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Discharges measured at this site are also affected by the pumping of water from this pond <br />for the truck cash system. This pumping began on September 18, 1984. <br />Review of Table 18 (Appendix A) shows this water to be a MgCa-S04 type. TOS values at <br />this site have remained relatively stable since 1981, indicating that the water quality of <br />spoils discharges into this pond have also stabilized. <br />Grassy Creek Drainage. Three monitoring sites lie ui thin the Grassy Creek drainage: <br />Surface water Site Sw•52-1, located upstream on Grassy Creek; NPDES Discharge Point 003, <br />also known as the Shop Reservoir or the Northwest Impoundment, located just north of the <br />mine shop area; and Surface Nater Site SW-S2-2, located approximately 0.1 mile downstream <br />of where NPDES 003 discharges into Grassy Creek. <br />Surface water Site SW-52-1. This site monitors the upper reaches of Grassy Creek which <br />are undisturbed by mining of the Seneca II Mine. Review of the hydrograph of monthly flow <br />readings shows low runoff in 1990 similar to 1967 to 1989 and significantly Less than 1982 <br />through 1986. <br />Review of Table 19 (Appendix A) shoos She eater at this site to be a CaM g-SO4HC03 type. <br />Increasing sulfate concentrations and slightly increasing TOS values are most likely due <br />to background conditions in the watershed above this site and the decreased runoff the <br />last four years. <br />NPDES Discharge Point 003. Hydrographs presented in Appendix E show that flow has <br />increased at this site since September 18, 1984, when operation of the truck wash <br />facilities began. water is siphoned from the wedge Impoundment (NPDES 002) into a holding <br />pond. Overf Low from the holding pond is diverted into the shop ditch which flows into <br />NPDES 003. water is pumped from the holding pond to the wash rack, drains into a settling <br />pond, and then into the same shop ditch. This operation has increased the flow at NPDES <br />003 while decreasing the flow at NPDES 002. Two other events that affected the tong-term <br />hydrograph include the diversion away from NPDES 003 of runoff from a fly ash pit operated <br />by Colorado-Ute Electric Association in October, 1980, and the diversion away from NPDES <br />003 of runoff contained in the Northwest Diversion Ditch (see the Seneca 11 Permit <br />Application, Exhibi[ 7-7, Surface water Hydrology Map and also [he 1982 Seneca II AHR) in <br />April, 1982. Finally, discharge volumes at the 003 site have been affected by the <br />reduction in diameter of the discharge culvert (36 inches to 6 inches) which occurred on <br />17 <br />