Remote Monitoring of Leaks in Storage Tanks using Electrical Resistance Tomography: Application at the Hanford Site

A field experiment was performed to evaluate the performance of electrical resistance tomography (ERT) to detect leaks from metal underground storage tanks. The test was carried out under conditions simulating those expected during actual remediation of a single shell tank located at the U. S. Department of Energy Hanford Reservation, Washington. A system was developed for the experiment to allow remote operation during the entire test. Approximately 54,000liters of concentrated sodium thiosulfate (simulating tank waste) were episodically released from a steel tank in a blind test lasting 110days (no knowledge of the release episodes during the course of the test were provided). ERT data were collected using an array of point electrodes installed in boreholes around the tank. Each day during the test a leak or no-leak condition was declared based solely on analysis of the electrical data. The success rate of the declarations made during the test was only 57%, however, further analysis carried out at the end of the test resulted in a significant improvement of the success rate. The results suggest that ERT, used either with custom built electrode arrays or existing steel cased wells, can provide an effective means of monitoring remediation or long-term integrity of underground storage tanks.