The Pullman-Moscow Regional Airport (PUW) in Pullman, WA, cut the ribbon on its new $154 million runway in October 2019. The 6,700-foot-long runway was rotated 5.5 degrees and extended 400 feet to a 7,100-foot-long length. The realignment and lengthening were done to comply with Federal Aviation Administration (FAA) design standards, improve airport procedures, and reduce winter weather-related flight cancellations.
The reconstruction and addition of impervious areas required
stormwater flow control and treatment measures to comply with most current
Washington State Department of Ecology General Use Level Designation (GULD)
standards. The Washington State Department of Transportation, FAA, and the City
of Pullman reviewed the project.
Engineers utilized underground detention instead of traditional land-based detention to save space and eliminate a pond that would attract wildlife and pose a safety risk to aircraft.
Engineers from Mead and Hunt considered a corrugated metal
pipe (CMP) and a cast-in-place concrete vault detention system. The engineers
selected the Contech CMP system based on cost savings. A split CMP detention
system was designed using 2,120LF of 120” and 195LF of 96” solid Aluminized Steel
Type 2 hydraulically connected with an upturned elbow in the 96” pipe to
overflow into the 120” pipe. Pretreatment is provided by two Contech CDS
The 120” CMP was placed under a parking lot and included a Stormwater Management StormFilter in a manhole configuration to provide water quality treatment. Vortex valves were used to optimize flow control discharge rates across a range of head values, allowing engineers to reduce the overall detention footprint by 15% - 20%. Contech also provided slotted drain to collect pavement runoff where a new taxiway connector met the existing terminal apron pavement.
This design required complex modeling from the engineer, which Contech assisted by providing technical system details and sizing calculations.
The systems were ordered during the winter to allow for fabrication for spring delivery. Challenging site conditions with wet clay soils made the installation difficult. The Covid pandemic was also a factor, requiring social distancing and the use of face masks.
“Contech staff provided useful information regarding optimal system layout, materials selection, facility sizing, construction expectations, and more from early in the design process all the way through construction,” said Bob Thayne, PE, Water Resources Engineer. “They were responsive, friendly, and helpful at all times.”