The deicing and anti-icing of aircraft and airfield surfaces is required by the Federal Aviation Administration (FAA) to ensure the safety of passengers; however, when performed without discharge controls in place, airport deicing operations can result in environmental impacts. In addition to potential aquatic life and human health impacts from the toxicity of deicing and anti-icing chemicals, the biodegradation of propylene or ethylene glycol (i.e., the base chemical of deicing fluid) in surface waters (i.e., lakes, rivers) can greatly impact water quality, including significant reduction in dissolved oxygen (DO) levels. Reduced DO levels can ultimately lead to fish kills. This Preliminary Data Summary provides information about the air transportation industry and the best practices being employed for aircraft and airfield deicing operations, as well as for the collection, containment, recovery, and treatment of wastewaters containing deicing agents. This study was conducted to meet the obligations of the EPA under Section 304(m) of the Clean Water Act, in accordance with the consent decree in Natural Resources Defense Council and Public Citizen, Inc. v. Browner (D.D.C. 89-2980, as modified February 4, 1997). EPA hopes that this study will serve as an objective source of information that can be used by airports, airlines, state and local regulators, and citizen groups.