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January 31, 2024 <br />Risk-Based Evaluation for Reuse of Stockpile Material for the Proposed Treatment <br />Wetland Project – City of San Leandro Water Pollution Control Plant <br /> <br /> 20240131-Terraphase-SanLeandro-TreatmentWetland-Risk-TM-DRAFT.docx Page 8 of 10 <br /> <br />available and appropriate) and COPC-specific toxicity values (CalEPA DTSC 2019b)4. The cumulative <br />cancer risk and noncancer HI were compared to the risk management goals of 1x10-6 and 1, respectively. <br />These risk management goals are used by CalEPA DTSC (2015, 2022a) and the California Office of <br />Environmental Health Hazard Assessment (OEHHA 2020) for determining whether risk management <br />action is warranted. <br />Tables 1a and 1b present the cumulative cancer risk and noncancer HI calculations, respectively, for <br />construction worker exposure to COPC in stockpiled soil. Tables 2a and 2b present the cumulative <br />cancer risk and noncancer HI calculations, respectively, for construction worker exposure to COPC in <br />sludge. As shown, the conservatively estimated cumulative cancer risk and noncancer HI for <br />construction worker exposure to COPC in both media are less than or equal to the risk management <br />goals. As a result, construction worker exposure to COPC in these media during the construction of the <br />proposed treatment wetland does not pose an unacceptable risk to human health. <br />Table: Cumulative Cancer Risk and Noncancer HI <br />for Construction Worker Exposure to COPC <br />Exposure Media Cumulative <br />Cancer Risk <br />Noncancer <br />HI <br />Stockpiled Soil 1x10-6 0.5 <br />Storage Pond Sludge 7x10-7 0.3 <br />Potential exposure of construction workers to lead in stockpiled soil and sludge is evaluated separately <br />from the assessment for other COPCs because CalEPA DTSC (2022b) evaluates the significance of lead <br />exposures using blood lead level as an index of exposure, rather than in terms of cancer risk or <br />noncancer HQ. CalEPA DTSC uses a soil screening level of 500 mg/kg to evaluate the potential <br />significance of occupational exposures to lead in industrial/commercial settings (CalEPA DTSC 2022b). <br />Exposure concentrations were calculated by estimating the UCLM lead concentrations in both media, <br />considering construction worker exposure to lead in the stockpiled soil and sludge during construction <br />of the treatment wetland. Because the Project may involve exposure to both media, an additional <br />exposure concentration for lead was calculated for the combined dataset. <br />Table: Refined Exposure Concentrations - UCLM (Lead) <br />Exposure Media Chemical Max Detect <br />(mg/kg) <br />95% UCLM <br />(mg/kg) <br />Stockpiled Soil Lead 3,100 420 <br />Storage Pond Sludge Lead 1,600 670 <br />Stockpiled Soil + Sludge Lead 3,100 440 <br />These exposure concentrations were compared to CalEPA DTSC’s soil screening level of 500 mg/kg. For <br />soil, the lead exposure concentration is less than this screening level indicating that construction worker <br /> <br />4 Consistent with CalEPA DTSC Regulation “Toxicity Criteria for Human Health Risk Assessment” (effective September <br />4, 2018) and USEPA's hierarchy of sources (USEPA 2003).