UNH: Pavement sealcoat a source of toxins in stormwa...( DURHAM N.H. Driveways and parking l...)

DURHAM, N.H. Driveways and parking lots may look better with a layer of sealcoat applied to the pavement, but the water running off the surface into nearby streams will be carrying more than just oxygen and hydrogen molecules. New research conducted at the University of New Hampshire Stormwater Center (UNHSC) indicates that sealcoat may contribute to increasingly significant amounts of polyaromatic hydrocarbons entering waterways from stormwater runoff.

Polyaromatic hydrocarbons, more commonly known as PAHs, are found in diesel and crude oil and are considered to be carcinogenic. Although small amounts of PAHs are typically found in the waters around the New Hampshire Seacoast, the sudden spike in the hydrocarbon concentrations in water draining from a university parking lot used for research caused Tom Ballestero, UNH associate professor of civil engineering, to be concerned about unknown impacts.

"Our society has been sealcoating pavement for decades and there are things we've never asked about," he says. "Now we're starting to probe and ask these questions."

Although it is intended to remain on the pavement surface, much of the sealcoat eventually washes or scrapes off and ends up in nearby streams and rivers, says Alison Watts, affiliate faculty member at the UNHSC. The PAHs from the sealcoat attach to organic matter, such as leaves or sediment, where they may be ingested by organisms or buried in other sediments.

As part of this N.H. Sea Grant-funded research, one-quarter acre of a parking lot located near the UNHSC was covered with coal tar-based sealcoat and one-third acre was covered with asphalt-based sealcoat. The remainder of the nine-acre lot was left unsealed. On-site stormwater drains off the parking lot and into a nearby swale. The PAH concentration was measured in the water and sediments coming from the sealcoated and unsealed parking lot sections.

Both types of sealcoat led to a surprisingly r
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