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Fish Creek by (SubTer[a, Inc., 1999) is -0.17 to 0.17. This change of slope would not have any significant long- <br />. term impact on the stream flow and/or water quality. The meandering character of Fish Creek, cutting through <br />fine-grained sediments, would facilitate the fast-healing process of any temporary changes in the streambed <br />gradient. <br />It should be noted that coal is mined beneath significant bodies of surface water, including the sea, in many nations <br />(Great Britain, Canada, Australia, Japan, Chile, and Turkey). The minimum cover to seabed for total extraction <br />(longwall mining) ranges in various nations from 60 meters (197 feet) in Japan to 213.4 meters (700 feet) in Nova <br />Scotia. The guidelines recommended by the U.S. Bureau of Mines (Wardell, 1976) state that, "any single seam of <br />coal beneath or in the vicinity of any body of surface water maybe totally extracted, whether by longwall mining or <br />by pillaz drawing, provided that for each I foot thickness of coal seam extracted a thickness of 60 feet of solid strata <br />cover exists between the proposed workings and the bed of the body of surface water." This shows that at the <br />Foidel Creek Mine the longwall operation extracting 9.5 feet of coal would be safe 570 feet under a seabed. <br />The conclusion of our studies of subsidence and the potential impacts of subsidence of the Fish and Foidel Creek <br />alluviums is that the mining in panels 12 Right through 16 Right will not have any detrimental impacts on the water <br />quantity and quality. <br />Additionally, Twentymile Coal Company conducted an exhaustive monitoring program on a selected segment of <br />Fish Creek and its alluvial valley floor during the period of 1992 through 1994. The program was required as a <br />result of the Division approving Twentymile's request to undermine and subside this selected section of Fish Creek <br />and its alluvial valley floor. The results of the program are summarized in Exhibit 7j, Fish Creek Alluvial Valley <br />Floor Study. The results have been submitted previously to the Division in the semi-annual subsidence reports for <br />1993 and 1994. <br />• The study also included the installation of eleven monitoring wells, two of which were completed in a shallow <br />bedrock unit and the remainder in the Fish Creek alluvium. The monitoring of these wells showed that the shallow <br />bedrock well experienced localized dewatering aver the mine workings, which had been predicted, and the <br />subsequent recovery to approximate premining conditions. The alluvial wells did not experience any significant <br />dewatering due to the undermining and subsiding of the valley floor. These data are summarized in Exhibit 7j. The <br />water quality in the wells was not significantly impacted by the subsidence that occurred in the study area. There <br />was a slight increase in some of the metals due to mobilization within the alluvium, but the concentrations were not <br />high enough to cause water quality problems. <br />Ground Water Inflow into the Mine <br />The ground water inflow into the proposed mine will originate mainly from the Wadge Coal Overburden Composed <br />of shales, siltstones, and sandstones. The average thickness of the Wadge Coal Overburden water-bearing strata is <br />about 75 feet. Hydrologic parameters of this strata were tested in 7 wells ('T'able 63A, Bedrock Hydraulic <br />Characteristics). <br />Analytical methods were used to calculate future ground water inflow from the Wadge Overburden strata. Two <br />types of inflows have been observed in the mine: 1) normal inflows from the Wadge Overburden and 2) localized <br />inflows from a fracture zone. The method for evaluating the normal flows was calibrated against past measured <br />inflows. The future inflows were then calculated using the calibrated model. The model was based upon the non- <br />leaky artesian formula ("Ilreis, 1935 and image well theory (Ferris, 1959 and Walton, 1962). The inflows from the <br />fracture zone were modeled using a constant drawdown analytical model (Jacob & Lohman, 1952). <br />For the analytical model, the Wadge Overburden was assumed to be really extensive except for recharge boundaries <br />on the north and east boundaries of the reclaimed Eckman Park Mine 1 (Figure X1). Since the spoils in the <br />.reclaimed surface mine lie against the Wadge Overburden and are of much higher transmissivity, they will act as <br />recharge boundaries. The mined area at any time (t) was assumed to be a well (W) with a radius (ro,;,,~) of a circle <br />APPROVED JUN 2 8 2000 <br />PR 99-OS 2.05-171.10 8/27/99 <br />