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in Table 1, the cumulative groundwater-grab sample analytical results are presented in Table 2, and the cumulative monitoring well groundwater sample analytical results are included in Table 4. Detectable concentrations of benzene have not been detected in any of the soil or groundwater monitoring well samples collected at the site, to date. MTBE has not been detected in any of the soil samples collected, to date. However, trace concentrations of MTBE were detected in two of the monitoring wells during the first sampling event in June 1998. MTBE was not detected in any of the wells during the sampling event in February 1999. The lateral and vertical extent of impacted soil is illustrated in a series of isoconcentration maps (Figures 4, 5 and 6) and isoconcentration cross-sections (Figures 7 and 8). The greatest mass of diesel hydrocarbons and aerial extent of impacted soil appears to be concentrated at a depth of approximately 15 feet bgs, which is within the zone of groundwater fluctuation (i.e., capillary fringe). At 15 feet bgs, soil impacted by concentrations of TPH-as-diesel above 100 mg/kg appears to extend up to 30 feet from the former UST (Figure 5). At 20 feet bgs, the concentration of TPH-as- diesel appears to decrease by at least an order of magnitude (Figure 6). Vertically, soil impacted by at least 1,000 mglkg of TPH-as-diesel appears to extend to at least 18 feet bgs (Figure 7). Laterally, impacted soil extends beyond the property boundary and under the Caltrans right-of-way. Again, the greatest mass of diesel hydrocarbons and aerial extent of impacted soil under the Caltrans right-of-way appears to be concentrated at a depth of approximately 15 feet bgs (Figures 5 and 8). Results of the groundwater-grab samples and groundwater samples from the monitoring wells indicate that groundwater impacted by diesel hydrocarbons extends less than 80 feet west, approximately 100 feet south and approximately 90 feet east of the former UST (Figure 9). The lateral extent of impacted groundwater is not defined to the north of the former UST, under State Highway 99. To date, the greatest concentration of petroleum hydrocarbons detected in groundwater was in the groundwater-grab sample collected from SB-2, immediately east of the former UST. This sample contained 590,000 micrograms per liter (µg/1) of TPH-as-diesel. The groundwater-grab sample collected from SB-7, directly beneath the former UST contained 13,000 µg11 of TPH-as-diesel, 2,800 µg/i of TPH-as-gasoline and 2.2 µg/i of benzene. Concentrations of TPH-as-diesel as high as 72,000 µg11 and TPH-as-gasoline as high as 970 µg11 were detected in groundwater-grab samples collected under the Caltrans right-of-way. 5