Wisconsin Administrative Code
Department of Natural Resources
NR 800 - Environmental Protection - Water Supply
Chapter NR 811 - Requirements For The Operation And Design Of Community Water Systems
Subchapter VII - Treatment
Section NR 811.42 - Treatment of water from surface water sources

Universal Citation: WI Admin Code ยง NR 811.42

Current through August 26, 2024

Treatment of water from surface water sources shall meet the following requirements:

(1) GENERAL REQUIREMENTS. All public water supply systems drawing water from lakes, rivers, streams, or other surface water sources shall, after the water is drawn, treat the water as provided in this chapter. In general and at a minimum, this treatment shall include coagulation, sedimentation, and filtration plus disinfection or membrane filtration plus disinfection. Filtration is required in all cases. Total plant removal and inactivation shall provide a minimum 99.9 percent (3-log) inactivation of Cryptosporidium and Giardia Lamblia plus 99.99 percent (4-log) inactivation of viruses.

(2) TREATMENT REQUIREMENTS. The following treatment requirements shall be met:

(a) Conventional plants consisting of coagulation, sedimentation, and filtration that meet the turbidity requirements in s. NR 810.29(1) are granted the following removal credits: 99.7 percent (2.5-log) Giardia Lamblia, 99.9 percent (3.0-log) Cryptosporidium and 99 percent (2-log) virus. The remaining 68 percent (0.5-log) Giardia Lamblia inactivation and 99 percent (2.0-log) virus inactivation shall be provided by CT disinfection. For conventional plants, a minimum of one-half of the required CT shall be provided after filtration.

(b) Log removal credit for membrane filtration shall be site specific as approved by the department.

(c) Additional treatment may be required by the department as provided in s. NR 810.35.

(d) The department may approve any request for a deviation from required treatment methods based on data which shows that the requirements of this chapter are unnecessary in the specific case.

(3) REDUNDANCY. All critical treatment components shall be provided with redundancy.

(4) CT VALUES. CT values for the inactivation of Giardia Lamblia, Cryptosporidium, and viruses can be found in ss. NR 810.47 to 810.62.

(5) CHLORINE RESIDUAL REQUIREMENTS. The free chlorine concentration in the water entering the distribution system shall be at least 0.2 mg/1 at the entry point to the distribution system and detectable throughout the distribution system or the total combined chlorine concentration shall be at least 1.0 mg/l at the entry point to the distribution system and detectable throughout the distribution system. Continuous chlorine residual monitoring of the water entering the distribution system shall be provided as required in ss. NR 809.74(2) and 810.38(2) (c).

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