Advance

The motion of the machine in a direction toward the face wall of the entrance pit.

Advance Rate

Forward progress over a given period of time; includes penetration rate, make-up time, downtime, and idle time; typically measured in feet or meters per shift.

Aerial Sewer

An unburied sewer (generally sanitary type), supported on pedestals or bents to provide a suitable grade line.

Aerobic

Presence of unreacted or free oxygen (O2).

Aggressive

A property of water which favors the corrosion of its conveying structure.