UNDERGROUND WASTE BARRIER STRUCTURES

Abstract: An underground waste barrier structure consisting of waste material, a first container formed of activated carbonaceous material enclosing the waste material, a second container formed of zeolite enclosing the first container, and clay covering the second container. The underground waste barrier structure is constructed by forming a recessed area within the earth, lining the recessed area with a layer of clay, lining the clay with a layer of zeolite, lining the zeolite with a layer of activated carbonaceous material, placing the waste material within the lined recessed area, forming a ceiling over the waste material of a layer of activated carbonaceous materi­ al, a layer of zeolite and a layer of clay, the layers cojoining with the respective layers forming the walls of the structure, and finally, covering the ceiling with earth.

Description: This invention relates to underground waste barrier structures. Reference is made to US-A-4430021 which discloses a chemical waste landfill, wherein a layer of activated carbon is used to remove any organic materials present. Radioactive and toxic waste materials are often stored in 208 liter (55 gallon) drums which are placed in underground trenches. While these trenches are typically lined with clay, it has been found that water leaking into the trenches can carry radioactive and toxic materials through the clay barrier into the surrounding earth, contaminating water supplies and creating an environmental hazard. This can occur because the drums corrode, rust or otherwise break or deteriorate, permitting the ground water to contact their contents. Even when the waste material is encapsulated within cement, the ground water can eventually leach radioactive or toxic materials from the cement. This is a particularly difficult problem to deal with because the ground water can contain organic materials which can foul or plug binders placed within the drums for the purpose of preventing radioactive or toxic materials from leaching out. Accordingly, the present invention resides in an underground waste barrier structure in which activated carbonaceous material is used for removing organic materials present in waste material, characterized in that said structure comprises a first container formed of activated carbonaceous material enclosing said waste material; a second contained formed of zeolite enclosing said first container; and earth covering said second container. The invention also includes a method of disposing of waste material using activated carbonaceous material for removing organic materials present therein, characterized by forming a recessed area within the earth; lining said recessed area with a first layer of zeolite; lining said layer of zeolite with a first layer of said activated carbonaceous material; placing said waste material within said lined recessed area; forming a ceiling over said waste material of a second layer of said zeolite on a second layer of said activated carbonaceous material, said layers cojoining with said respective first layers of zeolite and activated activated carbonaceous material; and covering said ceiling with earth. We have discovered a relatively inexpensive and permanent underground barrier structure capable of effectively preventing the dispersion of toxic or radioactive ions into the surrounding earth even when organic molecules are present. In order that the invention can be more clearly understood, convenient embodiments thereof will now be described, by way of example, with reference to the accompanying drawing which is a side view, in section, of an underground barrier structure. Referring to the drawing, 208 liter (55 gallon) steel drums 1 are placed within a space 2 enclosed by a multi-layered container 3 under earth 4. The inner layer of container 3 is a stiffener 5 which supports a layer of activated carbonaceous material 6. Surrounding activated carbonaceous material 6 is a second stiffener 7 which supports a layer of zeolite 8. Surrounding the layer of zeolite is a third stiffener 9 which supports a layer of clay 10. In preparing the underground waste barrier structure, a trench, hole, or other depression is formed in the earth. A typical trench might be 183 to 488 cm (6 to 16 feet) in width at the bottom, 358 to 549 cm (12 to 18 feet) wide at the top, with a height of about 368 to 914 cm, (12 to 30 feet) and with sides that slop at an angle of 5° to 10°. While not considered to be absolutely necessary, it is preferable to line the depression in the earth with a layer of clay to reduce the penetration of water into the cavity and increase the safety of the barrier. Suitable clays include nontronite, kandite, illite, and chlorite. The preferred clay is nontronite because it is effective, inexpensive, and readily available. The layer of clay is preferably from 7,62 to 15,24 cm (3 to 6 inches) in thickness as it is difficult to form thinner layers which are not broken, and thicker layers are usually unnecessary. If desired, a stiffener may be placed against a layer of clay to prevent it from falling within the cavity. Stiffeners may include materials such as plywood, "Micarta" laminates, sheet metal, and other types of material. In the next step tion, the depression is lined with a layer of zeolite. While synthetic zeolite may be used, natural zeolite (mineral) is preferred as it is much less expensive and it may be more effective in containing certain radioactive ions. Suitable zeolites includes clinoptilolite, erionite, chabazite, phillipsite, and mordenite. The preferred zeolite is erionite because it is readily available, has a fibrous structure (less permeable), and is more effective. The zeolite layer is preferably from 7,62 to 22,86 cm (3 to 9 inches) in thickness as thinner layers which may be breached and thicker layers are usually unnecessary. If desired, another stiffener can be placed against the zeolite layer to retain it in place. In the next step, a layer of activated carbonaceous material is placed against the inside of the depression, next to the zeolite. The purpose of the activated carbonaceous material is to remove any organic materials that may be present in the waste materials before they can reach the layer of zeolite, since organic materials tend to foul the zeolite and prevent it from effectively removing radioactive and toxic materials. Any type of activated carbonaceous material can be used, such as activated coconut shell and activated bone char. Preferably, the activated carbonaceous material is bone char as it is inexpensive and more effective than other activated carbonaceous materials. In addition, the activated carbonaceous material will also remove radioiodine and certain other radioactive species that may be present. The layer of activated carbonaceous material is preferably from 7,62 to 22,86 cm (3 to 9 inches) thick as thinner layers may be broken and thicker layers are usually unnecessary. A stiffener may also be placed against the layer of activated carbonaceous material to retain it in place. The radioactive or toxic waste material is then placed within the structure that has been formed. Typically, the waste material is in 208 liter (55-gallon drums, although it may also be in other forms. The drums may contain cement that contains the waste material or the drums may contain fluid or solid waste without cement being present. Radioactive wastes may be low to intermediate level wastes, and toxic wastes can include substances such as polychlorinated biphenyls, dioxane, trichloroethylene and other toxic materials. In the next step, a ceiling is formed over the container holding the waste. The ceiling is formed by applying the same layers used to form the walls but in reverse order. The materials forming the ceiling should cojoin with the same materials that form the walls so that each layer of the container completely surrounds the waste material. The completed structure is then covered with earth, typically to a depth of 30,48 to 183 cm (1 to 6 feet), depending upon radiation level and toxicity present.

Claims: An underground waste barrier structure in which activated carbonaceous material is used for removing organic materials present in waste material, characterized in that said structure comprises a first container formed of activated carbonaceous material enclosing said waste material; a second contained formed of zeolite enclosing said first container; and earth covering said second container. A structure according to claim 1, characterized in that the waste material is radioactive. A structure according to claim 1 or 2, characterized in that the activated carbonaceous material is bone char. A structure according to claim 1, 2 or 3, characterized in that the zeolite is a natural zeolite. A structure according to claim 4, characterized in that the natural zeolite is erionite. A structure according to any of claims 1 to 5, characterized in that first and second containers are each from 7.62 to 22.86 cm (3 to 9 inches) thick. A structure according to any of claims 1 to 6, characterized in that a third container of clay encloses the second container. A structure according to claim 7, characterized in that said third container is from 7,62 to 15,24 cm (3 to 6 inches) thick. A structure according to any of claims 1 to 8, characterized in that the waste material is sealed in steel drums. A structure according to any of claims 1 to 9, characterized in that said structure further comprises means for supporting the walls and ceiling of the first and second containers. A method of disposing of waste material using activated carbonaceous material for removing organic materials present therein, characterized by forming a recessed area within the earth; lining said recessed area with a first layer of zeolite; lining said layer of zeolite with a first layer of said activated carbonaceous material; placing said waste material within said lined recessed area; forming a ceiling over said waste material of a second layer of said zeolite on a second layer of said activated carbonaceous material, said layers cojoining with said respective first layers of zeolite and activated activated carbonaceous material; and covering said ceiling with earth.

Inventors: GRANT, DAVID CHARLES, SAHA, ANUJ KUMAR
Applicants: WESTINGHOUSE ELECTRIC CORPORATION
Application year: 1987
Main classification: G21F9
IPC codes: G21F9