Methods for environmental monitoring of DOE waste disposal and storage sites. Semiannual progress report, April 1--October 31, 1987

The authors have studied the precipitation of heavy metals by sulfide generated as a result of anaerobic sulfate respiration by sulfate-reducing bacteria. These bacteria are able to remove salts of mercury, lead, cadmium, nickel , and zinc from media that support sulfate respiration. A survey of metal-contaminated soils along East Fork Poplar Creek showed that all samples contained sulfate-reducing bacteria, but none had sufficient concentration of free sulfate to support active sulfate respiration. This situation represents a potential hazard in that sulfate-reducing bacteria can methylate mercury under conditions of low available sulfate, possibly releasing methyl mercury to the groundwater. The authors have proposed that amendment of soil with sulfate will promote sulfate respiration by bacteria. This would both enhance precipitation of heavy metals and also inhibit the formation of the toxic methylated metal compounds. Studies with soil columns demonstrated the feasibility of surface application of calcium sulfate to soil in providing sufficient concentration of sulfate at depths of at least 40 cm