SITE INFORMATION AND CORRESPONDENCE

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TAB1 - CHECKLIST OF REQUIRED ISA FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SiTES Site Name and Location: Nelson Ready Mix, 22700 South Highway 99, Ripon, San Joaquin County 1. Distance to production wells for municipal, domestic, agriculture, A well survey was not completed. The nearest water industry and other uses within 2000 feet of the site; supply well, Ripon City Well#12, is approximately 1,000 feet southwest of the site. 2. Site maps, to scale, of area impacted showing locations of former and existing tank systems, excavation contours and sample locations, boring and monitoring well elevation contours, Site maps are provided. gradients, and nearby surface waters, buildings, streets, and subsurface utilities; 0 3. Figures depicting lithology(cross section), treatment system diagrams; Boring logs were not provided. A treatment system was not operated at this site. 4. Stockpiled soil remaining on-site or off-site disposal(quantity); Approximately 522 cubic yards of soil were excavated and disposed at Forward Landfill in 8199. 5.-Monitoring.wells remaining-on-site;.fate,._Three_monitoring_wells-were_installed-in-5198,,and-destroyed in 6199. = - 6. Tabulated results of all groundwater elevations and depths to water; Groundwater levels vary from 10 to 20 feet below ground surface, and groundwater flow is to the north. 7. Tabulated results of all sampling and analyses: Post excavation groundwater monitoring results in Ng11 show TPHg at Detection limits for confirmation sampling 100, TPHd at 510, BTEX and MISE at<0.5. No indication of lead analysis. Lead analyses 8. Concentration contours of contaminants found and those remaining in soil According to the County, the lateral and and groundwater, and both on-site and off-site: vertical extent of soil and groundwater Lateral and 71 Vertical extent of soil contamination contamination has been defined. Lateral and Vertical extent of groundwater contamination 9. Zone of influence calculated and assumptions used for subsurface A remediation system was not operated at remediation system and the zone of capture attained for the soil and this site. Site cleanup by excavation and groundwater remediation system; removal of contaminated soil. w ❑ 10.Reports/information Unauthorized Release Form N❑ QMRs Boring logs PAR E] FRP � Other ❑ 11.Best Available Technology(BAT) used or an explanation for not using BAT,- Remove UST and contaminated soil,natural attenuation. 12.Reasons why background wasfis _ unattainable using BAT,• Diesel contamination remains in on-site soil and groundwater. 13.Mass balance calculation of substance A mass balance was not completed. Approximately 3,370 pounds of diesel treated versus that remaining; was removed during over excavation and removal of contaminated soil. ❑Y 14.Assumptions,parameters, calculations and model used in risk assessments, and fate and transport modeling; A risk assessment was not completed. 15. Rationale why conditions remaining at site will not adversely impact wafer quality, health, or other beneficial uses;and Remaining contamination will naturally attenuate. By: Comments: One 500-gallon gasoline UST was closed in place prior to 1983, and one 4,000-gallon diesel UST was removed in 4/95. Multiple borings and three monitoring wells identified soil and groundwater contamination. Site cleanup was completed by excavation and removal of contaminated soils. All three monitoring wells have been destroyed,and the site is now part of the Highway 99 and Jack Tone Road interchange. The City of Ripon Municipal Well#12 is D tC: approximately 1,000 feet southwest of the site. Well##12 is sealed to 150 feet and the first perforated interval is from 165 � D I to 190 feet bgs. Based on the information provided, Board staff concur with San Joaquin County's closure i recommendation.