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Extraction Well Installation Summary Report and Injection ARCADIS Well Installation Work Plan Former Occidental Chemical Corporation Facility Lathrop, California borehole to approximately 3 feet above the screen; 3 feet of#0/30 fine transition sand were placed above the sand pack to prevent grout from entering the sand pack.The borehole was then sealed with neat cement grout to 5 feet bgs. The well was left with a temporary well box and is awaiting vault construction associated with the future expansion of the groundwater treatment system. Water-table extraction wells EW-10, EW-11, and EW-17 were installed on January 29 and 30, 2013 using HSA drilling methodology and 12-inch augers.Wells EW-10, EW-11, and EW-17 were screened from approximately 10 to 40 feet bgs. Each well was constructed using a 6-inch-diameter 5-foot-long Schedule 80 PVC blank sump, followed by 6-inch-diameter stainless steel well screens with 0.010-inch slots. Blank 6-inch-diameter Schedule 80 PVC casing was installed from the top of the screen to approximately the ground surface. After the screen and casing were placed in the open borehole, a sand pack consisting of#2/12 Monterey sand was placed in the borehole to approximately 2 feet above the screen; 3 feet of#0/30 fine transition sand were placed above the sand pack to prevent grout from entering the sand pack.The borehole was then sealed with neat cement grout to 2 feet bgs. Each well was left with a temporary well box and is awaiting vault construction associated with the future expansion of the groundwater treatment system. 2.2.2 Well Development The new wells were developed between January 24 through March 7, 2013 by brushing,surging, airlifting, bailing,jetting, and pumping to remove fine-grained sediment and drilling fluids from the borehole and the sand pack.Temperature, pH, conductivity,turbidity, and volume removed were monitored during development. Development activities continued until all of the following were true: • visual observation indicated an improvement in the water clarity, • water-quality indicators stabilized after a minimum of 10 well casing volumes had been removed, and • no additional improvement in specific capacity was seen from development activities. Well development logs are included in Appendix B. 2.2.3 Well Replacement and Abandonment During development of extraction well EW-12B, it was discovered that the drilling mud had not been thinned appropriately prior to installing the well materials,causing the sand pack to bridge during placement and allowing neat cement grout to infiltrate the sand pack and screen. Due to the grout in the sand pack and screen, EW-12B was not a suitable extraction well and was abandoned and replaced lalhmp well ins llalion mport_final_(04-2913)d— 4