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i I f Site Investigation Work Plan Nella Oil Station #21 , 40052 Highway 41 , Oakhurst, California 11 3.0 PROPOSED SCOPE OF WORK As directed in their January 12 , 2009 letter, the SJCEHD required that Caltanks conduct a soil vapor survey to investigate the potential for vapor intrusion into on-site buildings at the subject site . The following details the soil vapor survey scope of work: 5. 1 Project Planning WRM will obtain the required boring permits and work plan approval from the SJCEHD . Underground Service Alert ( USA) will be notified a minimum of 48 hours prior to the installation of the soil borings to locate any utilities in the vicinity of the planned boring locations. Prior to initiating fieldwork, a site-specific health and safety plan ( HASP) will be prepared . The HASP will include safety procedures for work to be performed , chemical hazard information , site safety officers , and a medical emergency location . The HASP will be kept on site at all times during the site investigation work. 5.2 Soil Vapor Survey To evaluate potential vapor concentrations throughout the site, WRM will collect eight (8) on- and off-site soil vapor samples in accordance with the California Regional Water Quality Control Board Los Angeles Region , Interim Guidance for Active Soil Gas Investigation dated February 25 , 1997 ; the California Department of Toxic Substances Control Advisory — Active Soil Gas Investigations dated January 28, 2003 ; and the California Department of Toxic Substances Control Interim Final Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air, dated December 14 , 2004 and revised February 7, 2005 . Soil vapor points will be constructed by advancing a 4-inch diameter Geoprobe® MacroCore® sampler to approximately 5-feet bgs. Following removal of the MacroCore®, Teflon tubing fitted with a porous media and inserted into a 1 -inch diameter PVC casing , will be lowered to the total borehole depth . Approximately 1 -foot of sand will be placed on top of the screen through the PVC casing and added as the casing is removed allowing the sand evenly distribute in the borehole . Approximately 1 -foot of dry bentonite pellets will be added on top of the sand through the PVC casing . The PVC casing will be removed from the borehole and additional bentonite will be added to approximately 3-inches bgs and slowly hydrated . After sampling the tubing will be removed and the top of the borehole filled and patched to match the surrounding surface . WRM will wait at least 30-minutes after well construction to allow for subsurface equilibrium . i For each soil vapor sample, the system will be purged of approximately three system volumes prior to sampling to ensure that a representative soil vapor sample is collected . Immediately prior to sampling , a tracer gas will be applied to the sampling tubing at ground level and to the fittings to check seal integrity. The tracer gas will be included in the analytical suite to verify soil vapor sample reliability. ;Each soil vapor sample will be collected in laboratory provided containers at a flow rate of 100 to 200 milliliters per minute. 6