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31 October 1996 <br /> AGE-NC Project No 95-0113 <br /> Page 2 of 4 <br />' 2 3 GROUND WATER DEPTH AND FLOW DIRECTION <br /> Based on the San Joaquin County Flood Control and Water Conservation District map entitled Lines <br /> } of Equal Elevation in Water Wells - Fall 1993, ground water depth at the site is approximately 20 <br /> feet below surface grade (bsg) Regional flow direction in the area of the site is west to southwest <br /> However, flow direction can vary locally and with seasonal changes of ground water depth <br /> 1 <br /> 3.0. UNDERGROUND STORAGE TANK REMOVAL AND SAMPLING <br />' In Jul 1994 one 5,000-gallon and one 3,000-gallon gasoline USTs were removed from an area east <br /> Y z � <br /> of the maintenance building on the site by Goins Environmental Construction(GEC) of Sacramento, <br />' California Soil samples were collected from beneath the UST's following the tank removal by <br /> Geological Audit Services, Inc (GAS) for GEC Total petroleum hydrocarbons quantified as <br />' gasoline(TPH-g)and volatile aromatics (benzene,toluene, ethyl-benzene and total xylene BTE&X) <br /> were detected in t«o soil samples from the UST excavation Sample N-1, which was sampled from <br /> the northern side wall of the tank excavation at 11 feet,contained the highest concentration of TPH-g <br /> at 3,600 mg/kg (milligram per kilogram or parts per million ppinn) The highest concentrations,of <br /> BTE&X weie detected in the same sample, benzene and xylenes were detected at 70 and 400 ppm, <br /> respectively However, the highest concentration of total lead, 250 ppm, was detected in a different <br />' sample, E1, which was collected from the eastern wall of the tank excavation <br /> Soil removed during the UST excavation was stockpiled on-site and was subsequently sampled in <br />' August 1994 The samples were composited and analyzed for TPH-g, BTE&X and total Iead The <br /> sample contained 14 mg/kg of TPH-g and 15 mg/kg of total lead <br />' The soil sampling piocedures-,�e`re sununiarized in GAS,report, dated 09 September 1994 Analytical <br /> results of all soil samples are summarized on Table 1 The laboratory reports (MAI Laboratory ID <br />' Nos 36634 to 36637, 36771 to 36774 and 40667), QC reports and chain-of-custody forms are <br /> included in Appendix A <br /> Based upon laboratory results of soil samples from the UST removal, the PHS-EHD required further <br />' investigation to determine the extent of the hydrocarbon-impacted soil acid/oi ground water at the <br /> site <br /> 1 <br /> 4 0. SUBSURFACE INVESTIGATION <br />' Five borings were established by Advanced GeoEnvironmental,'Inc (AGE) in May 1995 Two <br /> borings(B 1 and B2) were drilled at an angle of 25' from vertical to the east (Figure 2) Borings B3 <br /> 1 i I <br /> ' r <br />