ASTM_D_6820_-_20.pdf

Designation:D682020Standard Guide forUse of the Time Domain Electromagnetic Method forGeophysical Subsurface Site Investigation1This standard is issued under the fixed designation D6820;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 This guide is one in a series of documents thatdescribe geophysical site investigation methods.1.1.2 Thisguidesummarizestheequipment,fieldprocedures,and interpretation methods for the assessment ofsubsurface materials and their pore fluids using the TimeDomain Electromagnetic(TDEM)method.This method is alsoknown as the Transient Electromagnetic(TEM)Method,and inthis guide is referred to as the TDEM/TEM method.TimeDomain and Transient refer to the measurement of a time-varying induced electromagnetic field.1.1.3 The TDEM/TEM method is applicable to the subsur-face site investigation for a wide range of conditions.TDEM/TEM methods measure variations in the electrical resistivity(or the reciprocal,the electrical conductivity)of the subsurfacesoil or rock caused by both lateral and vertical variations invarious physical properties of the soil or rock.By measuringboth lateral and vertical changes in resistivity,variations insubsurface conditions can be determined.1.1.4 Electromagnetic measurements of resistivity as de-scribed in this guide are applied in geologic studies,geotech-nical studies,hydrologic site investigations,and for mappingsubsurface conditions at waste disposal sites(1).2Resistivitymeasurements can be used to map geologic changes such aslithology,geological structure,fractures,stratigraphy,anddepth to bedrock.In addition,measurement of resistivity canbe applied to hydrologic site investigations such as the depth towater table,depth to aquitard,presence of coastal or inlandgroundwater salinity,and for the direct exploration for ground-water.1.1.5 This standard does not address the use of TDEM/TEMmethod for use as metal detectors or their use in unexplodedordnance(UXO)detection and characterization.While manyof the principles apply the data acquisition and interpretationdiffer from those set forth in this standard guide.1.1.6 General references for the use of the method areMcNeill(2),Kearey and Brooks(3),and Telford et al(4).1.2 Limitations:1.2.1 This guide provides an overview of the TDEM/TEMmethod.It does not provide or address the details of the theory,field procedures,or interpretation of the data.Numerousreferences are included for that purpose and are considered anessential part of this guide.It is recommended that the user ofthe TDEM/TEM method be familiar with the references citedand with the ASTM standards D420,D653,D5088,D5608,D5730,D5753,D6235,D6429 and D6431.1.2.2 This guide is limited to TDEM/TEM measurementsmade on land.The TDEM/TEM method can be adapted for anumber of special uses on land,water,ice,within a borehole,and airborne.Special TDEM/TEM configurations are used formetal and unexploded ordnance detection.These TDEM/TEMmethods are not discussed in this guide.1.2.3 The approaches suggested in this guide for the TDEM/TEM method are commonly used,widely accepted,andproven.However,other approaches or modifications to theTDEM/TEM method that are technically sound may be sub-stituted.1.2.4 This guide offers an organized collection of informa-tion or a series of options and does not recommend a specificcourse of action.This document cannot replace education,experience,and should be used in conjunction with profes-sional judgment.Not all aspects of this guide may be appli-cable in all circumstances.This ASTM standard is not intendedto represent or replace the standard of care by which theadequacy of a given professional service must be judged,norshould this document be applied without consideration of aprojects many unique aspects.The word standard in the title ofthis document means only that the document has been ap-proved through the ASTM consensus process.1.3 Precautions:1.3.1 It is the responsibility of the user of this guide tofollow any precautions in the equipment manufacturers rec-ommendations and to establish appropriate health and safetypractices.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 Jan.1,2020.Published January 2020.Originallyapproved in 2002.Last previous edition approved in 2018 as D6820 18.DOI:10.1520/D6820-20.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United StatesThis international standard was developed in accordance with internationally recognized principl