City of Casa Grande,
Water Reclamation Facility Expansion Phase 3 Design
- 24 Allen Bradley ControlLogix/CompactLogix PLCs
- Integrated video surveillance
- PLC programming coordinated among four different vendors
- Identification of existing plant deficiencies and solutions
- Guidance to contractors to ensure highest quality “as-built” documentation and owner’s ability to troubleshoot future problems
The City of Casa Grande (City) experienced rapid growth in early 2000, and despite the economic slowdown that started in 2007, the City has emerged as a center of economic growth within Pinal County Arizona. To accommodate the past and future growth potential, the City foresaw the need to have treatment and water reuse capacity to handle both current flows and the future growth, and recognized the need to expand their only Wastewater Reclamation Facility (WRF).
The City’s WRF was originally constructed as a mechanical plant in the early 1990s and later expanded to 4 mgd (average daily flow) in 2005, with both expansions designed by Carollo Engineers. In 2006, the City engaged Carollo to start planning the next expansion to 12 mgd, and in 2008, the planning and design phases were completed. In late 2007 and early 2008, the City and Carollo obtained funding from the Water Infrastructure Finance Authority (WIFA), which allowed the project to be bid by contractors in the fall of 2008. Construction commenced in April of 2009 with completion in 2012. The total funding provided by WIFA was $62.5M and the lowest responsive bidder (Hunter Contracting) was under $49M.
The design included several cost savings measures to optimize existing infrastructure including modification of the existing aeration basins to increase each basin capacity to 3 mgd and the addition of a new fourth basin to bring the capacity to 12 mgd. This approach saved approximately $20M in capital costs. The design included new disinfection facilities to replace the existing gas chlorine system with the largest on-site sodium hypochlorite generation system for a wastewater facility within Arizona.
The Phase 3 Expansion included some challenging aspects that were overcome by the entire project team. The major challenges entailed maintaining the existing WRF during construction activities. The design took into account these challenges and provided additional compartments and valves at key transition areas such as splitter boxes upstream of the aeration basins and the secondary clarifiers. Extensive workshops and coordination meetings were held by Hunter to coordinate the activities with the City operations staff and engineer to make sure that the permit limits were met at all times during construction.
The City’s expectations were exceeded and the final construction project came in under budget. The City, Hunter, and Carollo also worked together during the construction phase to improve other areas not in the original design. The low bid, as a result of the economic slowdown, allowed the team to rehabilitate areas that would have otherwise been slotted for future rehabilitation, which will result in lower operation costs. The facility was completed in time for the recent increase of wastewater flows, which are now past the prior capacity of the WRF.