In situ nitrogen permeability testing was undertaken in a borehole drilled between the No. 2 and No. 3 Tunnels at the Donkin-Morien Project. The object of this work was to assess whether the 'technique of in situ gas permeability testing could be used to assess changes in the sidewall rock integrity caused by the different excavation methods used to drive the two tunnels. After a description of the test site, equipment and procedures, the results are presented and discussed.