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Work Plan for Site Assessment Former Texaco Service Station Chevron Site ID 309075 September 30, 2009 • Methyl tertiary butyl ether (MTBE), ethanol, di-isopropyl ether (DIPE), ethyl tertiary butyl ether (ETBE), tertiary amyl methyl ether (TAME), tertiary butyl alcohol (TBA), 1,2-dichloroethane (1,2-DCA) and ethylene dibromide (EDB), also known as 1,2-dibromoethane, and ethanol by USEPA Method 8260B All down-hole drilling and sampling equipment will be steam-cleaned following the completion of each soil boring. Down-hole equipment will be washed in a tri-sodium phosphate or Alconox® 6W solution between samples. 3.6 MONITORING WELL INSTALLATION V Upon completion of the soil borings, the monitoring wells will be constructed using 2-inch outside diameter (OD) poly vinyl chloride (PVC) casing with a 10-foot screen interval of 0.010- inch slotted PVC screen. The shallow and deep water-bearing zone monitoring wells will be installed as described below. 3.6.1 Shallow Water-Bearing Zone The shallow water-bearing zone monitoring well will be constructed of schedule 40 PVC and the screen interval will be placed at approximately 65 feet to 75 feet bgs. A 2/12 sand filter pack will be placed around the well from the bottom of the borehole to approximately 1.5 feet above the screen interval followed by approximately 2 feet of hydrated coated bentonite chips. The remainder of the borehole annulus will be grouted using tremie piping to within approximately one foot of the ground surface. A traffic rated 12-inch diameter flush mounted well box will be installed in concrete at each location. The total well completion depth and screen interval will be determined based on observations in the field. Typical construction details of the shallow well are shown on Figure 3. 3.6.2 Deep Water-Bearing Zone The deep water-bearing zone monitoring well will be constructed of schedule 80 PVC and the screen interval will be placed at approximately 110 to 120 feet bgs. To minimize the potential for cross contamination between the shallow and deep water-bearing zones, the deep water bearing zone will be double-cased with steel conductor casing to approximately 80 feet bgs. The 8.625 inch OD conductor casing will be set in a 15.5 inch OD borehole. The space between the wall of the borehole and the outside of the conductor casing will be sealed at the base of the casing with approximately 2 feet of bentonite chips. Grout will then be tremied into the space to `- seal the remainder of the casing up to approximately 1foot bgs. Once the casing is set and sealed, an 8-inch diameter borehole will be advanced through the conductor casing to approximately 120 feet bgs and a 2 inch OD PVC casing will be installed. A 2/12 sand filter pack will be placed around the well from the bottom of the borehole to approximately 1.5 feet above the screen interval. The total well completion depth and screen interval will be determined based on observations in the field. Typical double cased monitoring well construction details are shown on Figure 4. \\arcadis-us\oficedata\Sacramento-CA\ENV\CHEVROM309075\6 Deliverables\Work Plan\Downgradient Wells\Work Plan for Downgradient Wells_379910950.doc 4 Ir.