An historic hydro-electric facility that has produced renewable energy for 81 years is getting a substantial overall starting today. Central Vermont Public Service is beginning extensive improvements to the company s Arnold Falls hydroelectric project, located on Mill Street along the Passumpsic River in Saint Johnsbury. The existing structures, similar to those originally constructed during the 19th Century for nearby mills, consist of two rock-filled, timber-crib dams with concrete abutments. Though the deteriorating timber dams will remain in place, new concrete dams will be built adjacent to them to ensure the facility s long-term future. This is a nice little site, producing an average of 1,112,328 kilo-watt hours of electricity annually over the past 10 years, CVPS spokesman Steve Costello said. At peak water flows, this facility can power 200 homes with clean, renewable energy. After construction, we expect slightly improved production, possibly as much as an additional 120,000 kilowatt-hours annually.The federally licensed generating station, which was built in 1928, includes two timber-crib dams separated by an island. The 189-foot north dam and 66-foot south dam consist of interlocked logs, which have a limited life span due to the riverine exposure and the inevitable decay of wood.CVPS made substantial repairs to the Arnold Falls dams in the 1940s. In 1976 and 1977, CVPS reconstructed the dams using logs from a local sawmill, and in recent years the company has made ongoing repairs. Compression of rotting logs has allowed the crest of the timber-crib structures to settle to the point that the improvements are necessary.The existing timber-crib dam structures will serve as coffer dams during construction. Although the timber-crib dams will remain submerged in the Passumpsic River after construction of the new dams, they will be somewhat visible and continue to represent the original structural design of the hydroelectric station. The new dams will be constructed one at a time, starting with the north dam. Bancroft Contracting Corp. of South Paris, Maine is expected to complete the project this fall.Each new dam will consist of a concrete structure cast in place immediately downstream of the existing timber-crib structures. Flashboards atop the north dam and a crest control system atop the south dam will stabilize the water level in the impoundment.Work on the $1.3 million project is not expected to reduce station generation during construction. We expect to be able to complete the project with minimal, if any, impact on power production, Costello said. That s good for our customers today, and the improvements mean the facility will continue to produce low-cost, no-emissions energy for our customers for years to come.The Arnold Falls facility is one of 20 owned and operated by CVPS across the state. Along with power supply contracts and other generation projects, they help provide CVPS customers with the lowest rates of any major utility in New England, according to the Edison Electric Institute, and Vermont with the lowest air emissions in the country.