Force Main Replacement Travels Under Agua Fria River

Cost: $6.78 million
Location: Surprise, Ariz.
Year: 2017-12-13
Size: 3.5 miles
Owner: EPCOR Water (USA) Inc.
Designers: GHD Inc.
Contractor: Achen-Gardner

In Maricopa County, Ariz., the only artery collecting wastewater for the Sun City West community is a critical force main built in 1979. The main stretches from El Mirage Road to the Northwest Valley Reclamation plant in the city of Surprise, Ariz., and had reached the end of its life. Replacing 3.5 miles of existing asbestos cement (AC) pipe with modern materials was chief among the project goals as the potential pipe failure posed risks to nearby communities. The main services more than 15,000 people.

“[The main] had experienced large commercial and residential development within 30 ft of its alignment and crossed under a 1,500-ft-wide river,” said Frederick Tack, senior civil engineer for GHD. “EPCOR Water had already experienced the failure of two smaller diameter AC sewer force mains in neighboring communities, so the risk to public health and the environment was high. The new 18-in. high-density polyethylene (HDPE) force main provides a stronger and more durable pipeline installed in a safer alignment.”

The project was completed in three phases, utilizing the construction manager at risk delivery method. First on the agenda was an alignment study to design 17,500 ln ft of 18-in. HDPE force main, including an integration system with the existing lift station. GHD, which planned, designed, permitted and coordinated the project, worked with local utilities, the city of Surprise, the Arizona State Land Department, and the Flood Control District of Maricopa Count to meet the client’s schedule requirements.

“I am most proud of the team effort between the owner, engineer and construction manager at risk contractor to overcome the many alignment and constructibility challenges and successfully complete the design and construction in less than 12 months,” Tack said.

One of the greatest challenges in completing the project was aligning the replacement pipe under the Agua Fria River, which required 1,600 ft of horizontal directional drilling requiring coordination with public stakeholders, Tack added.

“To cross the 1,500-ft river bed, the new force main needed to be installed adjacet to and 15-ft deeper than the exising force main, while the existing AC pipe remained in service,” Tack said. “The funds budgeted for the design and construction needed to be spent in just over 12 months’ time.”

Private stakeholders also entered the mix for coordinating alignment as the old main ran though residential and commercial areas. Tack said this was further complicated because the line could not be moved into local paved roadways due to a temporary right-of-way construction moratorium, which was put in place after a six-month detour associated with a major traffic intersection improvement project.

Despite those challenges, however, Tack said the project came together early and under the guaranteed maximum price. Concrete, epoxy-coated ductile iron, epoxy-coated reinforced concrete and polyvinyl chloride pipe were all evaluated for the project in addition to HDPE. Ultimately, HDPE pipe was selected because it has a higher resistance and longer life cycle for conveying wastewater.

Since construction completed, Tack said the pipe has performed admirably.

“The new HDPE force main is functioning well, the pump station is operating more efficiently, and the risk of a pipeline failure has been dramatically reduced,” Tack said.