After Maryland leaders and energy executives wrestled over the future of the Conowingo Dam for more than a decade — even reaching an agreement in 2019 only to see it thrown out by a judge — they hoped they finally had a deal that everyone could get behind.

But within weeks of a $341 million settlement announced in October, the Eastern Shore group Clean Chesapeake Coalition challenged the new environmental certification issued by Maryland for the dam’s owner Constellation Energy, arguing that their closed-door negotiations violated state law.

Among the concerns recently raised in an appeal the coalition submitted to state and federal regulators, the coalition argues that the closed-door negotiations locked Eastern Shore counties out of the process. The group also says the settlement doesn’t do enough to force Constellation to remove the accumulation of sediment that pours through the dam, polluting the bay.

The group’s appeal could disrupt the settlement brokered between Gov. Wes Moore’s administration, environmental advocates and Constellation, the energy powerhouse based in Baltimore. The governor, Constellation’s CEO and leading environmentalists stood side-by-side at the foot of the dam in October to unveil their new agreement.

Clean Chesapeake attorney Charles D. “Chip” MacLeod attended that announcement at Moore’s invitation but said he and Eastern Shore officials should have been allowed to weigh in on the settlement.

For Eastern Shore leaders, “this came out of nowhere,” MacLeod said.

“We’ve been scrambling ever since to understand: What is the deal? What does it really mean?” he said.

Just how serious a threat this coalition’s appeal poses to the dam’s relicensing remains to be seen.

MacLeod said the coalition will discuss taking their challenge to court if the Maryland Department of the Environment doesn’t grant their appeal. State environmental officials, meanwhile, traveled to Dorchester County last week to make their case to local officials on the settlement’s benefits.

The agreement is meant to pave the way for relicensing Conowingo, a nearly century-old dam that remains Maryland’s largest generator of renewable power, for another 50 years. The terms hinge on approval of the deal and state certification by federal energy regulators.

MDE was “puzzled” by the timing of the challenge, since a public comment period on the yearslong dam settlement closed in 2023, said Jay Apperson, an agency spokesman.

“It is reckless to come in at the end of the process and try to halt real progress for Maryland,” Apperson said.

He added that feedback from these Eastern Shore counties helped inform the new agreement’s dredging provisions, and disrupting the relicensing risks stalling or even eliminating dredge and other water quality-focused projects from the deal “because it will plunge us back into even more years of delay with no action.”

The agency will respond to the coalition’s submission “as appropriate,” Apperson said.

The Conowingo Dam served as a buffer for nearly 80 years, trapping and preventing sediment and agricultural runoff from flowing down the Susquehanna River, which supplies about half of the Chesapeake Bay’s fresh water. But as the reservoir north of the dam filled up in the last decade, the millions of tons of sediment and nutrients that had accumulated there became a growing threat to the bay’s health.

In heavy rains, those pollutants surge through the dam’s floodgates.

This sediment buildup deeply worries bay advocates, and re-permitting Conowingo, after its license lapsed in 2014, has not been easy.

After earlier efforts encountered legal troubles, former Gov. Larry Hogan’s administration reached a settlement requiring the dam’s operators to invest over $200 million into environmental projects.

After a suit from environmental groups, a federal court voided that deal in 2022, the same year Moore was elected governor.

The Moore administration and environmental advocates have touted their agreement as a big improvement over the scrapped Hogan deal.

Among its provisions is $18.7 million to study and potentially begin dredging behind the dam, a step also being studied by the U.S. Army Corps of Engineers.

In a statement, Constellation spokesperson Paul Adams pointed to years of “difficult negotiation” that resulted in a deal to preserve the dam’s operations.

“MacLeod’s filing risks to delay the implementation of this historic agreement and the many investments to protect Chesapeake Bay,” Adams said.

MacLeod, though, argued that dredging has already been studied extensively, and an appropriate agreement would include stronger provisions to ensure it happens. As the county attorney for Dorchester County, MacLeod said his group also has the backing of three other Eastern Shore counties: Cecil, Queen Anne’s and Kent.

Spokespeople and elected officials from Cecil, Queen Anne’s and Dorchester counties did not respond to emails Tuesday seeking clarification about their affiliation with the Clean Chesapeake Coalition, which formed in 2012.

Ronald Fithian, the Republican president of the Kent County Commission, is the coalition’s chairman and said his county fully supports the appeal. He expects the commission will commit financial support to the legal work at its next meeting.

For Fithian, a former waterman, the demands put on Eastern Shore communities to reduce bay pollution are unfair when so much of the estuary’s problems stem from nutrients flowing down from Pennsylvania through the dam.

The priorities of those Eastern Shore communities weren’t represented at the announcement event in October, Fithian said.

“I honestly came away from that thing pissed off,” he said.

The Eastern Shore group is not alone in raising alarm about the settlement.

Brookfield Renewable, a hedge fund-controlled company that owns two dams north of Conowingo on the Susquehanna, Holtwood and Safe Harbor dams in Pennsylvania, also submitted comments to federal regulators questioning terms of the settlement that imposed new requirements on its facilities despite being licensed separately.

Yet two environmental groups who sued over the Hogan administration’s dam settlement and helped broker the new one maintained Tuesday that the deal is the best outcome for the Susquehanna and the Chesapeake Bay.

Robin Broder, acting executive director of Waterkeepers Chesapeake, emphasized the 16 years of work by environmental advocates that went into securing these terms. The best way to protect the Chesapeake Bay and Lower Susquehanna River is to implement the settlement “promptly,” she said.

Lower Susquehanna Riverkeeper Ted Evgeniadis, whose group also sued over the prior settlement, has long wanted the silt dredged from behind the dam.

But this is no easy job, he said. It requires study and many regulatory approvals. Even if federal regulators relicense the dam tomorrow, Evgeniadis expects it would take at least four years for dredging to begin.

This agreement isn’t perfect, Evgeniadis said, but it’s a far better deal that the one inked under the Hogan administration.

“It needs to be implemented as soon as possible,” he said. “We’ve already spent a lot of time fighting over Conowingo Dam.”