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Geological Technics Inc. Page 10 35500 Welty Road,Vernalis,CA Report-Preixminary Environmental Site Assessment Project No. 248.2 February b, 1995 however the samples tested from the SB-1 boring (approximately 200 feet to the north of SB-2) did not contain detectable concentrations of the petroleum hydrocarbon compounds tested for. The laboratory analytical data show that petroleum hydrocarbons were detected in significant concentration in soil samples from the SB-2 boring. In particular, the laboratory data from the sample collected at 32 feet (the presumed capillary fringe) suggests that the shallow groundwater (±33') at this location may also be impacted. There may be multiple sources for the hydrocarbons detected in soil samples tested from SB-2. This supposition is based on the laboratory findings. The hydrocarbons detected in the soil column down to the capillary fringe were characterized by the laboratory as diesel, while the sample collected at the groundwater interface and the wipe sample had the signature of a heavier and oil-type hydrocarbon. One hypothesis for the difference of the two hydrocarbon types is that they may be sourced from different events/leaks. The oil at the presumed groundwater interface may have been sourced from the crude oil pipeline whereas the diesel range hydrocarbons may have been sourced from a fuel storage tank used to fire boilers at the former pumping station, from the Southern Pacific product pipeline, or from a tank installed and used during the operation of the labor camp's bus garage. The fact that no BTEX compounds were detected in the soil could indicate that they were not present in the crude oil to begin with. Another possibility is that these Compounds may have degraded with age, as is often the case, leaving behind heavier constituents. If this is the case, it can be assumed that the leak is sourced from the operation of the pumping station and thus would be over 50 years old. A third possibility is that the more volatile and soluble BTEX may have been entrained or dissolved into seeping recharge water in the unsaturated zone and thus transported into the aquifer below. The evidence from the Phase I Environmental Site Assessment indicates that Standard Oil operations may not have been the only potential source for the petroleum hydrocarbons in the subsurface. Labor camp operations taking place during the 1940's and 50's suggest that a bus and truck repair shop may have been operated on the Property. This could lead to the conclusion that one or more underground storage tanks possibly being present as either a source for refueling these vehicles or for storing waste oil from vehicle maintenance activities. Geological Technics Inc. recommends that the following assessment work be performed to better evaluate the environmental liability of this Property: