Aquifers of the United States

Aquifers of the United States
Name	Aquifers of the United States
Caption	Major aquifer systems in the contiguous United States
Location	United States
Type	Groundwater aquifers
Area	Varies by aquifer

Aquifers of the United States are the principal subsurface reservoirs that supply groundwater across the United States and its territories, underpinning municipal Los Angeles, agricultural irrigation in the Central Valley, and industrial users such as Pittsburgh and Houston. These aquifers include the Ogallala Aquifer, the Floridan Aquifer, and the Edwards Aquifer, and support ecosystems like the Everglades and rivers such as the Mississippi River; federal agencies including the United States Geological Survey and the Environmental Protection Agency coordinate studies, while state agencies in California, Texas, and Florida manage local regulation.

Overview and Classification

Groundwater storage in the United States is classified by hydrostratigraphic units such as unconfined sedimentary basins like the High Plains Aquifer (part of the Ogallala Aquifer), confined carbonate systems like the Floridan Aquifer, and fractured-rock aquifers in regions including the Appalachian Mountains, Rocky Mountains, and Sierra Nevada. Federal classifications follow frameworks used by the United States Geological Survey and the National Research Council (United States), distinguishing principal aquifers by extent, yield, and hydrogeologic characteristics; many maps derive from cooperative studies by the United States Department of Agriculture and the United States Fish and Wildlife Service in partnership with state geological surveys such as the California Department of Water Resources.

Major Regional Aquifers

Regional systems include the High Plains (Ogallala) Aquifer spanning Kansas, Nebraska, Texas, Oklahoma, and South Dakota; the Floridan Aquifer beneath Florida and parts of Georgia and Alabama; the Edwards Aquifer in central Texas; and the Basin and Range aquifers of the Great Basin in Nevada and Utah. Other significant systems are the Central Valley aquifer under Central Valley, California, the Atlantic Coastal Plain aquifers along the Atlantic Seaboard near New Jersey and North Carolina, and the fractured-rock aquifers of the New England states such as Massachusetts and Vermont. Transboundary features connect to Hudson Bay drainage and to international basins near Mexico–United States border areas including aquifers under Texas and Arizona.

Hydrogeology and Recharge/Discharge Processes

Hydrogeologic processes in U.S. aquifers involve porosity and permeability in materials ranging from unconsolidated Mississippian sands to Cambrian carbonates and Precambrian crystalline rocks studied by institutions like the Geological Society of America. Recharge occurs from precipitation over watersheds such as the Great Plains and from river leakage in systems like the Colorado River interacting with riparian zones near Boulder, while artificial recharge projects in California and Arizona augment storage. Discharge pathways include springs feeding the Santa Fe River, baseflow to streams including the Columbia River, and extraction by public suppliers in cities such as Denver and Phoenix; hydrologists at the University of California, Berkeley and Texas A&M University model these processes using principles established in publications of the American Geophysical Union.

Water Use, Management, and Legal Framework

Groundwater from principal aquifers supports irrigation in regions such as the Imperial Valley, municipal supply for New York City and Chicago, and industrial operations in Detroit and Los Angeles County. Management frameworks combine state doctrines—like prior appropriation in Colorado and correlative rights in California—with federal statutes such as the Safe Drinking Water Act and programs administered by the Bureau of Reclamation. Regional compacts and plans by entities including the Metropolitan Water District of Southern California, the Texas Water Development Board, and the Florida Department of Environmental Protection govern allocation, while interstate litigation (for example between Kansas and Nebraska) and agreements influence transboundary aquifer use.

Environmental Issues and Contamination

Aquifers face challenges from overdraft in the Ogallala Aquifer causing land subsidence in places like Houston and saline intrusion along coasts near Miami and Galveston, and contamination from point sources such as Superfund sites administered by the Environmental Protection Agency and nonpoint sources including agricultural runoff in the Mississippi River Basin. Specific contaminants include nitrates from Midwestern United States fertilizer use, volatile organic compounds near industrial corridors such as New Jersey's Meadowlands, and emerging contaminants tracked by researchers at the Centers for Disease Control and Prevention and the National Institutes of Health. Remediation and regulation involve cleanup programs under the Resource Conservation and Recovery Act and monitored natural attenuation projects coordinated with the United States Fish and Wildlife Service where aquifer health affects wetlands like the Okefenokee Swamp.

Monitoring, Mapping, and Research Methods

Monitoring networks run by the United States Geological Survey and state agencies collect well data, water-level records, and water-quality samples; large projects include the National Water-Quality Assessment (NAWQA) program. Mapping uses geophysical methods promoted by the American Geosciences Institute and numerical modeling tools developed in academia at institutions such as Massachusetts Institute of Technology and Stanford University employing MODFLOW and other codes endorsed by the International Association of Hydrogeologists. Remote sensing from Landsat and gravity-based observations by the Gravity Recovery and Climate Experiment have been used to infer aquifer depletion in the High Plains and Central Valley, informing policy decisions by agencies like the National Oceanic and Atmospheric Administration and guiding conservation projects run by nonprofits such as the Nature Conservancy.

Category:Water resources of the United States Category:Hydrogeology