WAT-1998-02 Abandoned Mines and Naturally Occurring Acid Rock Drainage on National Forest System Lands in Colorado


Overview report on the extensive CGS work on acid rock drainage on abandoned mine and natural sites across the state, in cooperation with the US Forest Service (USFS). 12 pages. Digital PDF download. WAT-1998-02D

From the Abstract

The CGS completed an inventory of environmental degradation associated with abandoned and inactive mines on National Forest System lands in Colorado. In the course of the inventory, areas with naturally occurring acid rock drainage were also noted. Approximately 18,000 abandoned mine-related features were inventoried, including about 900 features that are considered significant enough environmental problems to warrant further investigation. Water quality data, such as pH and conductivity were gathered at all features where water was present, such as draining adits, seepage at the toe of dumps and tailings, and standing water in shafts. Samples were taken where field tests indicated low pH and/or high conductivity, including several areas with naturally occurring acid rock drainage. Samples were analyzed for dissolved and total metals, and for selected anions. All mine locations and data collected by the field geologists were entered on field forms and, subsequently, into a computer database and GIS format.

With the information provided by the inventory, the Forest Service, in cooperation with other agencies, has been able to prioritize abandoned mines for reclamation. In most cases, cleanup is approached on a watershed basis. Mines in priority watersheds have been selected for reclamation first. Watersheds where studies prerequisite to cleanup are occurring include the upper Animas River, Willow Creek (tributary to the upper Rio Grande), Chalk Creek (tributary to the upper Arkansas River), the Uncompahgre River, and the Alamosa River.

During the inventory, evidence of naturally occurring water quality degradation was found in areas where little or no evidence of mining activity exists. These areas include the upper Alamosa River, the Middle Fork of Mineral Creek, Peekaboo Gulch, and Handcart Gulch. Water from these natural sources has been found to significantly exceed Colorado water quality standards for several metals.