Importance, Distribution, and Character of the Nation's Brackish Groundwater Resources

Nontraditional groundwater sources, such as moderately saline (brackish) groundwater, are increasingly being used for drinking water, oil and gas extraction, power generation, and other uses to supplement or replace the use of freshwater. This demand is likely to grow as fresh groundwater resources continue to decline. Demand could grow especially rapidly in some parts of the country where climate changes result in hotter and drier conditions. Despite the current and future need for alternative water supplies, brackish groundwater was last assessed at the national scale almost 50 years ago. Since that study, substantially more hydrologic and chemical data have been collected that can be used to improve the understanding of brackish waters.

The U.S. Geological Survey is reassessing the alternative water supply potential of significant brackish groundwater resources. Preliminary results indicate that almost one third (2.2 million km²) of the continental United States is underlain by brackish groundwater (dissolved-solids concentration between 1,000 and 10,000 mg/L) within the uppermost 3,000 ft of the land surface. This evaluation is likely an underestimate of the total resource because available data for mapping the distribution of brackish groundwater are scarce in some areas, especially for depths greater than 500 ft below land surface where brackish groundwater is more likely to occur. Most of the known brackish groundwater is within in the Western Mid-Continent region. Other significant reserves of brackish groundwater largely are found in the Atlantic and Gulf Coastal Plain, Eastern Mid-Continent, and Southwest Basins regions. The ability of brackish aquifers to produce at least 100 gal/min of water was greatest in the Southwest Basins (80 percent of wells) and least in the Western Mid-Continent region (8 percent of wells).