Maryland Wants to Muck Out Exelon Dam to Save Chesapeake Bay

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By Leslie A. Pappas

One “big and dirty flush” from a Maryland dam could wipe out decades of efforts to clean up the Chesapeake Bay.

The Conowingo Dam on the Susquehanna River, a hydroelectric power station owned by Chicago-based Exelon Corp., is no longer blocking pollution from contaminating the Chesapeake Bay, and Maryland is pushing a $3.9 million plan to start dredging the backed up muck to protect the estuary.

“The sediment has value, but it doesn’t have value if it’s leaking through the dam into the Chesapeake Bay,” Maryland’s Secretary of the Environment Ben Grumbles told Bloomberg BNA. “Pollution prevention is the key.”

Maryland Aug. 31 is expected to solicit plans to dredge 25,000 cubic yards of the nearly 200 million tons of sediment trapped by the dam as part of a pilot program to reduce pollution. But the program is only the start given that 2 million to 3 million cubic yards of sediment accumulates each year, Roy McGrath, director of the Maryland Environmental Service, told Bloomberg BNA.

While the dredging is only a small step, Grumbles said it’s one piece of a “holistic strategy” to restore and protect the Chesapeake Bay.

Dredging could buy Maryland the time it needs to look at steps to reduce upstream pollution that eventually flows into the bay. But removing the 31 million cubic yards of sediment needed to restore the reservoir to 1996 levels would cost nearly $3 billion, the U.S. Army Corps of Engineers estimated, with another 3 million cubic yards of sediment dredged each year at a cost of $267 million annually.

“We all need to continue pollution prevention efforts upstream,” Grumbles said.

Exelon Won’t Fund Dredging

Exelon Generation Co. LLC agrees the problem is upstream pollution, and the company has balked at paying for the dredging operation. Exelon has spent about $7.8 million studying the issue since 2010, company spokeswoman Deena O’Brien told Bloomberg BNA in an emailed statement. The company found 70 percent to 80 percent of the sediment that washes into the bay during storms comes from upstream sources, and not from the Conowingo Pond.

Maryland has pushed the power company to contribute more to the dredging solution, even threatening to block the company’s bid to renew a license from the Federal Energy Regulatory Commission to operate the dam.

“Exelon Generation believes protecting the vitality of the Chesapeake Bay is a multi-stakeholder, multi-state issue,” O’Brien said.

The company “will support” Maryland’s plan to solicit dredging bids though it will not play a formal role, she said.

Diminished Dam Could Drive New Standards

The dam has reached “dynamic equilibrium,” according to a 2016 report Maryland issued with the U.S. Army Corps of Engineers. Dynamic equilibrium means that over time, the same amount of pollution and sediment flowing into the Conowingo reservoir is also flowing out. That diminished storage capacity means that a million more pounds of phosphorus from the Susquehanna will flow into the bay each year, Grumbles said.

“Some people are fixated on these extreme events,” Donald F. Boesch, president of the University of Maryland Center for Environmental Science, which is studying the chemistry of sediment in the bay, told Bloomberg BNA, “but it’s the year-to-year pollution that really matters.”

That added pollution will make it even harder for Maryland to meet its goals under the Chesapeake Bay watershed cleanup plan, a pollution “diet” that aims to reduce levels of pollutants to certain federal standards by 2025. Maryland is one of six states and the District of Columbia that fall in the 64,000-square-mile watershed and must stay within federally mandated pollution discharge limits known as total maximum daily loads (TMDLs).

When Environmental Protection Agency first laid out those pollution limits in the 2010 Chesapeake Bay TMDL, the agency estimated the Conowingo trapped 55 percent of sediment, 2 percent of nitrogen, and 40 percent of phosphorus.

The EPA is conducting a midpoint assessment of nitrogen, phosphorus, and sediment levels in the bay to develop the next phase of cleanup, and the Conowingo’s reduced capacity may force states to meet even more stringent pollution reduction targets.

Dredging’s Value Questioned

While Maryland hopes the dredging plan will buy the time necessary to tackle upstream pollution, some researchers and groups involved in the bay cleanup question whether it is worth the cost.

Pollutants such as nitrogen are water soluble and will pass through the dam whether it gets dredged or not.

The 2016 sediment study by the U.S. Army Corps of Engineers concluded that nutrients from upstream “are a bigger threat to water quality than just the sediment,” Sarah Gross, an Army Corps spokeswoman, told Bloomberg BNA in an email.

Dredging the Conowingo Dam “would result in only minor water quality improvements” to the Chesapeake Bay and “would be required regularly, if not annually, to achieve any net improvement,” Gross said.

The Chesapeake Bay Foundation, an environmental group focused on the bay’s health, argues that upstream states such as Pennsylvania and New York must do more to reduce nitrogen, phosphorus, and sediment runoff before it gets into the watershed in the first place.

Joel D. Blomquist, a hydrologist with the U.S. Geological Survey in Baltimore who has monitored sediment for 30 years, said scientists need to learn more about how sediment moves now that the dams have reached a dynamic equilibrium.

“There’s legitimate debate around the question of needing to dredge,” Blomquist told Bloomberg BNA. “We need to continue to decrease the amount of phosphorus and the amount of fine-grain sediments reaching the Chesapeake Bay,” Blomquist said, but “there are multiple strategies to do that.”

To contact the reporter on this story: Leslie A. Pappas in Philadelphia at

To contact the editor responsible for this story: Rachael Daigle at

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