title: Chemical Considerations for an Updated National Assessment of Brackish Groundwater Resources.
abstract: Brackish groundwater (BGW) is increasingly used for water supplies where fresh water is scarce, but the distribution and availability of such resources have not been characterized at the national scale in the United States since the 1960s. Apart from its distribution and accessibility, BGW usability is a function of the chemical requirements of the intended use, chemical characteristics of the resource, and treatment options to make the resource compatible with the use. Here, we discuss relations between these three chemical factors using national-scale examples and local case studies. In a preliminary compilation of BGW data in the United States, five water types accounted for the major-ion composition of 70% of samples. PHREEQC calculations indicate that 57-77% of samples were oversaturated with respect to barite, calcite, or chalcedony. In the study, 5-14% of samples had concentrations of arsenic, fluoride, nitrate, or uranium that exceeded drinking-water standards. In case studies of the potential use of BGW for drinking water, irrigation, and hydraulic fracturing, PHREEQC simulations of a hypothetical treatment process resembling reverse osmosis (RO) showed that BGW had the potential to form various assemblages of mineral deposits (scale) during treatment that could adversely affect RO membranes. Speciation calculations showed that most boron in the irrigation example occurred as boric acid, which has relatively low removal efficiency by RO. Results of this preliminary study indicate that effective national or regional assessments of BGW resources should include geochemical characterizations that are guided in part by specific use and treatment requirements.
authors: P B
authors: PB
authors: McMahon
authors: U.S. Geological Survey, 12201 Sunrise Valley Dr., 431 National Center, Reston, VA, 20192.
authors: J K
authors: JK
authors: Böhlke
authors: Bureau of Reclamation, Denver Federal Center, Bldg. 67, Room 318, Denver, CO, 80225.
authors: K G
authors: KG
authors: Dahm
authors: U.S. Geological Survey, Denver Federal Center, Bldg. 53, Room G2226, Denver, CO, 80225.
authors: D L
authors: DL
authors: Parkhurst
authors: U.S. Geological Survey, 2255 North Gemini Drive, Flagstaff, AZ, 86001.
authors: D W
authors: DW
authors: Anning
authors: U.S. Geological Survey, 5231 South 19th Street, Lincoln, NE, 68512.
authors: J S
authors: JS
authors: Stanton
mesh_terms: D001151:Arsenic; D005618:Fresh Water; D060587:Groundwater; D014874:Water Pollutants, Chemical; D014881:Water Supply
chemical_list: D014874:Water Pollutants, Chemical; D001151:Arsenic