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13 Site History <br /> The facility at the site has been operatingas a gasoline station since 1969 In September 19 I the <br /> g p 9 ' <br /> underground storage tanks (USTs) and associated piping were removed from the site as part of a <br />' facility upgrade Laboratory analytical results of soil samples collected during the tank removal <br /> activities reported detectable concentrations of total petroleum hydrocarbons as gasoline (TPHg), <br />' benzene, toluene, ethylbenzene, and xylenes (BTEX), and ethylene dibromide (EDB) Based on <br /> these results, an assessment was conducted at the site in August 1992 which included a soil gas <br />' survey, drilling and soil sampling of seven soil borings, and converting four of the borings into <br /> groundwater monitor/extraction wells and three of the borings into soil vapor extraction wells A <br />' soil vapor extraction pilot test was subsequently performed on the vapor extraction wells A copy <br /> of the tank pull report prepared by Canonie Environmental (Canome) was forwarded to the office <br /> of San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) on <br />' December 17, 1991 A copy of the site assessment report prepared by Canome was forwarded on <br /> May 26, 1993 Based on the PHS/EHD's June 24, 1993 reply, an additional investigation was <br /> implemented by SEACOR in December 1993 Site activities included the advancement of four <br /> verification borings to define the limit of hydrocarbon impacted soils and re-sampling the <br />' groundwater monitor wells A Problem Assessment Report was prepared by SEACOR on May 31, <br /> 1994 <br /> 2.0 SITE CHARACTERISTICS <br /> 21 Hydrggeology <br /> The site is underlain by a yellowish-brown to light olive gray, fine to medium grained sand, to a <br /> depth of approximately 15 feet below ground surface (bgs) The sand overlies a very stiff, dark <br /> yellowish-brown clay which averages 5 feet in thickness A medium brown,fine to medium grained <br /> sand was encountered from approximately 20 feet bgs to approximately 30 feet bgs where a silty <br /> clay was observed by Canonie Groundwater is encountered in this sand under unconfined <br /> Iconditions <br /> F I f"5-W FRP q NMN15{g2-0I L +Enc W <br /> Aupu+12I I MVV <br /> I <br />