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<br />The text on Page 7-311 has been revised to make reference to <br />Exhibit 7-2B. <br />11. CDMG has noted that TDS (total dissolved solids) measurements <br />at monitoring Well 69-A are higher than those at Well 46-A. <br />The mean TDS value at 69-A (3378 mg/1) is approximately 35 <br />percent higher than the average at 46-A (2486 mg/1) for the <br />period of time that Well 69-A has been monitored (October 15, <br />1988 through September 30, 1991). While TDS values at 46-A <br />peaked on 10/27/86 (3498 mg/1) and have since been declining, <br />TDS levels at 69-A have been relatively stable. Well 69-A is <br />located about 6500 feet downgradient from 46-A, and it would <br />take over 100 years for a plume of high TDS alluvial water to <br />travel between these sites (using an average flow velocity of <br />0.13 ft/day for the Cow Camp Creek alluvium, calculated on <br />Page 7-271 of the permit). Therefore, the difference in TDS <br />levels at these two sites cannot be mining related and is most <br />likely attributable to natural conditions. Alluvial aquifers <br />are by nature heterogeneous, and there may be differences in <br />the mineral composition of the Cow Camp Creek alluvium at <br />these two sites. Also, alluvial water at 69-A has had a <br />longer residence time and therefore, more time to reach <br />geochemical equilibrium. The use of a digital geochemical <br />model would be required to further explain the difference in <br />TDS values at Wells 46-A and 69-A. <br />12. The comparison of surface water chemistry data to water use <br />standards in Section VIII.B.3.b. (starting on Page 7-317 of <br />the permit) was limited to data collected during the 1990 and <br />1991 water years for two reasons. First, a large volume of <br />surace water chemistry data has been collected at the Seneca <br />II Mine since 1986; a comparison of the entire post-1986 <br />database to water use standards would be cumbersome and time <br />consuming. The second, and perhaps most important reason for <br />limiting the comparison to 1990 and 1991 water year data, is <br />that water use standards used in the comparison were developed <br />by the Office of Surface Mining Reclamation and Enforcement in <br />1989. PWCC believes that is is inappropriate to compare water <br />use standards to water quality data collected prior to the <br />establishment of the standards. As discussed in Section <br />VIII.B.3.b., surface waters discharging from the Seneca II <br />Mine during water years 1990 and 1991 are, in general, quite <br />suitable for irrigation and/or livestock use, and PWCC is <br />confident that similar results would be found for water <br />quality data collected prior to the 1990 water year. <br />~13. The review of recently collected surface water quality data <br />has been expanded to examine in more detail future TDS values <br />at SW-52-2 and NPDES 003, starting on Page 7-324. <br />~4. The discussion of TDS concentrations at SW-S2-2 has been <br />expanded to address TDS levels during June, July, and August, <br />2 <br />