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

ASPECT CONSULTING 106 FINAL PROJECT NO. AS190583A-08  MAY 21, 2025 constituents detected at concentrations exceeding PCLs are summarized by constituent group in the following subsections. 6.5.4.1 Total Petroleum Hydrocarbons and PAHs There are six locations within the Log Pond where TPH-D+O remains in soil at concentrations exceeding the PCLs (Figure 6-C2). Five of these locations (LP-B-01, LP-B-03, LP-B-07, LP-B-08, and LP-MW-07) contain TPH-D+O above the PCLs in the sawdust layer, sampled at depths ranging from 35 to 41 feet bgs, with concentrations ranging from 6,300 mg/kg to 14,500 mg/kg. Concentrations of total cPAHs, total xylenes, naphthalene, 2-methylnaphthalene, acenaphthene, and dibenzofuran were also reported above their respective PCLs in one or more samples collected from the deep sawdust layer where TPH-D+O was reported above the PCL (Table 6-13) (naphthalene exceedance locations shown on Figure 6-C4). Groundwater samples collected from the deep wells, screened across the sawdust layer, did not contain TPH, PAHs, xylenes, or dibenzofuran above the PCLs, demonstrating empirically that those contaminants are not leaching from the sawdust layer to groundwater at levels that result in exceedances of the PCLs. The fill soil sample collected from boring LP-B-06 also contains TPH-D+O and total cPAHs (TMEQ) at concentrations above the PCLs (Table 6-13). Groundwater collected from downgradient well LP-MW-04 does not contain TPH-D+O above the PCLs but does contain total cPAH (TEQ) above the PCLs (Table 6-14). Total cPAH (TMEQ) concentrations exceeding but less than two times the PCL were left in-place in five locations at the limits of the Log Pond Chip Conveyer IA area (Figure 6-C3), with concentrations ranging from 0.127 mg/kg to 0.192 mg/kg relative to the PCL of 0.12 mg/kg (Table 6-13). Total cPAH (TEQ) concentrations were reported above the PCL in groundwater samples collected from two of the Log Pond wells (Figure 6-C3). Regardless of these and other cPAH exceedances in the Log Pond fill (Figure 6-C3), total cPAH (TEQ) concentrations were not reported above the PCL in groundwater samples collected from any of the shoreline wells or in the Seep-3 sample of intertidal seep discharge (Figure 6-C3). 6.5.4.2 Metals Within the Log Pond Area of Unit C, arsenic, copper, lead, mercury, and nickel are present in soil and groundwater at concentrations exceeding the PCLs. The data for those metals in Log Pond Area media are depicted on Figures 6-C5 through 6-C9 and are discussed in the following subsections. Zinc was also detected in one or more Log Pond Area soil samples at concentrations exceeding the soil PCL based on groundwater protection (Figure 6-C10; Table 6-9). However, zinc exceedances are not detected in Log Pond groundwater, indicating that zinc concentrations in the soil are protective of groundwater in accordance with MTCA (Figure 6-C10; Table 6-10). 6.5.4.2.1 Arsenic Arsenic above the PCL in Log Pond Area soil is limited to two locations in the Hazardous Waste Cage area (up to 26 mg/kg) and one location near the Log Pond’s center (21 mg/kg