Electrical detection of leaks in lined waste disposal ponds

A method for detecting and locating leaks in the plastic liner of a waste disposal pond has been implemented and tested at a site near Budmerice in Slovakia. The method is based on detecting electric current flowing through holes in the insulating lining membrane. Unlike similar methods employed elsewhere, this implementation allows monitoring for leaks that may develop during and after filling the pond with electrically inhomogeneous solid waste. To accomplish this goal, sensing electrodes were placed below the membrane during construction. In operation, current was passed between an electrode inside,the pond and another outside; the voltage caused by this current was observed on the buried sensing electrodes. The data were then processed to detect and locate any leaks in the membrane. An important practical concern is achieving acceptable detectability and location accuracy while using a sufficiently sparse grid of sensing electrodes. This problem was overcome by two processing steps: (1) calculating electrical potentials from the observed voltages and (2) performing a nonlinear inversion on subsets of the data. With this technique, observations made with a 10- x 8-m grid of electrodes, a relatively low-power current source, and a simple receiver can provide accurate location information, even for small leaks. In a blind test, the system accurately predicted the locations of six leaks that were subsequently verified visually. Five of the leaks were cuts in the plastic typically measuring less than 2 x 0.1 cm, whereas the sixth leak was a group of many small holes. For the five, the typical location accuracy was about 30 cm, comparable to the basic survey location accuracy of the sensing electrodes.