Toxic Element Analyses of Summer and Winter Storm-Water Sediment by Neutron Activation Analyses

To maintain the effectiveness of a storm-water detention/retention pond, the sediments accumulating at the bottom the pond must be periodically removed and treated for ultimate disposal. The required pond clean-outs may be executed during the winter months to minimize the impact on the pond’s operation and the recreational use of surrounding areas. However, the difference in trace element concentrations of storm-water sediments between the winter and summer months has not been fully investigated because most earlier studies focused on the summer season and sediment samples were seldom collected during the winter months. In this study, sediment samples were deliberately collected during both the winter and summer seasons at the same location. Neutron activation analysis (NAA) and prompt gamma ray techniques were used to determine the trace element concentration in the sediment samples, while a laser diffraction particle size analyzer and an optical microscope were used to analyze the sizes and shapes of sediment particles. The results show that the concentrations of Al, Na, and Cl in the winter samples are higher than those in the summer samples, while the concentrations of Ca and Mg in the summer sediment samples are higher than those in the winter sediment samples. The five regulated elements in both the summer and winter samples are higher than the Lowest Effect Level defined for sediment quality by the Government of Ontario, Canada. In the winter sample, the concentration of Cr is even higher than the Severe Effect Level. The concentrations of other detected elements are same level of concentration between the winter and summer sampled sludges.