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-23- The main stem of the Colorado River below Glenwood Springs, Colorado, has a drainage area of 6013 sq. miles. The natural flow of the stream is affected by trans-mountain diversions, storage reservoirs, power development, and diversions for irrigation of approximately 110,000 acres. The average discharge of the stream at Glenwood Springs, 'f or seventeen years of record, is 3,357 cfs. The maximum discharge on record occurred on June 25, 1983, and was 27,900 cfs. The 1984 water year maximum discharge is reported to have exceeded the previous maximum but the date of exceedance has not yet been published. The minimum discharge on record occurred on February 11, 1981-- 870 cfs. Selected chemical parameters and flow for the 1983 water year are presented in Table 3 for the Glenwood Springs U.S.G.S gaging station. Also given is the 1983 water year flows for the Colorado River near DeBeque, Colorado. The DeBeque gaging station is located approximately 54 river miles downstream of the Glenwood Springs station. The drainage area of the Colorado River at the DeBeque station is 7310 sq. miles. The Coal Ridge No. 1 surface facilities are proposed for location approximately 11 miles downstream of the gaging station at Glenwood Springs. The confluence of Harvey Gap with the Colorado River is approximately 20 miles downstream of the Glenwood Springs gaging station. The lowest average flows for the Colorado River in the area generally occur from September to March of each year, with February usually being the lowest flow month of the year. Highest flows are generally experienced in the month of June. Suspended solids levels within the Colorado River increase with increased flow. The opposite relationship exists with total dissolved solids, with the highest levels of TDS occurring during low flow. The Colorado River is a major source for irrigation water in the area. In general, the irrigation season is from April through October of each year. During these months, the levels of total dissolved solids are generally below 500 mg/1. During September and October, the TDS level in the Colorado River begins to rise to a point approaching or above 500 mg/1. This level is generally accepted as an indicator of moderate salinity hazard to plants, i.e., plants with a low salinity tolerance will experience decreased yield. There are thick alluvial bodies present along the Colorado River in the area of the mines. This alluvium is often used for agriculture. Water within the alluvium is a major source of shallow ground water for the region. The quantity and quality of water within the alluvium is intimately related to the water of the Colorado River, as the Colorado River is the major source of recharge for the alluvium. Conversely, this alluvium releases water back to the Colorado River during low-flow periods.