The West Basin Ocean Water Desalination Project
The potential Ocean Water Desalination Project (Project) would produce between 20 to 60 million gallons per day (MGD) of drinking water from the ocean. The 20 MGD capacity facility (Local Project) would generate approximately 21,500 acre-feet per year of high-quality, drinking water to meet local demand. The project also considers a potential expansion of the facility to produce up to 60 MGD of drinking water (Regional Project), to account for future needs in the region. A 20 MGD ocean water desalination facility could add approximately 10% of reliable water to the service area, further diversifying the District’s water supply portfolio.
The potential Project site would be at an 8 to 13 acre footprint in the existing 33 acre industrially zoned location within the El Segundo Generating Station (ESGS) at 301 Vista del Mar in the City of El Segundo, California. The key Project components would consist of a low velocity, screened intake system to deliver ocean water to the facility, reverse osmosis membrane technology, a brine discharge diffuser system to return concentrated seawater back to the ocean, and a drinking water delivery system to distribute potable water to the local and regional supply systems.
Ocean water desalination, with over 18,000 facilities in 150 countries, is one component of a water supply reliability solution used around the world. This added drinking or potable supply would enhance regional water reliability, especially during periods of drought and water scarcity (e.g., loss of snowpack in the Sierra Nevada Mountains, catastrophic interruptions of water supply and uncertain impacts of climate change).
The Project is being explored as one component of the District’s mission to provide safe and reliable water to the communities it serves through the following objectives:
- Diversify the District’s water supply portfolio to increase reliability in the near and intermediate term (5-15 years) and long term (15-30 years), while reducing reliance on imported water;
- Improve ability to adapt by developing a water supply that is less vulnerable to climate variations;
- Increase local control of water supplies and infrastructure;
- Improve the District’s ability to control water costs and provide long term price stability; and
- Develop a potable water supply that is cost effective and environmentally responsible.
How Does the Ocean Water Desalination Process Work?
The main ocean water desalination process involves removal of dissolved salts and impurities to produce high-quality clean drinking water. See figure above. The process involves the following steps:
- Intake: Ocean water passes through open ocean screened intake specifically designed to minimize impact to marine life with an opening that would not exceed 1 mm. Water is taken into the system at a velocity less than 0.5 feet per second ensuring minimal marine life impingement. The screens will be designed in accordance with the 2015 California Ocean Plan Amendment for desalination.
- Media Filtration: Filters remove coarse materials from the water, such as sand and sea shell pieces.
- Membrane Filtration: Fine membranes remove the microscopic material in the ocean water, such as bacteria.
- Reverse Osmosis: The filtered water is pumped under high pressure through reverse osmosis (RO) membranes to purify it, removing salt, minerals and any remaining viruses. This results in water that meets or surpasses state and federal drinking water requirements. The discarded salt water is referred to as brine.
- Post-Treatment: Due to the pure water quality that results from the RO process, minerals are added back to the water to stabilize it and prevent water pipes from corroding. The water is then disinfected so it is safe for drinking.
- Brine Disposal: The brine from the RO process is returned to the ocean where it reaches ambient salinity levels between 45 to 63 feet from the discharge point (depending on final design and operations) to minimize impacts on marine life. This avoids the creation of salt plumes or oxygen-starved areas on the seafloor. The 2015 Ocean Plan prescribes 328 feet to reach ambient salinity levles, but the Project discharge would be well below that threshold (45 to 63 feet).
General Project Information
Since its formation in 1947, West Basin Municipal Water District has undertaken a scientific and research-based approach to evaluating water management needs for the service area and implementing innovative water reliability solutions. During the multiple year drought of the 1980s, West Basin became a pioneer in water treatment technology by inaugurating a water recycling facility in 1995 which now purifies 40 million gallons per day of treated sewage and is world renowned for producing five unique types of customer-tailored water.
West Basin continues this innovative water solutions legacy through its partnerships in groundwater replenishment by expanding recycled water production, evaluating new purification technologies, and by building funding partnerships to increase access to water conservation programs for local residents and businesses. Now, as a coastal water agency, West Basin has undertaken its obligation to explore and evaluate a potential new reliable water source. The District is completing the California Environmental Quality Act (CEQA) process to examine the conversion of ocean water into drinking water with technologies that are environmentally responsible, energy-efficient and cost effective.