Salvaging Sediments 1/25/2007
Committee seeks new resting place for dredged materials from the Duluth-Superior Harbor

By Kathleen Schmitt

Every year, dredges remove approximately 100,000 cubic yards of sediment from Duluth-Superior Harbor shipping channels, enough to fill 45 Olympic-size swimming pools. For nearly three decades, most of the dredged material has been placed into Erie Pier, the Confined Disposal Facility (CDF) at the port. However, space is quickly running out, so members of the local Harbor Technical Advisory Committee (HTAC) are working to find ways to salvage much of the material rather than stockpiling it.

The 89-acre Erie Pier facility, owned by the Duluth Seaway Port Authority (DSPA) and operated by the U.S. Army Corps of Engineers, was designed to last 10 years and store one million cubic yards of material. By heightening its sides, the facility has managed to store over twice the expected amount, said Gene Clark, UW Sea Grant coastal engineering specialist. Clark chairs the HTAC dredging subcommittee. Together with representatives of the Corps and the DSPA, the subcommittee is preparing a management plan that focuses on promoting ways to re-use the dredged material. As a first step, the Corps spent $500,000 in 2006 to set up a washing operation at Erie Per that will help separate the material into different sizes, ranging from fine silts and clays to coarse sand. After sorting is complete, the material can be rechecked to ensure there is no environmental contamination and marketed to local cities, counties, and state agencies involved in construction projects, mine site reclamation, and landfill operations.

The hope is that reusing dredged material will eliminate the need to develop another CDF, which the Corps says may require up to 20 years for obtaining the necessary environmental agency permits and cost as much as $35 million. The draft plan will be completed in March 2007 and then submitted to the entire HTAC for review and approval.

Harbor maintenance dredging is essential to keep heavily loaded lakers moving freely into and out of the harbor, which handles the largest total cargo volume in the Great Lakes. For every inch of water depth that a port loses, a ship must reduce its load by about 250 tons.

Clark says developing the management plan for the Duluth-Superior Harbor could benefit other Great Lakes harbors as well. “Continuing to just stockpile this material is an issue at all of the Great Lakes ports,” he said. “Storage space is at a premium, and the material has many potential uses. It’s just too valuable not to reuse. If we’re successful with the implementation of our plan, it could serve as a model for other Great Lakes harbors.”