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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 5 of 10 nivosus), and the salt marsh wandering shrew (Sorex vagrans haliocoetes), are known to occur in the vicinity of the site but are unlikely to use it due to lack of suitable habitat (LSA 2020b). Several special- status fish species, such as longfin smelt (Spirinchus thaleichthys), North American green sturgeon (Acipenser medirostris), steelhead (Oncorhynchus mykiss), and chinook salmon (O. tshawytscha) inhabit the Bay and could briefly forage in the tidal slough during high tide; however, spawning, or rearing habitat is not present in the tidal slough for these fish species (LSA 2020b). The salt-pond-like habitat of the current storage basin is unlikely to support a balanced aquatic life community and is not likely to be used by waterfowl for foraging. As described above, the goal of the proposed treatment wetland is to provide a facility that reduces nitrate and micro-organic constituents in the WPCP effluent prior to discharge to the Bay. The impermeable liner fitted to the bottom and sides of the treatment wetland is expected to develop an algal mat to help support de-nitrification. Given the relatively shallow water depth of the proposed treatment wetland, this algal mat has the potential to provide a dietary source for zooplankton, such as copepods and rotifers, and/or the larvae of insects such as midges, mayflies, and dragonflies that typically inhabit surface sediments where they feed on algae and detrital matter. However, the clean fill placed on top of the stockpiled soil and sludge and the presence of the impermeable liner will prevent the potential for exposure of these aquatic organisms to metals in the buried soil and sludge. As a consequence, potential exposure pathways to the sludge/soil beneath the liner for birds feeding on emergent insects or waterfowl foraging in the treatment wetland, are considered incomplete. Furthermore, while the side slopes of the treatment wetland will be vegetated, they will be mowed to minimize the development of habitat that could be used by birds for perching, cover, or nesting, to ensure the insignificance of this exposure pathway for these receptors. Although there is evidence for the presence of small mammals at the Project site, the wetland environment is not the preferred habitat for these species. For example, the California ground squirrel prefers open grassland, oak woodlands, agricultural lands, and tends to avoid water (Smith et al. 2016). The pocket gopher typically occupies desert ranges with loose sandy soil for burrowing but can also be found in meadows and agricultural areas with cultivated soils. Distribution of this species is limited by hard soils and barriers, such as rivers and rock formations (Jones and Baxter 2004). Therefore, it is unlikely that these small mammals will be found burrowing or foraging close to the treatment wetland. Given the habitat preferences for these species, along with the placement of clean fill over the stockpiled soil/sludge and the impermeable liner, the potential exposure pathway for such small mammals to metals in the buried stockpiled soil and sludge is considered incomplete. A potential exposure pathway that could result in risk to ecological receptors is leaching of metals to groundwater. A distilled water waste extraction test (DI-WET) has been performed on the stockpile-soil samples and the recently collected sludge samples. The standard WET uses a dilute acid as the leaching medium to represent leaching of solids from landfill leachate, while the DI-WET is designed to represent leaching under natural field conditions. The DI-WET results showed the leachability of metals in stockpiled soil and sludge is very low, with DI-WET-extracted concentrations below or slightly above SFBRWQCB ESLs for fresh-water and salt-water habitats (SFBRWQCB 2019). The following table