Oxon Run Organics, Metals and Fecal Coliform Bacteria TMDL and Revised E. coli Revision TMDL

Oxon Run is a tributary to the Potomac River. The Oxon Run watershed is approximately 7,906 acres, or 12.4 square miles. The mainstem extends approximately 6.8 miles from its headwaters in Prince George’s County to the downstream end at the District/Maryland boundary—flowing into the southeastern section of the District before crossing back over the Maryland State line and discharging into the Potomac River. The length of the impaired segment within the District is approximately 2.9 miles. Approximately 26 percent of the watershed is located in the District; the remainder of the Oxon Run watershed is located in Maryland.  Oxon Run was listed in 1998 for elevated levels of bacteria, organics and metals. The total maximum daily loads (TMDLs) were approved for the Potomac River tributary parameters identified in the table below on December 15, 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 agreed to revise the applicable TMDLs to express daily loads. 

On July 25, 2014, EPA approved the E. coli TMDL for Oxon Run as a revision to the previous bacteria TMDL that was originally approved in 2004.  The revision incorporates the new water quality standard for Escherichia coli (E. coli) that the District promulgated in October 2005.  The load allocations specified in the original TMDL are still in effect; however, the revision provides a translation of those loads from fecal coliform to E. coli, which is the basis for the current bacteria water quality standard. A translator equation was developed from analysis of paired fecal coliform and E. coli sampling data collected from waters in the District. In addition to the translations to E. coli, the daily loading expressions for the new E. coli allocations are also provided.  The revisions are presented as an appendix to each existing watershed’s TMDL.  They provide information and calculations regarding the translation from fecal coliform to E. coli, as well as methodologies for calculating the daily load expressions.

The District Department of the Environment (DDOE) is working with EPA to collect/analyze data and revise the TMDLs for toxic parameters.  The table below lists the TMDL water bodies and pollutant pair with the current impairment status in the District’s 2014 Integrated Report.  In the table below, those water body/pollutant pairs categorized in 4a will be revised.  However, in several water bodies, recent data was insufficient to support an impairment determination, or the samples met water quality standards and therefore the water body/pollutant was removed from the impaired list for a particular pollutant.

Summary table of Oxon Runharlan cobe organics and metals TMDL parameters by segment and 2014 impairment listing status

Notes:
Categories reflect the District’s category definitions in the Integrated Report

Category 3 - There is insufficient available data and/or information to make a use support determination. In this case, they were previously in category 4a, now in category 3.

Category 4a - A State developed TMDL has been approved by EPA or a TMDL has been established by EPA for any segment-pollutant combination.

Delisted - Previously in Category 4a, now unlisted

Black boxes represent parameters not included in TMDLs.

For more information, please see the District’s 2014 Integrated Report.

The final approved TMDL documents for bacteria, metals and organics in Oxon Run are included below.  The revised metals and organic TMDL documents will be posted when available.