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Local municipalities also have similar practices regarding parking lot maintenance. For instance, the city of Birmingham doesn't treat parking lots, with the exception of patching pot holes or full replacement. "We patch them, but we don't refresh or seal them," said Lauren Wood, director of public services for Birmingham. "Parking lots, as a general rule, we just keep them safe and patch them."

Bloomfield Township Director of Public Works Tom Trice said the township doesn't sealcoat parking lots because he doesn't believe there is any added benefit to do so.

"We would never do that. There's no real reason to do it," he said. "It creates a maintenance headache because once you do it, you have to continue doing it. The sealcoat people will claim it extends the life of the asphalt by keeping the oil out, but the asphalt industry hasn't found that to be true."

In terms of alternative sealcoats, the industry standard in Michigan is coal tar based sealcoat, which manufacturers and applicators say is the most durable product available. Petroleum-based, or asphalt-based sealcoat, applicators say, doesn't have the same durability or shine that coal tar sealcoat offers, even though both are about the same price.

Arguments based on what works best, Ann Arbor's Naud said, aren't considering health and environmental factors.

"DDT worked really well," he said "Lead paint worked really well, but they had some environmental issues that we didn't know about for a long time."

Because of the wide availability of coal tar-based products in the middle and eastern regions of the United States, and because of its superior durability and look, the industry standard for sealcoat has been coal tar sealcoat, said Nick Whitehurst, president of True North Asphalt, in Rochester Hills.

However, due to the increasing number of bans and restrictions on coal tar-based sealcoat, the manufacturers have started producing an alternative, which is a petroleum-derivative sealcoat that Whitehurst said holds up better than traditional asphalt, or petroleum-based, sealcoat.

Sold under the name Black Diamond, manufacturers and suppliers of the product, such as Surface Coating Co., in Auburn Hills, say the product holds up well, and has a significantly lower PAH content, with suppliers saying the sealcoat is about two percent PAHs. Asphalt-based sealcoat, by comparison, has about .005 percent PAH.

The Black Diamond sealcoat is now approved for application in several locations where coal tar sealants are prohibited for use, such as Austin and San Antonio, Texas. However, the new alternative isn't permitted for use in Ann Arbor or Van Buren Township, which limit PAH content to .1 percent and one percent, respectively.

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