WQA with EPA Concurrence of MDE's Findings: Conowingo Dam/Lower Susquehanna River

Conowingo Dam/Susquehanna River watershed is located in the Lower Susquehanna River sub-basin of the Chesapeake Bay watershed. The Susquehanna River is a free flowing river, at least for the majority of its length (the river becomes tidally influenced a few miles downstream of the Conowingo Dam), that originates in Cooperstown, New York and flows 444 miles in a southern direction until it empties into the Chesapeake Bay in Havre de Grace, Maryland. The River drains approximately 27,504 square miles. The watershed draining to the mainstem Susquehanna River between the Pennsylvania-Maryland border and the Conowingo Dam is referred to as the Conowingo Dam/Susquehanna River watershed, and it covers approximately 125 square miles, of which only 18 square miles are located in Maryland.

The MD 8-Digit Conowingo Dam/Susquehanna River watershed consists of 1) the mainstem of the Conowingo Dam/Susquehanna River, which is fully occupied by the Conowingo Pool (the impoundment created behind the Conowingo Dam) for the entire length of the mainstem within Maryland, and 2) the nontidal tributaries within Maryland that drain to the pool. Thus, the use of the term “nontidal MD 8-Digit Conowingo Dam/Susquehanna River watershed” throughout this report will refer to solely the nontidal tributaries within Maryland draining to the Conowingo Pool. The Maryland Department of the Environment (MDE) has identified the waters of the nontidal MD 8-Digit Conowingo Dam/Susquehanna River watershed on the State’s 2010 Integrated Report as impaired by nutrients – phosphorus (1996) and sediments (1996). These impairments are only applicable to the nontidal MD 8-digit watershed. The Conowingo Pool is assessed separately, and therefore, the impoundment is not included as part of the analysis presented herein. The designated use of the nontidal MD 8-Digit Conowingo Dam/Susquehanna River watershed is Use I-P (Water Contact Recreation, Protection of Aquatic Life, and Public Water Supply).

The WQA presented below by MDE will address the 1996 sediments listing, for which a data solicitation was conducted, and all readily available data from the past five years have been considered. A WQA for eutrophication to address the nutrients/phosphorus listing was submitted to the EPA in 2011. The analysis presented in the report supports the conclusion that a TMDL for sediments is not necessary to achieve water quality standards in the nontidal MD 8-Digit Conowingo Dam/Susquehanna River watershed. Barring the receipt of contradictory data, this report will be used to support a revision of the 2010 Integrated Report sediment listing for the nontidal MD 8-Digit Conowingo Dam/Susquehanna River watershed from Category 5 (“waterbody is impaired, does not attain the water quality standard, and a TMDL is required”) to Category 2 (“waterbody is meeting some [in this case sediments-related] water quality standards, but with insufficient data to assess all impairments”), when MDE proposes the revision of the Integrated Report in 2012. 

Although the waters of the nontidal MD 8-Digit Conowingo Dam/Susquehanna River watershed do not display signs of a sediment impairment, the State reserves the right to require future controls in the watershed if evidence suggests that sediments from the basin are contributing to downstream water quality problems. For example, reductions will be required to meet allocations assigned to the Northern Chesapeake Bay Tidal Fresh Bay Water Quality Segment, as specified by the Chesapeake Bay Nutrient and Sediment TMDLs, established by EPA on December 29, 2010.


Water Quality Analysis of Sediment in the Conowingo Dam/Susquehanna River Watershed, Cecil and Harford Counties, Maryland

(Concurrence May 18, 2012)

EPA's Decision Letter

EPA's Decision Letter

MDE's Edits to EPA's Decision Letter

MDE's Decision Letter Edits

Main Report  WQA Conowingo_Susquehanna_Sediment.pdf (953KB)
Comment Response Document CRD Conowingo_Susquehanna_Sediment.pdf (7KB)

Contact Information

Please direct questions or comments concerning this project to Maryland's TMDL Program at (410) 537-3818.