Scientific Investigations Report 2006-5188
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006-5188
Since the late 1800s, mining and ore-processing activities in the South Fork Coeur d’Alene River basin have altered the water quality, aquatic biological, and hydrologic conditions in the 6,680‑mi2 Spokane River basin of northern Idaho and eastern Washington (fig. 1). Historical ore-processing activities resulted in large quantities of metal-rich tailings that were placed in and along streams (Long, 1998). The tailings have produced, and continue to produce, trace-metal-contaminated water (Hartz, 1993; Woods, 2001a; Woods, 2001b) and extensive deposits of trace-metal-contaminated sediment throughout the South Fork Coeur d’Alene River basin, the channel and flood plain of the main-stem Coeur d’Alene River (Spruill, 1993; Fousek, 1996; Bookstrom and others, 2001), and the lakebed of Coeur d’Alene Lake (Horowitz and others, 1995; Woods and Beckwith, 1997). Annual snowmelt runoff, frequent rain-on-snow events, and occasional floods continue to transport and redistribute trace-metal-contaminated sediments throughout the Coeur d’Alene River basin, into the Spokane River of eastern Washington (Maret and Skinner, 2000; Grosbois and others, 2001), and as far downstream as the Columbia River (Bortleson and others, 1994). The National Sediment Inventory (U.S. Environmental Protection Agency [USEPA], 1997) identified the Coeur d’Alene River and Lake as “areas of probable concern for sediment contamination,” the most severe contamination category in their assessment.
In 1998, USEPA initiated a Remedial Investigation/Feasibility Study (RI/FS) of the Spokane River basin under the authority of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980, which requires USEPA to evaluate contaminant release, fate, and transport. The Remedial Investigation (RI) phase involves data collection to characterize site conditions, development of conceptual models, determination of the nature and extent of trace-element contamination, and risk assessment for human health and the environment. The RI phase is followed by the Feasibility Study (FS) phase where remedial action alternatives are developed and evaluated.
Considerable effort is underway to mitigate the adverse environmental effects of past mining in the basin, primarily in the South Fork Coeur d’Alene River valley and its tributaries (Beckwith, 1998). The USEPA is directing cleanup of a Superfund site surrounding the defunct Bunker Hill Mine and ore-processing complex in Kellogg, Idaho (figs. 1 and 2). The State of Idaho, other Federal agencies, and the mining industry also are conducting site-specific sediment-removal, reclamation, and stream-channel rehabilitation projects. The USEPA is evaluating environmental contamination and remediation options in mining-affected areas outside the Superfund site in areas of the lower Coeur d’Alene River, its flood plain and adjacent wetlands, and the lakebed of Coeur d’Alene Lake (Beckwith, 1998). In addition, the USEPA and the Idaho Department of Environmental Quality currently are under court order to develop Total Maximum Daily Loads for a number of water bodies that do not support one or more designated uses in the Spokane River basin because of trace-metal contamination.
In support of these activities, streamflow and trace-metal chemistry data collected by the U.S. Geological Survey (USGS) during several previous and ongoing scientific studies at 10 USGS streamflow-gaging stations in the Spokane River basin were compiled and analyzed (table 1; figs. 1, 2). The data then were used to estimate annual trace-metal loads at the 10 stations for water years (WY) 1999–2003 or 1999–2004. Trace-metal loads for WY 1991–2003 or 1991–2004 also were estimated at four of the stations. The purpose of this report is to present and describe the results of the load estimations of dissolved and total cadmium (Cd), lead (Pb), and zinc (Zn) in numerous stream reaches in the Spokane River basin, Idaho and Washington, and to discuss inferences about metal transport and storage processes indicated by these results. The estimates in this study also were compared to earlier estimates of trace metal loads in the Spokane River basin as reported by Clark (2003).
