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iHistorical Background AGE-NC Project No 00-0764 Page 2 of 3 To mitigate an unauthorized release of petroleum hydrocarbons from the current UST excavation floor,the scope of work included the excavation of a limited volume of hydrocarbon-impacted soil and collection of soil samples ' excavated using a backhoe or an excavator to a depth of one to two feet below the depth Soil was exca g p of the UST inverts Soil was placed into an excavation soil bin for transportation to an appropriate landfill class i landfill at Waste Management at Kettleman Hills or class II landfill at Forward Landfill at Stockton Excavated soil was field screened for the presence of volatile organic compounds using an OVM,however,due to the release of waste fluids,all waste placed into the bins ' was disposed of at an appropriate landfill ' Following the excavation and sampling,clean and appropriate backfill was placed in the excavation PREVIOUS SITE INVESTIGATIONS On 23 and 24 October 2001,four soil probe bonngs(BI through 134)were advanced at the site under lie the oversight of the San Joaquin County Environmental Health Department(EHD) Probe borings were advanced in the former UST excavation as well as west,southwest,and east of the former UST area to collect soil and grab ground water samples Probe boring B 1 was advanced to a total depth ' of 65 feet bsg and borings B2 through B4 were advanced to 40 feet bsg Analytical data is presented in the attached tables Locations of the soil probe borings are illustrated on Figure 2 of the report ' The most intensely hydrocarbon-impacted soil was encountered in the area of the former USTs (boring 131), contaminants were not detected in analyzed soil samples collected from borings B2 through B4 At boring location B 1,petroleum hydrocarbons were detected in collected soil samples to depths of 30 feet bsg,but generally were not detected in soil samples collected at 40 feet bsg and below The highest hydrocarbon concentrations were encountered at depths between 10 and 20 feet bsg Hydrocarbon-impacted ground water was encountered in all four soil borings The highest ' concentration of dissolved hydrocarbons quantified as gasoline(TPH-g),diesel(TPH-d),and volatile aromatic compounds benzene, toluene, ethylbenzene, and total xylenes (BTEX) compounds were present in a water sample collected at 40 feet bsg from boring B 1 at the former UST area However, dissolved TPH-g and BTEX concentrations decreased radially northwest, southwest,and east away from the area of the UST release In addition, dissolved TPH and BTEX were detected at low concentrations in a grab ground water sample collected from 60 feet bsg in boring B 1 • Advanced GcoEnvironmental,Inc