Conowingo Dam

A new study from the U.S. Geological Survey agrees with an earlier U.S. Army Corps of Engineers study that there is too much sediment trapped in the reservoir behind the Conowingo Dam.

CONOWINGO — A study released by the U.S. Geological Survey echoes much of what has already been found of the Susquehanna River and its relationship to the Chesapeake Bay.

The 28-page report authored by Michael Langland shows the storage capacity for sediment behind the Conowingo Dam has reached its saturation point.

“The Conowingo Reservoir is at — or very near — filled to capacity,” Langland said Thursday.

As dire as it sounds, Langland said the situation is not an emergency.

“It doesn’t mean that the dam is filled to the top,” he said. “It means the capacity to trap is nearly extinguished.”

A study released in November by the U.S. Army Corps of Engineers concluded that, while there is an enormous sediment build-up, it is the content carried by the sediment that is the greater threat to the health of the bay.

Langland said the USGS report “is an expression of the (Corps of Engineers) report.” He added no decisions are made in either document.

“That has to be debated and decided by the people with the purse strings,” Langland said.

The USGS study looks at the movement of the sediment as it travels from the head of the river in New York, through two other hydroelectric facilities before coming to rest at the Conowingo Dam. The study analyzes the flow of water through the dams and looks at historical data measuring the amount of sediment both trapped and released.

From 1928 — the year the dam went into service — until 1940, 6.3 million tons of sediment was trapped in the Conowingo Reservoir each year. By the 1950s, regulations began to control soil erosion. From 1971 to 1990, the trapped sediment dropped to 2.6 million annually, with the most recent measure at 1.2 million tons.

“There’s always sediment flowing through the dam,” Langland said.

Nutrients in the sediment are the bigger issue, Langland said.

The Corps of Engineers study decided dredging the sediment from behind the dam would be too costly compared to the benefits.

“This is the third time I’ve been involved in a discussion on dredging,” Langland noted. “You cannot believe the number of (proposed) scenarios and possible dredge sites.”

One interesting piece of the discussion was the disposal of that sediment.

“There could be some use of the materials,” he said, such as potentially adding the dried matter to construction material mixtures. Storage and processing, however, would then become another issue.

In the meantime, Exelon Generation, the utility that owns Conowingo Dam, has agreed to pay $3.5 million for an enhanced water quality and sediment assessment upstream and downstream.

A team of scientists at the University of Maryland Center for Environmental Science will head the two-year study to determine the amount of sediment and associated nutrients present in major entry points to the Lower Susquehanna River Reservoir System and the upper Chesapeake Bay.

The study is intended to help policymakers determine the best management options to reduce this effect.

“With its long history of internationally recognized research on the Chesapeake Bay, the Horn Point Laboratory is well suited to perform this research,” said Mike Roman, director of the Horn Point Laboratory.

The city of Harrisburg, Pa., and Capitol Region Water have also recently agreed to an $82 million settlement with the EPA over the discharge of stormwater and wastewater into the Susquehanna River and Paxton Creek. Part of the agreement requires Harrisburg to update its treatment plant and collection systems.

Robert Judge, spokesman for Exelon, said this USGS study would provide valuable information.

“This analysis may be helpful to the parties working on a scientific regional solution to addressing the need for a clean Chesapeake Bay,” Judge said Friday via email.

Exelon is in the process of obtaining a 46-year operating license for the dam from the Federal Energy Regulatory Commission.

Langland said regardless of whether the sediment is removed, it would remain a continual problem.

“There’s a lot of opinions. Reservoirs are part of the problem, but are they a major or minor part,” he said. “The sediment levels are negligible. They come in, but they settle out.”

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