The largest fire in Johnson County history began on Saturday, May 26, and burned so hot it turned melted tire shreds into pyrolitic oil and created a plume of smoke that spanned the horizon for nearly 15 days.

While 7.5 acres of the Iowa City Landfill burned, the State Hygienic Laboratory - on behalf of Johnson County Public Health - tested air samples that were collected near the fire and from multiple locations in the county. The Laboratory also tested samples from a collection pool that held more than 100,000 gallons of volatile pyrolytic oil created when the tires that lined the landfill cell burned.

"Air samples were collected by Hygienic Laboratory staff that Sunday and on Memorial Day to assess the quality of the air in terms of chemical contaminants in the smoke plume," said Michael Wichman, Ph.D., associate director of Environmental Health Programs. "Air testing continued well into the next week in Coralville, and additional, urgent testing of pyrolytic oil byproduct was provided by our Ankeny staff."

The Laboratory assessed samples from 12 sites for potential exposure and background levels of various compounds. Volatile organic compounds (VOCs) identified as potential health concerns included benzene, toluene, 1,3-butadiene and styrene. Benzene and toluene were detected at concentrations of 8.27 and 8.64 parts-per-billion (ppb), respectively, at 1,000 feet from the fire. The concentrations for both compounds were above 10 ppb at the fire's edge.

The levels detected were considerably lower than the EPA lifetime Reference Concentration (RfC) of 95 ppb for benzene and 18,800 ppb for toluene. The levels also were less than exposure limits of 1,000 ppb and 150,000 ppb, respectively, for benzene and toluene recommended by the National Institute for Occupational Safety and Health.

Although the Hygienic Laboratory did not detect VOC concentrations at levels of concern for public health, additional observations by other University of Iowa researchers added to the environmental assessment. The UI Department of Chemistry detected carcinogenic polycyclic aromatic hydrocarbons at levels higher than those found regularly in large US cities. Particulate matter measurements by the UI Civil and Environmental Engineering Department and modeling by the UI Public Policy Center indicated that exposure to high fine particle concentrations (>35 μg/m3) also may have been an immediate concern for public health.

Johnson County Public Health issued a health advisory recommending that those in the path of the plume stay inside, particularly if they were elderly, children or people with a respiratory or heart condition.

Iowa City officials initially considered using a specialized wetting agent to extinguish the fire. Because of the low probability for success and the potential environmental hazards posed by the runoff, the city opted instead to contain the fire and let it burn itself out. Its strategy later shifted to a "stir, burn and cover" method that used heavy equipment to turn the burning tires to accelerate the combustion process, and then topped them with a layer of clay soil after combustion was nearly complete.

On June 10, the fire was covered and the plume greatly diminished. The pyrolytic oil was removed from the landfill and transported to incineration facilities in four different states and Canada.

"I cannot commend our staff enough for the long hours and rapid testing services that they provided to better understand the chemical makeup of the smoke as well as the oil byproduct," Wichman said. "Matt Mainprize, our environmental laboratory analyst, who performed much of the sampling and analyses, commented, 'This is why we are here. It is part of our job to provide testing services as needed, 24/7, 365 [days per year].'"