DEVELOPMENT OF GIS APPLICATION FOR RANKING AND PRIORITIZING MINE SITES FOR ASSESSMENT AND REMEDIATION IN CALIFORNIA

Within California, there are more than 40,000 inactive or abandoned mine sites in federal and state databases. It has been a long-standing challenge to assess and prioritize these sites for remediation, given limited budgets and staff time for federal, state, and local agencies. The United States Environmental Protection Agency (USEPA) Region 9, in cooperation with the California Department of Toxic Substances Control (CA DTSC) and the United States Geological Survey (USGS), is developing a Geographic Information System (GIS) application that will be used for ranking and prioritizing mine sites in California, for the purposes of Preliminary Assessment / Site Investigation by federal agencies, and consideration by state and local agencies for assessment and remediation. In addition to considering the commodities mined and the proximity to human population centers and recreational areas, the GIS application will take into account geologic factors based on the USGS mineral-deposit-type classification system. For each commodity mined, different deposit types will be different risk factors based on mineralogical and geochemical characteristics. For example, low-sulfide gold-Au vein deposits, the dominant deposit type for underground Au mines in the Mother Lode and the northern Sierra Nevada, have naturally occurring As, Pb, and other trace metals in waste rock and tailings, in addition to Hg contamination in mill tailings and at stamp mill sites where amalgamation was practiced. In contrast, historical placer Au mine sites typically have Hg contamination from amalgamation processing at selected features such as ground sluices and tunnel sluices, but do not have elevated As, Pb, or other metals. Although the project is not yet complete, criteria data layers have been identified. Efforts are underway to use the criteria data layers to process the universe of historical mine sites into manageable subsets, and to assign a USGS mineral-deposit type to each mine site.