Urban stormwater ponds: Evaluation of heavy metals and organic pollutants in stormwater and stormwater sediments

Urban runoff is generated by precipitation of rain and snowmelt on impervious surfaces. The increasing demand of urbanization causes contaminants to accumulate on roads, roofs and pathways. In turn, as runoff wash off these surfaces, contaminants such as heavy metals, particles and organic pollutants end up in the stormwater. Urban stormwater ponds improve water quality of runoff by facilitating contaminants in form of particles. To preserve the function of a stormwater pond accumulated sediment must periodically be removed.Therefore, upland disposal alternatives should be evaluated. This study examined stormwater sediment and outlet stormwater quality in seven and four ponds respectively in the vicinity of Halmstad. 7 heavy metals and 24 organic contaminants were analysed in both sediments and stormwater. Results showed metal and organic contaminant concentrations in stormwater pond discharge and sediment exceeding concentrations reported in guideline values. From the analysed heavy metals, Zn and Pb was considered the most critical contaminants. Heavier organic compounds were more frequently quantified than lighter ones, where 42 % of the analysed organic contaminants were quantified in at least one sample. Variability between inlets and outlets, between ponds and between sampling occasions was observed. The observed variability suggests that the contamination level is influenced by catchment area characteristics and activities. Significant correlation from Spearman’s rank correlation was found between the individual heavy metals (Cu, Cr, Ni, Pb and Zn), which suggest they originate from similar source