Ocotillo Water Reclamation Facility Expansion

For years, the City of Chandler had relied on their Airport Water Reclamation Facility (AWRF) to pump reclaimed water to the West Chandler area. However, the Ocotillo Water Reclamation Facility (OWRF) is located closer to many of the City’s reclaimed water uses such as the Ocotillo Management Group, the Gila River Indian Community, and the Ocotillo Recharge Wells. To accommodate the past and future growth potential in the West Chandler area, the City engaged Carollo to increase its treatment and water reuse capacity near its end users by expanding the OWRF with reliable, high quality reclaimed water.

Originally designed in 1984, the OWRF was a 10-million-gallon-per-day (mgd) wastewater treatment plant using a conventional activated sludge process with biological nutrient removal followed by tertiary filtration and disinfection. With completion of this Phase 1 Expansion, a membrane bioreactor (MBR) treatment train was added to the facility, increasing its overall rated capacity to 15.5 mgd. Carollo served as the lead design firm under this $122.6 million construction manager-at-risk (CMAR) project, working with joint venture contractors, Sundt Construction and McCarthy Building Companies.

To save capital costs while increasing treatment capacity, innovative approaches were employed, including the construction of combined facilities that could serve both the existing conventional and new MBR treatment trains and replace older, less efficient systems. The conventional and MBR trains now utilized shared Influent Pump Station, Headworks, Solids Handling, and Reclaimed Water Storage and Pumping facilities, as well as new Administration and Maintenance Facilities.

Being a “good neighbor” was a top priority for the City, given its physical location adjacent to residential and commercial stakeholders. A Community Advisory Panel (CAP) was established early on to provide input on strategies to minimize aesthetic impacts to the surrounding community. This CAP helped select the building architecture theme and provided valuable input to site screening strategies consisting of architecturally-pleasing block wall treatment, extensive landscaping, and undulating berms around the facility perimeter, all visualized through interactive 3D model videos and renderings. Extensive odor control for the various treatment facilities were also provided by covering process basins and directing the foul air to two-stage, biological odor-control treatment systems followed by carbon adsorption for polishing. Additionally, all noise-generating equipment were either located below-grade or enclosed within buildings with acoustical panels to attenuate noise impacts.

This project’s construction was documented on video in real-time through the use of drones. The captured footage not only helped stakeholders and community members remain abreast of the project’s advancement, but also allowed every team member to better understand day-to-day changes and needs and facilitated defensible discussions about next steps during weekly progress meetings.

Despite extensive construction activities demanding 30 scheduled shutdown events that impacted plant operations, this expansion project was completed on time, without ever exceeding permitted discharge requirements, and was delivered approximately $6.5 million under budget. The team used these cost savings to further improve areas of the OWRF that would have otherwise been slotted for future improvement, including the addition of a new secondary clarifier, medium-voltage standby generators, additional membrane cassettes, and a larger reclaimed water pipeline to the Gila River Indian Community (GRIC). In January 2019, these collective improvements resulted in the Arizona Department of Environmental Quality (ADEQ) approving an increase in the OWRF’s rated capacity from 15.5 mgd to 18.0 mgd, expanding the City’s distribution of Class A+ reclaimed water into the West Chandler area. Thanks to Carollo’s flexible and proactive facility planning, the plant can be further expanded up to 30 mgd in the future.