By: Angela B. Hurni
Angler Project to Filter Dulles Runway Runoff
Building a new airport runway isn’t exclusively about paving.
While a stable landing and take-off area is vital to airport operations, a runway’s design must also account for some of the chemicals used to ensure flight safety.
Angler Environmental of Manassas, Va., completed the installation of five biological treatment units alongside the new fourth runway at Washington Dulles International Airport Sept. 30.
The units are dry bioretention basins that filter chemicals — especially deicing material — that run off the runway by gravity filtration through a granular media bed.
The treatment units resemble rain gardens in makeup and function by mitigating glycol-containing runoff from deicing operations.
The Federal Aviation Administration requires airports that operate during icy conditions to perform deicing operations of aircraft and airfield pavement to ensure the safety of passengers and cargo operations. Deicing operations, if performed without proper discharge controls in place, can have a severe impact on the environment.
According to a 2004 study performed by the Environmental Protection Agency, airports discharge approximately 21 million gal. (79.8 million L) of aircraft deicing fluid (ADF) per year. A likely source of pollutants that causes fish kills, algae blooms and contamination to surface or ground waters is the ADF that is not properly recaptured, reused or treated before discharge.
As a result, airports are required to obtain the appropriate discharge permits to ensure that wastes from deicing operations are properly collected and treated.
Angler Environmental was hired to do just that.
Including this $1.5 million project, there are only 20 of these units in existence, said Dan Haberer, construction field operations manager of Angler Environmental,
Basically, he explained, “chemicals go through the biological treatment units, so when run-off leaves, it is clear.”
The units, designed by full-service engineering, construction and operations firm CH2M Hill, based in Colorado, are aesthetically pleasing with grass surrounding them.
“You could fly in and out of Dulles and never notice them,” Haberer said.
The material for each layer, or lift, for the biological treatment units is installed, then the elevation is checked to ensure “everything is within two-hundredths of a foot, to meet spec,” he said.
The amount of material installed for each lift can be broken down to 5,235 tons (4,750 t) of 2-in. (5 cm) stone; 3,706 tons (3,362 t) of 0.5-in. (1.27 cm) stone; and 3,586 tons (3,250 t) of 0.25-in. (0.64 cm) stone. Next, the 4-in. (10.2 cm) sand layer consisted of 3,490 tons (3,166 t), an 8-in. (20 cm) layer of soil mix measured 7,510 tons (6,813 t), and another sand layer, this one 6-in. (15.2 cm), consisted of 5,225 tons (4,740 t). The total tonnage installed was 28,752 tons (26,100 t).
Haberer also explained that “drainage pipe was installed at 0.02 percent of fall, and all pipe is checked with [a laser leveling system] to ensure proper elevation.”
The equipment on site had to be able to maneuver through wet conditions. The fleet consisted of wide-track, or low ground pressure, equipment that spreads the weight of a machine over a greater surface area; this allows mobility when regular equipment might sink and stick. Angler prefers smaller, more maneuverable equipment, preferably with full rotational capabilities, which permit access through existing, protected areas and reduce impact on sensitive natural habitats.
Up-to-date laser grading equipment is essential for finishing grades within inches. The right equipment can make the difference between a wetland and an upland or a stable bank versus one that will eventually slump and collapse.
Angler Environmental owns two Takeuchi TL150 compact track loaders retrofitted with laser leveling systems to assist with checking elevation. They were purchased from H&E Equipment.
While the machines were well-suited for wet conditions, the laser system needed some assistance.
One day, the TL150s were “installing the 4-in. layer of sand in the rain,” Haberer said. Workers had to secure umbrellas “to grade rods and tripods, as rain drops refract laser beams.”
The company rented a Doosan DX 300 long reach excavator from H&E for earthwork on this project. In addition, Angler has a Terex TA 30-ton (27 t) truck and a Dynapac CA250 84-in. (2.1 m) roller on rent-to-purchase, said Michelle Flinspach, Angler’s equipment specialist and sales representative for the Warrenton, Va., H&E Equipment branch.
Haberer also described other equipment frequently used on this type of job.
“We use a lot of swamp dozers with real wide pads,” he said, “and track trucks —dump trucks on tracks — because of the soft ground.”
Angler Environmental has three Virginia offices; one is its headquarters in Manassas, Va., and the other two are located in Richmond and Culpepper. The company also has an office in Hanover, Md. Haberer said that, in addition to Virginia and Maryland, the company has worked on projects in Delaware, Pennsylvania and West Virginia.
The Dulles project will add the first new runway since the airport was built in the 1960s. When the fourth runway opens, Dulles will be able to handle three parallel, simultaneous aircraft landings or takeoffs.
Construction of the fourth runway began in 2006. The north-south runway is 9,400 ft. (2,865 m) long and 150 ft. (45.7 m) wide and is scheduled to open in November.
It paves the way for the construction of a fifth runway at Dulles, which was approved by the FAA in 2005. No timeline has been set for its construction.
CH2M Hill has an equal partnership with contractor Carter Burgess and will conduct of variety of services on the project in addition to the design of the BTUs and the design of the runway, including airfield traffic, geometric, and airspace analyses and much more. The company has a global presence and has 136 project and area offices in the United States alone. CEG