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1 a Site Investigation and No Further Action Request Repo R$L Diesel Services, Project#051111 Ta6w Products site, reporting depth to water in their April 20, 2009 First Quarter 2009 GroundwaSIr►ce1954ter Monitoring Report at between 45-47 feet bgs. 2.2.3 Plume Characteristics The plume is primarily composed of TPH-D, BTEX and chlorinated hydrocarbons derived from used oil. The petroleum hydrocarbon constituents appear to be weathered, with benzene detected in only one sample from the site. No fuel oxygenates are present in the F plume. i The highest levels of TPH-D was found beneath the UST center at a concentration of 22,000 mg/kg; the highest BTEX compounds and chlo mated hydrocarbons (PCE)were found north of the former UST and directly under the former UST. Maximum concentrations, detected in 61 at 14 feet bgs, benzene, toluene, ethylbenzene, total xylenes and PCE were 2.55 ug/kg, F! 200 ug/kg, 97.3 ug/kg, 407 ug/kg, and 85.5 ug/kg, respectively. 2.3 Potential Pathway Analysis 2.3.1 Utility Corridors Utility corridors which may act as potential preferential pathways have not been fully evaluated at the site. The sensitive receptor survey did not provide any additional utility information that would identify potential pathways associated with utilities at the site. 2.3.2 Geologic Pathways The silty and sandy soils and limited clay identified at the site and during excavation activities at a nearby site (Pacific Pride, approximately D.5 miles north on the east side of West Lane) do not provide a significant barrier to petroleum hydrocarbons constituent migration, although some natural attenuation will occur within the unsaturated zone as the petroleum hydrocarbons disperse in the soil. Although silty clay at the site located from approximately 34- } 45 feet bgs may act as an impediment to downward migration of petroleum hydrocarbons and solvents to groundwater. 2.4 Potential Exposure Analysis BTEX constituents and chlorinated hydrocarbons can create an exposure risk in certain circumstances through volatilization and vapor intrusion from shallow soils and groundwater. Benzene is generally the constituent of greatest concern in these circumstances; however, levels of benzene present in the samples collected from the spill site and the identified uses of the spill site are not significant enough to indicate a vol tilization risk. Additionally, potential vapor intrusion into off-site buildings is unlikely due tot the lack of benzene detected in groundwater from the current investigation. °�'"� F 4