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EVALUATION OF RETENTION POND AND CONSTRUCTED WETLAND BMPS FOR TREATING PARTICULATE-BOUND HEAVY METALS IN URBAN STORMWATER RUNOFF
Citation:
MUTHUKRISHNAN, S. AND A. SELVAKUMAR. EVALUATION OF RETENTION POND AND CONSTRUCTED WETLAND BMPS FOR TREATING PARTICULATE-BOUND HEAVY METALS IN URBAN STORMWATER RUNOFF. Presented at 2006 World Water and Environmental Resources Congress , Omaha, NE, May 21 - 25, 2006.
Description:
Urban stormwater discharge during wet-weather flows is a major contributor to the pollution of many receiving waters. Heavy metals are of particular interest in stormwater runoff due to their toxicity, ubiquitousness, and their inability to degrade in the environment. The sources of heavy metals in urban stormwater runoff are numerous (e.g., highways, road surfaces, roofs) and the release of metals into the environment is governed by several complex mechanisms. These metals are either dissolved in the stormwater or bound to particulates and this chemical partitioning has a major effect on the occurrence, transport, fate, and biological effects of heavy metals in aquatic systems. 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 (<1 µm). 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. Sedimentation is believed to be the principal process by which vegetated control facilities and other BMPs improve runoff quality. It has been recognized that heavy metals in stormwater are primarily removed by sedimentation in pond BMPs and constructed wetlands, and these sediments may be toxic to benthic invertebrates and aquatic microorganisms. The geochemical partitioning of these metals should be an important consideration for BMP selection. Information on their particulate 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 following heavy metals were chosen based on an earlier screening procedure: Copper (Cu), Zinc (Zn), Lead (Pb), Chromium (Cr), Iron (Fe), Aluminum (Al), and Manganese (Mn). The research objectives include: (i) investigating the association of heavy metals 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 solid-phase chemical associations of heavy metals in cattail wetland sediments by selective sequential extraction procedures and thereby assessing the potential for sediment toxicity and heavy metal bioavailability. This investigation comprises the study of eight separate storm events (two rain events per season - spring, summer, fall, and winter) out of which three stormwater sampling events (two events in spring and one event in summer 2005) have been completed to date. Preliminary results showed that Fe and Al were primarily particulate-bound;