Gis-Based Geoenvironmental Assessments Of Watersheds Affected By Metal-Mining Activity

The environmental effects of metal mining activity are receiving ever increasing<br>attention from the public, regulators, land managers, and the mining industry. There are<br>several issues currently of primary interest: (1) assessment and remediation of<br>environmental problems at abandoned metal-mine sites; (2) prediction and mitigation (or<br>prevention) of potential environmental effects from future mining activity; (3) determination<br>of baseline conditions that existed in mineralized areas prior to mining (conditions which in<br>many mineralized areas were naturally degraded) and; (4) development of effective,<br>scientifically-realistic regulations to govern past, present, and future mining activity.<br>This paper summarizes a GIS-based approach developed to help address these issues.<br>Continually in refinement, our approach uses geologic and geochemical data layers to help<br>estimate potential environmental impacts of metal-mining activities on surrounding<br>watersheds. The approach is based on the fact that mineral-deposit geology as well as<br>geochemical processes exert fundamental and predictable controls on the environmental<br>conditions in mineralized areas prior to mining, and environmental conditions that result<br>from mining and mineral processing (Smith et al., 1994; Plumlee, in press). Similarly, the<br>geologic and geochemical characteristics of the rock units in the watersheds surrounding<br>mining districts and unmined mineralized areas can strongly influence the spatial extent and<br>magnitude of environmental impacts on the surrounding watersheds.<br>Results of prototype work in the State of Colorado are presented here with a focus on<br>environmental effects on surface-water quality; however, the techniques are generally<br>applicable, with appropriate changes in complexity of scale, for areas ranging in size from a<br>single watershed to a large state and for other environmental effects such as smelter<br>emissions and windblown solid contaminants. A second prototype for the State of<br>Montana is currently under development (S. Marsh, oral comm., 1995).