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Notification #1600-2018-0342-R3 Streambed Alteration Agreement October 28, 2019 Page 4 of 24 Sixty-four concrete -filled steel pipe piles, approximately 36 inches in diameter, will be driven along the inside edge of the cofferdam to provide support for the concrete floor and walls. The steel pipe piles will be installed by using a barge -mounted crane equipped with either a vibratory hammer or pile -driving impact hammer. Piles will be driven to the maximum depth feasible with a vibratory hammer before use of an impact hammer where feasible. Pile driving is likely to cause a small amount of mud heaving as it is displaced by the piles; the mud will be removed to achieve the correct elevation of the channel bottom. The mud removal will be done with either a clamshell excavator or a long-arm excavator and will be confined within the cofferdam walls. Following installation of the steel pipe piles, a reinforced concrete floor and the gate structure walls will be formed and poured. Two sides of the cofferdam will be used as forms. The concrete floor will be 69 feet wide, 69 feet long, and 6 feet thick, while the concrete walls will be 71.25 feet long, 22 feet high, and 6 feet thick. The metal gate will be attached to the concrete floor and walls by a barge -mounted crane. The cofferdam sheet pile along the inlet and outlet sides of the gate will be cut down by a diver using a torch to the level of the gate structure floor. The remaining portion of the sheet pile will be kept in place to prevent seepage under the gate structure. Rock protection will be placed at the transitions from the gate structure to the fixed wall to provide scour protection. The gate will be tested and put into service after construction of the gate structure controls and southern side of the fixed wall is completed. Construction of the northern side of the fixed wall will not take place until after the gate structure has been tested to confirm operability. Fixed Wall Construction Following installation of the gate structure cofferdam, work will begin on the fixed wall portion of the project. The fixed wall will extend approximately 800 feet from the north tip of Dad's Point Levee to the right bank of the San Joaquin River, at the Stockton Golf and Country Club. The fixed wall will consist of cellular flat -web steel sheet pile walls driven into the riverbed by a vibratory hammer. The walls will be constructed to be approximately 29 feet wide at the connection between cells and 34 feet wide and the widest part of each cell and will extend 10 feet above the mean water level at the entrance to Smith Canal. The sheet pile walls will be constructed using interlocking flat -web steel sheet piles that are approximately 20 inches wide and will be driven in a curved cellular design. The silt in the water between the sheet walls will be allowed to settle before being dewatered. The north end of the fixed wall will be integrated into the existing FEMA -accredited levee near the Stockton Golf and Country Club. This integration will be designed so that it will not affect the integrity of the existing levee system. Sheet pile wing walls will be driven along the levee perpendicular to the north end of the fixed wall, and the wing walls will be tied into the end of the fixed walls using interlocking sheet piles. Interlocking sheet piles will also be used at the Dad's Point tie-in, connecting the southernmost cell of the fixed wall to two parallel sheet pile walls driven into the end of Dad's Point. Granular material will be installed between the walls using a front-end loader. The granular material will consist of a sand and gravel mixture deposited to an elevation within 3 feet of the top of the sheet pile. Upon completion of construction, a locked security gate will be