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SECTIOMTW® Previous InvestlgWous Environmental mveMgations have been performed at the Shop 10 site since 1987 A summary of the previous environmental investigations is discussed below o The initial soil and groundwater assessment was conducted by Woodward-Clyde in 1987 Four groundwater monitoring wells (MW-1 through MW-4) were installed in the vicinity of the four 5,000-gallon USTs Groundwater sample results indicated that total petroleum hydrocarbons gasoline range (TPH-g) concentrations in groundwater ranged from 154 to 231 milligrams per liter (mg/L) and benzene concentrations ranged from 14 7 to 25 7 mg/L Twenty soil samples were collected and analyzed for TPH-g and benzene, toluene, ethylbenzene, and xylenes (BTEX) TPH-g concentrations soil samples were below detection limits in samples collected from NiW-1 through MW-3 and ranged from nondetect to 1,100 milligrams per kilogram (mg/kg) in soil samples collected from NM-4 Benzene concentrations ranged from nondetect to 7 7 mg/kg Toluene concentrations ranged from nondetect to 29 5 mg/kg, ethylbenzene concentration ranged from nondetect to 12 1 mg/kg, and xylenes concentrations ranged from nondetect to 55 2 mg/kg The lughest BTEX concentrations were detected in MW-4 between 20 and 30 feet bgs A soil and groundwater evaluation report was prepared summarizing the assessment (Woodward-Clyde, 987 o In 1989, the four USTs and a waste-oil UST were removed by Placer Tractor Service Soil samples were collected beneath the UST TPH-g concentrations in soil from beneath the gasoline and diesel fuel USTs ranged from 2 2 to 3,700 mg/kg and TPH diesel range (TPH-d) concentrations in soil from beneath the diesel and waste oil USTs ranged from 100 to 1,700 mg/kg, and 11 to 12 mg/kg, respectively o An additional site assessment was conducted by Woodward-Clyde between 1989 and 1990 Five additional groundwater monitoring wells (MW-5 through MW-9) were installed Twenty-four soil samples were collected and analyzed for TPH-g and BTEX BTEX was detected above laboratory detection limits in one soil sample collected from MW-7 at a depth of 30 feet bgs 0 4 mg/kg, 0 2 mg/kg, 0 1 mg/kg and 0 2 mg/kg, respectively TPH-g concentrations in the soil samples from the five borings were not detected above the laboratory detection lmvt TPH-g concentrations in groundwater ranged from nondetect to 3 4 mg/L BTEX concentrations in groundwater ranged from nondetect to 200 micrograms per liter (ug/L), nondetect to 8 ug/L, nondetect to 0 7 ug/L, and nondetect to 170 ug/L, respectively o A Problem Assessment Report (Woodward-Clyde, 1990) was prepared at the request of the CVRWQCB • A Supplemental Site Assessment (Alton Gsoscience, 19 92) was conducted to further delineate the extent, levels, and the type of petroleum hydrocarbons in soil and groundwater Three groundwater monitoring wells (MW-10 through MW-12) were installed and two soil borings were advanced (AB-1 and AB-2) Nineteen soil samples were collected and analyzed for TPH-g, TPH-d, and BTEX TPH-g were detected m two of 19 soil samples, and TPH-d were detected in one soil sample TPH-g ® T%iw7L9 so=gAL5TocKTOMREPORTD=7-AUGavw3commmA 2-1