SITE INFORMATION AND CORRESPONDENCE

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TABLE 1 -CHECKLIST OF REQUIRED DATA FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES Site Name and Location: Stockton Metropolitan Airport, 5000 S.Airport Way, Stockton, San Joaquin County(RB#390227) Y1 1. Distance to production wells for municipal, A 2015 sensitive receptor survey reported two(2)municipal water domestic, agriculture, industry and other uses supply wells located within 2,000'of the Site. The nearest well is within 2000 feet of the site. 350'southwest(up-gradient). The remaining well is 1,800' northwest(cross-gradient) The water supply wells were sampled in 1984(40 years after the USTs were installed), all results were non- detect. Y 2. Site maps, to scale, of area impacted showing In 8/87, 2/88, 2/90, 3/90, and 6/97, 16 USTs were removed from the locations of any former and existing tank Fuel Farm. Table 1 of the Closure Memo provides dates removed systems, excavation contours and sample and details of the USTs. Site maps and figures showing tanks locations, boring and monitoring well elevation location, excavations, building and residual pollutants were contours,gradients, and nearby surface waters, provided in investigation reports. building , streets, and subsurface utilities; Y 3. Figures depicting lithology(cross Site lithology consists of clay, silt and sand to 104', the total depth section), treatment system diagrams; investigated. An engineered remediation system was not required by the regulatory agency. N 4. Stockpiled soil remaining on-site or Approximately 350 yd soil was excavated 6/97. The fate of soil and the mass off-site disposal(quantity); estimate for excavated soil was not provided in the available reports. P5. Monitoring wells remaining on-site, Site monitoring wells MW-1 through MW-8 were-properly destroyed on e; 18 November 2015. 6. Tabulated results of all groundwater Tabulated data was provided in reports indicating depth to groundwater varied elevations and depths to water, from 32'bgs to 51'bgs. Groundwater flow direction was predominantly towards the northwest. Y 7. Tabulated results of all sampling All data was tabulated in various reports. Lead sampling was conducted as part of and analyses: the UST removal activities.Results appear to be representative of naturally Y❑ Detection limits for occurring levels of lead in soil and groundwater. confirmation sampling El Lead analyses FY7 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: TPH pollution is about 250'laterally and 104'vertically. Y❑Lateral and IEVertical extent of soil contamination Y Lateral and Vertical extent of groundwater contamination Y 9. Zone of influence calculated and assumptions used for subsurface No active remediation was performed. remediation system and the zone of capture attained for the soil and groundwater remediation system; 10.Reports/informationFY] Unauthorized Release Form ❑Y QMRs(35) 11/02 to 4/14 ❑Y Well and boring logs❑Y PAR ❑ FRP ❑Y Other Closure Requests, 6/12&/6/14 Y 11.Best Available Technology(BAT)used or Leak was stopped by removing tanks and piping(BAT). an explanation for not using BAT; Unable Reasons why background was/is not Residual soil pollution does not pose a threat to human health and UUnable usin BAT, groundwater pollution is predicted to be restored in 5 years. N 13.Mass balance calculation of substance Initial mass and residual mass estimates were not provided. treated versus that remaining; Y 14. Assumptions, parameters, calculations The site meets the State Water Board's Low Threat Closure Policy and model used in risk assessments,and criteria and the Consultant states site does not represent a significant fate and transport modeling; environmental or health risk. Y 15. Rationale why conditions remaining at Soil and groundwater pollution is limited in extent. Land use is not site will not adversely impact water quality, expected to change in the foreseeable future. Groundwater plume is health, or other beneficial uses;and stable and slowly decreasing in concentration. By: JLB Comments:Sixteen (16) USTs, including 15 installed between 1942-1945 by the US Army Air Corps that supported pilot training during WWII, were used to store gasoline, diesel and jet fuel and were removed from Date: 9/29/15 the Airport tank farm. Based on the stable and declining concentrations in groundwater, no foreseeable changes in land use, and no risks to human health from direct exposure soil, Regional Board staff concur with closure.