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N San Joaquin County DIRECTOR <br /> Environmental Health Department Donna Heran, REHS <br /> 2 600 East Main Street ASSISTANT REHS STANTDIRR <br /> y ` Stockton, California 95202-3029 Laurie Cotulla,REHS <br /> PROGRAM COORDINATORS <br /> • CCCarl Borgman, REHS <br /> 4�/FOP a� P Website: WWI%s19ov.or9/ehd Mike Huggins,REHS,RDI <br /> Phone: (209) 468-3420 Margaret Lagono,REHS <br /> Fax: (209) 464-0138 Robert McClellon,REHS <br /> Jeff Carruesco,REHS,RDI <br /> September 23, 2008 Kasey Foley, REHS <br /> Mr. Michael Karvelot <br /> Quik Stop Markets, Incorporated <br /> 4567 Enterprise Street <br /> Fremont, California 94538 <br /> Subject: Quik Stop Market No. 132 <br /> 3555 West Hammer Lane <br /> Stockton, California 95209 <br /> The San Joaquin County Environmental Health Department (EHD) has reviewed historical <br /> soil and groundwater analytical data for the above-referenced site and discussed the site <br /> information with the Central Valley Regional Water Quality Control Board (CVRWQCB) <br /> staff on September 17, 2008. <br /> Depth to groundwater has historically been reported between 6.95 and 18.45 feet below <br /> surface grade (bsg); however, since March 1996, depth-to-groundwater measurements have <br /> been reported between approximately 7 and 11.5 feet bsg. Of the eight remaining <br /> monitoring wells at this site, only MW-5, screened between 9 and 19 feet bsg, is screened <br /> across the first water-bearing zone identified at approximately 5 to 10 feet bsg. Monitoring <br /> wells MW-2, MW-3, and MW-8 are screened between 20 and 30 feet bsg; MW-4 is <br /> screened between 16.5 and 26.5 feet bsg; MW-6 is screened between 16 and 21 feet bsg; <br /> and MW-7 is screened between 17 and 23 feet bsg. .Data from quarterly groundwater <br /> monitoring events indicate that methyl tertiary-butyl ether (MTBE) concentrations were not <br /> reported in groundwater samples until March 1996, approximately five-and-a-half years <br /> after the initial petroleum hydrocarbon leak was detected. The EHD is concerned the <br /> MTBE plume may have migrated laterally in the permeable sand unit at approximately 10 <br /> feet bsg. This hypothesis is supported by high concentrations of MTBE reported in <br /> groundwater samples collected from soil boring SBA at 10 feet bsg in July 2001, and in <br /> groundwater samples collected from MW-5 during the quarterly monitoring events. The <br /> lateral extent of petroleum hydrocarbon contamination in the first water-bearing zone must <br /> be addressed. <br /> In addition, MTBE was detected at 39 micrograms per liter (lig/L) in groundwater samples <br /> collected at 42 feet bsg from ATC-5, the deepest soil boring, in March 1999. MTBE was <br /> also detected at 500 ug/L in groundwater samples collected at 29 feet bsg from soil boring <br />