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3 <br /> +`� S www secor com <br /> INTERNATIONAL 3017 Kilgore Road,Suite 100 <br /> S E C ® R INCORPORATED Rancho Cordova CA 95670 <br /> 916 861 0400 TEL <br /> . 916 861 0430 Fnx <br /> March 19, 2004 <br /> Ms Lori Duncan <br /> San Joaquin County Environmental Health Department MAR 2 6 2004 <br /> 304 East Weber Street, Third Floor <br /> Stockton, CA 95202 ENVIRONMENT HEATH <br /> PERMIT/SERVICES <br /> RE Work Plan for Additional Site Assessment and Interim Remediation <br /> 7-Eleven Store #32262 <br /> 2360 West Grant Line Road <br /> Tracy, California <br /> SECOR Project No 77EL 32262 03 0104 <br /> Dear Ms Duncan <br /> This work plan was prepared by SECOR International Incorporated (SECOR), on behalf of 7-Eleven <br /> Inc , to conduct additional offsite assessment, and onsite interim remediation at 7-Eleven store <br /> number 32262, located at 2360 West Grant Line Road in Tracy, California (Figures 1 and 2) The <br /> work plan was prepared in response to the San Joaquin County Environmental Health Department <br /> (SJCEHD) letter dated December 30, 2003 requesting a work plan to continue the investigation of <br /> the lateral and vertical extent of contamination at the site (Attachment A) The letter also requested <br /> a work plan for interim remediation to minimize migration of contamination offsite <br /> SITE BACKGROUND AND PREVIOUS INVESTIGATIONS <br /> In 1997, Fluor Daniel GTI conducted a Phase I environmental site assessment (ESA) On August 5, <br /> 1997, a follow-up Phase II ESA was performed No detectable concentrations of petroleum <br /> hydrocarbons, polynuclear aromatic hydrocarbons, or pesticides were found in the soil and <br /> groundwater samples <br /> Under the direction of a SJCEHD representative, ten soil samples were collected on May 2 and 3, i <br /> 2003, beneath the product lines (L1 through L4) and dispensers (D1 through D6) at depths between <br /> 3 5 feet and 4 5 feet below ground surface (bgs) The soil samples collected did not contain total <br /> petroleum hydrocarbons as gasoline (TPHg) or benzene, toluene, ethylbenzene, or total xylenes } <br /> (BTEX) above laboratory reporting limits (Table 1) Maximum reported concentrations of methyl-tert- <br /> butyl ether (MtBE) and tert-butyl alcohol (TBA) were 4 5 milligrams per kilogram (mg/kg) and 12 <br /> mg/kg, respectively (D1-4 0') <br /> During fuel line and dispenser upgrade activities on May 3, 2003, SECOR personnel collected grab <br /> water samples (W1 and W2) from tank pit observation wells TP-1 and TP-2, respectively (Figure 2 <br /> and 3) The samples were collected prior to UST removal and tank pit dewatering activities In May <br /> 2003 Depth to bottom of wells TP-1 and TP-2 were measured between 11 feet and 12 feet bgs <br /> MtBE, TBA, and tert-amyl methyl ether (TAME) were reported in sample W1 at concentrations up to <br /> 510,000 micrograms per liter (ug/L), 79,000 ug/L, and 1,500 ug/L, respectively (Table 2) During <br /> dewatering activities, approximately 199,090 gallons of impacted water and a calculated estimate of <br /> 243 8 pounds of MtBE were removed from the tank pit excavation Concentrations of MtBE, TBA, <br /> and TAME In water sample W3, collected from the open UST excavation on June 2, 2003 following <br /> dewatering activities, were significantly lower than pre-UST removal and tank pit dewatering <br /> activities (Table 2) <br /> • Due to contamination found in the soil and groundwater during upgrade activities and the discovery <br /> of air bubbles between the UST and outer lining, the SJCEHD required 7-Eleven to remove and <br /> 1 17 Elevenl7-11 Stores1322621Workplans132262 Offsite well install and interim remediation workplan doc <br /> f <br /> �` I <br />