Abandoned Mine Land

The Colorado Geological Survey conducted an Abandoned Mine Land Inventory (AMLI) project for the U.S. Forest Service (USFS) on National Forest System lands in Colorado from 1991 through 1998. The inventory identified physical and environmental hazards associated with mine features such as mine openings, waste rock dumps, tailings dumps, and mine structures. Approximately 18,000 individual mine features were inventoried.

Water located on or adjacent to these mine sites was initially assessed for pH, total dissolved solids, and flow quantity to identify adverse impacts to water quality. If these tests indicated significant degradation, full-suite water samples were taken for lab analysis of metallic and other constituents.

Portal of the Pennsylvania Mine in Summit County, upstream from Keystone Resort. Photo courtesy of Jeff Graves, Colorado Division of Reclamation, Mining and Safety.

Portal of the Pennsylvania Mine in Summit County, upstream from Keystone Resort. Photo courtesy of Jeff Graves, Colorado Division of Reclamation, Mining and Safety.

The driving force behind the project was the Federal Facilities Compliance Program, which is designed to bring federal facilities and lands into compliance with federal environmental laws including the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) (aka Superfund); the Resource Conservation and Recovery Act (RCRA); and the Clean Water Act (CWA) among other laws. The USFS Abandoned Mine Land Inventory Project was essentially a “discovery” process under CERCLA.

After the conclusion of the USFS-AMLI, CGS continued cooperation with the USFS to more fully characterize sites that contribute to significant environmental degradation. These ongoing mine site investigations continue to inform remediation actions by the USFS and others while helping to limit the impact of historic mining activities on affected watersheds.

For more detailed information on the AML Inventory download Abandoned Mines and Naturally Occurring Acid Rock Drainage on National Forest System Lands in Colorado (pdf).