Deicing pads are aircraft holding areas located near the runway. In cold weather, aircraft are treated here with deicing solution (primarily ethylene glycol) to remove or deice them before takeoff. Without deicing pads, aircraft treatment occurs at the gate, delaying airport traffic. This is especially problematic for Hartsfield because it is the world’s busiest passenger airport, handling nearly 100 million passengers per year. The new facility features four separate glycol retention/detention systems, each using 180 ft. of 48-in.- and 15-in.-diameter pipe buried 25 ft. deep. The pipe serves as a containment system for stormwater and deicing-solution runoff from the deicing pads.
Beneath each deicing area is a retention/detention system to capture deicing fluid and/or stormwater runoff. Hartsfield’s system is four 100- x 100-ft. holes containing three rows of Advanced Drainage System (ADS) polyethylene (PE) pipe buried 22-25 ft. deep. The pipe serves as a fluid-holding pen, slowing dispersal to the allowable outflow rate. At Hartsfield, the four containment systems are being built underneath the international concourse’s ramp area and are subject to the weight of a Boeing 747, nearly 400,000 lb. when empty, according to Boeing, the aircraft’s builder.
Atlanta-based Aviation Constructors Inc. was the prime contractor for the job, with SDL Environmental of Palmetto, GA, tasked with the preparation, installation, and finishing work. As anyone who has done work at a busy airport knows, there’s never a dull moment, but when you’re digging holes that are 100 ft. on a side and 30 ft. deep in a confined space, surrounded by as much action as you’ll find in a small war, the rules and restrictions are enough to drive strong men to drink.
“What started out to be a two- to three-month job turned out to take longer,” explains SDL’s Tom Boynton, reflecting on the difficulties inherent in the particular working environment. “Originally, the work was to be done at night, but we couldn’t get the productivity we needed, so we switched to daytime operations instead.” Daytime operations meant tedious, incessant, and time-consuming coordination with all the other activities taking place in the airport. Then there were the problems of weather, tight confines, and steep ramps in and out of the hole.
“Any hole deeper than 20 ft. has to be engineered,” Boynton points out. “Our excavators [John Deere 892 and two JD 200s] just dug their way down into the hole under the engineer’s direction and then drove their way out again.” Other equipment on the job, which employed 16 people at its height, included a 750 Deere dozer, Moxy and Bell off-road dumps, and an Ingersoll-Rand roller.
As to the installation of the plumbing, Boynton says, “Because of an aircraft’s weight and the deicing solution’s chemical nature, all containment-system material had to be strong, chemically inert, and watertight.” PE pipe fulfills these requirements and saved time and work compared to a concrete or ductile iron pipe installation. “Corrugated PE pipe is lighter than ductile iron or concrete, and it’s easy to assemble,” he explains.
SDL Environmental and design engineers refer to the pipe containment system as a “tuning fork” because of its three-pronged appearance. The name was coined during the design stage and has been used ever since. The containment-system layout consists of three rows of ADS 48-in.-diameter, N-12 ProLink WT pipe that are sealed on one end. The open ends feed into 15-in. tees of PE corrugated pipe. The smaller pipe provides the path to the city’s sanitary sewer system for deicing fluid runoff and to the airport’s existing drainage system for stormwater runoff. A manual gate valve controls fluid-flow direction. After installation, the tuning forks were covered with No. 89 gravel and then approximately 3,000-4,000 yd. of dirt. “Compaction was a real issue,” says Boynton, noting that airports are particular about that. “The soil that came out was a wet, silty clay. We had to mix in M10 sand to get it to compact properly.”
