Adding Power to a Non-Powered Dam: Mahoning Creek

More than 70 years in the making but less than a year in the execution, the 6-MW Mahoning Creek Hydroelectric Project, developed at an existing dam, is now providing clean, reliable power to residents in western Pennsylvania. 

By Kristina M. Johnson, E. Mark Garner, John R. Collins and John Strough

Kristina M. Johnson is chief executive officer, Mark Garner is managing director/hydropower, and John Collins is executive vice president and director of business development with Enduring Hydro LLC. John Strough is senior project manager with Hydro Consulting & Maintenance Services Inc.

The U.S. Army Corps of Engineers (USACE) broke ground on Mahoning Creek Dam, a flood control structure that also provides recreational opportunities in the Allegheny River basin in western Pennsylvania, in 1939. By 1941, the concrete dam was finished. The design included a conduit that would allow the potential energy of water stored behind the dam to be used to produce hydroelectric power. However, the plans to develop hydropower at this dam were postponed due to steel shortages associated with the country’s accelerating mobilization efforts for World War II.

Seventy-two years later, Enduring Hydro LLC, a Maryland-based company, fulfilled the vision of those early engineers. In a public-private partnership with the USACE’s Pittsburgh District and enabled by the 2009 American Recovery and Reinvestment Act and Pennsylvania Alternative and Clean Energy Program, Enduring Hydro constructed a 6-MW hydroelectric facility utilizing Mahoning Creek Dam.

The Mahoning Creek Hydroelectric Company Project is located on Mahoning Creek in Armstrong County, Pa. Mahoning Creek Dam is one of 16 facilities in the USACE’s Pittsburgh District used to provide flood protection to the lower Allegheny River Valley and upper Ohio River. This concrete gravity dam is 187 feet high and 926 feet long. The hydro project includes a 50-foot-high intake structure attached to the upstream face of the dam equipped with a removable trashrack and a vertical slide gate. A secondary penstock closure device, a butterfly valve, is located in a concrete vault downstream from the dam. A steel liner pipe was inserted into the existing conduit through the dam. Water is conveyed from the dam through a 1,090-foot-long, 10-foot-diameter buried penstock to the powerhouse containing two Francis turbines (4 MW and 2 MW) with two vertical-shaft generating units.

The electricity produced is transferred to West Penn Power at the nearest point of interconnection via an underground 1,200-foot-long 25-kV line. A 10-year power purchase agreement was in place before construction of the project began with ground-disturbing activities on Jan. 31, 2013. Commercial operations commenced on Dec. 26, 2013.

The Mahoning Creek project was designed to produce more than 20,000 MWh per year for more than 50 years, which is enough energy to power 1,800 homes with 100% clean electricity. Furthermore, this hydropower facility will avoid 20,000 tons of C02, 20 tons of N0x, and 460 grams of mercury emissions on an annual basis, equivalent to taking 4,000 cars off the road or planting 1,000,000 fully grown trees with respect to the reduction in greenhouse gas emissions.

The liner pipe was installed through Mahoning Creek Dam and the opening in the bulkhead plate was cut to ensure optimal transmission of water stored in the reservoir to the penstock when the roller gate is open.

In addition to the above-mentioned environmental benefits, retrofitting non-powered dams creates well-paying, highly-skilled crafts jobs, thereby economically empowering local communities. The project created more than 100 jobs utilizing local labor in Armstrong County. The project developer hired several Pennsylvania firms, including Hanlon Electric in Monroeville, Renick Brothers in Slippery Rock, and Hydro Consulting and Maintenance Services Inc. in York.

According to Oak Ridge National Laboratory’s “Assessment of Energy Potential at Non-Powered Dams in the United States,” an April 2012 study, there are 45 non-powered dams in the Commonwealth of Pennsylvania that could collectively provide hydropower capacity of 630 MW. From our experience, if these 45 projects were developed they potentially could create more than 10,000 jobs, power 200,000 homes, and take the equivalent of 400,000 cars off the road.

Innovations in the plant design

The hydro project was designed by Mead and Hunt of Madison, Wisc., under an original contract with Advanced Hydro Solutions (AHS) of Fairlawn, Ohio. Enduring Hydro bought Mahoning Creek Hydroelectric Company, the owner of the 50-year Federal Energy Regulatory Commission license, from AHS on July 31, 2012. We worked closely with Mead & Hunt and Kleinschmidt Associates of Pittsfield, Maine, to obtain the Section 404 and 408 permits from the USACE and the 401 Water Quality Certificate from the Commonwealth of Pennsylvania’s Department of Environmental Protection (PADEP), which needed to be in place before breaking ground in January 2013.

During the construction process, an intake structure on the upstream side of the dam was installed and then sealed before the concrete plug downstream was removed, obviating the need for a cofferdam. A dam liner pipe was inserted to connect with the penstock. The project’s penstock, supplied by Northwest Pipe Co. of Vancouver, Wash., is 10 feet in diameter and extends 1,090 feet downstream from Mahoning Creek Dam before bifurcating into two smaller sections. The bifurcated piece is located just before the penstock enters the powerhouse. In total, 54 pieces of 20 feet in length were placed and welded on site.

The Mahoning Creek Hydroelectric Company powerhouse contains a control room and two turbine-generator units. The 4-MW generator is shown in the foreground and the 2-MW generator is visible in the background.

The buried penstock bifurcates into two 110-foot-long sections, one 8-foot-diameter section and one 6-foot-diameter section. The hydro plant was designed so that during low-flow periods, only the 2-MW unit, which can generate power with a minimum flow of 120 cubic feet per second (cfs), operates. During the shoulder periods (flow between 350 and 500 cfs), we expect the 4-MW unit, which requires a minimum flow of 350 cfs, to operate. Finally, during the periods when water flows exceed 500 cfs, both the 2-MW and 4-MW units will produce power. Environmental considerations in the FERC license and the adaptive management plan with the USACE require a minimum bypass flow of 60, 40 and 30 cfs, during the low-, shoulder and high-flow periods, respectively.

All turbine components including the draft tubes, spiral cases, runner, distributor and shut-off valves were supplied by China Harbour Engineering Company Ltd. (CHEC) No. 9 of Beijing, China. The generators, switchgear, and control system were supplied by Hyundai Ideal of Mansfield, Ohio.

The project’s 10-foot-diameter penstock extends 1,090 feet downstream from Mahoning Creek Dam before bifurcating into two smaller sections just before the penstock enters the powerhouse.

The powerhouse’s switchgear and controls are sensitive, complex technologies. To mitigate the technological risk of installing separate interfaces in the powerhouse, Enduring Hydro worked with PCX of Clayton, N.C., to skid-mount the instrumentation controls prior to installation. PCX integrated various technologies in their factory and their expert team assembled a comprehensive skid that was installed in one piece in the powerhouse.

The dam liner pipe was installed and the opening in the bulkhead plate was cut, ensuring optimal transmission of water stored in the reservoir to the penstock when the roller gate, supplied by Steel-Fab of Fitchburg, Mass., is open. The valve vault built just downstream from the dam liner pipe includes the butterfly valve, supplied by Henry Pratt Co. of Aurora, Ill. This construction process required detailed planning and coordination between the Enduring Hydro team, FERC, and the USACE.

Innovations in the permitting, approval and construction process

To keep the project on schedule, the Enduring Hydro team worked diligently to obtain the permits and approvals required from the various stakeholders and governing agencies, including the USACE (Pittsburgh District, Great Lakes and Ohio River Division, and headquarters), FERC, PADEP and Pennsylvania Fish and Boat Commission (PAFBC).

To comply with the various regulatory processes and approvals and maintain the project’s tight construction schedule, Enduring Hydro planned the construction activities in stages. Each stage corresponded to the receipt of the regulatory approval over a four month period of time, as shown in Table 1 on page 16.

The Enduring Hydro team credits the strong public-private partnership with the USACE, FERC, PADEP, and PAFBC for the successful and timely completion of the project.


Enduring Hydro faced several major challenges while completing the project. First and foremost was obtaining the necessary permits and notices to proceed in a timely manner. Our consultants at Mead & Hunt and Kleinschmidt Associates were invaluable in helping us anticipate and address the concerns of these key regulatory partners to obtain all the approvals. This was the first greenfield hydroelectric project built in Pennsylvania in more than 20 years and therefore the first plant built at a USACE dam post-Hurricane Katrina with the new 408 permit requirement.

The second major challenge was the narrow site condition. The access point, from the McRae Furnace Bridge across a runoff stream from Mahoning Creek to the dam, was often referred to as a “bowling alley,” allowing for a single ingress and egress. This required efficient construction management in order to maintain the project’s tight construction schedule.

A third challenge involved assessing the geotechnical conditions where the penstock would be buried, prior to receiving the notice to proceed on ground-disturbing activities. Once we had full access to the site, we discovered that the solid rock foundation was deeper than originally anticipated. While the lack of solid rock led to less rock excavation, it did require proper filling material to be sourced and installed to support the penstock. The lack of rock also required the installation of rock anchors for the stilling basin wall between the penstock and the bank of the stilling basin just downstream of the dam.


As a result of the teamwork and collaboration between Enduring Hydro; its suppliers and vendors; and the USACE, FERC, PADEP and PAFBC, the project began commercial operations on Dec. 26, 2013. Achieving commercial operations prior to Jan. 1, 2014, allowed the project to qualify for the 1603 cash-back grant from the U.S. Treasury. Since commencing commercial operations, the project has produced about 12,000 MWh of electricity during the first half of 2014. We estimate the project will generate about 20,000 MWh in its first year of operation.

Effective Nov. 14, 2013, Mahoning Creek Hydroelectric Project was certified as a “Low Impact” facility by the Low Impact Hydropower Institute (LIHI) Certification Program, an independent non-profit organization. LIHI certification is granted to projects that comply with LIHI’s rigorous review process and meet its goals of achieving required clean energy benefits while meeting strict environmental standards.


The Mahoning Creek Dam powerhouse is named for E. Mark Garner, a long-time champion of hydropower throughout his 25 years in the industry. As an engineer, chief executive officer, and business leader, he has advocated for innovation and provided value engineering to improve hydropower into the 20th and 21st centuries. Through his leadership, Mahoning Creek Dam produced electricity in 2013, carrying out the vision of the original dam builders from 1939. We would also like to acknowledge the contributions of David Nammour and David Fox, project engineers; Jennifer Mesirow, controller; Ginger Lew, managing director; Marcus Switzer, compliance and regulatory; Andrew Longenecker, senior associate; and Smitha Ramakrishna, analyst, all part of the Enduring Hydro team.


About Enduring Hydro

The Enduring Hydro team is led by former U.S. Under Secretary of Energy Dr. Kristina Johnson, former chief executive officer of Voith Hydro Mark Garner, former chief finance officer of Constellation Energy John Collins, and former senior counselor to the White House National Economic Council Ginger Lew. Working with our senior associate Andrew Longenecker, controller Jennifer Mesirow, project engineers David Nammour and David Fox and chief of staff Marcus Switzer, this team brought on-line the first non-powered dam in Pennsylvania in more than 20 years. Our team is committed to helping clean our air by replacing carbon-based electricity with environmentally responsible, run-of-river hydropower at greenfield and brownfield sites.

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