Reduced Monitoring

Section 611.973  Reduced Monitoring a)         A supplier may reduce monitoring to the level specified in the applicable of subsections (a)(1) through (a)(13), subject to the limitation of subsection (a)(14), any time the LRAA is 0.040 mg/ℓ or less for TTHM and 0.030 mg/ℓ or less for HAA5 at all monitoring locations.  The supplier may only use data collected under the provisions of this Subpart Y or pursuant to Subpart I to qualify for reduced monitoring.  In addition, the source water annual average TOC level, before any treatment, must be 4.0 mg/ℓ or less at each treatment plant treating surface water or groundwater under the direct influence of surface water, based on monitoring conducted under either Section 611.382(b)(1)(C) or Section 611.382(d). 1)         A Subpart B system supplier that serves fewer than 500 persons may not qualify for reduced monitoring. 2)         A Subpart B system supplier that serves 500 to 3,300 persons qualifies for reduced monitoring to a minimum of one TTHM sample collected annually from the location and during the quarter with the highest single TTHM measurement and one HAA5 sample collected annually from the location and during the quarter with the highest single HAA5 measurement, with the two samples collected as one dual sample set if the highest TTHM and HAA5 measurements occurred at the same location and during the same quarter. 3)         A Subpart B system supplier that serves 3,301 to 9,999 persons  qualifies for reduced monitoring to a minimum of one dual sample set collected annually for TTHM from the location and during the quarter with the highest single TTHM measurement and one dual sample set collected annually for HAA5 from the location and during the quarter with the highest single HAA5 measurement. 4)         A Subpart B system supplier that serves 10,000 to 49,999 persons qualifies for reduced monitoring to a minimum of two dual sample sets collected quarterly from the locations with the highest TTHM and HAA5 LRAAs. 5)         A Subpart B system supplier that serves 50,000 to 249,999 persons qualifies for reduced monitoring to a minimum of four dual sample sets collected quarterly from the locations with the two highest TTHM and two HAA5 LRAAs. 6)         A Subpart B system supplier that serves 250,000 to 999,999 persons qualifies for reduced monitoring to a minimum of six dual sample sets collected quarterly from the locations with the three highest TTHM and three HAA5 LRAAs. 7)         A Subpart B system supplier that serves 1,000,000 to 4,999,999 persons qualifies for reduced monitoring to a minimum of eight dual sample sets collected quarterly from the locations with the four highest TTHM and four HAA5 LRAAs. 8)         A Subpart B system supplier that serves more than 5,000,000 persons qualifies for reduced monitoring to a minimum of 10 dual sample sets collected quarterly from the locations with the five highest TTHM and five HAA5 LRAAs. 9)         A groundwater system supplier that serves fewer than 500 persons qualifies for reduced monitoring to a minimum of one TTHM sample collected triennially from the location and during the quarter with the highest single TTHM measurement and one HAA5 sample collected annually from the location and during the quarter with the highest single HAA5 measurement, with the two samples collected as one dual sample set if the highest TTHM and HAA5 measurements occurred at the same location and during the same quarter. 10)         A groundwater system supplier that serves 500 to 9,999 persons qualifies for reduced monitoring to a minimum of one TTHM sample collected annually from the location and during the quarter with the highest single TTHM measurement and one HAA5 sample collected annually from the location and during the quarter with the highest single HAA5 measurement, with the two samples collected as one dual sample set if the highest TTHM and HAA5 measurements occurred at the same location and during the same quarter. 11)         A groundwater system supplier that serves 10,000 to 99,999 persons qualifies for reduced monitoring to a minimum of one TTHM dual sample set collected annually from the location and during the quarter with the highest single TTHM measurement and one HAA5 dual sample set collected annually from the location and during the quarter with the highest single HAA5 measurement. 12)         A groundwater system supplier that serves 100,000 to 499,999 persons qualifies for reduced monitoring to a minimum of two dual sample sets collected quarterly from the locations with the highest TTHM and highest HAA5 LRAAs. 13)         A groundwater system supplier that serves more than 500,000 persons qualifies for reduced monitoring to a minimum of four dual sample sets collected quarterly from the two locations with the highest TTHM and two highest HAA5 LRAAs. 14)         A supplier on quarterly monitoring must take dual sample sets every 90 days. b)         The supplier may remain on reduced monitoring as long as the TTHM LRAA does not exceed 0.040 mg/ℓ and the HAA5 LRAA does not exceed 0.030 mg/ℓ at each monitoring location (for a supplier with quarterly reduced monitoring) or each TTHM sample does not exceed 0.060 mg/ℓ and each HAA5 sample does not exceed 0.045 mg/ℓ (for a supplier with annual or less frequent monitoring).  In addition, the source water annual average TOC level, before any treatment, must not exceed 4.0 mg/ℓ at each treatment plant treating surface water or groundwater under the direct influence of surface water, based on monitoring conducted under either Section 611.382(b)(1)(C) or (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, 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, exceeds 4.0 mg/ℓ at any treatment plant treating surface water or groundwater under the direct influence of surface water, the supplier must resume routine monitoring under Section 611.971 or begin increased monitoring if Section 611.975 applies. d)         The Agency may return a supplier to routine monitoring by a SEP. BOARD NOTE:  Derived from 40 CFR 141.623 (2016).