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III IIIIIIIIIIIII III Doc Date:12H 1/ 02 01 • The operator has provided "worst case" calculations of the amount of depletion that might be suffered by the Williams Fork River through the contact of thA' Williams Fork alluvium and the subcropping "E" and "F" coals in which the Eagle No. 5 and No. 6 Mines are located, respectively. Inflow through the Middle sandstone subcrop was also included in the calculations. A total of 182 gpm inflow into the mines by this means was estimated. Since over 600 gpm is currently discharged into the Williams Fork and even larger amounts are permitted in anticipation of future mine expansion, there would be a net gain to the river from the active mining operation. There is potential for the largest streamflow depletion to occur after mining. After the underground coal mining activity has stopped, the mine workings and overlying and underlying depleted section will begin to fill and reestablish pre-mining water levels. During the period when the mine workings are filling and ground water levels in the affected aquifers are rebounding, the mine inflow waters will not be discharged to the surface and then to the rivers. Thus any depletions of surface water from stream/alluvial systems will not be augmented by mine water discharges and will continue until such time as an equilibrium is reestablished between the surface and ground water systems. The operator has estimated that the initial inflow rate will be approximately 1,500 gpm. This will decrease as the mine fills and the head differences are reduced between the mine and the various sources of the inflow. Using an average inflow rate of 750 gpm, the operator has calculated that the mine will take approximately 16 years to fill. As previously mentioned, the operator has furnished "worst case" calculations of the amount • of direct streamflow depletion resulting from inflow thru the subcrops of the coal seams being mined as well as the Middle sandstone. This figure was 182 gpm. As detailed in the Surface Water Section of this document, this depletion is insignificant to the Q-7-10 low flow of the Williams Fork River. During the active life of the mines, direct depletion of the quantity of water in the Trout Creek aquifer will occur as a result of pumping for mine and residential use. Empire Energy Corporation has two wells registered with the State Engineer that produce from the Trout Creek sandstone; these are the No. 5 Mine well and the Okie Plaza well. There is also a No. 5 A supplemental mine well located near the original mine well. The volume appropriated for the No. 5 Mine well is 4,0 acre feet/year. A total of 5.0 acre feet/ year is appropriated for the Okie Plaza well. After treatment, much of the water utilized from the No. 5 Mine well, is discharged into the Williams Fork River under NPDES permit. The Eagle No. 5 and No. 6 Mine workings may impact the quality of ground and surface water during mining following closure of the mines. Theeroof strata in the zone of caving, the floor strata, and the coal seams themselves will be sub,~ected to chemical weathering and leaching where in contact with mine inflow water. The chemical weathering and leaching will lead to ground water quality degradation. The degree of this degradation will depend on 1) the geochemistry of the affected strata; 2) the thickeness affected:strata in the zone of caving exposed to mine water; 3) the particle or fragment size distribution of caved overburden and coal strata; 4) the exposed surface areas of roof, floor, coal faces and coal pillars; 5) the geochemistry of the rock • dust used; 6 mining debris left in the mines; 7) the chemistry of back-stowed waste; and 8 the residency time of mine waters before discharging to the surface or to the overlying or underlying strata. -33-