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A spoil porosity of 15% was determined for the overburden. <br />Spoil spring discharge (Spoil Spring Recharge) - (Seepage into Low Wall) <br />Seepage into the Low Wall is approximately 18% of the total recharge. Spoil <br />Spring Discharge is approximately 82% of the total recharge. In the year <br />2000, the NPDES 001 discharge at the New Horizon #1 Mine showed an <br />average flow of 271,000 gallons per day or 320 acre-feet per year. The <br />NPDES 001 discharge is for practical purposes composed entirely of spoil <br />water. <br />Overall, there should be no detrimental impacts from the mining operation on <br />n-__W and rccvuar __. Gr-vilu u._. a water n iiu_ _w _ -__ aii <br />groundwater a__..ter flow ra`?c? recharge ill uic <br />spoil material will be increased, since the overburden aquifers have <br />historically had very low flow rates and also poor quality. These aquifers have <br />not been used for any wells in the surrounding area and cannot be considered <br />a water resource. The ground water aquifers below the Dakota coals, in the <br />Burro Canyon Formation, are used in surrounding wells and have better water <br />quality but 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 <br />these aquifers, which get their recharge from long distances away from the <br />mine operation. <br />3. Potential impacts of replaced spoil on groundwater quality. The operation has <br />disrupted the overburden above the Dakota coals and has removed the Dakota <br />coals, therefore, these are the only two stratigraphic zones that have been <br />affected. As described in the section on overburden water quality, the <br />pre-mine quality of the overburden water is poor with TDS generally in the <br />3000 ppm range and some ions exceeding limits for most water uses. The <br />primary potential for impacts to ground water quality occurs from increased <br />water infiltration causing an accelerated oxidation of pyrite in the spoil. Other <br />salts may also dissolve more readily in the highly permeable spoil. The minor <br />amounts of sulfuric acid produced can cause lower pH, which then results in <br />higher rates of dissolution of other chemical compounds in the spoil, resulting <br />in higher TDS. This water will saturate the spoil at the low-wall and form a <br />spring at the low point. Also, the spoil water can infiltrate into the low-wall <br />strata of the Dakota Sandstone formation. <br />Spoil Water Chemistry <br />Concerning impacts from the conversion of overburden to spoil, the available <br />data indicate that a small proportion of the overburden may produce acid <br />through, the oxidation of pyrite. Based on laboratory tests on overburden <br />cores, calcite is present throughout the overburden. Calcite serves two <br />functions. First, it buffers the pH of the water, which overall tends to slow the <br />29