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I Project No 58080-06-02 January 5, 1995 ' Page 2 estimated former locations of the Douglas Oil/Texaco USTs and pump island canopy are shown on ; the Site Plan, Figure 2 Previous environmental investigations were performed at the site between March 1991 and July 1994 by Uriah Environmental Services, Inc and EPM Technologies and included the drilling of 17 soil ' borings, the installation of three groundwater monitoring wells, the installation of one vapor extraction well and the chemical analysis of soil and groundwater samples Data from these ' investigations has revealed the existence of petroleum hydrocarbons in soil and groundwater beneath the subject site, A detailed summary of the previous investigative results is included in Geocon's previous status report entitled "Interim Environmental Assessment Status Report" dated August 31, 1994 As outlined in Geocon's August 1994 report, soil beneath the site is impacted with gasoline and diesel fuel petroleum hydrocarbons resultant from the historical operation of USTs at the site Soil impacted with petroleum hydrocarbons was identified primarily beneath the central, northern and southern portions of the site to a maximum depth of approximately 45 feet below ground = 1 surface (bgs) Groundwater beneath the site was reported to be impacted with total petroleum hydrocarbons as gasoline (TPHg), 1,2-Dichloroethane (DCA), 1,2-Dichloroethene (DCE), ' Trichloroethene (TCE), Tetrachloroethene (PCE) and Methyl Tert-Butyl Ether(MTBE) The depth to groundwater beneath the site (approximately 55 feet bgs) and the maximum depth of detectable petroleum hydrocarbons in soil (ap roximatel 45 feet bgs) suest hat the chemical compounds —� N in groundwater have migrated to beneath the subject site from offsite locations This is further supported by the fact that MTBE, used as a motor vehicle fuel additive, was not introduced into Northern California until the early 1980's after the former USTs were removed from the subject site The purpose of the services performed by Geocon was to complete the vertical and lateral ' delineation of petroleum hydrocarbons in soil and further evaluate whether the chemical compounds detected in groundwater are from offsite sources Data included herein will be used in the preparation of a Problem Assessment Report for submittal to the San Joaquin County Environmental ' Health Division ' ' i SUMMARY OF FIELD ACTIVITIES ' The following field activities were performed during the current phase of investigation completed by Geocon I 'I ' Eight exploratory borings(GB-6 through GB-11, MW-4 and MW-5) were advanced utilizing a CME 75 truck-mounted, hollow stern auger drill rig and a limited access hollow stem auger drill rig at the locations depicted on Figure 2 1 lie borings were advanced to depths between 1 46 and 71 feet bgs with borings GB-6, GB-7, GB-8, GB-9 and GB-10 completed as vapor extraction wells VW-2 through VW-6, respectively Boring GB-11 was backfilled with bentonite-cement grout to surface grade The %.apoi extraction and groundwater monitoring wells were completed at surface grade with locking traffic-rated well covers I � 1 i I I 1 I I I I I