ASTM D5126-90(1998)e1

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e1
Designation: D 5126 – 90 (Reapproved 1998)
Standard Guide for
Comparison of Field Methods for Determining Hydraulic
Conductivity in the Vadose Zone
This standard is issued under the fixed designation D 5126; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Paragraph 1.8 was editorially added in October 1998.
1. Scope obtained with each test method. A general description of each
test method, and special characteristics affecting applicability
1.1 This guide provides a review of the test methods for
is 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
ment techniques for determining unsaturated hydraulic conduc-
used for estimating the rate of water movement through clay
tivity include the instantaneous profile (IP) test method, and the
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
oped using borehole permeameter data, and using data ob-
predict contaminant movement, and to measure infiltration and
tained 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 3 10 to 1 3 10 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 experience and should be used in conjunction with professional
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.
infiltrometer test methods, air-entry permeameter test methods,
and borehole permeameter tests. Many empirical test methods
2. Referenced Documents
are used for calculating hydraulic conductivity from data
2.1 ASTM Standards:
D 653 Terms and Symbols Relating to Soil and Rock
D 2434 Test Method for Permeability of Granular Soils
This guide is under the jurisdiction of ASTM Committee D-18 on Soil and
(Constant Head)
Rock and is the direct responsibility of Subcommittee D18.21.02 on Vadose Zone
Monitoring.
Current edition approved Oct. 26, 1990. Published December 1990.
The boldface numbers in parentheses refer to a list of references at the end of
the text. Annual Book of ASTM Standards, Vol 04.08.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 5126
D 3385 Test Method for Infiltration Rate of Soils in the (b) Equipment compliance effects are minimal and may be
Field Using Double-Ring Infiltrometers disregarded or easily accounted for.
D 4643 Test Method for Determination of Water (Moisture) (c) The pressure of soil gas does not offer any impedance to
Content of Soil by the Microwave Oven Method 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 Terms and
(f) The soil is non-swelling, or the effects of swelling can
Symbols D 653.
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
rate of water into the soil from an infiltrometer or permeameter
decline of the water level within the ring, and the head for the
device. Infiltrometers typically measure conductivity at the soil
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
borehole permeameter methods, (constant and multiple head
D 4643).
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-
ponding water within a generally rectangular basin that may be
tration at the soil surface, (see Test Method D 2434), that is
as large as several metres on a side. The flow rate required to
influenced both by saturated hydraulic conductivity as well as
maintain a constant head of water within the pond is measured.
capillary effects of soil (4). Capillary effect refers to the ability
If the depth of ponding is negligible compared to the depth of
of dry soil to pull or wick water away from a zone of saturation
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 Another variant of the single ring infiltrometer is the
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.
4.1.1.2 Most infiltrometers generally employ the use of a
metal cylinder placed at shallow depths into the soil, and
include the single ring infiltrometer, the double ring infiltrom-
eter, and the infiltration gradient method. Various adaptations
to the design and implementation of these methods have been
employed to determine the field-saturated hydraulic conduc-
tivity of material within the unsaturated zone (5). The prin-
ciples of operation of these methods are similar in that the
steady volumetric flux of water infiltrating into the soil
enclosed within the infiltrometer ring is measured. Saturated
hydraulic conductivity is derived directly from solution of
Darcy’s Equation for saturated flow. Primary assumptions are
that the volume of soil being tested is field-saturated and that
the saturated hydraulic conductivity is a function of the flow
rate and the applied hydraulic gradient across the soil volume.
4.1.1.3 Additional assumptions common to infiltrometer
tests are as follows:
(a) The movement of water into the soil profile is one-
FIG. 1 Diagram of the Equipment for the Air-Entry Permeameter
dimensional downward. Technique (from Klute, 1986)
D 5126
4.1.3 Double Ring Infiltrometer: tube is then placed in the hole and sunken about 5 cm into the
4.1.3.1 The underlying principles and method of operation soil. The outer tube is then filled with water and a smaller inner
of the double ring infiltrometer are similar to the single ring tube is placed at the center of the outer tube. It is then driven
infiltrometer, with the exception that an outer ring is included into the soil. A top plate assembly (see Fig. 2) consisting of
to ensure that one-dimensional downward flow exists within water supply valves and standpipes for the inner and outer
the tested horizon of the inner ring. Water that infiltrated cylinders is installed. Water is then supplied to both cylinders.
through the outer ring acts as a barrier to lateral movement of The standpipe for the outer cylinder is allowed to overflow and
water from the inner ring (see Fig. 2). Double ring infiltrom- the standpipe gage for the inner cylinder is set at 0 by adjusting
eters may be either open to the atmosphere, or most commonly, the appropriate water supply values. After an equilibrium
the inner ring may be covered to prevent evaporation. For open period of approximately 1 h, the hole is saturated.
double ring infiltrometers the flow rate is measured directly
4.1.4.4 After saturation is achieved, the level of fall of water
from the rate of decline of the water level within the inner ring
in the inner standpipe, H, is recorded at given time intervals, t.
for falling head tests, or from the rate of water input necessary
H is recorded at least every 5 cm, for a total of at least 30 cm
to maintain a stable head within the inner ring for the constant
(Test 2). During this test, water in the outer standpipe remains
head case; for sealed double ring infiltrometers, the flow rate is
at a constant head.
measured by weighing a sealed flexible bag that is used as the
4.1.4.5 After the data is recorded, the inner reservoir is
supple reservoir for the inner ring (6).
again filled and the inner standpipe water level is set to 0. The
4.1.3.2 Refer to Test Method D 3385 for measuring infiltra-
system is allowed to re-equilibrate for a period of time at least
−2 −5
tion rates in the range of 10 to 10 cm/s. A modified
ten times as long as the time required to collect the first data
double-ring infiltrometer test method for infiltration rates from
set.
−5 −8
10 to 10 cm/s is also being developed.
4.1.4.6 After waiting, Test 2 is performed. The levels in the
4.1.4 Double Tube Test Method:
outer standpipe and inner standpipe are both brought to 0. Once
4.1.4.1 The double tube test method proposed by Bouwer
again the drop in the inner standpipe in cm, H, is recorded as
(6, 7, 8) has been described by Boersma (9) as a means of
a function of time, t. During the second test, however, water
measuring the horizontal, as well as the vertical, field-saturated
levels in both tubes drop simultaneously. Both tests are then
hydraulic conductivity of material in the vadose zone.
performed a second time or until the results of two consecutive
4.1.4.2 This test method as proposed by Bouwer (6, 7, 8)
runs are consistent.
utilizes two coaxial cylinders positioned in an auger hole. The
4.1.5 Air-Entry Permeameter:
difference between the rate of flow in the inner cylinder and the
4.1.5.1 The air-entry permeameter is similar to a single ring
simultaneous rate of combined flow from in the inner and outer
infiltrometer in design and operation in that the volumetric flux
cylinders is used to calculate K .
fs
of water into the soil within a single permeameter ring is used
4.1.4.3 A borehole is augured to the desired depth and a hole
to calculate field-saturated hydraulic conductivity. The primary
conditioning device is used to square the bottom of the hole.
differences between the two test methods are that the air-entry
The hole is then cleaned anda1to2cm layer of coarse
permeameter typically penetrates deeper into the soil profile
protective sand is placed in the bottom of the hole. An outer
and measures the air-entry pressure of the soil. Air-entry
pressure is used as an approximation of the wetting front
pressure head for determination of the hydraulic gradient, and
consequently field-saturated hydraulic conductivity.
4.1.5.2 The air-entry permeameter consists of a single ring,
typically 30 cm in diameter, sealed at the top, that is driven into
the soil approximately 15 to 25 cm. Water is introduced into the
permeameter through a standpipe, to the top of which is
attached a water supply reservoir. Water is allowed to infiltrate
into the soil within the permeameter ring, and the flow rate is
measured by observing the decline of the water level within the
reservoir. After a predetermined amount of water has
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