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Project No. S2170-07-12 <br />June 6, 2022 <br />VIA ELECTRONIC MAIL <br />Jeff Wong <br />San Joaquin County Environmental Health Department <br />1868 East Hazelton Avenue <br />Stockton, California 95205 <br />Subject: SOIL VAPOR ASSESSMENT WORKPLAN <br />STOCKTON EAST LINDSAY STREET <br />622 E. LINDSAY STREET AND 601 E. MINER AVENUE <br />STOCKTON, CALIFORNIA <br />CVRWQCB SITE #390705, <br />GLOBAL ID T0607700544 <br />Mr. Wong: <br />Geocon Consultants, Inc. (Geocon) is submitting this workplan to the San Joaquin County <br />Environmental Health Department (SJCEHD) for a soil vapor assessment at 622 E. Lindsay and <br />601 E. Miner Avenue (the Site) in Stockton, California (Figure 1). The soil vapor assessment will <br />include the installation of fourteen soil vapor wells and the collection and analysis of soil vapor <br />samples for volatile organic compounds (VOC). The California Department of General Services <br />(DGS) requested this assessment in response to the findings of our Phase II Environmental Site <br />Assessment (ESA), which identified the presence of tetrachloroethene (PCE) in soil vapor on the <br />southwestern portion of the Site at concentrations exceeding the San Francisco Bay Regional Water <br />Quality Control Board Environmental Screening Level (ESL) for PCE in soil vapor in a residential <br />setting. This DGS-owned surplus property is being assessed for the potential residential <br />redevelopment under Executive Order N-06-19 Affordable Housing Initiative. <br />This workplan summarizes background information related to the past operations on the Site, states the <br />purpose and objective of the soil vapor assessment, and describes the proposed field and sampling <br />activities and laboratory analyses. <br />BACKGROUND <br />The Site is a 0.85-acre vacant, irregularly-shaped parcel, located near downtown Stockton, California <br />in an area of commercial and residential land use. We performed a Phase I ESA of the Site in October <br />2019, which identified past site uses, including a channelized slough, residences, shops, auto sales, and <br />(most recently) a carwash. The carwash that operated on the Site (former Vintage Car Wash) is listed <br />as a closed leaking underground storage tank (LUST) regulatory case. The release of gasoline at the <br />former Vintage Car Wash impacted groundwater beneath the Site with petroleum products including <br />benzene. The release was investigated, monitored, and remediated between 1991 and 2013, when the <br />regulatory case was closed. The Central Valley Regional Water Quality Control Board (CVRWQCB) <br />closed the LUST case with residual contamination in groundwater in accordance with the State Water <br />Resources Control Board’s Low Threat Closure Policy (LTCP). However, because a change in the site <br />use is being considered from commercial to residential use, we identified possible vapor intrusion of <br />VOCs to indoor air of future residential structure(s) as a potential concern. We therefore recommended <br />and subsequently performed a Phase II ESA in December 2019 to assess these concerns.