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quality by a factor of 1 . 33 , and provides a margin of safety to ensure that the clarified supernatant released from the IR- 14 containment basin will meet state water quality standards . Therefore, the IR- 14 containment basin requires a 4 . 0-ft mean operational ponding depth . However, care must be taken not to increase ponding depth above the 2 .0=ft minimum too quickly. This may lead to dike saturation and promote dike instability. Operational experience has demonstrated that dike permeability typically reduces with time as percolation filters and traps fine sediments. Thus, a sufficiently slow increase in ponding depth will avoid piping, slumping, and other indicators of dike saturation and instability. Restricting the operational ponding depth to 4 ft should also reduce the likelihood of dike instability and provide an appropriate safety factor to ensure adequate solids removal . Consideration of realistic field conditions further reinforce the IR- 14 containment basin ' s conservative design . First, DMRP research indicates that under typical field conditions the actual depth of withdrawal may be significantly less than the WES Selective Withdrawal Model predicts . Solids retention should improve with decreased withdrawal depth. Second , field conditions may reduce dredge discharge rates below the design criterion . The design dredge discharge (3 , 560 cy/hr) reflects a minimum separation between the dredge plant and the placement site and thus a minimum discharge line length . Increasing the discharge line length also increases frictional losses and correspondingly reduces dredge discharge and extends basin retention time. The maximum pumping distance for Site IR- 14 to serve the extreme southern end of Reach III is 4 . 97 miles. Thus, actual dredge discharge rates will likely fall well below the design criterion and further improve basin solids retention . 2. 3. 4 Interior Earthworks The IR- 14 containment basin design specifically excludes secondary interior dikes — e .g. , multiple cells or spur dikes. Multiple cells are typically employed for continual or successive placement projects that cannot provide adequate time for dewatering the previous deposition . The projected dredging frequency for Reach III , once every 5 to 10 years, and the relatively small quantities anticipated with each operation, from 16 ,300 cy to 32,600 cy, do not warrant the use of multiple cells . Spur dikes are typically used in applications where the basin ' s size or configuration cannot provide adequate retention time. However, hydraulic analysis 20