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i From 15 to 30 feet below surface grade (bsg) is characterized by an orange brown silt with little or no plasticity and low consistency From 35 to 40 feet bsg is characterized by an orange brown Iclayey silt and an olive brown silt at 45 feet bsg PREVIOUS INVESTIGATIONS IAccording to records on file with the San Joaquin County Environmental Health Department (SJCEHD), four underground storage tanks (USTs) were formerly located on the property Three of the USTs were located in a common excavation, west of the on-site building, a fourth UST, presumably used for waste oil, was located south (behind) the on-site building In 1998, the four USTs were removed by Paydirt Excavation The USTs had been out of commission and empty at the time of removal Soil samples were collected from the UST excavation, former piping areas and dispenser island area Petroleum hydrocarbons were not Idetected in soil samples collected at the time of removal On 19 July 2004, three soil probe borings (B1 though B3) were advanced at the site utilizing a Ivan-mounted Geoprobe 5400 direct-push probing unit equipped with 1 125-inch probing rods Boring B1 was advanced in the former tank pit to a depth of approximately 30 feet bsg at which I point probe advancement ceased due to subsurface refusal as the result of pea gravel failing into the boring from the overlying tank pit Boring B2 was advanced as a continuation of BI, located 10 feet north of B1 dust outside the tank pit Samples were collected in boring B2 starting at 35 feet bsg to a total depth of 45 feet bsg Boring B3 was advanced in the former dispenser location to a total depth of 20 feet bsg Soil boring locations are depicted on Figure 2 I Samples were collected from the borings at discrete five-foot intervals using a 1 125" Geoprobe soil sampling assembly loaded with four six-inch brass sleeves A total of five soil samples were analyzed for petroleum hydrocarbon products The following target analytes were detected I • TPH-g was detected in soil samples collected from borings B 1 and B2 at a maximum concentration of 500 milligrams per kilogram (mg/kg) in boring B 1 at 25 feet bsg I • Toluene, ethylbenzene and xylenes were detected in borings B1 and B2 at maximum concentrations of 0 017 mg/kg toluene (B2-45), 0 017 mg/kg ethylbenzene (B2-45) and 6 3 mg/kg xylenes (B2-35) • EDB was detected in one soil sample at a concentration of 0 045 mg/kg(B2-35) No other target analytes were detected at or above laboratory detection limits in any of the samples analyzed IOn 20 and 21 July 2005, 3 soil borings were advanced to approximately 70 feet for installation of ground water monitoring wells Monitoring wells MW-1, MW-2 and MW-3 were installed to 70 Ifeet bsg and screened 50 to 70 feet bsg Quarterly ground water monitoring commenced on 05 August 2005