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Underground activities approved at the PSC are not predicted to add to the <br /> currently on-going salt loading of surface water, as all water that seeps into <br /> the underground mine workings is either expected to be consumed by dust <br /> control in the workings or is predicted to dilute the water in Pond 002. If all <br /> 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/I) compared to the TDS content of Pond 002 water (approximately 4,000 <br /> mg/I) because the pillars will not be removed during the proposed mining, <br /> resulting in minimal creation of waste rock (gob)in the workings. The <br /> mixing calculation indicates that, compared to the current water quality of <br /> Pond 002,the pumped mine water will improve the quality of water in the <br /> pond and its discharges to Little Grassy and ultimately Grassy Creek. <br /> Discharges of spoil leachate from the backfilled and reclaimed Seneca II <br /> Mine pits are expected to continue indefinitely, with the dissolved solids <br /> content of the spoil leachate declining over a long period of time (possibly <br /> centuries) as the chief source of dissolved solids in the spoil (pyrite)is <br /> exhausted. After underground mining is complete, the workings of the PSC <br /> are predicted to fill with water up to a maximum elevation equal to the portal <br /> elevation over a time period of less than 22 years. <br /> In addition to salt loading of streams, PSC activities are predicted to result in <br /> 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 <br /> of the stream, a degradation (i.e. increase in TDS)is expected to be observable <br /> in alluvial monitoring wells down-gradient of the mine site. The Division <br /> has previously found that in portions of the Little Grassy Creek drainage that <br /> are 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 PSC's water rights associated with this well. PSC 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 /> Page 17 of 27 <br />