What Lies Beneath 

DuPont concocted Sierra-Crete to turn waste into revenue, but in the process it created a much larger problem for itself.

The mysterious black goo first started oozing to the surface of roads in new Antioch housing subdivisions during a heat wave eight years ago. Homeowners complained about tracking the black gunk onto their floors and carpets. As time went on, during consecutive days of boiling-hot summer weather, the crud bubbled to the surface of other roads in eastern Contra Costa County. After things cooled down, the black liquid disappeared, but it left a white film stain on the asphalt, and eventually the roads cracked. Something really weird was going on beneath the streets. But what?

The stricken roads shared one thing in common: The base below the asphalt consisted of a new DuPont concrete product called Sierra-Crete, which had been made at the company's now-defunct Oakley plant.

Sierra-Crete was laid below 36 miles of asphalt under roads in new housing developments, parking lots, and school playgrounds in Contra Costa County between 1989 and 1996, DuPont says. About half of those 36 miles total are in Antioch, city officials say, including the Dallas Ranch housing subdivision and the parking lot of the Antioch Youth Sports Complex. The substance also was used in the parking lot at Ohara Park Middle School in Oakley and a school bus lane turnaround at Stoneman Elementary School in Pittsburg. County officials and DuPont are in the process of compiling a list of all the places Sierra-Crete was used.

The road material inspired a wave of still-raging litigation between developers, the city of Antioch, and DuPont, one of the world's largest chemical manufacturers. But for all the apparent shortcomings of Sierra-Crete, everyone could at least take solace that while the mysterious black ooze might have ruined some carpets and dirtied some sneakers, it didn't pose any health threat.

Then earlier this year, DuPont made a startling admission to county health officials. Recent testing of Sierra-Crete roads detected trace levels of dioxin, a probable human carcinogen.


When DuPont scientists came up with the idea for Sierra-Crete in 1986, it seemed like a cost-effective way to get rid of several thousand tons of iron chloride waste produced at the Oakley plant where it made titanium dioxide, a white pigment used in toothpaste and paint. Companies such as DuPont bear a "cradle-to-grave" responsibility for the toxic wastes they produce, and storing, handling, hauling, and disposing of such toxics in approved dump sites can put a significant dent in their bottom line.

Sierra-Crete was the lemonade that DuPont made from its toxic lemons. The product not only gave DuPont a way to unload iron chloride, but it even made some money in the process. The new product bore the stamp of environmental enlightenment -- after all, DuPont was recycling. "It was the most beneficial means identified for managing these materials," DuPont spokeswoman Sharon P. Justice said via e-mail.

Recycling waste into roadbase was not exactly a new idea. Shredded rubber tires, ground glass, and gypsum by-products from power plants have long been disposed of beneath roads. In 1986, the state agency now known as the Department of Toxic Substances Control gave DuPont the go-ahead to mix its iron chloride waste with cement, proclaiming the mixture nonhazardous. Still, there was a question about whether DuPont had a market for its mixture. Agency spokesman Ron Baker said DuPont initially considered peddling the product as a landfill cap. But ultimately, the company went in a different direction. DuPont obtained word from Caltrans that its concoction would qualify as a subsurface roadbase -- the layer right below the asphalt -- and Sierra-Crete was born.

DuPont advertised Sierra-Crete as a relatively cheap and environmentally safe alternative to more conventional cement roadbase. One ad exaggerated that Sierra-Crete was "revolutionizing the roadbase industry," proclaiming it stronger and more durable than other materials in its class. In reality, however, the revolution never happened. Annette Guiseppi-Elie, a senior remediation consultant for DuPont, said Sierra-Crete never sold anywhere outside of the East Bay and Tokyo. "It was pretty difficult to market," she said.

A few years after DuPont started marketing Sierra-Crete, state toxics regulators began expressing doubts about whether the product was actually nonhazardous. According to a department memo, tested samples of the roadbase taken 1991 and 1993 showed excessive amounts of vanadium, a toxic metal. The same memo noted that a preliminary evaluation by CalTrans recommended against using the highly acidic Sierra-Crete in future highway projects because of its "corrosivity."

Then in 1994, the Department of Toxic Substances Control levied a $200,000 fine against DuPont's Oakley plant for an array of alleged violations largely unrelated to Sierra-Crete. DuPont fought the enforcement order and the state ultimately dropped its case five years later. But according to DuPont, it stopped making Sierra-Crete in 1996, closing its entire Contra Costa facility two years later in a cost-cutting move.

Instead of revolutionizing the roadbase industry, Sierra-Crete's primary legacy seemed to be in the courts. Home developers such as Kaufman and Broad are suing DuPont for the cost of repairing or replacing roads, driveways, and storm drains allegedly corroded by Sierra-Crete. Last year the city of Antioch also filed suit against DuPont. Those lawsuits are grinding forward without resolution in Contra Costa County Superior Court. But otherwise, memories of Sierra-Crete seemed buried under so many miles of asphalt.

Then earlier this year DuPont discovered another legacy, to the alarm of county health officials.


Dioxin is one of the most toxic chemicals known to man. Exposure to high levels has been associated with several types of cancers, including lung cancer and lymphoma. Like mercury, once dioxin gets into the body it remains there for a long time. Although it first attracted public attention as a component of Agent Orange during the Vietnam War, most environmental dioxin originates in industrial pollution. Garbage incinerators and pulp mills are prime sources, but forest fires, volcanic eruptions, and even backyard barbecues produce the toxins.

Every year, major polluters such as DuPont must submit a report to the Environmental Protection Agency detailing their toxic emissions. But only since 2000 has the EPA required companies to include dioxins on their so-called Toxic Release Inventory. Once dioxin was added to the list, Guiseppi-Elie said, DuPont realized that the process used to create Sierra-Crete at the old Oakley facility might have produced dioxins.

To their credit, DuPont risk managers took the initiative and ordered testing of road sites in Contra Costa County where Sierra-Crete had been used. DuPont's local environmental consultant, Richard Wenning of Environ, did indeed find trace levels of the carcinogen, although they were well below legal limits for even residential soils and appeared to pose no health threat. Nevertheless, DuPont officials played it safe and reported the findings to county health officials. "They came forward with this information," said Michael Kent, the hazardous material ombudsman for the Contra Costa County Health Department. "They called us out of the blue one day and said, 'We realized there's dioxin in this stuff.'"

In response to the findings, county health officials have assembled a task force to investigate the issue. So far, the task force has concluded that DuPont's initial sampling was inadequate and that more extensive testing of the roads needs to be done. Of the ten spots DuPont tested, only one was from a public road; the rest were taken at the old Oakley factory. DuPont and its consultant also only obtained samples by wiping street surfaces. Public Health Director Wendell Brunner said he wanted soil samples taken as well. The county and DuPont are working to identify all the places where Sierra-Crete was used to develop a more comprehensive list of places to test. They hope to test those samples before the end of the year, Kent said.

Since its original disclosure, DuPont also has tested samples from the parking lots at Ohara Park Middle School and the Antioch Youth Complex, as well as the bus lane turnaround at Stoneman Elementary. DuPont's consultant concluded that the Sierra-Crete at the sites "makes a negligible contribution ... to a person's normal background exposure to dioxins."

Brunner said he and his staff want to do as much testing for dioxins as possible, so they can hopefully reassure the public. At the same time, he is cautious not to sound alarmist. "There is no immediate risk anywhere in the county," Brunner said.

Nonetheless, some residents are nervous about the idea of having toxic junk just outside their doors. One young mother, who lives on Tepee Court with her husband and their two- and four-year-old children in a subdivision where Sierra-Crete was used, only recently found out about the presence of dioxin. "I'm not comfortable with it at all. ... We don't let our kids go near it," she says, asking to remain anonymous for fear of reducing her home's value. But she's not ready to pick up and leave. "It would make us sad to have to move because of this. We love the neighborhood. I think we're all hoping it's going to be okay."

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