that are dependent on subsurface contrasts in density, velocity, or salinity, for example, will
not adequately resolve details of the geology in formations where these physical contrasts are
Limitations associated with borehole geophysical surveys are generally related to
individual tool response in different environments. As with surface geophysical techniques,
the proper tools should be selected for the individual application formation or borehole
conditions. Typical borehole geophysical surveying requires specialists trained in tool
operation and handling and data collection. Collected data will routinely require corrections
for borehole conditions prior to interpretation.
The potential for multiple interpretations of geophysical data results from the large
number of potential combinations of subsurface conditions that can occur to produce the
measured response. The limits in resolution and non uniqueness in interpretations of
geophysical methods should be recognized. Isolated surveys with no supporting information
should be carefully interpreted. Information from geophysical surveys should be utilized in
conjunction with other physical data to verify the initial interpretations of the geophysical
methods and provide constraints to remove some of the non uniqueness. In more complex
areas, surface to borehole and cross borehole geophysical methods may be considered to
delineate subsurface structure (Dobecki and Romig, 1985). However, application of multiple
geophysical methods at a site is not a guarantee that one survey will resolve the ambiguities
of another survey.
Equipment for performing many surface geophysical surveys is available from a
variety of sources, and include modern, computerized microprocessors and electronics.
Although the equipment can generally be operated by trained technicians, all aspects of data
collection, processing, and interpretation will require the oversight of a qualified geophysicist,
geologist, or ground water scientist having extensive experience with the equipment operation
and data interpretation. Borehole geophysical equipment is highly specialized and will
require a qualified contractor to obtain the logs.
Johnson and Johnson (1986) discuss some of the problems that are commonly
encountered when using geophysical techniques to investigate the shallow subsurface. These
Incorrect Method Applied Possible causes include lack of understanding of
geophysical technology, site conditions or survey objectives;
Poor Data Quality Possible causes include high ambient noise, poor field
procedures, improper use of equipment, faulty equipment, adverse geologic
conditions, or inexperienced operators;