Idaho Administrative Code, Rule 58.01.08, Section 58.01.08.300 - FILTRATION AND DISINFECTION | Idaho Administrative Code

01. General Requirements. 40 CFR 141.70 is herein incorporated by reference. Each public water system using a surface water source or ground water source directly influenced by surface water shall be operated by personnel, as specified in Sections 553 and 554, who have met state requirements for licensing of water system operators. (3-24-22)

02. Filtration. 40 CFR 141.73 is herein incorporated by reference. (3-24-22)

a. Each system which provides filtration treatment shall submit engineering evaluations, other documentation, or some combination of engineering evaluations and other documentation as required by the Department to demonstrate ongoing compliance with these rules. (3-24-22)

b. The Department will establish filtration removal credit on a system-by-system basis. Unless otherwise demonstrated to the satisfaction of the Department, the maximum log removal credit allowed for filtration is as follows:

Maximum Log Removal
Filtration Type	Giardia lamblia	Viruses	Cryptosporidium
Conventional	2.5	2.0	2.5
Direct	2.0	1.0	2.0
Slow sand	2.0	2.0	2.0
Diatomaceous earth	2.0	1.0	2.0
Microfiltration	3.0	0.5	3.0
Ultrafiltration	3.5	2.0	3.5
Nanofiltration	4.0	3.0	4.0
Reverse Osmosis	4.0	3.0	4.0
Alternate technology	2.0	0	2.0

(3-24-22)

c. Filtration removal credit shall be granted for filtration treatment provided the system is: (3-24-22)

i. Operated in accordance with the Operations Plan specified in Subsection 552.03.a.; and (3-24-22)

ii. The system is in compliance with the turbidity performance criteria specified under 40 CFR 141.73; and (3-24-22)

iii. Coagulant chemicals must be added and coagulation and flocculation unit process must be used at all times during which conventional and direct filtration treatment plants are in operation; and (3-24-22)

iv. Slow sand filters are operated at rates not to exceed one-tenth (0.1) gallons per minute per square foot or as approved by the Department; and (3-24-22)

v. Diatomaceous earth filters are operated at a rate not to exceed one point five (1.5) gallons per minute per square foot. (3-24-22)

03. Criteria for Avoiding Filtration. 40 CFR 141.71 is herein incorporated by reference. (3-24-22)

04. Disinfection. 40 CFR 141.72 is herein incorporated by reference. (3-24-22)

a. In addition to the disinfection requirements in 40 CFR 141.72, each system with a surface water source or ground water source directly influenced by surface water shall maintain a minimum of at least two-tenths (0.2) parts per million of chlorine in the treated water after an effective contact time of at least thirty (30) minutes at peak hour demand before delivery to the first customer. Effective contact time is either demonstrated or calculated. (3-24-22)

i. Demonstrated effective contact time is generally determined by tracer studies on a completed contact basin. Prior to conducting a tracer study, a testing plan shall be submitted to the Department for review and approval. The tracer chemical shall not be reactive with anything in the water or be consumed in the process. (3-24-22)

ii. Calculated effective contact time for tank type contact basins is based on tank baffling and inlet/ outlet configurations for the maximum hourly flow rate through that contact basin. Calculated effective contact time in a "pipeline type contact basin" (often called a pipeline contactor) is calculated by dividing the internal volume of the pipe by the maximum hourly flow rate through that pipeline contactor. (3-24-22)

b. The Department may allow a system to utilize automatic shut-off of water to the distribution system whenever total disinfectant residual is less than two-tenths (0.2) mg/l rather than provide redundant disinfection components and auxiliary power as required in 40 CFR 141.72(a)(2). An automatic water shut-off may be used if the system demonstrates to the satisfaction of the Department that, at all times, a minimum of twenty (20) psi pressure and adequate fire flow can be maintained in the distribution system when water delivery is shut-off to the distribution system and, at all times, minimum Giardia lamblia and virus inactivation removal rates can be achieved prior to the first customer. (3-24-22)

c. Each system which is required to provide filtration must provide disinfection treatment such that filtration plus disinfection provide at least 3-Log or ninety-nine and nine tenths percent (99.9%) inactivation/removal of Giardia lamblia cysts and at least 4-Log or ninety-nine and ninety-nine hundredths percent (99.99%) inactivation/ removal of viruses as specified in 40 CFR 141.72 and Section 300, and at least 2-Log or ninety-nine percent (99%) removal of Cryptosporidium as required by 40 CFR Part 141 , Subpart P or Subpart T However, in all cases the disinfection portion of the treatment train shall be designed to provide not less than five tenths (0.5) log Giardia lamblia inactivation, irrespective of the Giardia lamblia removal credit awarded to the filtration portion of the treatment train. (3-24-22)

05. Analytical and Monitoring Requirements. 40 CFR 141.74 is herein incorporated by reference. (3-24-22)

a. Each public water system which is required to provide disinfection shall monitor as follows: (3-24-22)

i. Each day the system is in operation, the purveyor shall determine the total level of inactivation of Giardia lamblia cysts and viruses achieved through disinfection based on CT99.9 values provided in 40 CFR 141.74(b)(3) (Tables 1.1 through 1.6, 2.1 and 3.1). (3-24-22)

ii. At least once per day, the system shall monitor the following parameters to determine the total inactivation ratio achieved through disinfection: (3-24-22)

(1) Temperature of the disinfected water at each residual disinfectant concentration sampling point; and (3-24-22)

(2) If using chlorine, the pH of the disinfected water at each chlorine residual sampling point. (3-24-22)

(3) The effective contact time, "T," must be determined each day during peak hour demand. Disinfectant contact time, "T," in pipelines used for Giardia lamblia and virus inactivation shall be calculated by dividing the internal volume of the pipe by the peak hour flow rate through that pipe. Effective contact time, "T," for all other system components used for Giardia lamblia and virus inactivation shall be determined by tracer studies or other evaluations or calculations acceptable to the Department. (3-24-22)

(4) The residual disinfectant concentrations at each residual disinfectant sampling point at or before the first customer, must be determined each day during peak hour demand, or at other times approved by the Department. (3-24-22)

iii. The purveyor may demonstrate to the Department, based on a Department approved on-site disinfection challenge study protocol, that the system is achieving disinfection requirements specified in Subsection 300.04 utilizing CT99.9 values other than those specified in 40 CFR 141.74(b)(3) (Tables 2.1 and 3.1) for ozone, chlorine dioxide, and chloramine. (3-24-22)

iv. The total inactivation ratio shall be calculated as follows: (3-24-22)

(1) If the system applies disinfectant at only one (1) point, the system shall determine the total inactivation ratio by either of the two (2) following methods: (3-24-22)

(a) One inactivation ratio (CTcalc/CT99.9) is determined at/or before the first customer during peak hour demand; or (3-24-22)

(b) Sequential inactivation ratios are calculated between the point of disinfectant application and a point at or before the first customer during peak hour demand. The following method must be used to calculate the total inactivation ratio: (3-24-22)

(i) Step 1: Determine (CTcalc/CT99.9) for each sequence. (3-24-22)

(ii) Step 2: Add the (CTcalc/CT99.9) values for all sequences. The result is the total inactivation ratio. (3-24-22)

(2) If the system uses more than one point of disinfectant application at or before the first customer, the system must determine the CT value of each disinfection sequence immediately prior to the next point of disinfectant application during peak hour demand. The sum of the (CTcalc/CT99.9) values from all sequences is the total inactivation ratio. (CTcalc/CT99.9) must be determined by the methods described in 40 CFR 141.74(b)(4)(i)(B). (3-24-22)

v. Log removal credit for disinfection shall be determined by multiplying the total inactivation ratio by three (3). (3-24-22)

vi. The Department may reduce the CT monitoring requirements specified under Section 300, for any system which demonstrates that the required inactivation levels are consistently exceeded. Reduced CT monitoring shall be allowed only where the reduction in monitoring will not endanger the health of consumers served by the water system. (3-24-22)

b. Residual disinfectant concentrations for ozone must be measured using the Indigo Method, or automated methods may be used if approved by the Department as provided for in 40 CFR 141.74(a)(2). (3-24-22)

c. Unfiltered Subpart H systems. 40 CFR 141.857(c) is herein incorporated by reference. (3-24-22)

d. As provided for in 40 CFR 141.74(b), the Department may specify interim monitoring requirements for unfiltered systems notified by the Department or U.S. Environmental Protection Agency that filtration treatment must be installed. Until filtration is installed, systems shall conduct monitoring for turbidity and disinfectant residuals as follows unless otherwise specified by the Department. (3-24-22)

i. Disinfectant residual concentrations entering the distribution system shall be measured at the following minimum frequencies, and samples must be taken at evenly spaced intervals throughout the workday.

Minimum Frequencies
Population	Samples/day
Less than 500	1
501 - 1000	2
1,001 - 2,500	3
Greater than 2501	4

(3-24-22)

ii. Turbidity shall be measured at least once per day at the entry point to the distribution system. (3-24-22)

iii. The Department may, at its discretion, reduce the turbidity monitoring frequency for any noncommunity system which demonstrates to the satisfaction of the Department: (3-24-22)

(1) A free chlorine residual of two-tenths (0.2) part per million is maintained throughout the distribution system; (3-24-22)

(2) The water source is well protected; (3-24-22)

(3) The total coliform MCL is not exceeded or a Level 1 or Level 2 Assessment has not been triggered in accordance with 40 CFR 141.859; and (3-24-22)

(4) No significant health risk is present. (3-24-22)

e. The Department may allow systems with surface water sources or ground water sources under the direct influence of surface water, to substitute continuous turbidity monitoring for grab sample monitoring as specified in 40 CFR 141.74(b)(2) and 40 CFR 141.74(c)(1) and Subsection 300.05. The Department may allow continuous turbidity monitoring provided the continuous turbidimeter is operated, maintained, standardized and calibrated per the manufacturer's recommendations. For purposes of determining compliance with turbidity performance criteria, discrete values must be recorded every four (4) hours water is supplied to the distribution system. (3-24-22)

f. The Department may allow systems using both a surface water source(s), or ground water source(s) under the direct influence of surface water, and one (1) or more ground water sources, to measure disinfectant residual at points other than the total coliform sampling points, as specified in 40 CFR 141.74(b)(6)(i) and 40 CFR 141.74(c)(3)(i) and Subsection 300.05. The Department may allow alternate sampling points provided the system submits an alternate monitoring plan to the Department for approval in advance of the monitoring requirement that demonstrates the alternative points are more representative of treated (disinfected) water quality within the distribution system. Heterotrophic bacteria, measured as heterotrophic plate count (HPC) as specified in 40 CFR 141.74(a)(1), may be measured in lieu of residual disinfectant concentration as outlined in 40 CFR 141.74(b)(6)(i). (3-24-22)

g. The Department may allow a reduced turbidity monitoring frequency for systems using slow sand filtration or technology other than conventional, direct, or diatomaceous earth filtration, as specified in 40 CFR 141.74(c)(1) and Subsection 300.05. To be considered for a reduced turbidity monitoring frequency, a system must submit a written request to the Department in advance of the monitoring requirement. (3-24-22)

06. Reporting and Recordkeeping Requirements. 40 CFR 141.75 is herein incorporated by reference. (3-24-22)

a. As provided in 40 CFR 141.75(a) and Section 300, the Department may establish interim reporting requirements for systems notified by the Department or U.S. Environmental Protection Agency that filtration treatment must be installed as specified in 40 CFR 141.75(a) and as referred to in Subsection 300.06. Until filtration treatment is installed, systems required to install filtration treatment shall report as follows: (3-24-22)

i. The purveyor shall immediately report to the Department via telephone or other equally rapid means, but no later than the end of the next business day, the following information: (3-24-22)

(1) The occurrence of a waterborne disease outbreak potentially attributable to that water system; (3-24-22)

(2) Any turbidity measurement which exceeds five (5) NTU; and (3-24-22)

(3) Any result indicating that the disinfectant residual concentration entering the distribution system is below two-tenths (0.2) mg/l free chlorine. (3-24-22)

ii. The purveyor shall report to the Department within ten (10) days after the end of each month the system serves water to the public the following monitoring information using a Department-approved form: (3-24-22)

(1) Turbidity monitoring information; and (3-24-22)

(2) Disinfectant residual concentrations entering the distribution system. (3-24-22)

iii. Personnel qualified under Subsection 300.01 shall complete and sign the monthly report forms submitted to the Department as required in Subsection 300.06. (3-24-22)

b. In addition to the reporting requirements in 40 CFR 141.75(b) pertaining to systems with filtration treatment, each public water system which provides filtration treatment must report the level of Giardia lamblia and virus inactivation/removal achieved each day by filtration and disinfection. (3-24-22)

07. Recycle Provisions. 40 CFR 141.76 is herein incorporated by reference. (3-24-22)

a. The Department shall evaluate recycling records kept by water systems pursuant to 40 CFR 141.76 during sanitary surveys, comprehensive performance evaluations, or other inspections. (3-24-22)

b. The Department may require a system to modify recycling practices if it can be shown that these practices adversely affect the ability of the system to meet surface water treatment requirements. (3-24-22)

Idaho Administrative CodeTitle IDAPA 58 - Environmental Quality, Department ofRule 58.01.08 - IDAHO RULES FOR PUBLIC DRINKING WATER SYSTEMSSection 58.01.08.300 - FILTRATION AND DISINFECTION

Idaho Administrative Code
Title IDAPA 58 - Environmental Quality, Department of
Rule 58.01.08 - IDAHO RULES FOR PUBLIC DRINKING WATER SYSTEMS
Section 58.01.08.300 - FILTRATION AND DISINFECTION