(1) The following special sealing methods may be required in situations where different techniques are necessary to protect aquifers.
(a) In drilled wells that penetrate an aquifer either within a consolidated or confining formation, sealing of the casing shall conform with one of the following procedures:
(i) an upper drill hole, at least three inches greater in diameter than the nominal size of the permanent well casing, shall extend from land surface to at least three feet into sound, consolidated formation. In no instance shall said upper drill hole extend less than 25 feet below land surface; and
(ii) unperforated permanent casing shall be installed to extend to this same depth, and the lower part of the casing shall be sealed into the rock formation with cement grout. The remainder of the annular space to land surface shall be filled with an appropriate sealing material (see Figure 2A at the end of this subchapter).
(2) If temporary surface casing is used in either of the above procedures, this casing shall be of sufficient diameter to conform to the upper drill hole specifications. Withdrawal of the temporary casing shall take place simultaneously with proper sealing of the annular space to land surface.