(a) Except as provided in subdivisions (d), (e) and (f) of this section, each buried transmission line, or distribution main operating at 125 psig (862 kPa) or more in a Class 3 or 4 location, must be installed with a minimum cover as follows:

(b) Except as provided in subdivisions (c), (d), (e) and (f) of this section, each buried distribution main, other than those specified in subdivision (a) of this section, must be installed with at least 24 inches (610 millimeters) of cover.

(c) Where a new distribution main is being inserted into an existing pipeline, the minimum depth of cover may be 18 inches (457 millimeters) provided openings are properly bridged to provide protection from shearing action and external damage.

(d) Where an underground structure prevents the installation of a transmission line or main with the minimum cover, the transmission line or main may be installed with less cover if it is provided with additional protection to withstand anticipated external loads.

(e) All pipe which is installed in areas actively cultivated for commercial farm purposes in at least two out of the last five years, as identified by the farmland operator, shall be installed with a minimum cover of 40 inches (1,016 millimeters) unless the farmland operator agrees to or requires a different depth.

(f) All pipe which is installed in a navigable river, stream, or harbor must have a minimum cover of 48 inches (1,219 millimeters) in soil or 24 inches (610 millimeters) in consolidated rock between the top of the pipe and the underwater natural bottom, (as determined by recognized and generally accepted practices). However, less than the minimum cover is permitted in accordance with subdivision (d) of this section.