SITE INFORMATION AND CORRESPONDENCE

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TABU - CHECKLIS9 T OF REQUIRED DA FOR NO f URTHER ACTION REQUESTS AT UNDERGROUND TANK SITES Site Name and Location: Tracy Auto Stereo, 10 West Grantilne, Tracy, Saiz Joaquin County Y 1. Distance to production wells for municipal, domestic, agriculture, Three water supply wells are within 2,000 feet of the industry and other uses within 2000 feet of the site; former USTs. The nearest downgradient well is 1,200 feet northeast of the site. ❑ 2. Site maps, to scale, of area impacted showing locations of,former and existing tank systems, Five USTs were removed in j excavation contours and sample locations, boring and monitoring well elevation contours, October 1993. Site maps are gradients, and nearby surface waters, buildings, streets, andsubsunface utilities, provided. Y❑ 3. Figures depicting lithology(cross section), treatment system diagrams; Boring logs and cross-sections show silty clay to 6 feet, and silty sand with silty clay lenses to 21 feet, the total depth explored. 0 4. Stockpiled soil disposed off-site(quantity); Approximately 190:cubic yards of excavated soil was transferred off- site to the Tracy Airport. 5. Monitoring wells remaining on-site, fate; One monitoring well remains northeast of the site. The well will be properly _ destroyed pending site closure. 6. Tabulated results of all groundwater elevations and depths to water; Groundwater levels varied from 6 to T feet below ground surface,and flow is to the northeast. 7. Tabulated results of al/sampling and analyses: Groundwater monitoringresults for the First Quarter 2001 are non- Defection limits for confirmation sampling detect forall constituents including MtBE and other fuel oxygenates at acceptable detection limits. Lead was analyzed in soil during tank Y❑Lead analyses removal activities of maximum concentrations of 9.6 mg/kg. } Y❑ S. Concentration contours of contaminants found and those remaining in soil' and groundwater, and both on-site and off-site: The lateral and vertical extent ofsoil and © Lateral and El Vertical extent of soil contamination groundwater contamination has been Latera!and 0 Vertical extent of groundwater contamination. defined 9. Zone of influence calculated and assumptions used for subsurface Remediation consisted of soil excavation remediation system and the zone of capture attained for the soil and to 10 feet Approximately 190 cubic yards groundwater remediation system; of con tamina ted soil was disposed off-site. 10.Reports/information q Unauthorized Release Form Y❑ QMRs Ej Boring logs 0 PAR FN 1 FRP rq Other(Site Closure Report,'5/2001) 11.Best Available Technology(BAT).used or an explanation for not using BAT; Remove contaminated soils and groundwater, verification monitoring. � "i2.Reasons-why background wa st '� Based on.thesoil_and groundwater_:grab samples, minor.contamination,. LEunattainable using BAT,• remains in shallow soil and groundwater. Quarterly sampling following soil excavation shows no groundwater contamination in the one monitoring well. { 13.Mass balance calculation of substance 0 treated versus that remaining The mass balance shows that 95% of contaminated soli has been excavated p and removed from the site. 14.Assumptions,parameters, calculations and model used in risk Based on the limited contamination, a risk assessment ❑ assessments, and fate and transport modeling; was not required. 15. Rationale why conditions remaining at site will not adversely Remaining contamination is limited. Contamination will ❑impact water quality, health, or other beneficial uses;and naturally degrade. By: Comments: The site is currently an auto stereo store. In October 1993, during construction of a right hand turn lane at West Grant Line Road and Holly Drive, five previouslyunknown USTs were discovered and removed. Soil contamination was identified during tank removal activities, and approximately 190 cubic yards of soil was excavated. Approximately 3,225 gallons of contaminated groundwater was also removed from the tank pit excavation. in April 2000, six soil borings Da e: were completed, and minor soil and groundwater contamination was4dentified. In September 2000, one monitoring well b (MW-1) was Installed, which has been monitored quarterly since.September 2000. MW-1 has been non-detect for all t Z3 Of constituents for the last three quarters. The site is covered with asphalt and concrete, which should limit leaching of contaminants into the groundwater. Based on the siteiinvestigation completed to date and the lack of groundwater contamination, Board staff concur with San Joaquin County's closure recommendation.