CAP’s dedicated professionals take their job seriously. We are caretakers and stewards of 336 miles of amazing infrastructure, and we work diligently at our jobs to ensure the long-term reliability of this critical water delivery system.

Much of that work is done during an outage where large-scale maintenance is planned months and years in advance. However, at CAP, not all outages are created equal. This winter’s outage wasn’t actually about performing maintenance. It was a visual inspection of two tunnels and one siphon on the west end of the system, valuable infrastructure that connects communities in central and southern Arizona. Because the CAP system was built to last, it’s an inspection that is only necessary to conduct every 15 years.

What happens during this inspection?

The inspection team looks for cracking and breaking in the precast liner panels and loss of mastic, the material that is used to fill the gaps between the liner joints. The team also looks for anomalies that would indicate a larger structural issue.

Sounds easy until you consider the difficulties of even entering the tunnels … since they are full of water. It took a team of CAP experts from approximately a dozen different departments to prepare for and conduct the inspection.

Two tunnels and one siphon were inspected. Buckskin Mountain Tunnel, which is nearly seven miles long, Burnt Mountain which is 0.6 miles long and Cunningham Wash Siphon, which is 0.7 miles long.

Prior to inspection, each had to be dewatered. The process to dewater is slightly different for each tunnel and siphon, but the result is the same: isolate the tunnel or siphon with a barrier and pump water out so crews have a safe working environment.

During this outage, several repairs were made in Buckskin Mountain Tunnel where old patches had failed or where the precast concrete tunnel liner segments were damaged due to normal use wear and tear. No need for repairs were found in Burnt Mountain Tunnel or Cunningham Wash Siphon.

It’s rare to delay repairs in dewatered tunnels and pipelines since accessing assets such as those are extremely involved, and inspections are many years apart.

Tunnel inspections – another way CAP’s water professionals work hard to deliver ensure a reliable water delivery system for Arizona.