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. EXECUTIVE SUMMARY Veisai, Incorporated (Veisai), on behalf of the Sacramento District Corps of Engineers (SD- COE) and the California Aslny National Guard (C ARNG), has prepared this Prelurunary Assessment/ Site Investigation Update (PA/Sl Update) Report summarizing the findings of work performed at the Stockton California Arany National Guard Complex in Stockton, California (Site) The PA/Sl Update is being performed to address residual environnnental issues identified In the PAISI report pi epai ed by Versai on behalf of the CARNG in May 2000 The Site is di-vided into four divisions 1) the Army Aviation 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 have not been identified at the Armory AASF Areas of concern identified at the AASF comprise the condition of groundwater in the area of the former 5,000-gallon fuel undeigiound storage tanks (USTs) removed in 1990, and a minor release of fuel to soil occun-ng in Apnl 2002 The findings of groundwater monitoring identified 110 rnicrogranrs per Inter (µg/L) of total petioleurn hvdiocarbons as gasoline (TPH-g) in one groundwater sample at the AASF This represents the second detection of trace concentrations of TPH-g the feast having occurred in May 1996 These detections indicate that very little iesidual contamination is likely present from the former USTs The spot adic detection of trace concentrations of TPH-g in the groundwater does not reflect a significant risk to human health or the emvrronrnent Therefore, Versar iecominends no furthei action for the unauthorized release from the minor fuel spill The presence of low concentrations (less than 500 milligrams per kilogram [mg/kg]) of extractable TPH in soils between the surface and five feet bgs at the location of the minor fuel release does not present a significant threat to human health or the envirorunent The results of soil sampling indicate that the impacted soils are not present at the 10-foot level and below Vertical migration of heavy hydrocarbons is typically limited to the soluble fraction, and is generally considered not a concern in shallow soils at concentrations less than 1,000 mg/kg Therefore, Versar recommends no further action for the unauthorized release from the nunoi fuel spill CSMS Areas of concern identified at the CSMS are petroleum hydrocarbons beneath the vehicle wash rack in the north portion of the building, elevated metals and petroleum hydrocarbons along the north facility boundary, petroleum hydrocarbons near the waste storage area, heavy metals near the sandblasting area, and pavement upwelling in the velucle storage area east of the building Laboratory analysis did not detect concentrations of extractable hydrocarbons or polychlorinated biphenyls (PCBs) in any of the samples collected from boring B29, located north of the vehicle 104700 4766 230/08SEPT2004 11