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Mr. Siddarth Sewalia 1 February 2011 Page 2 • Geosyntec will obtain a traffic control and encroachment permit from the City of Stockton for work in the right-of-way of South Argonaut Street; f • Geosyntec will mark the sampling locations with white paint and notify Underground Service Alert(USA North) at least 48 hours prior to the onset of subsurface activities; • All sampling locations will be cleared for underground utilities by a private underground utility locating service; and • Geosyntec will update the Site health and safety plan, as needed, in accordance with California Occupational Safety &Health Administration requirements. Sampling Procedures Soil gas sampling will be conducted in accordance with the joint Department of Toxic Substance Control (DTSC) and California Regional Water Quality Control Board, Los Angeles Region, (LA RWQCB) Advisory — Active Soil Gas Investigations guidance' with the leak check procedures incorporated from DTSC's March 2010 Draft Advisory — Active Soil Gas Investigation? Temporary soil gas probes will be installed to a target depth of 5 feet below ground surface (ft bgs). If there is a significant rain event (e.g., 'h inch or greater), the probes will not be installed until at least 72 hours have passed. At each location, a continuous core direct-push boring will be advanced to 5 ft bgs. Upon completion, the direct-push rods and core will be removed from the boring. The soil cores will be logged according to the Unified Soil Classification System (USCS) by the field geologist or engineer, under the supervision of a California Professional Geologist. A probe consisting of a 6-inch-long, '/4-inch-diameter stainless steel screened implant connected with a compression fitting to '/4-inch Nylaflow tubing will be installed in the boring. A sand filter pack will be placed within the borehole annulus around the probe and will extend from the base of the boring to a height of approximately 6 inches above the probe screen. Granular bentonite will be then placed in two lifts of approximately 3 inches each above the filter pack and will be hydrated as each lift is placed. The remainder of the borehole annulus will be backfilled with a thick bentonite-water slurry to seal the borehole annulus to ground surface. Following placement of the bentonite seal,the top end of each soil gas probe will be fitted with a 'DTSC and LA RWQCB,2003.Advisory—Active Soil Gas Investigations, 28 January 2003. 2 DTSC,2010.Draft Advisory—Active Soil Gas Investigations, March 2010. P:\PRJ2003REM\Wilbur-Ellis\Wr0250(JTF)\STOCKTON\S1.P Vapor Sampling\Work Plan\JTF Stockton Off-Site Soil Gas Sampling Work Plan.docx engineers I scientists I innovators