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M <br />Brown <br />Page 2 <br />August 24, 1999 <br />1998 AHR? Are concentrations for these parameters significantly higher than corresponding <br />baseline levels, and does the overall trend indicate increasing or decreasing concentrations for <br />these constituents? <br />3. In Table 9, SCC presents surface water agricultural standards from various references. In <br />our AHR review letter to SCC dated October 15, 1998, the Division recommended using the <br />Basic Standards and Methodologies for Surface Water for comparison with surface water <br />samples from the Seneca II-W Mine. Upon review of these standards and the corresponding <br />Classifications and Numeric Standards for the Upper Colorado River Basin, it is the Division's <br />understanding [hat [here are no metals standards for Segment l2 of the Yampa River Sub-basin. <br />This was also verified in Section III of SCC's Colorado Discharge Permit System permit. It is <br />commendable that SCC has attempted to identify applicable water quality standards for <br />comparison with analytical results and for the sake of discussion. However, please check the <br />referenced metals standards and other parameters in Table 9 for accuracy and applicability. It <br />may be appropriate to rename Table 9 as "Use-Suitability Standards". <br />4. Information presented in the 1998 AHR indicates that predictions for Hubberson Gulch <br />alluvium at Well WHAL7-2 have been exceeded, when comparing 1998 average TDS values to <br />predicted TDS values. Please provide an explanation for this exceedance of the PHC prediction. <br />5. For Well WOV 17 in the Wadge overburden, the predicted TDS concentration of 4295 <br />mg/1 has been significantly exceeded by an observed 1998 value of 8860 mg/l. The Division <br />notes that Well WOV 17 exhibited a premining value of 8043 mg/1, and the predicted value <br />(4295) was predicated on a premining value of 4072 mg/I. However, the original PHC prediction <br />estimated a 5.5% TDS increase in the overburden below the center pit. The observed 1998 TDS <br />concentration is an increase of approximately 9.2 % over the baseline value for Well WOV l7, <br />which appears to be an exceedance of the estimated 5.5% TDS increase. Please provide any <br />available information on the source of the high initial baseline TDS levels at this well location, <br />and provide an explanation for [he apparent exceedance of the PHC prediction. <br />6. With the exception of surface water site SW-S2W-FG4, observed 1998 TDS values for <br />surface water locations were all below the predicted TDS concentrations presented in the PHC. <br />The predicted value for TDS at site SW-S2W-FG4 on Sage Creek is 464 mg/l. The observed <br />1998 value was 655 mg/I. Please provide any available information on the source of the elevated <br />TDS level, and provide an explanation for the exceedance of the PHC prediction. <br />If you have any questions concerning my review of the 1998 AHR, please let me know. <br />m:\coal\mpbls2w98ahr <br />