Evaluation of Retention Pond and Constructed Wetland BMPs for Treating Particulate-bound Heavy Metals in Urban Stormwater Runoff

Author： Muthukrishnan Swarna Selvakumar Ariamalar

Publisher： Water Environment Federation

ISSN： 1938-6478

Source： Proceedings of the Water Environment Federation, Vol.2007, Iss.5, 2007-10, pp. : 969-990

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Abstract

The sources of heavy metals in urban stormwater runoff are diverse (e. g., highways, road surfaces, roofs) and the release of metals into the environment is governed by several complex mechanisms. Heavy metals in stormwater are associated with suspended particulate materials that vary from coarse (>75 μm) and fine particulates (<75 to 1 μm), to colloids (<1μm). Stormwater runoff investigations increasingly focus on evaluating quality and the effectiveness of adopting best management practices (BMPs) to minimize pollutant input, including heavy metals, to receiving waters. Heavy metals in stormwater are primarily removed by sedimentation in BMPs such as retention ponds and constructed wetlands; these sediments may be toxic to benthic invertebrates and aquatic microorganisms. Information on heavy metalsparticulate association is therefore a fundamental requirement prior to using wetland and pond BMPs for treatability studies. Research is being conducted at the U. S. EPA's Urban Watershed Research Facility in Edison, NJ to evaluate the effectiveness of retention pond and constructed wetland BMP mesocosms to remove particulate-bound heavy metals from roof and parking-lot stormwater runoff. The research objectives include: (i) investigating the association of selected heavy metals (Al, Cr, Cu, Fe, Mn, Pb, and Zn) with fine particulates (20 to 0.4 μm) in stormwater runoff; (ii) evaluating the relative removal of particulate-bound as well as dissolved heavy metals in retention ponds and cattail-wetland mesocosms; and, (iii) investigating the solidphase chemical associations of heavy metals in cattail wetland sediments and assessing the potential for sediment toxicity and heavy metal bioavailability. This investigation comprises the study of eight separate storm events; six sampling events have been completed to date. Preliminary results show that Al, Cr, Fe, and Pb are primarily particulate-bound (>20 μm) and Mn is mostly soluble. Cu and Zn are primarily associated with fine particulates (10 to 1 μm) and the dissolved fraction (<0.4 μm) in stormwater runoff. Also, the retention pond and cattail wetland mesocosms are effective in attenuating heavy metals, especially, Cu, Zn, Al, Cr, and Pb. Preliminary results are also presented for the chemical fractionation of cattail wetland sediments.