The National Risk Management Research Laboratory (NRMRL) of the U.S. Environmental Protection Agencys (U.S. EPAs) Office of Research and Development (ORD) has been conducting research to develop methods and tools for the evaluation of monitored natural recovery (MNR) of sediments contaminated with polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), mercury, and other legacy pollutants. This research is supporting a broad, national research program focused on contaminated sediments in U.S. waterways. This Research Summary provides a synopsis of a multiyear, interdisciplinary research project conducted by ORD, specifically NRMRL and the National Exposure Research Laboratory (NERL), at the Sangamo-Weston, Inc./Twelve-Mile Creek/Lake Hartwell PCB Contamination Superfund Site in Pickens County, South Carolina. The methods and tools described in this Research Summary are comprised of quantitative approaches for characterizing naturally-occurring mechanistic processes that are necessary to manage risk using MNR. The information developed in this project is expected to be used as a reference for site managers and Federal, State, and local regulators who may be considering MNR as a site remedy or monitoring the progress of MNR at a contaminated sediment site(s). The methods and techniques evaluated and optimized in this study also provide the broader sediment community with an approach for characterizing environmental processes controlling the risk associated with contaminated sediments.