Differential Tracing of Oily Waste and the Associated Water Mass by Tagging with Rare Earths

摘要

A method was developed for tagging oily waste with dysprosium and the associated fresh water with samarium. Neutron activation analysis permitted determination of rare earth concentrations as low as 40 ng/l in 15-ml water samples. Shipboard sampling procedures were developed that allowed measurement of the three-dimensional distribution of the spreading wastes and associated water. The method was applied in two field experiments that involved tracing oily wastes and polluted water from the Indiana Harbor Canal (IHC) into Lake Michigan. For a summer, floating-plume experiment, about 1400 shipboard samples were collected. Employment of the dual-tracer technique led to the following results: (1) after artificial mixing into the water column by a passing ship, the tagged oil did not immediately resurface, and (2) there were no distinguishable differences between the movement of the oil and water over 4 km of travel. During a winter, sinking-pluma experiment, 1200 lake-water samples were collected from a boat and from the raw-water intakes of Chicago's South Water Filtration Plant (SWFP). These data provided positive evidence of the intake of IHC effluent and oily waste at the SWFP. The different tracers for the oily waste and underlying water gave evidence of separate pathways to the SWFP, reflecting differing transport modes for surfaces and near-bottom waters. (ERA citation 04:017092)