Environmental Declaration WPCP 20240409

Home

January 31, 2024 Risk -Based Evaluation for Reuse of Stockpile Material for the Proposed Treatment Wetland Project— City of San Leandro Water Pollution Control Plant Therefore, metals in the untreated stockpile soil and sludge are unlikely to leach to groundwater, and by extension, also unlikely to reach the tidal slough, and the potential exposure pathway for special -status fish (and other marine life) in the tidal slough is therefore considered incomplete. Human Health Evaluation Based upon reasonably anticipated future use of the Project site, there will be no complete human exposure pathways to COPCs in stockpiled soil and storage pond sludge following the construction of the proposed treatment wetland. The stockpiled soil and sludge will be covered by clean fill, an impermeable liner, and 12-18 inches of water. Workers could be exposed to COPCs in the stockpiled soil and sludge during construction. Potential routes of exposure to COPCs in stockpiled soil and sludge would include incidental ingestion and dermal contact. Potential routes of exposure to COPCs in stockpiled soil would also include inhalation of volatiles and airborne particulates. Cumulative cancer risk and noncancer HI for construction workers assumed to be exposed to COPC concentrations in stockpiled soil or sludge over the course of a 6-month construction project were calculated. Separate risk estimates were calculated for stockpiled soil and sludge using exposure concentrations calculated for each media. The exposure concentrations for each COPC were equal to maximum detected concentrations in each media, with the exception of benzo(a)pyrene, PCBs (total) and arsenic in stockpiled soil. The exposure concentrations for these three COPC in stockpiled soil were based upon UCLM2 because they were identified as chemicals that would contribute most to cumulative risk/HI. This approach (i.e., refining the exposure concentrations for only the chemicals contributing most to the cumulative risk) is efficient in that it avoids calculations that would not materially affect the cumulative cancer risk and/or HI estimates. This approach is also conservative, because it uses the maximum detected concentrations, rather than UCLM, for many chemicals. Table: Refined Exposure Concentrations — UCLM (Stockpiled Soil) Chem Chemical Group SVOCS Benzo(a)pyrene PCBs _ PCBs (total) METALS Arsenic Max Detect 95% UCLM (mg/kg) (mg/kg) 2.8 0.23 6.7 0.68 20 1 _ 7.1 Attachment B provides the input and output tables from ProUCL. The risk and HI estimates3 use high -end exposure factors recommended by CaIEPA Department of Toxic Substances Control (DTSC 2019a) and USEPA (1991, 2011, 2014) for estimating reasonable RME (where 2 The UCLM calculations were performed using ProUCL (Version 5.2), including the Kaplan -Meier method for datasets with non -detects. 3 These risk and HI estimates conservatively assume that the measured concentrations of all COPC are entirely site - related (e.g., metals concentrations are not associated naturally occurring levels). 11 20240131-Terraphase-San Leandro -Treat mentWetIand-Risk-TM-DRAFT.docx Page 7 of 10