Seawater Barrier


In 1940 freshwater pumping wells along the coast of Los Angeles County began to be abandoned due to seawater intrusion. A cooperative study between the United States Geologic Survey's Water Resources Division and the Los Angeles County Flood Control District to investigate this critical situation determined in 1943 that immediate action was necessary to restrain the situation. Of the different alternatives, only artificial groundwater recharge was found to be economically feasible. Although storm water spreading basins could be used to recharge local unconfined aquifers, which lie directly beneath the ground surface, something different and innovative was necessary to reach those deeper confined aquifers containing by far the most fresh water.

Barriers Locations There exists three different barriers within LA County. The water which is injected is supplied by the Water Replenishment District, which purchases imported water from MWD, and reclaim water from West Coast Municipal Water District. The largest of these barriers is the West Coast Basin Barrier Project (WCBBP), which is an expansion of the original pilot study. The second largest barrier is the Dominguez Gap Barrier Project (DGBP). It began operation in 1971. The Alamitos Barrier Project was developed in conjunction with the Orange County Water District and crosses south of the County boundary. It went into operation in 1966.


Injection Well Vs. Spreading BasinsA bill passed by the California State Legislature in 1951, allowed the State Water Resources Board to fund various investigational groundwater recharge experiments being conducted by Los Angeles County utilizing injection wells. Results showed that seawater could be successfully displaced below a confined aquifer's confining cap or "aquiclude". This breakthrough, encouraged a pilot injection well program to be initiated along the coastline within the City of Hermosa Beach. By December 31, 1953, having proven that injection wells could be a useful tool to abate intrusion from the ocean, the Water Resources Board participation in the barrier project ceased. All capital costs since then to expand and improved the barriers have seen funded by the Los Angeles County Flood Control District.


The Second Largest Barrier is the Dominguez Gap Barrier Project (DGBP). It began operation in 1971. This barrier comprises of a line of 41 injection wells and 107 observation wells extend 12 miles from F Street to E street along the Dominguez Channel. The observation wells which are used to monitor water surface elevations and depth specific chloride levels, are located along the barrier alignment and placed between injection wells or situated off the immediate barrier alignment. Both reclaimed and imported water is used to be injected into the 200-foot Sand-Gaspur, 400-Foot Gravel and Gaspur Aquifers.

Dominguez Barrier alignment was selected based on comprehensive investigations which provided detailed geologic and hydrologic study of the Dominguez Gap area and determined the location, rate of movement, and rout of seawater intrusion. Based on these factors, the barrier alignment extends along the Dominguez Channel as north-to south alignment through Pacific Coast Highway and Southern Pacific Drive. The alignment then swerve west along Grant Street till it curves South-West along Alameda Street. To the west the alignment curves back inland along the E Drive and the then jogs one block south along Banning Boulevard to connect along the D Street. At D Street the alignment proceeds West through Avalon Boulevard and Wilmington Boulevard and then proceeds to the terminus located at Figueroa Street adjacent to the Interstate 110 Harbor Freeway.


In conjunction with the Orange County Water District (OCWD), the Alamitos Barrier Project (ABP) was initially proposed and constructed in 1964, partially in Orange County and partially in Los Angeles County. The project was designed to protect the groundwater supplies in C, B, A, and I zones of the Central Basin of Los Angeles County and the southwest portion of the Coastal Plain area in Orange County from the intrusion of seawater through the Alamitos Gap area. The project, which is comprised of 43 injection wells to provide a freshwater pressure ridge and 4 extraction wells to form a trough which breaks the landward gradient of intruding seawater, is located near the Los Angeles-Orange County line about two miles inland from the mouth of the San Gabriel River. To monitor the project performance, there are 226 observation wells along the barrier alignment, between injection wells, and spread out both landward and seaward in the vicinity of the barrier. The observation wells are used to monitor water surface elevations and depth specific chloride levels.

The delineation of the alignment was based on geologic and hydrologic conditions, the route of seawater intrusion, the extent of seawater intrusion, geographic location, and available land. The alignment arcs across the Alamitos Gap and is landward of the seal Beach Fault.

The Water Replenishment District of Southern California (WRD) purchases the water injected into the LA County side of the barrier and the OCWD purchases the water injected into the Orange County side of the barrier. Injected water is currently a blend of both imported and reclaimed water. The imported water is purchased from the Metropolitan Water District (MWD) and the reclaimed water is purchased from WRD's Advanced Water Treatment Facility which is operated by the Long Beach Water Department and receives source water from the LA County Sanitation Districts.