New Facility Rids Town of Arsenic

Between its founding in 1880 and the year 2000, the town of Buckeye, Ariz., saw its population grow to about 6,500 residents. Over the past five years, the town has experienced a population boom, growing to an estimated 40,000 residents. This meteoric growth in population had to be accompanied by major water infrastructure improvements.

One example of how the town has successfully dealt with this challenge is the Sundance Arsenic Treatment and Water Storage Facility. This campus has been designed to meet the needs of more than 23,000 projected residents, various commercial developments and schools. For this small town, a project of this magnitude could be overwhelming. But thanks to the efforts of Buckeye’s public works staff, the project’s engineer and the backing of a consortium of homebuilders, this project was completed to the satisfaction of all involved.

 

Early design

The first phase of design for the Sundance Water Storage Facility started in the spring of 2002. The project engineering company, RBF Consulting, worked closely with the town’s contract engineer, WC Scoutten, and operations staff to make provisions for future expansion to meet projected growth. These improvements included a 1.5-million-gal welded steel storage tank, onsite chlorine generation, pumping for two pressure zones and provisions for a future 3.5 million gal of storage and additional pumping. The project provided reliable service to residents with backup power, redundant pumping and electrical controls. Shortly after completing the first phase, the need for a second expansion became evident.

 

Keeping up with demand

In 2004, RBF was retained to complete the engineering design for the campus expansion. It was clear that this would need to be a fast-track project in order to keep up with development in the area. RBF coordinated again with Buckeye’s engineering and operations staff in the design of the proposed 2.5-million-gal tank and other associated improvements.

This cooperative effort expedited design and aided in early identification of potential issues. One example is the foresight that RBF and the town shared in anticipating the effects of a change in federal arsenic treatment standards during the first phase of design.

On Jan. 23, 2006, the U.S. Environmental Protection Agency (EPA) instated a new water quality law that reduced the acceptable amount of arsenic in water systems nationwide. While the first phase of expansion had easily met the previous standard of 50 ppb, the arsenic present in the water exceeded the new acceptable level of 10 ppb. In an effort to comply, the town of Buckeye and RBF worked to make big changes in their water treatment strategy.

 

Identifying the proper treatment

The arsenic treatment design began in 2004 when RBF was hired to perform a technological assessment of the community’s current water system. The team analyzed treatment technologies and their associated benefits and challenges and performed a comprehensive life cycle cost analysis for each process. After a thorough analysis, Pureflow Filtration was selected to provide an effective long-term solution for removing arsenic from the town’s water.

While the improvements were under design, the Sundance system was serving a new community of residents in a 2,000-acre development. Because any large-scale changes to the water system would take place in this residential area, an important aspect of the project was maintaining a good relationship with the community. Extensive public outreach efforts were undertaken to ensure that the neighbors were aware of the project’s impacts and benefits. RBF made presentations to the town’s design review board and the public. These meetings provided an opportunity to discuss the need for the project with citizens and present exhibits illustrating what the finished treatment facility would look like. The citizens of Buckeye ultimately decided to build a completely new arsenic treatment facility to meet the community’s needs and the water quality requirements set by the new federal law.

 

Construction process and obstacles

The Sundance Arsenic Treatment plant was designed as a 10-mgd arsenic treatment facility with the capacity to substantially improve the area’s water quality. RBF provided civil design and overall project management and coordination. They also worked with a provider of electrical design and programming, an arsenic treatment equipment vendor and a construction-manager-at-risk contractor. Various architectural, mechanical and structural subconsultants rounded out the design team.

Success of this project was heavily dependent on communication. As the design was being put together, engineers worked closely with Buckeye residents, staff, stakeholders and the contractor to facilitate the construction process. The engineers held weekly meetings to discuss concerns, suggestions and appropriate solutions; these meetings allowed community members to have a strong voice in the project as it took shape, and they clearly communicated their expectations. This helped to accelerate the project’s design approval and keep construction within federally imposed time frames.

The existing water supply facility was the only source of potable water and fire-flow supply for the Sundance community and surrounding residential and commercial developments. Keeping the existing water supply facility in operation while the arsenic treatment facility was being constructed and tested was one of the project’s major challenges.

Careful planning, phasing and coordination during both the design and construction phases of the project were necessary in order to complete the project without severely disrupting water service to the surrounding community. This was accomplished through scheduling other needed upgrades in conjunction with related construction, constructing during low-demand periods (October to May) and coordination with operation staff to ensure the availability of operators during construction.

The result of this extensive investigation, planning and teamwork is the Sundance Arsenic Treatment Plant and Water Storage Facility. This facility includes a state-of-the-art 10-mgd arsenic treatment facility and 3.5 million gal of storage capacity. It was one of the first facilities of its size in the state. The plant is fully automated though PLCs and SCADA controls, requiring minimal operator intervention.

In order to conserve as much water as possible, the design included two 200,000-gal floating decanter tanks to reclaim up to 99% of the backwash water from the plant and reduce wasted process water. The dual-tank design allows the system to be backwashed to one tank while reclaiming the backwash water from the other tank. The team also designed a sludge holding tank to facilitate the storage and disposal of sludge from the treatment process. The plant design included several pumping systems to effectively backwash the filters, reclaim the backwash water and transmit sludge.

Other improvements were made to the water supply facility in order to benefit the town’s operations staff, such as the design of an expanded onsite chlorine generation system, replacement of the existing flowmeter, addition of hose bibs for site water and the recoating of the existing 1-million-gal storage tank.

 

Milestones and legacy

Because an arsenic treatment plant of this nature was relatively new in its county, RBF worked closely with the Maricopa County Environmental Services Department (MCESD) to establish appropriate performance requirements for the plant’s construction. With the help of RBF, MCESD determined start-up procedures and testing requirements for future large-scale projects.

When this desert town was founded in 1880, did anyone dream that it would become a leader in drinking water technology? Probably not.

Nonetheless, the end result of this collaborative effort is an effective, centralized treatment plant and storage facility that will serve Buckeye residents for a long time.

Mike Worlton is manager for RBF’s Water Resources Department. Ryan Christensen is project manager for RBF. They can be reached at 602/467-2200 or by e-mail at mworlton@rbf.com.

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