What are the Different Uses of California

California - sewage pollution

Orange County's groundwater replenishment

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Orange County, California, is an urban area on the coast of the Pacific Ocean south of Los Angeles County. With a population of 3 million people in 2010, it is California's third largest county.

The challenge

The Orange County Water District (OCWD) is known for building one of the first facilities in the United States in 1976 to convert wastewater into purified water. This first project, called Water Factory 21, laid the groundwork for an expansion of the world's largest advanced water treatment system to recycle drinking water in 2008. While the project was not originally designed with ocean health in mind, it has billions of gallons of treated wastewater saved from being discharged into the ocean while providing clean water to hundreds of thousands of people in a drought-stricken area.

In the mid-1970s, Orange County's underground freshwater aquifer came on stream after a population boom and increased water demand. Saltwater from the ocean seeped inland and posed a threat to the county's drinking water supply. OCWD officials decided to build a facility that could purify the county's wastewater so that OCWD can inject the treated water back into the aquifer where it can acts as a barrier and prevents salt water from entering.

The facility, known as Water Factory 21, was capable of producing approximately 15 million gallons of clean water every day. As the county's population grew and more and more water was drawn from underground aquifers, salt water infiltration continued to be a problem. Drought was also common, resulting in frequent water shortages. At the time, the county's water supply came from groundwater, the Santa Ana River, and was also imported at significant cost from the Colorado River and Northern California. In times of drought, it was not as reliable to import more water.

Another problem for the county was that a large drainage pipe discharging treated wastewater from a sewage treatment plant into the ocean had reached capacity. If the water sources were to expand according to demand, the pipe would not be able to handle the additional volume.

Those in charge of the OCWD weighed up various expansion plans and looked for the cheapest option to support the water supply even during periods of drought, and finally conceived the “Groundwater replenishment system” (GWRS) project. As part of this plan, the OCWD, in partnership with the Orange County Sanitation District (OCSD), built the world's largest advanced water treatment system for the reuse of drinking water.

Actions Taken

The facility, built by OCWD and OCSD, started operations in 2008 and was initially able to produce 70 million gallons of clean water per day. In 2015 the facility expanded to 100 million gallons per day and the facility is currently expanding again to produce 130 million gallons per day in 2023.

How it works

Before entering the sewage treatment plant, the wastewater is first subjected to a more typical treatment process called secondary treatment. These include bar sieves, sand chambers, trickling filters, activated sludge, clarifiers and disinfection. After this process is completed, it is sent to the GWRS system. The system, designed by engineering firm CDM Smith, uses a three-stage cleaning process.

1 - The first step is microfiltration which is based on tiny polypropylene hollow fibers, similar to straws, with tiny holes in the sides that are 0.2 microns in diameter (1/300 the diameter of a human hair). By pulling water through the holes in the center of the fibers, suspended solids and pathogens are filtered out of the water.

Microfiltration uses tiny hollow polypropylene fibers that resemble straws and have holes in the sides that are 0.2 microns (1/300 the diameter of a human hair). By pulling water through the holes in the center of the fibers, suspended solids and pathogens are filtered out of the water. Photo © Orange County Water District

2 - During the second step, the water is subjected to reverse osmosis, in which pressurized water is forced through a fine membrane that removes pathogens and chemicals, including pharmaceuticals.

After microfiltration, the water is subjected to reverse osmosis, in which pressurized water is forced through a fine membrane that removes pathogens and chemicals, including pharmaceuticals. Photo © Orange County Water District

3 - The third step involves a final treatment with ultraviolet light, which disinfects the water by denaturing the DNA of any remaining pathogens. Hydrogen peroxide is also used to remove iron, tannins and low molecular weight organics through an advanced oxidation process that breaks the molecular bonds of remaining impurities. Minerals are added back to the water to buffer it and stabilize the pH before entering the distribution system.

A final treatment with ultraviolet light disinfects the water by denaturing the DNA of any remaining pathogens. and hydrogen peroxide is also used to remove iron, tannins and low molecular weight organics through an advanced oxidation process that breaks the molecular bonds of remaining impurities. Photo © Orange County Water District

Water treated with GWRS exceeds state and federal regulations for drinking water. (For more technical details, see Opens in New Window Technical Tour of Groundwater Refill System.) The treated water, groundwater, and surface water are subject to extensive monitoring at the Opens New Window Philip L. Anthony Water Quality Laboratory, where it is tested on more than 500 compounds (the EPA only regulates 90 so thousands of chemicals are unregulated). The laboratory tests water from approximately 1,500 locations across the basin, analyzes more than 20,000 samples each year, and reports more than 400,000 results. OCWD also offers regional tests of more than 200 drinking water wells for local drinking water suppliers.

After treatment, about a third of the volume produced is injected into deep wells along the coast, creating a freshwater barrier against the ingress of seawater. The remainder will be used to replenish the Orange County's aquifer. It does this by collecting the water in large ponds and then seeping it through sand and gravel by gravity to eventually be stored in an underground aquifer. While the percolation process can provide additional filtration, in the case of OCWD the water has already been near-distillation purified, and this step mainly serves as an extra layer of protection required by California drinking water regulators. This also offers a psychological benefit and helps reduce consumer reluctance to use recycled water to boost traditional sources of drinking water. Retailers pull the water from the basin through over 400 wells and forward it to consumers.

How successful was it?

The program currently delivers 100 million gallons per day, which is enough water to meet the needs of 850,000 people. The Orange County's aquarium provides approximately 2.5% of the total water supply to 77 million people in north and central Orange County. The facility is currently being expanded again, with a capacity of up to 130 million gallons per day expected in 2023.

While this system was initiated primarily to ensure clean water for residential and commercial use and was not initiated out of concern about the effects of discharging treated wastewater into the ocean, the system has still been estimated at an estimated 329 billion gallons since its introduction in 2008 creates recycled clean water. A significant portion of this water would likely have been discharged into the sea had the system never been built and implemented.

The system is still generating a waste stream. The cleaning process produces 85 percent by volume of clean water, while 15 percent is sent back to OCSD for further processing. At this point it looks like dark iced tea. Solids are separated and taken to a landfill. What is left is still discharged into the ocean through drainage pipes that carry the water into the ocean five miles at a depth of two hundred feet below the surface of the water.

OCSD also harvests methane and hydrogen. The hydrogen is used for hydrogen cars, and there is a charging station at the entrance gate.

The GWRS has served as a model for other places and has shown that recycling water in a relatively affluent metropolis can work and be widely accepted as a wastewater treatment solution. The district has partnered with Singapore, which has built and is now using at least three smaller facilities with similar technology. Numerous cities in California, the United States, and the world are currently considering whether wastewater reclamation could work for them.

Minerals are added back to the purified water to buffer it and stabilize the pH before entering the distribution system. Photo © Orange County Water District

Lessons learned

  • Public relations can never stop and must be early and often. Orange County learned from early failures in San Diego in 1994 and Los Angeles in 2000, where both tried and failed water recycling programs. In LA, social justice played a role as poorer areas were designated to receive the recycled water. San Diego has since built a (more expensive, more energy-intensive) ocean desalination plant.
  • OCWD has invested in working with schools to engage children, including an annual water festival for 5th and 6th grade students and classes for young adults taught by local community colleges. The district offers free factory tours to the public. The website is sophisticated and contains simplified explanations and videos, as well as libraries of more detailed reports.
  • The GWRS was very well received. Out of 158 articles about the operation published in magazines between 2000 and 2016, there was no negative coverage, with the majority of the articles being rated either neutral (72%) or positive (28%).
  • It was effective to teach the staff who run the facility how to speak publicly about their work without jargon, and to have them conduct the publicity and presentations instead of PR firms. California recently passed law allowing the facility to bottle a small portion of the water it produces. This means staff can bring the water to festivals and community fairs so people can see that the water is squeaky clean. The fear of drinking recycled water decreases with familiarity.
  • Having an aquifer to re-inject the water into offers a psychological benefit to alleviate public aversion. It also provides an extra layer of protection that ensures that the recycled water mixes with the natural groundwater.
  • Improvements in membrane technology have reduced the energy costs of reverse osmosis by 1970% since the '75s.
  • People often ask why the county doesn't desalinate seawater. Purifying salt water is more difficult and expensive than purifying wastewater. The sea water contains around 35,000 ppm of salts while the wastewater contains less than 2000 ppm.
  • It's a large financial company with a cost near $ 1 billion, and estimates to run the same program are closer to $ 2 billion today.
  • Over time, the rules have been refined as data has been received from bodies such as the GWRS. At the beginning of the program, the California drinking water department required the water to be stored underground for six months, which posed some infrastructural and technical challenges. Now the underground storage time has been reduced to three months.

Summary of funding

The total estimated cost of building GWRS is nearly $ 1 billion ($ 973 million, including $ 481 million for the first 70 million gallons per day). This was paid for by low interest federal loans of $ 135 million and low interest government loans of $ 167 million, with grants making the difference, including subsidies of $ 90 million from government agencies including the California Department of Water Resources and the Environmental Protection Agency, Metropolitan Water District of Southern California and others.

Importing water from other countries costs about $ 1,000 per hectare. The cost of water produced at GWRS is $ 525 per acre with subsidies or $ 850 per acre without subsidies.

Leading Organizations

Orange County's Sanitary District and Orange County's Water District

partner

CDM Smith (engineering)
Black and Veatch (technology)

resources

Opens in a new windowNewspaper coverage of drinking water recycling in the Orange County Water District's groundwater replenishment system

opens in new windowOrange County's Sanitary District

opens in a new windowOrange County Water District

Video: opens in a new windowVirtual tour: Groundwater replenishment system