Wisconsin Administrative Code › Department of Natural Resources › NR 800 - Environmental Protection - Water Supply › Chapter NR 810 - Requirements for the operation and maintenance of public water systems › Subchapter II - Surface Water Treatment and Groundwater Under the Direct Influence of Surface Water Treatment Operations › Section NR 810.31 - Disinfection requirements for Giardia lamblia and viruses

Current through June 24, 2024
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.