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4 currently programmed to rotate ozone sparging among the zones through sixteen 72 minute cycles per day. This is yielding 19.2 hours of ozone sparging in every 24 hour day. 5.0 SOIL VAPOR SURVEY ' 6.1 Purpose of Investigation A soil vapor survey was requested by the San Joaquin County Environmental Health Division (SJCEHD), in a letter dated 6 March 2009, to evaluate the potential vapor intrusion threat from 1 possible soil contamination in the former UST excavation areas. The SJCEHD approved the workplan submitted by JJW Geosciences, Inc. (JJW), dated 23 April 2009, that outlined the soil vapor survey, on 13 May 2009. 5.2 Soil Vapor Survey Underground Service Alert was.notified a .minimum of 48 hours before the soil vapor probes were placed in the subsurface, as required. Underground water and sewer lines were noted, and the probe locations moved and sited to avoid equipment, and all known buried utilities and features, such as ozone system lines, monitor,wells, sparge points, etc. On 17.June 2009, JJW retained TEG-Northern California, Inc. (TEG) (C-57 Lic. #706568) to install six soil vapor probes (SV-1 to SV-6), three around the former gasoline UST locations, L and three around the former diesel UST locations (figure 5) and collect and analyze the soil vapor. Soil vapor samples were collected from the six probes for on-site analysis following the California Department of Toxics Substances Control / Los Angeles Regional Water L, Quality Control Board (DTSC/LAWQCB) "29 January 2003 Advisory — Active Soil Gas Investigations" protocols (DTSC protocols). Three additional samples were also collected in sorbent tubes from around the diesel UST locations for off-site diesel analysis. The six, one- inch diameter probes were installed to .a depth of 5.0 feet below the surface. (bgs) using a hydraulically driven hammer mounted on a direct push Strataprobe rig. To sample each probe location, a new, disposable, inert nylaflow 118 inch tube was inserted through the center of the probe and was attached to the sampling port; at the bottom of the •probe, with a stainless steel post run fitting. Ail steel reusable components that come in contact the soil vapor were decontaminated by washing in Alconox solution and rinsed in potable water prior to use. The probe was withdrawn slightly to open the sampling port at the probe tip. After waiting a minimum of 20 minutes after probe emplacement for equilibration, the soil vapor sample was collected by the on-site mobile laboratory analyst with a glass syringe.' Prior to use, the.glass syringes were decontaminated by heating in an oven at 175 degrees Celsius for 25 minutes. �4 � While the sample was being drawn, a leak check compound, 1,1 difluoroethane, was applied around the probe rod, ground-surface interface, and exposed sample tubing as per DTSC protocols. The soil vapor sample was analyzed for 1,1 difluoroethane in addition to the analytes of interest by the mobile laboratory. The DTSC protocols recommended leak check reporting limit of 10 µg/L was used to determine if a leak in the sampling train and apparatus existed. No 1,1 difluoroethane was detected in any of the vapor samples reported at or above the DTSC recommended leak check compound reporting limit of 10 µg/L of vapor. Thus, the integrity of the sampling train and apparatus was shown to be intact and leak free. JJW GEOSCIENCES Inc.