Bear with me a little, the logic train is a little tortured. At the Bay Journal, Dammed-up soil could help heal abandoned mine land
Fertile sediment bottled up behind old mill dams in Pennsylvania is a relentless source of nutrient and sediment pollution in local waterways that flow toward the Chesapeake Bay. But it could become a prime ingredient in restoring another scourge in the state: abandoned mine land.
Documented as a sediment and nutrient pollution problem for the Bay about 15 years ago, legacy sediment is topsoil that ran off the land long ago from farm fields and logging areas throughout the Bay region and piled up behind mill dams, many of which date back to colonial times.
As the dams have been torn down or abandoned, the now-elevated streams seek their original course, cutting through the soft earth that buried them and sending the soil and attached nutrients into the water. Also, the gantlet of mill ponds buried and altered healthy stream channels that once were a braid of connected streams with floodplains buffering nearby land from rising water.
In Pennsylvania, the 126-square-mile Chiques Creek watershed is one of the largest sediment and nutrient polluters in Lancaster County, itself one of the Bay’s top sources of such pollutants with one of the highest concentrations of easily erodible legacy sediment. More than 400 old mill dams have been mapped in Lancaster County alone.
Primarily surrounded by farmland and urban development with scant forest cover, the Chiques watershed has 48 dam sites that have been identified through satellite imagery.
All but nine of the dams are gone, resulting in slow but persistent pollution from the easily erodible soil in the former mill ponds. About 70 million pounds of sediment from banks up to 8 feet high erode each year, washing toward the Susquehanna River and on to the Bay, according to the Susquehanna River Basin Commission.
Sediment makes the water murky, smothering fish habitat and blocking sunlight for underwater grasses. It also carries nutrients, which contribute to harmful algae blooms and the Bay’s oxygen-starved “dead zone.”
Partners in the Chiques Creek Legacy Sediment Removal Project would like to turn that problem into a solution. If the project secures enough funding, as much as 283,000 cubic yards of legacy sediment stranded on streamside terraces would be dug up at 10 sites. The nutrient-rich soil would be trucked or taken by train to spread on abandoned mine land, where vegetation struggles to grow in the acidic soil.
With an estimated price tag of about $10 million, the project is being assembled by the U.S. Department of Agriculture’s Natural Resources Conservation Service, the nonprofit Water Science Institute, and the Lancaster County commissioners and soil conservation district. NRCS has already provided $800,000 from its small watershed improvement program to study the idea’s potential.
So, by moving dirt out of the the old damn basins, you not only benefit the Bay by removing potential nutrient source, you also help heal the environmental scars from old mining. Sounds win win to me. Possible caveats include actually causing more sediments to move down the stream in the the course of trying to excavate it, and that sediments placed on the old acid mine sites will also continue to bleed nutrients.
Of course, another possible source for sediments to place on the acid mines is the legacy sediment that has built up behind Conowingo Dam (which come from the old dams, and farm fields). By taking sediments from behind the dam, they could restore the function of the dam as a nutrient trap, a function that has been lost as the pool behind the dam filled up with sediments. It certainly makes the whole process more simple. The problem is that dirt is cheap, dirt cheap, and moving it is expensive.