By Jeff Crider
Rapid population growth is making water an increasingly precious commodity across California, which faces a recent federal mandate limiting its consumption of Colorado River water to 4.4 million acre feet per year.
The federal mandate poses a significant challenge for state water agencies, which in the past have imported as much as 5.3 million acre feet of water from the Colorado River for their growing numbers of consumers.
As a result, many water districts in California are looking at other ways to make better use of their groundwater supplies in an effort to reduce their dependence on imported water.
Eastern Municipal Water District is one of several California water districts that’s using desalination—or brackish water treatment technology—to improve the quality of groundwater supplies, not only to generate additional sources of drinking water but to improve its ability to use existing aquifers for water storage purposes during wet years. The desalted water is pumped into a domestic water distribution system for sale to water customers.
Eastern serves 440,000 customers in a 555-square mile area of western Riverside County, about 70 miles east of Los Angeles. Eastern’s service area stretches from Temecula north to Moreno Valley, following the Interstate 215 corridor.
The district overlies extensive aquifers containing large quantities of marginally usable brackish groundwater. Total dissolved solids (TDS) in these basins range from 1,500-to-3,000 milligrams per liter (mg/L). Estimates of potential production from these basins range as high as 15,000 acre feet per year—an acre foot being the volume of water required to cover one acre of land one foot deep or about 325,900 gallons.
Tracking the terrain
The salinity problem stems in part from the fact that Eastern’s service area is trapped in a bowl, bordered by the 10,000-foot San Jacinto Mountains on the east and bands of rolling hills on the north, west and south. While the district receives freshwater runoff from the San Jacinto Mountains, much of that water becomes unusable as it seeps into Eastern’s underground aquifers.
The high quality basins to the east have water with TDS concentrations as low as 250 mg/L. As you travel west, you encounter basins with water with TDS levels of 500, 600, 1,000, 1,200, 1,500 and 2,000 mg/L. In the worst of these basins, TDS routinely exceeds 3,000 mg/L. Most of the water served by Eastern contains TDS concentrations below 700 mg/L—the same level as water imported from the Colorado River—but once TDS exceeds 1,000 mg/L, it rapidly loses its value as a source of irrigation supply.
“Underground water flowing west from the San Jacinto Mountains historically has picked up salts from the soil that have made the water less desirable the further west you go,” said Mike Garner, Eastern’s resource development administrator.
Growth equals salinity
The district’s service area has also been transformed during the past four decades from an agricultural area to a bedroom community for people working jobs in Los Angeles, Orange, San Diego and western Riverside counties.
“When you add the mix of human activity that has occurred in the area during the past hundred years with the reduction of agricultural pumping in the 1960s and ’70s, you wind up with increased salts trapped in a rising pool of unusable water that also threatens better quality water in other parts of the district,” Garner said. Indeed, the salinity of groundwater in some parts of Eastern’s service area has become so high that, again, it’s often unusable for agriculture.
Strategy over time
For 10 years, however, Eastern has been closely monitoring the flows and salinity content of waters going through its aquifers and has developed a strategy to make this water usable not just for agriculture but for the district’s growing population.
The strategy calls for construction of three desalination plants during the next five years that could eventually enable the district to remove 13 million or more gallons per day (gpd) of unusable water from local aquifers while adding over 10 million gpd of drinking water to its domestic water system.
The remaining three million gallons would consist of high salinity waste material that will be transported out of the area via a brine disposal pipeline. The brine is transported about 20 miles through a newly built pipeline and joins an existing brine disposal line. It continues to a special treatment plant in Orange County, where it’s further treated and disposed of into the Pacific Ocean.
Plant in the making
Eastern is currently constructing its first plant, a 4 million gallons per day (mgd) reverse osmosis (RO) plant in the community of Menifee. The plant is expected to be operational by next summer.
RO produces highly purified water by pumping brackish water at high pressures through a semi-permeable membrane, which allows water molecules to pass through but rejects salts and other contaminants that are flushed away for disposal.
Efficient use of the Menifee facility requires the district to operate wells where the unusable groundwater is located and to move the brackish water by pipelines to the desalination plant. Four wells have been established to supply the Menifee plant.
Another 4-mgd desalination plant is tentatively planned for the northeastern part of the city of Perris, while a third 4-mgd facility would be built in the Winchester area or as an expansion of the Menifee facility.
Leaving the door open
It’s likely that RO membranes will be used for all of the facilities. Desalination technologies continue to advance, however, and the district will evaluate the best available technology for each phase of the program.
“Construction of the desalination plants will enable us to increase our local supplies of drinking water, thereby reducing the need for Eastern to import additional water to satisfy our growing population,” Garner said. “It will also enable us to improve the integrity of our aquifers so that we can use them for storage purposes during wet years when surplus surface water is available at lower cost.”
When the bill comes due
While few can argue the merits of desalinating Eastern’s groundwater aquifer, the technology requires a significant upfront investment—not only in the technology but in the finished cost of desalinated water. Indeed, desalinated water will cost about $900 per acre foot compared to $430 for imported water.
Eastern was able to offset the higher costs of desalinated water by obtaining low interest construction loans from California’s Agricultural Drainage Loan Program and operating cost subsidiaries from Metropolitan Water District’s Recovery Program. These programs have been developed to encourage agencies to invest in the development of local water resources that reduce demand for imported water.
“As the cost of imported water increases and with improvements in desalination technology, the utilization of brackish groundwater will become increasingly cost effective,” Garner said.
The desalination program will yield benefits other than expanded water supplies, including: protection of adjacent high quality basins from the spread of rising brackish groundwater; salinity management; improved water recycling, and long-term improvements in local groundwater quality as salt is removed from the basin.
“In the long run, desalination technology will prove to be a prudent investment,” said John B. Brudin, Eastern’s general manager. “Not only will this technology help us better utilize our existing aquifers, but it will help us minimize our need for rate increases as the population continues to grow within our service area.”
Eastern hasn’t raised its water rates since 1996 and no increases are projected for the current fiscal year, which ends June 30, 2001. The average “retail” rate charged to customers is $653 per acre foot.
Eastern’s investments in desalination technology also lay the foundation for a more vibrant economy in the district’s service area.
“Due to the inland location of our district, it is necessary to construct pipelines to dispose of the brine waste generated by the desalination process,” said Charles J. Bachmann, Eastern’s assistant general manager for engineering.
“These are the same kinds of pipelines needed by semiconductor manufacturers and other high-tech businesses to dispose of their wastes. So, by laying the foundation for desalination plants in western Riverside County, we are signaling high-tech businesses that we have the ability to accommodate them.”
Eastern believes its construction of desalination plants—using RO membrane technology—and their related brine disposal lines will help the district minimize its water imports and make better use of its existing groundwater resources during a time of rapid population growth. The construction of brine lines to dispose of waste from the desalination plants will also strengthen the region’s economic base by creating an important component of the waste disposal infrastructure needed by high-tech businesses.
About the author
Jeff Crider, formerly public relations manager for USFilter Corp., is a Temecula, Calif.-based writer specializing in water issues. He can be reached at (909) 781-2240 or email: [email protected]