Sediment increase growing concern at Conowingo Dam

The Conowingo Hydroelectric Dam in the lower Susquehanna River provides more than half of Maryland's clean, renewable energy. But now concerns are turning to a dirty side effect of the dam, a build-up of sediment from upriver since the dam's completion 86 years ago.

"It's gotten to the point where some people say it's full," said Col. Trey Jordan, commander of the U.S. Army Corps of Engineers, Baltimore District.

There's an estimated 180 million tons of sediment behind the Conowingo Dam. To put that in perspective, that's enough to fill 80 M&T Bank Stadiums.

"During storm events and things, this huge amount of sediment, nitrogen, phosphorus is all released," said Ron Fithian, Kent County Commission president and chairman of the Clean Chesapeake Coalition "Comes roaring down the Chesapeake Bay with a vengeance and destroys any chance for the Chesapeake Bay to survive."

The Clean Chesapeake Coalition is a group of leaders from nine rural Maryland counties, who are pushing for the sediment behind the dam to be scooped out and moved elsewhere. It's a process called dredging.

"I'm here to tell you that the Chesapeake Bay is today, deader than it's ever been in its life," Fithian said. "And we think it's due to the sediment, the concentration of sediment."

The U.S. Army Corps of Engineers, Baltimore District, is wrapping up a three-year study on the issue. The Lower Susquehanna River Watershed Assessment was prompted by Tropical Storm Lee in September 2011.

The storm sent an estimated four million tons of scoured sediment, along with nitrogen and phosphorus, over the dam and into the Chesapeake Bay. Satellite photos taken from NASA's Terra satellite following Lee show a brown plume of water flowing to the bay. Though the picture is striking, Col. Jordan said the preliminary findings of the study tell a slightly different story.

"About 20 percent of the brownness entering the bay came from behind the dam," he said. "The other 80 percent we found, came from above the dam."

But Col. Jordan said the study also found that overall, sediment was not the biggest polluter of the bay following Tropical Storm Lee.

"Whether it was from behind the dam or upstream that reached the bay, that the sediment didn't cause the most impact to the bay, rather it was the nutrients," he said.

Still, Chip McLeod, attorney for the Clean Chesapeake Coaltion, said the 20 percent figure should not be downplayed.

"Even if it is just 20 percent, you have to ask yourself, 20 percent? What's the real number?" McLeod said. "Forget about percentages, what's the volume? It's a lot of pollution."

The assessment also explored options for dealing with the sediment, including the cost of dredging it. Col. Jordan estimates that dredging just 15 percent of it would come with a price tag of anywhere between a half-billion to $3 billion.

"If you wanted to take all 80 football stadiums out, we don't have a figure for that because it's astronomical," he said.

Conservationists like Lower Susquehanna Riverkeeper Michael Helfrich said the issue needs to be studied even further before any actions are taken.

"We don't know if it's cheaper to try and address the material upstream, or if it's cheaper to dredge," Helfrich said. "It's all about finding the most cost effective ways to deal with problems."

But with Exelon Corporation's license to operate Conowingo expiring on September 1st, some are pushing for action now. Under the current license, Exelon has no obligation to deal with the sediment, which sits in the 14 square mile Conowingo Pond behind the dam. The company is seeking a new 46-year license.


"The coalition firmly belives that no long-term license, should be issued for the operators of that dam, without some condition to dredge and then maintain the reservoir," McLeod said.


State Senator Bryan Simonaire, R-Anne Arundel, sponsored a resolution asking the federal government to authorize and help fund the dredging of the sediment. It passed the Senate, but died in the House.


"This is something that needs to be addressed, now," Sen. Simonaire said. "I think the federal government needs to be involved because it's not just a Maryland issue, but it's a regional issue as well."


The Federal Energy Regulatory Commission (FERC) is expected to issue Exelon a one-year license extension, while the company awaits the findings of several environmental impact studies.


"You don't want to spend money on something that's not going to be effective," said Kenneth Poletti, general manager of the Conowingo Dam. "So we want to make sure that whatever measures are taken, that they're effective and they're cost-effective for all stakeholders."


In the meantime, Helfrich said the states in the watershed should continue the work they've been doing to reduce the amount of pollutants they contribute to the bay.


"The biggest problem is that you can't really see improvement that much when you're looking at the body of water," Helfrich said. "But when you look at the science,

at the data, you can see that the numbers have gone down."


"I think we can all get there, if we don't find just one scapegoat, keep doing our work and we make sure that we address scienfically, the big issue behind me here," he added.


Exelon has spent five- to six-million dollars on more than 30 studies that will form the conditions for its license renewal. The new conditions are expected to include provisions for monitoring sediment levels. A draft of the U.S. Army Corps of Engineers study is expected in Septemeber, with the final report due later this year or early next.

Print this article Back to Top