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| Santa Monica Coastal Plain Groundwater Basin | |
|---|---|
| Name | Santa Monica Coastal Plain Groundwater Basin |
| Location | Los Angeles County, California |
| Coordinates | 34°00′N 118°27′W |
| Type | Alluvial groundwater basin |
| Area | ~260 km² |
| Aquifers | Dune, alluvial, and marine terrace deposits |
| Managed by | Multiple agencies including Los Angeles County Department of Public Works, City of Los Angeles, West Basin Municipal Water District, Metropolitan Water District of Southern California |
Santa Monica Coastal Plain Groundwater Basin The Santa Monica Coastal Plain Groundwater Basin underlies urbanized portions of Santa Monica, California, Venice, Los Angeles, Marina del Rey, Culver City, California, and parts of West Los Angeles and Beverly Hills, California. The basin is situated within the larger geological setting of the Los Angeles Basin and the Transverse Ranges, influenced by tectonics associated with the San Andreas Fault system and sedimentation from the Santa Monica Mountains. Urbanization, infrastructure, and coastal processes have shaped extraction, recharge, and quality issues documented by agencies such as the United States Geological Survey, California Department of Water Resources, and local water districts.
The basin occupies the western portion of the Los Angeles Plain where Quaternary deposits overlie Miocene and Pliocene formations mapped in studies by the United States Geological Survey. Hydrogeologic units include Holocene dune sands near the Pacific Ocean coast, Pleistocene marine terraces correlated with work from the California Geological Survey, and older alluvium described in publications by the Los Angeles County Department of Public Works. Groundwater flow is generally seaward toward coastal discharge zones including Santa Monica Bay and the Ballona Creek estuary, with hydraulic gradients influenced by pumping in municipal wells operated by entities like the City of Los Angeles Department of Water and Power and the West Basin Municipal Water District. Recharge sources include direct infiltration from episodic surface runoff from tributaries feeding the Santa Monica Mountains Conservancy lands, managed aquifer recharge projects linked to programs by the Metropolitan Water District of Southern California, and artificial recharge from recycled water and stormwater capture supported by the Los Angeles County Flood Control District.
Indigenous settlement by Chumash peoples in the coastal plain preceded Spanish colonial period activities centered on Mission San Gabriel Arcángel and the Rancho La Ballona land grant, which influenced early water use patterns. During the 19th and 20th centuries, development tied to the expansion of Los Angeles, California, the growth of Santa Monica Pier, and transportation corridors like the Pacific Electric Railway and later Interstate 10 intensified groundwater extraction for agriculture, industry, and municipal supply. Landmark projects such as importation of water by the Los Angeles Aqueduct and interstate initiatives involving the Colorado River Aqueduct altered reliance on local groundwater, while federal programs during the Great Depression and postwar era spurred urbanization. Post-World War II suburban expansion in Culver City, California and Mar Vista, Los Angeles drove well-field development overseen by agencies including the Los Angeles County Board of Supervisors.
Current management blends local water districts like the West Basin Municipal Water District and the City of Santa Monica water division with regional institutions such as the Metropolitan Water District of Southern California and regulatory oversight from the California State Water Resources Control Board. Demand is shaped by municipal supply contracts with the Los Angeles Department of Water and Power, industrial users tied to Los Angeles International Airport, and landscape irrigation regulations implemented by the California Urban Water Conservation Council. Resource strategies include conjunctive use plans coordinated with the Santa Monica Mountains Conservancy for managed aquifer recharge, stormwater capture projects funded through ballot measures like those endorsed by the Los Angeles County Board of Supervisors, and recycled water initiatives influenced by Assembly Bill 401-era policy frameworks. Monitoring networks maintained by the United States Geological Survey and county agencies track water levels, while allocation decisions sometimes reference case law from the Supreme Court of California and statutory directives from the California Water Code.
Industrial development in the coastal plain resulted in legacy contaminant sites investigated under programs administered by the United States Environmental Protection Agency and the California Department of Toxic Substances Control. Documented issues include volatile organic compound plumes similar to those addressed near Defense Fuel Support Point Norwalk and petroleum hydrocarbon impacts related to historical gasoline stations cataloged by the California State Water Resources Control Board. Coastal habitat loss in Santa Monica Bay and impacts to the Ballona Wetlands have been linked to altered groundwater-surface water interactions, prompting assessments by the National Oceanic and Atmospheric Administration and conservation groups like the Santa Monica Bay Restoration Commission. Emerging concerns include seawater intrusion influenced by lowered groundwater heads, evaluated in comparative studies referencing the Orange County Groundwater Basin and managed in part through desalination and replenishment planning by agencies such as the West Basin Municipal Water District.
Water governance in the basin involves overlapping jurisdictions of municipal governments including the City of Santa Monica, City of Los Angeles, and County of Los Angeles, together with special districts like the West Basin Municipal Water District and regional regulators such as the California State Water Resources Control Board. Legal instruments relevant to allocation and quality include the California Water Code, state well construction standards enforced under the California Department of Water Resources, and federal statutes implemented by the United States Environmental Protection Agency and the Safe Drinking Water Act. Local ordinances from the City of Santa Monica and regulatory actions by the Los Angeles County Department of Public Health have addressed well permitting, pumping limits, and contamination response, often coordinated through interagency agreements modeled after cooperative frameworks used elsewhere in Southern California.
Remediation projects have combined pump-and-treat systems, monitored natural attenuation strategies endorsed by the United States Environmental Protection Agency, and in situ treatment pilots supported by research partners such as the University of California, Los Angeles and the Southern California Coastal Water Research Project. Habitat restoration in coastal wetlands has involved collaboration between the California Coastal Conservancy, the Santa Monica Mountains Conservancy, and non-governmental organizations like the Nature Conservancy and the Heal the Bay advocacy group. Climate adaptation and resilience planning reference guidance from the California Natural Resources Agency and the Governor's Office of Planning and Research, integrating sea level rise scenarios from the National Research Council and funding mechanisms through state water bond measures and local general obligation bonds overseen by the Los Angeles County Treasurer and Tax Collector.