Opinion ID: 173200
Heading Depth: 2
Heading Rank: 2

Heading: ADF and the Denver Airport

Text: Plaintiffs do not challenge the district court's rendition of the historical facts. We begin by discussing some pertinent science and then summarize the history of ADF use at the Denver Airport and the problems that have and have not arisen.
ADF is mostly propylene glycol. When propylene glycol degrades in an anaerobic environment where sulfur is present, hydrogen-sulfide gas can be produced. Hydrogen sulfide has a characteristically offensive odor, which often accompanies sewage or rotten eggs. It can be smelled at very low concentrations in the air. Some people can detect it at one part per billion, and almost all recognize it at 300 parts per billion. Much higher levels, however, are required before it has recognized health effects. Eye irritation has been noted at between 5 and 30 parts per million  not billion; [m]arked eye and lung irritation occurs at 200 parts per million; and [b]reathing impairment and unconsciousness results at 1,000 parts per million. Bench Ruling at 12.
After ADF is used to deice an airplane, hydrogen-sulfide gas can enter Concourse B by two means. The ADF may degrade outside the concourse and the resultant gas then infiltrates the concourse. Or the ADF may mix with storm water and flow down through cracks in the tarmac. Because the concourse basement extends under the tarmac, this mixture can leak into the basement where the ADF degrades, producing hydrogen sulfide. Until practices at the Denver Airport changed in 2005, some planes could be fully deiced with ADF while at their gates. Beginning in 1997, employees of United Airlines and others who worked at Concourse B filed a number of complaints about the rotten-egg smell and about health effects that are symptoms of exposure to hydrogen sulfide. Some complaints linked the smell to degrading ADF. Maintenance logs and reports also indicated the presence of hydrogen sulfide in the basement, and one or two reports attributed the gas to ADF. A 1998 water-quality study made numerous recommendations to control the runoff of ADF into the Denver Airport's storm-water system. Perhaps the most significant episode occurred in 2001, when many people complained of a foul odor and burning eyes in the Red Carpet Club in Concourse B. Air testing detected concentrations of hydrogen sulfide above one part per million. The Tri-County Health Department found that the gas flowed from the basement level up to the Red Carpet Club through the elevator shafts. A report by URS Corporation, a consultant retained by Denver, concluded that the hydrogen sulfide came from degrading ADF. As a result, the elevator shafts next to the club were sealed and measures were taken to prevent ADF from leaking into the basement of Concourse B. Denver began a program (which was still in effect at the time of trial) to seal cracks in the tarmac around the concourse, thus preventing ADF from entering the ground. Despite these measures, in September 2005 maintenance logs reported toxic levels of hydrogen sulfide in a mechanical room in the basement of Concourse B and stated that employees were advised not to enter the room without proper safety equipment. Beginning about that time (the record does not provide a precise date), Denver limited the amount of deicing that could be conducted at the gates. Planes were directed to deicing pads away from the gates and the concourse basement. Gate deicing was restricted to a few portions of the plane in certain circumstances. (The district court found the evidence insufficient to determine Denver's motives for moving deicing from the gates  whether it was a response to this lawsuit or more a matter of efficiency and economics.) In addition, in 2006 Denver installed ventilation fans in two of the twelve basement sump rooms and, as of trial, it anticipated installing fans in the remaining sump rooms.
Even after full-plane deicing at the gates ceased at the Denver Airport, there were some reports of the odor of hydrogen sulfide in the basement of Concourse B. But the complaints were much fewer and not supported by objective evidence. The Center for Toxicology and Environmental Health, an independent engineering firm, conducted five air-quality tests between November 2005 and March 2008 at many sites in the concourse, but no hydrogen sulfide was detected. The district court concluded that currently the evidence does not establish levels of either propylene glycol or hydrogen sulfide that are dangerous to human health in the basement of Concourse B. Id. at 34. A United Airlines official testified in April 2008 that United had no intent to request full-plane gate deicing after this litigation ends. He said that there had been discussions two years earlier about testing the use of glycol-recovery vehicles at the gates, apparently to determine whether they could reduce the flow of ADF into the environment after full-plane deicing. But United then decided not to spend the money necessary to acquire the vehicles. An airport official testified that Denver had no plans to allow United to return to full-plane deicing at the gates. He explained that the airport had added deicing pads and that gate deicing could create traffic congestion as inbound aircraft waited for gates where deicing was taking place. He also said that gate deicing would require new infrastructure to collect overspray and runoff.