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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-007UTask Order W91238-05-F-0084 Version 2.0 1.0 INTRODUCTION Versar, Incorporated (Versar), on behalf of the Sacramento District Corps of Engineers (CESPK) and the California Army National Guard (CA ARNG), has prepared this Type II Work Plan - Addendum (WPA) detailing additional methods and procedures, and deviations from the existing Type II Work Plan (WP) for this project (Versar, Inc., 2005). The WPA is to be used to perform an additional response action (RA) at the Stockton California Army National Guard Complex in Stockton, California (Site). The work will be performed under General Services Administration (GSA) Contract No. GS-00E-0007L, Task Order W91238-05-F-0084, with the CESPK. Versar has been contracted to perform two actions as presented in the Scope of Work for Expanded Site Investigation and Removal of Copper Contaminated Soil and Potential Tear Gas Burial Site (SOW), California Army National Guard Armory, Stockton, California dated 17 June 2005 and a supplemental response action as presented in the Supplemental Scope of Work dated 8 September 2006. The Supplemental SOW is included as Appendix A to this WPA. 1.1 SITE LOCATION The removal actions are to be performed at the CA ARNG facility in Stockton, California. The Stockton CA ARNG facility is located in the central portion of the Sacramento Valley, just west of the Stockton Metropolitan Airport. The facility is divided into four divisions: 1) the Army Aviation and Support Facility (AASF); 2) the Combined Support and Maintenance Shop (CSMS); 3) the Field Maintenance Shop (FMS); and 4) the Armory. Figure 1 shows the location of the Stockton CA ARNG facility. Figure 2 shows the facility layout. 1.2 SITE HISTORY The area surrounding the Stockton CA ARNG facility has been a mix of airport and agricultural use for over 40 years. The AASF has been in existence since the early 1950s as an aircraft fueling station and was expanded to its present size of approximately 25 acres in 1974. The Armory, CSMS and OMS appear from aerial photographs to have been constructed in 1963. A Preliminary Assessment/Site Investigation (PA/SI) performed in 2000 (Versar, 2003) included a geophysical survey of the CA ARNG Stockton vehicle storage yard north of the CSMS. The survey was performed based on the testimony of workers who claim they remembered "tear gas canisters" having been buried at the Site. The geophysical survey identified the presence of one larger and two smaller subsurface anomalies at the Site. Investigation of the subsurface anomalies was performed during October 2005. The initial investigation uncovered trash and debris in the area of the large southernmost anomaly. Further excavation uncovered numerous one and five-gallon cans, and one and one-half gallon plastic jugs, suspected to be paint materials. The excavation was then extended approximately three feet west to investigate the debris. Soils in the west end of the excavation exhibited odors and free 104700.4965.300 Page 1-1 April 2007