ASTM D5126-90(2004)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: D5126 – 90 (Reapproved 2004)
Standard Guide for
Comparison of Field Methods for Determining Hydraulic
Conductivity in Vadose Zone
This standard is issued under the fixed designation D5126; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope obtained with each test method. Ageneral description of each
testmethodandspecialcharacteristicsaffectingapplicabilityis
1.1 This guide covers a review of the test methods for
provided.
determining hydraulic conductivity in unsaturated soils and
1.5 Field test methods used to determine unsaturated hy-
sediments. Test methods for determining both field-saturated
draulic conductivity in the field include direct measurement
and unsaturated hydraulic conductivity are described.
techniques and various estimation methods. Direct measure-
1.2 Measurement of hydraulic conductivity in the field is
menttechniquesfordeterminingunsaturatedhydraulicconduc-
used for estimating the rate of water movement through clay
tivityincludetheinstantaneousprofile(IP)testmethodandthe
liners to determine if they are a barrier to water flux, for
gypsum crust method. Estimation techniques have been devel-
characterizing water movement below waste disposal sites to
opedusingboreholepermeameterdataandusingdataobtained
predictcontaminantmovement,andtomeasureinfiltrationand
from desorption curves (a curve relating water content to
drainage in soils and sediment for a variety of applications.
matric potential).
Test methods are needed for measuring hydraulic conductivity
−2 −8
1.6 The values stated in SI units are to be regarded as
ranging from 1 310 to 1 310 cm/s, for both surface and
standard.
subsurface layers, and for both field-saturated and unsaturated
1.7 This standard does not purport to address all of the
flow.
safety concerns, if any, associated with its use. It is the
1.3 For these field test methods a distinction must be made
responsibility of the user of this standard to establish appro-
between “saturated” (K ) and “field-saturated” (K ) hydraulic
s fs
priate safety and health practices and determine the applica-
conductivity. True saturated conditions seldom occur in the
bility of regulatory limitations prior to use.
vadose zone except where impermeable layers result in the
1.8 This guide offers an organized collection of information
presence of perched water tables. During infiltration events or
or a series of options and does not recommend a specific
in the event of a leak from a lined pond, a “field-saturated”
course of action. This document cannot replace education or
condition develops. True saturation does not occur due to
2 experienceandshouldbeusedinconjunctionwithprofessional
entrapped air (1). The entrapped air prevents water from
judgment. Not all aspects of this guide may be applicable in all
moving in air-filled pores that, in turn, may reduce the
circumstances. This ASTM standard is not intended to repre-
hydraulic conductivity measured in the field by as much as a
sent or replace the standard of care by which the adequacy of
factor of two compared to conditions when trapped air is not
a given professional service must be judged, nor should this
present (2). Field test methods should simulate the “field-
document be applied without consideration of a project’s many
saturated” condition.
unique aspects. The word “Standard” in the title of this
1.4 Field test methods commonly used to determine field-
document means only that the document has been approved
saturated hydraulic conductivity include various double-ring
through the ASTM consensus process.
infiltrometertestmethods,air-entrypermeametertestmethods,
and borehole permeameter tests. Many empirical test methods
2. Referenced Documents
are used for calculating hydraulic conductivity from data
2.1 ASTM Standards:
D653 Terminology Relating to Soil, Rock, and Contained
Fluids
ThisguideisunderthejurisdictionofASTMCommitteeD18onSoilandRock
and is the direct responsibility of Subcommittee D18.21 on Ground Water and
Vadose Zone Investigations.
CurrenteditionapprovedJuly1,2004.PublishedJuly2004.Originallyapproved
´1 3
in 1990. Last previous edition approved in 1998 as D5126-90 (1998) . DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/D5126-90R04. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
The boldface numbers in parentheses refer to a list of references at the end of Standards volume information, refer to the standard’s Document Summary page on
the text. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D5126 – 90 (2004)
D2434 Test Method for Permeability of Granular Soils (a) The movement of water into the soil profile is one-
(Constant Head) dimensional downward.
D3385 Test Method for Infiltration Rate of Soils in Field
(b) Equipment compliance effects are minimal and may be
Using Double-Ring Infiltrometer
disregarded or easily accounted for.
D4643 Test Method for Determination of Water (Moisture)
(c) The pressure of soil gas does not offer any impedance
Content of Soil by Microwave Oven Heating
to the downward movement of the wetting front.
(d) The wetting front is distinct and easily determined.
3. Terminology
(e) Dispersion of clays in the surface layer of finer soils is
3.1 Definitions:
insignificant.
3.1.1 Definitions shall be in accordance with Terminology
(f) The soil is non-swelling, or the effects of swelling can
D653.
easily be accounted for.
3.2 Definitions of Terms Specific to This Standard:
4.1.2 Single-Ring Infiltrometer:
3.2.1 Descriptions of terms shall be in accordance with Ref
4.1.2.1 The single-ring infiltrometer typically consists of a
(2).
cylindrical ring 30 cm or larger in diameter that is driven
several centimetres into the soil. Water is ponded within the
4. Summary of Guide
ring above the soil surface. The upper surface of the ring is
4.1 Test Methods for Measuring Saturated Hydraulic Con-
often covered to prevent evaporation. The volumetric rate of
ductivity Above the Water Table—There are several test meth-
water added to the ring sufficient to maintain a constant head
ods available for determining the field saturated hydraulic
within the ring is measured.Alternatively, if the head of water
conductivity of unsaturated materials above the water table.
within the ring is relatively large, a falling head type test may
Most of these methods involve measurement of the infiltration
be used wherein the flow rate, as measured by the rate of
rateofwaterintothesoilfromaninfiltrometerorpermeameter
decline of the water level within the ring, and the head for the
device.Infiltrometerstypicallymeasureconductivityatthesoil
later portion of the test are used in the calculations. Infiltration
surface, whereas permeameters may be used to determine
is terminated after the flow rate has approximately stabilized.
conductivity at different depths within the soil profile. A
The infiltrometer is removed immediately after termination of
representative list of the most commonly used equipment
infiltration, and the depth to the wetting front is determined
includes the following: infiltrometers (single and double-ring
either visually, with a penetrometer-type probe, or by moisture
infiltrometers), double-tube method, air-entry permeameter,
content determination for soil samples (see Test Method
and borehole permeameter methods (constant and multiple
D4643).
head methods).
4.1.2.2 A special type of single-ring infiltrometer is the
4.1.1 Infiltrometer Test Method:
ponded infiltration basin. This type of test is conducted by
4.1.1.1 Infiltrometer test methods measure the rate of infil-
pondingwaterwithinagenerallyrectangularbasinthatmaybe
tration at the soil surface (see Test Method D2434) that is
as large as several metres on a side. The flow rate required to
influenced both by saturated hydraulic conductivity as well as
maintainaconstantheadofwaterwithinthepondismeasured.
capillary effects of soil (4). Capillary effect refers to the ability
If the depth of ponding is negligible compared to the depth of
ofdrysoiltopullorwickwaterawayfromazoneofsaturation
the wetting front, the steady state flux of water across the soil
faster than would occur if soil were uniformly saturated. The
surface within the basin is presumed to be equal to the
magnitude of the capillary effect is determined by initial
saturated hydraulic conductivity of the soil.
moisture content at the time of testing, the pore size, soil
4.1.2.3 Anothervariantofthesingle-ringinfiltrometeristhe
physical characteristics (texture, structure), and a number of
air-entry permeameter (see Fig. 1). The air-entry permeameter
other factors. By waiting until steady-state infiltration is
is discussed in 4.1.4.
reached, the capillary effects are minimized.
4.1.3 Double-Ring Infiltrometer:
4.1.1.2 Most infiltrometers generally employ the use of a
metal cylinder placed at shallow depths into the soil, and 4.1.3.1 The underlying principles and method of operation
of the double-ring infiltrometer are similar to the single-ring
include the single-ring infiltrometer, the double-ring infiltrom-
eter, and the infiltration gradient method. Various adaptations infiltrometer, with the exception that an outer ring is included
to the design and implementation of these methods have been to ensure that one-dimensional downward flow exists within
employed to determine the field-saturated hydraulic conduc- the tested horizon of the inner ring. Water that infiltrated
tivity of material within the unsaturated zone (5). The prin- through the outer ring acts as a barrier to lateral movement of
ciples of operation of these methods are similar in that the water from the inner ring (see Fig. 2). Double-ring infiltrom-
steady volumetric flux of water infiltrating into the soil etersmaybeeitheropentotheatmosphere,ormostcommonly,
enclosed within the infiltrometer ring is measured. Saturated theinnerringmaybecoveredtopreventevaporation.Foropen
hydraulic conductivity is derived directly from solution of double-ring infiltrometers, the flow rate is measured directly
Darcy’s Equation for saturated flow. Primary assumptions are from the rate of decline of the water level within the inner ring
that the volume of soil being tested is field saturated and that for falling head tests, or from the rate of water input necessary
the saturated hydraulic conductivity is a function of the flow to maintain a stable head within the inner ring for the constant
rate and the applied hydraulic gradient across the soil volume. headcase;forsealeddouble-ringinfiltrometers,theflowrateis
4.1.1.3 Additional assumptions common to infiltrometer measured by weighing a sealed flexible bag that is used as the
tests are as follows: supple reservoir for the inner ring (6).
D5126 – 90 (2004)
The hole is then cleaned anda1to 2-cm layer of coarse
protective sand is placed in the bottom of the hole. An outer
tube is then placed in the hole and sunken about 5 cm into the
soil.Theoutertubeisthenfilledwithwaterandasmallerinner
tube is placed at the center of the outer tube. It is then driven
into the soil. A top plate assembly (see Fig. 2) consisting of
water supply valves and standpipes for the inner and outer
cylinders is installed. Water is then supplied to both cylinders.
Thestandpipefortheoutercylinderisallowedtooverflowand
thestandpipegagefortheinnercylinderissetat0byadjusting
the appropriate water supply values. After an equilibrium
period of approximately 1 h, the hole is saturated.
4.1.4.4 Aftersaturationisachieved,theleveloffallofwater
in the inner standpipe, H, is recorded at given time intervals, t.
H is recorded at least every 5 cm, for a total of at least 30 cm
(Test 2). During this test, water in the outer standpipe remains
FIG. 1 Diagram of the Equipment for the Air-Entry Permeameter
at a constant head.
Technique (from Klute, 1986)
4.1.4.5 After the data is recorded, the inner reservoir is
again filled and the inner standpipe water level is set to 0. The
system is allowed to re-equilibrate for a period of time at least
ten times as long as the time required to collect the first data
set.
4.1.4.6 After waiting, Test 2 is performed. The levels in the
outerstandpipeandinnerstandpipearebothbroughtto0.Once
again the drop in the inner standpipe in cm, H, is recorded as
a function of time, t. During the second test, however, water
levels in both tubes drop simultaneously. Both tests are then
performedasecondtimeoruntiltheresultsoftwoconsecutive
runs are consistent.
4.1.5 Air-Entry Permeameter:
4.1.5.1 Theair-entrypermeameterissimilartoasingle-ring
infiltrometerindesignandoperationinthatthevolumetricflux
of water into the soil within a single permeameter ring is used
tocalculatefield-saturatedhydraulicconductivity.Theprimary
differences between the two test methods are that the air-entry
permeameter typically penetrates deeper into the soil profile
and measures the air-entry pressure of the soil. Air-entry
pressure is used as an approximation of the wetting front
FIG. 2 Diagram of the Equipment Used for Double-Tube Test
pressure head for determination of the hydraulic gradient, and
Method (from Klute, 1986)
consequently field-saturated hydraulic conductivity.
4.1.5.2 The air-entry permeameter consists of a single ring,
typically30cmindiameter,sealedatthetop,thatisdriveninto
4.1.3.2 Refer to Test Method D3385 for measuring infiltra-
−2 −5
thesoilapproximately15to25cm.Waterisintroducedintothe
tion rates in the range of 10 to 10 cm/s. A modified
permeameter through a standpipe, to the top of which is
double-ring infiltrometer test method for infiltration rates from
−5 −8
attached a water supply reservoir.Water is allowed to infiltrate
10 to 10 cm/s is also being developed.
into the soil within the permeameter ring, and the flow rate is
4.1.4 Double-Tube Test Method:
measuredbyobservingthedeclineofthewaterlevelwithinthe
4.1.4.1 The double-tube test method proposed by Bouwer
reservoir.Afterapredeterminedamountofwaterhasinfiltrated
(6, 7, 8) has been described by Boersma (9) as a means of
(based upon the estimated available storage of the soil interval
measuringthehorizontal,aswellasthevertical,field-saturated
containedwithinthering),andtheflowrateisrelativelystable,
hydraulic conductivity of material in the vadose zone.
infiltration is terminated and the wetted profile is allowed to
4.1.4.2 This test method as proposed by Bouwer (6, 7, 8)
drain. The air-entry value is the minimum pressure measured
utilizes two coaxial cylinders positioned in an a
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