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F <br /> .� TERRA VAC <br /> t UTILITY SURVEY <br /> I and <br /> ` PLUME STABILITY EVALUATION <br /> Former Chevron Service Station 9-4054 <br /> 2103 Country Club Boulevard <br /> Stockton California <br /> INTRODUCTION <br /> The site, located at 2103 Country Club Boulevard in Stockton California, was formerly a <br /> Chevron service station. The site is currently a vacant lot (Figure 1). Environmental <br /> investigations conducted at the site have confirmed the presence of petroleum hydrocarbons in <br /> vadose zone soils and groundwater beneath the site. The site is surrounded by light commercial <br /> and residential properties. <br /> i- <br /> Terra Vac, at the request of Chevron Products Company, has prepared the following study to <br /> identify potential preferential pathways adjacent to the site that may contribute to contaminant <br /> res <br /> i transport to adjacent properties. The report will also document result of a biodegradation <br /> evaluation with regard to plume stability. <br /> HYDROGEOLOGY <br /> Available boring logs depicting the subsurface Iithology show the saturated zone is composed of <br /> fine grain silt and clay with interbedded units of silty sand and sand. Historical groundwater <br /> monitoring data indicate that the water table has fluctuated from a depth of approximately 10 feet <br /> � to a depth of approximately 22 feet during the past 10 years. Fourth quarter 1996 groundwater <br /> monitoring data show the depth to water to be from 13.5 to 14.7 feet below the ground surface. <br /> Groundwater flow has been predominately northeast. The gradient has ranged from 0.0002 to <br /> 0.007. Groundwater velocity_has been calculated to be 2.25 feet per year (EA Engineering, <br /> Science and Technology, Inc., October 1, 1987, Report of Investigation Chevron SS 9-40.54). <br /> The nearest surface water (Smith Canal) is approximately 1300 feet south of the site and flows <br /> east to west. Smith canal is a potential recharge source for groundwater beneath the site. <br /> BENZENE PLUME <br /> Fourth quarter 1996 groundwater sampling and monitoring analytical data indicate detectable <br /> benzene concentrations in groundwater beneath the site. A summary of fourth quarter 1996 <br /> analytical datais included in Appendix A. Figure 2 illustrates the lateral extent of the dissolved <br /> benzene plume base on these data. <br /> 1 <br /> I <br /> Project 30-0212 <br /> April 17, 1997 <br /> i <br />