For Our Lakes and Rivers- The Dangers of Blacktop
A busy parking lot can become an unsuspected source for damage to the health of a water bodies as dust from the parking lot containing PAH’s run off into the water during a rainfall. (Photo Courtesy UW Extension Lakes Program)
By Krista Olson
The warm weather is here, and many homeowners are looking at their driveway, considering if they need to recoat the blacktop again. The harsh winter took a toll on many driveways, but what many homeowners don’t realize is their driveway may be adding to the demise of their favorite summertime getaway, and there are choices that lessen the impact on our lakes and rivers.
Blacktop suffers through repeated driving, shoveling, plowing, and other uses which create friction, wearing off the sealant of asphalt. The friction on a coal tar- based blacktop also creates a dust, which contains a known human carcinogen made up of about 200 polycyclic aromatic hydrocarbon (PAH) compounds.
The dust afterward is washed off as rain falls, often to untreated storm sewers that drain directly into a water body like the Wisconsin or Plover Rivers. Other water in parking lots of developed areas runs off into detention or settling ponds, accumulating the toxic sediments in one small area. After the sediments have settled for a period of years, that bottom soil can turn into a contaminating material at a seriously toxic level.
PAH are toxic to humans and wildlife, creating deformities and reducing the amount of offspring. It is particularly damaging to the animals that call the bottom sediment of a water body home, and often are the beginning of the food chain. This throws off the food chain, and has created a disruption in even mildly contaminated water bodies which in turn affects the water body as a whole as wildlife populations decline due to the break in the food chain.
The only way to remove the toxic sediments is to undertake an expensive dredging operation, and have the toxic material disposed of properly.
PAH are heavier in coal tar- based sealants, and not as prevalent in asphalt based sealants, as PAH concentrations in the coal/tar sealcoat products are about 1,000 times higher than in an asphalt-based product.
Wisconsin is one of just four states that implemented the ban on coal tar coatings, but unfortunately the products are still readily available online or through a few asphalt coaters. Outside of water bodies, PAHs are also a concern from the dust settling around homes and exposing the home’s occupants during everyday living activities in and around the home.
What can you do? If you plan on recoating a driveway or parking lot, check the label or with the contractor you are hiring to make sure the sealant is not coal tar based, but asphalt based.
You may end up having to recoat more often with an asphalt based product, but the environmental savings and decreased risk to your own health need to be weighed against getting an extra year or two by using coal tar based sealants. If you are planning new parking lot or driveway construction, consider other eco- friendlier alternatives such as impervious pavers, gravel, or impervious cement.
If you live on a water body, make sure any blacktopped areas drain into rain gardens or parts of the property that don’t drain directly into the water body. With more awareness homeowners can help correct runoff and contamination issues, and we will find that with each person doing their part it will add up to make a positive impact on the water we love.