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<br />Michael G. AI[avilla <br />Seneca Coal Company <br />Pace 2 <br />August 13, 1999 <br />significantly higher than corresponding baseline levels, and does the overall trend indicate <br />increasing or decreasing concentrations for 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 Yoast 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 that there are no metals standards for Segment 12 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 in Table 9 for accuracy and applicability. It may be appropriate to <br />rename Table 9 as "Use-Suitability Standards". <br />4. Information presented in the 1998 AHR indicates that predictions for Upper Grassy Creek <br />alluvium and spoil and Annand Draw alluvium and spoil have been exceeded, when comparing <br />1998 average total dissolved solids (TDS) values to predicted TDS values. Please provide an <br />explanation for these exceedances of the PHC predictions. In particular, the Division notes that <br />for ground water samples from the Annand Draw alluvium (well YAAL14), average TDS values <br />for 1998 are significantly elevated above the baseline levels. Please provide any available <br />information on the source of the elevated TDS levels. <br />5. For the Sage Creek alluvium and spoil, the predicted TDS concentration is 798 mg/I. <br />Two wells YSAL3 and YSAL8 located within the Sage Creek alluvium, show,TDS values for <br />1997 and 1998 that exceed the predicted concentration of 798 mg/I. It also appears that the mean <br />baseline TDS value for each of these wells exceeds the predicted PHC value of 798 mg/1. Please <br />provide an explanation for the apparent exceedance of the predicted PHC value. Because it <br />appears that the baseline values exceed the predicted value, SCC may want to consider revising <br />the PHC modeling and discussion contained in the permit document for Sage Creek alluvium and <br />spoil. <br />6. The PHC predicted value for TDS at site YSGS on Grassy Creek is 1337 mg/l. The <br />average TDS value for 1998 was 1570 mg/I, which exceeds the PHC prediction. On page 8 of <br />the AHR, SCC states [hat TDS values are affected more by the Seneca II Mine than the Yoast <br />Mine at site YSGS. This is consistent with the data presented in the 1998 AHR for the Seneca II <br />Mine. TDS values presented for site SW-S2-2 for the Seneca II Mine (located on Grassy Creek <br />below the Seneca II Mine and above site YSGS) ranged from 1670 ma/I in June to 2430 mg/1 in <br />September. The predicted TDS values for SW-S2-2 are 1233 mg/I in June and 2341 mg/1 in <br />September. This is slightly higher than the predicted TDS values for site SW-S2-2 and likely <br />