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Orange County Groundwater Replenishment System Expansion

Upgraded purification facility ensures locally controlled, potable water supply for Orange County.
  • Exterior view of Oxnard advanced water purification plant - Gannett Fleming.

    The 100-mgd facility is one of the largest advanced water purification plants of its kind in the world.

  • Interior view showing large collection of pressure vessels - Gannett Fleming.

    The expansion enabled the plant to replenish groundwater to serve 850,000 people daily.

  • Closeup view of a collection of bundled membranes encased in circular pressure vessels - Gannett Fleming.

    The treatment process includes the use of a multistage reverse osmosis process with energy recovery.

Orange County Water District

McCarthy Building Companies

Fountain Valley, California

Our Role
Testing and Startup Management.

100 mgd
Construction Cost
$174 million
New Construction
2 years, 4 months
  • 100 million gallons of high-quality, advanced treated water produced daily for Orange County
  • Treated water from the facility meets or exceeds state and federal drinking water standards
  • Energy-saving measures in the purification process design saves the district $100,000 annually
  • A successful model of high-volume advanced treatment for other communities

One of the largest advanced water purification facilities of its kind in the world produces 100 million gallons of potable water daily, enough for 850,000 people. The Orange County Groundwater Replenishment System (GWRS) purifies secondary effluent using a three-step process of microfiltration, reverse osmosis (RO), and ultraviolet light disinfection with hydrogen peroxide addition. Lime addition is included for stabilization of the final product. The Orange County Water District and Sanitation District jointly developed the treatment facility in response to an ever-increasing demand for potable water and groundwater replenishment.

An expansion of the GWRS in 2015 added two 7.5-million-gallon equalization tanks to the system, facilitating a flow equalization process that stores excess wastewater during the day and feeds the equalized flow to the plant at night during low flow periods. This allows purification to operate at a steady flow, increasing water production and reducing the unit cost of the water produced to $525 per acre-foot, significantly lower than the cost of imported water. Future expansion of the facility will bring the plant capacity to 130 million gallons per day.

What We Did

KEH, before becoming a business group of Gannett Fleming, provided testing, startup, and commissioning management, including field oversight, for the $174 million expansion project. Its work included coordination with vendors and suppliers to ensure that new equipment was properly integrated within existing systems. It also provided commissioning certification reports demonstrating the project’s full compliance with California regulatory requirements and energy codes.

The addition of 6,840 microfiltration membranes, 6,300 RO membranes, and 1,728 ultraviolet light lamps to the system increased treatment capacity by 30 mgd. Energy recovery devices (ERDs) added to the RO system recover the energy from the concentrate and use it to balance the fluxes within the system, resulting in approximately $100,000 annual energy cost savings. Post-treatment stabilization increases the water’s buffering capacity and decreases the variability of its acidity, maintaining the desired pH level. Testing and startup ensured that all new equipment and processes functioned as specified, enabling expanded GWRS operations to begin in Orange County as scheduled.

Key Features

  • Two equalization tanks facilitate flow equalization to reduce the unit cost of treated water to $525 per acre-foot.
  • Additional microfiltration membranes, RO units, and ultraviolet disinfection modules increased treatment capacity by 30 mgd.
  • Stabilization of treated water enables maintenance of desired pH level.

Sustainability Features & Outcomes

  • Advanced treatment reduces wastewater discharge into the Pacific Ocean, lessening impacts on the marine environment.
  • Reduced imports from the Sacramento-San Joaquin River Delta and Colorado River help protect those environments from water depletion.
  • Groundwater replenishment with treated water protects the Orange County Groundwater Basin by preventing seawater intrusion into freshwater aquifers.

Similar Projects: Water/Wastewater: Drinking Water, Engineering, Drinking Water: Water Treatment Plants, Water/Wastewater, Engineering: Water/Wastewater