2013-09-24_REVISION - C1981014 - Laserfiche WebLink

Home Browse Search

George Patterson September 19, 2013 Page 3 reasonable estimate of the inflow for the 1 North mine area. The 14- acre -foot inflow estimate is based on the observations provided by onsite personnel who were responsible for the dewatering of the mine and aware of discharges of dewatering water within the mine. The estimate is based on flow information for periods when water was not discharged to the 1 North area (pre -1987 and 1995) and the understanding that inflow and dewatering rates have decreased since areas have been mined. This is consistent with general ground water movement especially in the low permeable material surrounding the mine. When a coal seam is first mined, mine inflow is relatively high as the water in the coal seam drains into the mine, but as the water in the coal seam drains, the inflow rates decreases with time. Accordingly, the 14- acre -foot per year inflow rate was based on information from 1985, 1986 and 1995 and the general understanding that inflow rates are decreasing and was projected from the available information to estimate the inflow rate in the year 2000 for the start of our analysis. Conceptual Models As indicated in the July 19, 2013 evaluation prepared by our office, three conceptual models were prepared to analyze the timing of mine refilling to the elevation of the bottom of the MW -NW well casing and the elevation of the partial obstruction in the MW -NW well. Janet Binns has requested clarification of how the 3 North mining area was considered in the conceptual models and the potential connection of this area with the rest of the mine. The first of the three conceptual models considered the entire mine to be hydrogeologically connected and that the mine refills as a single hydrogeologic unit. In this conceptual model, the 3 North mining area was simply considered part of the entire mine volume which refills with the rest of the mine as water levels within the mine rose. Accordingly, the mine refilling timing calculation for Conceptual Model No. 1 included the 3 North area with the entire mine area. The second of the three conceptual models considered the filling the 1 North, I '/s North and 2 North mining areas as single hydrogeologic unit. This model assumed that the seals in the 1 North, 1 %2 North and 2 North areas hold perfectly to allow water entering these mining areas to remain sequestered. Accordingly, the mine refilling timing calculation for Conceptual Model No. 2 did not include the 3 North mining area because it was not included in the areas sequestered by the installed seals. The third of the three conceptual models considered the filling of the 1 North, 1 '/z North, 2 North and 3 North mine areas as a single hydrogeologic unit separate from the West Mains and the rest of the mine. This model assumes that the seals in the North areas do not restrict the localized flow of water, but that the North areas are hydrogeologically separated from the West Mains and the rest of the mine workings. Accordingly, the mine refilling timing calculation for Conceptual Model No. 3 included the 3 North mine area.