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<br />'! <br />Mr. Michael R. Neumann October 20, 1998 <br />[vlonigomzry Watson Americas. Inc. Page ~ <br />3. H-G Mine's long-term potential for further degradation of surface water <br />a) The USGS conducted a geochemical mass-balance study of the nearby Seneca II Coal Mine. The <br />results of [he study are reported in USGS Water-Resources Investigations Report 92-4187. The <br />study concluded that enough minerals are present in the reclaimed spoil to maintain TDS <br />concentrations in the spoil aquifer in the 3,000 - 4,000 mg/l range for hundreds to thousands of <br />years. Spoil spring TDS concentrations above 4,000 mg/1 have been reported at the Edna Mine <br />approximately 10 miles east. <br />b) Hayden Gulch Mine's post-mining water quality data from spoil springs and surface water spans <br />10 years. This time period is only a brief snapshot in time if the mine's impact to water quality <br />will span hundreds or thousands of years as predicted for the Seneca II Mine. Over such a long <br />period of time, the spoil aquifer at Hayden Gulch Mine would be expected to geochemically <br />evolve as minerals are dissolved from the spoils and eventually the source minerals are <br />exhausted. <br />c) It seems possible that TDS concentrations from Hayden Gulch Mine's spoil springs could <br />eventually exceed today's levels. If TDS from Hayden Gulch's lazgest spoil spring, RSP-4, <br />reaches 5,000 mg/l, the water will be unsuitable for livestock and wildlife watering. (The 5,000 <br />mg/1 threshold is based on Wyoming DEQ's 5,000 mg/1 use-suitability standard for livestock <br />watering that is referenced in the bond release submittal's hydrologic impact analysis.) RSP-4 <br />discharges directly into the streambed of Hayden Gulch. <br />d) The potential for further degradation of surface water quality by RSP-4 warrants additional <br />analysis; therefore, the Division requests that you submit an evaluation of that potential and the <br />projected impacts. The evaluation should include a prediction of RSP-4's maximum TDS level <br />and discharge. <br />If you have any questions, please call me. <br />Sincerely, <br />T~ I<..P~...e.~ <br />Tom Kaldenbach <br />Environmental Protection Specialist <br />cc: David Berry, CDMG <br />