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

ASPECT CONSULTING 112 FINAL PROJECT NO. AS190583A-08  MAY 21, 2025 Constituents that were not detected at concentrations greater than the PCLs in soil or groundwater samples collected within Unit D include TPH-G, dioxins/furans, and VOCs, metals, and SVOCs that are not included in the list above. The sample locations for constituents detected at concentrations exceeding the PCLs in Unit D are presented on Figures 6-D2 through 6-D10. The data for constituents detected at concentrations exceeding the PCLs are summarized by constituent group in the following subsections. 6.5.5.1 Total Petroleum Hydrocarbons and PAHs During the first IA, four IA areas within Unit D focused on the removal of TPH- contaminated soil: the Naval Reserve Parcel UST area, the Naval Reserve Parcel South area, the CN-B-2 area, and the Hydraulic Barker Vault area (Figure 6-D1). During the second IA, relatively high concentrations of cPAH left in-place in soil at the limits of the CN-B-2 area excavation were removed from the CN West and CN East areas (Figure 6-D1). Xylenes were the primary constituent targeted for IA in the UST 29/Latex Spill area; however, TPH and cPAHs were also present in soil in this area at concentrations exceeding the IA cleanup levels. The two IAs resulted in the removal of approximately 10,700 tons TPH- and cPAH-contaminated soil and 5,440 tons xylene- contaminated soil from the IA areas within Unit D (Figure 6-D1), as described by Aspect (2015a; 2021). Following the soil removals, the TPH PCLs are met in the Naval Reserve Parcel UST area, the Naval Reserve Parcel South area, the CN-B-2 area, and the Hydraulic Barker Vault area (Aspect, 2015a). In the Naval Reserve Parcel UST area and the CN-B-2/CN west area, soil concentrations of total cPAHs (TMEQ) meet the soil PCLs except for three samples in the saturated zone (Figure 6-D3). Following the first IA, four quarterly rounds of postexcavation confirmation groundwater monitoring at these four areas demonstrated that groundwater meets PCLs for TPH and PAHs, demonstrating the soil quality is protective of groundwater, and Ecology agreed that no further groundwater monitoring for those compounds was required for those areas (Aspect, 2015d). The PCL for xylenes were met in the UST 29/Latex Spill area except for two bottom samples, where the reported concentrations of total xylenes exceed the 0.23 mg/kg PCL based on soil leaching (Table 6-13; Figure 6-D4). Four quarterly rounds of postexcavation groundwater monitoring at the UST 29/Latex Spill area demonstrated that groundwater meets PCLs for TPH, xylenes, and ethylbenzene (Table 6-14). The confirmation groundwater data indicate that the residual soil xylenes concentrations are protective of groundwater in accordance with MTCA. However, low-level total cPAHs (TEQ) exceedances (up to 0.05 µg/L) have been reported in six of eight groundwater samples collected from well UST29-MW-101 (Figure 6-D3). West of well UST29-MW-101, no cPAH (TEQ) exceedances were detected in groundwater at shoreline monitoring wells REC6-MW-02 (within Unit C) or TM-MW-06 (Figure 6-S1). The combined removal of highly contaminated soil plus dewatering of the excavation throughout soil removal successfully remediated the high xylene concentrations in groundwater present at the UST29 location prior to the first IA.