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Response: The text on or about page 2.04-47 in Section 2.04.7, Hydrology <br />Description has been revised to address the comparison of hydraulic conductivity <br />and transmissivity values from SCCC's wells to the values reported by Robson and <br />Stewart (1990), but not on a depth-specific basis. Comparison using Robson and <br />Stewart's slug and pump test data for wells drilled to depths similar to those of <br />SCCC's wells is not possible because Robson and Stewart's well and/or test <br />interval depths were not included in their tables. PSCM estimated the test interval <br />depths for the tests reported by Robson and Stewart by comparing Wadge coal <br />elevations and land surface elevations at the reported test well locations. The <br />comparisons showed that, except in one well, the tested wells were in areas where <br />the depths to the tested intervals were significantly shallower than those of the <br />SCCC tests summarized in Table 2.04.7-T2. The test locations provided by Robson <br />and Stewart were presented using section, township, range, and section format, <br />which can result in fair degree of error for the estimated depths especially in steeper <br />terrain. Because the comparisons indicate the intervals tested as reported by <br />Robson and Stewart were significantly more shallow, and the estimated depth for <br />the one well that may be comparable to the SCCC tests has some degree of <br />uncertainty associated with the location information, direct comparisons of values <br />reported by Robson and Stewart were not included on a depth-specific basis. The <br />revised materials are included in this PAP response package. <br />b) Please remove from the permit application Figure 2.04.7-F7.2 and its discussion. <br />This figure and its discussion provides data on the hydraulic properties of a <br />marine beach sandstone unit (the Twentymile Sandstone) which diverges from <br />the topic in this part of the permit application, the hydraulic properties of a mud- <br />rich deltaic/back-barrier stratigraphic sequence (the Wadge overburden, coal, <br />and underburden). The contrast in depositional histories between the beach <br />sandstone unit and the Wadge sequence would have created significant <br />differences in these two hydrostratigraphic units' diagenesis and mechanical <br />properties, and these differences would result in contrasting hydraulic properties. <br />Response: Figure 2.04.7-F7.2 and related discussion have been removed from the <br />text. However, SCCC points out Figure 2.04.7-F7.2 and the related discussion <br />provided data on the Wadge coal and its overburden and underburden, not the <br />Twentymile Sandstone, and were intended to illustrate the overlap of results from <br />slug testing and pump testing in the hydrostratigraphic units that will be affected by <br />the proposed mining. <br />c) Please revise Figure 2.04.7-F7.1 so that it compares only slug test data of SCCC <br />and Robson and Stewart (1990), rather than slug test and permeameter data. The <br />Division does not consider comparison of data from well slug tests and <br />permeameter plugs from the lower member of the Williams Fork to be a valid <br />comparison because of the small volume of permeameter plugs compared to the <br />volume of rock tested in slug tests. Also, revise accordingly all other references <br />or uses of the data in Figure 2.04.7-F7.1 elsewhere in the permit application. <br />3