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<br />29 <br />1 <br />• shale and siltstone-sandstone together with the thicknesses of these two <br />t types of strata. The geometric mean permeability of the 23 values of <br />vertical permeability measured in the Raton formation (Table 1) is 0.39 <br />milli-darcys. This converts to a vertical hydraulic conductivity to water <br />at 63° F of 0.001 ft/d. and applies to the sandstone-siltstone strata. The <br />corresponding value far the shale is 0.00013 ft/d. (Table 1). The thickness <br />{ of shale and sandstone-siltstone encountered in various drill holes ranges <br />( widely. However, examination of several geophysical and lithologic logs <br />suggests that the first 225 ft. above the coal contains approximately 50 <br />percent shale and 50 percent siltstone-sandstone. Thus, the effective mean <br />conductivity to water flowing normal to the bedding planes is (Mc:~horter and <br />~ Sunada, 1977 r. ~• <br />f K L 225 = 2.3x10-4 ft/d. <br />1 a L1 + L2 112 + 113 <br />0.001 0.00013 <br />Kl K2 <br />The vertical hydraulic conductivity computed in this manner is observed to <br />• agree very closely with that obtained using the drawdown in LA 218A. <br />1 The current Maxwell Mine extends over an area of approximately <br />3.4xlO6ft2. Using a 65 percent extraction factor, the exposed roof area is <br />estimated to be 2.2x106ft2. The current perimeter of the workings forms a <br />rectangle with a perimeter length of 8700 ft. Eventually, the Maxwell Mine <br />may encompass 6 sq, mi. with an exposed roof area of 1.1x108ft2 and a peri- <br />meter length of 4.6x104ft. <br />i The calculations of mine inflow are made for three different cases, <br />differentiated by the va lue of coal transmissivity used. The model para- <br />meters for each case are summarized in Table 3. The transmissivity for <br />Case III is the mean of the two measured values. <br />i <br />• <br />I <br />