Natural major and trace element background geochemistry of selected soil profiles, Los Alamos, New Mexico
— Eric V. McDonald, Patrick A. Longmire, Paula M. Watt, Randall T. Ryti, and Steven L. Reneau

Background-elemental concentrations for 24 metals and nonmetals relevant to the Environmental Restoration Project at Los Alamos National Laboratory were determined for a variety of soils and geomorphic settings across the Pajarito Plateau. Approximately 175 soil samples were analyzed for background-elemental concentrations using HNO₃ (leachable element concentration) and HF (total element concentration) sample digestion techniques. Leachable background elemental concentrations in soils provide information for risk calculations relevant to the bioavailability of elements. Background elemental concentrations in soils on the Pajarito Plateau generally vary with parent material, the degree of soil development, and other factors. Soil B horizons typically have higher concentrations of several trace elements, including As, Be, Th, and U, relative to soil A and C horizons. Higher concentrations of these trace elements in B horizons may be due to higher abundances of chemically active phases that enhance the adsorption of metals, such as ferric (oxy)hydroxides and clay minerals. Variations in soil-elemental concentrations may also be related to mineralogical variations in soil parent materials. Background-elemental soil data are used to determine possible contamination or to establish clean-up levels based on the calculation of a horizon-specific upper tolerance limit (UTL) for each element.