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San Joaquin County Environmental Health Department Site Mitigation Program 8 December 2021 Page 3 – 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 and A protective cover will be placed over each soil vapor probe location. –  In accordance with the California Environmental Protection Agency/Department of Toxic Substances Control Advisory – Active Soil Gas Investigations (CalEPA/DTSC Advisory), dated July 2015, the soil vapor probes will be allowed to equilibrate for a minimum of 48-hours prior to purging and sampling. Additionally, per CalEPA/DTSC Advisory, if a rain event producing 0.5 inches or more in a 24-hour period, sampling will not be completed for a minimum of 5 days afterward.  Prior to sample collection, the soil vapor probes will be leak tested and purged, then sampled in general accordance with the CalEPA/DTSC Advisory.  The soil vapor samples will be collected in laboratory-provided passivated cannisters, which will be submitted under chain-of-custody documentation to a California-certified analytical laboratory for the following: – VOCsUSEPA Method TO-15; and – Methane using American Society for Testing Materials (ASTM) Method D1946.  The temporary soil vapor probes will be destroyed within 4 weeks of installation. The probes will be destroyed by overdrilling the temporary soil vapor probes the entire depth of the original boring and sealing the borehole with cement.  Investigation-derived waste generated during the drilling activities will be stored in a labeled 55- gallon drum which will be stored onsite pending waste profiling and offsite disposal. Reporting Haley & Aldrich will prepare a report documenting the completed soil and soil vapor sampling activities and summarizing the analytical results. A copy of this report will be submitted to SJCEHD to comply with their permitting requirements. Schedule Haley & Aldrich anticipates completing this work as soon as SJCDEH approves this Work Plan and issues the permit. We have currently scheduled Tuesday, 4 January 2022 as the initial drilling date. Haley & Aldrich will contact SJDEH to schedule an inspection upon issuance of the permit.