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<br />1 <br /> <br /> <br />i <br />J <br />Lam' <br /> <br />f <br /> <br /> <br /> <br /> <br /> <br />1 <br />1 <br />district seems to confirm this assumption. The inflow from the <br />surface streams into the Mains is anticipated to be very low, <br />because no subsidence fractures will be developed by driving six <br />entries at 80 foot centers. Darcy's Law was applied to calculate <br />the water inflow into the entries driven underneath the two <br />surface streams: <br />Q = (h/a)RhA <br />where: Q =water inflow into the mine; <br />h = hydraulic head above the mine; <br />a =thickness of low permeable strata above <br />the mine; <br />Rh = vertical hydraulic conductivity of the <br />strata above the mine; <br />A =area of entries underneath the streams. <br />The geometric and geologic characteristics of the study <br />areas were taken from geologic cross-sections and logs of <br />boreholes (GR-77-7, DH-59, and DH-26). However, the value of the <br />vertical permeability of the low permeable shales above the <br />entries was assumed using a range of values (K = 2.8 x 10-4 - 1.4 <br />x 10-3 ft/day) from a table published by Brown, et. al,(1972). <br />The resulting estimate of water seepage into the West Mains <br />is the following: <br />o Underneath Stevens Gulch, Q = 5.2 gpm; <br />o Underneath East Roatcap Creek, Q = 1.3 gpm. <br />These values should, again, be considered conservative. <br />Development of continuous fractures above the mains through at <br />least 400 feet of overburden into the stream beds without effects <br />of subsidence is not probable. <br />Another potential for increased water inflow into the mine <br />is through the seepage in the coal in areas where the mined coal <br />seam is subcropping into the saturated stream bed deposits. This <br />will occur on the West Mains underneath Stevens Gulch and during <br />the development of the South-west Panels near the seam outcrop <br />underneath East Roatcap Creek. <br />Two different methods were used to calculate the seepage <br />through the coal seam in a combination of confined and unconfined <br />flow and a constant head source. <br />One method provided by McWhorter (1981) is expressed in the <br />following equation: <br />where: Q = flow through <br />exposed coal; <br />T = transmissivity <br />G <br />the length of the <br />of the coal; <br />111'UHI6 Y.F.I I I:I LAti1~LT \NTti <br />