ASTM D6639-01
(Guide)Standard Guide for Using the Frequency Domain Electromagnetic Method for Subsurface Investigations
Standard Guide for Using the Frequency Domain Electromagnetic Method for Subsurface Investigations
SCOPE
1.1 Purpose and Application
1.1.1 This standard guide summarizes the equipment, field procedures, and interpretation methods for the assessment of subsurface conditions using the frequency domain electromagnetic (FDEM) method.
1.1.2 FDEM measurements as described in this standard guide are applicable to mapping subsurface conditions for geologic, geotechnical, hydrologic, environmental, agricultural, archaeological and forensic investigations as well as mineral exploration.
1.1.3 The FDEM method is sometimes used to map such diverse geologic conditions as depth to bedrock, fractures and fault zones, voids and sinkholes, soil and rock properties, and saline intrusion as well as man-induced environmental conditions including buried drums, underground storage tanks (USTs), landfill boundaries and conductive ground water contamination.
1.1.4 The FDEM method utilizes the secondary magnetic field induced in the earth by a time-varying primary magnetic field to explore the subsurface. It measures the amplitude and phase of the induced field at various frequencies. FDEM measurements therefore are dependent on the electrical properties of the subsurface soil and rock or buried man-made objects as well as the orientation of any subsurface geological features or man-made objects. In many cases, the FDEM measurements can be used to identify the subsurface structure or object. This method is used only when it is expected that the subsurface soil or rock, man-made materials or geologic structure can be characterized by differences in electrical conductivity.
1.1.5 The FDEM method may be used instead of the Direct Current Resistivity method (Guide D6431) when surface soils are excessively insulating (for example, dry or frozen) or a layer of asphalt or plastic or other logistical constraints prevent electrode to soil contact.
1.2Limitations:
1.2.1 This standard guide provides an overview of the FDEM method using coplanar coils at or near ground level and has been referred to by other names including Slingram, HLEM (horizontal loop electromagnetic) and Ground Conductivity methods. This guide does not address the details of the electromagnetic theory, field procedures or interpretation of the data. References are included that cover these aspects in greater detail and are considered an essential part of this guide (Grant and West, 1965; Wait, 1982; Kearey and Brook, 1991; Milsom, 1996; Ward, 1990). It is recommended that the user of the FDEM method review the relevant material pertaining to their particular application. ASTM standards that should also be consulted include Guide D420, Terminology D653, Guide D5730, Guide D5753, Practice D6235, Guide D6429, and Guide D6431.
1.2.2 This guide is limited to frequency domain instruments using a coplanar orientation of the transmitting and receiving coils in either the horizontal dipole (HD) mode with coils vertical, or the vertical dipole (VD) mode with coils horizontal (Fig. 2). It does not include coaxial or asymmetrical coil orientations, which are sometimes used for special applications (Grant and West 1965).
1.2.3 This guide is limited to the use of frequency domain instruments in which the ratio of the induced secondary magnetic field to the primary magnetic field is directly proportional to the ground's bulk or apparent conductivity (see 5.1.4). Instruments that give a direct measurement of the apparent ground conductivity are commonly referred to as Ground Conductivity Meters (GCMs) that are designed to operate within the "low induction number approximation". Multi-frequency instruments operating within and outside the low induction number approximation provide the ratio of the secondary to primary magnetic field, which can be used to calculate the ground conductivity.
1.2.4 The FDEM (inductive) method has been adapted for a number of special uses within a borehole, on water, or airborne. Discussions of these adaptations or methods are not included in this guide.
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Designation: D 6639 – 01
Standard Guide for
Using the Frequency Domain Electromagnetic Method for
1
Subsurface Investigations
This standard is issued under the fixed designation D 6639; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 1.2 Limitations:
1.2.1 This standard guide provides an overview of the
1.1 Purpose and Application:
FDEM method using coplanar coils at or near ground level and
1.1.1 This standard guide summarizes the equipment, field
has been referred to by other names including Slingram,
procedures, and interpretation methods for the assessment of
HLEM (horizontal loop electromagnetic) and Ground Conduc-
subsurface conditions using the frequency domain electromag-
tivity methods. This guide does not address the details of the
netic (FDEM) method.
electromagnetictheory,fieldproceduresorinterpretationofthe
1.1.2 FDEM measurements as described in this standard
data. References are included that cover these aspects in
guide are applicable to mapping subsurface conditions for
greater detail and are considered an essential part of this guide
geologic, geotechnical, hydrologic, environmental, agricul-
(Grant and West, 1965; Wait, 1982; Kearey and Brook, 1991;
tural, archaeological and forensic investigations as well as
Milsom, 1996;Ward, 1990). It is recommended that the user of
mineral exploration.
the FDEM method review the relevant material pertaining to
1.1.3 The FDEM method is sometimes used to map such
their particular application. ASTM standards that should also
diverse geologic conditions as depth to bedrock, fractures and
be consulted include Guide D 420, Terminology D 653, Guide
fault zones, voids and sinkholes, soil and rock properties, and
D 5730, Guide D 5753, Practice D 6235, Guide D 6429, and
saline intrusion as well as man-induced environmental condi-
Guide D 6431.
tions including buried drums, underground storage tanks
1.2.2 This guide is limited to frequency domain instruments
(USTs), landfill boundaries and conductive ground water
using a coplanar orientation of the transmitting and receiving
contamination.
coils in either the horizontal dipole (HD) mode with coils
1.1.4 The FDEM method utilizes the secondary magnetic
vertical, or the vertical dipole (VD) mode with coils horizontal
field induced in the earth by a time-varying primary magnetic
(Fig. 2). It does not include coaxial or asymmetrical coil
field to explore the subsurface. It measures the amplitude and
orientations, which are sometimes used for special applications
phase of the induced field at various frequencies. FDEM
(Grant and West 1965).
measurements therefore are dependent on the electrical prop-
1.2.3 This guide is limited to the use of frequency domain
erties of the subsurface soil and rock or buried man-made
instruments in which the ratio of the induced secondary
objects as well as the orientation of any subsurface geological
magnetic field to the primary magnetic field is directly propor-
features or man-made objects. In many cases, the FDEM
tionaltotheground’sbulkorapparentconductivity(see5.1.4).
measurements can be used to identify the subsurface structure
Instruments that give a direct measurement of the apparent
or object.This method is used only when it is expected that the
ground conductivity are commonly referred to as Ground
subsurface soil or rock, man-made materials or geologic
Conductivity Meters (GCMs) that are designed to operate
structure can be characterized by differences in electrical
within the “low induction number approximation”. Multi-
conductivity.
frequency instruments operating within and outside the low
1.1.5 The FDEM method may be used instead of the Direct
induction number approximation provide the ratio of the
Current Resistivity method (Guide D 6431) when surface soils
secondary to primary magnetic field, which can be used to
are excessively insulating (for example, dry or frozen) or a
calculate the ground conductivity.
layer of asphalt or plastic or other logistical constraints prevent
1.2.4 The FDEM (inductive) method has been adapted for a
electrode to soil contact.
numberofspecialuseswithinaborehole,onwater,orairborne.
Discussionsoftheseadaptationsormethodsarenotincludedin
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This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rock
this guide.
and is the direct responsibility of Subcommittee D18.01 on Surface and Subsurface
Characterization.
Current edition approved Feb 10, 2001. Published May 2001.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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