The Los Angeles County Department of Public Works operates and maintains three seawater barriers along Los Angeles County's coastline. Often unnoticed because of their underground nature, these facilities serve as Los Angeles basin's fresh water sentinels. They protect a significant portion of the area's drinking water supply from ocean water, which constantly attempts to migrate into existing aquifers. Treated imported and reclaimed water is injected deep into the underground aquifers to block this inland migration of saltwater.
Hydrologic Basis for Seawater Intrusion:
Fresh water which comes from the percolation of rain and river water into the ground accumulates within the different aquifers below the Los Angeles Basin. Originally there existed enough fresh water to completely displace any ocean water which might have migrated inland.
As larger and larger amounts of water are pumped up from underground for drinking water purposes, eventually there doesn't exist enough fresh water to keep the ocean water at bay. At this point seawater intrusion begins to spread landward, compromising domestic water supply wells. By the end of 1950, such a situation existed within Los Angeles County.
One method which has been proven successful to combat this problem and is currently in use by the Department is to construct a series of injection wells along the coastline which recharge the domestic water supply with imported water and advance treated reclaimed water which has undergone microfiltration, reverse osmosis and disinfection. This technique attempts to establish groundwater elevations greater than or equal to the original elevations within the different aquifers.