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Indoor-Surveys, Radon Potential Maps and Their Impacts on Radon Awareness in California

Indoor-Surveys, Radon Potential Maps and Their Impacts on Radon Awareness in California

Adapted from the presentation and printed with permission of the author, Ronald K. Churchill, Ph.D.

In a presentation at the 2016 International Radon Symposium held in San Diego, California, September 18-21, Ronald Churchill, Ph.D., of the California Department of Conservation, California Geological Survey (CGS), presented findings of the paper “Indoor-Surveys, Radon Potential Maps and Their Impacts on Radon Awareness in California.” The CGS and the California Department of Public Health (CDPH) have worked cooperatively on data collection, mapping and analysis of radon potentials in California. CGS radon activities are funded through an interagency agreement, by a portion of the CDPH State Indoor Radon Grant from U.S. Environmental Protection Agency (USEPA) and CGS matching funds.

The paper presents the historical origin and accuracy/inaccuracy of the pervasive perspective that California does not have significant radon problems. Additionally it explains the cooperative efforts of the CGS and CDPH to identify the state’s relatively small but significantly anomalous radon areas, documenting that California does have some local radon exposure issues. It also discusses how radon maps that have been created are used, especially by consultants required to address the radon exposure issue when preparing Phase 1 environmental reports for construction projects.

Historically, in the 1980s and 90s, the perception that radon was not a significant problem in California developed due to factors such as:
• small random radon surveys with limited ability to identify typical anomalous radon areas;
• radon authorities repeated statements that radon is only a problem in small isolated areas;
• lack of more detailed studies to identify such areas;
• disagreements between experts on who should test; and
• radon potential map shortcomings of existing USEPA and other mapping.

Since 2003, CGS has been developing advisory maps using indoor-radon data from CDPH surveys, uranium geochemical data, soil permeability data and geologic maps at 1:100,000 scale or larger. To date CDPH has completed 20 radon-screening surveys and CGS has completed 10 radon potential maps. Approximately 15 million Californians reside in areas with completed CGS radon potential maps.

The development of and access to these maps has increased awareness of radon in California as evidenced by additional website views and downloads. Improvements in distributing the information have come through:
• CDPH and CGS radon websites;
• CDPH online radon Zip Code database;
• CDPH—CGS cooperative radon surveys (all or parts of 20 counties);
• CGS geology based radon potential maps (10 maps completed since 2005—available online); and
• CGS 2016 online interactive radon potential map.

Some outcomes of the study are that:

• Recent radon potential maps by the CGS show that higher radon potential areas, not detected by the early surveys, do exist within some California counties.

• Availability of these maps on the web has facilitated their use by consultants in Phase 1 environment assessments, in real estate disclosure and by the public; increasing the visibility of radon as an environmental health issue in California.

• One county recently began requiring radon map review during preparation of geotechnical reports for construction projects. This has resulted in consideration of radon at several sites and a commitment to radon resistant construction at a new fire station.

For more information, review the paper at

Ronald K. Churchill, Ph.D.
Senior Engineering Geologist
California Geological Survey, California Department of Conservation