ELECTRICAL DETECTION OF LEAKS IN LINED WASTE-DISPOSAL PONDS

A method for detecting and locating leaks in the plastic liner of a wa ste disposal pond has been implemented and tested at a site near Budme rice in Slovakia. The method is based on detecting electric current fl owing 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 electric ally inhomogeneous solid waste. To accomplish this goal, sensing elect rodes 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 achievin g acceptable detectability and location accuracy while using a suffici ently sparse grid of sensing electrodes. This problem was overcome by two processing steps: (1) calculating electrical potentials from the o bserved voltages and (2) performing a nonlinear inversion on subsets o f the data. With this technique, observations made with a 10- x 8-m gr id of electrodes, a relatively low-power current source, and a simple receiver can provide accurate location information, even for small lea ks. 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, whe reas 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 su rvey location accuracy of the sensing electrodes.