More pollution has been sweeping past the Conowingo Dam since its reservoir filled with sediment a decade ago, allowing millions of pounds of nutrient pollution to wash downstream to the Chesapeake Bay and creating a costly cleanup problem.

But, some say they have — literally — dredged up a solution.

A new corporation, Conowingo Systems, proposes to excavate and remove some of the sediment building up behind the 94-foot-high dam on the Susquehanna River, thereby restoring its capacity to trap a portion of the pollution that would otherwise enter the Bay.

In December, the company unveiled a proposal to dredge as much as 20 million cubic yards of sediment — enough, it says, to fill the Great Pyramids of Giza more than six times. And they hope to start by the end of this year.

“We’re giving the jurisdictions a two-fer,” said Jeff Corbin, director of environmental policy and water markets with Restoration Systems, a North Carolina-based firm that offers market-based solutions to environmental problems and is a principal partner in Conowingo Systems. “We’re fixing the real problem for them, the sediment accumulation, and the second thing is we’re doing it in the most cost-effective way.”

The company says that the dredging would be paid for by selling water quality credits to others who need to offset the nutrient pollution they are generating elsewhere.

The idea is controversial. Dredging has long been considered an option too expensive to reasonably pursue, and many environmentalists contend the money is better spent elsewhere.

Dredging proponents say earlier cost estimates were dramatically overstated and that costs for other means of pollution reduction have been underestimated — and those alternatives, unlike dredging, would take years to produce results.

“This is a fix that happens relatively quickly” compared to land-based controls, said Deni Chambers, president of Northgate Environmental Management, which is partnering with Restoration Systems on the proposal.

A cloud over the cleanup

The Conowingo Dam has been a cloud over the Bay restoration effort for more than a quarter century. For decades after being completed in 1929, it trapped sediment and other pollutants washing down the Susquehanna, helping to reduce the amount of pollution reaching the Bay.

In the early 1990s, though, U.S. Geological Survey scientists warned that the 14-mile-long reservoir behind the dam was in danger of filling, at which point it would start sending more nutrients and sediment into the Bay, just 10 miles downstream.

When the Bay watershed states and U.S. Environmental Protection Agency completed their latest Bay cleanup plan in 2010, it was thought that the reservoir wouldn’t be filled until after the 2025 cleanup deadline. Therefore, any potential impact from Conowingo was not considered.

Workers extract samples of the sediment that has built up behind the Conowingo Dam on the Susquehanna River. Credit: Dave Harp / Bay Journal Media

Research in recent years, though, has concluded that the reservoir has reached its capacity and the threat has become reality. Computer models used by the Bay Program estimate that the annual loading of nutrients and sediment has grown by approximately 6 million pounds — which in turn increases the amount of pollution reductions needed to meet Bay cleanup goals.

That’s 12% beyond what states have committed to doing by 2025, and they are already struggling with that task. Further, the pollution would be most effectively controlled in Pennsylvania, which is upstream of the dam’s location in Maryland. But Pennsylvania is the farthest behind in meeting its goals.

The Bay Program in 2017 agreed to jointly support the development of a Conowingo cleanup plan that was separate from those being devised by individual states to meet their own goals.

The draft Conowingo plan, released in October, would cost more than $53 million annually to implement, and it warns that the states would ultimately have to shoulder the cost.

That price tag is within the range of a 2015 estimate produced by the Army Corps of Engineers and Maryland Department of the Environment, which put the dredging cost between $48 million and $267 million a year. As a result, most attention has focused on implementing various upstream practices such as forest buffers and cover crops, to help keep nutrients and sediment from ever reaching Conowingo.

Growing interest in dredging

Jeffrey Otto, who heads HarborRock, a New Jersey firm that has floated its own dredging idea, has put the annual dredging cost at $40 million a year, though he acknowledged that figure may not fully cover securing a site to hold, dewater and process the excavated material.

His New Jersey-based company envisions building a kiln at the site and turning the sand into stone pellets that would then be sold to make bricks, concrete and other similar products. “There’s huge demand for stone everywhere,” Otto said.

Pellet production is not likely to cover the full costs, so states or some other entity would still have to pay a “tipping fee” to overcome any shortfall.

But, Otto noted, because they can measure the amount removed, the nutrient reduction benefits can be better estimated than those produced by runoff control practices installed on hundreds of farms farther upstream. “That’s not too verifiable, right?” he said. “How are you going to know that you’re achieving that?”

“Looking at this stuff from a technical standpoint, it’s really kind of disappointing that dredging somehow doesn’t seem to be getting a fair shake,” Otto said.

Dredging has been championed by Maryland Gov. Larry Hogan, and his state funded a pilot project in December that took core samples, from the Pennsylvania state line to the dam, to analyze what is in the sediment.

Different types of material, whether sand, fine silt, or gravel pose different issues when it comes to dredging. And some are more valuable for reuse or resale than others.

Maryland Environment Secretary Ben Grumbles said his department has been briefed about the Conowingo Systems proposal and “we’re intrigued.”

Conowingo was built in 1928 to generate electricity, and it inadvertently acted as a trap for nutrient and sediment pollution flowing downstream to the Bay. Over the years, sediment buildup behind the dam has reduced its pollution-trapping capacity. Credit: Dave Harp / Bay Journal Media

He supports the creation of a panel of experts to determine the nutrient reduction value of dredging. He also supports exploring ways to involve the private sector in the project.

“It has our attention, and I think it should have other people’s attention, too,” Grumbles said, “because we’ve got to find ways to provide incentives for environmental restoration on a larger scale that has economics behind it.”

Little can happen until the Bay Program assembles an expert panel to estimate the nutrient reductions that might be associated with different amounts of dredging. That’s essential in determining how many credits can be created, and sold.

Environmental groups split

Many environmentalists have opposed dredging in the past.

Beth McGee, director of science and agricultural policy with the Chesapeake Bay Foundation, said that the reservoir would simply refill once dredging stops. She supports spending money to keep nutrients and sediment from flowing downstream, such as installing stream buffers, incentivizing the use of cover crops and encouraging farmers to take other conservation actions.

“You get much more benefits by spending money to prevent sediment from entering in the first place, such as by planting trees, that have all kinds of co-benefits like reduced flooding,” she said. “There really isn’t much co-benefit to dredging.”

McGee also noted that studies indicate the nutrients stored in the sediment are in forms that are not as harmful as those washing down the river, so any dredging project would have to carefully account for the actual benefits — something the expert panel would have to determine.

Not all environmental groups agree.

Ted Evgeniadis, the Lower Susquehanna riverkeeper, has long promoted dredging as part of the solution because it would help buffer the Bay from extreme storms such as Tropical Storm Agnes which, in 1972, caused widespread damage when it smothered much of the Bay with sediment and nutrients.

For decades, the Conowingo Dam trapped nutrient-laden sediment and reduced pollution from flowing to the Bay. Now, the reservoir behind the dam has filled with sediment and an additional 6 million pounds of nutrients are now flowing past the dam and reaching the Bay each year. Credit: Dave Harp / Bay Journal Media

Such storms not only carry sediment and other pollution washed off the land, but also scour built-up sediment from behind the dam. Because there is now much more sediment behind the dam than there was in 1972, Evgenladis noted, a similar event in the future would cause even more damage.

Further, he said, storms are expected to become more severe, and more frequent, as the climate warms.

“If we get another storm like Agnes, well forget it,” Evgeniadis said. “The Chesapeake Bay is dead, it’s absolutely dead. Forget about the work that’s been going on for the last 40 years because it doesn’t matter. That’s why dredging is so important.”

A market based solution?

Conowingo Systems’ work would start on a small scale but would be self-supporting, said Corbin, who has worked on the Bay for decades in positions with the Bay Foundation, the state of Virginia and the EPA.

The company envisions using the nutrient reductions from dredging to sell nitrogen credits, all or some of which could be purchased by the states to help offset the impacts of Conowingo. If the states weren’t interested, the credits could be sold to other regulated entities, such as municipal stormwater systems, as a more cost-effective way to meet Bay cleanup requirements.

“We’re going to jumpstart a robust, market-based water quality program,” Corbin said.

Conowingo Systems has not established a price for the credits, but expects it to be less than that of implementing the Conowingo cleanup plan.

But the company would take all of the financial risk while the nutrient market develops, potentially for years, even if it does not initially sell enough credits to fully cover costs, Corbin said.

“The goal here is that we will dredge enough to generate sufficient credits that the market can sustain,” Corbin said. “We will sell those credits, we will pay ourselves back, and generate enough money to go out and dredge again next year.”

The proposal intends to ultimately dredge sediment at a faster rate than it is coming in. Eventually, it envisions reducing sediment to its 1995 level — which means excavating 20 million cubic yards.

At that point the dam would be trapping enough sediment to fully offset the additional 6 million pounds of nitrogen that’s now going into the Bay, and it would require lesser amounts of dredging to maintain, especially as Pennsylvania implements runoff control practices to meet its own cleanup goals — which would reduce the amount of sediment and nutrients flowing downstream.

It is likely it could become less costly than efforts to control upstream pollution, Corbin said, most of which require ongoing annual payments to farmers, which might become more expensive over time.

“It is a complicated situation,” said Sam Merrill of Northgate. “We’ve dug ourselves a deep pit filled with sediment, and it’s going to take a bit to dig out of it. But, the benefits are huge”

This article originally appeared on BayJournal.com on January 19, 2021, and is republished with permission.


David M. Higgins II, Publisher/Editor

David M. Higgins was born in Baltimore and grew up in Southern Maryland. He has had a passion for journalism since high school. After spending many years in the Hospitality Industry he began working in...

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