Dredging

A horizontal auger hydraulic dredge will be used as the primary means of sediment dredging for the Phase 1 Remedial Action. Two dredges will be used to supplement each other to maintain continued sediment removal during equipment repositioning and a third dredge will be available as a back-up in the event of mechanical breakdown.

The three dredges selected for use on this project are Mudcat Model MC 2000 manufactured by Ellicott. The horizontal augers on these dredges are self-leveling and fully enshrouded along the back of the auger for environmental projects. This shroud minimizes the loss of material behind the auger and helps direct the flow of sediment and water to the pump intake.

Horizontal auger hydraulic dredges consist of a dredge pump mounted on a pontoon barge or directly on the suction pipe and a hydraulic system to raise and lower the suction pipe and auger-type cutterhead. The sediments are loosened by a rotating auger, partially enclosed in a metal housing, which moves the loosened sediments to the inlet of the suction pipe.

The dredges will move on a straight course across the river by way of a winch and cable system, the ends of which are secured to perpendicular anchor cables positioned at the perimeter of the work area.
Hydraulic dredging is the most effective means of reducing the re-suspension of sediments where underwater excavation is required. By controlling the speed at which the dredge suction pipe (or horizontal auger) moves through the sediments, as well as the depth of cut, pumping rate, and rotational speed of the auger, a trained operator can maintain a continuous movement of water in the dredge suction area to the intake pipe to capture the re-suspended sediments.

Sampling after the work has been completed is critical to ensure that all of the highest concentrations of PCBs have been removed. Sampling and surveys will be done to ensure that the agencies’ cleanup goals have been met.

This project will remove about 2 percent of the total volume of contaminated sediment in the lower part of the river, representing about 8.5 percent of the PCBs for the overall Fox River cleanup.

Area to be Dredged