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e-CFR data is current as of January 14, 2021

Title 40Chapter ISubchapter DPart 141Subpart V → §141.621

Title 40: Protection of Environment
Subpart V—Stage 2 Disinfection Byproducts Requirements

§141.621   Routine monitoring.

(a) Monitoring. (1) If you submitted an IDSE report, you must begin monitoring at the locations and months you have recommended in your IDSE report submitted under §141.605 following the schedule in §141.620(c), unless the State requires other locations or additional locations after its review. If you submitted a 40/30 certification under §141.603 or you qualified for a very small system waiver under §141.604 or you are a nontransient noncommunity water system serving <10,000, you must monitor at the location(s) and dates identified in your monitoring plan in §141.132(f), updated as required by §141.622.

(2) You must monitor at no fewer than the number of locations identified in this paragraph (a)(2).

Source water typePopulation size categoryMonitoring Frequency1Distribution system monitoring location total per monitoring period2
Subpart H:
   <500per year2
   500-3,300per quarter2
   3,301-9,999per quarter2
   10,000-49,999per quarter4
   50,000-249,999per quarter8
   250,000-999,999per quarter12
   1,000,000-4,999,999per quarter16
   ≥5,000,000per quarter20
Ground Water:
   <500per year2
   500-9,999per year2
   10,000-99,999per quarter4
   100,000-499,999per quarter6
   ≥500,000per quarter8

1All systems must monitor during month of highest DBP concentrations.

2Systems on quarterly monitoring must take dual sample sets every 90 days at each monitoring location, except for subpart H systems serving 500-3,300. Ground water systems serving 500-9,999 on annual monitoring must take dual sample sets at each monitoring location. All other systems on annual monitoring and subpart H systems serving 500-3,300 are required to take individual TTHM and HAA5 samples (instead of a dual sample set) at the locations with the highest TTHM and HAA5 concentrations, respectively. For systems serving fewer than 500 people, only one location with a dual sample set per monitoring period is needed if the highest TTHM and HAA5 concentrations occur at the same location and month.

(3) If you are an undisinfected system that begins using a disinfectant other than UV light after the dates in subpart U of this part for complying with the Initial Distribution System Evaluation requirements, you must consult with the State to identify compliance monitoring locations for this subpart. You must then develop a monitoring plan under §141.622 that includes those monitoring locations.

(b) Analytical methods. You must use an approved method listed in §141.131 for TTHM and HAA5 analyses in this subpart. Analyses must be conducted by laboratories that have received certification by EPA or the State as specified in §141.131.

[71 FR 488, Jan. 4, 2006, as amended at 74 FR 30958, June 29, 2009]

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