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Conowingo tango

Our view: How much pollution mitigation should a hydroelectric dam be expected to do? Debate over Susquehanna River facility needs to be put in reasonable context

As a candidate for governor, Larry Hogan frequently attacked Maryland's approach to fighting pollution entering the Chesapeake Bay, particularly the locally-assessed storm water cleanup fee — calling it a "rain tax" — while claiming the previous administrations had done nothing to prevent trapped sediment from cascading past the Conowingo Dam, which he viewed as the far bigger problem. His point was that Gov. Martin O'Malley and Lt. Gov. Anthony G. Brown, Mr. Hogan's Democratic opponent in the 2014 race, should not have been regulating "watermen, farmers and struggling families" and should have instead been protecting the bay from "federal and corporate neglect."

Three years later, Governor Hogan seems to regard his views on the Conowingo as vindicated. "Most people didn't seem to agree that it was a problem," Mr. Hogan recently concluded, telling reporters he is close to announcing a plan for the dam. "Now everyone seems to agree that it's a problem."

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All of which is, of course, a load of mud. To our knowledge, no one has ever suggested that silt, soil and sediment flowing down the Susquehanna River was not a problem for water quality. For decades, the Conowingo (and other smaller dams along the river and its tributaries), have essentially trapped these pollutants from flowing further downstream. Such pollution mitigation is not the point of a dam but a side benefit. As these reservoirs have filled up with silt, however, that benefit has diminished — and, in recent years, at a faster rate than some scientists had predicted and to the point where it's now regarded as full. What experts argued at the time, and continue to preach, is that it's not a choice of one or the other in terms of fighting pollution. Maryland and the other states in the Chesapeake watershed need to take an "all of the above" approach to protecting the bay from pollution, whether it comes from chicken manure, parking lot runoff, failing septic tanks, sewage spills or anything else.

The problem with pointing a finger at the Conowingo is that first, it's a difficult problem to "fix." The most obvious remedy would be to dredge all the sediment behind the dam and truck it to some upland location. But Governor Hogan's call for suggestions has so far produced some novel approaches such as using the silt to create pavers or countertops, dumping it into the ocean or turning it into concrete. That's welcome, but the proposals all appear to be costly and no more than "nibble" at the huge inventory of sediment, which the U.S. Army Corps of Engineers has already estimated would cost billions of dollars to remove. The second is that this isn't necessarily the pollution source that should be the top priority for Chesapeake Bay cleanup efforts.

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Governor is correct to insist on Conowingo dam cleanup.

Why? Because while that silt and sediment flowing over the Conowingo can certainly be described as pollution, it primary has an impact on the Chesapeake Bay's central stem, the deep water that already has problems with low dissolved oxygen. However, the sediment overflow doesn't really affect valued tributaries like the Potomac, Choptank, Chester or Pocomoke rivers, which contain some of the most critical and environmentally sensitive habitats in the watershed. Nor is it clear that dredging silt from behind the Conowingo (no matter what you do with the dredge material) is the most cost-effective way to reduce the muck coming from the Susquehanna or, in particular, the excess nitrogen and phosphorus those sediments contain.

Maryland may soon have little say on what happens to Conowingo dam.

That doesn't mean there isn't room for Mr. Hogan to help reduce water pollution from the Susquehanna. There certainly is. He might, for instance, force the owner of the Conowingo Dam — Exelon Corp. — to contribute money toward anti-pollution efforts. The goal might be to at least reduce "scouring," the tendency for severe weather to stir up sediment deposits behind the dam and worsen the situation. While we don't expect the company to dredge all of the millions of tons of sediment, it might be able to do enough to reduce this effect.

In the Conowingo, the governor has correctly identified a problem for Chesapeake Bay water quality, but he speaks of it in a misleading fashion, much as he did with the "rain tax." Mr. Hogan eventually came around on storm water pollution by making the fees optional while actually better enforcing anti-storm water rules. There's similar hope for the Conowingo, where any new approach to sediment control is welcome as long as it doesn't compromise the ongoing federal and state partnership and "pollution diet," the comprehensive plan to reduce all forms of pollution leading to the bay. It may prove, for example, more beneficial and cost-effective to reduce pollution going into the Susquehanna than to clean up sediment at the dam — but that's a strategy that only happens if science, and not political rhetoric, informs policy.

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