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Effects on Groundwater in the Rapid Creek Basin •~ "Mining coal in the Mesa Verde Group temporarily will dewater the rock adjacent to the underground mine. The adjacent rock, especially above the mine, will become rubbled and fractured because of subsidence during mining advancement. These subsidence effects will increase the permeability of rock in the mining vicinity and increase inflow of groundwater to the mine. The potentiometric surface (water level) will decline near underground mines because the increase in the permeability of the rock from fracturing and rub6ling also increases the storage capacity of the rock. The dewafering is temporary and water levels should return to premining levels after the underground mine is sealed. All pore spaces and fractures would become saturated after mining completion; saturation would occur after several years. Inflow of groundwater to the mine will increase as additional surface area in the mine is exposed to the water in coal and sandstone. Inflow probably would be small with decreased or no extraction of coat beneath streams, springs and Cabin Reservoir and because the Mesa Verde Group generally is a confining bed. • No critical aquifers would 6e dewatered by underground mining in the northwest part of the Rapid Creek basin. Water in the bedrock is the smallest part of the water ba: ~ for the basin and it is unused by the town of Palisade." (Brooks, 1986) Historic mine inflows are documented in the annual hydrologic reports. Total inflow appears to be fairly steady over time, with no seasonal variation. New areas of the mine have a higher inflow rate than areas that have already been developed. After an area has been developed, the area tends to dry out. Most water comes from the new (active) faces. The Graystone report in Appendix 7-3, Volume 2, evaluated the hydrologic characteristics of the Rollins Sandstone which lies 5-22' below the Cameo B- • 19-5 (Rev. 9/17/97)