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mine shop area; and Surface Water 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 11 Mine. Review of the hydrograph of monthly flow <br />readings shows, in 1993, the highest peak flow observed since 1986. <br />Review of Table 17 shows the water at this site to be a CaN g-504HC03 type. The 1993 <br />average TDS value of 731 mg/l falls within the historic range. <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. Overflow 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, end then into the same shop ditch. This operation has increased the flow at NPDES <br />003 while decreasing the flow et NPDES 002. Two other events that affected the long-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, end the diversion away from NPDES <br />003 of runoff contained in the Northwest Diversion Ditch (see the Seneca 11 Permit <br />Application, Exhibit 7-7, Surface Water Hydrology Map and also the 1982 Seneca II AHR) in <br />April, 1982. Finally, discharge volumes et the 003 site have been effected by the <br />reduction in diameter of the discharge culvert (36 inches to 6 inches) which occurred on <br />July 19, 1988. No comparison of this years' flows to prior years is presented since the <br />operation of the truck wash system tends to greatly influence the flow conditions at Pond <br />003. <br />Review of Table 15 shows a dramatic shift in water quality after 1984. Prior to [he [ruck <br />wash operation, the annual average 7DS of the flows at NPDES 003 ranged from 1225 to 1578 <br />mg/l. After the truck wash operation began, the TDS range increased to 2491, peaking at <br />3028 mg/l in 1990. The 1993 annual average is more than 200 mg/l Less than the 1990 <br />value. The water remains generally a MgC a-504 type, although the percentage of sulfates <br />have increased and bicarbonates have decreased since the beginning of the truck wash <br />operation. This water is of similar quality to that found at NPDES 002. <br />Surface Water Site SW-52-2. This site is the furthest downstream surface water site in <br />[he Little Grassy end Grassy Creek drainages prior to exiting [he permit area. Therefore, <br />14 <br />