A study recently published in the journal Science of the Total Environment* supports previous studies that conclude that coal tar-based asphalt sealcoats are a major source of polycyclic aromatic hydrocarbons (PAHs) in stormwater runoff. Scientists from the U.S. Geological Survey and Wisconsin Department of Natural Resources found PAHs at concentrations in the range of 40-80 ug/g (parts per million) in sediment in storm drains and runoff from a residential neighborhood in Madison, WI.
PAHs from coal tar-based asphalt sealants find their way into stormwater from sealcoated parking lots and driveways. Over time, asphalt sealcoats abrade and deteriorate into fine particles which are washed into storm drains. As these particles accumulate in stormwater detention ponds, coal-tar derived PAHs can reach levels that require the sediment to be disposed of in a licensed landfill (rather than land-applied, as would be done for uncontaminated sediments).
Recent experience in Minnesota highlights the financial liability faced by municipalities for disposal of contaminated stormwater sediment. While normal disposal costs for testing, mobilization, excavation, transportation and disposal can equal $40-$50/cubic yard of sediment, disposal of PAH contaminated sediment can raise that cost to $65 to $95/cubic yard.
Dane County, WI, twenty eight Minnesota Cities and the State of Washington have banned the use of coal tar-based asphalt sealants. Wisconsin municipalities that wish to avoid future costs related to disposal of PAH contaminated stormwater sediment will want to consider banning the use of coal tar-based asphalt sealcoats in the watersheds draining to their Municipal Separate Sewer Systems (MS4s).
For more information about efforts to eliminate the use of coal tar-based asphalt sealcoats in the Great Lakes Region see: http://www.pca.state.mn.us/ahx9qrk
* Selbig, W.R., R. Bannerman, S. Corsi, From Streets to Streams: Assessing the toxicity potential of urban sediment by particle size, Science of the Total Environment, Vol.444 (2013) pg. 381-391