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 809.566 - Compliance requirements for disinfection byproducts and disinfection residuals Stage 1 DBP

Universal Citation: WI Admin Code ยง NR 809.566

Current through August 26, 2024

(1) GENERAL REQUIREMENTS. The general requirements for compliance with this subchapter are as follows:

(a) If compliance is based on a running annual average of monthly or quarterly samples or an annual average and the water supplier for a public water system fails to monitor for TTHM, HAA5 or bromate, this failure to monitor shall be treated as a monitoring violation for the entire period covered by the annual average.

(b) If compliance is based on a running annual average of monthly or quarterly samples or averages and the water supplier's failure to monitor the public water system makes it impossible to determine compliance with MRDLs for chlorine and chloramines, failure to monitor shall be treated as a monitoring violation for the entire period covered by the annual average.

(c) All samples taken and analyzed under the provisions of this subchapter shall be included in determining compliance, even if that number is greater than the minimum required.

(d) If, during the first year of monitoring under s. NR 809.565, any individual quarter's average will cause the running annual average of that public water system to exceed the MCL, the public water system is out of compliance at the end of that quarter.

(2) COMPLIANCE REQUIREMENTS FOR DISINFECTION BYPRODUCTS.

(a) TTHMs and HAA5s. Compliance for TTHMs and HAA5s shall be based one of the following:
1. For public water systems monitored quarterly, compliance with MCLs in s. NR 809.561(3) shall be based on a running annual arithmetic average, computed quarterly, of quarterly arithmetic averages of all samples collected by the water supplier as prescribed by s. NR 809.565(2). If the running annual arithmetic average of quarterly averages covering any consecutive 4-quarter period exceeds the MCL, the public water system is in violation of the MCL and the water supplier shall notify the public pursuant to subch. VII, in addition to reporting to the department pursuant to s. NR 809.567. If the water supplier for a public water system fails to complete 4 consecutive quarters of monitoring, compliance with the MCL for the last 4-quarter compliance period shall be based on an average of the available data.

2. For public water systems monitored less frequently than quarterly, compliance with MCLs in s. NR 809.561(3) shall be based on an average of samples taken that year under the provisions of s. NR 809.565(2). If the average of these samples exceeds the MCL, the water supplier shall increase monitoring to once per quarter per treatment plant and the public water system is not in violation of the MCL until it has completed one year of quarterly monitoring, unless the result of fewer than 4 quarters of monitoring will cause the running annual average to exceed the MCL, in which case the public water system is in violation at the end of that quarter. Water supplier for public water systems required to increase monitoring frequency to quarterly monitoring shall calculate compliance by including the sample which triggered the increased monitoring plus the following 3 quarters of monitoring.

3. If the running annual arithmetic average of quarterly averages covering any consecutive 4-quarter period exceeds the MCL, the public water system is in violation of the MCL and the water supplier shall notify the public pursuant to subch. VII, in addition to reporting to the department pursuant to s. NR 809.567.

(b) Bromate. Compliance for bromate shall be based on a running annual arithmetic average, computed quarterly, of monthly samples or, for months in which the water supplier for the public water system takes more than one sample, the average of all samples taken during the month, collected by the water supplier as prescribed by s. NR 809.565(3) (b). If the average of samples covering any consecutive 4-quarter period exceeds the MCL, the public water system is in violation of the MCL and the water supplier shall notify the public pursuant to subch. VII, in addition to reporting to the department pursuant to s. NR 809.567. If the water supplier for a public water system fails to complete 12 consecutive months of monitoring, compliance with the MCL for the last 4-quarter compliance period shall be based on an average of the available data.

(c)Chlorite. Compliance for chlorite shall be based on an arithmetic average of each 3-sample set taken in the distribution system as prescribed by s. NR 809.565(3) (a) 2. and 3. If the arithmetic average of any 3-sample set exceeds the MCL, the public water system is in violation of the MCL and the water supplier shall notify the public pursuant to subch. VII, in addition to reporting to the department pursuant to s. NR 809.567.

(3) COMPLIANCE REQUIREMENTS FOR DISINFECTANT RESIDUALS.

(a) Chlorine and chloramines.
1. Compliance shall be based on a running annual arithmetic average, computed quarterly, of monthly averages of all samples collected by the water supplier for a public water system under s. NR 809.565(4) (a). If the average of quarterly averages covering any consecutive 4-quarter period exceeds the MRDL, the public water system is in violation of the MRDL and the water supplier shall notify the public pursuant to subch. VII, in addition to reporting to the department pursuant to s. NR 809.567.

2. In cases where chlorine and chloramines are used for residual disinfection during the year, compliance shall be determined by including together all monitoring results of both chlorine and chloramines in calculating compliance. Reports submitted pursuant to s. NR 809.567 shall clearly indicate which residual disinfectant was analyzed for each sample.

(b) Chlorine dioxide. Compliance shall be based on consecutive daily samples collected by the water supplier under s. NR 809.565(4) (b).
1. A public water system has an acute violation of the MRDL for chlorine dioxide when any daily sample taken at the entrance to the distribution system exceeds the MRDL and on the following day one or more of the 3 samples taken in the distribution system exceeds the MRDL. If both exceedances occur, the public water system is in violation of the MRDL and the water supplier shall take immediate corrective action to lower the level of chlorine dioxide below the MRDL and shall notify the public pursuant to the procedures for acute health risks in s. NR 809.951. Failure to take samples in the distribution system the day following an exceedance of the chlorine dioxide MRDL at the entrance to the distribution system shall also be considered an MRDL violation and the water supplier shall notify the public of the violation in accordance with the provisions for acute violations under s. NR 809.951.

2. A public water system has a nonacute violation for chlorine dioxide when any 2 consecutive daily samples taken at the entrance to the distribution system exceed the MRDL and all distribution system samples taken are below the MRDL. A water supplier for a public water system with a nonacute violation shall take corrective action to lower the level of chlorine dioxide below the MRDL at the point of sampling and shall notify the public pursuant to the procedures for nonacute health risks in subch. VII. Failure to monitor at the entrance to the distribution system the day following an exceedance of the chlorine dioxide MRDL at the entrance to the distribution system is also an MRDL violation and the water supplier shall notify the public of the violation in accordance with the provisions for nonacute violations under subch. VII.

(4) COMPLIANCE REQUIREMENTS FOR DISINFECTION BYPRODUCT PRECURSORS (DBPP). Compliance with disinfection byproduct precursors shall be determined as specified in s. NR 809.569(1). Water suppliers for public water systems may begin monitoring to determine whether Step 1 TOC removals can be met 12 months prior to the compliance date for the public water system. This monitoring is not required and failure to monitor during this period is not a violation. However, any water supplier that does not monitor during this period, and then determines in the first 12 months after the compliance date that it is not able to meet the Step 1 requirements in s. NR 809.569(1) (b) and therefore applies for alternate minimum TOC removal (Step 2) requirements, is not eligible for retroactive approval of alternate minimum TOC removal (Step 2) requirements as allowed pursuant to s. NR 809.569(1) (c) and is in violation. Water supplier may apply for alternate minimum TOC removal (Step 2) requirements any time after the compliance date. For public water systems required to meet Step 1 TOC removals, if the value calculated under s. NR 809.569(3) (a) or (b) is less than 1.00, the public water system is in violation of the treatment technique requirements and the water supplier shall notify the public pursuant to subch. VII in addition to reporting to the department pursuant to s. NR 809.567.

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