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State geologists and engineers brief Senate on brackish-water resources and desalination options
Summary
Experts from New Mexico Tech's Bureau of Geology and Jacobs Engineering told the Senate conservation committee that brackish groundwater exists across New Mexico in many basins; they outlined the steps required to evaluate supplies and the common reverse-osmosis treatment and disposal approaches used in municipal projects.
Stacy Timmons, Associate Director for Hydrogeology Programs at the New Mexico Bureau of Geology and Mineral Resources (New Mexico Tech), and Robert Fowley of Jacobs Engineering briefed the Senate conservation committee on the state's brackish-water resources and the technical steps required to consider desalination projects.
Timmons defined brackish water as groundwater typically above about 1,000 milligrams per liter total dissolved solids (TDS) and described statewide data-collection work the bureau has compiled. "Brackish water is water that's a little saltier than fresh," Timmons said, and she noted regional variation in chemistry: some basins have primarily sodium chloride salts while others are dominated by calcium sulfate. The bureau has compiled roughly 2,800 well samples with brackish water across New Mexico and identified basins where brackish resources are likely—including the Albuquerque, San Juan, Roswell, Capitan Reef, Estancia, Mesilla and Tularosa basins.
Timmons said site-by-site investigations are required before pursuing treatment: exploratory drilling, geophysics, aquifer testing, hydraulic testing and modeling. She emphasized that work supported with state funds should provide data back to state repositories under current water-data rules.
Robert Fowley described common municipal-scale treatment approaches and concentrate disposal options based on his work on the Alamogordo desalination plant and El Paso projects. "Treatment of brackish water ... is using reverse osmosis," Fowley said. He explained that reverse osmosis produces a low-TDS permeate stream and a concentrated waste stream (concentrate) that has three common disposal paths: evaporation ponds, deep-well injection and, in some cases, sanitary-sewer disposal where permitted. He described pilot testing requirements, typical recovery rates (roughly 80 percent permeate as a rule of thumb), and energy and cost considerations. Fowley estimated construction costs for a municipal-scale RO plant (historical figures) and noted Alamogordo's 1-million-gallon-per-day plant had used local elevation to reduce pumping energy needs.
Senators asked about constituent-specific issues such as radionuclides and oilfield contaminants, treatment recoveries for high-TDS sources, depth of wells in the Tularosa basin (many domestic wells sampled were shallower than 400 feet; the Alamogordo brackish well field included wells deeper than 1,000 feet), and permitting roles for the New Mexico Environment Department and the Office of the State Engineer. The presenters stressed careful site characterization and pilot testing prior to any full-scale plant, and they said disposal method selection depends on local hydrogeology and reuse opportunities.
Ending: Presenters told senators that brackish-water desalination is a proven option at municipal scale but requires detailed study, pilot testing and careful planning for concentrate disposal. The briefing was presented as preparatory material ahead of water-supply legislation that committee members expected to consider later in the week.
