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

ASPECT CONSULTING PROJECT NO. AS190583A-08  MAY 21, 2025 FINAL 91 specific volume extracted from the CMS area is unknown, but it was not insignificant. Oil- range TPH was the inferred constituent targeted for IA in the Heavy Duty Shop Sump area based on oily material observed within the sump structure during the Phase 1 ESA (AECOM, 2011). However, during the first IA, the results of field screening and soil sampling following removal of the sump structure did not indicate a release from the structure; therefore, no soil was removed in this area. Following the first IA, TPH and PAH IA soil cleanup levels were met in the Rail Car Dumper area, BA-MW-6 area, UST 70 area, and the REC2-MW-5 area (Figures 6-B2, 6-B3, and 6-B4, and Aspect, 2015a). Four quarterly rounds of postexcavation confirmation groundwater monitoring at those four areas demonstrated that groundwater meets PCLs for TPH and PAHs, and Ecology agreed that no further groundwater monitoring for those compounds is required for those areas (Aspect, 2015d). Likewise, during the second IA, TPH and PAH IA soil cleanup levels were met for the CMS excavation area (Figures 6-B2, 6-B3, and 6-B4, and Aspect, 2021). TPH soil cleanup levels were also met following removal of oily waste material from the Digesters Trench area (Figure 6-B2). Prior to the second IA, when the oily material remained in place, no TPH or PAH exceedances were detected in groundwater from well PM-MW-1 located near the western (downgradient) end of the Digesters Trench area; the groundwater data demonstrate limited leachability of hydrocarbons from the oily materials that were subsequently removed (Aspect, 2021). Well PM-MW-1 was excavated during the GF-B-12 excavation and is thus not displayed on Section 6 figures. Within the USTs 71, 72, 73 IA area, concentrations of TPH-D+O (Bunker C fuel oil) exceeded the 2,000 mg/kg PCL in five sidewall soil samples (remaining concentrations range up to 28,000 mg/kg TPH-D+O as measured by NWTPH-Dx) collected from two areas of the excavation (Figure 6-B2). In addition, concentrations of total cPAHs (TMEQ) exceeding the PCLs were reported in five of the compliance soil samples (located in the saturated zone) collected at the limits of the excavation (Figure 6-B3). Further soil excavation in those areas was impracticable due to the presence of massive concrete foundation structures (Aspect, 2015a). Samples of the inaccessible TPH-impacted soil were also analyzed for petroleum fractions (EPH analysis) to allow calculation of an area- specific soil TPH PCL for that soil, as presented below. 6.5.2.1.1.1 SITE-SPECIFIC SOIL TPH PCL FOR USTS 71, 72, 73 EXCAVATION AREA Four samples of the residual TPH-contaminated soil that could not be removed from the USTs 71, 72, 73 IA excavation area were submitted for laboratory analysis of hydrocarbon fractions using the EPH Method to allow the calculation of risk-based soil cleanup levels in accordance with MTCA (WAC 173-340-745(5)(b)(iii)(B)(III)). The TPH concentrations measured by the EPH analysis ranged from 16 to 88 percent of those measured by the NWTPH analysis for the four samples, and the distribution of petroleum fractions indicates Bunker C fuel oil. The results of the MTCAtph calculations for this area are detailed in Section F.1.1 of Appendix F. As discussed in Appendix F, the residual TPH concentrations in this area’s inaccessible soils are protective of industrial direct contact and leaching to groundwater. However, the