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Soil and Groundwater Investigation Quik Stop No 121 Page 2 bottom of the excavation Two grab water samples were also collected from the south end of the excavation using a disposable bailer and nylon string Approximately 200 cubic yards of pea-gravel were excavated from the tank area pnor to the removal of the three underground fuel tanks on March 26, 1998 and stockpiled on the southwest and west sides of the site The County requested that this material be sampled for contamination Seven discrete samples were collected from the stockpile for analysis of TPHGBTEX and oxygenates At this point, the open excavation at the subject site measured approximately 35'x 44' x 33'x 39' and ranged in depth from approximately 12 to 15 feet The existing canopy and the western footing of the canopy structure were exposed and being undermined by the collapsing, into the open pit, of the unexcavated pea-gravel that was beneath the concrete slab and canopy footings In addition, the native soil (sand) on the north and northwest sides of the excavation was, at times, collapsing into the open excavation (after the removal of the tanks and while excavating to collect samples of the native soil) Based on this, Quik Stop intended to place the stockpiled material back into the open excavation to shore-up the exposed canopy footings and to prevent further soil collapse as quickly as possible The six soil samples collected from the bottom of the excavation were reported by the laboratory to be free of detectable TPHG Soil sample S-2 was reported to have 15 milligrams per kilogram (mg/kg) of benzene Soil sample S-3 was reported to contain toluene at 1 I mg/kg and ethylbenzene at 21 mg/kg No other TPHG or BTEX compounds were reported in these six samples The laboratory did report oxygenates in all six soil samples Methyl-t-Butyl Ether(MTBE)was detected and ranged from 43 micrograms per kilogram (ug/kg) in S-1 to a high of 27,000 ug/kg in S-5 No other petroleum compounds were reported in these samples The two grab water samples (W-1 and W-2) were reported to contain detectable petroleum compounds, including 1,500 micrograms per liter (ug/l) TPHG in both W-1 and W-2, 3 to 4 ug/l benzene, toluene ranging from 11 to 23 ug/l, ethylbenzene ranging from 14 to 19 ug/l and total xylenes ranging from 200 to 270 ug/l In addition, MTBE was reported at 6,800 ug/l in W-1 and 5,900 ug/1 in W-2 These two water samples were also reported to contain 55 and 56 ug/l, respectively, of t-amyl methyl ether (t-AME) The laboratory also reported five of the seven stockpile soil samples to be free of detectable petroleum contamination Two of the seven samples (SP-2 and SP-3) were reported to contain MTBE at concentrations of 72 ug/kg and 11 ug/kg, respectively No other petroleum compounds were reported in these samples Based on data obtained during the tank excavations, visual observations, analytical laboratory results and the condition of the three fuel tanks at the time of their removal, San Joaquin County Public Health Services, Environmental Health Division required further investigation at the site to define the extent of soil and groundwater contamination •