Thanks to the July 7 Sunday LNP for the article on conditions at the Conowingo Dam (“Behind the dam, tons of pollution”). The Conowingo is now the third major dam on the lower Susquehanna River to have reached capacity, creating a series of policy challenges for Chesapeake Bay advocates, Pennsylvania and other states targeting upstream pollution sources with varying practices and levels of success.

It’s important to remember that most of these sources aren’t from current land use activities but the legacy of our past.

The most significant contributor to Lancaster County streams is from legacy sediment that remains after the abandonment or breaching of milldams. Often mistaken for bottomland pasture or flood plains next to steep stream banks, these sites are highly erodible pollution “hot spots” that contribute enormous amounts of sediment, phosphorus and nitrogen to our waterways and the Conowingo’s load.

One dam the Water Science Institute has monitored since its 2018 removal has released 5,000 tons and will likely continue to do so for decades. With hundreds of major erosion hot spots identified by Franklin & Marshall College and institute scientists, the problem’s scale quickly becomes apparent.

An institute report, funded by the National Resource Conservation Service and The Steinman Foundation, has examined legacy sediment restoration costs compared to other environmental practices. (Editor’s note: The Steinman Foundation is a local, independent family foundation funded by the companies that make up Steinman Communications; those companies include LNP Media Group.)

The Soil and Water Conservation Society Journal just published report results that illustrate the impact and opportunity of restorations and their implication for clean water goals. Given the magnitude of the challenge, a different dam strategy may be in order.

Joe Sweeney

Executive director

Water Science Institute