ILWACO, Wash. — What at first seemed like a brilliant way to get rid of mountains of old tires has given new meaning to the old saying about what paves the road to hell.
Two highways repaired with chunks of rubber are smoking and oozing a toxic, oily goo that is threatening nearby marshes on the Columbia River.
Digging out the mess will cost from $1 million to $3 million, officials estimate.
The state used the rubber from a million recycled tires in place of rock or gravel to provide 7,000 cubic feet of fill when it rebuilt a 150-foot stretch of state Route 100 last October.
The road runs atop an embankment above Baker Bay, a pretty inlet at the mouth of the Columbia River, tucked into the little curlicue at the state's southwest tip.
The first sign of trouble came in December when asphalt pavement laid over the fill began to crack, split and give off wisps of noxious smoke, with temperatures up to 160 degrees.
Some of that buried rubber had started burning, apparently through natural processes, similar to what heats up a compost pile. And as the rubber heats up, it releases a goo that oozes to the surface and flows onto the mud flats below, dangerously close to a saltwater marsh and freshwater wetlands.
It smells like creosote, with a burned-plastic undertone.
The underground combustion is generating toxins such as benzene, a known carcinogen, said Coast Guard Lt. Rob Myles.
Workers at the site must wear protective masks.
In southeastern Washington, a 350-foot stretch of a Garfield County road has been emitting smoke--and even flames--since January at the site of another repair job late last year that used chipped tires.
Both roads have been closed pending removal of the tires.
"They're going to go in and take the part that's burning out," said Dana Humphrey at the University of Maine.
Above-ground tire fires are not uncommon--in March, a huge tire dump fire in Philadelphia damaged an elevated highway that ran over the site.
But this rubber is underground, without enough air to allow complete combustion.
"There's never been a tire fire under a road. There's no history of methods to use," said Joe Zellibor, a former science advisor to the Scrap-Tire Management Council in the Rubber Manufacturers Assn. His expertise is being tapped by state officials.
Route 100 leads to Fort Canby State Park, where the expedition led by Meriwether Lewis and William Clark reached the Pacific in 1805.
The cleanup is complicated because eagles are nesting nearby and by the spring migration of ocean-bound salmon fingerlings, said biologist Thom Hooper of the state Department of Fish and Wildlife. And salmon spawning will begin in about a month.
While there are concerns about the effect on the wildlife of all of the heavy equipment and people to be used in the cleanup, there's a sense of urgency because the rubber in each tire contains hydrocarbon compounds equivalent to about a gallon of oil.
"We're here because there is potential for a million-gallon oil spill," said Myles of the Coast Guard's San Francisco-based oil-spill strike team.
Humphrey, a civil engineering professor, is completing a report on the problem for the Federal Highway Administration, which has encouraged use of recycled-tire materials.
Lessons learned here will help with future projects, Humphrey said. About 250 million used tires are discarded each year in the United States, and "we can use up a heck of a lot of tires even on small projects," he said.
His report surveyed 70 known projects using tire-chip fill.
At Ilwaco, the recycled rubber is piled to a maximum depth of 27 feet on a 4-foot gravel bed, topped with 3 to 5 feet of soil. In Garfield County, where the repair involved a gully, the tire layer is about 45 feet deep.
It's not known exactly what is happening to the 4- to 6-inch chunks of rubber buried beneath the two roadways.
"There are a lot of unknowns," said hazardous-materials specialist Melany Lee of the state Transportation Department, slogging through the mud below the tire-fill slope.
But it appears that the process is a lot like what produces heat in a compost pile, she said.
Pressure, water, microbes--"you wouldn't think they'd munch on tires, but they do"--and the rubber itself are combining to create chemical heat measured as high as 160 degrees at cracks in the road's surface and probably hovering around 450 degrees deep inside the embankment.
Humphrey offered a range of other possible factors, including heat generated by the rusting of wire from steel-belted radial tires, and sulfuric acid, a possible byproduct from bacterial breakdown of sulfur-containing rubber compounds.
The only other report of a similar heat reaction came in October from Colorado, where tires were used as fill along Interstate 70 in Glenwood Canyon. The reaction stopped when the upper part of the fill was removed, Humphrey said.