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which are separated by persistent rock partings. In the Jumbo Mountain area, the thickness of the B-Seam varies <br />• due to the local geology. On the north side, the B-Seam thins abruptly with portions of the upper two coal <br />benches being replaced by colluvium. Toward the south and west, the partings thicken and the B-Seam splits at <br />mid-seam. The minable portion of the B-Seam occurs at the top oT the seam where the upper benches combine <br />to attain a sufficient thickness. In the Jumbo Mountain Area, the B-Seam dips 4.6° to the northeast. <br />• <br />Primarily due to its relative hydraulic isolation, its low permeability, and limited recharge, the B-Seam in the Jumbo <br />Mountain area can not be considered a major regional or local aquifer. Hydrogeologically, the B-Seam is bounded <br />to the south and west by nearly vertical outcrops which limits recharge in these areas. To the north which is <br />downgradient topographically, alandslide has removed much of the B-Seam, and to the northeast, the B-Seam <br />subcrops in the valley of the North Fork. Discharge occurs along the subcrop tlowngradient tram the proposed <br />mining operation. <br />One well (JMB-121, located in the upper portion of Jumbo Mountain, has been completed in the B-Seam. The <br />total depth of this well was 627 Teet, and the static water level on July 21, 1994 was 619.77 Teet below the <br />ground surface. Based on monitoring wells in other mines in the area including West Elk, it is anticipated that the <br />water levels will follow the topography with a hydraulic gradient of approximately 0.05 ft/ft as illustrated in Figure <br />1 (a potentiometric map of the B-Seam). Further, there is no evidence that grountlwater levels are structurally <br />controlled. <br />Recharge to the B-Seam unit and deeper bedrock units is very limited and is estimated to be about 0.5 in/year or <br />about 3% of rainfall. This estimate is based using Dupuit-Forchheimer Theory, as follows: <br />KIh,T-h,zl = PLC <br />• <br />where: <br />h, =height of water table above impermeable layer at tap of hill (1100 ft) <br />h7 =height of water level in stream above impermeable layer j100 ft) <br />L =distance between top of hill and alluvial aquifer !11,900 Ttl <br />P =infiltration rate <br />K =hydraulic conductivity of strata (0.016 it/day (120 gpolf[) based on pumping test SG-11 <br />Hydraulic conductivity of the strata in the Jumbo Mountain Tract area is quite low and is expected to vary <br />between 0.033 ft/day and 0.00033 it/day. In calculating recharge for the system, the hydraulic conductivity of <br />strata was estimated to be 0.016 Tt/day. This conductivity value was based on a pumping test on SG-1 which <br />was completed in similar strata in the West Elk Mine area. <br />2 <br />