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Rock Creek Metals TMDLs

Monday, October 17, 2011

Rock Creek flows through Montgomery County, Maryland, and the northwest portion of Washington, DC, to join with the Potomac River. The watershed is 76.5 square miles with approximately 21 percent (or 15.9 square miles) in the District and 79 percent in Maryland.  Rock Creek was listed in 1998 for elevated levels of organics and metals in fish tissue and sediment in the Anacostia River. Subsequent water quality data suggested many of the pollutants of concern most likely did not contribute to the impairment, but total maximum daily loads (TMDLs) were required for lead, zinc, copper and mercury. The TMDLs were approved for upper and lower Rock Creek on February 27, 2004. 

The TMDLs were challenged in Friends of the Earth v. EPA 446 F.3d 140 (D.C. Cir. 2006) because the loads were not expressed in daily loads.  Following the case, a settlement agreement was reached between the US Environmental Protection Agency (EPA) and Anacostia Riverkeeper, Friends of the Earth, and Potomac Riverkeeper (Case No.: 1:09-cv-00098-JDB of January 15, 2009).  To meet the settlement requirements, EPA will revise the applicable TMDLs to express daily loads.  DDOE is working with EPA to collect/analyze data and revise the TMDLs for toxic parameters. 

The 2004 final approved TMDL documents and Draft revisions for metals in Rock Creek are included below.  The Draft revisions are presented in an appendix to the final 2004 TMDL and provide information and methodologies for calculating the daily load expressions in addition to minor updates to the hydrologic model. All other aspects of the TMDLs are the same.