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Extent and Origin of Soil Contamination Soil samples taken in the phased subsurface investigation of the site were analyzed for their content of total petroleum hydrocarbons as gasoline (TPHg), total petroleum hydrocarbons as diesel fuel (TPHd), and benzene, toluene, ethylbenzene, and xylenes (BETX) Soil samples taken m the most recent phase of investigation were analyzed, in addition, for total petroleum hydrocarbons as motor oil (TPHmo) and MTBE The results of soil analyses are summarized in Table 1, Summary of Results of Analyses of Soil Samples, 305 Hutcluns Street, Lodi, California Concentrations of all of these analytes, with the exception of MTBE, were found in some of the soil samples No MTBE was detected in soil samples No significant concentrations of TPH or BTEX hydrocarbons have been found in soil shallower than 15 feet bgs at the site In most places the shallowest TPH or BTEX soil contamination is at or below 20 feet bgs The deepest sigmficant TPH and BTEX soil contamination was found at 42 5 feet bgs in boring GB5 The maximum depth of significant petroleum hydrocarbon concentrations in soil appears to be limited to approximately 25 feet bgs in the northern portion of the site and 42 5 feet bgs in the southern portion Figure 2 illustrates the distribution of soil containing petroleum hydrocarbons in cross section These data show that the petroleum hydrocarbon-containing soil is situated largely below 20 feet bgs and above 42 5 feet bgs This region of fuel hydrocarbon-contaminated soil is well above the r top of the saturated zone As discussed previously, the depth to the water table measured in site investigations at 305 South Hutchins Street has ranged between 51 and 57 feet b s Thus, at least S 5 to 14 5 feet vertical distance s arates the deepest significant fuel hydrocarbon-contamination in soil from the top of the water table The approximate areal extent of soil contaminated with fuel hydrocarbons is illustrated in Figure 4 The lateral extent of contamination is well-delineated in the southern and western portions of the site Because few soil borings have been drilled north and east of the site, the lateral extent of soil contamination in those directions is only approximate GEOCON (1995) concluded that operations at both former service station locations at the site were responsible for releases of fuel hydrocarbons that resulted in the TPH and BTEX contamination of soil above the water table Extent and Origin of Ground Water Contamination TPHg and petroleum hydrocarbons within the diesel fuel range, as well as MTBE and chlorinated hydrocarbons, have been found dissolved in ground water on and offsite The results of analyses of ground-water samples are tabulated in Table 2 The dissolved concentrations of all analytes can be described as moderate to small The concentration of benzene, however, has frequently been found to be above the maxnumum contaminant level for drinking water Water from all five monitoring wells has contained dissolved fuel hydrocarbons Only water from MW4 has never contained MTBE Water from all five wells has contained dissolved chlorinated hydrocarbons 6