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s TAS 1 - CHECKLIST OF REQUIRED;; TA FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES Site Name and Location: 7-Eleven Store#2243-17647, 1048 Yosemite Avenue East, Manteca, San Joaquin County 1. Distance to production wells for municipal, domestic, agriculture, One public supply well is located 1000 feet north of the industry and other uses within 2000 feet of the site; site. No other wells are located within 500 feet of the site. ETI2. Site maps, to scale, of area impacted showing locations of former and existing tank Two 10,000-gallon and one systems, excavation contours and sample locations, boring and monitoring well elevation 6,000-gallon gasoline USTs contours, gradients, and nearby surface waters, buildings, streets, and subsurface utilities; were removed in 12/98. 3. Figures depicting lithology(cross section), treatment system diagrams; Site lithology consists of silty sand grading to a medium sand. The total depth investigated was 20 feet. E 4. Stockpiled soil disposed off site(quantify); Approximately 450 cubic yards of soil was excavated and transported offsite to a licensed disposal facility. 5. Monitoring wells remaining on-site, fate; Three monitoring wells(MW-1 to MW-3)were installed for this investigation. The three wells will be properly abandoned. 6. Tabulated results of all groundwater elevations and depths to water, The depth to water varied from 12 to 17 feet. The groundwater flow direction varied from northwest to east. 7. Tabulated results of all sampling and analyses: In 12/98,soil analyses reported TPHg(1.4 mg/kg),and MtBE (2.3 mg/kg). After overexcavation in 12/98 and resampling in 3/02, only M Detection limits for confirmation sampling MtBE(0.0026 mg/kg)was detected in soil. Grab groundwater sample ©Lead analyses results in 6/99 were 19,400 Ng/L for TPHg,and 126 lag/L for MtBE. in 7/03, groundwater results from monitoring wells were 0.561ag/L(MtBE). 0 8. Concentration contours of contaminants found and those remaining in soil The extent of contamination is defined by d groundwater, both on-Ab and off-site: on-site soil borings and monitoring wells. Y Lateral and Y Vertical extent of soil contamination Lateral and Vertical extent of groundwater contamination 9. Zone of influence calculated and assumptions used for subsurface Based on the limited extent of soil remediation system and the zone of capture attained for the soil and contamination,an engineered remediation groundwater remediation system; system was not required at this site. Q10.Reports/information 0 Unauthorized Release Form fourteen QMRs(1/00 to 7/03) 0 Boring logs 0 PAR F!] FRP Other Q11.Best Available Technology(BAT) used or an explanation for not using BAT; Remove USTs, overexcavation with offsite soil disposal, and natural attenuation. 12.Reasons why background was/is unattainable using BAT,' Decreasing concentrations have been attained at all monitoring wells. Minor soil contamination remains on-site. 13.Mass balance calculation of substance The consultant did not estimate remaining soil contamination. Minimal treated versus that remaining; contamination was defected in groundwater in 2003. N� 14.Assumptions,parameters, calculations and model used in risk A risk assessment was not required. assessments, and fate and transport modeling;and Q15. Rationale why conditions remaining at site will not adversely Soil contamination is limited in extent,and based on impact water quality, health, or other beneficial uses. fourteen sampling events, contamination is not continuing to leach to groundwater. Groundwater monitoring shows a decreasing trend in concentrations. By: Comments: Two 10,000-gallon and one 6,000-gallon gasoline USTs were removed from the subject site in 12198. JLB Multiple borings and three monitoring wells(MW-1 to MW-3) were completed in 2000 to delineate and monitor contamination at this site. Additional borings and grab sampling were completed in 1999 and 2003. In 1996, maximum Date: soil concentrations reported were TPHg(1.4 mg/kg), and MtBE(2.3 mg/kg). In 3/02 additional soil analyses detected only MtBE(0.0026 mg/kg). Grab groundwater monitoring results in 6/99 were 19,400 Ng/L for TPHg, and 126 pg/L for MtBE. 10/29/03 in 7/03 after 14 quarters of monitoring groundwater, monitoring well results were 0.56 pg/L for MTBE. Groundwater flow direction varied from northwest to east. Based on the limited extent of soil contamination and decreasing contaminant concentrations in groundwater, Board staff concur with San Joaquin County's Closure Recommendation.