All excavations required for the installation
of a building sewer shall be open trenchwork unless otherwise approved
by the Enforcement Officer. Pipelaying and backfill shall be performed
in accordance with Sections 3 through 6 of ASTM Specification C12,
except that no backfill shall be placed until the work has been inspected
and except that trench width measured at the top of the installed
pipe shall not exceed 24 inches.