2001-12-11_PERMIT FILE - C1981010A (4)

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COYPO'J„IHMI ~~ 5.0 DISCUSSION OF F,°_SULTS In the southern area of the mine (Well Site GZ), water levels decrease with increasing depth. Although ground-water movement is primarily along bedding planes, this water level relationship indicates that some docancaard, cross-bedding flow is present. Tdater moving within the Twenty Mile Sandstone loses much Less pressure head than water moving the same distance ~a within the less-permeable Upper Williams Fork Formation. Con- sequently, as ground water moves northward and docan-dip, the pressure relationship between the Twenty :Ii le Sandstone and -~ the Upper Williars Fork is reversed. In the more northern parts of the mine, water levels still decrease with increasing depth within the shallower sections of the Upper Williams Fork. Hoca- ever, the Tcaenty Mile Sandstone becomes a relatively high pres- `) ~ sure artesian aquifer. Ground caater sri11 moves primarily along bedding planes. North of the point of reversal of the pressure relationship, some upward, cross-bedding flow takes place within the Twenty Mile Sandstone and the Lowermost section of the Upper Williams Fork. Figure 5-1 displays a generalized view of the `~ probable configuration of equipotential lines and flora directions along a dip (north-south) section of the Trapper Mine. In the Big Bottom area, near the Yampa River, the ground-water level relationships are similar to the relation- ships in the northern mine area. That is, water levels decrease with increasing depth in the shallower strata, and then increase I~ to relatively high pressure conditions in deeper strata. A1- though.the cause of high pressures within the deeper strata is unknown, the Twenty Mile Sandstone or sandstone beds of the Upper Willimas Fork are likely sources of relatively high pres- sures. :~. ~ 5-1