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• <br /> Ms. Katie Hower SECOND DRAFT <br /> Chevron Pipe Line Company <br /> 24 January 1997 <br /> Page 2 <br /> both types of petroleum, the line was heated and incorporated a series of pump stations to <br /> facilitate flow. The pipeline north of Tracy was removed from service in the early 1950s and <br /> most sections of the pipeline were removed from the ground in the 1970s. <br /> The crude oil/Bunker C oil carried by the pipeline consisted of predominantly middle-to high- <br /> boiling petroleum hydrocarbons. These constituents have low solubility in groundwater and, <br /> therefore, demonstrate limited environmental mobility. Furthermore, because of the age of the <br /> releases (minimum of 40 years old),the petroleum associated with the Old Valley Pipeline is <br /> typically highly weathered and has lost the majority of the relatively low levels of volatile and <br /> water soluble constituents (e.g.,benzene,toluene,ethylbenzene, and xylenes [BTEX] and low <br /> molecular weight polynuclear aromatics [PNAs])present in the original oil. Weathering has <br /> likely occurred as a result of a combination of evaporation,biodegradation, and water <br /> solubilization. At many sites in the Bay Area and Central Valley with shallow groundwater <br /> tables,the vertical distribution of the residual petroleum is above and below the current water <br /> table,probably due to historical fluctuations in the water table. This distribution of petroleum <br /> below the water table allows for a direct assessment of its potential threat to groundwater, <br /> because the presence of petroleum in contact with groundwater functionally represents a long- <br /> term in situ leaching test. Old Valley Pipeline sites are assumed to have reached chemical <br /> equilibrium or steady-state conditions because of the age of the release. <br /> INVESTIGATION/MONITORING APPROACH <br /> At each site impacted by residual petroleum from the Old Valley Pipeline, CPL will evaluate <br /> the potential threat to groundwater and, if applicable.risks to human health. Because the <br /> potential source is essentially the same between sites, a consistent approach will provide data <br /> for this evaluation. Based on the lessons learned from investigations at several Old Valley <br /> Pipeline sites, the following approach will be used, as discussed below and presented in a flow <br />