f USING ERT TO LOCATE A HISTORICAL MINE TUNNEL

Existing tunnels in historical mine sites often serve as conduits for acid mine drainage thus, delineating them can be important in remediating these sites. In a recent field study, electrical resistivity tomography was successfully used to locate a tunnel in a former mining district in the Rocky Mountains of Colorado. Prior to the ERT survey, a combination of historical mine data and surface geophysical surveys were used to find the approximate location of the tunnel. This culminated in drilling of boreholes on both sides of the location of the tunnel. Cross-borehole ERT was then used to provide a final estimate of the tunnel location. Surface-to-hole ERT surveys were conducted near a second, known portion of the tunnel to determine the feasibility of finding the tunnel using only a single borehole. In addition to the ERT surveys, an electrode was placed inside the entrance to the tunnel and used to perform mise-a-la-masse (MALM) surveys with receiving electrodes at the surface and in the borehole.