EVALUATION OF THE EXTENT OF CONTAMINATED SEDIMENTS IN THE WEST BRANCHOF THE GRAND CALUMET RIVER, INDIANA-ILLINOIS, USA

The extent of contamination in river sediments is often not rigorously evaluated. In many cases, only surface sediment samples are taken. In other cases, entire sediment cores are composited for analysis, an ap proach that limits the ability to identify discrete zones of contamina tion. In addition, few studies include information on the mte of sedim entation. Composited sediment cores, subsamples of cores made at discr ete intervals, and surface samples were obtained from locations in the West Branch of die Grand Calumet River. The organic carbon content an d concentrations of up to 26 major, minor, and trace elements were det ermined. Sedimentation rates at the ten locations were estimated using Cs-137. The mean concentrations of metals in the surface samples were considerably higher than concentrations in samples obtained by the tw o coring approaches. Only by analyzing discrete subsamples was it poss ible to plot the concentrations by depth and location. This approach w as used to demonstrate that high levels of organic carbon and trace el ements are confined between river miles 5 and 7.5. Sedimentation rate information combined with chemical analyses of the same cores indicate that contamination of this part of the river began in the 1930s.