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fly ash pit (operated by the Hayden Station power plant) in October 1980 <br />and the diversion away from NPDES3 of runoff contained in the Northwest <br />Diversion Ditch (see the Seneca II Permit Application, Exhibit 7-7, <br />Surface Water Hydrology Map and the 1982 Seneca II AHR) in April 1982. <br />Discharge volumes at the site have also been affected by the reduction <br />in diameter of the discharge culvert (36 -inches to 6 -inches) that <br />occurred on July 19, 1988. A smaller volume pump and line from Pond 002 <br />to the truck wash was installed in August 2001. The truck wash was last <br />used in 2007. These pump lines, which were siphoning water out of Pond <br />002, were capped off on July 7, 2010. <br />This year's average flow value, 0.020 cfs, is below the historic (1980- <br />2016) average flow value, 0.130 cfs. This year's below average value is <br />due to retirement of the truck wash system. Review of the TDS plot <br />indicates a decreasing trend, with the peak value occurring in September <br />2002. <br />Surface Water Site SW -S2-2 (SSG2). <br />This site exists on Grassy Creek downstream of discharges from PSCM <br />Ponds 002 and 003, but upstream of Site SSG3 and Scotchman's Gulch <br />(Yoast Mine NPDES Pond 010). Review of the TDS plot indicates an <br />increasing trend, with the peak TDS occurring in August 2013. <br />Surface Water Site YSGS. <br />This site is the furthest downstream surface water site in the Little <br />Grassy, Scotchmans Gulch and Grassy Creek drainages after exiting the <br />PSCM permit area. Therefore, it is the most significant monitoring site <br />with respect to showing the cumulative effects of mining in this area. <br />It displays a relatively stable slightly increasing TDS trend, with the <br />peak value occurring in August 2013. <br />The PSCM PAP addresses potential impacts to surface water quality on <br />pages 2.05-84 to 91 (Vol. 1A). A summary of those impacts is presented <br />on Table 2.05.6(3), page 2.05.89. The Probable Hydrological Consequences <br />(PHC) focus on impacts caused by underground mine dewatering. As that <br />scenario has not occurred yet, the PHC predictions are not yet relevant. <br />14 <br />