Finding Buried
Objects
Real estate transactions happen in times to hinge on the
potential presence of buried objects such as historical underground
storage tanks, chemical storage drums, pipelines and others. In another
line of activity, safety of construction projects depends on exact
knowledge of buried objects in the planned excavation areas. Hitting an
unknown, high pressure gas line can and has caused loss of lives.
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We need tools to assist us in the exploration of
buried objects, and such tools should be capable of doing the work
without disturbing the surface.
The field of geophysics comes to our need.
Geophysics is a compounded word: geo plus physics.
Geo is earth in Greek, from Gaia,
the mythological goddess personifying earth. GAIA was Mother
Earth, an ancient primeval goddess who emerged at the creation of the
universe, second only to Khaos (Air). She was depicted as a
buxom, matronly woman, shown half risen from the earth, unable to
completely separate herself from her element. |
Physics derives from
Latin physica: natural science, from Greek physika: of
nature.
Physics is the science that deals with matter and
energy and their interactions. Physics includes such fields of
mechanics, optics, heat, electricity, magnetism, atomic structure, and
others. It is the study of how objects (from the very tiny to the very
big) behave.
Geophysics is the study of the physical properties of
the earth and the composition and movement of its component layers of
rock.
Geophysics is applied to mining exploration to detect zones that
could be characterized by physical properties such as magnetism, gravity
or conductivity. It studies the physics of the Earth, using the
physical principles underlying such phenomena as seismic waves, heat
flow, gravity, and magnetism to investigate planetary properties. It is
the study of the physical properties of rocks and minerals.
Assessment of contamination in the subsurface is done by
advancing test holes to the desired depths and collecting samples of
soil and/or groundwater. Drilling involves the inherent hazard of
colliding with unknown buried objects such as gas lines, power lines,
petroleum pipelines, fiber-optic arteries, water mains, underground
storage tanks and connected gasoline lines. Such encounters involve
great risks of explosions and attendant losses in life and property.
It is crucially important to identify buried utilities in
areas of intended excavations. Tools are needed that will identify
underground targets without actually intruding on the subsurface world.
Also, in the exploration for environmental liabilities in
real estate transactions, it is not uncommon to find records of historic
existence of underground tanks with no information on their ultimate
fate: Have they been removed? Are they still there? Where?
We need a tool that, with minimal interference with the
current conditions of the property will help us find buried objects.
The science of Geophysics has long used non-destructive
methods to identify subsurface characteristics of underlying rocks,
formations, minerals and groundwater. These tools are used today
extensively to assist in our environmental needs for the exploration of
subsurface features and buried objects.
In this and forthcoming articles we shall look at the
features and uses of these tools.
In assembling the articles we relied on information gleaned
from several sources on the World Wide Web. A major source has been a
U.S. EPA publication. All information copied, to the best of our
knowledge, has not been copyrighted. For lack of space, a general credit
and gratitude is hereby expressed to all other sources without
identifying any. They are easy to locate through key words in a good
search engine. We are biased to Google and a hearty appreciation to the
creators of this engine is hereby expressed.
Surface geophysical methods are generally non-intrusive and
can be employed quickly to collect subsurface data.
Data collected with geophysical tools are often difficult to
interpret because a given data set may not indicate specific subsurface
conditions. Instead, data provided by these tools indicate anomalies
which can often be caused by numerous features. As a result, geophysical
methods are most effectively used in combination with other site
information (e.g., data from different geophysical methods,
sampling and analytical tools, geological and historic records,
anecdotal information). A combination of these sources is often
necessary to resolve ambiguities in geophysical plots (i.e.,
the graphical representation of data produced by a specific method).
The most appropriate geophysical methods for UST site
investigations are:
- ground penetrating radar (GPR);
- electromagnetic methods;
- electrical resistivity;
- metal detection;
- seismic methods; and
- magnetometry.
All geophysical methods have limitations
that will affect their applicability at specific sites.
In the next articles we shall deal with each of these
methods. |
