Geophysical Investigation For Buried Drums: A Case Study

A vertical gradient magnetic survey was implemented over a 100 acre site to<br>locate isolated buried drums. Clusters of buried drums at the site had been<br>discovered and excavated during the course of previous investigations. The<br>survey was designed and field tested for the ability to detect a single drum<br>buried at a depth of up to 10 feet below the ground surface. Field tests<br>demonstrated that vertical gradient magnetic data collected on five-foot<br>centers would provide the best means for detecting isolated drums. High clay<br>content soils severely limited both electrical and ground penetrating radar<br>methods. Based on the field results and theoretical calculations, a minimum<br>anomaly criterion were established for deciding which vertical gradient<br>anomalies would be investigated. The vertical gradient magnetic contour maps<br>were then inspected and anomalies exceeding these criterion were targeted for<br>investigation. More than 1,000 anomalies were investigatedbytrenching with<br>a backhoe. Most of the trenched anomalies resulted in the discovery of<br>miscellaneous magnetic debris. Thirty-six of the trenched anomalies resulted<br>in the discovery of drums or drum fragments at depths of up to nine feet. The<br>results of this survey show that isolated drums were easily detectable at<br>depths of 10 feet. Careful management of this investigation was essential due<br>to the large number of anomalies and the complexity of coordinating heavy<br>equipment operations and the magnetometer surveys.