Water Quality Analyses (WQA) with EPA Concurrence of MDE's Findings: Middle Patuxent River

The Middle Patuxent River originates just south of Rt. 144 in the area of Cooksville.  The river flows southeast crossing under Rt. 32 and flowing directly through the University of Maryland Central Farm Area (UMFCA).  From the UMCFA the river continues south crossing under Rt. 108 and into the Middle Patuxent Environmental Area.  Continuing southeast the river crosses under Cedar Lane and Rt. 32 where it defines the northeast property of the Johns Hopkins University Applied Physics Laboratory.  The River merges with the Little Patuxent River just south of Interstate 95 near the town of Savage.

Middle Patuxent River (basin code 02131106), located in Howard County, Maryland, was identified on the State’s list of Water Quality Limited Segments (WQLSs) as impaired by zinc (Zn) (1996), sediments (1996), nutrients (1996), and impacts to biological communities (2004 listing).  The information used for listing Zn is suspect due in part to sampling and analysis methods available at the time, and assessment inconsistencies that led to the listing in 1996.

The report available below provides an analysis of recent monitoring data, which shows that the aquatic life criteria and designated uses associated with Zn are being met in the Middle Patuxent River watershed, and that the 303(d) impairment listings associated with Zn are not supported by the analyses contained herein.  The analyses support the conclusion that a TMDL for Zn is not necessary to achieve water quality standards.  Barring the receipt of contradictory data, this report will be used to support a Zn listing change for the Middle Patuxent River from Category 5 (“waterbodies impaired by one or more pollutants requiring a TMDL”) to Category 2 (“Surface waters that are meeting some standards and have insufficient information to determine attainment of other standards”), when the Maryland Department of the Environment (MDE) proposes the revision of Maryland’s 303(d) list for public review in the future.  The listings for sediments, nutrients, and impacts to biological communities will be addressed separately at a future date. 
Although the waters of the Middle Patuxent River watershed do not display signs of toxic impairments due to Zn, the State reserves the right to require additional pollution controls in the Middle Patuxent River watershed if evidence suggests that Zn from the basin is contributing to downstream water quality problems. 

Water Quality Analysis of Zinc in Middle Patuxent River, Howard County, Maryland

(Concurrence: July 2, 2009)

EPA's Decision Letter EPA's Decision Letter

Main Report

WQA_Middle_Patuxent_Zn.pdf (622KB)

Comment Response Document

CRD_Middle_Patuxent_Zn.pdf (7KB)

Contact Information

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