Brackish Groundwater as a Resource for the Nation

The U.S. Geological Survey has conducted a national assessment to gain a better understanding of the occurrence and distribution of brackish groundwater (BGW)(dissolved-solids concentration between 1,000 and 10,000 mg/L) as well as the geochemical and hydrogeologic characteristics of the resource. A conservative estimate for the volume of BGW for depths up to 3,000 ft below the land surface is more than 900 times the amount of saline groundwater (dissolved-solids concentration greater than 1,000 mg/L) currently used each year, and more than 40 times the amount of fresh groundwater (dissolved-solids concentration less than 1,000 mg/L) used. Compiled data indicated that in regions with the most BGW, many of the sampled wells that produce BGW have reported well yields that are at least 10 gal/min, with arid southwestern U.S. basins commonly providing yields of at least 100 or 1,000 gal/min. Consequently, BGW may be a substantial water resource available for potential use by the Nation, but further evaluation is needed to determine the sustainability of BGW development.

Brackish groundwaters were evaluated chemically to assess possible uses. Frequently, chemical constituents such as arsenic, barium, boron, fluoride, iron, nitrate, selenium, or uranium in untreated BGW exceed standards for drinking water, livestock or irrigation use; however, treatment may render the BGW usable, or the BGW may be suitable for use in energy development and industrial processes. Only 5 percent of the wells producing water with a dissolved-solids concentration of 1,000 mg/L or more exceeded a Langelier-Saturation Index (LSI) of 1 (increased scaling potential), and only 2 percent of samples had a LSI less than -1 (increased corrosion potential). The potential for BGW to form mineral deposits (scale) also was evaluated using PHREEQC software. Some minerals identified as potential scaling components include calcite, barite, and chalcedony (quartz), which vary depending on the source of the water.