Designation:D6820−20StandardGuideforUseoftheTimeDomainElectromagneticMethodforGeophysicalSubsurfaceSiteInvestigation1ThisstandardisissuedunderthefixeddesignationD6820;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope1.1PurposeandApplication:1.1.1Thisguideisoneinaseriesofdocumentsthatdescribegeophysicalsiteinvestigationmethods.1.1.2Thisguidesummarizestheequipment,fieldprocedures,andinterpretationmethodsfortheassessmentofsubsurfacematerialsandtheirporefluidsusingtheTimeDomainElectromagnetic(TDEM)method.ThismethodisalsoknownastheTransientElectromagnetic(TEM)Method,andinthisguideisreferredtoastheTDEM/TEMmethod.TimeDomainandTransientrefertothemeasurementofatime-varyinginducedelectromagneticfield.1.1.3TheTDEM/TEMmethodisapplicabletothesubsur-facesiteinvestigationforawiderangeofconditions.TDEM/TEMmethodsmeasurevariationsintheelectricalresistivity(orthereciprocal,theelectricalconductivity)ofthesubsurfacesoilorrockcausedbybothlateralandverticalvariationsinvariousphysicalpropertiesofthesoilorrock.Bymeasuringbothlateralandverticalchangesinresistivity,variationsinsubsurfaceconditionscanbedetermined.1.1.4Electromagneticmeasurementsofresistivityasde-scribedinthisguideareappliedingeologicstudies,geotech-nicalstudies,hydrologicsiteinvestigations,andformappingsubsurfaceconditionsatwastedisposalsites(1).2Resistivitymeasurementscanbeusedtomapgeologicchangessuchaslithology,geologicalstructure,fractures,stratigraphy,anddepthtobedrock.Inaddition,measurementofresistivitycanbeappliedtohydrologicsiteinvestigationssuchasthedepthtowatertable,depthtoaquitard,presenceofcoastalorinlandgroundwatersalinity,andforthedirectexplorationforground-water.1.1.5ThisstandarddoesnotaddresstheuseofTDEM/TEMmethodforuseasmetaldetectorsortheiruseinunexplodedordnance(UXO)detectionandcharacterizatio...
