Abandoned Mine Lands

Mine Dump in Leadville Historic Mining District

Prior to 1977 there were virtually no laws in the United States requiring that mines be reclaimed when mining was finished. Today the Colorado Division of Reclamation Mining and Safety is responsible for assuring that mined lands are restored under the Colorado Mined Land Reclamation Act and the Colorado Land Reclamation Act for the Extraction of Construction Materials. However, prior to those laws, when mining was completed, the companies just walked away leaving piles of waste and dug out holes. Thus, Colorado was left with an estimated 23,000 abandoned mine lands (AML).

Abandoned mines present very dangerous physical hazards to the public. High priority physical hazards identified by the Colorado Geological Survey for the USFS AML inventory are being jointly mitigated by the USFS and the Colorado Division of Reclamation, Mining, and Safety (DRMS). Mine workings are notorious for containing “bad air” including carbon monoxide, carbon dioxide, and hydrogen sulfide. These gases can kill unwary explorers of these old mines by asphyxiation. The old workings and structures can be very unstable and collapse without warning. Dangerous sites close to public access are being safeguarded through filling, capping, or gating the abandoned mine openings with engineered structures.

As yet, many mines remain open in Colorado, especially in the backcountry. People are injured and killed every year while “just exploring” abandoned mines. Don’t be a victim.


USFS Abandoned Mine Land Inventory Project

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) (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.

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.