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/. Quantitative lmpactr of Mining . <br />Waste, Water and Land (WWL) (1980) estimated the maximum inflows to the Maxwell (Golden <br />Eagle) Mine from roof and floor faces of the coal to be 120 gpm and 73 gpm respectively, <br />totalling 193 gpm. This estimate was based on room and pillar mining of a mine with an areal <br />extent of 6 square miles (1.7 x 10g ftZ) and a perimeter of 4.6 x 10° ft. The mine plan currently <br />includes a substantial amount of longwall mining, an areal extent of 3.99 x 10' 1tZ, and a <br />perimeter of 3.5 x 10° ft. The acreage is 20% of the projected build-out and the perireter is <br />77%a of the projected perimeter. This corresponds to an equivalent WWL worst case projection <br />of 85 gpm'. In 1993, Basin observed inflows at the Golden Eagle Mine of 208 gpm of which <br />74 gpm came from the roof and floors, 34 gpm came from leaks associated with drill holes and <br />shafts, and 100 gpm came from a fault. WWL's projection comes within 20% of accurately <br />predicting inflows associated with non-fault inflows. <br />Greystone re-examined the original data, recent water level data and information acquired from <br />drilling to prepare a more accurate estimate of inflows (Table 3A). Greystone assumt:s that the <br />Maxwell, Blue and Red coal seams are the predominant sources of water, with minor <br />contributions from channel sands with localized areal extent. WWL assumed that 225 feet of <br />overburden above the coal was saturated based on water level data acquired from well LA-221. <br />This value was considered the effective thickness of the leaking overburden. Examination of <br />representative drill hole data acquired since 1980 suggests that the water level can vary from • <br />195.4' to 484.2' above the top of the Maxwell Coal (Table 3B), and in fact the original logging <br />of holes LA-218 and LA-221 in 1976, prior to installation of casing, found a height of water <br />table above the top of the coal of 303.7' and 321.9' respectively. (See Figure 5 for locations). <br />Consequently, the same drawdown analysis was performed using a range of saturated <br />thicknesses. <br />Coal seam trartsmissiviry values from the WWL Report ranged from 0.56 to 1.98 ftZ/day, with <br />an average coal transmissivity of 1.27 ftZ/day. These established the three cases (I, II, and III). <br />Coal permeability was set at 2.1 x 10~" ft/day. The effective saturated thickness of the leaking <br />overburden aquifer was set at 195.4 ft for Case A, and 484.3 ft for Case B. They leakance <br />values ranged from 722 ft to 2137 ft with discharge to the mine per foot of perimeter ranged <br />from 0.152 to 0.448 ftZ/day (Table 4). These results were then applied to the perimeter and <br />Calculated using a transmissivity of 1.98 ft=/day, a coal permeability of 2. I x 10" k/day, and an effective <br />thickness of the overburden (bJ of 225 ft. <br />B = (1.98 k=/day x 225 ft / .00021 k/day)''Z = 1465 ft <br />q = (1.98 ft=/day z 225 k) /1465 k = .304 k= /day <br />Inflow from the face = (.304 k=/ day x 35,000 ft)/1.92 ft'/day/gpm = 55 gpm <br />Inflow from the roof = (2.1 z 10'' k/day) x (2.8 x 10' k=)/ 1.92 ft'/day/gpm =30 gpm <br /> <br />9 <br />