Located beneath the city of Torrance, California is a large underground water source just waiting to be tapped. It’s too salty.
The Southern California Water Reclamation District (WRD) is working on a solution as part of its brackish groundwater reclamation program. While the program includes numerous capital projects, one of its most critical efforts is the Torrance Groundwater Desalter Expansion (TGDE), which will treat this salty groundwater plume and provide up to 7,100 acre-ft per year of drinking water for up to 105,000 local residents.
The realization of this project, for which a formal opening was held on June 10, has required creative delivery, an extensive pilot and some coordinated logistics to manage multiple site constraints. When completed in 2028, the TGDE will include four new production wells, feedwater pipelines and additional treatment capacity at the Robert W. Goldsworthy Desalination Plant.
The desalination expansion shares its site with many other city functions, requiring careful planning and logistics as construction progresses.
Photo courtesy of McCarthy-Jacobs JV
Salty origins
How exactly did all that salt get to that particular body of water? This dates back to the 1900s, “when aggressive pumping in the region drew seawater inland. After that problem was solved by installing seawater intrusion barriers, essentially walls of injection wells that push clean drinking water into the ground, it trapped that plume in place,” explains Joel Blair, WRD’s engineering manager. “So we’ve been sitting on this huge volume of groundwater that couldn’t be used for local supply.”
Los Angeles County began installing these seawater barrier injection wells in the 1950s (the last ones were completed in 1964), and today, the West Coast Barrier includes 159 injection wells that protect aquifers from seawater pollution. This plume spans 14 square miles, which has made it impossible to pump groundwater in some areas.
In 2018, WRD held an initial meeting with a group of stakeholders about the possibility of joining efforts to clean up the plume. By 2021, a feasibility study had been completed.
Aggressive pumping in the region drew seawater inland in the early 20th century. This plume was trapped after seawater intrusion barriers were built starting in the 1960s.
Graphic courtesy of the Water Replenishment District
“We knew we wanted wells in the ground to extract the water, we wanted to treat it for potable use, and we wanted to deliver it to local water users. By 2024, the project was more defined, but not so defined that we knew all the details,” adds Blair.
To find the solution, WRD started a pilot program of water quality testing and treatment systems. Completed in 2024, the first phase of the pilot saw small production wells installed to understand the water attributes of the aquifers and various treatment systems tested.
“The delivery model allowed us to adjust the design and the characteristics of the treatment.”
—Joe Broughton, director of design and construction operations, Jacobs
“The pilot plant and operation was conceived like most pilots; it’s expected to help define or refine the project. In this case, we thought it would help us get into the process. But the opposite happened; the pilot showed that we didn’t need any of the unit processes, which is pretty rare,” says Joe Broughton, director of design and construction operations at Jacobs. “We realized we didn’t need nanofiltration, so at about 30 percent design, the pilot results caused the client, the owner’s advisory team, and the design-build entity to rethink the right scope for the project.”
Reverse osmosis is a very mechanical and above-ground process compared to traditional water and wastewater plants, Broughton explains. Water is moved at high pressure through a membrane with small pores, allowing clean water to escape and brackish material to remain.
“Brackish water requires significantly less pressure than seawater, in the 300 to 400 psi range,” he says. Seawater desalination requires about 1,000 psi. “For reference, home water pressure is typically 60 to 80 psi. We are adding two new reverse osmosis trains to the existing desalinator.”
Since the main technical challenge for this project is organic pollution, the use of reverse osmosis also ensures that WRD can always keep a train in cleaning mode while ensuring ease of operation, Blair says.
Although other, more advanced technologies were considered, this tried and true process was chosen to keep expansion simple and operational. “The real innovation was the strategy – we right-sized the project and a lot of good decisions along the way focused it on the right project at the right scale,” Blair says. “Since this is a progressive design build (PDB), we’re still providing input to the design team and piloting some technologies, including automatic strainers. We’re close to finishing it.”
Crews work to install feed water pipes for the desalination plant expansion project.
Photo courtesy of McCarthy-Jacobs JV
All on delivery
The Torrance desalination plant is WRD’s second major PDB project. “Since we knew the components and the general direction, but not all the details, PDB was a perfect fit. It allowed us to participate in the process as we went along and also allowed for faster delivery,” Blair says.
After the first phase of the pilot was completed, McCarthy-Jacobs joined as designer and builder in April 2024. PDB allowed the team to continue to refine the design as construction began, mitigating risk and cost, but also ensured an optimized facility for WRD.
“The most unique result so far is that the pilot drove quite a significant change in treatment processes, and we achieved it without any cost or schedule impact,” says Broughton. “The delivery model allowed us to right-size the project and treatment features, and package parts of the work so that construction would cause minimal disruption. That’s what a successful PDB should achieve: be agile and deliver work in a way that’s not purely linear.”
This evolution towards WRDs and the actual needs of the city made it a completely different project than it was at the RFQ stage, says Callie Nottingham, project manager, McCarthy-Jacobs JV. “It wasn’t because anyone did anything wrong, it was because of what the data from the groundwater system told us,” he says.
A vertical turbine pump in the maintenance yard in Torrance.
Photo courtesy of McCarthy-Jacobs JV
A little bigger
WRD’s existing desalination plant has a capacity of 5 million gallons per day, but the facility never reached that capacity because of its construction and the variability of water being drawn from the ground, Nottingham says. “We are upgrading this facility to approximately 3.5 mgd and expanding another 1.5 mgd. [At completion it will have] a total of about 7 mgd, essentially doubling capacity,” he continues. “Originally the plant was going to be 10 to 12 mgd, but pilot data showed that wasn’t feasible. We have continuously refined the design to reach the actual needs of the project.”
During groundwater modeling, the team also realized that they should avoid displacing contaminated plumes. Starting with hydrogeology, engineers identified the precise number of wells in the right locations, allowing for more streamlined scoping, Blair notes.
“Construction costs are approximately $185 million. With construction management and consulting services, approximately $200 million in total,” he adds.
The existing desalination plant is located in the Torrance maintenance yard, which houses public works, traffic, fleet maintenance, parks and recreation, and more.
“I don’t think I’ve ever seen a tighter place to build a project. The designers and superintendents looking at drawings and adjusting the scope and features to fit that small footprint is pretty remarkable,” says Broughton. “The pumping equipment is located below grade in vault-type structures, hidden from street view, unlike a typical well field where the equipment is above ground. Access is through door and hatch systems for proper maintenance.”
“We have continuously refined the design to reach the actual needs of the project.”
—Callie Nottingham, Project Manager, McCarthy-Jacobs JV
Construction began in November on the feedwater pipelines, facilitated by extensive utility mapping and ground-penetrating radar, says Chris Kostelny, senior project manager at McCarthy-Jacobs JV. “There are high-pressure oil lines, gas lines, water mains, sewers, everything we’re digging and crossing underneath. For the treatment plant, we coordinated with our building information modeling team to laser scan and map all the existing connections where we’re connecting to the plant, to make sure what we’re designing matches the existing conditions and everything will fit in the field.”
The contract was structured with multiple GMPs, although the Del Amo Pipeline was accelerated first and completed earlier this year because the City of Torrance had a paving moratorium and it had to be done before the street was repaved. “The early works package was a design-bid-build that started first to prepare the site for the expansion. The team has also completed pipeline for three of the new wells,” he says. “Next is the installation of Silverado wells 1, 2 and 3. GMP2, which covers the expansion of the treatment plant, is already approved.” GMP3, which includes the South Pipeline and the Fourth Well, was approved by the WRD Board on May 27.
Upon completion, TGDE will provide discounted water to the community, while WRD will be able to replenish and store water in a previously unused aquifer, Blair says.
“Part of the project also protects production wells for water users outside the plume, ensuring that contamination does not continue to migrate to clean wells,” he says. “We’re pretty unique in that we’re voluntarily cleaning up this plume. There are other contaminated plumes in the region, but usually there’s a regulatory order and a responsible party. We’re doing it because we think it’s the right thing to do and a smart use of our resources.”
