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

ASPECT CONSULTING PROJECT NO. AS190583A-08  MAY 21, 2025 FINAL 99 6.5.2.6 Other Constituent Exceedances Other constituent exceedances in Unit B groundwater consist of the following:  At well PM-MW-05, pentachlorophenol (PCP) and its degradation daughter product 2,4,6-trichlorophenol were detected in groundwater at concentrations exceeding their PCLs (Table 6-17). There is no documentation of historical usage of PCP in the pulp mill area or anywhere in the former mill. PCP has never been detected above the laboratory reporting limits in 215 soil samples analyzed for SVOCs (Table 6-1), including those collected from PM-MW-05 (Table 6-16). PCP was not detected in groundwater samples collected from downgradient wells PM-MW-02, PM-MW-04, PM-MW-07, and PM-MW-08, located between well PM-MW-05 and the shoreline (Figure 6-B1), indicating an incomplete transport pathway to marine surface water.  Vinyl chloride was detected above the groundwater PCL of 0.2 µg/L in both samples collected from well OPS-MW-01, at concentrations of 0.23 µg/L and 0.28 µg/L (Table 6-17). This well is located more than 800 feet from the shoreline. Vinyl chloride was not detected anywhere in Upland Area soil above the laboratory reporting limits (Table 6-1), and was not detected exceeding the PCL in any other Unit B groundwater samples indicating an incomplete transport pathway to marine surface water (Table 6-17). The detected concentrations at well OPS-MW-01 were also an order of magnitude below the 3.4 µg/L screening level for vapor intrusion. 6.5.2.7 Summary for Unit B The IA successfully removed TPH-contaminated soil from Unit B to meet the default soil industrial PCLs; however, soil TPH concentrations in two portions of the USTs 71, 72, 73 excavation exceed the proposed area-specific PCL. Groundwater immediately downgradient of both inaccessible soil occurrences had no detected TPH exceedances, but well UST71-MW-103 downgradient of the southern occurrence had consistent cPAH exceedances. In addition, TPH and cPAH exceedances were detected inconsistently in well UST71-MW-102 located on the downgradient edge of the middle of the excavation. The detections at UST71-MW-102 and -103 may be attributable to elevated turbidity of the groundwater samples. Outside of the two areas of inaccessible soil within the USTs 71, 72, 73 excavation area, there are no detected TPH soil exceedances remaining in Unit B Outside of the UST 71 area locations, cPAHs were detected sporadically in Unit B soil and groundwater at concentrations greater than the PCLs. In groundwater, concentrations of the metals arsenic, copper, lead, mercury, nickel, and zinc greater than the PCLs were detected throughout Unit B, with the most consistent and higher-magnitude exceedances detected in the Boilers area. At most other Unit B wells, the groundwater metals exceedances were inconsistently detected and relatively low-level in magnitude, although some exceed by 3 to 5 times the cleanup level. Of those dissolved metals, copper, nickel, and zinc exceeded PCLs in shoreline wells; and of those, copper and nickel were detected at concentrations greater than PCLs more than once only at shoreline wells RCD-MW-101, REC3-MW-1R, PM-MW-07 and UST70-MW-02. As observed in Unit A, there are not elevated soil nickel concentrations detected in Unit B and the detected dissolved nickel concentrations are higher in shoreline wells than in inland wells. The collective data suggest that the elevated shoreline groundwater nickel