Abstract Placement of solid wastes in dissolved caverns in salt is increasingly being viewed as an environmentally secure technology for low-toxicity wastes such as foundry sands (heavy metals), contaminated soil and other granular solid waste streams. Costs of salt cavern disposal probably eliminates their use for large volumes of non-toxic wastes, but permanent entombment of toxic materials in salt caverns is economically competitive to other alternative disposal or storage approaches. Salt caverns in Alberta and Saskatchewan at depths of 1,200-1,500 m are being used for disposal of non-toxic materials (non-hazardous oilfield wastes) and for storage of natural gas and liquids (propane, glycol, etc.). Low to medium toxicity oilfield wastes can be economically and securely placed in salt solution caverns using an engineered slurry approach. Effective cavern disposal requires a design and monitoring strategy to optimize cavern utilization and to demonstrate environmental security for waste containment. This article is conceptual in nature; however, its conclusions and observations are based firmly on extensive laboratory, field, and modeling experience in salt rocks, applied to caverns and to underground mines. P. 239

Abstract Slurry fracture injection (SFI) involves placement of solid wastes and water wider fracture pressures into deep geological formations. Currently, materials permitted for SFI include oily waste sand, "slops", produced muds, and produced water or waste water. Five years field experience has led to a good understanding of the SFI technology, and a regulatory frame- work is evolving in Alberta to permit SFI projects to proceed in an environmentally secure manner to meet the goals of the regulatory bodies as well as the goals of the oil companies. The approach to SFI operations is described, including geological arguments related to environmental security. Security is also based on careful regulatory control, design, site selection, and analysis. The application of SFI to other waste streams should help mitigate environmental issues for heavy oil development, as well as for other oil feld applications. P. 87

Abstract Massive injection of slurried solid waste generates permanent strains and displacements. These can be measured and analyzed to give useful information related to the shape and orientation of the injected body, and therefore lead to a monitoring approach based on accurate surface measurements of vertical movements or tilt We discuss waste emplacement, present information showing the magnitudes of the final deformations, and show how some displacement field features are sensitive to certain parameters, whereas others are insensitive. Tilt measurements continuously through time give the best possibility of accurate monitoring of the waste body. 1 INTRODUCTION Permanent disposal of terminal solid wastes can be achieved through landfilling, ocean dumping, mine placement, injection or placement into solution caverns in salt, or by subsurface fracture injection of a slurry of water and granulated waste. The latter approach has been used for disposal of drilling wastes comprising used mud, rock chips and cavings (Willson et al ., 1992), as well as sand co-produced with heavy oil (Dusseault and Bilak, 1993). Slurry injection of wastes is in many ways analogous to the geological emplacement of dykes and sills (pollard, 1987), cement slurry grouting under hydraulic structures such as dams (USDI, 1974), and hydraulic fracturing in the oil industry (Howard and Fast, 1970). Injection of wastes requires monitoring to insure containment, to give some idea of the shape and extent of the injected body, for assessment of surface displacements, for quality control during the process, and for legal protection and regulatory control. If the orientation of the injected waste body is dominantly vertical, does it pass through strata that otherwise would serve as seals to flow? Is the solid material confined to the near wellbore vicinity, or does it travel considerable distances as a slurry before the water content drops to the point where the waste is immobilized? Whatever reasonable assumptions are made as to confinement or shape, monitoring data are required to confirm the assumptions and to collect information over the time-history of waste injection. The injection well itself can be used for pressure build-up and decay tests, which, if the permeability and compressibility of the injected material is much different that the host rock, will yield highly averaged information about the waste zone transport properties, from which indirect deductions about orientation and shape may be possible. Special monitoring wells can be installed, but these give only punctual data, are useful only for a limited time, and for deep waste injection operations, monitoring wells are costly. ther wellbore methods such as geophysical logs or tracer tests are too local, subject to interpretative non-uniqueness, and are generally costly. High-resolution seismic 3-D surveys, repeated and suitably analyzed, give spatial evolution of seismic wave parameters (velocities, amplitudes, attenuations). These approaches are powerful if an accurate velocity model exists, and "time-slices" from successive survey periods will show changes as the body of immobilized. injected solids grows. Disadvantages are related to 3-D seismic survey costs, analysis time, interpretive models, and limited spatial resolution. Altered seismic properties must be related to the presence of the body using some assumptions, and the fact that local stresses are changing at the same time may cause interpretive difficulties. Microseismic methods using passive monitoring of emitted acoustic signals could be useful, but the technique must be further developed for systematic use as a monitoring tool for slurry waste injection. Perhaps after several field trials, these methods will become cheaper and more suitable.

Abstract Granular salt can be used to construct high performance permanent seals in boreholes which penetrate rock salt formations. These seals are described as seal systems comprised of the host rock, the seal material. and the seal rock Interface. The performance of these seal systems is defined by the complex interactions between these seal system components through time. The interactions are largely driven by the creep of the host formation applying boundary stress on the seal forcing consolidation of the granular salt. The permeability of well constructed granular salt seal systems is expected to approach the host rock permeability (<10 -21 m 2 (10 -9 darcy)) with time. The immediate permeability of these seals is dependent on the emplaced density. Laboratory test results such that careful emplacement techniques could result in immediate seal system permeability on the order of 10 -16 m 2 to 10 -18 m 2 (10 -4 darcy to 10 -6 darcy). The visco-plastic behavior of the host rock coupled with the granular salts ability to "heal" or consolidate make granular salt an ideal sealing material for boreholes whose permanent sealing is required. INTRODUCTION Effective sealing of penetrations (boreholes) in geologic materials is becoming increasingly important as it is recognized that groundwater resources need to be protected from potential contamination. Boreholes are drilled for a myriad of purposes including oil and gas production, water production, monitoring, site characterization, mineral exploration, and waste disposal. These boreholes penetrate all geologic environments and range in depth from very shallow to depths of up to several kilometers. In the undisturbed geologic system, potential contaminants are separated from freshwater aquifers by low permeability aquitards. Improper plugging, sealing, or abandonment of boreholes which penetrate aquitards can allow the borehole to act as a conduit between the contaminated and freshwater regions. The real or perceived failure of these seal systems to isolate contaminants from groundwater supplies can result in costly litigation and remediation, loss of public confidence and support, and destruction of groundwater resources. Borehole seal performance has been recognized as a potential environmental concern by numerous researchers (USEPA, 1987; National Research Council, 1985). Typical well abandonment requirements and practice include sealing of any water-producing zones by the use of cements. Open-hole cementing is typically done to plug abandoned wells, to assist in directional or follow-on drilling, to minimize or restrict lost circulation, or for isolation of specific zones in the borehole to restrict water inflow. Secondary pressure grouting may also be used to reduce the permeability of the surrounding host rock. High density drilling muds are also used in abandonment of oil and gas wells. Typical tests to assure borehole seal quality include a complete review of well construction data as well as Mechanical Integrity Tests (MITs) such as pressure tests of the seal system as a check for cracks and leaks in the casing and seal/rock interface. These tests are conducted at the top of the plug and are intended to assure immediate performance. The nature of the seal system construction (placement across production and freshwater zones) and test techniques (pressure tests at the top of the seal) suggest that this standard practice may not identify seal problems until performance is compromised because the test techniques may only sample a small part of the seal. Well founded concerns that such conventional cementitious seals will degrade with time or will otherwise be difficult or impossible to demonstrate permanent performance have led workers in radioactive waste disposal programs in the United States and elsewhere to develop new approaches to, and technology for the emplacement of truly permanent seals. or particular interest here is the approach being taken toward sealing of penetrations in bedded and domal salt formations. Native material (i.e., previously mined-out, granular salt) has been selected as the primary long-term component in these programs, in large part because of its natural compatibility with the host rocks. The experience acquired in evaluating seal materials and systems, necessitated by the requirement to ensure seal integrity and public safety over perhaps thousands of years has led the authors to develop new approaches to sealing boreholes through rock salt.

Abstract Geotechnical safety for a cavity field will be assessed on the basis of model computations. The statistical uncertainty of rock salt parameters as well as possible variations in the dimensions of a cavity field under design result in the necessity to carry out a parametric study. The purpose of the paper is to explain probabilistic modeling with respect to structural response computations, using sensitivity and uncertainty analysis. Probabilistic finite element computations have been carried out for a hexagonal cavity configuration, The results are discussed with respect to the variability of the following parameters and their interrelation: diameter, spacing, depth and height of the cavities, creep of the salt rock, and stiffness of the overburden. Introduction Salt deposits are being used not only as a source of minerals but increasingly also for the storage of primary energy reserves and for the permanent disposal of hazardous wastes. According to the favourable geomechanical properties of halite, namely steady state creep behavior, which allows the salt to close and to heal up any fissures or open gaps, a rock salt formation is functioning as a tight barrier. Moreover, rock salt allows the construction of large cavities without any particular support. However, the proper design of cavities for the different purposes requires: site specific investigations with respect to geological features, planning and determining the most favourable geometrical dimensions of the cavity configuration, e.g. diameter, spacing, height and depth. Besides that, the design of the cavities may demand for particular considerations for the different live stages concerning construction, operation and abandonment. The utilisation of salt cavities for the purpose of isolating hazardous wastes against the biosphere necessitates safety assessment with respect to long-term integrity of the host rock. P. 761