Current through Register Vol. 48, No. 38, September 20, 2024
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).
