•  Groundwater exploration-Geophysical Methods. Unit-II 1
  • Exploration geophysics is an applied branch of geophysics, which uses physical methods (such as seismic, gravitational, magnetic, electrical and electromagnetic) at the surface of the Earth to measure the physical properties of the subsurface, along with the anomalies in those properties.
  • Traditional solution: Drill several boreholes & install wells: Expensive Labor Intensive Time If site is contaminated: Disposal of contaminated core Clean equipment
  • Geophysical Investigations • Geophysical investigations involve simple methods of study made on the surface with the aim of ascertaining subsurface detail. This is achieved by measuring certain physical properties and interpreting them mainly in terms of subsurface geology.
  • Importance of Geophysical Investigations • These investigations are carried out quickly. • This means large area can be investigated in a reasonable short period and hence time is saved. • The geophysical instruments used in the field are simple, portable and can be operated easily. • This means fieldwork is not laborious.
  • Importance of Geophysical Investigations • Different inferences to suit different purposes can be drawn from the same field data, for example electric resistivity data can be interpreted for knowing subsurface of rock types, geological structures, groundwater conditions, ore deposits depth to the bed rock, etc. Hence the investigations are multipurpose. 6
  • ELECTRICAL RESISTIVITY METHOD • The electrical resistivity method involves the measurement of the apparent resistivity of soils and rock as a function of depth or position. • It is calculated by dividing the measured potential difference by the input current and multiplying by a geometric factor specific to the array being used and electrode spacing