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BLEW Soil Borings and Soil Vapor Sampling A total of seven (7) soil borings are proposed at the locations depicted on Figure 1. Soil borings will be advanced utilizing direct-push technology. The soil borings will be advanced to a terminal depth of approximately five feet-bgs to install temporary soil vapor wells. The temporary soil vapor wells shall generally consist of approximately 3/8" x 1.5" polyethylene vapor implants, 1/4" Teflon tubing, and 1/4" polycarbonate sample valves. The soil vapor well construction details will generally be as follows: the vapor implant will be embedded within an approximate 1' sand pack, followed by approximately 1' of dry granular bentonite, and a hydrated bentonite annular seal. The temporary soil vapor wells will be allowed to equilibrate for at least two hours prior to purging and sampling activities. Prior to sampling, a shut-in test will be conducted to check for leaks in the above- ground sampling system, and three volumes of air will be purged from the soil vapor well and sampling train. The purging rate will be set between 100 to 200 milliliters/minute (mL/min). Prior to and during purging and sampling, a leak test shall be performed utilizing helium and a shroud. Due to the EHD request for soil vapor analyses to include total petroleum hydrocarbons as diesel range organics(TPH-DRO), soil vapor sampling will be performed utilizing sorbent tubes and shall be analyzed by McCampbell Analytical of Pittsburg, California for volatile organic compounds (VOCs) and TPH- DRO by EPA Method TO-17. Soil vapor well installation and sampling will be conducted in general accordance with the Advisory—Active Soil Gas Investigations,California Department of Toxic Substances Control (DTSC), July 2015. Borehole Abandonment After sampling is complete, the soil vapor well tubing will be pulled out of the ground by hand, and the boreholes with be abandoned with neat cement and patched at the surface to substantially match original ground conditions. Reporting The results of the additional soil vapor sampling will be submitted to the EHD for review within 30 days of completion of field activities. Analytical results will be evaluated relative to the SFBRWQCB Environmental Screening Levels (ESLs) published in January 2019, and the screening levels established by the California Department of Toxic Substances Control, Human and Ecological Risk Office (HERO), Human Health Risk Assessment (HHRA),Note No. 3, June 2020. SCHEDULE The proposed schedule is contingent upon EHD reviewing and approving this Work Plan, Site access,and driller/field personnel availability. Work Plan for Additional Investigation 2546 French Camp Turnpike, Stockton,CA 95206 2