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NAS Report and EPA's Approach to Setting Limits for Radon in Drinking Water
The National Academy of Science has published a report that will provide
important inputs to EPA's development of a National Primary Drinking Water
Regulation (NPDWR) for radon. The regulation will include a Maximum Contaminant
Level (MCL) for radon in drinking water, as well as an Alternative Maximum
Contaminant Level (AMCL) and multi-media mitigation guidelines. The Safe
Drinking Water Act (SDWA), as amended, calls for the establishment of both
an MCL as well as an AMCL tied to the ambient outdoor radon in air level.
Setting the MCL will ultimately be a "risk management" decision
that considers a variety of information and analyses, including human health
risk, nationwide occurrence of radon in drinking water, performance of treatment
technologies, costs of treatment, and capabilities of analytical methods.
The Agency expects to publish a Health Risk Reduction and Cost Analysis
for various MCL options for public comment in February, 1999. A proposed
regulation will be published for public comment by August 6, 1999 and the
regulation will be promulgated in final form on August 6, 2000.
The SDWA requires the Agency to set a Maximum Contaminant Level Goal
(MCLG) at a level at which no known or anticipated adverse health effects
would occur, with a margin of safety. For known human carcinogens such
as radon, the MCLG is expected to be zero. The SDWA requires that the
MCL be set as close as feasible to the MCLG, using the recommended best
available treatment technology(ies), and taking into account costs to
public water systems of meeting the MCL.
As a first step in developing the MCL, EPA will consider the NAS estimates
of lifetime cancer risk associated with exposure to a unit concentration
(expressed in picoCuries per liter of radon). This information, together
with EPA's estimate of radon occurrence in U.S. public water supplies,
will be used in the development of a national estimate of the risk from
exposure to radon in drinking water. This national population risk estimate
will be a key element in the Agency's cost-benefit analysis of various
MCL options. Under the SDWA, the EPA Administrator must publish a determination
of whether or not the benefits of the MCL justify the costs. In addition,
small public water systems (those serving less than 10,000 people) may
be eligible for variances or exemptions.
The EPA also anticipates setting an AMCL for radon in drinking water.
The primary elements affecting the Agency's development of AMCL options
are NAS' estimates of the national average concentration of radon in outdoor
air and the transfer of radon in drinking water to radon in air. In addition,
multi-media mitigation guidelines, which the Agency must publish to accompany
the AMCL, will be developed in consideration of the Academy's recommendations
concerning the effectiveness of various radon in air risk reduction measures.
In summary, the Academy's recommendations are expected to be valuable
inputs into the process of development of the MCL for radon in drinking
water. In combination with consideration of a variety of other factors,
these recommendations are expected to help shape the proposed radon in
drinking water regulation. The Academy's recommendations with respect
to ambient outdoor radon in air levels and the air-to-water transfer factor
are expected to be formative in the development of the AMCL.
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