An Evaluation of the Toxicity of Accumulated Sediments in Forebays of Stormwater Wetlands and Wetponds

摘要

Forebays, small settling basins placed at the inlet of Stormwater Best Management Practices (BMPs), encourage sedimentation with the intention of pollutant consolidation and capture. Regularly, accumulated sediments are excavated to restore forebay storage volume and to further prevent contamination of downstream waterbodies during large storm events. Disposal measures for excavated solids would vary according to the toxicity of sediments. To test for the potential toxicity of forebay spoils, thirtystormwater wetland and wetpond forebays, of varying age, size, and upstream landuse were sampled across North Carolina and analyzed for 7 metals: cadmium, chromium, copper, iron, lead, nickel, and zinc. Ten of 30 sites were also sampled near the outlet structures for a spatial comparison of settled sediment pollutant presence. The relative toxicity of all sampled sediment metal concentrations was evaluated using existing aquatic health sediment guidelines and U.S. Environmental Protection Agency (EPA) standards for the land application of biosolids (40 CFR503). Twenty-two of 30 forebays exceeded sediment guidelines for aquatic health with respect to one or more.metals, emphasizing the need for routine forebay sediment removal. All samples were less than 40 CFR 503 limits with factors of safety ranging from 5 to 13, indicating that land application of forebay sediment is an acceptable means of disposal.