Current through Register Vol. 48, No. 38, September 20, 2024
Monitoring for Gross Alpha Particle Activity, Radium-226,
Radium-228, and Uranium
a) A CWS
supplier must monitor to determine whether it complies with Section
611.330(b),
(c), and (e). For monitoring gross alpha
particle activity, radium-226, radium-228, uranium, and beta particle and
photon radioactivity in drinking water, "detection limit" is defined as in
Section 611.720(c).
1) Applicability and Sampling Location for an
Existing CWS Supplier. An existing CWS supplier using groundwater, surface
water, or both groundwater and surface water must sample at every entry point
to the distribution system representing all sources the supplier uses (a
sampling point) under normal operating conditions. The supplier must take each
sample at the same sampling point, unless conditions make another sampling
point more representative of each source or the Agency designates a
distribution system location under subsection (b)(2)(C).
2) Applicability and Sampling Location for a
New CWS Supplier. A new CWS supplier or a CWS supplier using a new source of
water must begin initial monitoring for the new source within the first quarter
after beginning to use the source. A CWS supplier must conduct more frequent
monitoring as directed by the Agency in a SEP due to possible contamination or
changes in the distribution system or treatment processes that may increase the
concentration of radioactivity in the supplier's finished water.
b) Initial Monitoring. The Agency
may issue a SEP directing a CWS supplier to monitor for gross alpha particle
activity, radium-226, radium-228, and uranium for four consecutive quarters at
all sampling points. The Agency may revise the SEP waiving the final two
quarters of initial monitoring for a sampling point if the results of the
samples from the previous two quarters are below the detection limit. For gross
alpha particle activity, uranium, radium-226, and radium-228 monitoring, the
Agency may issue a SEP waiving the final two quarters of initial monitoring for
a sampling point if the results of the samples from the previous two quarters
are below the detection limit. If the average of the initial monitoring results
for a sampling point is above the MCL, the supplier must collect and analyze
quarterly samples at that sampling point until its results from four
consecutive quarters are at or below the MCL, unless the Agency issues a SEP
requiring another schedule as part of a formal compliance agreement.
c) Reduced Monitoring. The Agency may allow a
CWS supplier to reduce the future frequency of monitoring from once every three
years to once every six or nine years at each sampling point, based on certain
criteria:
1) If the average of the initial
monitoring results for each contaminant (i.e., gross alpha particle activity,
uranium, radium-226, or radium-228) is below the detection limit Section
611.720(c)(1)
specifies, the supplier must collect and analyze for that contaminant using at
least one sample at that sampling point every nine years.
2) For gross alpha particle activity and
uranium, if the average of the initial monitoring results for each contaminant
is at or above the detection limit but at or below one-half the MCL, the
supplier must collect and analyze for that contaminant using at least one
sample at that sampling point every six years. For combined radium-226 and
radium-228, the supplier must combine the analytical results. If the average of
the combined initial monitoring results for radium-226 and radium-228 is at or
above the detection limit but at or below one-half the MCL, the supplier must
collect and analyze for that contaminant using at least one sample at that
sampling point every six years.
3)
For gross alpha particle activity and uranium, if the average of the initial
monitoring results for each contaminant is above one-half the MCL but at or
below the MCL, the supplier must collect and analyze at least one sample at
that sampling point every three years. For combined radium-226 and radium-228,
the supplier must combine the analytical results. If the average of the
combined initial monitoring results for radium-226 and radium-228 is above
one-half the MCL but at or below the MCL, the supplier must collect and analyze
at least one sample at that sampling point every three years.
4) A supplier must use the samples it
collected during the reduced monitoring period to determine the monitoring
frequency for subsequent monitoring periods (e.g., if a supplier's sampling
point is on a nine year monitoring period, and the sample result is above
one-half the MCL, then the next monitoring period for that sampling point is
three years).
5) If a supplier has
a monitoring result exceeding the MCL while on reduced monitoring, the supplier
must collect and analyze quarterly samples at that sampling point until the
supplier has results from four consecutive quarters below the MCL, unless the
supplier enters into another schedule as part of a formal compliance agreement
with the Agency.
d)
Compositing. To fulfill quarterly monitoring requirements for gross alpha
particle activity, radium-226, radium-228, or uranium, a supplier may composite
up to four consecutive quarterly samples from a single entry point if analysis
is done within a year after collecting the first sample. The supplier must
treat analytical results from the composited sample as the average analytical
result to determine whether the supplier complies with the MCLs and the future
monitoring frequency. If the analytical result from the composited sample is
greater than one-half the MCL, the Agency may issue a SEP directing the
supplier to take additional quarterly samples before allowing the supplier to
sample under a reduced monitoring schedule.
e) A supplier may substitute a gross alpha
particle activity measurement for the required radium-226 measurement, provided
the measured gross alpha particle activity does not exceed 5 pCi/L. A supplier
may substitute a gross alpha particle activity measurement for the required
uranium measurement, provided the measured gross alpha particle activity does
not exceed 15 pCi/L.
1) The gross alpha
measurement must have a confidence interval of 95% (1.65 [SIGMA],
where [SIGMA] is the standard deviation of the net counting rate of the sample)
for radium-226 and uranium.
2) When
a supplier uses a gross alpha particle activity measurement in lieu of a
radium-226 or uranium measurement, the supplier must use the gross alpha
particle activity analytical result to determine the future monitoring
frequency for radium-226 or uranium.
3) If the laboratory does not detect gross
alpha particle activity, the supplier must use one-half the detection limit to
determine whether it complies and its future monitoring frequency.
BOARD NOTE: This Section derives from
40 CFR
141.26(a).
