Solids (dune sand and sandstone bedrock) and groundwater from in and around the site were analyzed to determine major element and metal concentrations (including uranium). High solid-phase concentrations of salts (mainly sodium chloride, calcium carbonate, and sodium/calcium sulfate) and slightly elevated uranium consistently occur in caliche horizons found above the water table. These caliche zones have not been associated with uranium in the past because their uranium concentrations are near average crustal abundance (2.7 ppm). However, uranium concentrations in solid samples from below the water table are much lower (< 1 ppm uranium). Distilled water and dilute acetic acid leaching of solid samples indicate that the uranium in the caliche zones is more leachable than samples from below the water table. Leachable element concentrations appear to be high enough to produce the surrounding shallow groundwater and contaminant plume geochemistry with elevated concentrations of sodium, calcium, chloride, sulfate, and uranium.
Natural dissolution versus precipitation of these caliche zones is probably an on-going process that reaches equilibrium with the shallow groundwater geochemistry. However, anthropogenic disturbances may have created conditions favorable for additional caliche dissolution. During the dump operations, caliche zones that may have remained above the water table for thousands of years could have become saturated, producing an associated dissolution of uranium and other elements to the groundwater.