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i (Basin 5-22) This basin is drained primarily by the San Joaquin River • I The closest surface water features to the site are San Joaquin River and Walker Slough located approximately 4,500 feet southwest of the site Water from the site drains into the San Joaquin River Deep Water Channel which is primarily used for commercial and recreational boating Based upon Iwell information obtained from the most recent quarterly monitoring event (03104), ground water flow direction is towards the southeast and is currently occurs at a depth of approximately 29 to 30 feet below surface grade (bsg) UNDERGROUND STORAGE TANK REMOVAL On 21 October 1999, three USTs and associated piping and dispenser islands were removed from the site by Stockton Service Station Equipment Company (SSSEC) of Stockton, California The USTs were Iocated in a common excavationn near the northern portion of the property The axis of each tank was oriented roughly east-west Approximately 150 cubic yards ofhydrocarbon-impacted Isoil were removed and stockpiled during excavation of the USTs Nine samples were collected beneath the USTs, six samples were collected beneath the dispenser area and two laboratory-composited soil samples were collected from the excavated stockpiled soil Methyl tertiarybutyl ether(MTBE),tertiarybutanol(TBA),tertiary-amyl methyl ether(TAME)were � . detected in each of the soil samples collected from the site Total petroleum hydrocarbons quantified as gasoline (TPH-g) were detected at concentrations as high as 3,849 milligrams per kilogram (mg/kg)beneath the western end of the center UST location Volatile aromatics including benzene, toluene, ethyl benzene and xylenes (BTEX) were detected at concentrations as high as 29,720 micrograms per kilogram (µg/kg) from the same sample location SOIL EXCAVATION IOn 20 April 2000, approximately 175 cubic yards of petroleum hydrocarbon-impacted soil were excavated from the former UST area Excavation was performed by SSSEC The highest concentrations of petroleum hydrocarbons,TPH-g and fuel additives were detected near the eastern end of the center UST(sample EN-16') Fuel oxygenating compounds,including MTBE, I TBA and TAME,were detected in each of the soil samples collected from the site at concentrations as high as 11,000 gg/kg TPH-g was detected at concentrations up to 12,000 mg/kg beneath the western end of the center UST location BTEX was detected at concentrations up to 1,800 mg/kg I (total xylenes) Analytical results of soil samples collected beneath the former USTs and piping area are summarized in Table 1 Advanced CeoEnvironmental,Inc