# 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 type | Population size category | Monitoring Frequency | Distribution system monitoring location total per monitoring period |
| --- | --- | --- | --- |
| Subpart H: | | | |
| | <500 | per year | 2 |
| | 500-3,300 | per quarter | 2 |
| | 3,301-9,999 | per quarter | 2 |
| | 10,000-49,999 | per quarter | 4 |
| | 50,000-249,999 | per quarter | 8 |
| | 250,000-999,999 | per quarter | 12 |
| | 1,000,000-4,999,999 | per quarter | 16 |
| | ≥5,000,000 | per quarter | 20 |
| Ground Water: | | | |
| | <500 | per year | 2 |
| | 500-9,999 | per year | 2 |
| | 10,000-99,999 | per quarter | 4 |
| | 100,000-499,999 | per quarter | 6 |
| | ≥500,000 | per quarter | 8 |
| All systems must monitor during month of highest DBP concentrations. | | | |
| Systems 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]