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• 1.0 INTRODUCTION Versar, Incorpoiated (Veisar), on behalf of the Sacramento District Corps of Engineeis (SD- COE) and the California Anny National Guard (CARNG), has prepared this Preliminary Assessment 1 Site Investigation Update (PAJSI Update) summarizing the findings of work perfortned at the Stockton California Army National Guaid Complex in Stockton, California (Site) The PA/SI Update was perfonned to address residual environmental issues identified in the PA/SI report prepared by Vei sat on behalf of the CARNG in May 2000 Figure 1 shows the location of the CARNG facility The Site is divided into four divisions 1) the An-ny AN lation and Support Facility (AASF), 2) the Combined Support and Maintenance Shop (CSMS), 3) the Operation and Maintenance Shop (OMS), and 4) the Armory Environmental concerns were not identified at the Armory Figure 2 shows the Site Layout Veisar's 2000 PA/Sl identified residual petroleum hydrocaibons in soil at two locations at the OMS and one location at the CSMS Buried objects in the vehicle stoiage area east of the CSMS were also investigated In the PA/Sl Update, the petroleum hydrocarbons in soil at the OMS and CSMS were furthei investigated, the buried objects east of the CSMS were excavated and secured on Site, and a recent fuel spill was assessed at the AASF . 11 Background The area surrounding the Stockton CARNG facility has been a mix of airport and agncultuial 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 piesent size of appioaimately 25 acres in 1974 The Armory, CSMS and OMS appeai from aenal photographs to have been constructed in 1963 1 1 1 AASF Aieas of concern at the AASF comprise the condition of groundwater in the area of three 5,000- gallon USTs removed in 1990, and a minor release of fuel to soil occurring to April 2002 The fuel storage for the AASF formerly used three 5,000-gallon steel USTs which were installed in the eaily 1950s These USTs were removed in 1990 The fonner USTs, shown on Figure 3, rested on a six-inch thick concrete slab The slab still remains in place at a depth estimated to be 11 feet bgs The fuel dispensers were originally located on the north side of the USTs During the 1974 expansion./modernization the dispensers were relocated 30 feet to the east ANTlation gasoline was reportedly stoied in the former USTs until the early 1960s when tuibine powered ancraft began replacing older piston-engine powered airplanes From approximately 1962 until 1989, JP-4 was stored in the former USTs The three 5,000-gallon USTs v ere taken out of operation in 1989 and were removed in January 1990 (Wallace-Kuhl, 1993) Five soil saniples were collected from beneath the tanks at the time iof l emoval Analytical results reported no detectable concentrations of fuel constituents from 104700 4766 230/09SEPT2004 1