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evaluate changes to the spring flow. The ground water aquifer below the Dakota coal, (the <br />Brushy Basin Member of the Morrison Formation) has much better water quality and will not be <br />affected by mining and reclamation at NHN Mine. Shale layers below the mined coals prevent <br />interaction between the spoil and this aquifer, which gets its recharge up dip and away from the <br />mine operations. <br />4) Containment Of Pit Inflow And Impacts On Water Ouality All runoff and pit pumpage <br />from disturbed areas will be routed through approved NPDES sedimentation pond(s). These <br />pond(s) will be designed and constructed to impound runoff and pit pumpage from areas <br />disturbed by mining and provide sufficient residence time to insure that the pond discharge water <br />chemistry meets the effluent requirements specified in the NPDES Permit. A review of the <br />chemical and flow data indicates that the potential for any discharge from any NPDES pond to <br />exceed receiving stream or federal standards is minimal. Past history of mine operations at the <br />New Horizon 2 Mine indicate very few exceedances of the standards over the years of <br />operations. <br />5) Potential Impacts Of Replaced Spoil On Groundwater Quality Since the mining <br />operation will disrupt the overburden above the LDx Seam and remove the LDx Seam, these are <br />the only two stratigraphic zones that will be affected by the operation. As described in the <br />section on overburden water quality, the pre -mine quality of the overburden water is poor, with <br />TDS generally in the 3000 ppm range and some ions exceeding limits for most water uses. The <br />primary potential for impacts to ground water quality will occur from increased water infiltration <br />causing an accelerated oxidation of pyrite in the backfill material. Other salts may also dissolve <br />more readily in the highly permeable backfill. The potential for minor amounts of sulfuric acid <br />production could cause lower pH, which would then result in higher rates of dissolution of other <br />chemical compounds in the spoil, resulting in higher TDS. The water draining through the <br />backfill will most likely not saturate the back fill south of Meehan Draw, (see Figure 2.05.6(3) -1) <br />but rather drain to the south and issue as a spring at the SS# 1 location. The backfill water north <br />of Meehan Draw will saturate the spoil at the low wall and form springs or seeps at the low <br />point(s). The backfill water north of Meehan Draw may also either migrate down dip across the <br />Meehan Draw "protection pillar" or into the side wall strata of the Dakota Sandstone Formation. <br />Spoil Water Chemistry Concerning impacts from the conversion of overburden to backfill <br />material, the available data indicate that a small proportion of the overburden may produce acid <br />through the oxidation of pyrite. Based on laboratory tests on overburden cores, calcite is present <br />throughout the overburden. Calcite serves two functions. First, it buffers the pH of the water, <br />which overall tends to slow the oxidation of pyrite, slowing the production of acid. Second, it <br />will neutralize the acid that is produced. The core samples that exhibited low paste pH are <br />surrounded by non -acid producing, calcite - bearing rocks. The water that contacts the low -paste <br />pH materials will have first reacted with calcite, and therefore developed a pH- buffer capacity of <br />its own. The groundwater monitoring data indicate that mixed overburden and interburden <br />Section 2.05.6(3) Page 19 November 2011 <br />