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J � � <br /> Stantec Consulting Services Inc. i <br /> .�. 3017 Kilgore Road Suite 100 <br /> Rancho Cordova CA 95670 <br /> i <br /> Tel:(916)861-0400 <br /> Fax:(916)861-0430 <br /> Stantec <br /> cj <br /> August 15, 2013 <br /> Ms. Lisa Medina i <br /> San Joaquin County <br /> Environmental Health Department <br /> 1868 East Hazelton Avenue <br /> I Stockton, CA 95202 <br /> RE: Site Closure Report <br /> 7-Eleven Store#14117.. <br /> i <br /> 2725 Country Club Boulevard <br /> Stockton, California <br /> Stantec Project Number` 185750063 <br /> Dear Ms. Medina: <br /> This report was prepared by Stantec Consulting Services Inc. (Stantec) on behalf of 7-Eleven <br /> Inc. (7-Eleven), to request site closure pursuant to the Low-Threat Underground Storage Tank <br /> Case Closure Policy (LTCP):for 7-Eleven store #14117, located at 2725 Country Club i <br /> Boulevard, in Stockton, California (Figures 1 and 2). <br /> 1 SITE BACKGROUND <br /> On July 17, 1998, three 10,000-gallon single-walled underground storage tanks (LISTS) were <br /> removed from the site. The UST excavation was extended to the east, and two new 10,000- <br /> gallon double-walled steel USTs were installed. The new tanks were installed in a tank pit <br /> located east of the original UST locations. Three ten-inch diameter Schedule 40 <br /> polyvinylchloride (PVC) conductor casings were installed in the new UST pit between the new <br /> tanks for the potential future installation of groundwater monitoring wells. <br /> i <br /> On September 29 and October 2, 1998, Fluor-Daniel GTI advanced six offsite (OSGP-1 through <br /> OSGP-6) and 11 onsite (GP-7 through GP-17) Geoprobe® soil borings. The offsite borings <br /> were located north of the 7-Eleven site in an apartment complex. The offsite borings did not <br /> contain detectable concentrations of petroleum hydrocarbons. The onsite borings contained <br /> benzene, total petroleum hydrocarbons as gasoline (TPHg), and methyl tertiary butyl ether <br /> (MtBE) at maximum concentrations of 12.5 milligrams per kilogram (mg/kg) (GP-17@20'), <br /> 42,900 mg/kg (GP-15@15'), and 234 mg/kg (GP-14@10'), respectively (Fluor Daniel GTI, <br /> 1998). <br /> j On May 13 and 14, 1999, four groundwater monitoring wells (MW-1 through MW-4) were <br /> installed'to 25 to 51 feet below ground surface (bgs). Benzene, TPHg, and MtBE in soil were <br /> reported at maximum concentrations of 2.89 mg/kg (MW-3@15'), 429 mg/kg (MW-3@15'), and <br /> 1.95 mg/kg (MW-3@15'), respectively (IT Corporation, 1999). <br /> f <br /> 4 r <br />{ i <br /> I <br />