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§ 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 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. | |
| ≥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. | |
| ≥500,000 | per quarter | 4 dual sample sets at the locations with the two highest TTHM and two highest HAA5 LRAAs. |