Laserfiche WebLink
underground mine water is not consumed in the workings, then the water will <br />be pumped from the portal area sumps to Pond 002. Table 2.05.6(3) of the <br />permit application contains a mass -balance mixing calculation of the pumped <br />underground mine water and the water in Pond 002. The underground mine <br />water is expected to have a much lower TDS content (approximately 1,050 <br />mg/1) compared to the TDS content of Pond 002 water (approximately 4,000 <br />mg/1) because the pillars will not be removed during the proposed mining, <br />resulting in minimal creation of waste rock (gob) in the workings. The mixing <br />calculation indicates that, compared to the current water quality of Pond 002, <br />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 Seneca II Mine pits are <br />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 <br />source of dissolved solids in the spoil (pyrite) is exhausted. After underground <br />mining is complete, the workings of the PSCM are predicted to fill with water <br />up to a maximum elevation equal to the portal elevation over a time period of <br />less than 22 years. <br />In addition to salt loading of streams, PSCM activities are predicted to result <br />in the following impacts: <br />Spoil leachate from the reclaimed surface mine pits will continue to load <br />alluvial ground water with salts in the Little Grassy, Grassy, and Cow Creek <br />drainages. As the alluvial/colluvial water quality closely mirrors the quality of <br />the stream, a degradation (i.e. increase in TDS) is expected to be observable in <br />alluvial monitoring wells down -gradient of the mine site. The Division has <br />previously found that in portions of the Little Grassy Creek drainage that are <br />in contact with previously disturbed lands, TDS increase over baseline <br />conditions is observable (Seneca II Mine findings). <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 <br />supply well located in the mine facilities area. The pumping rate will be <br />subject to SCCC's water rights associated with this well. PSCM predicts no <br />impacts to potential aquifers above the Trout Creek Sandstone from pumping <br />the well, based on the presence of thick intervening shale beds that act as <br />aquicludes. <br />Removing coal in the underground workings will cause ground water inflow <br />into the mine void, resulting in drawdown of the potentiometric surface in the <br />Wadge coal seam around the perimeter of the workings. The drawdown will <br />extend into beds immediately above and below the coal seam. Maximum <br />inflow of ground water into the workings is predicted to be 75 gallons per <br />minute, including less than 2 gallons per minute of predicted spoil leachate <br />17 <br />