Theory 
A magnetometer measures magnetic field strength in wide range units of gammas or nanoteslas (1 gammas = 1 nanotesla = 0.00001 gauss). Local variations, or anomalies, in the earth’s magnetic field are the result of disturbances caused mostly by variations in concentrations of ferromagnetic material in the vicinity of the magnetometer’s sensor. A buried ferrous object, such as a steel drum or tank, locally distorts the earth’s magnetic field and results in a magnetic anomaly. The common objective of conducting a magnetic survey at a hazardous waste or ground water pollution site is to map these anomalies and delineate the area of burial of the sources of these anomalies. The magnetic method may also be used at a site to map various geologic features, such as igneous intrusions, faults, and some geologic contacts that may play an important role in the hydrogeology of a ground water pollution site. 
Applications

A- Locating:

• Pipes, cables and ferrous metallic objects
• Buried military ordnance 
• Buried metal drums of contaminated or toxic waste, etc.
• Concealed mine shafts and adits.

B- Mapping

• Archaeological remains 
• Concealed basic igneous dykes 
• Metalliferous mineral lodes 
• Geological boundaries between magnetically contrasting
• lithologies, including faults
• Large-scale geological structures