Unlocking the Potential of Groundwater Replenishment Systems in Southern California

Water Infrastructure in Orange County

The Orange County Water District (OCWD) has established itself as a pioneering force in water conservation and sustainability through its Groundwater Replenishment System (GWRS). Situated in the semi-arid region of southern California, Orange County, with its current population of approximately 3,000,000, is projected to witness a growth of over 300,000 people by 2035. To meet the growing water demands of the region efficiently and environmentally, OCWD's GWRS plays a vital role by recycling water, offering a drought-proof supply, and serving almost 600,000 individuals daily.

Although less than one-third of California's precipitation occurs in southern California, it accommodates two-thirds of the state's population. While OCWD imports some water, this practice is not only costly but also energy-intensive. The challenge of water scarcity is exacerbated as other states and Mexico share similar resources, increasing demand amid declining precipitation levels. The primary water source for Orange County is a substantial groundwater basin with an annual yield of nearly 300,000 acre-feet of water. However, as early as the 1940s, the natural recharge of this basin couldn't keep up with the escalating water usage, necessitating a comprehensive approach to combat seawater intrusion into the drinking water supplies.

In response, OCWD initiated the groundwater replenishment program, a pivotal component of the region's water infrastructure, to safeguard the basin's integrity and reduce dependence on imported water. The Orange County GWRS successfully bridges the divide between water supply and demand.

Water Infrastructure: The Five-Step Process

1. Pre-purification: Before entering the GWRS, the Orange County Sanitation District subjects over 200 million gallons of wastewater daily to thorough pre-purification. This step involves a range of treatments such as bar screens, activated sludge, trickling filters, grit chambers, and clarifiers, effectively eliminating contaminants and ensuring wastewater disinfection. Stringent control over metals and chemicals maintains water quality standards.
2. Microfiltration: Microfiltration employs bundles of hollow polypropylene tubes through which water is drawn under a vacuum. These tubes feature minuscule pores that strain out solids, protozoa, bacteria, and even certain viruses.
3. Reverse Osmosis: Water undergoes reverse osmosis, where it is forced through semi-permeable polyamide molecular membrane bundles. Operating under high pressure, this process eliminates dissolved salts, organic chemicals, pharmaceuticals, and viruses. The outcome is exceptionally pure water, necessitating the addition of minerals to enhance stability.
4. Ultraviolet Light with Hydrogen Peroxide Treatment: In this phase, ultraviolet light combined with hydrogen peroxide treatment disinfects and oxygenates the water, breaking molecular bonds to neutralize any remaining contaminants.
5. Water Delivery: The OCWD's groundwater basin faces the constant threat of seawater intrusion. To create a protective buffer, about a third of the GWRS-produced water is channeled into seawater intrusion wells along the coastline. This water functions as a hydraulic barrier against seawater intrusion, safeguarding Orange County's water supply. The remaining treated water, approximately 65 million gallons per day, is transported to lakes in Anaheim. There, it undergoes natural filtration through sand and gravel, ultimately replenishing the groundwater basin in north and south-central Orange County with pristine drinking water.

Operational since 2008, Orange County's Groundwater Replenishment System stands as the world's largest advanced water purification system, providing up to 100 million gallons of potable water each day.

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