Since Conowingo Dam’s construction in 1929, sediments flowing down the Susquehanna River have been building up in its reservoir. Recent studies by the U.S. Geological Survey indicate that the reservoir is full, which means that more sediments and associated nutrients are washing downstream into Chesapeake Bay during storms. A 2015 study led by the Departments of Environment (MDE) and Natural Resources, the U.S. Army Corps of Engineers, Susquehanna River Basin Commission and EPA’s Chesapeake Bay Program (CBP) found that those sediments and nutrients are contributing to dissolved oxygen impairments in the Chesapeake Bay. CBP has calculated that an additional 6-million pounds of total nitrogen and 260,000 pounds of total phosphorus are now passing through Conowingo Dam and reducing dissolved oxygen levels in Chesapeake Bay.
Changing market conditions, stakeholder interest, and recent dredged material reuse guidance have renewed support for in-reservoir solutions as part of a comprehensive multi-state strategy to restore Chesapeake Bay. The Conowingo Sediment Characterization and Innovative Reuse and Beneficial Use pilot project will provide Maryland with better information on the quality of sediments behind the dam, dredging costs, dredged material reuse options, scalability, and feasibility for addressing Conowingo’s impacts. A revised request for proposals for this project was issued on November 13th, 2018 and Northgate-Dutra (ND) was awarded the contract in February 2019. To date ND has completed a literature and data review of existing sediment and bathymetric data behind Conowingo Dam and finalized a sediment characterization report describing the chemical and physical characteristics of Conowingo sediments.
The sediment characterization results will be used to categorize the dredged material according to MDE’s Innovative and Beneficial Reuse guidance and help determine environmentally safe reuse options. ND will be performing a Conowingo dredging demonstration in Fall of 2021, that will include additional sediment characterization and reuse evaluation of the dredge area, followed by an economic analysis to assess the market value of different Conowingo sediment reuses. Modeling tools are being evaluated to simulate different dredging scenarios and their influence on Chesapeake Bay water quality. The overall pilot project should be complete in spring of 2022. State partners on this pilot project include the Maryland Environmental Service, the Maryland Department of Natural Resources and the Maryland Geological Survey.
At the watershed scale, Maryland is working collaboratively with the CBP partnership on implementing a Conowingo Watershed Implementation Plan to reduce pollution in the Susquehanna River Basin upstream of Conowingo Dam. This work, coupled with Exlon’s pollution reduction and ecosystem restoration commitments in a settlement agreement with MDE, represent Maryland’s comprehensive strategy to reduce upstream and in-reservoir pollution and meet our 2025 Chesapeake Bay Restoration goals.
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