Conowingo’s, Bay’s mutual relationship finally ran its course
Dam can no longer hold back nutrients and Bay is paying the price. Who should foot the bill?
Editor’s note: This is part of a series of occasional articles examining issues related to the Chesapeake Bay Program’s “Midpoint Assessment” of Bay cleanup efforts.
For decades, the Chesapeake Bay’s biggest friend was the Conowingo Dam.
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 general 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 even larger.
Now, scientists say, the dam’s reservoir is filled and in a state of “dynamic equilibrium” — 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 out strategies to help the Bay — and its watershed — meet the 2025 cleanup deadline.
It’s possible that an answer could be reached as soon as December. But — as several committees within the state-federal Bay Program partnership have failed to coalesce around a solution — it’s also possible it won’t be resolved until well into the new year.
“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 Chesapeake Bay Total Maximum Daily Load, 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 TMDL, or “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.”
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 deep waters of the Upper Bay.
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 any additional reductions — is already lagging far behind in its cleanup. It needs to ramp up the pace of nitrogen reductions five-fold beyond recent efforts just to meet current goals.
“They are already struggling to achieve the reductions that we have quantified for them,” Davis-Martin said. “And the idea that they would be able to absorb a bunch of previously unaccounted-for loads may not be a viable alternative.”
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 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 under the TMDL in 2010.
Those allocations were made 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 other jurisdictions.
Efficiency vs. equity
But spreading the burden around 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.
“It’s a policy call,” McGee said, adding that the whole region should “share the pain.”
Those numbers could also 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. But financial responsibility would be shared through some kind of interstate trading mechanism, under which states in other parts of the watershed would send cleanup funds to those where the reductions would cost the least.
Though enticing in theory, 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.
“Would downstream states…really send money to areas that are doing more because it is more cost-effective?” McGee asked. “I don’t think so, especially if it means money going out of the state.”
Davis-Martin said he still thinks the idea is worth exploring, so policy makers can weigh their options. But, he agreed, states are unlikely to send their money elsewhere or even agree to give up federal funds so they could be sent somewhere else.
“The bottom line is no, it’s not viable,” he said.
Push Conowingo offsets beyond 2025?
Other actions could soften the burden and reduce costs. For instance, it’s 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 any suggestion of extending the 2025 deadline, calling it a “non-starter” at meetings.
Viewed in isolation, the Conowingo impact actually 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 meet water quality standards about 29 percent of the time during the summer. Under current model estimates, if all currently required nutrient reductions were made, the failure to account for Conowingo’s failed trapping capacity would mean standards would still be exceeded 3 percent of the time.
But, 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 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 more of that nutrient is leaking from soils than previously thought in areas with intense animal farming. 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.
Further, while the TMDL called for doing everything needed to achieve cleanup goals by 2025, no one expects water quality to reach the desired level until years later. That’s because the impacts from many nutrient reduction efforts, whether planting cover crops or installing forest buffers, take years to be felt in streams and show up in water quality monitoring.
If any needed actions are kicked beyond the deadline, meeting water quality goals would be further delayed — even as strains on the Bay ecosystem from climate change and population growth are expected to become even more intense.
Withstanding extreme events
The debate among policy makers over how to adjust the cleanup effort for the Conowingo’s lost nutrient trapping capacity does not directly deal with one issue: the potentially devastating impact of extreme weather events. Tropical Storm Lee in 2011, and the even more severe Tropical Storm Agnes in 1972, sent water, nutrients and sediment flooding into the Bay, in the process scouring huge amounts of those pollutants from behind the dam. With the Conowingo reservoir now essentially filled, even more material is available to be flushed into the Bay.
While most of the nutrients and sediment passing the dam — even during massive storms — come from the watershed upstream, the amount stirred up from the bottom of the reservoir can still be significant. And the Corps report found that an extreme storm today would scour more out of the reservoir than a similar event two decades ago.
But there’s no real way to remove sediment from the reservoir. Dredging enough to match what the dam used to trap each year would cost between $15 million and $270 million annually, according to the Corps report. Trying to maximize the dam’s trapping capacity by removing everything that’s accumulated since Conowingo was completed in 1929 would be prohibitively expensive.
Therefore, all of the management strategies on the table are aimed at dealing with nutrient problems under more “normal” weather conditions.
“You can’t manage for a 100-year or 200-year storm,” Batiuk said. “Nobody can manage for something like that.”
Instead, officials hope that by offsetting the annual increased loads, the Bay as a whole will become healthier, and better able to withstand big storms.
“Managing for the chronic condition guards against the extreme event because it allows the Bay to be more resilient,” Currey said. He pointed to the recovery of grass beds in the Susquehanna Flats. Grasses, once nearly vacant from the area, have rebounded so much since the late 1990s that they were able to withstand the massive influx from Tropical Storm Lee in 2011.
One of the reasons that Agnes was so devastating, scientists say, is that the Bay was already in a declining condition when the storm hit. Underwater grass beds — which were devastated by Agnes — had already been shrinking for years because of worsening water quality. Agnes pushed them over the edge.
Today, officials say the Bay is getting healthier. Nutrient trends are heading down — albeit slowly in many areas — and underwater grass beds are making a comeback. “It is a different system than back when Agnes hit the Bay,” Batiuk said.
It needs to be. Because after a friendship with Conowingo Dam that lasted nearly 80 years, the Bay now needs to look elsewhere for help.
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