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i i{ Site History Jackpot Food Mart, 1434 W Yosemite Ave , Manteca, CA Time Oil Property No 04-167 Based on the results of the most recent sampling event, it did not appear as though the concentrations and distribution of hydrocarbons in groundwater changed significantly since the previous sampling event While trace toluene concentrations appeared in W-6 during the December 1993 groundwater sampling event, no hydrocarbons were indicated during the July sampling event Depth to groundwater decreased across the site by approximately one foot since the previous sampling event, and groundwater flow changed from east in December 1993 to northeast in July 1994 These changes may have been due to seasonal variations or local agricultural irrigation, however, not enough data has been collected to definitively determine the cause Suantary of Findings Pertinent to Selection of Remediation System Based on data collected to date, it appears that the extent of hydrocarbon- impacted soil is well defined and remains limited to the area of the pump islands and north portion of the former tank bed Groundwater beneath the site does not appear to have been significantly impacted by hydrocarbons Soils at the site generally consist of fine to medium sands to a depth of approximately 15 feet This strata is underlain by a clay unit which is approximately 5 feet thick Fine to medium sand is present from a depth of 20 feet to the extent of each boring Groundwater has generally been encountered at depths of 16 to 17 feet below ground surface and flow direction has varied from east-southeast (November 1992) to east (December 1993) to northeast (July 1994) To evaluate remedial options, a vapor extraction pilot test was conducted at the subject site in December 1992 Results indicated that vapor extraction would be a feasible remedial alternative for remediating impacted soils beneath the site Comparison of Remedial Alternatives SEACOR's "Problem Assessment Report" dated May 31, 1994, contained an evaluation of several remedial technologies for cleanup of impacted soils in the vicinity of the former tank system soil excavation and disposal, soil excavation and on- site aeration, soil excavation and off-site aeration, and in-situ soil vapor extraction Based on the excellent results achieved during the vapor extraction pilot test and the low cost of installing and operating such a system, other remedial methods involving excavation were not considered feasible for soil cleanup Vapor extraction is the least expensive option, it can achieve rapid results, and it will not disrupt the business currently in operation Selection of Remedial Technology Vapor extraction is the proposed remedial technology to achieve cleanup of hydrocarbon-impacted soils beneath the subject site It is estimated that 3 existing wells (W-1, W-2, and W-4) will be utilized for the proposed vapor extraction system In addition, horizontal wells may be installed within the vapor extraction piping trenches to enhance remediation if hydrocarbon-impacted soils are encountered during system installation Although a radius of influence 5