Metro storm-water ponds are chemical soups

  • Article by: TOM MEERSMAN , Star Tribune
  • Updated: April 27, 2010 - 12:30 PM

White Bear Lake's proposed ban on some driveway sealants is a first step in keeping contaminants out of storm-water ponds.

The local neighborhood pond fringed with spring green looks attractive, but its muddy bottom is loaded with contaminants.

Metro communities from White Bear Lake and Maplewood to South St. Paul are discovering that their storm-water ponds are chemical soups of pesticides, fertilizers, pet wastes, oil, grease and other contaminants.

With an estimated 20,000 public storm-water ponds in the metro area, and thousands more privately owned by industries and homeowner associations, state pollution officials say they expect the problem to be widespread.

"It took us aback, frankly," said Mark Burch, White Bear Lake's public works director. "Especially when we figured out how much it would cost" to clean up.

On Tuesday, the city is poised to adopt the state's first ordinance -- and only the fourth in the nation -- to ban coal-tar sealants spread on driveways and parking lots. The sealants, among the worst culprits in the contamination, contain chemical compounds that are classified as likely carcinogens, and are known as PAHs (polycyclic aromatic hydrocarbons).

Sealant industry officials oppose the ban and dispute studies that have identified their products as the main source of pollution.

Burch stood recently next to one of the 60-inch culverts that drain storm water from dozens of streets into Varney Lake.

He stepped onto a delta of sediment and pointed to sandy islands in the water where ducks and Canadian geese were standing. "Their bellies aren't even wet," he said. "The water out there is just a few inches deep."

Because the lake is nearly full, Burch planned to excavate the sediment and debris. But he put the project on hold when he learned that the contaminant levels were so high that the soil would need to be trucked to a landfill for disposal. That would cost up to $250,000, he said, about three times the cost of extracting clean sediment, which could be re-used within the city for berms or fill.

A half-dozen other lakes in the city have the same problem, said Burch. Plans to dredge them are also on hold while the city cleans a few smaller ponds that were not contaminated.

MPCA warns of PAHs

Sealants are shiny black coatings used to protect underlying pavement in driveways and low-traffic parking lots for churches, restaurants, shopping centers, playgrounds and trails. They are usually applied every three to five years.

The PAHs that are the most serious pollutant come from coal tar-based sealants, according to a "white paper" on the issue by the Minnesota Pollution Control Agency (MPCA).

The compounds flake off as tiny dust particles as pavement weathers, said Judy Crane, the research scientist who coauthored the white paper. Those particles are carried into waterways, where they can kill aquatic insects, hurt frogs and other amphibians, and cause mouth tumors in fish.

The main concern for humans is the potential for breathing the chemicals if sediment is dredged, dried and used in parks where children play.

"I don't think we want to assume that every pond is contaminated," said Dale Thompson, supervisor of the municipal storm-water program for the MPCA, "but it's certainly widespread in the metro area, and we suspect it's going to be widespread outstate."

Burch said he can wait awhile to dredge the ponds, and hopes that research at the University of Minnesota may provide new ways to neutralize contaminated sediment to avoid costly disposal. But the state is facing hundreds of ponds that are nearly full, said Rep. Bev Scalze, DFL-Little Canada, and if they aren't dredged, oil, grease, coal tar and other wastes that run off streets will no longer be trapped and will flush into cleaner lakes and rivers.

"The ponds have done their job and accumulated mud and chemicals and debris," she said. "It was the right thing to do to require them. The question is, where do we go from here?"

Scalze authored a bill passed in 2009 that requires state agencies to stop using the coal tar sealants on parking areas and trails effective July 1. It also requires more than 200 metro cities to inventory their storm-water ponds.

"We have a great amount of pollution here in the ponds already," said Scalze. "But when you're talking about a possible carcinogen, it gets even more important."

Scalze wants to ban the sealants throughout the state, and said that a readily available alternative -- asphalt emulsion sealant -- provides the same protection for pavement without the environmental runoff problems. Such a prohibition, now being considered in Michigan, would affect commercial applicators most, said Scalze; some large retail chains, such as Lowe's and Home Depot, stopped selling coal tar-based sealants in recent years.

Industry officials are closely tracking White Bear Lake's proposed ordinance to ban the use of coal tar sealants. Only four other communities have adopted similar ordinances: Austin, Texas, and one of its suburbs; Dane County, Wis., and Washington, D.C.

Sealants not the only problem

Anne LeHuray, executive director for the Pavement Coatings Technology Council, a national trade association, said that PAHs come not only from coal tar, but also from natural sources and from incomplete combustion of many other coal and petroleum products, including oil, wood and even charcoal in barbecues.

Some studies show that vehicle emissions -- not coal tar -- are the main source of PAHs in the environment, LeHuray said, which means that banning sealants won't prevent buildup in storm-water ponds.

"Government is picking winners and losers in the marketplace, regardless of what the benefits are," said LeHuray, who also represents asphalt emulsion businesses. "If you try to ban a product that is not the source of the problem, you won't solve the problem."

The MCPA's Crane acknowledged that there are many sources of PAHs in the environment, but "coal tar sealant is coming up as a very important source." She has found high levels of PAHs in several ponds she has studied in the past year.

Randy Nugent, who owns a sealcoating firm in Hugo, said that a ban on coal tar sealants would not affect his business because he switched to the asphalt emulsion alternative years ago. The two products are basically the same in price and performance, he said, but his workers dislike coal tar because it burns their skin and smells bad. The only marginal advantage to coal tar, said Nugent, is that it can be applied in slightly cooler weather, adding a week or two to the work season in spring and fall.

"I'm not a tree-hugger," he said, "but why ruin the grass and the water if you don't have to?"

Tom Meersman • 612-673-7388

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