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Water runs through Conowingo Dam hydroelectric plant during an open house.
Water runs through Conowingo Dam hydroelectric plant during an open house. (Steve Ruark / Baltimore Sun Media Group)

Gov. Larry Hogan's administration is requiring the owner of Conowingo Dam to find a way to trap pollution that flows down the Susquehanna River and into the Chesapeake, threatening progress in cleaning up the bay.

For decades, pollution has built up behind the Conowingo. But the dam is now at its capacity and no longer traps sediment and nutrient runoff from across Pennsylvania.

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Maryland Environment Secretary Ben Grumbles said a set of "stringent environmental conditions" imposed Friday is part of a broader strategy to speed bay cleanup "and hold our partners accountable for doing their part to create a healthier watershed."

Dam owner Exelon Corp. needs a water quality permit from Maryland to get a federal license to continue operating. The state issued the new permit with a requirement that Exelon develop a plan to continue trapping the same amount of pollution the Conowingo always has — millions of pounds of nitrogen and hundreds of thousands of pounds of phosphorus every year.

Sediment and nutrients like nitrogen and phosphorus degrade the Chesapeake ecosystem by clouding waters and blocking sunlight, and by fertilizing algae blooms that strip the water of oyxgen.

The permit also requires Exelon to more frequently collect floating trash and debris that builds up at the dam's edge, potentially through a solar-powered trash wheel like one that has helped clean up Baltimore's Inner Harbor in recent years.

The administration had been working with Exelon and environmental groups for the past two years to find a long-term solution to prevent pollution from spilling through the Conowingo. But state officials said they had to abandon talks of a settlement with Exelon and impose the water quality conditions on the company because of a looming May deadline to keep the dam in compliance with the federal Clean Water Act.

Exelon officials said in a statement they "will continue to work with the state, local communities and environmental organizations to find a comprehensive and long-term solution" to address pollution concerns, while emphasizing that "the dam does not produce any pollution itself." The state and Exelon have been at odds over how much responsibility the company should take because of that.

"We are reviewing the State of Maryland's water quality certification now and will evaluate next steps to determine the long-term viability of the Conowingo Dam," they said.

The Conowingo was built in 1928. At that time, the 252 megawatts of electricity it produced made it the second-largest hydroelectric project in the United States, behind Niagara Falls, according to Exelon. It now produces 500 megawatts of power, enough for nearly 200,000 homes.

The dam costs $40 million a year to operate, the company said.

It sits about 10 miles from the Chesapeake in the lower Susquehanna, which collects runoff from a 27,000-square mile area covering half of Pennsylvania and parts of upstate New York. The river provides about half of the bay's fresh water, but also sends heavy loads of nitrogen and phosphorus from farms.

Exelon is in the midst of applying for a new federal license to operate the dam as a hydroelectric power station for the next 50 years. That process gave Maryland officials a rare chance to address Susquehanna River pollution, because the state water quality permit is a requirement for federal re-licensing.

"We're telling Exelon, in order to get their 50-year re-licensing, they have to take significant steps to reduce that problem," Grumbles said.

Environmental groups that have pressed Exelon to help address the problem and pay for solutions mostly praised the state's actions.

Alison Prost, acting vice president of the Chesapeake Bay Foundation, said she was glad to see that the permit requires Exelon to improve fish passage through the dam and also change the way it releases water to reduce harm to downstream fish. She said the permit "ensures a cleaner Bay, but gives Exelon clearly defined options for fulfilling its clean-up responsibilities."

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But Betsy Nicholas, executive director of Waterkeepers Chesapeake, said the document gives Exelon too much flexibility. The state is requiring Exelon to develop its plans for trapping sediment and nutrients by the end of next year. Until that plan is developed, she said, it won't be clear whether the company is adequately limiting the pollution.

"What happens with this waterway has a tremendous impact on the nation's largest estuary," she said. "We need to get it right."

Asked if the requirements ultimately could lead to higher electricity costs for Marylanders, a Hogan spokeswoman cited the flexibility Exelon is being given to develop a means of controlling the runoff. She said that will allow the company "to comply in a way that makes sense for their business model."

The work Exelon will be required to do is separate from a small dredging project the Hogan administration has ordered. Officials tapped a business partnership called Northgate-Dutra Joint Venture in December to explore how to remove some of the 31 million cubic yards of sediment that have built up behind the Conowingo.

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