An Evaluation of the Toxicity of Accumulated Sediments in Forebays of Stormwater Wetlands and Wetponds
- 214 Downloads
Forebays, small settling basins placed at the inlet of Stormwater Best Management Practices, 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 vary according to the toxicity of sediments. To test for the potential toxicity of forebay spoils, 30 stormwater wetland and wetpond forebays of varying age, size, and upstream landuse were sampled across North Carolina and analyzed for seven metals: cadmium, chromium, copper, iron, lead, nickel, and zinc. Ten of 30 sites were also sampled near the outlet structures for spatial comparison of settled sediment and pollutant presence. The relative toxicity of all sampled sediment metal concentrations was evaluated using existing aquatic health sediment guidelines and US Environmental Protection Agency standards for the land application of biosolids (40 CFR503). Of 30 sites, 17 exceeded sediment guidelines for aquatic health, emphasizing the need for routine forebay sediment removal. However, all samples were less than 40 CFR 503 limits with factors of safety ranging from 2.3 to 28, indicating that land application of forebay sediment is unlikely to pose an environmental threat. Additionally, forebay sediment tended to have lower metal toxicity than sediment collected at the pond or wetland outlet.
KeywordsSediment Forebays Stormwater wetlands Stormwater wetponds Water quality Land application
Several NCSU students and faculty assisted with data collection of this project: Cole Ammons, Robert Brown, Amelia Clark, W. Evan Corbin, Shawn Kennedy, Trisha Moore, Bill Price, and Erica Tillinghast. Public works officials in the following municipalities are very much appreciated: Apex Charlotte, Durham, and High Point. Each assisted with pond and wetland identification and location. Officials in Durham expended a substantial amount of effort in helping the research team and are especially thanked.
- Australian and New Zealand Environment and Conservation Council (ANZECC): Agriculture and Resource Management Council of Australia and New Zealand. (2000). Australian and New Zealand Guidelines for Fresh and Marine Water Quality: volume 2—Aquatic Ecosystems—Rationale and Background Information. http://www.mincos.gov.au/publications/australian_and_new_zealand_guidelines_for_fresh_and_marine_water_quality/volume_2
- Buchman (2008). NOAA Screening Quick Reference Tables, NOAA OF&R Report 08-1, Seattle WA, Office of Response and Restoration Division, National Oceanic and Atmospheric Administration, 34 pages.Google Scholar
- Canadian Council of Ministers of the Environment. 2001. Canadian Environmental Quality Guidelines. http://www.elaw.org/system/files/sediment_summary_table.pdf
- Gee, G. W., & Bauder, J. W. (1986). Methods of soil analysis, part 1. Physical and mineralogical methods–Agronomy Monograph no 9 (2nd ed.). Madison: American Society of Agronomy.Google Scholar
- Graham, E., & Lei, J. (2000). Stormwater management ponds and wetlands sediment maintenance. Water Quality Research Journal of Canada, 35(3), 525–539.Google Scholar
- Hardy, D., Myers, J., and Stokes, C. (2008) “Heavy metals in North Carolina soils, occurrence and significance.” North Carolina Department of Agriculture and Consumer Services: Agronomic Division. Raleigh, NC. http://www.ncagr.gov/agronomi/pdffiles/hmetals.pdf
- Johnson, J. 2007. “Evaluation of stormwater wetland and wet pond forebay design and stormwater wetland pollutant removal efficiency.” M.S. thesis. Raleigh, NC: North Carolina State University, Biological and Agricultural EngineeringGoogle Scholar
- Liebens, J. (2002). Heavy metal contamination of sediments in stormwater management systems: The effect of land use, particle size, and age. Environmental Geology, 41(3–4), 341–351.Google Scholar
- NOAA. (1999). Sediment Quality Guidelines developed for the National Status and Trends Program. http://response.restoration.noaa.gov/book_shelf/121_sedi_qual_guide.pdf
- OMOE, Ontario Ministry of the Environment. (2003). Stormwater management practices, planning, and design manual. Toronto, Canada. http://www.ene.gov.on.ca/envision/gp/4329e_preface.pdf
- Polta, R. (2004). A survey of regulations used to control the use and disposal of stormwater pond sediments in the United States and Canada. Metropolitan Council Environmental Services: EQA Report 04-542 (accessed 11/25/2008).Google Scholar
- Scarborough, R.W. and Mensinger, M.G. 2005. Evaluation of the storm water sediment control forebay at Anchorage Canal, South Bethany, DE. Delaware Department of Natural Resources and Environmental Control Division of Soil and Water Conservation Delaware Coastal Programs. Submitted to: Delaware Department of Transportation. Dover, DE. http://www.deldot.gov/stormwater/pdfs/SouthBethanyForebayMonitoringReport.pdf (accessed 2-10-10)
- Sonon, L. and Gaskin, J. (2009). Metal concentration standards for land application of biosolids and other by-products in Georgia. The University of Georgia College of Agricultural and Environmental Sciences: Cooperative Extension, Bulletin 1353. http://pubs.caes.uga.edu/caespubs/pubcd/B1353/B1353.htmla (last accessed 4/216/09).
- State of Minnesota Stormwater Advisory Group. 1997. “Storm-water and wetlands: planning and evaluation, guidelines for addressing potential impacts of urban storm-water and snow-melt runoff on wetlands.” http://www.pca.state.mn.us/publications/reports/wq-strm1-07.pdf (accessed 2-10-10).
- USEPA. (1983). Results of Nationwide Urban Runoff Program, Volume 1–Final Report. WH-554, Washington D.C.Google Scholar
- USEPA, (1996). Method 3050B: Acid digestion of sediments, sludges, and soils: revision 2. http://www.epa.gov/waste/hazard/testmethods/sw846/pdfs/3050b.pdf, last accessed 1/18/10
- VanLoon, G., Anderson, B. C., Watt, W. E., & Marsalek, J. (2000). Characterizing stormwater Sediments for ecotoxic risk. Water Quality Research Journal of Canada, 35(3), 341–364.Google Scholar