SITE INFORMATION AND CORRESPONDENCE

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TABtt T - CHECKLIST OF REQUIRED trATA FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES Site Name and Location: North Stockton Auto Service, 8709 North Davis Road,Stockton, San Joaquin County 1. Distance to production wells for municipal, domestic, agriculture, A well receptor survey identified four water supply industry and other uses within 2000 feet of the site; wells within 2,000 feet of the site. The nearest well is 75 feet northeast of the former tank pit. Y 2. Site maps, to scale, of area impacted showing locations of former and existing tank systems, Site maps are provided in the various reports. One excavation contours and sample Locations, boring and monitoring well elevation contours, p gradients, and nearby surface waters, buildings, streets, and subsurface utilities, 550-gallon waste oil UST was removed in May 2000. Y� 3. Figures depicting lithology(cross section), treatment system diagrams, Boring logs show silty sand to 32 feet,sand to 44 feet,and clay to 46 feet, the total depth explored. Y� 4. Stockpiled soil disposed off-site(quantity); Approximately 165 cubic yards of soil was disposed at Forward Landfill in December 2000. 5. Monitoring wells remaining on-site, fate; One monitoring well was installed and remains on-site. The well will be _ properly destroyed pending site closure. 0 6. Tabulated results of all groundwater elevations and depths to water; Groundwater levels varied from 32 to 34 feet below ground surface,and flow is to the east/northeast. 7. Tabulated results of all sampling and analyses: Groundwater monitoring results for samples collected in August 2001 are non-detect for all constituents including MtBE and other fuel Detection limits for confirmation sampling oxygenates at acceptable detection limits. Soil samples collected ©Lead analyses during UST removal in May 2000 reported lead at<5 mg/kg. 8. Concentration contours of contaminants found and those remaining in soil The lateral and vertical extent of soil and and groundwater,and both on-site and off-site: groundwater contamination has been Lateral and 171 Vertical extent of soil contamination defined. Confirmation sampling shows 1(❑ Lateral and "y�" Vertical extent of groundwater contamination contaminated soils were removed 0 9.Zone of influence calculated and assumptions used for subsurface Based on the limited contamination,site remediation system and the zone of capture attained for the soil and remediation beyond soil excavation and groundwater remediation system; disposal was not required. The site has been repaved with asphalt 10.Reports/information Iq Unauthorized Release Form Y❑ QMRs(6/01 to 8/01) El Boring logs El PAR El FRP El Other(Well installation Report, 7/2001) 11.Best Available Technology(BAT)used or an explanation for not using BAT, The UST and contaminated soils were removed. 0 12.Reasons why background wasrs Minor groundwater contamination remains below the tank pit area. The unattainable using BAT, contamination is limited in extent,and does not present a significant threat to water quality. 13.Mass balance calculation of substance Based on the removal of contaminated soils and the limited groundwater treated versus that remaining; contamination,a mass balance calculation was not required. 14.Assumptions,parameters, calculations and model used in risk Results of the risk assessment show that constituents assessments,and fate and transport modeling; identified in groundwater at the tank pit would be below MCLs at the receptor 75 feet away. 15. Rationale why conditions remaining at site will not adversely Remaining contamination is limited in extent. impact water quality, health, or other beneficial uses,and Contamination will naturally degrade. By: Comments: The site is an auto service center. One 550-galloon waste oil UST was removed in May 2000. Five soil borings were MH completed in September 2000,and petroleum hydrocarbon and VOCs were identified at 10 feet in one boring at the center of the tank pit. In November 2000, approximately 165 cubic yards of soil was removed and disposed at Forward Landfill. In January 2001, a groundwater grab sample(SB1A}identified low VOC and MtBE contamination at 35 feet in the center of the tank pit. One monitoring well was installed approximately 15 feet northeast of SB1A, and only chloroform was identified at 2.2 Ng/l in June 2001. Groundwater sampling completed in August 2001 did not identify any constituents using EPA Method 82608. The Date: receptor survey completed in February 2001 identified a domestic water supply well approximately 75 feet northeast of the former 11/7101 tank pit. Well construction details for the domestic well are unknown. This well was sampled in June 2001 and no contamination was identified using EPA Method 8260B. The soil contaminant mass has been removed and the remaining contamination in groundwater is limited in extent. The remaining groundwater contamination will naturally volatilize and degrade. Based on the site investigation and activities completed to date, Board staff concur with San Joaquin County's closure recommendation.