Alternatives for coal tar sealants

Since the mid-1900s, sealcoats with coal tar have been widely used on asphalt pavements to protect them and to keep them looking “new” or uniformly black. It has also been used in settings where vehicle gas and oil spills and drippings are expected.

A byproduct of coal processing, the coal tar pitch used in sealcoat is a known carcinogen and contains high levels - up to 50,000 parts per million (ppm), or 5 percent - of polycyclic aromatic hydrocarbons (PAHs). Some of these PAHs are reasonably anticipated human carcinogens, and pre-natal and early childhood developmental impacts are being studied.

Exposure to the PAHs in coal tar sealcoat can occur through inhalation of fumes or dust or direct contact with the liquid or dried product. Dried coal tar sealcoat wears away over time into PAH-laden dust that is washed by rainwater into streams, lakes and stormwater ponds, harming aquatic life and concentrating in sediments.

Depending on the condition of pavement, it may be replaced with concrete, stone, or permeable pavers. If years more life are expected, it may be preserved by alternative sealcoats. The most common replacement is asphalt-based, which when properly applied performs as well or better than coal tar, at similar cost.

Because MPCA, USGS, and other U.S. research has traced over 50 percent of PAH sediment contamination to coal tar sealcoats, the 2009 Minnesota legislature passed a law prohibiting State agencies from purchasing coal tar sealcoat products and encouraged cities to pass ordinances banning coal tar sealcoat in order to be eligible for state grants to help pay for pond cleanout. Twenty-eight Minnesota cities have now passed such bans.

Cities with dozens or hundreds of stormwater basins will incur huge costs in cleaning out, transporting, and disposing of sediments in order to maintain storage capacity and pollutant capture. Total cost per cubic yard of highly PAH-contaminated sediment can range from $65 to $100 per yard, and a modest clean-out will involve 2500 to 5000 cubic yards of sediment.

In the absence of a statewide ban, MPCA is encouraging voluntary coal tar sealcoat phase-out and supporting cities in developing and implementing local bans. Under a U.S. EPA Great Lakes Restoration Initiative grant, MPCA will push successful coal tar phase-out tools throughout the state and to other Great Lakes area states and provinces.

MPCA’s coal tar web pages provide resources for anyone interested in using alternatives on their own property or encouraging other audiences in their community to do so. Stormwater professionals and active local stakeholders can play individual and collective roles in this education and phase-out promotion, and it is readily integrated into other stormwater management education initiatives that communities may already have in place.

Additional resources

• Interactive map or list of contractors who have pledged not to apply coal tar sealcoat
• Guidance on choice and best application practices for alternatives to coal tar
• Information on coal tar-related activities in MPCA’s Stormwater regulatory program – including guidance for municipalities on cleaning up contaminated sediment
• Information on government and private sector actions to phase-out coal tar sealcoat

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