§ 141.132 Monitoring requirements.
(a) General requirements. (1) Systems must take all samples during normal operating conditions.
(2) Systems may consider multiple wells drawing water from a single aquifer as one treatment plant for determining the minimum number of TTHM and HAA5 samples required, with State approval in accordance with criteria developed under § 142.16(h)(5) of this chapter.
(3) Failure to monitor in accordance with the monitoring plan required under paragraph (f) of this section is a monitoring violation.
(4) Failure to monitor will be treated as a violation for the entire period covered by the annual average where compliance is based on a running annual average of monthly or quarterly samples or averages and the system's failure to monitor makes it impossible to determine compliance with MCLs or MRDLs.
(5) Systems may use only data collected under the provisions of this subpart to qualify for reduced monitoring.
(b) Monitoring requirements for disinfection byproducts—(1) TTHMs and HAA5—(i) Routine monitoring. Systems must monitor at the frequency indicated in the following table:
Routine Monitoring Frequency for TTHM and HAA5
| Type of system | Minimum monitoring frequency | Sample location in the distribution system |
|---|---|---|
| Subpart H system serving at least 10,000 persons | Four water samples per quarter per treatment plant | At least 25 percent of all samples collected each quarter at locations representing maximum residence time. Remaining samples taken at locations representative of at least average residence time in the distribution system and representing the entire distribution system, taking into account number of persons served, different sources of water, and different treatment methods. 1 |
| Subpart H system serving from 500 to 9,999 persons | One water sample per quarter per treatment plant | Locations representing maximum residence time. 1 |
| Subpart H system serving fewer than 500 persons | One sample per year per treatment plant during month of warmest water temperature. | Locations representing maximum residence time. 1 If the sample (or average of annual samples, if more than one sample is taken) exceeds the MCL, the system must increase monitoring to one sample per treatment plant per quarter, taken at a point reflecting the maximum residence time in the distribution system, until the system meets criteria in paragraph (b)(1)(iv) of this section. |
| System using only ground water not under direct influence of surface water using chemical disinfectant and serving at least 10,000 persons | One water sample per quarter per treatment plant 2 | Locations representing maximum residence time. 1 |
| System using only ground water not under direct influence of surface water using chemical disinfectant and serving fewer than 10,000 persons | One sample per year per treatment plant 2 during month of warmest water temperature. | Locations representing maximum residence time. 1 If the sample (or average of annual samples, if more than one sample is taken) exceeds the MCL, the system must increase monitoring to one sample per treatment plant per quarter, taken at a point reflecting the maximum residence time in the distribution system, until the system meets criteria in paragraph (b)(1)(iv) of this section. |
1 If a system elects to sample more frequently than the minimum required, at least 25 percent of all samples collected each quarter (including those taken in excess of the required frequency) must be taken at locations that represent the maximum residence time of the water in the distribution system. The remaining samples must be taken at locations representative of at least average residence time in the distribution system.
2 Multiple wells drawing water from a single aquifer may be considered one treatment plant for determining the minimum number of samples required, with State approval in accordance with criteria developed under § 142.16(h)(5) of this chapter.