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Jerry H. Koblitz <br />November 22, 1999 <br />Page 2 <br />Williams and Clark suggest on page 56 of their report that oxidation of <br />pyrite in spoil is the primary reaction that produces increased TDS in <br />reclaimed spoil aquifer water. The sulfur released by pyrite oxidation <br />combines with oxygen to form sulfate in the spoil aquifer water, thus <br />increasing the concentration of total dissolved solids. TDS levels remain <br />high until the available mass of pyrite is exhausted. Williams and Clark <br />calculate that for spoil containing 1.0% pyrite (by weigh[) it takes 1,600 <br />years to oxidize all of the pyrite (their Table l8). <br />Like the Seneca II Mine, the dominant anion in spoil aquifer water at <br />Chimney Rock would probably be sulfate; therefore, the oxidation of <br />pyrite will be the main source of increased TDS in spoil aquifer water at <br />Chimney Rock. The pyritic sulfur content in Chimney Rock's spoil <br />averaged 0.36% (by weight) in six samples (Table 4, Section 2.04.6 of <br />permit application). Pyrite is 53% sulfur (by weight); therefore, the <br />0.36% pyritic sulfur content indicates that pyrite comprises roughly <br />0.53% of the mass of Chimney Rock's spoil. Applying Williams and <br />Clark's 300-year exhaustion time for 0.20% pyrite, Chimney Rock's <br />spoil can be expected to generate high sulfate concentrations for at least <br />600 years. <br />3. PHC, Exhibit 10, predicted increasing TDS in spoil aquifer water based on regression <br />analysis of data from well W-16. The analysis predicts an increasing trend for TDS with <br />1294 mg/1 being reached in year 2004, the last yeaz of the projection. By analogy with the <br />USGS's Seneca Mine study, TDS levels at Chimney Rock can be expected to reach a long- <br />term plateau of elevated levels, and then eventually subside to premining levels when the <br />pyrite mass in the spoil is exhausted. What is the predicted TDS concentration for that loop <br />term plateau? <br />4. PHC, Exhibit 10, page 9, first paragraph. The 30% effective porosity that is assumed in <br />the seepage velocity calculation appears unreasonably high compared to reported total <br />porosity values of less than ]0% in the Fruitland formation in the Ignacio Blanco gas field <br />(30 miles away), and less than 19% in other upper Cretaceous lagoonal sandstone/coal <br />sequences (e.g. Seneca II Mine, Routt County Colorado). The Division recognizes the high <br />30% value may have been used in the calculation merely to emphasize that even if the <br />seepage velocity is very slow (as 30% effective porosity calculates), then any discharge of <br />spoil aquifer water to the alluvium that is going to occur would have occurred by now. <br />Without actual field data, though, please use in the analysis an effective porosity value that is <br />reasonable for the fine-grained sandstones of the Fruitland formation, such as 15%. Also, if <br />the effective porosity value used is no[ based on local field data, then please state so in the <br />permit application and explain the reason for using the specific value. <br />