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Former Town and County Chevron - 2 - 28 August 2001 <br /> 13336 Highway 88 East, Lockeford <br /> soil in the three monitoring well borings is 0.16 mg/kg at 31 feet in MW-3, and the deepest benzene <br /> concentration is 0.094 mg/kg at 36.5 feet in MW-3. <br /> Lithology encountered during drilling activities include silty sand and sandy silt to approximately 80 feet where a <br /> thin sand interval was encountered, and then clayey sand, silty clay,and silty sand to 120 feet. GeoSoly reports <br /> that the groundwater encountered in the thin sand interval at 80 feet is a perched aquifer. As presented in the San <br /> Joaquin County Flood Control and Water Conservation District,Lines of Equal Depth to Groundwater, <br /> Spring 1999 map,the depth to water in the Lockeford area is 100 to 110 feet. Therefore,the first water identified <br /> at 80 feet at this site may be a perched aquifer, and not part of the regional aquifer where water supply wells <br /> would be completed. <br /> The monitoring wells were purged and sampled in March 2001, and the only contaminant identified in <br /> groundwater was toluene in MW-2 at 5 micrograms per liter(µg/1). MtBE and other oxygenates were non-detect <br /> at appropriate detection limits. The second quarter monitoring event was completed in July 2001, and the only <br /> contaminant identified in groundwater was 1,2-dichloroethane in MW-1 at 1.0 µg/1. The reporting limit for <br /> 1,2-dichloroethane is 1.0 µg/1. GeoSoly included a revised contaminant mass estimate in the QMR, and reported <br /> the TPHg mass in soil at 1,186 pounds or 182 gallons at 6.5 pounds per gallon, and the benzene mass at <br /> 33 pounds or 5 gallons at 6.5 pounds per gallon. <br /> The current depth to groundwater is approximately 81 feet, and the groundwater flow direction calculated from <br /> both groundwater sampling events is to the south. The two Lockeford water supply wells that we required to be <br /> sampled are north and east of the site,respectively. The nearest water supply well in the direction of <br /> groundwater flow is 1,900 feet to the south. Based on the lack of groundwater contamination, the groundwater <br /> flow direction,and the lateral distance to existing water supply wells,the requirement to sample nearby <br /> Lockeford water supply wells is not necessary. <br /> Regional Board and County staffs discussed this site, and determined that based on the known extent of soil <br /> contamination and depth to water,the remaining concentration of benzene in soil, and the lack of MtBE <br /> contamination, continued groundwater monitoring is not required, and we believe it is appropriate to close this <br /> site. The County submitted a case closure recommendation to the Regional Board, and we will review the site <br /> file,and issue a No Further Action Required letter within 30 days. With the submittal of the Investigation and <br /> Quarterly Monitoring Reports, Mr. Ronald Nunan and Former Town and Country Chevron have met the <br /> requirements of the 22 December 1998, 13267 Order. <br /> If you have any questions,please call Marty Hartzell at(916)255-3115. <br /> GORDON LEE BOGGS <br /> Underground Tank Program Manager <br /> cc: Mr.Mark Owens,UST Cleanup Fund, State Water Resources Control Board, Sacramento <br /> Ms. Sandy Gill,UST Cleanup Fund, State Water Resources Control Board, Sacramento <br /> Mr. Jeffrey Wong, San Joaquin County Environmental Health Division, Stockton <br /> Mr.Frank Goldman,GeoSoly LLC, Sonoma <br />