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IV / vvvvvv secon corn E'& INTATIONAL 3017 Kilgore Road,Suite 100 S E C O R INCORPORATED Rancho Cordova,CA 95670 916-861-0400 TEL 916-861-0430 FAx March 19, 2004 Ms. Lori Duncan V L�C��UUJ San Joaquin County Environmental Health Department MAR 2 6 2004 304 East Weber Street, Third Floor Stockton, CA 95202 ENVIRONMENT HEALTH PERMIT/SERVICES RE: Work Plan for Additional Site Assessment and Interim Remediation 7-Eleven Store #32262 2360 West Grant Line Road Tracy, California SECOR Project No.: 77EL.32262.03.0104 Dear Ms. Duncan: This work plan was prepared by SECOR International Incorporated (SECOR), on behalf of 7-Eleven Inc., to conduct additional offsite assessment, and onsite interim remediation at 7-Eleven store number 32262, located at 2360 West Grant Line Road in Tracy, California (Figures 1 and 2). The work plan was prepared in response to the San Joaquin County Environmental Health Department (SJCEHD) letter dated December 30, 2003 requesting a work plan to continue the investigation of the lateral and vertical extent of contamination at the site (Attachment A). The letter also requested a work plan for interim remediation to minimize migration of contamination offsite. SITE BACKGROUND AND PREVIOUS INVESTIGATIONS In 1997, Fluor Daniel GTI conducted a Phase I environmental site assessment (ESA). On August 5, 1997, a follow-up Phase II ESA was performed. No detectable concentrations of petroleum hydrocarbons, polynuclear aromatic hydrocarbons, or pesticides were found in the soil and groundwater samples. Under the direction of a SJCEHD representative, ten soil samples were collected on May 2 and 3, 2003, beneath the product lines (1-1 through 1-4) and dispensers (D1 through D6) at depths between 3.5 feet and 4.5 feet below ground surface (bgs). The soil samples collected did not contain total petroleum hydrocarbons as gasoline (TPHg) or benzene, toluene, ethylbenzene, or total xylenes (BTEX) above laboratory reporting limits (Table 1). Maximum reported concentrations of methyl-tert- butyl ether (MtBE) and tort-butyl alcohol (TBA) were 4.5 milligrams per kilogram (mg/kg) and 12 mg/kg, respectively (D1-4.0'). During fuel line and dispenser upgrade activities on May 3, 2003, SECOR personnel collected grab water samples (W1 and W2) from tank pit observation wells TP-1 and TP-2, respectively (Figure 2 and 3). The samples were collected prior to UST removal and tank pit dewatering activities in May 2003. Depth to bottom of wells TP-1 and TP-2 were measured between 11 feet and 12 feet bgs. MtBE, TBA, and tert-amyl methyl ether (TAME) were reported in sample W1 at concentrations up to 510,000 micrograms per liter (ug/L), 79,000 ug/L, and 1,500 ug/L, respectively (Table 2). During dewatering activities, approximately 199,090 gallons of impacted water and a calculated estimate of 243.8 pounds of MtBE were removed from the tank pit excavation. Concentrations of MtBE, TBA, and TAME in water sample W3, collected from the open UST excavation on June 2, 2003 following dewatering activities, were significantly lower than pre-UST removal and tank pit dewatering activities (Table 2). Due to contamination found in the soil and groundwater during upgrade activities and the discovery of air bubbles between the UST and outer lining, the SJCEHD required 7-Eleven to remove and I:\7-Eleven\7-11 Stores\32262\workplans\32262 Offsite well install and interim remedlation workplan.doc J