The excavated material at the face may be transported to the surface using a high powered vacuum or air pressure system. Such systems have been used since the 1980s with rock and consolidated ground conditions being the most favorable for their use. As the use of vacuum microtunneling systems has spread, they have increasingly been applied to a broad range of ground conditions and to larger tunnel diameters (up to 3m). Vacuum extraction may be used in single-pass microtunneling or in pilot tube applications (where it can be used for the pilot tube installation itself and/or for the subsequent boring operations).