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ASPECT CONSULTING <br />84 FINAL PROJECT NO. AS190583A-08  MAY 21, 2025 <br />in sub-slab air samples collected beneath the warehouse meet screening levels based on <br />VI, and those in indoor air samples collected within the warehouse meet PCLs and are <br />comparable to ambient air samples collected outside the warehouse. However, benzene <br />and/or naphthalene were detected in indoor air or sub-slab soil gas at concentrations <br />exceeding the risk threshold for individual chemicals under commercial and unrestricted <br />land use scenarios. Therefore, VI is considered an exposure pathway of concern for <br />commercial and unrestricted land uses. <br />6.5.1.2 Unit A Outside Warehouse Subarea <br />This section discusses the portion of Unit A that is outside of the Warehouse Subarea. For <br />current conditions following the IA, the constituents that were detected in one or more <br />samples of Unit A media at concentrations exceeding their respective PCLs are as follows: <br /> TPH-G in soil <br /> TPH-D+O in soil <br /> Total cPAHs in soil <br /> Naphthalene in groundwater <br /> Copper and mercury in soil and groundwater <br /> Lead and zinc in soil <br /> Nickel in groundwater <br /> PCBs in soil <br /> Un-ionized ammonia in groundwater. <br />The data for constituents detected at concentrations exceeding the PCLs are summarized <br />by constituent group in the following subsections. <br />6.5.1.2.1 Petroleum Hydrocarbons and PAHs <br />Concentrations of TPH-G and/or TPH-D+O exceeding PCLs were detected in soil samples <br />collected at the REC1-MW-5 and REC1-MW-8 locations along the southern property <br />boundary to the west of the warehouse (within the saturated zone; Figures 6-A2 and 6-A3) <br />but were not detected above PCLs in groundwater (Table 6-14). <br />Total cPAH (TMEQ) exceedances were detected in three Unit A soil samples including a <br />25-foot-deep sample from GF-B-15A, located west of the warehouse (0.28 mg/kg). At <br />GF-B-15A, the shallower four soil samples had no cPAH exceedances, and the 25-foot <br />sample (with cPAH exceedance) had no detectable TPH (Table 6-13); those data suggest <br />that the low-level cPAH exceedance at depth is not attributable to the Upland Area <br />historical industrial operations. The soil PCL for total cPAH (TMEQ) is based on <br />protection of groundwater (with groundwater protective of discharge to the East <br />Waterway), and following completion of the interim action, there are no groundwater <br />cPAH exceedances in wells downgradient of these soil exceedance locations, nor <br />anywhere in Unit A (Figure 6-A4). The groundwater data demonstrate empirically that the <br />cPAH concentrations in Unit A soil appear to be protective of groundwater in accordance <br />with MTCA, subject to future long-term groundwater monitoring.