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-25- 3) Le ac hate from surface water seepage through waste piles may degrade the quality of both surface and ground water as a result of the proposed mining operations. All three of the underground mines (Dorchester, Newlin Creek and Twin Pines) will have to dispose of mine waste rock. When this material comes in contact with water, a leachate water is produced which is usually of poorer quality than the natural waters. If the leachate were to come in contact with natural surface or ground water, degraded water quality may result. The reclaimed spoils left by the one surface mine (G.E.C.) may also produce a leachate water. Similar effects as those described above could be expected from this leachate. In all likelihood, this impact has been occurring for many years as a result of the many unreclaimed mines in the area. The Inactive Mines Program identifies almost 600 acres of land directly disturbed by mining still in evidence. There is no available pre-mining water quality data to compare with the existing water quality. Therefore, it is impossible to quantify the magnitude of the water quality impact that has occurred. However, the impact of the anticipated operations will be small in comparison with these existing coal mining impacts. The impacts to the hydrologic balance due to the leachate water from the waste piles and spoils from the proposed mining operations will be minimized in several ways. The waste piles and spoils will be located above the peizometric surface limiting the leachate to dissolution from transient flow. The post-mining topography will be contoured to the approximate original contour, thus preventing the formation of impoundments and the resultant contamination of ground water recharge. Also the fills will be compacted, which will significantly reduce the infiltration of water. The proposed waste piles will be covered with non-toxic, non-acid-forming materials, which will also decrease contact between the waste and water. Water quality impacts will also be minimized if revegetation is successful. If adequate revegetation occurs, resultant higher evapotranspiration rates reduce the amount of infiltration, thereby reducing the amount of leachate produced. Therefore, no significant additional water quality impacts to leachate generation are anticipated. 4) Experience with underground mines in the Carbondale, Book Cliffs, Danforth Hills, and Yampa Coal Fields of the State, as well as in the Canon City area, indicates that mine inflows are not normally significant when ephemeral streams are undermined. Most of the streams to be undermined in the region are ephemeral and would not be expected to be significantly affected by mining. Flows in these ephemeral streams are concentrated in periods of snowmelt and high-intensity precipitation events. The stream gradients are steep and their channels contain little alluvium. For the above reasons, very little surface water is retained in the stream valleys long enough to infiltrate into the ground water system. Therefore, the amount of water observed reaching the mine workings is insignificant.