Idaho Admin. Code r. 58.01.08.300

Current through September 2, 2024

Section 58.01.08.300 - FILTRATION AND DISINFECTION

01.General Requirements. 40 CFR 141.70 is incorporated by reference.

02.Filtration. 40 CFR 141.73 is incorporated by reference.

a. The Department will establish filtration removal credit on a system-by-system basis. Unless otherwise allowed 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

b. Filtration removal credit will be granted for filtration treatment provided the PWS is:

i. Operated in accordance with the Operations Plan specified in Subsection 552.03.a.; and

ii. The PWS is in compliance with the turbidity performance criteria specified under 40 CFR 141.73; and

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

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

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

03.Criteria for Avoiding Filtration. 40 CFR 141.71 is incorporated by reference.

04.Disinfection. 40 CFR 141.72 is incorporated by reference.

a. Surface water sources or groundwater sources directly influenced by surface water must maintain a minimum of at least two-tenths (0.2) mg/l disinfectant residual in the treated water at peak hour demand before delivery to the first customer.

b. The Department may allow a PWS 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 PWS 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.

c. Each PWS 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 must 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.

05.Analytical and Monitoring Requirements. 40 CFR 141.74 is incorporated by reference.

a. Total inactivation ratio calculations: 40 CFR 141.74(b)(4)(i) and (ii) are incorporated by reference.

b. Log removal credit for disinfection must be determined by multiplying the total inactivation ratio by three (3).

c. Unfiltered Subpart H systems. 40 CFR 141.857(c) is incorporated by reference.

d. Unfiltered PWSs must monitor as required in 40 CFR 141.74(b) upon notification by the Department that filtration treatment must be installed.

e. During the period prior to filtration treatment installation, the Department may, at its discretion, reduce the turbidity monitoring frequency for any non-community system which demonstrates to the satisfaction of the Department:

i. A free chlorine residual of two-tenths (0.2) part per million is maintained throughout the distribution system;

ii. The water source is well protected;

iii. E. coli MCL is not exceeded or a Level 1 or Level 2 Assessment has not been triggered in accordance with 40 CFR 141.859; and

iv. No significant health risk is present.

06.Reporting and Recordkeeping Requirements. 40 CFR 141.75 is incorporated by reference.

a. As provided in 40 CFR 141.75(a) and Section 300, the Department may establish interim reporting requirements for PWSs 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, PWSs required to install filtration treatment must report as follows:

i. The purveyor will 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:

(1) The occurrence of a waterborne disease outbreak potentially attributable to that PWS;

(2) Any turbidity measurement which exceeds five (5) NTU; and

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

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

(1) Turbidity monitoring information; and

(2) Disinfectant residual concentrations entering the distribution system.

iii. Personnel qualified under Subsection 300.01 will complete and sign the monthly report forms submitted to the Department as required in Subsection 300.06.

b. In addition to the reporting requirements in 40 CFR 141.75(b) pertaining to PWSs with filtration treatment, each PWS which provides filtration treatment must report the level of Giardia lamblia and virus inactivation/removal achieved each day by filtration and disinfection.

07.Recycle Provisions. 40 CFR 141.76 is incorporated by reference.

a. The Department will evaluate recycling records kept by PWSs pursuant to 40 CFR 141.76 during sanitary surveys, comprehensive performance evaluations, or other inspections.

b. The Department may require a PWS to modify recycling practices if it can be shown that these practices adversely affect the ability of the PWS to meet surface water treatment requirements.

Idaho Admin. Code r. 58.01.08.300

Effective July 1, 2024