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Hydrology The Orchard Valley mine workings have the potential to deplete the quantity of ground water through mine included ground water inflows. The mining operation will induce inflows by dewatering the coal seam and the associated roof and floor strata as the mine workings advance. The mining operation may induce inflows from underlying or overlying units through: 1) the dewatering of fractures and faults which intersect both the mine workings and the ovezlying or underlying saturated horizons; or 2) the dewatering of overlying saturated horizons through subsidence related fractures produced by the mining operation. To date, however, the Orchard Valley mine has Daly encountered minor inflows to the underground workings. During the year 1983, approximately 300,000 gallons of water flowed into the mine. The source of ground water inflow to the mine is from perched, discontinuous, water-bearing sandstones overlying the "D" seam. These sandstones are of the lenticular character and the water bearing strata are only present sporadically within the permit area. It is anticipated that these locally perched ground water aquifers is strata _ directly above the workings will be dewatered through subsidence cracks or fractures. This predicted impact of dewatering these aquifers is considered to be insignificant in terms of volumes of mine inflow or impact on the overall hydrologic balance, based on the lack of appreciable amounts of ground water encountered above the "D" seam during exploration drilling activities. There are no wells within the area which derive water from ground water sources other than shallow eolluvial/alluvial deposits near the surface. No ground water monitoring wells have been installed or proposed in any saturated water bearing units above the "D" seam within the 5 year permit area, due to • difficulties in successfully locating a saturated unit to monitor. One such monitor well, however, is located outside of the 5-year permit area is Section 14 of T13S, R92W. The greatest potential for subsidence to have an effect on ground water is within the stream channels containing deposits of alluvium and colluvium. Two wells exist adjacent to the area which may be mined in the future and withdraw water from stream alluvium, one in Steven's Gulch (used by CWI) and the other to the north of the mine area east of the Morrell Cow Camp and near the Terror Creek drainage CNW 1!2 NW 1/4, Section 6, T13S, R91W). This latter well is located outside the area to be mined, and in an area where the overburden depth is is excess of .1,500 feet. The Steven`s Gulch well field, however, is within the area which may be undermined over the life of the mine and has an overburden depth of 660 feet. The applicant will continue to provide a yearly inflow study under a stipulation to the State permit. • 5