(1) The following special sealing methods may be required in situations where different techniques are necessary to protect aquifers.
(a) When permanent surface casing is installed, the well bore shall have a diameter of at least three inches greater than the surface casing for the introduction of sealing materials.
(b) A watertight seal shall be installed at the top of the gravel pack between the permanent surface and production casing.
(c) Sealing procedures and installation of gravel fill pipes are substantially the same as in ARM 36.21.659.
(d) If a temporary casing is used to maintain the oversized drill hole, the annular space to be sealed under conditions of ARM 36.21.659 and 36.21.660 shall be kept full with cement grout or bentonite clay grout as the temporary casing is withdrawn (see Figure 4B at the end of this subchapter).
(2) If a clay layer or other formation of low permeability is not encountered before reaching the top of the water-bearing zone, the upper drill hole and unperforated production casing shall extend to a minimum depth of 25 feet below land surface. Sealing procedures, installation of gravel fill pipes, and temporary casing are substantially the same as in ARM 36.21.659 and 36.21.660.