Woronoco Hydro LLC

Woronoco Forebay and Dam

The Westfield River has a 346 square mile drainage area whose flow is diverted into a 550 foot long penstock that drops 57.4 feet to the Woronoco power station.  Swift River purchased the land and facilities from International Paper Company (IPC) in June 2001. Hydro power was first developed at Woronoco in the early 1870's at Salmon Falls located 5 miles upstream of Westfield and 2 miles below Russell, Massachusetts.  IPC was successor to the Strathmore Paper Company who bought the paper mills from Fairfield Paper.

The Woronoco dam is a low hazard dam because it is anchored on top of a ledge outcropping that formed the original Salmon Falls.  The concrete structure of the North dam is only 15 feet high but forms a dam approximately 25 feet high and 307 feet long.  A south dam (constructed in 1950) is also a concrete structure, approximately 25 feet high and 315 feet long, which replaced the timber crib dam now submerged in the head pond. The concrete dam crest is equipped with pin sockets to support 30-inch flashboards.  IPC did not use the flashboards in later years because of its limited repair budget and inexperienced hydro operators.  However, Woronoco Hydro would like to study the feasibility of installing a crest gate on the dam to improve regulation of the head pond elevation by inflating a small rubber dam with compressed air to adjust the elevation to pass floods, downstream migrating fish and to sustain robust fishery living in the upstream wetland habitat.

An interim downstream fish passage chute was installed adjacent to the intake at the south end of the dam. The passage used an existing sluice gate formerly employed to pass ice and trash over the dam.  Several downstream passage effectiveness tests with Atlantic salmon smolt were conducted with unsatisfactory results.  So in March 2010. Woronoco moved the fish passage entrance over into the middle of 3/4" bar spaced trashracks designed to prevent smolt entrainment.  A third set of effectiveness tests were conducted in May and June 2010 with significantly improved passage results.

The gatehouse is approximately 40 feet wide housing a manually-operated trash rake.  Woronoco constructed a stop log gate in 2001 to dewater the forebay to replace rotted timbers under the gatehouse.  In 2002, SRHOCO repaired all the trashracks, replaced wooden beams with steel beams that support the racks and in 2006-2007 financed automation of the station, built a new interconnection with WMECO, relined the penstock and prepared to re-power two 450 kW Francis horizontal turbines as low flow turbines.

Bottom of Salmon Falls on the Westfield River from bridge above Woronoco powerhouse

In the early 1880's Horace A. Moses acquired a controlling interest in the fine writing paper mill of the Vernon Brothers.  Five water wheels were operating at Salmon Falls until a powerhouse for generation of electricity was built in 1916 to supply both Mill 1 and 2 with power most of the year.  Moses formed the Strathmore Paper Company in 1911.  Moses used the hydro to power "Strathmore Town," a village housing all the employees and all paper mill operations.

Woronoco powerhouse with bridge and Salmon Falls visible on right

There is a single 1,700 KW Francis turbine and 1,900 KW Westinghouse generator operating at Woronoco, which requires a design flow of 450 cfs at a net head of 55.4 feet.  Two 450 KW Leffel camelback turbines (with new runners in 1970's) were shutdown and abandoned in the 1980's because of leaks in their pressure cases and damaged runners.  Woronoco's FERC license renewal was issued in May 2002 authorizing expansion to reach 2,700 KW.

1,900 kW T-3 generator in cage and exciter for 450 kW T-2 generator on left before rehabilitation

    Since the 2,700 kW in the license would use less than the mean flow of the river, the owners may amend the FERC license to expand by adding a 1,100 KW vertical full Kaplan turbine.  Woronoco's optimized design capacity is between 3,450-3,900 KW.  After installation of the 1,100 kW Kaplan turbine, Woronoco Hydro's average annual generation is estimated to increase to 13,250 MWh from the historic average of 9,148 MWh annual long-term average. Financing of another unit would depend on a long-term PPA and the sale of Class I RECs.  The stage was to repower T-1 and T-2 by SRHOCO. T-2's rebuild can be followed by clicking on this link: Rehab of T-2. The previous FERC license included 30-inch flashboards on the dam and a lower tailrace in the pool downstream of the powerhouse.  A FERC amendment is needed to restore the head loss.

    Historic operations of the site reflects the secondary nature of hydro power production at the Strathmore Paper Company during its years of decline.  In the monthly production record (shown below) we can trace during the period from 1984 through 1993 when the output figures suggest that there were frequent breakdowns.  One such example is one that closed the hydro station from July 1989 until May 1990 a 10 month period during which the penstock was relined with concrete and all of the generating equipment was reconditioned.  During the 1980's the two low flow turbines were deteriorating and became less reliable.  Finally, in June 1993, the larger wheel was damaged beyond repair.  At that time, IPC ordered 2 new Francis runners to replace the original T-3 runners.  It was nearly two years later before the new equipment was installed and the station was put back on line in August 1997.  Operating data for the next two years showed an output jump, even without the two smaller turbines being operational.  However, in the summer of 1997, IPC closed the Woronoco paper mill and without employees, IPC abandoned its hydro station.  IPC did not retain trained staff to operate the hydro equipment to sell power into the ISO-NE grid.  The hydro plant was not restarted until IPC signed a purchase agreement with Swift River in September 2000, at which time as part of due diligence testing, IPC had to prove that the single large turbine would generate power.  IPC sold that power to a tenant that had rented Mill #2 to manufacture pelletized paper pellets for sale to the U-Mass boiler plant.  IPC's production history is as follows:

The plant has been automated since it was purchased for run-of-river operations and remote monitoring of all functions.

Woronoco three turbines after being restored to full operation in 2008

Power Sales Agreement

Since Woronoco Hydro started full time operations in February 2002, when the rehab of the intake, gates and equipment was complete, the hydro has supplied power to Mill #2 across the Westfield River and sold its surplus energy to WMECO at ISO market clearing rates. However, the load of Mill #2 is not large enough to take more than 10 to 15% of the station output, and it is intermittent since the plant does not operate during the weekends and some shifts.

Therefore, Woronoco is looking for a stable long-term contract to sell all of its output, including the generation from the capacity expansion that is described above.  The monthly average production for Woronoco is shown in the Graph in the Woronoco section of Operating Projects. It is also possible that the output of both Turners Falls and Woronoco could be sold together to a single customer.  For the monthly output of these two projects combined, refer to the graph shown in the section Energy Sales.  The advantage of the steady year round flow taken from the Turners Falls canal would help to offset the low summer flows characteristic of the Westfield River.  The owners are seeking a stable long-term PPA such that it can serve as the basis for project financing of the capacity addition proposed at Woronoco, including the reinstallation of the flashboards to raise the operating head.

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