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mine. Unfortunately the elevation below which confined ground water was en- <br /> countered is not known. <br /> A large portion of the permit area has been mined previously. The <br /> ground water conditions in the mined areas provide a valid analog of that which can <br /> be expected to exist in the post mining phase on presently undisturbed areas. Mining <br /> has disrupted the natural sequence of strata down to the coal seam and replaced the <br /> overburden with spoil. One consequence of this disruption is to provide improved <br /> vertical continuity. Deep percolation from precipitation moves downward until the <br /> relatively impervious contact between the spoil and the underburden is encountered. <br /> Water perched on this contact moves downdip and forms a small water table aquifer <br /> against the now buried highwall of the boxcut near the foot of the slope. Numerous <br /> springs are in evidence as a result. Exhibit 2.5-21 shows the location and qualitative <br /> indication of discharge of springs inventoried within the permit boundary. Most of <br /> the springs are located in or adjacent to areas that have been mined. Further <br /> discussions of the significance of the springs relative to their volumetric and salt ~ <br /> load contributions to Trout Creek are presented in Sections 2.5.2.4 and 2.5.2.6. <br /> Hydraulic Coefficients and Well Productivity - A number of aquifer tests <br /> have been performed within or immediately adjacent to the permit boundary. <br /> D'Appolonia (1977) reported the results of several tests in the vicinity of West Ridge <br /> on the south end of the study area. Watec (1978) conducted tests at the locations <br /> of wells GMC I and GMC S on the west side of Trout Creek. As part of this study, <br /> D'Appononia's well PM-7 at the foot of West Ridge was retested and tests were <br /> performed at wells 05-03-0005, IC, 05-01-0010, 05-01-0004. Data from the tests <br /> conducted by WWLL are tabulated in the section entitled, "Compilation of Field <br /> Data." Table 2.5-13 contains a summary of the hydraulic coefficients for the water <br /> bearing strata encountered. <br /> Aquifer tests performed by D'Appolonia and WWLL were all single hole tests. <br /> Watec (1978) attempted aquifer tests utilizing observation wells. However, the <br /> transmissivity of the materials tested is very small and Watec experienced difficulty <br /> keeping the well bore from dewatering. Also well-bore storage plays an important <br /> role in observed response in such tests and the multi-well tests were largely <br /> unsuccessful. D'Appolonia tests were conducted by pumping the well at a constant <br /> rate for a period, the duration of which varied from test to test, but was often about <br /> one hour. The drawdown during the recovery period following the cessation of <br /> pumping was measured and The Hvorslev (1951) method was used to derive estimates <br /> of transmissivity from the recovery data. The Hvorslev method utilized by <br />Revised 7-81 2.5-50 <br />