Journal-AWWA-2025-Clark-Final-Expansion-of-California-s-Celebrated-Groundwater-Replenishment-Project

•

FEATURE

Final Expansion of

California’s Celebrated

Groundwater

Replenishment Project

James H. Clark, Jeff Neemann, Mehul Patel, and Robert Thompson

Final Expansion of

California’s Celebrated

Groundwater

Replenishment Project

James H. Clark, Jeff Neemann, Mehul Patel, and Robert Thompson

Final Expansion of

California’s Celebrated

Groundwater

Replenishment Project

James H. Clark, Jeff Neemann, Mehul Patel, and Robert Thompson

42 JOURNAL AWWA • APRIL 2025

Key Takeaways

After two expansions since its

opening in 2008, Southern

California’s Groundwater

Replenishment System is at its

goal capacity of 130 mgd.

Through rigorous simulations

and full-scale testing, two special

districts determined the best

materials, methods, and designs

to overcome challenges to

ensure peak performance from

the expansion.

Efficiencies gained with

improved methods, advanced

technologies, and reviving an old

pipeline could save the districts

millions in energy costs.

Layout imagery by OCWD

JOURNAL AWWA • APRIL 2025 43

15518833, 2025, 3, Downloaded from https://awwa.onlinelibrary.wiley.com/doi/10.1002/awwa.2419, Wiley Online Library on [19/03/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

•

FEATURE Groundwater Replenishment in California

44 JOURNAL AWWA • APRIL 2025

s many aquifers around the world continue

to be depleted, especially in the western and

southwestern United States, a system that

can restore 130 mgd of processed water to

a region’s aquifer is getting plenty of attention. The

Groundwater Replenishment System (GWRS) in Southern

California first went into operation in 2008 and went

through two subsequent expansions. The GWRS has

become more than the world’s largest wastewater purifi-

cation system for indirect potable reuse—it just may be

the world’s most documented and toured water facility.

The plant draws visitors who safely sample the water, at

times with significant publicity. In 2014, 60 Minutes corre-

spondent Lesley Stahl visited the GWRS for the televised

news magazine’s segment about the plant’s innovative

designs. Stahl filled a clear plastic cup with processed water

that a mere 45 minutes earlier had been sewage. Her unvar-

nished critique, on camera: “To tell the truth, it wasn’t bad.”

The GWRS is a collaborative effort of the Orange County

Water District (OCWD) and the Orange County Sanitation

District (OC San); Black & Veatch provided final design,

planning, and construction support. The plant came on

line as a 70-mgd facility and added another 30 mgd with

its initial expansion in 2015. Another 30-mgd expansion

that began in 2020 brought the plant to its final 130-mgd

goal, using a variety of designs that optimized the oper-

ations, saved the agencies money, and kept the facility’s

footprint within planned parameters. Most important,

the final GWRS expansion enabled 100% of OC San’s re-

claimable wastewater flow to be recycled—a long-sought

milestone—and the total capacity is now enough to satisfy

the needs of one million people. (The accompanying side-

bar, “California’s GWRS Timeline,” provides a snapshot of

OCWD and OC San’s evolution.)

The treatment process includes microfiltration, reverse

osmosis (RO), and ultraviolet light with hydrogen perox-

ide. After treatment, the water either infiltrates into local

aquifers through recharge basins located in Anaheim,

Calif., or it is injected through various wells near the

coast. From the regulatory framework of indirect reuse,

the recycled water needs the buffer provided by the aqui-

fers before it can serve as a source for drinking water.

The Microfiltration Challenge

When design work began for the final expansion of the

GWRS, analysis determined that the footprint for the

new facilities was less than optimal if the plant used the

same type of microfiltration membranes. To address this,

the project teams initiated full-scale tests of two new

types of membranes that would require fewer units and

less space as a result of increased efficiency.

The microfiltration membrane design also considered

the quality of wastewater that would be used for recy-

cling at the expanded facilities. Pre-expansion, the GWRS

took its wastewater from OC San’s Plant No. 1 in Fountain

Valley, Calif., next to the GWRS facility. The final expan-

sion would mix in wastewater effluent from Plant No. 2,

which is 3 miles away in Huntington Beach, Calif. Plant No.

2’s water had a lower quality for recycling purposes, due to

its tributary collection system being adjacent to the ocean,

which created higher total dissolved solids and increased

ammonia and alkalinity in the influent; therefore, new

types of microfiltration membranes were examined.

CALIFORNIA’S GWRS TIMELINE

1933

The Orange County Water District is established.



1954

The Orange County Sanitation District (OC San) is

established.



1975

Water Factory 21, a water reclamation and desalting

facility and a precursor to the GWRS, begins producing

15 mgd of water.



2004

Groundbreaking takes place for the GWRS, which will

become the world’s largest water purification facility.



2008

The GWRS comes on line, producing 70 mgd of water.



2015

The initial expansion of the GWRS is completed,

increasing its capacity to 100 mgd.



2018

The GWRS produces 100,008,000 gallons in 24 hours,

setting a Guinness World Record for most wastewater

recycled into drinking water in a day.



2020

Construction begins on the final expansion of the GWRS.



2022

The GWRS receives wastewater from OC San Plant

No. 2, enabling it to recycle 100% of reclaimable

wastewater flows.



2023

The final 30-mgd expansion of the GWRS is completed

and dedicated, increasing total capacity to 130 mgd,

enough to serve one million people.

GWRS—groundwater replenishment system

•

FEATURE Groundwater Replenishment in California

JOURNAL AWWA • APRIL 2025 45

OCWD staff put the two newer polyvinylidene fluoride

(PVDF) membranes into full-scale cells, testing them and

collecting data for more than six months. These full-scale

tests supported procurement of the best-fit design to

handle the potential for high-fouling influent.

Once operations staff saw the effectiveness, they com-

petitively bid the membranes; the testing and selection

process saved the district $8 million over what was bud-

geted. The use of more chemically tolerant PVDF micro-

filtration membranes reduces the frequency of cleanings

and extends the service life of the membranes.

OCWD implemented a universal design for the micro-

filtration membrane system that could fit several types

of membranes, giving it flexibility in membrane selection

during the bidding process. This innovative design also

kept the expansion plans moving forward, even if all the

specifics weren’t yet finalized. Considering the space

limitations of the expanded plant, the delivery system

for chlorine, which is used for PVDF membrane cleaning,

was located in two separate areas at the GWRS to ease

chemical deliveries by trucks.

Repurposing a Little-Used Pipeline

Since the GWRS expansion would use wastewater from

a new source, a suitable pipeline was needed to link the

facilities. Three pipelines already connected OC San’s

Plant No. 1 (next to the GWRS) and Plant No. 2, and one

of the pipelines—a full 66 inches in diameter—was a

little-used overflow line. This line was originally built

in 1957, and after it was rebuilt with a new liner, it

would serve as the connector. Since the GWRS is uphill

from Plant No. 2, the rebuild was especially critical as

the line was changing from being gravity-driven to a

pressure line.

The 3-mile conveyance pipeline was relined with

fiberglass-reinforced plastic as part of a process consist-

ing of digging numerous “launch pits” along the route,

inserting the liner in a special mechanism and pushing it

through the pipeline to the next launch pit. Aside from a

few locations that required a steel liner for short distanc-

es, fiberglass-reinforced plastic was used throughout.

Relining gave the pipeline a second life and avoided

the challenges of trenching and tunneling a new pipeline

through a narrow right-of-way. In addition, the relining

process and the pipe’s large diameter are expected to re-

duce energy needs, ultimately saving $200,000 annually.

Interstage Boosting at RO Units

The expansion project closely examined the existing

facilities to determine whether upgrades or modifica-

tions were needed. When it came to the RO system, the

higher salt content in the new wastewater source meant

higher operating pressures. So rather than pumping the

water through all three RO stages using a single feed

pump, whereby the flow would be weaker at the end than

the beginning, an interstage booster pump was added

between the first and second stages to help balance the

flow and ultimately use less energy.

Interstage boosting was installed on the six new RO

units (each rated at 5 mgd) and retrofitted into the orig-

inal 15 units. This new system maintains the flows and

balances production, allowing the plant to achieve longer

run times between membrane cleanings. In addition,

flowmeters were installed on all stages of the units to

better track and analyze performance. Achieving more

constant flow should save more than $10 million in ener-

gy costs over the lifespan of the equipment while main-

taining an 85% recovery rate through the RO units.

Monte Carlo Simulations

Key parameters considered when designing a water recy-

cling system included temperatures, total dissolved sol-

ids, amount of salt, and the organic materials in the

water. A series of Monte Carlo simulations were used to

screen a variety of data from more than 1,000 scenarios

to determine the most probable water quality, which sub-

sequently guided the selection of equipment, pumps, and

pressure lines.

Treatment for the final expansion was designed using

the statistical analysis from Monte Carlo projections for

influent water quality. Ultimately, the design used the

95th percentile of quality to ensure the system wasn’t

over-designed for the occasional times when quality was

worse than expected. This simply means that during

those occasions, the plant wouldn’t produce as much

water for a short period.

Equalization Tanks

During the latest GWRS expansion, some key modi-

fications were taking place at OC San’s Plant No. 2 to

better optimize its performance. For instance, the RO

membranes are best operated at a constant feed rate

rather than a variable flow. Wastewater systems have

more activity during the day and less activity at night,

so to achieve a constant flow, OCWD installed two large

flow-equalization tanks for Plant No. 2; now the RO units

can hum along at a constant pace and keep production

going at maximum capacity. Flow-equalization tanks

were installed during the initial expansion at the GWRS

plant in 2015, and now the practice of using them before

RO treatment has become a common practice.

Other improvements at Plant No. 2 included the in-

stallation of a weir in the existing pipe. Instead of using

a pump station for the tanks, the water was intercepted

•

FEATURE Groundwater Replenishment in California

46 JOURNAL AWWA • APRIL 2025

much closer to the tanks and held with a new weir, saving

several thousand feet of piping. This configuration still

gives operators the option of allowing the treated water

from OC San to flow to the ocean for discharge if needed.

Treatment System Modifications

Plant No. 2 processes contain certain significant industrial

flows that are considered non-reclaimable; these must be

processed through a separate treatment train from the

GWRS-bound reclaimable flows for ocean outfall disposal.

The challenge was that Plant No. 2 was not designed to han-

dle separate treatment trains. The biggest area of concern

was the 340-mgd headworks facility, which includes flow

metering, screens, influent pumping, and grit removal.

OC San addressed this problem by dividing the existing

headworks facility into two treatment trains: reclaimable

and non-reclaimable, while maintaining 24-7 operations

at this critical facility. Adding to the complexity was the

requirement that the system could be recombined during

extreme wet-weather events.

The project team identified several integrated ap-

proaches, including new infrastructure, modifications

to existing equipment, and operational changes to allow

the headworks to serve the three process configurations.

New elements were installed to facilitate the separation

and recombining of the headworks facility:

• A new 75-inch diversion pipe

• Highly customized steel pipe fittings

• A vortex structure

• Seventeen large stainless-steel slide gates installed in

extremely constrained locations

New influent pumps were required to accommodate

the reduced flow on the non-reclaimable side, as was a

complete reprogramming of the headworks supervisory

control and data acquisition system to reconfigure the

extensive operational modifications.

Proceeding Despite the Pandemic

The final expansion of the GWRS was completed ahead

of schedule, despite construction taking place during the

COVID-19 pandemic and despite resulting supply-

chain disruptions worldwide. While many sectors were

locked down, this project was declared an essential pub-

lic service, so it was allowed to move forward. Social dis-

tancing, wearing masks, and other safety practices were

observed by all parties.

Among many COVID-related supply-chain issues, the

fiber-reinforced plastic piping needed to reline the 3-mile

conveyance pipe idled on ships offshore for a consider-

able time. Dozens of ships visible from the facility were

forced to wait for weeks to get into the Los Angeles or

Long Beach ports to unload. And while those shipping

issues prolonged the pipe relining, they didn’t delay the

final expansion’s debut.

Building Trust and Water Independence

The GWRS brings extraordinary water sustainability and

resilience to the Orange County Groundwater Basin, the

primary potable water supply for more than 2.5 million

people. Since its inception in 2008, the GWRS has pro-

duced more than 400 billion gallons of high-quality

water, building public trust along the way and demon-

strating the benefits of advanced water purification tech-

nologies. Even better, the plant’s success has further

reduced the need to import water from the Colorado

River or the State Water Project, which is a series of water

supply canals coming from Northern California.

Leaders from the OCWD, OC San, and Black & Veatch

worked closely throughout this project to fortify the

reliability of local drinking water supply and reduce the

region’s dependence on water imports. This collaboration

advanced many new water reclamation techniques, mak-

ing the region’s water customers the biggest winners.

About the Authors

James H. Clark is senior vice president at

Black & Veatch, Los Angeles, Calif.;

ClarkJH@bv.com.

Jeff Neemann is west managing director for Black &

Veatch, Irvine, Calif.

Mehul Patel is executive director of operations for the

Orange County Water District, Fountain Valley, Calif.

Robert Thompson is general manager of the Orange

County Sanitation District, Fountain Valley, Calif.

https://doi.org/10.1002/awwa.2419

AWWA Resources

• OneWater Nevada Advances A+ Water Recycling Project.

Teel L, Sundram V. 2024. Journal AWWA. 116:8:68. https://

doi.org/10.1002/awwa.2339

• Tapping Tomorrow: Houston’s Water Prospects for the

Next Century. Kommineni S, Petersen T, Bartlett J, et al.

2023. Journal AWWA. 115:8:36. https://doi.org/10.1002

/awwa.2161

• Are Utilities Ready for Advanced Water Treatment

Operator Training? Soltau S. 2024. Opflow. 50:6:6. https://

doi.org/10.1002/opfl.1975

These resources have been supplied by Journal AWWA staff.

For information on these and other AWWA resources, visit