One area of particular focus is aircraft deicing. Airlines apply deicing and anti-icing fluids to aircraft to ensure safe operation during winter storm events in accord with requirements of the Federal Aviation Administration (FAA). Airports have responsibility for clearing and deicing runway and taxiway surfaces.
Subject to the overriding imperative to maintain the safety of passengers and crew, airlines and airports are also committed to addressing the potential environmental concerns associated with deicing.
Aircraft deicing and anti-icing fluids are formulated to meet rigid SAE performance specifications and are generally composed of a freeze point depressant (most commonly propylene glycol), about 10% water, and 2% additives. The primary environmental concern associated with deicing fluid is the possibility of high oxygen depletion in receiving waters due to rapid biodegradation, which can have negative impacts on aquatic life. However, this concern is largely mitigated because of the nature of deicing operations. First, deicing fluid is usually applied in a diluted form, and when combined with other stormwater runoff, the concentration of propylene glycol in the stormwater is relatively low. Second, aircraft deicing occurs during the winter, which is a time when biodegradation is slow. Finally, airlines and airports take numerous measures to limit the amount of deicing fluid that ends up in stormwater. While the toxicity of additives had been some concern in the past, fluid manufacturers – driven by demand from their airline customers – have reformulated fluids so that they are essentially non-toxic. In addition, manufacturers continue to make progress towards developing fluids that exert lower oxygen demand in receiving waters.
At the same time, airlines use sophisticated technology and operational procedures to apply deicing fluid and limit the amount applied to each aircraft. Airports use a variety of measures to limit the discharge of deicing fluid in stormwater, including the use of glycol collection systems, which include dedicated deicing pads and collection systems, or the use of glycol recovery vehicles. Finally, in many cases airports recycle collected deicing fluid, divert stormwater with deicing fluid to a public wastewater treatment facilities, or limit the amount of deicing fluid that is discharged into stormwater runoff at any given time.
Regulation of Airport Stormwater Runoff
Airport stormwater runoff currently is regulated under the Environmental Protection Agency’s stormwater National Pollutant Discharge Elimination System (NPDES) program. The NPDES program is administered either by individual states, or in the absence of a state program, by EPA under the Multi-Sector General Permit. Individual permits are issued for each airport based on the conditions at the airport. Permits issued under the NPDES program ensure that deicing runoff is properly treated to prevent adverse impacts to the environment. The existing stormwater permitting process works well for deicing runoff because it allows local jurisdictions to determine the best approach to regulating deicing runoff and taking into account the unique characteristics of each airport’s physical size, volume of traffic, operations, climate, and nearby waterways. This approach protects the environment by ensuring that the permit addresses the conditions at the airport, and does not apply an arbitrary standard that is not realistic or necessary for the airport’s operations.