National Primary Drinking Water Regulations: Long Term 2 Enhanced Surface Water Treatment Rule, 654-786 [06-4]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 71, Number 3 (Thursday, January 5, 2006)]
[Rules and Regulations]
[Pages 654-786]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 06-4]



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Part II





Environmental Protection Agency





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40 CFR Parts 9, 141, and 142



National Primary Drinking Water Regulations: Long Term 2 Enhanced 
Surface Water Treatment Rule; Final Rule

Federal Register / Vol. 71, No. 3 / Thursday, January 5, 2006 / Rules 
and Regulations

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 9, 141, and 142

[EPA-HQ-OW-2002-0039; FRL-8013-1]
RIN 2040--AD37


National Primary Drinking Water Regulations: Long Term 2 Enhanced 
Surface Water Treatment Rule

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: EPA is promulgating National Primary Drinking Water 
Regulations that require the use of treatment techniques, along with 
monitoring, reporting, and public notification requirements, for all 
public water systems that use surface water sources. The purposes of 
the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) are to 
protect public health from illness due to Cryptosporidium and other 
microbial pathogens in drinking water and to address risk-risk trade-
offs with the control of disinfection byproducts.
    Key provisions in the LT2ESWTR include the following: 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.
    EPA believes that implementation of the LT2ESWTR will significantly 
reduce levels of infectious Cryptosporidium in finished drinking water. 
This will substantially lower rates of endemic cryptosporidiosis, the 
illness caused by Cryptosporidium, which can be severe and sometimes 
fatal in sensitive subpopulations (e.g., infants, people with weakened 
immune systems). In addition, the treatment technique requirements of 
this regulation will increase protection against other microbial 
pathogens like Giardia lamblia.

DATES: This final rule is effective on March 6, 2006. The incorporation 
by reference of certain publications listed in the rule is approved by 
the Director of the Federal Register as of March 6, 2006. For judicial 
review purposes, this final rule is promulgated as of January 5, 2006.

ADDRESSES: EPA has established a docket for this action under Docket ID 
No. EPA-HQ-OW-2002-0039. All documents in the docket are listed on the 
www.regulations.gov Web site. Although listed in the index, some 
information is not publicly available, i.e., CBI or other information 
whose disclosure is restricted by statute. Certain other material, such 
as copyrighted material, is not placed on the Internet and will be 
publicly available only in hard copy form. Publicly available docket 
materials are available either electronically through 
www.regulations.gov or in hard copy at the Water Docket, EPA/DC, EPA 
West, Room B102, 1301 Constitution Ave., NW., Washington, DC. The 
Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through 
Friday, excluding legal holidays. The telephone number for the Public 
Reading Room is (202) 566-1744, and the telephone number for the Water 
Docket is (202) 566-2426.

FOR FURTHER INFORMATION CONTACT: Daniel C. Schmelling, Standards and 
Risk Management Division, Office of Ground Water and Drinking Water (MC 
4607M), Environmental Protection Agency, 1200 Pennsylvania Ave., NW., 
Washington, DC 20460; telephone number: (202) 564-5281; fax number: 
(202) 564-3767; e-mail address: schmelling.dan@epa.gov. For general 
information, contact the Safe Drinking Water Hotline, telephone number: 
(800) 426-4791. The Safe Drinking Water Hotline is open Monday through 
Friday, excluding legal holidays, from 9 a.m. to 5 p.m., Eastern time.

SUPPLEMENTARY INFORMATION:

I. General Information

A. Who Is Regulated by This Action?

    Entities potentially regulated by the LT2ESWTR are public water 
systems (PWSs) that use surface water or ground water under the direct 
influence of surface water (GWUDI). Regulated categories and entities 
are identified in the following chart.

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                Category                  Examples of regulated entities
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Industry...............................  Public Water Systems that use
                                          surface water or ground water
                                          under the direct influence of
                                          surface water.
State, Local, Tribal or Federal          Public Water Systems that use
 Governments.                             surface water or ground water
                                          under the direct influence of
                                          surface water.
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    This table is not intended to be exhaustive, but rather provides a 
guide for readers regarding entities likely to be regulated by this 
action. This table lists the types of entities that EPA is now aware 
could potentially be regulated by this action. Other types of entities 
not listed in this table could also be regulated. To determine whether 
your facility is regulated by this action, you should carefully examine 
the definition of public water system in Sec.  141.3 of Title 40 of the 
Code of Federal Regulations and applicability criteria in Sec.  
141.700(b) of today's rule. If you have questions regarding the 
applicability of the LT2ESWTR to a particular entity, consult one of 
the persons listed in the preceding section entitled FOR FURTHER 
INFORMATION CONTACT.

Abbreviations Used in This Document

ASTM American Society for Testing and Materials
AWWA American Water Works Association
[deg]C Degrees Centigrade
CDC Centers for Disease Control and Prevention
CFE Combined Filter Effluent
CFR Code of Federal Regulations
COI Cost-of-Illness
CT The Residual Concentration of Disinfectant (mg/L) Multiplied by the 
Contact Time (in minutes)
CWS Community Water Systems
DAPI 4',6-Diamindino-2-phenylindole
DBPs Disinfection Byproducts
DBPR Disinfectants/Disinfection Byproducts Rule
DE Diatomaceous Earth
DIC Differential Interference Contrast (microscopy)
EA Economic Analysis
EPA United States Environmental Protection Agency
GAC Granular Activated Carbon
GWUDI Ground Water Under the Direct Influence of Surface Water
HAA5 Five Haloacetic Acids (Monochloroacetic, Dichloroacetic, 
Trichloroacetic, Monobromoacetic and Dibromoacetic Acids)
ICR Information Collection Rule (also Information Collection Request)
ICRSS Information Collection Rule Supplemental Surveys

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ICRSSM Information Collection Rule Supplemental Survey of Medium 
Systems
ICRSSL Information Collection Rule Supplemental Survey of Large Systems
IESWTR Interim Enhanced Surface Water Treatment Rule
Log Logarithm (common, base 10)
LRAA Locational Running Annual Average
LRV Log Removal Value
LT1ESWTR Long Term 1 Enhanced Surface Water Treatment Rule
LT2ESWTR Long Term 2 Enhanced Surface Water Treatment Rule
MCL Maximum Contaminant Level
MCLG Maximum Contaminant Level Goal
MG Million Gallons
M-DBP Microbial and Disinfectants/Disinfection Byproducts
MF Microfiltration
NPDWR National Primary Drinking Water Regulation
NTTAA National Technology Transfer and Advancement Act
NTU Nephelometric Turbidity Unit
OMB Office of Management and Budget
PE Performance Evaluation
PWS Public Water System
QC Quality Control
QCRV Quality Control Release Value
RAA Running Annual Average
RFA Regulatory Flexibility Act
RO Reverse Osmosis
SAB Science Advisory Board
SBAR Small Business Advocacy Review
SDWA Safe Drinking Water Act
SWAP Source Water Assessment Program
SWTR Surface Water Treatment Rule
TCR Total Coliform Rule
TTHM Total Trihalomethanes
UF Ultrafiltration
UMRA Unfunded Mandates Reform Act

Table of Contents

I. General Information
    A. Who Is Regulated by This Action?
II. Summary of the Final Rule
    A. Why Is EPA Promulgating the LT2ESWTR?
    B. What Does the LT2ESWTR Require?
    1. Source water monitoring
    2. Additional treatment for Cryptosporidium
    3. Uncovered finished water storage facilities
    C. Will This Regulation Apply to My Water System?
III. Background Information
    A. Statutory Requirements and Legal Authority
    B. Existing Regulations for Microbial Pathogens in Drinking 
Water
    1. Surface Water Treatment Rule
    2. Total Coliform Rule
    3. Interim Enhanced Surface Water Treatment Rule
    4. Long Term 1 Enhanced Surface Water Treatment Rule
    5. Filter Backwash Recycle Rule
    C. Concern with Cryptosporidium in Drinking Water
    1. Introduction
    2. What is Cryptosporidium?
    3. Cryptosporidium health effects
    4. Efficacy of water treatment processes on Cryptosporidium
    5. Epidemic and endemic disease from Cryptosporidium
    D. Specific Concerns Following the IESWTR and LT1ESWTR
    E. New Information on Cryptosporidium Risk Management
    1. Infectivity
    2. Occurrence
    3. Analytical methods
    4. Treatment
    F. Federal Advisory Committee Recommendations
IV. Explanation of Today's Action
    A. Source Water Monitoring Requirements
    1. Today's rule
    a. Sampling parameters and frequency
    b. Sampling location
    c. Sampling schedule
    d. Plants operating only part of the year
    e. Failing to monitor
    f. Providing treatment instead of monitoring
    g. Grandfathering previously collected data
    h. Ongoing watershed assessment
    i. Second round of monitoring
    j. New source monitoring
    2. Background and analysis
    a. Sampling parameters and frequency
    b. Sampling location
    c. Sampling schedule
    d. Plants operating only part of the year
    e. Failing to monitor
    f. Grandfathering previously collected data
    g. Ongoing watershed assessment
    h. Second round of monitoring
    3. Summary of major comments
    a. Sampling parameters and frequency
    b. Sampling location
    c. Sampling schedule
    d. Plants operating only part of the year
    e. Failing to monitor
    f. Providing treatment instead of monitoring
    g. Grandfathering previously collected data
    h. Ongoing watershed assessment
    i. Second round of monitoring
    j. New source monitoring
    B. Filtered System Cryptosporidium Treatment Requirements
    1. Today's rule
    a. Bin classification
    b. Bin treatment requirements
    2. Background and analysis
    a. Basis for targeted treatment requirements
    b. Basis for bin concentration ranges and treatment requirements
    3. Summary of major comments
    C. Unfiltered System Cryptosporidium Treatment Requirements
    1. Today's rule
    a. Determination of mean Cryptosporidium level
    b. Cryptosporidium treatment requirements
    c. Use of two disinfectants
    2. Background and analysis
    a. Basis for Cryptosporidium treatment requirements
    b. Basis for requiring the use of two disinfectants
    c. Filtration avoidance
    3. Summary of major comments
    D. Options for Systems to Meet Cryptosporidium Treatment 
Requirements
    1. Microbial toolbox overview
    2. Watershed control program
    a. Today's rule
    b. Background and analysis
    c. Summary of major comments
    3. Alternative source
    a. Today's rule
    b. Background and analysis
    c. Summary of major comments
    4. Pre-sedimentation with coagulant
    a. Today's rule
    b. Background and analysis
    c. Summary of major comments
    5. Two-stage lime softening
    a. Today's rule
    b. Background and analysis
    c. Summary of major comments
    6. Bank filtration
    a. Today's rule
    b. Background and analysis
    c. Summary of major comments
    7. Combined filter performance
    a. Today's rule
    b. Background and analysis
    c. Summary of major comments
    8. Individual filter performance
    a. Today's rule
    b. Background and analysis
    c. Summary of major comments
    9. Demonstration of performance
    a. Today's rule
    b. Background and analysis
    c. Summary of major comments
    10. Bag and cartridge filtration
    a. Today's rule
    b. Background and analysis
    c. Summary of major comments
    11. Membrane filtration
    a. Today's rule
    b. Background and analysis
    c. Summary of major comments
    12. Second stage filtration
    a. Today's rule
    b. Background and analysis
    c. Summary of major comments
    13. Slow sand filtration
    a. Today's rule
    b. Background and analysis
    c. Summary of major comments
    14. Ozone and chlorine dioxide
    a. Today's rule
    b. Background and analysis
    c. Summary of major comments
    15. Ultraviolet light
    a. Today's rule
    b. Background and analysis
    c. Summary of major comments
    E. Disinfection Benchmarking for Giardia lamblia and Viruses
    1. Today's rule
    2. Background and analysis
    3. Summary of major comments
    F. Requirements for Systems with Uncovered Finished Water 
Storage Facilities
    1. Today's rule

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    2. Background and analysis
    a. Types and sources of contaminants in open reservoirs
    b. Regulatory approaches to reduce risk from contamination in 
open reservoirs
    c. Definition of uncovered finished water storage facility
    3. Summary of major comments
    G. Compliance Schedules
    1. Today's rule
    2. Background and analysis
    3. Summary of major comments
    H. Public Notice Requirements
    1. Today's rule
    2. Background and analysis
    3. Summary of major comments
    I. Reporting Source Water Monitoring Results
    1. Today's rule
    2. Background and analysis
    3. Summary of major comments
    J. Analytical Methods
    1. Analytical methods overview
    2. Cryptosporidium methods
    a. Today's rule
    b. Background and analysis
    c. Summary of major comments
    3. E. coli methods
    a. Today's rule
    b. Background and analysis
    c. Summary of major comments
    4. Turbidity methods
    a. Today's rule
    b. Background and analysis
    c. Summary of major comments
    K. Laboratory Approval
    1. Cryptosporidium laboratory approval
    a. Today's rule
    b. Background and analysis
    c. Summary of major comments
    2. E. coli laboratory approval
    a. Today's rule
    b. Background and analysis
    c. Summary of major comments
    3. Turbidity analyst approval
    a. Today's rule
    b. Background and analysis
    c. Summary of major comments
    L. Requirements for Sanitary Surveys Conducted by EPA
    1. Today's rule
    2. Background and analysis
    3. Summary of major comments
    M. Variances and Exemptions
    1. Variances
    2. Exemptions
V. State Implementation
    A. Today's Rule
    1. Special State primacy requirements
    2. State recordkeeping requirements
    3. State reporting requirements
    4. Interim primacy
    B. Background and Analysis
    C. Summary of Major Comments
VI. Economic Analysis
    A. What Regulatory Alternatives Did the Agency Consider?
    B. What Analyses Support Today's Final Rule?
    C. What Are the Benefits of the LT2ESWTR?
    1. Nonquantified benefits
    2. Quantified benefits
    a. Filtered PWSs
    b. Unfiltered PWSs
    3. Timing of benefits accrual (latency)
    D. What Are the Costs of the LT2ESWTR?
    1. Total annualized present value costs
    2. PWS costs
    a. Source water monitoring costs
    b. Filtered PWSs treatment costs
    c. Unfiltered PWSs treatment costs
    d. Uncovered finished water storage facilities
    e. Future monitoring costs
    f. Sensitivity analysis--influent bromide levels on technology 
selection for filtered plants
    3. State/Primacy agency costs
    4. Non-quantified costs
    E. What Are the Household Costs of the LT2ESWTR?
    F. What Are the Incremental Costs and Benefits of the LT2ESWTR?
    H. Are there Increased Risks From Other Contaminants?
    I. What Are the Effects of the Contaminant on the General 
Population and Groups within the General Populations that Are 
Identified as Likely to be at Greater Risk of Adverse Health 
Effects?
    J. What Are the Uncertainties in the Risk, Benefit, and Cost 
Estimates for the LT2ESWTR?
    K. What Is the Benefit/Cost Determination for the LT2ESWTR?
    L. Summary of Major Comments
    1. Cryptosporidium occurrence
    a. Quality of the ICR and ICRSS data sets
    b. Treatment of observed zeros
    2. Drinking water consumption
    3. Cryptosporidium infectivity
    4. Valuation of benefits
    a. Valuation of morbidity
    b. Valuation of lost time under the enhanced cost of illness 
(COI) approach
VII. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review
    B. Paperwork Reduction Act
    C. Regulatory Flexibility Act
    D. Unfunded Mandates Reform Act
    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination With 
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children from 
Environmental Health and Safety Risks
    H. Executive Order 13211: Actions that Significantly Affect 
Energy Supply, Distribution, or Use
    I. National Technology Transfer and Advancement Act
    J. Executive Order 12898: Federal Actions to Address 
Environmental Justice in Minority Populations or Low-Income 
Populations
    K. Consultations with the Science Advisory Board, National 
Drinking Water Advisory Council, and the Secretary of Health and 
Human Services
    L. Plain Language
    M. Analysis of the Likely Effect of Compliance with the LT2ESWTR 
on the Technical, Financial, and Managerial Capacity of Public Water 
Systems
    N. Congressional Review Act
VIII. References

II. Summary of the Final Rule

A. Why Is EPA Promulgating the LT2ESWTR?

    EPA is promulgating the Long Term 2 Enhanced Surface Water 
Treatment Rule (LT2ESWTR) to further protect public health against 
Cryptosporidium and other microbial pathogens in drinking water. 
Cryptosporidium is a protozoan parasite that is common in surface water 
used as drinking water sources by public water systems (PWSs). In 
drinking water, Cryptosporidium is a particular concern because it is 
highly resistant to chemical disinfectants like chlorine. When 
ingested, Cryptosporidium can cause acute gastrointestinal illness, 
which may be severe and sometimes fatal for people with weakened immune 
systems. Cryptosporidium has been identified as the cause of a number 
of waterborne disease outbreaks in the United States (details in 
section III.C).
    The LT2ESWTR supplements existing microbial treatment regulations 
and targets PWSs with higher potential risk from Cryptosporidium. 
Existing regulations require most PWSs using surface water sources to 
filter the water, and those PWSs that are required to filter must 
remove at least 99 percent (2-log) of the Cryptosporidium (details in 
section III.B). As explained in the proposal for today's rule (68 FR 
47640, August 11, 2003) (USEPA 2003a), new data on the occurrence, 
infectivity, and treatment of Cryptosporidium in drinking water 
indicate that existing regulations are sufficient for most PWSs. A 
subset of PWSs with greater vulnerability to Cryptosporidium, however, 
requires additional treatment.
    In particular, recent national survey data show that the level of 
Cryptosporidium in the sources of most filtered PWSs is lower than 
previously estimated, but also that Cryptosporidium levels vary widely 
from source to source. Accordingly, a subset of filtered PWSs has 
relatively high levels of source water Cryptosporidium contamination. 
In addition, data from human health studies indicate that the potential 
for Cryptosporidium to cause infection is likely greater than 
previously recognized (details in section III.E). These findings have 
led EPA to conclude that existing requirements do not provide adequate 
public health protection in filtered PWSs with the highest source water 
Cryptosporidium levels. Consequently, EPA is establishing risk-targeted 
additional treatment requirements for such filtered PWSs under the 
LT2ESWTR.

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    For PWSs that use surface water sources and are not required to 
filter (i.e., unfiltered PWSs), existing regulations do not require any 
treatment for Cryptosporidium. New survey data suggest that typical 
Cryptosporidium levels in the treated water of unfiltered PWSs are 
higher than in the treated water of filtered PWSs (USEPA 2003a). Thus, 
Cryptosporidium treatment by unfiltered PWSs is needed to achieve 
comparable public health protection (details in section III.E). 
Further, results from recent treatment studies have allowed EPA to 
develop standards for the inactivation of Cryptosporidium by ozone, 
ultraviolet (UV) light, and chlorine dioxide (details in section IV.D). 
Based on these developments, EPA is establishing requirements under the 
LT2ESWTR for all unfiltered PWSs to treat for Cryptosporidium, with the 
required degree of treatment depending on the source water 
contamination level.
    Additionally, the LT2ESWTR addresses risks in uncovered finished 
water storage facilities, in which treated water can be subject to 
significant contamination as a result of runoff, bird and animal 
wastes, human activity, algal growth, insects, fish, and airborne 
deposition (details in section IV.F). Existing regulations prohibit the 
building of new uncovered finished water storage facilities but do not 
deal with existing ones. Under the LT2ESWTR, PWSs must limit potential 
risks by covering or treating the discharge of such storage facilities.
    Most of the requirements in today's final LT2ESWTR reflect 
consensus recommendations from the Stage 2 Microbial and Disinfection 
Byproducts (M-DBP) Federal Advisory Committee. These recommendations 
are set forth in the Stage 2 M-DBP Agreement in Principle (65 FR 83015, 
December 29, 2000) (USEPA 2000a).

B. What Does the LT2ESWTR Require?

1. Source Water Monitoring
    The LT2ESWTR requires PWSs using surface water or ground water 
under the direct influence (GWUDI) of surface water to monitor their 
source water (i.e., the influent water entering the treatment plant) to 
determine an average Cryptosporidium level. As described in the next 
section, monitoring results determine the extent of Cryptosporidium 
treatment requirements under the LT2ESWTR.
    Large PWSs (serving at least 10,000 people) must monitor for 
Cryptosporidium (plus E. coli and turbidity in filtered PWSs) for a 
period of two years. To reduce monitoring costs, small filtered PWSs 
(serving fewer than 10,000 people) initially monitor just for E. coli 
for one year as a screening analysis and 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 all small unfiltered PWSs, must monitor for 
Cryptosporidium for one or two years, depending on the sampling 
frequency (details sections IV.A).
    Under the LT2ESWTR, specific criteria are set for sampling 
frequency and schedule, sampling location, using previously collected 
data (i.e., grandfathering), providing treatment instead of monitoring, 
sampling by PWSs that use surface water for only part of the year, and 
monitoring of new plants and sources (details in section IV.A). The 
LT2ESWTR also establishes requirements for reporting of monitoring 
results (details in section IV.I), using analytical methods (details in 
section IV.J), and using approved laboratories (details in section 
IV.K).
    The date for PWSs to begin monitoring is staggered by PWS size, 
with smaller PWSs starting at a later time than larger ones (details in 
section IV.G). Today's rule also requires a second round of monitoring 
to begin approximately 6.5 years after the first round concludes in 
order to determine if source water quality has changed to a degree that 
should affect treatment requirements (details in section IV.A).
2. Additional Treatment for Cryptosporidium
    The LT2ESWTR establishes risk-targeted treatment technique 
requirements to control Cryptosporidium in PWSs using surface water or 
GWUDI. These treatment requirements supplement those established by 
existing regulations, all of which remain in effect under the LT2ESWTR.
    Filtered PWSs will be classified in one of four treatment 
categories (or ``bins'') based on the results of the source water 
Cryptosporidium monitoring described in the previous section. This bin 
classification determines the degree of additional Cryptosporidium 
treatment, if any, the filtered PWS must provide. Occurrence data 
indicate that the majority of filtered PWSs will be classified in Bin 
1, which carries no additional treatment requirements. PWSs classified 
in Bins 2, 3, or 4 must achieve 1.0- to 2.5-log of treatment (i.e., 90 
to 99.7 percent reduction) for Cryptosporidium over and above that 
provided with conventional treatment. Different additional treatment 
requirements may apply to PWSs using other than conventional treatment, 
such as direct filtration, membranes, or cartridge filters (details in 
section. IV.B). Filtered PWSs must meet the additional Cryptosporidium 
treatment required in Bins 2, 3, or 4 by using one or more treatment or 
control processes from a ``microbial toolbox'' of options (details in 
section. IV.D).
    The LT2ESWTR requires all unfiltered PWSs to provide at least 2-log 
(i.e., 99 percent) inactivation of Cryptosporidium. If the average 
source water Cryptosporidium level exceeds 0.01 oocysts/L based on the 
monitoring described in the previous section, the unfiltered PWS must 
provide at least 3-log (i.e., 99.9 percent) inactivation of 
Cryptosporidium. Further, under the LT2ESWTR, 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 (details in section IV.C).
3. Uncovered Finished Water Storage Facilities
    Under the LT2ESWTR, PWSs with uncovered finished water storage 
facilities must take steps to address contamination risks. Existing 
regulations require PWSs to cover all new storage facilities for 
finished water but do not address existing uncovered finished water 
storage facilities. Under the LT2ESWTR, PWSs using uncovered finished 
water storage facilities must either cover the storage facility or 
treat the storage facility discharge to achieve inactivation and/or 
removal of 4-log virus, 3-log Giardia lamblia, and 2-log 
Cryptosporidium on a State-approved schedule (details in section. 
IV.F).

C. Will This Regulation Apply to My Water System?

    The LT2ESWTR applies to all PWSs using surface water or GWUDI, 
including both large and small PWSs, community and non-community PWSs, 
and non-transient and transient PWSs. Wholesale PWSs must comply with 
the requirements of today's rule based on the population of the largest 
PWS in the combined distribution system. Consecutive PWSs that purchase 
treated water from wholesale PWSs that fully comply with the monitoring 
and treatment requirements of the LT2ESWTR are not required to take 
additional steps for that water under today's rule.

III. Background Information

    The sections in this part provide summary background information 
for

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today's final LT2ESWTR. Individual sections address the following 
topics: (A) Statutory requirements and legal authority for the 
LT2ESWTR; (B) existing regulations for microbial pathogens in drinking 
water; (C) the problem with Cryptosporidium in drinking water; (D) 
specific public health concerns addressed by the LT2ESWTR; (E) new 
information for Cryptosporidium risk management in PWSs; and (F) 
recommendations from the Stage 2 M-DBP Advisory Committee for the 
LT2ESWTR. For additional information on these topics, see the proposed 
LT2ESWTR (USEPA 2003a) and supporting technical material where cited.

A. Statutory Requirements and Legal Authority

    The Safe Drinking Water Act (SDWA or the Act), as amended in 1996, 
requires EPA to publish a maximum contaminant level goal (MCLG) and 
promulgate a national primary drinking water regulation (NPDWR) with 
enforceable requirements for any contaminant that the Administrator 
determines may have an adverse effect on the health of persons, is 
known to occur or has a substantial likelihood of occurring in public 
water systems (PWSs) with a frequency and at levels of public health 
concern, and for which, in the sole judgement of the Administrator, 
regulation of such contaminant presents a meaningful opportunity for 
health risk reduction for persons served by PWSs (section 1412 
(b)(1)(A)).
    MCLGs are non-enforceable health goals and are to be set at a level 
at which no known or anticipated adverse effects on the health of 
persons occur and which allows an adequate margin of safety (sections 
1412(b)(4) and 1412(a)(3)). EPA established an MCLG of zero for 
Cryptosporidium under the Interim Enhanced Surface Water Treatment Rule 
(IESWTR) (63 FR 69478, December 16, 1998) (USEPA 1998a). In today's 
rule, the Agency is not making any changes to the current MCLG for 
Cryptosporidium.
    The Act also requires each NPDWR for which an MCLG is established 
to specify a maximum contaminant level (MCL) that is as close to the 
MCLG as is feasible (sections 1412(b)(4) and 1401(1)(C)). The Agency is 
authorized to promulgate an NPDWR that requires the use of a treatment 
technique in lieu of establishing an MCL if the Agency finds that it is 
not economically or technologically feasible to ascertain the level of 
the contaminant (sections 1412(b)(7)(A) and 1401(1)(C)). The Act 
specifies that in such cases, the Agency shall identify those treatment 
techniques that would prevent known or anticipated adverse effects on 
the health of persons to the extent feasible (section 1412(b)(7)(A)).
    The Agency has concluded that it is not currently economically or 
technologically feasible for PWSs to determine the level of 
Cryptosporidium in finished drinking water for the purpose of 
compliance with a finished water standard. As described in section 
IV.C, the LT2ESWTR is designed to protect public health by lowering the 
level of infectious Cryptosporidium in finished drinking water to less 
than 1 oocyst/10,000 L. Approved Cryptosporidium analytical methods, 
which are described in section IV.K, are not sufficient to routinely 
determine the level of Cryptosporidium at this concentration. 
Consequently, the LT2ESWTR relies on treatment technique requirements 
to reduce health risks from Cryptosporidium in PWSs.
    When proposing an NPDWR that includes an MCL or treatment 
technique, the Act requires EPA to publish and seek public comment on 
an analysis of health risk reduction and costs. This includes an 
analysis of quantifiable and nonquantifiable costs and health risk 
reduction benefits, incremental costs and benefits of each alternative 
considered, the effects of the contaminant upon sensitive 
subpopulations (e.g., infants, children, pregnant women, the elderly, 
and individuals with a history of serious illness), any increased risk 
that may occur as the result of compliance, and other relevant factors 
(section 1412(b)(3)(C)). EPA's analysis of health benefits and costs 
associated with the LT2ESWTR is presented in the Economic Analysis of 
the LT2ESWTR (USEPA 2005a) and is summarized in section VI of this 
preamble. The Act does not, however, authorize the Administrator to use 
a determination of whether benefits justify costs to establish an MCL 
or treatment technique requirement for the control of Cryptosporidium 
(section 1412(b)(6)(C)).
    Finally, section 1412(b)(2)(C) of the Act requires EPA to 
promulgate a Stage 2 Disinfectants and Disinfection Byproducts Rule 
within 18 months after promulgation of the LT1ESWTR, which occurred on 
January 14, 2002. Consistent with statutory requirements for risk 
balancing (section 1412(b)(5)(B)), EPA is finalizing the LT2ESWTR in 
conjunction with the Stage 2 DBPR to ensure parallel protection from 
microbial and DBP risks.

B. Existing Regulations for Microbial Pathogens in Drinking Water

    This section summarizes existing rules that regulate treatment for 
pathogenic microorganisms by PWSs using surface water sources. The 
LT2ESWTR supplements these rules with additional risk-targeted 
requirements, but does not withdraw any existing requirements.
1. Surface Water Treatment Rule
    The Surface Water Treatment Rule (SWTR) (54 FR 27486, June 29, 
1989) (USEPA 1989a) applies to all PWSs using surface water or ground 
water under the direct influence (GWUDI) of surface water as sources 
(i.e., Subpart H PWSs). It established MCLGs of zero for Giardia 
lamblia, viruses, and Legionella, and includes the following treatment 
technique requirements to reduce exposure to pathogenic microorganisms: 
(1) Filtration, unless specific avoidance criteria are met; (2) 
maintenance of a disinfectant residual in the distribution system; (3) 
removal and/or inactivation of 3-log (99.9%) of Giardia lamblia and 4-
log (99.99%) of viruses; (4) maximum allowable turbidity in the 
combined filter effluent (CFE) of 5 nephelometric turbidity units (NTU) 
and 95th percentile CFE turbidity of 0.5 NTU or less for plants using 
conventional treatment or direct filtration (with different standards 
for other filtration technologies); and (5) watershed protection and 
source water quality requirements for unfiltered PWSs.
2. Total Coliform Rule
    The Total Coliform Rule (TCR) (54 FR 27544, June 29, 1989) (USEPA 
1989b) applies to all PWSs. It established an MCLG of zero for total 
and fecal coliform bacteria and an MCL based on the percentage of 
positive samples collected during a compliance period. Coliforms are 
used as an indicator of fecal contamination and to determine the 
integrity of the water treatment process and distribution system. Under 
the TCR, no more than 5 percent of distribution system samples 
collected in any month may contain coliform bacteria (no more than 1 
sample per month may be coliform positive in those PWSs that collect 
fewer than 40 samples per month). The number of samples to be collected 
in a month is based on the number of people served by the PWS.
3. Interim Enhanced Surface Water Treatment Rule
    The Interim Enhanced Surface Water Treatment Rule (IESWTR) (63 FR 
69478, December 16, 1998) (USEPA 1998a) applies to PWSs serving at 
least 10,000 people and using surface water or

[[Page 659]]

GWUDI sources. Key provisions established by the IESWTR include the 
following: (1) An MCLG of zero for Cryptosporidium; (2) Cryptosporidium 
removal requirements of 2-log (99 percent) for PWSs that filter; (3) 
more stringent CFE turbidity performance standards of 1.0 NTU as a 
maximum and 0.3 NTU or less at the 95th percentile monthly for 
treatment plants using conventional treatment or direct filtration; (4) 
requirements for individual filter turbidity monitoring; (5) 
disinfection benchmark provisions to assess the level of microbial 
protection that PWSs provide as they take steps to comply with new DBP 
standards; (6) inclusion of Cryptosporidium in the definition of GWUDI 
and in the watershed control requirements for unfiltered PWSs; (7) 
requirements for covers on new finished water storage facilities; and 
(8) sanitary surveys for all surface water systems regardless of size.
    The IESWTR was developed in conjunction with the Stage 1 
Disinfectants and Disinfection Byproducts Rule (Stage 1 DBPR) (63 FR 
69389, December 16, 1998) (USEPA 1998b), which reduced allowable levels 
of certain DBPs, including trihalomethanes, haloacetic acids, chlorite, 
and bromate.
4. Long Term 1 Enhanced Surface Water Treatment Rule
    The Long Term 1 Enhanced Surface Water Treatment Rule ( LT1ESWTR) 
(67 FR 1812, January 14, 2002) (USEPA 2002a) builds upon the microbial 
control provisions established by the IESWTR for large PWSs through 
extending similar requirements to small PWSs. The LT1ESWTR applies to 
PWSs that use surface water or GWUDI as sources and that serve fewer 
than 10,000 people. Like the IESWTR, the LT1ESWTR established the 
following: 2-log (99 percent) Cryptosporidium removal requirements by 
PWSs that filter; individual filter turbidity monitoring and more 
stringent combined filter effluent turbidity standards for conventional 
and direct filtration plants; disinfection profiling and benchmarking; 
inclusion of Cryptosporidium in the definition of GWUDI and in the 
watershed control requirements for unfiltered PWSs; and the requirement 
that new finished water storage facilities be covered.
5. Filter Backwash Recycle Rule
    The Filter Backwash Recycling Rule (FBRR) (66 FR 31085, June 8, 
2001) (USEPA 2001a) requires PWSs to consider the potential risks 
associated with recycling contaminants removed during the filtration 
process. The provisions of the FBRR apply to all PWSs that recycle, 
regardless of population served. In general, the provisions include the 
following: (1) PWSs must return certain recycle streams to a point in 
the treatment process that is prior to primary coagulant addition 
unless the State specifies an alternative location; (2) direct 
filtration PWSs recycling to the treatment process must provide 
detailed recycle treatment information to the State; and (3) certain 
conventional PWSs that practice direct recycling must perform a one-
month, one-time recycling self assessment.

C. Concern With Cryptosporidium in Drinking Water

1. Introduction
    EPA is promulgating the LT2ESWTR to reduce the public health risk 
associated with Cryptosporidium in drinking water. This section 
describes the general basis for this public health concern through 
reviewing information in several areas: the nature of Cryptosporidium, 
health effects, efficacy of water treatment processes, and the 
incidence of epidemic and endemic disease. Further information about 
Cryptosporidium is available in the following documents: 
Cryptosporidium: Human Health Criteria Document (USEPA 2001b), 
Cryptosporidium: Drinking Water Advisory (USEPA 2001c), and 
Cryptosporidium: Risks for Infants and Children (USEPA 2001d).
2. What Is Cryptosporidium?
    Cryptosporidium is a protozoan parasite that lives and reproduces 
entirely in one host. Ingestion of Cryptosporidium can cause 
cryptosporidiosis, a gastrointestinal (GI) illness. Cryptosporidium is 
excreted in feces. Transmission of cryptosporidiosis occurs through 
consumption of water or food contaminated with feces or by direct or 
indirect contact with infected persons or animals (Casemore 1990).
    In the environment, Cryptosporidium is present as a thick-walled 
oocyst containing four organisms (sporozoites); the oocyst wall 
insulates the sporozoites from harsh environmental conditions. Oocysts 
are 4-5 microns in length and width. Upon a host's ingestion of 
oocysts, enzymes and chemicals produced by the host's digestive system 
cause the oocyst to excyst, or break open. The excysted sporozoites 
embed themselves in the surfaces of the epithelial cells of the lower 
small intestine. The organisms then begin absorbing nutrients from 
their host cells. When these organisms sexually reproduce, they produce 
thick- and thin-walled oocysts. The host excretes the thick-walled 
oocysts in its feces; thin-walled oocysts excyst within the host and 
contribute to further host infection.
    The exact mechanism by which Cryptosporidium causes GI illness is 
not known. Factors may include damage to intestinal structure and 
cells, changes in the absorption/secretion processes of the intestine, 
toxins produced by Cryptosporidium or the host, and proteins that allow 
Cryptosporidium to adhere to host cell surfaces (Carey et al. 2004).
    Upon excretion, Cryptosporidium oocysts may survive for months in 
various environmental media, including soil, river water, seawater, and 
human and cattle feces at ambient temperatures (Kato et al. 2001, 
Pokorny et al. 2002, Fayer et al. 1998a and 1998b, and Robertson et al. 
1992). Cryptosporidium can also withstand temperatures as low as -20 
[deg]C for periods of a few hours (Fayer and Nerad 1996) but are 
susceptible to desiccation (Robertson et al. 1992).
    Cryptosporidium is a widespread contaminant in surface water used 
as drinking water supplies. For example, among 67 drinking water 
sources surveyed by LeChevallier and Norton (1995), 87 percent had 
positive samples for Cryptosporidium. A more recent survey of 80 medium 
and large PWSs conducted by EPA detected Cryptosporidium in 85 percent 
of water sources (USEPA 2003a). Cryptosporidium contamination can come 
from animal agriculture, wastewater treatment plant discharges, 
slaughterhouses, birds, wild animals, and other sources of fecal 
matter.
    Because different species of Cryptosporidium are very similar in 
morphology, researchers have focused on genetic differences in trying 
to classify them. However, discussion on Cryptosporidium taxonomy is 
complicated by the fact that even within species or strains, there may 
be differences in infectivity and virulence. Cryptosporidium parvum (C. 
parvum) has been the primary species of concern to humans. Until 
recently, some researchers divided C. parvum into two primary strains, 
genotype 1, which infects humans, and genotype 2, which infects both 
humans and cattle (Carey et al. 2004). In 2002, Morgan-Ryan et al. 
proposed that genotype 1 be designated a separate species, C. hominis. 
Additional Cryptosporidium species infecting other mammals, birds, and 
reptiles have been documented. In some cases, these species can infect 
both immunocompromised (having weakened immune systems) and

[[Page 660]]

otherwise healthy humans (Carey et al. 2004).
3. Cryptosporidium Health Effects
    Cryptosporidium infection is characterized by mild to severe 
diarrhea, dehydration, stomach cramps, and/or a slight fever. 
Incubation is thought to range from 2 to 10 days (Arrowood 1997). 
Symptoms typically last from several days to 2 weeks, though in a small 
percentage of cases, the symptoms may persist for months or longer in 
otherwise healthy individuals.
    Symptoms may be more severe in immunocompromised persons (Frisby et 
al. 1997, Carey et al. 2004). Such persons include those with AIDS, 
cancer patients undergoing chemotherapy, organ transplant recipients 
treated with drugs that suppress the immune system, and patients with 
autoimmune disorders (e.g., Lupus). In AIDS patients, Cryptosporidium 
has been found in the lungs, ear, stomach, bile duct, and pancreas in 
addition to the small intestine (Farthing 2000). Immunocompromised 
patients with severe persistent cryptosporidiosis may die (Carey et al. 
2004). Besides the immunocompromised, children and the elderly may be 
at higher risk from Cryptosporidium than the general population 
(discussed in section VII.G).
    Studies with human volunteers have demonstrated that a low dose of 
C. parvum (e.g., 10 oocysts) is sufficient to cause infection in 
healthy adults, although some strains are more infectious than others 
(DuPont et al. 1995, Chappell et al. 1999, Okhuysen et al. 2002). 
Studies of immunosuppressed adult mice have demonstrated that a single 
viable oocyst can induce C. parvum infections (Yang et al. 2000, 
Okhuysen et al. 2002). The lowest dose tested in any of the human 
challenge studies was 10 oocysts. Because drinking water exposures are 
generally projected to be at lower levels (e.g., 1 oocyst), statistical 
modeling is necessary to project the effects of such exposure. 
Following the advice of its Science Advisory Board (SAB), EPA has 
developed a range of models to predict effects of exposure to low doses 
of Cryptosporidium. These models are discussed in section VI and in the 
LT2ESWTR Economic Analysis (USEPA 2005a).
    The degree and duration of the immune response to Cryptosporidium 
is not well characterized. In a study by Chappell et al. (1999), 
volunteers with IgG Cryptosporidium antibodies in their blood were 
immune to low doses of oocysts. The ID50 (the dose that infects 50 
percent of the challenged population) was 1,880 oocysts for those 
individuals compared to 132 oocysts for individuals that tested 
negative for those antibodies. However, earlier studies did not observe 
a correlation between the development of antibodies after 
Cryptosporidium infection and subsequent protection from illness 
(Okhuysen et al. 1998).
    No cure for cryptosporidiosis is known. Medical care usually 
involves treatment for dehydration and nutrient loss. Certain 
antimicrobial drugs like Azithromycin, Paromomycin, and nitazoxanide, 
the only drug approved for cryptosporidiosis in children, have been 
partially effective in treating immunocompromised patients (Rossignol 
et al. 1998). Therapies used to treat retroviruses can be helpful in 
fighting cryptosporidiosis in people with AIDS and are more effective 
when used in conjunction with antimicrobial therapy. The effectiveness 
of antiretroviral therapy is thought to be related to the associated 
increase in white blood cells rather than the decrease in the amount of 
virus present.
4. Efficacy of Water Treatment Processes on Cryptosporidium
    EPA is particularly concerned about Cryptosporidium because, unlike 
pathogens such as bacteria and most viruses, Cryptosporidium oocysts 
are highly resistant to standard disinfectants like chlorine and 
chloramines (Korich et al. 1990, Ransome et al. 1993, Finch et al. 
1997). Consequently, control of Cryptosporidium in most treatment 
plants is dependent on physical removal processes. However, due to 
their size (4-5 microns), oocysts can sometimes pass through filters.
    Monitoring data on finished water show that Cryptosporidium is 
sometimes present in filtered, treated drinking water (LeChevallier et 
al. 1991, Aboytes et al. 2004). For example, Aboytes et al. (2004) 
analyzed 1,690 finished water samples from 82 plants. Of these, 22 
plants had at least one positive sample for infectious Cryptosporidium 
(1.4 percent of all samples were positive). All positive samples 
occurred at plants that met existing regulatory standards and many had 
very low turbidity.
    Waterborne outbreaks of cryptosporidiosis have occurred even in 
areas served by filtered surface water supplies (Solo-Gabriele and 
Neumeister, 1996). In some cases, outbreaks were attributed to 
treatment deficiencies, but in others, the treatment provided by the 
water system met the regulatory requirements in place at that time. 
These data indicate that even surface water systems that filter and 
disinfect can still be vulnerable to Cryptosporidium, depending on the 
source water quality and treatment effectiveness.
    Certain alternative disinfectants can be more effective in treating 
for Cryptosporidium. Both ozone and chlorine dioxide have been shown to 
inactivate Cryptosporidium, albeit at doses much higher than those 
required to inactivate Giardia, which has typically been used to set 
disinfectant doses (summarized in USEPA 2003a). Studies have also 
demonstrated a synergistic effect of treatment using ozone followed by 
chlorine or monochloramine (Rennecker et al. 2000, Driedger et al. 
2001). Significantly, UV light has recently been shown to achieve high 
levels of Cryptosporidium inactivation at feasible doses (summarized in 
USEPA 2003a).
    Other processes that can help reduce Cryptosporidium levels in 
finished water include watershed management programs, pretreatment 
processes like bank filtration, and additional clarification and 
filtration processes during water treatment. Further, optimizing 
treatment performance and achieving very low levels of turbidity in the 
finished water has been shown to improve Cryptosporidium removal in 
treatment plants (summarized in USEPA 2003a).
5. Epidemic and Endemic Disease From Cryptosporidium
    Cryptosporidium has caused a number of waterborne disease outbreaks 
since 1984 when the first was reported in the United States. Data from 
the Centers for Disease Control and Prevention (CDC) include ten 
outbreaks caused by Cryptosporidium in drinking water between 1984 and 
2000, with approximately 421,000 cases of illness (CDC 1993, 1996, 
1998, 2000, and 2002). The most serious outbreak occurred in 1993 in 
Milwaukee; an estimated 403,000 people became sick (MacKenzie et al. 
1994), and at least 50 Cryptosporidium-associated deaths occurred among 
the severely immunocompromised (Hoxie et al. 1997). Further, a study by 
McDonald et al. (2001) using blood samples from Milwaukee children 
suggests that Cryptosporidium infection was more widespread than might 
be inferred from the illness estimates by MacKenzie et al. (1994).
    The number of identified and reported outbreaks in the CDC database 
is believed to substantially understate the actual incidence of 
waterborne disease outbreaks and cases (Craun and Calderon 1996, 
National Research Council 1997). This under reporting is

[[Page 661]]

due to a number of factors. Many people experiencing gastrointestinal 
illness do not seek medical attention. Where medical attention is 
provided, the pathogenic agent may not be identified through routine 
testing. Physicians and patients often lack sufficient information to 
attribute gastrointestinal illness to any specific origin, such as 
drinking water, and few States have an active outbreak surveillance 
program. In addition, if drinking water is investigated as the source 
of an outbreak, oocysts may not be detected in water samples even if 
they are present, due to limitations in analytical methods. 
Consequently, outbreaks may not be recognized in a community or, if 
recognized, may not be traced to a drinking water source.
    In addition, an unknown but probably significant portion of 
waterborne disease is endemic (i.e., isolated cases not associated with 
an outbreak) and, thus, is even more difficult to recognize. In an 
outbreak, if the pathogen has been identified, medical providers and 
public health investigators know what to look for. In endemic disease, 
there is no investigation, so the illness may never be identified, or 
if it is, it may not be linked to a source (e.g., drinking water, 
person-to-person transmission). In addition, where a pathogen is 
identified, lab results may not be reported to public health agencies.
    Because of this under reporting, the actual incidence of 
cryptosporidiosis associated with drinking water is unknown. However, 
indications of this incidence rate can be roughly extrapolated from 
different sources. Mead et al. (1999) estimated approximately 300,000 
total cases of cryptosporidiosis annually that result in a physician 
visit, with 90 percent of these attributed to waterborne (drinking 
water and recreational water) and secondary transmission. This estimate 
is based on the percentage of stools that test positive for 
Cryptosporidium and applying this percentage to the approximately 15 
million physician visits for diarrhea each year. While the fraction of 
cryptosporidiosis cases that result in a physician visit is unknown, 
Corso et al. (2003) reported that during the 1993 outbreak in 
Milwaukee, medical care was sought in approximately 12 percent of all 
cryptosporidiosis cases.
    Surveillance data from the CDC for 2001 show an overall incidence 
of 1.5 laboratory diagnosed cases of cryptosporidiosis per 100,000 
population (CDC, 2002). Although the fraction of all cryptosporidiosis 
cases that are laboratory confirmed is unknown, during the 1993 
Milwaukee outbreak, 739 cases from an estimated 403,000 cases total 
were confirmed by a laboratory (MacKenzie et al., 1994). These data 
indicate a ratio of 1 laboratory confirmed case per 545 people 
estimated to be ill with cryptosporidiosis.
    A few studies have attempted to determine exposure in certain areas 
by measuring seroprevalence of Cryptosporidium antibodies (the 
frequency at which antibodies are found in the blood). Detection of 
such antibodies (seropositivity), however, does not mean that the 
person actually experienced symptoms of cryptosporidiosis. An 
individual can be asymptomatically infected and still excrete oocysts. 
Seroprevalence, though, is still a method for estimating the exposure 
to Cryptosporidium that has occurred within a limited time period (the 
antibodies may last only a few months).
    Frost et al. (2001) conducted a paired city study, in which the 
serological response of blood donors in a city using ground water as 
its water source was compared to that of donors in a city using surface 
water as its source. Rates of seropositivity were higher (49 vs. 36 
percent) in the city with the surface water source. A similar study in 
two other cities (Frost et al. 2002) showed a seropositivity rate of 54 
percent in the city served by surface water compared to 38 percent in 
the city served by ground water. These studies suggest that drinking 
water from surface sources may be a factor in the higher rates of 
seropositivity.

D. Specific Concerns Following the IESWTR and LT1ESWTR

    In the LT2ESWTR, EPA is addressing a number of public health 
concerns that remain following implementation of the IESWTR and 
LT1ESWTR. These are as follows:
     The need for filtered PWSs with higher levels of source 
water Cryptosporidium contamination to provide additional risk-based 
treatment for Cryptosporidium beyond IESWTR or LT1ESWTR requirements;
     The need for unfiltered PWSs to provide risk-based 
treatment for Cryptosporidium to achieve equivalent public health 
protection with filtered PWSs; and
     The need for PWSs with uncovered finished water storage 
facilities to take steps to reduce the risk of contamination of treated 
water prior to distribution to consumers.
    EPA and stakeholders identified each of these issues as public 
health concerns during development of the IESWTR (USEPA 1994, 1997). 
However, the Agency was unable to address these concerns in those 
regulations due to data gaps in the areas of health effects, 
occurrence, analytical methods, and treatment. Consequently, EPA 
followed a two-stage strategy for microbial and disinfection byproducts 
rules. Under this strategy, the IESWTR and LT1ESWTR were promulgated to 
provide an initial improvement in public health protection in large and 
small PWSs, respectively, while additional data to support a more 
comprehensive regulatory approach were collected.
    Since promulgating the IESWTR and LT1ESWTR, EPA has worked with 
stakeholders to collect and analyze significant new information to fill 
data gaps related to Cryptosporidium risk management in PWSs. The next 
section presents EPA's evaluation of these data and their implications 
for both the risk of Cryptosporidium in filtered and unfiltered PWSs 
and the feasibility of steps to limit this risk. In addition, the 
Agency has evaluated additional data related to mitigating risks with 
uncovered finished water storage facilities, which are presented in 
section IV.F.

E. New Information on Cryptosporidium Risk Management

    EPA and stakeholders determined during development of the IESWTR 
that in order to establish risk-based treatment requirements for 
Cryptosporidium, additional information was needed in the following 
areas: (1) The risk associated with a given level of Cryptosporidium 
(i.e., infectivity); (2) the occurrence of Cryptosporidium in PWS 
sources; (3) analytical methods that would suffice for making site-
specific source water Cryptosporidium density estimates; and (4) the 
use of treatment technologies to achieve specific levels of 
Cryptosporidium disinfection (USEPA 1997).
    In today's final LT2ESWTR, EPA is promulgating risk-based 
Cryptosporidium treatment requirements for filtered and unfiltered 
PWSs. The Agency believes that the critical data gaps in the areas of 
infectivity, occurrence, analytical methods, and treatment that 
prevented the adoption of such an approach under earlier regulations 
have been addressed. The new information that the Agency and 
stakeholders evaluated in each of these areas and its significance for 
today's LT2ESWTR are summarized as follows. See section VI.L for a 
summary of public comments on EPA's use of Cryptosporidium infectivity 
and

[[Page 662]]

occurrence data in assessing benefits of the LT2ESWTR.
1. Infectivity
    Infectivity relates the probability of infection to the number of 
Cryptosporidium oocysts that a person ingests. It is used to predict 
the disease burden associated with a particular Cryptosporidium level 
in drinking water. Information on Cryptosporidium infectivity comes 
from dose-response studies where healthy human volunteers ingest 
different numbers of oocysts (i.e., the ``dose'') and are subsequently 
evaluated for signs of infection and illness (i.e., the ``response'').
    Prior to the IESWTR, data from a human dose-response study of one 
Cryptosporidium isolate (IOWA) had been published (DuPont et al. 1995). 
Following IESWTR promulgation, a study of two additional isolates (TAMU 
and UCP) was completed and published (Okhuysen et al. 1999). This 1999 
study also reanalyzed the IOWA study results. The measured infectivity 
of Cryptosporidium oocysts varied over a wide range in the Okhuysen et 
al. (1999) study. The UCP oocysts were much less infective than the 
IOWA oocysts, and the TAMU oocysts were much more infective.
    EPA analyzed these new data for the proposed LT2ESWTR using two 
different dose-response models. This analysis suggested that the 
overall infectivity of Cryptosporidium is greater than was estimated 
for the IESWTR (USEPA 2003a). Specifically, EPA estimated the mean 
probability of infection from ingesting a single infectious oocyst 
ranges from 7 to 10 percent. This infection rate is approximately 20 
times higher than the estimate of 0.4 percent used in the IESWTR.
    Since the publication of the proposed LT2ESWTR, EPA has evaluated 
three additional studies of Cryptosporidium infectivity. EPA also 
received a recommendation from the SAB that it analyze Cryptosporidium 
infectivity data using a wider range of models. Accordingly, EPA re-
estimated Cryptosporidium infectivity using the new data and six 
different dose-response models, including the two models used at 
proposal. Estimates from the new data and models for the probability of 
infection from ingesting a single infectious oocyst range from 4 to 16 
percent. A detailed discussion of the models and their varying 
assumptions is provided in the LT2ESWTR Economic Analysis (USEPA 
2005a).
    As is apparent from these results, substantial uncertainty about 
the infectivity of Cryptosporidium remains in several areas. These 
include the variability in host susceptibility, response at very low 
oocyst doses typical of drinking water ingestion, and the relative 
infectivity and occurrence of different Cryptosporidium isolates in the 
environment. To address this uncertainty, EPA conducted its health risk 
reduction and benefits analyses using a representative range of model 
results. In the summary tables for these analyses, three sets of 
estimates are presented: A ``high'' estimate based on the model that 
showed the highest mean baseline risk; a ``medium'' estimate, based on 
the models and data used at proposal, which also happens to be in the 
middle of the range of estimates produced by the six models using the 
newly available data; and a ``low'' estimate, based on the model that 
showed the lowest mean baseline risk.
    These estimates should not be construed as upper and lower bounds 
on illnesses avoided and benefits. For each model, a distribution of 
effects is estimated, and the ``high'' and ``low'' estimates show only 
the means of these distributions for two different model choices. The 
detailed distribution of effects is presented for the proposal model in 
the Economic Analysis (USEPA 2005a). Further, the six dose-response 
models used in this analysis do not cover all possible variations of 
models that might have been used with the data, and it is possible that 
estimates with other models would fall outside the range presented. 
However, as discussed in the Economic Analysis, EPA believes that the 
models used in the analyses reflect a reasonable range of results based 
on important dimensions of model choice.
    Regardless of which model is chosen, the available infectivity data 
suggest that the risk associated with a given concentration of 
Cryptosporidium is most likely higher than EPA had estimated for the 
IESWTR. This finding supports the need for increased treatment for 
Cryptosporidium as required under the LT2ESWTR.
2. Occurrence
    Information on the occurrence of Cryptosporidium oocysts in 
drinking water sources is a critical parameter for assessing risk and 
the need for additional treatment for this pathogen. For the IESWTR, 
EPA had no national survey data on Cryptosporidium occurrence and 
relied instead on several studies that were local or regional. After 
promulgating the IESWTR, EPA obtained data from two national surveys, 
the Information Collection Rule (ICR) and the ICR Supplemental Surveys 
(ICRSS), which were designed to provide improved estimates of 
occurrence on a national basis.
    The ICR included monthly sampling for Cryptosporidium and other 
water quality parameters from the sources of approximately 350 large 
PWSs over 18 months. The ICRSS involved twice-per-month Cryptosporidium 
sampling from the sources of a statistically random sample of 40 large 
and 40 medium PWSs over 12 months. In addition, the ICRSS required the 
use of an improved analytical method for Cryptosporidium analysis that 
had a higher method recovery (the likelihood that an oocyst present in 
the sample will be counted) and enhanced sample preparation procedures.
    EPA analyzed ICR and ICRSS data using a statistical model to 
account for factors like method recovery and sample volume analyzed. As 
described in more detail in EPA's Occurrence and Exposure Assessment 
for the LT2ESWTR (USEPA 2005b), the ICR and ICRSS results demonstrate 
two main differences for filtered PWSs in comparison to Cryptosporidium 
occurrence data used for the IESWTR:

    (1) The occurrence of Cryptosporidium in many drinking water 
sources is lower than was indicated by the data used in IESWTR. For 
example, median Cryptosporidium levels for the ICR and ICRSS data 
are approximately 0.05/L, which is nearly 50 times lower than the 
median IESWTR estimates of 2.3 oocysts/L (USEPA 1998a).
    (2) Cryptosporidium occurrence is more variable from location to 
location than was shown by the data considered for the IESWTR. This 
finding demonstrates that, although median occurrence levels are 
below those estimated for the IESWTR, a subset of PWSs contains 
Cryptosporidium levels that are considerably greater than the 
median.

    These results, therefore, indicate that Cryptosporidium levels are 
relatively low in most water sources, but a subset of sources with 
relatively higher concentrations may require additional treatment. 
These findings support a risk-targeted approach for the LT2ESWTR 
wherein additional Cryptosporidium treatment is required only for 
filtered PWSs with the highest source water pathogen levels.
    Only the ICR provided data to evaluate Cryptosporidium occurrence 
in unfiltered PWS sources. The median Cryptosporidium level among 
unfiltered PWS sources was 0.0079 oocysts/L. This level is 
approximately 10 times lower than the median level for filtered PWS 
sources.
    When the Cryptosporidium removal that filtered PWSs achieve is 
taken into account, these occurrence data suggest that unfiltered PWSs 
typically have

[[Page 663]]

higher concentrations of Cryptosporidium in their treated water than 
filtered PWSs. EPA has estimated that on average, conventional 
filtration plants remove around 99.9 percent (3-log) of the 
Cryptosporidium present in the source water. Most unfiltered PWSs, 
however, provide no treatment for Cryptosporidium. If an unfiltered PWS 
had a source water Cryptosporidium level 10 times lower than a filtered 
PWS and the filtered PWS achieved 3-log Cryptosporidium removal, then 
the Cryptosporidium level in the treated water of the unfiltered P