The Colorado Geological Survey conducted an Abandoned Mine Land (AML) Inventory 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.

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); 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.

Since the completion of the USFS-AML Inventory Project, CGS has been cooperating with the USFS on more fully characterizing those sites that contribute to significant environmental degradation.  These investigations have informed remediation actions by the USFS to help limit the mine site’s impact on affected watersheds.

Click here for the report on Abandoned Mines and Naturally Occurring Acid Rock Drainage on National Forest System Lands in Colorado