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The Dam is Not So Threatening After All, Geologists Say

Federal geologists once warned that the silt trapped behind Conowingo dam was “a time bomb,” threatening to choke the life out of Chesapeake Bay. The mass of muck piled up behind the dam over the years is enough to fill M&T Bank Stadium 80 times over. And a major storm could hurl tons of it through the flood gates down river and into the bay, destroying grass beds and suffocating oyster bars.

But those fears may have been overwrought. According to a new state-federal study, only 20 percent of the mud that turned the Upper Bay into a brown mess after Tropical Storm Lee in 2011 came from behind the dam. The rest came from upstream.

What that means, says Colonel Trey Jordan, commander of the Baltimore District of the Corps of Engineers, is that those worried about sediment in Chesapeake Bay would have “a better target of opportunity” if they concentrated on the 80 percent of the sediment that’s “coming from upstream of the dam.”

That doesn’t mean there’s nothing to fear, adds Don Boesch, president of the University of Maryland Center for Environmental Science. But this study suggests the sediment issue is “not a game changer in terms of what we’re trying to achieve in bay water quality.”

The findings, announced at a U.S. Senate hearing, appear to undercut the arguments of Eastern Shore lawmakers who have claimed the sediment is a greater threat to the bay than farm field run-off or leaking septic systems. But State Senator Steve Hershey, who represents the Upper Shore, was not impressed. He said the study was “just a way of taking the focus off the Conowingo Dam.”

The sediment in an underwater delta that stretches 14 miles up the Susquehanna River behind the dam is “low hanging fruit” that could easily be cleaned up, reducing problems in the bay without requiring his constituents to abide by new rules, he argued.

But Colonel Jordan says the cost is prohibitive; anywhere from $500 million to $3 billion to dredge just back to 1996 levels. And that doesn’t count an additional $250 million in annual maintenance dredging. You would get more bang for your buck by making sure upstream, and downstream, communities adhered to the watershed implementation plans, or WIPS, drafted as part of the bay pollution diet known as TMDLs.

That would “take care of the vast majority of the sediment issues, the nutrient issues that are mandated by the TMDLs,” he said.

Doug Myers, a Chesapeake Bay Foundation scientist, says the “low hanging fruit” argument comes from people who want to avoid dealing with their “piece of the pie” in bay clean up. “There’s lots of pieces of the pie, there’s lots of sources of nitrogen, phosphorous and sediment and many of the impairments that are happening to the bay are in local water bodies,” he says.

It’s pretty difficult for someone on one local water body that has its own problems to point to others, he says. “It’s really a local problem and so we really need to be dealing with all the pollution sources in all the local water bodies collectively to clean up the Bay.

Exelon Corp. which owns the dam, has applied to renew its federal operating license, which expires September 1st. It has been negotiating with state and federal officials about what to do with the sediment.

Vicki Will, an Exelon vice president, said during a tour of the dam the company is still trying to understand the impact that storms scouring out the sediment would have on the bay.

U.S. Senator Ben Cardin, who presided at the hearing, says it isn’t clear to him how to deal with the septic issue, but that the Corps of Engineers study “made a very strong case that it was not what we thought it was a year or two ago.”

Meanwhile, Richard Gray, the mayor of Lancaster, Pa., shakes his head at the arguments in Maryland. Lancaster has invested heavily in green infrastructure to clean the storm water run-off that flows to Chesapeake Bay. But when you see Maryland fighting against bay clean-up programs “that makes it far more difficult for in Pennsylvania to do it.”

“We’re removed from the Chesapeake Bay,” he says. “A lot of the people in the city of Lancaster really don’t know or don’t care about the Chesapeake Bay. So, when they see people that are directly involved opposing efforts to clean it up it makes it more difficult for us in Pennsylvania to convince our constituency that they should do it.”