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Notification #1600-2018-0342-R3 Streambed Alteration Agreement October 28, 2019 Page 3 of 24 once reaching its design elevation The test pile program will also include conducting five cone penetration tests (CPTs) across the cellular sheet pile wall alignment. CPTs will involve pressing a sensor mounted on a 2 - inch -wide sectional pole into the channel bottom from a barge -mounted rig, with additional sections being added as the pole is pressed further into the channel bed. Gated Wall Construction Cofferdam Installation Construction and installation of the gate structure will begin by installing a metal sheet pile cofferdam to dewater the work area and allow dry work on the foundation and walls for the gate structure. To form the cofferdam, sheet piles will be driven using a barge -mounted crane equipped with a vibratory hammer. The cofferdam sheet piles will be sized to form the foundation of the gate structure, approximately 71 by 71 feet, and will be the same height as the gate structure, extending 10 feet above the mean water level at the entrance to Smith Canal. The cofferdam will be constructed over a 1 -month period Dewatering Procedures Dewatering of the cofferdam area will begin upon completion of the cofferdam installation and will continue during the entire installation of the gate structure. The cofferdam will need to be continuously dewatered. Initial dewatering will take place prior to placement of the foundation. Procedures will be put into place to manage the silt that will likely be removed during the initial dewatering activities. The silt will be allowed to settle within the cofferdam to limit silt discharged during dewatering; accordingly, it will be stored onsite and will settle on the channel floor. The cofferdam is assumed to have a low continuous inflow, resulting in a work area that is not watertight, and a sump pump and generator will be used to remove excess water if it reaches a predetermined level. Should continuous dewatering be needed, silt curtains will be used around the discharge area to contain silt and allow it to settle. Dredging Prior to construction of the gate structure and fixed wall, up to 8,650 cubic yards of the channel bottom may be dredged along the length of the fixed wall alignment to provide a level surface, and an additional area may be dredged to allow barge access for pile driving during periods when water surface elevations may be low, which will limit barge access (Exhibit A). Dredging will occur where the fixed wall ties into high ground at the golf course, where the fixed wall ties into Dad's Point, and where the gate structure will be built. Material will be dredged using a combination of a long-arm excavator, a dragline excavator, and a clamshell excavator, and silt curtains may be used along the limits of dredging. All dredged material will be disposed of at an upland site with no connectivity to waters of the United States. Gate Structure Construction and Installation Construction and installation of the gate structure will commence once construction of the cofferdam is complete. Construction of the gate structure will take approximately 6 months.