Final TMDLs Approved by EPA: Rock Creek

Rock Creek is a free-flowing stream that originates near the town of Laytonsville in Montgomery County, Maryland and flows 23 miles in a southeasterly direction until it empties into the tidal Potomac River in Washington, D.C.   The watershed is located in the Middle Potomac River sub-basin of the Chesapeake Bay watershed within both Montgomery County, Maryland and Washington, D.C.   The entire watershed comprises 52,761 acres, of which 39,273 acres are located within Montgomery County, Maryland.

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 (Water Contact Recreation, and Protection of Nontidal Cold Water Aquatic Life), and 2) the Rock Creek mainstem and its tributaries in between Route 28 and Muncaster Mill Road, which are designated as Use IV (Water Contact Recreation, Protection of Aquatic Life and Recreational Trout Waters).    

The Maryland Department of the Environment (MDE) has identified the waters of the Rock Creek watershed on the State’s 2010 Integrated Report as impaired by nutrients (1996) and impacts to biological communities (2002).   Because scientific research supports that phosphorus is generally the limiting nutrient in freshwater aquatic systems, the 1996 nutrients listing was refined in the 2008 Integrated Report to identify phosphorus as the specific impairing substance.   Therefore, the listed impairment of phosphorus will henceforth be referred to in this report and the term “nutrients” should be read as interchangeable with “phosphorus” in this case.

Once approved by EPA, the document, available below, establishes a TMDL for Nutrients (Phosphorus) in the Rock Creek watershed.   A data solicitation for nutrients was conducted by MDE in 2009, and all readily available data from 1998 up to the time of the TMDL development have been considered.   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 TMDL for sediment was approved by EPA in 2011.   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 Phosphorus in the Rock Creek Watershed, Montgomery County, Maryland 

(Approved on September 26, 2013)

EPA's Decision Letter EPA's Decision Letter (999KB)
Main Report

Rock_Creek_NutTMDL_fa.pdf (1,540KB)

Point Source Technical Memorandum

Rock_Nutrient_PS_techmemo_fa.pdf (30KB)

Nonpoint Source Technical Memorandum

Rock_Nutrient_NPS_techmemo_fa.pdf (17KB)

Comment Response Document

Rock_Creek_NutTMDL_CRD_fa.pdf (150KB)

Additional Supporting Information

Biological Stressor Identification Rock Creek Watershed Report

Rock_Creek_BSID_Report.pdf (1,110KB)

Biological Stressor Identification Methodology

Biological Stressor Identification Methodology(459KB)


Contact Information

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