This report presents maps of water depths (or bathymetry) and thickness of impounded (and previously impounded) bottom sediment in the study area and describes the collection of 20 sediment-grab samples (top 4 in. of sediment), 31 sediment-core samples (depth composited from 550 in., depending on the total depth of the sediment), and 12 measurements of PCB concentrations in the water column by means of a passive water-sampling system (PISCES). The report discusses the occurrence and geographic distribution of elements and organic compounds in the bottom sediment, as well as the potential adverse effects that these contaminants pose to aquatic organisms and humans. Throughout this report, the implications of these sediment data are discussed in terms of sediment-management options, such as sediment removal, and other river-restoration methods. Finally, this report details possible past and present source areas of polychlorinated biphenyls (PCBs) to the water, biota, and sediment of the lower Neponset River.