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Site Background Information: Bob's Muffler Page 2 of 5 or monitoring wells and septic tanks located within a 2,000-foot radius of the site. The nearest ground water wells were two City of Manteca wells (No. 7 and No. 19), located approximately 2,300 feet northeast of the site,and one commercial well located approximately 1,000 feet southeast of the site. In addition, ground water monitoring wells were observed approximately 300 feet ' northwest, 1,000 feet northwest, and 1,500 feet southeast of the site.No other receptors, including septic tanks, were identified within the 2,000-foot radius. UNDERGROUND STORAGE TANK REMOVAL ' AGE has been informed that one 10,000-gallon leaded gasoline underground storage tank (UST), one 8,000-gallon unleaded gasoline UST,and one 550-gallon waste oil UST were removed from the site in 1988.During UST removal activities,soil samples were collected and analyzed from beneath the ends of each UST. Total xylenes were detected at a concentration of 230 micrograms per kilogram (µg/kg) in a soil sample collected from the base of the gasoline UST (Tank No. 2) ' excavation at a depth of 15 feet bsg.Total petroleum hydrocarbons quantified as motor oil(TPH-mo) were detected at a concentration of 97 milligrams per kilogram (mg/kg) in a soil sample collected at a depth of 12 feet bsg from the base of the waste oil UST (Tank No. 3) excavation. However, laboratory detection limits were elevated and may not have indicated low concentrations of petroleum hydrocarbon compounds above standard reporting levels.According to an Environmental Health Department (EHD) inspection report, soil discoloration and petroleum hydrocarbon odors were noted beneath Tank No. 1 and Tank No. 2. Additional information regarding history of the UST use,tank tests,product inventory, and repairs ' are not known to AGE. PREVIOUS SUBSURFACE INVESTIGATION ' On 05 February 1999,AGE advanced four soil probe borings at the site.Probe borings B-1 and B-2 were advanced within the formerUST No.2 andNo. 1 excavations to depths of 40.25 and 25.25 feet bsg,respectively.Probe boring B-3 was advanced within the former waste oil UST No.3 excavation ' to 20.25 feet bsg. The fourth boring, B-4,was advanced northwest of the former dispenser islands to 20.25 feet bsg. • Total petroleum hydrocarbons quantified as gasoline (TPH-g) and volatile aromatic compounds toluene, ethylbenzene, and xylenes were detected in the soil samples collected between 20 and 25 feet bsg from all of the borings at concentrations as high as 670 mg/kg ' and 13 mg/kg(xylenes),respectively,in soil sample B2-20.25';TPH-mo was detected in soil samples collected between 20 and 25 feet bsg in borings B-2 through B-4 at a maximum concentration of 120 mg/kg (B2-20.25'). Fuel oxygenating compounds, including methyl 1 Advanced GeoEnvironmental,Inc.