U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993, Water-Resources Investigations Report 94-4015

Potential Anhydrite Precipitation Associated With Deep Injection of Ground-Water Brine from Paradox Valley, Colorado

Abstract

Seepage and discharge of ground-water brine into the Dolores River in Paradox Valley, a collapsed diapiric salt anticline located in southwestern Colorado, increase the dissolved-solids load of the Colorado River annually by about 2.0 x 10⁸ kilograms. In order to abate this natural contamination, the U.S. Bureau of Reclamation plans to pump about 3,540 cubic meters per day of brine from 12 shallow wells located along the Dolores River. The brine, with a salinity of 250,000 mg/L, will be piped to the deepest (4.88 kilometers) injection well in the world, and injected mainly into the Mississippian Leadville Limestone.

Results of geochemical modeling indicate and water-rock experiments confirm that a huge mass of anhydrite, about 10,000 kilograms per day, likely will precipitate from this brine when heated to 120 °C at 500 bar--the temperature and pressure conditions in the Leadville aquifer. Precipitation of anhydrite could increase by a factor of two or more if the injected brine were allowed to mix with the highly incompatible formation water of the Leadville aquifer and if, as expected, the Mg in this brine dolomitizes the calcite of the aquifer. Dilution of the brine with river water, precipitation of its SO₄ and/or addition of precipitation inhibitors prior to injection are possible remedial actions.