SITE INFORMATION AND CORRESPONDENCE

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` y TABLE 1 -CHECKLIST OF REQUIRED DATA FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES Site Name and Location: Vanco Truck Plaza, 9033 W. Charter Way, tockton, San Joaquin County(RB#399967) Y 1. Distance to production wells for municipal,domestic, a municipal water supply is located 500'northeast, agriculture, industryand other uses within 2000 feet of the.site. o e domestic well is 9300'northwest, and one domestic 11 is 1900'south of the site. Y 2. Site maps, to scale, of area impacted showing locations of 1 May 2003, an unauthorized release from the USTs any former and existing tank systems, excavation contours and s rstem was discovered during dispensers and piping sample locations, boring and monitoring well elevation u grades. contours, gradients, and nearby surface waters, buildings, streets, and subsurface utilities; Y 3. Figures depicting lithology(cross section), treatment system Site lithology consists of clay, silt,and sand to 100', the diagrams; I total depth investigated. Y 4. Stockpiled soil remaining on-site or off-site disposal(quantity); Approximately 300 cubic yards of excavated soil was transp,orted to Forward Landfill in Manteca. y 5. Monitoring wells remaining on-site, fate; I Seven monitoring we Its(MW-1 through MW-7)will be property abandoned. 6. Tabulated results of all groundwater Depth to groundb tater varied from 16'to 29'bgs. Groundwater Now elevations and depths to water; direction varied t vm east to northwest. Groundwater gradient varied from 0.0003 to 0.1 P15 ft/ft. �,. r7. Tabulated-results-of-all sampling_ _AIl_data_adequafely_tabula.Ted in various.reports,including closure report. and analyses: Detection limits for confirmation sampling ❑N Lead analyses LyJ 8. Concentration contours of contaminants found and those remaining in soil and The extent of the identified groundwater, and both on-site and off.-site: contamination shown in applicable reports. Latera!and El Vertical extent of soil contamination Latera!and Vertical extent of groundwater contar ination 9. Zone of influence calculated and assumptions used for subsurface remediation An engineered remedlation was not. system and the zone of capture attained for the soil and groundwater remediation required by the regulatory agency. system; 10.Reports 1 information ❑Y Unauthorized Release Form FYI MRs 97 from 8104 to 9108 FY] Well and boring logs10 PAR FRP FY-1 Other Closure Report(6110) Y 11.Best Available Technology(BA T) used or an explanation for not USTs piping and dispensers trench soil removal and, using BAT, I natural attenuation. attainable Reasons why background was/is Minor residual oil and groundwater contamination remains on-site. using BAT; y 13.Mass balance calculation of substance treated The consultant estimates 0.16 gallons of TPH-d remain in groundwater, while 467 gallons of TPH-d remain in soil. versus that remaining, Y 14. Assumptions,parameters, calculations and The regulatory ger:cy did not require a soil vapor survey,tlue to the model used in risk assessments, and fate and location of residual soil and groundwater contaminants(mainly TPHg transport modeling; and TPHd in fu l island), limited threats from unsaturated zone vapor intrusion from ong chain hydrocarbons, distance to building(-30'), and no change in site use(service station). A mitigation plan was proposed fort a current owners/operators to address gross contamination 3nd direct contact from contaminated soils during future UST system rei novaL :y- 15. Rationale why conditions remaining at site Soil and grouni fwater contamination reportedly is limited in extent. will not adversely impact water quality, health, or Land use(com ercial)is not expected to change in the foreseeable other beneficial uses;and future. Vapor ir trusion and residual soil contamination risk have been addressed. Wa er quality goals will be reached in 1 ear. By. JL B Comments:In May 2003, an unauthorized release fr m the USTs system was discovered during dispensers and piping upgrades from the subject Site. Based uj Pon 17 quarters of groundwater monitoring showing a T1'4 stable plume with declining concentrations, the limi ed extent of contamination remaining in soil and 0 1 0 groundwater, no foreseeable changes in land use, a 7d limited threats from groundwater,soil and soil vapor intrusion, Regional Board staff concur with San Joa juin County's Closure Recommendation. I