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SECTION 3.0 SUMMARY OF PREVIOUS INVESTIGATIONS • A Problem Assessment Report (Woodward-Clyde, 1990) was prepared at the request of the CVRWQCB 1 • In 1992, Alton Geoscience (Alton) conducted a Supplemental Site Assessment (Alton Geoscience, 1992) 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 Concentrations of TPH- g were detected in two of the 19 soil samples, and a concentration of TPH-d was detected in one soil sample TPH-g concentrations in soil ranged from non-detect to 270 mg/kg, and TPH-d concentrations ranged from non-detect to 12 mg/kg Benzene was detected above laboratory detection limits in four soil samples with soil concentrations ranging from non- detect to 4 4 mg/kg Toluene was detected above laboratory detection Iimits in two soil ' samples with soil concentrations ranging from non-detect to 17 mg/kg Ethylbenzene was detected above laboratory detection limits in two soil samples with soil concentrations ranging from non-detect to 5 5 mg/kg Xylenes were detected above laboratory detection limits in two soil samples with soil concentrations ranging from non-detect to 30 mg/kg Alton Geoscience sampled groundwater monitoring wells MW-7, MW-8, and MW-10 through MW-12 Groundwater monitoring wells MW-1 through MW-6, and MW-9 were dry TPH-g and BTEX concentrations decreased in groundwater monitoring wells MW-7 and t MW-8 TPH-g concentrations in the new monitoring wells ranged from non-detect (MW-12) to 5,600 mg/L (MW-10) TPH-d concentrations ranged from non-detect (MW-11 and MW- 12) to 1 8 mg/L (MW-10) • A limited vapor extraction pilot test was conducted by Alton in September 1992 (Alton, 1992) to evaluate the feasibility of using soil vapor extraction as a remedial alternative Soil vapor extraction (SVE) was considered a feasible remediation alternative (Alton, 1992) • An additional environmental site investigation was conducted by Environmental Assessors Inc ' in 1993 to evaluate the horizontal and vertical extent of petroleum hydrocarbons in soil and groundwater Six additional groundwater monitoring wells MW-13, MW-14, MW-16, MW-19, MW-20, and MW-24 and four soil borings SB-15, SB-17, SB-18, and SB-22 were installed Selected soil samples were collected and analyzed to a depth of 75 feet bgs for TPH-g and BTEX TPH-g concentrations in soil ranged from nondetect to 350 mg/kg, benzene ' concentrations ranged from nondetect to 4 7 mg/kg, toluene concentrations ranged from nondetect to 37 mg/kg, ethylbenzene concentrations ranged from nondetect to 7 2 mg/kg, and xylenes concentrations ranged from nondetect to 47 mg/kg Groundwater concentrations for TPH-g ranged from non-detect (MW-14, MW-16, MW-19, MW-20 and MW-24) to 1 gg/L (MW-13) Existing groundwater monitoring wells (MW-7, MW-10, MW-11, and MW-12) were sampled during this investigation Groundwater concentrations for TPH-g and BTEX S 4PROJtAI04010004%HOP10SSHOPIOSILOOC 3-2 URS G'a'iner WOed mrd Clyde