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Report:Groundwater-quality Monitoring-November 28, 2000: 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 Figure 2. Evaluation of the results of analyses of samples of groundwater recovered from i' those wells on May 11, 2000 and analyses of soil samples from the well borings and an array of push-probe borings, together with information regarding groundwater flow directions, sources of J leakage of fuel hydrocarbons into the subsurface and other i 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.) -- 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 NOVEMBER 28, 2000 GROUNDWATER SAMPLING AND ANALYIS On November 28, 2000, the second round of groundwater-quality monitoring was _ .: conducted using monitoring wells MW-1 through MW-7, which were installed at the site in April 2000. The well locations are shown on Figure 2. Ms Lori Duncan, REHS was present on site to represent the SJCPHS and observed some of the procedures described f: i ...; below. 2.1 Groundwater Elevations and Flow Direction To initiate the November 2000 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). These measurements and the computed groundwater table elevations are recorded in Table 1. In the period between May 11 and November 28, 2000, the groundwater table had fallen about one foot. The groundwater elevation data presented in Table 1 was used to construct the water table contours for November 28, 2000 shown on Figure 2. The general direction of flow r ' through the subsurface where the fueling station infrastructure was formerly located is to the north-northeast (approximately north, 20 degrees east). However, as can be seen on 1 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 groundwater table topography was not well developed in the water table contours that were constructed from depths to groundwater measured in the seven monitoring wells on May 11, 2000. However, as was noted at the time, there was an sic