(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.