Sampling Purpose: The U.S. Geological Survey Water Resources Division collected bed-sediment samples from the Illinois River Basin for the National Water Quality Assessment Program (NAWQA) in 1996 and 1997. A composite core or grab sample was collected and analyzed for particle size, carbon (organic, carbonate, total), metals, polynuclear aromatic hydrocarbons, organochlorines, fungicides, insecticides, herbicides, industrial and miscellaneous compounds, and polychlorinated biphenyls. Sediment subsamples were analyzed for both inorganic and organic contaminants and were sieved separately; therefore, each inorganic and organic sample was considered a discrete sample within the database. However, the same site information and particle size data were entered for both the inorganic sample and its organic counterpart. Lower quantitation limits for all contaminants were provided in several reports from the National Water Quality Laboratory. Note that this data set contained several additional contaminants that were not included in the database.