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The Colorado Division of Minerals and Geology has prepared four reclamation <br />feasibility reports for the Upper Animas River Basin (Appendices 10A, B, C, and D of <br />the UAA). Remediation of historical mine sites in the upper Animas will utilize the most <br />feasible methods on a site-by-site basis according to waste characterization, site access, <br />and disposal restrictions. <br />Surface Hvdrolosic Controls <br />Most hydrologic controls are preventative measures in that they inhibit or prevent the <br />process of acid formation and/or heave metal dissolution. If it is possible to prevent <br />water from entering a mine, or coming into contact with sulfide ores or wastes, this can <br />be the best; most cost effective approach. Here are excerpts on surface hydrologic <br />controls from Herron et al (1999, p. 27). <br />Diversion ditches are effective where run-on water is degraded by flowing over <br />or through mine waste, or into mine working. Diversion ditches can also be <br />used to intercept shallow groundwater that may enter mine waste. In some <br />cases, mine drainage can be improved by flowing through waste rock. Mine <br />drainage must be sampled above and below a waste rock pile to determine <br />whether the waste rock is actually degrading the water quality. <br />Mine waste removal and consolidation is effective where there are several small <br />mining waste piles in an area, or where there is a large pile in direct contact with <br />flowing water. The method is simply to move reactive material away from <br />~vater sources. <br />Stream sealins or diversion involves moving the water sources away from <br />reactive materials. Or sealingilining streams to prevent surface inflows into <br />shallow mine workings through slopes, shafts, or fracture systems. It may <br />include lining or grouting/sealing the streambed or bedrock <br />Revegetation is often used in combination with other hydrologic controls above. <br />Revegetation by itself can be a very effective method of reducing heavy metal <br />concentrations, particularly where much of the metals come from erosion of <br />mining waste into a stream. Revegetation also reduces the amount of water that <br />infiltrates a waste pile, thereby reducing leachate production. The roots of <br />growing plants also have been shown to produce carbonates through respiration. <br />In addition and often in conjunction to these methods, mine waste piles may be <br />capped and amended with neutralizing agents (e.g. limestone, lime, fly ash). A cap can <br />only reduce surface moisture infiltration. Throughflow and groundwater upwelling can <br />also occur and the impervious cap could result in increased humidity to the mine waste <br />resulting in increased salt formation and eventual loading to nearby streams. The <br />effectiveness of the amendment depends upon many site-specific factors. <br />6 <br />