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ASPECT CONSULTING <br />100 FINAL PROJECT NO. AS190583A-08  MAY 21, 2025 <br />concentrations may be attributable to release of naturally occurring nickel due to <br />geochemical interactions from anaerobic Upland Area groundwater mixing with <br />oxygenated seawater within the nearshore fill material. No metals exceedances were <br />detected in intertidal porewater samples collected on the downgradient edge of Unit B. <br />The existing analytical data for Unit B soil and groundwater provide sufficient information <br />for the development and evaluation of cleanup action alternatives in accordance with MTCA. <br />6.5.3 Unit C <br />The Former Log Pond occupies a large proportion of Unit C, as depicted on Figure 6-C1. <br />As discussed in Section 2.4.4.1, the Former Log Pond fill materials are markedly different <br />from the dredge fill placed across most of the rest of the Upland Area. Given the distinct <br />nature of the Former Log Pond fill and its contamination characteristics relative to the rest <br />of Unit C, the Former Log Pond area of Unit C is discussed on its own in Section 6.5.4. <br />This section discusses the portion of Unit C outside of the Former Log Pond. The <br />explorations and IA areas within Unit C, including IA compliance soil sample locations, <br />are depicted on Figure 6-C1. For current conditions following the IAs, the constituents <br />detected in one or more samples of Unit C media outside of the Former Log Pond at <br />concentrations exceeding their respective industrial PCLs are as follows: <br /> TPH-D+O in soil and groundwater <br /> Total cPAHs and naphthalene in soil and groundwater <br /> Lead and zinc in soil <br /> Arsenic, copper, and mercury in soil and groundwater <br /> Vinyl chloride in groundwater <br />Constituents that were not detected at concentrations greater than the industrial PCLs in <br />soil or groundwater samples from Unit C, outside of the Former Log Pond, include <br />TPH-G, BTEX, PCBs, VOCs except vinyl chloride, dioxins/furans, and the SVOCs and <br />metals not specifically included in the previous list. <br />The sample locations for constituents detected at concentrations exceeding the PCLs in <br />Unit C are presented on Figures 6-C2 through 6-C11. The data for constituents detected at <br />concentrations exceeding PCLs are summarized by constituent group in the following <br />subsections. <br />6.5.3.1 Total Petroleum Hydrocarbon and PAHs <br />During the first IA, TPH (gasoline- and oil-range) and copper were the contaminants <br />targeted for removal from the SHB-MW-1 (Small Hydraulic Barker) area located within <br />Unit C (Figure 6-C1). The SHB-MW-1 area IA removed 210 tons of contaminated soil, <br />and the IA soil cleanup levels for TPH and PAHs were met at the limits of the excavation <br />(Figures 6-C2 and 6-C3). Four quarterly rounds of postexcavation confirmation <br />groundwater monitoring for the area demonstrated that groundwater meets PCLs for TPH. <br />However, groundwater concentrations of total cPAHs (TEQ) exceeding the PCL were <br />detected in one of the SHB-MW-1 area compliance wells (SHB-MW-101, Figure 6-C3) <br />during the first of eight groundwater sampling events; the concentrations were below the