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5.0 SUMMARY AND CONCLUSIONS <br /> Partner conducted an Additional Subsurface Investigation at the subject property to further evaluate the <br /> potential impact of PCE to soil, groundwater, soil gas, and/or indoor air as a consequence of a release or <br /> releases from the former on-site dry cleaning facility and known PCE impacts to soil gas. The scope of the <br /> Additional Subsurface Investigation included the advancement of four borings (131 through 134) and the <br /> installation of two temporary sub-slab soil gas probes(SS-5 and SS-6)to facilitate the collection and analysis <br /> of soil,groundwater,and/or soil gas samples,as well as the collection and analysis of four indoor air samples <br /> (IAQ-1 through IAQ-4) and one ambient air sample (AMB-1). Four soil samples,two groundwaters samples, <br /> 10 soil gas samples, and five air samples were analyzed for PCE. <br /> Subsurface lithology encountered in the upper 30 feet bgs consisted of a varying combination of sandy silt <br /> and silt. From 31 to 40 feet bgs, the subsurface consisted predominantly of medium- to coarse-grained <br /> sand. Groundwater was encountered during this investigation between 36.1 and 36.7 feet bgs. <br /> PCE was not detected in the analyzed soil and groundwater samples at concentrations exceeding regulatory <br /> screening criteria. <br /> PCE was detected in soil gas at concentrations ranging between 250 and 7,000 pg/m3. PCE was also detected <br /> in the previous sub-slab soil gas samples (SS-1 through SS-4) at concentrations ranging between 2,000 and <br /> 13,000 pg/m3. The extent of the PCE impacts appears to be limited to soil gas and decreases with depth <br /> beneath the subject property. The highest concentrations of soil gas impacts appear to be limited to the <br /> east interior of the former dry cleaning facility (Suite 30813), presumably where on-site dry cleaning <br /> operations occurred. The regulatory exceedances indicate evidence of a release and represent a potential <br /> concern to human health and/or the environment. However, PCE was not detected in indoor air at <br /> concentrations exceeding applicable regulatory screening criteria, which indicates there is no discernable <br /> vapor intrusion concern for the subject property occupants at this time. <br /> Partner recommends additional steps to address the identified subsurface impacts to soil gas. At a <br /> minimum, additional investigation and implementation of a mitigation strategy to address the subsurface <br /> soil gas impacts appears warranted. <br /> Additional Subsurface Investigation Report PARTNER <br /> Project No.23-400162.14 <br /> July 31,2023 <br /> Page 11 <br />