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Report:Groundwater-quality Monitoring—May 30, 2001: 7500 West Eleventh Street, Tracy, CA. Page 3 1.5 Distribution of Hydrocarbons in the Subsurface The site characterization program conducted during April and May 2000 included installation of seven groundwater-quality monitoring wells at the locations shown on r. Figure 2. Evaluation of the results of analyses of samples of groundwater recovered from those wells on May 11, 2000 and analyses of soil samples from the well borings and an J array of push-probe borings, together with information regarding groundwater now 71 directions, sources of leakage of fuel hydrocarbons into the subsurface and other information gathered by the site characterization program yielded an interpretation that the site was affected by a primary plume of diesel and gasoline that affected both soil and groundwater, a secondary plume of diesel and gasoline, and dispersed low concentrations of a variety of hydrocarbons in shallow soils having sources different from those of the primary and secondary plumes of diesel and gasoline. (The San Joaquin Company 2001 b.) - Figure 2 is a plan view of the site showing the extent of the primary and secondary plumes of diesel and gasoline and the areas in which shallow soils are affected by other -'` dispersed hydrocarbons. Figures 3, 4 and 5 illustrate the distribution of petroleum hydrocarbons along sections A-A', B-B' and C-C', the locations of which are also shown on Figure 2. 2.0 MAY 30, 2001 GROUNDWATER SAMPLING AND ANALYIS On May 30, 2001, the third round of groundwater-quality monitoring was conducted using monitoring wells MW-I through MW-7, which were installed at the site in April 2000. The well locations are shown on Figure 2. ,i 2.1 Groundwater Elevations and Flow Direction To initiate the May 30, 2001 sampling program, the depth to groundwater in each of the seven monitoring wells was measured using a conductivity probe. The water table elevations were computed relative to mean sea level (MSL). Those measurements and the computed groundwater table elevations are recorded in Table 1. In the period between November 28, 2000 and May 30, 2001, the groundwater table had risen about 0.5 feet. The groundwater elevation data presented in Table 1 was used to construct the water table contours for May 30, 2001 shown on Figure 2. The general direction of flow through the subsurface where the fueling station infrastructure was formerly Iocated is to the north-northeast (approximately north, 20 degrees east), as it was when last computed for conditions on November 28, 2000. As can be seen on the figure, there is a significant curvature to the water table's contour lines in that area, but that curvature is less pronounced in areas further to the south and east where the contours, as interpreted on Figure 2, indicate a groundwater flow direction closer to true north. This feature of the groundwater flow iii the area can be attributed to the presence of the clays and silty clays in the area around MW-3, that, as is shown in cross-section A-A' on Figure 4, separates sic