Designation:D5785/D5785M−20StandardPracticefor(AnalyticalProcedure)forDeterminingTransmissivityofConfinedNonleakyAquifersbyUnderdampedWellResponsetoInstantaneousChangeinHead(SlugTest)1ThisstandardisissuedunderthefixeddesignationD5785/D5785M;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope*1.1Thispracticecoversdeterminationoftransmissivityfromthemeasurementofthedampedoscillationabouttheequilibriumwaterlevelofawell-aquifersystemtoasuddenchangeofwaterlevelinawell.Underdampedresponseofwaterlevelinawelltoasuddenchangeinwaterlevelischaracterizedbyoscillatoryfluctuationaboutthestaticwaterlevelwithadecreaseinthemagnitudeoffluctuationandrecoverytoinitialwaterlevel.Underdampedresponsemayoccurinwellstappinghighlytransmissiveconfinedaquifersandindeepwellshavinglongwatercolumns.1.2ThisanalyticalprocedureisusedinconjunctionwiththefieldprocedureTestMethodD4044/D4044Mforcollectionoftestdata.1.3Limitations—Slugtestsareconsideredtoprovideanestimateoftransmissivityofaconfinedaquifer.Thistestmethodrequiresthatthestoragecoefficientbeknown.As-sumptionsofthispracticeprescribeafullypenetratingwell(awellopenthroughthefullthicknessoftheaquifer),buttheslugtestmethodiscommonlyconductedusingapartiallypenetrat-ingwell.Suchapracticemaybeacceptableforapplicationunderconditionsinwhichtheaquiferisstratifiedandhorizon-talhydraulicconductivityismuchgreaterthanverticalhydrau-licconductivity.Insuchacasethetestwouldbeconsideredtoberepresentativeoftheaveragehydraulicconductivityoftheportionoftheaquiferadjacenttotheopenintervalofthewell.Themethodassumeslaminarflowandisapplicableforaslugtestinwhichtheinitialwater-leveldisplacementislessthan0.1or0.2ofthelengthofthestaticwatercolumn.1.4ThispracticeforanalysispresentedhereisderivedbyvanderKamp(1)2basedonanapproximationoftheunder-dampedresponse...
