A group working to create a disposal site for dredged sediment from around Portland’s waterfront has identified three potential locations in Portland Harbor to bury the mud.

The Portland Harbor Non-Federal Dredge Workgroup will outline its proposal and provide other details about plans for a confined aquatic disposal – or CAD – cell to the Waterfront Alliance, a group of Portland and South Portland marine interests at 4 p.m. Tuesday on the third floor of the Gulf of Maine Research Institute at 350 Commercial St.

A CAD cell is a hole dug into the harbor bottom that is filled with dredged material and capped. It would contain dredged material from Portland Harbor’s public and private piers, which are slowly being choked by mud.

The dredge work group, made up of volunteer representatives from marine businesses, port agencies and environmental advocacy groups, as well as federal and local permitting agencies, has been working since January to locate, design and permit a CAD cell. CAD cells have been used in Boston Harbor, Rhode Island and California. A Portland Harbor CAD cell would be a first for Maine.

Bill Needleman, Portland’s waterfront coordinator, said the CAD cell would provide an environmentally safe and cheaper alternative to other sediment disposal options.

Important navigation routes are maintained and dredged by the U.S. Army Corps of Engineers. But wharf owners and abutting shoreside land owners are responsible for dredging outside the federal channel.

Much of the mud around Portland’s 200-year-old wharves is believed to be laced with contaminants from long-departed industries and modern-day storm water runoff. Contaminated mud may not be dumped at sea at the federally approved dump site off Portland.

Needleman said that dumping a cubic yard of sediment at sea costs about $22 compared to $100 for land-side disposal, which makes it unaffordable for many of the 20 private and public wharves, and another half-dozen transportation and fuel terminals in Portland Harbor.

The dredge work group has been working with the lobstermen who use Portland wharves to berth their boats to identify potential sites for the CAD cell that would have the least impact on fishing. Needleman said it would be up to the Portland Harbor Commission and several federal and state environmental and other permitting agencies to approve the project. He said the U.S Army Corps of Engineers has estimated such a project can take between two and 10 years to complete. He said he hopes the design and permitting can be in place within the next year. Then the effort will switch to finding money to build the CAD cell. He said the project could cost $6 million to $10 million.

Charlie Poole, whose family has owned Union Wharf since the mid-1800s, said dredging is essential to keep wharves open. Poole, a member of the dredge work group, said there has been no dredging around Union Wharf since the mid-1990s, when new regulations banned contaminated dredged material from the sea dump site off Portland. He said at one section of Union Wharf, where he once tied a 38-foot fishing boat in the 1970s, the mud bottom is visible at low tide.

Roger Hale Sr., who owns Deakes and Holyoke wharves, called the CAD cell a great idea. He said the last time the wharves were dredged was in 1985 and 1990 when he spent $125,000 to remove the silt that had built up around the piers.

“That is when we could take it out to sea,” said Hale.

Frank Strout, of Cape Elizabeth, a lobsterman who berths his boat at Union Wharf and is in the working group, said lobstermen are not worried about any impact on fishing grounds in Portland Harbor.

“The need is so great for a project like this. We are losing docking space,” said Strout.

Strout said he met with members of the two local lobster councils and found a lot of support for the Portland Harbor project.