Environmental Enlightenment #73

By Ami Adini - Reissued July 1, 2010

This is a SHORT, LIGHT and SIMPLE newsletter. Its purpose is to rekindle in the initiated terminology they have once learned, and enlighten the uninitiated on terms they may have heard but never known the meaning of.

How to Find Buried Objects
Magnetic Methods

[The text in this article has been extracted from a publication by the United States Environmental Protection Agency.]

This is the last of a series of articles on using the science of geophysics to detect buried objects.

Magnetometers are useful at underground storage tank (UST) sites for locating tanks and piping made of ferrous materials. Although highly sensitive magnetometers have been developed that can detect the void space within large buried objects of any material (e.g., fiberglass tanks), this technology is not often used in UST investigations because many cultural interferences present at UST sites will mask the effect.

Magnetometers that are commonly used at UST sites work by measuring the earth's total magnetic field at a particular location. Buried ferrous materials distort the magnetic field, creating a magnetic anomaly. There are two methods for measuring these anomalies--the total field method and the gradient method. The total field method utilizes one magnetic sensing device to record the value of the magnetic field at a specific location. The gradient method uses two sensors, one above the other. The difference in readings between the two sensors provides gradient information which helps to minimize lateral interferences. Total field magnetic methods are often used at sites with few cultural features. Gradiometer methods can be used in culturally complex areas. As a result, gradiometers are more applicable for UST sites.

Magnetometers may be useful for reconnaissance surveys of UST sites because they are very fast and relatively inexpensive.

Potential cultural interferences include steel fences, vehicles, buildings, iron debris, natural soil minerals, and underground utilities. Gradiometer methods are useful for minimizing these interferences.

Power lines are an additional source of interference that can be neutralized with the use of very sophisticated equipment that synchronizes readings with the oscillating electrical current.

Some magnetometers are very simple and do not have a data recording or processing ability. They indicate the presence of iron with a sound or meter and can be used as a rapid screening tool.

Magnetometers that record data can, with the aid of data processing software, be used to estimate the size and depth of ferrous targets.

You can find past issues of our  "Environmental Enlightenment" at amiadini.com Wealth of information about environmental site assessments in the real estate transactions and issues concerning assessment and cleanup of contamination in the subsurface soil and groundwater.

Call me if you have any questions. There are no obligations.

Ami Adini
Ami Adini & Associates, Inc.
Environmental Consultants
Underground Storage Tank Experts
323-913-4073; 323-667-2336 fax

Ami Adini is a mechanical engineer, California Registered Environmental Assessor, Level II, and president of AMI ADINI & ASSOCIATES, INC. (AA&A), an environmental consulting firm specializing in all phases of environmental site assessments, rehabilitation of contaminated sites and upgrading of underground storage tank facilities. AA&A supplies practical solutions to environmental concerns using the highest standards of ethics and integrity while providing its clients with maximum return on their investments.