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"People are willing to get over the 'yuck' factor to have a safe and reliable supply of water"

Operational since January 2008, the world's largest advanced water purification system for potable reuse – the Groundwater Replenishment System in Orange County, California – is a state-of-the-art water purification project that can produce up to 100 million gallons (379,000 cubic meters) of high-quality water every day, enough to meet the needs of nearly 850,000 residents.

The Groundwater Replenishment System (GWRS) provides a drought-proof and reliable supply of high-quality water in a manner that is environmentally sensitive and cost-effective. Treated wastewater is purified with a three-step advanced process, then injected to create a seawater intrusion barrier that protects the Orange County Groundwater Basin as well as pumped to recharge basins where it naturally percolates into groundwater. Leading the way in water recycling in semi-arid southern California, other counties are following in the footsteps of the Orange County Water District (OCWD) and turning to water reuse to address their water supply challenges. We interview Mehul Patel, Executive Director of Operations for OCWD, to hear the ins and outs of this pioneering yet now long-standing system, as well as recent developments. 

Can you tell us briefly about your career path and your current role at the Orange County Water District?

I am currently the Executive Director of Operations for OCWD. I started at OCWD in 1996 as a student intern while working on my master’s degree in college. I was helping do research on the lab scale treatment technologies that were being considered for the eventual GWRS project. Eventually I was hired full time as an engineer and was lucky enough to be involved in the pilot testing, demonstration testing, pre-design, design, construction and eventual start-up of the GWRS project. This led to several promotions along the way until I got to my current position as an executive director.

For this project to come to fruition it had to be accepted and that meant educating about the benefits and safety of recycled water

The GWRS pioneered potable reuse and is a model for other regions in the U.S. and the world. What were the keys to its success at a time when other water recycling initiatives proposed in California didn’t materialize?

Over 2 decades we have seen a much broader understanding by the public of the importance of water reuse for water supply and reliability

From the beginning, public education was a priority for our leadership. We knew that in order for this project to come to fruition it had to be accepted by the public and that meant educating legislators, regulators, stakeholders and the general public about the benefits and the safety of recycled water. We embarked on an extensive public outreach campaign during the design phase of the project and it has continued to this day. Our outreach efforts include a robust tour program that brings thousands of people each year to our facility to see the treatment process up close; an active speakers’ bureau that goes into the community to offer presentations about the Groundwater Replenishment System; a bottled water campaign that allows us to bring samples of the GWRS water into the community for people to taste, see and smell; educational resources and programs for schools and teachers; and informational materials available on our website.

Can you comment on the role of public awareness and acceptance of potable reuse, and how it has evolved?

Over the past two decades we have seen a much broader understanding by the public of the importance of water reuse for water supply and reliability, but also a much stronger sense of confidence in the quality of the water. Education is the key to this level of acceptance. 20 years ago people weren’t as engaged with water issues or where their water came from, so the concept of reuse was unappealing to the general public. But teaching people about water supply and management and the need for new water supplies lays the groundwork for understanding the importance of water reuse. We find overwhelming support of the concept of reuse, and specifically our project, from people who have come on a tour of our facility and learned the facts. People are willing to get over the ‘yuck’ factor in order to have a safe and a reliable supply of water.

How does the OCWD manage seawater intrusion to protect the Orange County Groundwater Basin, and why is this important? What percentage of the water purified at the GWRS is injected into the seawater barrier?

OCWD manages seawater intrusion by using a series of strategically placed monitoring wells throughout the groundwater basin to determine the extent of the intrusion. In addition, OCWD maintains a 3D groundwater model that helps us model the flow of groundwater as well as groundwater usage throughout the basin. Constituents like chloride are key indicators of seawater intrusion. The main management technique is to operate a series of thirty-six individual injection wells sites located along the coast in the cities of Huntington Beach and Fountain Valley. These sites consist of over one hundred individual injection wells where purified water from the GWRS is injected at various depths. About 30% or up to 30 mgd of the purified water from GWRS is used for the seawater barrier.

How have water purification technologies and regulatory requirements evolved in recent years?

Water purification technologies like technologies in other sectors continues to evolve. They are capable of greater constituent removal and prices of advanced technologies are becoming more competitive with conventional technologies. These include RO membranes with greater salt and contaminant rejection capability while operating at lower pressure than those produced just five years ago. Low pressure membrane technologies like MF and UF are offering more choices while standardizing to a certain extent on membrane polymer material type. There is also a larger offering of products for advanced oxidation including UV/peroxide, UV/free chlorine, and UV/Ozone technologies.

The difference in cost between GWRS and desalination is very significant – desalinated water is more than twice the amount of GWRS water

In California the regulations for potable reuse have evolved greatly within the last ten years. The finalization of the Groundwater Replenishment Recharge Projects regulations in 2014 and Surface Water Augmentation regulations in 2018 were real game changers. They now offer a specific regulatory framework for groundwater recharge and reservoir augmentation reuse applications.

How do the operating costs of the GWRS compare to the costs of importing water or other measures to augment the water supply (such as seawater desalination) or curb the demand (such as conservation and increasing network efficiency)?

GWRS water is comparable in cost to untreated imported water, but several hundred dollars an acre-foot less than treated imported water. The difference in cost between GWRS water and desalinated water is very significant – desalinated water is more than twice the amount of GWRS water. Conservation is a much more challenging area to quantify because the costs range and fluctuate a great deal depending on the method of conservation.

How would it compare to other alternatives if you consider environmental costs, such as the impact on marine or land-based ecosystems and the carbon footprint?

The GWRS offers a favourable carbon footprint and allows for a reduction in the amount of ocean discharge of treated secondary effluent

The GWRS compares favourably with other alternatives such as imported water or seawater desalination. It offers a favourable carbon footprint output based on the energy requirements of the alternatives. It does also allow for a reduction in the amount of ocean discharge of treated secondary effluent in north Orange County.

Can you tell us about the GWRS Final Expansion Project?

The GWRS Final Expansion will expand the output of the current facility from 100 mgd to 130 mgd. This will then allow the project to reach its ultimate build out as was planned during the original project’s conception. It also allows the Orange County Sanitation District (OC San) to reuse all of the reclaimable secondary effluent wastewater it currently produces. The project adds additional microfiltration, reverse osmosis, and UV/Advanced Oxidation treatment capacity. It also allows for the GWRS to receive secondary effluent wastewater feed water to come from a second OC San facility known as Plant 2 located in Huntington Beach, California. Currently, the GWRS is fed by OC San’s Plant 1 facility located adjacent to OCWD in Fountain Valley, California. Bringing in this additional source of feed water involves using an existing gravity-based pipeline that connects the two OC San wastewater treatment plants that will be slip-line to allow for it to function as a pressurized pipeline. Finally, flow equalization storage tanks and a pumping station will be constructed at OC San Plant 2 to help convey the additional required feed water to GWRS. The total project cost is $300 million and will be complete in the first quarter of 2023.

As water supply challenges mount, other Californian counties are turning more and more to water reuse using groundwater recharge or surface water augmentation. In addition, California is in the midst of regulating direct potable reuse. What do you think is the outlook for indirect and direct water reuse in the state as it faces potentially drier conditions in the future?

I think the outlook is great for a greater implementation of potable reuse across California. The regulations currently in place and the finalization of the direct potable reuse regulations come at an opportune time given the severity of the current drought plaguing the entire southwest of the United States. California is especially impacted by the current drought and with cycles becoming more extreme, it is only natural to assume reuse has to play a larger role in meeting future water supply needs. Reuse along with greater conservation and protection of our existing supplies (like groundwater) are absolutely essential to meet future water demands in all of California.