PEPPERELL -- Swift River Hydro is planning to begin the removal and replacement of its wooden penstock at the Pepperell Hydro plant within the next couple of weeks. Plans have been in place for months to remove the 60-year-old wooden apparatus, which carries water from the Nashua River dam under the Main Street bridge to the plant's turbines; the company will replace it with a sturdier, longer-lasting steel tube, said Swift River Hydro operations manager Wayne Bailey.

"This could change, it's based on a couple of things, but basically the plan right now is to start removal of the penstock in early October," said Bailey.

The job should take until January 2013, meaning the hydro plant will be out of commission for about four months. During that time, the headgate, which is the entrance to the penstock through the dam, will be closed, causing the water to pour over the edge of the dam during that period of time.

The penstock's imminent replacement is necessary, according to Bailey; it was last replaced in 1950 and its expected life span is approximately 50 years.

"We're on borrowed time now," said Bailey.

The company opted for steel this time around for several reasons. First and foremost, it's expected to last anywhere from 65 to 85 years. It will require less maintenance like patchwork and vegetation removal and it will operate more efficiently.

"We get the same amount of power for a slightly smaller diameter," said Bailey.

The current penstock has a diameter of 13 feet and is 600 feet long; the new one will have a diameter of 12 feet, according to Conservation Administrator Paula Terrasi.

And with the fact that it won't be consistently leaking, which is something that is to be expected with a wooden penstock, "It should definitely improve the output of the station," said Bailey.

As for the current construction going on at the dam, building crews are carving a notch into the cement in order to direct fish attempting to swim downstream and prevent them from entering the penstock, according to Terrasi. Currently, the fish have no way to do so except through the headgate.

"(Employees of Pepperell Hydro) don't want the fish going into the penstock because they just get ground up," said Terrasi.

The only downfall of the notch, as is true with any dam, is that there is no way for the fish to swim back upstream, except to install a fish ladder to assist them, which would be excessively costly.

"It's a one-way trip (for the fish)," said Terrasi.

The construction crews are also working on repairing sections of the dam, called flashboards, as needed. They are prone to ice damage during the winter, according to the Pepperell Hydro manager Peter Clark.

"When we get a lot of rain, a lot of things come over the edge of the dam. If a big log comes over, it could take out a section of the flashboards," said Terrasi.

Pepperell Hydro produces approximately one and a half megawatts per hour and has an agreement to sell the power to Reading Municipal Power. Swift River Hydro owns four other hydro plants; the next closest is Turner Falls Hydro on the Connecticut River.