---
kind: "section"
citation: "40 C.F.R. § 141.623"
title: "40"
number: "141.623"
heading: "Reduced monitoring."
url: "https://uscodex.org/cfr/40/141.623"
---

# §141.623. Reduced monitoring.

- (a) You may reduce monitoring to the level specified in the table in this [paragraph (a)](#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](/cfr/40/subpartL.md) 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)](/cfr/40/141.132.md?p=b-1-iii) or [§ 141.132(d)](/cfr/40/141.132.md?p=d).
- (b) You may remain on reduced monitoring as long as the TTHM LRAA ≤0.040 mg/L and the HAA5 LRAA ≤0.030 mg/L at each monitoring location (for systems with quarterly reduced monitoring) or each TTHM sample ≤0.060 mg/L and each HAA5 sample ≤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 ≤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)](/cfr/40/141.132.md?p=b-1-iii) or [§ 141.132(d)](/cfr/40/141.132.md?p=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](/cfr/40/141.621.md) or begin increased monitoring if [§ 141.625](/cfr/40/141.625.md) applies.
- (d) The State may return your system to routine monitoring at the State's discretion.

## Notes

### Source

Source: 71 FR 488, Jan. 4, 2006, unless otherwise noted.

### Authority

Authority: 42 U.S.C. 300f, 300g-1, 300g-2, 300g-3, 300g-4, 300g-5, 300g-6, 300j-4, 300j-9, and 300j-11.

### Source

Source: 40 FR 59570, Dec. 24, 1975, unless otherwise noted.