GEOLOGIC SOURCES OF RADON IN KENTUCKY: PRELIMINARY ANALYSIS

The Kentucky Geological Survey and the University of Kentucky College of Nursing are collaborating to study radon in Kentucky. KGS is using detailed statewide digital geologic maps to better delineate geologic areas of higher radon potential. Through the College of Nursing partnership, KGS acquired a statewide data set of 60,763 in-home radon measurements. Each individual radon measurement was assigned to a geologic map unit based on reported location (latitude-longitude). There are statistically significant differences in radon measurements between geologic units of different age and lithology. Most units exhibit high variability in radon measurements, but each unit can be distinguished by its maximum and average (mean or median) value.

Spatial patterns of high radon measurement and their correlation with geologic units in the large data set suggest and support several different possible sources or pathways of radon in Kentucky. Selected bedrock units contain higher concentrations of uranium and independently produce elevated levels of radon. They include Devonian black shales, certain bedrock sandstone or limestone units, Ohio River alluvium, and Pleistocene glacial outwash to varying degrees. Landscape evolution processes, especially karst dissolution, locally result in progressive concentration of insoluble residue, typically including uranium, in the soil; in these areas, the soil overlying the bedrock is the source of elevated radon. Voids, empty fractures, and caverns in karst areas attract soil gases as a region of lower pressure/potential, leading to elevated concentrations of radon in these areas. Areas of extensive limestone outcrops, which coincide with the karst areas of Kentucky, contain the most consistently high radon measurements in the state. These include the Lexington Limestone and Mississippian Slade Formation, St. Louis Limestone, Ste. Genevieve Limestone, and Upper Mississippian (Chester) limestone units. Faults have been known to leak radon in some areas; private industry at one point used high-resolution mapping of airborne radon to delineate possible fault and fracture traces. Ongoing studies will attempt to improve our understanding of the relative importance and spatial distribution of these varying processes.