CONOWINGO — Concerns about the sediment-filtering capacity of a dam on the lower Susquehanna River in northeast Maryland and related environmental issues must be addressed in the broader context of trying to improve water quality efforts throughout the Chesapeake Bay region, officials said Monday at a U.S. Senate field hearing.
Construction of the Conowingo Dam in the late 1920s created a detainment area for some of the sediments and nutrients flowing down the Susquehanna toward the bay. But officials say the ability of the reservoir to hold additional sediment is reaching capacity, and heavy rain events sometimes send sediment and pollutants flowing through the dam toward the bay.
U.S. Sen. Ben Cardin said after conducting Monday’s field hearing that discussions about the dam reinforced the need to take a comprehensive approach to protecting and improving water quality in the bay, including existing efforts to reduce the total maximum daily load, or TMDL, of pollutants going into the bay, and the development of watershed implement plans throughout the region.
Sediment management at the dam has become an issue as its owner, Exelon Power, is asking federal regulators for a 46-year renewal of its operating permit.
“The overall strategy for the bay as represented by the TMDL enforcement mechanisms and the watershed implementation plans are vital to this evaluation process,” Cardin, D-Md., said after Monday’s hearing.
An Army Corps of Engineers study found that areas upstream from the dam contribute far more sediment flowing to the bay during major storm events than what is stirred up in the reservoir and sent over the dam.
“These sources deliver more sediment and nutrients and, therefore, more impacts on the bay ecosystem, than do the scoured sediment and associated nutrients from the reservoir behind the Conowingo Dam,” said Col. J. Richard Jordan III, commander of the Corps’ Baltimore District.
Jordan told Cardin that reservoirs behind the Conowingo and other dams on the river are in a state of “dynamic equilibrium,” with scouring during heavy storms sending sediment from the reservoirs flowing toward the bay while also creating more space to hold sediment coming from upstream.
But Joe Gill, secretary of the Maryland Department of Natural Resources, pointed out that scouring events are occurring at much lower water levels than previously thought and thus happening more frequently. Officials need more information to determine the effect of the lower-level scouring on water quality in the bay, he added.
While dredging the Conowingo reservoir to increase its storage capacity is one option, Jordan said dredging behind the dam and depositing the spoils upland would be prohibitively expensive, perhaps more than $250 million a year, while providing only marginal benefits and “very little bang for your buck downstream.”
While officials continue to study the sediment issue, Genevieve LaRouche, a field office supervisor for the U.S. Fish and Wildlife Service, said the permit review process for Exelon provides an opportunity to address the related issue of how the dam affects the movement of migratory fish, particularly American shad, river herring and the American eel, in the lower Susquehanna. She said the technology exists to make fish passage mechanisms at the dam more efficient and cost-effective.
Exelon’s operating permit for the dam expires later this year, but it likely will be allowed to continue operating under an interim permit while further studies are done and state and federal regulators consider whether to renew the permit and under what conditions.
“We don’t have all the technical information necessary,” Cardin said. “…. It’s complicated to figure out how to provide the best protection of the bay for future generations.”