3815_PGSF WMVD Pkg 2_Vol 4-2_03.03.2026_BXWA_Certified

ASPECT CONSULTING PROJECT NO. AS190583A-08  MAY 21, 2025 FINAL 83 (0.074 µg/m3) land use scenarios (Tables 6-15b and 6-15c). Benzene was detected in all the indoor air samples and in one of the ambient air samples at concentrations exceeding the PCL for the unrestricted land use; however, the concentration of benzene detected in the November 2014 ambient air sample (1.3 µg/m3; collected downwind of Marine View Drive and BNSF mainline, but upwind of the warehouse ) is similar to those detected in indoor air samples (1.2 µg/m3 to 1.3 µg/m3; Table 6-15c) suggesting that benzene in indoor air has the potential to be influenced by area background sources, such as Marine View Drive, diesel locomotives on the BNSF mainline, and/or neighboring industrial operations. However, the degree to which background sources may influence benzene concentrations inside the warehouse, if any, is unknown. For example, the ambient air sample collected west of the warehouse in February 2013, during onshore winds, was nondetect for benzene. Tables 6-15a, 6-15b, and 6-15c also calculate the cumulative carcinogenic risk represented by the combined concentrations of benzene and naphthalene, which is compared against MTCA’s 1 x 10-5 (1E-05) acceptable cumulative risk threshold. The calculated cumulative carcinogenic risk for each future use scenario is less than the MTCA risk threshold. Hydrocarbon concentrations detected in samples of sub-slab air collected below the floor slab also meet screening levels for commercial and unrestricted uses. However, naphthalene was detected in one sub-slab soil gas sample, at a concentration of 13 µg/m3, which exceeds the soil gas PCLs for unrestricted and commercial land use of 2.5 µg/m3 and 11 µg/m3, respectively. In conclusion, for commercial and unrestricted use scenarios, hydrocarbon concentrations in sub-slab air samples collected beneath the warehouse meet screening levels based on VI, and those in indoor air samples collected within the warehouse meet PCLs and are comparable to ambient air samples collected outside the warehouse. However, benzene and/or naphthalene were detected in indoor air or sub-slab soil gas at concentrations exceeding the risk threshold for individual chemicals under commercial and unrestricted land use scenarios. Therefore, VI is considered an exposure pathway of concern for commercial and unrestricted land uses. 6.5.1.1.3 Metals Arsenic and copper were detected above the groundwater PCLs in monitoring well BCT-MW-103, located within the Warehouse Subarea (Table 6-8). Dissolved arsenic was detected in the only groundwater sample analyzed for arsenic from well BCT-MW-103 at a concentration of 9.61 µg/l, which is only slightly above the PCL of 9 µg/l, based on Site background. Copper was detected above the PCL in groundwater at well BCT-MW-103 in two of four sampling events (Table 6-8). There are no detected concentrations of arsenic or copper in soil above the PCLs, which are based on natural background. 6.5.1.1.4 Warehouse Subarea Summary Petroleum-impacted soil remains beneath the warehouse, where historical bulk storage facilities existed, but the soil does not pose a direct contact risk (i.e., it’s not accessible because it’s covered by the warehouse) and empirical data demonstrate that the soil, which is currently capped by existing warehouse, is not creating exceedances of PCLs for groundwater. For commercial and unrestricted use scenarios, hydrocarbon concentrations