OXFORD — Major rehabilitation for the Thompson Lake dam in Oxford has been a long time coming. The first piece in a series of repair projects will be completed in about three weeks. The project was approved at Oxford’s 2020 annual Town Meeting with a budget of $521,350. It is expected to come in at least $30,000 under budget when completed.

Looking upstream at the Thompson Lake dam in Oxford, as Bancroft Contracting prepares to install a temporary coffer dam. Nicole Carter/Advertiser Democrat

Bancroft Contracting of South Paris began work on the dam on Sept. 11, including staging, removing old and compromised stop logs, and repairing the east gate of the dam. Bancroft is also adding 14 inches of concrete reinforcement to the original wall that was built using hand-cut stone masonry.

A replacement sluice for the stop logs has been shipped from the manufacturer in Canada and is scheduled for installation next week. The sluice can be raised and lowered using electricity, a major improvement over the stop logs which were immovable and starting to bulge from years of pressure.

A coffer dam was installed around the east gate of the Thompson Lake dam so it could be repaired. The temporary dam will be removed after the new electrically powered sluice as been been installed in the gate. Nicole Carter/Advertiser Democrat

During this fall’s rehabilitation phase, water to the east gate was blocked by a temporary coffer dam. The lake level was dropped starting on Sept. 8 by removing the stop logs from the west gate; those logs will be replaced before winter and that gate will go under similar repair and sluice replacement in the future.

The central sluice’s gate can be operated manually or with electricity; it has been the sole tool in managing the dam’s operation and Thompson Lake water levels.

Myron Petrovski of MBP Consulting has worked with towns throughout Maine on dam inspections, maintenance and management, including Oxford’s Welchville dam. He is well acquainted with the Thompson Lake dam and was hired by the town to oversee Bancroft’s construction work.

Petrovski provided a tour of the dam project on Nov. 13, ahead of the delivery of the new sluice for the east gate.

By Oct. 9 the coffer dam was installed, sealing the east gate so Bancroft could stage the area for removing the stop logs from the east sluice and repair the gate. Nicole Carter/Advertiser Democrat

“The east and west gates are controlled by wooden boards, stop logs,” he explained. “They are the same system but the west, which is open now, has a shallower sluice. The east sluice, which is being rehabbed, is much deeper.

Looking downstream above the east gate of the Thompson Lake dam. Forms are in place for protective concrete to be poured and a new electrically powered sluice will be installed next week. Nicole Carter/Advertiser Democrat

“To repair the east gate, Bancroft had to build a temporary, coffer dam which is made of steel sheets and installed by crane. When the work is done it will be removed as one of the last steps.”

The submerged logs at the bottom of the east sluice could not be reached and had begun moving and shifting. Some repair was done over the last few years, but the stop logs could suddenly fail and not be stopped quickly, Petrovsky said, adding that if the dam failed it could take a week or two to stop the flow, making the lake level drop significantly.

“So the wooden stop logs will be replaced with electrically operated gates,” he said. “The other issue is the dam itself, the stone masonry is open joints and water can easily go through and create conditions for deterioration of the body of the dam. It is the same with the vegetation growing along it, it should be controlled.

“That leakage needs to be stopped. They’re adding concrete on the face of the dam. It is about 14 inches thick. It adds an extra barrier. You can see where the concrete has been poured, and where they have placed forms for more to be added around the east gate.”

The gate is being delivered by Nov. 21. It will be installed the last week of the month. Once that is done, Bancroft will remove the coffer dam and decommission the work site. They are expected to complete this phase of the overall rehabilitation by mid-December.

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