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G i GEOMATRIX gel cleanup. Laboratory services were provided by AEN. Analytical data sheets provided by the laboratory are included in Appendix C. Groundwater samples collected on 15 March 1996 were analyzed for BTEX by EPA Method 8020 and ' TPH-G by a modified version of EPA Method 8015. These samples were not analyzed for TPH-D because the two previous groundwater monitoring events and results of fingerprint characterization of soil samples indicated that diesel is not present in groundwater and soil at the site. Laboratory services ' were provided by GTEL Environmental Laboratories, Inc. of Concord, California. Analytical data sheets provided by the laboratory are included in Appendix C. ' 6.0 RESULTS Field screening results and analytical results for soil samples collected from the confirmation soil boring (SB6) and the additional borings (SB7 through S1314) are summarized in Table 3 and are displayed ' graphically on the cross sections in Figures 3 and 4. As described in Section 5.0, the results of finger- print characterization indicated that the petroleum hydrocarbons present in soil beneath the site were gasoline. Gasoline constituents were present in soil samples from borings SB6 through SB9. Gasoline ' constituents were not present in soil samples from borings SB 10 through S1314. Groundwater elevations are summarized in Table 4. Groundwater elevation contours based on water levels measured on 17 November 1995 are shown on Figure 5. The groundwater gradient on 17 November 1995 was 0.028 to the north. Groundwater elevation contours based on water levels measured on 15 March 1996 are shown on Figure 6. The groundwater gradient on 15 March 1996 was 0.036 to the north/northwest. ' Analytical results for groundwater samples collected on 17 November 1995 and 15 March 1996 b Yt l� P y ' Geomatrix are summarized in Table 5. For the groundwater samples collected on 17 Novenber 1995, the laboratory reported that TPH-D was present in samples collected from wells MW-1, MW-3, and MW-4 using the standard TPH-D analysis; however, the concentrations of TPH-D were reduced to less ' than the detection limit (50 gg/�) in samples that were filtered prior to analysis. This indicates that material reported as TPH-D in the standard analysis is not from diesel dissolved in groundwater but ' reflects a false positive due to other sources. A complete discussion of false-positive results for TPH-D due to other sources was included in the Geomatrix 17 July 1995 "Groundwater Monitoring Results, 540 North Aurora Street, Stockton, California." 7.0 RECOMMENDATIONS In August 1995, SJCEHD staff indicated that the LOFT Manual should be used to evaluate the need for, and scope of, corrective action at this site. However, the LUFT Manual is currently undergoing revi- - cion. As input to the revision efforts, guidance has been published by the State Water Resources 6