Pole-dipole array electrical potential distributions are calculated for a geomembrane-lined liquid impoundment having single or multiple leaks. A three-dimensional numerical model is employed to represent a small circular leak in the highly resistive plastic liner. The liquid waste material, the liner, and the soil under the impoundment are simulated by infinite horizontal layers, with approximate corrections for the finite size of the impoundment. Parametric curves for a single leak show that with optimum selection of electrode spacing and positioning and other field survey parameters leaks can be detected effectively. To identify and resolve the presence of a cluster of leaks, the potential measurements must be made close to the liner and the detector dipole spacing must be smaller than the separation of the leaks. The results also indicate that the survey speed may be increased when portable leak detection equipment employing a vertical dipole detector is used.