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

ASPECT CONSULTING PROJECT NO. AS190583A-08  MAY 21, 2025 FINAL 63 concentrations that are protective of direct contact by industrial workers and soil leaching to groundwater. The values considered for each exposure pathway are described in the following subsections. Table 5-3 presents the criteria incorporated into the soil PCL derivation for the protection of industrial workers and the resulting PCLs applied for the RI. Table 5-4 presents the criteria incorporated into the soil PCL derivation for the Warehouse Subarea for the protection of commercial workers and the resulting PCLs applied for the RI. Note that Tables 5-3 and 5-4 only include constituents that were detected in samples of either soil or groundwater collected from the Upland Area; constituents not detected in either medium are not presented to make the table more manageable. 5.3.2.1 Direct Contact Exposure Pathway Soil concentrations protective of direct human contact under industrial land use are the more stringent of the MTCA standard Method C soil cleanup levels 23 and, as described below, selected MTCA Method A industrial soil cleanup levels. For the Warehouse Subarea, soil concentrations protective of direct human contact for unrestricted land use are the standard MTCA Method A or Method B unrestricted land use soil cleanup levels. Most MTCA Method A soil cleanup levels are based on either direct contact using the standard Method B equations (WAC 173-340-745[5][b]) or protection of groundwater for drinking water (potable) use. The highest beneficial use of Upland Area groundwater is discharge to marine water, not drinking water. Therefore, the Method A soil cleanup levels based on groundwater protection are not applicable, and this pathway is addressed separately using the most stringent groundwater criteria in accordance with MTCA (described below). In addition, the Method A industrial soil cleanup levels based on direct contact are covered by including standard Method C cleanup levels in the PCL derivation. For the purposes of the RI, the Method A industrial soil values that were included in the derivation of soil PCLs include arsenic (background-based), lead (no Method C value), total PCBs (an applicable or relevant and appropriate requirement [ARAR] from the federal Toxic Substances Control Act [TSCA]), and petroleum mixtures (TPH-G, TPH-D, and TPH-O). 5.3.2.2 Soil Leaching to Groundwater Exposure Pathway Soil concentrations protective of the highest beneficial use of groundwater were calculated conservatively using Ecology’s variable parameter three-phase partitioning model (WAC 173-340-747(5)) and the most stringent groundwater criteria for protection of VI and marine water quality (described above). Separate values were developed for unsaturated and saturated soil (MTCA-default dilution factors of 20 and 1, respectively), in accordance with WAC 173-340-747(4)(e). MTCA-default parameters (WAC 173-340-747(4) and (5)) were used in the three-phase model, except that a Site-specific soil fractional organic carbon content (foc) of 0.0079 (0.79 percent) was used for calculating soil-water partition coefficients (Kd = Koc × foc) for organics, in accordance with WAC 173-340-747(5)(b)(i). This is the average foc value from 24 Upland Area soil samples collected during the 2012 23 From Ecology’s Cleanup Level and Risk Calculation (CLARC) database (February 2023). https://fortress.wa.gov/ecy/clarc/CLARCHome.aspx