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HYDROLOGY REPORT Introduction The water year of October 1983 to September 1984 was one of the wettest years in recent times at the North Thompson Creek Mines. A total of 28.76 inches of precipitation fell at the mine's rain gauge near Number Three Mine (Appendix 1). An average precipitation amount for this period is 20 inches. The highest 24-hour precipitation event occurred on June 7, 1984, when 2.6 inches of precipitation was recorded. A ten-year 24-hour event for the Thompson Creek Area is 2.7 inches; therefore, this event in all practical purposes could be classified as a ten-year, 24-hour event. Much damage resulted from this snow/rain storm. Many Aspen trees near the mine site collapsed under the weight of the snow. All together several acres of Aspen forests in this region were decimated. In terms of damage to the mine site, very little problems occurred. Our site drainage system completely contained the surface runoff from this storm and no discharges occurred to North Thompson Creek. The flow in North and Middle Thompson Creeks during the spring runoff were at very high levels. Unfortunately, the weir at the west end of Snow- mass Coal Company's permit area washed out in June and no high runoff data was obtained. However, the weir recorded a water flow of 174 cfs just M before it washed out. Using this data, it is estimated that the peak run- off flow in North Thomspon Creek was in excess of 300 cfs. It is estimated that a total yearly flow in North Thompson Creek is close to 700 acre-feet. This number will be more accurate in 1985 when Snowmass Coal Company has all its flumes in and operational, Surface Water Quality Appendix 2 contains all the water quality data obtained from the North Thompson Creek and Roaring Fork River during the period October 1983 to September 1984. The data for the Roaring Fork River suggests that the Loadout facility is having no impact on the Roaring Fork. All of the analy- tical data is consistent with the pre-permit mean data. When the data for the North Thompson Creek Upstream and Downstream samples are compared with the pre-permit mean values it is apparent that the chemical make-up of the creek has has changed very little. A comparison between the North Thompson Creek Upstream and Downstream samples indicate that the lower sampling point has a higher value of Calcium, Magnesium, Sulfate, and Dissolved Solids. These levels are slightly increased due to the chemical composition of the ground water being pumped from the