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1{(1Wp1 V rcdi�uN ew.Mwrm4�'. 4. Sampling Rationale and Design Up to four additional judgmental sample locations will be selected on the Stockton Fire Department Station 3 property. Samples will be collected in the vicinity of the USTs,AST, and former piping;and in areas down-gradient of the USTs. Proposed sample locations are presented on Figure 4(Appendix A). Surface(0 to 0.5 feet bgs)and subsurface soil samples will be collected from the proposed borings to assess whether contamination exists at the site related to previous site activities, including LUSTs as well as surface spills around the former USTs. A direct-push drilling rig will be used to advance borings to the desired sampling depths.At both the Stockton Fire Department Station 3 site and the vacant parcel to the south of the Stockton Fire Department Station 3 property, soil samples will be collected from the surface,at 2.5 feet bgs, and at approximately 5- foot intervals to a depth of 15 feet bgs. Soil samples will be analyzed for TPH-g,TPH-d,and TPH-mo by EPA Method 8015; for volatile organic compounds(VOCs) (including BTEX and MTBE)by EPA Method 8260; and for metals, including mercury,by EPA Method 6010/7473. 4.2.2 Soil Gas Sampling Soil gas samples will be collected at two judgmental boring locations to evaluate whether LUSTs from the City of Stockton Fire Department Station 3 property have resulted in concentrations of volatile constituents in soil gas that have the potential to migrate upwards through soils and impact receptors,Figure 4(Appendix A). Judgmental sampling will be used to assess concentrations of volatile constituents in soil gas above the point of release from the former gasoline UST and from below the slab of the fire house structure, where workers are most likely to be exposed. Soil gas samples will be collected from the two boring locations; one above the former gasoline UST and one beneath the slab of the Stockton Fire Department Station 3 building. Soil gas samples will be collected at approximately 1.5 feet bgs at the former gasoline UST location and sub-slab beneath the fire station and analyzed for VOCs by Method TO-15. 4.2.3 Groundwater Sampling Groundwater beneath the site will be investigated at the 12 proposed boring locations to evaluate whether LUSTs from the City of Stockton Fire Department Station 3 property have resulted in the release of contaminants to groundwater. Groundwater samples will be analyzed for TPH-g, TPH-d,and TPH-mo by modified EPA Method 8015 and for VOCs(including BTEX and MTBE)by EPA Method 8260.Previous investigations at the site have encountered groundwater at depths of approximately 39 feet bgs,thus grab groundwater sampling depths are anticipated to be approximately 40 to 45 feet bgs. 1102693.1501.0188 4-2 EI Conciho No.2