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1 INTRODUCTION <br /> • <br /> This report summarizes the results of a subsurface investigation conducted at former Exxon <br /> Retail Site (RS) 7-3942, located at 4444 North Pershing Avenue, Stockton, California(Figure 1) <br /> At the request of ExxonMobil Oil Corporation (ExxonMobil), ETIC Engineering, Inc (ETIC) <br /> oversaw the drilling of one exploratory boring (EB1) and the installation of three injection point <br /> pairs (IPI-IP3) (Figure 2) The work was performed to further define the vertical extent of <br /> hydrocarbon-impacted soil and groundwater, to construct wells for subsequent air spargzng tests, <br /> and to collect soil and groundwater samples needed for subsequent laboratory benchscale testing <br /> of the applicability of oxidant injection as a remedial option for the site The Aar Sparging Pilot <br /> Test Report was submitted in November 2004 The Work Plan for Benchscale Study and <br /> Oxidant Infection Pilot Tests was submitted in December 2004 and was approved by the <br /> Regional Water Quality Control Board in February 2005 The laboratory benchscale tests <br /> proposed in the work plan are currently being performed <br /> Soil and groundwater samples collected from the exploratory boring and injection point pairs <br /> were analyzed for petroleum hydrocarbons to assess the vertical extent of hydrocarbon impact, <br /> and were analyzed for a suite of general minerals as part of the benchscale study to evaluate the <br /> effects of injecting ozone and hydrogen peroxide into the subsurface The injection point pairs <br /> were used to perform air sparging tests, which provided additional information needed to assess <br /> if in situ chemical oxidation using a combination of ozone and hydrogen peroxide is a viable <br /> option as a remedial technology The general mineral suite analytical results will be submitted <br /> . under separate cover in the benchscale study report <br /> Scope of Work <br /> The investigation consisted of the following activities <br /> • Prior to field work, a permit for the installation of the three injection point pairs and one <br /> exploratory boring was obtained from the San Joaquin County Environmental Health <br /> Department (SJCEHD) on 14 September 2004 <br /> • ETIC personnel marked the three proposed injection point pair locations and one <br /> exploratory boring location as indicated on Figure 2, and Underground Service Alert was <br /> contacted prior to drilling A licensed utility line locator cleared the marked drilling <br /> locations <br /> • On 17 September 2004, the boreholes were vacuum cleared to 8 feet The boreholes <br /> were drilled from 20 to 22 September with a truck-mounted rotary drill, using hollow- <br /> stem continuous-flight augers <br /> • Soil samples from the boreholes were collected and logged during drilling at intervals of <br /> approximately 5 feet in the vadose zone and then continuously in the saturated zone to <br /> the total depth of the boreholes to characterize subsurface lithology Selected soil <br /> samples were retained for laboratory analysis based on significant lithologic changes <br /> and/or organic vapor analyzer measurements <br /> G 1Projects%739421MA5TER5WP4PR1204UPRtcxt&c 1 <br />