This report presents geochemical data collected during an investigation of contaminant attenuation within the unconsoidated overburden and shallow bedrock at the Weldon Spring chemical plant site. The data consist of chemical analyses of water samples from 20 groundwater and 5 surface-water sites, mineralogic and chemical analyses of about 70 overburden samples, results from laboratory sorption experiments, and chemical and mineralogic characterization of sludge and interstitial water samples from raffinate pit 3. Concentrations of dissolved nitrite plus nitrate ranging from 24 to 1,100 milligrams per liter as nitrogen were detected in samples from four shallow (less than 110 feet deep) bedrock monitoring wells near the raffinate pits. The samples from these wells generally had increased concentrations of calcium, magnesium, sodium, sulfate, dissolved solids, lithium, and strontium. Concentrations of dissolved uranium (3 to 1 10 micrograms per liter) were detected in samples from all four of these wells. Samples from unconsolidated overburden units at the site consist mainly of silt-size particles (as much as 82 percent of the less than 2-millimeter size fraction) with lesser quantities of clay-and sand-size particles. The predominant mineral in the bulk (less than 2 millimeters) fraction is quartz (36 to 98 percent) with lesser quantities of feldspars, clay minerals, and calcite. Quartz also was the predominate mineral in the clay-size (less than 2 micrometers) fraction. Generally, clay minerals comprise less than 10 percent of the overburden, with the clay till containing the largest average quantities. The predominant clay type is montmorillonite (50 to 95 percent of the total clay minerals). Calcite and other carbonate minerals constitute between an average of 0.7 percent (Ferrelview Formation) and 20 percent (residuum) of the overburden mineralogy. Average contents of Iron ranged from 1.4 percent in the loess to 2.4 percent in the Ferrelview Formation and clay till. More than 95 percent of the lead and 89 percent of the vanadium in a simulated leachate was removed from solutions equilibrated with the Ferrelview Formation or clay till at fixed pH values ranging from 4.5 to 9.0 in laboratory experiments. The maximum sorption of molybdenum (greater than 97 percent) occurred at a fixed pH 4.5 in solutions in contact with either unit. Less than 41 percent of molybdenum was removed at a fixed pH of 7.0 in solutions in contact with either unit and less than 5 percent was removed at a fixed pH of 9.0. At fixed pH values, the maximum sorption of uranium (greater than 97 percent) occurred in solutions at pH 4.5 in contact with the clay till. Slightly larger quantities of sorption (more than 98 percent) occurred in unadjusted solutions in contact with the Ferrelview Formation at initial pH values of 4.5 and 7.0. Conditions least conducive to uranium sorption were at a fixed pH of 7.0 in contact with the clay till where only 52 percent of uranium was removed. Less than 15 percent of sulfate, 19 percent of nitrite plus n...
