Prior to groundwater pumping in a region, the seaward movement of freshwater prevents seawater from encroaching coastal aquifers. An interface between freshwater and seawater is maintained with denser seawater underlying freshwater. When groundwater is pumped from a coastal aquifer, lower water levels can allow the freshwater-seawater interface to move inland eventually impacting wells nearest the coast.
Seawater intrusion is the only undesirable result limited to largely coastal areas.
Central Coast seawater intrusion
Reports of seawater intrusion into the Salinas Basin began as early as 1946. The extent of seawater intrusion has moved farther inland due to continuing overdraft conditions for municipal and agricultural uses.
- Recommendations to Address the Expansion of Seawater Intrusion in the Salinas Valley Groundwater Basin (Monterey County Water Resources Agency, October 2017)
- Monterey County Water Resources Agency website
- Seawater intrusion in the Salinas Valley: Central Coast Watershed Wiki (CSU - Monterey Bay)
Southern California Seawater Intrusion
Groundwater pumping from as early as the 1920’s caused landward seawater intrusion into Southern California coastal aquifers. To combat this, in the 1950’s, sets of closely spaced wells were installed to inject high-quality fresh water into aquifers to create barriers to the encroaching saltwater.
- Saltwater Intrusion in Los Angeles Area Coastal Aquifers—the Marine Connection (USGS)
- Battling Seawater Intrusion in the Central & West Coast Basins (Water Replenishment District, Technical Bulletin)
More information at the USGS Seawater Intrusion page.