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w . Site History Jackpot Food Mart, 1434 W Yosemite Ave,Manteca,CA Time Oil Property No 04-157 Additional Site Investioation - December 1993 On December 2, 1993, a drill ng was utilized to advance 4 soil borings in the vicinity of the former tanks Prior to the Implementation of field activities, SECOR's workplan dated October 12, 1993 was submitted for agency review Verbal authorization to proceed with the proposed work was received from the PHSIEHD on November 27, 1993 During field activities, soils were found to consist of fine to medium sands to a depth of approximately 15 feet This strata was underlain by clay Because the previous Investigation Indicated that the clay unit may be acting as an aquitard, all bonngs were discontinued at a depth of 16 5 feet below ground surface to prevent possible impacts to groundwater beneath the site Soil samples collected from depths of 10 5 to 11 feet and 15 5 to 16 feet in each boring were submitted to an analytical laboratory and analyzed for gasoline and its constituents Hydrocarbons were not detected in any of the soil samples submitted for analyses On December 2, 1993, the groundwater wells were developed and sampled Prior to purging, an easterly gradient was determined by measuring the depth to groundwater in each well (approximately 16 feet below ground surface) Analyses identified 0 06 ppb toluene in the sample collected from W6, however, contaminants were not detected in the remaining samples A copy SECOR's "Problem Assessment Report"was forwarded to the PHSIEHD and CRWQCB on June 1, 1994 This report recommended the installation of a vapor extraction system to address the small amount of impacted sod Although trace concentrations of toluene were present in the groundwater sample collected from W6, SECOR's report did not recommend the implementation of a groundwater cleanup system Time Oil concurred with these recommendations In their response dated May 24, 1994, the PHSIEHD requested that quarterly groundwater monitoring be Implemented until the investigation and cleanup of the site are deemed adequate Submittal of Final Remedial Pian & Quarterly Groundwater MonitonnglStatus Report- Third Quarter 1994 On September 7, 1994 three copies of SECOR's"Final Remedial Plan and Quarterly Summary Report" was forwarded to the appropriate regulatory agencies This report presented the analytical results of groundwater samples collected from monitoring wells during the third quarter of 1994, summarized assessment data, and presented recommendations for a cleanup system to remediate hydrocarbon- impacted soils at the subject site Groundwater Sampling Results-July 1994 On July 28, 1994, samples were collected from each of the monitoring wells at the subject site Groundwater with a northeasterly flow was encountered at depths of 16 10 feet to 17 42 feet which was approximately one foot lower than it was during the previous sampling event Groundwater flow had changed from east to northeast since the previous sampling event Hydrocarbons were not indicated in any of the samples submitted for analyses Comparison of Remedial Alternatives SECOR'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 sod vapor extraction 3