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Overall, there should be no detrimental impacts from the mining operation on groundwater <br />flow and recharge rates. It is definite that ground water flow and recharge in the spoil <br />material will be increased, since the overburden aquifers have historically had very low flow <br />rates and also poor quality. These aquifers have not been used for any wells in the <br />surrounding area and cannot considered a water resource. The ground water aquifers below <br />the Dakota coals, in the Burro Canyon Formation, are used in surrounding wells and have <br />better water quality but they will not be affected by the mining and reclamation of this site. <br />Shale layers below the mined coals prevent interaction between the spoil and these aquifers, <br />which get their recharge from long distances away from the mine operation. <br />C) Potential impacts of replaced spoil on groundwater quality <br />Since the operation has disturbed the overburden above the Dakota coal seam and has <br />removed the Dakota coal, these are the only two stratigraphic zones that have been affected <br />by this operation. The water quality of the overburden is usually poor with a TDS of over <br />3000 ppm. The primary potential for impacts to ground water quality occurs from increased <br />water infiltration causing an accelerated oxidation of pyrite in the spoil. Other salts may also <br />dissolve more readily in the highly permeable spoil. The minor amounts of sulfuric acid <br />produce can cause lower pH, which then results in higher rates of dissolution of other <br />chemical compounds in the spoil, resulting in higher TDS. Also, the spoil water can infiltrate <br />into the low wall strata of the Dakota Sandstone formation. <br /> <br />• <br />0 SL-12 DRAFT 20AUG10.wPd 39