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. 1k Stantec Consulting Corporation .. 57 Lafayette Circle 2nd Floor Lafayette CA 94549 Tel:(925)299-9300 Fax:(925)299-9302 StanWc September 11, 2009 Terrence Fox �+ Task Order Manager California Department of Transportation 2015 E. Shields Ave. Suite 100 Fresno, CA 93728 Reference: Work Plan for Site Closure, Caltrans Shop 10 Maintenance Facility Stockton,California { Dear Mr. Fox: This work plan was prepared by Stantec Consulting Corporation (Stantec) on behalf of the California Department of Transportation, District 6 (Caltrans)to provide a description of work tasks leading to a Request for Site Closure of the Caltrans Shop 10 Maintenance Station, located at 1603.So. B Street, Stockton (the Site; Figures 1 and 2). BACKGROUND , The Site is located adjacent to the Caltrans District Office located at,1976 E Charter Way at the comer of Charter Way and B Street in the City of Stockton, California (Figure 1). The Site occupies approximately four acres including a two-story office building and.,temporary permit building, parts warehouse, and maintenance shop (Shop 10). Outside areas for truck washing and water treatmerrt, machining, and highway maintenance equipment storage exist in the southwestern portion of the property(Figure2). The property is owned by Caltrans and is used for the storage and maintenance of state vehicles and highway maintenance equipment. In 1978, one 5,000-gallon UST with unknown contents was reportedly removed from the Site due to a detected leak. In 1989,three 5,000-gallon gasoline USTs, one 5,000-gallop diesel UST, and one 1,000- gallon waste oil UST were removed from the Site. Soil samples beneath the tanks and lines were found to contain up to 3,700 milligrams per kilogram (mglkg)total petroleum hydrocarbons, as gasoline (TPH-g), 1,700 mglkg total petroleum hydrocarbons, as diesel (TPH-d)and 25 mg/kg benzene- A previous mass estimate estimated approximately 3,320 pounds of hydrocarbon in vadose zone and'capillary fringe soils and 240 pounds in groundwater prior to treatment. l j ' Between 1987 and 1996, 25 groundwater monitoring.wells and 2 va3por extraction wells (VM-1 and VM-2) were installed at the Site to assess the vertical and lateral extent of contamination. The highest soil levels were found in two borings in the area of the former USTs, VM-1 and:MW-14. Soil samples from these borings found up to 11,000 mg/kg TPH-g and 440 mg/kg benzene at 20 feet below ground surface (ft bgs); 13,000 mglkg TPH-g and 440 mg/kg benzene at 30 ft bgs; and 3,000 mg/kg TPH=g and 840 mg/kg benzene at 40 ft bgs. Thirteen of the monitoring wells were destroyed and the remaining twelve groundwater wells are included in the current groundwater monitoring program- The Site has been on a quarterly groundwater monitoring schedule since 1990 and will continue monitoring on a semi-annuai basis as directed by the San Joaquin County, Environmental Health Department (EHD) in a letter,dated July 1, 2009. The next groundwater sampling event is scheduled in December 2009. Previous Sensitive Receptor Data Neighboring properties include residential and commercial uses to the north, west, and south. The San Joaquin County Fairgrounds property borders the Site to the west. A local Well survey was performed for the Site in 2000 and reported that there did not appear to be any private or public wells within 500 feet of the L\Prolects\CALTRANSIShop 10\20091Closurelclosure work plan fnl.doo