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...

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ASTM D5126-16e1 - Standard Guide for Comparison of Field Methods for Determining Hydraulic Conductivity in Vadose Zone
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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
1
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
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
1
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.
2
a given professional service must be judged, nor should this
The boldface numbers in parenthe
...

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