36.21.641 INNER CASING
(1) Inner casing installed through caving formations, or for sealing out water of poor quality, and installed without driving, may be of lighter weight than specified by the table under ARM 36.21.640. Such lightweight pipe shall have a wall thickness equal to or greater than a minimum wall thickness of .188 inch. All inner casing shall be of steel, in new or like new condition, being free of pits or breaks; or shall be of polymerized vinyl chloride conforming with American Society for Testing and Materials Specification F480-81 per ARM 36.21.645. Inner casing installed in a well shall extend or telescope at least 4 feet into the lower end of the well casing. In the event that more than one string of inner casing is installed, each string shall extend or telescope at least 4 feet into the adjacent larger diameter inner casing.
(2) In the event inner casing must be driven, it must meet the specifications of ARM 36.21.640.