ASTM D5126-16e1

Standard Guide for Comparison of Field Methods for Determining Hydraulic Conductivity in Vadose Zone

SIGNIFICANCE AND USE
5.1 Saturated hydraulic conductivity measurements are made for a variety of purposes varying from design of landfills and construction of clay liners to assessment of irrigation systems. Infiltrometers are commonly used where infiltration or percolation rates through a surface or subsurface layer are desired. Evaluation of the rate of water movement through a pond liner is one example of this kind of measurement. Penetration of the liner by a borehole would invalidate the measurement of liner permeability. It has been noted that small-ring infiltrometers are subject to error due to lateral divergence of flow. Therefore, techniques using very large (1 to 2-m diameter) infiltration basins have been recommended for measuring the very slow percolation rates typically needed for clay liners. The air-entry permeameter can be used instead of infiltrometer tests to avoid lateral divergence of flow. However, because a cylinder must be driven into the media tested, the actual soil column tested may be disrupted by introduction of the cylinder, especially in structured soils.  
5.2 Borehole tests for determining saturated hydraulic conductivity are applicable for evaluating the rate of water movement through subsurface layers. For slowly permeable layers, an accurate method of measuring the rate of water movement into the borehole will need to be developed. Use of a flexible bag as a reservoir that can be periodically weighed is advisable for these conditions. A number of mathematical solutions for borehole outflow data are available (Stephens et al. (17), Reynolds et al. (18), and Philip (19)).  
5.3 Information on unsaturated flow rates is needed to design hazardous waste landfills and impoundments where prevention of flow of contaminants into groundwater is needed. Of the test methods available, the primary differences are cost and resultant bias and precision. The instantaneous profile test method appears to provide very reliable data because it uses a large volume of so...
SCOPE
1.1 This guide covers a review of the test methods for determining hydraulic conductivity in unsaturated soils and sediments. Test methods for determining both field-saturated and unsaturated hydraulic conductivity are described.  
1.2 Measurement of hydraulic conductivity in the field is used for estimating the rate of water movement through clay liners to determine if they are a barrier to water flux, for characterizing water movement below waste disposal sites to predict contaminant movement, and to measure infiltration and drainage in soils and sediment for a variety of applications. Test methods are needed for measuring hydraulic conductivity ranging from 1 × 10−2 to 1 × 10−8 cm/s, for both surface and subsurface layers, and for both field-saturated and unsaturated flow.  
1.3 For these field test methods a distinction is made between “saturated” (Ks) and “field-saturated” (Kfs) hydraulic conductivity. True saturated conditions seldom occur in the vadose zone except where impermeable layers result in the presence of perched water tables. During infiltration events or in the event of a leak from a lined pond, a “field-saturated” condition develops. True saturation does not occur due to entrapped air (1).2 The entrapped air prevents water from moving in air-filled pores that, in turn, may reduce the hydraulic conductivity measured in the field by as much as a factor of two compared to conditions when trapped air is not present (2). Field test methods should simulate the “field-saturated” condition.  
1.4 Field test methods commonly used to determine field-saturated hydraulic conductivity include various double-ring infiltrometer test methods, air-entry permeameter test methods, and borehole permeameter tests. Many empirical test methods are used for calculating hydraulic conductivity from data obtained with each test method. A general description of each test method and special characteristics affecting applicabili...

General Information

• Status: Published
• Publication Date: 30-Jun-2016
• ICS: 07.060 - Geology. Meteorology. Hydrology
• Technical Committee: D18 - Soil and Rock
• Drafting Committee: D18.21 - Groundwater and Vadose Zone Investigations

Relations

• Replaces: ASTM D5126/D5126M-16 - Standard Guide for Comparison of Field Methods for Determining Hydraulic Conductivity in Vadose Zone
• Effective Date: 01-Jul-2016
• Refers: ASTM D3740-23 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Nov-2023
• Refers: ASTM D3740-19 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Oct-2019
• Refers: ASTM D3385-18 - Standard Test Method for Infiltration Rate of Soils in Field Using Double-Ring Infiltrometer
• Effective Date: 01-Mar-2018
• Refers: ASTM D4643-17 - Standard Test Method for Determination of Water Content of Soil and Rock by Microwave Oven Heating
• Effective Date: 01-Feb-2017
• Refers: ASTM D653-14 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Aug-2014
• Refers: ASTM D3740-12a - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-May-2012
• Refers: ASTM D3740-12 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Mar-2012
• Refers: ASTM D653-11 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Sep-2011
• Refers: ASTM D3740-11 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Sep-2011
• Refers: ASTM D3740-10 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Mar-2010
• Refers: ASTM D3385-09 - Standard Test Method for Infiltration Rate of Soils in Field Using Double-Ring Infiltrometer
• Effective Date: 01-Mar-2009
• Refers: ASTM D653-09 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Jan-2009
• Refers: ASTM D653-08a - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Dec-2008
• Refers: ASTM D653-08 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Nov-2008

Overview

ASTM D5126-16e1 is a standardized guide developed by ASTM International outlining the comparison and selection of field methods for determining hydraulic conductivity in the vadose zone. Hydraulic conductivity is a critical property of unsaturated soils and sediments, relevant to applications such as landfills, clay liners, waste disposal sites, and soil drainage systems. This guide provides a comprehensive review of various test methods for assessing both field-saturated and unsaturated hydraulic conductivity, emphasizing the significance of appropriate field measurement techniques for environmental and geotechnical site investigations.

Key Topics

• Field vs. Laboratory Methods: ASTM D5126-16e1 focuses on field test methods rather than laboratory tests, underlining the importance of in-situ measurements for hydraulic conductivity due to the natural variability and heterogeneity of soils.
• Saturated vs. Field-Saturated vs. Unsaturated Conductivity: The guide differentiates between true saturated (Ks), field-saturated (Kfs), and unsaturated hydraulic conductivity. True saturation is rare in most vadose zones; thus, field-saturated conditions that account for entrapped air are emphasized.
• Test Methods Reviewed:
  • Single- and double-ring infiltrometers
  • Air-entry permeameters and ponded infiltration basins
  • Borehole permeameters, including constant and falling head tests
  • Direct measurement and estimation techniques for unsaturated conductivity, such as the instantaneous profile and gypsum crust methods, and mathematical analysis of outflow data
• Empirical and Analytical Approaches: Guidelines on using empirical formulas and analytical solutions to interpret infiltration and outflow data for estimating hydraulic conductivity.

Applications

The ASTM D5126-16e1 standard is essential for:

• Design and Evaluation of Liners: Assesses whether clay liners in waste containment or water management structures effectively limit water flux and contaminant migration.
• Environmental Impact Assessment: Characterizes water movement below waste disposal sites to predict the risk of groundwater contamination.
• Agricultural and Irrigation Studies: Measures infiltration and drainage properties in soils and sediments to improve irrigation management and soil conservation.
• Subsurface Engineering: Evaluates hydraulic conductivity in situ for site characterization in construction, remediation, and environmental monitoring projects.
• Selection of Field Methods: Assists engineers, geologists, and hydrologists in selecting appropriate test procedures based on site-specific conditions, required accuracy, budget, and depth of investigation.

Related Standards

• ASTM D653: Terminology relating to soil, rock, and contained fluids.
• ASTM D2434 (Withdrawn): Constant head permeability testing for granular soils.
• ASTM D3385: Field infiltration rate measurement using the double-ring infiltrometer.
• ASTM D4643: Determination of soil moisture content by microwave oven heating.
• ASTM D6026: Guidance on the use of significant digits in geotechnical data reporting.
• ASTM D3740: Requirements for agencies engaged in soil and rock testing.

Practical Value

Adopting ASTM D5126-16e1 ensures standardized, reliable, and comparable field data when determining hydraulic conductivity in unsaturated soils. The document supports accurate risk assessments for groundwater protection, efficient engineering designs for liners and barriers, and scientifically sound environmental monitoring practices. Selecting the suitable field test method based on this guide helps minimize measurement bias and errors, optimize costs, and improve the reliability of site characterizations across diverse geotechnical and environmental projects.

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Keywords: ASTM D5126-16e1, hydraulic conductivity, vadose zone, unsaturated soils, field methods, infiltrometer, permeameter, soil permeability, environmental site assessment, clay liner, groundwater protection, infiltration test.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
´1
Designation: D5126 − 16
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.
ε NOTE—The designation was editorially corrected to match the units of measurement statement in October 2016.
1. Scope* and borehole permeameter tests. Many empirical test methods
are used for calculating hydraulic conductivity from data
1.1 This guide covers a review of the test methods for
obtained with each test method.Ageneral description of each
determining hydraulic conductivity in unsaturated soils and
testmethodandspecialcharacteristicsaffectingapplicabilityis
sediments. Test methods for determining both field-saturated
provided.
and unsaturated hydraulic conductivity are described.
1.5 Field test methods used to determine unsaturated hy-
1.2 Measurement of hydraulic conductivity in the field is
draulic conductivity in the field include direct measurement
used for estimating the rate of water movement through clay
techniques and various estimation methods. Direct measure-
liners to determine if they are a barrier to water flux, for
menttechniquesfordeterminingunsaturatedhydraulicconduc-
characterizing water movement below waste disposal sites to
tivityincludetheinstantaneousprofile(IP)testmethodandthe
predictcontaminantmovement,andtomeasureinfiltrationand
gypsum crust method. Estimation techniques have been devel-
drainage in soils and sediment for a variety of applications.
opedusingboreholepermeameterdataandusingdataobtained
Test methods are needed for measuring hydraulic conductivity
−2 −8
from desorption curves (a curve relating water content to
ranging from 1×10 to1×10 cm/s, for both surface and
matric potential).
subsurface layers, and for both field-saturated and unsaturated
flow.
1.6 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
1.3 For these field test methods a distinction is made
standard.
between “saturated” (K ) and “field-saturated” (K ) hydraulic
s fs
conductivity. True saturated conditions seldom occur in the
1.7 All observed and calculated values shall conform to the
vadose zone except where impermeable layers result in the
guidelines for significant digits and rounding established in
presence of perched water tables. During infiltration events or
Practice D6026.
in the event of a leak from a lined pond, a “field-saturated”
1.7.1 The method used to specify how data are collected,
condition develops. True saturation does not occur due to
2 calculated,orrecordedinthisstandardisnotdirectlyrelatedto
entrapped air (1). The entrapped air prevents water from
theaccuracytowhichthedatacanbeappliedindesignorother
moving in air-filled pores that, in turn, may reduce the
uses, or both. How one applies the results obtained using this
hydraulic conductivity measured in the field by as much as a
standard is beyond its scope.
factor of two compared to conditions when trapped air is not
present (2). Field test methods should simulate the “field- 1.8 This standard does not purport to address all of the
saturated” condition. safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
1.4 Field test methods commonly used to determine field-
priate safety and health practices and determine the applica-
saturated hydraulic conductivity include various double-ring
bility of regulatory limitations prior to use.
infiltrometertestmethods,air-entrypermeametertestmethods,
1.9 This guide offers an organized collection of information
or a series of options and does not recommend a specific
course of action. This document cannot replace education or
ThisguideisunderthejurisdictionofASTMCommitteeD18onSoilandRock
experienceandshouldbeusedinconjunctionwithprofessional
and is the direct responsibility of Subcommittee D18.21 on Groundwater and
judgment. Not all aspects of this guide may be applicable in all
Vadose Zone Investigations.
CurrenteditionapprovedJuly1,2016.PublishedJuly2016.Originallyapproved
circumstances. This ASTM standard is not intended to repre-
ɛ1
in 1990. Last previous edition approved in 2010 as D5126–90(2010) . DOI:
sent or replace the standard of care by which the adequacy of
10.1520/D5126-16E01.
a given professional service must be judged, nor should this
The boldface numbers in parentheses refer to a list of references at the end of
the text. document be applied without consideration of a project’s many
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
D5126 − 16
unique aspects. The word “Standard” in the title of this other factors. By waiting until steady-state infiltration is
document means only that the document has been approved reached, the capillary effects are minimized.
through the ASTM consensus process.
4.1.1.2 Most infiltrometers generally employ the use of a
metal cylinder placed at shallow depths into the soil, and
2. Referenced Documents
include the single-ring infiltrometer, the double-ring
2.1 ASTM Standards:
infiltrometer, and the infiltration gradient method. Various
D653Terminology Relating to Soil, Rock, and Contained
adaptationstothedesignandimplementationofthesemethods
Fluids
have been employed to determine the field-saturated hydraulic
D2434Test Method for Permeability of Granular Soils
conductivity of material within the unsaturated zone (5). The
(Constant Head) (Withdrawn 2015)
principles of operation of these methods are similar in that the
D3385Test Method for Infiltration Rate of Soils in Field
steady volumetric flux of water infiltrating into the soil
Using Double-Ring Infiltrometer
enclosed within the infiltrometer ring is measured. Saturated
D3740Practice for Minimum Requirements for Agencies
hydraulic conductivity is derived directly from solution of
Engaged in Testing and/or Inspection of Soil and Rock as
Darcy’s Equation for saturated flow. Primary assumptions are
Used in Engineering Design and Construction
that the volume of soil being tested is field saturated and that
D4643Test Method for Determination of Water (Moisture)
the saturated hydraulic conductivity is a function of the flow
Content of Soil by Microwave Oven Heating
rate and the applied hydraulic gradient across the soil volume.
D6026Practice for Using Significant Digits in Geotechnical
4.1.1.3 Additional assumptions common to infiltrometer
Data
tests are as follows:
(a)The movement of water into the soil profile is one-
3. Terminology
dimensional downward.
3.1 Definitions:
(b)Equipment compliance effects are minimal and may be
3.1.1 Forcommondefinitionsoftermsinthisstandard,refer
disregarded or easily accounted for.
to Terminology D653.
(c)Thepressureofsoilgasdoesnotofferanyimpedanceto
3.2 Descriptions of other related terms can be found in Ref
the downward movement of the wetting front.
(3).
(d)The wetting front is distinct and easily determined.
(e)Dispersion of clays in the surface layer of finer soils is
4. Summary of Guide
insignificant.
4.1 Test Methods for Measuring Saturated Hydraulic Con-
(f)The soil is non-swelling, or the effects of swelling can
ductivity Above the Water Table—There are several test meth-
easily be accounted for.
ods available for determining the field saturated hydraulic
4.1.2 Single-Ring Infiltrometer:
conductivity of unsaturated materials above the water table.
4.1.2.1 The single-ring infiltrometer typically consists of a
Most of these methods involve measurement of the infiltration
cylindrical ring 30 cm or larger in diameter that is driven
rateofwaterintothesoilfromaninfiltrometerorpermeameter
several centimetres into the soil. Water is ponded within the
device.Infiltrometerstypicallymeasureconductivityatthesoil
ring above the soil surface. The upper surface of the ring is
surface, whereas permeameters may be used to determine
often covered to prevent evaporation. The volumetric rate of
conductivity at different depths within the soil profile. A
water added to the ring sufficient to maintain a constant head
representative list of the most commonly used equipment
within the ring is measured.Alternatively, if the head of water
includes the following: infiltrometers (single and double-ring
within the ring is relatively large, a falling head type test may
infiltrometers), double-tube method, air-entry permeameter,
be used wherein the flow rate, as measured by the rate of
and borehole permeameter methods (constant and multiple
decline of the water level within the ring, and the head for the
head methods).
later portion of the test are used in the calculations. Infiltration
4.1.1 Infiltrometer Test Method:
is terminated after the flow rate has approximately stabilized.
4.1.1.1 Infiltrometer test methods measure the rate of infil-
The infiltrometer is removed immediately after termination of
tration at the soil surface (see Test Method D2434) that is
infiltration, and the depth to the wetting front is determined
influenced both by saturated hydraulic conductivity as well as
capillary effects of soil (4). Capillary effect refers to the ability either visually, with a penetrometer-type probe, or by moisture
content determination for soil samples (see Test Method
ofdrysoiltopullorwickwaterawayfromazoneofsaturation
faster than would occur if soil were uniformly saturated. The D4643).
magnitude of the capillary effect is determined by initial
4.1.2.2 A special type of single-ring infiltrometer is the
moisture content at the time of testing, the pore size, soil
ponded infiltration basin. This type of test is conducted by
physical characteristics (texture, structure), and a number of
pondingwaterwithinagenerallyrectangularbasinthatmaybe
as large as several metres on a side. The flow rate to maintain
a constant head of water within the pond is measured. If the
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
depth of ponding is negligible compared to the depth of the
Standards volume information, refer to the standard’s Document Summary page on
wetting front, the steady state flux of water across the soil
the ASTM website.
4 surface within the basin is presumed to be equal to the
The last approved version of this historical standard is referenced on
www.astm.org. saturated hydraulic conductivity of the soil.
´1
D5126 − 16
4.1.2.3 Anothervariantofthesingle-ringinfiltrometeristhe
air-entry permeameter (see Fig. 1). The air-entry permeameter
is discussed in 4.1.4.
4.1.3 Double-Ring Infiltrometer:
4.1.3.1 The underlying principles and method of operation
of the double-ring infiltrometer are similar to the single-ring
infiltrometer, with the exception that an outer ring is included
to make sure that one-dimensional downward flow exists
withinthetestedhorizonoftheinnerring.Waterthatinfiltrated
through the outer ring acts as a barrier to lateral movement of
water from the inner ring (see Fig. 2). Double-ring infiltrom-
etersmaybeeitheropentotheatmosphere,ormostcommonly,
theinnerringmaybecoveredtopreventevaporation.Foropen
double-ring infiltrometers, the flow rate is measured directly
from the rate of decline of the water level within the inner ring
for falling head tests, or from the rate of water input necessary
to maintain a stable head within the inner ring for the constant
headcase;forsealeddouble-ringinfiltrometers,theflowrateis
measured by weighing a sealed flexible bag that is used as the
supple reservoir for the inner ring (6).
4.1.3.2 Refer to Test Method D3385 for measuring infiltra-
FIG. 2 Diagram of the Equipment Used for Double-Tube Test
−2 −5
tion rates in the range of 10 to 10 cm/s. A modified
Method (from Klute, 1986)
double-ring infiltrometer test method for infiltration rates from
−5 −8
10 to 10 cm/s is also being developed.
soil.Theoutertubeisthenfilledwithwaterandasmallerinner
4.1.4 Double-Tube Test Method:
tube is placed at the center of the outer tube. It is then driven
4.1.4.1 The double-tube test method proposed by Bouwer
into the soil. A top plate assembly (see Fig. 2) consisting of
(6, 7, 8) has been described by Boersma (9) as a means of
water supply valves and standpipes for the inner and outer
measuringthehorizontal,aswellasthevertical,field-saturated
cylinders is installed. Water is then supplied to both cylinders.
hydraulic conductivity of material in the vadose zone.
Thestandpipefortheoutercylinderisallowedtooverflowand
4.1.4.2 This test method as proposed by Bouwer (6, 7, 8)
thestandpipegagefortheinnercylinderissetat0byadjusting
utilizes two coaxial cylinders positioned in an auger hole. The
the appropriate water supply values. After an equilibrium
differencebetweentherateofflowintheinnercylinderandthe
period of approximately 1 h, the hole is saturated.
simultaneousrateofcombinedflowfromintheinnerandouter
4.1.4.4 Aftersaturationisachieved,theleveloffallofwater
cylinders is used to calculate K .
fs
in the inner standpipe, H, is recorded at given time intervals, t.
4.1.4.3 Aboreholeisauguredtothedesireddepthandahole
H is recorded in most cases at least every 5 cm, for a total
conditioning device is used to square the bottom of the hole.
minimumof30cm(Test2).Duringthistest,waterintheouter
The hole is then cleaned anda1to 2-cm layer of coarse
standpipe remains at a constant head.
protective sand is placed in the bottom of the hole. An outer
4.1.4.5 After the data is recorded, the inner reservoir is
tube is then placed in the hole and sunken about 5 cm into the
again filled and the inner standpipe water level is set to 0. The
system is allowed to re-equilibrate for a period of time, a
minimum ten times as long as the time needed 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
FIG. 1 Diagram of the Equipment for the Air-Entry Permeameter
Technique (from Klute, 1986) pressure is used as an approximation of the wetting front
´1
D5126 − 16
pressure head for determination of the hydraulic gradient, and 4.1.7 Empirical Methods—Saturated Hydraulic Conductiv-
consequently field-saturated hydraulic conductivity. ity:
4.1.7.1 A number of empirical methods have been devel-
4.1.5.2 The air-entry permeameter consists of a single ring,
oped for estimation of hydraulic conductivity from grain size
typically30cmindiameter,sealedatthetop,thatisdriveninto
data (Shepard (11)). Shepard suggested that hydraulic conduc-
thesoilapproximately15to25cm.Waterisintroducedintothe
tivity could be predicted from the following:
permeameter through a standpipe, to the top of which is
a
attached a water supply reservoir.Water is allowed to infiltrate
K 5 cd (1)
into the soil within the permeameter ring, and the flow rate is
where:
measuredbyobservingthedeclineofthewaterlevelwithinthe
c = a dimensionless constant found through regression
reservoir.Afterapredeterminedamountofwaterhasinfiltrated
analysis,
(based upon the estimated available storage of the soil interval
d = the mean pore throat or particle diameter, and
containedwithinthering),andtheflowrateisrelativelystable,
a = an exponent generally ranging from 1.65 to 1.85.
infiltration is terminated and the wetted profile is allowed to
drain. The air-entry value is the minimum pressure measured
4.1.7.2 Values for c and a were found to vary substantially
overthestandingwaterinsideofthepermeameterringattained
depending on the degree of sorting of particles and the amount
during drainage. Once the minimum pressure is achieved, the of induration. Both c and a decreased as the degree of sorting
permeameter is removed, and the depth to the wetting front is
became poorer and as the induration increased. The amount of
determined (10). secondary porosity (“structure” in soils, or “fractures” in rock
and sediment) is also expected to affect the values for c and a.
4.1.6 Borehole Permeameter:
Estimatesof Kforaparticularvalueof dvariedbynearlythree
4.1.6.1 Borehole permeameter test methods encompass a
orders of magnitude depending on the choice of values for c
wide range of test designs, methods of operation, and methods
and a(11).
of solution. The common feature among the different types of
borehole tests is that the rate of water infiltration into a
4.2 Test Methods for Measuring Unsaturated Hydraulic
cylindrical borehole is used to determine field-saturated hy-
Conductivity:
draulic conductivity. One of the most popular borehole infil-
4.2.1 Instantaneous Profile Test Method (IP):
tration tests is the constant-head borehole infiltration test,
4.2.1.1 Several references, including Watson (12), describe
wherein the flow rate necessary to maintain a constant water
the IP test method. The relationship between water potential
levelwithinaboreholeismeasured.Thesteadystateflowrate,
andhydraulicconductivitycanbedeterminedbymeasuringthe
borehole geometry, borehole radius (r), and depth of ponding
rate of drainage and water potential and then solving a form of
within the borehole (h), along with certain capillary
the Richards equation. The Richards equation solves for the
parameters, are typically used in the solution. Hence, by change in water content through time for non-steady, uniform,
accounting for capillary effects, borehole test methods attempt
unsaturated flow by relating water potential and unsaturated
to measure field-saturated hydraulic conductivity rather than hydraulic conductivity.
infiltration rate. Another variation of this test consists of
4.2.1.2 ToconductanIPtest,asmallbasinisconstructedin
conducting multiple constant head borehole infiltration tests
which water is ponded. Neutron access tubing and a nest of
withinthesameborehole.Differentwaterlevelsareestablished
tensiometers at varying depths are installed in the center of the
within the borehole for each individual test. Results from one
basin. Water is ponded in the basin until the wetting front
or more tests at different ponded heights are solved simultane-
passesthebottomofthehorizonbeinginvestigated.Movement
ously to independently find hydraulic conductivity and capil-
of the wetting front is detected with a neutron probe. The soil
larity. basin is then covered to reduce evaporation and water content
and water potential are measured periodically as water drains
4.1.6.2 Borehole infiltration tests are the only currently
downward under the influence of gravity.
available tests that can measure field-saturated hydraulic con-
4.2.2 Gypsum Crust Test Method:
ductivity at depth within the unsaturated zone. Borehole tests
may be conducted at great depth within the unsaturated zone,
4.2.2.1 Thegypsumcrusttestmethodissimilartoinfiltrom-
and are frequently used to measure the variability of conduc-
eter methods in that the rate of water flux across an infiltrative
tivity with depth by conducting tests at selected horizons
surface is measured.Acrust composed of varying mixtures of
within an advancing borehole.
gypsum and coarse sand is poured over the surface of an
exposedexcavatedcylinderofsoil.Afterthecrustcures,water
4.1.6.3 During constant head borehole tests, water is intro-
is ponded on the crust. The presence of the crust causes
duced into a cylindrical borehole and maintained at a prede-
unsaturated conditions to form in the soil beneath the crust.
termined level. This may be accomplished by use of a float
valve connected to an external water supply reservoir, or with 4.2.2.2 The cylinder of soil is instrumented with a nest of
tensiometers to measure water potential below the gypsum
a Mariotte-siphon device (2, 10). The flow rate into the
boreholenecessarytomaintainthewaterattheprescribedlevel crust.Therateoffluxofwaternecessarytomaintainaconstant
head over the gypsum crust and the diameter of the cylinder is
is measured at various times. The flow rate at steady state is
also recorded (13, 14).
used in the solution of field-saturated hydraulic conductivity.
The dimensions and geometry of the borehole and the depth to
4.2.3 Empirical Test Methods—Unsaturated Hydraulic
the water table are also needed for the solution. Conductivity:
´1
D5126 − 16
4.2.3.1 A number of empirical test methods have been of magnitude, but may be of use where relative differences in
developed to estimate unsaturated hydraulic conductivity from permeability between materials or across water content ranges
other hydraulic parameters. Van Genuchten (15) and Mualem is of interest.
(16) developed methods for predicting unsaturated hydraulic
NOTE 1—The quality of the result produced by this standard is
conductivity from the desorption curve (that relates water
dependent on the competence of the personnel performing it, and the
content to water potential) and from K measurements. Reyn-
suitability of the equipment and facilities used. Agencies that meet the
s
olds and Elrick (2) developed a borehole permeameter method criteria of Practice D3740 are generally considered capable of competent
and objective testing/sampling/inspection/etc. Users of this standard are
for measuring a fitting parameter used for estimating unsatu-
cautionedinthatcompliancewithPracticeD3740doesnotinitselfassure
rated hydraulic conductivity according to a model proposed by
reliable results. Reliable results depends on many factors; Practice D3740
Gardner. The fitting parameter is found by solving simultane-
provides a means of evaluating some of those factors.
ousequationsdevelopedfromboreholewaterfluxdatafortwo
ponded heights. The two ponded height test method is dis-
6. Report: Test Data Sheets
cussed further in 6.4. Infiltration data can be used to estimate
6.1 The reporting requirements for each test vary substan-
hydraulic conductivities by solving the Green-Ampt or Philips
tially. However, the variability of hydraulic conductivity in
Eq. (4).
soils, and the sensitivity of some test methods to factors such
as textural stratifications, anisotropic conditions, changes in
5. Significance and Use
temperature or barometric pressure, initial and final water
5.1 Saturated hydraulic conductivity measurements are
contents, and depth to groundwater, suggest that a detailed
madeforavarietyofpurposesvaryingfromdesignoflandfills
descriptionofeachtestsiteberecorded.Recordasaminimum
and construction of clay liners to assessment of irrigation
the following general information (data):
systems. Infiltrometers are commonly used where infiltration
6.1.1 Soil series (for comparison to existing data),
or percolation rates through a surface or subsurface layer are
6.1.2 Soil horizon characteristics above and below layer
desired. Evaluation of the rate of water movement through a
tested (to help interpret deviations from theoretical response),
pond liner is one example of this kind of measurement.
6.1.3 Initial and final water content (measure or describe
Penetration of the liner by a borehole would invalidate the
subjectively depending upon method and to identify which
measurement of liner permeability. It has been noted that
numerical solution is most applicable),
small-ring infiltrometers are subject to error due to lateral
6.1.4 General climatic conditions (for example, barometric
divergenceofflow.Therefore,techniquesusingverylarge(1to
pressure, temperature, precipitation, cloud cover to estimate
2-m diameter) infiltration basins have been recommended for
evaporation, pressure responses, accumulation of precipitation
measuring the very slow percolation rates typically needed for
that might bias results),
clay liners. The air-entry permeameter can be used instead of
6.1.5 Diameter of borehole or infiltration ring (parameter
infiltrometerteststoavoidlateraldivergenceofflow.However,
used in solution),
because a cylinder must be driven into the media tested, the
6.1.6 Rate of outflow, infiltration, or drainage (parameter
actual soil column tested may be disrupted by introduction of
used in solution),
the cylinder, especially in structured soils.
6.1.7 Water potential (tensiometer) readings (parameter
5.2 Borehole tests for determining saturated hydraulic con-
used in solution),
ductivity are applicable for evaluating the rate of water
6.1.8 Temperature of water used, and
movement through subsurface layers. For slowly permeable
6.1.9 Chemical composition of water used.
layers, an accurate method of measuring the rate of water
6.1.10 Record data in accordance with Practice D6026 and
movement into the borehole will need to be developed. Use of
Test Method D2434, or Test Method D3385 as appropriate for
aflexiblebagasareservoirthatcanbeperiodicallyweighedis
the test and for significant digits and rounding.
advisable for these conditions. A number of mathematical
6.1.11 Names of personnel performing test and developing
solutions for borehole outflow data are available (Stephens et
report.
al. (17), Reynolds et al. (18), and Philip (19)).
6.2 Infiltrometer Tests:
5.3 Information on unsaturated flow rates is needed to
6.2.1 Infiltrometer tests are useful for measuring the rate of
design hazardous waste
...