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Hayden averaged 15.90 inches for 1951 through 1980. Average monthly precipitation . ranged from 1.18 inches in February to L60 inches in December. Average monthly temperature at Hayden for 1951 through 1980 ranged from 17.0° F in January to 66.3° F in July. Daily temperature extremes range from less than -20° F in the winter to over 90° F in the summer (1951-1986, NOAA). Land surface elevations at the mine site range from about 6,800 feet to about 8,240 feet. The fond surface for the proposed mine area drains to Hubberson Gulch and Dry Creek. Streamflow within the mine area is intermittent and primarily results from snowmelt and precipitation events. The U.S. Geological Survey operated a stream gage on Hubberson Gulch just upstream from Dry Creek from July 1979 through September 1981. The drainage area at this site is about 8.08 square miles. The daily Streamflow ranged from zero in the late summer months to 30 cubic feet per second (cfs) on April 20, 1980. The records show that the Streamflow is highly dependent on snowmelt. For April, May and June, streamflow averaged 3.52 cfs, 2.4b cfs and b.52 cfs, respectively, and for the remainder of the year the average streamflow ranged from 0.02 cfs in August to 0.22 cfs in March (1979-1981, USGS). WATER REQUIREMENTS 1, The water uses at the Seneca 11-W Mine will include domestic and industrial components. The domestic component will include water used by Peabody employees at the mine headquarters complex for drinking, washing, and sanitary purposes. Domestic wastewater disposal will consist of a septic tank and non-evaporative leach field system. The annual water demand for domestic purposes is estimated to be about I.0 acre-foot per year, and daily demands should be fairly constant throughout the year. The industrial component will include water uses for dust suppression and miscellaneous purposes. The water demands for industrial purposes are estimated to be about 25,0 acre-feet per year. Most of this requirement is for dust suppression purposes, so the monthly demands should be proportional to the net evaporation rates for free water surfaces. The net evaporation rate is the difference between gross lake evaporation and effective precipitation. For the Hayden area, the net lake evaporation is estimated to be 26.46 inches per year and to range from zero during December through February to 5.40 inches in July. The monthly water requirements for industrial uses range from zero during December through February to 5.1 acre-feet in July. The derivation of the monthly evaporation rates are shown in Table 1. The monthly water • demands for the Seneca II-W Mine are shown in Table 2. 2