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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 . 47 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