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Groundwater Well Installation Work Plan Sharpe Army Depot Lathrop, California 3.2.1 Well Construction Well construction activities and materials will conform to the sections below. Special consideration and care will be taken during construction to ensure that the casing and screen are joined correctly and in a manner that does not place excess pressure or stress on each joint. Well construction diagrams for the extraction and monitoring wells are presented in Figures 9 through 11.The drilling subcontractor will have a State of California C-57 license, and a copy of the certificate will be kept onsite. Each well boring will be advanced to its total depth using a truck-mounted mud rotary or sonic drill rig. Before installation,the downhole equipment,tools, and well materials are freed of solvents, oils, grease, paint, and dirt. If the supervising Project Geologist determines that the well screen or casing is not clean, steam-cleaning of the drill bit and rods, well screen and casing, or other equipment and tools will be performed before installation. 3.2.1.1 Well Casing Blank well casing for extraction wells will be flush-threaded 8-inch diameter, Schedule 80 polyvinyl chloride (PVC). Blank well casing for monitoring wells will be flush-threaded 4-inch diameter, Schedule 40 PVC.Sections of casing will be received from the supplier in polyethylene protective wrappers with sealed ends to limit exposure to potential contaminants.The casing will not be removed from the wrapping until installation. After the borehole has been drilled to the proposed total depth, the well screen and casing will be lowered into the center of the borehole.The well screen and casing will be plumb and centered in the hole using centralizers placed at the top and bottom of the screened interval, as described below. The preliminary design for the proposed wells is as follows: • EWC6 and EWC7 (Table 1, Figure 9) o Blank casing from the ground surface to 112 ft bgs o Screened casing from 112 to 122 ft bgs o Blank casing sump from 122 to 127 ft bgs • EWC8 and EWC9 (Table 1, Figure 10) o Blank casing from the ground surface to 120 ft bgs o Screened casing from 120 to 130 ft bgs o Blank casing sump from 130 to 135 ft bgs • EWCC7 (Table 1, Figure 11) o Blank casing from the ground surface to 140 ft bgs o Screened casing from 140 to 150 ft bgs o Blank casing sump from 150 to 155 ft bgs • MW549C and MW550C(Table 1, Figure 12) o Blank casing from the ground surface to 100 ft bgs o Screened casing from 100 to 110 ft bgs • MW551B (Table 1, Figure 12) o Blank casing from the ground surface to 75 ft bgs o Screened casing from 75 to 85 ft bgs Ahtna Environmental,Inc. 10