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Technical Memo  Page 8 August 16, 2024 <br />Peabody – CDPS Permit Supplement <br />determine compliance with the WQBEL. Compliance with the WQBEL should be assessed <br />for each sampling event. <br />4.RP Determination for Peabody Drainages <br />Conditions for the drainages downstream of the outfalls at the Seneca Mine Complex have <br />been maintained throughout the period of study, in that no new inputs of selenium have been <br />added to these drainages over the course of study. Therefore, steady-state conditions have <br />been maintained for over 10 years (2012 – 2024). As shown in Table A-1, fish tissue <br />concentrations across multiple sampling events for Bond and Cow Camp creeks demonstrate <br />that fish tissue concentrations are at steady-state. <br />•For example, mean selenium concentrations for Creek Chub from sites in Bond Creek <br />range from 2.15 to 4.23 mg/kg dw, with White Sucker ranging from 2.20 to 3.21 <br />mg/kg dw which characterizes whole body fish tissue samples collected across 10 <br />years of data collection, 2012 - 2024. <br />•Additionally, mean tissues by species for those collected in 2024 were maintained <br />within the range of 2012 – 2024. <br />The fish tissue elements supersede water column elements in the 2016 Criterion when fish <br />tissues are at steady-state; this concept should, therefore, also be prioritized in determination <br />of RP as well as impairment/attainment status. This approach has been utilized in other states <br />such as the approach proposed and approved by EPA Region 4 and Mississippi Department <br />of Environmental Quality (MDEQ) for the Black River Basin (Little and Middle Bywy <br />creeks, and Big Bywy Ditch) in which site-specific application of fish tissues were used to <br />show absence of RP (i.e., mean of whole-body tissues sampled were below the EPA’s whole- <br />body criterion of 8.5 mg/kg dw). In this case, absence of RP resulted in the removal of <br />numeric selenium limits from the discharge permit (MDEQ 2023). <br />For Bond and Cow Camp creeks there have been no exceedances of the 8.5 mg/kg dw <br />criterion for whole-body fish tissues over the course of the study from 2012 - 2024. <br />Therefore, there should be no risk of reproductive effects on the fish populations in these <br />streams. As invertebrate populations are less sensitive to the effects of selenium than fish <br />populations are, there is therefore no risk to aquatic life. The information presented above <br />suggests that if a waterbody is in steady-state and mean fish tissues by species are below the <br />federal selenium whole-body criterion of 8.5 mg/kg dw, it should be determined that there is <br />no RP, resulting in removal of numeric selenium limits from the discharge permit.