The new Phoenix Metro light-rail line, which will cover 20 mi. (32 km) through the cities of Phoenix, Tempe and Mesa, Ariz., is expected to begin carrying passengers on Dec. 26, 2008. The light-rail is designed to carry 3,000 to 5,000 passengers per hour and will ultimately have the capacity to transport the same number of people as a six-lane freeway, up to 15,000 people per hour.

Clearing a 30-ft. (9.1 m) path for the light-rail through crowded city corridors is no easy feat. Every buried power line, communications cable, gas line, water main, and sewer pipe must be located and moved. This requires careful planning and execution to avoid damage to existing lines, the results of which could potentially be catastrophic in terms of dollars and public health and inconvenience.

To safely and cost effectively accomplish this task, Archer Western Contractors, who was awarded a $95 million contract to build a 4.3-mi. (6.9 km) section of the light-rail in downtown Phoenix, called upon Specialized Services Company (SSC), a subcontractor who is known for its accomplishments in vacuum technology.

SSC relied on the System 4000, a vacuum excavator that uses a combination of air, water, and suction, to quickly and safely expose buried utilities along five light-rail line sections. This allowed contractors to speed up their work and avoid delays.

“Vacuum technology utilizing air is currently the safest method available for exposing utilities and underground infrastructures,” Arvid Veidmark, owner of SSC, said.

In recent years, utility regulations often prohibited any mechanical exploration within a few feet of a known pipeline or cable, which makes vacuum or hand digging the only option. Vacuum excavation allows contractors to avoid many of these concerns with the least amount of surface disruption.

The System 4000 vacuum uses 95 percent air at a volume of 100 psi (6.9 bar). Additionally, the system uses 5 percent water, which helped break up soil more quickly.

With the System 4000, SSC excavated the material into a 450-gal. (1,700 L) rear mounted collection canister. The material was then reused for backfill at the completion of the locating project.

“Air offers higher performance in most soils, greater efficiency, lower cost, and is less invasive than water,” Arvid said. “For every dollar spent on vacuum potholing services for transportation projects, the overall project experiences a savings of $4.62.”

Despite the size of this project, there were no vacuum potholing conflicts. Valley Metro officials expressed confidence that they would meet the Dec. 26, 2008 deadline.

For more information, visit www.valleymetro.org.

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