Design And Management of Salt Solution Caverns For Toxic Waste Disposal
Authors: Dusseault M.B. , Davidson B.C. 
Published: March 2010

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 (&gt;105 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.

Introduction

Disposal of Wastes

There is a need for economic disposal methods for industrial wastes, including non-toxic, toxic, as well as low-level radioactive materials. Wastes may be liquid, solid, or mixed. Some industrial wastes can be cleaned easily, other wastes can be recycled, but there remain significant volumes of wastes that do not degrade and cannot be recycled. Whether they are hazardous or not, permanent means of disposal must be found. Permanent disposal methods must meet stringent criteria:Disposed wastes should have extremely small probabilities of negative interaction with the biosphere.The disposal technology should be relatively straightforward and flexible in its capacity to handle a variety of waste materials.Procedures for transporting, handling, and disposing of wastes must be safe, meeting requirements of environmental and occupational health and safety agencies.Disposal sites must be permanent, not impair current and future surface land use, and must not require long-term permanent maintenance (e.g.: &gt; 10 years).The cost of the disposal method must allow it to operate economically.The approach for permanent disposal must be acceptable to society. (Note that acceptance comes only through clear understanding of all processes).

This article discusses a disposal technology for toxic waste designed to meet these criteria. The method uses caverns created in geologically stable salt strata; it is called SCD (Solution Cavern Disposal) for brevity. A method is described to create an "engineered waste slurry" tailored to individual wastes. Closure of the cavity and waste compaction over time will permanently entomb the toxic wastes.

In this article, use of the term "permanent" implies secure entombment for periods no less than 105 - 106 years. Current radioactive waste disposal criteria are designed to meet 10,000 (104) year security limits(1, 2), whereas present approaches to landfilling of wastes often mean groundwater contamination within decades(1,2).