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i 3,4 Soil Analytical Results In this section, laboratory results are discussed in sequence from youngest (Modesto Channel) to oldest (3rd Riverbank Channel) All samples were analyzed only for Total Petroleum Hydrocarbons in the diesel range by EPA method 8015 The laboratory report is in Appendix B One soil sample was collected from the base of the Modesto Channel in GT-20 (sample GT-20- 41 5', Table 1) No diesel fuel was detected in the sample Two samples were collected in boring GT-21, where hydrocarbon odors were detected during drilling Diesel fuel was detected in the sand at the base of the Modesto Channel (50 feet) at 4100 mg/kg ,(parts per million) The sample from the underlying aquitard at 55 feet contained no diesel above the 50 mg/kg detection limit(Table 1) F One soil sample was collected from the I" Riverbank aquifer Sample GT-20-60 5 contained no detectable hydrocarbons Three samples were collected from the 2nd Riverbank aquifer Samples GT-20-70 5'and GT-18-80 5' were below the detection limit Diesel fuel was detected at 2 7 mg/kg in GT-12B-100' at the basal contact of the aquifer The sample from the underlying aquitard at 1 l 1 feet was below the detection limit M One sample was collected from the base of the 3rd Riverbank aquifer in GT-12B A concentration of 16 mg/kg was reported by the laboratory, but the lab noted that the chromatogram did not resemble the standard diesel chromatogram 3 5 Water Analytical Results Twenty groundwater samples were collected for analysis The results are given in Table 3, and the laboratory report is in Appendix D No sample was collected from GT-9, which had been nun over by a truck and was broken off at ground level The casing was plugged by mud and is being repaired by V&W Drilling No diesel fuel was detected in GT-12A, GT-13B, GT-1513, GT-17A, GT-17B or GT-21 Concentrations in the other wells ranged from 57 µg/1 in GT-13A to 370 µ.g/1 in GT-14B However, the laboratory noted that most of the chromatograms did not match the standard diesel chromatogram This is particularly true of the samples from the 2"d and 3rd Riverbank aquifers The laboratory data are contoured for each aquifer in Figures 13-15 Like the plume within the Modesto aquifer (contoured in 1996-2000 when groundwater was present in this aquifer), the plume within the I" Riverbank aquifer is relatively large and trends generally northeast-southwest As noted in the Fourth Quarter 2004 Report, it appears to be centered east of the former UST facility, where the maximum concentration presently appears to be approximately 250 µg/1 (however, concentrations have exceeded 600 µg/1 in GT-6 in the recent past) The limits of the plume in this aquifer are now fairly well defined With a concentration only 7 parts per billion above the detection limit, well GT-13A is essentially at the western margin of the plume The southern margin is defined by CPT-5, GT-17A, and GT-9 The aquifer does not extend as far south as CPT-5 (Figure 3), and the concentration in GT-17A was below the detection limit Although no sample was collected from GT-9, previous samples from that well have either been 8