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layer makes draining off all ponded water in this manner unlikely . As discussed , differential settling of the various size fractions of the sediment results in partial segregation of the dredged material within the containment basin . Coarser sand- and gravel - sized particles settle nearer the inlet, while finer particles concentrate nearer the weir . The sand-sized fraction , concentrated nearer the inlet , should experience relatively little consolidation because of its low initial water content. However, the fine material ' s greater consolidation will likely form one or more depressions nearer the weirs . To remove the ponded water that remains in these areas, a drainage trench must connect each depression to a sump excavated adjacent to one or more weirs. During this phase of operations , the weir crest must be raised to prevent the premature release of the ponded water which , as a result of the excavation , will likely contain a high concentration of suspended solids . Clarified water can then be released over the weir as soon as effluent turbidity standards are met. Following the removal of all remaining ponded water, evaporative drying will eventually form a crust over the layer of fine-grained material nearer the weir. This crust will trap water beneath its surface and retard continued evaporation . In addition , the desiccation cracks which quickly form in the crust will hold rainwater and limit further drying . Therefore, complete drying will require additional trenching . Initially, a perimeter trench can be excavated by dragline or clamshell operating from the crest of the containment dike . More intensive trenching must wait until a crust of significant thickness (greater than 5 to 6 in . ) has developed on the deposition surface . The crusted surface will allow the use of conventional low ground pressure equipment . A network of radial or parallel trenches should then be constructed throughout the area of fine sediment deposition . The depth of each trenching operation will be dictated by the slumping resistance of the semiliquid layer beneath the crust . Based on the projected mean thickness of the deposition to be placed in the IR- 14 containment basin (<2 . 0 ft, Section 3 . 3 ), adequate drying should require no more than two successive trenching operations . As an alternative to intensive trenching, the dried surface crust can be transferred to a more well-drained area of coarser material nearer the inlet . This would expose the wetter under layers and restore a relatively high rate of evaporative drying . The dewatering process will continue until the crust extends over the entire depth of the deposition layer. The time required to complete this phase of site operation will depend on the physical characteristics of the sediment, as well as climatic conditions (e . g . , rainfall , relative humidity, season , etc . ) . During the entire dewatering phase of the site operation, the weir must be operated to control the release of residual 37