(1) The following special sealing methods may be required in situations where different techniques are necessary to protect aquifers.

(2) An upper drill hole having a diameter of at least 3 inches greater than the outside diameter of the production casing shall be drilled to extend from land surface into a clay or other formation of low permeability overlying the water-bearing zone. The annular space to this depth shall be filled with sealing material. If the clay or other impermeable formation is at or near land surface, the upper drill hole and unperforated production casing shall extend to a minimum depth of 18 feet below land surface, provided that the casing does not pass through the impermeable zone. A suitable bridge shall be installed in the annular space between the gravel pack and the sealing material. A gravel fill pipe may be installed for injecting gravel prior to sealing the top of the gravel pack

(see ARM 36.21.656 for definition of a suitable bridge) . Special care shall be taken to insure that the seal is watertight around the injection pipe. The injection pipe shall be capped with a watertight seal or plug (see Figure 4A at the end of this sub-chapter) .