Dishing the Dam Dirt, Dealing with Sediment at the Conowingo Dam


CONOWINGO DAM, Md.—A 14-mile reservoir behind the Conowingo hydroelectric generating dam in northern Maryland stops 2 million pounds of sediment every year from flowing into the Chesapeake Bay. But another one million pounds get through, burying underwater grasses that support sea life and adding to the bay’s myriad pollution problems.

The reservoir that stores the sediment, essentially dirt and other material carried by the water, is expected to reach capacity within 20 years, after which all of the sediment will get through the dam, putting the bay’s health further at risk.

Exelon Power, which owns the Conowingo Dam, is negotiating a new license with the Federal Energy Regulatory Commission that would last for 46 years. State officials and others say the time is now to resolve the sediment buildup.

“This is the moment in time when these issues will be addressed,” said Ann Swanson, executive director of the Chesapeake Bay Commission, a tri-state legislative assembly representing Maryland, Virginia and Pennsylvania.

State and federal agencies are studying possible solutions, with the three-year Lower Susquehanna River Watershed Assessment to be completed by September 2014.

But the solutions will not be simple, and the question remains: Who will pay for them?

“There’s no silver bullet in this,” said Bruce Michael, resource assessment service director for the Maryland Department of Natural Resources, who is working on the study. “We’re not going to come up with one magical thing that’s going to be cheap that we’ll be able to implement quickly.”

Exelon Power is waiting to see what the study finds before making any conclusions on who will fund it.

“Exelon believes it should be a shared approach,” said Robert Judge, Mid-Atlantic regional manager of Exelon Power’s communications. “Exelon thinks this needs to be a regional discussion, to look at the models and see what the next steps would be.”

Swanson said the cost would be prohibitive and far exceed what Exelon makes from power generation.

“It’s widely recognized that no one entity could pay for this,” she said.

And after all, it is not Exelon’s sediment. If the Conowingo Dam was not there, all of the sediment flowing through New York and Pennsylvania down the Susquehanna River would pass freely into the bay.

Sediment comes from the land, said Harry Campbell, Pennsylvania executive director of the Chesapeake Bay Foundation.

It is dirt. It is clay. It is little pieces of earth, matter that settles at the bottom of a liquid.

It comes from construction sites, agricultural fields, poorly maintained logging operations, roadside ditches—any place that doesn’t have adequate vegetation to hold soil in place.

Environmentalists call these vegetation buffer zones, areas of grass and trees that hold dirt in place during rainstorms.

Parking lots, roads and large areas of flat cement do not have buffer zones, and the oils, pollutants and sediment from the roads find their way into waterways when it rains, a process called stormwater runoff.

When it reaches the bay, it settles on top of underwater plants, burying them and preventing future root growth. The plants might have been food or home to other marine life, and shelter for fish and crabs.

While nutrients like sediment, nitrogen and phosphorous are necessary in very small amounts, in large quantities, they disturb the balance of the ecosystem.

“Nature is seeking equilibrium,” Campbell said.

The small soil particles block out sunlight, which interferes with photosynthesis in underwater plants and grasses, decreasing oxygen that is important for sustaining aquatic life.

“As that cumulatively takes effect in large areas of the bay, it has a deleterious impact on the healthy condition of the bay,” Campbell said.

Environmentalists have been working to limit stormwater runoff as a solution to the sediment buildup behind the dam, but that effort relies on a cooperative effort among New York, Pennsylvania and Maryland.

The Susquehanna River begins in Cooperstown, N.Y., and the sediment load increases substantially south of Harrisburg, Penn. The river ultimately contributes 25 percent of the Chesapeake Bay’s total sediment load.

The Conowingo Dam is about five miles from the Pennsylvania border and 10 miles from the bay, and there are three dams north of it in Pennsylvania.

But the reservoirs behind the other dams are full, and only the Conowingo has storage left to hold sediment.

Exelon Power is studying possible solutions as part of its negotiation process that began with a pre-application in 2009. The Federal Energy Regulatory Commission asked that Exelon file a sediment management plan with its final application next year.

Among the possibilities are dredging the Conowingo Pond, the 14-mile reservoir that still has storage capacity north of the dam, and using the sediment for a number of different projects—from parklands to quarries, maybe even brick-making, Swanson said.

Another option would be to allow sediment to pass through the dam at certain times of the year that might be less damaging for the bay, but that would interfere with the dam’s operation and would need Exelon’s support, Michael said.

“It’s going to be difficult environmentally and infrastructure-wise,” Campbell said, explaining that the sediment is like wet concrete and could be toxic and very difficult to move.

The Lower Susquehanna River Watershed Assessment will be releasing a list of possible solutions over the next six months. Michael hopes the public will get involved.

But even if the sediment storage issues at the dam are resolved, Campbell said they are a temporary fix to an ongoing problem.

There’s a myriad of technical and economic considerations to deal with what’s behind those dams, Campbell said. And they don’t solve the long-term problem of sediment entering the river to begin with.

“It’s sort of like putting a bandaid on a gunshot wound,” he said. “If we don’t turn off the sources—the sources coming in from the land—if we don’t get a handle on that, they may buy us time but not a solution. You have to start at the source.”

Even if we remove that sediment, it will accumulate again behind the dam, he said. It buys time, but also does not deal with the quantity of nitrogen or phosphorous entering the bay, which could be controlled by decreasing stormwater runoff.

Campbell said some argue Exelon Power should be responsible for dealing with the sediment since they own the dam. But others say it is not their sediment.

“That’s going to be a point of conversation,” he said. “If there is anything that can and should be done technologically and economically, who undertakes the lion’s share?”

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