2018-11-19_PERMIT FILE - C2010089A (6)

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Backfilling of pit walls and continued irrigation adjacent to the permit boundary will allow ground water levels to recover as demonstrated by the 80% recovery of the water levels at GW - N8 in less than 20 years. The ground water from the Dakota bedrock zones has not been used to date because of poor quality and low production potential. Further, the "bedrock" seepage water will continue to flow tributary to Tuttle Draw maintaining the hydrologic balance of the San Miguel River. Infiltrating irrigation water on the reclaimed backfill will also travel the path of least resistance and issue at the SS# 1 location as increased flows tributary to Tuttle Draw and The San Miguel River. The impact of the backfill material on the ground water flow and recharge is therefore minimal. Two quarters (6 months) prior to initiation of mining activity at NHN, flow and water quality monitoring (field parameters) at the SS# 1 location will be resumed in order to detect and evaluate changes to the spring flow. The ground water aquifer below the Dakota coal, (the Brushy Basin Member of the Morrison Formation) has much better water quality and will not be affected by mining and reclamation at NHN Mine. Shale layers below the mined coals prevent interaction between the spoil and this aquifer, which gets its recharge up dip and away from the mine operations. 4) Containment of Pit Inflow and Impacts on Water Ouality All runoff and pit pumpage from disturbed areas will be routed through approved NPDES sedimentation pond(s). These pond(s) will be designed and constructed to impound runoff and pit pumpage from areas disturbed by mining and provide sufficient residence time to insure that the pond discharge water chemistry meets the effluent requirements specified in the NPDES Permit. A review of the chemical and flow data indicates that the potential for any discharge from any NPDES pond to exceed receiving stream or federal standards is minimal. A copy of the approved NPDES permit is on file at the New Horizon North Mine office and is available for review at the Division's request. 5) Potential Impacts of Replaced Spoil on Groundwater Quality Since the mining operation will disrupt the overburden above the LDx Seam and remove the LDx Seam, these are the only two stratigraphic zones that will be affected by the operation. As described in the section on overburden water quality, the pre -mine quality of the overburden water is poor, with TDS generally in the 3000 ppm range and some ions exceeding limits for most water uses. The primary potential for impacts to ground water quality will occur from increased water infiltration causing an accelerated oxidation of pyrite in the backfill material. Other salts may also dissolve more readily in the highly permeable backfill. The potential for minor amounts of sulfuric acid production could cause lower pH, which would then result in higher rates of dissolution of other chemical compounds in the spoil, resulting in higher TDS. The water draining through the backfill will most likely not saturate the back fill south of Meehan Draw, (see Figure 2.05.6(3)-1) but rather drain to the south and issue as a spring at the SS# 1 location. Spoil Water Chemistry Concerning impacts from the conversion of overburden to backfill material, the available data indicate that a small proportion of the overburden may produce acid Section 2.05.6(3) Page 19 March 2018 (TR -16)