tions would provide the 11,300 Bq m-3. For the high-potential region, mitigation of the 23 highest-concentration homes would provide the required health-risk reduction. However, in both cases, to obtain the absolute minimum number of dwellings to be mitigated would require that 100% of the dwellings in the community be monitored to ensure finding the highest concentration homes. It is unlikely that such a high level of participation can be achieved, so alternative strategies would need to be adopted. Because there are more high-concentration dwellings to find, an extensive but not exhaustive survey of the community could identify enough high concentration homes to provide the needed health-risk reduction at a cost that would be less than the cost of implementing and maintaining a water-treatment facility.

One cost-effective approach to solicit participation would be to send a notice to ratepayers with their water bills asking whether they know what their indoor radon concentration is, and that if it is above 150 Bq m-3 in the home, they might be eligible for mitigation at no cost. The solicitation could also indicate that if the owner were interested in participating, a free test kit would be provided. It is essential that long-term monitoring of radon concentrations be performed in order to provide a reliable estimate of the risk reduction potential. This approach might provide a utility with an initial indication of the availability of high-concentration homes that could be used in developing a health-risk reduction plan. It is the committee's judgment that such an approach is unlikely to identify all the homes that would have to be mitigated to provide an equivalent health-risk reduction, but it would provide a cost-effective way to test the possibility of using the multimedia approach in a utility's operating region.

Scenario 5: Use of New Radon-Resistant Construction

As discussed in chapter 8, the effectiveness of radon-resistant construction is highly uncertain. The committee feels that it is not now possible to quantitatively assign radon-risk reduction potential to such construction practices. In many areas of the country, home construction is not contributing a substantial number of new dwellings to the community. To take credit for using radon-resistant techniques, new houses would have to be connected to existing water supplies. 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. Thus, it is necessary to estimate what the concentrations would have been in the new homes if they had not been built to be radon-resistant. The potential for radon in these homes will depend on the geology of the area. Assuming that the geology of the area is reasonably uniform, so that existing homes are on geologically comparable soils, a statistically valid survey

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