Risk Assessment of Radon in Drinking Water (1999) / Chapter Skim
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9 Multimedia Approach to Risk Reduction
9 Multimedia Approach to Risk Reduction
Pages 180-197
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From page 180... ...
is required to publish guidelines, including criteria, for establishing multimedia approaches to mitigate radon levels in indoor air that will result in an equivalent or greater reduction in the health risk posed by radon in the area served by a public water supply that contains radon in concentrations greater than the MCL but less than or equal to the AMCL. The objective of this chapter is to describe the considerations involved in performing a quantitative evaluation of the health-risk reductions that would be achieved by reducing the concentration of radon in the water relative to those achieved through such multimedia activities as mitigating homes to reduce their average indoor radon concentrations.
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From page 181... ...
It does not, however, imply that in any given dwelling, the contribution to the airborne radon concentration from water at the AMCL will equal Ma,,~,bien~. The available data regarding ambient-air concentrations and transfer factors are limited but adequate for estimation of MTF and Ma,,~,bien~, and the committee determined that the best estimate of the AMCL that can be derived from the available data is the ratio of the estimated arithmetic means: AMCLeSt= M~]
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From page 182... ...
The committee makes no recommendation or endorsement of a specific value and is using this assumption only in order to provide a framework for the following discussion of potential risk-reduction scenarios for implementing a multimedia mitigation program. EQUIVALENT RISK-REDUCTION SCENARIOS To estimate the health-risk reductions that are obtained by treating water to remove radon or mitigating homes to reduce indoor 222Rn, it is necessary to consider all the associated risks.
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From page 183... ...
In general these factors would not produce sufficient cost differences between meeting the AMCL and meeting the MCL to constitute an incentive to consider a multimedia mitigation program. Thus, the only cases where it is of practical interest to consider implementation of a multimedia program is for water systems in which the radon concentration in the water is between the MCL and the AMCL.
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From page 184... ...
for the acquisition of an appropriate water-treatment system is $275,000 plus annual O&M costs of $23,000, so multimedia mitigation might be considered as a cost-effective alternative. Scenarios 2-4: Effects of Distribution of Radon in Indoor Air On the basis of previously described scenario, an important consideration in deciding on the feasibility of the multimedia approach relative to the watertreatment approaches is whether a subpopulation of dwellings can be identified that would provide the needed equivalent health-risk reduction when their airborne radon concentrations were reduced sufficiently.
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From page 185... ...
which provided a statistically valid survey of the distribution of indoor radon concentrations in homes. Each home in the survey was classified by the EPA radon potential region associated with its location.
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From page 186... ...
Thus, the mitigation of a fraction of the homes that exceed the current EPA guidance level would actually produce a larger health risk reduction than mitigation of the water would provide even if the radon concentration in the water supply approached the AMCL. The ability to obtain the required health-risk reduction by mitigating fewer homes might make the multimedia approach more financially attractive.
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From page 187... ...
If in the future, the extent of radon reduction in new radon-resistant homes could be reliably estimated, then the following framework could be used to incorporate it into a multimedia mitigation program. Radon-resistant construction will reduce the indoor radon concentration to a fixed fraction of the value it would have been if conventional construction practices had been used.
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From page 188... ...
Suppose that one community has water with a radon concentration between the MCL and the AMCL and another community has low radon concentrations in its water but high radon concentrations in its indoor air. Could the water utility mitigate the air concentrations in dwellings in the low-waterradon community to produce the equivalent health-risk reduction that would have been obtained by lowering the water concentration of 222Rn in the other community?
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From page 189... ...
A policy decision would be needed as to whether such dwellings could be included in a multimedia mitigation program and would raise an important equity question, in that water ratepayers would be charged for the mitigation of homes that are not being served by their utility and whose occupants are not contributing to the payment of the costs of the radonabatement program. Scenario 7: Use of Outreach, Education, and Incentives Another possible approach to reducing the indoor air concentrations of radon is to enlist homeowners in the identification and mitigation of homes with high radon concentrations.
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From page 190... ...
The CRCPD surveys indicated that states with radon testing as part of their real-estate transactions requirements also had high-awareness. Furthermore, the surveys indicated that home mitigation was lower for homes with indoor air concentrations less than the EPA-recommended action level of 150 Bq m-3.
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From page 191... ...
Several studies have described the problems of communicating risk to the general public; a broad review of radon-related risk communication was done by the EPA's Science Advisory Board (1995~. A telephone survey was used to assess information about homeowners with indoor air concentrations greater than 740 Bq m-3 (Field and others 1993~.
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From page 192... ...
Indoor radon concentrations have been measured in about 350,000 dwellings with the cost of the measurement usually paid by the homeowner. About 45,000 homes with radon concentrations above 400 Bq m-3 have been found.
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From page 193... ...
The programs described above indicate that public apathy about the potential risks of exposure to radon has generally remained despite numerous and sometimes costly public education efforts. On the basis of these reported results, the committee concludes that an education and outreach program would be insufficient to provide a scientifically sound basis for claiming equivalent health-risk reductions and that an active program of mitigation of homes would be needed to demonstrate health-risk reduction.
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From page 194... ...
Thus, non-economic considerations such as equity, fraction of homes mitigated, and other related matters are expected to play a large role in the evaluation of multimedia mitigation programs and might ultimately constitute the deciding factor in whether such a program is undertaken. In any planning process, a carefully designed program of public education will be essential to provide a perspective on the tradeoffs in the risks being proposed and the health and economic costs and benefits that will be produced by the various alternatives.
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From page 195... ...
. If a multimedia approach to the radon problem involves mitigation of air in specifically targeted homes, water utilities will have to oversee the installation, operation, and maintenance of mitigation systems in individual homes.
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From page 196... ...
It is likely that many very small water utilities whose water contained radon concentrations exceeding the MCL but not the AMCL could not muster the resources or mount the effort required to propose such a program formally. EPA, state agencies, and perhaps the water associations should develop mechanisms to assist small public water supplies in decision-making regarding multimedia mitigation programs.
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From page 197... ...
EPA and the state agencies responsible for water quality will continue to be faced with the problem that the health risks arising from the presence of radon in drinking water are essentially associated with the water's contribution to the indoor air concentration. With an average transfer coefficient of 10=, the increment of indoor radon that emanates from water will generally be smaller than the average concentration of radon already present in the dwellings from other sources.
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