2018-01-31_PERMIT FILE - C2009087A (2)

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RULE 2 - PERMITS • At YSG5, the proposed downstream compliance point under SMCRA, ambient iron concentrations were diluted by the mine effluent to 97% of the previously measured concentration. It should be noted that reported iron concentrations are affected by variable detection limits (0.02 to 0.1 mg/L), and the use of the detection limit in averaging where the laboratory reported "less than" values. At downstream compliance point YSG5, measured summer low flows were as low as 20 gpm, due to reinfiltration of surface water into valley alluvium. Mixing calculations at YSG5 are therefore of questionable precision. Discharge of mine - affected groundwater to alluvial aquifers will have negligible effects. As estimated in the discussion above, the inflow of poor - quality groundwater to the alluvial aquifer would only be 0.046 gpm, less than a tenth of a percent of the combined dry- season spoil spring discharge (66 gpm in September 2005) in the Little Grassy Creek basin, and less than two- tenths of a percent of the measured summer low flow in Little Grassy Creek (28 gpm at Pond 002). Exposure of materials by mining- related surface disturbance and contact of disturbed area runoff with these materials, infiltration and drainage from coal storage any potential surface discharge of excess mine drainage flows may result in changes in runoff or discharge water chemistry. Surface water in the mine area is generally a calcium - sodium, mixed -anion type, although chemistry may vary to include calcium- magnesium mixed anion, sodium - potassium bicarbonate, and sodium - potassium mixed anion types. The most probable potential change in. runoff water chemistry would be a shift from a mixed anion type toward a calcium- magnesium sulfate type due to the weathering and leaching of exposed surface materials. Additionally, as discussed above, mine inflow • discharges may contribute additional iron to surface water under some circumstances, while not exceeding water quality standards. Mine inflows would actually dilute ambient TDS concentrations in surface waterways. PSCM's proposed surface drainage and sediment control measures, specifically limitations on total surface disturbance and collection of disturbed area runoff as close as reasonably feasible to the disturbance source area, will be effective in limiting runoff exposure to stockpiled materials and consequent leaching. The fact that the materials which will be exposed, including overburden, soils, coal, and mine development waste materials, have been determined as not potentially acid- or toxic - forming (Section 2.04.6) is an important factor which will also limit the potential for any significant changes in surface water chemistry. While minor changes in surface water chemistry may occur as a result of mining and related operations, limited surface disturbance areas, corresponding limited disturbed area runoff volumes, and consumptive use of mine water discharge will minimize any potential for significant changes in water chemistry for the receiving drainages. In addition, disturbed area runoff and any residual mine water discharge flows will be buffered by significantly greater volumes of normal runoff from undisturbed drainage basin areas during most times of the year. Potential increases in TSS levels will be effectively, addressed on a short-term basis by establishment and operation of the drainage and sediment control system, consumptive use of mine water discharge, and compliance under the required CDPS permits with applicable monitoring requirements and discharge effluent limitations. Reclamation and restoration of effective surface drainage conditions will address all potential mining and related surface water impacts over the long -term. Culvert installation and diversion construction may temporarily affect surface drainage patterns, and construction activities may result in increases in sediment contributions both during construction PSCM Permit App. 2.05 -90 Revision 03/05/10