The products, used mostly on private driveways and parking lots, contain high concentrations of toxic compounds called polycyclic aromatic hydrocarbons. These substances have been linked to tumors, deformities and other problems in fish and aquatic organisms and are believed to be carcinogenic to humans.
As the sealant wears down, its compounds are washed into storm drains, streams and lakes.
Lake Ballinger, on the border of Mountlake Terrace and Edmonds, was found to have unusually high concentrations of hydrocarbons in a study released last year by the U.S. Geological Survey. The lake was one of 40 lakes studied around the nation.
Its pollution likely has accumulated over decades, said Curt Brees, public works director for the city of Mountlake Terrace.
Coal-based sealant has been used little, if at all, in Washington state in recent years, according to local contractors.
"If it hasn't been banned, it should have been banned before this," said Tom Niebruegge, owner of JB Asphalt Paving in Edmonds. "It's nasty."
Legislators who sponsored the bill to ban the sealants said the condition of Lake Ballinger was a major motivator.
Rep. David Frockt, D-Seattle, the bill's prime sponsor, said hearing about the lake "really piqued my interest in this thing." Rep. Mary Helen Roberts, D-Edmonds, signed on as a co-sponsor largely because of Lake Ballinger, she said.
The bill was approved by the Legislature and signed by Gov. Chris Gregoire last month. Some cities around the nation, including Washington, D.C., have banned the sealants but Washington is the first state to do so.
The sealants are used to protect asphalt from deterioration. They are used much more extensively on the East Coast than in the West, according to the U.S. Geological Survey, but have been used in all parts of the country.
John Julnes, owner of Tilco Vanguard paving in Maltby, said coal tar has one advantage over petroleum-based asphalt sealants.
"It's the only seal coat that protects your asphalt against oil and gas intrusion," Julnes said. "Others do not." Niebruegge said coal-tar sealants cause oil and gas to bead up rather than penetrate the surface.
Still, the drawbacks outweigh the benefits, Julnes said.
"I stopped using it probably 20 years ago because it's very costly, and when it steams up it burns your skin," he said.
Gas stations formerly used coal-based sealants to protect their parking lots, Julnes said.
"I don't really know of anyone that uses it," he said. "It's not even available locally anymore."
Niebruegge, too, pointed out that the substance can burn people who use it.
"It puts out a gas or a fume or something," he said. "You're supposed to grease yourself down before applying it."
Airports also have historically used coal-based sealants on runways, Julnes said.
Paine Field director Dave Waggoner said the airport formerly used coal-based sealants on runway aprons but hasn't now for more than five years.
"We have no current projects using this type of sealant," he said.
The PAH pollution in Lake Ballinger likely found its way there by runoff from Highway 99, Brees said.
"A lot of Lake Ballinger is receiving waters from the Highway 99 corridor -- Edmonds, Lynnwood, all those parking lots, all those car lots, all those driveways," he said. "Through creeks and storm drainage systems it makes its way to the lake."
Once there, the particles settle at the bottom. Trying to clean them up, Brees said, would be expensive and could cause more damage through disturbance.
"I think the best venue is to make sure they're not used from this point forward."
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