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9 0 <br />Ms. Vicki McCartney <br />April 21, 2005 <br />Page 3 <br />CPT/Direct-Push Borings and Sample Collection <br />To evaluate conditions surrounding the site, approximately twelve boring locations will be <br />advanced onsite and offsite to provide a comprehensive view of the extent of petroleum <br />hydrocarbon impact (Figure 2). Each boring location will consist of a CPT and a direct -push <br />boring. Approximately nine boring locations will be performed on the Chevron property. <br />Two boring locations are proposed in the area of the City of Stockton Maintenance Yard to <br />the southwest of the site and one boring location is proposed in the area of the motel to the <br />west of the site. Completion of the off site borings is dependent on obtaining access to <br />each property. <br />The CPT borings will be advanced to at least 50 feet below ground surface (bgs) to assess <br />petroleum hydrocarbon impact and soil lithology and stratigraphy at locations shown in <br />Figure 2. The total boring depths and soil and groundwater sampling intervals will be <br />determined by field instruments and observations made during the sampling program. The <br />borings will be extended until either probe -refusal or until "clean" soils and groundwater are <br />encountered. During completion of the CPT borings, the soil and groundwater column will <br />be screened for volatile petroleum hydrocarbons using a Membrane Interface Probe (MIP). <br />Adjacent to each CPT borehole, a direct -push boring will be advanced to collect discrete <br />soil and groundwater samples. Information from the MIP will be used to target specific <br />depth intervals at which soil and groundwater samples will be collected during the direct - <br />push borings. Selected soil and groundwater samples, collected during completion of the <br />direct -push borings will be submitted for chemical analysis for the analytical parameters <br />described below. <br />Soil and Groundwater Analytical Parameters <br />Soil and groundwater samples from each direct -push boring will be submitted for chemical <br />analysis. All soil and groundwater samples submitted for chemical analysis will be <br />analyzed for Total Petroleum Hydrocarbons reported as gasoline (TPHg), diesel (TPHd), <br />and motor oil (TPHmo) by EPA Method 8015M, and benzene, toluene, ethylbenzene, and <br />total xylenes by EPA Method 82608. A silica -gel clean-up will be performed on all samples <br />submitted for analysis for TPHd and TPHmo. TPHd and TPHmo analyses will be <br />performed on the samples before and after the silica -gel cleanup. In addition, all soil and <br />groundwater samples will be analyzed for methyl tertiary butyl ether (MtBE), di -isopropyl <br />ether (DIPE), tertiary amyl methyl ether (TAME), ethyl tertiary butyl ether (EtBE), tertiary <br />butyl alcohol (TBA), ethyl dibromide (EDB), 1,2 dichloroethane (1,2 -DCA), ethanol, and <br />methanol by EPA Method 8260. <br />N:\Files\Projects\Chevron\Retail\#9-2033\REPO RTS\2005Add n'IAssessmentworkPla n.doc <br />