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

ASPECT CONSULTING 98 FINAL PROJECT NO. AS190583A-08  MAY 21, 2025 footprint prior to the second IA. The second IA removed the presumptive source of PCBs to groundwater in that area while also removing a large quantity of contaminated groundwater during dewatering of the large excavation. In accordance with the RI/FS Work Plan (Aspect, 2013c), three soil samples collected during the RI with the highest concentrations of total PCBs were also submitted for analysis of PCB congeners to support future work in the East Waterway RI/FS; each of the three samples was collected from Unit B (from explorations BA-MW-02, PM-B-06, and PM-B-07; Figure 2-4). Of these, only the soil sample collected from BA-MW-02 is representative of current conditions; the soil PCB congener data for this sample is provided on Table 6-19. Figure 6-B14 presents histograms of PCB congener composition (as weight percent of total PCB congener concentration) for the three soil samples. The sample histograms can be compared to plots of congener composition (by weight percent) for the common PCB Aroclors,35 including the three Aroclors detected in Upland Area soil (Aroclors 1016, 1254, and 1260), which are presented in Appendix J. In Figure 6-B14, nondetected congeners are plotted as zero, so the histogram pattern is not obscured by numerous nondetections (if plotted as one-half the reporting limit). The distribution of PCB congeners appears generally consistent with the detected Aroclors in the samples: lighter molecular weight congeners constitute a greater percentage of the total PCB concentration in the BA-MW-02 sample (with detectable Aroclor 1016), whereas the PM-B6 and PM-B7 samples (with detectable Aroclors 1254 and 1260) both have a greater percentage of moderate-molecular-weight congeners. 6.5.2.4 Un-Ionized Ammonia Un-ionized ammonia was not detected above the 0.035 mg/L PCL in groundwater samples collected from any of the shoreline wells in Unit B (Figure 6-S3). Un-ionized ammonia was detected above the PCL in one of two porewater samples collected from the PW-03 location (0.14 mg/L; Table 6-12). Each of the un-ionized ammonia concentrations detected in Unit B intertidal porewater was less than the NOEC of 0.46 mg/L (Kendall and Barton, 2004), and they are in the range of background concentrations in Puget Sound sediments (USGS, 2010). 6.5.2.5 Sulfide Total dissolved sulfide concentrations in groundwater were below the PCL at each of the six Unit B shoreline wells. High total dissolved sulfide concentrations were detected in three of four intertidal porewater samples collected from two locations beneath the dock and downgradient of the former Boilers area in February and August 2014 (8.8 to 23.5 mg/L at PW-03; nondetect to 9.1 mg/L at PW-04). However, applying the more reliable DGT sulfide sampling methodology in February 2015, hydrogen sulfide (H2S) was not detected at either porewater sample location (Table 6-12). The data indicate that the prior variable detections of total dissolved sulfide are attributable to mineral sulfides in the samples, not H2S. 35 Obtained from http://www.epa.gov/epawaste/hazard/tsd/pcbs/pdf/aroclorplots.pdf.