Soil-Gas Radon Concentrations in Selected Rock Units and Sediments in Ellis County, North-Central Kansas

Radon is a naturally occurring inert gas produced by the radioactive decay of uranium. Uranium is found in nearly all types of rocks and sediments. Radon-222 (Rn222), the most common isotope of radon, has a half-life of four days. The health risk associated with long term exposure to radon is lung cancer. The lungs are exposed to alpha radiation from the decay of radon and its progeny (radiogenic isotopes or daughter elements). The United States Environmental Protection Agency (USEPA) has SCI a guideline of 4 picocuries per liter (pCi/L) average annual concentration of radon in homes. Above this level, concentration reduction measures should be taken. The two major sources of radon concentrations in homes are either soil gas entering the home or the use of radon-bearing water. Soil gas enters the home by the stack effect, which is due to the pressure difference between the soil gas and the air inside the home. The soil-gas radon concentration in rocks and sediments is controlled by I) the uranium content of the mineral matter, 2) the location of the uranium relative to pore space in the rock or sediment, and J) the moisture content of the rock or sediment Marine shales, loess, volcaniclastic alluvial conglomerates, sandstones and carbonates are lithologies in geologic terranes that are typically major radon producers. Previous uranium studies in western Kansas identified Pleistocene volcanic ash, the Smoky Hill Chalk, Ogallala Group, Greenhorn Limestone, Graneros Shale, Carlile Shale, loess and oil field brine as containing anomalously high concentrations of uranium Thirty-five homes in Ellis County were screened for radon concentrations by the USEPA and the Kansas Department of Health and Environment (KDHE); 46% of the homes had radon concentrations above 4 pCi/L. In this study, 48 passive alpha-track radon detectors were used to measure soil-gas radon concentrations from 10 different geologic units in Ellis County, Kansas: Pleistocene volcanic ash, loess, Ogallala, Smoky Hill, Fort Hays, Blue Hill, Fairport, Greenhorn, Graneros, and sediments contaminated with oil-field brine All of the geologic units have average soil-gas radon concentrations less than the typical radon gas concentrations in natural soils The highest concentrations were detected in the Fairport Chalk at 534 pCi/L, Graneros Shale at 458 pCi/L and the loess deposits at 423 pCi/L. The geologic unit with the highest mean is the loess deposits, followed by the Blue Hill Shale and the Fairport Chalk. The geologic units with the lowest mean values are the Pleistocene volcanic ash and the Fort Hays Limestone The large variance in the soil-gas radon concentrations from each geologic unit may be due to differences in soil moisture content, porosity, or uranium content. These characteristics would affect the radon emanation process and may not be homogeneous in the geologic units.