A reconnaissance study was made of occurrence of arsenic in the Dry Creek basin in northern California where the U.S. Army Corps of Engineers proposes to construct Warm Springs Dam. The purpose of the study, made from August through November 1974, was to determine the extent of any potential arsenic problems that may affect Lake Sonoma which would form behind the dam. Samples of sediment, water, and biota were collected and analyzed for arsenic content.
Results of the study indicate that arsenic presents a potential problem only in the Little Warm Springs Creek area. Samples of the geothermal water from that area contained 140 micrograms of arsenic per litre of water--almost two and one-half times the maximum allowable concentration for drinking water. However, the contribution of arsenic to the proposed lake would be minimal because discharge of the geothermal water in the area is estimated to be only about 0.01 cubic foot per second (0.0003 cubic metre per second).
Analyses of limited numbers of biota samples indicated that there is no biomagnification of arsenic through the food chain. Concentrations of arsenic in fish and benthic invertebrates collected from water containing high levels of arsenic were similar to concentrations in samples collected from water with low arsenic content. Concentrations of arsenic on sediment were low throughout the project area.
