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Work plan forAdditona/Groundwater Assessment <br /> Former Chevron Service Station 94054 <br /> March 19, 2010 <br /> 3.6 MONITORING WELL INSTALLATION <br /> Upon completion of the offsite soil borings, the monitoring wells will be constructed using 2 inch <br /> outside diameter(OD) poly vinyl chloride (PVC) casing with a 10 foot screen interval of 0.010 <br /> inch slotted PVC screen. The B zone monitoring wells will be installed as described below. <br /> 3.6.1 B Zone Monitoring Wells <br /> The B zone monitoring wells will be constructed of schedule 80 PVC and the screen interval will <br /> be placed at approximately 40 to 50 feet bgs. To minimize the potential for cross contamination <br /> between the A zone, the B zone will be double-cased with steel conductor casing to <br /> approximately 35 feet bgs. The 8.625 inch OD conductor casing will be set in a 15.5 inch OD <br /> borehole. The space between the wall of the borehole and the outside of the conductor casing <br /> will be sealed at the base of the casing with approximately 2 feet of bentonite chips. Grout will <br /> then be tremied into the space to seal the remainder of the casing up to approximately 1 foot <br /> bgs. Once the casing is set and sealed, an 8-inch diameter borehole will be advanced through <br /> the conductor casing to approximately 50 feet bgs and a 2 inch OD PVC casing will be installed. <br /> A 2/12 sand filter pack will be placed around the well from the bottom of the borehole to <br /> approximately 1.5 feet above the screen interval followed by approximately 3.5 feet of hydrated <br /> bentonite chips. The remainder of the borehole annulus will be grouted using tremie piping to <br /> within approximately one foot of the ground surface. A traffic rated 12 inch diameter flush <br /> mounted well box will be installed in concrete at each location. The total well completion depth <br /> and screen interval will be determined based on observations in the field. Typical double cased <br /> monitoring well construction details are shown on Figure 3. <br /> 3.6.2 Monitoring Well Development and Sampling <br /> The newly installed groundwater monitoring wells will be developed a minimum of 48 hours <br /> following installation. If possible ARCADIS will coordinate sampling of the newly installed wells <br /> with the regularly-scheduled semiannual groundwater monitoring and sampling event. The <br /> groundwater samples will be placed on ice, cooled to approximately 4 degrees °C, and <br /> transported to a State of California certified laboratory under chain-of-custody documentation. <br /> The groundwater samples will be analyzed for the following constituents: <br /> • TPH-GRO [C6-C12] by USEPA Method 8015B <br /> • BTEX by USEPA Method 8260B <br /> • MTBE, TAME, 1,2-DCA, TBA and EDB by USEPA Method 8260B <br /> 3.6.3 Surveying <br /> A California State Licensed Surveyor will survey the newly installed wells. The well casing will <br /> be surveyed to the nearest 0.01 feet in elevation to the existing site elevation datum located with <br /> I',CA5FP\Data\Aproject\ENV\CHEVRON\94054\6 DeliverablesMork Plans,2010\TempMork Plan for Site Assessment_4E21010950.doc 5 <br />