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

The Little Patuxent River watershed is located in the Patuxent River region of the Chesapeake Bay watershed within Maryland.  The Little Patuxent River originates just north of Route 70 near the Howard County Landfill.  The river flows southeast through the heavily suburbanized area of Columbia crossing under Route 29 just south of Lake Kittamaqundi.  The Little Patuxent River continues southeast crossing under Route 32 where the Middle Patuxent River joins the Little Patuxent River in the town of Savage.  The Little Patuxent River, now larger due to the influx of the Middle Patuxent River, continues to flow southeast crossing under Route 295, through the southwest corner of the Fort Meade Military Reservation, and through the northeast section of the Patuxent Research Refuge.  The Little Patuxent River joins the Patuxent River just southeast of the Patuxent Research Refuge between the towns of Bowie and Crofton just before the Routes 3 and 450.

The Little Patuxent River watershed (assessment unit ID: MD-02131105) was identified in Maryland’s Integrated Report as impaired by cadmium (listed in 1996), nutrients (1996), sediment (1996), and impacts to biological communities (2006).  Centennial Lake located within the watershed as identified as impaired by nutrients (1998) and sediment (1998).  The Centennial Lake listings have been addressed by TMDLs approved in 2002.  The cadmium listing has been addressed by a Water Quality Analyses (WQA), submitted in 2008, showing no impairment.  The 1996 nutrients listing was refined in the Integrated Report by identifying phosphorus as the specific impairing substance.  Consequently, for the purpose of this report the terms nutrients and phosphorus will be used interchangeably.  The listings for sediment and impacts to biological communities will be addressed separately at a future date.

A data solicitation for information pertaining to pollutants, including nutrients, in the Little Patuxent River basin was conducted by MDE in January 2005, and all readily available data from the past five years have been considered.  Currently, Maryland’s water quality standards do not contain specific numeric criteria for nutrients.  Nutrients typically do not have a direct impact on aquatic life; rather, they mediate impacts through excessive algal growth leading to low dissolved oxygen.  Therefore, the evaluation of potentially eutrophic conditions due to nutrient over-enrichment will be based on whether nutrient-related parameters (i.e., dissolved oxygen levels and chlorophyll a concentrations) are found to impair designated uses in the Little Patuxent River watershed (in this case, protection of aquatic life and wildlife, fishing, and swimming).

Recently, MDE developed a biological stressor identification (BSID) methodology to identify the most probable cause(s) of the existing biological impairments in Maryland 8-digit watersheds based on the suite of available physical, chemical, and land use data.  The BSID analysis for the Little Patuxent River watershed indicates inorganic pollutants and flow/sediment stressors are associated with impacts to biological communities; these findings will be addressed separately. The BSID analysis for the Little Patuxent River watershed did not identify any nutrient-related stressors present and/or nutrient-related stressors showing a significant association with degraded biological conditions.  The results of the BSID study, combined with the analysis of recent water quality data presented in the report available below, indicate that the Little Patuxent River watershed is not being impaired by nutrients.

The analysis, available below, supports the conclusion that a TMDL for nutrients is not necessary to achieve nutrient related water quality standards in the Little Patuxent River watershed.  Although the waters of the Little Patuxent River watershed do not display signs of eutrophication, the State reserves the right to require future controls in the watershed if evidence suggests that nutrients from the basin are contributing to downstream water quality problems.  Reductions may be required by the forthcoming Chesapeake Bay TMDL, currently under development and scheduled to be completed by the EPA at the end of 2010.

Barring the receipt of contradictory data, the report will be used to support a revision of the nutrients (i.e., phosphorus) listing for the Little Patuxent River watershed, from Category 5 (waterbody is impaired, does not attain the water quality standard, and a TMDL is required) to Category 2 (waterbodies meeting some [in this case nutrients-related] water quality standards, but with insufficient data to assess all impairments) when MDE proposes the revision of the Integrated Report.

Water Quality Analysis of Eutrophication for the Little Patuxent River Basin in Anne Arundel and Howard Counties, Maryland

(Concurrence March 15, 2010)

EPA's Decision Letter

EPA's Decision Letter

Main Report

WQA_Little_Pax_eutro.pdf (546KB)

Comment Response Document

CRD_Little_Pax_eutro.pdf (7KB)

Additional Supporting Information

Biological Stressor Identification Little Patuxent River Watershed Report

BSID_LittlePatuxentRiver.pdf (697KB)

Biological Stressor Identification Methodology Report

BSID Methodology.pdf (459KB)


Contact Information

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