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review of ground water impacts is documented in a memorandum to file SL-03 dated March 25, 1999. The Division's review identified the following hydrolo;ic impacts. Surface Water Impacts: Hayden Gulch Nline has desraded the quality of water Flowing in the stream channel of Hayden Gulch within one mile downstream from the mine. This conclusion is based on a comparison of pre-minins and post-mining water quality data 2. The degradation in Hayden Gulch is an approximate 400 mg11 increase in total dissolved solids (TDS) during springtime flow. The increase has raised TDS from a premining level of azound 1000 mg/l, to a postmining level of around 1400 mg/l. 3. The degradation in Hayden Gulch will persist for hundreds to thousands of years before returning to pre-mining levels. This projection is based on an analogy with a U.S. Geological Survey geochemical mass-balance study at the nearby Seneca II Mine. The degradation increase in TDS in Hayden Gulch is due mainly to an increase in the concentration of sulfate. The origin of the sulfate most likely is the oxidation of pyrite in the spoil in the former pit. Spoil spring RSP-4 (next to County Road 53) and pond HG-8 are both fed by water discharging from the pit, and both dtrectly discharge into the Hayden Gulch stream. 5. The degradation in Hayden Gulch will not violate State or Federal surface water laws. 6. The degradation in Hayden Gulch will no[ constitute material damage in Hayden Gulch because the quantity of water flowing in Hayden Gulch stream is inadequate to support irrigation use and the quality of water in the stream has always been too poor for higher level uses. The water flowing in Hayden Gulch will remain suitable for livestock watering. There is a stock watering pond in Hayden Gulch. The degradation in Hayden Gulch will not cause material damage downstream from Hayden Gulch because of dilution from another stream, the East Fork of [he Williams Fork River. Amass-balance calculation indicates the degradation in Hayden Gulch will increase the TDS concentration in the East Fork less than 4% during periods of low flow. This increase is the same amount predicted in the mining and reclamation permit's discussion of the probable hydrologic consequences. Ground Water Impacts: 8. Amass-balance analysis indicates that sulfate-rich water discharging from the reclaimed Hayden Gulch pit will not degrade ground water because virtually all of the water from the pit dischazges into the surface waters of Hayden Gulch via spoil spring RSP-4 and Hayden Gulch Mine Page 13 May 25. 1999 Phase II/III Bond Release