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
by
Yousif K. Kharaka (U.S. Geological Survey; Menlo Park, Calif.),
William C. Evans (U.S. Geological Survey; Menlo Park, Calif.), Gil Ambats
(U.S. Geological Survey; Menlo Park, Calif.), and James J. Thordsen (U.S.
Geological Survey; Menlo Park, Calif.)
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.
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