Nondestructive testing (NDT) techniques to detect contained subsurface hazardous waste

Abstract

A systematic and comprehensive study was conducted to detect buried containers with nondestructive testing (NDT) remote-sensing techniques. Seventeen techniques were considered but only four were ultimately selected. Those four were electromagnetic induction (EMI), metal detection (MD), magnetometer (MAG), and ground penetrating radar (GPR). The containers — both steel and plastic — varying in size from 5 gal to 55 gal were buried in known distributions in a wide variety of soils; also, some were submerged in water. Five diverse field sites were used. As a result of the work at the five field sites, a relatively complete picture has emerged concerning the strengths and weaknesses of the four NDT subsurface container location techniques. GPR is the only reliable method to detect plastic containers, but it has limitations. GPR, EMI, and MD all suffer severe loss of detection ability when the background electrical conductivity exceeds 40 millimhos/meter. In dry sandy soil EMI, GPR, and MAG are all capable of picking up a single 55-gal steel drum to a depth of at least 10 feet. The MAG method works well for steel under all subsurface conditions, and GPR can usually pickup the side walls of the excavations where waste in dumped. Application of signal enhancement techniques (background suppression) can be expected to enhance NDT utility.