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 feas ible alternative to current waste management practices. Disposal in solutio ned caverns in salt strata can provide environmental security over geologic time (> 10(5) yr) because salt caverns will slowly close onto the solid wa stes, isolating them from the formation fluid flow systems. Because this me thod is permanent (non-retrievable), ensuring the long-term isolation of th e wastes from biosphere interaction is fundamental to this technology. Perm anent secure isolation can be achieved by choosing appropriate disposal sit es, 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 to xicity 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 o ccurs in compacting slurries is presented. Salt cavern disposal is technica lly founded on petroleum engineering, geology, hydrogeology, rock mechanics and geochemistry. Suitable salt deposits are almost always found in sedime ntary basins where petroleum development exists; therefore, salt cavern dis posal for toxic oil field wastes is a natural application.