For decades, Conowingo Dam was the Chesapeake Bay’s biggest friend.
Even before scientists realized the Bay was sick from too much nitrogen and phosphorus, the 94-foot concrete wall on the Bay’s largest tributary was holding back tens of millions of pounds of the nutrients that would have fueled even more greenish algae blooms.
The friendship was severely tested at times. Tropical Storm Agnes flushed huge amounts of stored sediment from behind the dam and into the Bay, smothering grass beds and oyster reefs, and causing havoc. And migratory fish were none too happy that it became nearly impossible to swim up the Susquehanna River to spawn, despite huge investments in “fish elevators.”
But without the dam, more nutrients and water-clouding sediment would have poured into the Bay for most of the past century. Algae blooms would have been more intense, and oxygen-starved dead zones would have been larger.
Now, scientists say, the dam’s reservoir can hold no more nitrogen, phosphorus, or sediment — what comes into the reservoir goes out.
The Bay’s best friend has nothing more to give.
And now, state and federal policy makers must figure out who has to pick up the slack.
Should it be the upstream states, where the nutrients and sediment originate? Or, because the entire Bay benefitted from past reductions, should the whole region share the pain? Since the job ahead is going to be harder, should states get more time to offset the Conowingo effect?
It’s one of the stickiest questions that decision makers face as they map strategies to help the Bay — and its watershed — meet the 2025 cleanup deadline imposed by the 2010 Chesapeake Bay Total Maximum Daily Load, the bay’s “pollution diet.”
“It’s probably the decision that will be the most challenging to the partnership because it is potentially so divisive,” said James Davis-Martin, Bay coordinator with the Virginia Department of Environmental Quality and chair of the Bay Program’s Water Quality Goal Implementation Team. “It can set the us-against-them mentality in place.”
No more ‘free ride’
The Bay Program is in the midst of a “midpoint assessment” of the 2010 clean up plan, which set nutrient and sediment caps for each state and river. The resulting pollution reductions were intended to reduce algal blooms, improve water clarity and enhance oxygen levels to sustain fish, crabs, oysters and other aquatic life.
States were to take all needed actions by 2025 to achieve those reductions — including planting cover crops, installing stream buffers and upgrading wastewater treatment plants. But the pollution diet also called for a review in 2017, during which the states and the U.S. Environmental Protection Agency were to assess progress, weigh new information and make any needed course corrections by the end of that year.
Few issues have changed more than Conowingo since 2010.
When the TMDL was written, the EPA assumed that the dam’s reservoir was trapping as much as 20 percent of the nitrogen and 50 percent of the phosphorus coming down the Bay’s largest tributary as it had for decades — and that it would continue to do so through 2025.
But research shows that’s no longer so. A review by the U.S. Geological Survey found that Conowingo has been trapping fewer and fewer nutrients since the 1990s, and sometime in the last few years reached the point where it essentially was no longer retaining nutrients and sediment.
“The free ride is over,” said Robert Hirsch, a USGS research hydrologist whose work a few years ago was the first to show the dam was starting to leak more nutrients downstream. “What comes in basically goes out under the current situation.”
Recent reports by the U.S. Army Corps of Engineers and the Bay Program’s Scientific and Technical Advisory Committee reached the same conclusion.
That lost trapping capacity has masked improvements made upstream. USGS monitoring shows that the amount of nitrogen and phosphorus in the lower Susquehanna River above the dam has decreased since the early 1990s. But because nutrients are no longer effectively being trapped in the reservoir, there has been little net change in the amount passing Conowingo and entering the Bay. In the last two decades, nitrogen levels measured below the dam have decreased slightly, while those for phosphorus have increased a bit.
The upshot is this: Because of the dam’s diminished trapping capacity, the nutrient reductions called for in the Susquehanna watershed by the TMDL are no longer enough to meet dissolved oxygen goals in the Upper Bay’s deep waters .
Who bears the burden?
Computer modeling done for the Corps estimated that to meet oxygen goals without Conowingo’s help, areas upstream of the dam would need to keep an additional 2.4 million pounds of nitrogen and an extra 270,000 pounds of phosphorus annually from getting into the Susquehanna. Those would require 9 percent greater nitrogen and 38 percent greater phosphorus reductions from now to 2025.
In an appendix to the TMDL, the EPA said that if the Conowingo reservoir did fill prior to 2025, it would consider assigning steeper cuts to areas of Pennsylvania, Maryland and New York upstream of the dam to make up the difference.
But some question whether that is fair, or realistic. Pennsylvania — which would bear the brunt of additional reductions — is already lagging far behind in its cleanup. It needs to ramp up the pace of nitrogen reductions five-fold just to meet current goals.
“The idea that they would be able to absorb a bunch of previously unaccounted-for loads may not be a viable alternative,” Davis-Martin said.
And, some question whether all of the additional responsibility should be placed upstream of the dam, as the Bay has been a major beneficiary of the dam’s past reductions.
“We have collectively reaped the benefits of the reservoir and its trapping capacity, and maybe there is a reasonable expectation that we share the consequence of that trapping capacity being lost,” Davis-Marin said.
Beth McGee, senior water quality scientist with the Chesapeake Bay Foundation, said the debate about who bears the burden results from bad timing. The nutrients from Conowingo are considered “new” only because scientists didn’t recognize that the reservoir was nearly filled when nutrient allocations were made to states and rivers in 2010.
Those allocations were based on several principles, including that places with the greatest impact on the Bay bear the greatest cleanup burden, but also that as a matter of equity, everyone must share in the task.
If the dam’s fading benefit had been recognized in 2010, McGee said, those additional nutrients would have been divided across the watershed using that formula.
“We would have factored in the new way Conowingo was behaving, and I don’t think anyone would have debated it,” she said.
Under that scenario, areas upstream of the dam would still have to undertake the greatest action — because they have the greatest impact — but some of the burden would be spread among downstream jurisdictions.
Efficiency vs. equity
But spreading the burden comes at a price, literally.
Modeling estimates in the Corps’ report suggest that meeting the water quality goals would require almost twice the reductions — 4.4 million pounds of nitrogen and 410,000 pounds of phosphorus — if spread using the allocation formula. That’s mainly because the Susquehanna has a greater impact on dissolved oxygen levels in the Upper Bay than almost any other part of the watershed. Spreading the burden would likely increase the cleanup cost by millions, if not tens of millions, of dollars.
Those numbers could increase. The computer models used to make those nutrient reduction estimates are being updated and improved with new research. Final estimates won’t be available until late next spring. Officials don’t expect them to change dramatically, but say it’s more likely the needed reductions would increase than decrease.
Some have argued for a hybrid approach in which actions to offset Conowingo would be carried out wherever, and however they could be done most cheaply,b ut with financial responsibility shared through interstate trading, under which states in other parts of the watershed would send cleanup funds to those where the reductions would cost the least.
Though enticing, that option is unlikely. Right now, Bay Program officials say the tools do not exist to support such decisions. And even if they did, most are skeptical that politically, states would willingly send their cleanup money elsewhere. All states still have substantial work to meet their own TMDL goals — reductions necessary to not only meet Bay water quality goals, but also those within their own tributaries.
Push Conowingo offsets beyond 2025?
Other actions could soften the burden and reduce costs. For instance, it is possible states may be able to reduce more of one nutrient and less of the other if it would achieve the same overall water quality goal. If it is less expensive to control phosphorus than nitrogen, a state could opt to spend more on the cheaper option, if the Bay benefit is the same.
“I don’t think that will be the total solution, but it may help,” said Lee Currey, science services director of the Maryland Department of the Environment and co-chair of the Bay Program Modeling Workgroup. “I think that would be something to add to the menu of how we solve the problem, but not a solution by itself.”
Another idea put forward is that states would continue to be required to meet current nutrient reduction goals by 2025, but they would be allowed extra time to offset the impact of Conowingo.
“One of the guiding principles we’ve been operating on since 2010 is adaptive management,” Davis-Martin said. “It is not unreasonable to say new science requires that we adapt our timeline.”
But the EPA has opposed suggestion of extending the 2025 deadline, calling it a “non-starter” at meetings.
Viewed in isolation, the Conowingo impact seems small. The primary impact of the extra nutrients is on dissolved oxygen in one relatively small area, the deepwater portion of the Upper Bay.
Right now, that area lacks enough dissolved oxygen to support aquatic life about 29 percent of the time during the summer. Under current model estimates, if all currently required nutrient reductions were made, but Conowingo’s impact is not offset water quality standards would be exceeded 3 percent of the time.
That may seem small, but as McGee said, “we need to plan for it. Otherwise, what is the difference between 3 and 5 percent, or 5 and 6 percent? I think you need to draw a line in the sand.”
Indeed, other factors that have changed since 2010 will also pose challenges. Preliminary estimates suggest that offsetting the impacts of climate change on Bay water quality by 2025 might require a level of nutrient reductions similar to those needed to offset Conowingo’s lost trapping capacity. Also, additional phosphorus reductions are likely to be needed in parts of the watershed because in areas with intense animal farming more of that nutrient is leaking from soils than previously thought. Population growth and development will produce more nutrient pollution as well.
“If you start to add all of those up but don’t account for them, then you won’t get back to a healthy system,” said Rich Batiuk, associate director for science with the EPA Bay Program Office.
By Karl Blankenship
Frederick S. Patt says
Well written. This make the case clear that the inability of the Conowingo to continue blocking the flow of nutrients and pollution from the Susquehanna is not the fault of the dam or its owners, but rather the watershed upstream from the dam.
William McMillan says
A possible solution would be to install dredging equipment above the dam and mine the nutrients. Resell them to help offset the cost. Of course, something more has to be done with the upriver pollution, but certainly this could help.
joe diamond says
William, I can’t help but think something like that is possible. A solar de watering set up to lighten the sludge before shipment….rail cars are already there…and a system to redistribute the nutrient laden sludge back where crops grow must be possible. I bet there is a lot more that usable nutrients in the sludge but I have not been able to find anyone working in this area. Large scale mine operations do no move mountains…..bet there is a way!
joe