Current through Register Vol. 48, No. 38, September 20, 2024
a) Sample Siting Plans
1) A supplier must develop a written sample
siting plan that identifies sampling sites and a sample collection schedule
that are representative of water throughout the distribution system. These
plans are subject to Agency review and revision. The supplier must collect
total coliform samples according to the written sample siting plan. Monitoring
required by Sections
611.1054
through
611.1058
may take place at a customer's premises, a dedicated sampling station, or
another designated compliance sampling location. Routine and repeat sample
sites and any sampling points necessary to meet the requirements of Subpart S
must be reflected in the sampling plan.
2) A supplier must collect samples at regular
time intervals throughout the month, except that systems that use only ground
water and serve 4,900 or fewer people may collect all required samples on a
single day if they are taken from different sites.
3) A supplier must take at least the minimum
number of required samples even if the system has had an E. coli MCL violation
or has exceeded the coliform treatment technique triggers in Section
611.1059(a).
4) A supplier may conduct more compliance
monitoring than is required by this Subpart AA to investigate potential
problems in the distribution system and use monitoring as a tool to assist in
uncovering problems. A supplier may take more than the minimum number of
required routine samples and must include the results in calculating whether
the coliform treatment technique trigger in Section
611.1059(a)(1)(A)
and (a)(1)(B) has been exceeded only if the
samples are taken in accordance with the existing sample siting plan and are
representative of water throughout the distribution system.
5) A supplier must identify repeat monitoring
locations in the sample siting plan. Unless the provisions of subsection
(a)(5)(A) or (a)(5)(B) are met, the supplier must collect at least one repeat
sample from the sampling tap where the original total coliform-positive sample
was taken, and at least one repeat sample at a tap within five service
connections upstream and at least one repeat sample at a tap within five
service connections downstream of the original sampling site. If a total
coliform-positive sample is at the end of the distribution system, or one
service connection away from the end of the distribution system, the supplier
must still take all required repeat samples. However, the Agency may grant a
SEP that allows an alternative sampling location in lieu of the requirement to
collect at least one repeat sample upstream or downstream of the original
sampling site. Except as provided for in subsection (a)(5)(B), a supplier
required to conduct triggered source water monitoring under Section
611.802(a)
must take ground water source samples in
addition to repeat samples required under this Subpart AA.
A) A supplier may propose repeat monitoring
locations to the Agency that the supplier believes to be representative of a
pathway for contamination of the distribution system. A supplier may elect to
specify either alternative fixed locations or criteria for selecting repeat
sampling sites on a situational basis in a standard operating procedure (SOP)
in its sample siting plan. The supplier must design its SOP to focus the repeat
samples at locations that best verify and determine the extent of potential
contamination of the distribution system area based on specific situations. The
Agency may, by a SEP, modify the SOP or require alternative monitoring
locations as the Agency determines is necessary.
B) A GWS supplier that serves 1,000 or fewer
people may propose repeat sampling locations to the Agency that differentiate
potential source water and distribution system contamination (e.g., by sampling
at entry points to the distribution system). A GWS supplier that has a single
well and which is required to conduct triggered source water monitoring may, as
allowed by a SEP, take one of its repeat samples at the monitoring location
required for triggered source water monitoring under Section
611.802(a).
The supplier must justify an Agency determination that the sample siting plan
remains representative of water quality in the distribution system. If approved
by a SEP, the supplier may use that sample result to meet the monitoring
requirements in both Section
611.802(a)
and this Section.
i) If a repeat sample taken
at the monitoring location required for triggered source water monitoring is E.
coli-positive, the supplier has violated the E. coli MCL and must also comply
with Section
611.802(a)(3).
If a supplier takes more than one repeat sample at the monitoring location
required for triggered source water monitoring, the supplier may reduce the
number of additional source water samples required under Section
611.802(a)(3)
by the number of repeat samples taken at that location that were not E.
coli-positive.
ii) If a supplier
takes more than one repeat sample at the monitoring location required for
triggered source water monitoring under Section
611.802(a),
and more than one repeat sample is E. coli-positive, the supplier has violated
the E. coli MCL and must also comply with Section
611.803(a)(1).
iii) If all repeat samples taken at the
monitoring location required for triggered source water monitoring are E.
coli-negative and a repeat sample taken at a monitoring location other than the
one required for triggered source water monitoring is E. coli-positive, the
supplier has violated the E. coli MCL, but is not required to comply with
Section
611.802(a)(3).
6) The Agency may, by a SEP,
review, revise, and approve, as appropriate, repeat sampling proposed by a
supplier under subsections (a)(5)(A) and (a)(5)(B). The supplier must justify
an Agency determination that the sample siting plan remains representative of
the water quality in the distribution system. The Agency may determine that
monitoring at the entry point to the distribution system (especially for
undisinfected ground water systems) is effective to differentiate between
potential source water and distribution system problems.
b) Special Purpose Samples. Special purpose
samples, such as those taken to determine whether disinfection practices are
sufficient following pipe placement, replacement, or repair, must not be used
to determine whether the coliform treatment technique trigger has been
exceeded. Repeat samples taken under Section
611.1058
are not considered special purpose samples, and must be used to determine
whether the coliform treatment technique trigger has been exceeded.
c) Invalidation of Total Coliform Samples. A
total coliform-positive sample invalidated under this subsection (c) does not
count toward meeting the minimum monitoring requirements of this Subpart AA.
1) The Agency may, by a SEP, invalidate a
total coliform-positive sample only if the conditions of subsection (c)(1)(A),
(c)(1)(B), or (c)(1)(C) are met.
A) The
laboratory establishes that improper sample analysis caused the total
coliform-positive result.
B) The
Agency, on the basis of the results of repeat samples collected as required
under Section
611.1058(a),
determines that the total coliform-positive sample resulted from a domestic or
other non-distribution system plumbing problem. The Agency cannot invalidate a
sample on the basis of repeat sample results unless all repeat samples
collected at the same tap as the original total coliform-positive sample are
also total coliform-positive, and all repeat samples collected at a location
other than the original tap are total coliform-negative (e.g., a Agency cannot
invalidate a total coliform-positive sample on the basis of repeat samples if
all the repeat samples are total coliform-negative, or if the system has only
one service connection).
C) The
Agency has substantial grounds to believe that a total coliform-positive result
is due to a circumstance or condition that does not reflect water quality in
the distribution system. In this case, the system must still collect all repeat
samples required under Section
611.1058(a),
and use them to determine whether a coliform treatment technique trigger in
Section
611.1059
has been exceeded. To invalidate a total coliform-positive sample under this
subsection (c)(1), the decision and supporting rationale must be documented in
writing and approved and signed by the Agency, as a SEP. The Agency must make
this document available to USEPA and the public. The written documentation must
state the specific cause of the total coliform-positive sample, and what action
the supplier has taken, or will take, to correct this problem. The Agency may
not invalidate a total coliform-positive sample solely on the grounds that all
repeat samples are total coliform-negative.
2) A laboratory must invalidate a total
coliform sample (unless total coliforms are detected) if the sample produces a
turbid culture in the absence of gas production using an analytical method
where gas formation is examined (e.g., the multiple-tube fermentation
technique), produces a turbid culture in the absence of an acid reaction in the
presence-absence (P-A) coliform test, or exhibits confluent growth or produces
colonies too numerous to count with an analytical method using a membrane
filter (e.g., membrane filter technique). If a laboratory invalidates a sample
because of such interference, the supplier must collect another sample from the
same location as the original sample within 24 hours after being notified of
the interference problem, and have it analyzed for the presence of total
coliforms. The supplier must continue to re-sample within 24 hours and have the
samples analyzed until it obtains a valid result. The Agency may, by a SEP,
waive the 24-hour time limit on a case-by-case basis. Alternatively, the Agency
or any interested person may file a petition for rulemaking, under Sections 27
and 28 of the Act, to establish criteria for waiving the 24-hour sampling time
limit to use in lieu of case-by-case extensions.
BOARD NOTE: Derived from
40 CFR
141.853.