Your Water

Groundwater & Seawater Barriers

Groundwater

Prior to the District's formation in 1947, the average resident (in what would be considered the West Basin service area) solely relied on groundwater. Today, West Basin customers can count on a more diverse mix of water resources to ensure a more reliable supply of water for our service area: 10% groundwater, 57% imported water, 14% recycled water and 19% conserved water.

The West Coast Groundwater Basin 

The District's groundwater supply is extracted from its namesake West Coast Groundwater Basin that underlies much of the service area.

Pumping Rights

Because the West Coast Groundwater Basin is adjudicated (i.e. the amount to be extracted each year has been determined by a court decision), the rights to the amount of groundwater extracted each year remain virtually the same. Total adjudicated pumping rights in the West Coast Groundwater Basin remain above 50,000 AFY.

The average amount of water extracted from the West Coast Groundwater Basin by our customer agencies over the past five years (FY19-FY23) is approximately 20,000 acre-feet per year (AFY). Groundwater pumping in the West Basin service area is on an upward trajectory (e.g. approx. 17,000 AF was pumped in FY19; and more than approx. 25,000 AF of groundwater pumped for FY24).

This presents considerable opportunities to:

  • Increase groundwater pumping,
  • Replenish the groundwater basin with purified recycled water, and
  • Offset the need to import drinking water (subject to restrictions during drought yeras) from hundreds of miles away

Water Replenishment District 

The entity responsible for maintaining and replenishing the West Coast Groundwater Basin is the Water Replenishment District of Southern California (WRD). They replenish the basin with a mix of imported water and recycled water. They are also responsible for protecting the groundwater basin from seawater intrusion. To prevent ocean water from seeping in and ruining the fresh groundwater, WRD, in partnership with Los Angeles County, injects high-quality recycled water into the West Coast Seawater Barrier.

See also the District's current Urban Water Management Plan to get more details about how groundwater plays a role in its pat, present and future portfolio.

West Coast Groundwater Basin

The West Coast Groundwater Basin (Basin) underlies 160 square miles in the southwestern part of the Los Angeles Coastal Plain in Los Angeles County. The Basin extends southwesterly along the coast from the Newport-Inglewood Uplift to the Santa Monica Bay. The Basin provides groundwater to approximately eleven cities and unincorporated areas of Los Angeles County. This average annual production is roughly 52,000 Acre-feet (AF), which accounts for 20% of total retail demands.

In 1961, the Basin was adjudicated. The adjudication limits the allowable annual extraction of groundwater per water rights holder within West Basin in order to prevent seawater intrusion and an unhealthy groundwater level. As part of the adjudication, the court appointed the California Department of Water Resources (DWR) to serve as Watermaster to account for all water rights and groundwater extraction amounts per year.

Since the adjudicated groundwater production is substantially higher than the natural recharge of the Basin, the California State Legislature in 1959 created the Water Replenishment District of Southern California (WRD) to manage, regulate and replenish the Basin. Each year WRD determines the amount of supplemental recharge that is needed for the Basin based upon annual groundwater extractions and groundwater levels. As part of the recharge and protective duties, WRD procures imported water and recycled water for the West Coast Basin Barrier Project and Dominguez Gap Barrier Project to prevent seawater intrusion.

Through the coordination of the Los Angeles County Public Works Department, DWR, and WRD, the West Coast Groundwater Basin is managed and maintained to provide the utmost water quality and reliability for the region.

For further information on the West Coast Groundwater Basin please visit the Water Replenishment District’s website at http://www.wrd.org and the California Department of Water Resources at https://water.ca.gov/Water-Basics/Groundwater.

Seawater Barriers

With our proximity to the ocean here in southwest Los Angeles County, seawater has the potential to seep into the aquifers and mix with groundwater, making it too salty to drink. Protecting the groundwater aquifer is important because it can store up to one million acre-feet (one acre-foot equals approximately 326,000 gallons) of drinking water, which is more than the water contained in the largest reservoir in Southern California.

There are two aquifers that West Basin draws water from: the West Coast Groundwater Basin and the Central Groundwater Basin.

To prevent seawater intrusion, a seawater barrier was constructed. A seawater barrier is a series of injection wells positioned like a dam between the ocean and the groundwater aquifer. These wells inject water along the barrier to ensure that the water level near the ocean stays high enough to keep the seawater from seeping into the aquifer. A combination of West Basin’s high quality recycled water and imported water is injected into the seawater barriers. There are two seawater barriers that receive this combination of water: the West Coast Basin Seawater Barrier and the Dominguez Gap Barrier.

The Los Angeles County Flood Control District (LACFCD) owns, operates, and maintains the barrier projects. The Water Replenishment District of Southern California (WRD) purchases all of the water that is injected into the barriers. WRD protects the basin through groundwater replenishment, deterrence of sea water intrusion, and groundwater quality monitoring of contamination through assessments on water pumped from the WRD service area.

West Coast Basin Seawater Barrier

In an effort to decrease our dependence on imported water where appropriate, the amount of high-quality recycled water injected into the seawater barrier has steadily increased from 50% to 75%. West Basin’s recently completed Phase IV water recycling project has made this increase possible, resulting in a decrease in the amount of imported water needed for the barrier (from 50% to 25%), allowing approximately 5,000 acre-feet of imported water to be conserved each year. In addition, recycled water is produced locally, making it more reliable than imported water, which is subject to drought, regulation, and changes in weather patterns.

West Basin is working with WRD to increase the amount of recycled water injected into the Barrier to 100% to further conserve imported water supplies and provide a more reliable, high quality source of water to the aquifer.

Dominguez Gap Barrier

The Dominguez Gap Barrier is similar to the West Coast Barrier, in that clean water is injected into the groundwater basin to prevent seawater from mixing into the drinking water supply. The Dominguez Gap Barrier is located along the Dominguez Channel in the Cities of Wilmington and Carson. The Barrier currently receives approximately 1,000 acre-feet per year of high-quality recycled water.

The LACFCD provides water to the Dominguez Gap Barrier from their Terminal Island Treatment Plant. They also operate and maintain the barrier. West Basin is coordinating with the Los Angeles Department of Water and Power, WRD, and the LACFCD to develop plans for serving recycled water to supplement a portion of the Dominguez Gap Barrier from West Basin’s satellite water recycling facility in Carson.

At this time, it is estimated that West Basin could potentially serve the Dominguez Gap Barrier up to approximately 1 MGD (million gallons per day) of high-quality recycled water from the Carson Facility. The proposed expansion will bring the total amount of recycled water to almost 50%, with the remaining 50% imported water.