SITE INFORMATION AND CORRESPONDENCE

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for TABLE 1 - CHECKLIST OF REQUIRED D TA FOR NO,FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES Site Name and Location: Tracy Auto Stereo, 10 West Grantline,Tracy, San Joaquin County 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 Y excavation contours and sample locations, boring and monitoring well elevation contours, October 1993. Site maps are gradients, and nearby surface waters, buildings, streets, and subsurface utlikies; 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. ETI 4. Stockpiled soil disposed off-site(quantity); Approximately 190,cubic yards of excavated soil was transferred off- site to the Tracy Airport �Y 5. Monitoring wells remaining on-site, fate; One monitoring well remains northeast of the site. The well will be property destroyed pending site closure. 0 6. Tabulated results of all groundwater elevations and depths to water; .Groundwater levels varied from 6 to 7 feet below ground surface, and flow is to the northeast. 7.Tabulated results of all sampling and analyses: Groundwater monitoring results for the First Quarter 2001 are non- detect for all constituents including MtBE and other fuel oxygenates at Detection limits for confirmation sampling acceptable detection limits. Lead was analyzed in soil during tank Lead analyses removal activities at maximum concentrations of 9.6 mg/kg. 0 8. Concentration contours of contaminants found and those remaining in soil The and groundwater, and both on-site and off-site: lateral and vertical extent of soil and F1Latera!and Vertical extent of soil contamination groundwater contamination has been Lateral and Vertical extent of groundwater contamination defined. fq 9. Zone of influence calculated and assumptions used for subsurface Remediation consisted of soil excavation EKI remediation system and the zone of capture attained.for the soil and to 10 feet. Approximately 190 cubic yards groundwater remediation system; of contaminated soil was disposed off-site. 10.Reports/information 0 Unauthorized Release Form QMRs f 0 Boring logs E PAR N❑ FRP Other(Site Closure Report 512001) 11.Best Available Technology(BA7) used or an explanation for not using BAT, Remove contaminated soils and groundwater, verification monitoring. 12.Reasons why background wads Based on the.soi!and groundwater grab samples, minor contamination unattainable 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 treated versus that remaining; The mass balance shows that 95% of contaminated sail has been excavated and removed.from the site. 14.Assumptions,parameters,calculations and model used in risk Based on the limited contamination,a risk assessment 0 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 f impact water quality, health, or other benerrcial 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 previously unknown 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 Date: were completed,and minor soil and groundwater contamination was identified. In September 2000, one monitoring well (MW-1)was installed, which has been monitored quarterly since September 2000. MW-1 has been non-detect for all Z3 Q( 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 site investigation completed to date and the lack of groundwater contamination, Board staff concur with San Joaqui,?County's closure recommendation.