§ 141.623. Reduced monitoring.

Code of Federal Regulations

Title 40. Protection of Environment

Chapter I. ENVIRONMENTAL PROTECTION AGENCY

Subchapter D. WATER PROGRAMS

Part 141. NATIONAL PRIMARY DRINKING WATER REGULATIONS

Subpart V. STAGE 2 DISINFECTION BYPRODUCTS REQUIREMENTS

Current through July 3, 2019

§ 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 frequency 1 Distribution system monitoring location per monitoring period
Subpart H:         
   <500    monitoring may not be reduced.
   500-3,300 per year 1 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.
   3,301-9,999 per year 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.
   10,000-49,999 per quarter 2 dual sample sets at the locations with the highest TTHM and highest HAA5 LRAAs.
   50,000-249,999 per quarter 4 dual sample sets-at the locations with the two highest TTHM and two highest HAA5 LRAAs.
   250,000-999,999 per quarter 6 dual sample sets-at the locations with the three highest TTHM and three highest HAA5 LRAAs.
   1,000,000-4,999,999 per quarter 8 dual sample sets-at the locations with the four highest TTHM and four highest HAA5 LRAAs.
   [GREATER THAN EQUAL TO] 5,000,000 per quarter 10 dual sample sets-at the locations with the five highest TTHM and five highest HAA5 LRAAs.
Ground Water:         
   <500 every third year 1 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.
   500-9,999 per year 1 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.
   10,000-99,999 per year 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.
   100,000-499,999 per quarter 2 dual sample sets; at the locations with the highest TTHM and highest HAA5 LRAAs.
   [GREATER THAN EQUAL TO] 500,000 per quarter 4 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, >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.

Cite as 40 C.F.R. § 141.623