National Primary Drinking Water Regulations; Announcement of the Results of EPA's Fourth Review of Existing Drinking Water Standards, 59623-59645 [2024-15807]

Download as PDF 59623 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations EPA-APPROVED VIRGINIA REGULATIONS AND STATUTES State citation State effective date Title/subject * * Explanation [former SIP citation] EPA approval date * * * * * * * 9 VAC 5, Chapter 20 General Provisions * * * * * Part II Air Quality Programs * 5–20–204 ......... * Nonattainment Areas ...... * * * 2/15/23 * * * * 7/23/2024, [Insert Federal Register Citation]. * * * * * * List of nonattainment areas revised to include Giles County locality for the primary sulfur dioxide standard. * AGENCY: July 23, 2024. EPA is not accepting public comment on the review results. FOR FURTHER INFORMATION CONTACT: Samuel Hernandez, Environmental Protection Agency, Office of Ground Water and Drinking Water, Standards and Risk Management Division, (Mail Code 4607M), 1200 Pennsylvania Avenue NW, Washington, DC 20460; telephone number: (202) 564–1735; email address: hernandez.samuel@ epa.gov. SUPPLEMENTARY INFORMATION: Abbreviations and acronyms: The following acronyms and abbreviations are used throughout this document. The Safe Drinking Water Act (SDWA) requires the U.S. Environmental Protection Agency (EPA or the agency) to conduct a review every six years of existing national primary drinking water regulations (NPDWRs) and determine which, if any, are appropriate for revision. The purpose of the review, called the Six-Year Review, is to evaluate available information for regulated contaminants to determine if any new information on health effects, treatment technologies, analytical methods, occurrence, exposure, implementation, and/or other factors provides a basis to support a regulatory revision that would improve or strengthen public health protection. While EPA has recently completed several significant revisions to existing regulations and other regulatory revisions are currently underway, based on this periodic review of all NPDWRs, there are no additional candidates for regulatory revision at this time. 2,4-D—2,4-Dichlorophenoxyacetic acid ADWR—Aircraft Drinking Water Rule BAT—Best Available Technology CFR—Code of Federal Regulations CVOC—Carcinogenic Volatile Organic Contaminant CWS—Community Water System DBCP—1,2-Dibromo-3-Chloropropane DBP—Disinfection Byproduct DEHA—Di(2-ethylhexyl)adipate DEHP—Di(2-ethylhexyl)phthalate EPA—U.S. Environmental Protection Agency EQL—Estimated Quantitation Level FBRR—Filter Backwash Recycling Rule GWR—Ground Water Rule HAA5—Haloacetic Acids (five) (sum of monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid) ICR—Information Collection Request IRIS—Integrated Risk Information System LT2—Long-Term 2 Enhanced Surface Water Treatment Rule MCLG—Maximum Contaminant Level Goal MCL—Maximum Contaminant Level MDBP—Microbial and Disinfection Byproduct MDL—Method Detection Limit MRDLG—Maximum Residual Disinfectant Level Goal DATES: [FR Doc. 2024–16121 Filed 7–22–24; 8:45 am] ADDRESSES: BILLING CODE 6560–50–P ENVIRONMENTAL PROTECTION AGENCY 40 CFR Part 141 [EPA–HQ–OW–2023–0572; FRL 7946–01– OW] National Primary Drinking Water Regulations; Announcement of the Results of EPA’s Fourth Review of Existing Drinking Water Standards Environmental Protection Agency (EPA). ACTION: Results of regulatory review. SUMMARY: ddrumheller on DSK120RN23PROD with RULES1 * VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 PO 00000 Frm 00033 Fmt 4700 Sfmt 4700 * * MRDL—Maximum Residual Disinfectant Level MRL—Minimum Reporting Level NAS—National Academy of Sciences NCWS—Non-Community Water System NDWAC—National Drinking Water Advisory Council NPDWR—National Primary Drinking Water Regulations NRC—National Research Council NTP—National Toxicology Program PCBs—Polychlorinated biphenyls PCE—Tetrachloroethylene PQL—Practical Quantitation Limit PT—Proficiency Testing PWS—Public Water System RfD—Reference Dose RSC—Relative Source Contribution RTCR—Revised Total Coliform Rule SDWA—Safe Drinking Water Act SDWIS—Safe Drinking Water Information System SWTR—Surface Water Treatment Rule TCDD—Tetrachlorodibenzo-p-dioxin TCE—Trichloroethylene TCR—Total Coliform Rule TNCWS—Transient Non-Community Water System TTHM—Total Trihalomethanes (sum of four THMs: chloroform, bromodichloromethane, dibromochloromethane, and bromoform) TT—Treatment Technique USGS—U.S. Geological Survey Table of Contents I. General Information A. Does this action apply to me? B. How can I get copies of this document and other related information? II. Statutory Requirements for the Six-Year Review III. Regulations Included in the Six-Year Review 4 IV. EPA’s Protocol for Reviewing the NPDWRs Included in This Action A. What was EPA’s review process? B. How did EPA conduct the review of the NPDWRs? 1. Initial Review 2. Health Effects E:\FR\FM\23JYR1.SGM 23JYR1 59624 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations ddrumheller on DSK120RN23PROD with RULES1 3. Analytical Feasibility 4. Occurrence and Exposure Analysis 5. Treatment Feasibility 6. Risk-Balancing 7. Other NPDWR Revisions V. Results of EPA’s Review of NPDWRs A. Overview of Six-Year Review 4 Results B. Chemical Phase Rules/Radionuclides Rules 1. Key Review Outcomes 2. Summary of Review Results 3. Select NPDWRs with New Information Not Appropriate for Revision C. Microbial Contaminants Regulations VI. References regulation shall be promulgated in accordance with this section, except that each revision shall maintain, or provide for greater, protection of the health of persons.’’ Pursuant to the 1996 SDWA Amendments, EPA completed and published the results of its first Six-Year Review (Six-Year Review 1) on July 18, 2003 (68 FR 42908, USEPA, 2003), the second Six-Year Review (Six-Year Review 2) on March 29, 2010 (75 FR 15500, USEPA, 2010a) and the third Six-Year Review (Six-Year Review 3) on January 11, 2017 (82 FR 3518, USEPA, I. General Information 2017a). A. Does this action apply to me? During the Six-Year Review 1, EPA This action itself does not impose any identified the Total Coliform Rule (TCR) requirements on individual people or as a candidate for revision.1 In Six-Year entities. Instead, it notifies interested Review 2, EPA identified four NPDWRs corresponding to acrylamide, parties of EPA’s review of existing epichlorohydrin, tetrachloroethylene national primary drinking water (PCE), and trichloroethylene (TCE) as regulations (NPDWRs) and its candidates for revision. In Six-Year conclusions about which of these Review 3, eight NPDWRs were listed as NPDWRs may warrant regulatory candidates for revision, including: revisions at this time. The Six-Year Review is not a final regulatory decision chlorite, Cryptosporidium (under SWTRs), Giardia lamblia, haloacetic to revise or not revise an NPDWR, but acids (HAA5), heterotrophic bacteria, rather a planning process that involves Legionella, total trihalomethanes more detailed analyses of factors (TTHM), and viruses (under SWTRs). relevant to deciding whether a rulemaking to revise an NPDWR should EPA also announced that the NPDWRs for acrylamide and epichlorohydrin be initiated. were no longer candidates for revision B. How can I get copies of this document due to low opportunity for further and other related information? reduction of public health risk through 1. Docket. EPA has established a regulatory revision (82 FR 3525, USEPA, docket for this action under Docket ID 2017a). In this document, EPA is announcing No. EPA–HQ–OW–2023–0572. Publicly the results of the fourth Six-Year Review available docket materials are available (Six-Year Review 4). EPA’s electronically on www.regulations.gov announcement of whether to identify an or in hard copy at the EPA Docket Center, WJC West Building, Room 3334, NPDWR as a candidate for revision (pursuant to SDWA section 1412(b)(9)) 1301 Constitution Ave. NW, is not a regulatory decision. Instead, Washington, DC. The Docket Center’s hours of operations are 8:30 a.m. to 4:30 announcing that an NPDWR is a candidate for revision formally initiates p.m., Monday through Friday (except a regulatory process that involves more Federal Holidays). For further detailed analyses of health effects, information on the EPA Docket Center analytical constraints, treatment services and the current status see: feasibility, occurrence, benefits, costs, https://www.epa.gov/dockets. 2. Electronic Access. You may access and other policy considerations relevant this Federal Register document to informing an NPDWR revision effort. electronically from https://www.federal The Six-Year Review results do not register.gov. obligate the agency to revise an NPDWR if EPA determines during the regulatory II. Statutory Requirements for the Sixprocess that revisions are no longer Year Review appropriate and discontinues further Under the Safe Drinking Water Act (SDWA), as amended in 1996, EPA must 1 The NPDWRs apply to specific contaminants/ parameters or groups of contaminants. Historically, periodically review existing NPDWRs and, if appropriate, revise them. Section when issuing new or revised standards for these contaminants/parameters, EPA has often grouped 1412(b)(9) of the SDWA states: ‘‘The the standards together in more general regulations, Administrator shall, not less often than such as the Total Coliform Rule, the Surface Water Treatment Rule or the Phase V rules. In this action, every six years, review and revise, as however, for clarity, EPA discusses the drinking appropriate, each national primary water standards as they apply to each specific drinking water regulation promulgated regulated contaminant/parameter (or group of under this title. Any revision of a contaminants), not the more general regulation in which the contaminant/parameter was regulated. national primary drinking water VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 PO 00000 Frm 00034 Fmt 4700 Sfmt 4700 efforts to revise the NPDWR. Similarly, when EPA announces that a particular NPDWR has not been identified as a candidate for revision it means that the agency has concluded that it is not appropriate for revision at this time based on available information. The criteria that EPA has applied to help identify when an NPDWR might be considered as a ‘‘candidate for revision’’ are, at a minimum, that the regulatory revision presents a meaningful opportunity to improve the level of public health protection, and/or achieve cost savings while maintaining or improving the level of public health protection. III. Regulations Included in the SixYear Review 4 Table 1 of this document lists all 94 NPDWRs established to date. The table also reports the maximum contaminant level goal (MCLG) and, where applicable, the maximum contaminant level (MCL). The MCLG is ‘‘set at the level at which no known or anticipated adverse effects on the health of persons occur and which allows an adequate margin of safety’’ (SDWA section 1412(b)(4)). The MCL for each applicable NPDWR, is the maximum permissible level of a contaminant in water delivered to any user of a public water system (PWS) and generally ‘‘is as close to the maximum contaminant level goal as is feasible’’ (SDWA section 1412(b)(4)(B)). If it is not ‘‘economically or technically feasible to ascertain the level of the contaminant,’’ EPA can require the use of a treatment technique (TT) in lieu of establishing an MCL. The treatment technique(s) must prevent known or anticipated adverse health effects ‘‘to the extent feasible’’ (SDWA section 1412(b)(7)(A)).2 In the case of disinfectants (e.g., chlorine, chloramines, chlorine dioxide), the values reported in the table are not MCLGs and MCLs, but maximum residual disinfectant level goals (MRDLGs) and maximum residual disinfectant levels (MRDLs). 2 Under limited circumstances, SDWA section 1412(b)(6)(A) gives the Administrator the discretion to promulgate an MCL or TT that is less stringent than the most protective feasible standard that ‘‘maximizes health risk reduction benefits at a cost that is justified by the benefits.’’ Similarly, SDWA section 1412(b)(5) authorizes the Administrator to promulgate an MCL or TT that is less stringent than the most protective feasible standard if the more protective standard would increase the level of other contaminants in drinking water or interfere with the efficacy of treatment techniques or process used for compliance with other NPDWRs. Under those circumstances, EPA is to promulgate feasible a MCL or TT rule to ‘‘minimize the oversall risk of adverse health effects’’ while avoiding an increase in health risks from other contaminants. E:\FR\FM\23JYR1.SGM 23JYR1 59625 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations As part of the fourth Six-Year Review, EPA did not consider information after December 2021, unless otherwise noted. EPA identified 15 NPDWRs for which there has either been a recently completed, an ongoing, or a pending regulatory action. EPA did not conduct a detailed review of these 15 NPDWRs for the Six-Year Review 4. These include the ongoing Lead & Copper rulemaking activities and the potential revisions 3 of the Microbial and Disinfection Byproduct Rules (MDBP). The MDBP effort contemplates potential regulatory revisions for the NPDWRs covering the following contaminants: (Bromate, Chloramines, Chlorine Dioxide, Chlorine, Chlorite, Cryptosporidium, Giardia lamblia, Haloacetic acids, Heterotrophic bacteria, Legionella, Total Trihalomethanes, Turbidity, & Viruses). The EPA did not include in this SixYear Review cycle the recently promulgated per-and polyfluoroalkyl substances (PFAS) regulations.4 The PFAS regulations, promulgated in April 2024, established 6 new NPDWRs. The EPA anticipates that once the PFAS regulations go into effect and sufficient information regarding compliance monitoring becomes available, those NPDWRs will be subject to a more detailed regulatory review under a future Six-Year Review cycle. This document describes the detailed review of the remaining 73 NPDWRs. section IV of this document describes the Six-Year Review 4 protocol, and section V of this document describes the review results. Please see USEPA (2024a) for more details. ddrumheller on DSK120RN23PROD with RULES1 TABLE 1—LIST OF NPDWRS Contaminants/parameters MCLG (mg/L) 1 3 MCL or TT (mg/L) 2 3 Contaminants/parameters MCLG (mg/L) 1 3 Acrylamide ........................................... Alachlor ................................................ Alpha/photon emitters .......................... Antimony .............................................. Arsenic ................................................. Asbestos .............................................. Atrazine ................................................ Barium ................................................. Benzene ............................................... 0 ........................... 0 ........................... 0 (pCi/L) ............... 0.006 .................... 0 ........................... 7 (million fibers/L) 0.003 .................... 2 ........................... 0 ........................... TT ......................... 0.002 .................... 15 (pCi/L) ............. 0.006 .................... 0.010 .................... 7 (million fibers/L) 0.003 .................... 2 ........................... 0.005 .................... 0 ........................... 0.7 ........................ n/a 5 ...................... 0 ........................... 0 ........................... n/a ........................ 0 ........................... 0.05 ...................... 10 (ppt) ................. TT. 0.7. 0.060. 0.0004. 0.0002. TT. 0.001. 0.05. 10 (ppt). Benzo[a]pyrene .................................... Beryllium .............................................. Beta/photon emitters ........................... Bromate ............................................... Cadmium ............................................. Carbofuran ........................................... Carbon tetrachloride ............................ Chloramines (as Cl2) ........................... Chlordane ............................................ Chlorine (as Cl2) .................................. Chlorine dioxide (as ClO2) ................... 0 ........................... 0.004 .................... 0 (millirems/yr) ...... 0 ........................... 0.005 .................... 0.04 ...................... 0 ........................... 4 ........................... 0 ........................... 4 ........................... 0.8 ........................ 0.0002 .................. 0.004 .................... 4 (millirems/yr) ...... 0.010 .................... 0.005 .................... 0.04 ...................... 0.005 .................... 4.0 ........................ 0.002 .................... 4.0 ........................ 0.8 ........................ 0 ........................... 0 ........................... 0.0002 .................. 0.002 .................... 0.04 ...................... 0.1 ........................ 10 ......................... 1 ........................... 0.2 ........................ 0 ........................... 10 (ppt) ................. TT. TT. 0.0002. 0.002. 0.04. 0.1. 10. 1. 0.2. 0.001. 10 (ppt). Chlorite ................................................ Chromium (total) .................................. Copper ................................................. Cryptosporidium ................................... 0.8 ........................ 0.1 ........................ 1.3 ........................ 0 ........................... 1.0 0.1 TT TT 0.2 ........................ 0.07 ...................... 0.2 ........................ 0.4 ........................ 0 ........................... 0 ........................... 0.6 ........................ 0.2 ........................ 0.07 ...................... 0.2 ........................ 0.4 ........................ 0.006 .................... 0.0002 .................. 0.6 ........................ 10 (ppt) ................. 0 (ppt) ................... 0 (ppt) ................... Hazard Index 12 of 1. 0.5 ........................ 0 ........................... 0 (pCi/L) ............... 0.05 ...................... 0.004 .................... 0.1 ........................ 0 ........................... 10 (ppt). 4.0 (ppt). 4.0 (ppt). Hazard Index of 1. Cyanide (as free cyanide) ................... 2,4-Dichlorophenoxyacetic acid (2,4-D) Dalapon ............................................... Di(2-ethylhexyl)adipate (DEHA) .......... Di(2-ethylhexyl)phthalate (DEHP) ....... 1,2-Dibromo-3- chloropropane (DBCP) 1,2-Dichlorobenzene (oDichlorobenzene). 1,4-Dichlorobenzene (pDichlorobenzene). 1,2-Dichloroethane (ethylene dichloride). 1,1-Dichloroethylene ............................ cis-1,2-Dichloroethylene ...................... trans-1,2-Dichloroethylene ................... Dichloromethane (methylene chloride) 1,2-Dichloropropane ............................ Dinoseb ................................................ Diquat .................................................. E. coli ................................................... Endothall .............................................. Endrin .................................................. Epichlorohydrin .................................... Ethylbenzene ....................................... Ethylene dibromide (EDB) ................... Fluoride ................................................ Giardia lamblia 4 .................................. Glyphosate ........................................... Haloacetic acids (HAA5) ..................... Heptachlor ........................................... Heptachlor epoxide .............................. Heterotrophic bacteria 6 ....................... Hexachlorobenzene ............................. Hexachlorocyclopentadiene ................. Hexafluoropropylene oxide dimer acid (HFPO–DA). Lead ..................................................... Legionella ............................................ Lindane ................................................ Mercury (inorganic) .............................. Methoxychlor ....................................... Monochlorobenzene (Chlorobenzene) Nitrate (as N) ....................................... Nitrite (as N) ........................................ Oxamyl (Vydate) .................................. Pentachlorophenol ............................... Perfluorohexane sulfonic acid (PFHxS). Perfluorononanoic acid (PFNA) ........... Perfluorooctane sulfonic acid (PFOS) Perfluorooctanoic acid (PFOA) ............ PFAS Mixture (HFPO–DA, PFBS, PFHxS, & PFNA). Picloram ............................................... Polychlorinated biphenyls (PCBs) ....... Radium 226/228 (combined) ............... Selenium .............................................. Simazine .............................................. Styrene ................................................ 2,3,7,8-TCDD (Dioxin) ......................... 0.075 .................... 0.075 .................... Tetrachloroethylene ............................. 0 ........................... 0.005. 0 ........................... 0.005 .................... Thallium ............................................... 0.0005 .................. 0.002. 0.007 .................... 0.07 ...................... 0.1 ........................ 0 ........................... 0 ........................... 0.007 .................... 0.02 ...................... 0 ........................... 0.1 ........................ 0.002 .................... 0 ........................... 0.7 ........................ 0 ........................... 4.0 ........................ 0.007 .................... 0.07 ...................... 0.1 ........................ 0.005 .................... 0.005 .................... 0.007 .................... 0.02 ...................... MCL,10 TT 8 11 ...... 0.1 ........................ 0.002 .................... TT ......................... 0.7 ........................ 0.00005 ................ 4.0 ........................ Toluene ................................................ Total coliforms 7 8 ................................. Total Trihalomethanes (TTHM) ........... Toxaphene ........................................... 2,4,5-TP (Silvex) .................................. 1,2,4-Trichlorobenzene ........................ 1,1,1-Trichloroethane ........................... 1,1,2-Trichloroethane ........................... Trichloroethylene ................................. Turbidity 6 ............................................. Uranium ............................................... Vinyl Chloride ...................................... Viruses ................................................. Xylenes (total) ...................................... 1 ........................... n/a ........................ n/a 9 ...................... 0 ........................... 0.05 ...................... 0.07 ...................... 0.2 ........................ 0.003 .................... 0 ........................... n/a ........................ 0 ........................... 0 ........................... 0 ........................... 10 ......................... 1. TT. 0.080. 0.003. 0.05. 0.07. 0.2. 0.005. 0.005. TT. 0.030. 0.002. TT. 10. ........................ ........................ ......................... ......................... MCL or TT (mg/L) 2 3 0.5. 0.0005. 5 (pCi/L). 0.05. 0.004. 0.1. 3 ×10 ¥8. 1 MCLG: the maximum level of a contaminant in drinking water at which no known or anticipated adverse effect on the health of persons would occur, allowing an adequate margin of safety. Maximum contaminant level goals are nonenforceable health goals. 3 Additional information can be found at https:// www.epa.gov/system/files/documents/2022-04/ mdbp-rule-revisions-charge-to-the-ndwac.pdf. 4 On April 26, 2024, the EPA promulgated legally enforceable drinking water standards to address VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 PFAS known to occur individually and as mixtures in drinking water (89 FR 32532). The NPDWRs sets limits for five individual PFAS: (perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), perfluorohexane sulfonic acid (PFHxS), perfluorono nanoic acid (PFNA), hexafluoropropylene oxide PO 00000 Frm 00035 Fmt 4700 Sfmt 4700 dimer acid (HFPO–DA, commonly known as GenX Chemicals)); and also established a limit for mixtures of any two or more of the following four PFAS: (PFNA, PFHxS, perfluorobutane sulfonic acid (PFBS), and HFPO–DA). E:\FR\FM\23JYR1.SGM 23JYR1 59626 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations 2 MCL: the maximum level allowed of a contaminant in water which is delivered to any user of a public water system. TT: any action, process, or procedure required of the water system that leads to the reduction of the level of a contaminant in tap water that reaches the consumer. 3 Units are in milligrams per liter (mg/L) unless otherwise noted. Milligrams per liter are equivalent to parts per million. For chlorine, chloramines, and chlorine dioxide, values presented are MRDLG and MRDL. 4 The current preferred taxonomic name is Giardia duodenalis, with Giardia lamblia and Giardia intestinalis as synonymous names. However, Giardia lamblia was the name used to establish the MCLG in 1989. Elsewhere in this document, this pathogen will be referred to as Giardia spp. or simply Giardia unless discussing information on an individual species. 5 There is no MCLG for all five haloacetic acids. MCLGs for some of the individual contaminants are: dichloroacetic acid (zero), trichloroacetic acid (0.02 mg/L), and monochloroacetic acid (0.07 mg/L). Bromoacetic acid and dibromoacetic acid are regulated with this group but have no MCLGs. 6 Includes indicators that are used in lieu of direct measurements (e.g., of heterotrophic bacteria, turbidity). 7 The Aircraft Drinking Water Rule (ADWR) 40 CFR part 141 subpart X, promulgated October 19, 2009, covers total coliforms and E. coli. 8 Under the RTCR, a PWS is required to conduct an assessment if it exceeded any of the TT triggers identified in 40 CFR 141.859(a). It is also required to correct any sanitary defects found through the assessment. 40 CFR 141.859(c). 9 There is no MCLG for total trihalomethanes (TTHM). MCLGs for some of the individual contaminants are: bromodichloromethane (zero), bromoform (zero), dibromochloromethane (0.06 mg/L), and chloroform (0.07 mg/L). 10 A PWS is in compliance with the E. coli MCL unless any of the conditions identified under 40 CFR 141.63(c) occur. 11 Under the GWR in 40 CFR 141.402, a ground water system that does not provide at least 4-log treatment of viruses and has a distribution system RTCR sample that tests positive for total coliform is required to conduct triggered source water monitoring to evaluate whether the total coliform presence in the distribution system is due to fecal contamination in the ground water source. The system must monitor for one of three State-specified fecal indicators (i.e., E. coli, coliphage, or enterococci). 12 The Hazard Index is an approach that EPA uses to determine the health concerns associated with mixtures of certain PFAS in finished drinking water. The Hazard Index is made up of a sum of fractions. Each fraction compares the level of each PFAS measured in the water to the associated health-based water concentration. IV. EPA’s Protocol for Reviewing the NPDWRs Included in This Action ddrumheller on DSK120RN23PROD with RULES1 A. What was EPA’s review process? This section provides an overview of the process EPA used to review the NPDWRs discussed in this document. The protocol document, ‘‘EPA Protocol for the Fourth Review of Existing National Primary Drinking Water Regulations,’’ contains a detailed description of the process the agency used to review the NPDWRs (USEPA, 2024c). The foundation of this protocol was developed for the Six-Year Review 1 based on the recommendations of the National Drinking Water Advisory Council (NDWAC, 2000) and has undergone minor clarifications during each Six-Year Review cycle (USEPA, 2024c). Figure 1 presents an overview of the Six-Year Review protocol and the possible review outcomes. The objective of the Six-Year Review process is to identify and prioritize NPDWRs for possible regulatory revision. The two major outcomes of the detailed review are either (1) the NPDWR is not appropriate for revision and no action is necessary at this time or (2) the NPDWR is a candidate for revision. The reasons why EPA might list an NPDWR as ‘‘not appropriate for revision at this time’’ could include: • Recently completed, ongoing, or pending regulatory action: The NPDWR was recently completed, is being reviewed under an ongoing action, or is subject to a pending action. • Ongoing or planned health effects assessment: The contaminant or contaminants regulated by the NPDWR has an ongoing or planned health effects assessment. • No new information: EPA did not identify any new relevant information for the contaminant since the last SixYear Review that indicates changes to the NPDWR may be appropriate. VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 • Data gaps/emerging information: New information indicates a possible change to the MCLG and/or MCL but changes to the NPDWR are not appropriate due to data gaps and emerging information that needs to be evaluated. • Low priority and/or no meaningful opportunity: New information indicates a possible change to the MCLG and/or MCL but changes to the NPDWR are not appropriate at this time due to one or more of the following reasons: (1) possible changes present negligible gains in public health protection; (2) possible changes present limited opportunity for cost savings while maintaining the same or greater level of health protection; and/or (3) possible changes are a low priority because of competing workload priorities, limited return on the administrative costs associated with rulemaking, and the burden on states and the regulated community associated with implementing any regulatory change that would result. Alternatively, the reasons why an NPDWR could be listed as a candidate for revision are that the regulatory revision presents a meaningful opportunity to improve the level of public health protection, and/or achieve cost savings while maintaining or improving the level of public health protection. Individual regulatory provisions that are evaluated as part of the Six-Year Review process include: MCLG, MCL, MRDLG, MRDL, TT, best available technology (BAT), and other requirements, such as monitoring requirements. For example, the microbial regulations include TT requirements because no reliable, affordable, and technically feasible method is available to measure the microbial contaminants covered by those regulations. These TT requirements rely on the use of indicators that can be measured in PO 00000 Frm 00036 Fmt 4700 Sfmt 4700 drinking water, such as detection of total coliforms as an indicator of a potential pathway for pathogenic contamination in the distribution system. As part of the Six-Year Review 4, EPA evaluated new information related to the use of those indicators to determine if a meaningful opportunity to improve the level of public health protection exists. Results of EPA’s review of the microbial regulations are presented in section V of this document. Basic Principles EPA applied several basic principles to the Six-Year Review process: • The agency sought to avoid redundant review efforts. Because EPA has reviewed information for certain NPDWRs as part of recently completed, ongoing, or pending regulatory actions, these NPDWRs were not subject to detailed review under the Six-Year Review process. • The agency does not believe it is appropriate to consider revisions to NPDWRs for contaminants with an ongoing or planned health effect assessment where the MCL is set equal to the MCLG or that were set at the level at which health risk reduction benefits were maximized at a cost justified by the benefits in accordance with SDWA section 1412(b)(6)(A)). This principle stems from the fact that any new health effects assessment may affect the MCL via a change in the MCLG or the assessment of the benefits associated with the MCL. EPA notes that these NPDWRs are not appropriate for revision and no action is necessary if the health effects assessment would not be completed during the review cycle. • In evaluating the potential for new information to affect NPDWRs, EPA assumed no change to existing policies and procedures for developing NPDWRs. For example, in determining whether new information affected the feasibility of analytical methods for a contaminant, the agency assumed no E:\FR\FM\23JYR1.SGM 23JYR1 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations change to current policies and procedures for calculating practical quantitation limits. • EPA may consider whether there is new public health risk information to justify accelerating review and potential revision of a particular NPDWR before the next review cycle. Procedures EPA also applied the following procedures in the review process: • EPA considered new information from health effects assessments that were completed by the information cutoff date. Assessments completed after this cutoff date will be reviewed by EPA during the next review cycle. • During the review, EPA identified areas where relevant information, which is needed to determine whether a revision to an NPDWR may be appropriate, was either: inadequate, 59627 unavailable (i.e., data gaps), or emerging. To the extent EPA is able to fill data gaps or fully evaluate the emerging information, the agency will consider the information as part of the next review cycle. • Finally, EPA assured that the scientific analyses supporting the review were consistent with the agency’s peer review policy (USEPA, 2015a). Figure 1: Six-Year Review Protocol Overview and Review Outcomes NPDWRs Under Review NPDWRs reviewed in recent or ongoing action? Yes No Health effects assessment (HEA) in process or planned?* Yes No i; New information to suggest possible changes (i.e., to an MCLG, MCL, Treatment Technique and/or other re tory revisions)? !Uncertain- emerging infomtation Outcome: No action at this time Yes i !___ No Data sufficient to support regulatory revision? No Yes Meaningful opportunity for health risk reduction for persons served by PWSs and/or cost savings while maintaining/improving public health protection? Outcome: Candidate for Revision ddrumheller on DSK120RN23PROD with RULES1 B. How did EPA conduct the review of the NPDWRs? The protocol for the Six-Year Review 4 is organized as a series of questions to inform an assessment as to the appropriateness of revising an NPDWR. These questions are logically ordered into a decision tree. This section provides an overview of each of the review elements that EPA considered for each NPDWR during the Six-Year Review 4, including the following: initial review, health effects, analytical feasibility, occurrence and exposure, treatment feasibility, risk balancing, and other NPDWR revisions. The final review combines the findings from all these review elements to recommend whether an NPDWR is a candidate for revision. Further information about the review elements is described in the VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 *Contaminants with an HEA process that have an MCL based on practical quantitation limits and are greater than the MCLG are passed to the next question to evaluate the potential to revise the MCL. protocol document (USEPA, 2024c). The results of the Six-Year Review are presented in section V of this document. 1. Initial Review EPA’s initial review of all the contaminants included in the Six-Year Review 4 involved a simple identification of the NPDWRs that have either been recently completed or are being reviewed in an ongoing or pending action since the publication of Six-Year Review 3. In addition, the initial review also identified contaminants with ongoing health effects assessments that have an MCL equal to the MCLG. Excluding such contaminants from a more detailed review in the Six-Year Review 4 prevents duplicative agency efforts. PO 00000 Frm 00037 Fmt 4700 Sfmt 4700 2. Health Effects The principal objectives of the health effects review are to identify: (1) contaminants for which a new health effects assessment indicates that a change in the MCLG might be appropriate (e.g., because of a change in cancer classification or a change in reference dose (RfD)), and (2) contaminants for which new health effects information indicates a need to initiate a new health effects assessment. To meet the first objective, EPA reviewed the results of health effects assessments completed since promulgation of each NPDWR. To meet the second objective, the agency conducted a systematic literature search, to capture more recently published peer-reviewed studies on relevant health effects via the oral route E:\FR\FM\23JYR1.SGM 23JYR1 ER23JY24.000</GPH> Yes No 59628 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations of exposure for the general population as well as sensitive subpopulations including children. The results of the literature search were used to survey the health effects literature that has become available since the previous review cycle, identify any emerging issues for a contaminant, and identify data gaps to inform future health assessment nominations. ddrumheller on DSK120RN23PROD with RULES1 3. Analytical Feasibility When establishing an NPDWR, EPA identifies a practical quantitation limit (PQL), which is the lowest achievable level of analytical quantitation during routine laboratory operating conditions within specified limits of precision and accuracy (50 FR 46880, USEPA, 1985). EPA has a separate process in place to approve new analytical methods for drinking water contaminants; therefore, review and approval of potential new methods is outside the scope of the SixYear Review protocol. EPA recognizes, however, that the approval and adoption in recent years of new and/or improved analytical methods may enable laboratories to quantify contaminants at lower levels than was possible when NPDWRs were originally promulgated. This ability of laboratories to measure a contaminant at lower levels could affect its PQL, the value at which an MCL is set when it is limited by analytical feasibility. Therefore, the Six-Year Review process includes an examination of whether there have been changes in analytical feasibility that could possibly change the PQL for the subset of the NPDWRs that reach this stage of the review. To determine if changes in analytical feasibility could possibly support changes to PQLs, EPA relied primarily on two approaches to develop estimated quantitation levels (EQLs), which are based on either (1) minimum reporting levels (MRLs) obtained as part of the Six-Year Review 4 Information Collection Request (ICR), or (2) method detection limits (MDLs) from EPAapproved laboratory protocols. An MRL is the lowest level or contaminant concentration that a laboratory can reliably achieve within specified limits of precision and accuracy under routine laboratory operating conditions using a given method. The MRL values provide direct evidence from actual monitoring results about whether quantitation below the PQL using current analytical methods is feasible. An MDL is a measure of analytical sensitivity, representing the minimum reported concentration that can be distinguished from blank results with 99 percent confidence. MDLs have VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 been used in the past to derive PQLs for regulated contaminants. EPA used the EQL as a threshold for occurrence analysis to help the agency assess for a meaningful opportunity to improve public health protection. It should be noted, however, that the use of an EQL does not necessarily indicate the agency’s intention to promulgate a revised MCL based on the new PQL. Any change in the PQL for a contaminant could be part of future rulemaking efforts if EPA decides to initiate a regulatory revision for the contaminant. 4. Occurrence and Exposure Analysis EPA conducted the occurrence and exposure analysis in conjunction with other review elements to determine if an NPDWR revision would provide a meaningful opportunity to improve public health by: • estimating the extent of contaminant occurrence, i.e., the number of PWSs in which contaminants occur at levels of interest (health-effectsbased thresholds or analytical method limits), and; • evaluating the number of people potentially exposed to contaminants at these levels. To evaluate national contaminant occurrence under the Six-Year Review 4, EPA reviewed data from the Six-Year Review 4 ICR database (SYR 4 ICR database) and other relevant sources. EPA collected SDWA compliance monitoring data and treatment technique information through use of an ICR (84 FR 58381, USEPA, 2019). EPA requested that states, as well as Tribes and territories with primacy voluntarily submit their compliance monitoring data and treatment technique information for regulated contaminants in PWSs. Specifically, EPA requested the submission of compliance monitoring data, treatment technique information, and related details collected between January 2012 and December 2019 for regulated contaminants and related parameters (e.g., water quality indicators). Forty-six states plus 13 other jurisdictions (Washington, DC, territories, and Tribes) provided data. The assembled data constitute the largest, most comprehensive set of drinking water compliance monitoring data and treatment technique information ever compiled and analyzed by EPA to inform decision making, containing almost 71 million analytical records from approximately 140,000 PWSs, serving approximately 301 million people nationally. Through extensive data management efforts, quality assurance evaluations, and PO 00000 Frm 00038 Fmt 4700 Sfmt 4700 communications with state data management staff, EPA established the SYR 4 ICR dataset (USEPA, 2019). The number of states and PWSs represented in the dataset varies across contaminants because of variability in state data submissions and contaminant monitoring schedules. EPA considers that these data are of sufficient quality to inform an understanding of the national occurrence of regulated contaminants and related parameters. Details of the data management and data quality assurance evaluations are available in the supporting document (USEPA, 2024d). The resulting database is available online on the Six-Year Review website at https://www.epa.gov/ dwsixyearreview. 5. Treatment Feasibility An NPDWR either identifies an MCL or establishes enforceable TT requirements. When promulgating an MCL or enforceable treatment technique requirements, to determine feasibility, EPA identifies the best technology, treatment techniques, and other means which EPA finds, after examination for efficacy under field conditions and not solely under laboratory conditions, are available (taking cost into consideration). When promulgating an MCL, EPA also lists the technology, treatment techniques, or other means which are feasible for purposes of meeting the MCL. EPA reviews treatment feasibility to ascertain if available technologies meet BAT criteria for a hypothetical more stringent MCL, or if new information demonstrates an opportunity to improve public health protection through revision of an NPDWR TT requirement. To be a BAT, the treatment technology must meet several criteria such as having demonstrated consistent removal of the target contaminant under field conditions. Although treatment feasibility and analytical feasibility are considered together in evaluating the technical feasibility requirement for an MCL, historically, treatment feasibility has not been a limiting factor for MCLs. The result of this review element is a determination of whether treatment feasibility would pose a limitation to revising an MCL or provide an opportunity to revise the NPDWR TT requirement. 6. Risk-Balancing EPA reviews the risk-balancing analysis underlying some NPDWRs to examine how a potential regulatory revision would address tradeoffs in risks associated with different contaminants. Under this review, EPA considers whether a change to an MCL and/or TT E:\FR\FM\23JYR1.SGM 23JYR1 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations will increase the public health risk posed by one or more contaminants, and, if so, the agency considers revisions that will balance overall risks. This review element is relevant only to the NPDWRs included in the microbial and disinfection byproduct (MDBP) rules, which were promulgated to address the need for risk-balancing between microbial and disinfection byproduct (DBP) requirements, and among differing types of DBPs. NPDWRs for microbials and disinfectants and DBPs were not reviewed during SixYear Review 4 due to ongoing regulatory action initiated by Six-Year Review 3. 7. Other NPDWR Revisions In addition to possible revisions to MCLGs, MCLs, and TTs, EPA evaluated whether other revisions are needed to other regulatory provisions in NPDWRs, such as monitoring and system reporting requirements. EPA focused this review element on issues that were not already being addressed through alternative mechanisms, such as a recently completed, ongoing, or pending regulatory action. EPA also reviewed implementation-related NPDWR concerns that were ‘‘ready’’ for rulemaking—that is, the problem to be resolved had been clearly identified, along with specific options to address the problem that could be shown to either clearly improve the level of public health protection or represent a meaningful opportunity for achieving cost savings while maintaining the same 59629 level of public health protection. The result of this review element is a determination regarding whether EPA should consider revisions to the monitoring and/or reporting requirements of an NPDWR. V. Results of EPA’s Review of NPDWRs A. Overview of Six-Year Review 4 Results Table 2 of this document, lists the results of EPA’s review of the 88 NPDWRs assessed during Six-Year Review 4, along with the principal rationale for the review outcomes. Table 2 includes the 15 NPDWRs that have ongoing or pending regulatory actions. TABLE 2—SUMMARY OF SIX-YEAR REVIEW 4 RESULTS ddrumheller on DSK120RN23PROD with RULES1 Outcome Regulated contaminants Not Appropriate for Revision at this Time. Recently completed, ongoing or pending regulatory action. Bromate ............................................... Chloramines (as Cl2) ........................... Chlorine Dioxide (as ClO2) .................. Chlorine (as Cl2) .................................. Chlorite ................................................. Copper ................................................. Cryptosporidium (IE, LT1) 1 ................. Giardia lamblia. Haloacetic acids (HAA5). Heterotrophic bacteria. Lead. Legionella. Total Trihalomethanes (TTHM). Turbidity. Viruses (SWTR, IE, LT1).1 Not Appropriate for Revision at this Time. Health effects assessment in process or contaminant nominated for health assessment. Alpha/photon emitters .......................... Arsenic ................................................. Beta/photon emitters ............................ Chromium (total) .................................. Ethylbenzene ....................................... Mercury (inorganic). Polychlorinated biphenyls (PCBs). Radium 226/228 (combined). Uranium. No new information, NPDWR remains appropriate after review. Asbestos .............................................. Benzo(a)pyrene ................................... Chlorobenzene ..................................... Dalapon ................................................ Di(2-ethylhexyl)adipate (DEHA) ........... Di(2-ethylhexyl)phthalate (DEHP) ........ 1,2-Dibromo-3-chloropropane (DBCP) trans-1,2-Dichloroethylene. Dinoseb. E. coli. Endrin. Ethylene dibromide. 2,4,5-TP (Silvex). New information, but no revision recommended because . . . Low priority and/or no meaningful opportunity. Acrylamide ........................................... Alachlor ................................................ Antimony .............................................. Atrazine ................................................ Barium .................................................. Benzene ............................................... Beryllium .............................................. Cadmium .............................................. Carbofuran ........................................... Carbon Tetrachloride ........................... Chlordane ............................................ Cryptosporidium (LT2) 1 ....................... 1,2-Dichlorobenzene ............................ 1,4-Dichlorobenzene ............................ 1,2-Dichloroethane ............................... 1,1-Dichloroethylene ............................ cis-1,2-Dichloroethylene ...................... Dichloromethane .................................. 2,4-Dichlorophenoxyacetic acid (2,4-D) 1,2-Dichoropropane ............................. Dioxin (2,3,7,8-TCDD) ......................... Diquat. Endothall. Epichlorohydrin. Glyphosate. Heptachlor. Heptachlor Epoxide. Hexachlorobenzene. Hexachlorocyclopentadiene. Lindane. Methoxychlor. Oxamyl (Vydate). Pentachlorophenol. Picloram. Selenium. Simazine. Styrene. Tetrachloroethylene (PCE). Thallium. 1,2,4-Trichlorobenzene. 1,1,1-Trichloroethane. 1,1,2-Trichloroethane. Toluene. Total Coliform. Toxaphene. Trichloroethylene (TCE). Vinyl Chloride. Xylenes. Emerging information and/or data gaps. Cyanide (as free cyanide) ................... Fluoride. Nitrate. Nitrite. Candidate for Revision ..... New information. None. 1 Regulation abbreviations: Aircraft Drinking Water Rule (ADWR), Ground Water Rule (GWR), Revised Total Coliform Rule (RTCR), Surface Water Treatment Rule (SWTR), Interim Enhanced Surface Water Treatment Rule (IE), Long Term 1 Enhanced Surface Water Treatment Rule (LT1), and Long Term 2 Enhanced Surface Water Treatment Rule (LT2). VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 PO 00000 Frm 00039 Fmt 4700 Sfmt 4700 E:\FR\FM\23JYR1.SGM 23JYR1 59630 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations EPA has identified no appropriate candidates for revision at this time. EPA’s Office of Ground Water and Drinking Water is currently engaged in several ongoing and potential regulatory actions, in addition to being involved in the efforts to successfully implement recently promulgated rules including: • Developing a proposal to revise the Microbial and Disinfection By-Product Rules, including eight NPDWRs listed as candidates for revision in Six-Year Review 3 (85 FR 61680, USEPA, 2020a). • On December 6, 2023, EPA published the proposed rule ‘‘National Primary Drinking Water for Lead and Copper: Improvements’’ (88 FR 84878, USEPA, 2023a). • In January 2024, EPA announced its commitment to promulgate a National Primary Drinking Water Regulation for Perchlorate by May 2027.5 • On April 26, 2024, EPA published the PFAS final rule ‘‘PFAS National Primary Drinking Water Regulation’’ (89 FR 32532, USEPA, 2024a). • On May 24, 2024, EPA published the final rule ‘‘National Primary Drinking Water Regulations: Consumer Confidence Reports’’ (89 FR 45980, USEPA, 2024b). Therefore, when evaluating the review results described in sections V.B and V.C of this document, EPA also considered competing workloads and potential diversion of resources from these other planned, ongoing, and pending higher priority efforts within the drinking water office. B. Chemical Phase Rules/Radionuclides Rules The NPDWRs for chemical contaminants, collectively called the Phase Rules, were promulgated between 1987 and 1992, following the 1986 SDWA amendments. In December 2000, EPA promulgated final radionuclide regulations, which had been issued as interim rules in July 1976. 1. Key Review Outcomes EPA has decided that it is not appropriate at this time to revise any of the NPDWRs covered under the Phase or Radionuclides Rules (Table 2 of this document). These NPDWRs were determined not to be candidates for revision for one or more of the following reasons: • ongoing/pending regulatory action warrants waiting for further review; • no new information was identified to suggest possible changes in MCLG/ MCL; • new information did not present a meaningful opportunity for health risk reduction or cost savings while maintaining/improving public health protection; • emerging information and/or data gaps create substantial uncertainty. In addition, EPA is announcing that the NPDWRs for trichloroethylene (TCE) and tetrachloroethylene (PCE) are no longer candidates for revision at this time. In March 2010, as an outcome of the second cycle of Six-Year Review, EPA listed the TCE and PCE NPDWRs as candidates for revision (75 FR 15500, USEPA, 2010a). TCE and PCE were not reviewed under Six-Year Review 3 because regulatory revisions were being considered as part of plans to address regulated and unregulated Carcinogenic Volatile Organic Contaminants (cVOCs) in a group rule (75 FR 3525, January 21, 2010; 82 FR 3531, USEPA, 2017a). However, after evaluating currently available information for both of these chemicals, the EPA concludes that these NPDWRS are not appropriate for revision at this time because minimal reductions in health risks would be associated with any revisions to these regulations. Given resource limitations, competing workload priorities, and administrative costs and burden to states to adopt any regulatory changes associated with rulemakings, as well as limited potential health benefits, these NPDWRs are considered a low priority and are no longer candidates for revision at this time. Section V.B.2 of this document describes the results of the review organized by each review element. Section V.B.3 of this document includes a description of the new information gathered by EPA for select contaminants that EPA determined are not candidates for revision at this time due to emerging information or data gaps or no meaningful opportunity for health risk reduction. The contaminants discussed in detail in section V.B.3 of this document are cyanide, fluoride, nitrate, nitrite, TCE, and PCE. Review results organized by contaminant for the Chemical Phase and Radionuclides Rules can be found in the ‘‘Chemical Contaminant Summaries for the Fourth Six-Year Review of National Primary Drinking Water Regulations’’ (USEPA, 2024e). 2. Summary of Review Results Initial Review After conducting the initial review, as described in section IV.B.1 of this document, EPA identified two chemical contaminants (lead and copper) with NPDWRs that were considered as part of a recently completed action, and which are also currently part of an ongoing or pending regulatory action. EPA published the Lead and Copper Rule Revisions in January 2021 and published the proposed Lead and Copper Rule Improvements on December 6, 2023. EPA did not evaluate lead and copper in Six-Year Review 4 because such effort would be redundant with these recent and ongoing rulemakings. EPA also identified contaminants with ongoing or planned EPA health effects assessments. As of December 31, 2021, nine chemical or radiological contaminants reviewed had ongoing or planned formal EPA health effects assessments. Table 3 of this document below lists the contaminants with ongoing or planned EPA assessments at the time of the Six-Year Review 4 cutoff date and the current status of those reviews. EPA did not conduct a detailed review of these nine chemical and radiological contaminants under Six-Year Review 4. ddrumheller on DSK120RN23PROD with RULES1 TABLE 3—SIX-YEAR REVIEW CHEMICAL/RADIOLOGICAL CONTAMINANTS WITH ONGOING OR PLANNED EPA HEALTH ASSESSMENTS Chemical/radionuclide Status 1 Alpha/photon emitters ........... EPA Office of Air and Radiation (OAR) is conducting a review of alpha and beta photon emitters. Additional information about this effort can be found at in the Federal Register (87 FR 15988, USEPA, 2022a) or at: https://sab.epa.gov/ords/sab/r/sab_apex/sab_ bkup/advisoryactivitydetail?p18_id=2616&clear=18&session=8694491614209. Inorganic arsenic is being assessed by the EPA IRIS Program. The assessment status can be found at: https://iris.epa.gov/ ChemicalLanding/&substance_nmbr=278. EPA/OAR is conducting a review of alpha and beta photon emitters. Additional information about this effort can be found at in the Federal Register (87 FR 15988, USEPA, 2022a) or at: https://sab.epa.gov/ords/sab/r/sab_apex/sab_bkup/ advisoryactivitydetail?p18_id=2616&clear=18&session=8694491614209. Arsenic ................................... Beta/photon emitters ............. 5 Additional information can be found at https:// www.epa.gov/sdwa/perchlorate-drinking-water. VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 PO 00000 Frm 00040 Fmt 4700 Sfmt 4700 E:\FR\FM\23JYR1.SGM 23JYR1 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations 59631 TABLE 3—SIX-YEAR REVIEW CHEMICAL/RADIOLOGICAL CONTAMINANTS WITH ONGOING OR PLANNED EPA HEALTH ASSESSMENTS—Continued Status 1 Chemical/radionuclide Chromium VI (as part of total Cr). Ethylbenzene ......................... Mercury .................................. PCBs ..................................... Radium 226/228 .................... Uranium ................................. Chromium VI is being assessed by the EPA IRIS Program. The assessment status can be found at: https://iris.epa.gov/ ChemicalLanding/&substance_nmbr=144. Ethylbenzene is being assessed by the EPA IRIS Program. The assessment status can be found at: https://iris.epa.gov/ ChemicalLanding/&substance_nmbr=51. Inorganic Mercury Salts is being assessed by the EPA IRIS Program. The Assessment status can be found at: https://iris.epa.gov/ ChemicalLanding/&substance_nmbr=1522. PCBs are being assessed by the EPA IRIS Program. The assessment status can be found at: https://iris.epa.gov/ChemicalLanding/ &substance_nmbr=294. EPA/OAR is conducting a review of radium. Additional information about this effort can be found at in the FEDERAL REGISTER (87 FR 15988, USEPA, 2022a) or at: https://sab.epa.gov/ords/sab/r/sab_apex/sab_bkup/advisoryactivitydetail?p18_ id=2616&clear=18&session=8694491614209. Uranium is being assessed by the EPA IRIS Program. The assessment status can be found at: https://iris.epa.gov/ChemicalLanding/ &substance_nmbr=259. 1 Additional information on the status of EPA IRIS Program assessments can be found in the EPA IRIS Program Outlooks at https://www.epa.gov/iris/iris-programoutlook. Regarding the ongoing health assessment for Chromium VI (hexavalent chromium), on October 20, 2022 the EPA published its draft ‘‘IRIS Toxicological Review of Hexavalent Chromium [Cr(IV)]’’ (87 FR 63774, USEPA, 2022b). This draft health effects assessment, which includes a comprehensive evaluation of potential health effects, preliminarily categorizes hexavalent chromium as likely carcinogenic to humans via the oral exposure pathway. The final IRIS assessment was not available as of the publication of this document and for consideration as part of Six-Year Review 4. When this human health assessment is final, EPA will carefully review the conclusions and consider all relevant information to determine whether the assessment by EPA, a more detailed review was undertaken. Of the chemicals that underwent a more detailed review, EPA identified 29 contaminants for which an updated RfD and/or the cancer risk assessment (from oral exposure) or new relevant non-EPA assessments might support a change to the MCLG. These 29 chemicals were further evaluated as part of the Six-Year Review 4 to determine whether they were candidates for regulatory revision. Table 4 of this document lists the chemicals with available new health effects information and the sources of the relevant new information. As shown in this table, 15 chemical contaminants have information that could support a lower MCLG, and 14 contaminants have new information that could support a higher MCLG. NPDWR for chromium is a candidate for revision. After the initial review was completed, EPA identified 71 chemical and radiological NPDWRs that were appropriate for detailed review. Health Effects The principal objectives of the health effects assessment review were to identify: (1) contaminants for which a new health effects assessment indicates that a change in MCLG might be appropriate (e.g., because of a change in cancer classification or an RfD), and (2) contaminants for which the agency has identified new health effects information suggesting a need to initiate a new health effects assessment. For chemicals that were not excluded due to an ongoing or planned health effects TABLE 4—CHEMICALS WITH NEW HEALTH ASSESSMENTS THAT COULD SUPPORT A CHANGE IN MCLG Chemical Relevant new assessment 15 Contaminants with Potential to Decrease the MCLG ddrumheller on DSK120RN23PROD with RULES1 Antimony ................................................................................................... Cadmium .................................................................................................. Carbofuran ................................................................................................ Cyanide ..................................................................................................... cis-1,2-Dichloroethylene ........................................................................... Endothall ................................................................................................... Fluoride ..................................................................................................... Hexachlorocyclopentadiene ...................................................................... Methoxychlor ............................................................................................ Oxamyl ...................................................................................................... Selenium ................................................................................................... Styrene ..................................................................................................... Toluene ..................................................................................................... 1,2,4-Trichlorobenzene ............................................................................. Xylenes ..................................................................................................... CalEPA, 2016. ATSDR, 2012. USEPA OPP, 2008. USEPA IRIS, 2010b. USEPA IRIS, 2010c. USEPA OPP, 2015b. USEPA OW, 2010d. USEPA IRIS, 2001. CalEPA, 2010a. USEPA OPP, 2017b. ATSDR, 2003. CalEPA, 2010b. Health Canada, 2014. USEPA PPRTV, 2009a. Health Canada, 2014. 14 Contaminants with Potential to Increase the MCLG Alachlor ..................................................................................................... Atrazine ..................................................................................................... Barium ...................................................................................................... Beryllium ................................................................................................... 2,4-Dichlorophenoxy-acetic acid (2,4-D) .................................................. 1,2-Dichlorobenzene ................................................................................. 1,4-Dichlorobenzene ................................................................................. VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 PO 00000 Frm 00041 Fmt 4700 USEPA OPP, 2007a. USEPA OPP, 2018a. USEPA IRIS, 2005. USEPA IRIS, 1998. USEPA OPP, 2017c. ATSDR, 2006. ATSDR, 2006. Sfmt 4700 E:\FR\FM\23JYR1.SGM 23JYR1 59632 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations TABLE 4—CHEMICALS WITH NEW HEALTH ASSESSMENTS THAT COULD SUPPORT A CHANGE IN MCLG—Continued Chemical Relevant new assessment 1,1-Dichloroethylene ................................................................................. Diquat ....................................................................................................... Glyphosate ................................................................................................ Lindane ..................................................................................................... Picloram .................................................................................................... Simazine ................................................................................................... 1,1,1-Trichloroethane ................................................................................ Details of the health effects assessment review of the chemical and radiological contaminants are documented in the ‘‘Results of the Health Effects Assessment for the Fourth Six-Year Review of Existing Chemical and Radionuclide National Primary Drinking Water Standards’’ (USEPA, 2024f). ddrumheller on DSK120RN23PROD with RULES1 Analytical Feasibility EPA performed analytical feasibility analyses for the contaminants that reached this portion of the review. These contaminants included the 15 chemical contaminants identified under the health effects assessment review as having potential for a lower MCLG. EPA evaluated whether there were any analytical limitations to lowering the MCL to the potential MCLG. EPA also evaluated an additional 22 contaminants with MCLs higher than the current MCLGs due to analytical limitations at the time of rule promulgation. The document ‘‘Analytical Feasibility Support Document for the Fourth Six-Year Review of National Primary Drinking Water Regulations: Chemical Phase and Radionuclides Rules’’ (USEPA, 2024g) describes the process EPA used to evaluate whether changes in PQL are possible in those instances where the MCL may be limited by analytical feasibility. Table 5 of this document shows the outcomes of EPA’s analytical feasibility review for two general categories of VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 USEPA USEPA USEPA USEPA USEPA USEPA USEPA IRIS, 2002. OPP, 2020b. OPP, 2017d. OPP, 2004. OPP, 2020c. OPP, 2018b. IRIS, 2007b. drinking water contaminants: (1) contaminants where health effects assessments indicate potential for lower MCLGs, and (2) contaminants where existing MCLs were limited by analytical feasibility at the time of promulgation and new information indicates a potential to reduce the PQL. • A health effects assessment indicates potential for lower MCLG. This category includes the 15 contaminants identified in the health effects review as having potential for a lower MCLG. EPA reviewed the available information to determine if analytical feasibility could limit the potential for MCL revisions. The current PQL is not a limiting factor for seven of the 15 contaminants identified by the health effects review as potential candidates for lower MCLGs (cis-1,2-dichloroethylene, fluoride, hexachlorocyclopentadiene, oxamyl, selenium, toluene, and xylenes). For the remaining eight contaminants, the current PQL is higher than the potential new MCLG, so EPA evaluated whether there is an opportunity to lower the PQL. The evaluations indicated that all but one contaminant (antimony) have potential for a lower PQL, although not to the potential MCLG. Consequently, analytical feasibility may limit potential MCL revisions for the remaining seven contaminants (Table 5 of this document). • Existing MCLs are based on analytical feasibility. This category includes 22 contaminants with existing PO 00000 Frm 00042 Fmt 4700 Sfmt 4700 MCLs that are greater than the associated MCLGs due to analytical constraints at the time of rule promulgation. Two of the contaminants (thallium and 1,1,2-trichloroethane) are non-carcinogenic and have a non-zero MCLG, and the remaining 20 contaminants are carcinogens with MCLGs equal to zero. EPA evaluated whether the PQL could be lowered for each of these contaminants. The evaluations indicated that all but five (benzo[a]pyrene, DBCP, DEHP, ethylene dibromide, PCBs) of the 22 contaminants evaluated have potential for a lower PQL (Table 5 of this document). Where analytical feasibility evaluations indicated the potential for a PQL reduction, Table 5 of this document lists the type of data that support this conclusion. The types of data considered include laboratory proficiency tests (PT), method detection limits (MDL) from EPA-approved methods, and minimum reporting level (MRL) from the SYR 4 ICR dataset. The methods to evaluate each of these data types to identify potential to reduce PQLs are described in the analytical feasibility support document (USEPA, 2024g). Where the evaluations indicated that the current PQL remained appropriate, Table 5 shows of this document ‘‘Data do not support PQL reduction.’’ EPA found information supporting potentially lower MCLs for 31 out of 37 contaminants evaluated. E:\FR\FM\23JYR1.SGM 23JYR1 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations 59633 TABLE 5—ANALYTICAL FEASIBILITY REASSESSMENT RESULTS Current PQL (μg/L) Contaminant Analytical feasibility reassessment result (and source of new information) 1 15 Contaminants Identified Under the Health Effects Review as Having Potential for Lower MCLG Antimony ..................................................................................... Cadmium ..................................................................................... Carbofuran .................................................................................. Cis-1,2-dichloroethylene ............................................................. Cyanide ....................................................................................... Endothall ..................................................................................... Fluoride ....................................................................................... Hexachlorocyclopentadiene ........................................................ Methoxychlor ............................................................................... Oxamyl ........................................................................................ Selenium ..................................................................................... Styrene ........................................................................................ Toluene ....................................................................................... Xylenes ....................................................................................... 1,2,4-Trichlorobenzene ............................................................... 6 2 7 5 100 90 500 1 10 20 10 5 5 5 5 Data do not support PQL reduction. PQL reduction supported (MDL, MRL). PQL reduction supported (MDL). PQL not limiting. PQL reduction supported (MDL). PQL reduction supported (MDL, MRL). PQL not limiting. PQL not limiting. PQL reduction supported (MDL, MRL, PT). PQL not limiting. PQL not limiting. PQL reduction supported (MDL, MRL, PT). PQL not limiting. PQL not limiting. PQL reduction supported (MDL, MRL, PT). 22 Contaminants with MCLs Limited by Analytical Feasibility and Higher than MCLGs Benzene ...................................................................................... Benzo[a]pyrene ........................................................................... Carbon tetrachloride ................................................................... Chlordane .................................................................................... 1,2-Dibromo-3-chloropropane (DBCP) ....................................... 1,2-Dichloroethane ...................................................................... Dichloromethane ......................................................................... 1,2-Dichloropropane .................................................................... Di(2-ethylhexyl)phthalate (DEHP) ............................................... Ethylene dibromide ..................................................................... Heptachlor ................................................................................... Heptachlor epoxide ..................................................................... Hexachlorobenzene .................................................................... Pentachlorophenol ...................................................................... PCBs ........................................................................................... 2,3,7,8-TCDD (dioxin) ................................................................. Tetrachloroethylene .................................................................... Thallium ....................................................................................... Toxaphene .................................................................................. 1,1,2-Trichloroethane .................................................................. Trichloroethylene ......................................................................... Vinyl chloride ............................................................................... 5 0.2 5 2 0.2 5 5 5 5 0.05 0.4 0.2 1 1 0.5 0.00003 5 2 3 5 5 2 PQL reduction supported (MDL, MRL, PT). Data do not support PQL reduction. PQL reduction supported (MDL, MRL, PT). PQL reduction supported (MDL). Data do not support PQL reduction. PQL reduction supported (MDL, MRL, PT). PQL reduction supported (MDL, MRL, PT). PQL reduction supported (MDL, MRL, PT). Data do not support PQL reduction. Data do not support PQL reduction. PQL reduction supported (MDL). PQL reduction supported (MDL). PQL reduction supported (MDL, MRL). PQL reduction supported (MDL). Data do not support PQL reduction. PQL reduction supported (MRL). PQL reduction supported (MDL, MRL). PQL reduction supported (MRL). PQL reduction supported (MRL, PT). PQL reduction supported (MDL, MRL, PT). PQL reduction supported (MDL, MRL, PT). PQL reduction supported (MDL, MRL, PT). 1 The information source codes refer to the method detection limit (MDL), minimum reporting level (MRL), and proficiency testing (PT) data analyses. See USEPA (2024g) for further information. ddrumheller on DSK120RN23PROD with RULES1 Occurrence and Exposure Using the SYR 4 ICR database, EPA conducted an assessment to evaluate national occurrence of regulated contaminants and estimate the potential population exposed to these contaminants. The details of the current chemical occurrence analysis are documented in the ‘‘Analysis of Regulated Contaminant Occurrence Data from Public Water Systems in Support of the Fourth Six-Year Review of National Primary Drinking Water Regulations: Chemical Phase Rules and Radionuclides Rules’’ (USEPA, 2024h). Based on quantitative benchmarks which were identified in the health effects and analytical feasibility VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 analyses, EPA conducted the occurrence and exposure analysis for 31 contaminants. This analysis shows that 27 of the 31 contaminants assessed rarely occur at levels above the identified benchmark (e.g., potential MCLG or PQL). For these 27 contaminants, monitoring results only exceeded benchmarks in a very small percentage (i.e., less than 0.5 percent) of systems, which serve a very small percentage of the population, indicating that revisions to NPDWRs are unlikely to provide a meaningful opportunity to improve public health protection at the national level. Therefore, these 27 contaminants were not further considered as candidates for regulatory revision. The other four PO 00000 Frm 00043 Fmt 4700 Sfmt 4700 contaminants (cyanide, fluoride, TCE, and PCE) occurred at rates ranging from 0.57 to 9.1 percent of systems within the SYR 4 ICR dataset and 3.4 to 6.3 percent of the population served by those systems. Additional considerations for cyanide, fluoride, TCE, and PCE are discussed in section V.B.3 of this document. Table 6 of this document lists the numerical benchmarks used to conduct the occurrence analysis, the total number of systems with mean concentrations exceeding a benchmark, and the estimated population served by those systems. These average concentration-based evaluations are intended to inform the Six-Year Review, not to assess compliance with regulatory standards. E:\FR\FM\23JYR1.SGM 23JYR1 59634 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations TABLE 6—OCCURRENCE AND POTENTIAL EXPOSURE ANALYSIS FOR CHEMICAL NPDWRS Current MCL (ug/L) Contaminant Benchmark 1 (ug/L) Number (and percentage) of systems with a mean concentration 2 higher than benchmark Population served by systems with a mean concentration higher than benchmark (and percentage of total population) Contaminants Identified Under the Health Effects Review as Having Potential for Lower MCLG Cadmium ....................................................................................................................... Carbofuran .................................................................................................................... Cyanide ......................................................................................................................... cis-1,2-Dichloroethylene ................................................................................................ Endothall ....................................................................................................................... Fluoride 4 ....................................................................................................................... Hexachlorocyclopentadiene .......................................................................................... Methoxychlor ................................................................................................................. Oxamyl .......................................................................................................................... Selenium ....................................................................................................................... Styrene .......................................................................................................................... Toluene ......................................................................................................................... 1,2,4-Trichlorobenzene ................................................................................................. Xylenes (total) ............................................................................................................... 5 40 200 70 100 4,000 50 40 200 50 100 1,000 70 10,000 1 5 50 10 50 900 40 1 9 30 0.5 60 0.5 80 182 37 328 7 (0.36%) (0.02%) (0.85%) (0.01%) 0 4,479 (9.05%) 0 1 (<0.01%) 3 7 (0.02%) 91 (0.18%) 89 (0.17%) 14 (0.03%) 15 (0.03%) 23 (0.05%) 430,823 (0.16%) (0.02%) 8,134,220 (3.43%) 42,215 (0.02%) 0 17,058,830 (6.30%) 0 22,536 (0.01%) 3 52,677 (0.02%) 84,988 (0.03%) 27,473 (0.01%) 5,256 (<0.01%) 126,201 (0.05%) 34,728 (0.01%) 83 (0.16%) 90 (0.17%) 1 (<0.01%) 60 (0.11%) 215 (0.41%) 41 (0.08%) 1 (<0.01%) 3 (0.01%) 6 (0.02%) 0 7 (0.11%) 432 (0.83%) 71 (0.14%) 2 (0.01%) 2 (<0.01%) 297 (0.57%) 24 (0.05%) 319,633 (0.12%) 766,891 (0.28%) 240 (<0.01%) 181,041 (0.07%) 360,289 (0.13%) 34,800 (0.01%) 900 (<0.01%) 32,710 (0.01%) 17,278 (0.01%) 0 2,311 (<0.01%) 15,811,810 (5.76%) 57,541 (0.02%) 335 (<0.01%) 50 (<0.01%) 12,755,926 (4.65%) 307,275 (0.11%) 3 49,409 Contaminants with MCLs Higher than MCLGs (Limited by Analytical Feasibility) Benzene ........................................................................................................................ Carbon tetrachloride ...................................................................................................... Chlordane ...................................................................................................................... 1,2-Dichloroethane ........................................................................................................ Dichloromethane ........................................................................................................... 1,2-Dichloropropane ...................................................................................................... Heptachlor ..................................................................................................................... Heptachlor epoxide ....................................................................................................... Hexachlorobenzene ...................................................................................................... Pentachlorophenol ........................................................................................................ 2,3,7,8-TCDD (dioxin) ................................................................................................... Tetrachloroethylene (PCE) ............................................................................................ Thallium ......................................................................................................................... Toxaphene .................................................................................................................... 1,1,2-Trichloroethane .................................................................................................... Trichloroethylene (TCE) ................................................................................................ Vinyl chloride ................................................................................................................. 5 5 2 5 5 5 0.4 0.2 1 1 0.00003 5 2 3 5 5 2 0.5 0.5 1 0.5 0.5 0.5 0.1 0.1 0.1 0.9 0.000005 0.5 1 1 3 0.5 0.5 ddrumheller on DSK120RN23PROD with RULES1 1 Benchmark screening levels were set to either potential maximum contaminant level goals (MCLGs) or estimated quantitation levels (EQLs), depending on the contaminant. For more information see USEPA (2024g). 2 Results are based on long-term means generated by substituting one-half the MRL for each non-detection record. For results based on substituting the value of the full MRL or zero see USEPA (2024h). 3 Oxamyl and carbofuran have health endpoints associated with acute exposure and are not appropriate for long-term mean estimates. Results show the number of systems with at least one detection exceeding the benchmark. 4 Estimates represent naturally occurring fluoride concentrations. Quality assurance steps were taken to exclude samples from fluoridated water systems. See USEPA (2024i) for details. In addition, EPA performed a source water occurrence analysis for the 15 chemical contaminants in which updated health effects assessments indicated the possibility to increase (i.e., render less stringent) the MCLG values. EPA conducted this analysis to assess for meaningful opportunity to achieve cost savings while maintaining or improving the level of public health protection. The data available to characterize contaminant occurrence was limited because a comprehensive dataset to characterize drinking water source quality is not available. Data from the U.S. Geological Survey (USGS) National Water Quality Assessment program and the U.S. Department of Agriculture Pesticide Data Program water monitoring survey provide useful insights into potential contaminant occurrence in source water. The analysis of the available contaminant occurrence data for potential drinking VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 water sources indicated relatively low contaminant occurrence in the concentration ranges of interest, and consequently, no meaningful opportunity for system cost savings by increasing the MCLG and MCL for these 15 contaminants. The results of this analysis were documented in ‘‘Occurrence Analysis for Potential Source Waters for the Fourth Six-Year Review of National Primary Drinking Water Regulations’’ (USEPA, 2024j). Treatment Feasibility Currently, all of the MCLs for chemical and radiological contaminants are either (1) set equal to the MCLGs, (2) limited by analytical feasibility, or (3) set at the level at which health risk reduction benefits were maximized at a cost justified by the benefits; none are currently limited by treatment feasibility. EPA considers treatment feasibility after identifying PO 00000 Frm 00044 Fmt 4700 Sfmt 4700 contaminants with the potential to lower the MCLG/MCL that constitute a meaningful opportunity to improve public health. No such contaminants were identified in the occurrence and exposure analysis described above. Treatment techniques were promulgated for two of the chemical and radiological contaminants that were subject to a detailed review in Six-Year Review 4. Acrylamide and epichlorohydrin occur in drinking water as treatment impurities and are primarily introduced as residuals in polymers and copolymers used for water treatment. There are no standardized analytical methods for their measurement in water; instead of sampling, water systems must certify to the State in writing that they use products meeting the specifications in the NPDWR. To evaluate the potential to revise the NPDWRs for these contaminants, EPA obtained data from E:\FR\FM\23JYR1.SGM 23JYR1 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations NSF on analyses for approval of products against NSF/ANSI Standard 60, which are based on EPA’s regulation. NSF certification data shows that manufactured products contain acrylamide and epichlorohydrin impurity levels far below the current regulatory standard. Specifically, the mean residual acrylamide concentration of certified products is one-fifth of the current regulatory level and the 90th percentile is one-half. There were no samples with detections of residual epichlorohydrin. The available data indicates that the majority of tested products already pose lower health risks than required under the current TT, and therefore, revisions are a low priority. EPA is not listing acrylamide and epichlorohydrin as candidates for revision at this time. See USEPA (2024k) for details. Other Regulatory Revisions In addition to possible revisions to MCLGs, MCLs, and TTs, as a part of the Six-Year Review 4, EPA considered whether other regulatory revisions to NPDWRs are needed to address implementation issues, such as revisions to monitoring and system reporting requirements. EPA used the protocol to evaluate which implementation issues to consider (USEPA, 2024c). EPA’s protocol focused on items that were not already being addressed, or had not yet been addressed, through alternative mechanisms (e.g., as a part of a recent or ongoing rulemaking). EPA compiled information on implementation-related issues associated with the Chemical Phase Rules. EPA also identified unresolved implementation issues and concerns from previous Six-Year Reviews. The complete list of implementation issues related to the Phase and Radionuclides Rules is presented in ‘‘Consideration of Other Regulatory Revisions in Support of the Fourth Six-Year Review of the National Primary Drinking Water 59635 Regulations: Chemical Phase Rules and Radionuclides Rules’’ (USEPA, 2024l). The agency focused on the following five implementation issues in the SixYear Review 4: • Use of an alternative MCL for nitrate in Noncommunity Water Systems (NCWSs) • Frequency of nitrate monitoring in Transient Noncommunity Water Systems (TNCWS) • Frequency of nitrite monitoring • Total nitrate-nitrogen plus nitritenitrogen MCL • Total cyanide screening for free cyanide Table 7 of this document provides a brief description of the five issues and identified potential ways of addressing them. Please see section V.B.3. of this document for a discussion of these contaminants and their review outcomes. Please see USEPA (2024l) for a more detailed description and estimated scope of these issues. TABLE 7—CHEMICAL RULE IMPLEMENTATION ISSUES IDENTIFIED THAT FALL WITHIN THE SCOPE OF AN NPDWR REVIEW Implementation issue Description of issue Nitrate Alternative MCL in Non-community Water Systems. EPA evaluated the possibility of removing or further restricting the options for some NCWSs to use an alternative nitrate-nitrogen MCL of up to 20 mg/L. The nitrate-nitrogen MCL specified for PWSs in 40 CFR 141.62 is 10 mg/L and is based on the critical health endpoint of methemoglobinemia in children under six months of age. 40 CFR 141.11 provides States the discretion to use an alternative MCL of 20 mg/L for non-community water systems (NCWS). This alternative MCL is allowed under certain conditions—including that water would be unavailable to children under six months of age. Monitoring requirements for nitrate-nitrogen are specified in the introductory text to 40 CFR 141.23, which states that ‘‘Non-transient, non-community water systems shall conduct monitoring to determine compliance with the maximum contaminant levels specified in § 141.62 in accordance with this section. Transient, non-community water systems (TNCWS) shall conduct monitoring to determine compliance with the nitrate and nitrite MCL in §§ 141.11 and 141.62 (as appropriate) in accordance with this section.’’ Potential concerns with the current rule provisions were identified as: • The alternative MCL does not address any nitrate-induced health concerns beyond methemoglobinemia and • While § 141.11 allows the use of the alternative MCL by all eligible NCWS, § 141.23 implies that only TNCWS, a subcategory of NCWS, are eligible to use the alternative MCL. To determine the scope of this issue, the agency reviewed state drinking water regulations and analyzed SYR 4 ICR nitrate compliance data and identified nominal application of the alternative nitrate MCL by NCWSs. In addition, the nitrate and nitrite human health assessments are currently being evaluated by the EPA IRIS program. An updated assessment could inform the potential health effects of nitrate exposure to levels between 10 and 20 mg/L on adult populations. EPA will consider all available and updated human health assessments as it conducts future cycles of the six-year review. Currently, community water systems (CWSs) and NTNCWSs are required to monitor for nitrate quarterly if a sample is greater than or equal to 50 percent of the nitrate MCL (§ 141.23). TNCWSs are required to monitor for nitrate annually (§ 141.23(d)(4)). In the preamble to the 1991 final Phase II rule, the agency describes TNCWSs as being subject to the quarterly monitoring requirement stating that ‘‘EPA has decided to retain the 50 percent trigger for increased nitrate monitoring in the case of nitrate and also to extend this requirement to TWSs’’ (56 FR 3566, USEPA, 1991). EPA notes the conflict between the regulatory text and the preamble. To evaluate whether it may be appropriate to revise the nitrate NPDWR, the agency analyzed compliance monitoring data collected under the SYR 4 ICR. EPA found that while the majority of TNCWSs that reported detections equal or greater than 50 percent of the nitrate MCL did not conduct quarterly monitoring afterward, the number of these systems appears relatively small. Due to the limited scope of this issue, EPA is not revising the monitoring requirements at this time but will consider monitoring requirements if NPDWRs are revised in the future. ddrumheller on DSK120RN23PROD with RULES1 Nitrate Monitoring Frequency in Transient Noncommunity Water Systems. VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 PO 00000 Frm 00045 Fmt 4700 Sfmt 4700 E:\FR\FM\23JYR1.SGM 23JYR1 59636 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations TABLE 7—CHEMICAL RULE IMPLEMENTATION ISSUES IDENTIFIED THAT FALL WITHIN THE SCOPE OF AN NPDWR REVIEW— Continued Implementation issue Description of issue Nitrite Monitoring Frequency ..................... According to 40 CFR 141.23(e)(1), all PWSs were required to monitor for nitrite once between January 1, 1993, and December 31, 1995. If this initial sample was less than 50 percent of the MCL (10 mg/L), systems ‘‘shall monitor at the frequency specified by the State‘‘. Though the nitrite monitoring frequency is not explicitly stated in the CFR, EPA’s guidance provides that this frequency should be at least once every 9-year compliance cycle (USEPA, 2020d). EPA is aware that some States may not require systems to conduct routine nitrite monitoring when sample results are less than 50 percent of the MCL. Because sample results below the MCL are not reported to EPA, the scope of this issue is uncertain. To address this uncertainty, EPA analyzed State regulations and nitrite compliance monitoring data to characterize the frequency of nitrite monitoring. Results indicated that a majority of systems monitored for nitrite at least once during the last 9-year compliance cycle (2011–2019). EPA intends to work with States to encourage more systems to sample for nitrite at least once during each 9-year compliance cycle. In 40 CFR 141.62, the MCL for nitrate is specified as 10 mg/L and the MCL for total nitrate and nitrite is also specified as 10 mg/L. Sampling and analytical requirements as specified in 40 CFR 141.23, however, only included nitrate and left total nitrate and nitrite monitoring up to the discretion of States. Using Safe Drinking Water Information System (SDWIS) compliance data, EPA is aware that at least half of the States allow total nitrate/nitrite analysis to determine compliance with the nitrate MCL. To characterize monitoring practices for the nitrate MCL, the Agency analyzed Six-Year Review 4 compliance monitoring data for both nitrate and total nitrate/nitrite. This evaluation aims to serve as a baseline to assess nitrate monitoring practices in the future, in response to the 2020 EPA guidance outlining best practices when using total nitrate/nitrite analysis for monitoring compliance with the nitrate MCL. EPA is not revising the monitoring requirements at this time but will consider monitoring requirements in § 141.23 if NPDWRs are revised in the future, to incorporate best practices similar to those described in recent guidance (USEPA, 2020e). Total Nitrate and Nitrite Analysis for Nitrate MCL Monitoring. 3. Select NPDWRs With New Information Not Appropriate for Revision The NPDWRs discussed in this section had new information identified, but EPA has determined they are not appropriate for revision at this time due to: (1) data gaps or emerging information that are necessary for EPA to evaluate as part of a review or; (2) new information that suggests low or no meaningful opportunity to provide greater public health protection. Examples of data gaps and emerging information identified during the review include an analytical monitoring challenge, a compliance reporting limitation, and an anticipated health effects assessment being developed by another U.S. Federal Agency. Specific details about the data gaps and emerging information identified during the review for on cyanide, fluoride, nitrate, nitrite, TCE, and PCE are provided below. ddrumheller on DSK120RN23PROD with RULES1 Cyanide EPA published the current MCL and MCLG of 0.2 mg/L (200 mg/L) for free cyanide on July 17, 1992 (57 FR 31776, USEPA, 1992). In 2010, EPA published an IRIS assessment (USEPA, 2010b), which identified a new reproductive health effect endpoint that supports decreasing the MCLG from 200 mg/L to 4 mg/L. Analytical feasibility information identified in Six-Year Review 3 and Six-Year Review 4 VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 supports a PQL reduction to as low as 50 mg/L. In Six-Year Review 3, cyanide was listed as ‘‘low priority’’ due to low occurrence at levels below the current MCL. Analysis of Six-Year Review 4 occurrence data identified greater occurrence with 328 systems serving 8.1 million people with mean concentrations above 50 mg/L (see Table 6 of this document). However, occurrence was limited to few states (USEPA, 2024h). EPA considered these occurrence results and the potential for a meaningful opportunity to improve the level of public health protection. Two analytical monitoring challenges complicate interpretation of the occurrence data. As described in section V.B.2 of this document, an analytical artifact created by ascorbic acid pretreatment of drinking water samples, which had been disinfected with chloramines, can result in false positives for free cyanide (USEPA, 2020f). An EPA guidance document (USEPA, 2020f) identified solutions to address this analytical challenge, but the general awareness of the availability of this guidance is uncertain. Second, EPA is aware that some systems analyze samples for total cyanide, and if the results are lower than the MCL, these systems report the total cyanide results as free cyanide. Systems may achieve cost savings by analyzing samples for total cyanide; however, using results for total cyanide instead of free cyanide could potentially overestimate the PO 00000 Frm 00046 Fmt 4700 Sfmt 4700 actual occurrence of free cyanide. Free and total cyanide results cannot be distinguished in the Six-Year Review 4 ICR dataset because the Safe Drinking Water Information System (SDWIS) State-version that many primacy agencies use to manage SDWA compliance monitoring data does not have an analyte code for total cyanide. Because the numerical benchmark used for occurrence is significantly lower than the current cyanide MCL, some of the reported concentrations may be for total cyanide. Therefore, the Six-Year Review 4 occurrence analysis likely overestimates free cyanide occurrence. For these reasons, EPA does not believe it is appropriate to list the cyanide NPDWR as a candidate for revision at this time. EPA intends to help address these data gaps by continuing to disseminate the 2020 guidance on analytical methods for cyanide and may consider an additional analyte code for total cyanide in the SDWIS reporting system. Further discussion of the cyanide monitoring issues can be found in USEPA (2024h). Fluoride EPA published the MCL and MCLG of 4.0 mg/L for fluoride on April 2, 1986 (51 FR 11396, USEPA, 1986) based on the critical health endpoint of crippling skeletal fluorosis. EPA also established a secondary MCL/MCLG at 2.0 mg/L to protect against cosmetically objectionable dental fluorosis E:\FR\FM\23JYR1.SGM 23JYR1 ddrumheller on DSK120RN23PROD with RULES1 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations (discoloration and/or pitting of teeth). Certain drinking water systems may choose to fluoridate finished water as a public health protection measure for reducing the incidence of cavities. The U.S. Public Health Service (PHS) recommendation for the optimal community water fluoridation level is 0.7 mg/L (U.S. Department of Health and Human Services, 2015). The decision to fluoridate a community water supply is made by the state or local municipalities and is not required by EPA or any other federal entity. Fluoride is also added to various consumer products, such as toothpaste and mouthwash. EPA has reviewed the NPDWR for fluoride in prior Six-Year Reviews. As a result of Six-Year Review 1, EPA requested that the National Research Council (NRC) of the National Academies of Sciences (NAS) conduct a review of the health and exposure data on orally ingested fluoride. In 2006, the NRC published the results of its review and concluded that severe dental fluorosis can be an adverse health effect (NRC, 2006). The NRC report recommended that EPA develop a doseresponse assessment for severe dental fluorosis as the critical health endpoint and update an assessment of fluoride exposure from all sources. In 2010, EPA published Dose Response Analysis for Noncancer Effects (USEPA, 2010d), which was considered under Six-Year Review 3. For more information, please see Appendix C of the Six-Year Review 3 Health Effects Assessment for Existing Chemical and Radionuclide National Primary Drinking Water Regulations— Summary Report (USEPA, 2016). In SixYear Review 3, EPA did not recommend the fluoride NPDWR for revisions citing limited agency resources, prioritization of other contaminants, ongoing health effects research, and other factors that were anticipated to reduce the U.S. population’s exposure to fluoride via drinking water (82 FR 3531, USEPA, 2017a). In Six-Year Review 4, EPA again considered the 2010 EPA assessment to derive a lower potential MCLG of 0.9 mg/L. Review results are provided in section V.B.2. of this document. Available published literature on other health effect categories including neurotoxicity and behavior, reproduction and development, endocrine effects, and cancer were reviewed in the EPA assessment (USEPA, 2010d). However, based on the review of the available literature at the time, EPA determined that the data for these other health effects associated with fluoride exposure were insufficient to support their selection as critical VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 effects for potential MCLG derivation (USEPA, 2010d). EPA is aware of ongoing efforts by the National Toxicology Program (NTP) to conduct a systematic review and meta-analysis of the published literature on developmental neurotoxicity for fluoride. In May 2023, NTP released the Draft ‘‘NTP Monograph on the State of the Science Concerning Fluoride Exposure and Neurodevelopmental and Cognitive Health Effects: A Systematic Review’’ (NTP, 2023); however, the NTP systematic review and meta-analysis are not health assessments that could be used to directly inform the derivation of a potential MCLG. Due to emerging research published on developmental neurotoxicity after fluoride exposure coupled with competing workloads and other ongoing high priority actions (see section V.A of this document.), EPA has decided that the fluoride NPDWR is not a candidate for revision at this time. In addition, the NTP has not made a final decision about the report’s developmental neurotoxicity systematic review conclusions and has not formally released a final report. Following publication of the final NTP report, EPA will consider the systematic review and meta-analysis conclusions regarding developmental neurotoxicity to inform the agency’s future development of a health effects assessment for fluoride. See USEPA (2024f) Appendix B for more information. Nitrate and Nitrite EPA published the MCLs and MCLGs for nitrate (10 mg/L) and nitrite (1 mg/ L) based on the critical endpoint of methemoglobinemia (blue baby syndrome) on January 30, 1991 (56 FR 3526, USEPA, 1991). Nitrate and nitrite were not reviewed in detail under SixYear Review 3 due to ongoing IRIS assessments at that time. Although the development of the IRIS assessment for nitrate and nitrite was suspended in December 2018, EPA has restarted development of their health assessment for nitrate and nitrite as indicated in the October 2023 IRIS Program Outlook. The agency recently released the ‘‘Protocol for the Nitrate and Nitrite IRIS Assessment (Oral)’’ for public comment on November 9, 2023 (88 FR 77310, USEPA, 2023b). EPA plans to evaluate whether a revision of the nitrate and nitrite NPDWRs is appropriate, once the final IRIS assessment is available. Trichloroethylene (TCE) and Tetrachloroethylene (PCE) The NPDWR for TCE was published on July 8, 1987 (52 FR 25690, USEPA, 1987) and the NPDWR for PCE was published on January 30, 1991 (56 FR PO 00000 Frm 00047 Fmt 4700 Sfmt 4700 59637 3526, USEPA, 1991). Both TCE and PCE are classified as carcinogens and have MCLGs and MCLs of zero and 5 mg/L, respectively. The MCLs were based on analytical feasibility at the time of rule promulgation. TCE and PCE were both listed as candidates for revision in SixYear Review 2, based on updated analytical feasibility, treatment, and occurrence information. In 2011, EPA announced plans to address a group of regulated and unregulated carcinogenic volatile organic contaminants (cVOCs) in a single regulatory effort. The eight regulated contaminants that were evaluated for the cVOCs group regulation included benzene, carbon tetrachloride, 1,2-dichloroethane, 1,2dichloropropane, dichloromethane, PCE, TCE, and vinyl chloride. In SixYear Review 3, these contaminants were categorized under recent, ongoing, or planned regulatory action and were not reviewed. The cVOC group regulation was not promulgated, as a result these eight contaminants were reviewed again during Six-Year Review 4. EPA has determined that TCE and PCE are no longer candidates for revision at this time based on updated information. In Six-Year Review 2, EPA assessed analytical information that supported reducing the PQL and evaluated occurrence for TCE and PCE at 0.5 mg/ L. As shown in Tables 5 and 6 of this document, EPA identified information in Six-Year Review 4 that again supported assessing occurrence at that level. The average TCE concentration exceeded 0.5 mg/L in 297 systems, representing 0.57 percent of the systems assessed nationwide and serving approximately 13 million people. Similarly, the average PCE concentration exceeded 0.5 mg/L in 432 systems, which represent 0.83 percent of the approximately 50,000 PWSs assessed nationwide and serve approximately 16 million people. These occurrence results are consistent with the Six-Year Review 2 estimates (75 FR 15500, March 29, 2010, USEPA, 2010a). The most recent final IRIS assessments for TCE (USEPA, 2011) and PCE (USEPA, 2012) were completed after the Six-Year Review 2 results were published and have been selected as the health assessments relevant to chronic toxicity for TCE and PCE in Six-Year Review 4 (USEPA, 2024f). The updated IRIS assessments maintained the classification of ‘‘carcinogenic to humans,’’ and therefore do not support a change to the MCLGs of zero for either TCE or PCE. Based on the Six-Year Review 4 occurrence estimates described above, EPA considered if there was a potential for an increase in E:\FR\FM\23JYR1.SGM 23JYR1 59638 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations human health protection at the lower identified level. To evaluate this potential, EPA examined the cancer risk level associated with the current MCLs (5 mg/L) and the screening level (0.5 mg/ L) using updated occurrence and health effects information from Six-Year Review 4. The cancer risk levels at the current MCLs for TCE and PCE are 1 × 10¥5 (USEPA, 2011) and 3.0 × 10¥7 (USEPA, 2012), respectively. These cancer risk levels correspond to excess lifetime cancer cases of 10 and 0.3 cases per million people, respectively. At the screening level of 0.5 mg/L, the risk per million people would be 1 case for TCE and 0.03 cases for PCE. The implied number of baseline cancer cases over a 70-year exposure period is unlikely to exceed 120 total cases for TCE and 5 total cases for PCE. This corresponds to annual averages of 1.7 and 0.07 cases for TCE and PCE, respectively. This new information identified since Six-Year Review 2 indicates that revising the MCLs for either TCE or PCE would result in relatively small health risk reductions among the exposed population and would divert significant resources from other planned and ongoing work. Therefore, EPA has determined that TCE and PCE are considered ‘‘low priority’’ and are no longer candidates for revision. ddrumheller on DSK120RN23PROD with RULES1 C. Microbial Contaminants Regulations As discussed in section III of this document, the initial review branch of the review protocol identifies NPDWRs that have recently been recently competed or are being reviewed in ongoing or pending regulatory actions. Excluding such contaminants from a more detailed review in the Six-Year Review 4 prevents duplicative Agency efforts. Based on the initial review and considering the ongoing rulemaking activities for the Microbial and Disinfection Byproduct Rules, EPA did not perform a more detailed review for the Surface Water Treatment Rule (SWTR), the Interim Enhanced Surface Water Treatment Rule (IESWTR), the Long-Term 1 Enhanced Surface Water Treatment Rule (LT1ESWTR), and the Stage 1 and Stage 2 Disinfectants and Disinfection Byproducts Rules. The following microbial contaminant regulations were subject to a more detailed review for the Six-Year Review 4: • Revised Total Coliform Rule (RTCR) • Long Term 2 Enhanced Surface Water Treatment Rule (LT2) • Ground Water Rule (GWR) • Aircraft Drinking Water Rule (ADWR) • Filter Backwash Recycling Rule (FBRR) VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 Background information on each of the microbial contaminant regulations is presented in the subsequent sections. EPA is conducting its first detailed review of the RTCR and the ADWR as part of the Six-Year Review. The RTCR and the ADWR were excluded from a detailed review in Six Year Review 3 because they were promulgated in 2013 and 2009, respectively. These microbial contaminants regulations establish treatment technique (TT) requirements in lieu of MCLs, except in the RTCR, EPA also established an MCL for Escherichia coli (E. coli) and TT requirements for total coliform. In accordance with the SixYear Review Protocol, during the sixyear review process, EPA assesses whether new health risk, analytical methods, or treatment information indicate possible TT revision. For the RTCR, the regulatory review determines whether new information indicates potential revision to the MCL for E. coli. The elements of the RTCR, LT2, GWR, and ADWR regulations that were reviewed for Six-Year Review 4 were: health effects, analytical feasibility, occurrence and exposure, and treatment feasibility. For the RTCR, LT2, GWR, and ADWR regulations, the EPA did not find any new relevant information as it relates to analytical feasibility. For all the other elements reviewed a summary of the findings is included in the subsequent sections. In addition, detailed information about the review is provided in the ‘‘Six-Year Review 4 Technical Support Document for Microbial Contaminant Regulations’’ (USEPA, 2024m). At this time, none of the reviewed microbial contaminant rules are being identified as a candidate for regulatory revision. 1. Revised Total Coliform Rule Background EPA promulgated the Revised Total Coliform Rule (RTCR), a revision to the Total Coliform Rule, on February 13, 2013 (78 FR 10269, USEPA, 2013). The Total Coliform Rule (TCR) was promulgated on June 29, 1989 (54 FR 27544, USEPA, 1989). The purpose of the revision was to increase public health protection through the reduction of potential entry pathways for fecal contamination into distribution systems. The TCR required all public water systems (PWSs) to monitor for the presence of total coliforms and Escherichia coli (E. coli)) in the distribution system at a frequency dependent on the size (population served by) of the system. Under the TCR, a maximum contaminant level PO 00000 Frm 00048 Fmt 4700 Sfmt 4700 (MCL) was established based on the presence or absence of total coliforms with the intent to address contamination that could enter into distribution systems. The RTCR revised the TCR to eliminate the MCL for total coliforms and established an MCLG and MCL for E. coli of zero. The RTCR also requires PWSs that have an indication of coliform contamination (e.g., as a result of total coliform positive samples, E. coli MCL violations or performance failure) to find and assess the problem, identify sanitary defects and take corrective action. There are two levels of assessments (i.e., Level 1 and Level 2) based on the severity or frequency of the problem. Summary of Review Results Information available for national occurrence and exposure indicates that both routine total coliform and E. coli positive rates have decreased after the implementation of RTCR. EPA concludes that no regulatory revisions to the RTCR are appropriate at this time based on the review of available information. Health Effects Collier et al. (2021) estimated the collective U.S. disease burden attributable to over a dozen waterborne illnesses from infectious pathogens found in the distribution system (vibriosis, campylobacteriosis, cryptosporidiosis, giardiasis, Legionnaire’s disease, salmonellosis, shigellosis, infections by nontuberculous mycobacteria (NTM), norovirus, Shiga-toxin-producing E. coli, otitis externa, pneumonia, and septicemia). These researchers estimated the total disease burden at approximately 7.15 million cases annually, with an estimated 118,000 hospitalizations and 6,630 deaths. In this analysis, waterborne disease is understood to include gastrointestinal, respiratory, and systemic disease attributable to both drinking-water and non-drinking-water exposure. From further evaluation of this study’s cases, Gerdes et al. (2023) determined 1.13 million of these illnesses were attributable to drinking water. According to the estimates presented in these studies, the opportunistic pathogens (Legionella, Nontuberculous Mycobacteria (NTM), and Pseudomonas) impose a greater public health burden than the fecal pathogens. Of the estimated 7.15 million infectious waterborne illnesses in 2014 in the United States, drinking water exposure caused 40 percent of hospitalizations and 50 percent of deaths. E:\FR\FM\23JYR1.SGM 23JYR1 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations Occurrence and Exposure To evaluate potential pathogenic contamination in distribution systems EPA analyzed national compliance monitoring data from the SYR 4 ICR dataset (USEPA, 2019. EPA assessed the trends that may be associated with the implementation of the RTCR and found a statistically significant decline for total coliform positive results from years of 2014–2015 to 2018–2019 (i.e., before and after the implementation of RTCR respectively). The result suggests that the presence of these indicator organisms in the distribution system was declining. The trend of declining positive total coliform results was observed across different types of public water systems, water sources (ground water versus surface water), and system sizes (small versus large). With respect to the fecal contamination indicator E. coli, the observed decreasing trend was not supported by a statistical test of significance. EPA also found that the absolute number of E. coli positives were low, suggesting that the treatment techniques are effective (USEPA, 2024m). ddrumheller on DSK120RN23PROD with RULES1 Treatment Feasibility In this section as part of Six-Year Review process, EPA evaluated new information about tools and treatment techniques. Since the major treatment technique requirements under the RTCR are assessments followed by corrective actions (if total coliform and/or E. coli are detected), EPA evaluated the effectiveness of such requirements by comparing total coliform and E. coli positive rates after completion of either Level 1 or Level 2 assessments (USEPA, 2024m). EPA found about an 80 percent decrease in both routine total coliform and E. coli positive rates, two months after completion of RTCR assessments for systems having a monthly monitoring schedule. These analytical results and newly compiled information suggest that the ‘‘find and fix’’ approach prescribed under the provisions of assessments and corrective action within RTCR appears to work as intended for reducing the microbial occurrence in distribution systems and may be improving public health protection from microbial risks (as indicated by a substantial drop of the total coliform and E. coli positive rates following completion of corrective actions to respond to assessments). VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 2. Long Term 2 Enhanced Surface Water Treatment Rule Background EPA promulgated the Long Term 2 Enhanced Surface Water Treatment Rule, hereafter referred to as ‘‘LT2’’, on January 5, 2006 (71 FR 654, USEPA, 2006a). The LT2 applies to all PWSs that use surface water or ground water under the direct influence of surface water. The LT2 builds upon the IESWTR and the LT1 by improving control of microbial pathogens and by focusing on systems with elevated Cryptosporidium contamination risk. The purposes of the LT2 are to protect public health from illness arising from exposure to Cryptosporidium and other microbial pathogens in drinking water and to prevent significant increases in risks that might occur when systems implement drinking water disinfection byproduct rules. Key provisions in the LT2 include: source water monitoring for Cryptosporidium (with a screening procedure to reduce monitoring costs for small systems); risk-targeted Cryptosporidium treatment by filtered systems with the highest source water Cryptosporidium levels; inactivation of Cryptosporidium by all unfiltered systems; criteria for the use of Cryptosporidium treatment and control processes; and covering or treating uncovered finished water storage facilities. The LT2 requires PWSs using surface water or ground water under the direct influence of surface water to monitor their source waters for Cryptosporidium and/or E. coli to identify additional treatment requirements. PWSs must monitor their source water (i.e., the influent water entering the treatment plant) over two different timeframes (defined as Round 1 and Round 2) to determine the occurrence of Cryptosporidium. Monitoring results determine the extent of Cryptosporidium treatment requirements under the LT2. According to the LT2 rule requirements, all PWSs were to complete Round 2 by 2021. To reduce monitoring costs, small filtered PWSs (serving fewer than 10,000 people) which initially monitor for E. coli for one year as a screening analysis, are required to monitor for Cryptosporidium only if their E. coli levels exceed specified trigger values. Small filtered PWSs that exceed the E. coli trigger, as well as small unfiltered PWSs, must monitor for Cryptosporidium for one or two years, depending on the sampling frequency. The LT2 also requires all unfiltered PWSs to provide at least 2 to 3-log (i.e., PO 00000 Frm 00049 Fmt 4700 Sfmt 4700 59639 99 to 99.9 percent) inactivation of Cryptosporidium. Further, under the LT2, unfiltered PWSs must achieve their overall inactivation requirements (including Giardia lamblia and virus inactivation as established by earlier regulations) using a minimum of two disinfectants. Under the LT2, PWSs with uncovered finished water reservoirs (UCFWR) must either cover the storage facility or treat the water leaving the storage facility to achieve inactivation and/or removal of 4-log virus, 3-log Giardia lamblia and 2log Cryptosporidium using a protocol approved by the state (USEPA, 2006a). Most finished water reservoirs for surface water systems are covered. All PWSs with UCFWRs are under administrative orders or compliance agreements to cover or treat their UCFWR. Summary of Review Results From a review of the literature on Cryptosporidium health effects, EPA concludes that there is no new health information to suggest a need to modify the LT2. In addition, EPA determined that no regulatory revisions to the microbial toolbox options are appropriate at this time. During SixYear Review 4, EPA did not consider disinfection profiling information since EPA is evaluating overall filtration and disinfection requirements in the SWTRs as part of the on-going consideration of potential revisions to the MDBP rules. For more information regarding EPA’s review of treatment feasibility see the ‘‘Six-Year Review 4 Technical Support Document for Microbial Contaminant Regulations’’ (USEPA, 2024m). Health Effects Since 1995, cryptosporidiosis has been a nationally notifiable disease, meaning healthcare providers and laboratories that diagnose cases of laboratory-confirmed cryptosporidiosis are required to report cases to their local or state health departments, which in turn report the cases to CDC. Since 2012, there have been four reported outbreaks of cryptosporidiosis from public water systems to CDC. The four outbreaks together resulted in a total of 201 recorded illnesses, 2 hospitalizations, and no deaths (CDC, 2022). Although cryptosporidiosis is a nationally notifiable disease, additional outbreaks may go unreported to CDC or may have been recorded as of uncertain causes. In addition, since CDC’s National Outbreak Reporting System is specifically focused on outbreaks, it does not capture rates of endemic disease of cryptosporidiosis from drinking water. E:\FR\FM\23JYR1.SGM 23JYR1 59640 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations ddrumheller on DSK120RN23PROD with RULES1 Occurrence and Exposure Based on the LT2 source water monitoring results, filtered systems were classified in one of four risk categories (Bins 1–4) to determine additional treatment needed. Systems in Bin 1 are not required to provide additional Cryptosporidium treatment. Systems in Bins 2–4 must achieve 1.0– 2.5 log of treatment (i.e., 90 to 99.7 percent reduction for Cryptosporidium) over and above that provided by conventional treatment, depending on the Cryptosporidium concentrations. Filtered PWSs must meet the additional Cryptosporidium treatment requirements in Bins 2, 3, or 4 by selecting one or more technologies from the microbial toolbox to ensure source water protection and management, and/ or Cryptosporidium removal or inactivation. All unfiltered water systems must provide at least 99 or 99.9 percent (2 or 3-log) inactivation of Cryptosporidium, depending on their monitoring results. All filtered systems that provide 5.5 log treatment for Cryptosporidium are exempt from monitoring and subsequent bin classification. Six years after the initial bin classification following a first round of monitoring, filtered systems were required to conduct a second round of monitoring. Round 2 monitoring began in 2015. Round 2 monitoring was implemented to understand year-to-year variability for occurrence of Cryptosporidium. The difference observed between occurrence at the time of the ICR Supplemental Surveys and the LT2 Round 1 monitoring indicates year-to-year variability (USEPA, 2017a). Limited occurrence data for Cryptosporidium was available to EPA in response to the SYR 4 ICR since fewer than 1 percent of the Cryptosporidium monitoring records provided actual concentration levels with units of oocysts/L; however, the data about system binning for about 300 PWSs serving populations larger than 10,000 was provided. Those data indicate that the percentage of PWSs potentially moving to an ‘‘action bin’’ based on Round 2 monitoring would not be substantially higher than the percentage estimated based on modeling conducted during the LT2 review included as part of the Six-Year Review 3, thus suggesting no change to the review decision made under Six-Year Review 3. Treatment Feasibility The LT2 includes a variety of treatment and control options, VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 collectively termed the ‘‘microbial toolbox,’’ that PWSs can implement to comply with the LT2’s additional Cryptosporidium treatment requirements. Most options in the microbial toolbox carry prescribed credits toward Cryptosporidium treatment and control requirements. The LT2 Toolbox Guidance Manual (USEPA, 2010e) provides guidance on how to apply the toolbox options. For the Six-Year Review 4, EPA reviewed additional research into the relationship between ultraviolet light (UV) dose and log inactivation. Some studies showed the same log inactivation at UV doses lower than those reported in previous EPA guidance, and other studies showed log inactivation at UV doses higher than those contained in the guidance. Since there is not a consensus of log inactivation at levels significantly lower than EPA prior published guidance, EPA concludes that the new information does not support changes to the UV dose table. EPA also reviewed new information pertaining to technologies, which have not been included in the existing LT2 toolbox guidance manual, and which may be effective for the removal or inactivation of protozoa including Cryptosporidium. In addition, EPA also reviewed new technologies that water systems may be employing to improve treatment performance for complying with the MDBP rules, e.g., turbo coagulation and powdered activated carbon. Initiatives by states and EPA’s Area Wide Optimization Program were evaluated as well. EPA found that this new information appears insufficient to develop quantification criteria for inactivation and removal credit for Cryptosporidium. 3. Ground Water Rule Background EPA promulgated the Ground Water Rule (GWR) in 2006 (71 FR 65574, USEPA, 2006b) to provide protection against microbial pathogens in PWSs using ground water sources. The rule establishes a risk-based approach to target undisinfected ground water systems that are vulnerable to fecal contamination. In addition to the protection provided by the RTCR and GWR monitoring requirements, systems that do not disinfect are also protected by the sanitary survey provisions of the GWR and the treatment technique provisions of the RTCR. The GWR required compliance beginning December 1, 2009. Since the triggered source water monitoring provision was built upon the PO 00000 Frm 00050 Fmt 4700 Sfmt 4700 compliance monitoring results of total coliform and E. coli under the TCR and later RTCR, implementation of the GWR was not yet completed for the period of time covered by the Six-Year Review 3 ICR (2006–2011). The RTCR was promulgated in 2013 and became effective on April 1, 2016. EPA expected that implementation of the RTCR might impact the percent of ground water systems that would be triggered into source water monitoring and taking any corrective actions under the GWR. Therefore, the effects of the GWR and the RTCR implementation in addressing vulnerable ground water systems were not reviewed during the Six-Year Review 3 process. Summary of Review Results The information considered during this review suggest that microbial pathogens have been detected in untreated ground water samples which show no presence of fecal indicators, however these studies are limited in quantity and the prevalence of endemic disease from microbial contamination of untreated ground water cannot be well characterized with the available information (USEPA, 2024m). Additional and more robust studies are needed to further understand the magnitude of the issue. EPA concludes that no regulatory revisions to the GWR are appropriate at this time. Health Effects Waterborne pathogens can cause mild to severe illnesses (Wallender et al., 2014). These illnesses may include; acute gastrointestinal illness (AGI) with diarrhea, abdominal pain/discomfort, nausea, vomiting, conjunctivitis, aseptic meningitis, and hand-foot-and-mouth disease. Infections from some waterborne pathogens (e.g., Campylobacter) may cause long-term implications, such as reactive arthritis, Guillain-Barré syndrome, and irritable bowel syndrome (Keithlin et al., 2014). Other more severe illnesses include hemolytic uremic syndrome (HUS) (kidney failure), hepatitis, and bloody diarrhea (WHO, 2004). Some studies have indicated that waterborne pathogens such as adenovirus, enteroviruses, hepatitis A, norovirus, rotavirus, Salmonella, Giardia, Cryptosporidium, and Shigella have been found in untreated ground water samples (Borchardt et al., 2012; Wallender et al., 2014; Stokdyk et al., 2020). Human enteric viruses have been detected in drinking water free of bacterial indicators, such as total coliform. With total coliform detections rates similar to the average rate for E:\FR\FM\23JYR1.SGM 23JYR1 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations ddrumheller on DSK120RN23PROD with RULES1 undisinfected community PWSs in the U.S, Borchardt et al. (2012) estimated a six to 22 percent attributable risk for enteric illness from viruses present in the communities’ drinking water. In another study, Burch et al. (2022) found that noncommunity wells had higher infection risk than community wells. Burch et al. (2022) found the annual risk was relatively high for all pathogens combined in the study, while the average daily doses for individual pathogens were low, indicating that significant risk results from sporadic pathogen exposure. Studies by Fout et al. (2017) and Stokdyk et al. (2020) found that total coliform (and other indicators like E. coli, somatic phage, HF183, and Bacteroidales-like HumM2) tend to have high specificity, meaning that absence of the indicator provides relatively strong assurance that water is free of viral and other pathogens, but also have low sensitivity, meaning that presence of the indicator does not necessarily predict presence of pathogens. Occurrence and Exposure Similar to the RTCR, EPA examined the national compliance monitoring data collected for the Six-Year Review 4 to understand how total coliform and E. coli, indicators of contamination behaved before and after implementation of the GWR, as well as understanding how level of contamination for high risk undisinfected ground water systems have changed. As noted, GWR monitoring is based on initial monitoring under the RTCR. If a system has a positive total coliform sample (based on routine coliform monitoring under the RTCR), the system must test that sample for the presence of E. coli. Under the GWR, ground water systems that do not provide at least 4log treatment of viruses and are notified of a routine positive total coliform sample collected under RTCR must collect and analyze at least one source water sample for E. coli or other fecal indicators from each ground water source (well) within 24 hours. If the triggered source water sample has a positive for E. coli the ground water systems must take corrective action. EPA conducted a distribution system total coliform/E. coli data exploration and analysis effort to identify findings that could inform the risk reduction of the fully implemented GWR, as well as characterize high risk systems. The national average total coliform and E. coli rates (i.e., total number of positives divided by total number of samples) before and after implementation of the GWR were VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 calculated using Six-Year Review 3 and Six-Year Review 4 datasets. The analytical results were grouped by system sizes and disinfection status (i.e., disinfecting versus and undisinfected). The period of analysis was from 2007– 2008 (before the GWR was implemented) to 2014–2015 (after the completed implementation of the first round of sanitary surveys under the GWR). The total coliform rates across different system categories decreased, suggesting that there may be less pathogenic contamination pathways and so potentially less microbial exposure, corresponding to the period when the GWR was being implemented. This downward change is supported by a statistical significance test. The declining count of the fecal contamination indicator, E. coli was not supported by a test of statistical significance. Yet numbers of E. coli positives were consistently low, which may indicate low exposure to fecal contamination. EPA performed a more specific analysis using a statistical model focused on the most vulnerable water systems, the undisinfected ground water systems. EPA conducted statistical modeling focused on examination of total coliform levels in small ground water systems to account for their infrequent sampling and relatively low level of monitoring observations compared to larger systems that monitor more frequently. There are approximately 45,000 undisinfected ground water systems associated with total coliform records collected and less than 1 percent population among the population served by the public community water systems in the U.S. (based on SYR 4 ICR data). Most undisinfected ground water systems serve small permanent populations or transient populations. EPA found that the smallest systems (serving a population fewer than 1,001) have higher median total coliform rates than undisinfected larger systems. In addition, the analysis indicates that median occurrence rates for many undisinfected transient systems may have fallen, from four to three percent total coliform detection rate from 2011 to 2019. Another finding from the statistical modeling is that the number of non-community systems that have high total coliform detections in the systems serving fewer than 1,001 people has remained roughly the same, about 7,000 undisinfected ground water systems, when running a comparison using Six-Year Review 3 and Six-Year Review 4 ICR data with a threshold of five percent rate of total coliform positive detections, which is the PO 00000 Frm 00051 Fmt 4700 Sfmt 4700 59641 threshold that triggers a Level 1 Assessment in the RTCR. For statistical analysis of E. coli detection rates, there was not sufficient data to make estimates of averages and numbers of systems exceeding high levels. Two implications of these modelling results should be noted as it relates to estimating potential exposure and occurrence. One is that the noncommunity systems serving fewer than 1,001 have total coliform positive rates around two to four percent, while a study of 14 community systems served by untreated ground water in Wisconsin found that a total coliform positive rate of 2.3 percent was associated AGI burden (Borchardt et al, 2012). EPA concludes, however, that studies indicating microbial disease burden at total coliform positive levels found in high-risk systems are limited in number as mentioned in the Health Effects section, as well as in geographic scope. Another implication from the results of this statistical analysis is that the remaining systems with very high total coliform rates could suggest compliance challenges among small ground water systems. In addition to evaluating trends with indicators under RTCR to evaluate protection for vulnerable ground water systems, EPA also considered the results from the GWR requirement for triggered source water sampling. The sample results indicate that there is a small percent of positive source water E. coli detections ranging from 0.76 percent to 1.99 percent of E. coli samples for noncommunity systems which are primarily undisinfected systems, and 250 out of 270 of source water E. coli detections were associated with undisinfected systems serving fewer than 500 people. The other fecal indicators, coliphage and enterococci were used very infrequently, and data was insufficient to evaluate. Low incidence of fecal indicators may indicate low exposure to fecal contamination among undisinfected ground water systems. Treatment Feasibility Per treatment technique requirements under the GWR, there are two scenarios that trigger ground water systems to take corrective actions: (1) positive results of the triggered source water monitoring, and (2) significant deficiencies found during Sanitary Survey (EPA was not able to assess sanitary surveys directly given data limitations). EPA evaluated whether treatment was improving under the GWR by using the RTCR occurrence analysis data to consider total coliform rates before and after the GWR was implemented. E:\FR\FM\23JYR1.SGM 23JYR1 ddrumheller on DSK120RN23PROD with RULES1 59642 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations EPA developed a systematic approach to identify disinfection status of ground water systems for each of the years included in the Six-Year Review ICR datasets and found that the percentage of ground water systems that were disinfecting had increased consistently from 2007–2008 (before the GWR was implemented) to 2014–2015. This finding of an increasing number of systems disinfecting could be attributable to systems taking corrective actions to address positive results after triggered source water monitoring. The analytical results presented in the ‘‘SixYear Review 4 Technical Support Document for Microbial Contaminant Regulations’’ (USEPA, 2024m) also indicate that disinfecting ground water systems had substantially lower total coliform positive rates than undisinfected ground water systems. In addition, EPA also observed that the total coliform positive rates decreased after completion of the first round of sanitary surveys under the GWR among ground water systems. onboard drinking water, as well as selfinspections of each aircraft water system and immediate notification of passengers and crew when violations or specific situations occur. 4. Aircraft Drinking Water Rule Health Effects Limited new literature is available on the presence of microbial pathogens in aircraft drinking water. Handschuh et al. (2015) found that long-haul flights were significantly poorer in terms of microbial water quality than short haul flights. A follow-up study by Handschuh et al. (2017) demonstrated that there is a diversity of microorganisms within the aircraft drinking water supply chain. Other studies have also found microbial contaminants present in aircraft drinking water, including Pseudomonas aeruginosa, enterococci, clostridia, and Salmonella (WHO, 2009; Schaeffer et al., 2012). Tracking an illness back to contaminated water served on an aircraft presents a technical challenge. Most disease incubation periods are longer than the duration of a flight, and even if it is possible to determine that a disease was incurred in air travel, it may be difficult to determine if the route of transmission was from beverages, food, or close proximity of people, and to determine whether transmission happened on board the aircraft or at an air terminal. Background EPA promulgated the Aircraft Drinking Water Rule (ADWR) on October 19, 2009 (74 FR 53590, USEPA, 2009b). The primary purpose of the ADWR is to ensure that safe and reliable drinking water is provided to aircraft passengers and crew. This entails providing air carriers with a feasible way to comply with SDWA and NPDWRs. The existing NPDWRs were designed for traditional, stationary public water systems not mobile aircraft water systems that are operationally different. For example, aircraft fly to multiple destinations throughout the course of any given day and may board drinking water from sources at any of these destinations. Aircraft board water from airport watering points via temporary connections. Aircraft drinking water safety depends on a number of factors including the quality of the water that is boarded from these multiple sources, the care used to board the water, and the operation and maintenance of the onboard water system and the water transfer equipment. The ADWR’s provisions protect against disease-causing microbiological contaminants through the required development and implementation of aircraft water system operations and maintenance plans. The ADWR’s provisions include: routine disinfection and flushing of the water system, air carrier training requirements for key personnel, and periodic sampling of the VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 Summary of Review Results The ADWR is a unique rule within the context of the SDWA. This rule applies only to aircraft engaged in interstate commerce with onboard systems that provide water for human consumption through pipes. These aircraft water systems board finished water for human consumption and regularly serve an average of at least twenty-five individuals daily, at least 60 days out of the year. Human consumption includes water for drinking, hand washing, food preparation, and oral hygiene. From a review of available technical information within the scope of the review, EPA concludes that there is no new information to suggest that regulatory revisions to the ADWR are appropriate at this time. Occurrence and Exposure The Aircraft Reporting and Compliance System (ARCS) is used to facilitate the reporting of aircraft water system data under the ADWR. Air carriers subject to the ADWR must report to EPA about their inventory of aircraft water system fleet; the date the operations and maintenance plan was developed; the date the coliform PO 00000 Frm 00052 Fmt 4700 Sfmt 4700 sampling plan was developed; the date the aircraft water system sampling plan(s) was incorporated into the aircraft water system Operations and Maintenance plan; the date the Operations and Maintenance plan(s) was incorporated into the U.S. Federal Aviation Administration (FAA) accepted air carrier Operation and Maintenance program; the frequency for routine disinfection and flushing, and the corresponding routine total coliform sampling frequency; and the date for routine disinfection and flushing, routine coliform sampling dates and results, and corrective actions (when applicable). For Six-Year Review 4, EPA downloaded and reviewed compliance monitoring data available in ARCS as of May 2021. Approximately 140,000 records of aircraft water systems compliance monitoring data for total coliform and E. coli samples were available in ARCS from February 2011 through May 2021, including results reported for more than 70 different makes/models of aircraft. These results were used to characterize the positivity rates of total coliform and E. coli in aircraft water systems on an annual basis for the years that data were available (2011–2021) and for the subset of years 2012 through 2019. This approach removes potentially confounding considerations associated with evaluating data for calendar year 2020 when a large number of aircraft PWS were inactive due to COVID–19, as well as years 2011 and 2021 for which the ARCS data evaluated represents partial years. Monitoring data broken down by year for the years 2012–2019 shows an average annual total coliform positivity rate of 5.46 percent, with a median of 5.63 percent, a minimum of 3.76 percent and a maximum of 7.03 percent. The total coliform positivity rate decreased on an annual basis from 2012–2019. The average E. coli positivity rate was 0.26 percent, and the median rate was also 0.26 percent, with a minimum of 0.17 percent and a maximum of 0.33 percent. The E. coli positivity rate also decreased on an annual basis. Treatment Feasibility Under the ADWR, air carriers routinely disinfect and flush aircraft water systems at the frequency recommended by the water system manufacturer or, if not specified by the manufacturer, they may choose from one of four options. If corrective disinfection and flushing is chosen or required, air carriers follow the procedures in their O&M plans. Unscheduled flight disruptions to E:\FR\FM\23JYR1.SGM 23JYR1 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations perform corrective disinfection and flushing can be minimized by shutting off the water or preventing the flow of water to the taps. Before allowing unrestricted access to the aircraft water system, a complete set of follow-up samples must be collected and submitted for analysis after the disinfection and flushing event if triggered by a total coliform-positive sample and must be reported as total coliform-negative if triggered by an E. coli-positive sample. One study was identified that examined the effectiveness of disinfection and flushing procedures to prevent coliform persistence in aircraft water systems (Szabo et al., 2019). That study showed that coliforms were not persistent on the aircraft plumbing surfaces, and coliforms were not detected after disinfection and flushing. However, it noted an exception for the aerator installed in the lavatory faucet which was coliform positive after disinfection with ozone and mixed oxidants; disinfection with glycolic acid and quaternary ammonia showed no detectable coliforms on aerators after 30 minutes of soaking in the disinfectants. Each aircraft water system must be inspected by the air carrier at least every 5 years according to the procedures in their O&M plans. At a minimum, the self-inspection procedures for an aircraft water system must include inspection of the storage tank, distribution system, supplemental treatment, fixtures, valves, and backflow prevention devices. Any deficiencies detected must be addressed, and any deficiency that is unresolved within 90 days of identification of the deficiency must be reported to EPA. ddrumheller on DSK120RN23PROD with RULES1 5. Filter Backwash Recycling Rule EPA promulgated the Filter Backwash Recycling Rule (FBRR) on June 8, 2001 (66 FR 31086, USEPA, 2001a). The rule aimed to increase public health protection by addressing microbial contaminant risks associated with filter backwash recycling practices. The rule required certain systems to return recycled filter backwash water, sludge thickener supernatant, and liquids from dewatering processes to a location in the system such that all filtration processes of a system are employed, or at an alternate location if approved by the State. In addition, the rule required systems that employ conventional filtration or direct filtration to notify States of their recycling practices by June 8, 2004, and after then to keep and retain records on file about their recycle flows for subsequent review and evaluation by the State. There are no VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 ongoing monitoring requirements associated with the FBBR. EPA reviewed available State data collected under the ICR; however, the EPA did not identify any new and relevant information that would indicate that revisions to the NPDWR at this time are appropriate. VI. References ATSDR. 2003. Toxicological Profile for Selenium. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry (ATSDR). https://hero.epa.gov/hero/ index.cfm/reference/details/reference_ id/2990677 ATSDR. 2006. Toxicological Profile for Dichlorobenzenes. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry (ATSDR). https://hero.epa.gov/ hero/index.cfm/reference/details/ reference_id/5160103 ATSDR. 2012. Toxicological Profile for Cadmium. Atlanta (GA): U.S. Department of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry (ATSDR). https://hero.epa.gov/ hero/index.cfm/reference/details/ reference_id/2509015 Borchardt, M.A., S.K. Spencer, B.A. Kieke, Jr., E. Lambertini, and F.J. Loge. 2012. Viruses in Nondisinfected Drinking Water from Municipal Wells and Community Incidence of Acute Gastrointestinal Illness. Environmental Health Perspectives, 120(9): 1272–1279. Burch T.R., J.P. Stokdyk, N. Rice, A.C. Anderson, J.F. Walsh, S.K. Spencer, A.D. Firnstahl and M.A. Borchardt. 2022. Statewide Quantitative Microbial Risk Assessment for Waterborne Viruses, Bacteria, and Protozoa in Public Water Supply Wells in Minnesota. Environmental Science & Technology. 56(10): 6315–6324. CalEPA. 2010a. Public Health Goal for Methoxychlor in Drinking Water. EPA– HQ–OW–2016–0627–0033. Sacramento, CA: California Environmental Protection Agency (CalEPA), Office of Environmental Health Hazard Assessment. https://hero.epa.gov/hero/ index.cfm/reference/details/reference_ id/10489852 CalEPA. 2010b. Public Health Goal for Styrene in Drinking Water. Sacramento, CA: California Environmental Protection Agency (CalEPA), Office of Environmental Health Hazard Assessment. https://hero.epa.gov/hero/ index.cfm/reference/details/reference_ id/10489854 CalEPA. 2016. Public Health Goal for Antimony in Drinking Water: 2016 Update. Sacramento, CA: California Environmental Protection Agency (CalEPA), Office of Environmental Health Hazard Assessment. https:// hero.epa.gov/hero/index.cfm/reference/ details/reference_id/10489864 PO 00000 Frm 00053 Fmt 4700 Sfmt 4700 59643 Centers for Disease Control and Prevention (CDC). 2022. National Outbreak Reporting System Dashboard. Atlanta, Georgia: U.S. Department of Health and Human Services, CDC. Accessed November 2022. Available from URL: wwwn.cdc.gov/norsdashboard. Collier, S.A., L. Deng, E.A. Adam, K.M. Benedict, E.M. Beshearse, A.J. Blackstock, B.B Bruce, G. Derado, C. Edens, K.E. Fullerton and J.W. Gargano. 2021. Estimate of burden and direct healthcare cost of infectious waterborne disease in the United States. Emerging Infectious Diseases. 27(1): 140. Fout, G.S., M.A. Borchardt, B.A. Kieke Jr., and M.R. Karim. 2017. Human virus and microbial indicator occurrence in publicsupply groundwater systems: metaanalysis of 12 international studies. Hydrogeology Journal. 25(4): 903. Gerdes, M.E., S. Miko, J.M. Kunz, E.J. Hannapel, M.C. Hlavsa, M.J. Hughes, M.J. Stuckey, L.K.F. Watkins, J.R. Cope, J.S. Yoder, V.R. Hill, and S.A. Collier. 2023. Estimating Waterborne Infectious Disease Burden by Exposure Route, United States, 2014. Emerging Infectious Diseases. 29(7): 1357. Health Canada. 2014. Guidelines for Canadian Drinking Water Quality. Guideline Technical Document. Toluene, Ethylbenzene and Xylenes. Ottawa, Ontario: Health Canada. https:// hero.epa.gov/hero/index.cfm/reference/ details/reference_id/3049488 Handschuh, H., J. O’Dwyer, and C.C. Adley. 2015. Bacteria that travel: the quality of aircraft water. International Journal of Environmental Research and Public Health, 12(11): 13938–13955. Handschuh, H., M.P. Ryan, J. O’Dwyer and C. C. Adley. 2017. Assessment of the bacterial diversity of aircraft water: identification of the frequent fliers. PLoS One, 12(1): e0170567. Keithlin, J., J. Sargeant, M.K. Thomas, and A. Fazil. 2014. Systematic review and metaanalysis of the proportion of Campylobacter cases that develop chronic sequelae. BMC Public Health 14: 1–19. National Drinking Water Advisory Committee (NDWAC). 2000. Recommended Guidance for Review of Existing National Primary Drinking Water Regulations. November 2000. National Research Council (NRC). 2006. Fluoride in drinking-water: A Scientific Review of EPA’s Standards. The National Academies Press, Washington, DC. National Toxicology Program (NTP). 2023. NTP Board of Scientific Counselors Working Group Report on the Draft State of the Science Monograph and the Draft Meta-Analysis Manuscript on Fluoride. Research Triangle Park, NC: U.S. Department of Health and Human Services, National Institutes of Health, National Institute of Environmental Health Sciences, NTP. Schaeffer, F., K. Tower, and A.S. Weissfeld. 2012. What’s Up with Aircraft Drinking Water? Clinical Microbiology Newsletter, 34(2): 9–13. Stokdyk J.P., A.D. Firnstahl, J.F. Walsh, S.K. Spencer, J.R. de Lambert, A.C. Anderson, E:\FR\FM\23JYR1.SGM 23JYR1 ddrumheller on DSK120RN23PROD with RULES1 59644 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations L.W. Rezania, B.A. Kieke Jr. and M.A. Borchardt. 2020. Viral, bacterial, and protozoan pathogens and fecal markers in wells supplying groundwater to public water systems in Minnesota, USA. Water Research. 178: 115814. Szabo, J.; M. Rodgers; J. Mistry; J. Steenbock; and J. Hall. 2019. The effectiveness of disinfection and flushing procedures to prevent coliform persistence in aircraft water systems. Water Supply. 19 (5): 1339–1346. https://doi.org/10.2166/ ws.2018.195. U.S. Department of Health and Human Services Federal Panel on Community Water Fluoridation. 2015. U.S. Public Health Service Recommendation for Fluoride Concentration in Drinking Water for the Prevention of Dental Caries. Public Health Reports. 2015 Jul– Aug; 130(4):318–31. doi: 10.1177/ 003335491513000408. USEPA. 1985. National Primary Drinking Water Regulations; Volatile Synthetic Organic Chemicals; Final Rule and Proposed Rule. 50 FR 46880. November 13, 1985. USEPA. 1986. National Primary and Secondary Drinking Water Regulations; Fluoride; Final Rule. 51 FR 11396. April 2, 1986. USEPA. 1987. National Primary Drinking Water Regulations; Synthetic Organic Chemicals; Monitoring for Unregulated Contaminants; Final Rule. 52 FR 25690. July 8, 1987. USEPA 1989. Drinking Water; National Primary Drinking Water Regulations; Total Coliforms (including Fecal Coliforms and E. coli); Final Rule. 54 FR 27544. June 29, 1989. USEPA. 1991. National Primary Drinking Water Regulations-Synthetic Organic Chemicals and Inorganic Chemicals; Monitoring for Unregulated Contaminants; National Primary Drinking Water Regulations Implementation; National Secondary Drinking Water Regulations; Final Rule. 56 FR 3526. January 30, 1991. USEPA. 1992. Drinking Water; National Primary Drinking Water RegulationsSynthetic Organic Chemicals and Inorganic Chemicals; National Primary Drinking Water Regulations Implementation. 57 FR 31776. July 17, 1992. USEPA. 1998. Toxicological Review of Beryllium and Compounds. EPA/635/R– 98/008. Washington, DC: U.S. Environmental Protection Agency (USEPA). https://hero.epa.gov/hero/ index.cfm/reference/details/reference_ id/999207. USEPA. 2001. Integrated Risk Information System (IRIS) Chemical Assessment Summary: Hexachlorocyclopentadiene. Washington, DC: U.S. Environmental Protection Agency (USEPA), Office of Research and Development, National Center for Environmental Assessment. https://hero.epa.gov/hero/index.cfm/ reference/details/reference_id/10509468. USEPA. 2001a. National Primary Drinking Water Regulations: Filter Backwash Recycling Rule. 66 FR 31086. June 8, 2001. VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 USEPA. 2002. IRIS Toxicological Review of 1,1-Dichloroethylene in Support of Summary Information. EPA/635/R02/ 002. Washington, DC: U.S. Environmental Protection Agency (USEPA), National Center for Environmental Assessment, Office of Research and Development. https:// hero.epa.gov/hero/index.cfm/reference/ details/reference_id/10721895. USEPA. 2003. National Primary Drinking Water Regulations; Announcement of Completion of EPA’s Review of Existing Drinking Water Standards. Notice. 68 FR 42908. July 18, 2003. USEPA. 2004. Reregistration Eligibility Decision (RED) for Lindane. Washington, DC: U.S. Environmental Protection Agency (USEPA), Office of Prevention, Pesticides and Toxic Substances. https:// hero.epa.gov/hero/index.cfm/reference/ details/reference_id/10492448. USEPA. 2005. Toxicological Review of Barium and Compounds (CAS No. 7440– 39–3) in Support of Summary Information on the Integrated Risk Information System (IRIS) (Revised). EPA/635/R–05/001. Washington, DC: U.S. Environmental Protection Agency (USEPA). https://hero.epa.gov/hero/ index.cfm/reference/details/reference_ id/11311280. USEPA. 2006a. National Primary Drinking Water Regulations: Long-Term 2 Enhanced Surface Water Treatment Rule; Final Rule. 71 FR 654. January 5, 2006. USEPA. 2006b. National Primary Drinking Water Regulations: Ground Water Rule; Final Rule. 71 FR 65574. November 8, 2006. USEPA. 2007a. Acetochlor/Alachlor: Revised Cumulative Risk Assessment for the Chloroacetanilides to Support the Proposed New Uses on Alachlor and Acetochlor. Washington, DC: U.S. Environmental Protection Agency (USEPA), Office of Prevention, Pesticides, and Toxic Substances. https://hero.epa.gov/hero/index.cfm/ reference/details/reference_id/10492629. USEPA. 2007b. Toxicological Review of 1,1,1-Trichloroethane. EPA/635/R–03/ 013. Washington, DC: U.S. Environmental Protection Agency (USEPA). https://hero.epa.gov/hero/ index.cfm/reference/details/reference_ id/3004991. USEPA. 2008. Carbofuran. HED Revised Risk Assessment for the Notice of Intent to Cancel (NOIC). EPA–HQ–OPP–2007– 1088–0034. Washington, DC: U.S. Environmental Protection Agency (USEPA), Office of Prevention, Pesticides, and Toxic Substances. https://hero.epa.gov/hero/index.cfm/ reference/details/reference_id/10494332. USEPA. 2009a. Provisional Peer-Reviewed Toxicity Values for 1,2,4Trichlorobenzene, CASRN 120–82–1. EPA/690/R–09/065F. Cincinnati, OH: U.S. Environmental Protection Agency (USEPA), Office of Research and Development, National Center for Environmental Assessment, Superfund Health Risk Technical Support Center. https://hero.epa.gov/hero/index.cfm/ reference/details/reference_id/10255709. PO 00000 Frm 00054 Fmt 4700 Sfmt 4700 USEPA. 2009b. National Primary Drinking Water Regulations: Drinking Water Regulations for Aircraft Public Water Systems. 74 FR 53590. October 19, 2009. USEPA. 2010a. National Primary Drinking Water Regulations; Announcement of the Results of EPA’s Review of Existing Drinking Water Standards and Request for Public Comment and/or Information on Related Issues. 75 FR 15500. March 29, 2010. USEPA. 2010b. Toxicological Review of Hydrogen Cyanide and Cyanide Salts. EPA/635/R–08/016F. Washington, DC: U.S. Environmental Protection Agency (USEPA). https://hero.epa.gov/hero/ index.cfm/reference/details/reference_ id/723657. U.S. EPA. 2010c. Integrated Risk Information System (IRIS) Chemical Assessment Summary: cis-1,2-Dichloroethylene, CASRN 156–59–2. Washington, DC: U.S. Environmental Protection Agency (USEPA), Office of Research and Development. https://hero.epa.gov/hero/ index.cfm/reference/details/reference_ id/10493648. USEPA. 2010d. Fluoride: Dose-Response Analysis for Non-Cancer Effects. EPA/ 820/R–10/019. Washington, DC: U.S. Environmental Protection Agency (USEPA), Office of Water. https:// hero.epa.gov/hero/index.cfm/reference/ details/reference_id/10493692. USEPA. 2010e. Long Term 2 Enhanced Surface Water Treatment Rule: Toolbox Guidance Manual. EPA 815–R–09–016. April 2010. https://www.epa.gov/ dwreginfo/long-term-2-enhancedsurface-water-treatment-rule-documents. USEPA. 2011. Trichloroethylene; CASRN 79– 01–6. Integrated Risk Information System (IRIS) Chemical Assessment Summary. Last Revised September 28, 2011. Retrieved from https://iris.epa.gov/ ChemicalLanding/&substance_ nmbr=199. USEPA. 2012. Tetrachloroethylene (Perchloroethylene); CASRN 127–18–4. Integrated Risk Information System (IRIS) Chemical Assessment Summary. Last Revised February 10, 2012. Retrieved from https://iris.epa.gov/ ChemicalLanding/&substance_ nmbr=106. USEPA. 2013. National Primary Drinking Water Regulations: Revisions to the Total Coliform Rule; Final Rule. 78 FR 10269. February 13, 2013. USEPA. 2015a. Peer Review Handbook 4th Edition. October 2015. Available online at: https://www.epa.gov/sites/default/ files/2015-10/documents/epa_peer_ review_handbook_4th_edition_october_ 2015.pdf. USEPA. 2015b. Endothall: Human Health Risk Assessment in Support of Registration Review, and the Petition to Re-Evaluate Tolerances for Livestock, and Remove the Restriction that Prohibits Livestock from Drinking Treated Water. EPA–HQ–OPP–2015– 0591–0012. Washington, DC: U.S. Environmental Protection Agency (USEPA), Office of Chemical Safety and Pollution Prevention, Health Effects E:\FR\FM\23JYR1.SGM 23JYR1 ddrumheller on DSK120RN23PROD with RULES1 Federal Register / Vol. 89, No. 141 / Tuesday, July 23, 2024 / Rules and Regulations Division. https://hero.epa.gov/hero/ index.cfm/reference/details/reference_ id/10494329. USEPA. 2016. Six-Year Review 3—Health Effects Assessment for Existing Chemical and Radionuclide National Primary Drinking Water Regulations—Summary Report. EPA 822–R–16–008. USEPA. 2017a. National Primary Drinking Water Regulations; Announcement of the Results of EPA’s Review of Existing Drinking Water Standards and Request for Public Comment and/or Information on Related Issues. 82 FR 3518. January 11, 2017. USEPA. 2017b. Oxamyl Draft Human Health Risk Assessment in Support of Registration Review. Washington, DC: U.S. Environmental Protection Agency (USEPA), Office of Chemical Safety and Pollution Prevention, Health Effects Division. https://hero.epa.gov/hero/ index.cfm/reference/details/reference_ id/10532947. USEPA. 2017c. 2,4–D Revised Human Health Risk Assessment for Registration Review. Washington, DC: U.S. Environmental Protection Agency (USEPA), Office of Chemical Safety and Pollution Prevention, Health Effects Division. https://hero.epa.gov/hero/index.cfm/ reference/details/reference_id/10532862. USEPA. 2017d. Glyphosate: Draft Human Health Risk Assessment in Support of Registration Review. EPA–HQ–OPP– 2009–0361–0068. Washington, DC: U.S. Environmental Protection Agency (USEPA), Office of Chemical Safety and Pollution Prevention. https://hero.epa. gov/hero/index.cfm/reference/details/ reference_id/10532909. USEPA. 2018a. Draft Atrazine Human Health Risk Assessment for Registration Review. EPA–HQ–OPP–2013–0266–1256. Washington, DC: U.S. Environmental Protection Agency (USEPA). https:// hero.epa.gov/hero/index.cfm/reference/ details/reference_id/10533087. USEPA. 2018b. Simazine: Human Health Risk Assessment for Registration Review and to Support the Registration of Proposed Uses on Citrus Fruit (Crop Group 10–10), Pome Fruit (Crop Group 11–10), Stone Fruit (Crop Group 12–12), Tree Nuts (Crop Group 14–12), and Tolerance Amendment for Almond Hulls. Washington, DC: U.S. Environmental Protection Agency (USEPA), Office of Chemical Safety and Pollution Prevention. https://hero.epa. gov/hero/index.cfm/reference/details/ reference_id/10533123. USEPA. 2019. Information Collection Request Submitted to OMB for Review and Approval; Comment Request; Contaminant Occurrence Data in Support of the EPA’s Fourth Six-Year Review of National Primary Drinking Water Regulations. 84 FR 58381. October 31, 2019. USEPA. 2020a. Microbial Disinfection Byproducts Rules: Public Meeting to Inform Potential Rule Revisions. Notice. 85 FR 61680. September 30, 2020. USEPA. 2020b. Diquat. Human Health Risk Assessment for the Establishment Of A VerDate Sep<11>2014 17:25 Jul 22, 2024 Jkt 262001 Tolerance Without U.S. Registration For Residues in/on Crop Subgroup 6C Dried Shelled Pea and Bean (Except Soybean). EPA–HQ–OPP–2017–0291–0009. Washington, DC: U.S. Environmental Protection Agency (USEPA), Office of Chemical Safety and Pollution Prevention. https://hero.epa.gov/hero/ index.cfm/reference/details/reference_ id/10533339. USEPA. 2020c. Picloram Draft Human Health Risk Assessment in Support of Registration Review. Washington, DC: U.S. Environmental Protection Agency (USEPA), Office of Chemical Safety and Pollution Prevention, Health Effects Division. https://hero.epa.gov/hero/ index.cfm/reference/details/reference_ id/10533340. USEPA. 2020d. ‘‘The Standardized Monitoring Framework: A Quick Reference Guide.’’ EPA 816–F–20–002. May 2020. https://www.epa.gov/ dwreginfo/standardized-monitoringframework-quick-reference-guide. USEPA. 2020e. Use of Total Nitrate and Nitrite Analysis for Compliance Determinations with the Nitrate Maximum Contaminant Level (WSG 213). November 30, 2020. https:// www.epa.gov/sites/default/files/2021-01/ documents/wsg_213_nitrate_wsg_11-302020_signed_508-compliantfinal.pdf. USEPA. 2020f. Clarification of Free and Total Cyanide Analysis for Safe Drinking Water Act (SDWA) Compliance Revision 1.0. EPA 815–B–20–004. June 2020. USEPA. 2022a. Request for Nominations for the Science Advisory Board Radionuclide Cancer Risk Coefficients Review Panel. 87 FR 15988. March 21, 2022. USEPA. 2022b. Availability of the Draft IRIS Toxicological Review of Hexavalent Chromium. 87 FR 63774. October 10, 2022. USEPA. 2023a. National Primary Drinking Water Regulations for Lead and Copper: Improvements (LCRI). 88 FR 84878. December 6, 2023. USEPA. 2023b. Availability of the Protocol for the Nitrate and Nitrite IRIS Assessment (Oral). 88 FR 77310. November 9, 2023. USEPA. 2024a. PFAS National Primary Drinking Water Regulation. 89 FR 32532. April 26, 2024. USEPA. 2024b. National Primary Drinking Water Regulations: Consumer Confidence Report Rule Revisions. 89 FR 45980. May 24, 2024. USEPA. 2024c. EPA Protocol for the Fourth Review of Existing National Primary Drinking Water Regulations. EPA 815–R– 24–018. USEPA. 2024d. Data Management and Quality Assurance/Quality Control Process for the Fourth Six-Year Review Information Collection Request Dataset. EPA 815–R–24–017. USEPA. 2024e. Chemical Contaminant Summaries for the Fourth Six-Year Review of Existing National Primary Drinking Water Regulations. EPA 815–S– 24–002. USEPA. 2024f. Results of the Health Effects Assessment for the Fourth Six-Year PO 00000 Frm 00055 Fmt 4700 Sfmt 4700 59645 Review of Existing Chemical and Radionuclide National Primary Drinking Water Standards. EPA 815–R–24–020. USEPA. 2024g. Analytical Feasibility Support Document for the Fourth SixYear Review of National Primary Drinking Water Regulations. EPA 815–R– 24–015. USEPA. 2024h. Analysis of Regulated Contaminant Occurrence Data from Public Water Systems in Support of the Fourth Six-Year Review of National Primary Drinking Water Regulations: Chemical Phase and Radionuclides Rules. EPA 815–R–24–014. USEPA. 2024i. Review of Fluoride Occurrence for the Fourth Six-Year Review. EPA 815–R–24–021. USEPA. 2024j. Occurrence Analysis for Potential Source Waters for the Fourth Six-Year Review of National Primary Drinking Water Regulations. EPA 815–R– 24–019. USEPA. 2024k. Support Document for the Fourth Six-Year Review of Drinking Water Regulations for Acrylamide and Epichlorohydrin. EPA 815–R–24–023. USEPA. 2024l. Consideration of Other Regulatory Revisions in Support of the Fourth Six-Year Review of the National Primary Drinking Water Regulations: Chemical Phase Rules and Radionuclides Rule. EPA 815–R–24–016. USEPA. 2024m. Six-Year Review 4 Technical Support Document for Microbial Contaminant Regulations. EPA 815–R– 24–022. Wallender, E.K., E.C. Ailes, J.S. Yoder, V.A. Roberts, and J.M. Brunkard. 2014. Contributing factors to disease outbreaks associated with untreated groundwater. Ground Water. 52(6): 886–97. World Health Organization (WHO). 2004. Guidelines for Drinking-Water Quality, Third Edition. Volume 1: Recommendations. https://www.who.int/ publications/i/item/9789241547611. WHO. 2009. Guide to hygiene and sanitation in aviation, 3rd edition. https://www. who.int/publications/i/item/97892415 47772. Michael S. Regan, Administrator. [FR Doc. 2024–15807 Filed 7–22–24; 8:45 am] BILLING CODE 6560–50–P ENVIRONMENTAL PROTECTION AGENCY 40 CFR Part 180 [EPA–HQ–OPP–2023–0221; FRL–11818–01– OCSPP] Trichoderma Atroviride Strain AT10; Exemption From the Requirement of a Tolerance Environmental Protection Agency (EPA). ACTION: Final rule. AGENCY: This regulation establishes an exemption from the requirement of a SUMMARY: E:\FR\FM\23JYR1.SGM 23JYR1

Agencies

ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 89, Number 141 (Tuesday, July 23, 2024)]
[Rules and Regulations]
[Pages 59623-59645]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-15807]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 141

[EPA-HQ-OW-2023-0572; FRL 7946-01-OW]


National Primary Drinking Water Regulations; Announcement of the 
Results of EPA's Fourth Review of Existing Drinking Water Standards

AGENCY: Environmental Protection Agency (EPA).

ACTION: Results of regulatory review.

-----------------------------------------------------------------------

SUMMARY: The Safe Drinking Water Act (SDWA) requires the U.S. 
Environmental Protection Agency (EPA or the agency) to conduct a review 
every six years of existing national primary drinking water regulations 
(NPDWRs) and determine which, if any, are appropriate for revision. The 
purpose of the review, called the Six-Year Review, is to evaluate 
available information for regulated contaminants to determine if any 
new information on health effects, treatment technologies, analytical 
methods, occurrence, exposure, implementation, and/or other factors 
provides a basis to support a regulatory revision that would improve or 
strengthen public health protection. While EPA has recently completed 
several significant revisions to existing regulations and other 
regulatory revisions are currently underway, based on this periodic 
review of all NPDWRs, there are no additional candidates for regulatory 
revision at this time.

DATES: July 23, 2024.

ADDRESSES: EPA is not accepting public comment on the review results.

FOR FURTHER INFORMATION CONTACT: Samuel Hernandez, Environmental 
Protection Agency, Office of Ground Water and Drinking Water, Standards 
and Risk Management Division, (Mail Code 4607M), 1200 Pennsylvania 
Avenue NW, Washington, DC 20460; telephone number: (202) 564-1735; 
email address: [email protected].

SUPPLEMENTARY INFORMATION: 
    Abbreviations and acronyms: The following acronyms and 
abbreviations are used throughout this document.

2,4-D--2,4-Dichlorophenoxyacetic acid
ADWR--Aircraft Drinking Water Rule
BAT--Best Available Technology
CFR--Code of Federal Regulations
CVOC--Carcinogenic Volatile Organic Contaminant
CWS--Community Water System
DBCP--1,2-Dibromo-3-Chloropropane
DBP--Disinfection Byproduct
DEHA--Di(2-ethylhexyl)adipate
DEHP--Di(2-ethylhexyl)phthalate
EPA--U.S. Environmental Protection Agency
EQL--Estimated Quantitation Level
FBRR--Filter Backwash Recycling Rule
GWR--Ground Water Rule
HAA5--Haloacetic Acids (five) (sum of monochloroacetic acid, 
dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and 
dibromoacetic acid)
ICR--Information Collection Request
IRIS--Integrated Risk Information System
LT2--Long-Term 2 Enhanced Surface Water Treatment Rule
MCLG--Maximum Contaminant Level Goal
MCL--Maximum Contaminant Level
MDBP--Microbial and Disinfection Byproduct
MDL--Method Detection Limit
MRDLG--Maximum Residual Disinfectant Level Goal
MRDL--Maximum Residual Disinfectant Level
MRL--Minimum Reporting Level
NAS--National Academy of Sciences
NCWS--Non-Community Water System
NDWAC--National Drinking Water Advisory Council
NPDWR--National Primary Drinking Water Regulations
NRC--National Research Council
NTP--National Toxicology Program
PCBs--Polychlorinated biphenyls
PCE--Tetrachloroethylene
PQL--Practical Quantitation Limit
PT--Proficiency Testing
PWS--Public Water System
RfD--Reference Dose
RSC--Relative Source Contribution
RTCR--Revised Total Coliform Rule
SDWA--Safe Drinking Water Act
SDWIS--Safe Drinking Water Information System
SWTR--Surface Water Treatment Rule
TCDD--Tetrachlorodibenzo-p-dioxin
TCE--Trichloroethylene
TCR--Total Coliform Rule
TNCWS--Transient Non-Community Water System
TTHM--Total Trihalomethanes (sum of four THMs: chloroform, 
bromodichloromethane, dibromochloromethane, and bromoform)
TT--Treatment Technique
USGS--U.S. Geological Survey

Table of Contents

I. General Information
    A. Does this action apply to me?
    B. How can I get copies of this document and other related 
information?
II. Statutory Requirements for the Six-Year Review
III. Regulations Included in the Six-Year Review 4
IV. EPA's Protocol for Reviewing the NPDWRs Included in This Action
    A. What was EPA's review process?
    B. How did EPA conduct the review of the NPDWRs?
    1. Initial Review
    2. Health Effects

[[Page 59624]]

    3. Analytical Feasibility
    4. Occurrence and Exposure Analysis
    5. Treatment Feasibility
    6. Risk-Balancing
    7. Other NPDWR Revisions
V. Results of EPA's Review of NPDWRs
    A. Overview of Six-Year Review 4 Results
    B. Chemical Phase Rules/Radionuclides Rules
    1. Key Review Outcomes
    2. Summary of Review Results
    3. Select NPDWRs with New Information Not Appropriate for 
Revision
    C. Microbial Contaminants Regulations
VI. References

I. General Information

A. Does this action apply to me?

    This action itself does not impose any requirements on individual 
people or entities. Instead, it notifies interested parties of EPA's 
review of existing national primary drinking water regulations (NPDWRs) 
and its conclusions about which of these NPDWRs may warrant regulatory 
revisions at this time. The Six-Year Review is not a final regulatory 
decision to revise or not revise an NPDWR, but rather a planning 
process that involves more detailed analyses of factors relevant to 
deciding whether a rulemaking to revise an NPDWR should be initiated.

B. How can I get copies of this document and other related information?

    1. Docket. EPA has established a docket for this action under 
Docket ID No. EPA-HQ-OW-2023-0572. Publicly available docket materials 
are available electronically on www.regulations.gov or in hard copy at 
the EPA Docket Center, WJC West Building, Room 3334, 1301 Constitution 
Ave. NW, Washington, DC. The Docket Center's hours of operations are 
8:30 a.m. to 4:30 p.m., Monday through Friday (except Federal 
Holidays). For further information on the EPA Docket Center services 
and the current status see: https://www.epa.gov/dockets.
    2. Electronic Access. You may access this Federal Register document 
electronically from https://www.federalregister.gov.

II. Statutory Requirements for the Six-Year Review

    Under the Safe Drinking Water Act (SDWA), as amended in 1996, EPA 
must periodically review existing NPDWRs and, if appropriate, revise 
them. Section 1412(b)(9) of the SDWA states: ``The Administrator shall, 
not less often than every six years, review and revise, as appropriate, 
each national primary drinking water regulation promulgated under this 
title. Any revision of a national primary drinking water regulation 
shall be promulgated in accordance with this section, except that each 
revision shall maintain, or provide for greater, protection of the 
health of persons.''
    Pursuant to the 1996 SDWA Amendments, EPA completed and published 
the results of its first Six-Year Review (Six-Year Review 1) on July 
18, 2003 (68 FR 42908, USEPA, 2003), the second Six-Year Review (Six-
Year Review 2) on March 29, 2010 (75 FR 15500, USEPA, 2010a) and the 
third Six-Year Review (Six-Year Review 3) on January 11, 2017 (82 FR 
3518, USEPA, 2017a).
    During the Six-Year Review 1, EPA identified the Total Coliform 
Rule (TCR) as a candidate for revision.\1\ In Six-Year Review 2, EPA 
identified four NPDWRs corresponding to acrylamide, epichlorohydrin, 
tetrachloroethylene (PCE), and trichloroethylene (TCE) as candidates 
for revision. In Six-Year Review 3, eight NPDWRs were listed as 
candidates for revision, including: chlorite, Cryptosporidium (under 
SWTRs), Giardia lamblia, haloacetic acids (HAA5), heterotrophic 
bacteria, Legionella, total trihalomethanes (TTHM), and viruses (under 
SWTRs). EPA also announced that the NPDWRs for acrylamide and 
epichlorohydrin were no longer candidates for revision due to low 
opportunity for further reduction of public health risk through 
regulatory revision (82 FR 3525, USEPA, 2017a).
---------------------------------------------------------------------------

    \1\ The NPDWRs apply to specific contaminants/parameters or 
groups of contaminants. Historically, when issuing new or revised 
standards for these contaminants/parameters, EPA has often grouped 
the standards together in more general regulations, such as the 
Total Coliform Rule, the Surface Water Treatment Rule or the Phase V 
rules. In this action, however, for clarity, EPA discusses the 
drinking water standards as they apply to each specific regulated 
contaminant/parameter (or group of contaminants), not the more 
general regulation in which the contaminant/parameter was regulated.
---------------------------------------------------------------------------

    In this document, EPA is announcing the results of the fourth Six-
Year Review (Six-Year Review 4). EPA's announcement of whether to 
identify an NPDWR as a candidate for revision (pursuant to SDWA section 
1412(b)(9)) is not a regulatory decision. Instead, announcing that an 
NPDWR is a candidate for revision formally initiates a regulatory 
process that involves more detailed analyses of health effects, 
analytical constraints, treatment feasibility, occurrence, benefits, 
costs, and other policy considerations relevant to informing an NPDWR 
revision effort. The Six-Year Review results do not obligate the agency 
to revise an NPDWR if EPA determines during the regulatory process that 
revisions are no longer appropriate and discontinues further efforts to 
revise the NPDWR. Similarly, when EPA announces that a particular NPDWR 
has not been identified as a candidate for revision it means that the 
agency has concluded that it is not appropriate for revision at this 
time based on available information.
    The criteria that EPA has applied to help identify when an NPDWR 
might be considered as a ``candidate for revision'' are, at a minimum, 
that the regulatory revision presents a meaningful opportunity to 
improve the level of public health protection, and/or achieve cost 
savings while maintaining or improving the level of public health 
protection.

III. Regulations Included in the Six-Year Review 4

    Table 1 of this document lists all 94 NPDWRs established to date. 
The table also reports the maximum contaminant level goal (MCLG) and, 
where applicable, the maximum contaminant level (MCL). The MCLG is 
``set at the level at which no known or anticipated adverse effects on 
the health of persons occur and which allows an adequate margin of 
safety'' (SDWA section 1412(b)(4)). The MCL for each applicable NPDWR, 
is the maximum permissible level of a contaminant in water delivered to 
any user of a public water system (PWS) and generally ``is as close to 
the maximum contaminant level goal as is feasible'' (SDWA section 
1412(b)(4)(B)). If it is not ``economically or technically feasible to 
ascertain the level of the contaminant,'' EPA can require the use of a 
treatment technique (TT) in lieu of establishing an MCL. The treatment 
technique(s) must prevent known or anticipated adverse health effects 
``to the extent feasible'' (SDWA section 1412(b)(7)(A)).\2\ In the case 
of disinfectants (e.g., chlorine, chloramines, chlorine dioxide), the 
values reported in the table are not MCLGs and MCLs, but maximum 
residual disinfectant level goals (MRDLGs) and maximum residual 
disinfectant levels (MRDLs).
---------------------------------------------------------------------------

    \2\ Under limited circumstances, SDWA section 1412(b)(6)(A) 
gives the Administrator the discretion to promulgate an MCL or TT 
that is less stringent than the most protective feasible standard 
that ``maximizes health risk reduction benefits at a cost that is 
justified by the benefits.'' Similarly, SDWA section 1412(b)(5) 
authorizes the Administrator to promulgate an MCL or TT that is less 
stringent than the most protective feasible standard if the more 
protective standard would increase the level of other contaminants 
in drinking water or interfere with the efficacy of treatment 
techniques or process used for compliance with other NPDWRs. Under 
those circumstances, EPA is to promulgate feasible a MCL or TT rule 
to ``minimize the oversall risk of adverse health effects'' while 
avoiding an increase in health risks from other contaminants.

---------------------------------------------------------------------------

[[Page 59625]]

    As part of the fourth Six-Year Review, EPA did not consider 
information after December 2021, unless otherwise noted. EPA identified 
15 NPDWRs for which there has either been a recently completed, an 
ongoing, or a pending regulatory action. EPA did not conduct a detailed 
review of these 15 NPDWRs for the Six-Year Review 4. These include the 
ongoing Lead & Copper rulemaking activities and the potential revisions 
\3\ of the Microbial and Disinfection Byproduct Rules (MDBP). The MDBP 
effort contemplates potential regulatory revisions for the NPDWRs 
covering the following contaminants: (Bromate, Chloramines, Chlorine 
Dioxide, Chlorine, Chlorite, Cryptosporidium, Giardia lamblia, 
Haloacetic acids, Heterotrophic bacteria, Legionella, Total 
Trihalomethanes, Turbidity, & Viruses).
---------------------------------------------------------------------------

    \3\ Additional information can be found at https://www.epa.gov/system/files/documents/2022-04/mdbp-rule-revisions-charge-to-the-ndwac.pdf.
---------------------------------------------------------------------------

    The EPA did not include in this Six-Year Review cycle the recently 
promulgated per-and polyfluoroalkyl substances (PFAS) regulations.\4\ 
The PFAS regulations, promulgated in April 2024, established 6 new 
NPDWRs. The EPA anticipates that once the PFAS regulations go into 
effect and sufficient information regarding compliance monitoring 
becomes available, those NPDWRs will be subject to a more detailed 
regulatory review under a future Six-Year Review cycle. This document 
describes the detailed review of the remaining 73 NPDWRs. section IV of 
this document describes the Six-Year Review 4 protocol, and section V 
of this document describes the review results. Please see USEPA (2024a) 
for more details.
---------------------------------------------------------------------------

    \4\ On April 26, 2024, the EPA promulgated legally enforceable 
drinking water standards to address PFAS known to occur individually 
and as mixtures in drinking water (89 FR 32532). The NPDWRs sets 
limits for five individual PFAS: (perfluorooctanoic acid (PFOA), 
perfluorooctane sulfonic acid (PFOS), perfluorohexane sulfonic acid 
(PFHxS), perfluorononanoic acid (PFNA), hexafluoropropylene oxide 
dimer acid (HFPO-DA, commonly known as GenX Chemicals)); and also 
established a limit for mixtures of any two or more of the following 
four PFAS: (PFNA, PFHxS, perfluorobutane sulfonic acid (PFBS), and 
HFPO-DA).

                                                                 Table 1--List of NPDWRs
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                             MCL or TT (mg/L) 2 3      Contaminants/                               MCL or TT (mg/L) 2 3
     Contaminants/parameters          MCLG (mg/L) 1 3                                   parameters          MCLG (mg/L) 1 3
--------------------------------------------------------------------------------------------------------------------------------------------------------
Acrylamide......................  0......................  TT.....................  Giardia lamblia     0......................  TT.
                                                                                     \4\.
Alachlor........................  0......................  0.002..................  Glyphosate........  0.7....................  0.7.
Alpha/photon emitters...........  0 (pCi/L)..............  15 (pCi/L).............  Haloacetic acids    n/a \5\................  0.060.
                                                                                     (HAA5).
Antimony........................  0.006..................  0.006..................  Heptachlor........  0......................  0.0004.
Arsenic.........................  0......................  0.010..................  Heptachlor epoxide  0......................  0.0002.
Asbestos........................  7 (million fibers/L)...  7 (million fibers/L)...  Heterotrophic       n/a....................  TT.
                                                                                     bacteria \6\.
Atrazine........................  0.003..................  0.003..................  Hexachlorobenzene.  0......................  0.001.
Barium..........................  2......................  2......................  Hexachlorocyclopen  0.05...................  0.05.
                                                                                     tadiene.
Benzene.........................  0......................  0.005..................  Hexafluoropropylen  10 (ppt)...............  10 (ppt).
                                                                                     e oxide dimer
                                                                                     acid (HFPO-DA).
Benzo[a]pyrene..................  0......................  0.0002.................  Lead..............  0......................  TT.
Beryllium.......................  0.004..................  0.004..................  Legionella........  0......................  TT.
Beta/photon emitters............  0 (millirems/yr).......  4 (millirems/yr).......  Lindane...........  0.0002.................  0.0002.
Bromate.........................  0......................  0.010..................  Mercury             0.002..................  0.002.
                                                                                     (inorganic).
Cadmium.........................  0.005..................  0.005..................  Methoxychlor......  0.04...................  0.04.
Carbofuran......................  0.04...................  0.04...................  Monochlorobenzene   0.1....................  0.1.
                                                                                     (Chlorobenzene).
Carbon tetrachloride............  0......................  0.005..................  Nitrate (as N)....  10.....................  10.
Chloramines (as Cl2)............  4......................  4.0....................  Nitrite (as N)....  1......................  1.
Chlordane.......................  0......................  0.002..................  Oxamyl (Vydate)...  0.2....................  0.2.
Chlorine (as Cl2)...............  4......................  4.0....................  Pentachlorophenol.  0......................  0.001.
Chlorine dioxide (as ClO2)......  0.8....................  0.8....................  Perfluorohexane     10 (ppt)...............  10 (ppt).
                                                                                     sulfonic acid
                                                                                     (PFHxS).
Chlorite........................  0.8....................  1.0....................  Perfluorononanoic   10 (ppt)...............  10 (ppt).
                                                                                     acid (PFNA).
Chromium (total)................  0.1....................  0.1....................  Perfluorooctane     0 (ppt)................  4.0 (ppt).
                                                                                     sulfonic acid
                                                                                     (PFOS).
Copper..........................  1.3....................  TT.....................  Perfluorooctanoic   0 (ppt)................  4.0 (ppt).
                                                                                     acid (PFOA).
Cryptosporidium.................  0......................  TT.....................  PFAS Mixture (HFPO- Hazard Index \12\ of 1.  Hazard Index of 1.
                                                                                     DA, PFBS, PFHxS,
                                                                                     & PFNA).
Cyanide (as free cyanide).......  0.2....................  0.2....................  Picloram..........  0.5....................  0.5.
2,4-Dichlorophenoxyacetic acid    0.07...................  0.07...................  Polychlorinated     0......................  0.0005.
 (2,4-D).                                                                            biphenyls (PCBs).
Dalapon.........................  0.2....................  0.2....................  Radium 226/228      0 (pCi/L)..............  5 (pCi/L).
                                                                                     (combined).
Di(2-ethylhexyl)adipate (DEHA)..  0.4....................  0.4....................  Selenium..........  0.05...................  0.05.
Di(2-ethylhexyl)phthalate (DEHP)  0......................  0.006..................  Simazine..........  0.004..................  0.004.
1,2-Dibromo-3- chloropropane      0......................  0.0002.................  Styrene...........  0.1....................  0.1.
 (DBCP).
1,2-Dichlorobenzene (o-           0.6....................  0.6....................  2,3,7,8-TCDD        0......................  3 x10 -8.
 Dichlorobenzene).                                                                   (Dioxin).
1,4-Dichlorobenzene (p-           0.075..................  0.075..................  Tetrachloroethylen  0......................  0.005.
 Dichlorobenzene).                                                                   e.
1,2-Dichloroethane (ethylene      0......................  0.005..................  Thallium..........  0.0005.................  0.002.
 dichloride).
1,1-Dichloroethylene............  0.007..................  0.007..................  Toluene...........  1......................  1.
cis-1,2-Dichloroethylene........  0.07...................  0.07...................  Total coliforms 7   n/a....................  TT.
                                                                                     8.
trans-1,2-Dichloroethylene......  0.1....................  0.1....................  Total               n/a \9\................  0.080.
                                                                                     Trihalomethanes
                                                                                     (TTHM).
Dichloromethane (methylene        0......................  0.005..................  Toxaphene.........  0......................  0.003.
 chloride).
1,2-Dichloropropane.............  0......................  0.005..................  2,4,5-TP (Silvex).  0.05...................  0.05.
Dinoseb.........................  0.007..................  0.007..................  1,2,4-              0.07...................  0.07.
                                                                                     Trichlorobenzene.
Diquat..........................  0.02...................  0.02...................  1,1,1-              0.2....................  0.2.
                                                                                     Trichloroethane.
E. coli.........................  0......................  MCL,\10\ TT 8 11.......  1,1,2-              0.003..................  0.005.
                                                                                     Trichloroethane.
Endothall.......................  0.1....................  0.1....................  Trichloroethylene.  0......................  0.005.
Endrin..........................  0.002..................  0.002..................  Turbidity \6\.....  n/a....................  TT.
Epichlorohydrin.................  0......................  TT.....................  Uranium...........  0......................  0.030.
Ethylbenzene....................  0.7....................  0.7....................  Vinyl Chloride....  0......................  0.002.
Ethylene dibromide (EDB)........  0......................  0.00005................  Viruses...........  0......................  TT.
Fluoride........................  4.0....................  4.0....................  Xylenes (total)...  10.....................  10.
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ MCLG: the maximum level of a contaminant in drinking water at which no known or anticipated adverse effect on the health of persons would occur,
  allowing an adequate margin of safety. Maximum contaminant level goals are nonenforceable health goals.

[[Page 59626]]

 
\2\ MCL: the maximum level allowed of a contaminant in water which is delivered to any user of a public water system. TT: any action, process, or
  procedure required of the water system that leads to the reduction of the level of a contaminant in tap water that reaches the consumer.
\3\ Units are in milligrams per liter (mg/L) unless otherwise noted. Milligrams per liter are equivalent to parts per million. For chlorine,
  chloramines, and chlorine dioxide, values presented are MRDLG and MRDL.
\4\ The current preferred taxonomic name is Giardia duodenalis, with Giardia lamblia and Giardia intestinalis as synonymous names. However, Giardia
  lamblia was the name used to establish the MCLG in 1989. Elsewhere in this document, this pathogen will be referred to as Giardia spp. or simply
  Giardia unless discussing information on an individual species.
\5\ There is no MCLG for all five haloacetic acids. MCLGs for some of the individual contaminants are: dichloroacetic acid (zero), trichloroacetic acid
  (0.02 mg/L), and monochloroacetic acid (0.07 mg/L). Bromoacetic acid and dibromoacetic acid are regulated with this group but have no MCLGs.
\6\ Includes indicators that are used in lieu of direct measurements (e.g., of heterotrophic bacteria, turbidity).
\7\ The Aircraft Drinking Water Rule (ADWR) 40 CFR part 141 subpart X, promulgated October 19, 2009, covers total coliforms and E. coli.
\8\ Under the RTCR, a PWS is required to conduct an assessment if it exceeded any of the TT triggers identified in 40 CFR 141.859(a). It is also
  required to correct any sanitary defects found through the assessment. 40 CFR 141.859(c).
\9\ There is no MCLG for total trihalomethanes (TTHM). MCLGs for some of the individual contaminants are: bromodichloromethane (zero), bromoform (zero),
  dibromochloromethane (0.06 mg/L), and chloroform (0.07 mg/L).
\10\ A PWS is in compliance with the E. coli MCL unless any of the conditions identified under 40 CFR 141.63(c) occur.
\11\ Under the GWR in 40 CFR 141.402, a ground water system that does not provide at least 4-log treatment of viruses and has a distribution system RTCR
  sample that tests positive for total coliform is required to conduct triggered source water monitoring to evaluate whether the total coliform presence
  in the distribution system is due to fecal contamination in the ground water source. The system must monitor for one of three State-specified fecal
  indicators (i.e., E. coli, coliphage, or enterococci).
\12\ The Hazard Index is an approach that EPA uses to determine the health concerns associated with mixtures of certain PFAS in finished drinking water.
  The Hazard Index is made up of a sum of fractions. Each fraction compares the level of each PFAS measured in the water to the associated health-based
  water concentration.

IV. EPA's Protocol for Reviewing the NPDWRs Included in This Action

A. What was EPA's review process?

    This section provides an overview of the process EPA used to review 
the NPDWRs discussed in this document. The protocol document, ``EPA 
Protocol for the Fourth Review of Existing National Primary Drinking 
Water Regulations,'' contains a detailed description of the process the 
agency used to review the NPDWRs (USEPA, 2024c). The foundation of this 
protocol was developed for the Six-Year Review 1 based on the 
recommendations of the National Drinking Water Advisory Council (NDWAC, 
2000) and has undergone minor clarifications during each Six-Year 
Review cycle (USEPA, 2024c). Figure 1 presents an overview of the Six-
Year Review protocol and the possible review outcomes.
    The objective of the Six-Year Review process is to identify and 
prioritize NPDWRs for possible regulatory revision. The two major 
outcomes of the detailed review are either (1) the NPDWR is not 
appropriate for revision and no action is necessary at this time or (2) 
the NPDWR is a candidate for revision.
    The reasons why EPA might list an NPDWR as ``not appropriate for 
revision at this time'' could include:
     Recently completed, ongoing, or pending regulatory action: 
The NPDWR was recently completed, is being reviewed under an ongoing 
action, or is subject to a pending action.
     Ongoing or planned health effects assessment: The 
contaminant or contaminants regulated by the NPDWR has an ongoing or 
planned health effects assessment.
     No new information: EPA did not identify any new relevant 
information for the contaminant since the last Six-Year Review that 
indicates changes to the NPDWR may be appropriate.
     Data gaps/emerging information: New information indicates 
a possible change to the MCLG and/or MCL but changes to the NPDWR are 
not appropriate due to data gaps and emerging information that needs to 
be evaluated.
     Low priority and/or no meaningful opportunity: New 
information indicates a possible change to the MCLG and/or MCL but 
changes to the NPDWR are not appropriate at this time due to one or 
more of the following reasons: (1) possible changes present negligible 
gains in public health protection; (2) possible changes present limited 
opportunity for cost savings while maintaining the same or greater 
level of health protection; and/or (3) possible changes are a low 
priority because of competing workload priorities, limited return on 
the administrative costs associated with rulemaking, and the burden on 
states and the regulated community associated with implementing any 
regulatory change that would result.
    Alternatively, the reasons why an NPDWR could be listed as a 
candidate for revision are that the regulatory revision presents a 
meaningful opportunity to improve the level of public health 
protection, and/or achieve cost savings while maintaining or improving 
the level of public health protection.
    Individual regulatory provisions that are evaluated as part of the 
Six-Year Review process include: MCLG, MCL, MRDLG, MRDL, TT, best 
available technology (BAT), and other requirements, such as monitoring 
requirements.
    For example, the microbial regulations include TT requirements 
because no reliable, affordable, and technically feasible method is 
available to measure the microbial contaminants covered by those 
regulations. These TT requirements rely on the use of indicators that 
can be measured in drinking water, such as detection of total coliforms 
as an indicator of a potential pathway for pathogenic contamination in 
the distribution system. As part of the Six-Year Review 4, EPA 
evaluated new information related to the use of those indicators to 
determine if a meaningful opportunity to improve the level of public 
health protection exists. Results of EPA's review of the microbial 
regulations are presented in section V of this document.
Basic Principles
    EPA applied several basic principles to the Six-Year Review 
process:
     The agency sought to avoid redundant review efforts. 
Because EPA has reviewed information for certain NPDWRs as part of 
recently completed, ongoing, or pending regulatory actions, these 
NPDWRs were not subject to detailed review under the Six-Year Review 
process.
     The agency does not believe it is appropriate to consider 
revisions to NPDWRs for contaminants with an ongoing or planned health 
effect assessment where the MCL is set equal to the MCLG or that were 
set at the level at which health risk reduction benefits were maximized 
at a cost justified by the benefits in accordance with SDWA section 
1412(b)(6)(A)). This principle stems from the fact that any new health 
effects assessment may affect the MCL via a change in the MCLG or the 
assessment of the benefits associated with the MCL. EPA notes that 
these NPDWRs are not appropriate for revision and no action is 
necessary if the health effects assessment would not be completed 
during the review cycle.
     In evaluating the potential for new information to affect 
NPDWRs, EPA assumed no change to existing policies and procedures for 
developing NPDWRs. For example, in determining whether new information 
affected the feasibility of analytical methods for a contaminant, the 
agency assumed no

[[Page 59627]]

change to current policies and procedures for calculating practical 
quantitation limits.
     EPA may consider whether there is new public health risk 
information to justify accelerating review and potential revision of a 
particular NPDWR before the next review cycle.
Procedures
    EPA also applied the following procedures in the review process:
     EPA considered new information from health effects 
assessments that were completed by the information cutoff date. 
Assessments completed after this cutoff date will be reviewed by EPA 
during the next review cycle.
     During the review, EPA identified areas where relevant 
information, which is needed to determine whether a revision to an 
NPDWR may be appropriate, was either: inadequate, unavailable (i.e., 
data gaps), or emerging. To the extent EPA is able to fill data gaps or 
fully evaluate the emerging information, the agency will consider the 
information as part of the next review cycle.
     Finally, EPA assured that the scientific analyses 
supporting the review were consistent with the agency's peer review 
policy (USEPA, 2015a).
[GRAPHIC] [TIFF OMITTED] TR23JY24.000

B. How did EPA conduct the review of the NPDWRs?

    The protocol for the Six-Year Review 4 is organized as a series of 
questions to inform an assessment as to the appropriateness of revising 
an NPDWR. These questions are logically ordered into a decision tree. 
This section provides an overview of each of the review elements that 
EPA considered for each NPDWR during the Six-Year Review 4, including 
the following: initial review, health effects, analytical feasibility, 
occurrence and exposure, treatment feasibility, risk balancing, and 
other NPDWR revisions. The final review combines the findings from all 
these review elements to recommend whether an NPDWR is a candidate for 
revision. Further information about the review elements is described in 
the protocol document (USEPA, 2024c). The results of the Six-Year 
Review are presented in section V of this document.
1. Initial Review
    EPA's initial review of all the contaminants included in the Six-
Year Review 4 involved a simple identification of the NPDWRs that have 
either been recently completed or are being reviewed in an ongoing or 
pending action since the publication of Six-Year Review 3. In addition, 
the initial review also identified contaminants with ongoing health 
effects assessments that have an MCL equal to the MCLG. Excluding such 
contaminants from a more detailed review in the Six-Year Review 4 
prevents duplicative agency efforts.
2. Health Effects
    The principal objectives of the health effects review are to 
identify: (1) contaminants for which a new health effects assessment 
indicates that a change in the MCLG might be appropriate (e.g., because 
of a change in cancer classification or a change in reference dose 
(RfD)), and (2) contaminants for which new health effects information 
indicates a need to initiate a new health effects assessment.
    To meet the first objective, EPA reviewed the results of health 
effects assessments completed since promulgation of each NPDWR. To meet 
the second objective, the agency conducted a systematic literature 
search, to capture more recently published peer-reviewed studies on 
relevant health effects via the oral route

[[Page 59628]]

of exposure for the general population as well as sensitive 
subpopulations including children. The results of the literature search 
were used to survey the health effects literature that has become 
available since the previous review cycle, identify any emerging issues 
for a contaminant, and identify data gaps to inform future health 
assessment nominations.
3. Analytical Feasibility
    When establishing an NPDWR, EPA identifies a practical quantitation 
limit (PQL), which is the lowest achievable level of analytical 
quantitation during routine laboratory operating conditions within 
specified limits of precision and accuracy (50 FR 46880, USEPA, 1985). 
EPA has a separate process in place to approve new analytical methods 
for drinking water contaminants; therefore, review and approval of 
potential new methods is outside the scope of the Six-Year Review 
protocol. EPA recognizes, however, that the approval and adoption in 
recent years of new and/or improved analytical methods may enable 
laboratories to quantify contaminants at lower levels than was possible 
when NPDWRs were originally promulgated. This ability of laboratories 
to measure a contaminant at lower levels could affect its PQL, the 
value at which an MCL is set when it is limited by analytical 
feasibility. Therefore, the Six-Year Review process includes an 
examination of whether there have been changes in analytical 
feasibility that could possibly change the PQL for the subset of the 
NPDWRs that reach this stage of the review.
    To determine if changes in analytical feasibility could possibly 
support changes to PQLs, EPA relied primarily on two approaches to 
develop estimated quantitation levels (EQLs), which are based on either 
(1) minimum reporting levels (MRLs) obtained as part of the Six-Year 
Review 4 Information Collection Request (ICR), or (2) method detection 
limits (MDLs) from EPA-approved laboratory protocols.
    An MRL is the lowest level or contaminant concentration that a 
laboratory can reliably achieve within specified limits of precision 
and accuracy under routine laboratory operating conditions using a 
given method. The MRL values provide direct evidence from actual 
monitoring results about whether quantitation below the PQL using 
current analytical methods is feasible. An MDL is a measure of 
analytical sensitivity, representing the minimum reported concentration 
that can be distinguished from blank results with 99 percent 
confidence. MDLs have been used in the past to derive PQLs for 
regulated contaminants.
    EPA used the EQL as a threshold for occurrence analysis to help the 
agency assess for a meaningful opportunity to improve public health 
protection. It should be noted, however, that the use of an EQL does 
not necessarily indicate the agency's intention to promulgate a revised 
MCL based on the new PQL. Any change in the PQL for a contaminant could 
be part of future rulemaking efforts if EPA decides to initiate a 
regulatory revision for the contaminant.
4. Occurrence and Exposure Analysis
    EPA conducted the occurrence and exposure analysis in conjunction 
with other review elements to determine if an NPDWR revision would 
provide a meaningful opportunity to improve public health by:
     estimating the extent of contaminant occurrence, i.e., the 
number of PWSs in which contaminants occur at levels of interest 
(health-effects-based thresholds or analytical method limits), and;
     evaluating the number of people potentially exposed to 
contaminants at these levels.
    To evaluate national contaminant occurrence under the Six-Year 
Review 4, EPA reviewed data from the Six-Year Review 4 ICR database 
(SYR 4 ICR database) and other relevant sources. EPA collected SDWA 
compliance monitoring data and treatment technique information through 
use of an ICR (84 FR 58381, USEPA, 2019). EPA requested that states, as 
well as Tribes and territories with primacy voluntarily submit their 
compliance monitoring data and treatment technique information for 
regulated contaminants in PWSs. Specifically, EPA requested the 
submission of compliance monitoring data, treatment technique 
information, and related details collected between January 2012 and 
December 2019 for regulated contaminants and related parameters (e.g., 
water quality indicators). Forty-six states plus 13 other jurisdictions 
(Washington, DC, territories, and Tribes) provided data. The assembled 
data constitute the largest, most comprehensive set of drinking water 
compliance monitoring data and treatment technique information ever 
compiled and analyzed by EPA to inform decision making, containing 
almost 71 million analytical records from approximately 140,000 PWSs, 
serving approximately 301 million people nationally. Through extensive 
data management efforts, quality assurance evaluations, and 
communications with state data management staff, EPA established the 
SYR 4 ICR dataset (USEPA, 2019). The number of states and PWSs 
represented in the dataset varies across contaminants because of 
variability in state data submissions and contaminant monitoring 
schedules. EPA considers that these data are of sufficient quality to 
inform an understanding of the national occurrence of regulated 
contaminants and related parameters. Details of the data management and 
data quality assurance evaluations are available in the supporting 
document (USEPA, 2024d). The resulting database is available online on 
the Six-Year Review website at https://www.epa.gov/dwsixyearreview.
5. Treatment Feasibility
    An NPDWR either identifies an MCL or establishes enforceable TT 
requirements. When promulgating an MCL or enforceable treatment 
technique requirements, to determine feasibility, EPA identifies the 
best technology, treatment techniques, and other means which EPA finds, 
after examination for efficacy under field conditions and not solely 
under laboratory conditions, are available (taking cost into 
consideration). When promulgating an MCL, EPA also lists the 
technology, treatment techniques, or other means which are feasible for 
purposes of meeting the MCL. EPA reviews treatment feasibility to 
ascertain if available technologies meet BAT criteria for a 
hypothetical more stringent MCL, or if new information demonstrates an 
opportunity to improve public health protection through revision of an 
NPDWR TT requirement.
    To be a BAT, the treatment technology must meet several criteria 
such as having demonstrated consistent removal of the target 
contaminant under field conditions. Although treatment feasibility and 
analytical feasibility are considered together in evaluating the 
technical feasibility requirement for an MCL, historically, treatment 
feasibility has not been a limiting factor for MCLs. The result of this 
review element is a determination of whether treatment feasibility 
would pose a limitation to revising an MCL or provide an opportunity to 
revise the NPDWR TT requirement.
6. Risk-Balancing
    EPA reviews the risk-balancing analysis underlying some NPDWRs to 
examine how a potential regulatory revision would address tradeoffs in 
risks associated with different contaminants. Under this review, EPA 
considers whether a change to an MCL and/or TT

[[Page 59629]]

will increase the public health risk posed by one or more contaminants, 
and, if so, the agency considers revisions that will balance overall 
risks. This review element is relevant only to the NPDWRs included in 
the microbial and disinfection byproduct (MDBP) rules, which were 
promulgated to address the need for risk-balancing between microbial 
and disinfection byproduct (DBP) requirements, and among differing 
types of DBPs. NPDWRs for microbials and disinfectants and DBPs were 
not reviewed during Six-Year Review 4 due to ongoing regulatory action 
initiated by Six-Year Review 3.
7. Other NPDWR Revisions
    In addition to possible revisions to MCLGs, MCLs, and TTs, EPA 
evaluated whether other revisions are needed to other regulatory 
provisions in NPDWRs, such as monitoring and system reporting 
requirements. EPA focused this review element on issues that were not 
already being addressed through alternative mechanisms, such as a 
recently completed, ongoing, or pending regulatory action. EPA also 
reviewed implementation-related NPDWR concerns that were ``ready'' for 
rulemaking--that is, the problem to be resolved had been clearly 
identified, along with specific options to address the problem that 
could be shown to either clearly improve the level of public health 
protection or represent a meaningful opportunity for achieving cost 
savings while maintaining the same level of public health protection. 
The result of this review element is a determination regarding whether 
EPA should consider revisions to the monitoring and/or reporting 
requirements of an NPDWR.

V. Results of EPA's Review of NPDWRs

A. Overview of Six-Year Review 4 Results

    Table 2 of this document, lists the results of EPA's review of the 
88 NPDWRs assessed during Six-Year Review 4, along with the principal 
rationale for the review outcomes. Table 2 includes the 15 NPDWRs that 
have ongoing or pending regulatory actions.

                                  Table 2--Summary of Six-Year Review 4 Results
----------------------------------------------------------------------------------------------------------------
 
----------------------------------------------------------------------------------------------------------------
Outcome                                   Regulated contaminants
----------------------------------------------------------------------------------------------------------------
Not Appropriate for Revision at   Recently completed, ongoing or pending  Bromate...........  Haloacetic acids
 this Time.                        regulatory action.                     Chloramines (as      (HAA5).
                                                                           Cl2).              Heterotrophic
                                                                          Chlorine Dioxide     bacteria.
                                                                           (as ClO2).         Lead.
                                                                          Chlorine (as Cl2).  Legionella.
                                                                          Chlorite..........  Total
                                                                          Copper............   Trihalomethanes
                                                                          Cryptosporidium      (TTHM).
                                                                           (IE, LT1) \1\.     Turbidity.
                                                                          Giardia lamblia...  Viruses (SWTR, IE,
                                                                                               LT1).\1\
----------------------------------------------------------------------------------------------------------------
Not Appropriate for Revision at   Health effects assessment in process    Alpha/photon        Mercury
 this Time.                        or contaminant nominated for health     emitters.           (inorganic).
                                   assessment.                            Arsenic...........  Polychlorinated
                                                                          Beta/photon          biphenyls (PCBs).
                                                                           emitters.          Radium 226/228
                                                                          Chromium (total)..   (combined).
                                                                          Ethylbenzene......  Uranium.
                                 -------------------------------------------------------------------------------
                                  No new information, NPDWR remains       Asbestos..........  trans-1,2-
                                   appropriate after review.              Benzo(a)pyrene....   Dichloroethylene.
                                                                          Chlorobenzene.....  Dinoseb.
                                                                          Dalapon...........  E. coli.
                                                                          Di(2-               Endrin.
                                                                           ethylhexyl)adipat  Ethylene
                                                                           e (DEHA).           dibromide.
                                                                          Di(2-               2,4,5-TP (Silvex).
                                                                           ethylhexyl)phthal
                                                                           ate (DEHP).
                                                                          1,2-Dibromo-3-
                                                                           chloropropane
                                                                           (DBCP).
                                 -------------------------------------------------------------------------------
                                  New information,    Low priority and/   Acrylamide........  Heptachlor.
                                   but no revision     or no meaningful   Alachlor..........  Heptachlor
                                   recommended         opportunity.       Antimony..........   Epoxide.
                                   because . . .                          Atrazine..........  Hexachlorobenzene.
                                                                          Barium............  Hexachlorocyclopen
                                                                          Benzene...........   tadiene.
                                                                                              Lindane.
                                                                                              Methoxychlor.
                                                                          Beryllium.........  Oxamyl (Vydate).
                                                                          Cadmium...........  Pentachlorophenol.
                                                                          Carbofuran........  Picloram.
                                                                          Carbon              Selenium.
                                                                           Tetrachloride.     Simazine.
                                                                          Chlordane.........  Styrene.
                                                                          Cryptosporidium     Tetrachloroethylen
                                                                           (LT2) \1\.          e (PCE).
                                                                          1,2-                Thallium.
                                                                           Dichlorobenzene.   1,2,4-
                                                                          1,4-                 Trichlorobenzene.
                                                                           Dichlorobenzene.   1,1,1-
                                                                          1,2-Dichloroethane   Trichloroethane.
                                                                          1,1-                1,1,2-
                                                                           Dichloroethylene.   Trichloroethane.
                                                                          cis-1,2-            Toluene.
                                                                           Dichloroethylene.
                                                                          Dichloromethane...
                                                                          2,4-                Total Coliform.
                                                                           Dichlorophenoxyac  Toxaphene.
                                                                           etic acid (2,4-D). Trichloroethylene
                                                                          1,2-Dichoropropane   (TCE).
                                                                          Dioxin (2,3,7,8-    Vinyl Chloride.
                                                                           TCDD).             Xylenes.
                                                                          Diquat............
                                                                          Endothall.........
                                                                          Epichlorohydrin...
                                                                          Glyphosate........
                                                     -----------------------------------------------------------
                                                      Emerging            Cyanide (as free    Nitrate.
                                                       information and/    cyanide).          Nitrite.
                                                       or data gaps.      Fluoride..........
----------------------------------------------------------------------------------------------------------------
Candidate for Revision..........  New information.
                                  None.
----------------------------------------------------------------------------------------------------------------
\1\ Regulation abbreviations: Aircraft Drinking Water Rule (ADWR), Ground Water Rule (GWR), Revised Total
  Coliform Rule (RTCR), Surface Water Treatment Rule (SWTR), Interim Enhanced Surface Water Treatment Rule (IE),
  Long Term 1 Enhanced Surface Water Treatment Rule (LT1), and Long Term 2 Enhanced Surface Water Treatment Rule
  (LT2).


[[Page 59630]]

    EPA has identified no appropriate candidates for revision at this 
time.
    EPA's Office of Ground Water and Drinking Water is currently 
engaged in several ongoing and potential regulatory actions, in 
addition to being involved in the efforts to successfully implement 
recently promulgated rules including:
     Developing a proposal to revise the Microbial and 
Disinfection By-Product Rules, including eight NPDWRs listed as 
candidates for revision in Six-Year Review 3 (85 FR 61680, USEPA, 
2020a).
     On December 6, 2023, EPA published the proposed rule 
``National Primary Drinking Water for Lead and Copper: Improvements'' 
(88 FR 84878, USEPA, 2023a).
     In January 2024, EPA announced its commitment to 
promulgate a National Primary Drinking Water Regulation for Perchlorate 
by May 2027.\5\
---------------------------------------------------------------------------

    \5\ Additional information can be found at https://www.epa.gov/sdwa/perchlorate-drinking-water.
---------------------------------------------------------------------------

     On April 26, 2024, EPA published the PFAS final rule 
``PFAS National Primary Drinking Water Regulation'' (89 FR 32532, 
USEPA, 2024a).
     On May 24, 2024, EPA published the final rule ``National 
Primary Drinking Water Regulations: Consumer Confidence Reports'' (89 
FR 45980, USEPA, 2024b).
    Therefore, when evaluating the review results described in sections 
V.B and V.C of this document, EPA also considered competing workloads 
and potential diversion of resources from these other planned, ongoing, 
and pending higher priority efforts within the drinking water office.

B. Chemical Phase Rules/Radionuclides Rules

    The NPDWRs for chemical contaminants, collectively called the Phase 
Rules, were promulgated between 1987 and 1992, following the 1986 SDWA 
amendments. In December 2000, EPA promulgated final radionuclide 
regulations, which had been issued as interim rules in July 1976.
1. Key Review Outcomes
    EPA has decided that it is not appropriate at this time to revise 
any of the NPDWRs covered under the Phase or Radionuclides Rules (Table 
2 of this document). These NPDWRs were determined not to be candidates 
for revision for one or more of the following reasons:
     ongoing/pending regulatory action warrants waiting for 
further review;
     no new information was identified to suggest possible 
changes in MCLG/MCL;
     new information did not present a meaningful opportunity 
for health risk reduction or cost savings while maintaining/improving 
public health protection;
     emerging information and/or data gaps create substantial 
uncertainty.
    In addition, EPA is announcing that the NPDWRs for 
trichloroethylene (TCE) and tetrachloroethylene (PCE) are no longer 
candidates for revision at this time. In March 2010, as an outcome of 
the second cycle of Six-Year Review, EPA listed the TCE and PCE NPDWRs 
as candidates for revision (75 FR 15500, USEPA, 2010a). TCE and PCE 
were not reviewed under Six-Year Review 3 because regulatory revisions 
were being considered as part of plans to address regulated and 
unregulated Carcinogenic Volatile Organic Contaminants (cVOCs) in a 
group rule (75 FR 3525, January 21, 2010; 82 FR 3531, USEPA, 2017a). 
However, after evaluating currently available information for both of 
these chemicals, the EPA concludes that these NPDWRS are not 
appropriate for revision at this time because minimal reductions in 
health risks would be associated with any revisions to these 
regulations. Given resource limitations, competing workload priorities, 
and administrative costs and burden to states to adopt any regulatory 
changes associated with rulemakings, as well as limited potential 
health benefits, these NPDWRs are considered a low priority and are no 
longer candidates for revision at this time.
    Section V.B.2 of this document describes the results of the review 
organized by each review element. Section V.B.3 of this document 
includes a description of the new information gathered by EPA for 
select contaminants that EPA determined are not candidates for revision 
at this time due to emerging information or data gaps or no meaningful 
opportunity for health risk reduction. The contaminants discussed in 
detail in section V.B.3 of this document are cyanide, fluoride, 
nitrate, nitrite, TCE, and PCE.
    Review results organized by contaminant for the Chemical Phase and 
Radionuclides Rules can be found in the ``Chemical Contaminant 
Summaries for the Fourth Six-Year Review of National Primary Drinking 
Water Regulations'' (USEPA, 2024e).
2. Summary of Review Results
Initial Review
    After conducting the initial review, as described in section IV.B.1 
of this document, EPA identified two chemical contaminants (lead and 
copper) with NPDWRs that were considered as part of a recently 
completed action, and which are also currently part of an ongoing or 
pending regulatory action. EPA published the Lead and Copper Rule 
Revisions in January 2021 and published the proposed Lead and Copper 
Rule Improvements on December 6, 2023. EPA did not evaluate lead and 
copper in Six-Year Review 4 because such effort would be redundant with 
these recent and ongoing rulemakings. EPA also identified contaminants 
with ongoing or planned EPA health effects assessments. As of December 
31, 2021, nine chemical or radiological contaminants reviewed had 
ongoing or planned formal EPA health effects assessments. Table 3 of 
this document below lists the contaminants with ongoing or planned EPA 
assessments at the time of the Six-Year Review 4 cutoff date and the 
current status of those reviews. EPA did not conduct a detailed review 
of these nine chemical and radiological contaminants under Six-Year 
Review 4.

Table 3--Six-Year Review Chemical/Radiological Contaminants With Ongoing
                    or Planned EPA Health Assessments
------------------------------------------------------------------------
     Chemical/radionuclide                     Status \1\
------------------------------------------------------------------------
Alpha/photon emitters.........  EPA Office of Air and Radiation (OAR) is
                                 conducting a review of alpha and beta
                                 photon emitters. Additional information
                                 about this effort can be found at in
                                 the Federal Register (87 FR 15988,
                                 USEPA, 2022a) or at: https://sab.epa.gov/ords/sab/r/sab_apex/sab_bkup/advisoryactivitydetail?p18_id=2616&clear=18&session=8694491614209.
Arsenic.......................  Inorganic arsenic is being assessed by
                                 the EPA IRIS Program. The assessment
                                 status can be found at: https://iris.epa.gov/ChemicalLanding/&substance_nmbr=278.
Beta/photon emitters..........  EPA/OAR is conducting a review of alpha
                                 and beta photon emitters. Additional
                                 information about this effort can be
                                 found at in the Federal Register (87 FR
                                 15988, USEPA, 2022a) or at: https://sab.epa.gov/ords/sab/r/sab_apex/sab_bkup/advisoryactivitydetail?p18_id=2616&clear=18&session=8694491614209.

[[Page 59631]]

 
Chromium VI (as part of total   Chromium VI is being assessed by the EPA
 Cr).                            IRIS Program. The assessment status can
                                 be found at: https://iris.epa.gov/ChemicalLanding/&substance_nmbr=144.
Ethylbenzene..................  Ethylbenzene is being assessed by the
                                 EPA IRIS Program. The assessment status
                                 can be found at: https://iris.epa.gov/ChemicalLanding/&substance_nmbr=51.
Mercury.......................  Inorganic Mercury Salts is being
                                 assessed by the EPA IRIS Program. The
                                 Assessment status can be found at:
                                 https://iris.epa.gov/ChemicalLanding/&substance_nmbr=1522.
PCBs..........................  PCBs are being assessed by the EPA IRIS
                                 Program. The assessment status can be
                                 found at: https://iris.epa.gov/ChemicalLanding/&substance_nmbr=294.
Radium 226/228................  EPA/OAR is conducting a review of
                                 radium. Additional information about
                                 this effort can be found at in the
                                 Federal Register (87 FR 15988, USEPA,
                                 2022a) or at: https://sab.epa.gov/ords/sab/r/sab_apex/sab_bkup/advisoryactivitydetail?p18_id=2616&clear=18&session=8694491614209.
Uranium.......................  Uranium is being assessed by the EPA
                                 IRIS Program. The assessment status can
                                 be found at: https://iris.epa.gov/ChemicalLanding/&substance_nmbr=259.
------------------------------------------------------------------------
\1\ Additional information on the status of EPA IRIS Program assessments
  can be found in the EPA IRIS Program Outlooks at https://www.epa.gov/iris/iris-program-outlook.

    Regarding the ongoing health assessment for Chromium VI (hexavalent 
chromium), on October 20, 2022 the EPA published its draft ``IRIS 
Toxicological Review of Hexavalent Chromium [Cr(IV)]'' (87 FR 63774, 
USEPA, 2022b). This draft health effects assessment, which includes a 
comprehensive evaluation of potential health effects, preliminarily 
categorizes hexavalent chromium as likely carcinogenic to humans via 
the oral exposure pathway. The final IRIS assessment was not available 
as of the publication of this document and for consideration as part of 
Six-Year Review 4. When this human health assessment is final, EPA will 
carefully review the conclusions and consider all relevant information 
to determine whether the NPDWR for chromium is a candidate for 
revision.
    After the initial review was completed, EPA identified 71 chemical 
and radiological NPDWRs that were appropriate for detailed review.
Health Effects
    The principal objectives of the health effects assessment review 
were to identify: (1) contaminants for which a new health effects 
assessment indicates that a change in MCLG might be appropriate (e.g., 
because of a change in cancer classification or an RfD), and (2) 
contaminants for which the agency has identified new health effects 
information suggesting a need to initiate a new health effects 
assessment. For chemicals that were not excluded due to an ongoing or 
planned health effects assessment by EPA, a more detailed review was 
undertaken. Of the chemicals that underwent a more detailed review, EPA 
identified 29 contaminants for which an updated RfD and/or the cancer 
risk assessment (from oral exposure) or new relevant non-EPA 
assessments might support a change to the MCLG. These 29 chemicals were 
further evaluated as part of the Six-Year Review 4 to determine whether 
they were candidates for regulatory revision. Table 4 of this document 
lists the chemicals with available new health effects information and 
the sources of the relevant new information. As shown in this table, 15 
chemical contaminants have information that could support a lower MCLG, 
and 14 contaminants have new information that could support a higher 
MCLG.

   Table 4--Chemicals With New Health Assessments That Could Support a
                             Change in MCLG
------------------------------------------------------------------------
                Chemical                     Relevant new assessment
------------------------------------------------------------------------
           15 Contaminants with Potential to Decrease the MCLG
------------------------------------------------------------------------
Antimony...............................  CalEPA, 2016.
Cadmium................................  ATSDR, 2012.
Carbofuran.............................  USEPA OPP, 2008.
Cyanide................................  USEPA IRIS, 2010b.
cis-1,2-Dichloroethylene...............  USEPA IRIS, 2010c.
Endothall..............................  USEPA OPP, 2015b.
Fluoride...............................  USEPA OW, 2010d.
Hexachlorocyclopentadiene..............  USEPA IRIS, 2001.
Methoxychlor...........................  CalEPA, 2010a.
Oxamyl.................................  USEPA OPP, 2017b.
Selenium...............................  ATSDR, 2003.
Styrene................................  CalEPA, 2010b.
Toluene................................  Health Canada, 2014.
1,2,4-Trichlorobenzene.................  USEPA PPRTV, 2009a.
Xylenes................................  Health Canada, 2014.
------------------------------------------------------------------------
           14 Contaminants with Potential to Increase the MCLG
------------------------------------------------------------------------
Alachlor...............................  USEPA OPP, 2007a.
Atrazine...............................  USEPA OPP, 2018a.
Barium.................................  USEPA IRIS, 2005.
Beryllium..............................  USEPA IRIS, 1998.
2,4-Dichlorophenoxy-acetic acid (2,4-D)  USEPA OPP, 2017c.
1,2-Dichlorobenzene....................  ATSDR, 2006.
1,4-Dichlorobenzene....................  ATSDR, 2006.

[[Page 59632]]

 
1,1-Dichloroethylene...................  USEPA IRIS, 2002.
Diquat.................................  USEPA OPP, 2020b.
Glyphosate.............................  USEPA OPP, 2017d.
Lindane................................  USEPA OPP, 2004.
Picloram...............................  USEPA OPP, 2020c.
Simazine...............................  USEPA OPP, 2018b.
1,1,1-Trichloroethane..................  USEPA IRIS, 2007b.
------------------------------------------------------------------------

    Details of the health effects assessment review of the chemical and 
radiological contaminants are documented in the ``Results of the Health 
Effects Assessment for the Fourth Six-Year Review of Existing Chemical 
and Radionuclide National Primary Drinking Water Standards'' (USEPA, 
2024f).
Analytical Feasibility
    EPA performed analytical feasibility analyses for the contaminants 
that reached this portion of the review. These contaminants included 
the 15 chemical contaminants identified under the health effects 
assessment review as having potential for a lower MCLG. EPA evaluated 
whether there were any analytical limitations to lowering the MCL to 
the potential MCLG. EPA also evaluated an additional 22 contaminants 
with MCLs higher than the current MCLGs due to analytical limitations 
at the time of rule promulgation. The document ``Analytical Feasibility 
Support Document for the Fourth Six-Year Review of National Primary 
Drinking Water Regulations: Chemical Phase and Radionuclides Rules'' 
(USEPA, 2024g) describes the process EPA used to evaluate whether 
changes in PQL are possible in those instances where the MCL may be 
limited by analytical feasibility.
    Table 5 of this document shows the outcomes of EPA's analytical 
feasibility review for two general categories of drinking water 
contaminants: (1) contaminants where health effects assessments 
indicate potential for lower MCLGs, and (2) contaminants where existing 
MCLs were limited by analytical feasibility at the time of promulgation 
and new information indicates a potential to reduce the PQL.
     A health effects assessment indicates potential for lower 
MCLG. This category includes the 15 contaminants identified in the 
health effects review as having potential for a lower MCLG. EPA 
reviewed the available information to determine if analytical 
feasibility could limit the potential for MCL revisions. The current 
PQL is not a limiting factor for seven of the 15 contaminants 
identified by the health effects review as potential candidates for 
lower MCLGs (cis-1,2-dichloroethylene, fluoride, 
hexachlorocyclopentadiene, oxamyl, selenium, toluene, and xylenes). For 
the remaining eight contaminants, the current PQL is higher than the 
potential new MCLG, so EPA evaluated whether there is an opportunity to 
lower the PQL. The evaluations indicated that all but one contaminant 
(antimony) have potential for a lower PQL, although not to the 
potential MCLG. Consequently, analytical feasibility may limit 
potential MCL revisions for the remaining seven contaminants (Table 5 
of this document).
     Existing MCLs are based on analytical feasibility. This 
category includes 22 contaminants with existing MCLs that are greater 
than the associated MCLGs due to analytical constraints at the time of 
rule promulgation. Two of the contaminants (thallium and 1,1,2-
trichloroethane) are non-carcinogenic and have a non-zero MCLG, and the 
remaining 20 contaminants are carcinogens with MCLGs equal to zero. EPA 
evaluated whether the PQL could be lowered for each of these 
contaminants. The evaluations indicated that all but five 
(benzo[a]pyrene, DBCP, DEHP, ethylene dibromide, PCBs) of the 22 
contaminants evaluated have potential for a lower PQL (Table 5 of this 
document).
    Where analytical feasibility evaluations indicated the potential 
for a PQL reduction, Table 5 of this document lists the type of data 
that support this conclusion. The types of data considered include 
laboratory proficiency tests (PT), method detection limits (MDL) from 
EPA-approved methods, and minimum reporting level (MRL) from the SYR 4 
ICR dataset. The methods to evaluate each of these data types to 
identify potential to reduce PQLs are described in the analytical 
feasibility support document (USEPA, 2024g). Where the evaluations 
indicated that the current PQL remained appropriate, Table 5 shows of 
this document ``Data do not support PQL reduction.'' EPA found 
information supporting potentially lower MCLs for 31 out of 37 
contaminants evaluated.

[[Page 59633]]



          Table 5--Analytical Feasibility Reassessment Results
------------------------------------------------------------------------
                                                  Analytical feasibility
                                   Current PQL     reassessment result
          Contaminant             ([micro]g/L)      (and source of new
                                                     information) \1\
------------------------------------------------------------------------
  15 Contaminants Identified Under the Health Effects Review as Having
                        Potential for Lower MCLG
------------------------------------------------------------------------
Antimony.......................               6  Data do not support PQL
                                                  reduction.
Cadmium........................               2  PQL reduction supported
                                                  (MDL, MRL).
Carbofuran.....................               7  PQL reduction supported
                                                  (MDL).
Cis-1,2-dichloroethylene.......               5  PQL not limiting.
Cyanide........................             100  PQL reduction supported
                                                  (MDL).
Endothall......................              90  PQL reduction supported
                                                  (MDL, MRL).
Fluoride.......................             500  PQL not limiting.
Hexachlorocyclopentadiene......               1  PQL not limiting.
Methoxychlor...................              10  PQL reduction supported
                                                  (MDL, MRL, PT).
Oxamyl.........................              20  PQL not limiting.
Selenium.......................              10  PQL not limiting.
Styrene........................               5  PQL reduction supported
                                                  (MDL, MRL, PT).
Toluene........................               5  PQL not limiting.
Xylenes........................               5  PQL not limiting.
1,2,4-Trichlorobenzene.........               5  PQL reduction supported
                                                  (MDL, MRL, PT).
------------------------------------------------------------------------
 22 Contaminants with MCLs Limited by Analytical Feasibility and Higher
                               than MCLGs
------------------------------------------------------------------------
Benzene........................               5  PQL reduction supported
                                                  (MDL, MRL, PT).
Benzo[a]pyrene.................             0.2  Data do not support PQL
                                                  reduction.
Carbon tetrachloride...........               5  PQL reduction supported
                                                  (MDL, MRL, PT).
Chlordane......................               2  PQL reduction supported
                                                  (MDL).
1,2-Dibromo-3-chloropropane                 0.2  Data do not support PQL
 (DBCP).                                          reduction.
1,2-Dichloroethane.............               5  PQL reduction supported
                                                  (MDL, MRL, PT).
Dichloromethane................               5  PQL reduction supported
                                                  (MDL, MRL, PT).
1,2-Dichloropropane............               5  PQL reduction supported
                                                  (MDL, MRL, PT).
Di(2-ethylhexyl)phthalate                     5  Data do not support PQL
 (DEHP).                                          reduction.
Ethylene dibromide.............            0.05  Data do not support PQL
                                                  reduction.
Heptachlor.....................             0.4  PQL reduction supported
                                                  (MDL).
Heptachlor epoxide.............             0.2  PQL reduction supported
                                                  (MDL).
Hexachlorobenzene..............               1  PQL reduction supported
                                                  (MDL, MRL).
Pentachlorophenol..............               1  PQL reduction supported
                                                  (MDL).
PCBs...........................             0.5  Data do not support PQL
                                                  reduction.
2,3,7,8-TCDD (dioxin)..........         0.00003  PQL reduction supported
                                                  (MRL).
Tetrachloroethylene............               5  PQL reduction supported
                                                  (MDL, MRL).
Thallium.......................               2  PQL reduction supported
                                                  (MRL).
Toxaphene......................               3  PQL reduction supported
                                                  (MRL, PT).
1,1,2-Trichloroethane..........               5  PQL reduction supported
                                                  (MDL, MRL, PT).
Trichloroethylene..............               5  PQL reduction supported
                                                  (MDL, MRL, PT).
Vinyl chloride.................               2  PQL reduction supported
                                                  (MDL, MRL, PT).
------------------------------------------------------------------------
\1\ The information source codes refer to the method detection limit
  (MDL), minimum reporting level (MRL), and proficiency testing (PT)
  data analyses. See USEPA (2024g) for further information.

Occurrence and Exposure
    Using the SYR 4 ICR database, EPA conducted an assessment to 
evaluate national occurrence of regulated contaminants and estimate the 
potential population exposed to these contaminants. The details of the 
current chemical occurrence analysis are documented in the ``Analysis 
of Regulated Contaminant Occurrence Data from Public Water Systems in 
Support of the Fourth Six-Year Review of National Primary Drinking 
Water Regulations: Chemical Phase Rules and Radionuclides Rules'' 
(USEPA, 2024h). Based on quantitative benchmarks which were identified 
in the health effects and analytical feasibility analyses, EPA 
conducted the occurrence and exposure analysis for 31 contaminants.
    This analysis shows that 27 of the 31 contaminants assessed rarely 
occur at levels above the identified benchmark (e.g., potential MCLG or 
PQL). For these 27 contaminants, monitoring results only exceeded 
benchmarks in a very small percentage (i.e., less than 0.5 percent) of 
systems, which serve a very small percentage of the population, 
indicating that revisions to NPDWRs are unlikely to provide a 
meaningful opportunity to improve public health protection at the 
national level. Therefore, these 27 contaminants were not further 
considered as candidates for regulatory revision. The other four 
contaminants (cyanide, fluoride, TCE, and PCE) occurred at rates 
ranging from 0.57 to 9.1 percent of systems within the SYR 4 ICR 
dataset and 3.4 to 6.3 percent of the population served by those 
systems. Additional considerations for cyanide, fluoride, TCE, and PCE 
are discussed in section V.B.3 of this document. Table 6 of this 
document lists the numerical benchmarks used to conduct the occurrence 
analysis, the total number of systems with mean concentrations 
exceeding a benchmark, and the estimated population served by those 
systems. These average concentration-based evaluations are intended to 
inform the Six-Year Review, not to assess compliance with regulatory 
standards.

[[Page 59634]]



                     Table 6--Occurrence and Potential Exposure Analysis for Chemical NPDWRs
----------------------------------------------------------------------------------------------------------------
                                                                            Number (and     Population served by
                                                                          percentage) of     systems with a mean
                                          Current MCL    Benchmark \1\    systems with a    concentration higher
              Contaminant                   (ug/L)          (ug/L)      mean concentration   than benchmark (and
                                                                          \2\ higher than    percentage of total
                                                                             benchmark           population)
----------------------------------------------------------------------------------------------------------------
           Contaminants Identified Under the Health Effects Review as Having Potential for Lower MCLG
----------------------------------------------------------------------------------------------------------------
Cadmium...............................               5               1         182 (0.36%)       430,823 (0.16%)
Carbofuran............................              40               5       \3\ 7 (0.02%)    \3\ 49,409 (0.02%)
Cyanide...............................             200              50         328 (0.85%)     8,134,220 (3.43%)
cis-1,2-Dichloroethylene..............              70              10           7 (0.01%)        42,215 (0.02%)
Endothall.............................             100              50                   0                     0
Fluoride \4\..........................           4,000             900       4,479 (9.05%)    17,058,830 (6.30%)
Hexachlorocyclopentadiene.............              50              40                   0                     0
Methoxychlor..........................              40               1          1 (<0.01%)        22,536 (0.01%)
Oxamyl................................             200               9       \3\ 7 (0.02%)    \3\ 52,677 (0.02%)
Selenium..............................              50              30          91 (0.18%)        84,988 (0.03%)
Styrene...............................             100             0.5          89 (0.17%)        27,473 (0.01%)
Toluene...............................           1,000              60          14 (0.03%)        5,256 (<0.01%)
1,2,4-Trichlorobenzene................              70             0.5          15 (0.03%)       126,201 (0.05%)
Xylenes (total).......................          10,000              80          23 (0.05%)        34,728 (0.01%)
----------------------------------------------------------------------------------------------------------------
                  Contaminants with MCLs Higher than MCLGs (Limited by Analytical Feasibility)
----------------------------------------------------------------------------------------------------------------
Benzene...............................               5             0.5          83 (0.16%)       319,633 (0.12%)
Carbon tetrachloride..................               5             0.5          90 (0.17%)       766,891 (0.28%)
Chlordane.............................               2               1          1 (<0.01%)          240 (<0.01%)
1,2-Dichloroethane....................               5             0.5          60 (0.11%)       181,041 (0.07%)
Dichloromethane.......................               5             0.5         215 (0.41%)       360,289 (0.13%)
1,2-Dichloropropane...................               5             0.5          41 (0.08%)        34,800 (0.01%)
Heptachlor............................             0.4             0.1          1 (<0.01%)          900 (<0.01%)
Heptachlor epoxide....................             0.2             0.1           3 (0.01%)        32,710 (0.01%)
Hexachlorobenzene.....................               1             0.1           6 (0.02%)        17,278 (0.01%)
Pentachlorophenol.....................               1             0.9                   0                     0
2,3,7,8-TCDD (dioxin).................         0.00003        0.000005           7 (0.11%)        2,311 (<0.01%)
Tetrachloroethylene (PCE).............               5             0.5         432 (0.83%)    15,811,810 (5.76%)
Thallium..............................               2               1          71 (0.14%)        57,541 (0.02%)
Toxaphene.............................               3               1           2 (0.01%)          335 (<0.01%)
1,1,2-Trichloroethane.................               5               3          2 (<0.01%)           50 (<0.01%)
Trichloroethylene (TCE)...............               5             0.5         297 (0.57%)    12,755,926 (4.65%)
Vinyl chloride........................               2             0.5          24 (0.05%)       307,275 (0.11%)
----------------------------------------------------------------------------------------------------------------
\1\ Benchmark screening levels were set to either potential maximum contaminant level goals (MCLGs) or estimated
  quantitation levels (EQLs), depending on the contaminant. For more information see USEPA (2024g).
\2\ Results are based on long-term means generated by substituting one-half the MRL for each non-detection
  record. For results based on substituting the value of the full MRL or zero see USEPA (2024h).
\3\ Oxamyl and carbofuran have health endpoints associated with acute exposure and are not appropriate for long-
  term mean estimates. Results show the number of systems with at least one detection exceeding the benchmark.
\4\ Estimates represent naturally occurring fluoride concentrations. Quality assurance steps were taken to
  exclude samples from fluoridated water systems. See USEPA (2024i) for details.

    In addition, EPA performed a source water occurrence analysis for 
the 15 chemical contaminants in which updated health effects 
assessments indicated the possibility to increase (i.e., render less 
stringent) the MCLG values. EPA conducted this analysis to assess for 
meaningful opportunity to achieve cost savings while maintaining or 
improving the level of public health protection. The data available to 
characterize contaminant occurrence was limited because a comprehensive 
dataset to characterize drinking water source quality is not available. 
Data from the U.S. Geological Survey (USGS) National Water Quality 
Assessment program and the U.S. Department of Agriculture Pesticide 
Data Program water monitoring survey provide useful insights into 
potential contaminant occurrence in source water. The analysis of the 
available contaminant occurrence data for potential drinking water 
sources indicated relatively low contaminant occurrence in the 
concentration ranges of interest, and consequently, no meaningful 
opportunity for system cost savings by increasing the MCLG and MCL for 
these 15 contaminants. The results of this analysis were documented in 
``Occurrence Analysis for Potential Source Waters for the Fourth Six-
Year Review of National Primary Drinking Water Regulations'' (USEPA, 
2024j).
Treatment Feasibility
    Currently, all of the MCLs for chemical and radiological 
contaminants are either (1) set equal to the MCLGs, (2) limited by 
analytical feasibility, or (3) set at the level at which health risk 
reduction benefits were maximized at a cost justified by the benefits; 
none are currently limited by treatment feasibility. EPA considers 
treatment feasibility after identifying contaminants with the potential 
to lower the MCLG/MCL that constitute a meaningful opportunity to 
improve public health. No such contaminants were identified in the 
occurrence and exposure analysis described above.
    Treatment techniques were promulgated for two of the chemical and 
radiological contaminants that were subject to a detailed review in 
Six-Year Review 4. Acrylamide and epichlorohydrin occur in drinking 
water as treatment impurities and are primarily introduced as residuals 
in polymers and copolymers used for water treatment. There are no 
standardized analytical methods for their measurement in water; instead 
of sampling, water systems must certify to the State in writing that 
they use products meeting the specifications in the NPDWR. To evaluate 
the potential to revise the NPDWRs for these contaminants, EPA obtained 
data from

[[Page 59635]]

NSF on analyses for approval of products against NSF/ANSI Standard 60, 
which are based on EPA's regulation. NSF certification data shows that 
manufactured products contain acrylamide and epichlorohydrin impurity 
levels far below the current regulatory standard. Specifically, the 
mean residual acrylamide concentration of certified products is one-
fifth of the current regulatory level and the 90th percentile is one-
half. There were no samples with detections of residual 
epichlorohydrin. The available data indicates that the majority of 
tested products already pose lower health risks than required under the 
current TT, and therefore, revisions are a low priority. EPA is not 
listing acrylamide and epichlorohydrin as candidates for revision at 
this time. See USEPA (2024k) for details.
Other Regulatory Revisions
    In addition to possible revisions to MCLGs, MCLs, and TTs, as a 
part of the Six-Year Review 4, EPA considered whether other regulatory 
revisions to NPDWRs are needed to address implementation issues, such 
as revisions to monitoring and system reporting requirements. EPA used 
the protocol to evaluate which implementation issues to consider 
(USEPA, 2024c). EPA's protocol focused on items that were not already 
being addressed, or had not yet been addressed, through alternative 
mechanisms (e.g., as a part of a recent or ongoing rulemaking).
    EPA compiled information on implementation-related issues 
associated with the Chemical Phase Rules. EPA also identified 
unresolved implementation issues and concerns from previous Six-Year 
Reviews. The complete list of implementation issues related to the 
Phase and Radionuclides Rules is presented in ``Consideration of Other 
Regulatory Revisions in Support of the Fourth Six-Year Review of the 
National Primary Drinking Water Regulations: Chemical Phase Rules and 
Radionuclides Rules'' (USEPA, 2024l).
    The agency focused on the following five implementation issues in 
the Six-Year Review 4:

 Use of an alternative MCL for nitrate in Noncommunity Water 
Systems (NCWSs)
 Frequency of nitrate monitoring in Transient Noncommunity 
Water Systems (TNCWS)
 Frequency of nitrite monitoring
 Total nitrate-nitrogen plus nitrite-nitrogen MCL
 Total cyanide screening for free cyanide
    Table 7 of this document provides a brief description of the five 
issues and identified potential ways of addressing them. Please see 
section V.B.3. of this document for a discussion of these contaminants 
and their review outcomes. Please see USEPA (2024l) for a more detailed 
description and estimated scope of these issues.

Table 7--Chemical Rule Implementation Issues Identified That Fall Within
                      the Scope of an NPDWR Review
------------------------------------------------------------------------
               Implementation issue                 Description of issue
------------------------------------------------------------------------
Nitrate Alternative MCL in Non-community Water      EPA evaluated the
 Systems.                                            possibility of
                                                     removing or further
                                                     restricting the
                                                     options for some
                                                     NCWSs to use an
                                                     alternative nitrate-
                                                     nitrogen MCL of up
                                                     to 20 mg/L. The
                                                     nitrate-nitrogen
                                                     MCL specified for
                                                     PWSs in 40 CFR
                                                     141.62 is 10 mg/L
                                                     and is based on the
                                                     critical health
                                                     endpoint of
                                                     methemoglobinemia
                                                     in children under
                                                     six months of age.
                                                     40 CFR 141.11
                                                     provides States the
                                                     discretion to use
                                                     an alternative MCL
                                                     of 20 mg/L for non-
                                                     community water
                                                     systems (NCWS).
                                                     This alternative
                                                     MCL is allowed
                                                     under certain
                                                     conditions--includi
                                                     ng that water would
                                                     be unavailable to
                                                     children under six
                                                     months of age.
                                                    Monitoring
                                                     requirements for
                                                     nitrate-nitrogen
                                                     are specified in
                                                     the introductory
                                                     text to 40 CFR
                                                     141.23, which
                                                     states that ``Non-
                                                     transient, non-
                                                     community water
                                                     systems shall
                                                     conduct monitoring
                                                     to determine
                                                     compliance with the
                                                     maximum contaminant
                                                     levels specified in
                                                     Sec.   141.62 in
                                                     accordance with
                                                     this section.
                                                     Transient, non-
                                                     community water
                                                     systems (TNCWS)
                                                     shall conduct
                                                     monitoring to
                                                     determine
                                                     compliance with the
                                                     nitrate and nitrite
                                                     MCL in Sec.  Sec.
                                                     141.11 and 141.62
                                                     (as appropriate) in
                                                     accordance with
                                                     this section.''
                                                    Potential concerns
                                                     with the current
                                                     rule provisions
                                                     were identified as:
                                                        The
                                                        alternative MCL
                                                        does not address
                                                        any nitrate-
                                                        induced health
                                                        concerns beyond
                                                        methemoglobinemi
                                                        a and
                                                        While
                                                        Sec.   141.11
                                                        allows the use
                                                        of the
                                                        alternative MCL
                                                        by all eligible
                                                        NCWS, Sec.
                                                        141.23 implies
                                                        that only TNCWS,
                                                        a subcategory of
                                                        NCWS, are
                                                        eligible to use
                                                        the alternative
                                                        MCL.
                                                    To determine the
                                                     scope of this
                                                     issue, the agency
                                                     reviewed state
                                                     drinking water
                                                     regulations and
                                                     analyzed SYR 4 ICR
                                                     nitrate compliance
                                                     data and identified
                                                     nominal application
                                                     of the alternative
                                                     nitrate MCL by
                                                     NCWSs. In addition,
                                                     the nitrate and
                                                     nitrite human
                                                     health assessments
                                                     are currently being
                                                     evaluated by the
                                                     EPA IRIS program.
                                                     An updated
                                                     assessment could
                                                     inform the
                                                     potential health
                                                     effects of nitrate
                                                     exposure to levels
                                                     between 10 and 20
                                                     mg/L on adult
                                                     populations. EPA
                                                     will consider all
                                                     available and
                                                     updated human
                                                     health assessments
                                                     as it conducts
                                                     future cycles of
                                                     the six-year
                                                     review.
Nitrate Monitoring Frequency in Transient           Currently, community
 Noncommunity Water Systems.                         water systems
                                                     (CWSs) and NTNCWSs
                                                     are required to
                                                     monitor for nitrate
                                                     quarterly if a
                                                     sample is greater
                                                     than or equal to 50
                                                     percent of the
                                                     nitrate MCL (Sec.
                                                     141.23). TNCWSs are
                                                     required to monitor
                                                     for nitrate
                                                     annually (Sec.
                                                     141.23(d)(4)). In
                                                     the preamble to the
                                                     1991 final Phase II
                                                     rule, the agency
                                                     describes TNCWSs as
                                                     being subject to
                                                     the quarterly
                                                     monitoring
                                                     requirement stating
                                                     that ``EPA has
                                                     decided to retain
                                                     the 50 percent
                                                     trigger for
                                                     increased nitrate
                                                     monitoring in the
                                                     case of nitrate and
                                                     also to extend this
                                                     requirement to
                                                     TWSs'' (56 FR 3566,
                                                     USEPA, 1991).
                                                    EPA notes the
                                                     conflict between
                                                     the regulatory text
                                                     and the preamble.
                                                     To evaluate whether
                                                     it may be
                                                     appropriate to
                                                     revise the nitrate
                                                     NPDWR, the agency
                                                     analyzed compliance
                                                     monitoring data
                                                     collected under the
                                                     SYR 4 ICR. EPA
                                                     found that while
                                                     the majority of
                                                     TNCWSs that
                                                     reported detections
                                                     equal or greater
                                                     than 50 percent of
                                                     the nitrate MCL did
                                                     not conduct
                                                     quarterly
                                                     monitoring
                                                     afterward, the
                                                     number of these
                                                     systems appears
                                                     relatively small.
                                                     Due to the limited
                                                     scope of this
                                                     issue, EPA is not
                                                     revising the
                                                     monitoring
                                                     requirements at
                                                     this time but will
                                                     consider monitoring
                                                     requirements if
                                                     NPDWRs are revised
                                                     in the future.

[[Page 59636]]

 
Nitrite Monitoring Frequency......................  According to 40 CFR
                                                     141.23(e)(1), all
                                                     PWSs were required
                                                     to monitor for
                                                     nitrite once
                                                     between January 1,
                                                     1993, and December
                                                     31, 1995. If this
                                                     initial sample was
                                                     less than 50
                                                     percent of the MCL
                                                     (10 mg/L), systems
                                                     ``shall monitor at
                                                     the frequency
                                                     specified by the
                                                     State``. Though the
                                                     nitrite monitoring
                                                     frequency is not
                                                     explicitly stated
                                                     in the CFR, EPA's
                                                     guidance provides
                                                     that this frequency
                                                     should be at least
                                                     once every 9-year
                                                     compliance cycle
                                                     (USEPA, 2020d). EPA
                                                     is aware that some
                                                     States may not
                                                     require systems to
                                                     conduct routine
                                                     nitrite monitoring
                                                     when sample results
                                                     are less than 50
                                                     percent of the MCL.
                                                     Because sample
                                                     results below the
                                                     MCL are not
                                                     reported to EPA,
                                                     the scope of this
                                                     issue is uncertain.
                                                    To address this
                                                     uncertainty, EPA
                                                     analyzed State
                                                     regulations and
                                                     nitrite compliance
                                                     monitoring data to
                                                     characterize the
                                                     frequency of
                                                     nitrite monitoring.
                                                     Results indicated
                                                     that a majority of
                                                     systems monitored
                                                     for nitrite at
                                                     least once during
                                                     the last 9-year
                                                     compliance cycle
                                                     (2011-2019). EPA
                                                     intends to work
                                                     with States to
                                                     encourage more
                                                     systems to sample
                                                     for nitrite at
                                                     least once during
                                                     each 9-year
                                                     compliance cycle.
Total Nitrate and Nitrite Analysis for Nitrate MCL  In 40 CFR 141.62,
 Monitoring.                                         the MCL for nitrate
                                                     is specified as 10
                                                     mg/L and the MCL
                                                     for total nitrate
                                                     and nitrite is also
                                                     specified as 10 mg/
                                                     L. Sampling and
                                                     analytical
                                                     requirements as
                                                     specified in 40 CFR
                                                     141.23, however,
                                                     only included
                                                     nitrate and left
                                                     total nitrate and
                                                     nitrite monitoring
                                                     up to the
                                                     discretion of
                                                     States. Using Safe
                                                     Drinking Water
                                                     Information System
                                                     (SDWIS) compliance
                                                     data, EPA is aware
                                                     that at least half
                                                     of the States allow
                                                     total nitrate/
                                                     nitrite analysis to
                                                     determine
                                                     compliance with the
                                                     nitrate MCL.
                                                    To characterize
                                                     monitoring
                                                     practices for the
                                                     nitrate MCL, the
                                                     Agency analyzed Six-
                                                     Year Review 4
                                                     compliance
                                                     monitoring data for
                                                     both nitrate and
                                                     total nitrate/
                                                     nitrite. This
                                                     evaluation aims to
                                                     serve as a baseline
                                                     to assess nitrate
                                                     monitoring
                                                     practices in the
                                                     future, in response
                                                     to the 2020 EPA
                                                     guidance outlining
                                                     best practices when
                                                     using total nitrate/
                                                     nitrite analysis
                                                     for monitoring
                                                     compliance with the
                                                     nitrate MCL. EPA is
                                                     not revising the
                                                     monitoring
                                                     requirements at
                                                     this time but will
                                                     consider monitoring
                                                     requirements in
                                                     Sec.   141.23 if
                                                     NPDWRs are revised
                                                     in the future, to
                                                     incorporate best
                                                     practices similar
                                                     to those described
                                                     in recent guidance
                                                     (USEPA, 2020e).
------------------------------------------------------------------------

3. Select NPDWRs With New Information Not Appropriate for Revision
    The NPDWRs discussed in this section had new information 
identified, but EPA has determined they are not appropriate for 
revision at this time due to: (1) data gaps or emerging information 
that are necessary for EPA to evaluate as part of a review or; (2) new 
information that suggests low or no meaningful opportunity to provide 
greater public health protection. Examples of data gaps and emerging 
information identified during the review include an analytical 
monitoring challenge, a compliance reporting limitation, and an 
anticipated health effects assessment being developed by another U.S. 
Federal Agency. Specific details about the data gaps and emerging 
information identified during the review for on cyanide, fluoride, 
nitrate, nitrite, TCE, and PCE are provided below.
Cyanide
    EPA published the current MCL and MCLG of 0.2 mg/L (200 [micro]g/L) 
for free cyanide on July 17, 1992 (57 FR 31776, USEPA, 1992). In 2010, 
EPA published an IRIS assessment (USEPA, 2010b), which identified a new 
reproductive health effect endpoint that supports decreasing the MCLG 
from 200 [micro]g/L to 4 [micro]g/L. Analytical feasibility information 
identified in Six-Year Review 3 and Six-Year Review 4 supports a PQL 
reduction to as low as 50 [micro]g/L. In Six-Year Review 3, cyanide was 
listed as ``low priority'' due to low occurrence at levels below the 
current MCL. Analysis of Six-Year Review 4 occurrence data identified 
greater occurrence with 328 systems serving 8.1 million people with 
mean concentrations above 50 [micro]g/L (see Table 6 of this document). 
However, occurrence was limited to few states (USEPA, 2024h). EPA 
considered these occurrence results and the potential for a meaningful 
opportunity to improve the level of public health protection.
    Two analytical monitoring challenges complicate interpretation of 
the occurrence data. As described in section V.B.2 of this document, an 
analytical artifact created by ascorbic acid pretreatment of drinking 
water samples, which had been disinfected with chloramines, can result 
in false positives for free cyanide (USEPA, 2020f). An EPA guidance 
document (USEPA, 2020f) identified solutions to address this analytical 
challenge, but the general awareness of the availability of this 
guidance is uncertain. Second, EPA is aware that some systems analyze 
samples for total cyanide, and if the results are lower than the MCL, 
these systems report the total cyanide results as free cyanide. Systems 
may achieve cost savings by analyzing samples for total cyanide; 
however, using results for total cyanide instead of free cyanide could 
potentially overestimate the actual occurrence of free cyanide. Free 
and total cyanide results cannot be distinguished in the Six-Year 
Review 4 ICR dataset because the Safe Drinking Water Information System 
(SDWIS) State-version that many primacy agencies use to manage SDWA 
compliance monitoring data does not have an analyte code for total 
cyanide. Because the numerical benchmark used for occurrence is 
significantly lower than the current cyanide MCL, some of the reported 
concentrations may be for total cyanide. Therefore, the Six-Year Review 
4 occurrence analysis likely overestimates free cyanide occurrence. For 
these reasons, EPA does not believe it is appropriate to list the 
cyanide NPDWR as a candidate for revision at this time. EPA intends to 
help address these data gaps by continuing to disseminate the 2020 
guidance on analytical methods for cyanide and may consider an 
additional analyte code for total cyanide in the SDWIS reporting 
system. Further discussion of the cyanide monitoring issues can be 
found in USEPA (2024h).
Fluoride
    EPA published the MCL and MCLG of 4.0 mg/L for fluoride on April 2, 
1986 (51 FR 11396, USEPA, 1986) based on the critical health endpoint 
of crippling skeletal fluorosis. EPA also established a secondary MCL/
MCLG at 2.0 mg/L to protect against cosmetically objectionable dental 
fluorosis

[[Page 59637]]

(discoloration and/or pitting of teeth). Certain drinking water systems 
may choose to fluoridate finished water as a public health protection 
measure for reducing the incidence of cavities. The U.S. Public Health 
Service (PHS) recommendation for the optimal community water 
fluoridation level is 0.7 mg/L (U.S. Department of Health and Human 
Services, 2015). The decision to fluoridate a community water supply is 
made by the state or local municipalities and is not required by EPA or 
any other federal entity. Fluoride is also added to various consumer 
products, such as toothpaste and mouthwash.
    EPA has reviewed the NPDWR for fluoride in prior Six-Year Reviews. 
As a result of Six-Year Review 1, EPA requested that the National 
Research Council (NRC) of the National Academies of Sciences (NAS) 
conduct a review of the health and exposure data on orally ingested 
fluoride. In 2006, the NRC published the results of its review and 
concluded that severe dental fluorosis can be an adverse health effect 
(NRC, 2006). The NRC report recommended that EPA develop a dose-
response assessment for severe dental fluorosis as the critical health 
endpoint and update an assessment of fluoride exposure from all 
sources.
    In 2010, EPA published Dose Response Analysis for Noncancer Effects 
(USEPA, 2010d), which was considered under Six-Year Review 3. For more 
information, please see Appendix C of the Six-Year Review 3 Health 
Effects Assessment for Existing Chemical and Radionuclide National 
Primary Drinking Water Regulations--Summary Report (USEPA, 2016). In 
Six-Year Review 3, EPA did not recommend the fluoride NPDWR for 
revisions citing limited agency resources, prioritization of other 
contaminants, ongoing health effects research, and other factors that 
were anticipated to reduce the U.S. population's exposure to fluoride 
via drinking water (82 FR 3531, USEPA, 2017a). In Six-Year Review 4, 
EPA again considered the 2010 EPA assessment to derive a lower 
potential MCLG of 0.9 mg/L. Review results are provided in section 
V.B.2. of this document.
    Available published literature on other health effect categories 
including neurotoxicity and behavior, reproduction and development, 
endocrine effects, and cancer were reviewed in the EPA assessment 
(USEPA, 2010d). However, based on the review of the available 
literature at the time, EPA determined that the data for these other 
health effects associated with fluoride exposure were insufficient to 
support their selection as critical effects for potential MCLG 
derivation (USEPA, 2010d). EPA is aware of ongoing efforts by the 
National Toxicology Program (NTP) to conduct a systematic review and 
meta-analysis of the published literature on developmental 
neurotoxicity for fluoride. In May 2023, NTP released the Draft ``NTP 
Monograph on the State of the Science Concerning Fluoride Exposure and 
Neurodevelopmental and Cognitive Health Effects: A Systematic Review'' 
(NTP, 2023); however, the NTP systematic review and meta-analysis are 
not health assessments that could be used to directly inform the 
derivation of a potential MCLG. Due to emerging research published on 
developmental neurotoxicity after fluoride exposure coupled with 
competing workloads and other ongoing high priority actions (see 
section V.A of this document.), EPA has decided that the fluoride NPDWR 
is not a candidate for revision at this time. In addition, the NTP has 
not made a final decision about the report's developmental 
neurotoxicity systematic review conclusions and has not formally 
released a final report. Following publication of the final NTP report, 
EPA will consider the systematic review and meta-analysis conclusions 
regarding developmental neurotoxicity to inform the agency's future 
development of a health effects assessment for fluoride. See USEPA 
(2024f) Appendix B for more information.
Nitrate and Nitrite
    EPA published the MCLs and MCLGs for nitrate (10 mg/L) and nitrite 
(1 mg/L) based on the critical endpoint of methemoglobinemia (blue baby 
syndrome) on January 30, 1991 (56 FR 3526, USEPA, 1991). Nitrate and 
nitrite were not reviewed in detail under Six-Year Review 3 due to 
ongoing IRIS assessments at that time. Although the development of the 
IRIS assessment for nitrate and nitrite was suspended in December 2018, 
EPA has restarted development of their health assessment for nitrate 
and nitrite as indicated in the October 2023 IRIS Program Outlook. The 
agency recently released the ``Protocol for the Nitrate and Nitrite 
IRIS Assessment (Oral)'' for public comment on November 9, 2023 (88 FR 
77310, USEPA, 2023b). EPA plans to evaluate whether a revision of the 
nitrate and nitrite NPDWRs is appropriate, once the final IRIS 
assessment is available.
Trichloroethylene (TCE) and Tetrachloroethylene (PCE)
    The NPDWR for TCE was published on July 8, 1987 (52 FR 25690, 
USEPA, 1987) and the NPDWR for PCE was published on January 30, 1991 
(56 FR 3526, USEPA, 1991). Both TCE and PCE are classified as 
carcinogens and have MCLGs and MCLs of zero and 5 [micro]g/L, 
respectively. The MCLs were based on analytical feasibility at the time 
of rule promulgation. TCE and PCE were both listed as candidates for 
revision in Six-Year Review 2, based on updated analytical feasibility, 
treatment, and occurrence information.
    In 2011, EPA announced plans to address a group of regulated and 
unregulated carcinogenic volatile organic contaminants (cVOCs) in a 
single regulatory effort. The eight regulated contaminants that were 
evaluated for the cVOCs group regulation included benzene, carbon 
tetrachloride, 1,2-dichloroethane, 1,2-dichloropropane, 
dichloromethane, PCE, TCE, and vinyl chloride. In Six-Year Review 3, 
these contaminants were categorized under recent, ongoing, or planned 
regulatory action and were not reviewed. The cVOC group regulation was 
not promulgated, as a result these eight contaminants were reviewed 
again during Six-Year Review 4. EPA has determined that TCE and PCE are 
no longer candidates for revision at this time based on updated 
information.
    In Six-Year Review 2, EPA assessed analytical information that 
supported reducing the PQL and evaluated occurrence for TCE and PCE at 
0.5 [micro]g/L. As shown in Tables 5 and 6 of this document, EPA 
identified information in Six-Year Review 4 that again supported 
assessing occurrence at that level. The average TCE concentration 
exceeded 0.5 [micro]g/L in 297 systems, representing 0.57 percent of 
the systems assessed nationwide and serving approximately 13 million 
people. Similarly, the average PCE concentration exceeded 0.5 [micro]g/
L in 432 systems, which represent 0.83 percent of the approximately 
50,000 PWSs assessed nationwide and serve approximately 16 million 
people. These occurrence results are consistent with the Six-Year 
Review 2 estimates (75 FR 15500, March 29, 2010, USEPA, 2010a).
    The most recent final IRIS assessments for TCE (USEPA, 2011) and 
PCE (USEPA, 2012) were completed after the Six-Year Review 2 results 
were published and have been selected as the health assessments 
relevant to chronic toxicity for TCE and PCE in Six-Year Review 4 
(USEPA, 2024f). The updated IRIS assessments maintained the 
classification of ``carcinogenic to humans,'' and therefore do not 
support a change to the MCLGs of zero for either TCE or PCE. Based on 
the Six-Year Review 4 occurrence estimates described above, EPA 
considered if there was a potential for an increase in

[[Page 59638]]

human health protection at the lower identified level. To evaluate this 
potential, EPA examined the cancer risk level associated with the 
current MCLs (5 [micro]g/L) and the screening level (0.5 [micro]g/L) 
using updated occurrence and health effects information from Six-Year 
Review 4. The cancer risk levels at the current MCLs for TCE and PCE 
are 1 x 10^-5 (USEPA, 2011) and 3.0 x 10^-7 (USEPA, 
2012), respectively. These cancer risk levels correspond to excess 
lifetime cancer cases of 10 and 0.3 cases per million people, 
respectively. At the screening level of 0.5 [micro]g/L, the risk per 
million people would be 1 case for TCE and 0.03 cases for PCE. The 
implied number of baseline cancer cases over a 70-year exposure period 
is unlikely to exceed 120 total cases for TCE and 5 total cases for 
PCE. This corresponds to annual averages of 1.7 and 0.07 cases for TCE 
and PCE, respectively. This new information identified since Six-Year 
Review 2 indicates that revising the MCLs for either TCE or PCE would 
result in relatively small health risk reductions among the exposed 
population and would divert significant resources from other planned 
and ongoing work. Therefore, EPA has determined that TCE and PCE are 
considered ``low priority'' and are no longer candidates for revision.

C. Microbial Contaminants Regulations

    As discussed in section III of this document, the initial review 
branch of the review protocol identifies NPDWRs that have recently been 
recently competed or are being reviewed in ongoing or pending 
regulatory actions. Excluding such contaminants from a more detailed 
review in the Six-Year Review 4 prevents duplicative Agency efforts. 
Based on the initial review and considering the ongoing rulemaking 
activities for the Microbial and Disinfection Byproduct Rules, EPA did 
not perform a more detailed review for the Surface Water Treatment Rule 
(SWTR), the Interim Enhanced Surface Water Treatment Rule (IESWTR), the 
Long-Term 1 Enhanced Surface Water Treatment Rule (LT1ESWTR), and the 
Stage 1 and Stage 2 Disinfectants and Disinfection Byproducts Rules. 
The following microbial contaminant regulations were subject to a more 
detailed review for the Six-Year Review 4:

 Revised Total Coliform Rule (RTCR)
 Long Term 2 Enhanced Surface Water Treatment Rule (LT2)
 Ground Water Rule (GWR)
 Aircraft Drinking Water Rule (ADWR)
 Filter Backwash Recycling Rule (FBRR)

    Background information on each of the microbial contaminant 
regulations is presented in the subsequent sections. EPA is conducting 
its first detailed review of the RTCR and the ADWR as part of the Six-
Year Review. The RTCR and the ADWR were excluded from a detailed review 
in Six Year Review 3 because they were promulgated in 2013 and 2009, 
respectively.
    These microbial contaminants regulations establish treatment 
technique (TT) requirements in lieu of MCLs, except in the RTCR, EPA 
also established an MCL for Escherichia coli (E. coli) and TT 
requirements for total coliform. In accordance with the Six-Year Review 
Protocol, during the six-year review process, EPA assesses whether new 
health risk, analytical methods, or treatment information indicate 
possible TT revision. For the RTCR, the regulatory review determines 
whether new information indicates potential revision to the MCL for E. 
coli.
    The elements of the RTCR, LT2, GWR, and ADWR regulations that were 
reviewed for Six-Year Review 4 were: health effects, analytical 
feasibility, occurrence and exposure, and treatment feasibility. For 
the RTCR, LT2, GWR, and ADWR regulations, the EPA did not find any new 
relevant information as it relates to analytical feasibility. For all 
the other elements reviewed a summary of the findings is included in 
the subsequent sections. In addition, detailed information about the 
review is provided in the ``Six-Year Review 4 Technical Support 
Document for Microbial Contaminant Regulations'' (USEPA, 2024m).
    At this time, none of the reviewed microbial contaminant rules are 
being identified as a candidate for regulatory revision.
1. Revised Total Coliform Rule
Background
    EPA promulgated the Revised Total Coliform Rule (RTCR), a revision 
to the Total Coliform Rule, on February 13, 2013 (78 FR 10269, USEPA, 
2013). The Total Coliform Rule (TCR) was promulgated on June 29, 1989 
(54 FR 27544, USEPA, 1989). The purpose of the revision was to increase 
public health protection through the reduction of potential entry 
pathways for fecal contamination into distribution systems. The TCR 
required all public water systems (PWSs) to monitor for the presence of 
total coliforms and Escherichia coli (E. coli)) in the distribution 
system at a frequency dependent on the size (population served by) of 
the system. Under the TCR, a maximum contaminant level (MCL) was 
established based on the presence or absence of total coliforms with 
the intent to address contamination that could enter into distribution 
systems. The RTCR revised the TCR to eliminate the MCL for total 
coliforms and established an MCLG and MCL for E. coli of zero. The RTCR 
also requires PWSs that have an indication of coliform contamination 
(e.g., as a result of total coliform positive samples, E. coli MCL 
violations or performance failure) to find and assess the problem, 
identify sanitary defects and take corrective action. There are two 
levels of assessments (i.e., Level 1 and Level 2) based on the severity 
or frequency of the problem.
Summary of Review Results
    Information available for national occurrence and exposure 
indicates that both routine total coliform and E. coli positive rates 
have decreased after the implementation of RTCR. EPA concludes that no 
regulatory revisions to the RTCR are appropriate at this time based on 
the review of available information.
Health Effects
    Collier et al. (2021) estimated the collective U.S. disease burden 
attributable to over a dozen waterborne illnesses from infectious 
pathogens found in the distribution system (vibriosis, 
campylobacteriosis, cryptosporidiosis, giardiasis, Legionnaire's 
disease, salmonellosis, shigellosis, infections by non-tuberculous 
mycobacteria (NTM), norovirus, Shiga-toxin-producing E. coli, otitis 
externa, pneumonia, and septicemia). These researchers estimated the 
total disease burden at approximately 7.15 million cases annually, with 
an estimated 118,000 hospitalizations and 6,630 deaths. In this 
analysis, waterborne disease is understood to include gastrointestinal, 
respiratory, and systemic disease attributable to both drinking-water 
and non-drinking-water exposure. From further evaluation of this 
study's cases, Gerdes et al. (2023) determined 1.13 million of these 
illnesses were attributable to drinking water. According to the 
estimates presented in these studies, the opportunistic pathogens 
(Legionella, Nontuberculous Mycobacteria (NTM), and Pseudomonas) impose 
a greater public health burden than the fecal pathogens. Of the 
estimated 7.15 million infectious waterborne illnesses in 2014 in the 
United States, drinking water exposure caused 40 percent of 
hospitalizations and 50 percent of deaths.

[[Page 59639]]

Occurrence and Exposure
    To evaluate potential pathogenic contamination in distribution 
systems EPA analyzed national compliance monitoring data from the SYR 4 
ICR dataset (USEPA, 2019. EPA assessed the trends that may be 
associated with the implementation of the RTCR and found a 
statistically significant decline for total coliform positive results 
from years of 2014-2015 to 2018-2019 (i.e., before and after the 
implementation of RTCR respectively). The result suggests that the 
presence of these indicator organisms in the distribution system was 
declining. The trend of declining positive total coliform results was 
observed across different types of public water systems, water sources 
(ground water versus surface water), and system sizes (small versus 
large). With respect to the fecal contamination indicator E. coli, the 
observed decreasing trend was not supported by a statistical test of 
significance. EPA also found that the absolute number of E. coli 
positives were low, suggesting that the treatment techniques are 
effective (USEPA, 2024m).
Treatment Feasibility
    In this section as part of Six-Year Review process, EPA evaluated 
new information about tools and treatment techniques. Since the major 
treatment technique requirements under the RTCR are assessments 
followed by corrective actions (if total coliform and/or E. coli are 
detected), EPA evaluated the effectiveness of such requirements by 
comparing total coliform and E. coli positive rates after completion of 
either Level 1 or Level 2 assessments (USEPA, 2024m).
    EPA found about an 80 percent decrease in both routine total 
coliform and E. coli positive rates, two months after completion of 
RTCR assessments for systems having a monthly monitoring schedule.
    These analytical results and newly compiled information suggest 
that the ``find and fix'' approach prescribed under the provisions of 
assessments and corrective action within RTCR appears to work as 
intended for reducing the microbial occurrence in distribution systems 
and may be improving public health protection from microbial risks (as 
indicated by a substantial drop of the total coliform and E. coli 
positive rates following completion of corrective actions to respond to 
assessments).
2. Long Term 2 Enhanced Surface Water Treatment Rule
Background
    EPA promulgated the Long Term 2 Enhanced Surface Water Treatment 
Rule, hereafter referred to as ``LT2'', on January 5, 2006 (71 FR 654, 
USEPA, 2006a). The LT2 applies to all PWSs that use surface water or 
ground water under the direct influence of surface water. The LT2 
builds upon the IESWTR and the LT1 by improving control of microbial 
pathogens and by focusing on systems with elevated Cryptosporidium 
contamination risk. The purposes of the LT2 are to protect public 
health from illness arising from exposure to Cryptosporidium and other 
microbial pathogens in drinking water and to prevent significant 
increases in risks that might occur when systems implement drinking 
water disinfection byproduct rules.
    Key provisions in the LT2 include: source water monitoring for 
Cryptosporidium (with a screening procedure to reduce monitoring costs 
for small systems); risk-targeted Cryptosporidium treatment by filtered 
systems with the highest source water Cryptosporidium levels; 
inactivation of Cryptosporidium by all unfiltered systems; criteria for 
the use of Cryptosporidium treatment and control processes; and 
covering or treating uncovered finished water storage facilities.
    The LT2 requires PWSs using surface water or ground water under the 
direct influence of surface water to monitor their source waters for 
Cryptosporidium and/or E. coli to identify additional treatment 
requirements. PWSs must monitor their source water (i.e., the influent 
water entering the treatment plant) over two different timeframes 
(defined as Round 1 and Round 2) to determine the occurrence of 
Cryptosporidium. Monitoring results determine the extent of 
Cryptosporidium treatment requirements under the LT2. According to the 
LT2 rule requirements, all PWSs were to complete Round 2 by 2021. To 
reduce monitoring costs, small filtered PWSs (serving fewer than 10,000 
people) which initially monitor for E. coli for one year as a screening 
analysis, are required to monitor for Cryptosporidium only if their E. 
coli levels exceed specified trigger values. Small filtered PWSs that 
exceed the E. coli trigger, as well as small unfiltered PWSs, must 
monitor for Cryptosporidium for one or two years, depending on the 
sampling frequency. The LT2 also requires all unfiltered PWSs to 
provide at least 2 to 3-log (i.e., 99 to 99.9 percent) inactivation of 
Cryptosporidium. Further, under the LT2, unfiltered PWSs must achieve 
their overall inactivation requirements (including Giardia lamblia and 
virus inactivation as established by earlier regulations) using a 
minimum of two disinfectants.
    Under the LT2, PWSs with uncovered finished water reservoirs 
(UCFWR) must either cover the storage facility or treat the water 
leaving the storage facility to achieve inactivation and/or removal of 
4-log virus, 3-log Giardia lamblia and 2-log Cryptosporidium using a 
protocol approved by the state (USEPA, 2006a). Most finished water 
reservoirs for surface water systems are covered. All PWSs with UCFWRs 
are under administrative orders or compliance agreements to cover or 
treat their UCFWR.
Summary of Review Results
    From a review of the literature on Cryptosporidium health effects, 
EPA concludes that there is no new health information to suggest a need 
to modify the LT2. In addition, EPA determined that no regulatory 
revisions to the microbial toolbox options are appropriate at this 
time. During Six-Year Review 4, EPA did not consider disinfection 
profiling information since EPA is evaluating overall filtration and 
disinfection requirements in the SWTRs as part of the on-going 
consideration of potential revisions to the MDBP rules. For more 
information regarding EPA's review of treatment feasibility see the 
``Six-Year Review 4 Technical Support Document for Microbial 
Contaminant Regulations'' (USEPA, 2024m).
Health Effects
    Since 1995, cryptosporidiosis has been a nationally notifiable 
disease, meaning healthcare providers and laboratories that diagnose 
cases of laboratory-confirmed cryptosporidiosis are required to report 
cases to their local or state health departments, which in turn report 
the cases to CDC. Since 2012, there have been four reported outbreaks 
of cryptosporidiosis from public water systems to CDC. The four 
outbreaks together resulted in a total of 201 recorded illnesses, 2 
hospitalizations, and no deaths (CDC, 2022). Although cryptosporidiosis 
is a nationally notifiable disease, additional outbreaks may go 
unreported to CDC or may have been recorded as of uncertain causes. In 
addition, since CDC's National Outbreak Reporting System is 
specifically focused on outbreaks, it does not capture rates of endemic 
disease of cryptosporidiosis from drinking water.

[[Page 59640]]

Occurrence and Exposure
    Based on the LT2 source water monitoring results, filtered systems 
were classified in one of four risk categories (Bins 1-4) to determine 
additional treatment needed. Systems in Bin 1 are not required to 
provide additional Cryptosporidium treatment. Systems in Bins 2-4 must 
achieve 1.0-2.5 log of treatment (i.e., 90 to 99.7 percent reduction 
for Cryptosporidium) over and above that provided by conventional 
treatment, depending on the Cryptosporidium concentrations. Filtered 
PWSs must meet the additional Cryptosporidium treatment requirements in 
Bins 2, 3, or 4 by selecting one or more technologies from the 
microbial toolbox to ensure source water protection and management, 
and/or Cryptosporidium removal or inactivation. All unfiltered water 
systems must provide at least 99 or 99.9 percent (2 or 3-log) 
inactivation of Cryptosporidium, depending on their monitoring results. 
All filtered systems that provide 5.5 log treatment for Cryptosporidium 
are exempt from monitoring and subsequent bin classification.
    Six years after the initial bin classification following a first 
round of monitoring, filtered systems were required to conduct a second 
round of monitoring. Round 2 monitoring began in 2015. Round 2 
monitoring was implemented to understand year-to-year variability for 
occurrence of Cryptosporidium. The difference observed between 
occurrence at the time of the ICR Supplemental Surveys and the LT2 
Round 1 monitoring indicates year-to-year variability (USEPA, 2017a).
    Limited occurrence data for Cryptosporidium was available to EPA in 
response to the SYR 4 ICR since fewer than 1 percent of the 
Cryptosporidium monitoring records provided actual concentration levels 
with units of oocysts/L; however, the data about system binning for 
about 300 PWSs serving populations larger than 10,000 was provided. 
Those data indicate that the percentage of PWSs potentially moving to 
an ``action bin'' based on Round 2 monitoring would not be 
substantially higher than the percentage estimated based on modeling 
conducted during the LT2 review included as part of the Six-Year Review 
3, thus suggesting no change to the review decision made under Six-Year 
Review 3.
Treatment Feasibility
    The LT2 includes a variety of treatment and control options, 
collectively termed the ``microbial toolbox,'' that PWSs can implement 
to comply with the LT2's additional Cryptosporidium treatment 
requirements. Most options in the microbial toolbox carry prescribed 
credits toward Cryptosporidium treatment and control requirements. The 
LT2 Toolbox Guidance Manual (USEPA, 2010e) provides guidance on how to 
apply the toolbox options.
    For the Six-Year Review 4, EPA reviewed additional research into 
the relationship between ultraviolet light (UV) dose and log 
inactivation. Some studies showed the same log inactivation at UV doses 
lower than those reported in previous EPA guidance, and other studies 
showed log inactivation at UV doses higher than those contained in the 
guidance. Since there is not a consensus of log inactivation at levels 
significantly lower than EPA prior published guidance, EPA concludes 
that the new information does not support changes to the UV dose table.
    EPA also reviewed new information pertaining to technologies, which 
have not been included in the existing LT2 toolbox guidance manual, and 
which may be effective for the removal or inactivation of protozoa 
including Cryptosporidium. In addition, EPA also reviewed new 
technologies that water systems may be employing to improve treatment 
performance for complying with the MDBP rules, e.g., turbo coagulation 
and powdered activated carbon. Initiatives by states and EPA's Area 
Wide Optimization Program were evaluated as well. EPA found that this 
new information appears insufficient to develop quantification criteria 
for inactivation and removal credit for Cryptosporidium.
3. Ground Water Rule
Background
    EPA promulgated the Ground Water Rule (GWR) in 2006 (71 FR 65574, 
USEPA, 2006b) to provide protection against microbial pathogens in PWSs 
using ground water sources. The rule establishes a risk-based approach 
to target undisinfected ground water systems that are vulnerable to 
fecal contamination. In addition to the protection provided by the RTCR 
and GWR monitoring requirements, systems that do not disinfect are also 
protected by the sanitary survey provisions of the GWR and the 
treatment technique provisions of the RTCR.
    The GWR required compliance beginning December 1, 2009. Since the 
triggered source water monitoring provision was built upon the 
compliance monitoring results of total coliform and E. coli under the 
TCR and later RTCR, implementation of the GWR was not yet completed for 
the period of time covered by the Six-Year Review 3 ICR (2006-2011). 
The RTCR was promulgated in 2013 and became effective on April 1, 2016. 
EPA expected that implementation of the RTCR might impact the percent 
of ground water systems that would be triggered into source water 
monitoring and taking any corrective actions under the GWR. Therefore, 
the effects of the GWR and the RTCR implementation in addressing 
vulnerable ground water systems were not reviewed during the Six-Year 
Review 3 process.
Summary of Review Results
    The information considered during this review suggest that 
microbial pathogens have been detected in untreated ground water 
samples which show no presence of fecal indicators, however these 
studies are limited in quantity and the prevalence of endemic disease 
from microbial contamination of untreated ground water cannot be well 
characterized with the available information (USEPA, 2024m). Additional 
and more robust studies are needed to further understand the magnitude 
of the issue. EPA concludes that no regulatory revisions to the GWR are 
appropriate at this time.
Health Effects
    Waterborne pathogens can cause mild to severe illnesses (Wallender 
et al., 2014). These illnesses may include; acute gastrointestinal 
illness (AGI) with diarrhea, abdominal pain/discomfort, nausea, 
vomiting, conjunctivitis, aseptic meningitis, and hand-foot-and-mouth 
disease. Infections from some waterborne pathogens (e.g., 
Campylobacter) may cause long-term implications, such as reactive 
arthritis, Guillain-Barr[eacute] syndrome, and irritable bowel syndrome 
(Keithlin et al., 2014). Other more severe illnesses include hemolytic 
uremic syndrome (HUS) (kidney failure), hepatitis, and bloody diarrhea 
(WHO, 2004).
    Some studies have indicated that waterborne pathogens such as 
adenovirus, enteroviruses, hepatitis A, norovirus, rotavirus, 
Salmonella, Giardia, Cryptosporidium, and Shigella have been found in 
untreated ground water samples (Borchardt et al., 2012; Wallender et 
al., 2014; Stokdyk et al., 2020).
    Human enteric viruses have been detected in drinking water free of 
bacterial indicators, such as total coliform. With total coliform 
detections rates similar to the average rate for

[[Page 59641]]

undisinfected community PWSs in the U.S, Borchardt et al. (2012) 
estimated a six to 22 percent attributable risk for enteric illness 
from viruses present in the communities' drinking water. In another 
study, Burch et al. (2022) found that noncommunity wells had higher 
infection risk than community wells. Burch et al. (2022) found the 
annual risk was relatively high for all pathogens combined in the 
study, while the average daily doses for individual pathogens were low, 
indicating that significant risk results from sporadic pathogen 
exposure. Studies by Fout et al. (2017) and Stokdyk et al. (2020) found 
that total coliform (and other indicators like E. coli, somatic phage, 
HF183, and Bacteroidales-like HumM2) tend to have high specificity, 
meaning that absence of the indicator provides relatively strong 
assurance that water is free of viral and other pathogens, but also 
have low sensitivity, meaning that presence of the indicator does not 
necessarily predict presence of pathogens.
Occurrence and Exposure
    Similar to the RTCR, EPA examined the national compliance 
monitoring data collected for the Six-Year Review 4 to understand how 
total coliform and E. coli, indicators of contamination behaved before 
and after implementation of the GWR, as well as understanding how level 
of contamination for high risk undisinfected ground water systems have 
changed.
    As noted, GWR monitoring is based on initial monitoring under the 
RTCR. If a system has a positive total coliform sample (based on 
routine coliform monitoring under the RTCR), the system must test that 
sample for the presence of E. coli. Under the GWR, ground water systems 
that do not provide at least 4-log treatment of viruses and are 
notified of a routine positive total coliform sample collected under 
RTCR must collect and analyze at least one source water sample for E. 
coli or other fecal indicators from each ground water source (well) 
within 24 hours. If the triggered source water sample has a positive 
for E. coli the ground water systems must take corrective action. EPA 
conducted a distribution system total coliform/E. coli data exploration 
and analysis effort to identify findings that could inform the risk 
reduction of the fully implemented GWR, as well as characterize high 
risk systems.
    The national average total coliform and E. coli rates (i.e., total 
number of positives divided by total number of samples) before and 
after implementation of the GWR were calculated using Six-Year Review 3 
and Six-Year Review 4 datasets. The analytical results were grouped by 
system sizes and disinfection status (i.e., disinfecting versus and 
undisinfected). The period of analysis was from 2007-2008 (before the 
GWR was implemented) to 2014-2015 (after the completed implementation 
of the first round of sanitary surveys under the GWR). The total 
coliform rates across different system categories decreased, suggesting 
that there may be less pathogenic contamination pathways and so 
potentially less microbial exposure, corresponding to the period when 
the GWR was being implemented. This downward change is supported by a 
statistical significance test. The declining count of the fecal 
contamination indicator, E. coli was not supported by a test of 
statistical significance. Yet numbers of E. coli positives were 
consistently low, which may indicate low exposure to fecal 
contamination.
    EPA performed a more specific analysis using a statistical model 
focused on the most vulnerable water systems, the undisinfected ground 
water systems. EPA conducted statistical modeling focused on 
examination of total coliform levels in small ground water systems to 
account for their infrequent sampling and relatively low level of 
monitoring observations compared to larger systems that monitor more 
frequently.
    There are approximately 45,000 undisinfected ground water systems 
associated with total coliform records collected and less than 1 
percent population among the population served by the public community 
water systems in the U.S. (based on SYR 4 ICR data). Most undisinfected 
ground water systems serve small permanent populations or transient 
populations.
    EPA found that the smallest systems (serving a population fewer 
than 1,001) have higher median total coliform rates than undisinfected 
larger systems. In addition, the analysis indicates that median 
occurrence rates for many undisinfected transient systems may have 
fallen, from four to three percent total coliform detection rate from 
2011 to 2019. Another finding from the statistical modeling is that the 
number of non-community systems that have high total coliform 
detections in the systems serving fewer than 1,001 people has remained 
roughly the same, about 7,000 undisinfected ground water systems, when 
running a comparison using Six-Year Review 3 and Six-Year Review 4 ICR 
data with a threshold of five percent rate of total coliform positive 
detections, which is the threshold that triggers a Level 1 Assessment 
in the RTCR. For statistical analysis of E. coli detection rates, there 
was not sufficient data to make estimates of averages and numbers of 
systems exceeding high levels.
    Two implications of these modelling results should be noted as it 
relates to estimating potential exposure and occurrence. One is that 
the non-community systems serving fewer than 1,001 have total coliform 
positive rates around two to four percent, while a study of 14 
community systems served by untreated ground water in Wisconsin found 
that a total coliform positive rate of 2.3 percent was associated AGI 
burden (Borchardt et al, 2012). EPA concludes, however, that studies 
indicating microbial disease burden at total coliform positive levels 
found in high-risk systems are limited in number as mentioned in the 
Health Effects section, as well as in geographic scope. Another 
implication from the results of this statistical analysis is that the 
remaining systems with very high total coliform rates could suggest 
compliance challenges among small ground water systems.
    In addition to evaluating trends with indicators under RTCR to 
evaluate protection for vulnerable ground water systems, EPA also 
considered the results from the GWR requirement for triggered source 
water sampling. The sample results indicate that there is a small 
percent of positive source water E. coli detections ranging from 0.76 
percent to 1.99 percent of E. coli samples for non-community systems 
which are primarily undisinfected systems, and 250 out of 270 of source 
water E. coli detections were associated with undisinfected systems 
serving fewer than 500 people. The other fecal indicators, coliphage 
and enterococci were used very infrequently, and data was insufficient 
to evaluate. Low incidence of fecal indicators may indicate low 
exposure to fecal contamination among undisinfected ground water 
systems.
Treatment Feasibility
    Per treatment technique requirements under the GWR, there are two 
scenarios that trigger ground water systems to take corrective actions: 
(1) positive results of the triggered source water monitoring, and (2) 
significant deficiencies found during Sanitary Survey (EPA was not able 
to assess sanitary surveys directly given data limitations). EPA 
evaluated whether treatment was improving under the GWR by using the 
RTCR occurrence analysis data to consider total coliform rates before 
and after the GWR was implemented.

[[Page 59642]]

    EPA developed a systematic approach to identify disinfection status 
of ground water systems for each of the years included in the Six-Year 
Review ICR datasets and found that the percentage of ground water 
systems that were disinfecting had increased consistently from 2007-
2008 (before the GWR was implemented) to 2014-2015. This finding of an 
increasing number of systems disinfecting could be attributable to 
systems taking corrective actions to address positive results after 
triggered source water monitoring. The analytical results presented in 
the ``Six-Year Review 4 Technical Support Document for Microbial 
Contaminant Regulations'' (USEPA, 2024m) also indicate that 
disinfecting ground water systems had substantially lower total 
coliform positive rates than undisinfected ground water systems. In 
addition, EPA also observed that the total coliform positive rates 
decreased after completion of the first round of sanitary surveys under 
the GWR among ground water systems.
4. Aircraft Drinking Water Rule
Background
    EPA promulgated the Aircraft Drinking Water Rule (ADWR) on October 
19, 2009 (74 FR 53590, USEPA, 2009b). The primary purpose of the ADWR 
is to ensure that safe and reliable drinking water is provided to 
aircraft passengers and crew. This entails providing air carriers with 
a feasible way to comply with SDWA and NPDWRs. The existing NPDWRs were 
designed for traditional, stationary public water systems not mobile 
aircraft water systems that are operationally different. For example, 
aircraft fly to multiple destinations throughout the course of any 
given day and may board drinking water from sources at any of these 
destinations. Aircraft board water from airport watering points via 
temporary connections. Aircraft drinking water safety depends on a 
number of factors including the quality of the water that is boarded 
from these multiple sources, the care used to board the water, and the 
operation and maintenance of the onboard water system and the water 
transfer equipment.
    The ADWR's provisions protect against disease-causing 
microbiological contaminants through the required development and 
implementation of aircraft water system operations and maintenance 
plans. The ADWR's provisions include: routine disinfection and flushing 
of the water system, air carrier training requirements for key 
personnel, and periodic sampling of the onboard drinking water, as well 
as self-inspections of each aircraft water system and immediate 
notification of passengers and crew when violations or specific 
situations occur.
Summary of Review Results
    The ADWR is a unique rule within the context of the SDWA. This rule 
applies only to aircraft engaged in interstate commerce with onboard 
systems that provide water for human consumption through pipes. These 
aircraft water systems board finished water for human consumption and 
regularly serve an average of at least twenty-five individuals daily, 
at least 60 days out of the year. Human consumption includes water for 
drinking, hand washing, food preparation, and oral hygiene. From a 
review of available technical information within the scope of the 
review, EPA concludes that there is no new information to suggest that 
regulatory revisions to the ADWR are appropriate at this time.
Health Effects
    Limited new literature is available on the presence of microbial 
pathogens in aircraft drinking water. Handschuh et al. (2015) found 
that long-haul flights were significantly poorer in terms of microbial 
water quality than short haul flights. A follow-up study by Handschuh 
et al. (2017) demonstrated that there is a diversity of microorganisms 
within the aircraft drinking water supply chain.
    Other studies have also found microbial contaminants present in 
aircraft drinking water, including Pseudomonas aeruginosa, enterococci, 
clostridia, and Salmonella (WHO, 2009; Schaeffer et al., 2012). 
Tracking an illness back to contaminated water served on an aircraft 
presents a technical challenge. Most disease incubation periods are 
longer than the duration of a flight, and even if it is possible to 
determine that a disease was incurred in air travel, it may be 
difficult to determine if the route of transmission was from beverages, 
food, or close proximity of people, and to determine whether 
transmission happened on board the aircraft or at an air terminal.
Occurrence and Exposure
    The Aircraft Reporting and Compliance System (ARCS) is used to 
facilitate the reporting of aircraft water system data under the ADWR. 
Air carriers subject to the ADWR must report to EPA about their 
inventory of aircraft water system fleet; the date the operations and 
maintenance plan was developed; the date the coliform sampling plan was 
developed; the date the aircraft water system sampling plan(s) was 
incorporated into the aircraft water system Operations and Maintenance 
plan; the date the Operations and Maintenance plan(s) was incorporated 
into the U.S. Federal Aviation Administration (FAA) accepted air 
carrier Operation and Maintenance program; the frequency for routine 
disinfection and flushing, and the corresponding routine total coliform 
sampling frequency; and the date for routine disinfection and flushing, 
routine coliform sampling dates and results, and corrective actions 
(when applicable).
    For Six-Year Review 4, EPA downloaded and reviewed compliance 
monitoring data available in ARCS as of May 2021. Approximately 140,000 
records of aircraft water systems compliance monitoring data for total 
coliform and E. coli samples were available in ARCS from February 2011 
through May 2021, including results reported for more than 70 different 
makes/models of aircraft. These results were used to characterize the 
positivity rates of total coliform and E. coli in aircraft water 
systems on an annual basis for the years that data were available 
(2011-2021) and for the subset of years 2012 through 2019. This 
approach removes potentially confounding considerations associated with 
evaluating data for calendar year 2020 when a large number of aircraft 
PWS were inactive due to COVID-19, as well as years 2011 and 2021 for 
which the ARCS data evaluated represents partial years.
    Monitoring data broken down by year for the years 2012-2019 shows 
an average annual total coliform positivity rate of 5.46 percent, with 
a median of 5.63 percent, a minimum of 3.76 percent and a maximum of 
7.03 percent. The total coliform positivity rate decreased on an annual 
basis from 2012-2019. The average E. coli positivity rate was 0.26 
percent, and the median rate was also 0.26 percent, with a minimum of 
0.17 percent and a maximum of 0.33 percent. The E. coli positivity rate 
also decreased on an annual basis.
Treatment Feasibility
    Under the ADWR, air carriers routinely disinfect and flush aircraft 
water systems at the frequency recommended by the water system 
manufacturer or, if not specified by the manufacturer, they may choose 
from one of four options. If corrective disinfection and flushing is 
chosen or required, air carriers follow the procedures in their O&M 
plans. Unscheduled flight disruptions to

[[Page 59643]]

perform corrective disinfection and flushing can be minimized by 
shutting off the water or preventing the flow of water to the taps. 
Before allowing unrestricted access to the aircraft water system, a 
complete set of follow-up samples must be collected and submitted for 
analysis after the disinfection and flushing event if triggered by a 
total coliform-positive sample and must be reported as total coliform-
negative if triggered by an E. coli-positive sample. One study was 
identified that examined the effectiveness of disinfection and flushing 
procedures to prevent coliform persistence in aircraft water systems 
(Szabo et al., 2019). That study showed that coliforms were not 
persistent on the aircraft plumbing surfaces, and coliforms were not 
detected after disinfection and flushing. However, it noted an 
exception for the aerator installed in the lavatory faucet which was 
coliform positive after disinfection with ozone and mixed oxidants; 
disinfection with glycolic acid and quaternary ammonia showed no 
detectable coliforms on aerators after 30 minutes of soaking in the 
disinfectants.
    Each aircraft water system must be inspected by the air carrier at 
least every 5 years according to the procedures in their O&M plans. At 
a minimum, the self-inspection procedures for an aircraft water system 
must include inspection of the storage tank, distribution system, 
supplemental treatment, fixtures, valves, and backflow prevention 
devices. Any deficiencies detected must be addressed, and any 
deficiency that is unresolved within 90 days of identification of the 
deficiency must be reported to EPA.
5. Filter Backwash Recycling Rule
    EPA promulgated the Filter Backwash Recycling Rule (FBRR) on June 
8, 2001 (66 FR 31086, USEPA, 2001a). The rule aimed to increase public 
health protection by addressing microbial contaminant risks associated 
with filter backwash recycling practices. The rule required certain 
systems to return recycled filter backwash water, sludge thickener 
supernatant, and liquids from dewatering processes to a location in the 
system such that all filtration processes of a system are employed, or 
at an alternate location if approved by the State. In addition, the 
rule required systems that employ conventional filtration or direct 
filtration to notify States of their recycling practices by June 8, 
2004, and after then to keep and retain records on file about their 
recycle flows for subsequent review and evaluation by the State. There 
are no ongoing monitoring requirements associated with the FBBR.
    EPA reviewed available State data collected under the ICR; however, 
the EPA did not identify any new and relevant information that would 
indicate that revisions to the NPDWR at this time are appropriate.

VI. References

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2 Enhanced Surface Water Treatment Rule; Final Rule. 71 FR 654. 
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Water Regulations for Aircraft Public Water Systems. 74 FR 53590. 
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of Registration Review. Washington, DC: U.S. Environmental 
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Radionuclide Cancer Risk Coefficients Review Panel. 87 FR 15988. 
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USEPA. 2022b. Availability of the Draft IRIS Toxicological Review of 
Hexavalent Chromium. 87 FR 63774. October 10, 2022.
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and Copper: Improvements (LCRI). 88 FR 84878. December 6, 2023.
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USEPA. 2024a. PFAS National Primary Drinking Water Regulation. 89 FR 
32532. April 26, 2024.
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Confidence Report Rule Revisions. 89 FR 45980. May 24, 2024.
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Process for the Fourth Six-Year Review Information Collection 
Request Dataset. EPA 815-R-24-017.
USEPA. 2024e. Chemical Contaminant Summaries for the Fourth Six-Year 
Review of Existing National Primary Drinking Water Regulations. EPA 
815-S-24-002.
USEPA. 2024f. Results of the Health Effects Assessment for the 
Fourth Six-Year Review of Existing Chemical and Radionuclide 
National Primary Drinking Water Standards. EPA 815-R-24-020.
USEPA. 2024g. Analytical Feasibility Support Document for the Fourth 
Six-Year Review of National Primary Drinking Water Regulations. EPA 
815-R-24-015.
USEPA. 2024h. Analysis of Regulated Contaminant Occurrence Data from 
Public Water Systems in Support of the Fourth Six-Year Review of 
National Primary Drinking Water Regulations: Chemical Phase and 
Radionuclides Rules. EPA 815-R-24-014.
USEPA. 2024i. Review of Fluoride Occurrence for the Fourth Six-Year 
Review. EPA 815-R-24-021.
USEPA. 2024j. Occurrence Analysis for Potential Source Waters for 
the Fourth Six-Year Review of National Primary Drinking Water 
Regulations. EPA 815-R-24-019.
USEPA. 2024k. Support Document for the Fourth Six-Year Review of 
Drinking Water Regulations for Acrylamide and Epichlorohydrin. EPA 
815-R-24-023.
USEPA. 2024l. Consideration of Other Regulatory Revisions in Support 
of the Fourth Six-Year Review of the National Primary Drinking Water 
Regulations: Chemical Phase Rules and Radionuclides Rule. EPA 815-R-
24-016.
USEPA. 2024m. Six-Year Review 4 Technical Support Document for 
Microbial Contaminant Regulations. EPA 815-R-24-022.
Wallender, E.K., E.C. Ailes, J.S. Yoder, V.A. Roberts, and J.M. 
Brunkard. 2014. Contributing factors to disease outbreaks associated 
with untreated groundwater. Ground Water. 52(6): 886-97.
World Health Organization (WHO). 2004. Guidelines for Drinking-Water 
Quality, Third Edition. Volume 1: Recommendations. https://www.who.int/publications/i/item/9789241547611.
WHO. 2009. Guide to hygiene and sanitation in aviation, 3rd edition. 
https://www.who.int/publications/i/item/9789241547772.

Michael S. Regan,
Administrator.
[FR Doc. 2024-15807 Filed 7-22-24; 8:45 am]
BILLING CODE 6560-50-P

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