Effects of copper and acidic mine drainage on sediment and water quality in Keswick Reservoir, Shasta County, California

Iron Mountain Mine has historically been the largest contributor of toxic concentrations of copper to the Sacramento River. In addition to degradation of water and sediment quality, copper poses potential toxicity risks to sensitive aquatic species in the Sacramento River below Keswick Dam.; A mechanistic approach was developed to examine the transport and fate of copper in Keswick Reservoir, to estimate concentrations of copper species discharged to the Sacramento River, and to evaluate effects of alternative reservoir operations on disturbance and transport of contaminated sediments. Field studies were conducted in support of this study to characterize morphology, hydrodynamics, and water quality in Keswick Reservoir.; An existing suite of finite element models was adapted to the Keswick Reservoir system. pH and copper speciation equations were incorporated within the framework of the water quality model, RMA11, tested on a simplified system network, and applied to a finite element network representation of Keswick Reservoir. Simulation boundary conditions included existing (peaking power) discharges versus a steady discharge from Spring Creek Power Plant, together with average and worst case (i.e., spill) discharges from Spring Creek Debris Dam. Alternative hypothetical scenarios were used to examine effects of reservoir operations and discharges from the debris dam on copper concentrations in the water column and sediments.; Simulation results showed a correlation between water column constituent concentrations and power plant outflow rates. Simulated peak water column copper concentrations were 1.5 to 3 times higher under peaking power operations than under steady flow conditions at the power plant. Simulations of copper species' concentrations showed Cu2+, the copper species most toxic to aquatic organisms, to be the dominant form of copper under peaking power cycle operations, but that CuCO3 concentrations dominated under the hypothetical steady flow conditions applied at Spring Creek Power Plant.; Modeling techniques developed in this study can serve as a useful tool for evaluation of alternatives for remediation or enhancement of water quality in surface water systems receiving acidic and heavy metal contaminant discharges from mines or industrial sources and may be used in support of efforts to develop effective management strategies for preservation of fresh water resources.