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 IV - Inactivation Toolbox Components and CT Tables
Section NR 810.46 - Inactivation toolbox components

Universal Citation: WI Admin Code § NR 810.46

Current through August 26, 2024

(1) CALCULATION OF CT VALUES.

(a) CT is the product of the disinfectant contact time (T, in minutes) and disinfectant concentration (C, in milligrams per liter). Water suppliers for systems with treatment credit for chlorine dioxide or ozone under sub. (2) or (3) shall calculate CT at least once each day, with both C and T measured during peak hourly flow as specified in s. NR 809.563(1), Table R.

(b) Water suppliers for systems with several disinfection segments in sequence may calculate CT for each segment. In this section, "disinfection segment" means a treatment unit process with a measurable disinfectant residual level and a liquid volume. Under this approach, water suppliers for systems shall add the Cryptosporidium CT values in each segment to determine the total CT for the treatment plant.

(2) CT VALUES FOR CHLORINE DIOXIDE AND OZONE.

(a) Public water systems receive the Cryptosporidium treatment credit for chlorine dioxide by meeting the corresponding chlorine dioxide CT values found in s. NR 810.56 fortheapplicablewater temperature, as described in sub. (1).

(b) Systems receive the Cryptosporidium treatment credit for ozone by meeting the corresponding ozone CT values found in s. NR 810.61 fortheapplicablewater temperature.

(3) SITE-SPECIFIC STUDY. The department may approve alternative chlorine dioxide or ozone CT values to those referenced in sub. (2) on a site-specific basis. The department shall base this approval on a site-specific study a water supplier for a system conducts that follows a department-approved protocol.

(4) ULTRAVIOLET LIGHT. Public water systems receive Cryptosporidium, Giardia lamblia, and virus treatment credits for ultraviolet (UV) light reactors by achieving the corresponding UV dose values shown in s. NR 810.62. Water suppliers for the systems shall validate and monitor UV reactors as described in pars. (b) and (c) to demonstrate that they are achieving a particular UV dose value for treatment credit.

(a) UV dose table. The treatment credits listed in the dose table in s. NR 810.62 are for UV light at a wavelength of 254 nm as produced by a low pressure mercury vapor lamp. To receive treatment credit for other lamp types, water suppliers for the systems shall demonstrate an equivalent germicidal dose through reactor validation testing, as described in par. (b). The UV dose values in this table are applicable only to post-filter applications of UV in filtered systems and to unfiltered systems.

(b) Reactor validation testing. Systems shall use UV reactors that have undergone validation testing to determine the operating conditions under which the reactor delivers the UV dose required in par. (a), also known as the validated operating conditions. These operating conditions shall include flow rate, UV intensity as measured by a UV sensor, and UV lamp status.

1. When determining validated operating conditions, water suppliers for the systems shall account for the following factors: UV absorbance of the water; lamp fouling and aging; measurement uncertainty of on-line sensors; UV dose distributions arising from the velocity profiles through the reactor; failure of UV lamps or other critical system components; and inlet and outlet piping or channel configurations of the UV reactor.

2. Validation testing shall include the following: Full scale testing of a reactor that conforms uniformly to the UV reactors used by the system and inactivation of a test microorganism whose dose response characteristics have been quantified with a low pressure mercury vapor lamp.

3. The department may approve an alternative approach to validation testing.

1. Water suppliers for the systems shall monitor their UV reactors to determine if the reactors are operating within validated conditions, as determined under par. (b). This monitoring shall include UV intensity as measured by a UV sensor, flow rate, lamp status, and other parameters the department designates based on UV reactor operation. Water suppliers for the systems shall verify the calibration of UV sensors and shall recalibrate sensors in accordance with a protocol the department approves.

2. To receive treatment credit for UV light, systems shall treat at least 99.9% of the water delivered to the public during each month by UV reactors operating within validated conditions for the required UV dose, as described in pars. (a) and (b). Systems shall demonstrate compliance with this condition by the monitoring required under subd. 1.

Disclaimer: These regulations may not be the most recent version. Wisconsin may have more current or accurate information. We make no warranties or guarantees about the accuracy, completeness, or adequacy of the information contained on this site or the information linked to on the state site. Please check official sources.

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.