In 2013, the Minnesota Legislature banned the sale and use of coal tar-based sealants, effective January 1, 2014. Coal tar-based sealants can no longer be sold or applied legally in Minnesota. These products were commonly applied to asphalt driveways, parking lots, and some recreational trails to protect the underlying asphalt. However, they contain high concentrations of chemicals called polycyclic aromatic hydrocarbons (PAHs), which can be carcinogenic.
PAHs in coal tar-based sealants are released into the environment through volatilization into the air and as dust when the sealant breaks up over time. This dust can be tracked into homes or transported to nearby soils and waters via stormwater runoff. An MPCA sediment study found that coal-tar sealants contributed 67% of total PAHs in 15 metro-area stormwater ponds. High concentrations of PAHs have accumulated in some stormwater pond sediments around the state. Research conducted by the MPCA, the Metropolitan Council, the U.S. Geological Survey, and the University of New Hampshire Stormwater Center shows that coal tar-based sealants are an important source of PAHs to urban waterways.
This is a concern for local governments responsible for managing stormwater ponds and disposing of sediments that have been excavated from them. Alternatives to coal tar-based sealants, such as asphalt-based sealants, have far lower concentrations of PAHs.
Coal-tar based sealcoat: Environmental concerns (wq-strm4-12)- Contamination of stormwater pond sediments by Polycyclic Aromatic Hydrocarbons in Minnesota (tdr-g1-07)
Sediment removal guidance
- The soil reference values (SRVs) to protect human health are found on the cleanup guidance webpage.
- Managing Stormwater Sediment Best Management Practice Guidance (wq-strm4-16)
Worksheet: Summary of stormwater pond sediment testing results (wq-strm4-79)- Hydraulic dredging for removal of stormwater pond sediments
A short video highlighting key topics for sediment removal projects supplements the guidance document and provides a few visual examples associated with the removal of sediment from stormwater collection and conveyance systems. These guidance documents do not provide a comprehensive list of everything that should be considered when managing a sediment removal project, but they can help highlight important steps to be taken by those responsible for performing a sediment removal project.
Resources
- PAHs and coal tar-based sealcoats (USGS)
- Coal-Tar Sealcoat, Polycyclic Aromatic Hydrocarbons, and Stormwater Pollution (U.S. EPA)
- Use of Compost to Biodegrade Sediments Contaminated with Polycyclic Aromatic Hydrocarbons
Pavement Sealcoat a Source of Toxins in Stormwater Runoff- Assessment of Water Quality of Runoff from Sealed Asphalt Surfaces (U.S. EPA)
- Summary of Coal Tar-based Sealant Bans/Restrictions in the U.S. (tdr-g1-12)
- Sediment studies web page