Abstract

Radon is a radioactive gas of geologic origin that is found in many buildings in sufficient concentrations to represent a health hazard to building occupants. High concentrations of radon may exist where favorable geologic conditions are present, but non-geologic factors also affect indoor-radon levels. Non-geologic factors are difficult to quantify, but geologic conditions can be evaluated to determine the distribution and characteristics of radon-hazard areas where elevated indoor-radon levels are more likely to occur.

Geologic factors were used to identify potential radon-hazard areas in southwestern Utah by mapping: (1) possible point sources for radon, including known uranium occurrences, and (2) generalized sources, including uranium-enriched rocks found at the surface or beneath well-drained, porous, and permeable soils, and soils derived from uranium-enriched rocks. Potential radon-hazard areas in southwestern Utah are widespread, and are generally underlain by silicic igneous rocks and low-grade metasedimentary deposits. The results of 36 indoor measurements of radon levels in southwestern Utah confirm predictions that levels are highest, with an arithmetic mean of 8.8 picocuries per liter (pCi/L) (325.6 Becquerels per cubic meter [Bq/m³]), in hazard areas defined by geology, and are significantly lower, 2.4 pCi/L (88.8 Bq/m³), outside of hazard areas.

More detailed investigations to identify radon-hazard areas were conducted in St. George, and are planned in Sevier County, with partial funding from the U.S. Environmental Protection Agency under the Congressionally-mandated State Indoor Radon Grant Program.