2009-323A - Laserfiche WebLink

Home Browse Search

a Once the basin produces effluent that meets the required turbidity standards, the contractor should then maintain the necessary ponding depth by increasing the weir crest elevation at about the same rate as sediment builds within the basin. The contractor should install additional weir boards at the point the depth of flow over the weir crest approaches the width of the boards to be added. As the basin nears its design capacity, the contractor must reduce his operational ponding depth to ensure that the elevation of the ponded water remains a minimum of Z ft below the elevation of the dike crest, the minimum allowable freeboard for the IR- 14 containment facility. Continuing to meet effluent standards may require that the contractor reduce the dredge output or operate the dredge intermittently to provide the required retention time. During periods when the dredge remains idle, the contractor may also find it necessary to grade and distribute the mounds of coarser material deposited nearer the dredge discharge outlet to increase the plan area of the ponded water and thereby improve the basin ' s retention performance and effluent quality. Under no circumstances shall the contractor allow the dredged material to mound above the elevation of the dike crest . 3 .4 Weir Operations During Decanting Following the completion of dredging operations, the contractor must continue to operate the weir system and slowly release the clarified surface water that remains ponded within the basin over the weir crest by incrementally removing weir boards . The process , known as decanting, continues until all residual ponded water within the basin at the completion of dredging is released over the weirs. To maintain effluent quality throughout the decanting process, the contractor should allow the flow over the weirs to drop essentially to zero before removing another set of weir boards. The contractor may be required to grade the deposited dredged material to drain isolated pockets of water so that this water may also be released over the weirs. If at any time during the decanting process monitoring shows effluent turbidity to exceed perniitted standards, the contractor must again add weir boards until testing of the ponded water that remains within the basin confirms that turbidity has returned to acceptable limits . While decanting proceeds, the contractor may begin to dismantle and remove the dredge pipeline. Working from the site back toward the ICWW, the contractor must plan the operation to ensure that all residual water contained within the pipeline drains to the ICWW. - 17 -