Published on IDRA Global Connections Winter 2020 Issue
By Mr. Michael Markus, General Manager, Orange County Water District
The Orange County Water District (OCWD; the District), located in Orange County, California, manages a large groundwater basin that provides 77% of the potable water needs for 2.5 million people. It’s a very arid region that receives only about 14 inches (360 millimeters) of rain each year and has cyclical droughts. There are 19 retail water agencies that pump water from the basin, which means the District needs to recharge about 100 billion gallons or 375 million cubic meters (m3) of water each year to maintain high pumping levels and a healthy groundwater basin that is free from seawater intrusion and land subsidence.
The chart below shows various supplies used to refill the basin and looks much like an investment portfolio. Just like an investment portfolio, it is diversified to reduce risk and maximize return. Like any good investment firm, the Orange County Water District looks for investment opportunities that will help put reliable water back into the basin at reasonable cost OCWD currently gets 17% of its supply for the groundwater basin from natural recharge or rainfall, which is variable and dependent on unreliable hydrology.
Santa Ana River flows (20%) are the result of wastewater discharges from the upper Santa Ana Watershed treatment plants. OCWD diverts this river water into recharge basins where it percolates down into the groundwater basin. The District has an adjudicated right to a certain amount of that flow, but the current flow could be reduced by as much as 50% due to increased upstream recycling.
Stormwater capture (15%) takes place behind Prado Dam in Riverside County. OCWD has been working with the U.S. Army Corps of Engineers (the Corps), a federal agency that owns and operates the dam, to capture up to 7 billion gallons (26.5 million m3) of stormwater annually. The Corps holds stormwater behind the dam and after the storm passes, slowly releases water so that OCWD can divert and recharge the water in its downstream recharge basins. By doing so, the District captures a large amount of water that would be otherwise lost to the Pacific Ocean.
Untreated imported water (18%) from Northern California and the Colorado River costs one and a half times as much as groundwater but is a necessary supply to maintain high pumping levels. However, this water may not be available for purchase during a drought.
At 30% of our water portfolio, the Groundwater Replenishment System (GWRS) is the most reliable source and provides the highest quality water that is recharged. The GWRS is a partnership with the Orange County Sanitation District and is the world’s largest potable reuse project. It uses advanced technology consisting of microfiltration, reverse osmosis and ultraviolet light with hydrogen peroxide to purify secondary treated wastewater to near distilled drinking water quality. This water is injected into a seawater barrier and pumped to recharge basins where it naturally percolates into the groundwater basin. The project came online in January 2008, producing 70 million gallons per day (mgd) or 265,000 cubic meters per day (m3/d) of recycled water. Its initial expansion in May 2015 increased its production to 100 mgd (378,500 m3/d) and OCWD recently broke ground for the final expansion, which will bring an additional 30 mgd (113,500 m3/d) for a total of 130 mgd (492,000 m3/d) of recycled water when it comes online in 2023. That is enough drinking water for 1 million people.
The GWRS features many benefits. It creates a new local water supply, reuses a wasted resource, increases water supply reliability, costs less than desalinated water and imported water, uses onehalf the energy it takes to import water and one-third the energy to desalinate seawater, and improves the quality of water in the basin. We feel water reuse is a sound investment for the future.
OCWD is constantly looking for reliable, costeffective water supplies to strengthen its portfolio both now and well into the future.