ASSESSING THE RISK OF CONTAMINATED SEDIMENTS DURING SMALL DAM REMOVAL PROJECTS IN THE LONG ISLAND SOUND WATERSHED

Anthropogenic activities like urban and industrial wastewater discharge, releasing organic-rich sediments through irrigation practices, domestic sewage discharge through septic systems, and the burning of fossil fuels results in the accumulation of heavy metals in river systems. Dams in these river systems can disrupt the ecosystem by modifying the biological and physical characteristics of river channels and floodplains. The sediment trapped behind these dams often contains contaminants of anthropogenic origin including trace metals. This project focuses on three dams to be removed in the Long Island Sound Watershed: the Patchogue River Dam in Westbrook, CT, the Bladens River Dam in Seymour, CT, and the Wards Millpond Dam in Branford, CT. Surface sediment samples and cores were collected from above these dams. To assess the potential risk of downstream contamination after dam removal, we analyzed the distribution of heavy metals in dam impoundments. Sediment characteristics were acquired using the loss on ignition method to calculate percent organic matter, sieving and laser particle analysis to determine the sediment grain size, acid digestion of sediments using EPA Method 3050B, followed by flame atomic absorption spectroscopy to measure the metal concentration in the digest solutions. GIS analysis of the watersheds showed a similar land use profile, although the Branford River Watershed contains more developed area. Results show a strong covariance in metals, organic matter, and grain size. The cores from Westbrook and Branford locations show a higher concentration in surface sediments, while the Seymour location shows peaks in metal concentration at depth. Concentrations are highest in the Branford River Watershed, with zinc exceeding the probable effect level (PEL) threshold and copper and cadmium exceeding the threshold effect level (TEL) in core surface sediments (0-5cm). Peaks in cadmium, zinc, and mercury from the Westbrook and Seymour Watersheds exceed the TEL. Ultimately, developing a cost-effective methodology for testing these impounded sediments will aid in identifying dams for removal and the restoration of the natural Long Island Sound Watershed.