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GEOMATRIX Drive, and to the north by Beechnut Avenue(Figure 2). The fuel oil was stored in a concrete- lined reservoir and was conveyed by pipeline to a nearby rail yard. Alden Park is situated directly over the former site of the reservoir, and adjoining properties consists of single- and multi-family residential dwellings. The subsurface soil in the project area is underlain by approximately 3 to 5 feet of fill consisting of silty clay with fine sand. The fill is underlain by silty to sandy clays, sandy silts, sands, and occasional gravely horizons. The water table is approximately 8 feet bgs. Shallow Igroundwater beneath the project area is prohibited from use as domestic or municipal supply by the City of Tracy Municipal Code for reasons unrelated to the presence of degraded Bunker C fuel oil. Chevron initiated an assessment of subsurface conditions in 1986 and completed it in 1996. A summary of the results of the site investigations is provided in Geomatrix's "Results of Additional Soil and Groundwater Characterization,"dated September 20, 1996. The results of ' these site investigations conducted by Geomatrix and other consultants indicated that residual oil is present in shallow soils beneath the park and surrounding residential areas. The residual oil has been observed in primarily two forms: visibly oily material (described as either"tar- like"or"an oily residue"), which has been observed 5 to 8 feet bgs in the immediate vicinity of ' the former reservoir, or small, asphalt-like particles mixed with the soil,which has been observed in shallow soil in the vicinity of and adjacent to the park. In addition, separate-phase ' oil is present on the shallow groundwater table beneath the park. Due to the heavy and degraded nature of the oil and the Site's hydrogeologic conditions, the oil beneath the Site is considered to be relatively immobile and insoluble. This is confirmed by the fact that dissolved tpetroleum constituents are generally not found in groundwater downgradient of the separate- phase oil. The results of the soil and groundwater assessment performed by Geomatrix and others on ' behalf of Chevron were used to select COPCs for the health risk assessment (HRA). The HRA was performed to evaluate the potential human health risks associated with the presence of chemicals in the subsurface. Several chemicals, classified as polycyclic aromatic ' hydrocarbons, were identified as COPCs in soil. COPCs were not identified in groundwater. Based on the conceptual model for the Site,potential receptors included on-site residents and ' maintenance workers. Exposure pathways evaluated for all receptors included dermal contact with soil, incidental soil ingestion, inhalation of vapors, and inhalation of particulates (i.e., ' 1:\D.—Safe\6000s\6115.020\SMP.dm 2