2019-12-31_REVISION - C1981022 (15)

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to the ground water regime. Though the Sanborn Creek operation mined both the B and C seams that had been mined before at the old Somerset Mine, the Sanborn Creek Mine was not connected to the old workings and was protected by a 100-foot buffer. The old Somerset mine is thought to be flooded and that buffer was apparently successful in protecting the newer operation from inundation from the old workings. The 100-foot buffer was maintained by advance drilling to find the location of the old workings. Mine water inflow into the Sanborn Creek workings is estimated to be 425 gpm or less. The old Somerset Mine had an inflow rate of 0.15667 gpm/acre for the 1,500 acres of development in the mine that was below the level of the North Fork River. Projecting this rate to the 2,600 acres of the Sanborn Tracts yields an inflow of 407 gpm. The operator has rounded this figure to 425 gpm in the PAP. It is not known at the time of this findings document what the source of the mine inflow water was during the spontaneous combustion event in 1999. The operator has also projected an additional 235 gpm discharge from the old Somerset Mine, which has the potential to reach the North Fork of the Gunnison via the alluvial system. This is considered to be extremely unlikely; however, the projection is used in the CHIA to allow for absolute worst-case prediction. The following are potential sources for inflow: (a) The North Fork of the Gunnison River is 750 feet to the south and 100 feet above the proposed B-seam workings and 40 feet above the C-seam workings. Groundwater is expected to travel down dip from the river through the coal and overburden into the mine workings. Because of the low permeability of the coal and overburden, calculations have shown that these flows should be minor. The flows can be expected to occur with a considerable lag time. There will be a comparable diminution of flow in the North Fork, but mine pumping will return this amount to the river, minus that used in the mine. The cone of depression from dewatering of the strata will only extend to the boundary of the North Fork and will not adversely impact any wells. (b) The potential exists that the mine may encounter water inflow from faults and fractures. No particular faults have been identified. The largest fault that the old Somerset Mine encountered had a sustained inflow of 120 gpm, which contributed 50 percent of the total inflow. (c) The Sanborn Creek workings undermined portions of two abandoned mines - the Oliver Mine and the Hawk's Nest Mine. The Oliver Mine was mined in the 1930's and is thought to be flooded. An exposure of the workings adjacent to the old county road formerly discharged water at a rate of a few gallons per minute. About 90 percent of the workings of this mine lie downdip of the discharge point. 20