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The tracer compound, 1,1-DFA, was detected in one of the analyzed soil gas samples (B1-SG15). According <br /> to the DTSC, detection of tracer compound at concentrations of less than 10 times the laboratory RL of the <br /> target analyte are considered insignificant. For the purposes of this investigation, the lowest RL (6.9 pg/m3 <br /> for PCE) was utilized for comparison, resulting in a significance threshold of 69 pg/m3. The 1,1-DFA <br /> concentration detected in soil gas sample 131-SG15 (32 pg/m3) does not exceed the significance threshold. <br /> Therefore, this limitation is not anticipated to materially impact the findings of this investigation. <br /> Refer to Table 3 for a summary of the soil gas sample PCE laboratory analysis results. <br /> 4.6 Indoor Air Sample Data Analysis <br /> PCE was detected in each of the indoor air samples at trace concentrations above the laboratory method <br /> detection limits (MDLs); however, these detections do not exceed the commercial/industrial ESL of 2.0 <br /> pg/m3. <br /> Refer to Table 4 for a summary of the indoor air sample PCE laboratory analysis results. <br /> 4.7 Discussion <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 308B), 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 /> Additional Subsurface Investigation Report PARTNER <br /> Project No.23-400162.14 <br /> July 31,2023 <br /> Page 10 <br />