Hydrogeochemistry of sulfide and arsenic-rich tailings and alluvium along Whitewood Creek, South Dakota (Part 1 of 3 parts)

During 100 years prior to 1977, Whitewood Creek, SD, received about 1 billion tons of arsenic-rich and sulfide-mineral rich tailings from gold mining operations. A hydrogeochemical investigation conducted in 1983-84 focused on four local study areas on the flood plain where tailings deposits exist on top of moderately permeable alluvium. Piezometers in the alluvium beneath the tailings commonly show As at concentrations near or above the Primary Drinking Water Limit of 0.05 mg/l. Water supply wells on the flood plain are situated in alluvium in areas away from tailings where As levels in groundwater are below this limit. In these wells, selenium levels are generally above the limit of 0.01 mg/l. Suggested remedial measures and the likely persistence of these contaminants are discussed.