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to Pond 002. Table 2.05.6(3)-T1 of the permit application. contains a mass-balance <br />mixing calculation of the pumped underground mine water and the water in Pond 002. <br />The underground mine water is expected to have a much lower TDS content <br />(approximately 1,050 mg/1) compared to the TDS content of Pond 002 water <br />(approximately 4,000 mg/1) because the pillars will not be removed during the <br />proposed mining, resulting in minimal creation of waste rock (gob) in the workings. <br />The mixing calculation indicates that, compared to the current water quality of Pond <br />002, the pumped mine water will improve the quality of water in the pond and its <br />discharges to Little Grassy and ultimately Grassy Creek. <br />Discharges of spoil leachate from the backfilled pits proposed for transfer from Seneca <br />II are expected to continue indefinitely, with the dissolved solids content of the spoil <br />leachate declining over a long period of time (possibly centuries) as the chief source of <br />dissolved solids in the spoil (pyrite) is exhausted. After underground mining is <br />complete, the workings of the PSCM are predicted to fill with water up to a maximum <br />elevation equal to the portal elevation over a time period of less than 22 years. <br />In addition to salt loading of streams, PSCM activities are predicted to result in the <br />following impacts: <br />¦ Spoil leachate will continue to seep into bedrock in the downdip ends of the <br />reclaimed surface mine pits that are proposed for transfer to the PSCM. The seepage <br />continues to create a plume in the Wadge coal seam where the workings are not in <br />the flow path of the spoil leachate. The underground. mine workings will be <br />developed in the current surface mine plume as indicated by apparent spoil leachate <br />encountered in Wadge seam monitoring well immediately west of Pond 002. The <br />spoil leachate plume develops at a rate similar to the underground mine's leachate <br />plume. The spoil leachate is predicted to have higher TDS (approximately 4,000 <br />mg/1) compared to the underground mine water (approximately 1,050 mg/1). <br />¦ Spoil leachate from the surface mine pits will continue to load alluvial ground water <br />with salts in the Little Grassy, Grassy, and Cow Creek drainages. As the <br />alluvial/colluvial water quality closely mirrors the quality of the stream, a <br />degradation (i.e. increase in TDS) is observable in alluvial monitoring wells <br />down-gradient of the mine site. The Division has previously found that in portions <br />of the Little Grassy Creek drainage that are in contact with previously disturbed <br />lands, TDS increase over baseline conditions is observable (Seneca II Mine findings, <br />permit C-80-005). <br />¦ The potentiometric surface of the Trout Creek Sandstone will continue to be <br />depressed by the mine operator's pumping of water from this unit in their supply <br />well located in the mine facilities area. The pumping rate; will be subject to SCCC's <br />water rights associated with this well. PSCM predicts no impacts to potential <br />aquifers above the Trout Creek Sandstone from pumping the well, based on the <br />presence of thick intervening shale beds that act as aquicludes. <br />Peabody Sage Creek Mine 24 May 7, 2010