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Regional Assessment of Ground-Water Quality in the Basin and Range, Rio Grande, Coastal Basins, and Central Valley Aquifer Systems of the Southwestern United States

Aquifers are an important source of ground water for many cities and agricultural communities in the arid and semiarid southwestern United States. The quality of this ground water is of concern because of the general scarcity of renewable water supplies in the region. To address this concern, the National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey is conducting a regional analysis of water quality in the principal aquifer systems (U.S. Geological Survey, 2003) in the Southwest: the Basin and Range basin-fill aquifers in Nevada, Utah, and Arizona; the Rio Grande aquifer system in New Mexico and Colorado; and the Coastal Basin aquifers and the Central Valley aquifer system in California. These principal aquifers consist primarily of unconsolidated basin-fill deposits with similar land- and water-use practices, and water-quality issues. Withdrawals from these aquifers accounted for about one-third of ground water used for irrigation in the United States in 2000 (Maupin and Barber, 2005). More than 36 million people live above these aquifers, and almost one-half of the water used for public supply in the region is ground water. Information collected by the NAWQA Program on natural contaminants in ground water, such as dissolved solids (salinity) and arsenic, and contaminants related to human activities, such as nitrate and pesticides, is available for many basins in the Southwest.

Topics selected for the assessment of water quality in the Basin and Range, Rio Grande, Coastal Basins, and Central Valley Aquifer Systems:

  • Salinity in ground and surface water – What are the sources and sinks of dissolved solids, and are concentrations changing over time? Report and findings
  • Land use effects on shallow ground water – How do differences in land use, chemical use, irrigation, and other land-management practices help explain differences in the occurrence and distribution of selected constituents? (SIR 2007-5179)
  • Water quality in the Carbonate-Rock Aquifer of the Great Basin – To what degree is this regional aquifer system affected by hydrogeologic and environmental factors? (SIR 2005-5232)
  • Factors affecting water quality in basin-fill aquifers used for drinking-water supply - What natural factors, such as geology and climate, or human factors such as land and water use, influence selected constituents in ground water used for drinking?  
  • Statistical models of factors that influence the vulnerability of aquifers to contamination – How can we quantify natural and human factors that affect the distribution of a constituent, such as nitrate in ground water, and assess where changes in water quality are likely to occur?  

Featured Publications
(View complete list)

  • Salinity in ground and surface water – What are the sources and sinks of dissolved solids, and are concentrations changing over time? Report and findings
  • Land use effects on shallow ground water – How do differences in land use, chemical use, irrigation, and other land-management practices help explain differences in the occurrence and distribution of selected constituents? (SIR 2007-5179)

General Information

Informational handout about the Basin and Range, Rio Grande, Coastal Basins, and Central Valley Aquifer Systems studies (PDF format, 1Mb)

Detailed information on the hydrogeology of the Basin and Range, Rio Grande, Coastal Basins, and Central Valley Aquifer Systems can be accessed through the USGS Ground Water Atlas of the United States

For more information, contact:
Susan Thiros, Hydrologist

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