Talen Energy shares details on Spillway Upgrade Project, efforts to prioritize safety, reduce impacts

In this photo by Middle Susquehanna Riverkeeper Association Board President Michael Kinney, the Lake Chillisquaque spillway is shown to the left of the dam. The update project will close the section of Chilisuagi Trail (and the Planet Walk) between the dam and the boat launch parking lot for most of the duration of the project, which is expected to last approximately 12-18 months.

In an effort to prioritize safety and minimize impacts to visitors to the Montour Preserve, neighbors and local communities and the wildlife that calls the region home, Talen Energy has been carefully planning and making modifications to its impending Spillway Upgrade Project near Lake Chillisquaque’s manmade dam, according to Talen Energy Director of Corporate Communications Taryne Williams.

This includes lowering the lake’s water level, using controlled, low-leveled blasts to loosen and remove rock (in place of more intensive blasting) and timing excavation and construction phases to avoid peak migration and nesting timelines, she said.

“In addition to protecting the safety of visitors to the Montour Preserve and neighbors in the community, the project contractors will focus on minimizing impacts on wildlife and their habitats,” she said of the project, which will begin excavation in May. “This includes the eagles that nest at the Montour Preserve and the birds that are there during their migratory journey.”

A necessary upgrade
A high-rainfall event in 2018, where 4-6 inches of precipitation fell within 24 hours, led to erosion of the spillway for Lake Chillisquaque at the Montour Preserve.

Immediate repairs and improvements were made, but it was apparent the structure needed a long-term upgrade, and the event triggered an effort with the PA Department of Environmental Protection and Army Corps of Engineers that has led to a new Spillway Update Project that is preliminarily kicking off at the preserve and expected to last upwards of 18 months.

“This project represents an opportunity to upgrade and modernize the spillway to improve its functionality and extend its longevity,” said Williams. “The project will expand the spillway and install a drop structure that will help slow the flow of water from the lake during significant rainfall events. After an extensive three-year permit review and approval process, we look forward to completing it.” 

A dam spillway is a safety structure that allows excess water to flow out of a reservoir in a controlled way, preventing the dam from overtopping and failing. It is, basically, an extra safety measure, for those living downstream, according to Bob Stoudt, director of the Montour Area Recreation Commission.

“The spillway is an engineered component of the dam — essentially a reinforced, man-made channel — which allows water to safely flow in a controlled manner around the dam into Chillisquaque Creek during times of extremely high flows,” he said during an interview with The Daily Item. “The structure protects the dam from damage, thereby protecting downstream homes and properties.”

That theme of safety will be a priority that permeates the project from start to finish, according to Williams. As a precautionary measure, lake levels will be lowered throughout the project to minimize the impact of any significant precipitation events.

“An emergency plan for the lake already exists, and that plan will be used in the event of an significant rainfall event,” she said. “Talen has met with the local EMAs regarding the project, and they are aligned. Additionally, a tabletop exercise that includes Talen and EMA partners is also scheduled.”

Impacts to wildlife have also been scrutinized beforehand, according to Williams, who said that a bald eagle study was done using the US Fish and Wildlife Service’s online mapping tool to determine that eagle nests are outside of the “defined mitigation area” and the excavation and construction phases of the project “will be completed before the migratory birds return to the Montour Preserve. No impacts to fish or other inhabitants of the lake are expected.”

Preliminary work has started
This early preparation for the project has already begun and will include laying stone for a construction entrance, staging equipment, erecting fencing, installing silt socks and performing some minor excavation work.

Excavation phase
According to Williams, during the excavation phase, the existing spillway channel will be expanded to accommodate a roller compacted concrete (RCC) drop structure and stilling basin. This phase is expected to start next month and last through late summer. 

“While the majority of the excavation will be done using heavy equipment, it will be necessary to use controlled, low-level blasts to loosen and remove select sections of rock below the surface of the existing spillway channel,” said Williams. “In order to keep the lake, preserve and its visitors and inhabitants safe, the blasting will consist of small, controlled blasts that engineers characterize as being of a magnitude similar to a tractor trailer driving by on a 2-lane road.”

Williams added that it is estimated that this will occur approximately once a week for a handful of weeks, last for only a few minutes each, and be limited to daytime hours.

“The project specifications require that the contractor adhere to rigorous standards regarding the blasting operations. Each event must be approved by PADEP and notifications will be made to neighbors well in advance. Updates also will be posted on the project website,” she said. “Access to nearby areas at the Preserve will be limited and traffic controlled immediately before and during these short blasts.”

According to Willliams, excavated material will be hauled to a disposal area on the Montour plant property. 
“Increased truck traffic is expected during business hours on weekdays in summer and early fall,” she said. “The project team will coordinate with the applicable agencies on necessary permitting and work to minimize disruption.”   

Construction and restoration
Following excavation, the roller-compacted concrete (RCC) drop structure and stilling basin will be constructed on site and stalled within the existing auxiliary spillway channel “to safely convey spillway discharges to the valley floor,” according to Williams.

“This phase is expected to take place from late summer to late fall, with finish work potentially occurring in spring 2027 following the project’s winter pause,” she said.

Final grading will be completed during the restoration phase.

“Disturbed areas will be restored with grass, which is the preferred cover to support inspections and observe deficiencies,” Williams said. “Grass cover will support permanent stabilization of the site.”

For more info
Talen Energy plans to provide updates on the project via its own dedicated website – www.spillwayupgrade.com – where the public can sign up to receive updates directly and check out graphics, timelines and more. Updates can also be found via social media sites for the Montour Area Recreation Commission and Middle Susquehanna Riverkeeper Association.