entire community against the risks to the occupants of the houses being mitigated. The benefits of the risk-reduction program will go only to the people in the homes that are mitigated rather than to all those who use the water supply and are exposed to radon in the drinking water, so there are questions of fairness that will need to be addressed by the state that establishes the multimedia mitigation program and the utility that implements it. It can be shown statistically that there would be a net public-health benefit to the community if the highest-concentration homes, particularly in the medium-and high-potential areas of the country were mitigated. However, it might be difficult to convince residents whose homes are not treated that the net health benefits to the community, the net economic benefits to the utility, and the benefits to the water-users justify their small increased risk associated with the radon in the water.
Another problem is related to the accounting of the health-risk reduction and the potential natural variability of the indoor concentration of radon. Few homes have been continuously monitored over long periods, but where they have been (Steck 1992), a substantial variability can be observed even in the absence of any changes in construction or in the normal mode of living in the homes. That variability means that there could be increases or decreases in the health-risk reduction obtained by the mitigation of any specific dwelling. It is difficult to assess how much such variability would affect the total aggregate indoor-radon reduction obtained by the mitigation of a number of dwellings. Thus, the committee recommends that a margin of safety be designed into any multimedia mitigation plan. The committee suggests that there be a 10–20% excess in the cumulative amount of indoor radon mitigation performed to ensure that there will always be an equivalent or higher health-risk reduction.
The committee has presented a scenario in which the risks in one community have been traded for the risks in another with a resulting identical or improved public-health effect and a commensurate economic benefit to both communities. Thus, from the viewpoint of public health, it would be reasonable to take the cost-effective solution. However, residents in the community whose water is going untreated, in exchange for reduced risks to those living in what were high-airborne-concentration homes in the other community, are not likely to be in favor of such a solution even if it does result in a smaller increase in their water costs than would occur if their water were treated. 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. Because of the sensitivity of the equity issue, the assistance of risk communication experts will be needed in both the planning and implementation stages of public education programs.