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Greenfield Water Reclamation Plant Phase III Expansion

City of Mesa, Town of Gilbert and Town of Queen Creek, AZ
Gilbert, Arizona
Mesa digester

Project Overview

Award-winning expansion and rehabilitation of an end-of-the-line plant serving three municipalities

In 2015, the City of Mesa, Town of Gilbert, and Town of Queen Creek in Arizona embarked on a large-scale project to expand their jointly owned Greenfield Water Reclamation Plant (GWRP), a key regional facility whose treated water is used for a variety of uses including irrigation of golf courses, crops, fields, and greenbelts; the recharge of groundwater supplies; and water rights exchange for potable drinking water for human consumption and domestic use.

Faced with the consistent growth and development being observed across these three municipalities, the GWRP was rapidly approaching its previous rated capacity of 16 mgd and demanded its third expansion to keep up with these momentous changes. Carollo supported the resulting Greenfield Water Reclamation Plant Phase III Expansion Project’s conceptual planning and 18-month detailed design stage, and then served as a primary consultant for procurement and construction activities that commenced in November 2017.

This project faced numerous challenges associated with expanding and rehabilitating an end-of-the-line plant that needed to be continuously operated, all against the backdrop of a working environment constrained by the global COVID-19 pandemic. Still, through value engineering and resilient collaboration, Carollo’s project and subconsultant teams realized the following achievements:

  • Saved $25 million in construction costs by optimizing the secondary treatment process with 4-stage Bardenpho, fine-bubble diffused aeration, increased mixed liquor recycle pumping capacity, and side-stream recycle treatment that integrates a centrate and return activated sludge reaeration basin (CaRRB) process within the aeration basins.
  • Implemented solids retention time (SRT) control in the aeration basins to improve sludge settleability in the downstream secondary clarifiers and, in turn, facilitate more robust, consistent operations that still complied with nutrient permit limits.
  • Incorporated new technologies to address ongoing plant operations and maintenance (O&M) issues, including outside-in cloth media tertiary filtration to replace existing media, chlorination-dechlorination to replace problematic UV disinfection, and sludge screening to reduce fibrous material in the digesters and biosolids.
  • Replaced, reconfigured, and rewired aged infrastructure, including 20 programmable logic controllers (PLCs) and 60 variable frequency drives (VFDs), sequenced through 130 critical tie-ins that were thoroughly developed through detailed maintenance of plant operations (MOPO) planning.
  • Prioritized the safety of over 100 on-site personnel by developing and enforcing stringent COVID-19 safety protocols and mitigated supply shortages and factory delays by leveraging additional local vendors and suppliers as well as subconsultants’ self-perform crews.

As a result of these successful tasks, the project was not only completed within its contract milestones and on schedule but also experienced zero unplanned outages, protected the safety of work groups, and hosted numerous public outreach activities with local communities. Furthermore, the savings that Carollo extracted were reallocated to removing and replacing the failed coating systems within the plant’s existing digester sludge storage tank and digester vessel.

Reaching substantial completion in August 2020 and final completion in November 2020, the GWRP now handles up to 30 mgd annual average day flow (AADF) in liquids and 38 mgd AADF equivalent in solids, reliably producing Class A+ reclaimed water and Class B biosolids for beneficial reuse.

Results and Highlights

Plant expansion that added 14 mgd in treatment capacity to meet increasing regional demands

Real-time operational strategies to extract all available capacity from existing infrastructure while bringing new facilities online

$170 million in construction costs and $206 million in total project costs

Project completed under budget to allow for an additional $1.7 million in supplemental improvements

Project Awards and Accolades

2021 Project of the Year

American Society of Civil Engineers (ASCE), Arizona

2021 Public Works Project of the Year – Environment

American Public Works Association (APWA), Arizona

2021 Engineering Excellence Grand Award – Waste and Storm Water

ACEC, Arizona

2021 Best Project – Water/ Environment

ENR Southwest

2021 Reuse Project of the Year

Arizona WateReuse

2021 Wastewater Project of the Year

AZ Water Association

2021 Top Projects

Water & Wastes Digest

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