Section 303(d) of the federal Clean Water Act (CWA) and the U.S. Environmental Protection Agencys (EPA) implementing regulations direct each state to identify and list waters, known as water quality limited segments (WQLSs), in which current required controls of a specified substance are inadequate to achieve water quality standards. For each WQLS listed on the Integrated Report of Surface Water Quality in Maryland (Integrated Report), the State is required to either establish a Total Maximum Daily Load (TMDL) of the specified substance that the waterbody can receive without violating water quality standards, or demonstrate via a Water Quality Analysis (WQA) that water quality standards are being met (CFR 2007). The waters of Seneca Creek (MD basin code 02140208), located in Montgomery County, have been identified on the Integrated Report under Category 5 as impaired by nutrients (1996), sediments (1996), and impacts to biological communities (2002). All impairments are listed for non-tidal streams. The 1996 suspended sediment listing was refined in the 2008 Integrated Report to a listing for total suspended solids. Similarly, the 1996 nutrients listing were refined in the 2008 Integrated Report and phosphorus was identified as the specific impairing substance. Consequently, for the purpose of this report the terms nutrients and phosphorus will be used interchangeably. The listings for sediments and impacts to biological communities will be addressed separately at a future date.