Final TMDLs Approved by EPA: Patuxent River Upper

The Patuxent River Upper is a free flowing stream that originates at the discharge of the Rocky Gorge Reservoir near Interstate 95 and flows 28 miles in a southeasterly direction until it joins the Patuxent River, only a few miles upstream of the river’s tidal boundary. The watershed is located in the Patuxent River sub-basin of the Chesapeake Bay watershed within Howard, Anne Arundel, and Prince George’s Counties, Maryland and covers approximately 56,446 acres. Both the Little Patuxent River and the Rocky Gorge Reservoir empty into the Patuxent River Upper. There is one “high quality”, or Tier II, stream segment (Benthic Index of Biotic Integrity (BIBI) and Fish Index of Biotic Integrity (FIBI) aquatic life assessment scores > 4 (scale 1 – 5)), which is the mainstem of the Patuxent River Upper between the river’s confluence with Horsepen Branch to the immediate downstream confluence with the an unnamed tributary, located within the watershed requiring the implementation of Maryland’s antidegradation policy. Also, approximately 0.3% of the watershed area is covered by water (i.e., streams ponds, etc.). The total population in the watershed is nearly 165,898.

MDE has identified the waters of the Patuxent River Upper watershed on the State’s 2008 Integrated Report as impaired by nutrients – nitrogen and phosphorus (1996), sediment (1996), bacteria (2002 and 2008), methylmercury - Cash Lake (2004), and impacts to biological communities (2006). The designated use of the Patuxent River Upper mainstem and its tributaries is Use I (Water Contact Recreation and Protection of Aquatic Life).

The TMDL, available below, addresses the 1996 sediments listing, for which a data solicitation was conducted, and all readily available data from the past five years were considered. The TMDL sets the maximum load limit for sediments, and provides load allocations to point and nonpoint sources. A Water Quality Analysis (WQA) for eutrophication to address the nutrients (nitrogen and phosphorus) listing was approved by EPA in 2007, and the watershed was delisted for bacteria in 2002 (relisted in 2008 – mainstem only from Old Queen Anne's Bridge Road to the river’s confluence with the Little Patuxent River). A methylmercury TMDL for Cash Lake is scheduled to be submitted to the EPA in 2010. In the 2012 Integrated Report, the listing for impacts to biological communities will include the results of a stressor identification analysis. 

Total Maximum Daily Load of Sediment in the Patuxent River Upper Watershed, 
Anne Arundel, Howard, and Prince George's Counties, Maryland

(Approved on September 30, 2011)

EPA's Decision Letter EPA's Decision Letter 
(Does not include MDE's requested revisions)
MDE's Edits to EPA's Decision Letter MDE's Decision Letter Edits (35KB)
Main Report UpperPatx_Sed_TMDL_Final  (2,099KB)
Point Source Technical Memorandum UpperPatx_Sed_TMDL_PS_techmemo_Final (24KB)
Nonpoint Source Technical Memorandum Upper Patx_Sed_TMDL_NPS_techmemo_Final (14KB)
Comment Response Document UpperPatx_Sed_TMDL_CRD_Final (7KB)

Additional Supporting Information

Biological Stressor Identification Patuxent River Upper Watershed Report (633KB)
Biological Stressor Identification Methodology (459KB)
Nontidal Sediment TMDL Methodology Report (361KB)
Addendum to the Nontidal Sediment TMDL Methodology Report (23KB)


Contact Information

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