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

ASPECT CONSULTING PROJECT NO. AS190583A-08  MAY 21, 2025 FINAL 79 installation of the planned monitoring well, but soil sampling was still completed at this location to a depth of 6 feet (exploration location was renamed REC2-B-22 when the well was not completed). Two samples of porewater were also collected from an intertidal seep location (SEEP-1) along the shoreline of the off-loading dock slip (Figure 6-A1). Collocated samples of indoor air and sub-slab air29 were collected during two sampling events from three locations within the warehouse and were analyzed to evaluate the potential VI risk within the warehouse attributable to concentrations of petroleum hydrocarbons in shallow subsurface soil and groundwater. Because a building of concern exists within which indoor air sampling could be conducted, the sampling was conducted to determine what impact VI was having on its indoor air, thus constituting a Tier 2 VI evaluation in accordance with Ecology (2022) VI guidance. An ambient outdoor air sample was also collected at a location upwind of the warehouse to measure area background air quality during both sampling events, in accordance with Ecology (2022); because of differences in wind direction at the times of the two sampling events, the locations of these background samples differed between events (Back-AA-1 and Back-AA-2; Figure 6-A1). The sample locations for constituents detected at concentrations exceeding the PCLs in Unit A following the two IAs are presented on Figures 6-A2 through 6-A11. The Warehouse Subarea occupies approximately half of Unit A, as depicted on Figure 6-A1. As discussed in Section 5.1.1.2 and Section 5.3, a potential future change in land use from industrial to commercial is considered for the warehouse. Given the different exposure scenario and PCLs for the Warehouse Subarea if that land use conversion occurs, it is discussed on its own in Section 6.5.1. Section 6.5.2 describes the portion of Unit A that is outside, and downgradient of, the Warehouse Subarea. 6.5.1.1 Warehouse Subarea of Unit A The Warehouse Subarea of Unit A consists of those portions of land that are covered by the warehouse structure, which sits on the property line to the east, and on the Site boundary to the south (Figure 6-A1). The north and west extent of the Warehouse Subarea is defined by the 30-foot lateral distance for evaluating vapor intrusion into an existing structure. The constituents that were detected in one or more samples of Warehouse Subarea soil or groundwater at concentrations exceeding their respective PCLs are as follows:  TPH-G in soil and groundwater  Diesel- and/or oil-range total petroleum hydrocarbons (TPH-D+O 30) in soil  Xylenes in soil  Total cPAHs in soil  Naphthalene in soil 29 Air in void space beneath warehouse floor slab. 30 In the tables and figures, “TPH (D+O)” refers to the sum of detected diesel- and oil-range TPH concentrations as described in Section 6.2.6.