Southern California’s Groundwater Replenishment Systems

Water Infrastructure – Orange County Water District’s (OCWD) Groundwater Replenishment System (GWRS) is a leader in recycling water and providing potable, drought-proof water in an economical and environmentally sound way. Located in southern California’s semi-arid region, Orange County is home to about 3,000,000 people with projected growth of more than 300,000 people by 2035. Orange County’s GWRS provides enough drinking water for almost 600,000 people each day.Less than a third of California’s precipitation falls in southern California, yet two-thirds of California’s population lives there. OCWD imports some water, but importing is expensive and energy-intensive.

This gave birth to the OCWD’s water infrastructure, ground water replenishment program in an effort to protect the basin and decrease dependence on imported water. Orange County’s GWRS bridges the supply and demand gap.

Water Infrastructure

To make wastewater drinkable, it goes through a five-step process:
1. Pre-purification. Prior to going to GWRS, the Orange County Sanitation District removes many impurities from more than 200 million gallons of wastewater per day in this step. The treatment includes bar screens, activated sludge, trickling filters, grit chambers, and clarifiers that remove contaminates and disinfect the wastewater. Metals and chemicals
in the wastewater are strictly controlled to ensure water
quality standards.

Step 2. Microfiltration. Microfiltration uses bundles of hollow polypropylene tubes. Under a vacuum, the water is forced through small pores in the tubes that are tiny enough to strain out any solids, protozoa and bacteria, as well as some viruses.

Step 3. Reverse Osmosis. This process forces water through encased, semi-permeable polyamide molecular membrane bundles. Under high pressure, the water passes through the membranes sifting out any dissolved salts, organic chemicals, pharmaceuticals and viruses. The result is water so pure minerals are added to the water to buffer and stabilize it.

Step 4. Ultraviolet light with hydrogen peroxide treatment disinfects and oxygenates the water, destroying any trace contaminants that may still be present by breaking their molecular bonds.
To improve the settling of un-dissolved particles, calcium hydroxide and cationic polymers are mixed with water to settle out any remaining particles.

Step 5. Water Delivery. Orange County’s groundwater basin is subject to seawater intrusion. As water is pumped out of the basin and the water level drops, seawater can seep into the basin.

To create a protective barrier, OCWD pumps about a third of the water produced by GWRS into seawater intrusion wells along the coast. The water acts as a hydraulic barrier to seawater intrusion and protects Orange County’s water supply. The remaining purified water (65 million gallons per day), are piped to lakes in Anaheim where it undergoes natural filtration though sand and gravel, recharging north and south-central Orange County’s groundwater basin with fresh drinking water.

Orange County’s Groundwater Replenishment System has been operational since 2008 and is the world’s largest advanced water purification system, delivering up to 100 million gallons of potable water daily.