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• <br /> ' occur in zones. If the composition of the landfill is generally homogenous and nonmetallic, the <br /> contours tend to form large closures representing low values. If the fill material consists of both <br /> ' nonmetallic and metallic debris that varies significantly throughout the landfill, the contours tend <br /> to occur as numerous small closures representing both high and low values. <br /> 1 Limitations <br /> ' There are inherent limitations associated with the EM(TC and IPC) and VMG techniques that may <br /> not allow for the detection of all subsurface features of interest. These limitations are related to the <br /> construction of the object, its size and depth of burial, and its proximity to other above or below <br /> ' ground features. In general, as the distance between a subsurface object and the respective <br /> geophysical instrument increases, the intensity of the associated field decreases, thereby making <br /> detection more difficult. In addition, above and below ground objects, such as buildings, debris, <br /> ' utilities,above ground electric lines,etc.,typically produce interference that may mask effects from <br /> nearby buried features (targets). <br /> ' Apart from the physical limitations of the instruments and the unwanted effects from secondary <br /> objects,the ability to detect subsurface features is also dependent upon the density of data acquisition <br /> points. If the distance between data acquisition points is significantly larger than the size of the <br /> ' subsurface feature, then this object may not be detectable. <br /> ' A-3 <br />