Orange County Water District (OCWD) is working with the coastal and inland water agencies and cities in Orange County, Calif., to shift ground water pumping (6.5 billion gallons this year) to lessen the strain on OCWD's seawater barrier. The seawater barrier holds back the Pacific Ocean from infiltrating and contaminating the fresh water in the ground water basin, which provides water for 2.3 million residents. The Coastal Pumping Transfer Program, which will shift pumping from along the coastal area to inland areas, is needed due to the recent four-year drought in the Santa Ana River watershed and to relieve pressure on the seawater intrusion barrier until expansion improvements are completed in 2007.
During the 1950s and 1960s, the ocean moved about three miles inland in Orange County, due to increased ground water use and the resulting decreased water levels in the ground water basin. This resulted in seawater contamination of wells, which had to be decommissioned.
In the 1970s, OCWD installed an underground fresh water barrier to hold back the ocean. The barrier consisted of 26 injected wells along the coast that injected purified wastewater underground to create a fresh water mound above sea level, preventing ocean intrusion. Because of increased ground water use over the years, OCWD now is at a point where the barrier must be expanded. An additional eight wells will be installed to increase the amount of purified water that can be injected from 5 million gallons to 40 million gallons per day.
In the interim, OCWD has worked out an innovative solution to minimize the stress on the existing barrier by moving the pumping inland and reducing the pumping along the coast. Coastal water agencies and cities will pump less water and rely on more imported water, while inland cities will pump more ground water and use less imported water. The program is designed so that there is no cost difference for the participants, even though some will pump cheaper ground water and others will use more imported water, which costs more than double.
Eventually, a new water purification and water supply project, called the Groundwater Replenishment System, will be on-line in 2007 and produce about 40 million gallons of water per day to expand and rejuvenate the seawater barrier that currently only receives 5 million gallons per day. Gradual refilling of the ground water basin by recharge of the Santa Ana River and natural rainfall also will help reduce stress on the seawater barrier.