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 809.63 - Requirements for reduced and increased monitoring for Stage 2 DBP

Universal Citation: WI Admin Code ยง NR 809.63

Current through August 26, 2024

(1) REDUCED MONITORING. The department may reduce the monitoring frequency when the LRAA is less than or equal to 0.040 mg/L for TTHM and less than or equal to 0.030 mg/L for HAA5 at all compliance monitoring locations. Systems may only use data collected in compliance with s. NR 809.565 and under this section to qualify for reduced monitoring. In addition, the source water annual average TOC level, before any treatment, must be d4.0 mg/L at each treatment plant treating surface water or GWUDI, based on monitoring conducted under s. NR 809.565(2) (c) 2m. The reduced sampling frequency and number of sample sites are given in Table Z:

Table Z

Reduced Stage 2 Monitoring Frequency and Number of Sites

Source Water Type

Population Size Category

Monitoring Frequency

Distribution System Monitoring Location Total per Monitoring Period

Surface Water or GWUDI

less than 500

Annual

Monitoring may not be reduced.

500 to 3,300

Annual

1 TTHM and 1 HAA5 at the respective locations and quarters with the highest individual DBP; 1 dual sample set per year if the highest TTHM and HAA5 measurements occurred at the same location and quarter.

3,301 to 9,999

Annual

2 dual sample sets: one at the location and during the quarter with the highest TTHM single measurement, one at the location and during the quarter with the highest HAA5 single measurement.

10,000 to 49,999

quarterly

2 dual sample sets at the locations with the highest TTHM and highest HAA5 LRAAs

50,000 to 249,999

quarterly

4 dual sample sets at the locations with the two highest TTHM and two highest HAA5 LRAAs

250,000 to 999,999

quarterly

6 dual sample sets at the locations with the three highest TTHM and three highest HAA5 LRAAs

1,000,000 to 4,999,999

quarterly

8 dual sample sets at the locations with the four highest TTHM and four highest HAA5 LRAAs

5,000,000 or more

quarterly

10 dual sample sets at the locations with the five highest TTHM and five highest HAA5 LRAAs

Groundwater

less than 500

every third year (triennial)

1 TTHM and 1 HAA5 at the respective locations and quarters with the highest individual DBP; 1 dual sample set per year if the highest TTHM and HAA5 measurements occurred at the same location and quarter.

500 to 9,999

Annual

1 TTHM and 1 HAA5 at the respective locations and quarters with the highest individual DBP; 1 dual sample set per year if the highest TTHM and HAA5 measurements occurred at the same location and quarter.

10,000 to 99,999

Annual

2 dual sample sets: one at the location and during the quarter with the highest TTHM single measurement, one at the location and during the quarter with the highest HAA5 single measurement

100,000 to 499,999

quarterly

2 dual sample sets at the locations with the highest TTHM and highest HAA5 LRAAs

500,000 or more

quarterly

4 dual sample sets at the locations with the two highest TTHM and two highest HAA5 LRAAs
(a) Water suppliers for public water systems on quarterly monitoring shall take dual sample sets every 90 days.

(b) Public water systems on annual monitoring and surface water or GWUDI systems serving 500 to 3,300 people may use a single site if the highest TTHM and HAA5 concentrations occur at the same time and place. Any such public water system may be required to take individual TTHM and HAA5 samples, instead of a dual sample set, at sites identified as the highest TTHM and HAA5 sites, respectively. If separate sites for individual TTHM and HAA5 samples are used, then the TTHM sample shall be collected during the quarter with highest historical TTHM levels and the HAA5 sample shall be collected during the quarter with the highest historical HAA5 level.

(c) Only data collected under the provisions of s. NR 809.565 and under this section may be used to qualify for reduced monitoring.

(d) To remain on reduced monitoring, a public water system shall meet the following conditions:
1. Public water systems on a quarterly reduced monitoring schedule may remain on that reduced schedule as long as the TTHM LRAA <= 0.040 mg/L and the HAA5 LRAA <= 0.030 mg/L at each monitoring location.

2. Public water systems on an annual or less frequent reduced monitoring schedule may remain on that reduced schedule as long as each TTHM sample <= 0.060 mg/L and each HAA5 sample <= 0.045 mg/L.

3. In addition to subds. 1. and 2., for a surface water or GWUDI system, the source water annual average TOC level, before any treatment, shall be <= 4.0 mg/L, based on monitoring conducted under s. NR 809.565(2) (c) 2m.

(e) If the LRAA based on quarterly monitoring at any monitoring location exceeds either 0.040 mg/L for TTHM or 0.030 mg/L for HAA5 or if the annual (or less frequent) sample at any location exceeds either 0.060 mg/L for TTHM or 0.045 mg/L for HAA5, or if the source water annual average TOC level, before any treatment, is >4.0 mg/L at any treatment plant treating surface water or groundwater under the direct influence of surface water, the water supplier shall resume routine monitoring under s. NR 809.61 or begin increased monitoring under sub. (2).

(f) The department may return a public water system to routine monitoring, at any time, at the department's discretion.

(2) CONDITIONS REQUIRING INCREASED MONITORING.

(a) A public water system that is required to monitor at a particular location annually or less frequently than annually under s. NR 809.62 or 809.63(1), shall increase monitoring to dual sample sets once per quarter at all locations if a TTHM sample is >0.080 mg/L or a HAA5 sample is >0.060 mg/L at any location.

(am) Water suppliers shall conduct increased monitoring under this paragraph at the monitoring locations in the monitoring plan developed under s. NR 809.62 beginning on the date identified in s. NR 809.60(3) for compliance with this subchapter. The public water system shall remain on increased monitoring until it qualifies to return to routine monitoring under s. NR 809.61.

(b) Samples shall be taken every 90 days plus or minus 5 days beginning from the date of collection of the original sample that exceeded the MCL for either TTHM or HAA5.

(3) MCL VIOLATION DETERMINATION. A public water system is in violation of the MCL when the LRAA for TTHM or HAA5 exceeds the MCLs in s. NR 809.561(3), calculated based on four consecutive quarters of monitoring or the LRAA calculated based on fewer than four quarters of data if the MCL would be exceeded regardless of the monitoring results of subsequent quarters.

(4) RETURN TO ROUTINE MONITORING. The department may return a public water system to routine monitoring once the water supplier has completed increased monitoring for at least four consecutive quarters and the LRAA for every monitoring location is <= 0.060 mg/L for TTHM and <= 0.045 mg/L for HAA5.

(5) VIOLATION OF MONITORING REQUIREMENTS. A public water system is in violation of the monitoring requirements if the water supplier fails to monitor during a quarter and for each subsequent quarter that the monitoring result would have been used in calculating a LRAA.

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