Determination of Background Metal and Radionuclide Soil Concentrations. S. M. Rood, G. A. Harris, and G. J. White, Idaho National Engineering Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-3960
To support risk assessment efforts at the Idaho National Engineering Laboratory (INEL) background concentrations of metals and radionuclides in soil are necessary. Knowledge of background concentrations assists in determining which metals and radionuclides at potentially contaminated waste sites are a result of past activities and should, subsequently, be evaluated in the baseline risk assessment. As part of a site-wide risk assessment at the INEL, which is 2,350 km2, it became necessary to determine regional background concentrations of metals and radionuclides in soil. Metals evaluated include those on the U.S. Environmental Protection Agency's Contract Laboratory Program list and the radionuclide evaluated were: americium-241, cesium-137, potassium-40, plutonium(Pu)-238, Pu-239, Pu-240, radium-228, strontium-90, thorium(Th)-228, Th-230, Th-232, uranium(U)-234, and U-238. Previously, there had been several small, localized studies of background concentrations of metals and radionuclides in surficial soil (i.e., 0-10 cm) at, and in the vicinity of, the INEL. The approach for determining background soil concentrations made the best use of all available information by combining these studies, when possible, to form a database of regional concentrations. The prime considerations for combining these studies were representativeness and comparability. Items included to determine the comparability of the studies include whether the collected soil samples were composites or grab samples, the depth of sample collection, analytical methods used, and soil type. Methods for comparison of composite background samples with non-composite site soil samples are presented along with the determined background values at the INEL. A meta-analysis procedure was used to analyze these studies to provide a regional background data set that can be used at the INEL and surrounding areas. No additional soil samples had to be collected saving both time and financial resources.