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f • and/or inspection services, as required . Responsibility for the initial placement operation at Site IR- 14 remains to be determined. The Addendum is organized as follows. Chapter 2 . 0 first outlines basic elements of the IR- 14 weir design as described in the site 's original Management Plan, then presents preliminary minor revisions to the IR- 14 weir system that are intended to improve performance without requiring significant alteration of the weirs ' basic structure. Chapter 3 .0 presents guidelines for operating the modified weir system that the selected contractor must follow before, during, and immediately after dredging. Chapter 4 . 0 presents inspection criteria designed to ensure the stability and safety of the site' s containment dikes . Chapter 5 . 0 presents additional criteria for maintaining a vegetative cover on the containment dikes to facilitate the required inspections. 2. 0 WEIR DESIGN REVISIONS 2. 1 Elements of the Predominant Weir Design This section presents the basic elements of the preliminary design for the IR- 14 weir structure. As described in the site 's original Management Plan, the preliminary design for the IR- 14 weir structure follows the predominant weir design now in use within the Jacksonville District, as well as the design installed at almost all FIND containment facilities built since 1991 . This design features a parallel arrangement of three to four pile-supported weir stacks, each stack formed by a corrugated metal half- pipe. Removable flashboards key loosely into vertical 1-beam channels to form a vertical barrier across the otherwise open side of each half-pipe. This face acts as a dam to retain water within the basin. Under ideal conditions (that is, no leakage between the boards or around the boards ' ends), water may only exit the basin by passing over the weir' s crest, that is, the top board in the stack. Adding or removing weir boards allows the operator to maintain the crest elevation to just below the ponded water surface elevation. In this manner, the weir maintains effluent quality by discharging only the clarified surface layer from which almost all suspended sediment has already settled. The total weir crest length (that is, the combined length of the weir crests of each weir stack) reflects the length needed to maintain the withdrawal depth less than the minimum 2 . 0 -ft ponding depth (Section 3 . 3 . 1 ) . Withdrawal depth refers to the theoretical depth of the surface layer of water selectively withdrawn over the weir crest . For the weir to function as intended and maintain effluent turbidity within acceptable standards, the basin must provide sufficient retention to allow the finest sediment component to settle from the weirs ' design withdrawal depth. Given that the suspended sediment concentration within the ponded water increases with depth, - 2 -