Carollo (in conjunction with other subconsultants) was selected for the Phase II Expansion design of the Greenfield WRP. Located in Gilbert, Arizona and jointly owned by the City of Mesa, Town of Gilbert, and Town of Queen Creek, the plant was built in phases to meet the wastewater treatment needs of the rapidly growing communities. Phase I of the Greenfield WRP consisted of a site master plan, design, and the construction of the South Lift Station, equalization basin, and associated pipelines. Phase 1 began operation in March 2000 with a design capacity of 4.3 mgd. The original Basis of Design Report (BDR), developed in 1997, planned an ultimate water reclamation plant with a capacity of 43 mgd. However, significant increases in projected growth for the communities resulted in the need to update the original BDR. Per the BDR update completed by Carollo, the current site master planning is for an ultimate treatment capacity of 52 mgd with one train out of service and solids treatment equivalent to 64 mgd.

The Phase II Expansion project consisted of a 16-mgd liquid reclamation facility; 24 mgd equivalent of solids treatment, including 16 mgd from Greenfield WRP and 8 mgd from the Mesa Southeast WRP; and modifications to the Southeast WRP to allow the transfer of solids to the Greenfield WRP. The plant is designed to meet Arizona Department of Environmental Quality (ADEQ) Class A+ reclaimed water quality standards. Effluent will be utilized for irrigation, recharge, and exchange with the Gila River Indian Community. The solids treatment system was designed to produce Class B dewatered sludge.

Project elements include:

• Influent pumping and screening
• Biological nutrient removal
• Tertiary filtration
• Cloth disk filters
• UV disinfection
• Sludge thickening and anaerobic digestion
• Centrifuge dewatering
• Effluent pumping
• Odor control and noise abatement
• Administration and maintenance facilities
• Berming/screening for site aesthetics and security

Construction utilized the Construction Manager At Risk (CMAR) alternative project delivery method. Coordination between Carollo and the CMAR included initial partnering workshop; weekly progress meetings with Owners; development of early procurement documents for long-lead equipment items; overall project scheduling; and overall project cost development. CMAR representatives were integrated with the design team in a remote field office at the project site throughout the design phase.