SITE INFORMATION AND CORRESPONDENCE_FILE 2

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�' r tiABLE 1 -CHECKLIST OF REQUiRELI DAT FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES Site Name and Location: Southland (7-Eleven)Store #20304,455 Grant Line Road,Tracy,San Joaquin County Y 1. Distance to production wells for municipal, domestic, agriculture, industry Five water supply wells are within Y.mile of the and other uses within 2000 feet of the site; site. Four wells are upgradienticross-gradient, with the nearest well located 800'SW.One downgradient well is 1,900'NE of the site. All wells are greater than 150'bgs. Y❑ 2. Site maps, to scale, of area impacted showing Ibcations of former and existing tank systems, excavation contours and sample locations, boring and monitoring well elevation contours, gradients, and nearby surface waters, buildings, streets, and subsurface utilities, 3. Figures depicting lifhology(cross section), treatment system diagrams; Attempted to use groundwater extraction withair stripper,but ineffective. The site was overexcavated. r 4. Stockpiled soil remaining on-life or off-site disposal(quantity); 270 yds'of soil removed from the tank pit and dispensingisland and hauled off-site. 7 5. Monitoring wells remaining on-site, fate, Nine monitoring and two extraction wells are installed on-site. San Joaquin County has proposed decommissioning these wells pending the Regional Board's concurrence with the closure recommendation. _ 6. Tabulated results of all groundwater elevations and depths to water; Shallow roNNEfl w direction. uof the site and varies from 2 to 7' with a NNE flow direction. 0 7. Tabulated results of all sampling and analyses: TPHg at 1,700 mg/kg and low levels of BTEX were detected in soil after the 1998 overexcavation. Low levels of BTI)(and TPHg were detected in groundwater 71 Detection limits for confirmation sampling during the 3 March 1999 monitoring event. MtBE was not detected above F1 Lead analyses 0.005 mg11 In any of the monitoring wells. 8. Concentration contours of contaminants found and those remaining in soil Minor contamination was found in two and groundwater, and both on-site and off-site: monitoring and one extraction well. There is no indication of off-site plume migration. ❑Y Latera!and �Y Vertical extent of soil contamination Lateral and F9_1 Vertical extent of groundwater contamination NA 9. Zone of influence calculated and assumptions used for subsurface Although attempted,no subsurface remediation remediation system and the zone of capture attained for the soil and system was used at this site. groundwater remediation system; 10.Reports/information 0 Unauthorized Release Form QMRs(Dates)1186—3/99 Well and boring logs PAR FRP Other(report name) 1999 Post Remediation/Closure Rpt. 11.Best Available Technology(BAT)used or an explanation for not using BAT,- The former tank pit and pump island were overexcavated. 0 12.Reasons why backgrourid-was is unattainable using BAT; ❑Y 13.Mass balance calculation of substance treated versus that remaining; An estimated 1.1 lbs of benzene and 16 lbs of TPHg remain in soil,whereas 0.0002 lbs of benzene and 0.0027 lbs of TPHg are dissolved in groundwater. 0 14.Assumptions,parameters, calculations and model used in risk Np 1isk assessments or modeling conducted at this site. assessments,.and fate and transport modeling; 0 15.Rationale why conditions remaining at site will not adversely As sued in IT Corps'closure summary,source area impact wafer quality, health, or other beneficial uses;and concentrations declined up to 96 percent and the remaining residual contamination should biodegrade over time. NA 16.WET or TCLP results B , Comments: In 1986,two of three 10,000-gallon gasoline tanks failed leak tests. During the site investigation,free product was yY, , detected in groundwater,which led the installation of 16 monitoring wells. In 1989, the three tanks and the fuel-dispensing island Dwere removed from the site. From 1993 to 1996,groundwater extraction wells were installed in an attempt to extract and treat a E: groundwater. The system was shut down due to the inability to depress groundwater. In 1998, approximately 9 J� g y ty p gample 2eveale of contaminated soil was excavated from beneath the former tanks and dispensing island. Confirmation samples revealed TPHg at l 1,700 mg/kg and low STEX concentrations in soil. Results of a March 1999 monitoring event showed minor benzene and TPHg contamination in two monitoring wells(MW 1 and 16)and only benzene in one extraction well(GEW-1). MtBE and other fuel - oxygenates were below detectable levels the groundwater samples. The water supply wells extend deeper than 150'bgs. Based on the information provided,groundwater does not appear to be significantly impacted by site conditions. Staff concurs with San Joaauin County's closure recommendation.