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Chevron Environmental Management Company Soil and Groundwater Investigation Report Tracy Byron Road Project affected soil areas. Data from several boring logs indicate that petroleum penetrated vertically downward and laterally using preferential pathways (sandy soil) for migration. However, this was not consistent throughout the site. In other areas upper clayey soil is more affected than lower laying sands. In addition, in some boring logs two different layers of residual petroleum-affected soil were present, separated by a non-affected soil interval. Based on the analytical results, observations, and interpretations of subsurface conditions beneath the TBRP, the residual petroleum affecting soil and groundwater is not easily soluble,has a high viscosity, and moves very slowly and unevenly. Movement of the contaminant is promoted by sandy preferential pathways, and is not characterized by an even plume shape. 7.1 RECOMMENDATIONS • Soil and groundwater in the vicinity of SB-2, SB-3, and SB-6 are not fully characterized and the lateral extent of residual petroleum is not known. Although this is an agricultural area and there are no residential properties in the immediate vicinity,per the CTA, SAIL is recommending further investigation in the vicinity of these borings. • Soil and groundwater in the vicinity of borings SB-8 through SB-12 is not fully characterized and the lateral extent of residual petroleum is not known, and therefore requires further assessment. • SAIC recommends that no additional investigation be conducted in the vicinity of borings SB-13 through SB-16 since soil and groundwater appear to be delineated in this area. • Soil and groundwater affected by residual petroleum in vicinity of borings SB-19, SB-22 through SB-26, and SB-36 is not fully characterized and the lateral extent of residual petroleum is not known, and therefore requires further assessment. • Soil and groundwater affected by residual petroleum is present in the vicinity of borings SB-28, SB-30, and SB-33 through SB-35. Additional assessment is warranted in the vicinity of these borings. In conclusion, SAIC recommends additional borings are warranted in the above-referenced areas to fully delineate affected soil and groundwater south of West Byron Road. Therefore, SAIC suggests drilling step-out borings in the southern direction from West Byron Road to further investigate the lateral and vertical extent of affected soil and groundwater. SAIC recommends that soil and grab groundwater samples be collected from step-out borings. Based on well driller reports reviewed, the domestic wells identified were constructed with sanitary seals 50 feet or greater,pump groundwater from deeper water-bearing zones, and appear to be separated from the known affected soil intervals by multiple fine-grained strata of various thicknesses. Based on SAIC's grab groundwater samples collected from the water supply wells,it appears that dissolved petroleum constituents are not threatening the water supply and that further sampling or testing of water supply wells is not warranted. Furthermore, the vertical component of affected soil appears to be defined beneath the site and is unlikely to be a source of dissolved petroleum constituents that could impact the water supply wells. 12