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Science for Watershed Decisions on Abandoned Mine Lands: Review of Preliminary Results, Denver, Colorado, February 4-5, 1998

The Role of Geoenvironmental Maps and Statewide Assessments in Prioritizing Watersheds for Remediation of Abandoned Mine Lands

By S.E. Church,¹ T.C. Sole,² D.B. Yager,³ and A.E. McCafferty⁴

The Abandoned Mine Land (AML) Initiative is based on the premise that watersheds affected by acid-mine drainage should be prioritized so that the resources spent on remediation will have the greatest benefit on impacted streams. A U.S. Geological Survey national-scale survey is underway which will show the effect of acid mine drainage (AMD) on the surface waters of the contiguous United States. This survey shows that the existing water-quality and trace-element data are insufficient to determine the magnitude of the AMD impact on the Nation's waters. Water-quality sampling generally has not been done sufficiently close to AMD sources to accurately delineate the impact. River bed-sediment geochemical data would provide another, more integrated method to evaluate AMD at a watershed scale. Sediment data can be equally as useful as water-quality data because trace-element concentrations in sediment typically are elevated downstream of abandoned mines, because mine wastes and tailings are introduced into and transported by the stream, and because enrichment in sediment occurs as pH increases and dissolved metals sorb to iron oxy/hydroxides.

There are a variety of mineral-deposit types. The environmental responses of each to surface weathering reflect their geologic setting, size of the mining disturbance, and climatic variables. In general, when mineral deposits are produced, those mineral-deposit types that cause the greatest potential threats to the environment are: (1) those that contain abundant fine-grained pyrite in the waste rock, (2) those where large tonnages of material are disturbed, (3) those that occur in rocks that have a low capacity to neutralize the acidity released, and (4) those deposits that meet the above criteria and which are located in moist climates. Combining the knowledge of mineral deposits, ecoregions, and climatic data will lead to a better understanding of those regions in the western United States where the environmental effects of AMD from historic mines are most likely to impact the Nation's surface waters.

The GeoEnvironmental Map (GEM) was developed to integrate geologic information, environmental characteristics of different mineral-deposit types, and available water-quality data to evaluate the effect of mining on surface waters. The initial GEM (Plumlee and others, 1995) for Colorado and some information contained in its successor for Montana (McCafferty and others, 1998, this volume) were used by decision makers in these two states to evaluate watersheds proposed for study under the AML Initiative. GEMs are valuable tools for communication of multidisciplinary geologic data with land-use planners, State and local officials, and the general public. Both GEM products were prepared from existing digital data. Future GEM products created for the statewide watershed prioritization in phase one of the AML Initiative would be more useful if biologic resource data were incorporated because the aquatic data provide important indications of receptor response to AMD. In addition, water-quality data were not adequately represented in the two initial GEM products. Because of the transitory nature of the biologic and water-quality data, these data sets are more difficult to incorporate into the GEM analysis.

During a recent USGS workshop on database needs, workshop personnel evaluated the existing digital geologic databases needed to produce a GEM product for the 13 western states. Only New Mexico and Wyoming have complete geologic, geochemical, and geophysical database coverages. Current hydrologic and biologic databases were not assessed. The remaining western states have various database deficiencies which should be filled before a GEM effort for these states are undertaken. Evaluation of existing data and incorporation of mine-inventory data collected by the States and the Federal land-management agencies also are essential components of this database-building process. We must begin a new, more collaborative phase of AML planning to meet the future expectations of the general public for effective environmental remediation on Federal lands.

¹U.S. Geological Survey, MS 973, P.O. Box 25046, Denver Federal Center, Denver, CO 80225 (schurch@usgs.gov)

²U.S. Geological Survey, MS 973, P.O. Box 25046, Denver Federal Center, Denver, CO 80225 (tsole@usgs.gov)

³U.S. Geological Survey, MS 973, P.O. Box 25046, Denver Federal Center, Denver, CO 80225 (dyager@usgs.gov)

⁴U.S. Geological Survey, MS 964, P.O. Box 25046, Denver Federal Center, Denver, CO 80225 (anne@usgs.gov)

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