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mine shop area; and Surface Veter Site SV-52-2, located approximately 0.1 mile downstream of where NPDES 003 discharges into Grassy Creek. • Surface Vater Site SY-S2-1. This site monitors the upper reaches of Grassy Creek which are undisturbed by mining of the Seneca 11 Mine. Review of the hydrograph of monthly flow readings shows lower than normal flows for this year. Review of Table 17 shows the water at this site to be a CaNg-504X[03 type. The 1994 average TDS value of 744 mg/l falls within the historic range. NPDES Discharge Point 003. Mydrographs presented in Appendix E show Chat flow has increased at [his site since September 18, 1984, when operation of the truck wash facilities began. Pater is siphoned from the Yadge Impoundment (NPDES 002) into a holding pond. Overflow from the holding pond is diverted into the shop ditch which flows into NPDES 003. Pater is pumped from the holding pond to the wash rack, drains into a settling pond, and then into the same shop ditch. This operation has increased the flow at NPDES 003 while decreasing the flow at NPDES 002. Two other events that affected the long-term hydrograph include the diversion away from NPDES 003 of runoff from a fly ash pit operated by Colorado-Ute Electric Association in October, 1980, and the diversion away from NPDES • 003 of runoff contained in the Northwest Diversion Ditch (see the Seneca II Permit Application, Exhibit 7.7, Surface Pater Hydrology Map and also the 1982 Seneca II AHR) in April, 1982. Finally, discharge volumes at the 003 site have been affected by the reduction in diameter of the discharge culvert (36 inches to 6 inches) which occurred on July 19, 1988. No comparison of this years' flows to prior years is presented since the operation of the truck wash system tends to greatly influence the flow conditions at Pond 003. Review of Table 15 shows a dramatic shift in water quality after 1984. Prior to the truck wash operation, the annual average TDS of the flows at RPDES 003 ranged from 1225 to 1578 mg/l. After the truck wash operation began, the annual average TDS range increased from 2491 to 3094 mg/l, with this year's TDS being the highest. The water remains generally a MgCa-504 type, although the percentage of sulfates have increased and bicarbonates have decreased since [he beginning of the truck wash operation. This water is of similar quality to chat found at NPDES 002. Surface Pater Site SV-52-2. This site is the furthest downstream surface water site in • the Little Grassy and Grassy Creek drainages prior to exiting the permit area. Therefore, 14