Wisconsin Administrative Code
Department of Natural Resources
NR 800 - Environmental Protection - Water Supply
Chapter NR 809 - Safe Drinking Water
Subchapter III - Maximum Contaminant Levels, Maximum Residual Disinfectant Levels, Monitoring, Analytical Requirements and Control of Disinfection Byproducts, Disinfection Residuals and Stage 1 and Stage 2 DBP
Section NR 809.561 - Maximum residual disinfectant level goals (MRDLGs), and maximum contaminant levels (MCLs) for disinfection byproducts, maximum residual disinfectant levels (MRDLs) and best available treatment

Universal Citation: WI Admin Code § NR 809.561

Current through August 26, 2024

(1) MAXIMUM RESIDUAL DISINFECTANT LEVEL GOALS. MRDLGs for disinfectants are as follows:

Disinfectant residual	MRDLG (mg/L)
Chlorine ........................	4 (as Cl2)
Chloramines .....................	4 (as Cl2)
Chlorine dioxide ..................	0.8 (as ClO2)

(2) MAXIMUM CONTAMINANT LEVELS. The maximum contaminant levels (MCLs) for disinfection byproducts are as follows:

Disinfection byproduct	MCL (mg/L)
Total trihalomethanes (TTHM) .....	0.080
Haloacetic acids (five) (HAA5) .....	0.060
Bromate ................	0.010
Chlorite ................	1.0

(3) MAXIMUM RESIDUAL DISINFECTANT LEVELS.

(a) The maximum residual disinfectant levels (MRDLs) for disinfectants are as follows:

Residual Disinfectants	MRDL (mg/L)
Chlorine ......................	4.0 (as C12)
Chloramines ...................	4.0 (as C12)
Chlorine dioxide ................	0.8 (as ClO2)

(b) To achieve compliance with the maximum residual disinfectant levels identified in this subsection, water suppliers shall control treatment processes by reducing disinfectant demand and by controlling disinfection treatment processes to reduce disinfectant levels.

(c) Free chlorine or total chlorine may be measured for demonstrating compliance with the chlorine MRDL. Combined chlorine or total chlorine may be used for demonstrating compliance with the chloramine MRDL.

(4) BEST AVAILABLE TREATMENT. The department, pursuant to section 1412 of the Safe Drinking Water Act and related regulations applicable to public water systems, identifies the following as the best available treatment technology, treatment techniques or other means available for achieving compliance with the maximum contaminant levels for disinfection byproducts identified in sub. (1):

Disinfectant byproduct	Best available treatment
TTHM and HAA5	Enhanced coagulation or enhanced softening or GAC10, with chlorine as the primary and residual disinfectant. Enhanced coagulation or enhanced softening, plus GAC10; or nanofiltration with a molecular weight cutoff = 1000 Daltons; or GAC20.
TTHM and HAA5 in Consecutive Systems	Systems serving = 10,000: Improved distribution system and storage tank management to reduce residence time, plus the use of chloramines for disinfectant residual maintenance. Systems serving < 10,000: Improved distribution system and storage tank management to reduce residence time.
Bromate	Control of ozone treatment process to reduce production of bromate.
Chlorite	Control of treatment processes to reduce disinfectant demand and control of disinfection treatment processes to reduce disinfectant levels.

(5) ALTERNATIVE TREATMENT. The department may approve the use of alternative treatment not listed in sub. (4), if a water supplier demonstrates to the department, using pilot studies or other means, that the alternative treatment is sufficient to achieve compliance with the MCLs in sub. (2).

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