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Work Plan for the Former Two 20,000-Gallon USTs Location at Stockton AASF California Army National Guard EXECUTIVE SUMMARY ESA This Work Plan(WP)was prepared for the California Army National Guard(CA ARNG) under contract to the United States Army Corps of Engineers,Sacramento District. This WP was pre- pared to assess whether the soils and groundwater in the area surrounding the former underground storage tank(UST)location at the CA ARNG Stockton Army Aviation and Support Facility(AASF) have been impacted with petroleum constituents.The evaluation will be accomplished as follows: • Drilling five soil borings and up to five contingent soil borings surrounding the two former 20,000-gallon UST locations and collect soil and groundwater samples;analyze samples to determine whether total petroleum hydrocarbons(TPH)as gasoline(TPHG)and as diesel (TPHD);benzene,toluene,ethylbenzene,and xylenes(BTEX);oxygenates;and lead are present downgradient of the UST location.If soil samples from the initial five borings show indication of impacts(discoloration,odors,or photoionization detector[PID] readings above background), additional soil borings may be completed. Based on the investigation results,the three existing groundwater monitoring wells(MWs)may be destroyed(with approval from the Regional Water Quality Control Board [RWQCB] and CA ARNG). ES.2 The Stockton AASF is located at 2000 Stimson Road, Stockton,California,95206 (Figure ES-1)and includes a former refueling area with dispenser island and the location of three 5,000-gallon USTs(removed); a wash pad(rack);two 20,000-gallon USTs(removed); and existing 15,000-gallon and 20,000-gallon USTs. ES.3 The investigation described in this WP is to only include the area of the two former 20,000-gallon USTs. Information pertaining to and describing the areas adjacent to the two former 20,000-gallon USTs(the three 5,000-gallon USTs and fuel spill area)has been included to help describe the areas adjacent to the two former 20,000-gallon USTs,and provide the only available/ current sample data to date within the vicinity.The AASF previously contained a fuel island for fueling aircraft,with associated dispensers and fuel lines originating from all the USTs.The source of petroleum impacts to be investigated at this site is the location of two USTs(20,000 gallons each). The two 20,000-gallon USTs were removed and replaced in the mid-1990s. During removal and excavation of the three adjacent 5,000-gallon USTs and associated piping,soil samples were collected.Based on soil sample analyses,releases of diesel fuel and jet fuel had occurred within the vicinity of the three adjacent 5,000-gallon USTs(Versar,Inc.,2004). It is unknown whether soil removed from the excavation was placed back into the UST excavation pit or if the remaining space was filled with clean fill material. 1.0 SITE DESCRIPTION 1.1 Site Location The AASF is located in one of four divisional areas at 2000 Stimson Road, Stockton,California (95206).The divisional areas comprise the AASF,the Combined Support and Maintenance Shop (CSMS),the Field Maintenance Shop(FMS),and the Armory. Figure 1-1 shows the general layout of the areas and site features. KAWprocess\00251\CA ARNG\Stockton AASF WP\FINAL\WP text.doc 1 June 2007