Groundwater Replenishment System’s Initial Expansion Adds Production, Efficiency

By Michael R. Markus & Mehul Patel

In 2008, the Groundwater Replenishment System (GWRS) made history as the largest water purification and reuse project of its kind in the world. In 2015, the GWRS made history again as its Initial Expansion came online, providing an additional 30 million gallons of water per day (MGD) to the Orange County Groundwater Basin.

The Orange County Water District (OCWD) and Orange County Sanitation District (OCSD) have pioneered water recycling for nearly 40 years through Water Factory 21 and the Groundwater Replenishment System (GWRS). The GWRS incorporates reverse osmosis (RO), microfiltration (MF), and ultra-violet (UV) light with hydrogen peroxide technologies to purify highly-treated secondary effluent from OCSD. OCWD recharges the purified water to the groundwater basin and protects the basin from saline intrusion through injection wells paralleling the coastline.

The GWRS increases Orange County, California’s water independence by providing a locally controlled, drought-proof supply of safe, high-quality water that meets and exceeds state and federal drinking water standards. The $142 million GWRS Initial Expansion increases output to 100 MGD (enough for 850,000 people) at a typical average cost of $520 an acre-ft.

Goals and ObjectivesGoals and Objectives

With the GWRS Initial Expansion, OCWD set out to not only increase water production, but to make the GWRS even more efficient.

The original purpose of the GWRS Initial Expansion was two-fold: 1) to additionally capture and treat wastewater and recharge Orange County’s groundwater basin with flow normally discharged to the ocean by increasing the capacity of the GWRS by 30 MGD; and 2) to reduce operating costs (energy and chemical) by optimizing the performance of the existing system based on data from operation of the original GWRS. An additional goal was to develop a concept to equalize secondary effluent flow in order to maximize the capacity of the entire facility (original project and the expansion).

The Initial Expansion has resulted in positive social, economic, environment and industry impacts.

Savings and Water Reliability

While other agencies were facing severe local water shortages, the expansion allowed OCWD to increase pumping levels of the Orange County Groundwater Basin during California’s historic four-year drought. At one-half the cost of imported water supplies from Northern California and the Colorado River, pumping more local groundwater resulted in significant savings for the 19 agencies OCWD serves.

The Initial Expansion also helps to provide water diversity in an arid region and it better helps meet the long-range plan developed by the Metropolitan Water District of Southern California to maintain and improve the reliability of Southern California’s water supply. In May 2015, the California State Water Resources Control Board (SWRCB) imposed emergency water restrictions on all urban water suppliers within the OCWD service territory. These restrictions required the suppliers to reduce their total water demands by an average of 25 percent. In February 2016, the SWRCB modified the emergency restrictions and gave a credit for recently developed new drought resilient water supplies. The GWRS Initial Expansion project qualified for a 7 percent credit which means the urban water suppliers within the OCWD service territory now only need to reduce their total water demands by an average of 18 percent.

Environmental Windfalls, Water Recycling

The Initial Expansion protects the environment by reducing the amount of water taken from the Colorado River and State Water Project. It also helps maintain Orange County’s active lifestyle in a dry, desert-like region; helps protect the environment by reusing even more of a precious resource; the GWRS uses approximately one-half the amount of energy that is required to transport water from Northern California to Southern California; and uses one-third the energy required to desalinate seawater.

By reusing a precious resource, the GWRS also provides peak wastewater flow disposal relief and indefinitely postpones the need for OCSD to construct a new ocean outfall. It eliminates the environmental impacts construction has to the shoreline and marine wildlife by diverting treated wastewater flows that would otherwise be discharged to the Pacific Ocean. In addition, the Initial Expansion Project helps keep the groundwater basin within safe levels to avoid subsidence.

Optimized Performance with Flow Equalization Optimized Performance with Flow Equalization

One of the challenges to maintaining wastewater flows to the GWRS was that the OCSD facility did not receive and treat sufficient wastewater flow at night. An additional goal in building the expansion was to develop a concept to equalize secondary effluent flow in order to maximize the capacity of the entire GWRS facility.

A flow equalization plan was developed that would help increase daily production to the full 100 MGD production capacity by storing excess wastewater during the day in equalization tanks when it is available and feeding the equalized flow to the plant at night during low flow periods. This allows the GWRS purification processes to operate at a steady flow, simplify operation, increase water production and reduce the unit cost of the water produced.

Increased Energy EfficiencyIncreased Energy Efficiency

OCWD reduced GWRS operating costs by optimizing the performance of the existing system based on data from operation of the original GWRS. The reverse osmosis system of the original GWRS, consisting of 15 RO units, each designed with three stages, lacked some critical instrumentation to allow evaluation of performance of individual stages. Further, the feed pressure required for operation of RO was approximately 190 pounds per square inch (psi), resulting in concentrate stream pressure of 125 psi. As part of the Initial Expansion, Energy Recovery Devices were added to six new RO trains to recover the energy from the concentrate and use it to balance the fluxes within the system, reduce energy consumption and potentially improve performance of the overall system. Preliminary estimates indicate that the ERDs will save approximately 29 kilowatt (kW) per RO skid and have a payback period of approximately five years. This will result in approximately $23,000 energy cost savings per year for each RO skid and upwards of $100,000 per year in total savings.

Another optimization enhancement was the replacement of the lime feed system with a Tekkem system to provide post treatment stabilization. The original post-treatment system at the GWRS included degasification and addition of dry hydrated lime that includes lime silo, slurry make-up system and transfer pump. OCWD experienced difficulties in operating and maintaining treated water pH due to lack of process control and accuracy of the lime slurry make-up system. The GWRS Initial Expansion addressed these difficulties on several fronts, including 1) modification of treated water quality goals to allow operation at a more stabilized point with respect to pH and alkalinity, 2) process modifications to improve operation of existing system, and 3) use of a different lime addition system (Tekkem).

The new system provides a greater level of flexibility and reliability in meeting finished water quality targets to minimize corrosion and enhance groundwater recharge operations.

Positive Public and Community RelationsPositive Public and Community Relations

The GWRS Initial Expansion has received positive attention from national and international media including CBS Morning News, Buzzfeed, Bloomberg and 60 Minutes.

The success of the GWRS and the Initial Expansion have also resulted in greater public trust of water reuse and has placed a spotlight onto the tremendous potential advanced water purification technology has to help solving serious water shortages in California, the United States and around the globe.

The GWRS is an achievement in innovation that has allowed OCWD to live up to its commitment to water reliability, sound planning and investment, and exceptional water quality for the region of Orange County. More importantly, it has been a catalyst for technology innovation and creative water solutions in other communities around the world.

Applications to Others in the IndustryApplications to Others in the Industry

Agencies from across the entire globe have traveled to Orange County to tour the GWRS and learn the political, regulatory, and technical processes needed to implement a similar water reclamation system. The Santa Clara Water Valley District and agencies in San Diego and Los Angeles counties are planning or have constructed similar advanced water treatment plants since implementation of the GWRS. The GWRS Initial
Expansion is replicable and provides a blueprint for agencies wishing to:

  • Implement water reuse projects
  • Implement advanced water purification technologies for indirect potable reuse
  • Maximize energy efficiencies for the RO process
  • Optimize process control of the lime feed system

Leaders of the Orange County Water District and the Orange County Sanitation District were visionary in their pursuit of the GWRS and their understanding of water reuse and its potential as a new water resource. The partnership to develop and expand the GWRS has significantly assisted in the advancement of water reuse throughout the world. The GWRS has been replicated elsewhere in the United States, such as Florida, California, Texas, and Colorado and in Australia. Additionally, the GWRS’s water quality research and data aided Singapore in building its world renowned “New Water” project.


Michael R. Markus, P.E., D.WRE, F.ASCE, is the general manager of the Orange County Water District.

Mehul Patel is the director of water production for the Orange County Water District.

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