How to Find Buried Objects.
(The material in this article has been provided by US EPA publications)
resistivity, also referred to as galvanic electrical methods, is
occasionally useful at UST sites for determining shallow and deep
geologic and hydrogeologic conditions. By measuring the electrical
resistance to a direct current applied at the surface, this geophysical
method can be used to locate groundwater/contaminant pathways, clay
lenses and sand channels, perched water zones and depth to groundwater,
and occasionally, large quantities of residual and floating product.
variety of electrode configurations can be used depending on the
application and the resolution desired. Typically, an electrical
current is applied to the ground through a pair of electrodes. A second
pair of electrodes is then used to measure the resulting voltage. The
greater the distance between electrodes, the deeper the investigation.
Because various subsurface materials have different resistivity values,
measurements at the surface can be used to determine the vertical and
lateral variation of underlying materials.
Electrical resistivity has a number of limitations:
must be in direct contact with soil; if concrete or asphalt are
present, holes must be drilled for inserting the electrodes and then
refilled when the survey is complete.
The distance between outside electrodes must be 4 to 5 times the depth of investigation.
may be limited by both highly conductive or highly resistive surface
soils. If shallow clays and extremely shallow groundwater are present,
most of the current may concentrate at the surface. Although the
condition is very rare, the presence of thick, dry, gravelly material
(or massive dry material) at the surface may prevent the current from entering the ground.