Final TMDLs Approved by EPA: Rock Creek

Rock Creek is a free flowing stream that originates near the town of Olney in Montgomery County, Maryland and flows 23 miles in a southeasterly direction until it empties into the tidal Potomac River in Washington, DC. The watershed is located in the Middle Potomac River sub-basin of the Chesapeake Bay watershed within both Montgomery County, Maryland and Washington, DC. The entire watershed comprises 52,761 acres, of which 39,267 acres are located within Montgomery County, Maryland.

The North Branch of Rock Creek originates at Mount Zion, Maryland and discharges into the Rock Creek mainstem in Rockville, Maryland. There are two impoundments located in the watershed: Needwood Lake and Lake Bernard Frank. 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 Rock Creek watershed is approximately 307,000.

The Maryland Department of the Environment (MDE) has identified the waters of the Rock Creek watershed on the State’s 2008 Integrated Report as impaired by nutrients – phosphorus (1996, Needwood Lake – 1998, and Lake Bernard Frank - 1998), sediments (1996), bacteria (2002 listing), and impacts to biological communities (2002). The designated use of the Rock Creek mainstem and its tributaries is Use I (Water Contact Recreation and Protection of Nontidal Warmwater Aquatic Life), except for 1) the Rock Creek mainstem and its tributaries and the North Branch Rock Creek and its tributaries above Muncaster Mill Road, which are designated as Use III (Nontidal Coldwater), and 2) the Rock Creek mainstem and its tributaries in between Route 28 and Muncaster Mill Road, which are designated as Use IV (Recreational Trout Waters). 

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 TMDLs set the maximum load limit for sediments, and provides load allocations to point and nonpoint sources. A TMDL for bacteria was approved by the EPA in 2007.  Water Quality Analyses (WQAs) for eutrophication to address the Needwood Lake and Lake Bernard Frank nutrients/phosphorus listings were approved by the EPA in 2003. A phosphorus TMDL to address the Maryland 8-digit (MD 8-digit) watershed nutrients/phosphorus listing is scheduled to be submitted to the EPA in 2010 or 2011, and 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 Rock Creek Watershed,
Montgomery County, Maryland

(Approved on September 29, 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 Rock_Creek_Sed_TMDL_Final  (1628KB)
Point Source Technical Memorandum Rock_Creek_Sed_TMDL_PS_techmemo_Final (23KB)
Nonpoint Source Technical Memorandum Rock_Creek_Sed_TMDL_NPS_techmemo_Final (14KB)
Comment Response Document Rock_Creek_Sed_CRD_Final (28KB)

Additional Supporting Information

Biological Stressor Identification Rock Creek Watershed Report (368KB)
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.