Kristin Karlsson

Temporal trends in stormwater pond sediment quality were evaluated by conducting field sediment surveys in 1998 and 2006. A sediment removal process in 2006 was also assessed. Results show that, for both years, the sediment closest to the inlet had the lowest concentrations of metals. The results from 1998 showed no significant differences in sediment heavy metal concentrations depth while the results from 2006 showed a decreasing trend with depth. A significant difference between the two years could be seen for Cr, Cu, and Pb. The water phase in the pond showed a difference before and after the removal of sediment. The water samples after emptying showed higher concentrations of metals as a result of disturbing and re-suspending the bottom sediment. No significant difference could be found in the samples taken from the bottom sediment before the removal of the sediment and from the sediment pile formed during the removal process. The total heavy metal concentration in water exceeded the threshold limits for the selected quality guidelines and, according to soil quality guidelines, the sediment would be classified moderately serious to serious.

A mixture of sediment and water is formed during the cleansing of catch basins. This paper discusses the concentration levels and distribution of numerous metals and organic carbon (OC) in the water phase of this mixture. The results show that due to the high concentrations of metals in the water phase, the catch basin mixture should be treated before it reaches a recipient. Three sites with different types of area and traffic intensity were sampled. Four fractions were analyzed: unfiltered, dissolved (<0.2 µm), colloidal (0.22 µm to 1 kD [kilodalton]), and truly dissolved (<1 kD). The results of the unfiltered fraction show high concentrations of metals and OC in the catch basin mixture. A comparison of Canadian and Swedish Environmental Protection Agency guidelines and the catch basin mixtures shows that concentrations exceeded the threshold values for As, Cd, Cr, Cu, Ni, Pb, and Zn. Compared with samples from a reference lake in the area, the unfiltered fraction showed high concentrations of all elements. OC seems to have a large impact on the overall speciation of trace metals in the catch basin mixture. To trace the sources of the particulate fraction in the unfiltered samples, Al-normalization was used. Al-normalization indicated that Ca, K, Mg, Na, Mn, Ba, Co, and Cr concentrations could be explained by mineral particles used as traction control. Furthermore, the trace elements As, Cu, Pb, Zn, and Ni were all enriched in the catch basin mixture.