Design and management of salt solution caverns for toxic waste disposal

Disposal of low-level radioactive and toxic industrial wastes in dissolved caverns in salt deposits represents a safe, practical and economically feasible alternative to current waste management practices. Disposal in solutioned caverns in salt strata can provide environmental security over geologic time (> 10(5) yr) because salt caverns will slowly close onto the solid wastes, isolating them from the formation fluid flow systems. Because this method is permanent (non-retrievable), ensuring the long-term isolation of the wastes from biosphere interaction is fundamental to this technology. Permanent secure isolation can be achieved by choosing appropriate disposal sites, and by properly engineering a waste slurry which will compact over time when subjected to the stresses of a closing cavern. This article discusses engineered waste slurries designed to address the toxicity level of candidate waste materials. Issues related to site selection criteria,site investigation techniques, and decommissioning strategies are also discussed. Some experimental results showing how porosity reduction occurs in compacting slurries is presented. Salt cavern disposal is technically founded on petroleum engineering, geology, hydrogeology, rock mechanics and geochemistry. Suitable salt deposits are almost always found in sedimentary basins where petroleum development exists; therefore, salt cavern disposal for toxic oil field wastes is a natural application.