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16 SOFA <br /> Enwonmental Technology Inc _ <br /> 3.2 On-site Areas of Environmental Concern <br /> A review of previous preliminary investigations conducted by ETS and Applied <br /> ' Consultants on the subject site indicated that the site was a gasoline station <br /> since 1950 and that four underground storage tanks were decommissioned and <br /> removed from the property on July 10. 1990 A subsequent investigation <br /> Indicated that an unauthorized release of petroleum hydrocarbons had <br /> occurred and that both the soil and groundwater had been Impacted The <br /> limits of the groundwater contamination has not been evaluated <br /> ' Elevated concentrations of Total Petroleum Hydrocarbons (TPH) and purgeable <br /> aromatic hydrocarbons (BTEX) were detected in soil samples obtained from the <br /> /gasoline tank excavation, the product line excavation, and in each of the three <br /> borings which were converted into monitoring wells (MW-1, MW-2, and MW-3) <br /> The highest TPH concentration, 3,300 mg/kg was detected in the soil sample <br /> obtained from boring B-3 (MW-3) at a depth of 65 5 feet Free product was also <br /> encountered in the product line excavations. <br /> Elevated concentrations of Total Petroleum Hydrocarbons (TPH) and purgeable <br /> aromatic hydrocarbons (BTEX) have been detected in groundwater samples <br /> ' obtained from monitoring wells MW-1, MW-2, and MW-3 The highest TPH <br /> concentration, 18,000 ug/1 was detected in the water sample obtained from <br /> MW-1. TPH and BTEX have not been detected in the groundwater samples <br /> obtained form MW-2 and MW-3 in the first two quarters in 1993 (AC report <br /> dated 11 January 1993 and 9 April 1993). <br /> The depth to groundwater is approximately 65 to 70 feet below ground surface <br /> ' (BGS) at the subject site According to Mr. Michael Infurna of the San Joaquin <br /> Public Health Services, and historic groundwater elevation data (Table 3), the <br /> groundwater elevation in this area fluctuates more than 20 feet, seasonally <br /> The highest concentrations of petroleum hydrocarbons have been detected <br /> along the_e pro erg tv,line, up gradient of both the fuel dispensing island <br /> and the former tank excavation, The groundwater flow direction in the area of <br /> the subject site has been reported to vary over time from west to north and <br /> back to west. <br />' 4.0 SUBSURFACE INVESTIGATION <br />' In accordance with San Joaquin County Environmental Health Division letter <br /> dated August 31, 1994 to UHI, SOTA proceeded with plans for the delineation <br /> of the soil and groundwater at the subject site The workplan included drilling, <br /> subsurface sampling and installation of three monitoring wells, which included <br />' two 'off-site" monitoring wells (MW-7 and MW-9) to the southeast and east of <br /> the U-haul Center, respectively, and MW-8, drilled "on-site" in the western <br /> portion of the site The monitoring well construction permits were obtained <br /> from the San Joaquin County Environmental Health Division SOTA also <br /> obtained encroachment permits from the County of San Joaquin Department of <br /> Public Works for drilling monitoring wells MW-7 and MW-9 in the public right of <br /> way- <br /> 3 <br />