ASTM_D_5912_-_96e1.pdf

Designation:D 5912 96e1Standard Test Method for(Analytical Procedure)Determining Hydraulic Conductivityof an Unconfined Aquifer by Overdamped Well Response toInstantaneous Change in Head(Slug)1This standard is issued under the fixed designation D 5912;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(e)indicates an editorial change since the last revision or reapproval.e1NOTENote 5 was added editorially in December 1996.1.Scope1.1 This test method covers the determination of hydraulicconductivity from the measurement of inertial force free(overdamped)response of a well-aquifer system to a suddenchange in water level in a well.Inertial force free response ofthe water level in a well to a sudden change in water level ischaracterized by recovery to initial water level in an approxi-mate exponential manner with negligible inertial effects.1.2 The analytical procedure in this test method is used inconjunction with the field procedure in Test Method D 4044 forcollection of test data.1.3 LimitationsSlug tests are considered to provide anestimate of hydraulic conductivity.The determination of stor-age coefficient is not possible with this test method.Becausethe volume of aquifer material tested is small,the valuesobtained are representative of materials very near the openportion of the control well.NOTE1Slug tests are usually considered to provide estimates of thelower limit of the actual hydraulic conductivity of an aquifer because thetest results are so heavily influenced by well efficiency and borehole skineffects near the open portion of the well.The portion of the aquifer that istested by the slug test is limited to an area near the open portion of the wellwhere the aquifer materials may have been altered during well installation,and therefore may significantly effect the test results.In some cases thedata may be misinterpreted and result in a higher estimate of hydraulicconductivity.This is due to the reliance on early time data that is reflectiveof the hydraulic conductivity of the filter pack surrounding the well.Thiseffect was discussed by Bouwer.2In addition,because of the reliance onearly time data,in aquifers with medium to high hydraulic conductivity,the early time portion of the curve that is useful for this data analyses istoo short(for example,HlnRe/rw!5F1.1lnH/rw!1A 1 B lnD 2 H!/rw#L/rwG21(2)if D 5 Hln Re/rw5F1.1lnH/rw!1CL/rwG21(3)NOTE2Other analytical solutions are given by Hvorslev4and Cooperet al;5,6however,they may differ in their assumptions and applicability.NOTE3Bouwer2provided discussion of various applications andobservations of the procedure described in this test method.NOTE4Test Method D 4104 describes the analytical solution follow-ing Cooper et al.5NOTE5The use of the symbol K for the term hydraulic conductivityis the predominant usage in ground-water literature by hydrogeologists,whereas,the symbol k is commonly used for this term in soil and rockmechanics and soil science.5.Significance and Use5.1 Assumptions of Solution:5.1.1 Drawdown(or mounding)of the water table aroundthe well is negligible.5.1.2 Flow above the water table can be ignored.5.1.3 Head losses as the water enters or leaves the well arenegligible.5.1.4 The aquifer is homogeneous and isotropic.5.2 Implications of Assumptions:5.2.1 The mathematical equations applied ignore inertialeffects and assume that the water level returns to the static levelin an approximate exponential manner.5.2.2 The geometric configuration of the well and aquiferare shown in Fig.1,that is after Fig.1 of Bouwer and Rice.25.2.3 For filter-packed wells,Eq 1 applies to cases in whichthe filter pack remains saturated.If some of the filter pack isdewatered during testing,rc2should be replaced by thefollowing:rccorrected!51 2 n!ra21 nrw2#0.5(4)where:n5 short-term specific yield of the filter pack,ra5 uncorrected well casing radius,andrw5 borehole radius.NOTE6Short term refers to the duration of the slug test.6.Procedure6.1 The overall procedure consists of conducting the slugtest field procedure(see Test Method D 4044)and analysis ofthe field data that is addressed in this test method.6.2 The water level data are corrected so that the differencebetween the original static water level and the water levelduring the test is known.This difference in water level at time“t”is denoted as“yt”.6.3 The dimensionless coefficients of A,B,and C aredetermined graphically based on their relationship with L/rw.An example of the curves relating A,B,and C to L/rwis givenin Fig.2,that is after Fig.3 of Bouwer and Rice.27.Calculation7.1 Determine ln(Re/rw)using Eq 2 or Eq 3,as appropriate.7.2 Plot at a semilogarithmic scale the relationship of“y”onthe log scale versus elapsed time on the arithmetic scale.4Hvorslev,M.J.,“Time Lag and Soil Permeability in Ground-Water Observa-tions,”Waterways Experime