This document, upon approval by the U.S. Environmental Protection Agency (EPA), presents a Water Quality Analysis (WQA) of sediment in the Potomac River Lower North Branch (LNB) watershed (basin number 02141001) (2010 Integrated Report of Surface Water Quality in Maryland Assessment Unit ID: MD-02141001). Section 303(d) of the federal Clean Water Act (CWA) and the EPAs 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, the State is 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 that water quality standards are being met (CFR 2010). The Maryland Department of the Environment (MDE) has identified the waters of the Potomac River LNB watershed on the States 2010 Integrated Report as impaired by sediments (1996), nutrients phosphorus (1996), methylmercury (2002), metals cadmium (1996), low pH (1996), and impacts to biological communities (2002) (MDE 2010a). The designated use of the Potomac River LNB mainstem, Mill Run and its tributaries, and an unnamed tributary to the Potomac River LNB mainstem near Pinto, Maryland and its tributaries is Use I-P (Water Contact Recreation, Protection of Aquatic Life, and Public Water Supply). All other tributaries in the Potomac River LNB watershed are designated as use III-P (Nontidal Cold Water and Public Water Supply) (COMAR 2010a,b,c,d,e).