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Weston Solutions, Inc. <br /> Remedial Action Work Plan for the San Joaquin County Human Services Agency Site—Stockton, California <br /> PREVIOUS INVESTIGATIONS <br /> ■ If the site qualifies for Low Threat Closure Policy criteria, demonstrate how each of <br /> the criteria is met. <br /> In April 2014, WESTON prepared a Groundwater Data Gap Investigation Work Plan to <br /> address the EHD concerns with the Low-Risk Closure Request Report. EHD approved the <br /> Work Plan in May 2015. <br /> In July 2015, the Central Valley Water Board became the lead agency for the Site, and in <br /> March 2018, the Central Valley Water Board requested the following: <br /> ■ Conduct a Sensitive Receptor Survey to identify public and private water supply wells <br /> and surface water bodies within 1,000 feet of the Site. <br /> ■ Prepare a Work Plan to install and sample permanent soil gas wells near the southeast <br /> corner of the building. <br /> ■ Collect soil samples near former USTs that contained waste oil or unknown contents <br /> and analyze the samples for TPH-g,TPH-d,total oil and grease(TOG),volatile organic <br /> compounds (VOCs), semi-VOCs (SVOCs), polychlorinated biphenyls (PCBs), <br /> polycyclic aromatic hydrocarbons (PAHs), and Title 22 metals. <br /> ■ Collect soil samples near former gasoline USTs near well MW-3A for TPH-g and <br /> VOCs. <br /> ■ Collect and analyze soil samples to sufficiently assess methyl tertiary butyl ether <br /> (MTBE) concentrations at the Site. <br /> In May 2018, four cone penetrometer testing (CPT) borings were drilled to collect soil <br /> lithology and groundwater samples at locations downgradient of the Site. Two borings(CPT-1 <br /> and CPT-2) were drilled on the east side of South Sutter Street and two borings (CPT-3 and <br /> CPT-4) were drilled further downgradient on a vacant lot owned by the City of Stockton <br /> (Figure 2-2). Low concentrations of TPH-g and benzene were detected in the groundwater <br /> sample from boring CPT-2, indicating that this boring is located at the downgradient extent of <br /> the dissolved hydrocarbon plume originating from the former USTs. TPH-g, TPH-d, and <br /> benzene, toluene, ethylbenzene, or xylenes (BTEX) were not detected in the samples from <br /> borings CPT-3 and CPT-4, indicating that the dissolved hydrocarbon plume does not extend <br /> into the area east of the vacant building (former restaurant). <br /> 2-6 Febraary 2021 <br />