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Work Plan for Groundwater Monitoring Well Installation,
<br /> Soil Gas and Groundwater Investigation,
<br /> and Groundwater Monitoring
<br /> Army Aviation Support Facility, Stockton, California
<br /> • Implement a quarterly groundwater gauging and testing program to estimate the direction
<br /> and magnitude of groundwater flow across the site and to evaluate concentrations of
<br /> contaminants in groundwater;
<br /> • Implement a quarterly reporting program to document groundwater gauging and testing
<br /> results; and
<br /> • Develop a preliminary assessment regarding the need for future actions and/or
<br /> recommendations for site closure, as appropriate to the data, and submit that assessment
<br /> concurrent with findings from the fourth quarter groundwater gauging and testing event.
<br /> All activities associated with the proposed scope of work will be performed to meet the
<br /> CVRWQCB's directives pursuant to the Clean Water Act and California's Porter-Cologne Water
<br /> Quality Act.
<br /> 1.2 SITE LOCATION
<br /> Information provided in this and subsequent sub-sections has been derived chiefly from the
<br /> 2008 URS SI Report, along with anecdotal information provided by CVRWQCB and CA ARNG
<br /> representatives.
<br /> The site is located adjacent to 2000 Stimson Road, Stockton, California (Figure 1; Appendix A).
<br /> The site is one of four divisional areas at the CA ARNG facility, including the Field Maintenance
<br /> Shop (FMS), the Combined Support Maintenance Shop (CSMS), and the Armory. The general
<br /> site layout and related features are show in Figure 2.
<br /> 1.3 SITE DESCRIPTION AND HISTORY
<br /> The Stockton AASF and three other divisional areas are State-owned facilities operated by the
<br /> CA ARNG. The FMS, CSMS, and Armory make up the three other CA ARNG divisional areas.
<br /> The AASF includes a maintenance building (hangar), work bays and shop, supply areas, a
<br /> latrine, offices, various storage sheds, concrete pads and ramps, a former refueling area with
<br /> dispenser island (removed), three 5,000-gallon USTs (removed), an active wash rack, a former
<br /> wash rack (based on anecdotal information provided by site representatives, and evidenced by
<br /> an abandoned vertical drain line), two 20,000-gallon USTs (removed), an existing 15,000-gallon
<br /> UST, and an existing 20,000-gallon above-ground storage tank (AST). The approximate
<br /> locations of these existing and former features are indicated in Figure 2.
<br /> The three former 5,000-gallon USTs were installed in the 1950's and stored aviation gasoline
<br /> and later Jet Propulsion (JP)-4. They were removed in 1990 by Wallace-Kuhl. These three steel,
<br /> single-walled USTs rested on a 6-inch concrete slab, left in place during UST removal, at an
<br /> estimated depth of 11 feet below ground surface (bgs). During an expansion project completed
<br /> in 1974, the fuel dispensers associated with these USTs were moved from the north side to the
<br /> east side of the USTs, approximately 30 feet from the tanks. Soil samples collected during
<br /> removal and excavation of the USTs and their associated piping indicated that releases of
<br /> gasoline and jet fuel have impacted site soil (URS, 2008).
<br /> The two former steel, single-walled 20,000-gallon USTs, reportedly removed in the mid-1990's,
<br /> were situated within a cement-lined pit where approximately half of their surface area extended
<br /> above grade. The former 20,000-gallon USTs historically contained JP-4/8 fuels (URS, 2008).
<br /> Upon removal, they were replaced by the 20,000-gallon AST presently storing JP-8 fuel. The
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