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Trench proposed to be dug across Kennebec River for new sewer line in Augusta

Currently, due to a failed pipe, there is only one pipe carrying wastewater from the east side of the Kennebec River to the treatment plant on the west side.

AUGUSTA — A forthcoming multimillion-dollar project to build a new sewer line underneath the Kennebec River will be challenging, officials concede, but doing nothing is especially risky.

If an existing pipe were to fail, district officials said they won’t have any way to move wastewater from the east, where 20-30% of its flow comes from, to the west side of the Kennebec.

So, it would pollute the capital region’s landmark river instead of being treated.

“If it should fail, it will be the lead story in Maine for days as wastewater flows into the Kennebec while we scramble to find some sort of remedy,” said Andy Begin, assistant general manager and chief engineer for the Greater Augusta Utility District. “This is our one chance for probably the next 100 years to install a pair of new pipes that will improve our resiliency.”

The new pipe aims to ensure that wastewater from the east side of Augusta can continue to make it across the river to be treated. But the project involves a river crossing that officials didn’t want to do, to fix a pipe that is no longer working, in a way they didn’t want to do it, with money they didn’t want to spend. All with careful timing to avoid interfering with wildlife and the environment.

Right now, since a second, smaller pipe was discovered to be plugged up and to have failed in 2016 and taken out of service, there is only one, 20-inch pipe built of car iron in 1963 that carries wastewater in the sewer system from the east side of the Kennebec River to the treatment plant on the west side.

In 1998, a 20-inch sewer line that crossed the Kennebec River in Winslow broke, spewing some 605,000 gallons of sewage into the river before it could be fixed. It prompted advisories in Vassalboro and Augusta, downstream, warning residents at the time not to swim in the river, and in the town of Phippsburg clam digging was halted until the pipe could be fixed that year.

The roughly $3 million project in Augusta will involve pipe crossing the river from a spot below Riverview Psychiatric Center on the east side to below the district’s wastewater treatment plant off Jackson Avenue on the west side. It will bring a new, 16-inch high density polyethylene pipe under the Kennebec River, in addition to the 20-inch existing pipe that will be refurbished later in the project, for sewer. And, since a trench will be dug for the new sewer pipe already, a new 16-inch water line will be put in across the river too, though it won’t be hooked into the water system until later.

District officials had hoped to bring the new sewer line under the river by horizontal drilling, but efforts to do so in 2018 failed because the material under the river — including rock and cobble — was too loose and collapsed onto itself.

So now the proposal is to cross the river through a more traditional, and more costly, trench that will be dug mostly by a large excavator on a barge. The excavator will remove soil from the trench across the river, and place it just downstream to be put back later. Then the new pipes will be put in and reburied.

The work could begin in August and last two or three months, Begin recently told Augusta Planning Board members who approved some tree cutting alongside the river required to make way for the project.

Navigation by boats on the river could see some brief interruption during the project, though Begin and Brian Tarbuck, general manager of the utility district, said that could depend on the size of the boat. They said canoes, kayaks and boats with low draft could move around the project easily but a larger vessel or a sailboat with a keel could need to be in the deepest part of the channel.

So when the excavation work is taking place in the deepest part of the channel a larger or keeled vessel may not be able to pass through. They said that would be for a couple of days, at most, because they expect the excavation to move pretty rapidly once it starts.

Trucks going to and from the west side work site will cross the Kennebec River Rail Trail but the trail is expected to remain open. Begin said they don’t anticipate doing any damage to the trail but if they do, they would fix it.

“We chose this method because we did not want to build a cofferdam across the Kennebec,” Begin told Planning Board members recently, referring to a temporary barrier built in or around a body of water. “We just didn’t see that as a really good plan and I think the environmental impacts would have been worse than what we’re proposing now. We’ve been playing a delicate balance with regulators and I think we have a good solution.”

Begin said the timing of the project is planned to try to be done removing trees before June so it doesn’t take place during bat mating season. And the timing is also meant to limit the potential impact on sturgeon and Atlantic salmon in the Kennebec River. He said officials will likely monitor the turbidity of the water during construction, and could stop work if the river gets too stirred up.

The failed 2018 drilling effort cost about $300,000 and to date work on the project has exceeded $1 million, according to Tarbuck. He anticipates it will cost about $3 million total, though that could vary depending on what additional steps are required to obtain permits for the project from the Army Corps of Engineers and state Department of Environmental Protection.

Tarbuck said district rates to cover the expense of the project may have to increase in 2022, though he said it is too soon to know as the district is seeking grant and loan funding to potentially help pay for the work.

The site of the new project is about 60 feet north of the existing sewer line that still functions, to avoid working too near the existing line, potentially risking puncturing it during the work.

The new pipes will be installed, tested, and put into service before the old existing pipe is shut down so it can be refurbished and returned to use.

John Turner, engineering services manager and Clean Water State Revolving Fund program manager for the state Department of Environmental Protection, said underwater river crossings for sewer lines are fairly common, and there are usually a number of such crossings every year as utilities maintain and improve their systems.

A 1999 survey (which True said hasn’t been updated since then) indicated that there were 137 underwater river crossings, totaling 35,000 feet, in 94 municipalities and sewer districts that convey wastewater in Maine. More than half of them had been in operation for more than 20 years and the oldest had been installed in 1958. The study indicated there was no regular or periodic testing of underwater river crossings in Maine.

Begin said the pipes being replaced and refurbished in Augusta were installed in 1963.

A temporary, roughly 70-foot trestle will also be built as part of the project, on the west side, acting as cribbing to help move pieces of pipe into the river and providing access, for digging, to the tidal area that would not have enough water to work on from a barge.

The old, no longer functioning 8-inch sewer pipe will be repaired and repurposed to carry fiber optic conduit to allow communications between the district’s plant, office and remote pump stations. Tarbuck said use of additional capacity in that pipe, for more communications lines, will be offered to the city, state and possibly private entities.