Portland Harbour faces high bill for CAD storage

Portland Harbour, Maine. https://www.portlandharbordredge.info/
Portland Harbour, Maine. https://www.portlandharbordredge.info/

At an estimated cost of USD30 million, Portland Harbour, Maine, officials are concerned that storage of dredged materials from proposed work at 69 sites along the Fore River could eat considerably into the economic benefits of the operation.

Testing of the sediment for contaminants, as well as identification of potential confined aquatic disposal (CAD) cell sites, has already incurred expenses of USD600,000 in the form of grants from the U.S. Environmental Protection Agency and Maine Department of Environmental Protection.

Unfortunately, with some areas not having been dredged for 70 years, sediments in the port are polluted by industrial runoff from foundries and tanneries which used to operate along the river, well before the US 1972 Clean Water Act came into being. This means that rather than being dumped out at sea as with many conventional dredging operations, they will instead have to be disposed of by digging a hole in the sediment underwater, dumping the contaminated sediment, and covering it with a layer of sediment, in a process known as a CAD cell.

Thanks to silt washed upriver as well as occasional bursts of storm water and sewer runoff, many of the berths, which were in use have been rendered completely unusable, with boat operators having to push their way out using poles in many places or seek berthing elsewhere.

Portland Harbour Commission has hired Campbell Environmental Group to consult on the dredging operation, and designated a 122 m x 122 m area for the CAD, which will be 15 m deep and will allow 212.5 m3 of contaminated sediment to be stored, capped by conventional sediment around 2ft below the surface at MLLT. The US Army Corps of Engineers, which consults on many of the dredging operations in the US’ inland waterways, claimed that getting permits for a CAD cell design, as well as engineering and construction, can take up to a decade.

The proposed site for the CAD cell, which is to be constructed by local engineering firm Stantec, lies further down the Fore River. “The more we dredge over here, the bigger a hole we have to dig over there,” said Glenn Daukas, senior geologist at Campbell Environmental Group.

The Portland Harbour Commission and city governments in Portland and South Portland are banding together to try to attain the USD200,000 in necessary permits for the operation, which would allow dredging work to be undertaken at the 69 potential sites. Dredging operation will be funded by the individual wharf owners, who will consult to establish how much material needs to be removed, and pay a tipping fee for the dredging operation.