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v <br /> ASSOCIATESATC <br /> I NC . <br /> groundwater samples were collected for chemical analyses. Analytical results of the soil, soil <br /> vapor, and groundwater samples collected delineated the horizontal extent of petroleum <br /> hydrocarbon contamination in the vicinity of the former gasoline UST locations. Analytical <br /> results for chemical analyses are summarized in Tables 1, 2, and 3. <br /> During this phase of work, the collected soil, grab groundwater, and soil vapor samples were also <br /> submitted for geophysical analysis to determine if natural biodegradation of petroleum <br /> constituents was occurring beneath the site. Soil samples from significantly different lithological <br /> units encountered during drilling were submitted for the following geophysical analyses: falling <br /> head permeability, percent moisture, porosity, dry bulk density, soil pH, percent organic content, <br /> and carbon to nitrogen to phosphorus (C:N:P) ratios. Grab groundwater samples were field <br /> monitored for oxidation-reduction potential and submitted for laboratory analysis of carbon <br /> dioxide, alkalinity, nitrate, sulfate, and ferrous iron. Soil vapor samples were submitted for <br /> laboratory analysis of oxygen, carbon dioxide, nitrogen, and methane. Analytical results of <br /> geophysical analysis are summarized in Tables 1, 2, and 3. This phase of work was detailed in <br /> Smith Technology Corporation's Additional Soil and Groundwater Report, Fayette <br /> Manufacturing Corporation, 7675 West Eleventh Street, Tracy, California, dated January 31, <br /> 1997. <br /> Based on the results of previous site investigations, ATC prepared a technical report that <br /> �., considered three remedial alternatives for soil and groundwater at the site. Soil and groundwater <br /> remedial alternatives that were evaluated included natural attenuation with groundwater <br /> monitoring; excavation of remaining petroleum impacted soil; and in-situ vapor extraction with air <br /> sparging. Natural attenuation of the petroleum hydrocarbons beneath the site was selected as the <br /> preferred remedial choice. A more detailed discussion of the remedial alternatives was included in <br /> ATC's Problem Assessment Report & Corrective Action Plan for 7675 West Eleventh Street, <br /> Tracy, California, dated April 1, 1998. <br /> Between September 1996 and June 1997, groundwater samples collected from each of the site's <br /> monitoring wells were analyzed for specific geochemical parameters to assess intrinsic <br /> bioremediation occurrence at the site. In addition, grab groundwater samples were collected from <br /> soil borings during this time period and were also analyzed for specific geochemical parameters. <br /> Based upon geotechnical and geochemical data collected from groundwater and/or soil underlying <br /> the project site, this study concluded intrinsic bioremediation may be taking place in the <br /> contaminant plume beneath the site. Biodegradation appears to be continuing in an aerobic and <br /> anaerobic environment. Chemical data suggests the contaminant plume is stable since it appears <br /> that petroleum hydrocarbon concentrations are not significantly increasing in the wells. A more <br /> detailed discussion of the natural attenuation at this site is contained in Smith Technology <br /> Corporation's Additional Soil and Groundwater Report, Fayette Manufacturing Corporation, <br /> 7675 West Eleventh Street, Tracy, California, dated January 31, 1997. Geochemical trends from <br /> the results are summarized in Table 6. <br /> w:\17861\reportsknodeling.doc 2 <br />