SEARSPORT, Maine — A major dredging project in Searsport Harbor that has been in the works for more than a decade is slowly moving forward, though environmental activists fear that the $12 million effort could dislodge toxins in the silt and harm Penobscot Bay.

The U.S. Army Corps of Engineers earlier in April released a draft feasibility study and environmental impact assessment on the maintenance and expansion of the federal navigation channel in the harbor that leads to Mack Point, Maine’s second-busiest industrial port. The public has until May 6 to share comments on the project with the engineers.

Advocates say that maintaining and improving the channel is necessary to the continued economic viability of the port.

“I would say it’s extremely important,” John Henshaw, executive director of the Maine Port Authority, said Friday.

But longtime environmental activist Ron Huber of Penobscot Bay Watch cautioned against moving too quickly on the project.

“If shipping is going to supersize, as so much else is, then Searsport may need to expand that outer area — but this has yet to be proven,” he wrote Friday in an email to the BDN. “If it is so, then the Corps must err on the precautionary side and ensure that mercury, dioxin and other wastes are not to be dumped into the bay in contaminated spoils.”

He and others are worried that the dredged materials might be disposed of too close to the mouth of the Passagassawakeag River. According to the Army Corps of Engineers, the materials would be dumped either at the Penobscot Bay Disposal Site, located about six miles from the project area, or at the alternative Rockland Disposal Site in the lower part of Penobscot Bay — 25 miles to the south.

Henshaw said that Searsport is second only to Portland in terms of the numbers of cargo vessels that dock there, carrying a diverse load of goods including energy products, wind turbine components, salt, and clay slurry for the papermaking industry.

The federal navigation channel in the harbor was authorized to be dug out to a depth of 35 feet by the River and Harbor Act of 1962. Since then, there has been no maintenance to the channel, according to Barbara Blumeris of the Army Corps of Engineers. In 2000, Congress authorized the Army Corps of engineers to see if there were any “improvements to the project that were advisable,” she said Friday from her office in Concord, Mass. But because the area is “low-shoaling,” there hasn’t been much silting up. The feasibility study calls for the removal of about 37,000 cubic yards of maintenance material, she said.

However, a much larger amount of silt and sediment — 892,000 cubic yards — would be dredged to improve the channel, if the project continues as proposed. That would allow the Army Corps of Engineers to deepen the existing entrance channel and turning basin from 35 feet to 40 feet at low water. It also would widen the entrance channel from 500 feet to 650 feet and create a maneuvering area in Long Cove near the State Pier at Mack Point.

The project has nothing to do with DCP Midstream’s controversial and now defunct bid to build a propane terminal and tank storage facility at Mack Point, according to Henshaw. But opponent group Thanks But No Tank has a notice on its website encouraging “every Penobscot Bay resident” to consider writing and asking the Army Corps of Engineers to complete a full environmental impact statement and to hold a public hearing “for a job of this magnitude. Letters should perhaps focus on the expansion dredging, not the maintenance part.”

Deepening and maintaining the channel is important for safety purposes, argued David Gelinas of the Penobscot Bay & River Pilots Association. Larger vessels require more water, he said, and insurance underwriters now are requiring ships operate with more draft, too.

“Imagine an airport, where you built a runway 48 years ago and never maintained it. We have to go in,” he said Thursday about dredging efforts. “The level of activity in Searsport and the level of increased activity there does justify a deepening of the channel. … For us, we’re trying to make it safer. We’re trying to get a larger margin of safety, not just to maintain what we’re doing.”

Public comments on the project should be sent no later than May 6, 2013, to the U.S. Army Corps of Engineers, New England District, Engineering and Planning Division (ATTN: Ms. Barbara Blumeris), 696 Virginia Road, Concord, Mass., 01742-2751 or by email to