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

ASPECT CONSULTING PROJECT NO. AS190583A-08  MAY 21, 2025 FINAL 101 PCLs in seven subsequent sampling events (Table 6-14). In addition, groundwater samples collected from well SHB-MW-101 have shown sporadic exceedances of copper and mercury (Table 6-10). Outside of the SHB-MW-1 IA area, gasoline-range TPH and BTEX were not detected above the PCLs in soil or groundwater. However, concentrations of TPH-D+O, total cPAHs (TEQ), and naphthalene above respective PCLs were detected in soil and groundwater in other localized, discrete areas of Unit C (Figures 6-C2, 6-C3, and 6-C4, respectively), as discussed below. 6.5.3.1.1 GF-9 Area Along the southeast corner of the former Log Pond in Unit C, TPH and PAH exceedances were detected in soil and groundwater within the GF-9 area identified (based on boring GF-B-9) during the Phase 2 ESA (Aspect, 2013a), and investigated further as part of the RI/FS. Although the TPH detected in groundwater in this area is within the diesel range (C10 to C25 carbon range), the groundwater samples’ chromatographic pattern does not resemble a diesel fuel standard (indicated by the laboratory’s X qualifier; Table 6-14). This fact, with the relatively higher detected concentrations of noncarcinogenic PAHs (ncPAHs) (naphthalene, along with anthracene, fluorene, fluoranthene, phenathrene, and pyrene), indicate a creosote/coal tar source rather than fuel source for the detected hydrocarbons. Detected concentrations of TPH-D+O (up to 680 µg/L) and naphthalene (up to 210 µg/L) in groundwater from well GF9-MW-03 exceeded respective PCLs when sampled in 2013–2014. However, when sampled again in March 2017, naphthalene was well below the PCL; TPH was not analyzed for (Table 6-14). Naphthalene is readily degradable, particularly in aerobic conditions, and the groundwater field parameter data from well GF-MW-03 may suggest slightly more oxidizing conditions (change from negative to positive ORP; Table 6-11) starting in 2017 following years of infiltrating oxygenated water in the absence of pavement. The fact that the elevated naphthalene concentrations were more than a quarter of the TPH concentrations is consistent with a creosote/coal tar, not fuel, source. No groundwater exceedances for TPH or naphthalene were detected in wells GF9-MW-01 or GF9-MW-02 located on the downgradient side of GF9-MW-3, nor in well GF9-MW-04 located upgradient of it, indicating a relatively limited area of groundwater impact (Figures 6-C2 and 6-C4). Note that the naphthalene groundwater PCL is based on VI, and the maximum detected groundwater concentrations in the area are an order of magnitude below the 4,700 µg/L surface water quality standard (Table 5-1). 6.5.3.1.2 Hydraulic Barker Area Total PCBs were the contaminants targeted for removal from the Hydraulic Barker area during the second IA (Figure 6-C1). However, the area also included petroleum contamination, with a TPH-D+O concentration of 7,710 mg/kg detected in a sample of saturated soil (12-foot depth) collected at the HB-MW-1R replacement well location. No soil TPH exceedances were detected at the original well HB-MW-1, located several feet away. The second IA removed 268 tons of PCB-contaminated soil and the IA soil cleanup levels for PCBs were met at the limits of the excavation (Figure 6-C12). Final excavation verification samples from the Hydraulic Barker area were also analyzed for TPH and