Wis. Admin. Code Department of Natural Resources NR 810.31

Current through November 25, 2024

Section NR 810.31 - Disinfection requirements for Giardia lamblia and viruses

A public water system that uses groundwater under the direct influence of surface water and does not provide filtration shall provide disinfection treatment specified in sub. (1) within 18 months after the department determines that the groundwater source is under the influence of surface water. A system that filters and uses surface water or groundwater under the direct influence of surface water as a source shall provide the disinfection treatment specified in sub. (2) when filtration is installed. Failure to meet any requirement of this section is a treatment technique violation.

(1) DISINFECTION REQUIREMENTS FOR PUBLIC WATER SYSTEMS USING GROUNDWATER UNDER THE DIRECT INFLUENCE OF SURFACE WATER THAT DO NOT PROVIDE FILTRATION.

(a) The disinfection treatment shall be sufficient to ensure at least 99.9% (3 log) inactivation of Giardia lamblia cysts and 99.99% (4 log) inactivation of viruses, every day the system serves water to the public. Each day a system serves water to the public, the water supplier shall calculate the CT value from the system's treatment parameters using the procedure specified in s. NR 810.38(1) (d), and determine whether this value is sufficient to achieve the specified inactivation rates for Giardia lamblia cysts and viruses. Water suppliers for systems using a disinfectant other than chlorine shall demonstrate to the department through on-site challenge studies or other information that the system is achieving required minimum inactivation rates.

(b) The disinfection system shall have either redundant components, including an auxiliary power supply with automatic start-up and alarm to ensure that disinfectant application is maintained continuously while water is being delivered to the distribution system, or automatic shut-off of water delivery to the distribution system whenever there is less than 0.2 mg/l of residual disinfectant concentration in the water. If the department determines that automatic shut-off of delivery of water to the distribution system would cause an unreasonable risk to health or property, the disinfection system shall have redundant components.

(c) The residual disinfectant concentration in the water entering the distribution system, measured as specified in s. NR 809.563(2), Table R, may not be less than 0.2 mg/l for more than 4 hours.

(d)

1. The residual disinfectant concentration in the distribution system, measured as total chlorine, combined chlorine, or chlorine dioxide, as specified in s. NR 809.563(2), Table R, may not be undetectable in more than 5% of the samples each month, for any 2 consecutive months that the system serves water to the public. Water in the distribution system with a heterotrophic bacteria concentration less than or equal to 500/ml, measured as heterotrophic plate count (HPC) as specified in s. NR 809.311(1), Table F, is deemed to have a detectable disinfectant residual for purposes of determining compliance with this requirement. Thus, the value "V" in the following formula cannot exceed 5% in one month for any 2 consecutive months.

V = c + d + e/a + b x 100

where:

a = number of instances where the residual disinfectant con centration is measured.

b = number of instances where the residual disinfectant concentration is not measured but heterotrophic bacteria plate count (HPC) is measured.

c = number of instances where the residual disinfectant concentration is measured but not detected and no HPC is measured.

d = number of instances where no residual disinfectant concentration is detected and where the HPC is [GREATER than] 500/ml.

e = number of instances where the residual disinfectant concentration is not measured and HPC is [GREATER than] 500/ml.

2. If the department determines, based on site specific considerations, that a public water system has no means for having a sample transported and analyzed for HPC by a certified laboratory under the requisite time and temperature conditions required in s. NR 809.311(1), Table F, and that the system is providing adequate disinfection in the distribution system, the requirements of subd. 1. do not apply.

(2) DISINFECTION REQUIREMENTS FOR PUBLIC WATER SYSTEMS WHICH PROVIDE FILTRATION. Each public water system that provides filtration treatment shall provide disinfection treatment as follows:

(a) Disinfection treatment shall be sufficient to ensure that the total treatment processes of that system achieve at least 99.9% (3 log) inactivation or removal of Giardia lamblia cysts and at least 99.99% (4 log) inactivation or removal of viruses, as determined by the department.

(b) The residual disinfectant concentration in the water entering the distribution system, measured as specified in s. NR 809.563(2), Table R, may not be less than 0.2 mg/l for more than 4 hours.

(c)

1. The residual disinfectant concentration in the distribution system, measured as total chlorine, combined chlorine or chlorine dioxide, as specified in s. NR 809.563(2), Table R, may not be undetectable in more than 5% of the samples each month, for any 2 consecutive months that the system serves water to the public. Water in the distribution system with a heterotrophic bacteria concentration less than or equal to 500/ml, measured as heterotrophic plate count (HPC) as specified in s. NR 809.311(1), Table F, is deemed to have a detectable disinfectant residual for purposes of determining compliance with this requirement. Thus, the value "V" in the following formula may not exceed 5% in one month, for any 2 consecutive months.