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Mr. Tom Kaldenbach <br />October 19, 2000 <br />Page 2 <br />quantities of Lennox coal in the spoil material at the Spring Creek site probably result in larger <br />sulfate concentrations and enhanced weathering ofcarbonate minerals." <br />This suggests that at least initially, and for an undefined period, spoil pyrite content relates to and <br />influences water quality. Spoil bodies with lower pyrite concentrations can be expected to exhibit <br />better water quality. Other factors such as dilution and pH are influential as well and will, over the <br />long run, also play a significant role in determining the prevailing long-term water quality <br />characteristics. Positively trending sulfate accumulation patterns and corresponding increases in <br />TDS have been observed in the backfill wells established at Trapper, however, overall <br />concentrations to date vary widely from site to site as do the rates of increase. Trapper has revised <br />the PHC text to incorporate these factors into the discussion. <br />6.) This sentence has been revised to refer to average pyrite percentages and corresponding oxidation <br />time estimates derived from core sample values only. Again, pyrite estimates derived from <br />regraded spoil samples are no longer being utilized. <br />7.) The "worst case scenario" being referenced is one in which the entire mass of pyrite available in <br />the spoil body is oxidized. Mechanisms such as piping might physically reduce the spoil mass in <br />contact with groundwater and thereby limit complete pyrite oxidation. Other factors, such as <br />minimal infiltration combined with microbial activity, might also result in oxygen depletion from <br />the system effectively reducing pyrite oxidation. The PHC text has been revised to better define <br />this term. <br />8.) The text has been revised to explain the conversion from percent pyritic sulfur to percent pyrite. <br />9.) The text has been revised to explain this calculation in more detail per your request. <br />l0.) Trapper has considered the Division's suggestion that Third White Sandstone inflows might be <br />diluting the spoil water in the GF-5 area and improving the appazent water quality exhibited at this <br />site. The hydraulic gradient in the Third White Sandstone in this area generally trends towards the <br />northwest. For water to be flowing into the pit from the Third White, a significant departure from <br />the prevailing direction of groundwater flow would be required. The gradient to the northwest that <br />hes historically been depicted in the Third White in this area exceeds the gradient that exists <br />between the potentiometric surfaces at wells GB-2 and GF-5. This infers the prevailing direction <br />of groundwater flow would still be away from A pit in this area. <br />Trapper has also examined the water quality exhibited in well GB-2 and compared it to samples <br />from well GF-5. The sulfate content at well GB-2 is typically higher that the sulfate content <br />measured at GF-5. If waters from the aquifer monitored by well GB-2 (Third White) were diluting <br />presumably sulfate rich waters from the spoil aquifer monitored at well GF-5, the opposite <br />relationship would prevail (i.e. higher sulfate values at well GF-5). It would seem that a <br />significant quantity of high quality inflow water would be necessary to dilute "typical" spoil water <br />as characterized in the USGS study to the quality levels shown in well GF-5. Trapper notes that <br />the recharge zones of the Third White Sandstone have for the most part been mined throughout <br />