Abstract

The Ontario Ministry of the Environment and the United States Environmental Protection Agency have singled out contaminated sediments as a major environmental problem. Many previous studies have evaluated the types and concentrations of contaminants captured in urban stormwater detention ponds. It was found that the concentrations of regulated compounds in sludge/sediments from stormwater detention ponds exceeded the Lowest Effect Level (LEL) of the Guidelines for the Protection and Management of Aquatic Sediment in Ontario. This study focused on the evaluation of the characteristics of stormwater sediments from different types of neighbourhoods. Neutron Activation Analysis (NAA) was used in the analysis of the compositions of sediments.

Four different stormwater ponds around the cities of Burlington and Hamilton, Ontario, Canada were sampled in the summer of 2005. Two ponds are located in residential areas, one is located in highway/commercial areas and the other is located in commercial/light industrial areas. Our measurement shows that the particle sizes range from 20 µm to 1258 µm and the particles had irregular shapes. Thirty-two elements were found in the sediments and nine among these thirty-two elements were below the NAA detection limit. Seven elements were detected with a concentration higher than 1000 ppm, six elements had a concentration between 100ppm and 1000ppm, and the remaining ten elements had a concentration lower than 100ppm.

The main compositions (above 1000ppm) of the dried sludge included Ca > Al > Fe > K > Mg > Na > Ti. The trace compositions (below 1000 ppm) included Mn > Cl > Ba > Sr > Zn > Cr > V > La > Nd > As > Co > Sc > Br > Sm > Th > Eu. Five regulated elements were detected by NAA. The concentrations of Cr, Fe, Mn and Zn in a residential area pond were higher than the LEL; the concentrations of Fe, Mn, Zn and As in another residential area pond were higher than the LEL while the concentration of Cr in the second residential area pond was above the SEL. The concentrations of Fe, Zn, Mn and As in a highway/commercial area pond were higher than the LEL while the concentration of Cr there was above the SEL. The concentrations of Fe, Zn, Mn and As in a commercial/light industrial area pond were higher than the LEL and the concentration of Cr there was higher than the SEL.

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