Woodrow Wilson Bridge
Potomac River, Maryland
500,000 cubic yards
In the winter of 2000-2001, Weanack received the first 340,000 cy of a three phase dredge operation totaling 500,000 cy. The material was barged from the Woodrow Wilson Bridge replacement/expansion project (WWB) and offloaded at the dock here by both mechanical (excavator to truck) and, in later phases, by hydraulic (mud pump & pipes) means. The WWB is the I-95/I-495 bridge crossing the Potomac River just below Washington, DC.
Hydraulic offloading was by a closed-loop design in which mud was pumped in carrier-water through a pipe to the placement basin. The mud and carrier-water separated in the basin resulting in a pool of water on the low end of the basin and mud building up on the other end. A water pump moved the basin water back to supply/charge the mud pump at the dock. The water was recycled many times and, in effect, was part of a ‘wet conveyor’ system. This closed loop design eliminates the need for release of excess water from a “flow through” or “weir-discharge” system for a marginal cost. The water recycling, or no-discharge, system removes the need for a weir outflow, monitoring of discharged effluent (and potential non-compliance issues) or concerns about impacts to native receiving waters.
The material was placed into a basin created from an old sand and gravel mining pit which had been reshaped using compacted clays left behind by mining to form a “bathtub” to receive the sediment. The mined area was unproductive and farming had been abandoned. Placement of the fertile mud greatly improved the productivity of the field. In 2003, crops were grown on the upper portion of the placed material and the crop yields were comparable to the best native or un-mined soils in the area.
About half of the WWB basin’s capacity has been used to date and the basin awaits the next project(s) to fill the basin and restore the entire field to it’s former, pre-mining agricultural productivity.