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Seneca 11 Mine June 2014 <br />SL -6 Phase 111 Bond Release Request <br />Appendix 7 -6e, Sediment Pond 008 Permanent Impoundment Demonstration. There are no <br />other permanent impoundments with the Seneca II permit area. <br />Hydrology <br />Basic Standards Interim Narrative Standard for Ground Water (CWIQCC Regulation 41.5(C)(6)). <br />The Seneca II Mine Permit alluvial ground water point of compliance ( GWPOC) is Well SFAL72 <br />(aka, Twentymile Coal Company Well 008- AU -3), which is located in the Fish Creek alluvium <br />less than one mile downstream of the Bond Creek ( NPDES Pond 008 basin) confluence. It is <br />approximately four miles downstream of the Seneca permit boundary. This GWPOC was <br />established in Technical Revision 47 (TR -47), approved in 2009, and is located in Attachment 7- <br />3, Tab 7 of the Seneca II Mine permit document. <br />Table 1 in Attachment E provides the alluvial GWPOC water quality standards established in <br />TR -47. Table 2 (Attachment E) provides a statistical summary of the water quality for the past <br />three years (2011 to 2013) collected at Well SFAL72. The only standard that was exceeded was <br />iron (0.35 mg /l, dissolved) with values ranging between 2.88 and 5.16 mg /l. However, total <br />recoverable iron values for the last three years upstream at all spoils springs (SSSPG9 at Seneca; <br />and SSSPGI and SSSPG2 at the adjacent Peabody Sage Creek Mine (PSCM)) were less than 0.71 <br />mg /l; and NPDES discharges (NPDES8 at Seneca and NPDES4 at the PSCM) were less than <br />0.32 mg /l. Therefore, the high iron values observed at Well SFAL72 are not likely to be the result <br />of discharges from the Seneca II Mine or the PSCM. The high levels of iron displayed at Well <br />SFAL72 are more likely the result of naturally occurring organic matter and plant debris present <br />in the alluvium (Hem, 1989, pg. 77) at this particular location. The GWPOC standard for iron in <br />the adjacent Grassy Creek alluvium, established in TR -47, is 14.1 mg /l. This indicates that for the <br />region, high ambient levels of iron are present. <br />TR -47 also addressed bedrock aquifers. Bedrock GWPOC wells were deemed to be not <br />necessary, based on the absence of the potential for the mine to negatively impact the quality of <br />bedrock ground water. This is due to the low hydraulic conductivities of the bedrock units. <br />Other factors, including attenuation and dilution, further limit water quality impacts to a close <br />down gradient proximity. Furthermore, confining layers isolate mine- impacted water bearing <br />units from the nearest usable aquifer, the Trout Creek Sandstone, which lies approximately 300 <br />26 <br />