The U.S. Forest Ser Vice Abandoned Mine Land Inventory In Colorado: Background, Progress, And Preliminary Findings

The U.S. Forest Service (USFS) and the Colorado Geological Survey (CGS) are continuing a cooperative agreement to identify sites<br>of environmental degradation associated with abandoned and inactive mines on Colorado’s USFS administered lands. The USFS<br>Abandoned Mine Land inventory Project is a “discovery” process and is a precursor to the Environmental Protection Agency’s<br>“Preliminary Assessment” process. identification of environmentally degraded sites may lead to a formal Preliminary Assessment.<br>The inventory process begins in the office and involves reviewing existing mining and geologic literature, previous mine inventory<br>work, current and historical maps, water quality information, and aerial photographs. During field investigation, each mine feature<br>is given a unique identification number. Field geologists collect data on the physical and geographic characteristics of the mine<br>features along with information on any water emanating from or interacting with the mine features. This information is used to assign<br>a qualitative environmental degradation rating to the individual mine feature. Guidelines for the rating system are given to field<br>personnel to facilitate consistency within the data set.<br>All data collected are entered into a computer database. From a computer perspective, both location and attribute data are being<br>collected. Therefore, the data are well suited for integration into a geographic information system (GIS) creating a geo-referenced<br>data set.<br>The USFS Abandoned Mine Land Inventory Project began in 1991 and is ongoing. To date, field inventories of the Arapaho,<br>Roosevelt, Pike, and Rio Grande National Forests have been completed. Work in the San Isabel, San Juan, White River, Gunnison,<br>Uncompahgre, and Grand Mesa National Forests is in progress. Through the 1994 field season approximately 9,667 mine features<br>(openings, dumps, tailings, highwalls, etc.) have been inventoried.<br>In the course of field investigations, evidence of naturally occuring water quality degradation has been found in various parts of the<br>state. The geology and hydrology of these areas are conducive to producing waters from springs and seeps with relatively high<br>concentrations of metals and low pH. These areas usually exhibit hydrothermal alteration of the country rock in addition to vein<br>mineralization. Many of these occurrences are in, or associated with, volcanic terranes. However, some occurrences are known<br>in areas of metamorphic, sedimentary, and igneous terranes.<br>As inventoried mine sites exhibiting environmental degradation progress from identification to site characterization and remediation,<br>it will be important to clearly identify the goals of remediation. Sites that occur in areas of naturally degraded water should, if<br>possible, have background conditions characterized in addition to mine site characterization. Remediation goals for minecontaminated<br>waters can then be set at realistic levels.