Wastewater rehabilitation work wins project of the year in Arizona

The AZ Water Association (Arizona) has named the 91st Avenue Wastewater Treatment Plant Digester 1 Rehabilitation in the City of Phoenix as the wastewater treatment plant (WWTP) project of the year, recognizing the proactive planning, collaborative process and design innovations that resulted in an efficient implementation of upgrades to this critical public infrastructure.

The need for upgrades to the plant to protect public health was identified by the City of Phoenix through their asset management program. GHD worked with PCL Construction, the general contractor, to determine what rehabilitation work would be most effective, and the City actively encouraged design innovations throughout the rehabilitation process. It was determined that appropriate rehabilitation activities would include the removal of the existing steel dome, pipe and appurtenances, repair of concrete and steel structures, and the design, fabrication, and construction of a new steel dome and features. The project delivery method allowed PCL Construction and GHD to collaborate from the very beginning of the process, allowing them to identify and mitigate impacts and challenges that could compromise the schedule or cost of the project.

The GHD team conducted a condition assessment, topographic survey, 3D-scanning, and mapping of the existing components in order to develop a holistic approach and design construction documents for the concrete repairs and steel dome removal, as well as the replacement of one 56-year-old digester, which is a 1.2 million gallon, above ground concrete tank, that is 90 feet in diameter and 30 feet tall with fixed steel cover.

Prior to construction, PCL implemented two mock-ups to ensure realistic conditions were created, which enabled the team to identify and correct any constructability issues before construction began on Digester 1. The coordination between GHD and PCL resulted in a lasting solution that will serve the City of Phoenix for years to come.

“The successful management of such a large and complex project requires multi-discipline approaches to develop, design, and deliver the rehabilitation of such aging infrastructure,” said GHD Project Manager Frederick Tack. “This is a significant project, rehabilitating large public infrastructure, that has demonstrated the value and benefit of effective life cycle planning and budgeting to meet the wastewater treatment and water reuse needs of the community.”

Originally built in the early 1960’s, the 91st Avenue WWTP is the largest in Arizona with an ultimate permitted design flow of 230 MGD. It includes seven individual activated sludge treatment systems operated in parallel, and also serves as a reclamation plant that provides an average of 60 MGD to the Palo Verde Nuclear Generating Station (PVNGS) for reuse. The project team was able to prepare the design and construction documents within six months, and PCL Construction completed the demolition, rehabilitation, and dome replacement in just over 12 months. By November 2016, the work was substantially completed and Digester 1 was turned back over to the 91st Avenue Wastewater Treatment Plant for operation.

The AZ Water Association is a nonprofit educational organization for water/wastewater professionals dedicated to preserving and enhancing Arizona's water environment, and serves as the Arizona section of the American Water Works Association (AWWA) and the Arizona member association of the Water Environment Federation (WEF). The 2017 awards were presented at its 90th annual conference and exhibition in Phoenix, AZ, May 3-5 2017.

GHD is one of the world’s leading professional services companies operating in the global markets of water, energy and resources, environment, property and buildings, and transportation. Privately owned by our people, we deliver engineering, architecture, environmental and construction services to public and private sector clients across five continents and the Pacific region. Committed to creating lasting community benefit, we connect the knowledge, skill and experience of our 8500 people with innovative practices, technical capabilities and robust systems. See http://www.ghd.com/.

PCL is a group of independent construction companies that carries out work across the United States, Canada, the Caribbean, and in Australia. These diverse operations in the civil infrastructure, heavy industrial, and buildings markets are supported by a strategic presence in 31 major centers. Together, these companies have an annual construction volume of more than $7 billion, making PCL one of the largest contracting organizations in North America. See http://www.pcl.com/.