Favorite Build: Foster’s Insight on the DIW Pond Expansion

• June 26, 2026

Precision Tunneling Under Active Runways: The DIW Pond Expansion

Every project leaves an impression, but for Foster, one build stands above the rest. Though his career has spanned many successful endeavors, the West Gates DIW Pond Expansion at Denver International Airport remains a defining moment of technical challenge and professional growth. The project was essential to stop airplane de-icing fluid from contaminating local waters, protecting the environment beneath one of the world's busiest airports. Foster noted that the complexity was increased as mining took place directly under active taxiways and runways, requiring the team to solve problems on the fly with a beautiful view of the planes and the mountains. Ultimately, this project reinforced the importance of field collaboration, ensuring that even the most complex airport infrastructure can be delivered successfully under extreme schedule and operational pressure.

A Project of Unmatched Complexity

The DIW Pond Expansion project brought together a wide range of challenging technical elements:

• Excavation of six distinct tunnels totaling 4,400 linear feet using a modified 132 inch diameter single shield tunnel boring machine named Maverick
• Construction under active taxiways, a runway and an active de-icing pad with zero disruption to airport operations
• Installation of 72 inch and 90 inch fiberglass reinforced plastic pipe along with a 1 million gallon storage tank
• Construction of a major pump station equipped with four high capacity pumps and four pond cells totaling 21.6 million gallons of capacity

Engineering in Extreme Conditions

What made the project truly memorable wasn't just its scale, but the precision required to build directly beneath a functioning airfield. In lieu of buying new equipment, the team modified an existing open face tunnel boring machine to handle everything from cohesive sandstone to loose, non-cohesive soils that threatened tunnel stability.

The environment demanded constant adaptability, particularly because the site faced extreme winter weather, strict FAA regulations and severe staffing shortages caused by rigorous airport background checks. Construction operations had to change radically to coordinate around de-icing pad closures. The short-handed team had to work fourteen consecutive 12+ hour days to install a critical slide rail system less than 10 feet from the active tarmac, a high stakes task that no one on the crew had ever attempted before.

Rising to the Challenge

Foster is especially proud of how the team navigated these geological and logistical obstacles while stepping up to fill the gaps on a short-handed crew. He began his role as the tunnel field engineer but quickly expanded his responsibilities to work on the pump station, complete all the pipeline tie-ins in each shaft and build all of the sluice gate actuators onsite. The pressure of the project provided the perfect environment for professional development. By jumping into the field intensive work and becoming "one of the guys," Foster became a true expert on the project by the end of the mining portion. He remains forever grateful to the Project Manager, as they were the only two team members who stayed for the entire duration of the build.

Lessons That Last

Working on a build of this magnitude continued to shape Foster's professional philosophy, which centers on the vital relationship between office staff and field crews. The experience proved that being able to adjust on the fly is critical as new challenges arise hour to hour. Most importantly, the project demonstrated that listening to the experience of the men and women in the field is vital for project success, establishing a lifelong passion for the specialized world of tunneling.