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If there is any company equipped with the knowledge, expertise and manpower to take on a project as large as the Holtwood Hydro Plant expansion in Pennsylvania, The Walsh Group is one of the top names that come to mind.

Walsh has 14 regional offices throughout the United States and one in Canada, and it has completed many major projects throughout these regions. When the opportunity arose to bid the Holtwood Hydro Plant expansion, The Walsh Group knew it was ready to take on the challenge. The project broke ground in January 2010 and is scheduled for completion in March 2013.

The 100-year-old Holtwood Hydro plant is located on the Susquehanna River near Lancaster, Pa., and is owned by PPL Corp., Allentown, Pa. The hydroelectric facility currently features 10 turbines with a capacity of 108 megawatts.

When complete, the expansion will add two more turbines that will more than double the capacity by generating 125 additional megawatts – or enough energy to power 100,000 homes. When installed, the two turbines – manufactured by Voith Hydro of York, Pa. – re­portedly will be among the largest turbines in operation in the United States. The entire expansion project is budgeted at $434 million.

“We meet weekly with the owners and the other subcontractors to discuss the construction schedule as well as the plant’s operating schedule,” notes Dan Lucas, program manager at Walsh.

“Although it has been a struggle to maintain the aggressive schedule, Walsh has fallen behind to-date. However, utilizing good planning, good communication and good teamwork, Walsh is confident the project will be completed on time over the next 24 months.”

Saving Fish

PPL has considered the environmental impact to the migratory fish at the site since the construction of the fish-lift in 1996. “In addition to increasing the plant’s operating capacity, we will also improve the attraction flows to the fish-lift entrances for the migrating American Shad and River Herring that spawn in the Susquehanna river,” Lucas says. This will be accomplished by widening and deepening the plant’s tailrace not only to handle twice the water volume with the new turbines, but also to create a 4-to-7 foot per second flow velocity channel to attract the migrating fish to the fish-lift for further upstream travel.

“The new Kaplan-style hydro turbines also ensure greater fish survivability,” says Dale Zeisloft, senior project manager at PPL. “Studies show a survival rate of more than 96 percent for downstream fish migration through the Kaplan turbines in the new plant, which is a significant improvement over the 10 Francis-style units in the existing powerhouse.”

Another major player in tackling this project is the design team at Kleinschmidt Associates, Strasburg, Pa., an engineering firm whose expertise is focused on hydroelectric and dam projects. President and CEO Dr. Jacob Palmer claims he has a particular passion for projects such as Holtwood because the energy produced is renewable and non-climate changing. “Additionally, we are able to improve the native fish population and add recreational benefits to the neighboring communities,” he says. “PPL is a particularly good steward for the environment.”

Working Together

Palmer says working with Walsh has been a positive experience, where the design is being modified to assist with the constructability and/or sequencing of the work. For instance, the two companies worked collaboratively during construction of the Unit No. 1 draft tube extension tunnel. This portion of the work involved constructing a 34-foot-wide by 18-foot-tall tunnel located 65 feet below the top of a massive gravity concrete water diversion wall. To reduce the time and expenses, Walsh and Kleinschmidt have altered the tunnel boring sequence to allow for the new permanent center wall of the tunnel to be constructed early in the tunneling process so that it can be used for temporary support. This will allow simultaneous excavation of the remainder of the tunnel on each side of the new wall to be completed without any additional temporary supports for the tunnel roof.

To prepare the site for the construction of the new powerhouse, rock excavation had to be performed. Prior to this portion of the work, Walsh crews built a cofferdam to close off the existing forebay. “The excavation portion was a major undertaking,” Zeisloft says. “Crews had to drill, blast and excavate down 130 feet to achieve the depths needed for the new power station’s foundation.”

The blasting to remove the rock was performed by Maine Drilling & Blasting. The blasting had to be done in very controlled, six-foot sections to install the more than 16 miles of rock bolt anchors and dowels needed to stabilize the site.

The Ideal Mix

Concrete work began in December 2010. “Walsh teams have spent a significant amount of time to create the ideal concrete mix for this project,” Lucas says. “We believe we’ve come up with the best formulation that combines strength and longevity with setting speed for the mass concrete specifications.”

With more than 67,300 cubic yards of concrete for the project, Walsh built an on-site batch plant.

Hydro Consulting & Maintenance Services (HCMS) will assemble and install the new 65-megawatt Kaplan turbines and generators. “Because of the complexity of this project, coordinating this portion with HCMS was especially critical to the success of the project,” Lucas notes.