Waste Asphalt Doesn't Pollute Groundwater, UF Researchers Say

June 4, 1998

GAINESVILLE — Old asphalt scraped off roads does not bleed toxins into groundwater and is safe to use as construction fill, according to tests by University of Florida engineers.
The tests were spurred in part by fears that piles of old asphalt at asphalt plants were allowing toxins into the environment, said Tim Townsend, an assistant professor of environmental engineering sciences.

They were also spurred by new federal regulations calling for reducing the amount of old asphalt recycled into new roads, likely raising the need for alternative ways to dispose of it, said Allan Brantley, a recent environmental engineering sciences graduate.

“If I dig a hole and it has water in it, can I use this material as back fill — is it a clean fill?,” said Brantley, who conducted the tests as part of his master’s thesis on the subject.

When workers grind and mill roads to resurface them, the mixture of asphalt, sand and rock they remove is known as reclaimed asphalt pavement. In Florida, resurfacing generates between 750,000 and 1 million tons of the material each year, with most of it recycled into hot asphalt mix and reapplied to roads or highways, said Gale Page, state flexible pavement materials engineer for the Florida Department of Transportation.

Workers build up piles of the old pavement, and concerns have been raised about rain water filtering through the piles and leaching toxins into groundwater, Page said. Because of these concerns, DOT does not commonly use the material as fill, he said.

For the tests, Brantley and Tim Townsend, an assistant professor of environmental engineering sciences, used material from two roads and four piles of asphalt around the state, each containing material from several nearby roads or surfaces. The roads were Indian Town Road in Palm Beach County and Interstate 10 in Suwannee County. The asphalt piles were located in Lake City, Jacksonville, Miami and Tampa.

The researchers subjected water passed through the material to the Environmental Protection Agency’s standard toxicity test as well as tests aimed at mimicking outdoor conditions for pavement piles.

In the EPA test, the researchers immersed the material in water-filled containers, then stirred the contents with a machine for several hours. Pollutants including heavy metals, polynuclear aromatic hydrocarbons and volatile organic compounds were found to be at levels below federal standards or were not detected, Brantley said.

In the other tests, the researchers put pavement and water in stainless steel cylinders that were four feet high and six inches in diameter. With some cylinders, they collected and tested the water as it dripped through the pavement. With others, they let the water saturate the pavement for 14 days before collecting and testing it.

Lead was the only pollutant detected at levels above the EPA standard, but it only exceeded it by a small margin in one unsaturated cylinder and three saturated cylinders. No other pollutant levels were found above the federally determined safe standards, the researchers found.

“The lead more than likely came from leaded gasoline or crankcase oil,” Brantley said.

Page, the DOT engineer, said road builders can save more money recycling old pavement into new pavement than by using it as construction fill. But the study suggests the material could be used as fill more commonly in the future, he said.

“The study confirms that we could use the material in fill should it become economically feasible,” he said.