The distribution of trace water around brine leaks in the avery island salt mine: Implications for the natural migration of water in salt

Abstract

The natural distribution of water in the Avery Island domal salt has been investigated by performing trace water content analysis on 64 samples collected systematically at the 210 and 270 meter levels of the International Salt Compan mine. Specific attention was given to salt near an internal shear zone which is the apparent source of several mine leaks. No discernible migration of brine into the adjacent salt was observed from the meteoric leak at the 210 m level. Extensive water enrichment (>1000 mg/kg) was limited to 30 meters from the formation water leak at the 270 m level. The water contents of coexisting samples near the formation water leak are highly variable. If water is moving from; this leak into the adjacent normal salt it is not doing so by way of a uniform diffusion process. Petrographic examination of polished salt samples reveals that fluid inclusions occur mainly in healed fractures. The water content of a sample depends on the density of such fractures. Natural movement of water in the salt appears to occur mainly through microfractures and possibly along crystal boundaries rather than by the diffusion of brine through crystals. One possible zone of enhanced water content may occur along a possible bedding plane which intersects a mine leak. This suggests that any natural movement of fluid not associated with fractured salt may occur preferentially along bedding planes. The method of brine migration under natural conditions, the occurrence of fluid inclusions (i.e., fracture vs. nonfracture-fill inclusions), and the water content of salt will be helpful in evaluating the migration of brine in response to the thermal and/or pressure gradient which will be created by the emplacement of radioactive waste.