Final TMDLs Approved by EPA: Little Patuxent River

The Little Patuxent River is a free flowing stream that originates just north of Route 70 near the Howard County Landfill and flows 38 miles in a southeasterly direction until it joins the Patuxent River. The watershed is located in the Patuxent River sub-basin of the Chesapeake Bay watershed within both Howard and Anne Arundel Counties, Maryland and covers approximately 66,214 acres. From its headwaters, the river flows southeast through the densely urban town of Columbia, crossing under Route 29 just south of Lake Kittamaqundi. The river continues southeast crossing under Route 32, where the Middle Patuxent River joins the Little Patuxent River in the town of Savage, thereby significantly increasing the flow. The river continues to flow southeast crossing under Route 295, through the southwest corner of the Fort Meade Military Reservation, through the northeast section of the Patuxent Research Refuge, and it finally joins the Patuxent River just southeast of the Patuxent Research Refuge, between the towns of Bowie and Crofton, just before the Route 3 and Route 450 intersection. 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 antidegradation policy. Also, approximately 0.2% of the watershed area is covered by water (i.e., streams ponds, etc.). The total population in the watershed is nearly 266,000.

MDE has identified the waters of the Little Patuxent River watershed on the State’s 2008 Integrated Report as impaired by cadmium (1996), nutrients – phosphorus (1996, Centennial Lake - 1998), sediment (1996, Centennial Lake - 1998), and impacts to biological communities (2006). The designated use of the Little Patuxent River mainstem and its tributaries downstream of Old Forge Bridge is Use I (Water Contact Recreation and Protection of Aquatic Life), upstream of US Route 1 is Use IV-P (Recreational Trout Waters), and in between US Route 1 and Old Forge Bridge is Use I-P (Water Contact Recreation, Protection of Aquatic Life, and Public Water Supply).

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 cadmium was approved by the EPA in 2008, and a WQA for eutrophication to address the nutrient (phosphorus) listing was approved by the EPA in 2010. A TMDL of phosphorus and sediments for Centennial Lake was approved by the EPA in 2002. 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 Little Patuxent River Watershed, 
Howard and Anne Arundel 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 Lil_Patx_Sed_TMDL_Final  (2,108KB)
Point Source Technical Memorandum Lil_Patx_Sed_TMDL_PS_techmemo_Final (25KB)
Nonpoint Source Technical Memorandum Lil_ Patx_Sed_TMDL_NPS_techmemo_Final (14KB)
Comment Response Document Lil_Patx_Sed_TMDL_CRD_Final (7KB)

Additional Supporting Information

Biological Stressor Identification Little Patuxent River Watershed Report (698KB)
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.