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<br />extent of each surface within and proximate to the permit <br />area. <br />Although some seasonal variability has been observed at select <br />wells, the effects of this variability on the depicted <br />potentiometric surfaces is minimal, limited to small changes <br />in local gradients. The following c~ilculations demonstrate <br />this point. Gradients were measured t~etween the wells listed <br />below based on the potentiometric surfaces depicted on <br />Exhibits 7-2 through 7-4. Again, the surfaces were <br />constructed using the overall arithmetic means of valid water <br />levels. A second set of gradients bet~reen the same wells were <br />calculated using only valid baseline water levels collected <br />during the spring season (March 15 to July 1). <br />Spring Season <br />Map Gradient Gradient <br />YOV27-YOV28 (Wa.dge Overburden) .1637 ft/ft .1613 ft/ft <br />YW26-YW28 (Wadge Coal) .1511 ft/ft .1523 ft/ft <br />YWU17-YWU30 (Wadge Underburden) .1310 ft/ft .1303 ft/ft <br />The gradients calculated above using spring season water <br />levels were :Tightly lower between t:he Wadge overburden and <br />underburden wells, and were slightly ktigher between the Wadge <br />coal wells. In no instance were the differences in gradients <br />(ft/ft) greater than .0024, which is a minimal difference. <br />~/~ 19. During the February 1, 1995 meeting between SCC and the CDMG, <br />the CDMG admitted the exhibits which show the potentiometric <br />surfaces were: temporarily misplaced, have been located, and do <br />not need to k~e provided. <br />~Q 20. SCC has revised the "Introduction" to the "Site-Specific <br />Hydrogeology" section of Tab 7 to provide more specific <br />identification of geologic units monitored at the Yoast Mine <br />and how these units compare stratigraphically with regional <br />stratigraphy and aquifers. <br />~~ 21. Pages 39, 41, 42, 43, 46, 47, 48, 50, 51, and 54 of Tab 7 have <br />been modified to explain the significance of 1 mg/1 in the <br />ground .water quality discussion. <br />22. Laboratory analytical techniques commonly used by contract <br />laboratories for trace metals occasionally require dilution of <br />the sample a:nalyte in order to obtain reliable measurements, <br />~ depending on the instrumentation and the presence of <br />additional m~atals and compounds in the sample. This dilution <br />process may result in an occasional report of a higher <br />detection limit if the analysis finds no detectable <br />concentration of the trace metal. <br />