History will have a lot to say about 2021, the year when vaccines began to overtake the COVID virus and the world began to climb out of a pandemic.

At Southern California’s Yorba Linda Water District, 2021 was just as momentous: It was the year when the Yorba Linda Water District and the Orange County Water District began operations at the largest single-site ion-exchange PFAS treatment facility in the United States.

Yorba Linda Water District is one of 19 water districts and municipalities in north and central Orange County that provide water from the Orange County Groundwater Basin. The PFAS facility is one of 36 treatment sites being built in Orange County by the end of 2023.

SINGLE-SITE ADVANTAGES

The new level of treatment is required because of rising concerns about PFAS found in some areas of the groundwater basin, which provides close to 80% of the water used by 2.5 million people in north and central Orange County, just south of Los Angeles County.

Although most of the treatment facilities in the county will be installed at individual wells, the single-site approach, taking place in Placentia at the Yorba Linda Water District headquarters, was chosen for the Yorba Linda Water District facility for several reasons. Foremost, testing showed that all nine wells operated by the Yorba Linda Water District are affected by PFAS limits set by California regulators.

The centralization of the Yorba Linda Water District facility has several advantages:

-It is more efficient to monitor operations with minimal staffing.

-It is easier to take old well sites offline and bring new sites online.

-It is easier to keep water moving by simply rerouting if a unit has to be taken offline for  maintenance or emergency service.

-In addition, because of the short distances between the wellfields and the treatment plant, running pipes from the wells to the central site was more manageable than for other districts.

CAREFUL MONITORING

Orange County Water District funded the $25 million project. In addition to the 22 ion-exchange vessels that comprise the treatment system, the project includes a 25 mgd booster pump station and a 1,000 kW backup generator.

In addition to construction costs, the Orange County Water District is paying up to $75 per acre-foot of produced groundwater to offset operational costs for the treatment facility, according to John Brundahl, Yorba Linda Water District production superintendent. Those costs include two new staff members, including Todd Colvin, chief water systems operator.

Although the facility is permitted to produce 19 mgd of treated water, it is capable of producing 25 mgd, according to Colvin. The water system has more than 25,000 customer connections, primarily residential.

The Orange County Water District serves as the umbrella groundwater management agency overseeing the pumping of water from the basin’s wells. Because of the importance of maintaining water levels in the aquifer, the district closely monitors and limits the amount of water each agency can withdraw through a simple pricing mechanism.

ALLOCATING SOURCES

Yorba Linda Water District and fellow members of the Orange County Water District are retail distributors of drinking water in their communities. Some districts serve a single city while others are special districts crossing city lines and sometimes serving unincorporated areas of Orange County. Besides its namesake city, the Yorba Linda Water District supplies parts of Placentia, Brea, Anaheim and unincorporated areas of Orange County. The district’s headquarters and treatment plant are located in Placentia.

To protect the levels and quality of the water in the Orange County Groundwater Basin, member agencies agree to use the high-quality, low-cost groundwater for set percentages of their needs. Yorba Linda’s basin pumping percentage is no more than 77% of its needs; pumping above that amount is subject to additional charges.

The balance of the water needed to meet consumer demand is purchased wholesale from the Municipal Water District of Orange County, out of water that the Metropolitan Water District of Southern California imports from surface water reservoirs in northern California and the Colorado River.

Colvin says that using groundwater is important for several reasons, including the closer controls the local agencies have on the basin water. But it is a pocketbook issue as well: “Any member that goes over its percentage pays the same price for that water that they pay for imported water.”

BEING PROACTIVE

The concern over the PFAS hazards in water sources across the country is not new. By the second half of the past decade, the U.S. EPA and independent researchers were investigating the growing amount of these chemicals found in drinking water and their possible links to cancer and other diseases.

In August 2019 when the California State Water Resources Control Board updated its guidelines for water agencies to follow in detecting and reporting PFAS, the Orange County Water District and its members had already been tracking their levels and were ready to move ahead with a pilot project to avoid conflict with new regulatory standards.

District officials had also launched a proactive search for solutions. Rather than wait for new enforceable standards that could put the Yorba Linda Water District and its sister agencies in violation of new state standards, the district board agreed to shut down the affected wells in light state advisory levels and begin importing water until the chemicals could be removed.

The $25 million cost of the Yorba Linda plant included 11 pairs of AqueoUS Vets PF12-520 LP ion-exchange resin systems in treatment vessels each larger than a pickup truck. It also paid for plumbing to connect them to the wells and to the distribution system.

REGULATING FLOW

Each pair of vessels is  arranged in a parallel lead-lag configuration that makes one vessel the “worker,” expected to remove essentially all PFAS. The second vessel serves as a polisher to remove any remaining contaminants. A computer system manages the paired ion-exchange units, which maximizes resin life by ensuring each pair is not left idle for 24 hours, while also idling a unit to allow  operators to inspect the resin, perform maintenance or reload fresh resin.

The resin media works similar to the pellets homeowners have long used to reload household water softeners. Rather than dissolve, however, the resin pellets in the ion-exchange vessels are chemically engineered to attract and hold onto targeted substances such as PFAS.

Colvin says the key to operating the new system is to maintain water flows that allow the resin to do its work as water passes through the vessels. “We generally operate each train from about 600 to 1,600 gpm,” he says. That flow rate assures that the water gets at least two minutes contact time with the resin while ensuring that the flow is distributed evenly.

Flows that are too slow can lead to channeling of the water stream across the resin such that some pellets get more or less contact. That can necessitate resin exchanges before a full charge of resin is expended. Under optimal operations, Colvin says, “Each vessel is supposed to run 14 months at the volume we expect of it. Then we can turn to the other half of the pair.”