Current through Register Vol. 48, No. 38, September 20, 2024
a)
General. The requirements of this Subpart Y constitute NPDWRs. The regulations
in this Subpart Y establish monitoring and other requirements for achieving
compliance with MCLs based on LRAAs for TTHM and HAA5, and for achieving
compliance with MRDLs for chlorine and chloramine for certain consecutive
systems.
b) Applicability. A
supplier is subject to these requirements if its system is a CWS or a NTNCWS
that uses a primary or residual disinfectant other than ultraviolet light or
which delivers water that has been treated with a primary or residual
disinfectant other than ultraviolet light.
c) A supplier must comply with the
requirements in this Subpart Y as follows:
1)
The supplier's monitoring frequency is specified in Section
611.971(a)(2).
A) If a supplier is required to conduct
quarterly monitoring, it must begin monitoring in the first full calendar
quarter that includes the applicable compliance date set forth in this
subsection (c).
B) If a supplier is
required to conduct monitoring less frequently than quarterly, it must begin
monitoring in the calendar month recommended in the IDSE report prepared under
Section
611.921 or
Section
611.922
or in the calendar month identified in the Subpart Y monitoring plan developed
under Section
611.972,
but in no instance later than 12 months after the applicable compliance date
set forth in this subsection (c).
2) If a supplier is required to conduct
quarterly monitoring, it must make compliance calculations at the end of the
fourth calendar quarter that follows the compliance date and at the end of each
subsequent quarter (or earlier if the LRAA calculated based on fewer than four
quarters of data would cause the MCL to be exceeded regardless of the
monitoring results of subsequent quarters). If a supplier is required to
conduct monitoring less frequently than quarterly, it must make compliance
calculations beginning with the first compliance sample taken after the
compliance date.
3) The Agency may,
by a SEP, determine that the combined distribution system does not include
certain consecutive systems based on factors such as receipt of water from a
wholesale system only on an emergency basis or receipt of only a small
percentage and small volume of water from a wholesale system. The Agency may
also determine that the combined distribution system does not include certain
wholesale systems based on factors such as delivery of water to a consecutive
system only on an emergency basis or delivery of only a small percentage and
small volume of water to a consecutive system.
BOARD NOTE: Implementation of this Subpart Y occurred in
stages during October 1, 2012 through October 1, 2014, depending on population
served. See
40 CFR 141.620(c)(1) through
(c)(5). The Board removed the now-obsolete
implementation dates.
d) Monitoring and Compliance
1) Suppliers Required to Monitor Quarterly.
To comply with Subpart Y MCLs in Section
611.312(b)(2),
the supplier must calculate LRAAs for TTHM and HAA5 using monitoring results
collected under this Subpart Y, and it must determine that each LRAA does not
exceed the MCL. If the supplier fails to complete four consecutive quarters of
monitoring, it must calculate compliance with the MCL based on the average of
the available data from the most recent four quarters. If the supplier takes
more than one sample per quarter at a monitoring location, it must average all
samples taken in the quarter at that location to determine a quarterly average
to be used in the LRAA calculation.
2) Suppliers Required to Monitor Yearly or
Less Frequently. To determine compliance with Subpart Y MCLs in Section
611.312(b)(2),
the supplier must determine that each sample taken is less than the MCL. If any
sample exceeds the MCL, the supplier must comply with the requirements of
Section
611.975.
If no sample exceeds the MCL, the sample result for each monitoring location is
considered the LRAA for that monitoring location.
e) Violation for Failure to Monitor. A
supplier is in violation of the monitoring requirements for each quarter that a
monitoring result would be used in calculating an LRAA if the supplier fails to
monitor.
BOARD NOTE: Derived from
40 CFR
141.620.
