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SOIL GAS INVESTIGATION WORK PLAN APN 139-224-090 530 NORTH STANISLAUS STREET STOCKTON, SAN JOAQUIN COUNTY,CALIFORNIA 95202 April 11,2024 1.0 INTRODUCTION This work plan was prepared by Condor Earth(Condor)to describe proposed Phase II Environmental Site Assessment (ESA) investigation activities at 530 North Stanislaus Street, Stockton, California (Figure 1, Appendix A, Site). Condor Earth (Condor) conducted a Phase I ESA dated XXXXX on the Site. During the ESA investigation, there are at least five high-risk off-Site properties identified including automotive repair and dry-cleaning operations that were in close proximity to the Site. Due to the likelihood of chlorinated solvent use, a vapor encroachment condition(VEC) could not be ruled out for the Site without further investigation. This soil gas investigation work plan will be conducted for the Housing Authority of the County of San Joaquin(Client). The proposed work includes advancing a total of two (2) direct push borings to 5.5 feet below ground surface(bgs)within the parking area on the eastern portion of the Site to install temporary soil gas probes. All work will be performed by a State-licensed (C-57 drilling license) drilling contractor under supervision of a Condor geologist. 2.0 SITE PREPARATION Condor will obtain the necessary drilling permits from the San Joaquin County Environmental Health Department (SJCEHD) prior to scheduling field activities with the sub-contractors and notifying Underground Services Alert(USA). The proposed boring locations will be marked with white paint and USA will be notified at least 48 hours in advance of the fieldwork to locate and identify underground utilities in and near the work area. In addition, a private utility locator will be contracted to scan and identify potential subsurface piping and other anomalies, such as any remaining underground storage tanks(USTs). Prior to initiating fieldwork at the Site, all field personnel will familiarize themselves with the Site- Specific Health and Safety Plan (HASP) and a tailgate safety meeting will be held prior to commencement of fieldwork on location. The HASP pertains to field activities and includes information on potential hazards expected to be encountered at the Site,personal protective equipment, and directions to and telephone numbers for the nearest hospital.A copy of the HASP is included in Appendix B. 3.0 PROPOSED FIELD ACTIVITIES A total of two (2) subsurface soil gas sampling probes will be installed on the eastern portion of the Site. The temporary soil gas sampling points will be installed in general accordance with the Department of Toxic Substances Control (DTSC) and the Regional Water Quality Control Board's (RWQCB) guidelines set forth in the California Environmental Protection Agency's Advisory —Active Soil Gas Investigations, dated 2015. At each of the two locations, a C-57 licensed driller will advance direct push sample rods to depths of 5.5 feet bgs. Temporary soil gas wells within the borings will be constructed with Nylaflow tubing and nylon screen. The screen will be placed at a depth of approximately 5.0 feet bgs in the middle of a one- foot-thick sand filter pack. The filter pack will be overlain with six inches to one-foot of bentonite chips followed by hydrated bentonite to the base of the next sandpack interval or to the ground surface. Prior to purging and sampling,the wells will be allowed to sit for at least two hours to equilibrate. �1 CONDOR