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Site History Jackpot Foal Mart, 1434 W Yosemite Ave,Manteca,CA Time Oil Property No 04167 occurring Analyses identified low concentrations of hydrocarbons in the soil samples collected from GP- 1 at 9 5 - 10 feet bgs (116 ppm gasoline, 1 23 ppm ethylbenzene, and 6 71 ppm xylenes), GP-1 at 14 5 - 15 feet bgs (159 ppm gasoline, 0 282 ppm ethylbenzene, and 1 08 ppm xylenes), GP-2 at 9 5 - 10 feet bgs (77 9 ppm gasoline and 0 246 ppm xylenes), and GP-2 at 14 5 - 15 feet bgs (242 ppm gasoline, 0 341 ppm ethylbenzene, and 1 60 ppm xylenes) None of the other samples contained detectable concentrations of hydrocarbons Samples analyzed for TOC were found to contain concentrations ranging from 170 ppm to 2,000 ppm Following 20 days of incubation, bacterial counts for the samples collected from GP-3 ranged from 3 5 X 106 to 4 6 X 107 colony forming units per gram of soil for gasoline-utilizing bacteria, 4 1 X 106 to 4 7 X 107 colony forming units per gram of soil for THB, and 3 4 X10 6 to 5 3 X 106 colony forming units per gram of soil for BTEX-utilizing bacteria Because the PHSIEHD expressed a desire to conduct some soil transport modeling to determine if the remaining hydrocarbons may impact groundwater beneath the site, samples collected from each distinct soil strata in GP-1 (1 5 feet bgs (finer-grained sand), 12 feet bgs (coarser-grained sand), and 15 5 feet bgs (clay)) were analyzed for air permeability, total porosity, coarse grain size analysis, bulk density, and moisture content Analyses suggest that only minor concentrations of hydrocarbons remain in very limited areas beneath the subject site When compared to concentrations observed during previous investigations, it appears as though there has been a general decrease in hydrocarbon concentrations remaining in soils Additionally, plate counts suggest that sufficient populations of hydrocarbon-utilizing bacteria and total heterotrophic bacteria are present in the site's sods to support intrinsic bioattenuation of the soil impacts Accordingly, Time requested that the PHSIEHD consider site closure based on the following 1 The extent of soil impacts at the subject site is limited and well defined, and concentrations observed during the Geoprobe survey are generally lower than those observed in samples collected from similar areas during previous site investigations 2 Benzene was not present in any of the soil samples collected during the Geoprobe investigation 3 Sufficient bacterial populations exist in the site's soils to biodegrade the remaining hydrocarbons 4 The potential for vertical migration of the remaining hydrocarbons is limited, as the site is covered with asphalt and a lens of clay is present over the top of the first-encountered groundwater These site conditions also limit the potential for exposure to the impacted sods 5 Groundwater is not impacted Nine groundwater sampling events have been conducted over a period of four years Only two samples have ever contained hydrocarbons the sample from MW-3 to November 1992 (0 55 ppb xylenes) and the sample from MW-6 in December 1993 (0 06 ppb toluene) Hydrocarbon contaminants have not been observed in the seven additional groundwater sampling events conducted from July 1994 to May 1996 Time Oil's Third Quarter 1996 status report and SECOR's "Confirmation Sampling Report and Request for Closure" dated October 9, 1996, were forwarded to the PHSIEHD and CRWQCB on October 22, 1996 9