New Signal Butte Water Treatment Plant Allows Mesa Citizens to Thrive
An Investment in the Future: State-of-the-Art Signal Butte Plant Delivers Safe, Reliable Water Supply to Mesa Citizens
In Mesa, Arizona, one of the largest capital investment projects in its history turned operational nearly a year ago. The Signal Butte Water Treatment Plant (SBWTP), a 24 million-gallon-per-day (MGD) facility with capacity for future expansion to 48 MGD, came online last summer. Designed and constructed for $126 million, the SBWTP uses cutting-edge technologyto provide clean, safe drinking water to citizens.
Located at the northeast corner of Signal Butte and Elliot roads, the SBWTP treats Colorado River water supplied by the Central Arizona Project (CAP) canal. This 336-mile system extends from Lake Havasu in western Arizona to just south of Tucson, and serves roughly 80 percent of the state’s population. Access to the CAP supports the City of Mesa’s goal to fulfill 90 percent of water demand through renewable surface water. This, in turn, will help to build groundwater reserves that can be used during periods of drought.
Black & Veatch designed the city’s new water treatment plant, which employs multiple processes for maximum operational flexibility and treatment of varying raw water qualities. State-of-the-art water treatment systems include ozone for the water oxidizer, sand-ballasted flocculation for sedimentation, granular-activated carbon for the filters, and sodium hypochlorite as the main disinfectant.
The project included construction of process basins, piping galleries, chemical feed facilities and sludge handling facilities as well as an operations building featuring a laboratory, control room, and maintenance areas. Sundt Construction, Inc. (Sundt) delivered construction services under a construction manager at risk (CMAR) method.
A Compressed Project Schedule
Construction of the state-of-the-art plant began in June 2016. The project team was tasked with building an operations building, a raw water flow control and pH adjustment facility, ballasted flocculation facilities, ozone generators, ozone contactors, deep-bed biological filtration facilities, solids residuals facilities, mechanical dewatering facilities and chemical buildings.
The scope of work also called for various improvements to the site’s existing electrical building and standby power generation equipment, as well as site work for roads, parking, drainage, fencing, landscaping, and lighting.
The original construction contract would have resulted in substantial completion occurring in October 2018 – well past the peak water demand season in summer. To expedite project activities, Sundt proposed a multi-phased approach that allowed construction to commence four months earlier than planned.
The work was ultimately separated into two packages. The first included earthwork, under-slab piping and constructing the concrete foundations of the treatment complex and recovered water basin structures. The second package consisted of constructing the remainder of the complex.
This tactic also reduced project costs and eased the procurement of critical equipment. “The CMAR and the city negotiated two separate guaranteed maximum price (GMP) packages based on 90 percent design, with an allowance for 90 percent to 100 percent in design changes to speed up the procurement time,” explains Greg Ayres, Vice President of Sundt’s Industrial Division.
Collaboration Speeds Construction
To achieve the aggressive construction schedule, Sundt utilized the Last Planner System from the Lean Construction Institute. This production management tool benefits design and construction teams in three key ways:
- It simplifies design management responsibilities by helping team members better understand the roles, responsibilities and actions of each discipline.
- It enhances communication and coordination, which increases efficiency and speeds decision-making.
- It improves schedules by reducing design rework,as any necessary design clarifications/corrections are done before work begins in the field.
Through the Last Planner System, members of the SBWTP project team collaborated to provide input and define their commitments for the final schedule. According to Ayres, the planning sessions required “all project stakeholders to create detailed activities and resource requirements that support the as-planned schedule. Six-week look-ahead schedules were reviewed and updated each week and were the basis of a weekly work plan (WWP).”
The WWP consisted of a production plan in which quantity goals, as well as weekly manpower requirements, were established in accordance with the overall project schedule. Each week during construction, the entire project team carefully monitored and updated the project schedule and WWP.
“Completed activities were evaluated from a ‘lessons learned’ perspective in order to measure and record team members’ abilities to meet the committed objectives and improve on future planning activities,” Ayres notes.
In addition to finding creative ways to accelerate project delivery, the project team also had to consider impacts to the surrounding area. The plant sits on a 40-acre site in the middle of a large neighborhood.
“Noise was mitigated through work hour restrictions, and we addressed occasional noise concerns by installing noise barriers (when practical) or by remedying complaints immediately. Also, efforts were made to schedule large concrete pours before or after daily rush hour traffic routines,” Ayres says.
Designers also factored in the local community when planning the aesthetics of the water treatment complex. As a result, the architectural style for building exteriors blend with the environment and landscape screening strategically limits views from the surrounding neighborhood. In addition, certain facilities were installed below-grade to minimize visual impacts.
Ultimately, substantial completion was achieved in June 2018 – well ahead of the original schedule – with final construction activities wrapping up in November 2018.
Advanced Water Treatment Capabilities
The SBWTP is one of three water treatment plants used by the City of Mesa to treat up to 186 million gallons daily for over a half-million people. While every facility uses conventional treatment methods, filtration, fluoridation and chlorine disinfection, only the Signal Butte location uses ozone disinfection. This advanced technology is key to helping the city meet its goal of exceeding the requirements of the existing national primary drinking water regulations, specifically the U.S. Environmental Protection Agency’s Stage 2 Disinfectants/Disinfection Byproducts Rule.
“The new Signal Butte Water Treatment Plant was designed with ozone generators and deep-bed, biologically active, granular-activated carbon filters, which remove total organic carbon to reduce disinfectant byproducts,” Ayres says. “This allows the city to meet the goal of having disinfectant byproduct total trihalomethanes below 80 percent of the local-running annual average requirement.”
In addition, a “bleach” solution is generated on-site for chlorine disinfection that reduces hazardous chemicals stored at the plant. Water is recovered from the residuals captured in the process and recycled into drinking water. Also, ballasted flocculation works with the ozone disinfection system to improve the barriers to pathogens while decreasing the level of suspected contaminants in drinking water.
The Future Vision
Roughly 80 percent of water used by Mesa residents comes from the Salt, Verde, and Colorado rivers, while the remainder is sourced from 31 deep aquifer wells in the area. Groundwater will continue to provide the balance of water needed during peak demand periods until the SBWTP can be expanded, which is scheduled for 2025 but is subject to future bond authorizations and demand growth.
According to city officials, this innovative piece of infrastructure serves as a foundation for future economic vitality in the area.
“Everything begins with water, and Mesa would not be able to continue to grow and prosper without the new Signal Butte Water Treatment Plant and other investments in infrastructure,” says Mayor John Giles.
Mesa’s water meets over 100 state and federal drinking water standards, including standards for metals, microbiologic, organic and inorganic chemicals and radionuclides. With the addition of the state-of-the-art Signal Butte facility, the city can even more successfully achieve its vision of providing a safe, reliable water supply to citizens now and in the future.
Photos courtesy of Robby Brown, Sundt Construction, Inc.