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<br />Artificial Recharge of Ground Water in Colorado
<br />A Statewide Assessment
<br />
<br />Abandoned Metal Mines
<br />
<br />Inactive underground metal-mining districts throughout Colorado were also investigated to
<br />determine their potential water storage capacities, Three evaluation criteria were used to identify
<br />potential underground water storage sites:
<br />
<br />a) Water quality considerations
<br />Many of Colorado's metal-mining districts contain sulfide mineralization in such abundance
<br />that water becomes acidic and contaminated with heavy metals within the mines, This is part
<br />of the reason that several former mining districts have been designated as EP A Superfund
<br />sites, Examples include the LeadvilIe, Gilman (near Eagle), and Summitville mining
<br />districts, Yet, on the basis of a map showing metal-mine drainage hazards in Colorado
<br />(Plumlee and others, 1995), probable water quality characteristics within mining districts can
<br />be identified based on the ore type found there, Only mining districts determined to have
<br />minimal adverse effects on water quality were selected for further study, Twenty-five metal
<br />mining districts in the state were judged to potentially have good water quality, justifying
<br />further study,
<br />
<br />b) Volumetric considerations based on the total amount of ore production
<br />The 25 mining districts selected, based on favorable water quality characteristics, were
<br />assessed for their total amount of ore production, Several CGS and USGS sources were used
<br />for this research (Vanderwilt, 1947; Cappa, ] 998; Lovering and Goddard, 1950; Beatty,
<br />Landis, and Thompson, ]990; Scarbrough, 200]; Cappa and Bartos, in press), In all of these
<br />districts, the estimated ore production is a combination of all of the mines that compose each
<br />district, which is commonly more than 10 individual mines, Because metal mines have never
<br />been required to publicly disclose mine production data, volumes, or detailed mine maps,
<br />only rough estimates of total ore production are available, For the same reason, detailed
<br />information regarding the maximum depths of the mines in the districts, the amount of
<br />ground-water inflow into the mines at various depths, water loss through fractured rock,
<br />amount of dewatering required during production (if any), and other information necessary
<br />for a comprehensive evaluation of each mining district's potential as a water storage site is
<br />commonly lacking from the public record,
<br />
<br />c) Water storage capacity considerations
<br />Based on the estimated tonnage of ore produced in each of the 25 metal mining districts with
<br />good to moderate water quality, the maximum potential water storage capacity of each
<br />district was calculated, Using a tonnage factor of 12,5 (12,5 cubic feet ofrock per ton of
<br />ore), the volume of ore produced was estimated, An additional volume was separately added
<br />to account for the non-ore mining of development workings such as access tunnels, drifts,
<br />cross cuts, and shafts, A rough estimate of 50 percent of total ore production was used in this
<br />calculation of additional, non-ore volume, Therefore, the total volume of mine workings
<br />equals] ,5 times the volume of ore produced, Each mine in each district is different, of
<br />course, but as previously stated, detailed underground mine records are generally not
<br />available to the public, The ore volumes and non-ore volumes were added for each district,
<br />and the total volume was then converted to acre-feet The volumes calculated by this method
<br />are considered to be maximum potential water storage volumes, Because of the limited data
<br />and highly variable characteristics of ground water in the mountainous terrain, and the
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