Areas of the United States with elevated screening levels of 222Rn

As part of an Environmental Protection Agency/State cooperative program, 38 of the 48 contiguous states have successfully conducted probability-based surveys of indoor 222Rn. These surveys produced short-term screening measurements in approximately 55,000 randomly selected houses. An objective common to all surveys was to identify geographic regions within the state with elevated screening levels of 222Rn. This paper examines the survey results as they relate to this objective. The 38 states were partitioned into 225 geographic regions and summary statistics of 222Rn concentrations (e.g., arithmetic mean, geometric mean, percentage of houses exceeding a specified level) and associated 95% confidence intervals were calculated for each region. Twenty-four of the 225 regions had arithmetic means exceeding 222 Bq m-3 (6 pCi L-1); these are analyzed in detail