The Potomac River Montgomery County watershed, which is located predominately in Montgomery County, MD, covers 89,617 acres. Small portions also extend into Frederick County, MD (448 acres) and Washington, DC (1,369 acres). The watershed contains the mainstem of the Potomac River within Montgomery County and all tributaries except Seneca Creek and Cabin John Creek. The watershed encompasses numerous sub-watersheds, including Little Monocacy River, Broad Run, Horsepen Branch, Muddy Branch, Watts Branch, Rock Run, and Little Falls Branch. Several highly developed areas occur in the watershed including parts of Gaithersburg, Rockville, Bethesda, and Chevy Chase.
The Potomac River Montgomery County watershed (basin code 02140202) was identified on the 2008 Integrated Report under Category 5 as impaired by nutrients and sediments—non-tidal 8-digit watershed (1996 listings); impacts to biological communities—1st through 4th order streams (2006 listing); and toxics: polychlorinated biphenyls (PCBs) in fish tissues—non-tidal 8-digit watershed (2008 listing). The 2008 Integrated Report specified that the designated use impaired by nutrients and sediment is Aquatic Life and Wildlife. The 1996 suspended sediment listing was refined in the 2008 Integrated Report to a listing for total suspended solids. Similarly, the 1996 nutrients listing was refined in the 2008 Integrated Report, and phosphorus was identified as the specific impairing substance. Consequently, for the purpose of this report the terms “nutrients” and “phosphorus” will be used interchangeably. The listings for sediments, impacts to biological communities, and PCBs in fish tissues will be addressed separately at a future date.
Barring the receipt of contradictory data, the report available below, will be used to support a revision of the phosphorus listing for the Potomac River Montgomery County watershed, from Category 5 (“waterbody is impaired, does not attain the water quality standard, and a TMDL is required”) to Category 2 (“waterbodies meeting some [in this case nutrients-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 Montgomery County do not display signs of eutrophication, the State reserves the right to require future controls if evidence suggests that nutrients from the watershed are contributing to downstream water quality problems. For instance, reductions will be required to meet allocations assigned to the Potomac Tidal Fresh Bay Water Quality Segment by the Chesapeake Bay TMDL, established by EPA on December 29, 2010.
Water Quality Analysis of Eutrophication for the Potomac River Montgomery County Watershed, Montgomery and Frederick Counties, Maryland
(Concurrence May 18, 2012)
EPA's Decision Letter
Please direct questions or comments concerning this project to Maryland's TMDL Program at (410) 537-3818.
1800 Washington Boulevard, Baltimore, MD 21230