2012 Construction
Rehab Progress

Pepperell Hydro Company LLC

Swift River Hydro Operations Company (SRHOCO) purchased the Pepperell dam and hydro facilities from the liquidators of the Pepperell Paper Company in 2004.  Built in 1918, the hydro plant was designed for 3 vertical Francis turbines selected for a 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 will be replaced in 2012 before it is damaged by winter ice and spring floods. Of the original Leffel B turbines, the T-1 runner was replaced in 1997 with an American Hydro Corp. runner with greater efficiency.  SRHOCO bought the plant in 2004 and purchased and installed a new runner fabricated by American Hydro Corp for T-3 in 2005.  T-2 was 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 B2 runner in T-2 connected to a new 675 kW Dong Fang generator. The new equipment, together with installation of an Atlas Polar trash rake and PLC controlled switchgear with remote sensors and pond level controls increased long-term average production to 7,123 MWh per year.

Pepperell Dam behind Main St. Bridge and penstock in 2004 when SRHOCO bought the project.

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 hydropower producing green energy on the Nashua River for more than a century was nearly lost. The PPC story is typical of many mills 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 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 sites where river flows and head combine for efficient hydro generation.  Plants at existing dams were located at such efficient hydro sites, so repowering them helps 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 to 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 lighting strike on National Grid's interconnecting transmission line during a fall storm) 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 station wiring, windows and to rebuild 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 began to sell all of its output to ISO at local nodal marginal prices. In March 2011, bundled energy, capacity and RECs started to be sold to the Reading Municipal Light Department (RMLD) on a 15-year contract.

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 by the state's RPS.  Thus the price of RECs is expected to rise over time.

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

From 11 proposals were received, Mass Technology Collaborative (MTC) selected Pepperell Hydro's proposal to re-power, upgrade and re-commission SRHOCO's newly acquired hydro project.  MTC signed a 10-year REC Purchase Contract that provided credit support for Swift River's repower project financing but without sufficient financing to replace the penstock  Thus, SRHOCO is seeking a commercial and SBA 504 loan refinancing, and possibly a Treasury 1603 grant to help refund 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 a 12 ft diameter steel pipe installed on 8 steel saddles.  Competitive penstock budget bids were received from both American and Canadian suppliers of wood, fiberglass, steel and concrete pipe.  Pepperell is ready to solicit bids from general contractors or a nearby experienced construction company that has built similar penstock and civil construction projects in river/wetland locations for reconstruction in the summer 2012.

Pepperell's 600 volt to 69 kV substation transformers were renovated in June 2007

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 before acquiring the projectIn studying the proposed 2012 construction, Pepperell has made engineering studies and collected equipment bids to bring the project up to 2.2 MW from its present 1.92 MW by installing more efficient runners at T-1 and T-2, and installing a minimum flow discharge turbine at the dam.  A 51 kW pump turbine will be used to discharge water into the bypass reach, as proposed during consultation with the resource agencies who have pressured FERC to force Pepperell to get an exemption from licensing so that the agencies will be able to order Pepperell to construct a downstream fish passage facility for alewife and shad.  Fay Engineering has simulated with the latest daily flow records the potential to increase long-term average annual production to nearly 8,000 MWh per year.  Pepperell is replacing its T-1 runner and gate case following an accident in April 2011 that damaged the equipment.  Kiser Hydro submitted the low cost bid for replacing the equipment, which will increase the runner's capacity from 640 kW to 850 kW.  A similar replacement of the Leffel B2 runner is being evaluated along with the location of the fish passage facilities that will be constructed in 2012.  The capital budget variations were evaluated and with the RMLD bundled commodity sales agreement we find that each addition of more efficient equipment results in slightly greater production.  The table below shows the estimated long-term production from daily flow simulations averaged over the period from 1970 through 2010:

Monthly Average Flows and Estimated Output After Rehabilitation with more efficient equipment


Average Flow Rates (cfs)

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

T-1 Kiser + T-B2 + T-3 + min flow t/g Output (MWh)

T-1 Kiser + T-2 Kiser + T-3 + min flow t/g Output (MWh)





























































Annual Total or Annual Average





    Swift River Hydro Operations delivered the T-2 generator that it planned to install after the project was purchased and in the second year SRHOCO installed the rehabilitation Leffel B2 turbine at T-2.  The T-2 turbine was machined and balanced at the SRHOCO machine shop in Wilbraham, MA and a PLC automated switchgear was designed and installed by Olson Electric of nearby Methuen. This was the first phase of the work that will be continued in 2012

T-2 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 original 1.92 MW of capacity designed and installed in 1918.  The plant is now qualified as a Settlement Only Generator (SOG) and receives monthly capacity payments from ISO-NE, which is transferred to RMLD along with the sale of energy and RECs to RMLD. 

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 uncertainty because in 2007 and 2011during the spring floods the 60- year old penstock was damaged by ice and logs that had passed over the dam to break steel bands around the penstock and to puncture the dovetailed wood staves.  The penstock was repaired by SRHOCO, but to pay for it, Pepperell Hydro took out an emergency $225,000 life extension loan to extend the penstock's life a few more years.  Over 275 steel bands were replaced and four of the nearly 70 saddles that support the penstock were replaced. It is, however, time to replace the whole penstock as the current one lives on borrowed time.  We propose to replace the wood with a steel penstock that needs only 8 saddles.


The wooden penstock was replaced about 1955.  Look at the number of concrete saddles it used.

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.  Pepperell plans to mobilize in June 2012 to replace the penstock with a steel penstock in 2 plus months.  There are several concrete and equipment repairs planned during the summer shutdown.

The haul road for removing the old penstock and installing the steel penstock was built in May 2011.

Annual repair of flashboards is necessary in spring after ice out. Note crew safety harness are used.

The concrete wall protecting the penstock was washed out by overflow from storm drains in the bridge.

Pepperell Hydro repaired a wall along the river beside its wooden penstock in 2010. Today there is a sturdy interlocking concrete block wall anchored into the embankment, covered with riprap that cannot be undermined by river flows or road drainage.

In July 2012, Pepperell Hydro received a commitment letter from Webster Five Cents Savings Bank for refinancing of its existing loan together with a new SBA loan for 40% of a $5.3 loan to replace the 60+ year old wooden penstock with a steel penstock, and at the same time replacing two of the existing runners with Kiser Hydro turbines of greater efficiency and capacity and installation of a min-flow turbine to be located at the dam beside a new downstream fish passage facility.  PHC decided to prepare for a FERC license application and worked throughout 2012 on consultation for the design of the fish passage and min flow discharge rate (cfs flow).  Click on the report of the construction which began when the intake gates were closed and penstock removed in September 2012.


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