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August 17, 199,6 Interim Investigation Report Au g Marci's Diesel Ste a,ice 3i.te Stockton, California 3.0 CONCLUSIONS Soil samples were collected at five-ft vertical intervals, beginning roughly at the bottom of the former tank excavation, and extending to a depth of 80 ft below grade Laboratory analysis of the samples detected diesel fuel in all of the samples, generally at high concentrations Review of historic groundwater data indicate that diesel fuel was detected in samples collected from MW 1, located adjacent to the tank excavation, during three of the eieven sampling events performed ,1 since April 1992 Gasoline was also detected in most of the soil samples at concentrations ranging from 52 7 to 800 ppm The split samples analyzed by Sparger Technologies indicated the material detected was not characteristic of typical gasoline This may suggest that gasoline present in the soil may be very weathered or that the compounds detected are representative iv the more volatile portions of diesel fuel Benzene and toluene were not detected in any of the soil samples, but benzene was ' detected in MW 1 during three of the eleven groundwater sampling events ` It appears, based on the above findings, that high concentrations of diesel fuel throughout the soil profile may be impacting groundwater beneath the site Based on the high diesel concentrations in the soil, it also appears possible the groundwater will continue to be affected in the future While benzene has been detected in the groundwater during a few of the monitoring events, the lack of benzene in overlying soil suggests there is no source for the benzene in contamination associated with the former underground tank This may be due to degradation of contamination in the soil or the lack of benzene in the contaminant source ,1 IL r ' 524-001 - 6 - LusH GEOSCiENCES [ _ a4iS i......... r.-lJ. .9x...k.3lldk.iS 4y • i �$WYd41d.wJYYh{.od4•��t .0". '�jYiH _ L � — __ - - —