Dane County Regional's Glycol Recovery System Goes Underground

Robert Nordstrom
Published in: 

In 1991, Madison, Wisconsin's Dane County Regional Airport was one of the first airports in the Midwest to build a glycol recovery system. The system essentially consisted of a pond that held aircraft deicing runoff that was treated with aeration until it could be discharged into a local waterway or the sanitary sewer system, depending on its biochemical oxygen demand (BOD) concentration.

These days, however, environmental regulations are more stringent, effluent storage and treatment technologies more sophisticated and public awareness of environmental hazards more acute. The airport consequently broke ground for a new $3.8 million underground glycol retention system in August 2008, with Mead & Hunt providing architectural and engineering services.

Project manager Dave Elder reflects on the airport's evolution: "Since the early '90s, when the retention pond was built, improvements at the airport have slowly encroached on the original system and made it less effective. In the early '90s, regulations on deicing fluids were just coming out. Since then new storage and treatment technologies have become available."

FAA standards regarding the pond's location also became a factor. In the mid-'90s, the FAA stated that standing water should not lie closer than 5,000 feet to turbine runways and taxiways. The pond at Dane County Regional, which lay approximately 1,000 feet from runways, was exempt from the requirement through a grandfather clause; but it was not a long-term solution. The airport placed wire netting over the pond to discourage birds and other wildlife, but pond maintenance still became a headache, recalls Mike Kirchner, the airport's director of engineering.

Pushed Underground

A ramp project ultimately provided the definitive impetus for a new glycol retention system. "We had to extend our air carrier ramp to the south, which was where the retention pond was located," explains Kirchner. "We didn't have room to build another lagoon at the distance from the runways that the FAA requires, so we decided to construct underground storage tanks to hold the runoff and a pump station to disperse the runoff to nearby Starkweather Creek or the sanitary sewer system, depending on water analysis."

Facts & Figures

Project: Glycol Retention System

Location: Dane County (WI) Regional Airport

Cost: $3.8 million

Estimated Maintenance/Utility Costs: $40,000 - $45,000/year

Construction: August 2008 - November 2009

Architectural/Engineering Consultant: Mead & Hunt

General Contractor: Howard Immel


Mechanical Systems: J. F. Ahern Co.

Control Systems: Crane Engineering

Masonry: Monona Masonry

Earthwork: Mandt Sandfill Trust

Electrical: Electric Construction Inc.

Paving: Payne & Dolan

Key Benefits: Replaced open pond with automated underground storage and dispersal system

The new system samples, tests, stores and discharges storm water that may be contaminated with aircraft deicing fluids. The facility includes a storm water collection system, an influent pump station and effluent pump station and three underground storage tanks with the capacity to hold 1.1 million gallons of runoff. The tanks, which are set just below grade, lie beneath a new parking lot.

Cheryl Zegers, project manager for general contractor Howard Immel, notes that the storage tanks' subterranean location upped their design requirements - specifically, the amount of weight they could hold.

"Engineering wise, it's more than just placing concrete under the ground," explains Zegers. "The high groundwater in the area makes them buoyant. We had to work closely with our precast concrete contractor to make sure we would be able to carry the weight of vehicles on top. They were designed to support a six-wheel, 22K wheel load."

How It Works

During the deicing season (usually October through April in Wisconsin), storm water flows to the influent pump station, where it is tested. Based on BOD levels, the water is discharged either to nearby Starkweather Creek or the underground storage tanks.

Discharges to the creek are regulated by the Wisconsin Department of Natural Resources. Storm water pumped to the storage tanks is held until it complies with the Madison Metropolitan Sewerage District's standards for discharge into the city's sanitary sewer system. The goal is to provide a steady and controllable flow to the city's sanitary sewer in accordance with the airport's discharge permit.

During the warmer months (May to September), storm water flows into a new detention basin, where it is dispersed by gravity to the creek at a controlled rate. A sheer gate valve installed on the pipeline to the creek is closed when deicing operations begin and opened in the spring when storm water meets requirements for discharge. A check valve prevents backflow into the detention basin when the creek is at flood stage.

The system includes water analyzers at both ends: at the inflow to determine whether the water should be discharged to the creek or the underground tanks, and at the storage tank side to determine the BOD concentration of the water sent to the treatment plant.

Effluent pump station under construction.

Initial & Ongoing Costs

Fully 95% of the $3.8 million project was funded through the FAA Airport Improvement Program; the remaining 5% was funded through state grants and local airport funds. The airport expects utility costs for the new system to average $30,000 per year and maintenance expenses to cost $10,000 to $15,000.

"We've only had the system up and running for a year, so we don't know for sure what the exact costs will look like," Kirchner qualifies.

Operating costs for the previous system were less, he notes, but it was a more basic system. Without effluent analyzers, effluents were held in the pond until they degraded enough to be dispersed into the local waterways. With the new system, more effluents are dispersed to the sewerage district for treatment. The airport is billed according to the amount of water sent as well as the amount of treatment needed.

Before committing to the new glycol recovery system, the airport evaluated the possibility of constructing a small wastewater treatment center on the airport grounds. "The cost for such a facility was extremely high," says Kirchner. "However, we set up this system to be able to make a transition to an onsite treatment facility if the utility company one day says it will no longer treat our water."

Ready for Winter

The bulk of the work was completed between May and October 2009 (after the deicing season) to allow the previous system to stay in operation while the new one was built. Pump buildings and a 24-foot wet well, however, were constructed during the deicing season.

Glycol management system layout plan

"We did as many things as possible during the deicing season so we could complete the new system without impacting the existing system," notes Elder.

Effluent pump station.

Influent pump station.

Andy Platz, group leader and vice president of Aviation Services for Mead & Hunt, is pleased that the new system allows aircraft to be deiced at their respective gates.

"The system is low maintenance and provides for warm weather water quality enhancements," he reflects. "The underground tanks reduce wildlife concerns on the airport grounds. Plus, all of our goals were achieved without disrupting airport operations."

Kirchner is also pleased with the results. "Without a doubt," he states confidently, "this system does a good job dealing with our glycol runoff. I can run the system remotely from a computer. I can control the pumps and view various data. Generally speaking, though, the system pretty much runs automatically. All we have to do is switch our deicing activities from summer mode to winter mode, and coordinate with the sewerage district about when to pump effluents for treatment."


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