Final TMDL Approved by EPA: Patuxent River Lower Watershed

The Patuxent River is the largest river completely located in Maryland, and the basin lies between two large metropolitan areas – Baltimore, Maryland and Washington, D.C. The Patuxent River is comprised of eight separate MD 8-digit watersheds. The Patuxent River Lower watershed is located in Anne Arundel, Calvert, Charles, Prince George’s, and St Mary’s Counties. The watershed starts at the outlet of the Patuxent River Middle watershed, approximately 5 miles north of the town of Lower Marlboro. It encompasses the Patuxent River mainstem and all tributaries until the confluence with the Chesapeake Bay. A considerable portion of the watershed is tidal, and the navigable portion is crossed by two bridges. One bridge is located on RT 231 in the town of Benedict which is approximately the middle of the watershed. The other bridge is located on RT 4 near the confluence of the Patuxent River and the Chesapeake Bay.  The Patuxent River Lower watershed is located solely within the Coastal Plain Province of Maryland. According to the Chesapeake Bay Program’s Phase 5.3.2 watershed model, the total drainage area of the Maryland 8-digit watershed is approximately 205,500 acres, not including water/wetlands. Approximately 1,800 acres of the watershed area is covered by water.
There are five “high quality,” or Tier II, stream segments (BIBI and FIBI aquatic life assessment scores > 4 [scale 1-5]) located within the Patuxent River Lower watershed. Tier II segments require the implementation of Maryland’s anti-degradation policy.
The Patuxent River Lower watershed is associated with five assessment units in Maryland’s Integrated Report: a non-tidal 8-digit watershed (02131101) and four estuary portions – Upper Patuxent Tidal Fresh (PAXTF) Lower Patuxent River Mesohaline (PAXMH), Middle Patuxent River Oligohaline (PAXOH), and Lower Chesapeake Bay Mesohaline (CB5MH-MD) segments.
The TMDL, available below, only addresses the non-tidal portion of the watershed. Sediment TMDLs for the tidal estuaries were established as part of the Chesapeake Bay TMDLs in 2010. A data solicitation for TSS was conducted by MDE in March 2016, and all readily available data have been considered. 
The TMDL, available below, will ensure that watershed sediment loads are at a level to support the designated uses for the Patuxent River Lower watershed, and more specifically, at a level to support aquatic life. 

Total Maximum Daily Load of Sediment in the Non-tidal Patuxent River Lower Watershed, Anne Arundel, Calvert, Charles, Prince George's and Saint Mary's Counties, MD

(Approved on July 2, 2018)

EPA's Decision Letter EPA's Decision Letter (8,654KB)
​Fact Sheet Patuxent_River_Lower_Sed_TMDL_FactSheet.pdf (365KB)
Main Report

Patuxent_River_Lower_Sed_TMDL_final.pdf (1,803KB)

Point Source Technical Memorandum Patuxent_River_Lower_Sed_TMDL_PS_TechMemo.pdf (53KB)
Nonpoint Source Technical Memorandum Patuxent_River_Lower_Sed_TMDL_NPS_TechMemo.pdf (33KB)
Comment Response Document Patuxent_River_Lower_Sed_TMDL_CRD.pdf (17KB)

Additional Supporting Information

Biological Stressor Identification Patuxent River Lower Watershed Report (612KB)

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.