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9 March 2020 Page 3 — Polynuclear aromatic hydrocarbons(PAHs) using USEPA Method 8270; — Diesel range petroleum hydrocarbons(TPHd)and motor oil range petroleum hydrocarbons(TPHmo) using USEPA Method 8015 mod. • Upon completion of the soil sampling,each boring will be backfilled with cement grout, in accordance with San Joaquin County Environmental Health Department permit requirements. • Soil cuttings generated from the sampling will be placed in a labeled 55-gallon drum,which will be temporarily stored on the Site in a secure location pending waste profiling and future transportation and disposal by a California-licensed waste hauler. Soil Vapor Sampling Haley&Aldrich will install and sample temporary soil vapor probes at five locations at the Site(Figure 1). To perform this sampling, Haley&Aldrich will conduct the following activities: • A private utility locator will be used to scan for underground utilities in the vicinity of the proposed soil vapor sampling locations. • Five borings will be advanced to a total depth of approximately 5.5 feet bgs using a hand auger. A temporary soil vapor probe will be installed in each boring at a depth of approximately 5 feet bgs.Small diameter(1/4-inch)Teflon®tubing,fitted with a filter at the bottom to prevent particulate infiltration,will be placed in the boring at approximately 5 feet bgs.Approximately 12 inches of filter pack sand will be placed around the tubing inlet in the bottom of the boring (from 4.5 to 5.5 feet bgs).After installation of the sand pack,the borehole will be backfilled to the surface with hydrated bentonite.Once the construction of the soil vapor probe is complete, the tubing will be capped with an air-tight valve.A flush-mounted well box or protective cover will be placed over each soil vapor probe location. Soil vapor probes will be allowed to equilibrate for a minimum of 48 hours prior to purging and sampling. Per California Department of Toxic Substances Control (DTSC)guidance,if a rain event producing more than a half inch of rain occurs in a 24-hour period,sampling will not be completed for a minimum of five days afterward. • Prior to sample collection,the soil vapor probes will be leak tested and purged,then sampled in general accordance the California Environmental Protection Agency/Department of Toxic Substances Control Advisory—Active Soil Gas Investigations(CalEPA/DTSCAdvisory),dated July 2015. • Soil vapor samples will be submitted following standard environmental handling methods and under chain-of-custody documentation to a California-certified analytical laboratory for the following: — VOCs using USEPA Method TO-15; — Fixed gases(oxygen,carbon monoxide, and methane)analysis using ASTM Method 1946D. • The temporary soil vapor probes will be destroyed within four weeks of installation.The probes will be destroyed by gently pulling out the Teflon®tubing,then tamping down the hydrated bentonite to ensure closure of the small diameter(1/4-inch)opening.