P-703.2 Drainage pipe in filled ground. Where a building sewer or building drain is installed on filled or unstable ground, the drainage pipe shall conform to one of the standards for ABS plastic pipe, cast-iron pipe, copper or copper alloy tubing, or stainless steel drainage systems, type 304 and 316LPVC plastic pipe or polypropylene plastic pipe indicated in Table P-702.3. When drainage is installed in filled or unstable ground, it shall be of cast iron or hard temper copper tube of a weight not less than type "L" or stainless steel drainage systems, Type 304 and 316L. Pipe shall be supported on concrete piers with spacing consistent with Table 308.5, or a constant bed of concrete or clevis hangers attached to reinforcing rods in the concrete floor above the piping.
* * *
Exception: The repair or replacement of an existing combined building sewer as of the initial adoption date of this code. The size of such replacements shall comply with Section 1109.2.