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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 20240131-Terraphase-SanLeandro-TreatmentWetland-Risk-TM-DRAFT.docx Page 3 of 10 Additional Sludge Sampling In October of 2023, Terraphase collected 10 sludge samples from the central and eastern portions of the polishing pond. The samples were collected on a grid, with five samples each in the central portion and eastern portions of the polishing pond. No additional samples were collected from the western portion of the pond. The samples were collected using a plastic tube, which was lowered from the side of a raft. Depending on the substrate, approximately 6 and 12 inches of sludge was collected. Following sampler dewatering, each sludge sample was placed in a plastic tub, where it was manually homogenized using a stainless-steel trowel or similar tool. The samples were then placed in laboratory-provided jars. The jars were labeled and placed in a cooler for transport to the analytical laboratory, Enthalpy Analytical, under chain-of-custody procedures. Each of the samples was analyzed for: • Title 22 Metals [United States Environmental Protection Agency (USEPA) Method 6010] • Deionized-water-extracted (DI-WET) metals [USEPA Methods 1311 modified and 6010] • Total petroleum hydrocarbons [USEPA Method 8015] • Polychlorinated biphenyls (PCBs) [USEPA Method 8082] • Organochlorine pesticides [USEPA Method 8081] • Moisture content [ASTM D2216] Tables A-1 (stockpiled soil) and A-2 (storage pond sludge), which are provided in Attachment A, present the sampling results for each media. Each table provides a sample-by-sample comparison to the following potentially relevant generic screening levels: • Wetland Foundation Material Concentration Guidelines (SFBRWQCB 2000) • Environmental Screening Levels (ESLs; SFBRWQCB 2019) for the following scenarios: − Soil Direct Exposure [Construction Worker] − Soil Leaching to Groundwater [Drinking Water] − Soil Leaching to Groundwater [Non-Drinking Water] − Aquatic Habitat Goal [Fresh Water Ecotox] − Aquatic Habitat Goal [Saltwater Ecotox] The identification of chemical concentrations above these screening levels does not necessarily mean that unacceptable risk could exist. Rather, screening levels help identify sampling results that may warrant additional evaluation. They provide a means for reviewing datasets by segregating concentrations that indicate a higher potential for health significance from those that indicate a low potential. In this case, they have been used to help understand the nature and extent of chemicals in stockpiled soil and sludge and determine which chemicals be considered site-related COPC. Based upon this screening, the following chemicals were detected in one or more samples at concentrations greater than these generic screening levels and are considered to be COPC in this risk evaluation.