Computed solid phases limiting the concentration of dissolved constituents in basalt aquifers of the Columbia Plateau in eastern Washington. Geochemical modeling and nuclide/rock/groundwater interaction studies
A speciation-solubility geochemical model, WATEQ2, was used to analyze geographically-diverse, ground-water samples from the aquifers of the Columbia Plateau basalts in eastern Washington. The ground-water samples compute to be at equilibrium with calcite, which provides both a solubility control for dissolved calcium and a pH buffer. Amorphic ferric hydroxide, Fe(OH)/sub 3/(A), is at saturation or modestly oversaturated in the few water samples with measured redox potentials. Most of the ground-water samples compute to be at equilibrium with amorphic silica (glass) and wairakite, a zeolite, and are saturated to oversaturated with respect to allophane, an amorphic aluminosilicate. The water samples are saturated to undersaturated with halloysite, a clay, and are variably oversaturated with regard to other secondary clay minerals. Equilibrium between the ground water and amorphic silica presumably results from the dissolution of the glassy matrix of the basalt. The oversaturation of the clay minerals other than halloysite indicates that their rate of formation lags the dissolution rate of the basaltic glass. The modeling results indicate that metastable amorphic solids limit the concentration of dissolved silicon and suggest the same possibility for aluminum and iron, and that the processes of dissolution of basaltic glass and formation of metastable secondary minerals are continuing even though the basalts are of Miocene age. The computed solubility relations are found to agree with the known assemblages of alteration minerals in the basalt fractures and vesicles. Because the chemical reactivity of the bedrock will influence the transport of solutes in ground water, the observed solubility equilibria are important factors with regard to chemical-retention processes associated with the possible migration of nuclear waste stored in the earth's crust.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 5057161
- Report Number(s):
- PNL-4089; ON: DE82021962
- Country of Publication:
- United States
- Language:
- English
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58 GEOSCIENCES
BASALT
MATHEMATICAL MODELS
SOLUBILITY
GROUND WATER
GEOCHEMISTRY
RADIOACTIVE WASTE DISPOSAL
AMORPHOUS STATE
CALCITE
CLAYS
COLUMBIA RIVER
EQUILIBRIUM
HYDROLOGY
IRON HYDROXIDES
SILICA
UNDERGROUND DISPOSAL
WASHINGTON
ZEOLITES
ALKALINE EARTH METAL COMPOUNDS
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
CHALCOGENIDES
CHEMISTRY
FEDERAL REGION X
HYDROGEN COMPOUNDS
HYDROXIDES
IGNEOUS ROCKS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
IRON COMPOUNDS
MANAGEMENT
MATERIALS
MINERALS
NORTH AMERICA
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
RIVERS
ROCKS
SILICON COMPOUNDS
SILICON OXIDES
STREAMS
SURFACE WATERS
TRANSITION ELEMENT COMPOUNDS
USA
VOLCANIC ROCKS
WASTE DISPOSAL
WASTE MANAGEMENT
WATER
052002* - Nuclear Fuels- Waste Disposal & Storage
580400 - Geochemistry- (-1989)