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surface (i . e . , deposition layer plus ponding) of less than 2 . 6 in ./hr. These rates are slow enough to allow close <br /> continual monitoring of the entire dike perimeter. However, ponding depth should not be permitted to <br /> increase beyond a maximum of 5 ft (5 . 8 ft at the weir) . Dike stability should be monitored continuously <br /> during periods when ponding depth is maintained above the 2-ft minimum . <br /> Optimal operating efficiency requires that flow through the containment basin approachs plug flow <br /> to the greatest degree possible. Uneven flow distribution — evidenced by irregular sediment deposition , <br /> channelization , and short-circuiting — increases flow velocities, reduces retention time, and promotes <br /> sediment resuspension . If inspection reveals an irregular deposition pattern , the inlet pipe should be <br /> repositioned to produce a more uniform depositional surface . <br /> Last, the incoming slurry should be periodically monitored at the containment basin inlet to confirm <br /> or refine dredge output specifications , including volumetric output and slurry solids content . These <br /> parameters , in combination with the actual duration of dredging, can be used as an independent measure of <br /> deposition volume to determine remaining site capacity. Additionally, the computed deposition volume can <br /> be used with pre - and post- dredging bathymetric surveys of the channel and , following placement and <br /> dewatering of the deposition layer, topographic surveys within the containment basin to refine the bulking <br /> factor employed to translate in situ dredging volume to required storage volume . Also, within the same <br /> monitoring program , the quality of dredged sediment should be established by laboratory analysis of grain <br /> size distributions, settling velocities, specific gravity, and Atterberg limits . <br /> 3 .3 Weir Operation <br /> Weir operation — that is, controlling the ponding depth and flow rate over the weir by adjusting the <br /> weir crest elevation — is the procedure most critical to maintaining effluent quality during dredging and <br /> decanting operations . Operational requirements extend to the period during and immediately after <br /> containment basin construction . Initially, the weir crest elevation should be set as high as necessary to <br /> prevent unwanted release of stormwater and groundwater seepage . Before the site ' s initial use, the site <br /> operator will periodically release ponded stormwater and groundwater seepage during regularly scheduled <br /> inspections. <br /> 30 <br />