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• alluvium is much smaller than 25 inches due to evapotranspiration and the <br />fact that not all the precipitation falls on the area at the same time. <br />Assuming the precipitation and temperature patterns at Paonia, Colorado, <br />are similar to these at the Bear No. 3 Mine, it is estimated that 4.4, inches of <br />precipitation would accumulate during the winter months. This water would <br />infiltrate the alluvium under the Bear No. 3 facilities early in the spring, <br />prior to any significant amounts of evapotranspiration. Infiltration of 4.4 <br />inches of water would contribute 2.71 acre-feet of water to the alluvium. <br />This infiltration is 0.8 percent of the average monthly flow through the <br />alluvium. The large amount of dilution in the alluvial material will mitigate <br />any effects of contamination in the alluvium. Water quality in the <br />infiltrating water would have to be 30 times greater than background <br />concentrations to increase the concentration of any parameter by 25 percent. <br />3. Surface Water Effects <br />Mining activities at the Bear No. 3 Mine are not expected to degrade the <br />water quality of the North Fork of the Gunnison River. The disturbed area <br />for the Bear No. 1, 2, and 3 Mines is less than 30 acres in size, and is <br />extremely small in comparison to the entire North Fork of the Gunnison <br />drainage basin. The small contribution of surface water nmoff from the <br />Bear disturbed.area will be diluted by flow in the North Fork of the <br />Gunnison River. The Bear No. 3 sediment pond rarely discharges, and any <br />effluent is required to meet NPDES discharge standards. <br />The water quality of the North Fork of the Gunnison River is not expected <br />to be impacted by water that infiltrates the alluvium of the Bear No. 3 <br />facilities area. The small contribution to the flow of the river is <br />insignificant. Any water which enters the alluvium will be diluted by <br />ground water flowing through the alluvium. The ground water flow through <br />the alluvium will be further diluted by the greater flow in the North Fork of <br />the Gunnison River. The average annual flow in the river is 82.3 times <br />larger than the ground water flow through the alluvium. <br />4. Conclusion <br />An assessment of the probable hydrologic consequences of the mining <br />operation and an assessment of the probable cumulative impact of all <br />anticipated mining in the general area on the hydrologic balance has been <br />made. This document entitled "Cumulative Hydrologic Impacts of Mining to <br />the North Fork of the Gunnison River" is on file at the Division offices and <br />may be reviewed during normal business hours. It has been updated to <br />incorporate additional anticipated impacts that may result from the approval <br />• of Permit Revision No. 2. Pursuant to Rule 2.07.6(2)(c), the Division fords <br />that the Bear mining operation has been designed to minimize hydrologic <br />22 <br />