SITE INFORMATION AND CORRESPONDENCE CASE 2

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BLE 1 -CHECKLIST OF REQUIRED DATA FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES Site Name and Location: Former Western Lift,Case#2, 3430 S.EI Dorado St.,Stockton, San Joaquin County(RB#391189) Y1 1. Distance to production wells for municipal,domestic, A 2003 sensitive receptor survey reported no water agriculture, industry and other uses within 2000 feet of the site. supply wells within 2,000'of the site.A site domestic well was properly destroyed in 12-96. Y 2. Site maps, to scale, of area impacted showing locations of any Prior to 1984, one 1,000-gallon gasoline UST was former and existing tank systems, excavation contours and removed. Site maps and figures were provided in sample locations, boring and monitoring well elevation investigation reports. contours,gradients, and nearby surface waters,buildings, streets,and subsurface utilities; =73. Figures depicting lithology(cross Site lithology consists of clay,silt,and sand to 90', the total depth section), treatment system diagrams; investigated. N 4. Stockpiled soil remaining on-site or The fate of excavated soil is not documented. off-site disposal(quantity); y 5. Monitoring wells remaining on-site, Six(6)remaining Case#2 monitoring wells(MW-6,MW-7, MW-8A, and MW-9 ate; through MW-11)and eleven(11)remediation wells(VEW-1 through VEW-7, and ASW-1 through ASW-4) will be properly destroyed prior to closure. YJ 6. Tabulated results of all groundwater Depth to groundwater varied from 22'bgs to 39'bgs. Groundwater flow elevations and depths to water; direction was towards the northeast. Groundwater gradient varied from 0.001 ft/ft to 0.002 ft/ft. 7. Tabulated results of all sampling All data adequately tabularized in various reports. and analyses: FYIDetection limits for confirmation sampling IS Lead analyses 8. Concentration contours of contaminants found and those remaining in The horizontal and vertical extent of the soil and groundwater, and both on-site and off-site: petroleum contamination are confined to - the property limits. El Lateral and 0 Vertical extent of soil contamination Lateral and FY1 Vertical extent of groundwater contamination 9.Zone of influence calculated and assumptions used for subsurface Soil vapor extraction (SVE)and air remediation system and the zone of capture attained for the soil and sparging(AS) were implemented from groundwater remediation system; 1 2005 to 2012. 10.Reports/information❑Y Unauthorized Release Form MY QMRs(58)3-98 to 12-12 My Well and boring logs 1 PAR [] FRP ❑y Other Site Conceptual Model& Closure Report, 4-13 _YJ 11.Best Available Technology(BAT) used or an UST removal and implementation of an engineered SVE/AS explanation for not using BAT; I system. Y 12. Reasons why background was/is Residual soil contamination and groundwater pollution remain onsite. attainable using BAT, Groundwater plume is decreasing in concentration and should be restored through natural processes in about 26 years. Y 13.Mass balance calculation of Consultant estimated initial TPH mass as 13,705 lbs. in soil and 88 lbs. in substance treated versus that groundwater.SVE removed approximately 4,100 lbs. of TPH in soil. An remaining; estimated 4.5 lbs. of TPH remain in groundwater. Y 14. Assumptions,parameters, Site did not pass LTCP for Vapor Intrusion(J&E Model 10 benzene risk from calculations and model used in risk groundwater to soil vapor)and Direct Contact(Ethybenzene at>5'bgs); assessments, and fate and transport however, USTCUF recommended case for closure. Consultant states site reuse modeling; does not represent a significant human health risk with engineering controls in new construction. y 15. Rationale why conditions Soil and groundwater contamination reportedly are confined to the property remaining at site will not adversely boundaries.Land use(commercial)is not expected to change in the foreseeable impact water quality, health, or other future. Consultant estimated time to reach WQGs as 2039. Groundwater plume beneficial uses;and is stable and decreasing in concentration. By: JLB Comments:Prior to 1984, one 1,000-gallon gasoline UST was removed at the subject site. TPHg discovered as a result of routine domestic well monitoring. The domestic well was properly destroyed in 1996.Based on Date: the limited extent of soil and groundwater pollution remaining on-site, and slowly declining concentrations, 7/16/2013 commercial land use, and with engineering controls and Level C protection for any future construction, Regional Board staff concur with San Joaquin County's Closure Recommendation.