Laserfiche WebLink
Technical Memo  Page 6 August 16, 2024 <br />Peabody – CDPS Permit Supplement <br />For states such as Idaho and Mississippi that already have EPA-approved site-specific and/or <br />state-based criteria for multiple waterbodies, there is a continued emphasis on fish-tissue <br />based elements superseding water-column based elements if the waterbody is at steady-state. <br />The state of Minnesota also adopted a site-specific selenium criterion using the EPA’s tissue <br />elements, but adopted less stringent water column elements that appropriately reflected the <br />biogeochemical factors resulting in selenium bioaccumulation. <br />For states such as Kentucky, water column values can be utilized as a trigger to necessitate <br />fish tissue monitoring. However, if the water column values trigger this monitoring <br />requirement but fish tissues are not in exceedance, then there is no exceedance. This further <br />reiterates the EPA’s intent that fish tissue elements supersede water column elements. <br />3.2 Use of Fish Tissues for Conducting RP Analysis for Discharge Permits <br />In EPA 2024c, use of tissue elements rather than water column elements to determine RP is <br />discussed, with guidance included related to the four criterion elements that can be used for <br />deriving water quality based effluent limits (WQBELs) pursuant to 40 CFR 122.44(d)(1). <br />Based on EPA 2024c, if a state or authorized tribe believes that the EPA's national CWA <br />section 304(a) recommended selenium tissue criterion elements are not appropriate for a <br />waterbody capable of supporting fish, it can develop a site-specific value for a water column <br />element using the bioaccumulation factor (BAF) or mechanistic biodynamic model (MBM) <br />approach. That said, the recommended primacy of the fish tissue criterion elements set <br />forward in the 2016 Criterion allows National Pollutant Discharge Elimination System <br />(NPDES) permitting authorities to develop innovative NPDES implementation guidance (i.e., <br />state or tribal implementation procedures) for the expression of WQBELs based solely on <br />fish tissue criterion elements. Therefore, the WQBEL could be expressed in milligrams per <br />kilogram dry weight based on fish tissue selenium criterion elements (i.e., whole-body of 8.5 <br />mg/kg dw or egg/ovary of 15.1 mg/kg dw). For this reason, in some cases, NPDES <br />permitting authorities could consider incorporating a permit reopener clause with respect to <br />the selenium WQBEL. If fish tissue data reported during the permit cycle or information <br />about new or increasing selenium inputs indicate that the receiving stream fish tissue <br />concentrations are not at steady-state, this could constitute cause for permit modification. <br />This guidance suggests that the fish tissue WQBELs could be derived at permit issuance with <br />the caveat that the fish tissue limits are applicable unless there is new information that <br />precludes fish tissue from being assumed to be in steady-state (e.g., increasing fish tissue <br />concentrations, new or increasing selenium inputs). <br />Furthermore, EPA states that if the NPDES permitting authority has site-specific, steady- <br />state fish tissue data that were collected under and met appropriate quality-assurance <br />procedures, those data may be used directly to assess RP.