Report: Conowingo Dam More Serious Threat to Bay Health Than Previously Thought

A Bay Journal article (2016-03-11) announced the findings of the multi-year Lower Susquehanna River Watershed Assessment study, which concluded that the Conowingo Dam no longer has the ability to trap nutrients and sediment from the Susquehanna River. This threatens the efforts to clean up the Chesapeake Bay and may require additional pollutant offsets by Bay watershed states if they are to meet their 2025 restoration goals under the Bay Total Maximum Daily Load. From the article:

The $1.4 million study, led by the Army Corps of Engineers and the Maryland Department of the Environment, comes at a time when the state-federal Bay Program partnership has embarked on a multi-year effort to assess and update cleanup goals by the end of next year — a task made harder by the Conowingo situation. …

For decades, the 100-foot-high dam had helped Bay cleanup efforts by trapping a portion of the sediment and nutrients coming down the Susquehanna River, and keeping them from reaching the Chesapeake. While it has long been known that the dam’s reservoir was reaching its storage capacity, that day was thought to be further in the future. As a result, the 2010 Bay cleanup plan did not anticipate the impact of the reservoir filling on Chesapeake water quality.

But the new report concludes that Conowingo and two upstream dams, Safe Harbor and Holtwood, “are no longer trapping sediment and the associated nutrients over the long term.” Instead, the dams delay a portion of the sediment and nutrients coming down the river during dry years, only to have that material flushed into the Bay during years with higher than average rainfall.

The article also included responses from various stakeholders:

The report “puts more onus on all of us to recognize that Conowingo needs to be addressed, and with a sense of urgency,” Maryland Environment Secretary Ben Grumbles said. The contributions of nitrogen, phosphorus and sediment pollution from behind the dam and upriver are “important,” he said. …

Charles “Chip” MacLeod, an attorney who represents the Clean Chesapeake Coalition, a group of mostly rural Maryland counties, said the report affirms the coalition’s long-held position that the issue of the Conowingo reservoir must be addressed to meet Bay goals.

“This justifies a sense of urgency; as our efforts and expenditures in Maryland to improve Bay water quality are otherwise being inundated by upstream pollution,” he said.

In an emailed statement, Exelon spokesman Marshall Murphy emphasized the dam’s importance to Maryland, calling it the state’s second largest generator of renewable energy. In the statement, the company vowed to “continue to work with key stakeholders” to ensure the health of the lower Susquehanna and the Bay.

The report found that the Conowingo was not only releasing nutrients and sediment during large storm events, such as Tropical Storm Lee in 2011, but during normal operational conditions. However, the article explained that addressing the issues posed by Conowingo remain challenging:

Computer modeling done for the report showed that meeting water quality goals without the dam’s help would require an additional 2.4 million pounds of nitrogen reductions and an extra 270,000 pounds of phosphorus reductions from the Susquehanna each year.

That’s problematic because Pennsylvania —which supplies the vast majority of nutrients in the Susquehanna basin — is also lagging far behind in meeting its Bay cleanup goals, making additional nitrogen and phosphorus reductions from the river even more difficult. …

But the report discounted the potential of dealing with the problem by dredging the reservoir, as some including the coalition have suggested. When it comes to dredging, the report said, “ecosystem benefits are minimal and short lived, and the costs are high.” Dredging to roughly keep pace with what the dam historically trapped would cost between $15 million and $270 million annually, it said.

Useful Links

Lower Susquehanna Watershed Assessment Website

Lower Susquehanna Watershed Assessment Final Report

Prior Conduit Street Coverage of Conowingo Dam