Project: Groundwater Replenishment System
Jurisdiction: Orange County, Calif.
Agencies: Water District and Sanitation District
Designer: Cambridge, Mass-based CDM
Date completed: January 2008
Cost: $480.9 million
Last year, Orange County, Calif., cut the ribbon on its Groundwater Replenishment (GWR) System, which cleans treatedwith a three-step process — microfiltration, reverse osmosis, and ultraviolet light and hydrogen peroxide — so it eventually can be consumed as drinking and be used to prevent seawater intrusion. The project is reducing the amount of treated wastewater that is discharged into the Pacific Ocean, protecting groundwater sources and supplementing local drinking water supplies.
The system has the capacity to produce 70 million gallons per day (mgd) of near-distilled quality water. Approximately 35 mgd is injected into a seawater barrier to prevent ocean water from contaminating the groundwater supply, and the remaining 35 mgd are pumped to spreading basins in Anaheim where it mixes with Santa Ana River water and other imported water sources, then percolates into the groundwater basin, which is tapped by local water utilities.
In the GWR System, secondary effluent from the Orange County Sanitation District passes through a low-pressure microfiltration membrane process that removes small suspended particles, protozoa, bacteria and some viruses from the water. Next is the reverse osmosis step, in which the water is directed under high pressure through thin membranes that eliminate salts, viruses, pesticides, and most organic compounds, creating near-distilled quality water. In the final stage, ultraviolet light and hydrogen peroxide combine to create an oxidation reaction that breaks down organic compounds through an accelerated decomposition process. After purification, the water is injected along the coast to maintain a seawater intrusion barrier and sent to the groundwater basin where it blends with other waters and is buffered with natural minerals. It takes six months to a year or longer before the water is pumped from wells into the drinking .
Read the main story, "A new frontier," to learn more about how membranes are playing a critical role in helping communities stretch the water supplies.