Publication Summary

There are numerous abandoned metals mines and inactive mining districts in Washington State. Inactive and abandoned mines, waste rock dumps, and tailings can be the source of contaminated water, including acid rock drainage, that has the potential to severely impact nearby streams. Almost no data are available to evaluate the extent of the problem.

There are numerous abandoned metals mines and inactive mining districts in Washington State. Inactive and abandoned mines, waste rock dumps, and tailings can be the source of contaminated water, including acid rock drainage, that has the potential to severely impact nearby streams. Almost no data are available to evaluate the extent of the problem.

The purpose of this screening level study was to investigate streams near selected mining districts for water quality and sediment quality impacts. The project was the first application in Washington mining districts of EPA ultra-clean methods for measuring toxic metals at water quality criteria levels. As the first systematic investigation of mining district impacts on water and sediment quality, the results from this study were intended to identify the significant parameters for future sampling projects. Findings from this study highlighted districts that required follow-up sampling to define the extent of impacts. The study results will also aid watershed planning through identification of water quality impaired streams.

Water and sediment samples were collected in streams draining ten metals mining districts in eastern Washington. Samples were collected upstream and downstream of the districts and analyzed for metals and general chemistry parameters. Discharges from several individual mines and tailings facilities were also sampled. Field work took place in June 1997 for characterization of high-flow conditions, and in October 1997 for low-flow conditions.

Water quality impacts are seasonal in most districts, with maximum degradation commonly occurring during high-flow. Results showed increases in metals concentrations in the streams that drain most districts, in some cases by an order of magnitude or more. Iron, zinc, and lead were most frequently present in elevated concentrations. State water quality standards for zinc, cadmium, and/or copper were exceeded in three streams. Iron problems were pervasive in the study area. None of the mine or tailings water discharges met water quality standards. Impacts were subtle in some districts where a significant distance separated upstream and downstream samples.

Metals concentrations in sediments from four streams substantially exceeded sediment quality guidelines. Zinc, copper, arsenic, cadmium, and silver were common contributors to the exceedences.

Among the general chemistry parameters, sulfate and total dissolved solids appeared to be the most useful indicators of water quality and sediment quality impacts from mining. A ratio of sulfate to total dissolved solids above 20% was found to adequately identify exceedences of water quality and sediment quality standards or guidelines.

Link to EIM data for User Study ID MinesII