The North Branch of the Potomac River delineates the border between Maryland and West Virginia from its origin at the Fairfax Stone in West Virginia to its confluence with the South Branch of the Potomac near Oldtown, Maryland. The Potomac River Lower North Branch (LNB) is defined as the portion of the North Branch Potomac River extending 53 miles from the river’s confluence with the Savage River to its confluence with the South Branch Potomac River. The Potomac River LNB watershed is located in the North Branch Potomac River sub-basin of the Chesapeake Bay watershed within Allegany County, Maryland and covers approximately 114 square miles. There are no “high quality,” or Tier II, stream segments (Benthic Index of Biotic Integrity (BIBI) and Fish Index of Biotic Integrity (FIBI) aquatic life assessment scores > 4 (scale 1-5)) located within the watershed requiring the implementation of Maryland’s anti-degradation policy. Also, approximately 0.4% of the watershed is covered by water (i.e., streams, ponds, etc.). The total population in the Potomac River LNB watershed is approximately 50,420.
The Maryland Department of the Environment (MDE) has identified the waters of the Potomac River LNB watershed on the State’s 2010 Integrated Report as impaired by sediments (1996), nutrients – phosphorus (1996), methylmercury (2002), metals – cadmium (1996), low pH (1996), and impacts to biological communities (2002). The designated use of the Potomac River LNB mainstem, Mill Run and its tributaries, and an unnamed tributary to the Potomac River LNB mainstem near Pinto, Maryland and its tributaries is Use I-P (Water Contact Recreation, Protection of Aquatic Life, and Public Water Supply). All other tributaries in the Potomac River LNB watershed are designated as use III-P (Nontidal Cold Water 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 low pH was approved by the EPA in 2005, and a WQA for cadmium was approved by EPA in 2006. The watershed was also delisted for methylmercury in the 2010 Integrated Report. 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 Potomac River LNB 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 Potomac River LNB 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.
Although the waters of the Potomac River LNB 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 Potomac River Tidal Fresh Chesapeake 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 Potomac River Lower North Branch, Allegany County, Maryland
(Concurrence May 18, 2012)
EPA's Decision Letter
MDE's Decision Letter Edits
Please direct questions or comments concerning this project to Maryland's TMDL Program at (410) 537-3818.
1800 Washington Boulevard, Baltimore, MD 21230