CRYOCELL is currently the only known containment technology able to fully isolate and contain a hazardous waste site. Among CRYOCELL's features . . .
CRYOCELL effectively isolates and contains virtually all types of in-situ waste sites which are subject to underground contamination or have underground contamination such as:
All types of Chemical, Biological and Radioactive Wastes. CRYOCELL provides long-term hermetic enclosure for low-level and high-level rad wastes, TRU (transuranic), and mixed wastes.
Radioactive heat can increase the cost of maintaining frozen soil barriers. Any radioactive heat source in close proximity to a barrier would increase the cost by an estimated $3,000 per year per megacurie. Radioactivity in typical waste sites is dispersed rather than locally concentrated, there is no fundamental problem to maintain the ice against heat generation. Furthermore, where design permits, CRYOCELL is located away from the heat source, effectively eliminating this concern.
Deuterated and tritiated water, being isotopic variants of ordinary H2O, are completely soluble in ordinary ice, eliminating the solubility factor. However, the remaining factors provide sufficiently great impedance so that expected diffusion time for T2O through a CRYOCELL barrier is many times its half life (12 years). The solubility factor is present for all tritiated compounds other than T2O. (Please refer to the appendix for a discussion of CRYOCELL containment of TCE.)
Frozen soil barriers are highly effective against molecular diffusion due to the following factors:
For a brief discussion of molecular diffusion as specifically related to frozen soil barriers, please refer to the appendix. The scientific basis for determining molecular diffusion through frozen soil barriers is presented in Dash, J.G., "Ice Technology for Hazardous Waste Management," Waste Management, Vol. 11 No. 4, January 1991, pages 183-189.
In the case of extremely dry soils, moisture can be supplemented. Soil moisture of 14% to 18% is considered optimum under most site conditions and most sites have sufficient soil moisture content to meet this criteria. If any porosity remains in the barrier, it is sealed by moisture drawn into the barrier from the surrounding soil or from local aquifers or water sources. (Please refer to the appendix for a discussion of the moisture addition technique.)
No. CRYOCELL is frozen slowly in order to draw only pure water into the barrier. This process occurs in nature when pure water ice is formed in a salt water environment. The slow freezing action excludes all contaminants, confining them inside the barrier.
Maintenance costs for a 10-acre site with a stabilized barrier under "favorable" soil conditions can range from $2,000 to $4,000 per month. Once the CRYOCELL system is in place there is only scheduled maintenance required.
Not at all. One of the advantages of CRYOCELL containment is that it allows time for land use decisions and all other site closure steps to be properly initiated while ensuring the health and safety of on-site personnel and minimizing or precluding off-site releases of contaminants during remediation activities. Furthermore, CRYOCELL is compatible with all forms of remediation including cryogenic remediation technologies, soil washing, pump and treat systems, vacuum extraction, ionic extraction, solvent extraction, bioremediation, incineration, in-situ and other vitrification technologies, and excavation. Since CRYOCELL provides economical containment for indefinitely long periods, it provides time for implementation of proven remediation technologies or can allow for developmental research to improve the cost-effectiveness of the chosen clean-up method.
Due to CRYOCELL barrier wall thickness and the tremendous insulation properties of soil, established barriers are able to "coast" without power for more than two years before there is any danger to the barrier's integrity.
Ground freezing was specifically developed as a civil engineering dewatering and soil stabilization technique to address structural or water incursion problems in unconsolidated soils. Heterogeneous soil types (i.e., rocks, boulders, gravel and sand), uncontrollable subsurface water flow, or other undesirable soil conditions (layers of different soil types, i.e., a weak layer) are all overcome by a properly designed and effective frozen soil barrier.
Moisture content of the soil is a key factor in design of the design of the freeze plant and ground influencing equipment. Ground freezing is routinely used in civil engineering in the vadose zone, extending several hundred (or several thousand) feet below the water table. The level of soil moisture does not materially impact barrier formation. The low barrier core temperature causes moisture present in the soil to rapidly freeze while water from adjacent soil volume is drawn toward and made part of the barrier.
As an example, power cost for barrier formation in soil with 36% moisture content will be approximately 9% higher in the initial freeze-down period than soil with a 16% moisture content. This added electrical power is necessary to freeze the additional water volume in the soil and is calculated according to well-established thermal principals.
Once the barrier is fully formed and stabilized, maintenance costs are materially unaffected by higher soil moisture content.
CRYOCELL barriers maintain a core temperature of -30°C to -37°C to assure that all pore water, including interfacial films (latent water), is frozen. Some unfrozen water may persist in certain soil types at temperatures as low as -30°C, however, the design temperature of CRYOCELL is safely below the freezing point of all common brines. (Please refer to Moisture Addition Methodology in the Appendix.)
There is no intrinsic limit to a CRYOCELL working lifespan. There are no underground moving parts. If corrosion or earth movement cause failure of an underground pipe, it can be replaced. Corrosion does not pose a serious problem at a typical site. Also, certain brines used in ground freezing projects have anti-corrosive properties and inhibit degradation of soil influencing equipment. Repairs and on-going maintenance can be performed in-situ and these repairs are accomplished in a fully isolated, contained and stabilized environment.
CRYOCELL has the highest earthquake resistance known. CRYOCELL barriers are self-healing-in cases of shear fracture, sintering will occur naturally to reseal the edges. If earth movement causes an open fracture, the barrier can be repaired by introducing additional moisture to any damaged area and preferentially refreezing the affected area.
No. Only benign brines, i.e., salt water, aqueous ammonia, propylene glycol are used in CRYOCELL refrigeration systems. In emergency response situations that demand rapid response, LN2 may be used.
Molecular diffusion is a process in which solutes migrate through a host material without involving flow of the host. The rate of transport involves several factors: the inherent properties of the material and the solute, the porosity of the host, the concentration gradient, the temperature, and the thickness of material. There are three possible routes for molecular migration through frozen ground: in increasing importance, they are bulk diffusion through crystalline ice, vapor transport, and surface transport. Fundamental and applied studies of diffusion have been carried on for many years, and a substantial literature has been developed.
Bulk Diffusion through Crystalline Ice: The diffusion constants in bulk ice of light impurity molecules such as NaCL and HNO3 at -15° C are in the range of 4 x 10-9 cm2 per second; based on this, the diffusion through a 5m thick section of ice would yield a concentration ratio of C/C0 < 10-21 in 104 years. The diffusion constants of heavier ions and molecules are smaller still.
Vapor Transport: : Gases and volatile impurities may migrate through the pore spaces of partially saturated soil. Factors affecting the rate include the fineness of the soil, the dependence of vapor pressure on temperature, adsorption on soil grains, and the connectivity of the pore spaces. The vapor pressure of all volatile substances decreases at lower temperature, most strongly in materials of relatively low volatility. Even more important than the lowering of vapor pressure is the adsorption on solid substrates. Adsorption tends to bind all liquids and vapors to exposed surfaces, with greater permanence as temperature is lowered. The vapor pressure of the adsorbed material is typically lower than that of the pure liquid, and its decrease with temperature is typically stronger. The amount adsorbed depends on the fineness of the soil, i.e., the surface area available for adsorption. The gas phase transport process is interrupted through repeated adsorption and desorption, which slows the rate enormously due to the dwell time in the adsorbed state. Surface Transport can take place through surface films adsorbed on the soil grains and through the interfacial films between ice and the soil particles. In the case of relatively dry frozen soils, where major fractions of the pore spaces are free of ice, the former may dominate; where the pore spaces are nearly filled, the latter will be more important. The rate depends on the materials, the temperature, and the thickness and connectivity of the film. Lowered temperature reduces the rate, as does reduced thickness; both are coupled in the case of the ice-soil grain films. A fundamental difference between ice in bulk and ice in frozen ground exists at the ice-soil grain interfaces, where unfrozen water can persist well below the normal freezing point. Observations in natural soils and in powders show that a thin liquid film can remain in stable equilibrium, down to temperatures as low as -40° C. Impurity solubilities and diffusion constants in these unfrozen films are comparable to their values in bulk water. The film thickness decreases sharply as temperature falls below the bulk melting point; this and the intrinsic decrease of diffusion constants produces a very strong drop in diffusion rate at lower temperature. A calculation of transport by this mechanism in a 15 meter barrier of saturated moderately fine grained soil at -15° C estimated C/Co < 10-16 in 104 years.
In the hypothetical case of an underground tank leaking a plume of pure TCE into dry soil, a cryogenic barrier situated within the moisture-free TCE region would have to be maintained at a temperature below its freezing point, -73°C. This could be accomplished by the use of liquid nitrogen as refrigerant. This technically possible remedy is unnecessarily expensive to install and maintain; furthermore, the case is an extremely unlikely one. Several factors combine to provide much more efficient designs.
To contain a plume of TCE or any other liquid, a barrier would normally be situated outside the plume, not within it. In typical situations the soil contains a sufficient amount of moisture for a hermetic and efficient frozen soil barrier at -30°C against all fluids, including those with low freezing points. The soil need not be initially water-saturated at the location of the surrounding region by the temperature gradient. If the leakage is not pure TCE, but a contaminant in water solution, the plume itself will supply all the water necessary to stop the migration. If the plume is pure TCE in very dry soil, then a -30° C barrier outside the plume could be constructed by freezing the outer layer of refrigeration pipes, injecting sufficient water to saturate the adjacent soil, and then freezing the inner layer of pipes. This procedure is detailed in the CRYOCELL patent.
By design, a CRYOCELL barrier maintains a core temperature of -35ūC. By maintaining this core temperature throughout a design thickness of 10' to 45', a "vapor trap" is formed which will stop movement of organic and other soil vapors. Moisture present in the soil, from distances of as far as 1,000', will be drawn to the cold region. This adds moisture, which becomes ice, strengthening the barrier against waste migration. If contaminants are water-borne, water within the contaminant plume will become part of the barrier while excluding contaminants from the developing ice crystals. This has the effect of concentrating the contaminants inside the forming barrier, which is desirable for removal or treatment purposes. Should soil moisture need to be adjusted, moisture addition pipes (perforated well casings) are typically installed in the area between the double wall of freeze pipes and serve several purposes. Initially, if the soil lacks sufficient moisture to form an effective barrier, the moisture addition pipes are used to add water or steam to the soil to increase moisture content. In order to eliminate the possibility of migration due to moisture addition, the outer freeze pipes are activated first in order to form a frozen barrier to totally enclose the site. Only after the site has been enclosed is moisture added (if required) by means of the moisture addition pipes. Once the appropriate soil moisture content has been verified, the moisture addition pipes are evacuated and the inner row of freeze pipes are activated to complete the barrier.