Heavy metal discharges into Shasta Lake and Keswick reservoirs on the upper Sacramento River, California; a reconnaissance during low flow

Four out of seventeen streams entering the Shasta-Keswick Reservoir system in California contribute up to 94 percent of the heavy metal load into the upper Sacramento River under the low flow conditions which existed in the fall of 1974. Of these four streams, three contain acid mine drainage, with Spring Creek carrying more than 50 percent of the total load for every element analyzed except lead. The Pit River (the fourth stream) contains low concentrations of metals and has neutral pH values; but since it carries the greatest discharge, its computed loads also are high. The immediate danger to fishin the Shasta-Keswick region is not the contribution of acidity and toxic metals to the total load, but toxicity at the localized point of mixing where the acid streams mix with lake water. Zinc and cadmium, in addition to copper, are present in high concentrations for five of the seventeen streams and may exert significant synergistic effects. The presence of arsenic in some of the ore minerals suggests that it also may contribute to the toxicity of the mine drainage. (Woodard-USGS)