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Amo; Appendix C LIMITATIONS Total Field Magnetic Intensity TF Buried ferrous metal objects produce localized variations in the earth's magnetic field. The magnetic intensity associated with these objects depends on the mass of the metal and the distance the metal object is from the magnetometer sensor. As the distance between the object and the magnetometer sensor increases, the intensity of the associated field decreases, thereby making detection more difficult. In addition, the ability to detect a buried metal object is based on the intensity of these variations in contrast to the intensity of background variations. The intensity of background variations is based on the amount of above and below ground metal that is present within the survey area. Cultural features such as chain link fences, buildings, debris, railroad spurs, utilities,above ground electric lines, etc.typically produce magnetic variations with high intensities.These variations may mask effects from buried metal objects, or make it very difficult to determine whether the magnetic variations are associated with below ground metal or above/below ground cultural features. Metal Detector (MIDI • In general, the response of the electromagnetic metal detection instrument is proportional to the horizontal surface area of near surface buried objects (typically in the upper three or four feet). This relationship can be used to advantage in locating buried metal debris, buried reinforced concrete pads, and utilities. However, in the presence of above ground metal objects such as fences, walls, parked cars, and metal debris, this is no longer valid. In some instances, the presence of such objects can make it very difficult to determine whether the instrument responses are associated with below ground targets or above ground cultural features. As with terrain conductivity techniques, when multiple sources are present it may not be possible to identify individual targets. Ground Penetrating Radar GPR The ability to detect subsurface targets is dependent on site specific conditions. These conditions include depth of burial, the size or diameter of the target, the condition of the specific target in question, the type of backfill material associated with the target, and the surface conditions over the target. Typically, the GPR depth of detection will be reduced as the clay and/or moisture content in the subsurface increases. Therefore, it is possible that targets (UST's and utilities), buried greater than 2 to about 4 feet, may not be detectable by the GPR technique. i C-,