| Abstract: | A pile of pyrite cinders discharged from a former manufacturing facility rest upon the bottom of the St. Lawrence River adjacent to Clark Island. In situ capping was the selected remedy to control both the fine particle resuspension that produced a red mud cloud in the water, commonly formed on windy days, and the soluble metals concentrations originating from the pyrite pile. Metal mass balances around the pile allowed estimates of the pre‐capping release rates. Elevated concentrations above the pile were observed for eight metals; these included iron, lead, mercury, selenium, arsenic, copper, cadmium, and zinc. After iron, the highest concentration in the pyrite particles were cadmium and zinc present in the 1,000 mg/kg range. Mercury was the lowest at the 10 mg/kg level in the pyrite solids. For iron the soluble release rate was estimated to be 0.08 g/s, and the particle release was 0.8 to 1.2 g/s. A 30 cm cap consisting of particles 19 to 40 mm in diameter is proposed for the site. Its placement covers a ten‐hectare area and is expected to isolate the fine pyrite particles and prohibit their resuspension into the water column. Design estimates of steady state flux reduction efficiencies range from a low of 99.21 percent for iron to a high of 99.96 percent for copper. Breakthrough times to achieve these steady state flux reductions range from 100 to 3,800 years and metal porewater concentrations at 5 cm below the cap surface are estimated to be reduced by 83 percent. Although soluble metals will continue to be released from the pile zone, the flux of all the metals will be significantly reduced. © 2002 Wiley Periodicals, Inc. |
