National Brackish Groundwater Assessment: Previous Work

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Interest in the distribution and classification of brackish groundwater for use as a source of water supply has been longstanding. These studies provided valuable background for the National Brackish Groundwater Assessment.

A national compilation of data on mineralized (brackish) groundwater was completed in the 1960s (Feth and others, 1965). That study provided maps showing depth to the shallowest groundwater containing more than 1,000 mg/L of dissolved solids and chemical types of groundwater, serving as the primary source of information for subsequent assessments of the national distribution of brackish groundwater. Feth (1965b) also compiled a reference list of approximately 500 reports documenting saline groundwater conditions that "is by no means exhaustive, but it is representative of the types of information available and will serve to lead the reader into the literature." In addition, Feth (1981) and Richter and Kreitler (1991) summarized various models and mechanisms used to explain the spatial and temporal variability of dissolved solids in groundwater. Feth (1981) provided a national synthesis of chloride in natural waters, noting that the ratio of various other anions to chloride can be used to identify the source of brackish groundwater. Richter and Kreitler (1991) supplemented work by Feth and others (1965) with a map by Dunrud and Nevins (1981) showing the approximate extent of halite (sodium chloride salt) deposits, mapped locations of oil fields, estimates of the extent of seawater intrusion to coastal aquifers, and mapped saline springs and seeps to identify areas where brackish groundwater naturally occurs. Richter and Kreitler (1991) also provided a state-by-state summary of the occurrence of each source of groundwater salinization.

USGS Regional Aquifer-System Analysis (RASA) studies were conducted between 1978 and 1995 to define the regional geohydrology of the Nation's important aquifer systems. Maps showing dissolved-solids concentrations were published for many of these aquifer systems and compiled for the USGS Ground Water Atlas of the United States. In some cases, regional RASA studies included geochemical characterization and modeling, which assisted with understanding, interpolating, and extrapolating brackish water occurrence (for example, Busby and others, 1995).

Map of aquifer systems along the LA and TX coasts. Highest dissolved-solids located offshore of the Mississippi River delta.

Distribution of dissolved-solids concentrations and temperature in groundwater of the Gulf Coast Aquifer Systems, south-central U.S. Source: U.S. Geological Survey Water-Resources Investigations Report 88-4082, plate 5.

More recently, Androwski and others (2011) used previously published USGS reports to conduct a national assessment of the total volume of the saline (dissolved-solids concentration between 1,000 and 35,000 mg/L) component of the principal aquifers of the conterminous United States that could be available for desalination. The primary sources of dissolved-solids and aquifer-dimension information for that study were digital maps from the USGS Ground Water Atlas of the United States. No recently collected dissolved-solids data were used for the study, and depths to saline groundwater were estimated using simplistic assumptions and methods.

 

Examples of Regional Assessments of Brackish Aquifers

  • The USGS completed three pilot studies that use geochemical, geophysical, and geostatistical methods and previously published work to describe saline aquifers for the southern midcontinent, Mississippi embayment, and the southeastern United States. These "Challenge Area" studies were conducted from 2010 through 2012 to supplement the Groundwater Resources Program's freshwater regional groundwater availability assessments already underway in order to achieve a more complete picture of the Nation's groundwater availability.
  • Sandia National Laboratories assessed the relative availability and cost of using shallow (less than 2,500 feet (ft) below land surface) brackish groundwater as a water source for thermoelectric power generation in 17 western states (Tidwell and others, 2013). Sources of information for estimating the availability of brackish groundwater include volumetric estimates of brackish groundwater in Texas and Arizona, USGS water use information (Kenny and others, 2009), and data for wells in the USGS National Water Information System that contain brackish groundwater.
  • The Texas Water Development board is conducting the Brackish Resources Aquifer Characterization System (BRACS) study to provide a detailed characterization of brackish aquifers in Texas using geophysical bore-hole logs and available aquifer data.