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Type II Work Plan - Addendum UXO Construction Activities and Soil Removal Action Preliminary Assessment/Site Investigation Update California Army National Guard Facility Stockton, California Contract No GS-00E-007L/Task Order W91238-05-F-0084 Version 2.0 liquids. Based on the findings of potential soil contamination, and discussions with CA ARNG representatives, soil samples were collected from the south excavation for laboratory analysis. Figure 3 shows the former excavation and sample locations. Laboratory analysis of the soil samples detected low concentrations of petroleum hydrocarbons as gasoline (TPH-G, 1.26 mg/kg) and diesel (TPH-D, 115 mg/kg), and trace concentrations (less than one mg/kg) of 11 volatile organic compounds (VOCs). The detected VOCs were non- chlorinated and are typically found with fuel hydrocarbons. A total of 13 metals were also identified above the method detection limit. Of these, arsenic and vanadium were detected at concentrations exceeding the US EPA Preliminary Remediation Goal (PRG) for Industrial Soil (US EPA, 2004). Concentrations of arsenic and vanadium detected at the Site are believed to be representative of background conditions. Studies performed in California (Kearney, 1996) and the western United States (Shacklette and Boerngen, 1984) indicate that the detected concentrations fall well within observed ranges and are near the mean expected value. Similar concentrations of these metals were also detected at the copper sulfate contaminated soil removal site and at borings B11 and B19 located east of the CSMS. All visible, exposed construction debris and contaminated soil was removed from the excavation and properly containerized for disposal. The excavation was backfilled with clean fill. The northwest anomaly was excavated to a depth of four feet bgs, and the excavated material checked thoroughly for debris. No buried objects were detected. The northeast anomaly was excavated to a depth of seven feet bgs. A metal grounding/hold- down strap was unearthed and was removed. During May 2006 a geophysical investigation was performed at the south excavation. A report of the findings of the geophysical investigation (Versar, Inc., 2006) identified the potential extent of buried material associated with the former suspected CS (tear gas) excavation. A copy of the geophysical report is included as Appendix B. The findings of the report identified two anomalies in the unconsolidated fill west of the former excavation. The estimated surface extent of the anomalies is shown on Figure 4. Please note that the layout of the anomalies is based on two dimensional mapping. The length and depth are indicated in the Geophysical Report, but the width of the anomalies is estimated. Based on these data, Versar estimates between 300 and 400 cubic yards (bank yards) of potentially contaminated soil and debris may be present. Figure 5 depicts the proposed excavation area. 104700 4965 300 Page 1-2 April 2007