FARGO — Since temperatures started hitting the freezing point this fall, de-icing efforts have been pretty much a daily routine for planes taking off from Fargo's Hector International Airport.
The de-icing process happens in a ramp area near the airport's gates. Airline workers push planes to the area and spray a mixture of water and glycol — either ethylene glycol or propylene glycol — onto the plane's wings and fuselage.
While glycol can be toxic to animals, it isn't generally viewed as a danger to humans. In high concentrations, however, it can be problematic in the environment because it can decrease the availability of dissolved oxygen in a body of water.
Because of problems in the past, regulations were put in place for airports across the country outlining how glycol runoff is to be managed, said David Glatt, director of the North Dakota Department of Environmental Quality.
"Like anything we deal with, whether it's pesticides or anything else, it's the quantity, the concentration and the time period over which it is being applied," Glatt said, referring to glycol-based de-icing operations.
In North Dakota, airports and Air Force bases are required to manage glycol via a stormwater permit issued by the Department of Environmental Quality.
The permit applies to four regional airports: Devils Lake, Dickinson, Jamestown and Williston — and four commercial airports: Bismarck, Fargo, Grand Forks and Minot. It also applies to Air Force bases at Grand Forks and Minot.
The permit requires the facilities to conduct monthly inspections and sampling during de-icing operations, and annual reporting of de-icing activities.
Also, under the permit commercial airports and Air Force bases must consider recovering and recycling de-icing fluid, with options that include:
- Having a collection and recovery system
- Using vacuum trucks
- Storing and releasing controlled amounts to a sanitary sewer where allowed
- Collecting runoff in a pond where it can breakdown
- Directing runoff to grassy depressions, or infiltration areas
Fargo airport officials said concentrated de-icing mixtures draining off-site hasn't been a problem, even last winter when frequent bad weather required airlines to use about 73,000 gallons of glycol mixtures.
"In our situation, since it's already diluted to about 50% once they spray it on the airplane so little hits the ground there's really not much to work with," said Shawn Dobberstein, the airport's executive director, adding that when snow falls on glycol runoff, further dilution occurs.
"As it melts and so forth, it just dilutes it and there's nothing there and no concern," he said.
The glycol mix used for de-icing planes is typically orange in color and similar in nature to the coolant used in car and truck radiators. Glycol used for de-icing is sometimes called Type 1.
Another type of glycol mix, usually green in color, is more of an anti-icing concoction sprayed onto planes to prevent ice from reforming after take-off. The latter glycol mix, known as Type 4, is thicker and sticks better to airplane surfaces.
When snow and ice conditions are particularly severe, de-icing at the Fargo airport may occur on a taxiway closer to the runway, Dobberstein said.
Passenger planes are de-iced at a dedicated ramp area and the liquid runoff, also called effluent, pools in a low, paved area.
Workers use vacuums or pumps to move the liquid into tanks and from there the effluent typically goes into the city's sanitary sewer system, where it is ultimately treated at Fargo's wastewater treatment facility.
In the case of FedEx and UPS cargo planes, de-icing happens in a different area and effluent collects in grassy areas, where it usually dissipates in a short amount of time, airport officials said. Dobberstein said the same is the case for the rare times when passenger planes are de-iced on a taxiway.
Dobberstein added that next summer the airport plans to expand the cargo apron serving FedEx and UPS and as part of that work an underground containment system is planned that will be used to collect de-icing runoff.
At some point in the future that containment system, which could include a holding tank with a capacity of about 200,000 gallons, may be linked to the area where passenger planes are de-iced, airport officials said.
De-icing dynamics are similar at Minneapolis St. Paul International Airport, but on a much larger scale, according to airport officials.
Whereas airlines at the Fargo airport used less than 100,000 gallons of glycol last winter, airlines at the Twin Cities airport regularly use a million gallons a year.
To deal with such volumes, de-icing and anti-icing applications happen in a number of dedicated areas, including at the end of each runway.
The effluent is contained in a variety of ways and a good deal of it ends up at a glycol management facility on-site, where it is stored. From there, one of two things usually happens: The effluent is either recycled by a vendor, or it goes to the sanitary sewer system.
MSP officials said because de-icing and anti-icing applications can be expensive, airlines employ a variety of approaches to keep costs down.
One involves using carefully mixed concentrations of glycol depending on the air temperature, with more diluted concentrations adequate in warmer weather and heavier concentrations reserved for colder temps. Airlines will also clear planes of ice and snow using blasts of high-pressure air as a non-chemical option.
But even with today's modern de-icing systems, airlines sometimes have difficulty keeping up with Mother Nature, according to Toni Howell, MSP manager of environmental affairs.
"The weather always challenges us," Howell said.