This document, upon approval by the U.S. Environmental Protection Agency (EPA), establishes a Total Maximum Daily Load (TMDL) for sediment in the Potomac River Washington County watershed (basin number 02140501) (2008 Integrated Report of Surface Water Quality in Maryland Assessment Unit ID: MD-02140501). 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 required to either establish a 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 2010b). The Maryland Department of the Environment (MDE) has identified the waters of the Potomac River Washington County on the States 2008 Integrated Report as impaired by nutrients phosphorus (1996), sediments (1996), methylmercury (2002), impacts to biological communities (2002), and polychlorinated biphenyls (PCBs) in fish tissue (2008) (MDE 2008). The designated use of the Potomac River Washington County mainstem and its tributaries is Use I-P (water contact recreation, protection of aquatic life, and public water supply), except for Camp Spring Run, which is designated as Use III-P (nontidal cold water and public water supply) (COMAR 2010a,b,c). The TMDL established herein by MDE will address the 1996 sediments listing, for which a data solicitation was conducted, and all readily available data from the past five years have been considered. A Water Quality Analysis (WQA) for eutrophication to address the nutrients/phosphorus listing is scheduled to be submitted to the EPA in 2010. In the 2012 Integrated Report, the listing for impacts to biological communities will include the results of a stressor identification analysis, and the PCBs in fish tissue and methylmercury listings will be addressed at a future date. The Potomac River Washington County watershed aquatic life assessment scores, consisting of the Benthic Index of Biotic Integrity (BIBI) and Fish Index of Biotic Integrity (FIBI), indicate that the biological metrics for the watershed exhibit a significant negative deviation from reference conditions based on Marylands biocriteria listing methodology. The biocriteria listing methodology assesses the overall average condition of Marylands 8-digit (MD 8-digit) watersheds by measuring the percentage of sites, translated into watershed stream miles, that are assessed as having BIBI and/or FIBI scores significantly lower than 3.0 (on a scale of 1 to 5), and then calculating whether the percentage differs significantly from reference conditions (i.e., unimpaired watershed <10% of stream miles differ from reference conditions) (Roth et al. 2005; MDE 2008). The objective of the TMDL established herein is to ensure that watershed sediment loads are at a level to support the Use I-P/III-P designations for the Potomac River Washington County watershed, and more specifically, at a level to support aquatic life.