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Type 11 Work Plan - Addendum <br />OW Construction Activities and Soil Removal Action <br />Preliminary Assessment/Site Investigation Update <br />California Army National Guard Facility <br />Stockton, California <br />Contract No. GS-00E-007L/Task Order W9I238-05-F-0084 <br />Version 2.0 <br />1.0 SITE BACKGROUND <br />The area surrounding the Stockton CARNG facility has been a mix of airport and <br />agricultural use for over 40 years. The AASF has been in existence since the early 1950s <br />as an aircraft fueling station and was expanded to its present size of approximately 25 <br />acres in 1974. The Armory, CSMS and OMS appear from aerial photographs to have <br />been constructed in 1963. <br />A Preliminary Assessment/Site Investigation (PA/SI) performed in 2000 (Versar, 2000) <br />included a geophysical survey of the CA ARNG Stockton vehicle storage yard north of <br />the CSMS. The survey was performed based on the testimony of workers who claim they <br />remembered "Tear Gas Canisters" having been buried at the Site. The geophysical <br />survey identified the presence of one larger and two smaller subsurface anomalies at the <br />Site. <br />Investigation of the subsurface anomalies was performed during October 2005. The <br />initial investigation uncovered trash and debris in the area of the large southertunost <br />anomaly. Further excavation uncovered numerous one and five-gallon cans, and one and <br />one half gallon plastic jugs, suspected to be paint materials. The excavation was then <br />extended approximately three feet west to investigate the debris. Soils in the west end of <br />the excavation exhibited odors and free liquids. Based on the findings of potential soil <br />contamination, and discussions with CA ARNG representatives, soil samples were <br />collected from the south excavation for laboratory analysis. <br />Laboratory analysis of the soil samples detected low concentrations of petroleum <br />hydrocarbons as gasoline (1.26 mg/kg) and diesel (115 mg/kg), and trace concentrations <br />(less than one mg/kg) of 11 volatile organic compounds (VOCs). The detected VOCs <br />were non-chlorinated and are typically found with fuel hydrocarbons. A total of 13 <br />metals were also identified above the method detection limit. Of these, arsenic and <br />vanadium were detected at concentrations exceeding the US EPA Preliminary <br />Remediation Goal (PRG) for Industrial Soil (US EPA, 2004). <br />Concentrations of arsenic and vanadium detected at the Site are believed to be <br />representative of background conditions. Studies performed in California (Kearney, <br />1996) and the western United States (Shacklette and Boerngen, 1984) indicate that the <br />detected concentrations fall well within observed ranges and are near the mean expected <br />value. Similar concentrations of these metals were also detected at the copper sulfate <br />contaminated soil removal site and at borings B11 and B19, located east of the CSMS. <br />Exposed construction debris and contaminated soil were removed from the excavation <br />and properly containerized for disposal. The excavation was backfilled with clean fill. <br />104700.4965.300 Page C FSP-1 April 2007