Statutes, codes, and regulations
Code of Federal Regulations
Title 40 - PROTECTION OF ENVIRONMENTChapter I - ENVIRONMENTAL PROTECTION AGENCYSubchapter D - WATER PROGRAMSPart 141 - NATIONAL PRIMARY DRINKING WATER REGULATIONS
Subpart V - STAGE 2 DISINFECTION BYPRODUCTS REQUIREMENTS
Section 141.623 - Reduced monitoring

40 C.F.R. § 141.623

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Current through May 31, 2024
Section 141.623 - Reduced monitoring
(a) You may reduce monitoring to the level specified in the table in this paragraph (a) any time the LRAA is [LESS THAN EQUAL TO]0.040 mg/L for TTHM and [LESS THAN EQUAL TO]0.030 mg/L for HAA5 at all monitoring locations. You may only use data collected under the provisions of this subpart or subpart L of this part to qualify for reduced monitoring. In addition, the source water annual average TOC level, before any treatment, must be [LESS THAN EQUAL TO]4.0 mg/L at each treatment plant treating surface water or ground water under the direct influence of surface water, based on monitoring conducted under either § 141.132(b)(1)(iii) or § 141.132(d) .

Source water type Population size category Monitoring
frequency1		 Distribution system monitoring location per monitoring period
Subpart H:
[LESS THAN]500monitoring may not be reduced.
500-3,300per year1 TTHM and 1 HAA5 sample: 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; 1 dual sample set per year if the highest TTHM and HAA5 measurements occurred at the same location and quarter.
3,301-9,999per year2 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.
10,000-49,999per quarter2 dual sample sets at the locations with the highest TTHM and highest HAA5 LRAAs.
50,000-249,999per quarter4 dual sample sets-at the locations with the two highest TTHM and two highest HAA5 LRAAs.
250,000-999,999per quarter6 dual sample sets-at the locations with the three highest TTHM and three highest HAA5 LRAAs.
1,000,000-4,999,999per quarter8 dual sample sets-at the locations with the four highest TTHM and four highest HAA5 LRAAs.
[GREATER THAN EQUAL TO]5,000,000per quarter10 dual sample sets-at the locations with the five highest TTHM and five highest HAA5 LRAAs.
Ground Water:
[LESS THAN]500every third year1 TTHM and 1 HAA5 sample: 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; 1 dual sample set per year if the highest TTHM and HAA5 measurements occurred at the same location and quarter.
500-9,999per year1 TTHM and 1 HAA5 sample: 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; 1 dual sample set per year if the highest TTHM and HAA5 measurements occurred at the same location and quarter.
10,000-99,999per year2 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.
100,000-499,999per quarter2 dual sample sets; at the locations with the highest TTHM and highest HAA5 LRAAs.
[GREATER THAN EQUAL TO]500,000per quarter4 dual sample sets at the locations with the two highest TTHM and two highest HAA5 LRAAs.

1 Systems on quarterly monitoring must take dual sample sets every 90 days.

(b) You may remain on reduced monitoring as long as the TTHM LRAA [LESS THAN EQUAL TO]0.040 mg/L and the HAA5 LRAA [LESS THAN EQUAL TO]0.030 mg/L at each monitoring location (for systems with quarterly reduced monitoring) or each TTHM sample [LESS THAN EQUAL TO]0.060 mg/L and each HAA5 sample [LESS THAN EQUAL TO]0.045 mg/L (for systems with annual or less frequent monitoring). In addition, the source water annual average TOC level, before any treatment, must be [LESS THAN EQUAL TO]4.0 mg/L at each treatment plant treating surface water or ground water under the direct influence of surface water, based on monitoring conducted under either § 141.132(b)(1)(iii) or § 141.132(d) .
(c) 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, [GREATER THAN]4.0 mg/L at any treatment plant treating surface water or ground water under the direct influence of surface water, you must resume routine monitoring under § 141.621 or begin increased monitoring if § 141.625 applies.
(d) The State may return your system to routine monitoring at the State's discretion.

40 C.F.R. §141.623