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SAP/QAPP Addendum <br /> Lodi-125 N Stockton <br /> Final <br /> March 24,2025 <br /> The Phase II ESA produced the following findings,which can be found in Figure 2: <br /> o Concentrations of lead (up to 673 milligrams per kilogram [mg/kg]) and arsenic (up to 52.9 <br /> mg/kg) that may be associated with historical MGP operations. Several lead samples <br /> exceeded the EPA Regional Screening Level(RSL) for industrial soil,and two arsenic <br /> samples exceeded the upper-bound published background for the Site (Stantec,Inc. 2023). <br /> o One sub-surface soil sample at the location of the former UST contained residual <br /> hydrocarbons between 8 and 13 feet below ground surface (bgs). <br /> o Soil samples collected from beneath the equipment repair shop did not contain <br /> concentrations of petroleum hydrocarbons or volatile organic compounds (VOC) in <br /> exceedance of screening levels. <br /> o Soil gas samples contained concentrations of perchloroethylene (PCE) in exceedance of <br /> EPA commercial/industrial human health risk-based screening levels. Concentrations of <br /> PCE in samples collected from beneath the repair shop ranged from 690 to 800 micrograms <br /> per cubic meter [µg/m3]. One sample collected at a different location on the Site contained a <br /> concentration of trichloroethylene (TCE) of 17,000 µg/m3,potentially representing a <br /> separate VOC source apart from PCE-impacted groundwater.An asphalt patch like that of a <br /> small UST was found on the Site and can potentially be linked to the source of TCE in soil <br /> gas. <br /> 2.4 Geological Information <br /> The Site is within the Great Valley geomorphic province of California(Stantec,Inc. 2021).The Site is within <br /> an Eastern San Joaquin Subbasin of the San Joaquin Valley Groundwater Basin,comprised of an alluvial plain <br /> that stretches from the Sacramento Valley to the San Joaquin Valley.The local geology is characterized by <br /> undifferentiated Alluvium and Modesto/Riverbank Formations of the Pleistocene,Flood Basin Deposits <br /> (since the Pliocene),and the Laguna (Plio-Pleistocene) and Mehrten (late Miocene to Pliocene) Formations. <br /> Depth to groundwater at the Site is approximately 41 to 63 feet bgs and groundwater flow direction is <br /> assumed to be toward the south-southeast (Stantec,Inc.2021). <br /> 7 <br />