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Rob Zuber <br />Page 3 <br />December 9, 2016 <br />The Division has found the following notable exceedances of water quality standards in the data <br />within the 2015 AHR (please also see general discussions for manganese, ammonia, and other <br />constituents in Comments on Surface Water Quality section): <br />• Selenium concentrations at NPDES 13 exceed the Agricultural Use standard as well as the <br />Segment Be standard for Sage Creek. <br />• Total recoverable iron concentrations at YSGF5 exceed the Segment 13i standard for <br />Upper Grassy Creek. <br />• A total recoverable iron concentration at YSG5 exceeds the Segment 13j standard for <br />Lower Grassy Creek. <br />• A selenium concentration at YSG5 exceeds the Segment 13j standard for Lower Grassy <br />Creek. <br />• Selenium at YSSPG3 exceeds the Agricultural Use standard as well as the Segment Be <br />standard for Sage Creek. <br />Peabody listed these exceedances in Tables 12, 14, 16, and 18 in the AHR and provided some <br />discussion. <br />COMMENTS ON SURFACE WATER QUALITY <br />The exceedances for selenium are not unexpected. High selenium concentrations related to the <br />Yoast Mine are the subject of ongoing concentrations between Peabody and the CDPHE. <br />Most of the standard exceedances for manganese do not appear to be problematic, as the soils at <br />Yoast are not acidic. (The CDPHE agricultural standard for manganese only applies when <br />irrigation water is applied to acidic soils.) <br />The high level of total recoverable iron in Grassy Creek down gradient of the mine (YSGF5 and <br />YSG5) is not considered a significant issue by the Division. SCC notes in the AHR (page 14) <br />that the majority of pre -mining iron levels in streams also exceeded this strict aquatic life <br />standard. <br />Ammonia Nitrogen criteria are dependent on temperature and pH as outlined in an EPA <br />publication (Aquatic Life Ambient Water Quality Criteria for Ammonia — Freshwater, April <br />2013). The Yoast data were compared to criteria in this document, and no exceedances were <br />identified. <br />Mercury detection limits are an order of magnitude greater than the CDPHE standard. However, <br />this was discussed in past AHR reviews, and the Division determined that there is no reasonable <br />potential for mercury standards to be exceeded below the Yoast Mine (per a CDPHE analysis). <br />