ASTM_D_6639_-_01_2008.pdf

Designation:D663901(Reapproved 2008)Standard Guide forUsing the Frequency Domain Electromagnetic Method forSubsurface Investigations1This standard is issued under the fixed designation D6639;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 Purpose and Application:1.1.1 Thisguidesummarizestheequipment,fieldprocedures,and interpretation methods for the assessment ofsubsurface conditions using the frequency domain electromag-netic(FDEM)method.1.1.2 FDEM measurements as described in this standardguide are applicable to mapping subsurface conditions forgeologic,geotechnical,hydrologic,environmental,agricultural,archaeological and forensic investigations as wellas mineral exploration.1.1.3 The FDEM method is sometimes used to map suchdiverse geologic conditions as depth to bedrock,fractures andfault zones,voids and sinkholes,soil and rock properties,andsaline intrusion as well as man-induced environmental condi-tions including buried drums,underground storage tanks(USTs),landfill boundaries and conductive groundwater con-tamination.1.1.4 The FDEM method utilizes the secondary magneticfield induced in the earth by a time-varying primary magneticfield to explore the subsurface.It measures the amplitude andphase of the induced field at various frequencies.FDEMmeasurements therefore are dependent on the electrical prop-erties of the subsurface soil and rock or buried man-madeobjects as well as the orientation of any subsurface geologicalfeatures or man-made objects.In many cases,the FDEMmeasurements can be used to identify the subsurface structureor object.This method is used only when it is expected that thesubsurface soil or rock,man-made materials or geologicstructure can be characterized by differences in electricalconductivity.1.1.5 The FDEM method may be used instead of the DirectCurrent Resistivity method(Guide D6431)when surface soilsare excessively insulating(for example,dry or frozen)or alayer of asphalt or plastic or other logistical constraints preventelectrode to soil contact.1.2 Limitations:1.2.1 This standard guide provides an overview of theFDEM method using coplanar coils at or near ground level andhas been referred to by other names including Slingram,HLEM(horizontal loop electromagnetic)and Ground Conduc-tivity methods.This guide does not address the details of theelectromagnetic theory,field procedures or interpretation of thedata.References are included that cover these aspects ingreater 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 ofthe FDEM method review the relevant material pertaining totheir particular application.ASTM standards that should alsobe consulted include Guide D420,Terminology D653,GuideD5730,Guide D5753,Practice D6235,Guide D6429,andGuide D6431.1.2.2 This guide is limited to frequency domain instrumentsusing a coplanar orientation of the transmitting and receivingcoils in either the horizontal dipole(HD)mode with coilsvertical,or the vertical dipole(VD)mode with coils horizontal(Fig.2).It does not include coaxial or asymmetrical coilorientations,which are sometimes used for special applications(Grant and West 1965).1.2.3 This guide is limited to the use of frequency domaininstruments in which the ratio of the induced secondarymagnetic field to the primary magnetic field is directly propor-tional to the grounds bulk or apparent conductivity(see 5.1.4).Instruments that give a direct measurement of the apparentground conductivity are commonly referred to as GroundConductivity Meters(GCMs)that are designed to operatewithin the“low induction number approximation.”Multi-frequency instruments operating within and outside the lowinduction number approximation provide the ratio of thesecondary to primary magnetic field,which can be used tocalculate the ground conductivity.1.2.4 The FDEM(inductive)method has been adapted for anumber of special uses within a borehole,on water,or airborne.Discussions of these adaptations or methods are not included inthis guide.1This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rockand is the direct responsibility of Subcommittee D18.01 on Surface and SubsurfaceCharacterization.Current edition approved Dec.1,2008.Published January 2009.Originallyapproved in 2001.Last previous edition approved in 2001 as D6639 01.DOI:10.1520/D6639-01R08.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 1.2.5 The approaches suggested in this guide for the fre-quency domain method are the most commonly used,widelyaccepted and proven;however other lesser-known or special-ized techniques may be substituted if technically sound anddoc