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Bentonite used for annular seals shall be commercially prepared,powdered,granulated, pelletized,or chipped/crushed sodium montmorillonite clay. The largest dimension of pellets or chips shall be less than 1/5 the radial thickness of the annular space into which they are placed. Bentonite clay mixtures shall be thoroughly mixed with clean water prior to placement. A sufficient amount of water shall be added to bentonite to allow proper hydration. Depending on the bentonite sealing mixture used, 1 gallon of water should be added to about every 2 pounds of bentonite. Water added to bentonite for hydration shall be of suitable quality and free of pollutants and contaminants. Bentonite preparations normally require 1/2 to 1 hour to adequately hydrate. Actual hydration time is a function of site conditions and the form of bentonite used. Finely divided forms of bentonite generally require less time for hydration,if properly mixed. Dry bentonite pellets or chips may be placed directly into the annular space below water,where a short section of annular space, up to 10 feet in length, is to be sealed. Care shall be taken to prevent bridging during the placement of bentonite seal material. E. Radial Thickness of Seal. A minimum of two inches of sealing material shall be maintained between all casings and the borehole wall, within the interval to be sealed, except where temporary, conductor casing cannot be removed,as noted in Subsection B,page 15,above. A minimum of two inches of sealing material shall also be maintained between each casing,such as permanent conductor casing, well casing, gravel fill pipes, etc., in a borehole within the interval to be sealed,unless otherwise approved by the enforcing agency. Additional space shall be provided,where needed,for casings to be properly centralized and spaced and allow the use of a tremie pipe during well construction (if required), especially for deeper wells. F. Placement of Seal. Obstructions. All loose cuttings, or other obstructions to sealing shall be removed from the annular space before placement of the annular seal. 2. Centralizers. Well casing shall be equipped with centering guides or 'centralizers' to ensure the 2-inch minimum radial thickness of the annular seal is at least maintained. Centralizers need not be used in cases where the well casing is centered in the borehole during well construction by use of removable tools, such as hollow-stem augers. The spacing of centralizers is normally dictated by the casing materials used, the orientation and straightness of the borehole,and the method used to install the casing. Centralizers shall be metal,plastic,or other non-degradable material. Wood shall not be used as a centralizer material. Centralizers must be positioned to allow the proper placement of sealing material around casing within the interval to be sealed. Any metallic component of a centralizer used with metallic casing shall consist of the same material as the casing. Metallic centralizer components shall meet the same metallurgical specifications and standards as the metallic casing to reduce the potential for galvanic corrosion of the casing. -20-