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

ASPECT CONSULTING PROJECT NO. AS190583A-08  MAY 21, 2025 FINAL 69  UST 29/Latex Spill area  Hydraulic Barker Vault area The second IA included additional soil removal from the CN area (East and West), adjacent to the CN-B-2 excavation, within Unit D (Aspect, 2021). 6.2.5 Unit E The unit boundaries, current and historical features, and collective explorations for Unit E are depicted on Figure 6-E1; no IA work was conducted in Unit E. Historically, the primary use of Unit E was for timber storage by the Clark-Nickerson Lumber Company mill (late 1800s through early 1930s) (Figure 2-2). The area was later developed as the pulp/paper mill’s Wastewater Treatment Plant, and a portion of the area was used as a parking lot; the wastewater treatment plant infrastructure and the parking lot pavement remain in place. Unit E is the entirety of the City Utility Property as described in Section 2.1.1. 6.2.6 Data Presentation As described in Section 6.1, a very large RI data set is available from the combined Phase 2 ESA, RCRA closure, two IAs, and RI data collection efforts. Sample data representing soil or groundwater removed during the two IAs are not representative of current Upland Area conditions and are not included in the RI data set. Tables 6-1 and 6-2 are statistical summaries of the collective soil and groundwater data, respectively, representing current conditions for the Upland Area. The two tables present, for each constituent analyzed, the number of sample locations, the number of samples analyzed, the number of samples with detectable concentrations, the detection frequency (percent), the maximum detected concentration, and the number of samples with detected concentrations exceeding the PCL. Table 6-1 compares the soil data for each constituent against the PCL, which is the most stringent value addressing both industrial direct contact and groundwater protection as described in Section 5.3.2. However, the table also presents in a separate column the comparison of soil data to the industrial direct contact criteria. Distinguishing between criteria based on direct contact and groundwater protection (based on MTCA’s conservative predictive analysis) is pertinent to the data evaluation presented in Section 6.5 and to development and evaluation of remedial alternatives in the FS. Tables 6-3 and 6-4 are statistical summaries of the soil and groundwater data that represent conditions within the Warehouse Subarea. Table 6-3 compares the soil data for each constituent against the PCL, which considers commercial worker exposure (direct contact – unrestricted use) and groundwater protection. Table 6-4 compares the groundwater data for each constituent against the PCL, which considers protection of vapor intrusion for unrestricted land use. Based on the statistical summaries, Tables 6-7 through 6-22 present the soil, groundwater, sub-slab soil gas, indoor air, and beach porewater/seep data for analytes that were detected in samples of any Upland Area medium representing current conditions. The media- specific data tables include data for the entire Upland Area, organized by constituent group and by Site unit. The data for the Warehouse Subarea are presented separately, with