SITE INFORMATION AND CORRESPONDENCE

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V 4.0 CONCLUSIONS AND RECOMMENDATIONS 4.1 AASF Areas of concern identified at the AASF comprise the condition of groundwater in the area of the former 5,000-gallon fuel USTs removed in 1990, and a minor release of fuel to soil occurring in April 2002. The findings of groundwater monitoring identified 0.110 mg/L of TPH-g in one groundwater sample. This represents the second detection of trace concentrations of TPH-g, the first having occurred in May 1996. These detections indicate that very little residual contamination is likely present from the former USTs. The sporadic detection of trace concentrations of TPH-g in the groundwater, without related aromatic and carcinogenic compounds, does not reflect a significant risk to human health or the environment. Therefore, Versar recommends no further action for the unauthorized release from the minor fuel spill. The presence of low concentrations (less than 500 mg/kg) of extractable TPH in soils between the surface and five feet bgs at the location of the minor fuel spill does not present a significant threat to human health or the environment. The results of soil sampling indicate that the impacted soils are not present at the 10-foot level and below. Vertical migration of heavy hydrocarbons is typically limited to the soluble fraction, and is generally considered not a concern in shallow soils at concentrations less than 1,000 mg/kg (RWQCB, 2003). Therefore, Versar recommends no further action for the unauthorized release from the minor fuel spill. 4.2 CSMS Areas of concern identified at the CSMS are; petroleum hydrocarbons beneath the vehicle wash rack in the north portion of the building, elevated metals and petroleum hydrocarbons along the north facility boundary, petroleum hydrocarbons near the waste storage area, heavy metals near the sandblasting area, and pavement upwelling in the vehicle storage area east of the building. Laboratory analysis did not detect concentrations of extractable hydrocarbons or PCBs in any of the samples collected from boring B29, located north of the vehicle wash rack in the CSMS building. Previously identified hydraulic oil contamination,detected at 10 feet bgs in boring B7, appears to be limited to shallow soils in the vicinity of that boring. No further investigation is recommended for the vehicle wash rack area. A trace concentration of hydraulic oil-weight petroleum hydrocarbon previously detected at the former hazardous material storage shed was not confirmed during follow-up sampling. Two soil samples collected from boring B l Ob did not contain concentrations of extractable hydrocarbons, and metals concentrations were below regulatory guidelines. No further investigation is recommended for the former hazardous materials storage area. 104700.4766.230/08SEPT2004 11