Slant wells provide raw feed for California desalination plant

Spanish sustainable solutions company Acciona will build a seawater desalination plant in California, USA, that will provide water security for the area by mitigating the effects of drought and natural disasters on supply.

Finding reliable and sustainable water sources

The Doheny Ocean Desalination Plant will be located at Dana Point, a coastal city in California, located between Los Angeles and San Diego.

The area relies heavily on imported water, which is subject to disruption from drought and natural disasters, such as earthquakes, which are common in the region. The plant will provide fresh drinking water for both residential and business use in the South Orange County region, in addition to the current imported supplies.

Approximately 600,000 people residing in the South Orange County rely on imported water from the Colorado River and the State Water Project in northern California. Both these sources are currently experiencing water stress, with low reservoir levels and increased extraction.

Emergency management measures were instigated along the Colorado River by the federal government following droughts in 2021 and 2022. The current plan ends in 2026 and California is among the states now bargaining for water rights post-2026, with five proposals under discussion by the Colorado River basin states.

Fresh drinking water system using slant wells 

The proposed plant design will include up to five fully submerged slant wells, one mile of raw water pipeline and a treatment facility utilising reverse osmosis technology.

The slant wells, which will be used to provide the raw seawater, will be located below the ocean floor. This will help to avoid disturbing marine life in the immediate vicinity of the plant. The resultant brine will be mixed with treated water from an adjacent wastewater treatment plant in an existing ocean outfall pipe (San Juan Creek Ocean Outfall) and released back into the ocean, adhering to regulatory and environmentally preferred methods.

Utilising reverse osmosis technology

The plant will use reverse osmosis (RO) to desalinate the seawater (SWRO). RO produces 6.5 times less carbon emissions than traditional desalination technologies and is becoming widely adopted across the world as the need for clean, fresh sources of water increases.

Acciona has designed and continues to operate a number of SWRO plants in different parts of the world. Some of these include:

• The Port Stanvac plant in Adelaide, Australia, serves two million people and has a capacity of 300,000 m3/day. 
• The Al Khobar II plant in Saudi Arabia, provides drinking water to four million people with a capacity of 630,000 m3/day.
• Elsewhere in the US, the Tampa Bay SWRO facility serves a population of over 720,000 residents with a capacity of 108,675 m3/day.

Partners providing water security

Acciona was awarded the contract to design, construct and operate the plant by the South Coast Water District, alongside and J.R. Filanc Construction, two public partnering agencies, California State Parks, and Hazen. 

The partners will work with Acciona to decide the exact location of the slant wells, the design, and construction of conveyance and treatment facilities, as well as developing a carbon-neutral energy supply strategy.

Once complete, Acciona will lead the operation and maintenance of the plant for approximately 15 years.