Engineering Runoff Solutions

As EPA considers more stringent regulations on stormwater/deicing runoff, here’s a look at one alternative airports may want to consider.

Airport environmental managers know that the Environmental Protection Agency has been collecting data on the levels of deicing glycols and other contaminants in airport stormwater, and that mandatory stormwater management plans, and perhaps even prescriptive discharge limits, are on the horizon. The same managers also recognize that the airport is ultimately responsible for controlling discharge of pollutants to the environment. While airport stormwater runoff is particularly hard to treat using conventional means because it is cold, intermittent, and high-volume over short periods, an innovative approach using aerated gravel beds is proving to be an effective treatment for such contaminated stormwater.

These sub-surface flow (SSF) wetlands are insulated, aerated, and specifically engineered to remove glycol. In addition, they are easy to operate, requiring only minimal attention from airport staff, and their construction and operations and maintenance (O&M) costs are only a fraction of those of alternative conventional stormwater treatment facilities (less than 50 percent). A new facility of this sort is in its final design stages for Buffalo Niagara International Airport (BNIA).

Airports in cold weather areas use glycol-based aircraft deicing fluids (ADFs) for removing ice and snow from aircraft surfaces during winter and under frost conditions. Relatively concentrated, glycol-rich, spent ADFs (concentrate) may be collected from around the deicing pads; yet, significant parts of the spent ADFs at every airport end up in stormwater sewers and ditches, where they may be channeled into nearby streams.

The management of glycols varies from airport to airport. At some, sophisticated deicing pads and vacuum trucks are used to ensure the collection of up to as much as 65 percent of the glycols used. At others, little or none of the concentrate is recovered, and excess glycols and surface deicing chemicals are simply allowed to flow, drip, or blow into nearby sewers, ditches, and grassed areas.

Focusing on the Problem
Early emphasis for airport glycol management focused on the concentrate stream and ignored that portion of the spent ADF that entered stormwater systems. There are options for the off-site management of the glycol-rich concentrate.

In some cases, that which is vacuumed up or otherwise collected at deicing pads is sent to local municipal wastewater treatment plants. However, this option can be expensive and may be risky, as increasingly municipalities local to airports are reducing or eliminating taking such materials.

Alternatively, on- or off-site recycling or treatment plants such as anaerobic digesters, reverse osmosis plants, and distillation units can be used to manage the concentrate if there is a market for the recovered material. However, these concentrate management options usually also produce byproduct streams (sludges, residual water, gases/odors) that must in turn be managed, and they require extensive and expensive operations and maintenance by airport or contract staff.

No matter how concentrate collection operations are carried out, much of the spent glycols will end up in the usually huge volumes of stormwater runoff at airports. For these streams, off-site disposal or treatment is often not an option.

Federal regulations that establish baseline treatment for deicing liquids are scheduled for proposal in 2007, with the final rule scheduled for promulgation in 2009. Even at airports that now treat their concentrate on-site, or send it to an off-site wastewater treatment plant, the on-site management of glycol-contaminated stormwater runoff will increasingly have to be considered as well.

Therein lies the rub. Stormwater runoff at airports is often dilute and cold, with inconsistent flows and contaminant loadings. This makes it extremely difficult to treat. In the early stages of a rainfall event, accumulated contaminants in the catchment area (spilt fuels & lubricants, chemicals from cleaning operations, sewage leaks, oils and greases), especially those on impervious surfaces such as roads, parking areas, runways, aprons, and other paved areas, are washed off early in the storm (the “first flush”).

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