New findings on abandoned mines in southwest Colorado reveal what methods of investigation are most fruitful for watersheds

Researchers with the U.S. Geological Survey (USGS) have evaluated what different geologic, hydrologic, and biologic studies are most effective in cleaning up the watersheds affected by mining in southwest Colorado, and recently published their findings on-line and in print. USGS Professional Paper 1651, “Integrated Investigations of Environmental Effects of Historical Mining in the Animas River Watershed, San Juan County, Colorado.”

Acid drainage and toxic metals are a legacy of mining in many mountain watersheds throughout the western United States.

Application of the watershed approach has shown that it provides a cost-effective method for selecting abandoned mines for cleanup and restoration that can be applied by Federal, State, and local stakeholders groups and private entities.

This study demonstrates that a complete understanding of the nature and extent of hydrothermal alteration associated with the mineral deposits and the effect this alteration has, or had in the past, on water quality and native habitat must be carefully evaluated prior to initiation of remedial actions. The presence of extensive hydrothermal alteration exposed at the surface in the watershed limits the amount of biological recovery that reasonably can be expected and dictates the methods and costs of remediation projects.

The USGS report describes multidisciplinary studies of the geology and geochemistry of rock and sediment, the hydrology and water chemistry of streams and ground water, and the diversity and health of aquatic and terrestrial organisms in the Animas River watershed. The studies inventoried historical mines; defined geologic, structural, and geomorphological conditions that control acidity and release of potentially toxic trace elements; assessed fish distribution and habitat; collected and chemically analyzed hundreds of water, sediment, and mine- and mill-waste samples; conducted toxicity tests; analyzed macroinvertebrate and trout populations and biofilm to evaluate ecosystem health; defined hydrological regimes; evaluated plausible sources of trace elements to streams; and provided all data and maps in digital formats.

Studies in the 1,096-page report were conducted by USGS researchers as part of the Abandoned Mine Lands (AML) Initiative over a course of five fiscal years, 1997 to 2001. The AML was designed to provide technical assistance in support of Federal Land Management Agency (FLMA) actions to remediate contamination associated with abandoned hard rock mining activities and was part of a larger strategy by the U.S. Department of the Interior and the U.S. Department of Agriculture to coordinate activities for the cleanup of federal lands affected by AML. The strategy employed a watershed approach, in which contaminated sites were identified and remediated based on their effect on the water and ecosystem quality of a targeted watershed.

“Watersheds can have hundreds of active and abandoned sites that are potential sources of contamination. In order to demonstrate environmental improvements in a timely and cost-effective manner, the Federal agencies need to plan and implement remediation that is scientifically based, efficient, and invests resources where they would do the most good. In response to these needs, the USGS initiative developed a watershed approach, in which contaminated sites were prioritized and remediated based on their effect on the water and ecosystem quality in the affected watershed,” said Stan Church, USGS scientist and lead scientific editor of the report.