Rehab Progress

Pepperell Hydro Company LLC

    Swift River Hydro Operations Company (SRHOCO) purchased the dam and hydro facilities from the liquidators of the Pepperell Paper Company.  Built in 1918, the hydro plant was designed for 3 vertical Francis turbines selected for the net head of 28 feet and a design flow of 1,035 cfs.  The intake at the dam on the Nashua River is connected to the forebay of the powerhouse by a 13 foot diameter 600 foot long wood stave penstock.  This penstock was replaced over 60 years ago and should be replaced before it burst under the pressure of annual spring floods. Of the original Leffel B turbines, T-1 runner was replaced in 2001 with an American Hydro Corp. replacement runner of greater efficiency.  SRHOCO bought the plant in 2004 and immediately purchased a new runner from American Hydro Corp for T-3 in 2005.  T-2 had been taken out of service in 1962 and in the early 1980's the generator was cannibalized for parts.  SRHOCO's strategy then was to install a Leffel J turbine in T-2 connected to a new 675 kW Dong Fang generator. The new equipment, together with installation of an automatic trash rake and control system automation has increased long-term average production to 8 GWh per year.

Pepperell Dam behind Main Street Bridge Crossing the Penstock

    The Pepperell Hydro station was formerly the primary electricity supply for Pepperell Paper Company's (PPC) paper mill.  Manufacturing was located at that site in the mid 19th century because of its hydropower potential.  When the mill was closed in 2002, the powerplant operators were fired and the facility was maintained by a single security guard.  Thus, maintenance ceased at the dam and the hydro plant that generated renewable energy on the Nashua River for more than a century was nearly lost. The PPC story is typical of many mill towns in the Commonwealth.  Swift River Company (SRC) and its affiliate SRHOCO were formed to preserve the skills needed to finance and rehabilitate existing renewable energy projects and to preserve the civil structures and equipment that convert water into green, non-polluting electricity.  SRHOCO has acquired the engineering plans, shop drawings, repair equipment and skills necessary to maintain and operate hydro turbines and generators that have decades of useful life left before they must be replaced.

    Most importantly, Swift River believes that there are a few select locations where river flows and head combine for efficient hydro generation. Plants at existing dams are already located at such efficient hydro sites, and rebuilding them has helped Massachusetts to rely on local renewable energy resources.  The Massachusetts Green Power Partnership (MGPP) recognized this potential and awarded Pepperell Hydro Company with a 10-year contract to purchase renewable energy certificates (RECs) enabling the Webster Five Cents Savings Bank to finance purchase and rehabilitation of the century-old Pepperell hydro plant.  SRHOCO repaired or replaced one turbine at a time while continuing to generate power with the other turbines during the construction period in 2004 through 2006.

    SRHOCO has a machine shop with specialized tools and the shop equipment necessary restore the mechanical and electrical equipment but SRHOCO left the penstock to last, believing that it had at least another decade of useful life.  However, a fire (caused by a voltage system lighting strike on the interconnecting transmission line during a fall flood) burned out some of the new electrical control equipment, station wiring and one generator in the powerhouse.  Fire insurance funds then paid for replacement of all the wiring, windows and rebuilding of the damaged generator, leaving the plant in "like new" condition.. The hydro plant was disconnected from the rest of the paper mill across the river and now sell 100% of its output to ISO at the local nodal marginal price.

Pepperell Hydro Company's "like new" hydro plant was actually built in 1918

    In New England, reliance on locally generated "green" power is widely supported by consumers willing to pay more to increase the distribution systems share supplied by renewable hydro generated electricity.  When restructuring the electric sector, the state legislature mandated that renewable energy must increase annually by enforcing the Massachusetts Renewable Portfolio Standard (RPS) but hydro was omitted from the RPS. Therefore Pepperell Hydro applied and has been certified as a Class 1 generator in Connecticut and as a "new" source for the output of T-2 and T-3 in Rhode Island.  RECs represent the "renewable attribute" of hydropower that is separate from energy generation and may be sold to Connecticut and Rhode Island distribution companies.  (See Energy Sales and Green Certificates for an explanation of renewable energy certificates -- RECs).  Each year the share of renewable energy purchased by distribution companies must increase to levels set in the state's RPS.  Thus the price of RECs is expected to rise over time, unless there is a large jump in the supply of new green technologies growing faster than demand for electricity.

    You will note on your monthly electric bill, there is a small charge for development of renewable energy technology.  These funds are administered by the Massachusetts Technology Collaborative (MTC), which has initiated a large number of programs to stimulate the use of green energy technologies.  Among these programs, MTC signed a contract to purchase RECs for the next ten years from Pepperell Hydro.  From 11 proposals were received, 2 were hydro projects submitted by Swift River Company.  On November 13, 2003 MTC announced that it had selected Pepperell Hydro's proposal to re-power, upgrade and re-commission its existing hydro power project.  MTC signed a 10-year REC Purchase Contract that provided credit support for the Pepperell project financing but without sufficient financing to replace the penstock  Thus, SRHOCO is seeking a federal loan, grant or guarantee to help fund this "shovel ready" penstock replacement.  Pepperell Hydro has carried out engineering studies and determined that the best type of penstock to replace the 60 year old penstock would be another wood stave pipe built on rehabilitated saddles.  Competitive budget bids were received from both American and Canadian suppliers with about equal prices. Thus, if Stimulus Act funding were awarded to the project, an American supplier and nearby experienced construction company that has built many wood stave penstock are available for construction before the end of 2009.


Panoramic View of the forebay with intake gates before installation of the new automatic trash rake.

     For a comprehensive slideshow illustrating the need to replace the wood stave penstock, please copy this address in your browser:



T-3 Westinghouse 640 kW Generator and Woodward Governor in June 2003

    Automation and the redundancy of a third T/G set has increased long-term average annual output for the three units to 7,123 MWH, an increase of 3,715 MWH over the annual Base Period output averaged from 2000 to 2002.  The pre-rehab output data shows that the Pepperell Paper Company did not repair equipment when it was damaged and therefore operated its hydro plant intermittently during the last years the paper mill was viable.  Operations suffered due to frequent breakdowns and the retirement of trained staff once plans were made to close the paper mill.  SRHOCO bought the project after Fay Engineering prepared the Pepperell Production Study based on 40 years of hydraulic data collected at the USGS' East Pepperell gauge (located in the tailrace of the hydro station), which was a simulation of daily average output using headwater and tailwater rating curves for the site, estimated turbine efficiencies and a production simulation model for the period from 1970 to the present.  The table below shows simulated monthly average flows and monthly average production from one turbine, two turbines and three turbines.  This production model results resulted in SRHOCO's decision to install two new runners and a rewound generator.  Figure 13 of the Fay report is a graph of the actual monthly outputs generated by PPC for 2002 versus the long term average monthly curve for the period of record 1970 to 2002, estimated by the study and shows its close calibration.

Monthly Average Flows and Estimated Output After Rehabilitation of T-1 and T-2


Average Flow Rates (cfs)

T-1Optimized Output (MWh)

T-1 + T-2  Output (MWh)

T-1 + t-2 + t-3 Output (MWh)





























































Annual Total or Annual Average





    Swift River Hydro Operations delivered the T-2 generator that it plans to install as soon as the project had been purchased and in the second year installed the rehabilitation Leffel turbine as T-2.  The T-2 turbine was machined and balanced at the SRHOCO machine shop in Wilbraham, MA and new PLC automated switchgear was designed and installed by Olson Electric of nearby Methuen.

Generator parts being lifted into the powerplant to be cleaned and painted before installation.

    Today Pepperell Hydro is a fully restored renewable energy project.  Its equipment as been brought back to the 1920 kW of capacity installed in 1918.  The plant is now qualified as a Settlement Only Generator (SOG) and receive monthly payments for capacity as well as energy and REC income. 












Interior of the Pepperell Hydro station after capacity was restored to the plant's 1918 capacity level.

    The project has performed above expectations, but now faces great uncertainty because in 2007 during the spring floods the 60 year old penstock was damaged by a log that had come over the dam and punctured the wood stave penstock. The penstock was repaired by PHC taking out an emergency $250,000 life extension loan to extend the use of the penstock for another few years.  Over 250 steel bands were replaced and four of the nearly 70 saddles that support the penstock were replaced. However, it is now necessary to replace the whole penstock as the current one is living on borrowed time. 











Today's leaky penstock may be on its last legs!  Concrete cradles are now cracked and broken.


Wood stave penstock replaced about 1955 would be the most economical replacement penstock type.

Today's penstock shows the wood has deteriorated enough that weeds can root in the wet wood.

    For more information about the penstock replacement studies, please contact Pepperell Hydro Company at (978) 468-3999 and ask to receive the engineering studies of alternative penstock replacement materials and their costs.

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