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PEPPERELL — Yet another historical structure is getting some work done in downtown Pepperell.

Swift River Hydro’s penstock and pump facility repair project is scheduled to be underway in July. New England Infrastructure has been contracted to complete the $5 million project, which will update the existing 60-year-old wooden pipe that runs under the Main Street Bridge. The work is expected to have positive environmental impacts on the Nashua River and should be completed around late November.

Project Coordinator Martha Brennan says the primary objective is to replace the aged wood penstock with a steel one, something that will help with environmental concerns but also move the Pepperell hydro project onto a more environmentally-friendly track.

“Because steel is stronger and more rigid there is a net reduction in amount the of stuff sitting on river bed, in terms of environmental impact it will be better,” she said.

Steel is more durable and will require less maintenance and less saddles. Brenan says the new structure will require only 20 concrete footings, spaced about 60 feet apart.

Currently there are 75 support saddles that lie every 8 feet along the bypass-reach area, or riverbed, below it. Flooding in 2007 sent a log over the dam that punctured the penstock and damaged several of those saddles, requiring $250,000 in repairs and work to be done down in the riverbed.

“They are doing what they have to do right now and making sure they follow the rules, Swift River has good intentions for their projects and the river,” said Pepperell Conservation Administrator Paula Terrasi.

Swift River has been working with Terrasi on the project, primarily on a fish passageway. The U.S. Fisheries and Wildlife Service have begun a 10-year fish stocking project in the Nashua, downstream of the facility, and because the species are migratory, they have requested the inclusion of a passage to support their efforts.

“It is not going to be elaborate, but we have decided on installing a notch to the dam and plunge pool,” Brennan said.

Water is held up at the top of the dam by flashboards, intake structures take that water and send it down the 600 foot run of the penstock to the plant. Directly beside those intakes, a notch will be installed with a guidance boom to direct fish over the edge of the dam into a plunge pool below.

No upstream passage is being installed because of the expense, Brennan said, but Swift River is also pursuing a Federal Energy Regulatory Commission license which may include future provisions for additional passage structures.

“We have a preliminary permit so that when we build a new plant or buy and improve an old one we can be first in line for licensing,” she said.

When the facility was built in 1918 to provide power to the Pepperell Paper Company, FERC didn’t exist. It wasn’t until 1930 when the Federal Power Commission, a precursor to FERC, was formed. In 2004 when the plant was purchased by Swift River and re-purposed to provide municipal energy, now FERC license was necessary.

Currently, the Pepperell facility houses three turbines, two of which are operational.

According to Brennan, the project will include repairing the third, adding a fourth, smaller turbine by the dam and improve the efficiency of flow within the penstock, thus changing the power output from 7.2 gigawatt hours of electricity per year to 7.9 GWh, enough to power more than 1,700 homes.

Since it is an improvement, the company will need to pursue FERC recognition, either in the form of a license or exemption.

“When approved, we will get a set of conditions to comply with. We are currently meeting with state and federal agencies state about the licensing,” Brennan said.

FERC guidelines are tailored to specific sites and rivers and sometimes requirements are given a time frame, rather than made mandatory immediatley, according to Brennan. Like the fish passage, Swift River is also anticipating other possible FERC regulations like minimum flow.

“The project will keep a constant 40 (cubic feet per second) flowing to keep the downstream part wet,” Brennan said. “If it is completely dry from the dam on down, the habitat there could be lost.”

Passage installation coincides with the USFWS to begin introducing additional migrating species such as American shad, alewife, blueback herring and American eel.

Temporary diversion structures made from sandbags will be used to create de-watered working conditions during the project Brennan said. The wood and concrete from the existing structure will be disposed of and steel bands which hold the pipe together, recycled.

According to project engineers, Brennan said, there should be no impact to traffic on the bridge during construction.

Follow Luke Steere at twitter.com/LSNashobaPub.

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