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e-CFR data is current as of October 22, 2020

Title 40Chapter ISubchapter DPart 141Subpart V → §141.623


Title 40: Protection of Environment
PART 141—NATIONAL PRIMARY DRINKING WATER REGULATIONS
Subpart V—Stage 2 Disinfection Byproducts Requirements


§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 ≤0.040 mg/L for TTHM and ≤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 ≤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 typePopulation size categoryMonitoring
frequency1
Distribution system monitoring location per monitoring period
Subpart H:
   <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.
   ≥5,000,000per quarter10 dual sample sets—at the locations with the five highest TTHM and five highest HAA5 LRAAs.
Ground Water:
   <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.
   ≥500,000per quarter4 dual sample sets at the locations with the two highest TTHM and two highest HAA5 LRAAs.

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

(b) You may remain on reduced monitoring as long as the TTHM LRAA ≤0.040 mg/L and the HAA5 LRAA ≤0.030 mg/L at each monitoring location (for systems with quarterly reduced monitoring) or each TTHM sample ≤0.060 mg/L and each HAA5 sample ≤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 ≤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, >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.

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