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From Your Driveway to the Nearest Stream

May 28, 2008 - Thinking about resealing the driveway this summer? You might want to think twice about how to go about it, or whether to reseal the driveway at all.

There are basically two types of driveway sealants on the market today. The first type utilizes a base made from coal tar and the second utilizes a base made from asphalt. The bases make the difference in how toxic the sealant you put on your driveway is for you and any stream or lake in your neighborhood.

You might be thinking, "Wait a minute, what does my neighborhood stream or lake have to do with driveway sealant?" The reason is that research conducted in Austin, Texas, found high levels of polycyclic aromatic hydrocarbons, or PAHs, in some of their local streams. PAHs are linked to various health issues including cancer. The research was able to trace the PAHs back to pavement sealers used on parking lots and driveways. They found the average concentration of PAHs to be 1,600 times higher in liquid coal tar-based sealant products than in liquid asphalt-based sealant products. For this reason, coal tar-based sealants are a potentially higher health risk than asphalt-based sealants.

But how do these PAHs get from the driveway or parking lot into the neighborhood stream? When it rains or the snow melts, the stormwater carries with it little hitchhikers of whatever it hits or runs across, including pavement sealants. The polluted stormwater runoff, now containing PAHs, runs off the pavement to a storm drain or ditch which drains to the local stream. In the Austin study, they found that particles in runoff from parking lots sealed with coal tar sealants were as much as 65 times higher in total PAHs than runoff from unsealed pavement.

A report from the Great Lakes Environmental Center in March 2005 showed that coal tar sealants in sediments were toxic to aquatic life in streams at the concentrations observed in Austin streams.

So if you are considering sealing your driveway or parking area this summer, read the labels to avoid coal tar-based sealants and choose an asphalt-based sealant. The asphalt-based sealants may cost a bit more but they are more environmentally friendly and less toxic for you and our waters. Let's all do our part to keep Maine's lakes, rivers and streams healthy.

KATHY HOPPE May 22, 2008 Portland Press Herald

KATHY HOPPE is an environmental specialist with the Maine Department of Environmental Protection's Bureau of Land and Water Quality. E-mail your environmental questions to infoDEP@maine.gov or send them to In Our Back Yard, Maine DEP, 17 State House Station, Augusta, ME 04333.


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