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

ASPECT CONSULTING PROJECT NO. AS190583A-08  MAY 21, 2025 FINAL 115 comply with the PCL because that one reported concentration (135 mg/kg) is more than two times the PCL (96 mg/kg). No dissolved nickel exceedances were detected in well TM-MW-05 located generally downgradient of that soil location (Figure 6-D9). No dissolved nickel exceedances were detected in shoreline groundwater, including well REC6-MW-02, which is in Unit C, but downgradient of well UST29-MW-101, in porewater sample PW-07, or in any of the four seep samples collected from Unit D (Table 6-22; Figure 6-D9). 6.5.5.3 Un-ionized Ammonia No NH3 exceedances were detected in samples of groundwater collected from five shoreline monitoring wells, one intertidal porewater location, and four intertidal seep locations in Unit D. 6.5.5.4 Sulfide H2S concentrations exceeding the 0.002 mg/L PCL were detected in three of four intertidal seep locations (Seep-10, -11, and -13) and in the intertidal porewater location PW-07 adjacent to Seep-10 and -11 (Table 6-12; Figure 6-S1). Each of these intertidal water samples were collected within a few feet of the wooden bulkhead constructed for the former Naval Reserve facility. The surface sediments in this area contain abundant wood fragments and dimensional lumber, the decomposition of which may contribute to the observed elevated H2S concentrations. Total dissolved sulfide concentrations in the five shoreline wells commonly exceed the 0.05 mg/L PQL-based PCL, but there are no corresponding DGT data from which to document H2S concentrations in groundwater. The PW-07 porewater data provide an indication of the high bias in the total dissolved sulfide data for Unit D: total dissolved sulfide detections ranged from 2.7 to 15 mg/L compared with 0.114 mg/L H2S measured by DGT, although the samples were not concurrent (Table 6-12). 6.5.5.5 Summary for Unit D The IA excavations successfully removed petroleum-, cPAH-, and xylene-contaminated soil from Unit D (Naval Reserve Parcel UST area, the Naval Reserve Parcel South area, CN-B-2 area, Hydraulic Barker Vault area, and UST 29/Latex Spill area). Postexcavation confirmation groundwater monitoring for the five areas demonstrated that groundwater meets PCLs for TPH and xylenes, demonstrating that the IA’s intended source control was accomplished. Following the IA, only a single TPH-D+O soil exceedance remains (greater than 4,000 mg/kg at well TM-MW-05 south of the CN-B-2 IA area), and the empirical groundwater data indicate that the soil is protective of groundwater quality. Low-level exceedances of total cPAHs (TEQ) are detected in three inland wells within Unit D, but not in any of the wells positioned downgradient of them (and no exceedances in 10 shoreline wells). Groundwater exceedances for the metal’s arsenic, copper, mercury, and nickel are detected in one or more wells across Unit D; however, the groundwater exceedances were generally not consistent over time, and their locations indicate little, if any, correlation