Locating leaks in clay liners below bauxite residue deposits

Sources of leakage of contaminants to the ground water from old bauxite tailings impoundments at Kwinana in Western Australia have been repaired by the injection of chemical grout into defects in the basal clay liners. This work has required finding the precise location of the boundaries of the liner defects beneath 20 metres of residue. The techniques for finding leaks have involved measurements taken within piezometers installed by drilling to the top of the basal clay liners. The most important measurements for leak location are piezometric head, induced electric potential and liquor temperature. This paper illustrates the leak location techniques using as an example the most recently repaired leakage source at the southern end of Residue Area F. The leak location work has indicated some causes of liner defects including erosion by rainfall run-off prior to placement of the residue, and localised subsidence of the substrata.