Idaho Admin. Code r. 58.01.08.518

Current through September 2, 2024

Section 58.01.08.518 - ADDITIONAL DESIGN CRITERIA FOR SURFACE SOURCES

Performance criteria for surface water treatment facilities are set forth in Sections 300, 301, and 310. Surface water treatment systems must comply with applicable general design requirements in Section 503. In addition, the following design requirements apply specifically to surface water treatment facilities:

01.Engineering Design Requirements. The PWS must ensure that filtration and disinfection facilities for surface water or groundwater under the direct influence of surface water are designed, constructed and operated in accordance with all applicable engineering practices designated by the Department. The design of the water treatment plant must consider the worst raw water quality conditions that are likely to occur during the life of the facility.

02.Removal of Pathogens. Filtration facilities (excluding disinfection) must be designed, constructed and operated to achieve at least two (2) log removal of Giardia lamblia cysts, two (2) log removal of Cryptosporidium oocysts, and one (1) log removal of viruses, except as allowed under Subsection 518.09.b.

03.Disinfection. Disinfection facilities must be designed, constructed and operated so as to achieve at least point five zero (0.50) log inactivation of Giardia lamblia cysts; and

a. Two (2) log inactivation of viruses if using conventional and slow sand filtration technology; or

b. Three (3) log inactivation of viruses if using direct and diatomaceous earth filtration technology; or

c. Four (4) log inactivation of viruses if using alternate filtration technology.

d. Four (4) log inactivation of viruses if filtration treatment is not used.

04.Enhanced Disinfection. Higher levels of disinfection than specified under Subsection 518.03 may be required by the Department to provide adequate protection against Giardia lamblia and viruses.

05.Filter to Waste. For plants constructed after December 31, 1992, each filter unit must be capable of filter to waste. For plants constructed prior to December 31, 1992, each filter unit must be capable of filter to waste unless the PWS demonstrates through continuous turbidity monitoring or other means acceptable to the Department that water quality is not adversely affected following filter backwashing, cleaning or media replacement.

06.Continuous Turbidity Monitoring. For conventional, direct, membrane, and diatomaceous earth filtration technology, equipment must be provided to continuously measure the turbidity of each filter unit.

07.Continuous Monitoring of Disinfectant. Equipment must be provided and operated for continuous measurement of disinfectant residual prior to entry to the distribution system, unless the PWS serves fewer than three thousand three hundred (3,300) people.

08.Continuous Operation Required. Diatomaceous earth filtration facilities must include an alternate power source with automatic startup and alarm, or be designed in a manner to ensure continuous operation.

09.Acceptable Technology. The purveyor must select a filtration technology acceptable to the Department.

a. Conventional, direct, slow sand, diatomaceous earth, and membrane filtration technologies are generally acceptable to the Department on a case-by-case basis.

b. Alternate filtration technologies may be acceptable if the purveyor demonstrates all of the following to the satisfaction of the Department:

i. That the filtration technology:

(1) Is certified and listed by the National Sanitation Foundation (NSF) under Standard 53, Drinking Water Treatment Units - Health Effects, as achieving the NSF criteria for cyst reduction; or

(2) Removes at least ninety-nine percent (99%) (two (2) logs) of Cryptosporidium oocysts or surrogate particles and removes or inactivates at least ninety-nine percent (99%) (two (2) logs) of Giardia lamblia cysts or Giardia lamblia cyst surrogate particles in a challenge study acceptable to the Department.

ii. Based on field studies or other means acceptable to the Department, it must be demonstrated that the filtration technology has the following capabilities:

(1) In combination with disinfection treatment, consistently achieves at least ninety-nine percent (99%) (two (2) logs) removal of Cryptosporidium oocysts or surrogate particles and at least ninety-nine and nine tenths percent (99.9%) (three (3) logs) removal or inactivation of Giardia lamblia cysts and ninety-nine and ninety-nine hundredths percent (99.99%) (four (4) logs) removal or inactivation of viruses; and

(2) Meets the turbidity performance requirements of 40 CFR 141.73 (b).

10.Pilot Studies. The PWS must conduct pilot studies in accordance with the following requirements and in accordance with Subsection 501.19 for all proposed filtration facilities and structural modifications to existing filtration facilities, unless the Department modifies the requirements in writing:

a. The PWS must obtain the Department's approval of the pilot study plan before the pilot filter is constructed and before the pilot study is undertaken.

b. The design and operation of the pilot study must be overseen by an Idaho licensed professional engineer.

c. The PWS's pilot study plan must identify at a minimum:

i. The objectives of the pilot study;

ii. Pilot filter design;

iii. Water quality and operational parameters to monitor;

iv. Amount of data to collect; and

v. Qualifications of the pilot plant operator.

d. The PWS must ensure that the pilot study is:

i. Conducted to simulate conditions of the proposed full-scale design;

ii. Conducted for at least twelve (12) consecutive months or for a shorter period upon approval by the Department;

iii. Conducted to evaluate the reliability of the treatment system to achieve applicable water quality treatment criteria specified for filtration systems in 40 CFR 141.72 and 40 CFR 141.73; and

iv. Designed and operated in accordance with good engineering practices documented in references acceptable to the Department.

11.Redundant Disinfection. Surface water systems constructed after July 1, 1985, are required to install redundant disinfection components or maintain a backup unit on site as required to maintain constant application of disinfectant whenever water is being delivered to the distribution system.

Idaho Admin. Code r. 58.01.08.518

Effective July 1, 2024