As I drive around the Seacoast, I see a lot of people getting their driveways resealed. Perhaps people are anxious to get this done before the onset of winter. I wonder, though, if homeowners realize there are different types of sealcoats and that choosing the right one can help protect the environment and our health.
Most sealcoats are made of either an asphalt emulsion or a refined coal-tar pitch emulsion. Although the two sealcoats are similar in appearance and cost, coal-tar pitch sealers contain much higher levels of polycyclic aromatic hydrocarbons, more commonly known as PAHs. Present in crude oil and diesel fuel, these organic compounds are known to cause cancer. Incredibly, the concentrations of PAHs are up to 1,000 times higher in coal-tar-based sealcoats compared to asphalt sealers, posing a threat to fish and humans.
The UNH Stormwater Center has been studying the impact of coal-tar based sealcoats and found that soil at the edge of the pavement contained several hundred parts per million (ppm) of PAHs compared to less than 10 ppm where no sealcoat was applied. Soil samples taken three years after the initial application remained high in PAHs. This means that dust from sealed pavements, with elevated levels of carcinogens, can track to areas like playgrounds and homes.
The presence of high PAH concentrations in your driveway pose a threat to your family’s health. Studies at the Columbia Center for Children’s Environmental Health found that constant exposure to PAHs can affect cognitive development and cause asthma and other respiratory problems in children.
Toxic to aquatic life, the presence of PAHs is also on the rise in the sediments of Great Bay, adding yet another stress to the estuary and putting its health at risk. UNH researchers are currently trying to determine if sealants are the major source of PAHs to the estuary and hope to build a model that links the contaminant to its source.
Unlike many environmental choices, this one is fairly simple – avoid coal-tar based sealcoats in favor of asphalt-based ones or, better yet, no sealcoat at all. Home Depot and Lowes no longer sell coal-tar based sealcoats, but they are still available at some other retailers. You can tell if a product contains coal tar by looking at the materials list for words like “coal tar”, “refined coal”, “refined tar”, and “coal-tar pitch.” If you hire a commercial sealcoat company, insist they only use an asphalt-based sealer and only apply if the outside temperature is at least 60 degrees F, with no rain forecasted for at least two days after application.
Maintaining a driveway in New England is never easy. Constant freezing and thawing can lead to lots of cracks, often made worse by plowing, causing homeowners to protect their driveways by using a sealcoat every couple of years. However, proper repair of cracks in your driveway can delay and potentially avoid the need to sealcoat.
To repair driveway cracks, which can lead to pavement deterioration, homeowners typically use a cold asphalt patch to fill cracks. One new product now available is called GreenPatch, an environmentally friendly cold asphalt patch that does not contain petroleum based solvents. This makes GreenPatch a VOC compliant material that is healthier for your family.
As consumers, we are faced with many choices. If you are planning a new driveway, alternative surfaces such as gravel, concrete or porous pavement are great options as none of these require the use of sealants. Since most of us already have an asphalt driveway, the choice is even clearer – maintain your driveway to avoid the need to use sealants, and if sealants are necessary, never use a coal-tar based product