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

ASPECT CONSULTING PROJECT NO. AS190583A-08  MAY 21, 2025 FINAL 93 prior to analysis of cPAHs if turbidity was measured in the field to be greater than 25 NTU. Within Unit B, this included some of the samples collected from wells RCD-MW-101, UST71-MW-101, -102, and -103 (centrifuged samples are noted in Table 6-14). The wells with the highest detected total cPAHs (TEQ) concentrations— UST71-MW-102 and UST71-MW-103, which could not be effectively developed as described above—also have the highest turbidities measured, but the high-turbidity samples were centrifuged prior to PAH analysis. There is a reasonable weight of evidence to indicate that sample turbidity contributed to the cPAH exceedances in wells UST71-MW-102 and -103, but the data are inconclusive as to whether the sporadic cPAH exceedances elsewhere in Unit B groundwater samples can be attributed to high turbidity. At well BA-MW-05, the detected groundwater concentrations of the 2-methylnaphthalene and fluorene (Table 6-14) and dibenzofuran (Table 6-17) exceeded their PCLs. Naphthalenes and dibenzofuran are PAHs commonly associated with creosote-treated wood. Concentrations of dibenzofuran and 2-methylnaphthalene are below the PCLs in both groundwater samples collected from historical shoreline well BA-MW-07, located downgradient of well BA-MW-05. There are no surface water criteria for 2-methylnaphthalene or dibenzofuran; therefore, the groundwater PCLs are based on potable water (Table 5-1). Note that 2-methylnaphthalene is not routinely reported as part of the laboratory’s PAH analysis, and there are very limited soil data for it in Unit B. No concentrations of fluorene in Unit B soil exceeded the PCL (Table 6-13). Dibenzofuran was detected in 1 out of 85 Unit B soil samples analyzed for it, at a trace concentration (0.04 mg/kg) (Table 6-16). Given the very low frequency and magnitude of exceedance, limited to groundwater at a single location, dibenzofuran, fluorene, and 2-methylnaphthalene are not considered contaminants of concern within Unit B. 6.5.2.2 Metals Five IA areas within Unit B focused on the removal of soil contaminated with metals: Boiler/Baghouse area, GF-11 area (lead), GFB12 area (mercury), PM-B-6 area (copper and mercury), and REC5-MW-01 area (arsenic, copper, and lead) (Figure 6-B1). The Boiler/Baghouse area was initially excavated as part of the first IA, primarily because lead concentrations were detected above the industrial PCL in soil samples collected as part of the Phase 2 ESA (Aspect, 2013a). The Boiler/Baghouse area was further excavated during the second IA to remove copper, mercury, and zinc that were a suspected ongoing source to groundwater (Aspect, 2021). Approximately 11,200 tons of metals-contaminated soil were excavated from these five IA areas in total. The soil excavated from the GF-11 area was designated as characteristic hazardous waste and was treated and disposed of at a Subtitle C landfill, as described by Aspect (2015a). The 1,000 mg/kg IA soil cleanup level for lead (based on industrial) in unsaturated soil, equivalent to the PCL, was met at the limits of both of these excavation areas (Aspect, 2015a; Figure 6-B7). Concentrations of copper, mercury, and zinc exceeding the soil PCLs were detected in soil remaining at the limits of these excavation areas. Arsenic, copper, lead, mercury, nickel, and zinc are detected exceeding the PCLs in groundwater samples collected from select Unit B wells. The metals exceedances were detected primarily within the northwest area of Unit B, within the area of the former boilers/steam plant, baghouse, and hog fuel storage. The following sections describe the