EPA/530-SW-86-007
March 1986
DESIGN, CONSTRUCTION, AND EVALUATION
OF CLAY LINERS FOR
WASTE MANAGEMENT FACILITIES
Draft Technical Resource Document
for Public Comment
OFFICE OF SOLID WASTE AND EMERGENCY RESPONSE
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
Hazardous Waste Engineering Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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DISCLAIMER
This report was prepared by Dr. L. J. Goldman, R. S. Truesdale, G. L.
Kingsbury, C. M. Northeim, and A. S. Damle of the Research Triangle Institute
(RTI), Research Triangle Park, NC, under Contract Number 68-03-3149-1-2.
| The U.S. Environmental Protection Agency (EPA) Project Officer was M. H.
Roulier of the Hazardous Waste Engineering Research Laboratory, Cincinnati,
Ohio.
This is a draft technical resource document that is being distributed
by EPA for comment on the accuracy and usefulness of the information it
contains. The report has received extensive technical review, but the
Agency's peer and administrative review process has not yet been completed.
Therefore, it does not necessarily reflect the views or policies of the
Agency. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
Hpijf
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FOREWORD
The Environmental Protection Agency was created because of increasing
public and governmental concern about the dangers of pollution to the
health and welfare of the American people. Noxious air, foul water, and
spoiled land are tragic testimony to the deterioration of our natural
environment. The complexity of the environment and the interplay of its
components require a concentrated and integrated attack on the problem.
The Office of Solid Waste is responsible for issuing regulations and
guidelines on the proper treatment, storage, and disposal of hazardous
wastes to protect human health and the environment from the potential harm
associated with improper management of these wastes. These regulations are
supplemented by guidance manuals, technical guidelines, and technical
resource documents, made available to assist the regulated community and
facility designers in understanding the scope of the regulatory program.
Publications like this one provide facility designers with state-of-the-art
information on design and performance evaluation techniques.
This technical resource document is a compilation of all of the available
information relevant to the design, construction, and performance of clay-
lined waste management facilities. The broad topics covered are: clays;
geotechnical testing of soils; the compatibility of clays and chemical
wastes; the design, construction, and construction quality assurance of
clay liners; potential failure mechanisms; the performance of existing
facilities; and methods for predicting the useful life (transit time) based
on the modeling of leachate flow through soils.
Marcia Williams, Director
Office of Solid Waste
U.S. Environmental Protection Agency
m
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PREFACE
Subtitle C of the Resource Conservation and Recovery Act (RCRA) requires
the U.S. Environmental Protection Agency (EPA) to establish a Federal
hazardous waste management program. This program must ensure that hazard-
ous wastes are handled safely from generation until final disposition. EPA
issued a series of hazardous waste regulations under Subtitle C of RCRA
that are published in 40 Code of Federal Regulations (CFR) 260 through 265
and 122 through 124.
Parts 264 and 265 of 40 CFR contain standards applicable to owners and
operators of all facilities that treat, store, or dispose of hazardous
wastes. Wastes are identified or listed as hazardous under 40 CFR Part
261. Part 264 standards are implemented through permits issued by author-
ized States or EPA according to 40 CFR Part 122 and Part 124 regulations.
Land treatment, storage, and disposal (LTSD) regulations in 40 CFR Part 264
issued on July 26, 1982, establish performance standards for hazardous
waste landfills, surface impoundments, land treatment units, and waste
piles.
EPA is developing three types of documents for preparers and reviewers
of permit applications for hazardous waste LTSD facilities. These types
include RCRA Technical Guidance Documents, Permit Guidance Manuals, and
Technical Resource Documents (TRD's).
The RCRA Technical Guidance Documents present design and operating
specifications or design evaluation techniques that generally comply with
or demonstrate compliance with the Design and Operating Requirements and
the Closure and Post-Closure Requirements of Part 264.
The Permit Guidance Manuals are being developed to describe the permit
application information the Agency seeks and to provide guidance to appli-
cants and permit writers in addressing information requirements. These
manuals will include a discussion of each step in the permitting process
and a description of each set of specifications that must be considered for
inclusion in the permit.
The Technical Resource Documents present state-of-the-art summaries of
technologies and evaluation techniques determined by the Agency to constitute
good engineering designs, practices, and procedures. They support the RCRA
Technical Guidance Documents and Permit Guidance Manuals in certain areas
(i.e., liners, leachate management, closure covers, and water balance) by
describing current technologies and methods for designing hazardous waste
facilities or for evaluating the performance of a facility design. Although
emphasis is given to hazardous waste facilities, the information presented
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in these TRD's may be used for designing and operating nonhazardous waste
LTSD facilities as well. Whereas the RCRA Technical Guidance Documents and
Permit Guidance Manuals are directly related to the regulations, the informa-
tion in these TRD's covers a broader perspective and should not be used to
interpret the requirements of the regulations.
This document is a first edition draft being made available for public
review and comment. It has undergone review by recognized experts in the
technical areas covered, but Agency peer review processing has not yet been
completed. Public comment is desired on the accuracy and usefulness of the
information presented in this document. Comments received will be evaluated,
and suggestions for improvement will be incorporated, wherever feasible,
before publication of the second edition.
One original and one copy of all comments on this document should be
addressed to Docket Clerk, Office of Solid Waste (WH-562), U.S. Environmental
Protection Agency, 401 "M" Street, S.W., Washington, D.C. 20460. Comments
should list the docket number (F-86-CLDD-FFFFF) and should identify the
document by title and number; e.g. "Design, Construction, and Evaluation of
Clay Liners for Waste Management Facilities," (EPA/530-SW-86-007). The
comment period ends February 15, 1987.
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ABSTRACT
This Technical Resource Document is a compilation of all of the available
information on the design, construction, and evaluation of clay liners for
waste landfills, surface impoundments, and wastepiles. The information was
obtained from the literature and from in-depth interviews with design and
construction engineers and other knowledgeable individuals in both the
private and government sectors. As a consequence, some information is
presented for the first time in this document. The broad topics covered
are: clays, with emphasis on their composition, fabric, and hydraulic
conductivity; geotechnical test methods and soil properties including index
properties, soil classification, and hydraulic conductivity testing; clay
chemical compatibility, including a discussion of the mechanisms of interac-
tion and a comprehensive compilation of existing test data from the litera-
ture and private sources; construction and quality assurance; clay liner
failure mechanisms; the performance of existing clay liners based on case
studies of 17 sites; and clay liner transit time prediction methods featur-
ing an in-depth discussion of many available techniques and models.
VI
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TABLE OF CONTENTS
Chapter Page
Foreword iii
Preface iv
Abstract vi
Figures xiv
Tables xix
Acknowledgments xxii
1 Introduction 1-1
1.1 Scope 1-3
1.2 Summary of Current Practices 1-3
1.2.1 Investigation of Site Conditions
(Field) 1-3
1.2.2 Material Selection and Characterization
(Laboratory) 1-4
1.2.3 Develop Liner Design/Construction
Plans 1-5
1.2.4 Pilot Construction Test (Test Fill) .... 1-5
1.2.5 Construction 1-6
1.3 Analysis of Current Practices 1-7
1.3.1 Liner Material 1-7
1.3.2 Clod Size 1-7
1.3.3 Water Content 1-8
1.4 Summary 1-9
1.5 Reference 1-10
2 Clay Soil 2-1
2.1 Clay Minerals 2-2
2.1.1 Clay Mineral Structure 2-2
2.1.2 Clay Mineral Groups 2-4
2.2 Clay Formation and Occurrence 2-14
2.2.1 Clay Mineral Paragenesis 2-15
2.2.2 Clay Soil Formation and Occurrence 2-16
2.3 Clay Chemistry 2-18
2.3.1 Electrical Double-Layer Theory 2-18
2.3.2 Cation-Exchange Capacity and Cation
Affinity 2-22
2.3.3 Significance of the Electrical Double
Layer to Clay Liners 2-23
2.4 Clay Soil Fabric and Hydraulic Conductivity. . . . 2-23
2.4.1 Soil Porosity and Hydraulic
Conductivity 2-23
2.4.2 Soil Structure and Hydraulic
Conductivity in Compacted Soils 2-32
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TABLE OF CONTENTS (continued)
Chapter Page
2.5 References 2-40
3 Test Methods and Soil Properties 3-1
3.1 Introduction 3-1
3.2 Fundamental Relationships 3-2
3.2.1 Water Content 3-2
3.2.2 Density 3-2
3.2.3 Void Ratio 3-5
3.2.4 Porosity 3-5
3.2.5 Degree of Saturation 3-6
3.3 Atterberg Limits 3-6
3.4 Soil Classification 3-11
3.5.1 Grain Size Analysis 3-11
3.5-2 The Unified Soil Classification System. . . 3-16
3.5 Compaction 3-21
3.5.1 Fundamentals of Compaction 3-21
3.5.2 Compaction and Permeability 3-26
3.6 Field Measurement of Density and Moisture
Content 3-26
3.6.1 Traditional Methods 3-26
3.6.2 Nuclear Methods 3-29
3.7 Testing for Shear Strength 3-34
3.8 Hydraulic Conductivity Testing 3-35
3.8.1 Darcy's Law 3-37
3.8.2 Hydraulic Gradient 3-39
3.8.3 Permeability Measurement and Factors
That Influence Test Results 3-40
3.8.4 Laboratory Permeability Tests 3-52
3.8.5 Field Permeability Tests. ......... 3-61
3.9 References 3-65
4 Clay-Chemical Interactions and Soil Permeability. . . . 4-1
4.1 Parameters Determined in Permeability
Testing for Compatibility 4-2
4.2 Clay-Chemical Interactions that Influence
Permeability 4-3
4.2.1 Soil Fabric and Permeability 4-4
4.2.2 Dissolution by Strong Acids or Bases. . . . 4-13
4.2.3 Precipitation of Solids 4-13
4.2.4 Effect of Microorganisms. . 4-13
4.3 Measuring Clay-Chemical Compatibility
Through Permeability Testing 4-15
4.3.1 Measurement Devices 4-15
4.3.2 Test Setup 4-15
4.3.3 Compatibility of Materials With Test
Fluids 4-16
4.3.4 Effect of Backpressure 4-16
vm
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TABLE OF CONTENTS (continued)
Chapter
4.3.5 Effect of Hydraulic Gradient 4-16
4.3.6 Criteria for Concluding a Test
4.4 Summary of Available Research Data 4-18
4.5 Permeability Studies to Investigate
Clay-Chemical Interactions 4-27
4.5.1 Observations by Macey (1942) on
Effects of Organics on Fireclay 4-27
4.5.2 Tests With Kaolinite and Organic
Solvents by Michaels and Lin (1954) .... 4-27
4.5.3 Study by Buchanan (1964) of the Effect
of Naphtha on Montmorillonite 4-30
4.5.4 Study by Reeve and Tamaddoni (1965)
of the Effect of Electrolyte
Concentration on Permeability of a
Sodic Soil 4-31
4.5.5 Tests by van Schaik and Laliberte
(1968) of Permeability of Soils to a
Liquid Hydrocarbon 4-33
4.5.6 Study by Everett (1977) of Permeability
of Lacustrine Clay to Four Liquid Wastes. . 4-34
4.5.7 Tests by Sanks and Gloyna (1977) of
Permeability of Lacustrine Clay to
Liquid Waste 4-36
4.5.8 Investigation of the Effect of
Organic Solvents on Clays by
Green and Jones (1979) 4-36
4.5.9 Anderson's Study (1981) of the
Effects of Organics on Permeability .... 4-42
4.5.10 Schramm's Study (1981) of the
Permeability of Soil to Organic
Solvents 4-59
4.5.11 Evaluation by Monserrate (1982)
of the Permeability of Two Clays to
Selected Electroplating Wastes 4-64
4.5.12 Research by Brown, Green, and Thomas
(1983) on the Effect of Two Organic
Hazardous Wastes on Simulated
Clay Liners 4-67
4.5.13 Study by Brown, Thomas, and Green
(1984) of the Effect of Dilutions
of Acetone and Mixtures of Xylene
and Acetone on Permeability of a
Micaceous Soil 4-70
4.5.14 Tests by Brown, Thomas, and Green
(1984) to Determine the Permeability
of Micaceous Soil to Petroleum Products . . 4-71
IX
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TABLE OF CONTENTS (continued)
Chapter Page
4.5.15 Study by Brown and Thomas (1984) of
the Permeability of Commercially
Available Clays to Organics 4-71
4.5.16 Studies Conducted for EPA by Daniel
(1983) and Foreman and Daniel (1984)
at the University of Texas, Austin 4-79
4.5.17 Tests Conducted for Chemical
Manufacturers Association by Daniel
and Liljestrand (1984) 4-75
4.5.18 Study by Dunn (1983) of the Effects
of Synthetic Lead-Zinc Tailings
Leachate on Clay Soils 4-82
4.5.19 Studies by Acar and Others (1984)
on the Effect of Organics on Kaolinite. . . 4-86
4.5.20 Finding by Olivieri (1984) of
Impermeability of Montmorillonite to
Benzene 4-88
4.5.21 Study of Permeability of Clays to
Simulated Inorganic Textile Wastes
by Tulis (1983) 4-89
4.5.22 Tests Conducted by Engineering
Consulting Firms for Specific Applica-
tion (unpublished data) ..... 4-89
4.5.23 Tests Reported by Bentonite Companies . . . 4-102
4.6 References • 4-109
5 Current Practices 5-1
5.1 Design 5-2
5.1.1 Site Investigation. ..... 5-2
5.1.2 Liner Material Selection and
Characterization 5-6
5.1.3 Facility Design 5-13
5.1.4 Construction Specifications and CQA Plan. . 5-39
5.1.5 Design Case Studies 5-41
5.2 Clay Liner Construction: Methodology
and Equipment 5-45
5.2.1 Preinstallation Activities 5-45
5.2.2 Clay Liner Installation 5-47
5.2.3 Postinstallation Activities . 5-78
5.3 Quality Assurance and Quality Control 5-78
5.3.1 Key Terms . 5-80
5.3.2 Personnel ........... 5-83
5.3.3 Observations and Tests. 5-85
5.3.4 Documentation 5-100
5.4 Clayliner Design and Construction: Problems
and Preventive Measures 5-107
5.5 References 5-110
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TABLE OF CONTENTS (continued)
Chapter
6 Failure Mechanisms 6-1
6.1 Desiccation Cracks 6-1
6.1.1 Description 6-1
6.1.2 Studies of Cracking 6-2
6.2 Slope Instability 6-4
6.2.1 Description 6-4
6.2.2 Discussion of Slope Instability 6-4
6.3 Settlement 6-5
6.3.1 Description 6-5
6.3.2 Studies of Settlement 6-5
6.4 Piping 6-6
6.4.1 Description 6-6
6.4.2 Studies of Piping 6-7
6.5 Penetration 6-9
6.5.1 Description 6-9
6.5.2 Studies of Penetration 6-9
6.6 Erosion 6-9
6.6.1 Description 6-9
6.7 Cold Climate Operations 6-10
6.8 Earthquakes 6-12
6.9 Scouring - 6-16
6.10 Failures from Design or Construction Errors. . . . 6-17
6.11 References 6-18
7 Clay Liner Performance 7-1
7.1 Introduction 7-1
7.2 Case Studies 7-2
7.2.1 Criteria for Site Selection 7-2
7.2.2 Site A 7-5
7.2.3 Site B 7-7
7.2.4 Site C 7-10
7.2.5 Site D 7-13
7.2.6 Site E 7-19
7.2.7 Site F 7-22
7.2.8 Site G 7-26
7.2.9 Site H 7-29
7.2.10 Site 1 7-34
7.2.11 Site J 7-39
7.2.12 Site K 7-43
7.2.13 Site L 7-47
7.2.14 Site M 7-50
7.2.15 Site N 7-55
7.2.16 Site 0 7-61
7.2.17 Site P 7-64
7.2.18 Site Q 7-69
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TABLE OF CONTENTS (continued)
Chapter Page
7.3 Liner Types 7-72
7.3.1 Unlined Facilities 7-73
7.3.2 Recompacted Soil Liners 7-74
7.3.3 Admixed Liners 7-74
7.4 Site Characterization 7-75
7.4.1 Case Studies 7-76
7.5 Installation of Clay Liners 7-77
7.5.1 Installation Method 7-77
7.5.2 Quality Assurance/Quality Control
for Clay Liners 7-78
7.6 Waste Types 7-79
7.6.1 Free Liquids. 7-79
7.6.2 Stabilized or Solidified Liquids 7-82
7.6.3 Sludges and Solid Wastes 7-83
7.6.4 Waste Compatibility 7-84
7.7 Performance Monitoring 7-86
7.7.1 Unsaturated Zone Monitoring 7-86
7.7.2 Groundwater Monitoring 7-89
7.7.3 Leachate Level and Quality
Monitoring 7-90
7.8 Conclusions. 7-90
7.9 References 7-91
8 Clay Liner Transit Time Prediction Methods 8-1
8.1 Introduction 8-1
8.2 Background Considerations 8-1
8.2.1 Performance Criteria 8-1
8.2.2 Clay Liner System 8-2
8.2.3 General Equations ....... 8-4
8.3 Transit Time Prediction Methods 8-8
8.3.1 Simple Transit Time Equation 8-8
8.3.2 Modified Transit Time Equation 8-11
8.3.3 Green-Ampt Wetting Front Model 8-14
8.3.4 Transient Linearized Infiltration
Equation 8-17
8.3.5 Modified Transit Time Equation
with Diffusion. 8-20
8.3.6 Numerical Solutions . 8-21
8.4 Comparison of Different Approaches . 8-28
8.4.1 Basic Assumptions 8-29
8.4.2 Comparison With Performance Criteria
Based on Saturation Front ......... 8-31
8.4.3 Comparison Using Performance Criteria
Based on Solute Transport 8-34
8.5 Summary and Conclusions 8-38
8.6 Definition of Terms 8-41
8.7 References ..... 8-44
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TABLE OF CONTENTS (continued)
Chapter Page
Appendix
A Test Method Descriptions A-l
B A Partial List of Available Numerical Models to
Describe Flow and/or Solute Transport in
Partially Saturated Porous Media B-l
C Program LINERSOIL Modified Version of Program
SOILINER C-l
XI 1 1
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FIGURES
Number Page
1-1 Cross section of a segment of an idealized clay
liner system 1-2
2-1 Clay mineral tetrahedral sheet structure 2-3
2-2 Clay mineral octahedral sheet structure 2-3
2-3 Kaolinite group minerals 2-7
2-4 mite clay minerals 2-11
2-5 Chlorite and smectite minerals 2-13
2-6 Electrical double layer ........ ... 2-19
2-7 Effect of solution pH on clay mineral surface
charge (EPM) 2-21
2-8 Comparisons of clay mineral sizes and surface areas . . . 2-24
2-9 Clay soil fabrics 2-26
2-10 Fractures in glacial till 2-29
2-11 Root cast in glacial till 2-30
2-12 Permeable strata in glacial till deposit. . 2-31
2-13 Compaction curve from a standard compaction test 2-33
2-14 Compaction curves for different compact!ve efforts
applied to a siIty clay 2-35
2-15 Permeability as a function of molding water content
for samples of siIty clay prepared to constant
density by kneading compaction 2-36
2-16 The effect of dispersion on hydraulic conductivity. . . . 2-38
2-17 Effect of method of compaction on the permeability
of hydraulic conductivity of a si Ity clay 2-39
3-1 Schematic representation of soil illustrating the
fundamental relationships between the solid, liquid,
and air constituents 3-4
3-2 Consistency limits of cohesive soils 3-7
3-3 Device for determining the liquid limits of a
cohesive soil. The dish contains a grooved sample. . . . 3-8
3-4 Clay sample being grooved for liquid limit test 3-8
3-5 ' Rolling a clay sample for plastic limit test. ...... 3-10
3-6 Results of rolling clay with moisture content below
the plastic limit 3-10
3-7 Typical relationships between the liquid limit (LL)
and the plasticity index (PI) for various soils 3-12
3-8 Idealized particle size distribution curves for
well-graded, poorly-graded and gap-graded soils 3-15
3-9 Unified soil classification chart 3-17
xiv
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FIGURES (continued)
Number
3-10 Typical soil compaction curve illustrating maximum
dry density and optimum water content 3-22
3-11 Compaction curves for different compactive efforts
applied to a silty clay 3-24
3-12 Four types of compaction curves found from
laboratory investigation 3-25
3-13 Permeability as a function of molding water content
for samples of silty clay prepared to constant density
by kneading compaction 3-27
3-14 Influence of the method of compaction on the
permeability of silty clay 3-28
3-15 Schematic diagram of triaxial compression apparatus
for Q test 3-36
3-16 Effect of backpressure on permeability to water,
Sasumua clay 3-50
3-17 Apparatus for pressure cell method 3-53
3-18 Modified compaction permeameter 3-55
3-19 Detail of the base plate for a double-ring permeater. . . 3-56
3-20 Schematic of a constant head triaxial cell permeater. . . 3-58
3-21 Consolidation permeameter 3-60
3-22 Apparatus set-up for double-ring infiltrometer 3-62
3-23 Modified air-entry permeameter 3-64
4-1 Change in a pore diameter (400%) corresponding to a
permeability increase of 25,000% 4-5
4-2 Distribution of ions adjacent to a clay surface
according to the concept of the diffuse double layer. . . 4-8
4-3 Intrinsic permeabilities as a function of void space
(e) measured for different permeants 4-29
4-4 Coefficient of permeability of Ranger shale to
various chemicals 4-43
4-5 Permeability of the four clay soils to water (0.01N
CaS04) 4-47
4-6 Permeability of the four clay soils to acetic
acid 4-48
4-7 Permeability and breakthrough curves of the four
clay soils treated with aniline 4-49
4-8 , Permeability of the four clay soils to ethylene
glycol 4-50
4-9 Permeability of the four clay soils to acetone 4-51
4-10 Permeability of the four clay soils to methanol
and the breakthrough curve for the methanol-
treated mixed cation illitic clay soil 4-52
4-11 Permeability of the methanol-treated mixed cation
illitic clay soil at two hydraulic gradients 4-53
4-12 Permeability and breakthrough curves of the four
clay soils treated with xylene 4-54
xv
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FIGURES (continued)
Number Page
4-13 Permeability and breakthrough curves of the four
clay soils treated with heptane 4-55
4-14 Variation of intrinsic permeability with solvent
for each soil . 4-63
4-15 Permeability of White Store clay to 0.01 N calcium
sulfate, chromic acid (1 Molar) and zinc chloride
(1 Molar) as a function of moisture at compaction
(Data from Monseratte, 1982) 4-66
4-16 Hydraulic conductivity versus pore volume for
laboratory-compacted micaceous soil exposed to
kerosene at a hydraulic gradient of 91 4-72
4-17 Hydraulic conductivity versus pore volume for
laboratory-compacted micaceous soil exposed to
diesel fuel at a hydraulic gradient of 91 4-73
4-18 Hydraulic conductivity versus pore volume for
laboratory-compacted micaceous soil exposed to
paraffin oil at a hydraulic gradient of 91 4-74
4-19 Hydraulic conductivity versus pore volume for
laboratory-compacted micaceous soil exposed to
gasoline at a hydraulic gradient of 91 4-75
4-20 Hydraulic conductivity versus pore volume for
laboratory-compacted micaceous soil exposed to
motor oil at a hydraulic gradient of 91 .... 4-76
4-21 Permeability versus number of pore volumes of flow
for kaolinite permeated with methanol at a hydraulic
gradient of 250 or 300 4-81
4-22 Permeability versus hydraulic gradient for kaolinite
permeated in flexible-wall permeameters 4-83
4-23 Permeability versus hydraulic gradient for kaolinite
permeated in consolidation cell permeameters 4-84
4-24 Permeability versus hydraulic gradient for
kaolinite permeated in compaction mold cell 4-85
5-1 Compacted clay cutoff seal. . 5-17
5-2 Dike components and typical configurations 5-18
5-3 Methods of liner sidewall compaction 5-20
5-4 Liner design for collection system pipes and sump .... 5-26
5-5 Methods of keying-in liner segments 5-28
5-6 Liner material emplacement 5-49
5-7 Emplacement of liner material over foundation
excavation underneath a collection pipe ......... 5-50
5-8 Use of pulvi-mixer for clod size reduction. ....... 5-53
5-9 Moisture addition to liner material prior to
compaction 5-55
5-10 Joints and seepage along lift boundaries 5-57
5-11 Sketches of different types of roller feet 5-62
5-12 Various compacting rollers 5-63
xvi
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FIGURES (continued)
Number
5-13 Compaction on a 2(H) to 1(V) slope with a towed
sheepsfoot roller 5-66
5-14 Central plant mixing of bentonite and soil 5-68
5-15 Truck loaded bentonite spreader 5-70
5-16 Pneumatically fed bentonite spreader 5-72
5-17 Blending bentonite with soil using a disk harrow 5-74
5-18 Soil stabilizer mixing bentonite in place 5-75
5-19 Inflatable dome over a hazardous waste landfill 5-77
5-20 CQC test location and data summary 5-101
5-21 Statistical analysis of CQC test data 5-102
6-1 Location of past destructive earthquakes in the
United States 6-13
6-2 Differences in propagation of damage for eastern
and western earthquakes 6-13
7-1 Plan view of site A 7-6
7-2 Plan view of site B 7-8
7-3 Plan view of site C 7-11
7-4 Cross-sectional view of site C (vertical
dimensions are to scale) 7-12
7-5 Plan view of site D 7-15
7-6 Cross-sectional view of site D liner 7-18
7-7 Plan view of site E 7-20
7-8 Cross-sectional view of site F 7-23
7-9 Plan view of site G 7-27
7-10 Plan view of site H 7-30
7-11 Cross-sectional view of site H liner showing
details of leachate collection system and lysimeter
construction 7-31
7-12 Plan view of site I 7-37
7-13 Cross section of liner at site 1 7-38
7-14 Plan view of site J 7-40
7-15 Cross-sectional view of site J liner 7-42
7-16 Cross-sectional view of site K liner 7-44
7-17 Cross section of containment system at site L 7-48
7-18 Cross section of site M 7-51
7-19 Plan view of site M leachate collection and leak
detection systems 7-52
7-20 Plan view of site N 7-58
7-21 Cross-sectional view of site N liner and leachate
management systems 7-59
7-22 Cross section of site P showing relationship of
liner and dikes 7-65
7-23 Detailed cross section of site P liner 7-66
7-24 Cross section of site Q liner 7-71
7-25 Bentonite/soil liner constructed without
adequate CQA 7-80
7-26 Bentonite/soil liner installed with extensive CQA .... 7-81
xv n
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FIGURES (continued)
Number Page
8-1 Flow domain for leachate flow 8-3
8-2 Schematic of flow domain and assumed steady state
pressure head profile: Simple Transit Time Equation. . . 8-9
8-3 Schematic of flow domain and assumed steady state
pressure head profile: Modified Transit Time Equation. . 8-12
8-4 Green-Ampt infiltration model 8-15
8-5 Graphical solution to equation (16)—linearized
infiltration model 8-19
8-6 Graphical solution to equation (8.18)—transit time
equation with diffusion 8-22
8-7 Soil properties of hypothetical clay (solid line) and
sand (dashed line) for liner design, a) Unsaturated
hydraulic conductivity (cm/s) as a function of capillary
pressure (pF = log(-i|<), i)j in cm) b) Moisture content as
a function of capillary pressure 8-30
8-8 Extrapolation of transit times for solute transport,
for initial liner saturations of 50%, 80%, and 95%. . . . 8-39
xvi
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TABLES
No. Page
1-1 Technical Resource Documents 1-3
2-1 Clay Mineral Characteristics 2-5
3-1 Soil Tests Summarized in Appendix A 3-3
3-2 U.S. Standard Sieve Sizes and Their Corresponding
Open Dimension 3-14
3-3 Z/A of Various Soil Components 3-31
3-4 Summary of Potential Errors in Laboratory
Permeability Tests on Saturated Soil 3-42
3-5 Summary of Sources of Error in Estimating
Field Permeability of Compacted Clay Liners
from Laboratory Tests 3-43
3-6 Confidence Limits for Permeability (K) as a Function
of Number of Samples and the Mean Permeability 3-44
3-7 Test Results Showing Effect of Sample
Diameter on Permeability Measurements 3-47
4-1 Results of Permeability Tests With Organic Chemicals . . 4-19
4-2 Results of Permeability Tests With Wastes 4-25
4-3 Void Ratio and Coefficient of Permeability
Relationships for Calcium- and Sodium-Montmori1-
lonite Permeated by Water and Naphtha 4-32
4-4 Summary of Soil Permeability With Soltrol C and Water. . 4-32
4-5 Permeabilities Measured With Lacustrine Clay
Exposed to Water and Waste Liquids 4-37
4-6 Properties of Soils Tested 4-39
4-7 Classification of Clay-Organic Solvent Systems
According to Swell Properties 4-40
4-8 Percent Swell for Clay Soils in Contact With
Organic Liquids and Water 4-41
4-9 Grain Size Distribution, Mineralogy, and Properties
of the Four Clay Soils 4-45
4-10 Characteristics of Soils Used in Permeability Tests. . . 4-60
4-11 ' Permeability Coefficients (cm/s) Determined
in Soils Tested With Organic Solvents 4-61
4-12 Mean Conductivity of Each Soil to Each Fluid
Tested (Brown and Thomas, 1984) 4-78
4-13 Properties of Clay Soils Tested by Daniels and
Liljestrand (1984) 4-79
4-14 Leachate Characteristics 4-80
4-15 Permeability Test Results (Pennsylvania Case A) 4-92
4-16 Permeability Test Results (Pennsylvania Case B) 4-94
xix
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TABLES (continued)
No. Page
4-17 Chemical Characteristics of Waste Permeants, Project E . 4-98
4-18 Results of Permeability Tests, Project E ........ 4-100
4-19 Results of Permeability Tests, Project L 4-103
4-20 Initial and Final Permeabilities Determined
in Triaxial Cell Tests With Leachates, Project N . . . . 4-104
4-21 Effect of Concentrated Organics on a Treated
Bentonite Seal ..... 4-106
4-22 Permeability (cm/s) of a Treated Bentonite
Seal to Kerosene 4-107
5-1 Accessible Methods of Subsurface Exploration 5-7
5-2 Nonaccessible Methods of Subsurface Exploration 5-8
5-3 Factors Controlling Stability of Sloped Cut
in Some Problem Soils 5-23
5-4 Relative Volume Change of a Soil as Indicated
by PI and Other Parameters 5-34
5-5 Soil Volume Change as Indicated by LL and
Grain Size 5-34
5-6 Effect of Clod Size on Permeability of Laboratory
Compacted Clay 5-52
5-7 Compaction Equipment and Methods 5-60
5-8 Current QA Practices for Clay Liner Construction .... 5-96
5-9 Recommendations for Construction Documentation
of Clay-Lined Landfills by the Wisconsin Department
of Natural Resources 5-98
5-10 Elements of a Construction Documentation Report 5-99
5-11 Potential Clay Liner Design and Installation
Problems and Preventive Measures ..... 5-108
6-1 Relative Volume Change as Indicated by Plasticity
Index and Other Parameters 6-5
6-2 Volume Changes as Indicated by Liquid Limit
and Grain Size 6-5
7-1 Clay-Lined Facility Information 7-3
7-2 General Occurrence of Chemical Parameters in the
Groundwater at Site C 7-14
7-3 Lysimeter (L) and Leachate Collection System (LCS)
Liquid Volumes (gal) at Site H 7-33
7-4 • Monitoring Data for Site H 7-35
7-5 Heavy Metal Content and Percent Solids of Lime
Sludge Disposed at Site M ........... 7-54
7-6 Groundwater Monitoring Well Sample Analysis at
Site M . 7-56
7-7 Leachate Analysis at Site M 7-56
7-8 Leachate Volumes at Site M 7-57
7-9 Water Sample Analysis: BOD, COD, Total Coliform
and Fecal Col i form 7-62
xx
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TABLES (continued)
No. Page
8-1 Parameters Required in Different Transit Time
Prediction Methods 8-7
8-2 Results of Comparing Transit Time Prediction
Methods 8-32
8-3 Transit Time Estimation Using the Green-Ampt
Wetting Front Model 8-33
8-4 Transit Time Estimation Using the Transient
Linearized Infiltration Model 8-35
8-5 Transit Time Estimation Using a Numerical Solution
to the Flow Equation 8-36
8-6 Transit Time Estimation Using a Numerical Solution
to the Solute Transport Equation 8-40
xxi
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ACKNOWLEDGMENTS
The support of the U.S. Environmental Protection Agency, Cincinnati,
Ohio, and Dr. Mike Roulier, Technical Project Monitor, is greatly appreciated.
Dr. L. J. Goldman served as the Project Leader for Research Triangle
Institute and Ms. G. L. Kingsbury was Project Manager. The authors were
Dr. L. J. Goldman, Mr. R. S. Truesdale, Ms. G. L. Kingsbury, Ms. C. M.
Northeim, and Mr. A. S. Damle. Support services for the project were
contributed by Ms. D. S. Blank, Ms. K. B. Mohar, and Ms. J. L. Shirley.
The authors wish to acknowledge the firms, agencies, and individuals
who provided much of the information contained in this document. We also
wish to acknowledge the contributions made by those who reviewed and com-
mented on the manuscript:
Dr. J. K. Mitchell, Department of Civil Engineering, University of
California, Berkeley, California
Dr. W. E. Grube, U.S. Environmental Protection Agency, Cincinnati,
Ohio.
Dr. R. A. Griffin, Illinois State Geological Survey, Champaign, Illinois.
Dr. J. H. Williams, Missouri Department of Natural Resources, Roll a,
Missouri.
xxn
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CHAPTER 1
INTRODUCTION
A clay liner consists of one or more layers of cohesive soil that have
been compacted to achieve a low permeability. The purpose of a clay liner
in a waste management facility (landfill, waste pile, or surface impoundment)
is to serve as a barrier between waste materials and the hydrogeologic
environment by limiting seepage from the facility and to provide support
for overlying facility components.
A clay liner is usually constructed of native soil that contains
appreciable amounts of clay-sized particles; in some cases other materials,
such as bentonite, are mixed with the soil when it does not contain sufficient
clay. A clay liner may be overlain by one or more flexible membrane liners
and primary and secondary leachate collection (drain) systems. Figure 1-1
illustrates one possible liner configuration for a surface impoundment.
A compacted clay soil liner, because of its low permeability (hydraulic
conductivity), limits the steady-state seepage from a facility. In waste
management facilities the clay liner also is designed to delay the beginning
of seepage for the longest possible time (transit time) and to have sufficient
structural stability to support itself and other facility components that
may lie above it. Clay liners are used not only in waste management facil-
ities but also in many other applications such as water storage and conveyance
structures.
Although clay liners are a widely used technology, there is very
little information on their performance in limiting seepage from operating
waste facilities. [7.2.1; 7.3.2]* Performance predictions have been based
primarily on results from permeability tests conducted on laboratory-compacted
soils. Laboratory testing has provided a great deal of data that demonstrate
the permeability (hydraulic conductivity) that can be achieved with various
soil materials and compaction methods and how various types of wastes can
interact with soil materials to change this permeability. Even though it
is common practice to use such laboratory results to predict the field
behavior of a liner, there are few field data that confirm the validity of
laboratory-derived soil permeability values as a measure of field perme-
ability. There are some field data showing that permeability and seepage
rates for field-compacted clay soil liners are much greater than for
laboratory-compacted soils. [2.3.2; 3.8.3.1] Until more field data are
available on the performance of clay liners constructed with the best
current technology, permeabilities of laboratory-compacted soils should be
^Numbers in brackets refer to relevant sections of this document.
1-1
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Cover Soil and/or
Riprap
Not to scale.
Leachate Collection
System
Foundation
Bottom Liner-
Compacted Low
Permeability Soil
Component
Top Liner—
Synthetic Membrane
Bottom Liner-
Synthetic Membrane
Component
figure 1-1, Liner configuration for surface impoundment.
-------
regarded as a goal rather than an accurate estimate of the performance of
field-constructed clay liners.
1.1 SCOPE
The objective of this Technical Resource Document (TRD) is to provide,
in a single source, all of the available information on design, construction,
and performance of clay-lined waste management facilities. The broad
topics covered are: clay properties and characteristics [2.0]; geotechnical
testing of soils [3.0]; the compatibility of clays and chemical wastes
[4.0]; the design, construction, and construction quality assurance of clay
liners [5.0]; potential failure mechanisms [6.0]; the performance of exist-
ing facilities [7.0]; and methods of predicting the useful life (transit
time) based on the modeling of leachate flow through soils [8.0]. It
should be noted that the design and construction section [5.0] is limited
to practices currently in use by engineers. Information on recommended
practices is available in guidance documents issued by the USEPA Office of
Solid Waste, Washington, D.C.
One of the major sources of information for this document was a series
of in-depth interviews with over 30 design/construction engineers who have
hands-on experience with clay-lined facilities in all areas of the country.
Some of the material obtained in these interviews appears here, in print,
for the first time. Opinions and preferences stated in this document,
except when referenced to published material, were obtained from these
interviews and do not necessarily represent the preferences of the authors
or USEPA.
This document contains some soils information taken from a Technical
Resource Document on flexible membrane liners, Lining of Waste Impoundment
and Disposal Facilities (Haxo, 1983). Other important sources of information
were the published literature, discussions with researchers, interviews
with personnel from waste management companies and industries, and contacts
with State and Federal regulatory personnel. Waste management companies
and regulatory agencies were the primary sources for the information con-
tained in Chapter 7, Clay Liner Performance.
1.2 SUMMARY OF CURRENT PRACTICES
The following is a summary of major current practices in clay liner
construction that are believed to affect the permeability of the liner;
other aspects of earthwork (cut and fill volumes, etc.) are not covered.
The practices summarized are average or typical of a large number of the
cases observed by the authors at operating sites or in construction documenta-
tion. Instances of better or poorer practices were also frequently encoun-
tered by the authors.
1.2.1 Investigation of Site Conditions (Field)
Site investigations are conducted before construction to identify and
investigate borrow areas for liner material. The borrow area and the soils
1-3
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that will underly the liner are investigated through borings, pits, and
trenches cut across the area. In situ soil properties and groundwater
conditions are identified and taken into account in the design to avoid
structural problems such as hydraulic uplift (heaving) or settlement of the
soil underlying the liner. The foundation (soil) underlying the proposed
facility site is evaluated for structural properties through laboratory
tests on removed samples and in situ testing. [5.1.1; 5.3.3.2.1]
1.2.2 Material Selection and Characterization (Laboratory)
1.2.2.1 Foundation Soil--
Soil underlying the proposed facility must possess bearing and shear
strength adequate to support expected loading. If tests on samples examined
in the laboratory and onsite bearing tests show inadequate properties, the
site design and construction plans will include specifications that provide
for excavation and recompaction of an adequate foundation. [5.1.3.2.1;
6.2; 6.3].
1.2.2.2 Index Properties of Liner Materials—
Samples of soils from potential borrow areas are analyzed to determine
their index properties (grain size distribution, Atterberg limits, and
Unified Soil Classification). [3.3; 3.5.2; A-26; A-28; A-29; A-34; A-37]
This information is used to identify and reject undesirable materials
(i.e., low plasticity index or low fines content) and to select desirable
materials.
1.2.2.3 Engineering Properties of Liner Material —
A very important criterion for a suitable liner soil is whether it can
be compacted so that the_permeability (hydraulic conductivity), as measured
in the laboratory, is 10 7 cm/s or less. A number of engineering firms and
regulatory agencies have guidelines for the plasticity index and amount of
fines (amount passing a No. 200 sieve) and some have acceptance criteria
that consider only plasticity index or fines, but, at present, permeability
appears to be the most heavily weighted criterion.
Selection of a liner material that can be compacted to the required
permeability involves a series of laboratory tests of the engineering
properties of the candidate materials. A moisture content/density relation-
ship is established for the material by compacting samples of the material
at various moisture contents with a set compactive effort. [2.3.2; 3.4.1;
3.8.4.5; A-45; A-47; A-50] The optimum molding water content is the water
content at which the maximum dry density is achieved. The permeability
(hydraulic conductivity) of a sample of the soil compacted with the same
compactive effort at a water content slightly greater than optimum is
measured. [2.3.2; 3.4.2; 3.8] The relationship between density, moisture
content, compactive effort, and permeability derived from these data will
be used to develop construction specifications and, for quality control of
the construction process, to ensure that the water content is slightly
wetter than optimum and that compaction has been sufficient to achieve the
desired permeability. [3.4.2; 3.6; 5.1.4; 5.3.3.2,4] It is also necessary
to construct a test fill of the liner material prior to construction to
1-4
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confirm that the laboratory-derived relationship can be achieved in the
field. [1.2.4; 5.2.2.1.4; 5.3.3.1]
In addition to meeting permeability requirements, liner material must
be compatible with the waste it is meant to contain. A laboratory-compacted
sample of the soil will be tested to determine whether wastes or leachates
from the proposed facility will react with it to increase its permeability
and decrease its ability to control seepage from the facility. [4.3; 4.4;
7.6.4]
1.2.3 Develop Liner Design/Construction Plans
1.2.3.1 Lift and Liner Thickness—
The depth of loose soil laid down for compaction (lift thickness) is
selected so that the equipment and operating conditions will be capable of
imparting the required compactive effort throughout the lift. [5.2.2.1.1]
Minimum liner thickness is usually set by State or Federal regulations.
Beyond these minimums, liner thickness may be established on the basis of
the time required for liquid or waste to pass through the liner (transit or
containment time). [5.1.3.3; 7.7; 8.0] Greater than average liner thickness
may be specified at critical points such as the junction of the bottom and
side and below leachate collection lines or sumps. [5.2.2.1.1]
1.2.3.2 Compactive Effort-
Equipment and operating conditions (weight, number of passes, etc.)
are selected in conjunction with lift thickness to ensure that the same
compactive effort will be applied in the field as was used in the laboratory
to achieve the specified permeability. [3.4; 5.2.2.1.4] This selection
will be confirmed in the test fill. [1.2.4]
1.2.3.3 Adjust Design to Avoid Failure Mechanisms--
The design of the liner and the foundation (underlying soil) will be
adjusted to avoid common failure mechanisms, as appropriate:
Erosion [5.1.3.4; 6.6.2]
Freezing [5.1.3.4.3; 5.2.2.3.2; 6.7]
Piping [5.1.3.4.4; 6.4.3]
Slope instability [6.2]
Settlement [6.3]
Earthquake [5.1.3.4.6; 6.8]
Scouring (surface impoundments) [5.1.3.4.2; 6.9]
Hydraulic uplift (heaving) [5.1.3.4.7; 7.4].
1.2.4 Pilot Construction Test (Test Fill)
A small-scale construction test is conducted to determine whether the
selected combination of lift thickness, equipment, operational procedures,
moisture content, and density will result in the design permeability identi-
fied during the laboratory testing. [5.2.2.1.4; 5.3.3.1]
1-5
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1.2.5 Construction
1.2.5.1 Foundation Preparation—
The native soil is the foundation for the clay liner. The soil surface
will be, at a minimum, cleared, grubbed, stripped, and cleaned of organic
or otherwise deleterious material prior to placement of the liner material.
Resulting holes and depressions in the soil or underlying rock will be
filled. Where necessary, the soil may be excavated and recompacted using
standard earthmoving equipment. Water content and compactive effort will
be adjusted to give a firm surface for construction of the liner. The
surface may be proof-rolled to locate soft spots prior to placing liner
material. [5.2.1.1; 5.3.3.2.1]
1.2.5.2 Liner Material Preparation--
Soil material for the liner will be either excavated on site or brought
from a nearby borrow area. Areas containing material that is unsuitable
because the fines content is too low or because it contains rocks, organic
matter, etc., will be identified; material from these areas will be segre-
gated from the liner material and not used in the liner. [5.3.3.1; 7.5.1.2]
If the material is too dry or heterogeneous, construction equipment
will be used to mix it and the water content may be adjusted by addition of
water prior to placement. Adequate curing time must be allowed to enable
added water to penetrate all liner material uniformly. Stockpiles of liner
materials are often covered or seal-rolled to retard drying or erosion.
[5.2.2.1]
1.2.5.3 Material Placement-
Liner material will be hauled to the site from a stockpile or borrow
area and spread to the specified loose lift thickness as estimated with a
shovel blade or staff. [5.2.2.1.1] Rocks and other foreign material may
be removed if apparent. Clods that are larger than the lift thickness may
be reduced in size with a disc or harrow. [5.2.2.1.2; 5.3.3.2.2]
Water content of the soil will have been measured on samples from the
emplaced material. [3.6.2.2; A-6; A-7] If water content is less than
specified in the design, water will be added by spraying from a truck or
large hose before the soil is compacted. Adequate curing time must be
allowed. If the soil is too wet, it will be allowed to dry somewhat before
compaction. [5.2.2.1.3; 5.3.3.2.3]
1.2.5.4 Compaction—
.The soil is compacted using equipment such as sheeps-foot or rubber-
tired rollers until the density of the soil, at the specified moisture
content, has reached the value specified in the design. [5.2.2.1.4; 5.3.3.2.4]
During construction, density may be measured by direct methods such as the
sand cone or balloon but is more commonly measured with a nuclear density
gauge. [3.6.2.1; 5.3.3.2.4; 5.3.3.2.5; A-19; A-20; A-22] Samples of soil
may be taken during compaction to determine if the water content is close
enough to the design value. Alternatively, a nuclear moisture gauge may be
used.
1-6
-------
The top of a lift (layer of soil) may be scarified with a harrow or
other equipment so that there will be an adequate bond with the lift placed
above it. The edges of lifts are often beveled or overlapped to ensure
complete coverage. [5.1.3.3; 5.2.2.1.1]
1.2.5.5 Completion--
Upon completion of the liner, samples may be taken for laboratory
permeability measurements; alternatively, field permeability measurements
may be made on the completed liner.
The surface of the liner may be proof-rolled to seal it and prevent
erosion and the liner may be covered with a protective layer of soil to
reduce desiccation cracking if there will be considerable time before the
liner is placed in service or before a leachate collection system or flexible
membrane liner is placed over the clay liner. [5.1.3.4.5; 5.2.2.3.1;
6.1.3]
1.3 ANALYSIS OF CURRENT PRACTICES
The current practices discussed in this section are those that would
be most likely to improve clay liner performance (lower permeability) if
they were changed. Most of this analysis is based on laboratory studies of
the behavior of compacted soils; few field studies of the relationship
between construction practice and permeability have been conducted.
1.3.1 Liner Material
Changes in the amount of fines (material passing a No. 200 sieve) in a
soil strongly affect the relationship between compactive effort and water
content and the maximum density and permeability that can be achieved.
Consequently, efforts in the following areas are likely to result in a
liner with a more uniform and lower permeability:
Identification of the range of soil properties in the borrow
area
Determination of the water content, compactive effort,
density, and permeability relationships for all the major
and significantly different bodies of soil in the borrow
area, and verifying these relationships in a field-compacted
test fill
Sorting soils so that those delivered to the construction
site do not have properties significantly different from the
soils that were used in developing the construction specifica-
tions.
1.3.2 Clod Size
One laboratory study has shown that, for the same water content and
compactive effort, permeability increased as the size of the clods increased.
1-7
-------
The mechanism responsible has not been identified but it is assumed to be
nonuniform compaction, nonuniform moisture distribution, or inadequate
bonding between adjacent aggregates, leaving planes of weakness in the soil
sample and areas of higher permeability.
Efforts to reduce clod size during excavation and placement of the
soil for the liner would improve chances for achieving a lower permeability
in several ways:
A small clod is more likely to have a uniform water content;
the nonuniform water content of larger clods will lead to
differences in density and permeability after application of
the same compactive effort.
At any given water content, the material could be compacted
more uniformly because the range in clod sizes would be
smaller.
If water addition were necessary, the added water could be
distributed more evenly; shorter times would be required for
water to move from the outside to the inside of smaller
clods than of larger clods.
1.3.3 Water Content
Laboratory studies using homogenized soil samples that have been
ground to pass a 2-mm sieve have demonstrated that as water content is
increased several percentage points above optimum, the permeability of the
soil when compacted decreases sharply. Permeability may decrease by a
factor of 100 over a water content range of only 2.0 to 4.0 percent above
optimum.
During construction, a uniform water content slightly higher than the
optimum for maximum density is likely to result in lower permeabilities
than would water contents that are optimum or less. Considerable effort
may be required to control water content under field conditions but all
available information indicates that a considerable return may be realized
in terms of lower permeability.
1.3.4 Pilot Construction (Test Fill)
There are a number of differences between laboratory and field condi-
tions (uniformity of material, control of water content, compactive effort,
compaction equipment, etc.) that make it unlikely that permeabilities
measured on laboratory-compacted samples can be achieved during construction.
In addition, there are several processes and conditions that cannot be
examined or anticipated through laboratory work (e.g., control of desicca-
tion cracking, bonding of lifts, degree of compaction on sidewalls). Pilot
construction (test fill) provides an opportunity to verify that the materi-
als, equipment, and personnel that will be used to construct the liner can
1-8
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produce a liner that performs according to the design. Specific factors
that can be examined/tested during construction of a test fill to increase
the probability of achieving minimum permeability in the actual clay liner
are:
Preparation and compaction of foundation material to the
required bearing strength
Methods of controlling uniformity of material, clod size,
and water content
Types of equipment and estimates of operational conditions
(e.g., number of passes) required to achieve design density,
compactive effort, and permeability
Lift thickness and placement procedures necessary to achieve
uniformity of density throughout a lift and the absence of
apparent boundary effects between lifts or between placements
in the same lift
Procedures for protecting against desiccation cracking or
other site- and season-specific failure mechanisms for the
finished liner or intermediate lifts
Measuring the permeability on the test fill in the field and
collecting samples of field-compacted soil for laboratory
testing
Test procedures for controlling the quality of construction
Ability of different types of soil to meet permeability
requirements in the field
Skill and competence of the construction team.
1.4 SUMMARY
Clay liners are a widely used technology for management of hazardous
and nonhazardous wastes. Field data on the performance of clay liners or
on the effect of various construction procedures on the permeability of
liners are limited. Laboratory data show that low permeabilities (less
than 10 7 cm/s) can be achieved by compacting soils. The few case studies
that have been conducted suggest that permeabilities measured on laboratory-
compacted samples or on small-diameter intact samples are poor predictors
of performance of the actual liner. A large body of information exists
that suggests which aspects of construction practice, if changed, would be
most likely to improve liner performance and increase the certainty that
clay liners will exhibit uniform permeabilities with values approaching
those measured in the laboratory.
1-9
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1.5 REFERENCE
Haxo, H. E. et al. 1983. Lining of Waste Impoundment and Disposal
Facilities. SW-870, U.S. Environmental Protection Agency, Cincinnati,
Ohio.
1-10
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CHAPTER 2
CLAY SOIL
Clay liners are composed of layers of cohesive soil, engineered and
compacted to form a barrier to liquid migration. From an engineering
standpoint, soil has been defined as unconsolidated accumulations of solid
particles produced by the physical and chemical disintegration of rocks
(ASTM, 1985) or all materials in the surface layer of the Earth's crust
that are loose enough to be moved by a spade or shovel (Winterkorn and
Fang, 1975).
Soil may be viewed as a three-phase system composed of solids, liquids,
and gases. The solid phase is composed of inorganic and organic particles
of varying shapes and sizes. The liquid phase is usually an aqueous elec-
trolyte solution. The gaseous phase is basically air with variations in
composition resulting from biological activity and chemical processes in
the soil. Soils are normally characterized by the size and composition of
their solid (particulate) components, with air- and water-filled voids
considered together as porosity. However, the relative amounts of air and
water (usually expressed as the degree of saturation) also influence soil
behavior.
*
The term clay can be defined in several ways. Clay can refer to all
soil particles less than a given size, usually 2 urn (Mitchell, 1976). In
soils, this particle size range is composed of clay minerals and other
components. Clay minerals give a clay soil its plastic and cohesive proper-
ties. Other components of the clay size fraction include nonclay minerals
(e.g., marl and chalk), amorphous material, and organic material.
Geotechnical engineers use the term clay to refer to soils that contain
enough clay size particles to affect their behavior (Holtz and Kovacs,
1981). Because of its emphasis on the engineering properties of clay as a
liner material, this document uses the term clay to refer to clay soil,
with clay mineral being used when referring to mineralogy and clay size
being used when referring to particle size.
This chapter discusses the characteristics of clay soils and the clay
minerals that are important soil constituents. It is intended to give the
reader a brief overview of these materials, to present some basic defini-
tions, and to discuss the properties of clay soils and clay minerals that
influence the performance of clay liners. The formation and occurrence of
low-permeability, clay-rich soils are also discussed. For a more thorough
discussion of clay mineralogy or of the geotechnical behavior of soil, the
reader is referred to Grim (1962, 1968), Mitchell (1976), and Perloff and
Baron (1976).
2-1
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2.1 CLAY MINERALS
Clay minerals are hydrous silicates, largely of aluminum, magnesium,
and iron, that, on heating, lose adsorbed and constitutional water and
yield refractory material at high temperatures. Plasticity is another
characteristic of clay minerals and is largely due to an affinity of the
clay surface for water, resulting from a net negative charge on the surface
of a clay particle that causes it to adsorb water and other polar fluids.
This net negative surface charge results from defects in the clay mineral
crystal structure and from surface chemical reactions, as described below.
Because of their electrochemical surface activity and high surface area
(resulting from their small size and lamellar shape), clay minerals can
profoundly affect a soil's engineering behavior, even when present in small
quantities. Other soil minerals act predominantly physically to affect a
soil's behavior. As the clay content of a soil increases, the influence of
the clay fraction on its behavior also increases. The strong influence of
clay minerals on soil behavior can be illustrated by the addition of ben-
tonite to a granular soil. Bentonite is a clay material composed largely
of the clay mineral sodium montmorillonite. An addition of only 2 to 3
weight percent bentonite can reduce a soil's permeability when it is com-
pacted by 2 to 3 orders of magnitude (Kozicki and Heenan, 1983). The
influence of clay minerals on a soil's behavior increases with increasing
clay content to a range of 33 to 50 percent, at which point the none!ay
size material is essentially floating in a clay matrix and has little
effect on the engineering behavior of the soil (Mitchell, 1976; Holtz and
Kovacs, 1981).
2.1.1 Clay Mineral Structure
Most c-lay minerals have a sheet-like layered crystalline structure and
thus fall into the phyllosilicate mineral family. Exceptions are the clay
minerals attapulgite, palygorsite, and sepiolite, which have structures
composed of double chains of silica tetrahedra. These minerals are not
common in soils and are not discussed further in this document.
Clay mineral sheet structures consist of two different layer types,
one composed of tetrahedral units and the other of octahedral units, that
are arranged in different sequences to form the different clay minerals.
The tetrahedral unit is composed of silica tetrahedra in which four oxygens
surround a silicon atom in tetrahedral coordination (Figure 2-1). The
octahedral sheet, which is made up of cations octahedrally coordinated with
oxygen (Figure 2-2), occurs in two forms. If the cation is trivalent, only
two-thirds of the possible spaces in a layer are filled and the structure
is dioctahedral. The most commonly occurring dioctahedral sheet in clay
minerals is the gibbsite sheet, in which the cations are aluminum. If the
cation in the octahedral sheet is divalent, all of the available cationic
spaces are filled and the structure is termed trioctahedral. The most
commonly occurring trioctahedral sheet in clay minerals is the brucite
sheet, in which the cations are magnesium.
2-2
-------
Q and (~Ni = Oxygens Q and • * Silicons
Si
Si
(c)
(a) Silica tetrahedron.
(b) Silica tetrahedral sheet.
(c) Schematic of silica sheet. See Table 2-1.
Source: Lambe, 1958; Grim, 1968
Figure 2-1. Clay mineral tetrahedral sheet structure.
O and O * Hydroxyls or
oxygens
I Aluminums, magnesiums, etc.
Al
Al
(C)
(a) Octahedron.
(b) Octahedral sheet.
(c) Schematic of gibbsite octahedral sheet. See Table 2-1.
Source: Lambe, 1958; Grim, 1963
Figure 2-2. Clay mineral octahedral sheet structure.
2-3
-------
Isomorphous substitution, or the substitution of different, similar-
size cations for those present in the ideal crystal structure without a
change in structure, is common in clay minerals and is an important factor
in their behavior. Common cation replacement in clay minerals includes
aluminum (Al 3) for silicon (Si 4), magnesium (Mg+2) for aluminum (Al+3),
and ferrous iron (Fe 2) for magnesium (Mg 2) in the ideal tetrahedral and
octahedral sheets described above. Isomorphous substitution in clay minerals
results in a charge deficiency in the crystal structure and a net negative
charge on the mineral's surface.
The variety of cation substitutions, both in and between the crystalline
sheets, and the intergrowth of layers of different character results in the
diversity of actual clay minerals. However, despite the large number of
clay minerals, only a few are important soil-forming constituents. Table 2-1,
excerpted from Mitchell (1976), summarizes important chemical and physical
characteristics of the clay minerals that commonly occur in soils.
2.1.2 Clay Mineral Groups
This section describes the basic structural makeup of common clay
mineral groups. Although each clay mineral has a definite "ideal" structure,
many naturally occurring clays are complex and do not fit the ideal formulas
described herein. Mixed-layer clays can occur, with crystals containing
structural units of more than one clay mineral group. In addition, soils
composed of a single clay mineral or clay mineral group are relatively
rare; multimineral soils are more commonly encountered in most areas. In a
study of 137 soils across the United States, more than one clay mineral
occurred in about 70 percent of them (Lambe and Martin, 1953-1957).. There-
fore, it is not possible to predict soil behavior accurately by assuming
that only one clay mineral predominates through soil material. For more
information on clay minerals and their complex natures, the reader is
referred to Grim (1968) and Van Olphen (1963).
All clay minerals, except those with chain structure, may be roughly
categorized into four groups based on the height of the unit cell, the
composition of the sheets, and the kind of intersheet bonding that forms
the layers of unit cells. These groups are kaolinite, smectite, illite (or
mica-like), and chlorite. This grouping is convenient since members of the
same group have comparable engineering behavior (Mitchell, 1976). The
following subsections describe these groups and the mineral characteristics
that are important determinants of the engineering behavior of clay.
2.1.2.1 Kaolinite Minerals—
The basic structural unit (unit cell) of the kaolinite group is a 1:1
arrangement of a silica tetrahedral sheet and an alumina (gibbsite) octa-
hedral sheet (Figure 2-3). In the tetrahedral sheet, the tips of the
silica tetrahedra all point toward the center of the unit. The oxygen
atoms at the tips of the tetrahedra are common with one of the planes of
oxygens in the octahedral sheet and compose two-thirds of the octahedral
oxygens. The remaining positions in this plane are occupied by hydroxyls
that are located directly below each hexagonal hole in the network formed
2-4
-------
Type
Subgroup and
schematic
FABLE 2-1. CLAY MINERAL CMARACTERISIICS
Mineral
Ideal formula/unit cell
Cations
octahedral/tetrahedral
1.1 Kaolinite
Kaolinite
(OH)8
2.1 Illite
Ha Hoy site (Oll)g Si.jAI.,0,,,
(dehydrated)
(hydrated) (OH)8 Si4010-4H20
lllite
(K,H20)2(Si)8(A),Mg,fe), G 020(OH)4 (A) ,
ro
i
en
Vermiculite (OII)4(My.Ca)x(Si8_)< Alx)(Mg.Fe)6 020-YH20 (Ma,Fe)fi/(Si ,
x = 1-1.4, y = 8
Smectite
Montmorillonite (OII)4SiH(Al3 3/) Mg 66)02,,-nll20
Na 66
A13.34M9 66/S(«
2:1:1 Chlorite
Chlorite
(OHMSiAIMMg.Fe),. 0,11(2 1 laye! )
(M.|AI)0(OII)l;, (interlayer)
(Mgle),, (2:1 layer)/(Si ,AI )„
(Hg.AI),, interlayer
See notes at end of table
(cunt nun-ell
-------
TABLE 2-1 (continued)
IM
I
CTi
Mineral
Kaolinite
llalloysite
(dehydrated)
(hydra led)
mite
Vermicul i te
Montmori 1 Ion lie
Chlorite
Isomorphous
substitution
Little
Little
Si always replaced
by some Al. Balanced
by K between layers
Al for Si; net
charge of 1 to
1.4/unit cell
Mg for Al ; net
charge always =
0.66-/unit cell
Al for Si (2: I/layer)
Al for Mg (interlayer)
Interlayer bond
0-011
Hydrogen- s t rong
0-011
Hydrogen- strong
K ions-strong
Weak
0-0; 9.
Very weak
expanding lattice
0-011
Hydrogen-strong
Basal
Spacing
o
7.2A
O
7.2A
0
10. 1A
O
10A
O
10.5-14A
o
6A-conplete
separation
0
14A
CECe
(meq/lOOg)
3-15
5-10
5-40
10-40
100-150
80-150
10-40
Speci fie
surface (mVg)
10-20
35-70
65-100
40-80 primary
870 secondary
50-120 primary
700-840 secondary
Liquid
limit
(X)
30-110
35-55
50-70
60-120
100-900
44-47
Plastic
limit
25-40
30-45
47-60
35-60
50- 100
36-40
Shrinkage Activity
limit /Plasticity index
(%) \ %"~2,,iu l
25-29 0.5
0.1-0 5
15-17 0 5-1
8.5-15 1-7
After Mitchell (1976).
S indicates silica tetrahedral sheet
G indicates gibbsite octahedral sheet
B indicates brucite octahedral sheet.
K indicates potassium ions
0 indicates water layer
[wo formula units required per unit cell.
Arrow indicates source of charge deficiency.
Cation exchange capacity.
Equivalent Na listed as balancing cation.
-------
(a)
Oxygens
(OH) Hydroxyls
Aluminums
O Silicons
(b)
10.1 A
\
(0
Water Molecules
7
7.2 A
(a) Diagram of kaolinite structure.
(b) Hydrated haitoysite.
(c) Kaolinite or dehydrated halloysite.
G - Gibbsite sheet.
Source: Grim, 1963; Mitchell, 1976
Figure 2-3. Kaolinite group minerals.
2-7
-------
by the bases of the silica tetrahedral (Figure 2-3). The kaolinite basal
o
spacing is 7.2 A.
Minerals in the kaolinite group are composed of stacks of the 1:1
structural units (unit cells) described above. These unit cells are held
together by van der Waals forces and hydrogen bonding between the tetrahedral
sheets and the octahedral sheets of adjacent unit cells.. These bonds are
strong enough to preclude the introduction of water between the unit cells
and thus any inter!ayer swelling.
2.1.2.1.1 Kaolinite—Kaolinite is the most common mineral in this
group and consists of stacks of 1:1 unit cells comprised of silica tetrahe-
dral and gibbsite (Al) octahedral sheets. The stacks generally range from
0.05 to 2 urn in thickness and can attain thicknesses up to 4,000 (jm; the
stacks can range from 0.1 to 4 urn laterally. The specific surface area of
kaolinite is on the order of 10 to 20 m2/g of dry clay.
A small net negative charge on kaolinite particles results in a cation
exchange capacity of 3 to 15 meq/100 g. This charge has been attributed to
a small amount of isomorphous substitution in the silica or gibbsite sheets,
replacement of exposed hydroxyl hydrogens by exchangeable cations, broken
bonds around particle edges, or diffuse charges resulting from the large
size and surface accessibility of 0~2 and OH* molecules (Mitchell, 1976;
Winterkorn and Fang, 1975). The stacked crystal structure of kaolinite
results in a blocky form for this clay mineral and a larger size and lower
surface-to-volume ratio than other clay minerals. This low surface area,
combined with the relatively small negative surface charge, results in
kaolinite being the least electrochemically active and least plastic clay
mineral.
Because of the blocky structure of kaolinite particles, crystal edges
of this mineral group comprise 10 to 20 percent of the total crystal area
(Theng, 1974) and therefore exert a stronger influence on the electrochemical
behavior of these minerals than do the crystal edges of smectites or illites
(crystal edges comprise 2 to 3 percent of total crystal area for montmorillo-
nite; Theng, 1974). Broken bonds on these edges result in unsatisfied
valences that can be satisfied by cation or anion adsorption. However,
unlike the structurally generated negative charges on the platy crystal
surfaces, these charges are affected by the pH of the environment. Evidence
suggests that the edges are positively charged at low pH and negatively charged
at high pH. This results in kaolinite having a low cation exchange capacity
at low pH and higher cation exchange capacity at high pH (see Section
2.3.1). Kaolinite has a higher anion exchange capacity than most clay
minerals. This may result from the presence of replaceable hydroxyl ions
on the outside of structural sheets. Kaolinite thus has the ability to fix
certain negative ions (Deer et al., 1966).
Compared with other clay minerals, kaolinite has a lower affinity for
water, has a lower dispersivity (see Section 2.3), and does not achieve as
low a permeability upon compaction. On the other hand, because it is not
as electrochemically active, its behavior may be less affected by chemicals
than other clay minerals. Thus, a kaolinitic clay liner may have a higher
2-8
-------
permeability than liners composed of other clays, but the permeability of a
kaolinitic clay liner may not be as sensitive to changes in moisture content
or to chemical attack.
2.1.2.1.2 Halloysite—Halloysite is another kaolinite group mineral
that is a common soil constituent in some areas. This mineral occurs in
two forms: a nonhydrated type with a structural composition similar to
kaolinite and a hydrated form with a single layer of water interposed
between unit kaolinite layers (Figure 2-3). This layer increases the basal
o o
spacing to 10.1 A, compared with 7.2 A for nonhydrated halloysite and
kaolinite. Partially hydrated halloysite (metahalloysite) with basal
o
spacing from 7.4 to 7.9 A can also occur. The interlayer water molecules
in hydrated halloysite are believed to be in a rather flat hexagonal network
linked to each other and to adjacent halloysite layers by hydrogen bonding.
The hydrated form of halloysite occurs in cylindrical tubes of over-
lapping kaolinite sheets. The outside diameters of the tubes range from
0.05 to 0.20 urn, with a median value of 0.07 urn, and range in length from a
fraction to several micrometers. The specific surface area of halloysite
ranges from 35 to 70 mVg (Mitchell, 1976).
Because of the interlayer water sheet in hydrated halloysite, inter-
calation (introduction between the unit cells) of chemicals can occur.
This also results in a slightly higher cation exchange capacity for hy-
drated halloysite (5 to 40 meq/100 g) than for kaolinite (3 to 15 meq/100 g).
Halloysite also may be more affected by chemicals than kaolinite.
The interlayer water in halloysite is easily removed during drying,
and this dehydration is irreversible. Because of this phenomenon, soil
engineering tests on air-dried samples can give different results than
those performed on samples at the original field moisture content. For
this reason, it is especially important that laboratory tests on soils with
appreciable halloysite content be carried out on samples at the original
field moisture content (Holtz and Kovacs, 1981; Hilf, 1975).
2.1.2.2 Illite Minerals—
The illitic clay minerals are also known as the mica-like clay minerals
because of their structural similarity to hydrous micas. Illites are
composed of mica-like three-layer sandwiches with an octahedral sheet
between two silica tetrahedral sheets (2:1 layers). These "sandwich"
layers are in turn bound together by fixed or exchangeable cations. The
specific mineral species in this group are determined by differences in
octahedral sheet composition and the type of interlayer cations. Two
minerals in this group common in soils are illite and vermiculite.
2.1.2.2.1 111ite—Illite is an important constituent of clay soils
and has been described by Mitchell (1976) as "perhaps the most commonly
occurring clay mineral found in soils encountered in engineering practice."
Illite has almost the same crystalline structure as muscovite mica. This
structure is comprised of a silica-gibbsite-silica sandwich, with the tips
of the silica tetrahedra pointing toward the octahedral gibbsite sheet and
2-9
-------
the oxygens at the tips being common with the octahedral sheet (Figure 2-4).
Isomorphous substitution of aluminum for silicon in the tetrahedral sheet
results in a negative charge at the surface of these layers. This charge
is balanced by potassium, cesium, and ammonium ions between the 2:1 layers;
o
these ions fit tightly in the 1.32-A-radius holes in the bases of the
silica sheet and as a result are fixed in position and are not exchangeable.
Illite differs from muscovite in having less isomorphous substitution in
the tetrahedral sheet, a lower negative surface charge, and a lower amount
of potassium between the layers. The stacking of illite layers is also
more random, and illite occurs with a much smaller particle size than
muscovite.
In terms of properties important to clay liner performance, illite
lies between kaolinite and the smectite clay minerals. Although extensive
isomorphous substitution results in a net negative charge on the clay
mineral surface, the fixed potassium cations balance the charges and strongly
bond adjacent 2:1 sheets together. As a result, illite has intermediate
values for surface area (65 to 100 m2/g), cation exhange capacity (10 to
40 meq/100 g), swelling index, and activity. It is also intermediate in
its reaction to chemicals. Because of the strength of the interlayer
o
potassium bonding, the basal spacing of illite remains at 10 A when it is
exposed to polar liquids (Mitchell, 1976). The potassium ions effectively
prevent the intercalation of water, organic liquids, and other cations
(Deer et al., 1966).
2.1.2.2.2 Vermiculite—Vermiculite is a fairly common mineral in clay
soils and usually occurs with other clay minerals. Vermiculite has a 2:1
structure with a poorly organized octahedral sheet sandwiched between two
silica tetrahedral sheets (Figure 2-4). The octahedral sheet contains iron
and magnesium ions.
As with illite, isomorphous substitution of aluminum for silicon is
extensive in the tetrahedral sheet, resulting in a net negative charge on
the crystal surface. This positive charge deficiency is larger than that
of the smectite minerals (see Section 2.1.2.4) and is usually balanced by
interlayer layers of divalent cations and water. This larger charge defi-
ciency results in Vermiculite having the highest cation exchange capacity
of all clay minerals (Deer et al., 1966). The most common interlayer
cations in vermiculite are magnesium and, to a lesser extent, calcium.
The amount of water that is intercalated in vermiculite is less vari-
able than that in smectite and usually is limited to two layers of water
molecules. The interlayer spacing is therefore fairly constant for vermic-
ulite but varies to some extent depending on the cations present between
the layers. Vermiculites can absorb organic liquids between their layers
but take up less than the smectite minerals (Deer et al., 1966). The
primary specific surface area for vermiculite ranges from 65 to 100 m2/g.
This is within the range reported for montmorillonite and, as with montmoril-
lonite, the secondary (interlayer) surface area can reach very high values
(870 m2/g) (Mitchell, 1976).
2-10
-------
( j Oxygens. (OH) Hydroxyls. MB Aluminum, ( ) Potassium
O and • Silicons (One-Fourth Reolaced by Aluminums)
(a)
Exchangeable
fixed
\
(b)
(a) Diagram of illite structure
(b) Illite schematic.
(c) Vermiculite schematic
•2P— Water Molecule
10 to 14 A
114 A as
shown)
(c)
G - Gibbsite sheet.
B = Brucite sheet.
Source: Mitchell, 1976
Figure 2-4. Illite clay minerals.
2-11
-------
2.1.2.3 Chlorite Minerals--
Chlorite minerals in clay soils are almost always found in association
with other clay minerals. Chlorites are composed of 2:1 layers of silica
tetrahedral sheets surrounding a gibbsite or brucite octahedral sheet, with
another octahedral sheet between the 2:1 mica layers (Figure 2-5). Chlorites
thus may be termed 2:1:1 clay minerals.
Chlorites can have isomorphous substitution and may be missing a few
of the octahedral sheets between the 2:1 layers. This can result in some
swelling from water uptake between the layers. Chlorites are less active
than the smectites, have a cation exchange capacity similar to illite (10
to 40 meq/10 g), and may be similar to illite in engineering behavior.
2.1.2.4 Smectite Minerals—
The smectite group of clay minerals includes 2:1 minerals whose unit
cell is composed of an octahedral sheet sandwiched between two silica
tetrahedral sheets. The bonding between these 2:1 layers is by van der
Waals forces and cations that may be present to balance out structural
charge deficiencies in the 2:1 layer. This bonding is weak, and, as a
result, the layers are easily separated by adsorption of water or other
polag liquids. Thus, the interlayer spacing of smectites can vary from
9.6 A to complete separation, and this results in the high swelling behavior
and high activity of these clay minerals.
The smectite minerals may be divided into two groups, based on the
composition of the octahedral sheet. The montmorillonites have a diocta-
hedral , aluminum-based (gibbsite) octahedral sheet; the saponites have a
trioctahedral magnesium-based (brucite) sheet. Only montmorillonite is
commonly found in soils. The saponites are relatively unimportant as soil
constituents and are not discussed further in this document.
2.1.2.4.1 Montmorillonite—Montmorillonite is a 2:1 clay mineral with
a dioctahedral gibbsite sheet sandwiched between two silica tetrahedral
sheets (Figure 2-5). Extensive substitution of magnesium and other cations
for aluminum and aluminum for silicon results in a charge deficiency of 0.5
to 1.2 (usually 0.66) on the unit cell (Mitchell, 1976). Most of the
substitution in montmorillonite occurs in the octahedral gibbsite sheet,
usually one magnesium for every sixth aluminum. This results in a charge
on the mineral surface that is more diffuse or evenly spread than that of
vermiculite, which has mostly substitution of aluminum for silicon in the
outer, tetrahedral layers (Deer et a!., 1966; Winterkorn and Fang, 1975).
The charge deficiencies on the montmorillonite unit cells are balanced by
exchangeable cations between the unit cells, and, as a result, montmoril-
lonite exhibits a high cation exchange capacity (generally 80 to 150 meq/
100 g).
The bonding forces between unit cells of montmorillonite are weak, and
water and polar fluids can easily penetrate between the unit cell layers.
As a result, montmorillonite particles are very small and can be dispersed
o
to sheets of unit cell thickness (10 A) in water (Mitchell, 1976). The
specific surface area of montmorillonite is very high, with a primary
2-12
-------
T
T
(a)
Gibbsite
or brucite
Al
Si
Si
Si
Brucite
(b)
Several
water
Layers
1.4 nm
At
A;
*/
Several
water
Layers
T
nH2 0 layers and exchangeable cations
("^) Oxygens (Sw) Hydroxyls ^k Aluminum, iron, magnesium
O and 9 Silicon, occasionally aluminum
(a) Schematic diagram of chlorite.
(b) Schematic diagram of montmorillonite.
(c) Diagram of smectite structure.
Figure 2-5. Chlorite and smectite clay minerals.
2-13
-------
surface area of 50 to 120 m2/g and a secondary surface area (including
interlayer surfaces) of 700 to 840 m2/g. Because of its .high specific
surface and tendency to adsorb inter!ayer water, montmorillonite is very
susceptible to swelling and is the most active of the clay minerals.
Montmorillonite is especially sensitive to alteration by chemical attack.
The type of cations occupying the inter!ayer spaces strongly influences
the behavior of montmorillonite. The most commonly occurring interlayer
cation is calcium, a divalent cation. Like vermiculite, calcium-montmorillo-
nites usually take up two layers of water between the unit cell layers
(Deer et a!., 1966). This results in limited swelling to a maximum inter-
o
layer spacing of 19 A (Theng, 1974). However, when sodium is the inter-
layer cation, as occurs in the Wyoming bentonites (see 2.1.2.4.2), the
amount of interlayer water is not so limited and the interlayer spacing can
o o
range from 10 A (oven-dry) to over 50 A (Theng, 1974). This results in
high swelling, which is characteristic of sodium-montmorillonite; it can
expand to 13.8 times its dry volume when fully hydrated.
2.1.2.4.2 Bentonite—Bentonite is not a clay mineral. It is a rock
(or clay deposit) composed largely of the clay mineral montmorillonite.
The swelling and dispersive properties of this mineral give bentonite the
ability to lower the permeability of a soil, even when added in small
quantities (e.g., 1 to 3 percent by weight). The swelling capacity of
bentonite depends on its sodium-montmorillonite content. Low-swelling
bentonite has significant quantities of calcium-montmorillonite, which,
because of limited interlayer water uptake, does not swell to the extent of
sodium-montmorillonite. High-swelling sodium bentonite has a liquid limit
of 500 percent or more and can swell IS to 20 times in volume. Calcium
bentonite will increase in volume 0 to 5 times when wetted with water; this
swelling capacity has been reported to increase 700 to 1,000 percent by
treating calcium bentonites with a 0.25-percent solution of Na2C03 (Fisher,
1965).
Bentonite is formed by the weathering of volcanic ash. Environmental
conditions favorable to sodium bentonite formation are semiarid climate and
alkaline soil and groundwater. The type locality for bentonite is Wyoming,
and most sodium bentonite comes from the western United States and Canada
(Hosterman, 1985). Calcium or low-swelling bentonite is mainly obtained
from deposits in the Gulf Coastal Plain formed from weathering of volcanic
ash deposits (Hosterman, 1984).
2.2 CLAY FORMATION AND OCCURRENCE
This section presents some of the factors that influence the formation
and occurrence of clay soils in the United States. It is intended to help
the reader comprehend the complexity of soil-forming processes and the degree
of heterogeneity and variability that may be expected in naturally occurring
soils that may be used for clay liners. It is not intended to be a complete
treatise on the subject.
2-14
-------
2.2.1 Clay Mineral Paragenesis
Clay minerals are products of weathering or hydrothermal alteration,
with different minerals resulting from differences in physicochemical
conditions and differences in parent material (Deer et al., 1966). Clay
minerals may be found in their place of origin or may be transported and
deposited in sediments. In general, acid conditions favor the removal of
cations from the soil and kaolinite formation, and alkaline conditions
favor the formation of other clay minerals, with the predominant type(s) of
cation influencing the clay mineral species. A brief discussion of clay
mineral formation follows. A more complete discussion may be found in Grim
(1968), Keller (1964), and Weaver and Pollard (1973).
Kaolinite mineral deposits are formed primarily by the weathering of
alkali feldspars and other silicate minerals common to sialic rock types
such as granites and quartz diorite. Kaolinite occurs in residual, hydro-
thermal, and sedimentary deposits (Patterson and Murray, 1984). In the
soil environment, acidic conditions favor kaolinite formation through the
dissolution and removal of bases from the parent material. Kaolinite
formation is favored where alumina is abundant and silica is scarce.
Kaolinites may be formed in situ but are usually a product of weathering
and transport (Deer et al., 1966). Kaolinite minerals may be found alone
or in association with other clay minerals in soils. Kaolinite soils are
prevalent in the southeastern United States, where they are formed from
weathering, erosion, and redeposition of granitic material (Mason and
Berry, 1968) and in other humid regions with intense chemical weathering
and good drainage.
mites are formed from the degradation of muscovite and from the
alteration of other clay minerals. The formation of illite is favored by
alkaline conditions with high concentrations of alumina and potassium (Deer
et al., 1966); illite can be formed from smectites under these conditions.
Illite is very common in soils and is almost always found in association
with other clay minerals; its stability is responsible for its abundance.
Vermiculite in soils is formed from alteration of biotite by weather-
ing; it is usually found in association with other clay minerals in soils.
Chlorite is also commonly found in soils in association with other clay
minerals; it may be formed from the alteration of other clay minerals
(e.g., montmorillonite) in the presence of magnesia or by the degradation
of ferro-magnesian minerals. Alkaline environments rich in iron and mag-
nesium favor its formation.
In general, the formation of smectites is favored by alkaline conditions
and the presence of calcium and magnesium. However, smectites occur in
association with illite in the prairie soils of the midwest (pH 4.5 to 5).
Calcium is usually the dominant exchange cation in smectites, except for
deposits in the western United States, where high-sodium-montmorillonite-
content (sodium bentonite) clay deposits are formed from the alteration of
volcanic rocks. Montmorinonite is also found in soils formed by the
weathering of basic igneous rocks; poor drainage conditions promote the
2-15
-------
formation of montmorillonite in soils because magnesium is not removed
during weathering (Deer et al., 1966). High calcium and magnesium and low
potassium and sodium are also favorable to montmorillonite formation, as
are semiarid and arid climates (Mitchell, 1976).
2.2.2 Clay Soil Formation and Occurrence
Clay soils occur throughout the United States in a variety of deposi-
tional environments. The characteristics of a clay soil are influenced by
the parent material of the soil and the soil-forming processes (e.g.,
weathering, deposition). Clay soil may occur as transported soil or residual
soil. Transported clay soil includes soil laid down by water action (fluvial
soil) and soil deposited by ice action (glacial deposits). Residual soil
is soil that is chemically weathered in place from the parent bedrock
(USDI, 1974). Each of these soil-forming processes results in soils with
different characteristics. The processes involved in soil formation are
diverse and multivariate, resulting in a wide range of chemical and physical
variations.
2.2.2.1 Fluvial Soils-
Fine-grained, high-clay-content soils are found in the outer edges of
torrential outwash deposits or alluvial fans (deposits laid down where an
abrupt flattening of stream gradient occurs), especially in humid climates.
Other alluvial (steam laid) deposits can also have high clay contents;
sediments from older, slow-moving, meandering streams have a larger frac-
tion of fine-grained components (USDI, 1974). Overbank, floodplain deposits
laid down in still waters also tend to be fine-grained.
Individual strata of alluvial deposits can vary considerably, both
vertically and horizontally and in clay content and permeability (Freeze
and Cherry, 1979). A predominantly fine-grained floodplain or valley-fill
deposit should be expected to have many lenses or strata of coarse-grained,
permeable material. Complex vertical and lateral facies changes, from
fine-grained overbank deposits to coarse-grained river channel deposits,
are common in valley-fill and valley terrace deposits. These lateral
facies changes result from changes in a river course and changes in a flow
regime and reflect past and present geomorphic processes and environments.
Meandering stream deposits are especially variable in this regard because
of the continuous changes in river course common to this geomorphic envi-
ronment. Thus, there is much heterogeneity in alluvial sediments resulting
from textural variability. Hydraulic conductivities can vary more than 2
or 3 orders of magnitude in these deposits (Freeze and Cherry, 1979).
Because of this heterogeneity, knowledge of fluvial processes can be very
helpful when site investigations are conducted in areas of alluvial soils.
Alluvial deposits are found in river valleys across the United States, in
glaciated regions, and in the large intermountain basins of the Southwest
(Heath, 1984).
Lacustrine deposits are deposited by the still water of lakes. They
are fine-grained, finely stratified deposits with low permeability, high
compressibility, and low shear strength. Lacustrine deposits have flat
2-16
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surfaces and are surrounded by high ground (USDI, 1974). Near the edges of
lake deposits, alluvial influences can result in lenses of coarse-grained,
permeable material being interstratified with the fine-grained lake sedi-
ments. As with the valley-fill deposits, these heterogeneities can result
in rapid groundwater migration through the permeable layers. Lacustrine
deposits are common in glaciated regions, along the Gulf coastal plain, and
in the intermountain basins of the West (Freeze and Cherry, 1979).
Because they are laid down in still or slow-moving water, fine-grained,
low-permeability fluvial deposits tend to have a dispersed soil fabric (see
Section 2.4.1 for a discussion of fabric). However, flocculated fabrics
also can result from fluvial deposition. Fluvial soils tend to be aniso-
tropic with respect to permeability from stratification, with permeability
greater in the horizontal than in the vertical direction. In one study of
alluvial and lacustrine sediments (Johnson and Morris, 1962), 46 samples
had a greater horizontal than vertical hydraulic conductivity, 11 samples
were isotropic, and 4 samples had greater vertical conductivities. Horizon-
tal conductivities were 2 to 10 times larger than vertical conductivities
in this study.
2.2.2.2 Glacial Soils-
Glacial deposits are those that are laid down by the advances and
retreats of the North American continental ice sheets and by smaller moun-
tain glaciers in the Rocky Mountains, the Sierra Nevadas, and Alaska.
Glacial soils tend to be very heterogeneous because the source material of
a single soil can extend over hundreds of miles. Deposits of the glacier
proper are referred to as glacial-till or morainal deposits and are hetero-
geneous, well-graded deposits with particle sizes ranging from clay to
large boulders. They are deposited directly from glacial ice with little
or no sorting by moving water. The rock fragments are generally contained
in a matrix of fine silt and clay, resulting in a low-permeability soil
with considerable shear strength. These are excellent qualities for land-
fill sites and clay liner material. For these deposits, the fine clay
material can have a flocculated, random fabric because till is deposited in
mass from the wasting ice. Fine-grained glaciofluvial and glaciolacustrine
deposits tend to have a dispersed fabric because these deposits are fluvial
in origin (see preceding discussion on fluvial soils). However, flocculated
fabrics can result from fluvial deposition.
The heterogeneities common in glacial soils make a detailed site
survey necessary during investigations of a landfill site or borrow pit in
glacially deposited soils. Field permeability tests should be part of any
site surveys in glacial soils because of the potential for fractures and
stratified heterogeneities. Knowledge of glacial processes is very helpful
in delineating heterogeneities during a site investigation in glacial
soils.
2.2.2.3 Residual Soils-
Residual soils result from the in situ weathering of underlying bedrock
and are always present in the place where they have formed. The character
of a residual soil is determined by the parent bedrock and the type and
2-17
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degree of weathering to which it has been subjected (USDI, 1974). "Residual
soils are rare in glaciated regions because the action of ice removed such
soils during the last glaciation, and not enough time has passed since then
(10,000-12,000 years) for weathering processes to form new soils from rocks
in place. Residual soils generally occur where transported soils or surfi-
cial bedrock are absent (USDI, 1974).
The mineralogy and physical grain morphology for residual soils are
different from those of other soils. Residual soils are more leached than
glacial or fluvial soils, with lower lime, magnesium, and potash contents
and higher silica, alumina, and iron-oxide contents. Individual mineral
grains in residual soils tend to be more rounded and weathered (decomposed)
than in other soils. The fabric of residual soils can be flocculated, or
randomly oriented, as the mineral grains are formed in place and not
deposited with preferential orientation as are fluvial soils. However,
weathering processes can also result in dispersed fabric, depending on the
mineralogy of the soil and the geochemical environment (see Section 2.4.1.1),
Although most soils have unique compaction curves, for a residual
soil, compaction curves at a given compactive effort can change, depending
on the soil moisture content at the start of the test. This has been
attributed to the presence of halloysite (which exhibits irreversible
drying) and to particle breakdown during air drying and subsequent compac-
tion (Hilf, 1975). Irreversible changes during drying can also occur for
other soil types (see Section 3.8.3.1; Sangrey et al. 1976).
2.3 CLAY CHEMISTRY
2.3.1 Electrical Double-Layer Theory
Most clay mineral particles fall into the size range that defines
colloids. Colloids are particles that are sufficiently small to allow
interfacial forces to be significant in their behavior. For clay minerals
in soil environments, these interfacial forces are present as a charged
solid-solution interface that gives rise to an electrical or diffuse double
layer.
An electrical double layer is composed of a layer of charges fixed on
or within the surface of a solid and a layer of mobile ions of opposite
charge, or counter ions, distributed in the liquid adjacent to the surface.
These counter ions are weakly held close to the surface by electrostatic
forces and can be displaced with respect to the charged, solid surface with
movement of the liquid.
The theory of the diffuse double layer was originally developed by
Gouy (1910) and Chapman (1913), with later modifications by Stern (1924)
and others, to explain colloid behavior. Parks (1975) and Stumm and Morgan
(1970) describe several models of the double layer. A simple model is
illustrated in Figure 2-6. In this case, electrostatic attraction between
the adsorbent (negatively charged clay surface) and adsorbate (positive
ions in solution) results in a layer of cations at the surface (the Stern
2-18
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A.
Solid Surface
-Stern Plane
Solution
Gouy layer, charge = aG incl. charge
in Stern plane
Surface Charge = aa
B.
Concentration
of
Counter- and
Co- Ions in the
Double Layer
1
|: NV Counter-Ions, +
Cf* — ^^
l^-*" in Solution
I Co-Ions, —
1
1
Distance from Surface
After Parks, 1975.
Figure 2-6. Electrical double layer.
2-19
-------
layer) and a diffuse layer of cations in solution (the Gouy layer). The
cation concentration in the Gouy layer decreases with distance from the
negatively charged surface. The thickness of the Stern layer is fixed by
the hydrated radius of the adsorbed counter ions; the plane through the
center of the Stern layer counter ions is known as the Stern plane (Figure
2-6a). The thickness of the Gouy layer is defined as the distance from the
charged surface at which the cation and anion concentrations reach that of
the bulk solution. From this point, for a negatively charged surface,
cation concentrations increase and anion concentrations decrease as one
moves toward the surface (Figure 2-6b).
The negative surface charge that generates the electric double layer
around clay minerals may be attributed to two causes (Stumm and Morgan,
1970): (1) imperfections or substitutions in the crystal lattice of the
clay minerals (i.e., isomorphous substitution) and (2) charge deficiencies
arising from chemical reactions at the mineral surface. These surface
chemical reactions include those involving broken bonds at particle edges
and. noncleavage surfaces and the interactions of potential-determining ions
(H or OH ), with hydroxyl groups at the exposed surface of the clay parti-
cle. Isomorphous substitution is the major cause of negative surface
charge for all clay minerals except perhaps the kaolinite group. Surface
chemical reactions contribute about 20 percent of the surface charge for
smectites and may be the major source of surface charge for kaolinites
(Mitchell, 1976).
Negative surface charge from structural causes is not affected by the
pH of the solution surrounding the surface in question. However, charges
arising from surface chemical reactions are directly affected by solution
pH. Decreasing pH lessens the negative surface charge. For a given solution
and clay mineral, there is a characteristic pH, the pH , at which the
surface charge is zero. At pH values lower than pH , the surface becomes
positive and thus can act as an anion exchanger (Stumm and Morgan, 1970).
Figure 2-7 compares the effect of solution pH on surface charge, in
terms of electrophoretic mobility (EPM), for kaolinite and fuller's earth,
a clay material usually composed principally of calcium montmorillonite.
One may see that kaolinite is strongly affected by solution pH, with fuller's
earth being much less affected. This supports the contention that most of
the surface charge for kaolinite is due to surface chemical effects. Most
of the total surface charge of the 2:1 minerals (e.g., montmori11onite)
results from defects in the crystal structure inside the minerals and
therefore is less affected by changes in pH.
The thickness of the double layer of clay minerals results from a
balance between the electrostatic attraction force holding the diffuse
cation layer to the surface of the mineral and osmotic forces tending to
diffuse cations away from the mineral surface. The electrostatic attrac-
tion force depends on the mineral properties (i.e., surface charge), while
the osmotic forces depend upon the properties of the solution (including
dissolved ions) surrounding the clay mineral.
2-20
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1.0
I 05
S o
0- •
OS- S>-
•10'
9 10 11 12—• pH
for Fuller's earth
Source: Stumm and Morgan, 1970
Figure 2-7. Effect of solution pH on clay mineral surface charge (EPM).
2-21
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A more detailed discussion of these effects may be found in Mitchell
(1976) and in Chapter 4 of this document, which discusses the different
effects of chemicals on clay permeability. Quantitative treatment of the
electrical double layer also is discussed in Chapter 4. However, it is
difficult to apply the electrical double layer equations to predict the
behavior of clay soils because of the complexity of the system. Clay soils
are almost always composed of a variety of clay minerals, each with different
double layer characteristics.
2.3.2 Cation-Exchange Capacity and Cation Affinity
The cation-exchange capacity (CEC) of a clay mineral may be defined as
the excess of cations in the electrical double layer that can be exchanged
for other cations in the bulk solution (i.e., the shaded area in Figure 2-6b).
The three-layer (2:1) clay minerals exhibit the largest exchange capacities.
Typical CEC ranges for clay minerals are presented in Table 2-1. Ranges in
CEC result from variations in composition and environmental factors; a
given clay mineral does not have a single CEC value (Mitchell, 1976). It
should also be noted that because clay soils are rarely composed of a
single clay mineral and because other nonclay substances (e.g., sand and
rock flour) usually constitute a significant portion of the soil mass, the
cation exchange capacities of bulk soils are lower than those of pure clay
minerals.
Cations differ in their probability of being adsorbed by a colloid.
There is a well-defined affinity series of cations for clay mineral surfaces.
For cation-exchange equilibria dominated by electrical dipole interactions
between the cations and water molecules, the following affinity series
exist:
Cs
K
Na
and
> Sr > Ca > Mg > Be
Thus, affinity increases with decreasing ionic radius for a given cation
valence. This series does not apply to ion exchange sites that have affin-
ities for specific cations (e.g., interlayer illite potassium sites).
As predicted by double layer theory, clay minerals have a greater
affinity for bivalent cations than for monovalent cations and this selec-
tivity decreases with increasing solution ionic strength (Stumm and Morgan,
1970). In addition, the selectivity of clay surfaces for different ions in
a mixed ion system is temperature-dependent. Mass action effects (i.e.,
high concentrations of specific cations in solution) can override the
affinity series (Mitchell, 1976).
Cation exchange affects the double layer thickness and this, in turn,
can affect the permeability of clay soil through its effects on particle
arrangements. Replacement of a monovalent cation by a divalent cation
2-22
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results in a reduction in double layer thickness, lower interparticle
repulsion and dispersion, increased flocculation, and increased permeability
(see Section 2.4.2). This phenomenon is discussed in Chapter 4. The
properties of clay minerals with higher cation exchange capacities (e.g.,
montmorillonite) are more affected by cation exchange than those of clay
minerals with low cation exchange capacities (e.g., kaolinite). Cation
exchange capacity increases with increasing mineral surface area and surface
charge.
2.3.3 Significance of the Electrical Double Layer to Clay Liners
The thickness of the electrical double layer is an extremely important
determinant of the engineering properties of a clay soil. For clay soils,
increasing clay mineral electrical double layer thickness results in a more
dispersed fabric and lower hydraulic conductivity (see Section 2.3).
Reduction in electrical double layer thickness for clay minerals can occur
through desiccation, cation exchange, and interactions with certain chemicals
(see Chapter 4 for further discussion of clay/chemical interactions).
Reduction in double-layer thickness results in a more flocculated soil
structure and increased permeability. The effect of double-layer thickness
in a clay soil on its behavior also depends on the size and specific surface
area of the clay particles in the soil. The behavior of smaller clay
minerals, with higher specific surface area and surface charge (e.g.,
smectites), is more affected by changes in double-layer thickness than clay
minerals with lower specific surface areas (e.g., kaolinite). Relative
sizes of clay minerals are illustrated in Figure 2-8.
2.4 CLAY SOIL FABRIC AND HYDRAULIC CONDUCTIVITY
This section briefly discusses the fabric of fine-grained soils and
the engineering property of soils most relevant to clay liners; i.e., the
relationship of compaction to hydraulic conductivity (permeability). For
more information on these subjects, see Grim (1962, 1968), Mitchell (1976),
and Hilf (1975). A discussion of clay/chemical compatibility, including
the effects of chemicals on soil hydraulic conductivity, may be found in
Chapter 4 of this document.
2.4.1 Soil Porosity and Hydraulic Conductivity
Porosity and hydraulic (or fluid) conductivity are two fundamental
soil properties from the standpoint of fluid transport. The pore size of a
soil is the most important factor influencing the soil's hydraulic conduc-
tivity. Although a statistical relationship exists between porosity and
hydraulic conductivity for relatively uniform porous media (increasing
porosity increases hydraulic conductivity), it is difficult to relate
quantitatively porosity and hydraulic conductivity for clay soils (Mitchell,
1976). However, this relationship can be discussed qualitatively.
2-23
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(a)
Adsorbed water
Kaolinite crystal
(1000 X 100 nm)
Montmorillonite
crystal
(100 X 1 nm)
Edge View
Typical
Thickness
(nm)
Typical
Diameter
(nm)
Specific
Surface
(krn^/kg)
Montmorillonite
100-1000
0.8
(b)
Illite
30
10000
0.08
Chlorite
Kaolinite
30
50-2000
10000
300-4000
0.08
0.015
(a) Relative sizes of hydrated kaolinite and montmorillonite crystals.
(b) Relative sizes of clay minerals.
Source: Lambe, 1958
Figure 2-8. Comparisons of clay mineral sizes
and surface areas.
2-24
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The physical structure* of a soil determines its porosity and its
hydraulic conductivity. Two types of porosity may be delineated in soils:
primary and secondary. These types of porosity are controlled by, respec-
tively, the microstructure (fabric) and macrostructure of the soil, as
described below. In addition to primary and secondary porosity, macrostruc-
tural heterogeneities (e.g., sand lenses and sand seams) also influence the
hydraulic conductivity of a soil mass.
2.4.1.1 Soil Microstructure and Primary Porosity—
Primary porosity is the porosity of the soil mass or soil matrix and
is controlled by the microstructure or fabric of the soil, which is in-
fluenced by the particle size distribution and the arrangement of mineral
grains. Soils with low hydraulic conductivities have a significant percent-
age of fine material. Usually this fine-grained material is composed of
clay minerals. Clay minerals generally have flat, platy particle shapes.
The orientation of the clay platelets in the soil is one of the most important
parameters determining effective porosity and hence hydraulic conductivity
in fine-grained soils (Mitchell, 1976). Moreover, the primary cause of
microscale anisotropy in fine-grained soils is the orientation of clay
particles in a dispersed manner (Freeze and Cherry, 1979). Figure 2-9
illustrates some simple soil fabrics that can occur in clay soils. These
are simplified pictures. Much more complicated particle arrangements
usually occur, and a single soil may have many different zones of fabric.
In fine-grained, clayey soils, fabric can refer to the arrangement of
individual clay platelets (Figures 2-9a and 2-9b) or to the arrangement of
oriented groups of platelets (Figures 2-9c and 2-9d) and the relationship
of these platelets to larger mineral grains (silt and sand). A soil's
fabric helps determine its pore size. In a flocculated soil structure
(Figures 2-9a and 2-9c), the clay platelets or platelet groups tend to be
edge-to-face oriented. Soils with this fabric can be expected to have a
larger pore matrix with hydraulic conductivity that is fairly equal in all
directions. In a dispersed soil structure (Figures 2-9b and 2-9d), clay
platelets or platelet groups tend to be oriented face to face, resulting in
a deposit that is stratified on the microscale. A dispersed soil structure
will be anisotropic with respect to hydraulic conductivity with higher
matrix hydraulic conductivity in the horizontal direction (parallel to the
oriented clay particles) than in the vertical direction (perpendicular to
the oriented clay particles) (Mitchell, 1976). The pore size of a dispersed
soil structure is smaller than that of a flocculated structure.
Hydraulic conductivities in soils with dispersed fabrics tend to be
lower- than the hydraulic conductivities of similar soils with flocculated
structures. This phenomenon may be responsible for the difference between
the measured hydraulic conductivity of a clay compacted wet of optimum and
the hydraulic conductivity of the same clay compacted dry of optimum.
Although equal density can be achieved in both cases, the hydraulic conduc-
*Herein, structure refers to the physical arrangement of the soil
constituents.
2-25
-------
a.
b.
(a) Flocculated clay platelets.
(b) Dispersed clay platelets.
(c) Flocculated clay platelet groups.
(d) Dispersed clay platelet groups.
Source: From Holtz and Kovacs, 1981
d.
Figure 2-9. Clay soil fabrics.
2-26
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tivity of the soil compacted wet of optimum will be less (vertical direction)
than that of the soil compacted dry of optimum. This difference in hydraulic
conductivity can approach 2 orders of magnitude (Lambe and Whitman, 1979)
and can be attributed to the increased dispersion of clay platelets and the
resulting smaller pores when a soil is compacted at the higher moisture
content (Daniel, 1984). Mercury porosimetry data, reported by Acar and
Seals (1984) for kaolinite compacted to the same dry density, wet and dry
of optimum, suggest that higher hydraulic conductivities in dry of optimum
samples result from a bimodal pore size distribution; although the cumula-
tive porosity of the two samples is the same, the dry of optimum sample has
both large (~25 pm) and small (~5 x 10 2 urn) pore sizes, whereas the wet of
optimum sample has only the small pore size.
The fabric of an in situ clay soil is largely determined by soil-forming
processes responsible for its formation, its depositional environment, and
the action of postdepositional processes. A very important factor influen-
cing a clay soil fabric is the electrochemical environment at the time of
its deposition, including the mineralogy of the clay and the electrochemical
properties of the depositional medium. These factors influence the thick-
ness of the. electrical double layer surrounding the clay particles (see
Section 2.3 for a discussion of double-layer theory). Increasing the
double-layer thickness increases the dispersivity of clay particles, thus
decreasing their tendency to flocculate during deposition. Dispersed soil
fabrics tend to occur when a clay with exchangeable sodium is deposited in
water with a relatively low electrolyte level (Rogowski and Richie, 1984).
In addition, dispersed, anisotropic fabric may be developed in isotropic
soils from postdepositional shear or compressive forces (Mitchell, 1976).
Flocculated fabric can be created in virtually all depositional environments
(Holtz and Kovacs, 1981) and can result from postdepositional changes in
the soil environment (e.g., cation exchange).
2.4.1.2 Soil Macrostructure and Secondary Porosity—
Secondary porosity is controlled by the macrostructure of the soil and
encompasses the heterogeneities of soil deposits including joints, fissures,
root and animal holes, and other defects in the soil mass (Holtz and Kovacs,
1981). Joints, fissures, and/or holes can occur in any soil as a result of
stresses on the soil (i.e., earthquakes, slumping, and compression), desic-
cation, dissolution, or the action of vegetation or animals. In compacted
engineered soils, secondary porosity can result from poor quality control
of the compaction process or from desiccation of the liner after compaction.
.Secondary porosity affects the hydraulic conductivity of the entire
soil mass and generally overrides the effect of primary porosity. Thus, a
soil that is composed of material of low matrix hydraulic conductivity can
have a very high hydraulic conductivity because of secondary porosity.
Many natural clays have joints. Joints can result from postdepositional
expansion and contraction from wetting and drying. Joints and fissures in
preconsolidated clays result from shrinkage cracking and unloading. Cracks
can also occur in clays that have a water content consistently above the
shrinkage limit. These cracks have been postulated to result from syneresis—
2-27
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the formation of closely knit aggregates from the mutual attraction of clay
particles or from the removal of potassium by weathering. Figure 2-10
shows a fracture in a glacial till with a low matrix permeability. Root
systems can cause cracks by sucking up water, causing desiccation cracks to
develop in the soil mass, and can leave holes in the soil mass after rotting
away. Figure 2-11 shows a root cast in a till, including a fracture and a
zone of higher hydraulic conductivity material left after roots have decayed.
The ability of fissures or holes to heal in a soil depends largely
upon soil moisture content, soil plasticity, the size of the fissure or
hole, and ambient stress. Wetter, more plastic soils have a greater healing
capability (USDI, 1974). Certain organic chemicals can affect a soil's
self-healing capability by reducing a soil's moisture content and plasticity.
Zones of permeable material in a soil with low hydraulic conductivity
are generally referred to as lenses and seams and may be composed of silt
and sand. In certain soil deposits, lenses are isolated and discontinuous
and have little influence on the overall hydraulic conductivity of the soil
mass and on potential contaminant migration. However, in other soils,
these lenses may be continuous in one or more directions, in which case
they greatly increase a soil's overall hydraulic conductivity and provide
potential pathways for the rapid migration of contaminants in the groundwater.
Continuous zones of permeable material are usually deposited by moving
water and are common in river floodplain deposits, around the perimeter of
lake deposits, and in glacial outwash deposits. Permeable zones also may
be present in marine and glacial till deposits. Figure 2-12 depicts a sand
seam outcropping in an otherwise low hydraulic conductivity (KslO 7 cm/s)
glacial till. Leachate from a nearby landfill has migrated through this
sand seam and, by evaporating, has left white salt crystals that outline
the sand seam on the surface of the cut.
For residual soils, products of chemical weathering of rocks in place,
the primary and secondary porosity is influenced by the degree of weathering
and the composition and structure of the parent rock. Fractures and fissures
in the parent rock may persist in the weathered mass (although not in
highly weathered deposits), affecting the secondary porosity. Hydrothermally
deposited veins of quartz in the original rock can weather into veins of
sand in the resulting residual soil. In addition, for soils derived from
stratified rock, the different rock strata can result in a soil with strata
of different hydraulic conductivities.
Anisotropy and heterogeneity are common in all soils. Anisotropy and
heterogeneity can be attributed to the existence and variation of primary
and secondary porosity. On a small scale, the primary cause of anisotropy
in soils is the orientation of clay minerals and its effect on primary
porosity. On a larger scale, a relationship exists between heterogeneity
and anisotropy (Freeze and Cherry, 1979). Heterogeneities can be attrib-
uted largely to secondary porosity and stratification in low-permeability
soils. Trending heterogeneities, where transport parameters (e.g., hydraulic
conductivity) change gradually in a given direction, also exist in fine-
grained, low-permeability soils. Trending heterogeneities are most common
in soils deposited in deltas, alluvial fans, and glacial outwash plains
(Freeze and Cherry, 1979).
2-28
-------
--j^"~%;>®Ta^*
^;^j^
" •;#••
Source: Photo courtesy of Wisconsin Department of
Natural Resources
Figure 2-10. Fractures in glacial till. Note pen for scale (arrow).
2-29
-------
Source: Photo courtesy of Wisconsin Department of
Natural Resources
Figure 2-11. Root cast in glacial till. (Root cast is the lighter
colored material in the right center. Note
fracture that has developed along root cast
(arrow).)
2-30
-------
Source: Photo courtesy of Wisconsin Department of
Natural Resources
Figure 2-12. Permeable strata in glacial till deposit. (Permeable zone is the outlined
band across the center of photo. Note white salt crystals on surface of
permeable zone left by evaporating leachate flowing from a nearby
landfill.)
2-31
-------
It should be stressed that secondary porosity, if present and inter-
connected, can completely override the primary porosity of a soil mass,
making a deposit of low-permeability matrix material highly permeable. The
prevalence of heterogeneities in natural soil deposits is the primary
reason that hazardous waste containment facilities should be lined regardless
of the hydraulic conductivity of the in situ soil.
Heterogeneities and anisotropies in soils can lead to significant
differences between field and laboratory permeability measurements (01 sen
and Daniel, 1981; Griffin et al., 1985). There are at least three factors
contributing to this difference:
Most laboratory tests measure only vertical permeability,
while field permeability test results usually depend on both
vertical and horizontal permeability. In anisotropic soils,
horizontal permeability can be higher than vertical permeabil-
ity, resulting in higher field test results.
Bias in sample selection for those cohesive enough to withstand
handling and avoidance of cracked or broken samples. This
leads to a predominance of measurements of matrix permeability
rather than bulk permeability.
Samples taken for laboratory permeability tests are smaller
than the area covered by field tests. Field permeability
tests are more likely to include heterogeneities such as
fissures and zones of high-permeability material that can
significantly increase soil permeability.
Because of these factors, properly performed field permeability measure-
ments can give a more accurate estimate of soil permeability than can
laboratory permeability tests that are run on "undisturbed" samples (Griffin
et al., 1985; Day and Daniel, 1985). For soils with heterogeneities that
affect permeability, the larger the field permeameters or the more that are
used for a site investigation, the more accurate will be the measure of the
soil's permeability. These factors should be considered when the protective-
ness of potential hazardous waste facility sites is evaluated and during
the measurement of hydraulic conductivity of compacted clay liners.
2.4.2 Soil Structure and Hydraulic Conductivity in Compacted Soils
Compaction is the application of force to a soil to reduce the percent-
age of air-filled voids and thus to increase its density. For cohesive
soils, of which clay liners are composed, compaction with a given type and
amount of compactive effort at various water contents will result in a
compaction curve such as the one shown in Figure 2-13. Examination of this
curve shows that, with a given compactive effort, a maximum density is
achieved at a certain water content. This is the optimum water content for
this type and amount of compactive effort. The "S" lines in this figure
represent the computed relationship between water content and dry density
at a constant degree of saturation.
2-32
-------
s
z
19.0
18.5
t-
5 18.0
3
e
o
17.5
0.41
0.43
0.46
0.49
0.52
8 10 12 14 18 13
WATESt CONTENT w<%)
Source: Lamba, 1955
O
>
Figure 2-13. Compaction curve from a standard compaction test.
2-33
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Figure 2-14 illustrates that the moisture/density relationship for a
given soil also depends upon the type and amount of compactive effort.
This figure shows that the line of optimum moisture contents and maximum
dry density for these compactive efforts approximately parallels the line
of constant saturation. This figure also shows that the type of compactive
effort influences the shape of the moisture content/density curve (see
Chapter 3).
Much earthwork compaction is directed toward achieving structural
stability, as with roadbed or foundation compaction. For these applica-
tions, strength, stability, and resistance to changes in volume are the
important parameters. Density is used to control these parameters in the
field. Figures 2-13 and 2-14 illustrate that the same density can be
achieved either wet or dry of optimum. In many cases, foundations and
roadbeds are compacted dry of optimum for greater shear strength because
soil shear strength decreases with increasing moisture content (Mitchell,
1976). However, when cohesive soils are compacted to achieve lower hydraulic
conductivity, both the dry density (reduction of air voids) and the fabric
of the soil are important. Molding water content becomes important when
attempts are made to rearrange the fabric of the clay.
The reduction of hydraulic conductivity during the compacting of a
cohesive soil is a function of the following two processes:
The reduction of the voids in the soil
The rearrangement of the fabric of a soil to a more dispersed
structure.
In a dispersed soil structure, the clay mineral platelets are oriented in a
face-to-face fashion. A dispersed structure has smaller pores than a more
flocculated (edge-to-face) soil structure and also has more tortuous paths
for liquid movement through the soil, resulting in a lower hydraulic con-
ductivity.
Factors that influence the extent to which compaction acts on a cohe-
sive soil fabric to produce a more dispersed structure include:
Molding water content
Dispersivity of the clay minerals in a soil
Amount of compactive effort
Type of compactive effort.
Molding water content strongly influences the ease of rearranging clay
particles and particle groups under the compactive effort used (Mitchell
et a!., 1965; Carpenter, 1984). The profound effect of molding water
content on soil hydraulic conductivity is shown in Figure 2-15. This
figure illustrates that, for clay samples compacted to the same dry density
2-34
-------
I 1a
z
Jt
~ 17
5 18
14
10 15 20
WATER CONTENT (%)
25
No.
1
2
3
4
Layers
5
5
5
3
Blows per
Layers
55
26
12
25
Hammer
Mass
4.54 kg
5.54
4.54
2.50
Hammer
Drop
457 mm
457
457
305
(mod. AASHO)
(std. AASHO)
Source: Larnbe and Whitman, 1979
Figure 2-14. Compaction curves for different compactive efforts applied to a silty clay.
2-35
-------
o
9
CO
,0 1X10
1X10
'7
Q
Z
o
o
o
3
ir
o
1x10
"8
1x10
-9
Saturation = 95%
\
114
CO *"*
Z?5
^
UJ 5-
o I
cc
o
106
I ! I I I I I |
12 14 16 18
Kneading .
compaction curve ''•..
\
Density of Samples
i
20
Line of optimums
13 15 17 19
MOLDING WATER CONTENT (%)
Source: Mitchell, 1976
Figure 2-15. Permeability as a function of molding water content for samples
of silty clay prepared to constant density by kneading compaction.
2-36
-------
at different water contents, permeability decreases with increasing moisture
content, and this decrease can be more than 3 orders of magnitude (Mitchell,
1976). Permeability has also been shown to be strongly affected by the
amount and type of compactive effort used to reach the desired density
(Mitchell et al., 1965). Because of these phenomena, clay liner designs
should specify that clay liners be compacted wet of optimum and moisture
content, density, and compactive effort measured and controlled for proper
clay liner compaction. If only density is specified or measured and moisture
content and compactive effort are not carefully controlled, the specified
density can be achieved at too low a moisture content, resulting in a liner
with a higher hydraulic conductivity than required.
Soil dispersivity is affected by the double-layer thickness of the
clay minerals in the soil. Soils composed of minerals with thicker double
layers have higher dispersi-vities. The dispersivity of clay minerals in a
soil affects its hydraulic conductivity. Figure 2-16 illustrates this
phenomenon, showing that adding a chemical dispersant to a soil reduces
hydraulic conductivity upon compaction. (The chemical dispersant increases
the double-layer thickness of the clay minerals.)
A liner soil must be carefully screened as it arrives onsite to ensure
that the arriving soil type remains the same. If a change in soil type
occurs, it could have a lower dispersivity. If this soil is compacted
according to soil compaction parameters (density and moisture content)
developed for the original soil, a more permeable liner could result.
Thus, if the soil characteristics change during the construction of a clay
liner, it is necessary to reestablish density/moisture content/compactive
effort/hydraulic conductivity relationships for the new soil before it is
used as'a liner material.
The method of compaction also affects the hydraulic conductivity of a
compacted soil liner. Figure 2-17 illustrates that, for a cohesive soil
compacted to the same density, kneading compaction results in a lower
hydraulic conductivity than static compaction. This occurs because kneading
action introduces shear strains to the soil, which tends to realign particles
and results in a more dispersed soil fabric (Mitchell, 1976). This phenom-
enon occurs only for cohesive soils compacted wet of optimum because the
clay particles can be rearranged easily only at a high moisture content.
This phenomenon is the reason for a general preference for sheepsfoot
rollers for compacting clay liners; although equivalent densities at a
given moisture content may be obtained with a smooth-wheeled roller, the
kneading action of the sheepsfoot should result in lower hydraulic conduc-
tivities for most soils.
The effect of method of compaction on soil fabric is partly responsible
for the difference observed between field and laboratory compaction methods
(Lambe and Whitman, 1979). Laboratory compaction methods generally result
in permeabilities lower than those attained using field equipment (Dunn and
Mitchell, 1984; Day and Daniel, 1985). This is because compactive efforts
used in laboratory compaction tests are not the same as those produced by
specific field compaction equipment. Thus it is necessary to compact a
2-37
-------
1x10
,-5
u
o
u
a*
o
o
u
> 1x10'
-6
10 11
12 13 14 15
MOLDING WATER CONTENT
(% dry soil mass)
e
*N»
z
20.0
ia.o
>-
z
a
> 18.0
e
a
0=0.1
10 11 12 13 14
MOLDING. WATER CONTSN1
(% ary soil mass)
15
Source: Lambe, 1955.
Figure 2-16. The effect of dispersion on hydraulic conductivity. D = 0 is compaction
curve for a soil compacted in its natural state; D = 0.1 is a compaction
curve for a soil compacted with 0.1% (of dry soil weight) of sodium-
polyphosphate.
2-38
-------
ixio"5 H-
E
o
1x10
~6
Q
Z
O
o
o -r
3 1x10 7
I 5x10-8
a
Optimum water content
Static compaction
Kneading compaction
15 17 19 21 23 25 27
MOLDING WATER CONTENT (%)
108
> 10S
5 —
z «
S = 104
c
o
102
100
15 17 19 21 23 25 27
MOLDING WATER CONTENT (*>
o Knsadlng compaction 1* x 2.3' 3 mold
• Kneading compaction 3.5* x 1.4* 0 mold
» Static compaction 1* x 2.8* 0 moid
Source: Mitchell, 1976
Figure 2-17. Effect of method of compaction on the parmeability
(hydraulic conductivity) of a silty clay.
2-39
-------
test fill in the field and conduct permeability tests on this material to-
verify laboratory results (see Section 5.3.3.1.1).
2.5 REFERENCES
Acar, Y.B. and R. K. Seals. 1984. Clay Barrier Technology for Shallow
Land Waste Disposal Facilities. Hazardous Waste. 1(2):167-181.
ASTM. 1985. American Society of Testing Materials Annual Book of ASTM
Standards. Vol. 04.08.
Carpenter, G. W. 1982. Assessment of the Triaxial Falling Head Permeability
Testing Technique. Ph.D. dissertation, University of Missouri, Rolla,
MO.
Chapman, D. L. 1913. A Contribution to the Theory of Electrocapillarity.
Philosophica Magazine. 25(6):475-481.
Daniel, D. E. 1984. Predicting Hydraulic Conductivity of Clay Liners.
Journal of Geotechnical Engineering. 110(2):285-300.
Day, S. R. and D. E. Daniel. 1985. Hydraulic Conductivity of Two Prototype
Clay Liners. Eleventh Annual Research Symposium, U.S. Environmental
Protection Agency, Cincinnati, OH. EPA/600/9-85/013, p. 27-38.
Deer, W. A;, R. A. Howie, and J. Zussman. 1966. An Introduction to the
Rock-Forming Minerals. Longman Group Limited. London.
Dunn, R. J. and J. K. Mitchell, 1984. Fluid Conductivity Testing of Fine
Grained Soils. J. of Geotechnical Engineering. 110(11):1648-1665.
Fisher, W. L. 1965. Rock mineral resources of east Texas: Texas University
Bureau of Economic Geology. Report of Investigations 54. 439 pp.
Freeze, R. A., and J. A. Cherry. 1979. Groundwater. Prentice-Hall, Inc.
Englewood Cliff, New Jersey.
Gouy, G. 1910. Sur la Constitution de la Charge Electrique a la Surface
d'un Electrolyte. Anniue Physique (Serie 4) 9:457-468. Paris.
Griffin, R. A., B. L. Herzog, T. M. Johnson, W. J. Morse, R. E. Hughes, S.
F. J. Chou, and L. R. Follmer. 1985. Mechanisms of Contaminant
Migration Through a Clay Barrier-Case Study, Wilsonville, Illinois.
Eleventh Annual Research Symposium, U.S. Environmental Protection
Agency, Cincinnati, OH. EPA/600/9-85/013, p. 27-38.
Grim, R. E. 1962. Applied Clay Mineralogy. McGraw-Hill. New York.
Grim, R. E. 1968. Clay Mineralogy (second edition). McGraw-Hill. New
York.
2-40
-------
Heath, R. C. 1984. Groundwater Regions of the United States. Water
Supply Paper 2242. United States Geological Survey, Reston, Virginia.
Hilf, J. W. 1975. Compacted Fill. Chapter 7 in Foundation Engineering
Handbook. Eds., Winterkorn, H. F., and H-Y. Fang. Van Nostrand
Reinhold Co. New York.
Hosterman, J. W. 1984. Ball Clay and Bentonite Deposits of the Central
and Western Gulf of Mexico Coastal Plain, United States. U.S. Geological
Survey Bulletin 1558-C. USGS; Alexandria, VA.
Hosterman, J. W. 1985. Bentonite and fuller's earth resources of the
United States. Mineral Investigation Resources Map: MR-0092. U.S
Geological Survey; Alexandria, Virginia.
Holtz, R. D., and W. D. Kovacs. 1981. An Introduction to Geotechnical
Engineering. Prentice Hall, Inc. Englewood Cliffs, New Jersey.
Johnson, A. T., and D. A. Morris. 1962. Physical and Hydrological Proper-
ties of Water-Bearing Deposits From Core Holes in the Las Barros—
Kettleman City Area, California. USGS, Open File Department, Denver,
Colorado.
Keller, W. D. 1964. Processes of Origin and Alteration of Clay Mineral.
Eds., Rich, C. I., and G. W. Kunze Soil Clay Mineralogy. University
of North Carolina Press, Chapel Hill.
Kozicki, P., and D. M. Heenan. 1983. Use of Bentonite as a Soil Sealant
for Construction of Undersea! Sewage Lagoon Extension, Glenboro,
Manitoba. Shortcourse on Waste Stabilization Ponds, Winnipeg, Manitoba.
Lambe, T. W. and R. T. Martin. 1953-1957. Composition and Engineering
Properties of Soil. Highway Research Board Proceedings. 1-1953,
11-1954, III-1955, IV-1956, V-1957.
Lambe, T. W., and R. V. Whitman. 1979. Soil Mechanics (SI version). John
Wiley and Sons, Inc. New York.
Mason, B., and L. G. Berry. 1968. Elements of Mineralogy. W. H. Freeman
and Co. San Francisco.
Mitchell, J. K. 1976. Fundamentals of Soil Behavior. John Wiley and
Sons, Inc. New York.
Mitchell, J. K., D. R. Hooper, and R. G. Campanella. 1965. Permeability
of Compacted Clay. Journal of the Soil Mechanics and Foundations
Divisions, A.S.C.E. 91(SM4):41-65.
Olsen, R. E., and D. E. Daniel. 1981. Measurement of the Hydraulic Conduc-
tivity of Fine-Grained Soils. ASTM STP 746,:18-64. ASTM. Philadelphia,
Pensylvania.
2-41
-------
Parks, G. A. 1975. Adsorption in the Marine Environment. Eds., Riley, J.
P., and G. Skirrow. Chemical Oceanography 1. (second edition) 241-308.
Academic Press. New York.
Patterson, S. H. and H. H. Murray. 1984. Kaolin, Refractory Clay, Ball
Clay, and Hallosite in North America, Hawaii, and the Caribbean Region.
Prof. Paper 1300. U.S. Geological Survey. Alexandria, VA.
Perloff, W. H., and W. Baron. 1976. Soil Mechanics. Ronald Press Co.
New York.
Rogowski, A. S., and E. B. Richie. 1984. Relationship of Laboratory and
Field Determined Hydraulic in Compacted Clay Soils. Proceedings of
the 16th Mid-Atlantic Industrial Waste Conference. The Pennyslvania
State University, University Park, Pennsylvania.
Stern, 0. 1924. Zur Theorie der Elektrolytischen Doppelschrift. Zietschrift
Electrochem. 30:508-516.
Stumm, W. , and J. J. Morgan. 1970. Aquatic Chemistry. John Wiley and
Sons, Inc. New York.
Theng, B. K. G. 1974. The Chemistry of Clay-Organic Reactions. John
Wiley and Sons, Inc. New York.
U.S. Dept. of Interior (USDI). 1974. Earth Manual (second edition). U.S.
Government Printing Office, Washington, DC.
Van Olphen, H. 1963. An Introduction to Clay Colloid Chemistry. Wiley
Interscience. New York.
Weaver, C. E. , and L. D. Pollard. 1973. The Chemistry of Clay Minerals.
Developments in Sedimentology 15. Elesevier, Amsterdam.
Winterkorn, H. F., and H-Y. Fang. 1975. Soil Technology and Engineering
Properties of Soils. Chapter 1 in: Foundation Engineering Handbook.
Eds., Winterkorn, H. F. , and H-Y. Fang. Van Nostrand Reinhold. New York.
2-42
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CHAPTER 3
TEST METHODS AND SOIL PROPERTIES
3.1 INTRODUCTION
The engineering properties of soils are as varied as their chemical
compositions, their modes of formation, and their past and present environ-
mental settings. Consequently, when designing and constructing earthwork
projects, the design or construction engineer is faced with determining
whether or not a particular soil is suitable for its intended application.
To aid this decisionmaking process, a wide assortment of test procedures
have been developed that are used either to predict the probable engineering
performance of a soil (index tests) or to measure the soil performance
directly with respect to parameters of concern (e.g., permeability and
shear strength).
This chapter presents and discusses the soil testing procedures that
are of particular interest to designers of clay liners for hazardous waste
containment facilities. Emphasis is on determining Atterberg limits and
density, compaction, and permeability testing, with the bulk of the chapter
devoted to the latter.
Many test procedures have been standardized by organizations like the
American Society of Testing and Materials (ASTM) and are applied routinely
and uniformly by all competent soil testing groups (ASTM, 1983). Permeability
testing, on the other hand, has not been standardized. Different types of
permeability testing equipment are in current use, and test protocols also
can vary from laboratory to laboratory and even from test to test within a
laboratory. The situation is further complicated by the need to measure
not only the permeability to water but also, and perhaps more importantly,
the permeability to leachates or other complex chemical mixtures. In
addition, there is much discussion and controversy among soil experts
concerning interpreting permeability test results, the relationship between
field and laboratory permeability testing, and the relative merits of
different types of testing equipment and test protocols.
Many soil tests, because of their routine nature and the general
availability of the test protocols, are not discussed in detail this chapter.
However, capsule summaries of many important tests are provided in Appendix
A. These summaries have been taken directly from the EPA document Geotech-
m'cal Quality Assurance of Construction of Disposal Facilities (Spigolon
and Kelly, 1984). The summaries are intended only to give the reader
general information about the specific test methods. More detailed informa-
tion can be obtained from the references noted for each test. A list of
3-1
-------
the summarized tests contained in Appendix A is provided in Table 3-1.
Other important soil test procedures may be found in the ASTM Standards,
Part 19 - Natural Building Stones; Soil and Rock (ASTM, 1983).
One of the most commonly used pieces of field test equipment is the
nuclear moisture and density gauge. This device provides a rapid and
reliable means of making in-place field measurements of the moisture content
and density of soil. However, for accurate measurements in all test circum-
stances, it is necessary to understand the theoretical basis of the tests
and to be mindful of certain caveats regarding the application of nuclear
soil testing techniques. For these reasons, nuclear methods are described
in detail in Section 3.6.2.
3.2 FUNDAMENTAL RELATIONSHIPS
The presence of fluid- and gas-filled voids in soils is an inescapable
consequence of the particulate nature of the material. The multiphase
nature of soils is diagramatically represented in Figure 3-1, which depicts
the fundamental relationships of the weights and volumes of the basic
components of a soil mass. For soil engineering purposes, the important
parameters are unit weight, void ratio, porosity, and degree of saturation.
The measurements that are made to compute these parameters are the weight
and volume of the wet specimen, the weight of the same specimen after
drying, and the volume of the solids. Discussion of the appropriate standard
procedures for these measurements can be found in Laboratory Soil Testing,
U.S. Department of the Army (1970); in ASTM (1983); and in Appendix A of
this document.
3.2.1 Water Content
A fundamental property of any soil is its water content. This is
defined as the ratio, expressed as a percentage, of the weight of water in
a given soil mass to the weight of the solid particles.
3.2.2 Density
As a consequence of voids being an integral part of any soil, soil may
be considered to have two "densities." One of these densities, called the
specific density, is that of the solid particles. The other density,
called the unit weight or bulk density, is the density of the total soil
mass including water- and air-filled voids.
Specific gravity (of solids), Gs, is defined as the ratio of the
density of solid particles, P , at a stated temperature to the density of
distilled water, P , at 4 °C:
w
Ps Ws
Gs=F0rGs = V-TT ' <3.1)
w s 3w
3-2
-------
TABLE 3-1. SOIL TESTS SUMMARIZED IN APPENDIX A
Methoda
Method number
Parameter measured: water content
Standard oven-dry 1
Standard nuclear moisture/density gauge 2
Gas burner 3
Alcohol burning 4
Calcium carbide (speedy) 5
Microwave oven 6
Infrared oven 7
Parameter measured: unit weight
Standard laboratory volumetric 8
Standard laboratory displacement 9
Standard field sand-cone 10
Standard field rubber balloon 11
Standard field drive-cylinder 12
Standard nuclear moisture/density gauge 13
Parameter measured: specific gravity
Standard laboratory 14
Parameter measured: grain-size distribution
Standard sieve analysis (+200 fraction) 15
Amount of soil finer than No. 200 screen (wash) standard 16
Standard laboratory hydrometer (-200 fraction) 17
Pipette method for silt and clay fraction 18
Decantation method for silt and clay fraction 19
Parameter measured: liquid limit
Standard multipoint 20
Standard one point 21
Parameter measured: plastic limit
Standard laboratory 22
Parameter measured: cohesive soil consistency
Standard unconfined compression 23
Field expedient unconfined compression 24
Hand penetrometer 25
Hand-held torvane 26
Parameter measured: water content/density/compactive effort
25 blow standard Proctor compaction 27
25 blow modified Proctor compaction 28
Nonstandardized Proctor compaction 29
Rapid, one-point Proctor compaction 30
Rapid, two-point Proctor compaction 31
Hilf's rapid 32
Ohio Highway Department nest of curves 33
Harvard miniature compaction 34
aMethod numbers have been assigned for the sole purpose of providing an easy
way of finding the test method in the appendix. The number is meaningless
outside of the context of this document.
3-3
-------
WGCHT
VOLUMC
^»
4-
w
AIR
WATl*
TV.
Vw
MOI5T SOL
WC1CHT
w,
WATCH
VOLUMC
Vv
M
V,
SATURATED SOIL
Figure 3-1. Schematic representation of soil illustrating the fundamental
relationships among the solid, liquid, and air constituents.
3-4
-------
where
yw = the unit weight of water (1.00 g/cm3 or 62.43 lb/ft3) at 4 °C.
Dry unit weight (dry density) y , is defined as the weight of the
oven-dried soil solids per total volume of the wet soil mass:
W
Yd = -4 . (3.2)
Wet unit weight (wet density) y is the total weight (solids and
water) per unit volume of soil:
ym = n • (3.3)
Both wet and dry density are usually expressed in pounds per cubic foot
(lb/ft3).
3.2.3 Void Ratio
Void ratio, e, is the ratio of the volume of the voids to the volume
of the solids in a given soil mass:
V V - V
s s
where
Ws
V = volume of solids =
— VU I UH1C W I -3W I I *JO — 7^
s G y
s Jw
3.2.4 Porosity
Total porosity, n, is the ratio, usually expressed as a percentage, of
the total volume of the voids of a given soil mass to the total volume of
the soil mass:
V V - V
n = y^ x 100 = y-^ x 100 . (3.5)
Effective porosity is defined as that fraction of the total volume
through which flow can occur. If all of the pores and void space contrib-
uted to flow, the effective porosity would simply equal the volume of voids
divided by the total volume. However, some pores in soil are isolated or
3-5
-------
dead-end pores that do not contribute to flow. Water that is tightly
adsorbed to the wall of a fluid-conducting pore also decreases the flow
area and effective porosity. The total porosity typically ranges from 0.2
to 0.5 for clays; however, the effective porosity in clay is on the order
of 0.01 to 0.1 (Zimmie et al., 1981; Daniel, 1981).
3.2.5 Degree of Saturation
Degree of saturation, S, is the ratio (expressed as a percentage) of
the volume of the water in a soil mass to the total volume of the voids.
V
S = TT* • (3.6)
3.3 ATTERBERG LIMITS
Depending upon the water content, the consistency of a cohesive soil
may range from that of a viscous liquid to that of a very hard solid. This
range of consistencies may be arbitrarily divided into the four stages
illustrated in Figure 3-2, with the divisions between these states referred
to as the limits. These limits are called the Atterberg limits after the
Swedish soil scientist, A. Atterberg, who in 1911 developed a series of
tests for determining the plasticity of cohesive soils.
To understand the significance of the Atterberg limits, assume that a
very wet fine-grained soil is slowly dried. In the very wet condition, the
soil will act like a viscous liquid. As it dries, a reduction in volume
occurs that is very nearly proportional to the water loss. When the water
content is reduced to the value of the liquid limit, the soil consistency
becomes plastic (i.e., the soil mass can be shaped or deformed without
cracking). The liquid limit is defined as the water content, expressed as
a percentage of the weight of the oven-dried soil mass, at which the soil
shows a small but definite shear strength as it is dried. Conversely, with
increasing moisture, it is the water content at which the soil mass first
starts to become liquid under the influence of a standardized series of
shocks as delivered in the liquid limit test (U.S. Department of the Army,
1970; U.S. Department of Interior, 1974).
The liquid limit test is performed with the device illustrated in
Figure 3-3. This piece of equipment is designed so that the cup holding
the grooved soil sample is tipped up with a cam and allowed to drop onto
the hard surface below it, thereby supplying a "blow" to the soil sample.
Figure 3-4 is an illustration of the groove being cut into a soil sample.
The liquid limit is defined as the water content at which one-half inch of
the groove is closed after 25 blows (U.S. Department of Interior, 1974).
In practice, while it is hard to adjust the soil moisture so that the
groove closes at exactly 25 blows, the liquid limit can be determined by
3-6
-------
Stages of consistency
A
'Solid
state
Semisolid
state
Plastic state
Liquid state
Range indicated by
the plasticity index (PI)
PI = LL-PL
SL
PL
LL
Moisture content increasing
Source: U.S. Dept. of Interior, 1974
Figure 3-2. Consistency limits of cohesive soils.
3-7
-------
Figure 3-3. Device for determining the liquid limits of a cohesive soil.
The dish contains a grooved sampie.
Rgure 3-4. Clay sample being grooved for liquid limit test.
3-8
-------
plotting the water contents at which closure occurs with other blow counts
against the log of the number of blows needed to achieve groove closure.
This procedure produces a straight line known as the flow line from which
the water content corresponding to groove closure at 25 blows can be found
easily. This method is ASTM D 423-66 (ASTM, 1983).
A one-point liquid limit test also can be performed provided that the
practitioner is already familiar with the soils from which the sample is
obtained. This method is ASTM D 423-66 (ASTM, 1983). The basis for the
one-point procedure is the fact that the slopes of the flow lines for soils
within a given soil environment are generally constant. Therefore, if the
flow line slope, the water content, and the number of blows to obtain
closure at that water content are known, the liquid limit can be computed
from the following formula:
LL = WN ^ tan p , (3.7)
where
WN = water content of sample
N = number of blows required to close the groove
tan p = slope of the flow line.
The one-point test is usually performed on soil samples prepared to a
consistency that requires 20 to 30 blows to close the groove (U.S. Depart-
ment of the Army, 1970).
As the water content is reduced below the liquid limit, the soil mass
becomes stiffer and will no longer flow. The soil will continue to be
plastic (deformable) until the plastic limit is reached. The plastic limit
is defined as the water content, expressed as a percentage of the weight of
the oven-dried soil, where the soil begins to crumble when rolled into a
thread 1/8 inch in diameter (U.S. Department of the Army, 1970). The
rolling and crumbling are illustrated in Figures 3-5 and 3-6. The test
method for determining plastic index is ASTM D 0424-59.
As stated earlier, a soil mass will decrease in volume in proportion
to the amount of water removed. However, if enough water is removed, a
point will be reached below which very little shrinkage will occur. The
moisture content at this point, which is referred to as the shrinkage
limit, divides the solid from the semisolid phases in the soil consistency
continuum (Figure 3-2). Below the shrinkage limit, the soil is considered
a solid. In most fine-grained plastic soils, the plastic limit will be
appreciably greater than the shrinkage limit. However, for coarser grained
soils, with predominantly coarse silt and fine sand sizes, the shrinkage
limit will be near the plastic limit (U.S. Department of Interior, 1974).
3-9
-------
Figure 3-5. Rolling a clay sample for plastic limit test.
Figure 3-6. Results of rolling ciay with moisture content below the plastic limit.
3-10
-------
The test procedure for determining the shrinkage limit is ASTM D 427-61
(ASTM, 1983).
Very often the term plasticity index is encountered. It is the numer-
ical difference between the liquid limit and the plastic limit and re-
presents the range of moisture within which the soil remains plastic.
The plasticity index can be used to compute the activity, A, of a
cohesive soil. A is the ratio of the plasticity index to the percentage of
clay-size particles (smaller than 0.002 mm) and is an expression of the
plasticity of the clay fraction of the soil. The mineralogy of the clay
fraction is suggested by the activity, with low activity (less than 1)
characteristic of kaolinite, high activity (greater than 4) characteristic
of montmorillonite, and intermediate activity (1-2) characteristic of
ill He (Sowers and Sowers, 1970).
Soils may be grouped and located on a plasticity chart according to
their liquid limits and their plasticity indices (Figure 3-7). The loca-
tion of a soil on the chart provides a basis for estimating its engineering
properties based on knowledge of other tested soils that plot in the same
region of the chart. The plasticity chart is roughly divided into quadrants
by the "A" line and the 50-percent liquid limit line. Soils that plot
above the "A" line are classified clays; those below are not clays. The
50-percent liquid limit line is an arbitrary division between high and low
liquid limit soils. In general, soils plotting above the "A" line have low
permeabilities; for soils with the same liquid limit, the greater the plas-
ticity index the greater the strength at the plastic limit; compressibility
increases with increasing liquid limit (U.S. Department of Interior, 1974).
3.4 SOIL CLASSIFICATION
Based upon his early field work, Professor A. Casagrande of Harvard
University developed a soil classification system for grouping soils by a
plot of their plasticity index versus their liquid limit. In 1942, the
U.S. Army Corps of Engineers adopted this system for airfield work. The
system was modified slightly in 1947 to prevent dual classification of
soils; in 1952 the U.S. Bureau of Reclamation and the U.S. Army Corps of
Engineers, in consultation with Dr. Casagrande, adopted the system under
the title of the Unified Soil Classification System (USCS). The USCS is
descriptive, easy to use, adaptable to field or laboratory use, and takes
into account the soils' engineering properties. One of its greatest advan-
tages is that a soil can be classified readily by visual and manual examina-
tion .without extensive laboratory testing. The system is based on the size
distribution of the soil particles and the activity of the very fine grains
(U.S. Department of the Army, 1953; U.S. Department of Interior, 1974).
3.4.1 Grain Size Analysis
Within the USCS, soils are divided into coarse-grained and fine-grained
types. Coarse grains are larger than the openings in the U.S. Standard
Series No. 200 sieve; fine grains can pass through the No. 200 sieve. The
3-11
-------
ISO
160
140
120
X
UJ
0
z
100
80
60
40
SANOY CLAY, NORTHEASTERN NEW MEXICO
S1LTY LOESS, KANSAS-NEBRASKA
CLAYEY LOESS,KANSAS.
KAOLIN CLAY, DECOMPOSED GRANITE,SINGAPORE"
KAOLIN CLAY, RESIDUAL SOIL, CALI FORNIA
SILTY CLAY, SALT LAKE 8ASIN SEDIMENTS,UTAH.
PORTERVILLE CLAY "EXPANSIVE" (CALCIUM
8EIOELLITE ) , CALIFORNIA.
HALLOYSITE CLAY, SANDY , TRACE OF
MONTMORILLONITE, GUAM , MARIAN AS ISLANDS.
TULE LAKE SEDIMENTS (DIATOMACEOUS AND
PUMICE),NORTHERN CALIFORNIA
MONTMORILLONITE CLAY, SLIGHTLY ORGANIC,
GUAM, MARIANAS ISLANDS.
CLAY,GLACIAL LAKE DEPOSIT, NORTH DAKOTA
CLAY,"EXPANSIVE" (SODIUM MONTMORILLONITE)
GILA RIVER VALLEY, ARIZONA.
8ENTONITE.WYOMING AND SOUTH
DAKOTA.
30 100 120
LIQUID LIMIT
200
Source: U.S. Department of Interior, 1974
Figure 3-7. Typical relationships between the liquid limit
and the plasticity index for various soils.
3-12
-------
particle size distribution of coarse-grained soils can be determined readily
by a sieve analysis,, wherein the sample is passed through a set of sieves
and the material retained on each sieve is weighed (U.S. Department of the
Army, 1970). Sieve sizes commonly used are listed in Table 3-2.
The size distribution of particles smaller than the No. 200 sieve can
be determined by the hydrometer or by the pipette method based on Stokes1
Law, which relates the terminal velocity of a sphere flowing freely through
a fluid to the sphere's diameter. The relationship is expressed as:
where
V = terminal velocity of sphere, cm/s
Y = density of sphere, g/cm3
Yf = density of fluid, g/cm3
H = viscosity of fluid, g-s/cm2
D = diameter of sphere, mm.
The test assumes that Stokes1 Law can be applied to a mass of dispersed
soil particles of various shapes and sizes. The test is conducted by
treating the soil sample with a chemical dispersant and then mechanically
dispersing the sample in water to form a suspension. Hydrometer readings
or pipette samples at a specific depth in the column are taken every several
minutes, and Stokes' Law is used to compute the maximum grain size in
suspension.
Methods for determining grain size distribution are summarized in
Appendix A, Methods 15-19. Directions for conducting the tests can be
found in U.S. Department of the Army (1970) and in ASTM Method D422-63
(ASTM, 1980).
Grain size distributions are usually displayed graphically as illus-
trated in Figure 3-8, which plots graded and poorly graded distributions.
Well -graded soils have good representation of all particle sizes over a
fairly broad size range. A poorly graded soil may have an excess or defi-
ciency of particles within a certain size range (gap-graded or skip-graded),
or all the particles occur within a fairly narrow range.
The following coefficients have been defined to determine whether a
soil is well graded or poorly graded:
Coefficient of uniformity, C = 1 , and (3.9)
u U10
3-13
-------
TABLE 3-2. U.S. STANDARD SIEVE SIZES AND THEIR
CORRESPONDING OPEN DIMENSION
U.S. standard Sieve opening
sieve number (mm)
4 4.75
10 2.00
20 0.85
40 0.425
60 0.25
100 0.15
140 0.106
200 0.075
3-14
-------
CO
I—'
en
IOO
U 5 STANDARD SlfVf OWNING IN INCHf S U S STANDARD SIEVf NUMIE fti
6 43 J I'A I 14 '/, H 3 4 6 8 IO 14 16 2O 3O 40 5O 70 WO 140200
T
HvonoMfTt*
10
0
500
100 50
10
1 0.5
GRAIN SIZE MIUIMfrm
0.05
100
0001
COMICS
GftAVfl
cautse
[ fnt | COAMi | MIOtUM
SAND
IIHt
Sill OR ClAY
HO
IUVM Mrm
CLUJUCADOH
NAl WX
GRADATION CURVES
KWMCNO
Figure 3-8. Idealized particle size distribution curves for well-graded, poorly graded, and gap-graded soils.
-------
Coefficient of curvature, C = n *°n— , (3.10)
C UIQ x Ugo
where "D" with a numerical subscript represents the size that is larger
than a given percentage of the soil mass (as indicated by the subscript).
As an example, D10 = 0.5 mm means that 10 percent of the sample by weight
is smaller than 0.5 mm in diameter. To be well graded, the coefficient of
curvature (Cr) must be between 1 and 3 and, in addition, the coefficient of
\i
uniformity (C ) must be greater than 4 for gravels and greater than 6 for
sands. u
3.4.2 The Unified Soil Classification System (USCS)
Except for small editorial changes, the following sections (Sections
3.4.2 through 3.4.2.3.3) are taken directly from the Earth Manual (U.S.
Department of Interior, 1974).
Soils in nature seldom exist separately as gravel, sand, silt, clay,
or organic matter, but are usually found as mixtures with varying propor-
tions of these components. The Unified Soil Classification System (USCS)
is based on recognition of the type and predominance of the constituents,
considering grain size, gradation, plasticity, and compressibility. It
divides soils into three major divisions: coarse-grained soils, fine-
grained soils, and highly organic (peaty) soils. In the field, identifica-
tion is accomplished by visual examination for the coarse grains and by a
few simple hand tests for the fine-grained soils or fraction, as described
in the classification chart (Figure 3-9 and fully described in Section 3.4.2.3).
In the laboratory, the grain-size curve and the Atterberg limits can be
used in addition to visual examination. The peaty soils (Pt) are readily
identified by color, odor, spongy feel, and fibrous texture and are not
further subdivided in the classification system.
3.4.2.1 Field Classification—
A representative sample of soil (excluding particles larger than 3
inches) is first classified as coarse grained or fine grained by estimating
whether 50 percent, by weight, of the particles can be seen individually by
the naked eye. Soils containing more than 50 percent of individual particles
that can be seen are coarse-grained soils; soils containing more than 50
percent of particles smaller than the eye can individually distinguish are
fine-grained soils. (The No. 200 sieve size [74 urn] particles are about
the smallest that can be seen individually by the unaided eye.) If the
soil is predominantly coarse grained, it is then identified as being a
gravel or a sand by estimating whether 50 percent or more, by weight, of
the coarse grains are larger or smaller than the No. 4 sieve size (about
1/4 inch).
If the soil is a gravel, it is next identified as being "clean" (con-
taining few or no fines) or "dirty" (containing an appreciable amount of
fines). For clean gravels, final classification is made by estimating the
gradation: the well-graded gravels belong to the GW group, and uniform and
3-16
-------
CO
1
1— •
-~J
UNIFIED SOIL CLASSIFICATION
INCLUDING IDCNTlflCAIlON ANO OCSCNIPIION
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INFORMATION «tCK>t«tO fOA
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PL AS ncf r Y CHART
Source: U.S. Department of Interior, 1974
Figure 3-9. Unified soil classification chart.
-------
skip-graded gravels, the poorly graded gravels, belong to the GP group.
Dirty gravels are of two types: those with nonplastic (silty) fines (GM)
and those with plastic (clayey) fine (GC). The determination of whether
the fines are silty or clayey is made by three manual tests for fine-
grained soils (described in Section 3.5.2.3).
If a soil is a sand, the same steps and criteria are used as for the
gravels to determine whether the soil is a well-graded clean sand (SW),
poorly graded clean sand (SP), sand with silty fines (SM), or sand with
clayey fines (SC).
If a material is predominantly (more than 50 percent by weight) fine-
grained, it is classified into one of six groups (ML, CL, OL, MH, CH, OH)
by estimating its dilatancy (reaction to shaking), dry strength (crushing
characteristics), and toughness (consistency near the plastic limit) and by
identifying it as being organic or inorganic. (The test procedures and
behavior of the various groups of fine-grained soils for each of the hand
tests are shown on the classification chart (Figure 3-8) and are described
in Section 3.4.2.3).
Soils typical of the various groups are readily classified by the
foregoing procedures. Many natural soils, however, will have property
characteristics of two groups because they are close to the borderline
between the groups either in percentages of the various sizes or in plastic-
ity characteristics. For this substantial number of soils, borderline
classifications are used; i.e., the two group symbols most nearly describ-
ing the soil are connected by a hyphen, such as GW-GC.
If the percentages of gravel and sand sizes in a coarse-grained soil
are nearly equal, the classification procedure is to assume the soil is a
gravel and then continue the classification procedure using the chart until
the final soil group, say GC, is reached. Since it could have been assumed
that the soil is a sand, the correct field classification is GC-SC because
the criteria for the gravel and sand subgroups are identical. Similarly,
within the gravel or sand groupings, borderline classifications such as
GW-GP, GM-GC, GW-GM, SW-SP, SM-SC, and SW-SM can occur.
Proper classification of a soil near the borderline between coarse-
grained and fine-grained soils is accomplished by classifying it first as a
coarse-grained soil and then as a fine-grained soil. Such classifications
as SM-ML and SC-CL are common.
Within the fine-grained division, borderline classifications can occur
between low-liquid-limit soils and high-liquid-limit soils as well as
between silty and clayev materials in the same range of liquid limits. For
example, one may find ML-MH, CL-CH, and OL-OH soils; ML-CL, ML-OL, and
CL-OL soils; and MH-CH, MH-QH, and CH-OH soils.
3.4.2.2 Laboratory Classification—
Although most classifications of soil will be done visually and by
simple hand tests, the USCS has provided for precise delineation of the
3-18
-------
soil groups by gradation analyses and Atterberg limits tests in the labora-
tory. Laboratory classifications are often performed on representative
samples of soils which are to be subjected to extensive testing for shear
strength, compressibility, and permeability. They can also be used to
advantage in training the field classifier of soils to improve his ability
to estimate percentages and degrees of plasticity.
The grain-size curve is used to classify the soil as being coarse-
grained or fine-grained and, if coarse-grained, into gravel or sand using
the 50-percent criterion. Within the gravel or sand groupings, soils
containing less than 5 percent finer than the No. 200 sieve size are con-
sidered "clean" and are then classified as well-graded or poorly graded by
their coefficients of uniformity and of curvature. In order for a clean
gravel to be well-graded (GW), it must have both a coefficient of uniformity,
C , greater than 4 and a coefficient of curvature, C , between 1 and 3;
otherwise, it is classified as a poorly graded gravel (GP). A clean sand
having both C greater than 6 and C between 1 and 3 is in the SW group;
otherwise, it^is a poorly graded sand (SP).
"Dirty" gravels or sands are those containing more than 12 percent
fines, and they are classified as either silty or clayey by results of
their Atterberg limits tests as plotted on the plasticity chart shown in
Figure 3-8. Silty fines are those that have a PI less than 4 or that plot
below the "A" line. Clayey fines are those that have a PI greater than 7
and that plot above the "A" line.
Coarse-grained soils containing between 5 and 12 percent fines are
borderline cases between the clean and dirty gravels or sands (i.e., GS,
GP, SW, SP, GM, GC, SM, and SC). Similarly, borderline cases may occur in
dirty gravels and dirty sands where the PI is between 4 and 7 (GM-GC,
SM-SC). It is theoretically possible, therefore, to have a borderline case
of a borderline case; but this refinement is not used, and the rule for
correct classification is to favor the nonplastic one. For example, a
gravel with 10 percent fines, a C of 20, a C of 2.0, and a plasticity
index of 6, would be classified GW-GM rather than GW-GC.
If a soil is determined to be fine-grained by using the grain-size
curve, it is further classified into one of the six groups by plotting the
results of Atterberg limits tests on the plasticity chart, with attention
being given to the organic content. Inorganic, fine-grained soils with a
plasticity index greater than 7 and above the "A" line are CL or CH, depend-
ing on whether their liquid limits are less than 50 percent or more than 50
percent, respectively. Similarly, inorganic, fine-grained soils with a
plasticity index less than 4 or below the "A" line are ML or MH, depending
on whether their liquid limits are less than or more than 50 percent,
respectively. Fine-grained soils that fall above the "A" line but that
have a plasticity index between 4 and 7 are classified as ML-CL.
Soils below the "A" line that are definitely organic are classified as
OL if they have liquid limits less than 50 percent and as OH if the liquid
limits are above 50 percent. Organic silts and clays are usually distin-
3-19
-------
guished from inorganic silts, which have the same position on the plasticity
chart, by odor and by color. However, when the organic content is doubtful,
the material can be oven dried, remixed with water, and retested for liquid
limits. The plasticity of fine-grained organic soils is greatly reduced on
oven drying due to irreversible changes in the organic colloids. Oven
drying also affects the liquid limit of inorganic soils but to a much
smaller degree. A reduction in liquid limit after oven drying to a value
less than three-fourths of the liquid limit before oven drying is considered
positive identification of organic soils.
3.4.2.3 Field Identification Procedures for Fine-Grained Soils or Fractions-
These procedures are to be performed on the minus No. 40 sieve size
particles (approximately 1/64 inch). For field classification purposes,
screening is not intended; simply remove by hand the coarse particles that
interfere with the tests.
3.4.2.3.1 Dilatancy (Reaction to Shaking)—After removing particles
larger than No. 40 sieve size, prepare a pat of moist soil with a volume of
about one-half cubic inch. Add enough water if necessary to make the soil
soft but not sticky.
Place the pat in the open palm of one hand and shake horizontally,
striking vigorously against the other hand several times. A positive
reaction consists of the appearance of water on the surface of the pat,
which changes to a livery consistency and becomes glossy. When the sample
is squeezed between the fingers, the water and gloss disappear from the
surface, the pat stiffens, and finally it cracks or crumbles. The rapidity
of appearance of water during shaking and of its disappearance during
squeezing assist in identifying the character of the fines in a soil.
Very fine clean sands give the quickest and most distinct reaction,
whereas a plastic clay has no reaction. Inorganic silts, such as a typical
rock flour, show a moderately quick reaction.
3.4.2.3.2 Dry Strength (Crushing Characteristics)—After removing
particles larger than No. 40 sieve size, mold a pat of soil to the con-
sistency of putty, adding water if necessary. Allow the pat to dry com-
pletely by oven, sun, or air drying, and then test its strength by breaking
and crumbling between the fingers. This strength is a measure of the
character and quantity of the colloidal fraction contained in the soil.
The dry strength increases with increasing plasticity.
High dry strength is characteristic for clays of the CH group. A
typical inorganic silt possesses only very slight dry strength. Silty fine
sands and silts have about the same slight dry strength but can be distin-
guished by the feel when powdering the dried specimen. Fine sand feels
gritty, whereas a typical silt has the smooth feel of flour.
3.4.2.3.3 Toughness (Consistency Near Plastic Limit)—After removal
of particles larger than the No. 40 sieve size, a specimen of soil about
3-20
-------
one-half cubic inch in size is molded to the consistency of putty. If too
dry, water must be added and, if sticky, the specimen should be spread out
in a thin layer and allowed to lose some moisture by evaporation. Then the
specimen is rolled out by hand on a smooth surface or between the palms
into a thread about one-eighth inch in diameter. The thread is then folded
and rerolled repeatedly. During this manipulation the moisture content is
gradually reduced and the speciment stiffens, finally loses its plasticity,
and crumbles when the plastic limit is reached.
After the thread crumbles, the pieces should be lumped together and a
slight kneading action continued until the lump crumbles.
The tougher the thread near the plastic limit and the stiffer the lump
when it finally crumbles, the more potent is the colloidal clay fraction in
the soil. Weakness of the thread at the plastic limit and-quick loss of
coherence of the lump below the plastic limit indicate either inorganic
clay of low plasticity or materials such as kaolin-type clays and organic
clays that occur below the A-line.
Highly organic clays have a very weak and spongy feel at the plastic
1imit.
3.5 COMPACTION
Soil compaction is the rapid application of mechanical force to a soil
to increase its density. In the construction of clay liners, compaction is
done to decrease the permeability of the liner material. Compactive effort
is the term used to describe the amount of force applied to the soil. The
units of compactive effort are foot pounds of energy per cubic foot of soil
(ft-lb f/ft3) or joules per cubic meter (J/m3).
3.5.1 Fundamentals of Compaction
In a 1933 series of publications on soil compaction, R. R. Proctor
described a laboratory procedure that, in its modern form, has become the
standard method for determining the moisture, dry density, and compactive
effort relationship of compacted soils (Proctor, 1933). In the Proctor
compaction test, soil densification is achieved through the application of
a standard dynamic impact. A standard method has been adopted and described
in ASTM standard test method 0698-78 (ASTM, 1983). The test is performed
by placing 1 inch of test soil in a cylindrical compaction mold and dropping
a 5.5-pound weight onto its surface 25 times from a height of I foot. This
procedure is repeated for two subsequent 1-inch lifts (soil layers), result-
ing in a compacted sample with three lifts. The dry density of the compacted
sample is then determined. This procedure is repeated several times on
samples of the same soil at different moisture contents. When the testing
is completed, the water contents of the samples are plotted against the dry
densities achieved after compaction. This exercise produces a compaction
curve (also called a moisture density curve) as illustrated in Figure 3-10.
3-21
-------
19.0
^T 18.5
C*5
.E
2
O)
18.0
17.5
ine of Optimums
Maximum Dry
Optimum Water
Content
I I I
10 12 14
Water Content, w (%)
Source: Lambe, 1955
16 13
0.41
0.43
(Q
cc
0.46 3
0.49
0.52
Figure 3-10. typical soil compaction curve illustrating maximum dry density
and optimum water content.
3-22
-------
The illustration presents only one curve achieved with one compactive
effort. Changing the compactive effort will produce similar curves with
different optimums, with increasing compactive effort increasing the maximum
dry density and decreasing the optimum moisture content. A typical series
of compaction curves for a single soil at different compactive efforts is
presented in Figure 3-11. Note that changing the compactive effort also
can change the shape of the compaction curve.
The most important feature on the compaction curve is its peak, which
represents the maximum dry density that can be achieved with a given compac-
tive effort. The moisture content corresponding to this peak is called the
optimum water content. The line of optimums connects the maximum densities
and optimum water contents of compaction curves produced by different
compactive efforts applied to samples of the same soil. The line of optimums
runs nearly parallel to the zero air voids line (also called the 100-percent
saturation line), which represents the saturated water contents for different
dry densities of a given soil.
The compaction curves in Figure 3-11 clearly illustrate that, for a
given soil, compacted density is a function of soil moisture content and
compactive effort. Care must be taken in compaction tests to ensure that
moisture is evenly distributed through the soil mass. Winterkorn and Fang
(1975) point out that:
... to avoid irregular and meaningless moisture density curves
in laboratory and field tests on highly cohesive soils, it is
imperative that the moisture be evenly distributed throughout the
secondary soil aggregates. This may take from 1 to 7 days in the
case of highly cohesive soils to which water is added in the dry
condition.
The interpretation of compaction tests is not always straightforward.
Winterkorn and Fang (1975) point out:
. . . even properly performed tests may not yield the generally
expected paraboloid curves. Andrews et al. (1967) found two
optimum moisture contents for the compaction of Na-bentonite, one
at 100 percent H20 yielding 73 lb/ft3 and one at 50 percent H20
yielding 65 lb/ft3. Lee and Suedkamp (1972) reported the exist-
ence of four types of moisture-density curves [as shown in Figure
3-12]. They are (A) single-peak, (B) lh peak, (C) double peak,
and (D) oddly shaped with no distinct optimum moisture content.
They related the different types to the liquid limit ranges as
follows: LL<30, double and lh peaks; LL 30 to 70, typical single
peak; LL>70, peaked and oddly shaped curves.
These unusual curves are not likely to be encountered with clays suitable
for liners (Mitchell, J. K., 1985, Dept. of Civil Engineering, University
of California, Berkeley, personal communication).
3-23
-------
E
^
Z
19
18
17
16
15
14
10 15 20 25
WATER CONTENT (%)
Jo.
1
2
3
4
Layers
5
5
5
3
Blows per
Layers
55
26
12
25
Hammer
Mass
4.54 kg
5.54
4.54
2.50
Hammer
Drop
457mm (mod.AASHO)
457
457 (std. AASHO)
305
Source: Lambe and Whitman, 1979
Rgure 3-11. Compaction curves for different compactive efforts
applied to a silty clay.
3-24
-------
Type A
TypeC
TypeB
Type D
»
A
After Winterkorn and Fang, 1975
Rgure 3-12. Four types of compaction curves found from laboratory investigation.
3-25
-------
3.5.2 Compaction and Permeability
During installation of a clay liner, compaction is controlled by
measuring density and moisture content in each lift. However, these measure-
ments by themselves are meaningless unless they ultimately can be related
back to the permeability. (See Figures 3-13 and 3-14.)
Mitchell, Hooper, and Campanella (1965) investigated the relationship
between these variables and found that, at a given density, permeability
was very sensitive to variations in the molding water (moisture) content.
They performed a series of compaction tests on a silty clay, samples of
which were kneaded to constant density at different water contents. When
permeability tests were performed, the permeability increased slightly
between 12 and 18 percent molding water content but then decreased by
around 3 orders of magnitude as the water content increased from 18 to 19.5
percent. The decreased permeability corresponded to compaction performed
at water contents on the wet side of optimum; minimum permeability occurred
on the "wet-of-optimum" side of the compaction curve and not at the maximum
density. Mitchell et al. (1965) also found that, in the laboratory, lower
permeabilities are achieved with kneading compaction than with static
compaction. These phenomena are discussed in Chapter 2 of this report.
This discussion gives rise to the following conclusion: to achieve a
specified permeability, soil moisture, compactive effort, and dry density
must be carefully measured and controlled.
3.6 FIELD MEASUREMENT OF DENSITY AND MOISTURE CONTENT
Controlling clay compaction in the field so that a specified perme-
ability is achieved is done through control of the moisture content and
density. Methods for measuring moisture content are summarized in Appendix
A, Methods I through 7. Field density or unit weight measurements are
summarized in Methods 8 through 13. The following text discusses the more
commonly used techniques in more detail.
3.6.1 Traditional Methods
3.6.1.1 Density--
Two traditional methods are used for measuring density in the field.
In one type of test, a small hole is dug in the compacted fill and the
excavated material is saved and weighed. The volume of the hole is measured
by filling it with sand or liquid with a device that measures the amount of
material required to fill the hole. The sand cone and rubber balloon
methods are examples of this category of test (Appendix A, Methods 10 and
11).
Another technique is to drive a hollow cylinder into the fill, remove
a core, trim it to a known volume, and then determine its weight. This
drive-cylinder method (Appendix A, Method 12) and the sand cone and rubber
balloon methods take time because the sample must be oven dried before the
dry density can be determined.
3-26
-------
0>
"••
E
1x10
~6
§ 1X10'7
Q
Z
O
o
tr
Q
1x10
'8
1x10
-9
^
oc
0 106
I riii ii
12 14 16 18
N. .O
O
Kneading
compaction curve ''•-..
! I
20
Line of optimums
13 15 17 19
MOLDING WATER CONTENT (%)
Source: Mitchell, 1976
Rgure 3-13. Permeability as a function of molding water content for samples
of silty clay prepared to constant density by kneading compaction.
3-27
-------
1x10
-5
5x10
-6
E
o
> 1x10
-6
*
§ 5X10-7
Q
Z
O
o
U -7
-; 1x10 '
a 5x10~8
0
>
r
Optimum water content
I
Static compaction
Kneading compaction
15 17 19 21 23 25 27
MOLDING WATER CONTENT (%)
CO •*-
z «
UJ £
Q 2
> c
cr
o
108
106
104
102
100
15 17 19 21 23 25 27
MOLDING WATER CONTENT (%)
o Kneading compaction 1" x 2.3" 0 mold
• Kneading compaction 3.5" x 1.4* 0 mold
v Static compaction 1* x 2.8* 0 mold
Source: Mitchell, 1976
Rgure 3-14. Influence of the method of compaction
on the permeability of silty clay.
3-28
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3.6.2 Nuclear Methods
Nuclear gauges offer a faster and more convenient method for measuring
field density and moisture content than those methods described in Section
3.6.1 and are presently widely used for earthwork compaction quality control.
Nuclear gauges are designed to give very rapid measurements of density and
moisture content.
3.6.2.1 Nuclear Density Gauge—
Nuclear density gauges consist of a source of gamma rays, typically
Cs-137 (0.662 Mev), and a detector (or nest of detectors) separated horizon-
tally from the source. The gauges are used in two modes: a "back-scattering"
mode in which the gamma rays are directed, by collimation, downward into
the soil where they are scattered with some fraction reaching the detector
and a transmission mode in which the source is lowered into a hole in the
soil (2 to 12 inches deep) and the number of gamma rays penetrating the
soil to reach the detector on the surface is recorded. In the range of
densities of interest (70 to 160 lb/ft3), the gamma rays that reach the
detector decrease with increasing soil density.
Gamma rays interact with the electrons that are a part of the atoms
making up the soil. Two types of interactions are exploited for measuring
density. The primary interaction is Comptom scattering wherein the gamma
ray is deflected (scattered) by an electron and continues in a different
direction at a reduced energy. For the elements found in soil, Compton
scattering is the predominant reaction in the energy range above 100 keV.
The second interaction is photoelectric absorption wherein the gamma ray
gives up all its energy to an electron and is removed from the beam. The
frequency of this interaction becomes greater as the gamma ray energy
decreases from 100 keV. The probability of this reaction also increases
with the atomic number of the element.
The relative frequency of these two interactions is a function of the
soil's chemical composition. The effects can best be illustrated by first
considering the predominant reaction, Compton scattering, and then the
modification introduced by photoelectric absorption.
The Compton scattering cross section, i.e., the probability of a scat-
tering event, is proportional to the electron density of the medium. This
is given by:
De = Dm N I W. Z./A. , (3.11)
where
D = mass density of the medium
m J
N = Avogadro's number
W. = weight fraction of element
3-29
-------
Z. = atomic number of element
A. = atomic weight of element.
Thus, the electron density is related to the mass density by the factor Z/A
of the medium. The Z/A of the various soil components is given in Table 3-3.
Except for Fe203 (Z/A = 0:476), the major soil components have Z/A values
that fall within the range of 0.489 to 0.500. Thus, if Compton scattering
alone were responsible for the attenuation of the gamma rays, the mass
densities would be within a few tenths of a percent of the instrument gauge
indications except for soils containing appreciable amounts of Fe203.
Water also has a measurable effect on nuclear density measurements. Because
of its high Z/A, its electron density (per gram) is high. As a result, a
dry soil of a given density will produce a slightly lower nuclear gauge
density reading than a wet soil of the same mass density. The different
readings are a -consequence of the difference in the Z/A of the two soils
(Table 3-3; clay and clay + 10 percent H20).
Thus, with respect to the Compton scattering component, the gauge will
read iron-rich soils lower than their actual density and damp soils somewhat
higher than their actual density.
The cross section for the photoelectric effect interaction of gamma
rays with electrons is experimentally determined to be about proportional
to Z5/A. Thus, this effect becomes increasingly important for higher Z
elements such as calcium, which has a Z of 20. The other major earth ele-
ments—oxygen, silicon, and aluminum—have relatively low Z values (8, 14,
and 13, respectively), so the photoelectric effect for these is less than
for calcium. The consequence is that more gamma rays are absorbed per unit
of electron density in calcareous soils than in noncalcareous soils and the
nuclear gauge density reading is therefore higher than the actual density.
To minimize this effect, ASTM Standard 2922 (ASTM 1983) requires that
nuclear density gauge calibration blocks include two that bracket the
attenuation coefficient of soils and suggests limestone and granite. The
calibration curve is adjusted to fall halfway between the limestone and
granite data. As a result of this compromise, highly calcareous soils will
read 2 to 3 lb/ft3 high and highly siliceous soils will read 2 to 3 lb/ft3
low when measurements are made in the transmission mode. This effect is
exaggerated further in the backscattering mode, where the photoelectric
effect is greater. In the backscattering mode, highly calcareous soils
will read 3 to 4 lb/ft3 high and highly siliceous soils will read 3 to
4 lb/ft3 low.
Although iron is not a major component of the earth's crust, some
soils contain sufficient iron to affect the reading of a nuclear density
gauge. Biotite mica, other iron silicates, and iron oxides (e.g., goethite
and hematite) cure some of the more common iron-containing minerals in
soils; nuclear density measurements in soils containing iron minerals
should be made with care. Because the Z of iron is 26, the photoelectric
effect becomes quite important and the gauge will indicate a density higher
than the actual value when calibrated according to ASTM Standard 2922.
3-30
-------
TABLE 3-3. Z/A OF VARIOUS SOIL COMPONENTS
Components ^i/^i
Silica (Si02) 0.500
Feldspar (KAlSi308) 0.495
Lime (CaC03) 0.499
Alumina (A1203) 0.490
Soda (Na203) 0.489
Magnesia (MgO) 0.495
Clay (Al6Si2013) 0.496
Clay + 10% H20 0.502
Fe203 0.476
H20 0.555
3-31
-------
A method for overcoming the chemical composition error is to calibrate
the gauge against a series of sand cone tests performed on the soil of
interest. The precision of a series of sand cone tests is poorer than the
precision of nuclear gauge tests, but the accuracy is generally better if
the sand cone tests are done carefully. The ratio of the sand cone density
to the nuclear density may then be applied to the nuclear gauge reading to
achieve the corrected density.
When used in the backscattering mode, "surface roughness" may cause
inaccurate density measurements. If the soil surface is not a perfect
plane, air voids are formed between the gauge and the soil, reducing the
density of the volume beneath the gauge. A 50-mil air gap will result in a
density reading that is about 4 lb/ft3 low.
The uniformity of the soil density is also important in the backscatter-
ing mode. About 60 percent of the gauge response is from the top inch of
soil, 25 percent from the second inch, and 10 percent from the third inch.
Thus, while a gauge may be quoted as having 95 percent of its response from
a 3-inch depth, the response versus depth in this region is in no way
uniform. In summary:
Nuclear density gauges are factory calibrated to give compromised
measurements in two soil extremes. In highly calcareous dry
soils, the gauge will read high by 2 to 3 lb/ft3 at 120 lb/ft3 in
the transmission mode and in highly siliceous soils low by 2 to
3 lb/ft3. In the backscattering mode, the gauges are 3 to 4 lb/ft3
high and low, respectively, at 120 lb/ft3. The gauge would be
expected to read properly in clays with up to 10 to 12 percent
water content if no high Z elements such as calcium and iron are
present in appreciable quantities. Nuclear gauges will read
iron-rich soils lower than their actual density and damp soils
somewhat higher than their actual density.
In the backscattering mode, the nuclear gauge is sensitive to any
density variations in the upper 3 inches of soil and to the
flatness of the soil surface upon which the gauge rests.
It is customary to calibrate the nuclear gauge against a series
of sand cone tests to overcome chemical composition problems in
the field. A gauge reading (preferably in the transmission mode)
is taken, and then a sand cone test is made on the same volume
measured by the gauge. The average of the ratio of the sand cone
test to the gauge reading for a series of tests then becomes the
correction factor to be applied to the gauge reading. This
correction factor will apply as long as the chemical composition
of the soil does not change appreciably.
3.6.2.2 Nuclear Moisture Gauge—
Nuclear moisture gauges consist of a source of fast neutrons (usually
an americiurn-beryllium source) and a slow neutron detector mounted as close
to one another as possible. The principle of operation is that of neutron
3-32
-------
moderation, i.e., the slowing down of neutrons caused by elastic scattering
from the nuclei in the scattering medium. Hydrogen is an excellent moder-
ator because its nuclear mass is the same as the mass of a neutron and each
interaction with hydrogen results in a major energy loss to the neutron.
On the average, about 19 collisions with hydrogen nuclei will thermalize
the neutron, i.e., reduce its energy to that of the surrounding nuclei.
The other elements in the earth's crust are not nearly as effective—oxygen
requires about 158 collisions on the average and silicon 273. The readings
obtained with a nuclear moisture gauge are essentially independent of the
density of the medium because, except for hydrogen, the medium is nearly
transparent to the neutrons.
By using a slow neutron detector, i.e., one responsive only to thermal
neutrons, one can measure the number of neutrons themalized, which is a
function of the number of hydrogen atoms in the medium. In inorganic
soils, water provides the bulk of the hydrogen and thus the water content
can be measured. The greater the water content, the greater the number of
neutrons thermalized.
Because of the system's geometry, the gauge is most sensitive to the
hydrogen content in the immediate vicinity of the detector. At low moisture
contents, the neutron moves further from the source-detector position
before it has undergone enough collisions to thermalize it and is far enough
from the detector that the probability of returning to the detector is low.
On the other hand, a high moisture content will permit thermalization much
closer to the detector. This leads to the conclusion that the active
volume of measurement is a function of the moisture content.
Experimentally determined depths of measurement for a typical neutron
gauge give the following expression for the depth where 95 percent of the
detected interactions will occur:
D (inches) = 11 - 0.17 MC , (3.12)
where
MC = moisture content in pounds of water per cubic foot of soil.
When Equation (3.12) is applied to a hypothetical case, if a soil sample
has a density of 120 lb/ft3 and moisture content of 12 percent, it contains
14.4 pounds of water per cubic foot and the sensitive depth is 8.5 inches.
Note, however, that if the moisture is nonuniform, the gauge response will
be bi-ased toward the moisture content near the detector.
Another reaction can modify the gauge reading when certain soil elements
are present. Aside from the moderation interactions, certain elements have
a high probability of absorbing a neutron. The only ones normally found in
soil are iron and chlorine, the latter where saline soils exist. Thus,
coastal soils may contain sufficient chlorine to be significant and iron
oxide or silicate contents of 35 to 40 percent will cause errors. In
summary:
3-33
-------
Neutron gauges are useful for measuring the moisture content
of inorganic soils of uniform water content. Although the
sensitive depth of measurement may normally be 6 to 8 inches,
the response is biased toward the moisture content near the
detector.
If hydrogen-containing materials (including clay minerals)
other than water are present, the gauge will respond to this
hydrogen. Coastal soils may have sufficient chlorine content
to interfere, and high iron oxide or silicate content will
influence the moisture measurement.
In order to compensate for the soil compositions that may
affect the neutron response, it is customary to calibrate
the gauge against tests on the oven-dry soil. This is
generally done with the soil samples extracted for the
density calibration.
3.6.2.3 Modern Nuclear Density and Moisture Gauges—
Current nuclear gauges contain both density and moisture-measuring
components. A key pad, display unit, and microprocessor enable various
correction factors to be entered into the gauge for particular soils.
Operating manuals provide complete instructions for the use of the gauge
under various conditions. In addition, gauge manufacturers provide training
seminars on the proper use of their gauges, including safety considerations.
3.7 TESTING FOR SHEAR STRENGTH
The shear strength of a soil must.be known before an earthen structure
can be designed and built with assurance that the slopes will not fail (see
Chapter 5).
A soil mass may be considered to be a compressible skeleton of solid
particles. In saturated soils the void spaces are completely filled with
water; in partially saturated soils the void spaces are filled with both
water and air. Shear stresses are carried only by the skeleton of solid
particles, whereas the normal stress on any plane is carried by both the
solid particles and the pore water.
The development of shear in a saturated cohesive (clay) soil is com-
plex because an applied load is initially supported by the stress in the
pore water (neutral stress) and is not immediately transmitted to the soil
structure. Because of the very low permeability of clays, neutral stresses
are transmitted to the soil structure very slowly, sometimes requiring
months or years before the soil structure feels the full stress increase.
Another complicating factor is the attractive and repulsive interaction
between the clay particles (Sowers and Sowers, 1971).
The triaxial compression test is commonly used to measure the shear
strength of a soil under controlled drainage conditions. A triaxial com-
3-34
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pression chamber consists primarily of a head plate and a base plate separ-
ated by a transparent plastic cylinder (Figure 3-15). In the basic triaxial
test, a cylindrical specimen of soil, encased in a rubber membrane, is
placed in the chamber. Connections at the ends of the soil specimen permit
controlled drainage of pore water. The chamber is filled with water and
pressurized, thereby establishing a confining pressure on the specimen.
The specimen is then loaded axially to the point of failure. The axially
applied stress is called the "deviator stress." In general, a minimum of
three specimens, each under a different confining pressure, are tested to
establish the relation between shear strength and normal stress (U.S.
Department of the Army, 1970).
Three types of triaxial compression tests have been developed to
measure the shear strength of clays. The tests differ in the drainage
conditions established for the sample and shear stress application rate.
These tests are:
Consolidated-Drained (CD) Test or Slow (S) Test—The desired
confining stress is applied to the specimen and drainage is
allowed until 100-percent consolidation is achieved. The
rate of applied shear stress is slow enough that essentially
no change in the initial pore pressure occurs.
Consolidated-Undrained (CU) Test or Consolidated Quick (R)
Test—As in the CD test above, the derived confining stress
is applied to the specimen and drainage is allowed until
100-percent consolidation is achieved. No drainage is
allowed during the application of shear stress and the
specimen remains at a constant volume and water content.
Unconsol idated-Undrai ned (UU) Test or Quick (Q) Test—No
drainage is allowed during application of the confining
stress or during application of shear stress. The unconfined
compression test is a special case of the UU test with the
confining stress equal to zero. The principal stress differ-
ence at failure is called the unconfined compressive strength.
Detailed discussion of the protocols for shear strength testing and interpre-
tation of the test results are beyond the scope of this document. The
reader is referred to the U.S. Department of Interior (1974) and U.S.
Department of the Army (1970) for test protocols. Explanations of the
theory and interpretation of the test can be found in geotechnical engi-
neering texts such as Lambe and Whitman (1979) and Holtz and Kovacs (1981).
3.8 HYDRAULIC CONDUCTIVITY TESTING
Laboratory and field tests to quantify the hydraulic conductivity
(permeability) of low-porosity soils to water have been used for years.
Historically, information on permeability has been required to evaluate
seepage characteristics of soils in a variety of applications ranging from
earthen dams to septic tank drainage fields. These same test procedures
3-35
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'Dial Indicator
»
I Axial Load
Compression Chamber
Soil Sample
Pressure Gage
Valve C
Pressure
Regulator
Valve A
Air Pressure Una
Chamber
Pressure
Reservoir
Source: U.S. Department of the Army, 1970
Rgure 3-15. Schematic diagram of triaxial compression apparatus for Q test.
3-36
-------
have been adapted, with some modifications, to evaluate the performance of
compacted clay liners.
Hydraulic conductivity testing of clay liner material is used for
facility design, for construction quality control (CQC), and for clay/
chemical compatibility evaluation. CQC tests are conducted to ensure that
the hydraulic conductivity of an installed clay liner meets the performance
specification. A compatibility test is conducted to determine if a particular
soil's permeability is altered by a liquid waste with which it might come
in contact in a specific application. Chemical compatibility is discussed,
at length, in Chapter 4.
Theoretical knowledge has not yet reached the stage of providing reli-
able estimates of permeability. Thus, field and laboratory measurements
are needed. Standard procedures, however, have not been adopted for perme-
ability testing related to hazardous waste containment.
Effective porosity, pore-size distribution, fluid viscosity, and fluid
density determine the permeability of clay soils to fluids. Any action
that affects the soil's fabric may affect the effective porosity and, in
turn, the permeability. Such modification of the soil fabric might be
physical, as with soil compaction, or chemical, through the various processes
that can occur when a chemical waste interacts with the clay (see Chapter 4).
In general, the procedure for measuring the permeability of a compacted
soil is to enclose the sample tightly in a cylinder (permeameter) and then
to pass the liquid (permeant), usually under pressure, through the sample.
The pressure differential across the sample is expressed in terms of hydraulic
gradient (a dimensionless quantity) that is the pressure drop across the
sample divided by the sample's height. The gradient can be controlled by
superimposing air pressure above the permeant supplied to the sample and by
regulating the pressure applied at the effluent end of the column. High
hydraulic gradients reduce testing time by forcing permeant through the
sample at a greater rate than could be achieved with low gradients. However,
the amount of gradient may influence the test results.
3.8.1 Darcy's Law
Hydraulic conductivity (K) or permeability is a measure of how rapidly
a permeant fluid can move through porous soils under a hydraulic gradient.
Quantitatively, K is defined as the constant of proportionality in Darcy's
law (Equation 3.14). To calculate K for a given soil sample, one must be
able to measure the volumetric flow rate through the sample, the cross-
sectional area of the sample perpendicular to the direction of fluid flow,
and the hydraulic gradient across the sample.
The flow of liquids through clay has been found to obey Darcy's Law,
which states that the volumetric flow rate of water through a porous medium
is proportional to the cross-sectional area of the medium and to the hydraulic
gradient impressed across it. The constant of proportionality (K) is
defined as the soil's hydraulic conductivity. This is expressed in Equa-
tion (3-13):
3-37
-------
Q = KAh/L , (3.13)
where
Q = volumetric flow rate, cm3/s
K = hydraulic conductivity (permeability), cm/s
A = cross-sectional area of specimen, cm2
h = change in hydraulic head across the specimen, cm
L = length of sample, cm.
Note that h/L is the hydraulic gradient. Also note that although K
appears to have the dimensions of a velocity, this is an artifact due to
the cancellation of units. The true dimensions are cmVcm2 s (i.e., volume
per unit area per unit time). Darcy's Law assumes a direct proportionality
between the hydraulic gradient and the flow rate.
When fluids other than water are used, the permeability as defined
above will be different if the viscosity and/or density of the fluid differs
from that of water. It is convenient to define an intrinsic permeability
coefficient that considers these two parameters. The equation for intrinsic
permeability is:
k = K(j/pg , (3.14)
where
k = intrinsic permeability, cm2
K = permeability, cm/s
u = dynamic viscosity, g/cm s
p = density, g/cm3
g = gravitational constant, cm/s2.
A fluid's viscosity is a measure of its resistance to flow while its
density measures the degree to which gravity influences its flow behavior.
For liquids other than water, these two factors influence the fluid conduc-
tivity in a porous media.
Knowing the hydraulic conductivity of a clay enables one to calculate
the volumetric flow rate (Q) through a saturated, homogeneous liner composed
of that clay. Given a liner area (A) of 20,000 ft2 (about half an acre), a
liner thickness of 3 ft (L), 1 ft of water over the liner making L egual 4
(1 ft water + 3 ft of saturated liner), and a permeability (K) of 10 7 cm/s
(2.88 x io"4 ft/d), the volumetric flow rate from Equation (3.13) will be:
3-38
-------
Q = KAh/L
Q = (2.88 x 1Q~4 ft/d) (20,000 ft2) (4 ft/3 ft)
= 7.68 ftVd
= 57 gal/d.
Decreasing the permeability by a factor of 2 will halve the flow rate.
Note that this is the flow rate after equilibrium has been reached and
the liner is fully saturated. A time lapse will occur between the intrusion
of the leachate into the liner and its appearance at the bottom of the
liner. The topic of transit and breakthrough times is discussed in Chapter
8.
3.8.2 Hydraulic Gradient
It is necessary to conduct the tests with hydraulic gradients that are
substantially greater than those encountered in the field in order to
measure the permeability of compacted clay within a reasonably short time
period. The two implied conditions in the Darcy equation are that the flow
rate is directly proportional to the hydraulic gradient and that the relation-
ship between flow rate and hydraulic gradient is linear through the origin.
There is no single accepted hydraulic gradient for use in permeability
testing. Thus, gradients of 5 to 20 are recommended by some (Zimmie, 1981)
while gradients as high as 362 have been used by others (Brown and Anderson,
1982).
Over the past several decades, several studies have been aimed at
evaluating the validity of Darcy's law by measuring the dependence of per-
meability on hydraulic gradient. Oakes (I960), Hansbro (I960), Mitchell
and Younger (1967), and others have published data that indicate a depart-
ure from linearity at low hydraulic gradients. Bowles (1979) observes that
in clays a threshold gradient of 2 to 4 may be necessary to produce any
flow. The departure from linearity at low hydraulic gradients may not be
unexpected according to Yong and Warkentin (1975). The binding forces
between water molecules and clay surfaces, in effect, create immobilized
hydrodynamic layers of water surrounding each clay particle. The thickness
of these immobilized hydrodynamic layers depends upon the extent of inter-
action between the water and clay surfaces and upon the driving force for
flow. At sufficiently low hydraulic gradients, the "effective" pore diam-
eter available for flow could be decreased by the immobilized hydrodynamic
layers. Several workers, however, have attributed apparent threshold
gradients to experimental artifact.
The current regulations require that a landfill liner have a leachate
collection system that will ensure that the leachate depth over the liner
does not exceed 30 cm (1 ft). Thus, for liners exceeding 1 foot in thickness,
the hydraulic gradient will be less than 2. In view of the larger hydraulic
gradients used in laboratory tests, the question of the linearity of permea-
3-39
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bility with hydraulic gradient should be resolved, if meaningful translation
of laboratory results to the field situation is to be expected.
3.8.3 Permeability Measurement Factors That Influence Test Results
Permeability may be determined by either a constant head test or a
falling head test. In a constant head test, as implied by the name, the
test sample is subjected to the permeant fluid under a constant head (i.e.,
the hydraulic gradient is constant). In falling head tests, the head of
permeant fluid is allowed to decrease (fluid passes through the sample)
during the timed interval of the test.
Equations (3.15) and (3.16) are used to calculate permeability through
the methods of constant head and falling head, respectively.
For constant head, K = jjj= , and (3.15)
for falling head, K = | In , (3.16)
where
K = hydraulic conductivity, cm/s
L = length of soil path across which head is impressed, cm
Q = volumetric flow rate, cmVs
A = cross-sectional area of sample, cm2
h = hydraulic head, total hood
t = time interval over which the sample is collected (or readings
are taken)
a = cross-sectional area of in-flow column
hx,h2 = height of fluid in in-flow column at beginning of test
and at the end of test.
-The total head is actually comprised of three components: velocity,
elevation, and pressure head. Because the seepage velocity in geotechnical
problems is relatively low, the velocity head is insignificant compared to
elevation and pressure heads. As used in this report, total or hydraulic
head refers to the combination of the elevation difference between the
in-flow and the out-flow fluid levels and any applied pressure or vacuum
expressed as an equivalent height of water column.
3-40
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Most permeability test devices may be operated in the laboratory in
either the falling head or constant head mode, depending on the hydraulic
systems connected to the permeameter. Similarly,, in the field either a
constant head or a falling head test may be used to determine flow through
the soil. Theoretically, test results (i.e., the value of K that is cal-
culated) should be the same whether the measurements are made in a constant
head or falling head test.
Laboratory permeability tests are conducted to predict performance of
a natural or compacted clay liner in the field. Frequently, however, to
complete a test within a reasonable time frame, laboratory conditions are
established that differ substantially from conditions in the field (e.g.,
elevated hydraulic gradient). An understanding of the many factors that
affect permeability tests is necessary to extrapolate, in a meaningful way,
from test results to performance prediction.
Important factors that influence permeability measurements include
sample characteristics and preparation, permeant properties, design of the
test apparatus, and selection and control of variables during test perform-
ance. Another important factor that has not been addressed adequately is
inter!aboratory variability in permeability tests. Regarding variability
in permeability, Zimmie (1981) has concluded that, "One is always dealing
with orders of magnitude in permeability problems, and it is unrealistic to
expect results to agree within less than several hundred percent."
A summary compiled by Olson and Daniel (1979) of potential errors in
laboratory permeability tests is given in Table 3-4. ' The information is
based on reported permeability test results from several investigations.
Another summary of sources of error in estimating field permeability from
laboratory tests is given in Table 3-5. This table is reproduced from
Daniel (1981).
3.8.3.1 Sample Selection, Size, and Preparation—
Measuring the permeability of compacted fill is often accomplished by
bringing undisturbed samples into the laboratory. Samples obtained with
Shelby tubes or similar sampling devices are considered "undisturbed,"
although in reality this is not the case. Specifying sample selection,
sample size, sample preparation, and the number of samples subjected to
testing should be made based on adequately representing field conditions.
The number of samples and tests should be determined by the level of statis-
tical confidence desired combined with the precision and accuracy of the
test method employed. Confidence limits for permeability as a function of
numbers of samples have been determined by Mason et al. (1957) for tests
conducted in a laboratory pressure cell. Their results are shown in Table
3-6. Comparable data are not available for field measurements or for
measurements made on field-compacted samples.
Large samples tested in situ (see Section 3.8.5) may be of sufficient
size to include some macropores, holes, natural cracks, or sand lenses.
Such samples are more likely than much smaller samples to provide good
estimates of actual field performance. However, the time required for such
3-41
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TABLE 3-4. SUMMARY OF POTENTIAL ERRORS IN LABORATORY
PERMEABILITY TESTS ON SATURATED SOIL3
Source of error
Direction
of deviation of
measured permeability
from correct value
Ratio of measured
permeability to
correct value
Voids formed in sample
preparation
Smear zone formed
during trimming
Use of distilled water
as a permeant
Air in sample
Growth of microorganisms
Use of excessive hydraulic
gradient
Use of wrong temperature
Ignoring volume change
due to stress change
Flowing water in a direction
other than the one of
highest permeability
Performing laboratory
rather than in situ
tests
High
Low
Low
Low
Low
Low or high
Varies
High
Low
Usually low
0.005 to 0.1
0.1 to 0.5
0.001 to 0.1
<1 to 5
. 0.5 to 1.5
1 to 20
1 to 40
<0.0001 to 3
Data from Olson and Daniel (1979).
3-42
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TABLE 3-5. SUMMARY OF SOURCES OF ERROR IN ESTIMATING FIELD
PERMEABILITY OF COMPACTED CLAY LINERS FROM
LABORATORY TESTS3
Potential
sources of error
Laboratory K too
high or low?
Possible
number of
orders of magni-
tude of error
Compaction at a higher
water content in
laboratory than in field
Maximum size of clay
chunks smaller in
laboratory than in field
Deleterious substance (e.g.,
plant roots) present in
the field but not in
laboratory samples
Use of more compact!ve effort
in the laboratory than in
the field, resulting in
optimum water content being
higher in field than in
laboratory
Air in laboratory samples
Use of excessive hydraulic
gradient causing particle
migration
Lack of steady-state seepage
due to stress change
Sample size too small in
laboratory test
Desiccation cracks in field
Low
Low
Low
Low
Low
Low
High
Low
Low
1 to 3
1 to 2
1 to 3
1 to 3
0 to 1
0 to 1
0 to 1
0 to 3
No data
Reproduced from Daniel (1981).
3 A rough estimate based on available data.
3-43
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TABLE 3-6. CONFIDENCE LIMITS FOR PERMEABILITY (K) AS A
FUNCTION OF NUMBER OF SAMPLES AND THE
MEAN PERMEABILITY3
Number of samples
2
3
5
8
16
Confidence limit, AK
2.00 K
1.90 K
1.45 K
1.11 K
0.76 K
aData from Mason et al. (1957).
Confidence limits were computed with a variance of 0.1
(the lower limit of the variation observed in samples
taken from a given pit or site) and t-distribution value
appropriate to a 95-percent confidence limit.
3-44
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tests may be prohibitive, particularly if the purpose of the test is con-
struction quality control. Laboratory tests are performed on smaller
samples but have the advantage of a shorter test time and limited inter-
ruption of construction activities.
During the design phase of a clay liner construction project, samples
of clay soils are obtained from the site and subjected to a series of
laboratory tests, which include the measurement of their permeability in
the compacted state. The manner in which these samples are handled and the
procedures followed during compaction can greatly influence the test outcome.
At present, there are no accepted standard protocols for test sample prepara-
tion.
A recent study of test methods used by commercial soil laboratories
(Truesdale et a!., 1985) revealed that some used protocols requiring air
drying the soil while others required that it be maintained at or near the
field moisture content before clod size reduction. Reasons given for
drying were that it made it easy to break up clods, sieve the soil, and
obtain a very homogeneous soil mass for testing. The problem with drying,
however, is that there is no way of knowing if the dried soil can be rehy-
drated to its former condition. Sangrey et al. (1976) found that drying
and rewetting significantly altered the liquid limits of several clays.
Typically, rehydration took several weeks rather than the 24 hours commonly
allowed for most laboratory tests. More important was their finding that
some clays were irreversibly altered by drying.
Truesdale also found a variety of methods for reducing clod size and
obtaining a uniform representative sample for compaction. When dry soil
was used, the clod size reduction methods included grinding the clods in an
electric mill, breaking the clods up with a hammer, and manually crushing
them between a hand-held steel plate and a counter top. Typically, the
ground sample is passed through a No. 4 sieve before being rewet and compacted.
Wet samples were also handled in a variety of ways. These included
manually breaking the clods, forcing the moist clay through a No. 4 sieve,
and mixing and grinding the soil in a Hobart vegetable shredder.
Several techniques have been developed for compacting clay soil sam-
ples. In general, the soil is compacted in a cylindrical compaction mold.
If a fixed-wall permeation test is to be run, the clay can be compacted
directly in the permeameter, which in this instance serves as the compaction
mold. Alternatively, clay can be compacted in a separate compaction mold,
extruded, and then trimmed to fit the permeameter. At some facilities, a
split mold is used.
A variety of methods are available for compacting test samples in the
laboratory. Among these are:
Static Compaction—A hydraulic or mechanical press is used
to compress a predetermined weight of soil into a mold of
known volume (to find the required density).
3-45
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Impact Compaction—A drop-hammer is used to compact the
specimen. Often the compaction is done according to the
ASTM procedure for determining the moisture density curve.
The procedure is often modified to accommodate various-si zed
compaction molds.
Kneading Compaction—This may be accomplished with a device
known as a Harvard Miniature Compactor. Some investigators
think this device mimics the kneading compaction obtained in
the field with sheepsfoot rollers.
Manual Compaction—In some laboratories, soil samples are
weighed and pushed into a mold of known volume with a hand-
held ram or rod.
Recently, Dunn and Mitchell (1984) reported on a series of permeability
tests in which the only difference was the method of compacting the samples.
When samples were compacted by different methods to both 90 and 95 percent
of their maximum dry density, differences in their hydraulic conductivities
were notable. At both dry densities, the static compaction produced samples
with higher hydraulic conductivities than kneading, which was second highest,
or impact, which was lowest. Manual compaction methods were not tested.
The results of Dunn and Mitchell's (1984) study indicated that static
compaction produced replicate samples with the least effort. The higher
hydraulic conductivity obtained with this method correlates better with
field-compacted samples than the other commonly used compaction methods.
Regardless of the compaction method used in the laboratory, the final
sample should not be considered equivalent to the same material compacted
in the field, for several reasons. Field compaction is done with machines
whose size and compactive effort are not duplicated in the laboratory.
Clod sizes, which are very small and fairly well controlled in the laboratory,
are much more variable in the field, where clod size may range up to 6 or
8 inches or even greater in some cases. Finally, moisture content and
distribution in laboratory samples are controlled much more carefully than
in the field, where the combination of large clods and inadequate curing
(soaking) time after water addition may result in nonuniform moisture
distribution within a liner. The profound effect of moisture content on
permeability is discussed in Chapter 2 (Section 2.4.2).
The significance of sample diameter has been investigated by D'aniel
(1981-). His data show that permeability determined on the specimens tested
in the laboratory drastically underestimated the actual permeability of a
clay liner. Test results on different diameter samples of a compacted clay
liner are shown in Table 3-7. The average permeability of the in-place
liner was back-calculated from measured leakage rates and found to be
1 x 10 5 cm/s. Boynton and Daniel (1985) compacted test samples with
various diameters ranging between 15 and 6 inches. The measured hydraulic
conductivities showed an increased sample diameter, with the smallest
3-46
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TABLE 3-7. TEST RESULTS SHOWING EFFECT OF SAMPLE
DIAMETER ON PERMEABILITY MEASUREMENTS
Sample diameter (cm) Permeability (cm/s)
3.8 1 x io"7
6.4 8 x io"9
243.8 3 x IO"5
aData from Daniel (1981).
3-47
-------
diameter having the lowest conductivities. However, the highest and lowest
conductivities differed only by a factor of 2, which the authors did not
consider to be of practical significance.
Anderson and Bouma (1973) experimented with a series of cores of
different lengths to determine the effect of sample size on permeability.
They found that permeabilities for cores 17 cm in length were lower by
one-half an order of magnitude than for the 5-cm-length samples.
Whether a sample is compacted dry of optimum or wet of optimum can
profoundly influence the resulting permeability. Daniel (1981) reported
that the permeabilities of soils compacted dry of optimum might typically
be 10 to 1,000 times greater than permeabilities of the same soils compacted
wet of optimum (this phenomenon is discussed in Section 2.3). Because
moisture conditions at compaction can strongly influence permeability
measurements, gross errors in predicting field permeability from laboratory
tests may occur if compaction is performed at different water contents.
Permeability tests can be conducted with samples compacted at several
points in a range of moisture contents to ensure that actual field moisture
conditions are reproduced.
Another consideration is that equipment used to compact laboratory
samples does not resemble field compaction equipment. Lambe and Whitman
(1979), in comparing field and laboratory compaction efforts, have concluded
that generally the laboratory curves yield a somewhat lower optimum water
content than the actual field optimum.
In the field, a compacted low-permeability soil may display anisotropic
flow characteristics. The horizontal permeability (parallel to the plane
of compaction) of anisotropic soil may be much higher than the vertical
permeability (normal to the plane of compaction). Such a condition will
lead to predominantly horizontal flow. For in-place stratified clays, the
ratio of horizontal to vertical permeabilities may exceed 10 (Olson and
Daniel, 1979).
In contrast, however, Boynton and Daniel (1985) report that no aniso-
tropic flow was found in laboratory-prepared samples of fireclay compacted
wet of optimum. Anisotropic flow found in compacted soils may be the
result of poor lift bonding or variations in density within the test sample.
3.8.3.2 Hydraulic Gradient—
Since Darcy's law indicates a linear relationship between flow rate
and hydraulic gradient, many workers have used elevated hydraulic gradients
to reduce testing time. However, if hydraulic gradients are excessive,
piping (opening flow channels and increasing hydraulic conductivity) or
particle migration (blocking flow channels and reducing hydraulic conduc-
tivity) may occur and can significantly influence permeability measurement.
Although such effects can occur and have been reported (Daniel, 1981;
Mitchell and Younger, 1967), studies have been conducted at elevated gradients
with no evidence of piping or particle migration (Anderson, 1981).
3-48
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Excessive hydraulic gradients can result in deviations from Darcy's
law, which is only valid for laminar flow conditions. Even under gradients
as high as 361, however, velocities low enough to assure a Reynolds number
within the laminar flow regime are assured due to the very small particle
diameters in fine-grained soils.
Zimmie et al. (1981) have recommended use of hydraulic gradients
between 5 and 20 for laboratory studies. Research performed at Louisiana
State University has lead to the conclusion that tests conducted under
hydraulic gradients as high as 100 are "acceptable for testing, reducing
testing times to realistic and practical duration" (Acar and Field, 1982).
Dunn and Mitchell (1984) reported that increasing the gradient in steps
from 20 to 200 caused an irreversible decrease in hydraulic conductivity.
They attributed most of the observed changes to particle migration due to
seepage forces. They recommend that test gradients be kept as low as
possible while still allowing the test to be completed in a reasonable
time.
3.8.3.3 Sample Saturation—
A soil sample, even when compacted, has some degree of porosity. The
pores are filled with either gas (generally air) or liquid. Because water
cannot flow through a gas bubble, entrapped air within the interconnected
pores that form flow channels for the permeant fluid causes a reduction in
flow and a corresponding apparent decrease in permeability. Soaking the
sample from the bottom with the top open to the atmosphere may not result
in complete saturation. Smith and Browning (1942) found that in 200 specimens
soaked from the bottom, the degree of saturation averaged 91 percent, with
the lowest value at 78 percent.
The extent of the error in permeability measurement attributable to
entrapped gas bubbles is not fully known, although decreases in permeabil-
ity by factors ranging from 2 to 5 have been reported (Johnson, 1954).
The use of backpressure in permeability testing is considered by some
researchers to be necessary for saturating a soil sample. Matyas (1967),
investigating the effect of saturation on permeability, applied a back-
pressure of 5 psi to "saturate a clay specimen." According to his calcula-
tions, this pressure was not sufficient to guarantee complete saturation.
After the saturation attempt at the low pressure, the specimen was subjected
to different hydraulic gradients, and discharge velocities were measured.
Similar samples were saturated at 24 psi and at 70 psi. The plot of hydraulic
gradient versus discharge velocity is shown in Figure 3-16.
Matyas1 data indicate that at 5 psi backpressure the velocity gradient
plot does not pass through the origin and is nonlinear. However, when the
backpressure was raised to either 24 psi or 70 psi, the velocity gradient
relationship was found to be linear and to pass through the origin. The
apparent nonlinear velocity gradient relationship was attributed to the
presence of air in the voids. There was no evidence of a threshold gradient
(i.e., a gradient below which flow would not occur).
3-49
-------
3 X 10
r 5
2X 10
r 5
E
u
> 1 X 10'5
Back-pressure
Back-pressure = 5 psi
24 psi
• Back-pressure = 70 psi
Q_
Hydraulic Gradient
After Matyas, 1967
Figure 3-16. Effect of backpressure on permeability to water, Sasumua ciay.
3-50
-------
Matyas (1967) did not address the difference in the velocity gradient
relationships at backpressures of 24 and 70 psi. One might conclude that
the application of higher backpressures caused some particle rearrangement
resulting in lower observed permeability values. The lowest practical
backpressure to obtain saturation appears desirable in order to minimize
these effects. The effects can also be minimized if the backpressures are
increased incrementally and sufficient time is allowed between successive
increases so that high seepage forces do not develop in unsaturated portions
of the specimen. Daniel et al. (1984) reports using backpressures of 40 to
60 psi applied in 10-psi increments. Each increment is held for a period
ranging from several minutes to several hours. Full backpressure is main-
tained for 1 to 5 days before the test is begun.
3.8.3.4 Permeant Characteristics—
Permeant fluids that are commonly used to determine baseline permeabil-
ity values include deionized water, tap water, groundwater (representative
of a specific site) and standard permeant solution, typically 0.01 N calcium
sulfate or calcium chloride. The standard solution is intended to simulate
the hard water frequently used in the field during installation and subse-
quent hydration of a clay barrier.
While some researchers claim that use of different fluids can influence
baseline permeabilities, others do not believe the effects are significant
(Olson and Daniel, 1981). Recently, the trend has been toward using the
standard calcium solutions for initial saturation and baseline permeability
determinations.
In quality control and in compatibility testing, factors that influence
the flow characteristics of a permeant fluid will alter the apparent soil
permeability to that fluid. Because viscosity and density are temperature-
dependent properties of a fluid, seasonal temperature changes in the field
could influence the range of permeabilities to be anticipated. Large
variations in temperature over a test sample are unlikely, however. Soil
permeabilities are sometimes expressed as intrinsic permeabilities (see
Equation 3.15 in Section 3.8.1) to account for differences in flow properties
between different permeant fluids, or at different temperatures. However,
the use of the permeability coefficient, K, is much more common and is used
throughout the remainder of this section.
The presence of certain chemicals in permeant fluids has been shown to
alter the permeability of clay soils (see Chapter 4). Shrinkage of clay
particles may result from changes in interlayer spacing due to interaction
of chemicals with the clay particle's double layer. Changes in adsorbed
cations or the presence of salts or acids in the permeant fluid can also
effect significant permeability increases. Such effects are the reason for
conducting compatibility tests. Effects of chemical permeants may be
evident immediately after the permeant penetrates the sample, or the effect
may not be seen until one or more pore volumes have passed through the
sample. These effects are discussed fully in Chapter 4.
3-51
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3.8.3.5 Test Duration--
A number of factors can cause changes in permeability with time. It
is essential in permeability testing that flow through the sample be contin-
ued until stable permeability measurements are obtained. In compatibility
testing, several pore volumes of fluid should be passed through the sample
to ensure that any tendency toward an increased or decreased permeability is
observed. A final permeability cannot be established if the permeability
changes appreciably with time.
Changes in pore pressure cause changes in sample volume. In a constant
head test, some of the initial measured in-flow into the sample compensates
for the volume change rather than being the result of steady-state seepage
(Olson and Daniel, 1979). Permeability tests should be run long enough to
ensure that steady-state values are obtained.
Some clays exhibit thixotropic behavior; their internal structure and
flow characteristics change with time. These changes can increase permea-
bility with time because of larger effective pore sizes in the clay.
Mitchell et al. (1965) found measured permeabilities to be as much as six
times greater for samples tested at 21 days compared to samples tested
immediately after compaction. Dunn and Mitchell (1984) reported similar
results. Boynton and Daniel (1985) did not observe thixotropic changes in
stored samples; but they attributed this to their having compacted them dry
of optimum, whereas Mitchell et al. (1965) and Dunn and Mitchell (1984)
compacted wet of optimum.
Although not usually a significant factor, microorganisms present in
test samples have been shown to influence permeability by clogging the flow
channels with organic matter or with gases produced by the microorganisms.
Allison (1947) reported long-term permeabilities of sterile soils to be 8
to 50 times lower than the values of nonsterile soils.
3.8.4 Laboratory Permeability Tests
Examples of permeability test devices and the methods used for testing
are described briefly below. The emphasis of the discussion is on features
that distinguish the various devices and their advantages and disadvantages.
3.8.4.1 Pressure Cell--
The accepted standard test for laboratory determination of saturated
permeability in the agricultural sciences (but not the geotechnical sciences)
is called the pressure cell test. In this procedure a soil sample, which
may be an undisturbed core, a sample compacted in a mold, or a volume of
soil, is placed in a metal pressure cell. After the soil is initially
saturated, it is connected to a standpipe. The permeant fluid is introduced
through the standpipe and forced through the pressure cell under a falling
head. The standpipe may or may not be connected to a source of air pressure
to superimpose a pressure head over the fluid column. The pressure cell
apparatus for a falling head test is illustrated in Figure 3-17. A constant
head test could also be conducted in the pressure cell by measuring the
volume of the effluent forced through the sample within a timed interval.
3-52
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To drain
Porous plate
Overflow (Fixed leveO
Endcap
'0" ring aeais
Porous plate
T
H.
T
H2
u
Standpipe
To water source
for filling atandplpe
2-way stopcock
After Klute, 1965
Figure 3-17. Apparatus for pressure ceil method.
3-53
-------
Saturation of the sample core is usually accomplished by submerging
one end of the core in a pan of water for 16 hours with the other end open
to the air. This procedure may not be adequate to saturate the sample
completely prior to the permeability test. Vacuum wetting and fluctuating
external gas pressure are alternate saturation techniques that may be used
with the pressure cell.
3.8.4.2 Compaction Permeameter—
The compaction permeameter (also called a fixed-wall permeameter) has
been developed for testing permeant fluids with a compacted soil layer.
One advantage over the pressure cell is that the sample is compacted directly
in the permeability test device. As a result, a better seal is obtained
between the sample and the walls of the test vessel. To ensure a good
sidewall seal, some workers apply a bentonite slurry to the inside of the
chamber before the sample is introduced. Silicon grease has also been
tried. As with the pressure cell, the compaction mold may be used in
either a falling head test or a constant head test. The compaction permeam-
eter may be modified so that elevated pressures can be superimposed to
reduce the testing time. A modified compaction permeameter is illustrated
in Figure 3-18. Not shown on the diagram is the source of compressed air
with a water trap, regulator, and pressure meter. Also not shown is a
fraction collector with automatic timer that handles the collection and
isolation of effluent samples.
The sample is first leveled and sprayed with standard permeant fluid
to saturate it in the compaction mold. The fluid chamber is slowly filled
so as not to disturb the sample surface. The filled permeameter is allowed
to stand for a period of time (typically overnight or longer) to allow
hydration and swelling of the clay. Pressure is applied to the sample only
after it has completely hydrated.
In compatibility testing, baseline permeability determinations are
obtained with the standard permeant fluid before the test permeant is
introduced.
A recent modification of the compaction permeameter device is the
double-ring permeameter. This apparatus has been developed for use in
compatibility tests involving waste leachates that may cause sample volume
changes during testing (Anderson, 1983). In the double-ring permeameter
test, a soil sample is compacted in a cylindrical mold that is mounted on a
base plate with a short cylindrical section mounted on its upper surface
(Figure 3-19). Separate outlets in the inner and outer rings serve to
separate sidewall leakage from flow through the central soil matrix. This
type of device may be especially useful for tests with soils that are
liable to undergo volume changes during permeability testing. Also, the
double-ring permeameter is appropriate for use in compatibility tests that
involve liquids that may cause shrinkage of the sample due to development
of soil structure.
Testing in the double-ring permeameter begins by passing sufficient
standard permeant fluid through the soil to obtain stable baseline perme-
3-54
-------
Pressure intake
Sealing gaskets
Pressure release
Top plate
Clamping stud
Outlet
Base plate
Porous stone insert
Source: Anderson and Brown, 1981
Figure 3-18. Modified compaction permeameter.
3-55
-------
en
CTl
Permeameter
Base Plate
Outlet for
Inner Ring
Outlet for
Outer Ring
Outer Ring
Source: Anderson, 1983
Figure 3-19. Detail of the base plate for a double-ring permeameter.
-------
abilities for both the inner and outer compartments. If the permeability
of the outer compartment is significantly higher than that of the inner
compartment, the soil core is discarded and a new core is compacted in the
mold. After stable baseline permeabilities are obtained, the standard
permeant is replaced by the test fluid, which is then passed through the
sample. The volume passed through each compartment is measured and reported
based on the pore volume of that compartment.
Tests in the double-ring permeameter are usually conducted with a
constant elev.ated hydraulic gradient. They also can be performed as a
constant head test without superimposed air pressure. As in other tests,
100-percent saturation of the sample may not be achieved unless backpressure
is used.
Permeability value, leachate volume, and time increment are recorded
for discrete volumes of permeant fluid passed through both chambers during
a compatibility test. Permeability measurements are then plotted versus
the total number of pore volumes passed through the sample. Data plotted
in this way indicate changes in permeability that might be expected for a
clay liner in service over a period of time that corresponds to the number
of pore volumes exchanged in the test.
Because the double-ring device has been introduced only recently, a
criterion has not been established to determine what constitutes a signifi-
cant difference between the permeability in the central compartment and
•that in the annular space. This criterion needs to be developed if the
device is to be widely used.
3.8.4.3 Triaxial Cells--
Samples prepared for triaxial testing consist of cylindrical columns
of compacted soil-encased laterally with a flexible membrane (often latex
rubber) and enclosed at the ends with porous stones. The enclosed soil
sample is placed in a water-filled cell that can be pressurized to provide
a confining pressure on the sides of the sample (Figure 3-20). The sample
to be tested may be prepared in a compaction mold and extruded for testing
in the triaxial cell. Samples are typically 2 to 3 inches in diameter.
Undisturbed Shelby tube samples may also be tested.
Permeability tests are performed by passing permeant liquids upwards
into the sample under pressure while maintaining a lower pressure at the
exit port on the top of the sample. A confining pressure somewhat greater
than the pressure under which the liquids enter the soil is imposed to
press the flexible membrane firmly against the soil sample, preventing flow
along the sidewall. The confining pressure on the soil sample should be
selected to simulate the lateral pressures a material will experience in
the clay liner.
Sample saturation is accomplished by forcing a standard permeant
liquid upward through the sample. Backpressure may be applied to hasten
the dissolution of trapped air bubbles or gases generated by reactions
between permeant liquid and the sample. The use of backpressure ensures
3-57
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Ceil Pressure
Source
(Compressed Air)
Check Valve
Aluminum Alloy (Top and Bottom)
Plexiglass Cell
Pressurized Ceil Fluid
Polyethylene Top Cap
Porous Stone and Filter Paper
Test Sample Encased in Membrane
Porous Stone and Filter Paper
Polyethylene Bottom Pedestal
Tap
Water
Atmospheric Pressure
or Differential Back
Pressure Source
Back Pressure Source
(Compressed Air, Nitrogen
or Argon)
Graduated Burette for
Permeant Effluent
Collection
3-Way Valve for Parmeant
Effluent Sampling
• Polyethylene Tubing
Permeant Reservoir
Source: Haji-Ojafarr and Wright, 1982
Figure 3-20. Schematic of a constant head triaxial cell permeameter.
3-58
-------
complete saturation of the sample, a factor that probably contributes to
the good reproducibility of triaxial tests. Pressure regulators and elec-
tronic pressure transducers are used to monitor sample stress conditions
and to assess the saturation state within the sample during testing.
Sufficient standard liquid is passed through the sample to establish a
stable baseline permeability. The test permeant fluid is then introduced.
The test may be conducted as a constant head or falling head test. Per-
meability value, leachate volume, and time increment are reported for each
volume of test fluid passed through the sample. These data are used to
plot permeability versus pore volumes of test fluid passed.
Excellent precision (±20 percent) based on four samples has been
reported for the apparatus shown in Figure 3-20 (Haji-Djafari and Wright,
1982).
Questions have been raised about whether triaxial cells are appropriate
for compatibility testing of permeant fluids that may cause the soil sample
to shrink (Chapter 4). Because of the confining cell pressure, the flexible
membrane will contract with the soil sample so that shrinkage cracks that
could occur in a field situation and that might appear in fixed-wall devices
as sidewall leaks would not be simulated in the triaxial cell. Not all
researchers agree on this issue since the effect has not been demonstrated
clearly in comparative tests. Boynton and Daniel (1984) have shown that
cracks in desiccated and rewet samples would only partially close unless
substantial effective stress were applied.
Although conventional triaxial cells are not designed to withstand
concentrated chemical permeants, several modifications are possible to
minimize the problem of chemical attack on the test device. Polyethylene,
nylon, or Teflon fittings may be used in place of the customary brass or
steel fittings. The use of colostomy bags (of the type used in surgical
applications) in place of the conventional latex membrane has also been
reported for use with wastes such as gasoline (J. Withiam, D'Appolonia Con-
sulting Engineers, Inc., Pittsburgh, PA, personal communication, 1983).
Samples may also be wrapped in thin Teflon tape to prevent contact between
the permeant and the latex membrane.
3.8.4.4 Consolidation Cells--
Consolidation cells (consolidometers) are commonly used in the field
of geotechnical engineering to determine the compressibility and rate of
settlement of soils. Consolidation occurs when water is squeezed out of
the soil and is therefore a function of permeability. A fixed-ring consol-
idation cell can be used to measure permeability (Figure 3-21).
The consolidation cell method is routinely used in testing permeability
for applications such as earth dams, retaining walls, and slurry trenches.
The method has not been widely used in the evaluation of chemical compat-
ibility with clay liner material.
3-59
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Vertical Stress
T Pressure
Permeant Fluid
,n,et
Effluent
Outlet-
Outlet
O
LT V»V:X;.»:~:::/A:-:v^-vv.::::^/£-V U
Porous Stone
Figure 3-21. Consolidation permeameter.
3-60
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3.8.5 Field Permeability Tests
The methods described below for measuring permeability in the field
are frequently modified or adapted for specific sites or for specific types
of investigations.
3.8.5.1 Double-Ring Infiltrometer/Permeameter--
In the double-ring infiltrometer technique (ASTM-D3385), one open
metal cylinder is placed inside another, and both are driven into the soil.
The cylinders are then partially filled with water that is maintained at a
constant level in both rings. The amount of water added to maintain the
constant water level in the inner ring is the measure of the volume of
water that permeates the soil.
The metal cylinders may range from a few centimeters to a meter in
diameter. A piece of folded burlap or other suitable material is used to
protect the soil surface from puddling when water is first added to the
cylinders. The double-ring infiltrometer is illustrated in Figure 3-22.
Information on the accuracy of the method for fine-textured soils is
not available. However, good reproducibility and precision are indicated
by results of using double-ring tests at a low-level radioactive waste
disposal site (Luxmoore et al., 1981).
Care must be exercised in the installation of the cylinders to prevent
shatter or compaction of soil adjacent to the border. Air that may become
trapped below the advancing water front is another factor that can signifi-
cantly affect results. In long-term tests, corrections for evaporation are
needed.
3.8.5.2 Drum Tests—
A practical test to estimate permeability in the field may be conducted
with two 55-gallon steel drums. The top and bottom are removed from one of
the drums, forming a large steel pipe. The top is removed from the second
drum, but the bottom is kept intact. The drum with both ends removed is
forced into the soil. The second drum is placed close to the hollow drum,
and both drums are filled to a specified level with water. The drum pene-
trating the soil should be filled with fresh water for at least 24 hours
before any measurements are taken to reach stable saturation conditions.
After the test begins, measurements are recorded daily for 1 week or
longer if necessary. The drums are refilled every day to maintain the
water level close to the top. The amount of water that is lost from the
intact drum is a measure of the loss due to evaporation. The additional
water lost through the drum that penetrates the soil is the seepage volume.
The permeability may then be calculated based on the seepage volume and the
head used for the test (approximately 4 feet).
Compatibility testing can be conducted with the drum test by replacing
the water with the permeant fluid to be tested. Stable permeability measure-
ments with water should be obtained before the test fluid is introduced.
3-61
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CO
I
01
ro
Outer ring water level
Soil surface
Scale
Water level
Inner ring
Outer ring
Burlap (to prevent puddling)
Source: EPA/Army Corps of Engineers/USDA, 1977
Figure 3-22. Apparatus set-up for double-ring infiltrometer.
-------
The procedure described above is based on recommendations of the
Federal Bentonite Company for testing a bentonite seal designed for lagoons
or landfills. The specifications emphasize that the drum tests "are not of
sufficient accuracy to allow for precise permeability estimates" (Federal
Bentonite, 1982).
3.8.5.3 Modified Air-Entry Permeameter--
The air-entry permeameter technique tests the permeability of a 25-cm-
diameter cylindrical unit of undisturbed soil that is isolated by an infil-
tration cylinder driven into the soil. A head of water is applied and the
infiltration rate is measured until the wetting front is close to the
bottom of the cylinder. This is determined with an implanted tensiometer.
The basic equipment required and the experimental setup for air-entry
permeameter tests are shown in Figure 3-23 (U.S. EPA, 1984).
The saturated permeability is calculated as a function of the air
entry value of soil. Equations (3.17) and (3.18) are used:
"a ' '.in + G * L • <3'17>
where
P = air entry value of soil, expressed as pressure head in cm water
a at point of air entry
P . = minimum pressure head, cm water as determined by the maximum
m reading on the vacuum gauge
G = height of gauge above soil surface, cm
L = depth of wet front (depth of tensiometer), cm.
Saturated permeability is then calculated from:
K=2df L R? /CHt + L
where
dH
dt
= rate of fall of water level in reservoir just before closing
supply valve, cm/s
H. = height above soil surface of water level in reservoir at time
supply valve is closed, cm
R = radius of reservoir, cm
r '
R = radius of cylinder, cm.
3-63
-------
Soii surface
Reservoir
Vacuum guage
Supply valve
Tensiometer
Air escape valve
C-clamp
Gasket
Cylinder wall
Wetting front
After LLS. EPA, 1984
figure 3-23. Modified air-entry permeameter.
3-64
-------
Topp and Bins (1976) found that the air-entry permeameter gave reproduc-
ible values of permeability at various depths in a number of different
soils. They also found that results were consistent with values obtained
from determinations made on laboratory cores. Although the laboratory core
permeability was generally lower than the permeability determined by the
air-entry permeameter, this was probably due to lack of worm holes or
cracks in the laboratory samples. Aldabagh and Beer (1971) found the
method to be consistent and reasonable with variability substantially less
than the natural variation of soil.
As with other field methods, care must be exercised in the installation
of the cylinder to prevent shatter or compaction of soil adjacent to the
cylinder. The method is not appropriate for use on initially wet or nearly
saturated soils because the induced wetting from the addition of water
would not be well defined.
An advantage of the modified air-entry permeameter method over other
methods is the short time period (approximately 1 hour) that is required to
conduct the test. Although useful for quality control, the method is
probably not applicable to compatibility testing.
3.9 REFERENCES
Acar, Y. B., and S. D. Field. 1982. Organic Leachate Effects to Hydraulic
Conductivity in Fine-Grained Soil, Volume 1. Report No. GE-82/01,
Louisiana State University.
Aldabagh, A. S. Y., and C. E. Beer. 1971. Field Measurement of Hydraulic
Conductivity Above a Water Table with an Air-Entry Permeameter.
Transactions of the American Society of Agricultural Engineers.
14:29-31.
Allison, L. E. 1947. Effect of Micro-organisms on Permeability of Soil
Under Prolonged Submergence. Soil Science. 63:439-450.
Anderson, J. L., and J. Bouma. 1973. Relationships Between Saturated
Hydraulic Conductivity and Morphometric Data of an Argil lie Horizon.
Soil Science Society of America Proceedings. 37:408-413.
Anderson, D. C. and K. W. Brown. 1981. Organic Leachate Effects on the
Permeability of Clay Liners, pp. 119-130. In D. W. Shultz (ed.) Land
Disposal: Hazardous Waste. EPA-600/9-81-002b. National Technical
Information Service, Springfield, Virginia.
Anderson, D. C. 1981. Organic Leachate Effects on the Permeability of
Clay Soils. M.S. Thesis, Soil and Crop Sciences Department, Texas
A & M University, College Station, Texas.
Andrews, R. E. , J. J. Gawarkiewicz, and H. F. Winterkorn. 1967. Comparison
of the interaction of 3 clay minerals with water, dimethyl sulfoxide,
and dimethyl formamide. Highway Research Record. No. 209. pp. 66-78.
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ASTM. 1983. Annual Book of ASTM Standards, Part 19, Soil and Rock; Building
Stones. American Society for Testing and Materials, Philadelphia,
Pennsylvania.
Bouman, J., and L. W. Dekker. 1981. A Method of Measuring the Vertical
and Horizontal Saturated Hydraulic Conductivity of Clay Soils with
Macropores. Soil Science Society of America Journal. 45:662-663.
Bowles, J. E. 1979. Physical and Geotechnical Properties of Soils.
McGraw-Hill Book Company, New York. 478 pp.
Boynton, S. S., and D. E. Daniel. 1985. Hydraulic Conductivity Tests on
Compacted Clay. J. of Geotechnical Engineering. 111(4):465-478.
Brown, K. W., J. Green, and J. Thomas. 1982. The Influence of Selected
Organic Liquids on the Permeability of Clay Liners (draft). Texas
Agricultural Experiment Station, Soil and Crop Science Department,
College Station, Texas.
Daniel, D. E. 1981. Problems in Predicting the Permeability of Compacted
Clay Liners. In: Symposium on Uranium Mill Tailings Management, Fort
Collins, Colorado, pp. 665-675.
Daniel, D. E., S. J. Trantwein, S. S. Boynton, and D. E. Foreman. 1984.
Permeability Testing with Flexible Wall Permeameters. .Geotechnical
Testing Journal. 7(3):113-122.
Dunn, R. J., and J. K. Mitchell. 1984. Fluid Conductivity Testing of Fine
Grained Soils. J. of Geotechnical Engineering. 110(11):1648-1665.
Federal Bentonite, Division of Aurora Industries. 1983. Suggested Standard
Guidelines Technical Specifications Landfills/Lagoons (Obtained from
Federal Bentonite 1983). Montgomery, Illinois.
Haji-Djafari, S., and J. C. Wright. 1982. Determining the Long-Term
Effects of Interactions Between Waste Permeants and Porous Media.
Presented at American Society for Testing and Materials Second Symposium
on Testing of Hazardous and Industrial Solid Wastes. 26 p.
Hansbro, S. 1960. Consolidation of Clay with Special Reference to the
Influence of Verticle Sands Drains. In: Proceedings 18, Swedish
Geotechnical Institute, Stockholm, Sweden.
Holtz, R. D., and W. D. Kovacs. 1981. An Introduction to Geotechnical
Engineering. Prentice-Hall, Englewood Cliffs, New Jersey. 733 pp.
Johnson, A. I. 1954. Symposium on Soil Permeability. ASTM STP 163,
American Society for Testing and Materials, Philadelphia, Pennsylvania.
pp. 98-114.
3-66
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Klute, A. 1965. Laboratory Measurement of Hydraulic Conductivity of
Saturated Soil. In: Methods of Soil Analysis, C. A. Black, Ed.
Amer. Soc. of Agronomy, Madison, Wisconsin, pp. 210-220.
Lambe, T. W. 1955. The Permeability of Fine-Grained Soils. ASTM 163,
American Society for Testing and Materials, Philadelphia, Pennsylvania.
pp. 55-67.
Lambe, T. W., and R. V. Whitman. 1979. Soil Mechanics, SI Version.
John Wiley and Sons, Inc., New York. 553 pp.
Lee, D. Y. and R. J. Suedkamp. 1972. Characteristics of irregularly
shaped compaction curves of soils. Highway Research Record, No. 381,
p. 1-9.
Luxmoore, R. J., B. P. Spalding, and I. M. Munro. 1981. Areal Variation
and Chemical Modification of Weathered Shale Infiltration Characteristics.
Soil Science Society of America Journal. 45:687-691.
Mason, D. D., J. F. Lutz, and R. G. Peterson. 1957. Hydraulic Conductivity
as Related to Certain Soil Properties in a Number of Great Soil Groups—
Sampling Errors Involved. Soil Science Society of America Proceedings.
21:554-561.
Matyas, E. L. 1967. Air and Water Permeab.ility of Compacted Soils:
Permeability and Capillarity of Soils. Standard Technical Publication
417, ASTM, Philadelphia, Pennsylvania, pp. 160-175.
Mitchell, J. K. 1976. Fundamentals of Soil Behavior. John Wiley and
Sons, New York. 422 pp.
Mitchell, J. K., and J. S. Younger. 1967. Abnormalities in Hydraulic Flow
through Fine-Grained Soil. ASTM STP 417. pp. 106-139.
Mitchell, J. K., D. R. Hooper, and R. G. Campanella. 1965. Permeability
of Compacted Clay. Journal of the Soil Mechanics and Foundation
Division, ASCE. 91:41-66.
Oakes, D. J. 1960. Solids Concentration on Effects in Bentonite Drilling
Fluids. Clay and Clay Minerals. 8:252-273.
Olson, R. E., and D. E. Daniel. 1979. Field and Laboratory Measurements
of the Permeability of Saturated and Partially Saturated Fine-Grained
Soils. In: ASTM Symposium on Permeability and Groundwater Contaminant
Transport, Philadelphia, Pennsylvania. 67 pp.
Proctor, R. R. 1933. Fundamental Principles of Soil Compaction. Engineer-
ing News-Record. 111(9):245-258.
Sangrey, D. A., D. K. Noonan, and G. S. Webb. 1976. Variation in Atterberg
Limits of Soil Due to Hydration History and Specimen Preparation.
Soil Specimen Preparation for Laboratory Testing, ASTM STP 599, American
Society for Testing and Materials, pp. 158-168.
3-67
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Smith, R. M., and D. R. Browning. 1942. Persistent Water-Unsaturation of
Natural Soil in Relation to Various Soil and Plant Factors. Soil
Science Society of America Proceedings. 7:114-119.
Sowers, G. B., and G. F. Sowers. 1970. Introductory Soil Mechanics and
Foundations. The Macmillan Company, New York. 556 pp.
Spigolon and Kelley. 1984. Geotechnical Assurance of Construction of
Disposal Facilities. EPA 600/2-84-040, U.S. Environmental Protection
Agency, Cincinnati, Ohio.
Topp, G. C., and M. R. Binns. 1976. Field Measurement of Hydraulic Con-
ductivity with a Modified Air-Entry Permeameter. Canadian Journal
Soil Science. 56:139-147.
Truesdale, R. L., L. Goldman, J. Peirce, B. Cox, K. Witter, and T. Peel.
1985. Laboratory Methods for Testing the Permeability and Chemical
Compatibility of Inorganic Liner Material (in preparation).
U.S. Department of the Army. 1970. Laboratory Soils Testing. EM 1110-2-1906,
Office of the Chief of Engineers, Washington, D.C.
U.S. Department of the Army. 1953. The Unified Soil Classification System.
Corps of Engineers, Technical Memorandum No. 3-357, Volumes 1 and 3.
U.S. Department of the Army. 1977. Construction Control for Earth &
Rock-Fill Dams. EM 1110-2-1911, Washington, D.C.
U.S. Department of Interior. 1974. Earth Manual. U.S. Government Printing
Office, Washington, D.C. 810 pp.
U.S. Environmental Protection Agency. 1984. Soil Properties, Classification,
and Hydraulic Conductivity Testing (Draft). SW-925, Office of Solid
Waste and Emergency Response, Washington, D.C. 167 pp.
Winterkorn, H. F. , and H. Y. Fang. 1975. Foundation Engineering Handbook.
Van Nostrand Reinhold, New York.
Withiam, J. 1983. D'Appolonia Consulting Engineers, Inc. Personal communi-
cation.
Yong, R. N. , and B. P. Warkentin. 1975. Soil Properties and Behavior.
Elsever Scientific Publishing Company, New York. 449 pp.
Zimmie, T. F. , J. S. Doynow, and J. T. Warden. 1981. Permeability
Testing of Soils for Hazardous Waste Disposal Sites. In: Proceedings
of the Tenth International Conference on Soil Mechanics and Foundation
Engineering, Vol. 2, Stockholm, Sweden, pp. 403-406.
3-68
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CHAPTER 4
CLAY-CHEMICAL INTERACTIONS AND SOIL PERMEABILITY
It has been known for many years that the permeability of clay soils
may be drastically altered by chemicals present in the permeating liquid.
Apart from the many recent studies stemming from concern over the effects
of hazardous waste and waste leachates on clay liners, much research has
been carried out over the last several decades to determine the effects of
various chemicals on agricultural soils or on geological formations impor-
tant for oil production. The potential effects of certain organic fluids
on clay permeability were recognized as early as 1942, when Macey's experi-
ments with fireclay showed that the rates of flow for certain organic
liquids through clay were "of an enormously higher order than for water"
(Macey, 1942). Since Macey's experiments, many researchers have investi-
gated the effects of organic and inorganic fluids on clays in an effort to
elucidate the causes of the observed changes in permeability.
The current state of the knowledge in this area is complicated by the
dilemma of how to measure the permeability changes that appear to be caused
by clay-chemical interactions. The question of what types of permeameters
give valid measures of clay-chemical compatibility remains an important
issue. Because permeability studies with different fluids have been carried
out with different test protocols, different test devices, and different
clays, quantitative data comparisons cannot be made except in a few of the
more recent studies. Much can be learned from a review of the research
that has been carried out, however, and qualitative statements can be made
regarding the behavior of certain clays in the presence of many types of
fluids. Unifying theories of soil physics that explain the reported find-
ings have been advanced by several researchers. Such theories are useful
for predicting clay-chemical incompatibilities that could lead to perform-
ance failures in clay-lined hazardous waste disposal facilities.
This chapter presents the experimental findings that pertain to the
effects of chemicals on clay barrier permeability as well as the theories
and mechanisms proposed to explain the observed effects. Section 4.1
defines the terms most important in clay-chemical compatibility testing—
permeability (or, if the permeating liquid is water, hydraulic conductivity)
and intrinsic permeability. Section 4.2 is a discussion of the clay-chemical
interactions that influence soil permeability. A summary of the relevant
permeability studies is presented in Section 4.3. Approaches that have
been used in studies to determine clay-chemical compatibility and problems
associated with different test methods are addressed in Section 4.4.
Section 4.5 reviews in more detail permeability testing efforts that have
been carried out to measure clay-chemical interactions.
4-1
-------
4.1 PARAMETERS DETERMINED IN PERMEABILITY TESTING FOR COMPATIBILITY
When results of clay-chemical compatibility tests are compared, it is
important to understand the parameters that are being measured and calcu-
lated. The parameter usually determined in compatibility tests is permea-
bility, K, which is defined by Darcy's Law as expressed in Equation (4.1):
K = Q/Ai (4.1)
where
Q = volumetric flow rate (L3/t)
A = cross-sectional area of flow (L2)
i = hydraulic gradient (dimensionless).
K has units of length per unit time (e.g., cm/s). The density and viscosity
of the permeating liquid as well as the pore size distribution within the
soil matrix will influence the value of K. Hydraulic conductivity refers
to the value of K when the permeating fluid is water. Darcy's Law is limited
to saturated soil conditions and to laminar flow conditions.
In order to separate the effects of the liquid properties (viscosity
and density) from those of the medium (pore size distribution), a different
parameter, the intrinsic permeability, should be used. Intrinsic permeabil-
ity, usually referred to as k, is a property of the medium that is dependent
on the shape, size, and continuity of the pore spaces. Intrinsic permeabil-
ity is "a measure of the relative ease with which a porous medium can
transmit a liquid under a potential gradient. It is a property of the
medium alone and is independent of the nature of the liquid and of the
force field causing movement" (Lohman, 1972).
Intrinsic permeability, k, has units of length squared (e.g., cm2) and
is related to permeability, K, by Equation (4.2):
K = k£g or k= K pg ' (4'2)
where
p = density of the fluid (M/L3)
jj = dynamic viscosity of the fluid (M/Lt)
g = acceleration due to gravity (L/t2).
In clay-chemical compatibility testing, the value of K for a clay soil
permeated by a certain chemical is determined from measurements of the fluid
inflow or outflow. A change or lack of change in the value of K (when
compared to K for water or other baseline fluid) may be due to a combination
of two factors—
4-2
-------
Difference in the permeant fluid viscosity and density
(compared to baseline permeant fluid)
Change in porous medium characteristics as a result of clay-
chemical interactions.
In order to separate these effects, it is usually necessary to report
the results of the tests in terms of intrinsic permeability (k) both for
the tests with the baseline permeant fluid and for the tests with the
chemical permeant fluid in question. In practice, most researchers report
and discuss their test results in terms of permeability (K) rather than
intrinsic permeability (k). Provided the density and viscosity of the test
fluid (at the test temperature) are known, one could calculate k to corres-
pond to each K value reported. In general, only substantial permeability
changes are meaningful in clay-chemical compatibility testing. When large
changes in permeability are measured during the course of a test, the
clay-chemical interaction is apparent regardless of whether the k values
are computed and plotted.
4.2 CLAY-CHEMICAL INTERACTIONS THAT INFLUENCE PERMEABILITY
Mechanisms whereby the chemical nature of a permeant fluid may alter
clay soil permeability and theories to predict clay-chemical interactions
have been described by several researchers, among them Mitchell (1976),
Brown and Anderson (1980), Acar and Field (1982), Evans, Chaney, and Fang
(1981), Anderson and Jones (1983), Daniel (1982, 1983, 1984), Dunn (1983),
Monserrate (1982), Peirce (1984), and Griffin and Roy (1985). In addition
to laboratory and field permeability tests, methods such as X-ray diffraction,
shrink-swell measurements, settling tests, and other techniques have been
used to investigate the clay-chemical interactions that influence permeability.
Changes in the permeability of clay soils due to chemical interactions
may result from—
Alterations in soil fabric stemming from chemical influences
on the diffuse double layer surrounding clay particles
Dissolution of soil constituents by strong acids or bases
Precipitation of solids in soil pores
Soil pore blockage due to the growth of microorganisms.
The permeability of a soil may also be affected by the pore fluid
velocity; high velocities can displace small particles in the soil matrix.
The fluid flow velocity can also influence chemical interactions that
depend on the time of contact between the soil and some chemical component
of the permeating fluid. Thus, permeability and fluid flow velocity are
interrelated characteristics of a soil-permeant fluid system.
4-3
-------
4.2.1 Soil Fabric and Permeability
The permeability of any soil depends upon the geometric characteristics
of the area available for fluid flow. Influencing factors are the size,
shape, tortuosity, and degree of interconnection between the pore spaces.
The geometric arrangement of the soil particles will determine these pore
space characteristics.
The term "fabric" refers to the arrangement of particles, particle
groups, and pore spaces in a soil. Modes of particle association orienta-
tion in clay suspensions were described by van Olphen (1963) as "dispersed,"
"aggregated," "flocculated," or "deflocculated" (see discussion in Sec-
tion 2). Particle associations corresponding to these descriptors are
illustrated in Figure 2-10. Dispersion and flocculation represent the
extremes in soil fabric classification, and a chemical present in the
permeating liquid may influence the permeability of a clay soil by altering
the soil fabric toward either of these extremes. Figure 4-1 illustrates
how a change in pore diameter can drastically alter permeability.
A dispersed deflocculated soil fabric tends to have a large number of
very small pore spaces; with flocculation, relatively large-sized interpar-
ticle and interaggregate pores are formed. These large diameter pores can
cause drastic changes in the permeability of the clay soil since the flow
rate is proportional to the square of the diameter of the flow channel.
The pulling together of groups of clay particles into aggregates
results when cohesive forces between individual clay particles outweigh the
repulsive forces. The forces of attraction result from London-van der
Waals forces and do not vary significantly with the chemistry of the pore
water. Attractive forces are strongest close to the clay surface and
diminish rapidly with increasing distance from the surface.
The forces of repulsion between adjacent clay surfaces, however, are
primarily electrostatic and are influenced by the clay surface charge and
the chemistry of liquid adjacent to the clay surfaces. Interparticle
spacing is a function of the thickness of the diffuse double-layer cationic
clouds that form the Gouy layer of the diffuse double layer (Anderson and
Jones, 1983). (See also Section 2.3 and discussion below). In theory, the
direction of change in permeability associated with varying pore fluid
chemistry could be predicted if the variables that affect the thickness of
the diffuse double layer are known (Acar and Seals, 1984). However, the
heterogeneous mineral composition and wide particle-size distribution
common in many soils along with the complicated nature of chemical-soil
interactions make this difficult to accomplish in practice.
4.2.1.1 Diffuse Double-Layer Theory—
The theory of the diffuse double layer (also called the electrical
double layer) has evolved from the studies of colloid chemistry directed at
the description of surface interactions of small particles in a water-
electrolyte system. The description that follows is excerpted from Mitchell
(1976, pp. 112-113).
4-4
-------
Source: Anderson, 1981
Figure 4-1. Change in a pore diameter (400%) corresponding
to a permeability increase of 25,600%.
4-5
-------
In a dry clay, adsorbed cations are tightly held by the negatively
charged clay surfaces. Cations in excess of those needed to
neutralize the electronegativity of the clay particles and their
associated anions are present as salt precipitates. When the
clay is placed in water the precipitated salts go into solution.
Because the adsorbed cations are responsible for a much higher
concentration near the surfaces of particles, there is a tendency
for them to diffuse away in order to equalize concentrations
throughout. Their freedom to do so, however, is restricted by
the negative electric field originating in the particle surfaces
. . . The negative surface and the distributed charge in the
adjacent phase are together termed the DIFFUSE DOUBLE LAYER
The distribution of cations adjacent to a negatively charged clay
particle in suspension (the diffuse double layer) is depicted in Figure 4-2
(see also Figure 2-6). The distribution for a particular soil-water-
electrolyte system results from a balance between the tendency of the
cations to escape due to diffusion and the opposing electrostatic attrac-
tion of the clay surface for the cations. The Gouy-Chapman theory of the
diffuse double layer (Gouy, 1910; Chapman, 1913) is widely recognized, and
mathematical descriptions of the diffuse double layer have been formulated
for both planar and spherical surfaces.
Despite the fact that the Gouy-Chapman theory does not account for all
the factors that can influence the behavior of the soil-water-electrolyte
system, it has been useful as a generalized model for explaining clay-
chemical interactions that affect permeability. Since the thickness of the
double layer influences the level of interlayer and interparticle repulsion,
system variables that influence the double-layer thickness consequently
affect the physical interactions among clay particles.
The nature and thickness of the double layers, and thus the repulsive
forces, depend upon characteristics of clay particles and the pore fluid.
In general, the tendency for particles in suspension to flocculate decreases
with increased thickness of the double layer. An approximate quantitative
indication of the relative influences of several factors on the thickness
of the double layer is given by Equation (4.3) below (see Mitchell, 1976,
p. 118):
h
H = Dk
M
where
H = thickness of the double layer
D = dielectric constant of the medium
k = Boltzman constant (1.38 x 10"16 erg/K)
T = temperature in degrees Kelvin
4-6
-------
© ©
-
® ffi ^
Distance
Figure 4-2. Distribution of ions adjacent to a clay surface according
to the concept of the diffuse double layer.
4-7
-------
n0 = electrolyte concentration
e = unit electric charge, 16 x 10 6 coulomb
v = valence of cations in the pore fluid.
The thickness varies inversely with the valence of the cations present
and inversely with the square root of the concentration; the thickness
increases with the square root of the dielectric constant and the tempera-
ture, other factors remaining constant. Based on the Gouy-Chapman model,
Lambe (1958) noted that the following variables in the soil-water system
affect double-layer thickness and colloidal stability: dielectric constant,
electrolyte concentration, temperature, ionic valence, size of hydrated
ions present, pH, and anion adsorption.
It has been found that attractive forces exceed repulsive forces when
interlayer spacing is about 0.5 nm (Yong and Warkentin, 1975). Thus, a
sufficient reduction in repulsive forces (i.e., reduced double-layer thick-
ness) could "transform a massive, structureless, and slowly permeable clay
barrier into an aggregated, structured, and more permeable barrier"
(Anderson and Jones, 1983).
4.2.1.1.1 Dielectric Constant—The dielectric constant is a measure
of the ease with which molecules can be polarized and oriented in an electric
field (Mitchell, 1976, p. 113). It represents the ability of a fluid to
transmit a charge. Quantitatively, the static dielectric constant is
defined by D in Coulomb's equation (Equation 4.4), where F is the force of
electrostatic attraction between two charges, Q and Q1, separated by a
distance d.
F=Dd*' (4'4)
As the dielectric constant decreases, the fluid film surrounding the
clay that contains positive cations must be thinner for the negative surface
charge on the clay to be neutralized. For a constant surface charge, the
surface potential function will increase as the dielectric constant de-
creases. Since most organic liquids have dielectric constants substantially
lower than water, it is to be expected that the double-layer thickness
would be reduced (with an associated tendency toward flocculation) when an
organic liquid rather than water surrounds the clay particle. Due to the
effects of dielectric constant on the electrical double layer, there is a
relationship between the dielectric constant of an adsorbed fluid and
interlayer spacing exhibited by clay particles. In general, interlayer
spacing decreases with a decrease in the dielectric constant, although this
apparent relationship can be complicated by the other factors that affect
interlayer spacing.
4.2.1.1.2 Electrolyte Concentration—As the electrolyte concentration
in the pore fluid increases, the thickness of the double layer tends to
decrease, promoting flocculation. An analysis of the effect of electrolyte
concentration on the double layer indicates that an increase in concentration
4-8
-------
reduces the surface potential for the condition of constant surface charge.
Also, the decay of potential with distance is more rapid with increased
electrolyte concentration. In essence, the double layer is suppressed by
an increase in electrolyte concentration. Interparticle interactions
extend to much greater particle spacings for a low electrolyte concentration
(e.g., 0.83 x i(f4 M NaCl) than a higher concentration (e.g., 0.83 x lo"2 M
NaCl) (Mitchell, 1976, p. 122). The effect of salt concentration on the
behavior of clays has been discussed by Anderson (1981):
As salt concentration in interparticle spaces increases, the
cationic cloud is compressed closer to the clay surface, resulting
in a decrease in electrostatic repulsion and interlayer spacing.
Weiss (1958) noted the direct relationship between salt concentra-
tion and interparticle spacing in smectitic clay minerals in a
study using distilled water and several concentrations of sodium
chloride in water. Both distilled water and 0.01 N NaCl gave
infinite interlayer spacing values (the clay was completely
dispersed), while 1.0, 3.0, and 5.0 N NaCl gave interlayer
spacings of 0.93, 0.61, and 0.58 nm, respectively.
4.2.1.1.3 Temperature—An increase in temperature causes an increase
in double-layer thickness with a corresponding tendency toward dispersion.
However, the value of the dielectric constant for various fluids is also
affected by temperature, generally decreasing with increased temperature.
For water, the value of the product DT (Equation 4.3) is reasonably con-
stant, and temperature effects tend to cancel out..
4.2.1.1.4 Ionic Valence—The cation valence affects both the surface
potential and the thickness of the double layer. For solutions of the same
molarity and a constant surface charge, increasing the cation valence will
cause a decrease in the thickness of the double layer and a tendency toward
flocculation. It is also shown that an increase in valence will suppress
the midplane concentrations between parallel plates, leading to a decrease
in interplate repulsion (Mitchell, 1976, p. 122).
4.2.1.1.5 Size of Hydrated Ions—The smaller the size of the hydrated
ion, the closer it can approach the surface of the clay particle (Lambe,
1958). Thus, for a given cation valence, the thickness of the double layer
will tend to decrease with decreasing hydrated radii of double-layer cations.
4.2.1.1.6 p_H--Changes in pH can affect the thickness of the double
layer in several ways. The electrolyte concentration as well as the net
negative charge on the clay particle are influenced by the solution pH.
The formation of stable suspensions or dispersions of clay particles often
require high pH conditions. There are two ways in which pH can change the
surface charge that results from chemical reaction at the surface of the
clay particles. First, a high pH can cause dissociation of hydroxyl
groups at the edge of clay particles, increasing the net charge and expand-
ing the double layer. The dissociation reaction is given below:
H20
SiOH > SiO + H . (4.5)
4-9
-------
The higher the pH, the greater the tendency for the H to dissociate and
the greater the effective negative charge. Low pH discourages this dissoci-
ation, lowering the surface charge, reducing the thickness of the double
layer, and promoting flocculation (Evans et al., 1981; Mitchell, 1976,
p. 127).
Second, pH affects alumina exposed at the edges of clay particles.
Alumina ionizes positively at low pH and negatively at high pH. Thus, in
an acid environment, positive double layers may develop at the edges of
clay particles with H serving as the potential determining ion (Mitchell,
1976, p. 126).
Changes in pH do not significantly affect surface charge resulting
from isomorphous substitution of the crystal lattice of the clay mineral.
Thus, clays with most of their surface charge attributed to isomorphous
substitution (e.g., smectites and illites) are less affected by changes in
pH than the kaolinite minerals, which have most of their surface charge
resulting from surface chemical reactions (see Section 2.3).
4.2.1.1.7 Anion Adsorption—Adsorption of anions (e.g., Cl , P043,
and certain surfactants) by the clay particle can increase the net negative
charge and increase the double-layer thickness. Dispersion can occur as a
result.
4.2.1.2 Displacement of Water—
If adsorbed water within clay particles is displaced by a fluid with a
different dielectric constant or electrolyte concentration, the result may
be a change in the inter!ayer spaces of the clay. Such changes can cause
the clays to shrink and crack. This can result in the formation of large
conducting channels through the soil along with drastic increases in the
permeability. Desiccation of clays by certain organic fluids has been
reported by Anderson (1981) and others.
4.2.1.3 Cation Exchange--
Cations adsorbed in the diffuse double layer are exchangeable with
other cations in solution. In general, the affinity of a cation for a clay
increases with cation valence and decreases with increasing ionic radius
within an element group. (See Section 2.2.)
Cation exchange will usually result in a change in double layer thick-
ness. The thickness of the double layer decreases with+|ncreasing cation
valence for montmorillonite; replacement of Na with Ca results in a
reduction of inter!ayer basal spacing from over 4 nm to about 1.9 nm. For
montmorillonite, only two layers of water are incorporated between layers
when calcium is the adsorbed cation; with sodium, the number of water
layers between layers is practically unlimited. Thus, cation exchange can
cause double-layer collapse, desiccation and shrinkage, flocculation, and
increased permeability for certain clays.
Theng (1974) has summarized the importance of cation exchange in
clay-organic complexes:
4-10
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. . . Since uncharged polar organic molecules are adsorbed essen-
tially by replacement of the interlayer water, the behavior of
such molecules is likewise strongly influenced by the exchangeable
cation. Evidence is accumulating to show that, at least at low
water contents, cation-dipole interactions are of paramount
importance in their effect on the adsorption of polar organic
species by clay materials.
4.2.2 Dissolution by Strong Acids or Bases
Both organic and inorganic acids react with and dissolve aluminum,
iron, and silica in the crystal lattice of clay minerals. Strong bases can
have a similar effect. This dissolution can result in a release of mineral
fragments that may migrate from their original position and leave enlarged
pore spaces for conducting the permeant fluid through the clay. Anderson
and Jones (1983) have pointed out that "whether the permeability of the
clay barrier increases or decreases will depend on the fate of the migrating
particles." The increase in conducting pore size may give rise to an
increased permeability if the particles migrate through the clay mass. If
the particles lodge in pore constrictions, clogging the conducting pore
spaces, a decrease in permeability may result (Anderson and Jones, 1983).
Data originally reported by Pask and Davies (1945) show that sulfuric
acid dissolves 3, 11, and 89 percent of the aluminum present in kaolinite,
illite, and smectite. Other studies also suggest that kaolinite is less
soluble than smectite in strong acids (Grim, 1953).
4.2.3 Precipitation of Solids
The precipitation of solids in the soil-water system is controlled by
ionic concentration and equilibrium solubility. If the concentration of
certain ions exceeds the solubility limits, minerals such as gypsum (CaS04
2H20) or jarosite (KFe3(S04)2(OH)6) may precipitate from solution (Shepard,
1981; Dunn, 1983). Formation of such precipitates can clog pore spaces in
the soil matrix.
4.2.4 Effect of Microorganisms
The presence of microorganims can affect the mobility of fluids through
the soil. Fuller (1974) classified activity of microorganisms in terms of
three classes of chemical reactions: (1) oxidation and reduction, (2) miner-
alization and immobilization, and (3) reactions with organic constituents.
In certain circumstances, the attenuation of contaminants in soils is
drastically affected by microorganisms. Processes that can contribute to
attenuation of contaminants by microorganisms include the following (Fuller,
1974; Dunn, 1983):
Degradation of carbonaceous wastes
Transformation of cyanide to mineral nitrogen and denitrifi-
cation to nitrogen gas
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Oxidation-reduction reactions with metal ions
Reduction of sulfate to sulfide
Production of carbon dioxide from organic molecules
Production of simple organic acids
Production of humic and fumaric acids that can react with
trace contaminants
Production of organic species on which trace contaminants
can be adsorbed.
Apart from the benefits of attenuation, the physical presence of the
microorganisms as well as the gases produced as a result of the reactions
listed above can cause blockage in the conducting pore spaces within soils,
reducing the area for flow and decreasing permeability. This effect has
been noted in permeability tests, particularly when the permeant fluid is
conducive to the growth of microorganisms.
4.3 MEASURING CLAY-CHEMICAL COMPATIBILITY THROUGH PERMEABILITY TESTING
Permeability is a highly variable engineering property of soils, and
slight changes in the measurement technique or test equipment can cause
order of magnitude changes in the values determined (Mitchell et a!.,
1965). Because one is always dealing with orders of magnitude in permeabil-
ity testing, it is unrealistic to expect test results to agree within less
than several hundred percent (Zimmie, 1981). No widely accepted method
exists for measuring clay-chemical compatibility through permeability
testing. Thus, a variety of equipment and techniques have been employed in
this area of research. Some of the variables in test methods are described
in this section, and advantages and disadvantages are highlighted.
4.3.1 Measurement Devices
The permeability of clay soils to various liquids is usually determined
in either constant head or falling head tests in fixed-wall, flexible-wall,
or consolidation permeameters. Each category of test device can have many
variations. Fixed-wall permeameters that have been used in clay-chemical
compatibility testing include stainless steel permeameters, plexiglass
permeameters, thick-walled pyrex glass permeameters, glass cylinders, PVC
(polyvinyl chloride) tubes, and shrink tubing. Shrink tubing may, in fact,
lend to fixed-wall tests a major desirable feature of flexible-wall tests--
reduction in the possibility of sidewall leakage.
Tests with water and other solutions that do not interact with clays
have shown that comparable permeability measurements may be obtained through
different types of test devices. Everett (1977) measured the permeability
of Lacustrine clays in falling head tests over a 2-month test period in
three types of fixed-wall permeameters. Test results showed almost equivalent
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permeability readings in all test devices. Values measured were 9.0 x 10 9
cm/s in a commercial metal permeameter, 6.9 x 10 9 cm/s in PVC pipe, and
8.3 x 10 9 cm/s in shrink tubing.
Permeability tests performed in both fixed-wall and flexible-wall
tests at Duke University (Peirce, 1984; Peirce and Peel, 1985) also indicate
that comparable data can be obtained from the different devices. Test
fluids used in the Duke investigation did not significantly alter the soil
permeabilities as compared to baseline permeabilities obtained with 0.01 N
calcium sulfate. More than 100 tests were carried out. The reproducibility
of the permeability results suggests that side-wall leakage in fixed-wall
devices can be virtually eliminated through careful quality control during
sample preparation, compaction, and testing if the permeant fluid does not
alter the clay that is tested.
Test results may differ somewhat with different types of permeameters
when the test fluid is other than water (or comparable baseline fluid).
Daniel (1983) found that methanol in tests with kaolinite in three types of
permeameters produced similar curves (permeability versus pore volumes
passed through sample) but with compaction mold permeabilities somewhat
higher than values measured in flexible-wall or consolidation cells.
4.3.2 Test Setup
Whether permeability tests are carried out as constant head or falling
head should not affect the validity of the test results. Effectively, one
is doing the same thing in both tests. In the constant head test, readings
are converted to a flow rate; in the falling head test, readings are con-
verted to changes in head. Most of the permeability tests described in
this section are essentially constant head tests because of the very low
permeabilities of compacted clay soils. Test results reported by Monserrate
(1982), however, were computed as falling head permeabilities.
Buettner and Haug (1983) noted that leakage is the controlling factor
on how low a permeability can be measured. They measured total leakage
from their flexible-wall permeameter setup by placing a solid metal block
in the cell and monitoring the changes in inflow and outflow. Volume
change indicators with an accuracy of ±0.005 cm3 were used to determine the
leakage rate and also enabled the researchers to measure the change in
volume of clay soils due to consolidation or swelling. Buettner and Haug
found that if leakage is not_corrected for, the potential error at low
permeabilities (less than 10 12 cm/s) can be as high as 2 orders of magni-
tude.-
4.3.3 Compatibility of Materials with Test Fluids
A problem that has become apparent in testing organic fluids in triaxial
cells is the incompatibility between the commonly used latex membranes and
the fluid to be tested (Acar et al., 1984a; Foreman and Daniel, 1984).
Excessive deformations (i.e., wrinkling and expansion) in the membrane may
occur with possible effects on the test results. One technique used by
4-13
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Acar et al. (1984a) to alleviate problems resulting from incompatibility
was to wrap the samples with two rounds of 0.03-mm sheet teflon. After
placement around the wrapped samples, the membranes were coated with a
contaminant-resistant (silicon base) grease to decrease chemical diffusion.
Even with these provisions, however, acetone used as the test fluid was
found to diffuse through the membrane into the cell water. A procedure and
apparatus that can be used to test the membrane-permeant fluid compatibility
have been described by Rad and Acar (1984).
Foreman and Daniel (1984) also found a workable technique to be wrapping
the soil sample along with the top cap and base pedestal with two or three
revolutions of 15-cm (6-inch) -wide Teflon tape before placement of the
latex membrane. Long-term flexible-wall tests with heptane have been
carried out successfully with this method.
Materials compatibility has also been a problem in fixed-wall tests
with corrosive test fluids. Stainless steel permeameters and pressure
fittings were damaged in tests with chronic acid (Monserrate, 1982).
Several reseachers have used plexiglass devices with teflon fittings to
avoid such problems.
4.3.4 Effect of Backpressure
Slight deviations from full saturation have been shown to significantly
affect measured permeability values (Mitchell et al., 1965). Recognizing
this, some researchers include in the test method a saturation step involv-
ing backpressuring. Zimmie et al. (1981) noted that many permeability
determinations are made using backpressure to promote complete saturation
and then releasing or lowering the backpressure during the permeability
test. When this is done, dissolved gases immediately begin to come out of
solution, causing the measured permeability values to decrease. Zimmie
et al. (1981) concluded, "The maximum, fully saturated permeability value
should be determined. It is necessary to utilize backpressure to properly
saturate the specimen whether or not the actual permeability test utilizes
backpressure."
4.3.5 Effect of Hydraulic Gradient
Mitchell, Hooper, and Campanela (1965), in tests with a silty clay,
found evidence that rapid infiltration of water could cause migration of
fine particles that tended to plug conducting pore spaces and reduce flow
rates. Mitchell and Younger (1967) measured permeability to water of a
compacted silty clay as a function of hydraulic gradient. A gradual increase
in the gradient from 0 to 17 over 26 days resulted in a corresponding
increase in permeability from less than 5 x 10 7 to 5.4 x 10 6 cm/s. The
increase was approximately linear in the region of gradients of about 4 to
10, the curve of permeability versus hydraulic gradient tending to flatten
at the lower and higher gradients. The nonlinear behavior at the higher
gradients may have been the result of movement of fine soil particles.
Other researchers—01 sen (1965) and Hamilton (1979)—have reported data
4-14
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that show no significant effect of hydraulic gradient on either discharge
velocity or permeability to water.
Under a cooperative agreement with the U.S. Environmental Protection
Agency (EPA), Daniel (1982) investigated the effect of hydraulic gradient
on permeability. Water (actually 0.01 N calcium sulfate) as well as other
permeant fluids were tested at gradients of 10, 50, 100, and 300 in flexible-
wall cells, fixed-wall permeameters, and consolidation cells. The permea-
bility of kaolinite to water did not vary with hydraulic gradient in any
test device. Changes in hydraulic gradient caused a slight increase in
permeability for kaolinite permeated with methanol in flexible-wall cells.
In fixed-wall permeameters and consolidation cells, however, the trend was
for decreasing permeability with decreasing gradient in tests with methanol.
Due to large variations in the test data obtained for fixed-wall permeame-
ters, the results of the tests were somewhat inconclusive.
In other research funded by the EPA, Brown, Thomas, and Green (1984)
studied the effects of hydraulic gradient on the permeability of three clay
soils to two organic wastes—a xylene waste and an acetone waste. It was
concluded that hydraulic gradients of 31, 91, and 181 did not greatly
affect the permeabilities in either presaturated or unsaturated samples.
4.3.6 Criteria for Concluding a Test
Clay-chemical compatibility tests should be continued until all changes
in permeability resulting from the interaction of the chemical with the
clay have been observed. To satisfy this condition, compatibility tests
should be concluded only if the slope of the permeability versus time curve
does not vary significantly from zero (steady-state permeability has been
reached) and.at least one pore volume of fluid has passed through the clay.
If the first condition is not met, there is no assurance that reactions of
the chemical with the clay are complete. If the second condition is not
met, there is no assurance that the permeant has contacted all of the clay
in the column. In order to satisfy the above conditions, it is necessary
to determine the chemistry of both the influent and effluent (to detect
breakthrough) and report pore volumes through samples as well as real time.
(Conclusion from a workshop on Permeability Testing, Atlanta, GA, January
1984, unpublished.)
A statistical procedure was developed at Duke University (Monserrate,
1982; Peirce, 1984) to determine when a test should be concluded. Readings
of column level and time are taken at certain intervals throughout the
test. The hydraulic conductivity is computed for each time interval. From
this set of data the first 10 points are taken and a linear regression
analysis is performed to determine the slope of the hydraulic conductivity
vs. time curve. The first point is then dropped and another value is added
on the other end. The slope is calculated again, and so on. In the begin-
ning of the test this slope will be fairly large, but as the test progresses
it will decrease and approach zero when steady-state is obtained.
The criteria for when steady-state is obtained will be taken when two
criteria are met—
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When the slope at the curve does not vary significantly from zero
at the 95-percent confidence level, and
At least one pore-volume of the liquid is passed through the
sample (Pierce, 1984).
4.4 SUMMARY OF AVAILABLE RESEARCH DATA
Numerous studies pertaining to the effects of chemicals on clay soil
permeabilities have been carried out by researchers at universities and by
private firms across the country during the last few decades. Research has
been sponsored by the EPA, the Army Corps of Engineers, the Chemical Manu-
facturers Association, and others. Among the classes of compounds that
have been tested are aliphatic hydrocarbons, chlorinated aliphatics, aromatic
hydrocarbons, alcohols, glycols, ketones, carboxylic acids, amines, and
aromatic nitro compounds. In addition to tests with single-compound test
solutions, many studies have been carried out using complex chemical mix-
tures. In tests involving actual wastes or leachates (obtained by passing
water through wastes), the exact composition of the fluid is usually not
known although major components and important parameters are usually identi-
fied and quantified.
The results of some of the most significant permeability tests involving
specific organic solvents are presented in Table 4-1. The results of
permeability tests involving wastes are presented in Table 4-2.
Some of the studies summarized here and in more detail in Section 4.5
have shown that certain pure, concentrated organics can drastically alter
the permeability of clay soils under the conditions of the laboratory test.
These test results have led to widespread concern over the possible seepage
of wastes into the environment from clay-lined disposal facilities. It
should be emphasized that clay liners in disposal facilities are most often
in contact with leachate having much lower organic solvent concentrations
than the test solutions associated with the drastic permeability increases
seen in some laboratory studies. Laboratory studies performed with less
concentrated test solutions (either actual wastes or leachates or dilutions
prepared in the laboratory) do not appear to produce such effects.
Because of the wide variations in the soils used in clay liners and
the leachates to which they will be exposed during service, testing of the
actual liner/leachate system is necessary to confirm compability.
4.5 PERMEABILITY STUDIES TO INVESTIGATE CLAY-CHEMICAL INTERACTIONS
The major findings of various research efforts to investigate effects
on permeability of clay-chemical interactions are presented in this section.
4.5.1 Observations by Macey (1942) on Effects of Organics on Fireclay
As a result of permeability experiments with fireclay, Macey (1942)
concluded that the rates of flow of benzene, nitrobenzene, and pyridine
4-16
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TABLE 4-1. RESULTS OF PERMEABILITY TESTS WITH ORGANIC CHEMICALS
ALIPHATIC AND AROMATIC HYDROCARBONS
Heptane
Fixed-wall permeameter tests at high gradient with four clays showed rapid
permeability increases and breakthrough. The increase in permeability was
more than 3 orders of magnitude in an illite clay. Baseline permeabilities
were established in the same sample with 0.01 N calcium sulfate prior to
introducing the test solution. (Anderson, 1981)
Benzene
The flow rate of benzene through fireclay was of an enormously higher order of
magnitude than the flow rate for water. (Macey, 1942)
In a column test under a head of 701 cm (23 feet), signs of full penetration
throughout the clay material were observed after 36 days; in a similar column
with water as the permeant fluid the liquid level dropped less than 2.54 cm
(1 inch) over a 100-day period. Samples were 91 cm in height and 2.54 cm in
diameter. (White, 1976, unpublished data)
Following an initial decrease in permeability (compared to permeability to
deionized water established in a similar sample), total breakthrough occurred
on the eighth day of testing when Ranger shale was exposed to benzene in a
fixed-wall permeameter under low hydraulic gradient. (Green et a!., 1979)
Benzene did not penetrate compacted Ca-montmori11onite that was first
saturated with 0.01 N calcium sulfate even at hydraulic gradients as high at
150. (Olivieri, 1984)
In flexible-wall tests with a Georgia kaolinite, permeability decreased until
the tests were terminated. The final value was approximately 2 orders of
magnitude lower than the initial permeability. (Acar et al., 1984a)
Xylene
Following an initial decrease in permeability, total breakthrough occurred on
the 25th day of testing when fireclay was tested in a fixed-wall permeameter
under low hydraulic gradient. In Ranger shale, a slight decrease in
permeability was observed and remained steady until the test was terminated at
40 days. In Kosse kaoline, a slight decrease in permeability was followed by
an increase to about the initial level, which persisted until the test was
terminated at day 36; changes did not exceed half an order of magnitude.
(Green et al., 1979)
In column tests under very low gradient, intrinsic permeabilities were higher
than permeability to water by at least 1 order of magnitude in samples of Lake
Bottom, Nicholson, Fanno, Chalmers, and Canelo clays. Permeabilities were
(continued)
4-17
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TABLE 4.1 (continued)
Xylene (con.)
slightly higher than for water in three other soils. The samples (5.8 cm in
diameter and 5 cm in height) were presaturated with xylene. (Schramm, 1981)
Fixed-wall tests at high gradient with four clays showed permeability
increases and breakthrough followed by nearly constant permeabilities roughly
2 orders of magnitude higher than baseline permeabilities. Baseline
permeabilities were established in the same sample with 0.01 N calcium sulfate
prior to introducing the test solution. (Anderson, 1981)
In fixed-wall permeameter tests at high gradient, the permeability of an
unsaturated micaceous soil was 4 orders of magnitude higher when exposed to
xylene than when tested with 0.01 N calcium sulfate. (Brown et a!., 1984)
Xylene/Acetone
In fixed-wall permeameter tests at high gradient, the permeability of an
unsaturated micaceous soil to either pure acetone or pure xylene was greater
than the permeability determined for mixtures of the two solvents. The
permeability of a mixture of 87.5 percent xylene and 12.5 percent acetone was
lower by 3 orders of magnitude than the permeability measured with pure xylene
(though still higher than the permeability to 0.01 N calcium sulfate). When
the acetone component was increased to 75 percent, the permeability was
approximately the same as that determined with pure acetone (i.e., about 1.5
orders of magnitude greater than the permeability to 0.01 N calcium sulfate).
(Brown et al., 1984)
Kerosene (a mixture of aliphatics and aromatics)
In column tests under very low gradient, intrinsic permeabilities were higher
than permeability to water by approximately 1 order of magnitude in samples of
Lake Bottom, Nicholson, Fanno, Chalmers, and Canelo clays. Permeabilities
were slightly higher than for water in three other soils. The samples (5.8 cm
in diameter and 5 cm in height) were presaturated with kerosene. (Schramm,
1981)
In fixed-wall permeameter tests at high gradient, the permeability of an
unsaturated micaceous soil increased by 3 to 4 orders of magnitude compared
to the permeability determined with 0.01 N calcium sulfate. (Brown et al.,
1984)
Naphtha
The permeabilities of two clays (Na-saturated and Ca-saturated montmorillo-
nite) to naphtha were greater by several orders of magnitude than their
permeabilities to water. (Buchanan, 1964)
(continued)
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TABLE 4-1 (continued)
Soltrol C (a light hydrocarbon liquid)
Intrinsic permeabilities for samples tested with the light hydrocarbon were
significantly higher than the permeabilities measured in similar samples
exposed to water, (van Schaik, 1970)
Diesel Fuel
Fixed-wall permeameter tests at high gradient with an unsaturated micaceous
illite produced highly variable data inconsistent with the pattern of
permeability changes seen with other liquid hydrocarbons. Permeability was
greater by 1 to 2 orders of magnitude than the permeability measured with 0.01
N calcium sulfate in a similar sample. (Brown et al., 1984)
Paraffin Oil
In fixed-wall permeameter tests at high gradient with an unsaturated micaceous
illite, permeability was greater by about 1 order of magnitude than the
permeability measured with 0.01 N calcium sulfate in a similar sample.
Maximum values were obtained after the passage of one pore volume. (Brown et
al., 1984)
Gasoline
In fixed-wall permeameter tests at high gradient with an unsaturated micaceous
illite, permeability was greater by 1 to 2 orders of magnitude than the
permeability measured with 0.01 N calcium sulfate in a similar sample. (Brown
et al., 1984)
Motor Oil
In fixed-wall permeameter tests at high gradient with an unsaturated micaceous
illite, permeability increased by about 1 to 2 orders of magnitude as 2.5
pore volumes of fluid were passed through the sample. (Brown et al., 1984)
ETHERS
Dioxane
Kaolinite initially packed and permeated with water was permeated with
anhydrous dioxane until complete displacement of the water was achieved.
Replacement of water by dioxane was accompanied by about a 20- to 30-percent
increase in intrinsic permeability. This permeability was much lower,
however, than the values determined for kaolinite beds initially prepared with
dioxane. (Michaels and Lin, 1954)
(continued)
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TABLE 4-1 (continued)
KETONES
Acetone
In fixed-wall permeameter tests under low hydraulic gradient, three clays
showed slight decreases in permeability (compared to permeability to deionized
water established in a similar sample). All tests were concluded before 40
days. Less than 0.5 pore volumes were passed through the sample. (Green et a!.,
1979)
Fixed-wall permeability tests at high gradient with four clays showed initial
permeability decreases followed by increases compared to baseline. Baseline
permeabilities were established in the same sample with 0.01 N calcium sulfate
prior to introducing the test solution. Extensive shrinking and cracking in
the soils were observed after permeation. (Anderson, 1981)
In flexible-wall tests with a Georgia kaolinite, an immediate decrease in
permeability was followed by an increase, the final value stabilizing at
approximately double the initial permeability (Acar et al., 1984)
Acetone (high and low concentration)
An increase over baseline permeability (established with 0.01 N calcium
sulfate in similar samples) was seen in an unsaturated micaceous soil for
solutions where the acetone concentration was 75 or 100 percent. Samples
tested with lower concentrations of acetone did not show appreciable changes
in permeability compared to the 0.01 N calcium sulfate. Tests were carried
out in fixed-wall permeameters at high gradient. (Brown et al., 1984)
Acetone (low concentration)
Permeability decreased slightly in a Georgia kaolinite clay tested in a
flexible-wall permeameter with a solution containing a low concentration of
acetone (i.e., below 0.1 percent) prepared in 0.01 N calcium sulfate. (Acar
et al., 1984a)
ALCOHOLS, GLYCOLS, PHENOL
Methanol
Permeability decreased slightly (compared to permeability to deionized water
established in a similar sample) when Ranger shale was exposed to methanol
under low hydraulic gradient in a fixed-wall permeameter. The test was
terminated after 30 days. (Green et al., 1979)
Fixed-wall permeameter tests at high gradient with four clays showed steady
permeability increases compared to baseline. Baseline permeabilities were
established in the same sample with 0.01 N calcium sulfate prior to
introducing the test solution. Examination of the methanol-treated samples
revealed development of large pores and cracks. (Anderson, 1981)
(continued)
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TABLE 4-1 (continued)
Methanol (con.)
Test results with Lufkin clay in flexible-wall cells showed essentially no
change in permeability with time when samples were permeated with methanol.
The permeability to methanol was virtually the same as with 0.01 N calcium
sulfate. (Daniel, 1983)
At high hydraulic gradients, kaolinite was found to have a higher conductivity
to methanol than to water regardless of the permeameter types; fixed-wall,
flexible-wall, and consolidation permeameters were used. In the flexible-wall
and consolidation permeameters, kaolinite is about twice as permeable to
methanol as to water. (Foreman and Daniel, 1984)
Isopropyl Alcohol
In column tests under very low gradient, intrinsic permeabilities were higher
than permeability to water by almost 1 order of magnitude in samples of
Nicholson, Fanno, and Canelo clays. Permeability values were the same or
slightly higher than baseline in five other soils. The samples (5.8 cm in
diameter and 5 cm in height) were presaturated with the alcohol. (Schramm,
1981)
Glycerol
Permeability decreased slightly (compared to permeability to deionized water
established in a similar sample) when Ranger shale was exposed under low
hydraulic gradient to glycerol in a fixed-wall permeameter. The test was
terminated after 36 days. (Green et a!., 1979)
Ethylene Glycol
Fixed-wall permeameter tests at high gradient showed permeability decreases
compared to baseline followed by increases in three clays; a smectitic clay
showed an initial rapid increase followed by a slower but continuous increase
in permeability. Baseline permeabilities were established in the same sample
with 0.01 N calcium sulfate prior to introducing the test solution (Anderson,
1981)
In column tests under very low gradient, intrinsic permeabilities were an
order of magnitude lower than permeabilities to water in Chalmers clay, Mohave
clay,- and River Bottom sand. Values were slightly lower in Lake Bottom,
Nicholson, Canelo, and Anthony clays and slightly higher in Fanno clay. The
samples (5.8 cm in diameter and 5 cm in height) were presaturated with the
ethylene glycol. (Schramm, 1981)
~~~~~ (continued)
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TABLE 4-1 (continued)
Phenol (949 mg/L)
In column tests with a lacustrine clay (packed to discharge 2 ml/day), no
significant effect on permeability was noted when deionized water was replaced
by the phenol solution as the permeant fluid. (Sanks and Gloyna, 1977)
Phenol (low concentration)
Permeability decreased slightly in a Georgia kaolinite clay tested in a
flexible-wall permeameter with a solution containing a low concentration of
phenol (i.e., below 0.1 percent) prepared in 0.01 N calcium sulfate. (Acar
et al., 1984a)
Phenol (high concentration)
In flexible-wall tests with a Georgia kaolinite and a high-strength phenol
solution, an immediate decrease in permeability was followed by an increase,
the final value stabilizing at approximately double the initial permeability.
(Acar et al., 1984a)
AMINES
Aniline
Fixed-wall permeability tests at high gradient with four clays showed
permeability increases and breakthrough. Baseline permeabilities were
established in the same sample with 0.01 N calcium sulfate prior to
introducing the test solution. Extensive structural changes in the upper
half of the soil columns were observed following permeation with aniline. The
aggregated structure was characterized by visible pores and cracks on the
surface of the soils. (Anderson, 1981)
Pyridine
The flow rate of pyridine through fireclay was of an enormously higher order
of magnitude than the rate of flow for water. (Macey, 1942)
CHLORINATED ALIPHATICS
Carbon Tetrachloride
Permeability decreases slightly (compared to permeability to deionized water
established in a similar sample) when Ranger shale was tested under low
hydraulic gradient in a fixed-wall permeameter. The test was terminated after
14 days. (Green et al., 1979)
(continued)
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TABLE 4-1 (continued)
Trichloroethylene
Permeability decreased slightly (compared to permeability to deionized water
established in a similar sample) when fireclay was tested under low hydraulic
gradient in a fixed-wall permeameter. The test was terminated after 36 days.
(Green et al., 1979)
OTHER
Acetic Acid
Tests at high gradient in fixed-wall permeameters showed continuous
permeability decreases to baseline in two clays. Tests with .smectitic and
illite clays showed permeability increases after initial decreases. Baseline
permeabilities were established in the same sample with 0.01 N calcium sulfate
prior to introducing the test solution. The permeability decreases were
attributed to partial soil dissolution and migration of particles, which
temporarily clogged the fluid conducting pores. Progressive soil piping
eventually caused the increase in permeability. (Anderson, 1981)
Nitrobenzene
The flow rate of nitrobenzene through fireclay was of an enormously higher
order of magnitude than the flow rate for water. (Macey, 1942)
In flexible-wall tests with a Georgia kaolinite, permeability decreased until
the tests were terminated. The final value was approximately 2 orders of
magnitude lower than the initial permeability (Acar et al., 1984a)
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TABLE 4-2. RESULTS OF PERMEABILITY TESTS WITH WASTES
"Xylene Waste" (paint solvent containing xylene with 25 percent paint pigments
and trace amounts of water)
In fixed-wall permeameter tests, the permeability of three clay soils,
presaturated with 0.01 N calcium sulfate, increased rapidly upon exposure to
xylene waste after the cumulative flow exceeded 0.2 to 0.4 pore volume.
Permeabilities were 2 to 4 orders of magnitude greater than permeabilities
measured with 0.01 N calcium sulfate. Highest permeabilities measured on
initially unsaturated samples were greater by 1 to 2 orders of magnitude than
for samples that were initially saturated with the calcium sulfate. (Brown et
a!., 1983)
"Acetone Waste" (a chemical manufacturing waste containing 91.7 percent
acetone, 4 percent benzene, and 0.6 percent phenol)
In fixed-wall permeameter tests, the permeability of three clay soils,
presaturated with 0.01 N calcium sulfate, initially decreased (minimum
permeability at approximately 0.5 pore volume) and then steadily increased.
Permeabilities were 2 to 4 orders of magnitude greater than permeabilities
measured with 0.01 N calcium sulfate. Highest permeabilities measured on
initially unsaturated samples were greater by 1 to 2 orders of magnitude than
for samples that were initially saturated with the calcium sulfate. (Brown et
a!., 1983)
Perch!oroethylene Waste
There is evidence that a perch!oroethylene waste, which formed a separate,
denser than water phase, contributed to the failure of a clay liner at a
surface impoundment. (Personal communication, 1984)
"Acid Prowl" (pesticide wash of very low pH; higher viscosity than water)
After several days of exposure to a lacustrine clay packed in a fixed-wall
column, the water reacted with the soil to produce chlorine gas. Over a
5-week period, the flow of liquid from the column was irregular due to
clogging of pores by the gas. (Everett, 1977)
"Acid Wash" (42 percent sulfuric acid with about 5 percent organics; higher
viscosity than water)
Permeability of a lacustrine clay packed in shrink tubing increased by about 1
order of magnitude over a period of 19 days. The permeability was lower,
however, than values obtained when the soil sample was exposed to water.
(Everett, 1977)
~~~~(continued)
4-24
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TABLE 4-2 (continued)
"Mother Liquor" (an acid wash with pH of 0.37; higher viscosity than water)
Permeability of a lacustrine clay packed in shrink tubing was lower than the
value obtained when the soil sample was exposed to water. The waste may have
reacted with the soil, liberating gases and increasing pore pressures and
clogging flow. (Everett, 1977)
"Hydrazo Benzene" (33 percent methanol, 12.8 percent sodium hydroxide, 15.5
percent sodium formate, and 1.5 percent hydroazobenzene and azobenzene; more
viscous than water)
Permeability of a lacustrine clay packed in shrink tubing was slightly lower
than the value obtained when the soil sample was exposed to water. Tests were
carried out for 34 days under low gradient (less than 100 cm). (Everett,
1977)
"Acid Waste" (100 mM HC1/L)
Due to reaction with carbonates, much higher permeabilities were observed in
tests with lacustrine clay compared to permeabilities determined with
deionized water. (Sanks and Gloyna, 1977)
"Basic Waste" (100 mM NaOH/L)
Permeabilities in a lacustrine clay decreased compared to the values measured
with deionized water. (Sanks and Gloyna, 1977)
4-25
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through clay are "of an enormously higher order than for water." Analytical
reagent-grade organics were used. All the organic liquids passed through
the clay at flow rates 100,000 to 1,000,000 times greater than the flow
rate of water through the same clay. The high rates of flow produced
experimental difficulties because of the high resistance to flow of the
testing apparatus, and the experiments were finally abandoned. Differences
between the viscosities of the organic fluids and of water are not suffi-
cient to account for the very large permeability changes that were observed.
4.5.2 Tests With Kaolinite and Organic Solvents by Michaels and Lin (1954)
Michaels and Lin (1954) measured the permeability of high-purity
kaolinite to nitrogen gas, cyclohexane, acetone, dioxane, methanol, and
distilled water. Tests were also conducted to determine the effect of
replacement of one permeant liquid by another. The investigation was one
part of a broad program of fundamental research sponsored by the U.S. Army
Corps of Engineers and by industrial contributions and was carried out at
the Massachusetts Institute of Technology (MIT) Soil Stabilization Labora-
tory.
4.5.2.1 Test Method-
Permeability tests were conducted in a 5.1-cm (2-inch) -diameter fixed-
wall permeameter cell. Bed thickness was 1.1 to 1.8 cm. The base-exchange
capacity of the kaolinite was determined to be 5.0 ± 0.5 meq/100 g. Samples
were dried for 24 hours at 160 °C prior to saturation by the organic liquids
for the permeability test.
Prior to permeability testing, each sample was submerged in the fluid
to be tested (either organic liquid or water). The wetted samples containing
known amounts of clay were poured into the permeability cell, entrapped air
was removed, and the sample was consolidated by means of a confining piston.
Samples were consolidated to several void ratios (volume of voids/volume of
solid) for each test fluid. Void space was determined through column bulk
density and the true density of kaolinite.
For the permeability tests, a hydrostatic head not exceeding 10 percent
of the compaction pressure was maintained. Permeabilities were determined
for each void ratio. Permeability coefficients determined for separate
clay samples prepared with a given fluid and compacted to essentially the
same void ratio were found to be reproducible to within 10 percent.
The effect of change of fluid medium on the permeability of a confined
clay was determined through a series of desolvation experiments. Kaolinite
initially packed and permeated with water was subsequently permeated with
dioxane until the water was completely displaced (as evidenced by constant
permeability to dioxane). The dioxane was then displaced with acetone
under similar conditions. Finally, warm, dry nitrogen was passed through
the sample until the bed was solvent-free. Beds initially tested with the
organic liquids (methanol, dioxane, acetone, and cyclohexane) were similarly
treated with dry nitrogen until all solvent was removed.
4-26
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The permeability to nitrogen of the desolvated samples was then deter-
mined and compared to the permeability with the original permeant fluid.
4.5.2.2 Test Results —
The intrinsic permeabilities (cm2) of samples packed at different void
ratios, measured for organic solvents and for nitrogen, are shown in Figure
4-3. Predictably, the permeabilities increased with increasing void ratio.
The data also indicate that permeability at any given void ratio decreases
with increasing polarity of the permeant.
As a result of the desolvation experiments, the authors concluded
that:
Whatever specific effects these permeant liquids exert on the
kaolinite persist when the clay is thoroughly dried in the confined
state. The reduced permeabilities of kaolinite to these liquids
relative to the values observed for this clay to gas when packed
in the dry state apparently cannot be ascribed to adsorbed liquid
films, abnormally high liquid viscosities, or electro-osmotic
effects. ... It seems most probable, therefore, that the lower
permeabilities of kaolinite to. these liquids than to nitrogen are
caused by improved dispersion, and possibly more orderly packing
of the solids in more polar media.
Results of the desolvation experiments show the effect of replacement
of permeant fluid on the permeability of the kaolinite. For samples sedi-
mented from and initially permeated with methanol, dioxane, acetone, or
cyclohexane and then exhaustively permeated with warm, dry, nitrogen gas,
the final gas permeability is found to be equal, within the limits of
experimental accuracy, to the permeability to the initial permeant liquid
at the corresponding void ratio. This is particularly true at low void
ratios. An increase in permeability upon drying is observed if the initial
void ratio is high.
Specific observations by Michaels and Lin include the following:
Replacement of water by dioxane is, in all cases, accompanied
by about a 20- to 30-percent increase in permeability; the
dioxane permeabilities through these beds are, however, much
lower than the values determined for kaolinite beds prepared
initially in dioxane.
Replacement of the dioxane with acetone leads to a small
additional permeability increase approximately when water is
the initial permeant fluid.
Displacement and evaporation of the acetone with dry nitrogen
is accompanied by a great increase in permeability; the
magnitude of this increase is greatest for kaolinite samples
confined initially at high void ratios.
4-27
-------
Permeants
x - Water
0 - N2
Q - Cyclohexane
A - Acetone
A - Oloxane
+ - Methane1
1.0
gO.1
0.01
0.4
0.3
1.2
1.6
2.0
2.4
Source: Michaels and Lin, 1954
Figure 4-3. Intrinsic permeabilities as a function of void space (e)
measured for different permeants.
4-28
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4.5.2.3 Discussion--
Intrinsic permeabilities reported by Michaels and Lin cannot be directly
compared with permeability data from other tests because the measurement
procedure is unique. No information is provided about the amount of fluid
passed through the sample in determining each of the reported permeabilities.
While samples used in permeability tests are usually air-dried, the
clay samples used by Michaels and Lin were dried for 24 hours at 160 °C, a
condition that could cause irreversible changes in clays and organic matter.
It is possible that the adsorptive properties of the kaolinite were perma-
nently altered by this drying procedure. The kaolinite mineral, halloysite,
will not rehydrate if the interlayer water is removed.
4.5.3 Study by Buchanan (1964) of the Effect of Naphtha on Montmorilignite
Buchanan (1964) at Texas A&M University studied permeabilities of
sodium- and calcium-saturated montmorillonite when these clays were perme-
ated by water and naphtha. Permeabilities of the two clays to naphtha were
greater by several orders of magnitude than their permeabilities to water,
even with reductions in void ratios for the samples treated with naphtha.
The data also suggest that the permeability of the sodium-saturated clay is
more dramatically affected by the naphtha. Permeability differences were
thought to be at least partially due to the inability of naphtha to form an
immobilized liquid film on the clay mineral surfaces. Buchanan's data are
summarized in Table 4-3.
4.5.4 Study by Reeve and Tamaddoni (1965) of the Effect of Electrolyte
Concentration on Permeability of a Sodic Soil
Reeve and Tamaddoni (1965) of the U.S. Department of Agriculture
studied the effects of high-salt, high-sodium solutions on the permeability
of a highly sodic soil. California Waukena clay loam containing about 15
percent of expanding lattice-type clay was tested in the laboratory and in
the field.
4.5.4.1 Test Method-
Solutions of varying concentrations but with constant sodium adsorption
ratio (SAR) were used in the tests. Test solutions were prepared from
sodium chloride (NaCl) and calcium chloride (CaCl2) at SAR levels of 0 (100
percent CaCl2), 80 (a partially reclaiming solution), 180 (the equilibrium
solution of the natural soil), and °° (100 percent NaCl). For each SAR
level, seven ionic concentrations (63, 125, 250, 500, 1,000, 2,000, and
4,000 meq/L) were tested in a selected sequence. Laboratory tests were
carried out in fixed-wall 5.4-cm (2.125-inch) ID cylinders.
4.5.4.2 Test Results—
The test results indicate that permeability is a function of both the
absolute concentration and the SAR of the initial solution. Permeability
increased with increasing SAR value and ionic concentration. The permeabil-
ity-concentration relationship was found to depend markedly on the initial
solution concentration (i.e., if the initial solution concentration was
4-29
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TABLE 4-3. VOID RATIO AND COEFFICIENT OF PERMEABILITY RELATIONSHIPS
FOR CALCIUM- AND SODIUM-MONTMORILLONITE PERMEATED BY
WATER AND NAPHTHA
Clay
Cal cl urn-saturated
smectite
Sodi urn- saturated
smectite
Void
ratio
1.72
3.75
Water
Permeability
(cm/s)
1.6 x io"9
5.2 x 10"11
Void
ratio
1.52
1.31
Naphtha
Permeability
(cm/s)
6.4 x io"5
3.8 x io"5
Data from Buchanan (1964).
TABLE 4-4. SUMMARY OF SOIL PERMEABILITY WITH SOLTROL C AND WATER£
Soil
(bulk density in g/cm3)
Intrinsic
permeability (urn2) Permeability. K (cm/s)
Oil Water Oil
Water
Cavendish loamy sand 4.94
(bulk density: 1.44 g/cm2;
6 percent clay)
Chin sandy clay loam 0.73
(bulk density: 1.25 g/cm3;
18 percent clay)
Chin sandy clay loam 0.22
(bulk density: 1.38 g/cm3;
18 percent clay)
Lethbridge clay loam 0.51
(bulk density: 1.22 g/cm3;
37 percent clay)
9.38 4.8 x IO"3 3.0 x io"3
5.45 7.1 x IO"4 5.1 x IO"3
2.53 2.1 x io"4 1.4 x io"3
6.10 5.0 x IO"4 3.3 x IO"3
Data from van Schaik (1970).
4-30
-------
low, the range of permeability values with varying solution concentrations
was lower than if the initial solution concentration was high, and vice
versa.) Apparently the degree of flocculation or dispersion that occurred
with the application of the initial solution influenced the magnitude of
the permeability.
In some of the tests a large change in solution concentration (e.g.,
from 125 to 1,000 meq/L) was accompanied by a large increase in outflow due
to sidewall leakage as a consequence of the contraction of the previously
swollen mass.
In the test series in which initially low concentrations (63 meq/L)
were increased stepwise to 4,000 meq/L and then reduced to the initial
concentration, reproducibility of permeability values as a function of
concentration was good. These results suggested that a reversible swelling
process was occurring. In the test series in which initial concentrations
of 1,000 meq/L were increased to 4,000 meq/L and then reduced to 63 meq/L,
results showed a gradual decrease in permeability with a given solution
concentration. This was attributed to slaking or particle rearrangement
that led to permeability decreases that progressed with time.
The permeability of the Waukena soil to a saturated calcium sulfate
(CaS04) solution was an order of magnitude lower than the lowest values
measured with the test solutions.
Test results showed that intake rates measured in the field at high
electrolyte concentrations were approximately three times as great as
corresponding permeabilities measured in the laboratory. However, the
fractional change was essentially the same at equal electrolyte concentra-
tions.
4.5.5 Tests by van Schaik and Laliberte (1968) of Permeability of Soils
to a Liquid Hydrocarbon
Permeability data are reported by van Schaik (1970) for three soils
tested with tap water and with a light hydrocarbon liquid (trade name
Soltrol C). Permeability measurements were made on samples that had been
vacuum-saturated. The intrinsic permeabilities with the oil were first
reported by van Schaik and Laliberte (1968).
4.5.5.1 Test Results—
The saturated intrinsic permeability of the three samples varied
between 0.22 and 4.94 urn2 for water. For oil, the values ranged between
2.53 and 9.38 urn2. The data are summarized in Table 4-4.
4.5.5.2 Discussion—
The test apparatus used in the study was designed to measure properties
of unsaturated porous media. The number of pore volumes displaced by the
test fluid during the permeability determination was not reported. Details
of the test procedure used also were not given in the references cited. In
spite of these limitations, the intrinsic permeabilities are useful for
4-31
-------
comparing the relative permeabilities of the various soils to water and
oil. The increased permeabilities of the soils when exposed to the oil are
consistent with the later findings by Anderson (1981).
4.5.6 Study by Everett (1977) of Permeability of Lacustrine Clay to Four
Liquid Wastes
Everett (1977) investigated the permeability of lacustrine clays from
Bay County, Michigan, to four liquid wastes. The purpose of the study was
to establish the feasibility of a hazardous waste landfill in Bay County.
Three types of permeability test devices were used. The results of the
comparative tests with water show no significant differences in the perme-
abilities measured in the different devices.
The predominant mineral in the soil was quartz, estimated to be 40 to
50 percent. Clay minerals present were illite and chlorite, each at about
10 to 15 percent. Other important constituents were dolomite (20 to 25
percent) and calcite (10 to 15 percent). The clay fraction was reported to
average 18.1 percent. The mean cation exchange capacity of the soil (deter-
mined with ammonium acetate solution) was low.
Wastes used in the compatibility tests were "Acid Prowl," "Acid Wash,"
"Mother Liquor," and "Hydrazo Benzene." "Acid Prowl" is a pesticide wash
of very low pH. The "Acid Wash" was about 42 percent sulfuric acid in
water and also contained about 5 percent organics including dichlorobenzi-
dine, orthochloroaniline, and tars. The waste labeled "Hydrazo Benzene"
actually contained about 1.5 percent hydroazobenzene and azobenzene. Other
components were methanol (33 percent), sodium hydroxide (12.8 percent),
sodium formate (15.5 percent), and water (36.7 percent). The waste has a
pH of 12.10. The "Mother Liquor" was an acid wash (pH of 0.37) of unknown
use. All waste samples were more viscous than water.
4.5.6.1 Test Method-
Permeability to@water was measured in three different test devices—
commercial Soil Test units (fixed-wall, 10.2-cm [4-inch] diameter, 10.2-cm
[4-inch] sample height), PVC pipe (10.3-cm [4-inch] diameter, 15.2-cm
[6-inch] sample height), and shrink tubing (10.2-cm [4-inch] diameter,
15.2-cm [6-inch] length). Samples tested in the Soil Test units and the
shrink tubing were prepared in a standard Proctor mold according to ASTM
specifications for modified Proctor compaction (D-1557-70). The objective
of preparing the samples was to obtain uniform packing. The PVC pipe was
packed in a different manner, not specified.
Samples were saturated by backwashing with water for more than 2 weeks
before permeability data were recorded. Readings were taken over a 2-month
period to determine the permeability of the samples to water. After testing
with water, three shrink tube columns and the PVC pipe columns were tested
with wastes. Samples were allowed to saturate by backwashing with the
waste until the effluent showed the presence (by color or pH) of the waste.
4-32
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The tests were all conducted in falling head setups with a head of
less than 100 cm (39.37 inches). The metal test units were not used for
testing the wastes because of the corrosive nature of the wastes.
4.5.6.2 Test Results—
"Acid Prowl" was tested in the PVC column. After several days of
contact with the soil, chlorine gas became noticeable at the outlet pipe.
After 2 weeks, the gas was no longer apparent, and liquid flow from the
permeameter ceased. The column was allowed to stand with the waste fluid
head for 3 more weeks. During this time the fluid reacted irregularly.
This behavior was attributed to clogging of pores by chlorine gas generated
with the sample. Valid permeability readings could not be obtained.
"Acid Wash," "Mother Liquor," and "Hydrazobenzene" were tested in
shrink tubes. The permeabilities measured with the wastes were lower than
the corresponding permeabilities to water. This may be due in part to the
higher viscosity of the wastes compared to water. Values obtained after 19
days of testing with "Acid Wash" showed a slight increase in permeability
(about 1 order of magnitude) compared to the initial value. For "Mother
Liquor," test data with the waste showed permeability to be lower by more
than 2 orders of magnitude than values measured with water. These acid
wastes may have reacted with the soil-liberating gases, which would increase
pore pressures and consequently decrease the permeability. In tests with
hydrazobenzene, permeability values were slightly lower than values obtained
with water. Permeability data are compared in Table 4-5.
4.5.6.3 Discussion—
Although the compatibility tests were carried out for approximately 1
month, the volumes of liquid forced through the columns under the low
gradients had to be very small. The number of pore volumes displaced was
not specified. Sufficient data were not presented to determine quantita-
tively the effect attributable to the viscosity of the wastes.
4.5.7 Tests by Sanks and Gloy'na (1977) of Permeability of Lacustrine
Clay to Liquid Waste
Sanks and Gloya (1977) tested five simulated liquid wastes with three
clays in column tests to determine effects on permeability. The aqueous
waste solutions tested were chosen to be representative of materials that
might leak from containers of solid wastes. The various substances con-
tained acid, base, and heavy metals. Clays tested contained large percen-
tages of montmori1lonite. The columns were packed at densities low enough
to discharge 2 mL/day of distilled water at 152-cm (5-ft) head with an
allowable error of 10 percent. After the tests with water, the columns
were drained and refilled with the waste fluid to be tested.
Permeabilities with deionized water ranged from 4 x 10 8 to 1.2 x 10 7
cm/s. Much higher permeabilities were observed when the acid waste (100 mM
HC1/L) was passed through the columns due to reaction with carbonates.
Permeabilities decreased in tests with the basic waste (100 mM NaOH/L).
Phenol at 10 mM/L (940 mg/L) appeared to have little effact on permeability.
4-33
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TABLE 4-5. PERMEABILITIES MEASURED WITH LACUSTRINE CLAY
EXPOSED TO WATER AND WASTE LIQUIDS3
Day of
test data
1
3
5
15
19
29
32
34
3.4 x IQ'10
1.3 x 10"9
1.5 x 10"9
With
"acid wash"
7.1 x lo"11
No flow
2.9 x 10"10
5.8 x 10"10
6.9 x 10"10
Permeability (cm/s)
With water
6.7 x lo"7
6.5 x lo"7
5.7 x 10"7
With
"mother liquor"
9.Q x 10"10
1.0 x 10"9
8.3 x 10"10
2.1 x 10"9
3.1X10'10
4.0 x 10"7
6.0 x 10"7
5.1 x 10"7
With
"hydrazobenzene"
9.0 x lo"8
7.8 x io"8
No reading
. 1.3 x io"7
1.3 x IO"7
Data from Everett (1977).
4-34
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Heavy metals tested, HgCl2 at 30 mM/L (8,100 mg/L) and ZnS04x7H20 at
30 mM/L (8,610 mg/L), showed no effect except for one anomaly.
4.5.8 Investigation of the Effect of Organic Solvents on Clays by Green
and Jones (1979)
Under a grant from EPA's Kerr Environmental Laboratory, Ada, Oklahoma,
to the University of Texas at Dallas, Green, Lee, and Jones (1979) studied
the impacts of organic solvents on the shrink/swell behavior and permeability
of four clay soil materials--Ranger shale, fire clay, Kosse kaoline, and
Parker soil. The test results were compared to results with water. The
studies included extensive soil characterization. Soil properties are
summarized in Table 4-6. Organic solvents tested were benzene, xylene,
carbon tetrachloride, trichlorethylene, methanol, and glycol (Green et a!.,
1981, 1983).
4.5.8.1 Test Methods-
Swell properties of the clays in contact with water, the organic sol-
vents, and various solvent mixtures were investigated. The swell properties
were measured with a 6.4-cm-diameter consolidometer. Care was taken to
prevent evaporation. Clay core samples used in the tests were compacted at
optimum moisture content. In the consolidometer, samples were flooded with
the test fluid and measurements of the swell or shrink behavior were made
as a function of time.
. Permeability data were collected on 15 clay/solvent systems. Test
durations ranged from 8 to 40 days. Fixed-wall permeameters used in the
study were thick-walled Pyrex glass, and all joints were teflon-lined. The
test procedure was adapted from an ASTM method. Samples were compacted at
optimum moisture conforming to standard compaction procedures before trans-
fer to the permeameters. The test fluid was then introduced, the liquid
level being adjusted in an 8-mm graduated standpipe. Equilibrium permeabil-
ities were estimated from curves of K(cm/s) versus time. The number of
pore volumes of permeant fluid passed through the samples was not reported.
4.5.8.2 Test Results-
Each of the clay soils swelled to a greater extent when exposed to
deionized water than with any of the pure solvents tested. The shrink/swell
behavior of the various clays in water and in organic solvents is described
in Table 4-7. The final percent swells for the samples are listed in Table
4-8.
'Based on the swelling data for both pure solvents and for mixtures,
the authors concluded that "in mixtures of solvents, a clay will tend to
swell as though it were immersed in the component of higher dielectric
constant only" (Green et a!., 1979).
When Ranger shale was presented with benzene, breakthrough occurred on
the eighth day of testing. Breakthrough occurred at about day 25 in the
fire clay sample presented with xylene.
4-35
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TABLE 4-6. PROPERTIES OF SOILS TESTED1
Clays
Properties
Particle size distribution
(wt. %)
Clay
Silt
Sand
Total carbon (%)
Carbonate (%)
Cation exchange capacity
Atterberg limits
Plastic limit (moisture %)
Liquid limit (moisture %)
Optimum moisture content (%)
Corresponding dry density
(g/cm3)
Mineralogy (% of clay
fraction)
Kaol inite
Quartz
111 ite/mica
Chi ori te-montmori 11 oni te
Ranger
shale
40
59
1
0.60
0.32
54.4
36
46
17.5
1.73
24
28
24
10
Fire
clay
44
55
1.5
0.03
0
11.2
31
32
16
1.81
78
16
10
Negl igible
Kosse
kaoline
53
47
0
0.12
0
13.4
38
50
31
1.36
85
10
5
Negligible
Parker
soil
10.5
70.5
19
3.18
0.42
14.1
22
26
18
1.86
14
Negligible
37
49
Data from Green et al., 1979.
4-36
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TABLE 4-7. CLASSIFICATION OF CLAY-ORGANIC SOLVENT SYSTEMS
ACCORDING TO SWELL PROPERTIES3
Swelling
only
RS/H20
RS/glycerol
RS/methanol
RS/CC14
RS/TCE
KK/water
KK/acetone
FC/water
Swelling then
shrinking
RS/acetone
KK/xylene
FC/acetone
FC/TCE
FC/xylene (NS)
Shrinking then
swelling
RS/benzene
KK/TCE
FC/benzene
Shrinking
only
RS/xylene (NS)
KK/CC14 (NS)
FC/CC14 (NS)
RS = Ranger shale KK = Kosse kaoline
FC = Fire clay TCE = Trichloroethylene
NS = Net shrinkage (net swell
observed unless indicated
otherwise)
Reproduced from Green, Lee, and Jones, 1979.
4-37
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TABLE 4-8. PERCENT SWELL FOR CLAY SOILS IN CONTACT
WTH ORGANIC LIQUIDS AND WATER
Clay-soil
Ranger shale
Kosse kaoline
Fire clay
Solvent
Benzene
Benzene/acetone (3:l)c
Xylene
Carbon tetrachloride
Tri chl oroethy 1 ene
Acetone
Acetone/benzene (3:l)c
Acetone/water (1:1)
Methanol
Glycerol
Water
Xylene
Acetone
Water
Xylene
Carbon tetrachloride
Acetone
Water
Percent swell
0.05
5.75
-0.11
1.1
1.0
4.0
4.6
11.0
11.4
5.3
11.7
0.16
8.7
11.7
-0.25
-0.6
3.6
8.2
Adapted from Green et al., 1979.
Negative value indicates net shrinkage.
cMole percent.
Volume percent.
4-38
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For organic solvents other than benzene, a decrease in permeability of
Ranger shale was observed for 5 to 10 days. This decrease was followed by
stable readings at a minimum value. The permeability coefficients reported
are shown in Figure 4-4. Although there is some scatter in the measurements
characteristic of normal experimental error, the decreasing permeability
trends over the duration of the test period are evident. The largest
decrease in permeability compared to water is seen with glycerol. With
carbon tetrachloride, the decrease in permeability was followed by an
increase that continued to the end of the test period.
4.5.8.3 Discussion--
The authors based their final conclusion, an empirical relationship
for estimating the coefficient of permeability from dielectric constant of
the permeant and packed bulk clay density, on what they judged to be final
permeabilities. Their data do not indicate that stable permeabilities were
reached, however, in all of the solvent clay systems tested. Certainly the
permeabilities measured just prior to breakthrough could not be classified
as stable, yet these were used in obtaining the empirical equation to
predict permeability.
4.5.9 Anderson's Study (1981) of the Effects of Orgam'cs on Permeability
Anderson (1981) at Texas A&M University studied seven organic fluids
in comparative permeability tests. Four native clay soils were tested—two
with predominantly montmorillonite (smectitic) clay minerals but different
chemical properties, one with predominantly kaolinite minerals, and one
with predominantly illite. Each soil contained a minimum of 35 percent by
weight clay minerals and exhibited a baseline permeability of less than I x
10 * cm/s when compacted at optimum water content. Organic solvents tested
were reagent grade ethylene glycol, acetone, heptane, xylene (mixed isomers),
aniline, glacial acetic acid and methanol. The control fluid used to
establish the baseline permeability for each soil was a standard aqueous
solution of calcium sulfate (0.01 N CaS04). (Although it was not noted in
the initial publication of this research, the methanol used in the experi-
ment contained 20 percent water [Anderson 1982].)
Characteristics of the four soils used in the tests are presented in
Table 4-9. The percentage of soil voids filled with water at compaction at
optimum moisture content was approximately 75 percent for the two smectitic
clays and approximately 90 percent for the other two samples. The minimum
permeability for each sample occurred at or just above the optimum moisture
content (Anderson et al., 1981; Brown and Anderson, 1982).
4.5.9.1 Test Method--
Permeability was measured in constant head tests on soil cores compacted
at or above optimum water content. Pressurized compaction permeameters
with an air-induced elevated hydraulic gradient were used. For two montmor-
illonite clays, a gradient of 361.6 (equivalent to a hydraulic head of 42.2
m of water) was used. For the illite and kaolinite clay soils, a hydraulic
gradient of 61.6 (equivalent to a hydraulic head of 7 m of water) was
imposed. No signs of particle migration or turbulent flow resulted from
the elevated gradients.
4-39
-------
•t- Carbon Tetrachloride
a Xylene
4 Trichloroethylene
• Qeionizsd Water
0 Glycsrol
x Acetone
A Methanol
Source: Green, Lee, and Jones, 1979
Figure 4-4. Coefficient of permeability of Ranger shale to various chemicals.
4-40
-------
TABLE 4-9. GRAIN SIZE DISTRIBUTION, MINERALOGY, AND PROPERTIES
OF THE FOUR CLAY SOILS3
Clay soil
description
% Sand (>50 nm)
% Silt (50-2.0 nm)
% Clay (<2.0 nm)
Coarse clay (2.0-0.2 nm)
% of total.
Mineralogy
Fine clay (<0.2 nm)
% of total.
Mineralogy
Cation exchange capacity
(meq/100 g)
Total alkalinity (meq/100
Fe203 (%)
Organic matter (%)
CaC03 Equiv. (%)
Shrink-swell potential
Liquid limit
Plasticity index
Optimum water content
Maximum density (kN m )
Non-
calcareous
smectite
35-37
26-28
36-38
16
QZ-1
KK-2
MI-2
84
MT-1
24.2
g) 3.3
0.42
0.9
-
Very high
51-67
30-45
20.0
15.0
aAdapted from Anderson, 1981.
Key to mineralogy: MT = Smectite 1
KK = Kaolinite 2
I = Illite 3
Calcareous
smectite
7-8
42-44
48-50
25
MT-1
KK-2
QZ-3
75
MT-1
KK-3
36.8
129.2
0.2
3.0
33
Very high
58-98
34-72
21.5
14.4
= >40% QZ
= 10-40% MI
= <10% KH
Mixed
cation
kaolinite
39-41
17-18
42
33
KK-1
QZ-2
67
KH-1
MI-3
8.6
0.8
13.2
0.6
Trace
Mixed
cation
i 11 i te
14-15
38-39
47
61
1-1
QZ-2
39
1-1
MT-2
18.3
4.2
-
-
-
Moderate Moderate
41-60
18-30
20.0
16.3
= Quartz
= Mica or il
= Halloysite
-46
-27
19.0
16.6
lite
'Percent by dry weight.
4-41
-------
Special precautions were taken to minimize several sources of error
that occur frequently in permeability testing. At least one pore volume of
the CaS04 solution was passed through the soil cores to minimize trapped
air. Before the permeameter was pressurized, the top of the soil sample
was exposed to 10 cm of standard CaS04 solution for 48 hours. This procedure
helps to prevent channel formation and bulk flow and promotes sealing of
the permeameter sidewalls. Provision was made to view the effluent passing
through the soil sample so that trapped air or evidence of piping could be
monitored. Care was taken to minimize evaporative losses from the collected
effluent. Teflon fittings were used wherever possible to avoid deterioration
from exposure to the organic solvents.
After seating the soils at low pressure,, the selected gradient was
applied to the permeameter fluid chamber until stable permeability values
were obtained with the standard CaS04 solution. At this point, pressure
was released and permeameters were disassembled. Soil that had expanded
out of the mold was removed and additional standard leachate was passed
through the remaining sample in the permeameter. Percent swelling was
determined for each soil. At this point, the soil sample was assumed to be
completely saturated.
After the saturation step to ensure stable baseline permeability, the
remaining standard CaS04 solution was removed and replaced with one of the
organic solvents to be tested. The selected gradient was imposed and
between 0.5 and 2.0 pore volumes of fluid were passed through the sample in
the permeameter. The permeameters were then depressurized, disassembled,
and the cores removed and examined for evidence of structural changes.
Following the permeability tests of the noncalcareous smectite clay soil
with aniline, methanol, and ethylene glycol (all highly water-soluble),
water was reintroduced to the test columns and permeabilities were again
determined.
During the permeability tests, effluent was carried to an automatic
fraction collector, which separated the samples obtained from 10 permeameters
during specific time increments. The percentage of organic fluid in the
effluent samples was determined to develop breakthrough curves. A permea-
bility value, leachate volume, and time increment were obtained on each
volume of fluid passed through a sample.
4.5.9.2 Test Results--
Baseline permeability (two pore volumes) for the four soils is depicted
in Figure 4-5. Permeability data obtained for the various organics tested
are presented in Figures 4-6 through 4-13 (Anderson, 1981; Anderson et al. ,
1981; Brown and Anderson, 1982). Findings as described by the authors are
excerpted below:
Acetic Acid (glacial)--A11 four clay soils permeated with acetic
acid showed initial decreases in permeability . . . thought to be
due to partial dissolution and subsequent migration of soil
particles. These migrating particle fragments could lodge in the
fluid-conducting pores, thus decreasing cross-sectional area
available for fluid flow.
4-42
-------
10 —
u ""*
10'
NCNCALCAREOUS SMECTITE
CALCAREOUS SMECTITE
MIXED CATION KAOUN1TE.
MIXED CATION I LUTE
A
O
WATER (OQ1N CaSO4)
OS OO Q5 LO I.5 2.0 2.5
PORE VOLUMES
Source: Anderson, 1981
Figure 4-5. Permeability of the four ciay soils to water (0.01N CaSo4).
3,0
4-43
-------
NCNCALCAHEQUS SMECTITE
CALCAREOUS SMECTITE
MIXED CATION KADLJNITE
MIXED CATION I LUTE
ACETIC ACJD
Q5 LO 1.5
PORE VOLUMES
2.0
2.5
3.0
Source: Anderson, 1981
Figure 4-6. Permeability of the four clay soils to acetic acid.
4-44
-------
100-
8104*
i/
I
LU
NCNCALCAREOUS SMECTITE
CALCAREOUS SMECTITE
MIXED CATION KAOUNITE
MIXED CATION ILL1TE
Q5
Source: Anderson, 1981
as LO 1.5
PORE VOLUMES
2.0
2.5
3.0
Figure 4-7. Permeability and breakthrough curves of the four clay
soils treated with aniline.
4-45
-------
t
NONCALCAREOUS SMECTITE
CALCAREOUS • SMECTITE.
MIXED CATION KAOUNITE
MIXED CATION I LUTE
ETHYLENE GLYCOL
CXO
0.5 LO 1.5
PORE VOLUMES
2.0
2.5
3.0
Source: Anderson, 1981
Figure 4-8. Permeability of the four clay soils to ethylene glycol.
4-46
-------
NCNCALCAREQUS SMECTITE
CALCAREOUS SMECTITE
MIXED CATION KAOUNITE
MIXED CATION ILL1TE
ACETONE
10
Q5 LO 1.5
PORE VOLUMES
Source: Anderson, 1981.
Figure 4-9. Permeability of the four clay soils to acetone.
4-47
-------
I
-p.
00
-rj
(Q*
i
o
t
»£•
a
2.0
0)
3 g.
X (A
2 ~
a o
O 3
I*
2 =»"
3 D>
= 3
=r O
i-»- —
og
2.0.
8fl>
O"
m
(Q
3-
a
(D
C TJ L,
2 (0 (O
s
3)
m
o
r
P
01
o
r°
In
O
PERMEABILITY (cm/sec)
q o
j l I I i till41 | I l 11
% METHANOL
IN EFFLUENT _
O
o o
M I I I I I 1 *
O
r
fIN" CHANGED FROM HzO TO METHANOL—-
• o
-------
Q5
LO L5 2.0 2.5
PORE VOLUMES
3.0
Source: Anderson, 1981
Figure 4-11. Permeability of the methanol-treated mixed cation illitic clay soil
at two hydraulic gradients.
4-49
-------
lOOi
NCNCALCAREOUS SMECTITE
CALCAREOUS SMECTITE
MIXED CATION KAOL1NITE
MIXED CATION 1LUTE
XYLENE
0.5 LO 1.5
PORE VOLUMES
Source: Anderson, 1981
Figure 4-12. Permeability and breakthrough curves of the four clay
soils treated with xylene.
4-50
-------
NCNCALCAREOUS SMECTITE
CALCAREOUS SMECTITE
MIXED CATION KAOUNITE
MIXED CATION I LUTE
HEPTANE
0.5 LO 1.5
PORE VOLUMES
Source: Anderson, 1981
Figure 4-13. Permeability and breakthrough curves of the four clay
soils treated with heptane.
4-51
-------
Two of the soils treated with acetic acid (calcareous smectite
and mixed cation kaolinite) showed continuous permeability de-
creases throughout the test period. After passage of approximate-
ly 20 percent of a pore volume, the acid treated kaolinitic clay
generated a dark red-colored effluent . . . probably due to
dissolution of iron oxides. The acid treated calcareous smectite
began passing cream-colored foamy effluent after passage of about
28 percent of a pore volume. . . . The creamy material was probably
dissolved calcium, while the foam was the result of C02 liberation
from the dissolved carbonates.
Both noncalcareous smectite and the mixed cation illite eventually
showed permeability increases after . . . passage of 39 percent
and 62 percent of a pore volume, respectively. . . . Permeability
increases with both of these soils were probably due to progressive
soil piping that eventually cleared initially clogged pores.
Aniline—Both noncalcareous smectite and mixed cation illite had
breakthrough of aniline with concurrent permeability increases at
pore volume values (beTow 0.5). . . . Aniline broke through after
passage of one pore volume for the kaolinitic soil. The calcareous
smectite . . . permeability increased rapidly at first, but
showed substantial decrease concurrent with aniline breakthrough.
After the permeability decrease, this soil exhibited a slow but
steady permeability increase.
There were no signs of migrating soil particles in any effluent
samples. . . . Apparently, aniline is too weak a base to cause
significant dissolution of clay soil components. However, . . .
the organic base caused extensive structural changes in the upper
half of the soil cores. The massive structure of the four
soils . . . was altered by aniline into an aggregated structure
characterized by visible pores and cracks in the surface of the
soils.
Ethylene Glycol— . . . Permeability values indicated that it was
the ability of ethylene glycol to alter the soil fabric that was
the dominating influence on permeability. Three of the clay
soils treated with ethylene glycol showed initial permeability
decreases. The kaolinitic clay soil continued to undergo permea-
bility decreases as long as it was being tested. The illitic
clay soil began showing a permeability increase after passage of
0.5 pore volumes. In contrast, the calcareous smectite followed
its initial permeability decrease with a substantial increase, a
second decrease, and finally reached a nearly constant value that
continued until the end of the test period.
-The noncalcarecus smectitic clay soil treated with ethylene
glycol showed an initial rapid increase in permeability and a
slower but continuous increase after passage of 0.5 pore volume.
Acetone—All soils treated with acetone had initial permeability
decreases. These decreases continued until passage of approxi-
mately 0.5 pore volume. During passage of the next 0.5 pore
volume, however, the soils underwent large permeability increases.
One possible explanation for this sequence of permeability changes
is as follows:
4-52
-------
1. The higher dipole moment of acetone caused initial increase
in inter!ayer spacing between adjacent clay particles as
compared to water only.
2. As more acetone passed through the soil cores, more water
layers were removed from clay surfaces. Due to its larger
molecular weight, however, fewer acetone layers were adsorbed
than had adsorbed when water was the only fluid present.
This resulted in a larger effective cross-sectional area
available for fluid flow.
While acetone can displace water from clay surfaces due to its
higher dipole moment, it cannot form as many adsorbed fluid
layers as water due to its higher molecular weight.
Examination of the soil after acetone treatment showed extensive
shrinkage and cracking. Such soil shrinkage is usually associated
with dehydration, indicating that acetone had extracted water
from soil particle surfaces.
Methanol--Unlike soils treated with acetone, methanol-treated
soils underwent no initial permeability decrease.
Percent methanol in the effluent from the illitic clay soil
paralleled an increase in permeability of the soil. After passage
of 1.5 pore volumes, the hydraulic gradient was reduced from 61.1
to 1.85 and another pore volume of methanol passed. After an
initial decrease, permeability of the soil steadily increased at
the lower hydraulic gradient. ... No particle migration was
detected in effluent from methanol-treated cores, and therefore
soil piping was discounted as a mechanism for observed permeability
increases. Examination of methanol-treated soil cores revealed
development of large pores and cracks visible on the soil surface.
The lower dielectric constant of methanol may have caused a
decrease in inter!ayer spacing of the clay minerals present in
the soils and thereby promoted the structural changes.
Xylene--Xy!ene-treated soils showed rapid permeability increases
followed by nearly constant permeabilities roughly two orders of
magnitude greater than their permeabilities to water. Permeability
increases may be caused by ... structural changes in the
xylene-treated soils, exemplified by massive structure before
treatment and blocky structure after the soils were treated with
xylene.
Heptane—Permeability patterns for the heptane cores closely
approximated those shown by the xylene-treated cores (i.e., large
initial permeability increases). Following these initial large
increases, rate of permeability increase slowed until nearly
-constant permeability values were observed.
Only the calcareous smectitic clay showed . . . permeability to
heptane well below its permeability to xylene. The constant
permeability values eventually reached by the neutral nonpolar
treated cores were probably related to the limited ability of
these fluids to penetrate interlayer spaces of the clay minerals.
4-53
-------
4.5.9.3 Reintroduction of Water-
When the standard calcium sulfate solution was reintroduced to the
noncalcareous smectite test columns permeated with aniline, methanol, and
ethylene glycol, a subsequent decrease in the permeability (roughly 1 order
of magnitude) was observed. The final permeability (after one pore volume
of standard solution) remained well above the baseline permeability measured
prior to introduction of the organic solvents (Anderson, 1981).
4.5.9.4 Discussion—
Viscosity and density differences between the organic fluid and water
do not account for the large changes in permeability observed in the tests.
The data from these permeability tests illustrate the importance of passing
multiple pore volumes of fluid through the soil samples in order to deter-
mine the effects of solvents on permeability.
The work by Anderson has been criticized as being "unrepresentative of
real conditions" because pure organic solvents (rather than waste leachate)
were used in the permeability tests (Gray and Stoll, 1983). The test
results stand, however, as a demonstration of potential effects on clay
liners should they come in contact with certain types of undiluted organic
liquids.
The high gradients used in the tests have also been questioned (Zoeller,
1982; Gray and Stoll, 1983) since it is unlikely that gradients as high as
361 would be encountered in the field. The use of elevated gradients in
laboratory testing in order to reduce testing time is not uncommon. Although
the gradients used by Brown and Anderson were higher than those used by
most researchers, the permeability changes observed cannot be attributed to
the elevated gradients. Conditions were maintained well within the laminar
flow regime (i.e., Reynolds number was below 10) so that Darcy's Law for
computing the permeabilities remained valid. In general, the trends observed
in these tests are consistent with data from other researchers, and explana-
tions can be linked to the findings from clay-chemical complex studies.
Complete saturation in the compaction permeameter without backpressure
cannot be ensured. It is possible that air introduced with the permeant
fluids could have influenced the test results to some extent, but probably
by no more than one order of magnitude.
Finally, the use of fixed-wall permeameters for these studies has been
criticized (because of the potential for sidewall leakage) by advocates of
triaxial test methods. As there are advantages and disadvantages with
eithe'r method, the argument as to which test is most meaningful is finally
a matter of opinion.
_Acetic acid, a weak organic acid, has a dissociation constant of 1.75
x 10~5 in aqueous solution (pKa = 4.75) at 25 °C. Since glacial acetic
acid was used, the extent of ionization was a fraction of this. The perme-
ability decreases observed probably would have been followed by sharp
increases in permeability due to dissolution of the basic soil components
if a dilution had been used rather than glacial acetic acid. Progressive
4-54
-------
soil piping, as pointed out by Brown and Anderson, follows the soil dissolu-
tion and eventually results in large pores with an associated increase in
permeability.
This effect (i.e., increased permeability) is to be expected with
carboxylic acids or sulfonic acids in general. This is of particular
significance since carboxylic acids are among the biological degradation
products of a wide range of organic compounds. Soils that are high in
carbonates are most affected by acids (even weak acids such as acetic
acid), but other soil constituents such as Fe203 are also susceptible.
4.5.10 Schramm's Study (1981) of the Permeability of Soil to Organic
Solvents
Schramm (1981) evaluated permeabilities for eight soils tested with
kerosene, isopropyl alcohol, ethylene glycol, and mixed xylenes. Permeabil-
ity with water was also measured. A total of 211 column tests were run to
determine saturated permeabilities to the various test fluids. The research
was performed at the University of Arizona.
Clay content in the soils ranged from 1 percent in River Bottom sand
to 70 percent in Lake Bottom clay. Characteristics of the soils are pre-
sented in Table 4-10.
4.5.10.1 Test Method-
Permeabilities were obtained in glass or plexiglass cylinders through
the falling head method. Cylinders 5.8 cm in diameter were used in the
tests with soil packed to a depth of 5 cm. Soil was retained in the cylin-
ders by a galvanized screen glued to the cylinder. Prior to testing,
samples were immersed overnight in the test solvent. During the test, the
height of the solvent column above the soil surface varied between 6 and 2
cm. Six replicates were tested for every solvent-soil combination. Experi-
ments were repeated until a constant permeability value was obtained.
Length of runs varied from 1-1/2 minutes to several weeks. An analysis of
variance was performed to evaluate differences between intrinsic permeability
for the various soils and solvents.
4.5.10.2 Test Results—
A summary of the saturated permeability values (expressed in cm/h)
obtained from these tests is given in Table 4-11. It is notable that with
each soil tested the highest permeabilities were obtained with the nonpolar
organics, kerosene, and xylene. (Kerosene is a mixture of C12-C18 compounds
and includes both aliphatics and aromatics.)
Intrinsic permeabilities were also calculated to take into account
differences in viscosity and density for the various permeant fluids.
Analysis of the intrinsic permeability values included a one-way variance
test to determine if the intrinsic permeability varies significantly with
solvents or with soils. The intrinsic permeabilities for a given soil are
expected to be constant unless there is interaction between the soil and
the permeating liquid. The differences in intrinsic permeability with the
4-55
-------
TABLE 4-10. CHARACTERISTICS OF SOILS USED IN PERMEABILITY TESTS
en
en
Cation
Sol 1 exchange
Soil Clay Silt Sand paste capacity
Soil name order % % % pH (meq/100 g)
Lake Bottom clay Entisol 70.6 24.0 5.4 7.7 34.7
Nicholson Alfisol 49.0 47.0 3.0 6.7 37.0
Fanno Alfisol 46.0 19.0 35.0 7.0 33.0
Chalmers Mollisol 31.0 52.0 14.0 6.6 22.0
Canelo Alfisol 28.0 28.6 43.4 5.6 5.76
Anthony Entisol 15.0 14.0 71.0 7.8 10.0
Mohave Aridisol 11.1 37.0 52.0 7.3 10.0
River Bottom sand Entisol 1.0 2.0 97.0 7.2 2.0
Electrical
conductivity Column Soil
of saturated bulk surface
extract density area
(umho/cm) (g/cm3) (mVg)
1,111 1.52 142.0
176 1.53 120.5
392 1.48 122.1
288 1.53 95.6
240 1.72 35.0
328 1.87 49.8
615 1.78 38.3
210 1.80 3.6
Predominant
clay
minerals
Illite
Kaolinite
Vermiculite
Montmorillonite
Mica
Montmorillonite
Vermiculite
Montmorillonite
Mica
Mica
Kaolinite
Kaolinite
Mica
Adapted from Schramm (1981).
-------
TABLE 4-11. , PERMEABILITY COEFFICIENTS (cm/s) DETERMINED IN SOILS TESTED WITH
ORGANIC SOLVENTS
Solvent
Soil
Lake Bottom clay
Nicholson
Fanno
Chalmers
f- Canelo
Anthony
Mohave
River Bottom sand
5.
4.
I.
I.
5.
9.
1.
1.
Water
0 x 10
2 x 10"6
5 x 10"4
8 x 10
0 x 10
9 x 10
9 x 10
7 x 10
Kerosene
3.
9.
5.
3.
5.
2.
2.
3.
4 x io"4
5 x 10~5
2 x 10
8 x 10
6 x 10
0 x 10~4
6 x 10~3
4 x lo"2
Isopropyl
alcohol
2.1
2.3
3.1
2.3
3.5
9.5
1.6
5.8
x 10"4
x 10"5
x 10"3
x 10"5
x 10"5
x 10"5
x 10~3
x 10~3
Ethyl ene
glycol
1.
6.
3.
1.
1.
5.
2.
6.
1 x
8 x
0 x
8 x
4 x
8 x
0 x
4 x
10~5
io-7
io-4
io-6
ID'6
ID'6
ID'4
ID'4
Xylene
1.7 x
3.5 x
1.8 x
1.7 x
1.5 x
4.4 x
8.5 x
1.8 x
ID"3
10~4
ID'2
ID'4
ID"4
ID'4
10~3
io-2
Data from Schramm (1981).
-------
different solvents are shown in Figure 4-14 for five soils. The trend for
increased intrinsic permeability is readily apparent.
The analysis also shows rather uniform behavior of intrinsic permeabil-
ity for solvents in the different soil types, the Fanno, Mohave, and River
Bottom Sand having highest relative intrinsic permeabilities with all
organic solvents.
From the data summary and analysis of variance, Schramm (1981) concluded
that:
Calculated values of intrinsic permeability vary for the same soil
depending on solvent. However, the variation is relatively minor
compared to variation due to differences in soil properties among
several soils. . . .
Since intrinsic permeability values vary for the same soil depending
on solvent, the soil and solvents are interacting.
4.5.10.3 Discussion—
The test method used by Schramm differed significantly from that
employed by Anderson (1981) to measure permeability. Notable differences
include the following:
Gradients imposed on the sample were very low.
No estimate was made of the pore volumes passed through the
test samples.
Samples were presaturated with the test fluid rather than a
standard calcium-sulfate solution.
The impact of the low hydraulic gradient on the test results is not
known. The concept of "threshold gradient" has been postulated, although
there is no evidence of this effect in the results reported by Schramm.
Although Schramm reports that tests were continued until constant
permeability values were obtained, the criterion to establish an acceptable
difference in consecutive measurements was not discussed. There is no
indication of the number of pore volumes exchanged.
It may be argued that saturating the samples using the test permeant
fluid rather than water or a standard permeant solution is representative
of conditions typical for a liner in service in a land disposal application.
4.5.11 Evaluation by Monserrate (1982) of the Permeability of Two Clays
to Selected Electroplating Wastes
Monserrate (1982) at Duke University investigated the permeability of
two clays exposed to simulated electroplating wastes. The purpose of the
research was to examine the effect of compaction on the permeability response
of the two clays. The clays tested were a Wyoming bentonite and a White
4-58
-------
14
12-
10-
•
6'
4-
'8 2
I
I
LAKE BOTTOM CLAX
^^""^
H
M
a c.
< °
u
1 5-
a.
U 4.
Ul
5 3'
s
z
2'
1 •
0,
NICHOLSON
_n
2 ,
1
n .
CHAL.MZHS
, , |
••••M
•^•^H
Key:
MVTR •
STGL i
ISOP
KEHO
XYL
L
^^••^
• watsr
» Ethel yne Glycal
• Isopropyl
- Kerosine
« Xylene
f--1"^
ANTHONY
nr
^MMIM
n
CANZLO
, ,
"1
— .
•^MM
n
HATR ETGL ISOP KESO X2L WATS STGL ISOP JXRO
SOLVENTS
Source: Schramm, 1981
Figure 4-14. Variation of intrinsic permeability with solvent for each soil.
4-59
-------
Store clay from North Carolina. The White Store clay was reported to be an
active clay.
The simulated electroplating wastes used as permeant fluids were a
1-molar solution of zinc chloride (ZnCl2) (136.3 g/L, pH = 5.5) and a
1-molar solution of chromic acid (H2Cr04) (100 g/L, pH = 1.5).
4.5.11.1 Test Method-
Standard Proctor tests were conducted on each clay to establish the
relationship between water content and compacted density. Procedures
outlined in ASTM D-698 Method A (ASTM 1985) were followed. Permeability
studies were subsequently conducted at several different moisture contents.
For the permeability tests, the samples were prepared by mixing 0.01 N
calcium sulfate with the clay to achieve the desired moisture content. The
clays were compacted into either zinc-plated or lucite compaction permeameters
using compactive efforts comparable to those used in the standard Procter
tests. The compaction permeameters measure 4 inches (10.16 cm) in diameter
and 4.6 inches (11.68 cm) in height. Clays were compacted to a depth of
2 inches (5.08 cm). The compaction permeameters were adapted to allow measure-
ment of flow as the permeant fluid enters the unit. The data were evaluated
as a falling head test. A standard solution of deaired 0.01 N calcium
sulfate was used to saturate the sample prior to introducing the test
permeant fluids. The samples were exposed to the permeant fluids under
approximately 75 pounds of air pressure. In the permeability tests, a
statistical procedure was used to determine when enough data had been accumu-
lated to make a determination of the k value for a certain clay-permeant
fluid combination. (See details in Section 4.3).
4.5.11.2 Test Results-
Tests with bentonite showed that at moisture contents in the proximity
of the optimal compacted moisture content, permeabilities to calcium sulfate,
chromic acid, and zinc chloride were all on the order of 10 10 cm/s. At
lower moisture contents, the permeability to calcium sulfate was higher by
a factor of 2 than the permeability to the chromic acid test solution.
At wet-of-optimum water contents, however, the permeabilities determined
for the two fluids were nearly identical. The same low water content
divergence in permeability was observed for the zinc chloride test fluid,
although the magnitude of the difference was less.
The permeability of White Store clay to standard calcium sulfate
solution and to the test fluids is shown in Figure 4-15 as a function of
the moisture content at compaction. The White Store clay appeared to be
more sensitive than the bentonite clay to changes in compacted moisture
content. The permeability to the chromic acid test fluid aligns closely
with that of calcium sulfate at moisture contents higher than about 20 per-
cent (optimum moisture content = 21.5 percent). At lower than about 20 per-
cent moisture, the permeability to the chromic acid was higher than to
calcium sulfate. Zinc chloride test fluid showed permeabilities lower than
for calcium sulfate at low moisture.
4-60
-------
i
CTl
3.6 X 10
-7
-7
3.0 X 10
~ 2.4 X 10~7
8 7
E 1.8 X 10-7
a)
o_
,-7
1.2 X 10
6.0 X 10'8
CaSO,
i a. ao
Moisture Content at Compaction
Source: Monseratte, 1982
Figure 4-15. Permeability of White Store clay to 0.01 N calcium sulfate, chromic acid
(1 molar), and zinc chloride (1 molar) as a function of moisture at compaction.
-------
Monserrate (1982) concluded that for both bentonite and White Store
clays, the application of zinc chloride and chromic acid did not alter the
clay's permeability response, indicating that the structure of the clay, as
compacted, is the predominant influence in determining permeability. She
noted that the test results differed markedly from those of Coia (1981) who
carried out similar studies at Duke University using the chromic acid.
Monserrate noted that there was extensive corrosion of the steel
permeameters and some of the pressure fittings that were exposed to the
chromic acid test fluid.
4.5.12 Research by Brown. Green, and Thomas (1983) on the Effect of Two
Organic Hazardous Wastes on Simulated Clay Liners
Brown, Green, and Thomas (1983) at Texas A & M University reported
results of permeability tests in which clay soil samples representative of
three types of simulated clay liners were subjected to a xylene waste and
an acetone waste in both laboratory and field studies. The three clay
materials tested were predominantly kaolinite, mica, or bentonite. The
soils were blended with sandy loam soil to attain permeabilities in the
range of 1 x 10 7 to 1 x 10 8. The laboratory studies in fixed-wall perme-
ameters were directed at determining the influence of different initial
moisture contents and elevated gradients on the clay permeabilities. The
procedures used in the laboratory tests were similar to those described by
Anderson (1981) and Brown and Anderson (1982) in earlier permeability tests
with organics. The research was sponsored by the U.S. EPA.
The xylene waste, a paint solvent that was used to clean factory
sprayer lines, contained 25 percent paint pigments and trace amounts of
water. The acetone waste was a chemical manufacturing waste containing
91.7 percent acetone, 4 percent benzene, 0.6 percent phenol, and 3.7 percent
unknown.
4.5.12.1 Test Methods—
For the laboratory tests, soils were compacted wet of optimum to at
least 90 percent Proctor density. Prior to exposure to the waste solvents,
samples were saturated with 0.01 N calcium sulfate. Unsaturated cores were
also subjected to the permeability tests. Pressures of 5, 15, and 30 psi
(equivalent to hydraulic heads of 31, 91, and 181) were tested.
Twenty-eight field cells (1.5 m x 1.5 m x 1.8 m inside dimensions)
were constructed of reinforced concrete and lined with 100-mil high-density
polyethylene to facilitate leachate collection. The clay soils were com-
pacted with a vibratory compactor to 95 percent Proctor in two 7.5-cm-thick
lifts. The liquid waste to be tested was introduced into each cell through
a standpipe into barrels that were placed above the liners. A head of 1 m
of liquid (gradient of 7) was maintained throughout the test. Permeabilities
were calculated based on the volume of cell drainage collected during
discrete time intervals. Following the permeability tests, each cell was
disassembled and subjected to chemical and morphological analysis. The
wastes to be tested in the field cells were dyed with Automate Red B and
Fluorescent Yellow to facilitate detection within the sample cores.
4-62
-------
4.5.12.2 Laboratory Test Results--
To compare the results from the various tests, calculated permeabilities
were plotted as a function of the number of pore volumes of effluent that
passed through the sample. Permeabilities to standard calcium sulfate
solution on similar soils in the laboratory were generally found to be
reproducible to within 0.25 order of magnitude. Permeabilities increased,
however, when the organic-solvent wastes were substituted as the permeant
fluids. Permeability to the organic-solvent wastes was typically 2 to 4
orders of magnitude greater than the permeabilities measured with the
calcium sulfate solution. Presaturation with 0.01 N calcium sulfate appeared
to retard the effect of the permeant fluids on the samples (i.e., more pore
volumes were displaced before breakthrough occurred in the presaturated
samples). Highest permeabilities measured on initially unsaturated samples
were typically 1 to 2 orders of magnitude greater than for samples that
were initially saturated.
Permeability of the clay soils increased rapidly upon exposure to
xylene waste after the cumulative flow exceeded 0.2 to 0.4 pore volume.
The behavior of acetone was characterized by an initial small decrease in
permeability (minimum at approximately 0.5 pore volume), which was followed
by a steady increase in permeability. This behavior was explained as
follows: acetone first caused swelling of the clay soil with low concentra-
tions initially diffusing into the pores; as more of the water was displaced
by the solvent, shrinkage occurred.
Similar increases in permeability were observed for all three soil
types. The increase in permeability, however, for the bentonite samples
occurred after a larger pore volume was displaced.
If the permeability values calculated from the test data are plotted
as a function of pore volumes, the different hydraulic gradients used in
the experiments (31, 91, 181) have little influence on either the increase
in permeabilities observed or on the final values achieved. (This conclu-
sion holds for both presaturated and unsaturated samples [Brown et a!.,
1984]).
4.5.12.3 Field Test Results—
In the field studies, xylene had penetrated 10 of the 12 clay liners
within 12 months after installation; acetone had penetrated 2 of the liners
but at a slower rate. Increases in permeability of the bentonite clay soil
to xylene were more dramatic (as much as 2 orders of magnitude increase)
than of the other soils and occurred after passage of 0.5 pore volume of
permeant fluid. Kaolinitic and micaceous soils showed immediate increases
in permeability to xylene. Permeability values continued to increase as
more pore volumes of fluid passed through the sample. Increases of more
than 2 orders of magnitude were observed in some samples after passage of
two pore volumes of xylene.
Field tests with the acetone waste exposed to micaceous clay soil
showed a permeability decrease with the first 0.5 pore volume. This was
followed, however, by an increase in permeability. After two pore volumes
4-63
-------
had passed through the liner, the permeability was slightly higher than the
initial value measured.
Visual inspection of the clay liners following permeation by the
liquid wastes was facilitated by the dyes and by the paint pigment in the
xylene waste. Dyed surfaces observed throughout the liner indicated that
the liquid had moved through the soil through preferential channels rather
than in a clearly defined wetting front. Preferential channels were occa-
sionally found to extend from the top to the bottom of the liner. Evidence
that xylene moved through cracks in the liner or around blocky subangular
structural components was also obtained through chemical analysis of sections
of the permeated liners. The channels observed in the clays are attributed
to the displacement of water by the chemicals resulting in desiccation that
caused the clay to shrink and crack.
4.5.12.4 Discussion—
The results of this study, in close agreement with those previously
found by Brown and Anderson (1982), indicate that severe permeability
increases can occur when certain clay materials are in contact with concen-
trated organic solvents. Although the hydraulic heads used in the labora-
tory test procedures are higher than are likely to be encountered in the
field, the data suggest that the permeabilities measured are independent
of the hydraulic gradient used in the test. These results further support
the conclusions by Anderson based on tests involving a gradient of 361.
The effect of presaturation with calcium sulfate on the highest permea-
bilities is significant. Laboratory tests by other researchers (Green
et al., 1979; Foreman and Daniel, 1984) have also involved introducing the
test permeant fluid onto the unsaturated sample.
4.5.13 Study by Brown, Thomas, and Green (1984) of the Effect of Dilutions
of Acetone and Mixtures of Xylene and Acetone on Permeability of a
Micaceous Soil
To determine the effect of diluting a polar organic solvent with
water, Brown, Thomas, and Green (1984) measured the permeability of an
unsaturated micaceous compacted soil to several acetone-water dilutions.
Samples were tested at a gradient of 91 in laboratory tests with fixed-wall
permeameters. Solutions tested were 100, 75, 50, 25, 12.5, and 2 percent
acetone. Methods were similar to those used previously by Anderson (1981).
Compared to permeability to water (actually 0.01 N calcium sulfate),
an increase in permeability was seen for solutions where the concentration
of acetone was 75 percent or 100 percent. Samples permeated with lower
concentrations of acetone did not show appreciable changes compared to the
permeability to water.
Similar tests were conducted to determine the effect on permeability
of mixtures of xylene and acetone (Brown et al., 1984). For 100 percent
xylene, the permeability was reported to be 4 orders of magnitude greater
than the permeability to water (0.01 N calcium sulfate). When a mixture of
4-64
-------
87.5 percent xylene and 12.5 percent acetone was tested, the permeability
was dramatically reduced (i.e., more than 3 orders of magnitude below the
permeability to pure xylene). Values were comparable for a mixture contain-
ing 25 percent acetone and 75 percent xylene and for a 1:1 mixture. When
the acetone component was increased to 75 percent, however, the permeability
increased to approximately the value obtained in similar tests with pure
acetone. This value was about 1.5 orders of magnitude greater than the
permeability of the sample to 0.01 N calcium sulfate.
4.5.14 Tests by Brown, Thomas, and Green (1984) to Determine the
Permeability of Micaceous Soil to Petroleum Products
Brown, Thomas, and Green (1984) also reported permeability tests with
five commercial petroleum products. A compacted micaceous soil, unsaturated,
was permeated with the test fluids at a gradient of 91. The results of the
tests with kerosene, diesel fuel, paraffin- oil, gasoline, and motor oil are
shown in Figures 4-16 through 4-20, respectively. Conclusions of the tests
show that the micaceous soil is more permeable to these petroleum products
than to water (0.01 N calcium sulfate).
In tests with kerosene, the permeabilities were 3 to 4 orders of
magnitude higher than values measured with 0.01 N calcium sulfate in similar
samples. One-half the difference was achieved within the first 0.1 pore
volume. The permeability to paraffin oil was about 1 order of magnitude
greater than the comparable value to the calcium sulfate solution despite
its high viscosity. Maximum values were achieved by the passage of one
pore volume.
Test data obtained with diesel fuel were variable and did not appear
to increase along the patterns of most organics tested. No explanation is
offered for the unpredicted behavior. Values were, however, greater by 1
to 2 orders of magnitude than permeability to water. This was also the
case for gasoline. The test with motor oil showed a steady increase in
permeability from 2 x 10 7 cm/s at 0.5 pore volume to 1.5 x 10 6 cm/s at 3
pore volumes.
4.5.14.1 Discussion—
The data obtained in tests with the commercial petroleum products
illustrate the importance of extended permeability tests to allow passage
of several pore volumes of fluid. Earlier data indicate that the effects
of organic permeant fluids are retarded in tests where the samples are
presaturated with water (or 0.01 N calcium sulfate). The tests on unsatu-
rated. samples may serve as better estimators of maximum permeabilities that
may result when clay liners are exposed to petroleum products.
4.5.15 Study by Brown and Thomas (1984) of the Permeability of
Commercially Available Clays to Organics
To determine the effect of organic fluids on currently available clays
that are sold for sealing and lining impoundments, Brown and Thomas (1984)
tested permeabilities of three commercially available clays admixed with
sand.
4-65
-------
i64-
03
<
LU
a:
u
Q.
,6*-
io7-
LAS MICA
KEROSENE
NO N SATURATED
GRADIENT 91
• REP I
X REP 2
O REP3
1 PORE VOLUME 2
Source: Brown, Thomas, and Green, 1984
Figure 4-16. Hydraulic conductivity versus pore volume for laboratory compacted
micaceous soil exposed to kerosene at a hydraulic gradient of 91.
4-66
-------
.65-
CT>
o
«
u>
x
O
CO
<
UJ
UJ
Q.
-7
io-
,o8
O
o
o
o
1.0
2.0
PORE VOLUME'
g.o
LAB MICA
DIESEL FUEL
NONSATURATED
GRADIENT 91
• REP I
X REP 2
O REP 3
• REP 4
4.O
5.0
6.0
Source: Brown, Thomas, and Green, 1984
Figure 4-17. Hydraulic conductivity versus pore volume for laboratory compacted
micaceous soil exposed to diesel fuel at a hydraulic gradient of 91.
-------
u
>.67H
03
<
UJ
2
cr
LU
0.
io8
io9
LAB MICA
PARAFFIN OIL
NONSATURATED
GRADIENT 91
• REP. 1
X REP. 2
O REP 3
PORE VOLUME2
Source: Brown, Thomas, and Green, 1984
Figure 4-18. Hydraulic conductivity versus pore volume for laboratory compacted mica-
ceous soil exposed to paraffin oil at a hydraulic gradient of 91.
4-68
-------
LAB MICA
GASOLINE
NONSATURATED
GRADIENT 91
REP 4
PORE VOLUME2
Source: Brown, Thomas, and Green, 1984
Figure 4-19. Hydraulic conductivity versus pore volume for laboratory compacted
micaceous soil exposed to gasoline at a hydraulic gradient of 91.
4-69
-------
i66i
u
9)
at
>io7-
03
<
UJ
2
cc
LU
Q.
io8
io9-
LAB MICA
MOTOR OIL
NONSATURATED
GRADIENT 91
X RER 2
•PORE VOLUME2
Source: Brown, Thomas, and Green, 1984
Figure 4-20. Hydraulic conductivity versus pore volume for laboratory compacted
micaceous soil exposed to motor oil at a hydraulic gradient of 91.
4-70
-------
4.5.15.1 Test Method-
Each clay was mixed with sand to obtain a permeability to water of
about 1 x 10 8 cm/s. Smectite is the dominant mineral in soil CC1 (blue
bentonite) and soil CC2 (a synthetically treated bentonite); a micaceous
mineral is dominant in soil CCS (Ranger Yellow). The soils were compacted
at optimum moisture in 10-cm fixed-wall molds using a mechanical compactor
as described in ASTM Procedure 698-70.
The compacted soils were exposed to the test fluid without presatura-
tion. Following a 24-hour equilibrium period, a pressure of 15 psi
(equivalent to a hydraulic gradient of 91) was applied to the liquid surface.
Leachate passed through the samples was collected at intervals to allow
calculation of the soil permeability. Fluids tested in replicate were
water (0.01 N calcium sulfate), acetone, xylene, kerosene, diesel fuel,
gasoline, and used motor oil. A statistical analysis was performed to
establish the variance among the data set for each permeant fluid. Means
were separated using a Duncan's Multiple Range test at a significance level
of P = 0.05.
4.5.15.2 Test Results—
The test results for all permeant fluids are summarized in Table 4-12.
All of the organic fluids tested produced dramatic increases over the
corresponding permeabilities to water, the increase ranging from 1 to 5
orders of magnitude. Some of the increases, though large, were not statis-
tically significant compared to the permeabilities measured with water due
to the large variability seen in the tests. The increases in permeability
were significant for all clays permeated with xylene and for both the
smectitic clays when permeated by gasoline and kerosene.
Generally the increase in the micaceous clay permeability was less by
I order of magnitude than the increases seen in the smectitic clays. The
untreated bentonite (CC1) showed the greatest permeability increase in
response to each organic test fluid. Since the untreated bentonite is the
soil that is most subject to shrinkage and the micaceous soil is least
subject to shrinkage, these findings are consistent with the theory that
shrinkage resulting in greater spacing between peds is responsible for the
changes in soil permeability.
4.5.16 Studies Conducted for EPA by Daniel (1983) and Foreman and Daniel
(1984) at the University of Texas, Austin
Under a cooperative agreement with EPA, Daniel and others have carried
out research to address how the permeability of clay soils is affected by
hydraulic gradient and by the test device when the permeant fluid is other
than water. Permeability tests were performed using three different types
of test devices—flexible-wall cells, fixed-wall compaction mold permeame-
ters, and consolidation cell permeameters—at hydraulic gradients of 10,
50, 100, and 300. The three soils studied were a noncalcareous smectite
(Lufkin clay), a mixed-cation illite (from Hoytville, Ohio), and a commer-
cially processed kaolinite (Hydrite R). Fluids tested were water (actually
0.01 N calcium sulfate), methanol, and heptane (Foreman and Daniel, 1984).
4-71
-------
TABLE 4-12. MEAN CONDUCTIVITY OF EACH SOIL TO EACH FLUID TESTED
(Brown and Thomas, 1984)
Fluid
Water
Acetone
Xylene
Gasoline
Kerosene
Diesel fuel
Motor oil
CC1
3.61 x lo"8ba
5.05 x I0"5b
1.76 x lo"4a
1.96 x I0"4a
1.49 x io"4a
5.17 x lo"5b
6.13 x I0"6b
CC2
2.58 x I0"8b
1.41 x lo"6b
7.28 x I0"4a
9.07 x 10~5a
9.10 x I0"5a
4.53 x 10~5ab
2.13 x lo"6b
CCS
1.57 x lo"8b
2.51 x lo"7b
1.00 x lo"4a
6.19 x I0"5b
5.68 x lo"5b
6.29 x I0"7b
9.48 x I0"7b
aValues in a given column followed by the same letter do not differ
significantly (P = 0.05).
4-72
-------
4.5.16.1 Test Method-
Most of the tests for the project were flexible-wall tests. The
fixed-wall and consolidometer tests were performed to allow comparison of
the data from the different devices. Soil samples were compacted at or
slightly dry of optimum moisture content according to ASTM D-698. Soils
were scarified between each lift. Samples to be tested in flexible-wall
cells were extruded from the 10.2-cm (4-inch) -diameter compaction mold and
trimmed to a height of 9.4 cm (3.7 inches). Similar diameter samples with
a height of 11.9 cm (4.7 inches) were tested in the fixed-wall permeameter
setup. Samples tested in the consolidation cell were taken from the central
portion of a compacted 10.2-cm (4-inch) sample. The sample was trimmed to
a height of 1.90 cm (0.75 inch) and a diameter of 6.4 cm (2.5 inches).
Prior to the permeability measurements, the soil samples were saturated
with the permeant fluid to be tested. For the flexible-wall tests great
care was taken to completely saturate the samples. This was accomplished
through soaking under vacuum and backpressuring. During the permeability
tests, the backpressure was kept at about 2.8 kg/cm2 (40 psi) and the cell
pressure at 3.87 kg/cm2 (55 psi). The average effective stress was 1.05
kg/cm2 (15 psi) for tests at the lower hydraulic gradients; an average
effective stress of 1.76 kg/cm2 (25 psi) was used when the gradient was
300.
4.5.16.2 Test Results--
Test results with Lufkin clay in the flexible-wall cells showed essen-
tially no change in permeability with time when methanol was used as the
permeant fluid. Data were obtained for passage of about 0.9 pore volume.
The permeability to methanol was virtually the same as with 0.01 N calcium
sulfate (Daniel, 1983).
Methanol test results with the kaolinite show that when permeability
is plotted as a function of pore volumes of flow, the curves have similar
shapes for the three types of permeameters. The compaction mold yields
somewhat higher permeability results than the other two test devices. Test
data are shown in Figure 4-21.
Permeability values for the kaolinite at different hydraulic gradients
were obtained with water and with methanol in the different test devices.
The following conclusions were drawn:
At high hydraulic gradients (values of 150 or larger),
kaolinite has a higher conductivity to methanol than to
water regardless of permeameter type.
At high hydraulic gradients, the flexible-wall and consolida-
tion- cell permeameters yield similar hydraulic conductivities
for both methanol and water; kaolinite is roughly twice as
permeable to methanol as to water for these two types of
permeameters.
4-73
-------
-6
o
0)
05
\
£
o
>N
>
-a
c
o
o
3
O
Pore Volumes of Flow
Source: Foreman and Daniel, 1984
Figure 4-21. Permeability versus number of pore volumes of flow for kaolinite
permeated with methanoi at a hydraulic gradient of 250 or 300.
4-74
-------
At high gradients, use of compaction-mold permeameters leads
to large scatter in measured hydraulic conductivity. On the
average, compaction-mold devices showed kaolinite to be
approximately 10 times more permeable to methanol than to
water. The lowest values of K measured with the compaction-
mold devices are nearly identical to values measured with
the other two devices. It is possible that sidewall leakage
contributed to the causes ....
With flexible-wall permeameters and two liquids and one
soil, hydraulic gradient appears to have little effect on
hydraulic conductivity ....
With consolidation-cell permeameters, hydraulic gradient has
a very substantial effect on hydraulic conductivity. At a
hydraulic gradient of 50, K to methanol is only half of K to
water, but at gradients of 200 to 300, K to methanol is
twice as large as K to water ....
Figures 4-22, 4-23, and 4-24 show the effect of hydraulic gradient on
tests with kaolinite in flexible-wall cells, consolidation cells, and
fixed-wall permeameters, respectively. The scatter in the fixed-wall
permeameter data does not allow conclusions to be drawn although there
appears to be a trend to increased permeability with increased gradient.
4.5.17 Tests Conducted for Chemical Manufacturers Association by Daniel
and Liljestrand (1984)
In work sponsored by the Chemical Manufacturers Association (CMA),
Daniel and Liljestrand at the University of Texas at Austin carried out a
laboratory study of the permeability of five clay soils to six aqueous
fluids representative of waste leachates or actual liquid wastes. The
purpose of the testing was to determine if dilute organic/water mixtures
produced the increases in permeability demonstrated by other researchers
using concentrated organic liquids as permeant fluids.
The soils studied included Texas Lufkin clay (also used in tests at
Texas A&M) and four soils supplied by CMA (identified as SI, S2, S3, and S4)
from actual landfill sites. Properties of the clays are listed in Table
4-13. Permeability tests were not performed on the SI clay since its index
properties and mineralogy were similar to those of the S2 clay.
Permeant liquids used in the tests were: a leachate from a solid-waste
landfill (L2); two liquids (LI and L3) from industrial waste impoundments;
an aqueous solution containing methanol at 5 percent (50,000 ppm); an
aqueous solution saturated with xylene (near 196 ppm); and the leachate,
LI, spiked with chloroform (200 ppm) and trichloroethylene (200 ppm) to
simulate a landfill leachate contaminated with chlorinated hydrocarbons.
Water used to prepare the dilute methanol and xylene solutions was actually
0.01 N calcium sulfate. Characteristics of the leachates LI, L2, and L3
are listed in Table 4-14.
4-75
-------
-6
0 h
-------
10 0
200
3 0 0
Hydraulic Gradient
Source: Foreman and Daniel, 1984
Figure 4-23. Permeability versus hydraulic gradient for kaolinite
permeated in consolidation cell permeameters.
4-77
-------
-6
o
O)
tn
E
o
-7 _
0
c
o
o
o
0
-8
M e t h a n o
Water
O
o
0 100 200 30u
Hydraulic Gradient
Source: Foreman and Daniel, 1984
Figure 4-24. Permeability versus hydraulic gradient for kaolinite
permeated in compaction mold cell.
4-78
-------
TABLE 4-13., PROPERTIES OF CLAY SOILS TESTED BY DANIELS AND LILJESTRAND (1984)
Property
Natural water content (%)
Optimum water content (%)
Specific gravity
Percent finer than #200
sieve
Percent sand
Dominant minerals
i Secondary minerals
1C
Organic carbon content
(% of dry weight)
Cation exchange capacity
(meq/100 g)
Plasticity index
SI
23
17
2.73
93
7
Illite
Chlorite
1.46
10
21
S2
22
24
2.81
93
7
Chlorite
Smectite,
kaolinite
0.83
20
32
S3
47
31
2.71
94
6
Smectite
Kaolinite
1.39
40
59
S4
32
18
2.71
87
13
Quartz
Illite,
kaolinite
1.79
5
16
Lufkin clay
23
21
2.66
81
19
Smectite
Kaolinite,
illite
0.28
25
42
-------
TABLE 4-14. LEACHATE CHARACTERISTICS3
Parameter measured
or reported
Suspended solids (mg/L)
Dissolved solids (mg/L)
Volatile solids (mg/L)
Total organic carbon (TOC)
(mg/L)
Chemical oxygen demand (COD)
(mg/L)
Potential (ORP) (mV)
PH
Conductivity (pmho/cm)
Metals (mg/L)
Cr
Cu
Pb
Ni
Zn
Organics (mg/L)
Ethyl benzene
Toluene
Nitrotoluene
Dinitrotoluene
Formaldehyde
Dichlorobenzene
Aniline
Toluenediamine
LI
465
20,202
5,768
1,440
2,160
398
6.9
23,700
1.0
• 5.3
0.36
0.18
6.0
b
Leachates
L2
162
1,043
121
13
12
268
7.1
865
b
b
L3
107
4,593
1,052
82
120
130
496
1.5
4,620
b
•
0.120
0.035
8
117
14
8
4
2
aData from Daniel and Liljestrand, 1984.
Not reported.
4-80
-------
4.5.17.1 Test Method-
Permeability tests were carried out as described previously in Section
4.5.16. All testing was performed using flexible-wall permeameters and
hydraulic gradients of 150 or 200. Rates of flow were determined from the
rate of inflow for each test chamber.
4.5.17.2 Test Results—
The permeability tests were performed for several months, allowing the
passage of more than one pore volume of fluid for most soil/leachate combi-
nations. The permeabilities of the soils S2, S3, S4, and Lufkin clay appear
to be related to the plasticity index, the permeability decreasing with
increasing plasticity. For any one soil, the permeabilities to the various
liquids were all about the same. Permeabilities to the leachates did not
differ significantly from the permeability to water (actually 0.01 N calcium
sulfate). All permeabilities measured were 1 x 10 8 cm/s or lower. In
three of the four soils tested, the permeability to 196 ppm xylene was
slightly lower than the permeability to the 5 percent methanol. All perme-
abilities were plotted as a function of pore volumes of fluid passed through
the sample.
In addition to the permeability tests, Atterberg limits of the soils
were determined using the various test fluids and pure xylene and methanol
in place of water. Test fluids LI, L2, L3, and spiked LI did not signifi-
cantly alter the plasticity of any of the clay soils during the short-term
exposure of the test. Mixing any of the five soils with pure xylene or
pure methanol, however, caused a drop in the liquid limit and destruction
of the soil's tendency to be plastic. The dilute solutions of methanol
and xylene (as used in the permeability tests) had much less significant
effects on the plasticity. Only the soil S3 showed a large drop in plastic-
ity when mixed with the 5-percent methanol or the aqueous solution contain-
ing 196 ppm xylene.
The significance of Daniel and Liljestrand's findings is that they
appear to show that di1ute organic/water mixtures are not capable of causing
significant changes in the permeability of natural clay liners.
4.5.18 Study by Dunn (1983) of the Effects of Synthetic Lead-Zinc Tailings
Leachate on Clay Soils
Dunn (1983) evaluated the effects of a synthetic lead-zinc tailings
leachate, of low pH and containing large concentrations of heavy metals, on
the permeability of two clay soils. The permeability of the clays was
shown to be affected by the waste permeant, with cation exchange and precip-
itation apparently being the most important processes.
The soils used in the testing, Altamont soil and Rockville soil, had
been identified as potential liner construction materials. Altamont soil,
a "valley alluvium" with moderate plasticity, is a silty clay soil with I
or 2 percent shale fragments. Montmorillonite is the predominant clay
mineral in Altamont soil. Rockville soil, a yellow-brown silty clay with
high plasticity, is composed of the fine fraction from a sand and gravel
4-81
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plant. The predominant clay mineral is kaolin. This soil probably contained
microorganisms since some evidence of bacterial growth was noted in soil
that was stored for several months.
The permeant fluids tested were tap water, distilled water, and the
synthetic lead-zinc tailings leachate. Characteristics of this fluid were:
Conductivity 1,550 (jmho/cm
pH = 2.6
Lead = 5.8-15.0 mg/L
Zinc = 200 mg/L.
The leachate was prepared with zinc sulfate, lead sulfate, and lead nitrate.
Sulfuric acid was used to attain the desired pH.
Two tests with each clay were conducted with the synthetic leachate.
Permeabilities obtained with the test fluid were compared to the results of
samples tested with tap water and with distilled water. All the tests were
run at a compacted dry density of about 90 percent of maximum dry density
and at a water content approximately 1 to 2 percent above optimum. Tap
water was used for the molding water. Soil samples were prepared with
static compaction since this method was found to be most appropriate for
producing replicate samples at approximately the same dry density and water
content. The static compaction involves compressing the soil to a known
density with applied hydraulic pressure.
Tests were performed in a triaxial cell at a hydraulic gradient of 50.
Samples tested were 3.81 cm (1.5 inches) in diameter and 2.54 cm (1 inch)
thick. The samples were presaturated (using a backpressure technique) with
the fluid to be tested. Prior to permeability testing, the samples were
consolidated at 1.5 kg/cm2 (21.3 psi) effective stress. Permeability
measurements were carried out at an effective stress of 1.25 kg/cm2
(17.8 psi).
The permeability values measured in both soils exposed to the synthetic
leachate were higher than those measured with tap water. Values measured
with distilled water were lower than permeabilities measured with tap
water. The ultimate effect of the synthetic leachate on the permeability
to either soil could not be determined from the tests, however, because the
permeability values did not reach steady state during the duration of the
test (5,000 minutes or 3.5 days). The tests with tap water did appear to
reach steady state during this test.time.
For one Altamont sample, the measured permeability to the synthetic
leachate was approximately 2 orders of magnitude higher than that of tap
water. This appeared to correlate with a long curing period (the period of
time from compaction to the beginning of the permeability test). Thixotropic
alterations of the soil fabric may have occurred during this interval,
resulting in the higher K value.
4-82
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4.5.19 Studies by Acar and Others (1984) on the Effect of Qrganics on
Kao Unite
In research funded by EPA, Acar, Olivieri, and Field (Acar et al. ,
1984b and c) and Acar, Hamidon, Field, and Scott (Acar et al., 1984a)
studied the effect of four organic fluids on the saturated permeability of
Georgia kaolinite. The fluids tested—benzene, acetone, phenol, and nitro-
benzene—were chosen because they represent a wide range of dielectric
constants. Comparative tests were performed with 0.01 N calcium sulfate.
In addition to the pure solvents, 0.1 percent (1,000 ppm) solutions of
acetone and phenol prepared in 0.01 N calcium sulfate solutions were tested.
This research was carried out at Louisiana State University, Hazardous
Waste Research Center.
4.5.19.1 Test Method—
The kaolinite was cured at 32 percent moisture for 1 week before
compaction in a Harvard miniature mold at a compactive effort corresponding
to standard Proctor compaction. Sample dimensions were restricted to
3.55 cm in diameter and 3.8 to 5.1 cm in height.
Tests were conducted in triaxial cells with continuous backpressure.
Hydraulic gradients of less than 100 were used. Backpressures of 414 to
449 kPa (60 to 65 psi) were used to fully saturate the samples prior to the
permeability testing. Approximately one pore volume of 0.01 N calcium
sulfate was passed through the samples to establish the reference permeabil-
ity value. The influent liquid was then switched to the organic fluid to
be tested. Tests were continued until the permeability readings and the
effluent concentrations were stable.
A mercury intrusion method was used to characterize the p.ore size
distribution in the samples before and after permeation with the organic
test fluids and with the calcium sulfate (Acar et al., 1984b).
A fixed-wall test with acetone as well as flexible-wall tests at
variable effective stresses were also carried out in order to evaluate the
test scheme.
Free-swell and liquid limit tests were conducted with the organic
solutions and with the standard calcium sulfate to determine if these
properties were affected by the chemicals.
4.5.19.2 Test Results--
All tests with chemicals at low concentrations resulted in slight
decreases in permeability. It was found, however, that the chemicals
diffused through the flexible latex membrane so that the concentration of
the organics that actually permeated the soil sample could not be ascer-
tained.
Reference permeabilities in all kaolinite samples tested with pure
organics were between 5.0 x 10 8 cm/s and 6.0 x 10 8 cm/s. When pure
organic fluids were introduced into the test cells, an immediate decrease
4-83
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in permeability occurred. For acetone and phenol, this decrease was followed
by a permeability increase, the final value stabilizing at approximately
double the initial or reference value. In the tests with benzene and
nitrobenzene, the permeability decreased until the tests were terminated.
Final permeability values measured in these tests were 2 orders of magnitude
lower than the reference values.
When acetone was tested in a fixed-wall permeameter, the permeability
stabilized at 2 x 10 6 while tests under_comparable conditions in flexible-
wall cells yielded values between 6 x io"8 and 9 x io"8. The difference in
these test results is attributed to sidewall leakage in the fixed-wall test
resulting from sample shrinkage during permeation with acetone. The free-
swell tests also confirm that shrinkage would occur with acetone permeation.
Both swelling behavior and liquid limit determined with the specific
permeant fluid were found to relate to the changes in permeability measured.
The liquid limit and free swell were increased significantly with benzene
and nitrobenzene, slightly increased with phenol, and decreased with acetone.
Although absolute permeabilities were altered considerably by permeation
with the pure organic fluids, the mercury intrusion investigations showed
O
that the size and distribution of pores greater than 80 A were not signifi-
o
cantly affected. Since pores with diameters of less than 80 A are not
expected to contribute appreciably to the total flow, these results suggest
that physicochemical properties of the pore fluid close to the clay surfaces
lead to variations in flow characteristics.
4.5.20 Finding by Olivieri (1984) of Impermeability of Montmorillonite to
Benzene
Olivieri (1984) found that benzene did not penetrate compacted Ca-
montmorillonite that was first fully saturated with 0.01 N calcium sulfate
solution even at a hydraulic gradient as high as 150. This finding was
attributed to hydraulic pressures being less than the required flow initia-
tion pressure to two-phase flow (Acar and Seals, 1984).
4.5.21 Study of Permeability of Clays to Simulated Inorganic Textile
Wastes by Tulis (1983)
Tulis (1983) tested Wyoming bentonite, Grolley kaoline, vermiculite,
and White Store clay in compaction permeameters with alkaline metal hydrox-
ides.. Test solutions were ferrous hydroxide, cupric hydroxide, and manga-
nese hydroxide prepared from 1 N solutions of the respective sulfates by
adding sodium hydroxide until a precipitate formed. The final solutions
had pH readings as follows: ferrous = 12.9, manganese = 13.0, and cupric =
12.5. Test results show an increase in permeability of the bentonite when
it was exposed to the alkaline permeant fluids. The permeability of the
kaoline decreased with the application of the bases. Neither the field
clay nor the vermiculite showed any significant variation in permeabilities
with the test fluid.
4-84
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Cracks observed in the bentonite indicate that shrinkage was the
mechanism responsible for the observed increase in permeability.. The
decreased permeability of the kaoline was attributed to clogging
of the pore space by dispersed clay. All of the leachates from the tests
contained silica that had been dissolved by the alkaline solutions.
4.5.22 Tests Conducted by Engineering Consulting Firms for Specific
Application (unpublished data)
4.5.22.1 Tests Conducted by the Trinity Engineering Testing Corporation—
The tests discussed below were performed by the Trinity Engineering
Testing Corporation at the request of the Corpus Christi, Texas, City Water
Department (White, 1976).
4.5.22.1.1 Soil Characteristics and Test Method—A soil sample from a
proposed toxic waste landfill site was subjected to permeability testing
with isopropyl alcohol, benzene, and charcoal starter fluid. The material
tested was a subsurface clay. Composite samples were compacted at optimum
moisture content to a height of approximately 91.4 cm (36 inches) at 95.8
percent standard Proctor density in 2.54-cm (1-inch) inside diameter cylin-
ders. Each of the three organic fluids was added to a level of approximately
61 cm (24 inches) above the compacted soil samples. Water was tested in a
fourth sample. A constant pressure head of 7.01 m (23 feet) was imposed
with compressed air. Liquid level in each test cylinder was recorded every
4 hours until all the liquid had penetrated the full 91.4-cm (36-inch)
column of compacted material.
4.5.22.1.2 Test Results—In the experiments with isopropyl alcohol
and water as the test fluid, the total drop in liquid level was less than 1
inch over a 100-day period. In the column tested with the charcoal starter
fluid, liquid began dripping from the bottom of the test cylinder after 122
days. In the benzene test column, signs of full penetration throughout the
clay material were observed after 36 days.
In a second experiment series, two 91.4-cm (36-inch) compacted clay
soil samples were tested with benzene. The samples differed only in their
moisture content (sample A at 10 percent moisture and B at 20 percent
moisture). Sample A showed signs of full penetration of the benzene after
20 hours. Full penetration of benzene occurred after 32 days in sample B,
and all liquid passed through the sample in 71 days.
The conclusions drawn from the permeability tests are stated below:
Under optimum compaction, the clays are highly impermeable
to domestic water and, conversely, are very permeable to
lighter hydrocarbons.
When properly compacted to a finished thickness of 91.4 cm
(3 feet), the clays will serve as a suitable tank liner for
domestic water but will not contain the lighter hydrocarbons.
4-85
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Under optimum compaction, a 91.4-cm (3-foot) liner of the
clay in a tank 7.01 m (23 feet) deep containing benzene can
begin to leak within 36 days.
4.5.22.1.3 Discussion—Although the soil sample used in the Trinity
Engineering experiments is not adequately characterized, the results of the
test clearly indicate potential for large permeability increases resulting
from exposure to concentrated nonpolar hydrocarbons. The apparatus and
test procedures used differ substantially from those used in permeability
tests conducted by other investigators.
The data also illustrate the importance of moisture content during
compaction. The performance of clay-soil liner in contact with chemicals
such as benzene could be drastically influenced by the uniformity of the
moisture content when the liner material was installed and compacted.
4.5.22.2 Test Data Submitted to Pennsylvania Department of Environmental
Resources—
The Pennsylvania Department of Environmental Resources has received
data pertinent to clay liner/chemical compatibility. The data pertain to
specific sites and specific wastes and were submitted to the State by
consulting engineers. Testing procedures vary and information needed to
evaluate the data is not always provided in the reports. All test results
show the clay liner permeabilities to be "within the range required" after
exposure to the wastes tested.
Report A deals with tests to evaluate effects on a liner material in
contact with a waste comprised of one part oil contaminated soil and four
parts water. For the permeability tests, samples were air dried and then
recompacted, at ±2 percent of optimum moisture content, to 95 percent of
maximum dry density. Stainless steel molds 10.2 cm (4 inches) in diameter
and 11.7 cm (4.6 inches) in height were used. After trimming, the molded
sample was transferred to a constant head permeability device. A back-
pressure was applied to two of the four samples during saturation with 0.01
N calcium sulfate solution. Permeability measurements with the calcium
sulfate showed no significant differences between the results for samples
with or without backpressure. Thus, it was concluded that the effect of
entrapped air was minimal.
After permeability tests with the standard calcium sulfate, the liner
samples were placed in contact with the test fluid, sealed, and placed on a
rocking table for 30 days. Three of the samples were tested with the waste
fluid and one with calcium sulfate solution. After 30 days, the samples
were drained and the permeability tests repeated. Reported results are
shown in Table 4-15.
No discernible color change was observed after a 30-day exposure to
the waste fluid. No shrinkage along the sides of the mold was observed,
although a change in height of approximately 0.64 cm (0.25 inch) was
reported.
4-86
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TABLE 4-15. PERMEABILITY TEST RESULTS3
(Pennsylvania Case A)
Coefficient of permeability
Sample
AC
BC
C
D
With 0.01 N CaS04
1.1 x
5.9 x
9.4 x
1.7 x
lO'7
lO'8
lO'8
io-7
(cm/s)
After exposure to test fluid
1.2
3.9
1.1
Not
x 10-7d
x IO"8
x IO"7
tested
aTest data reported to Pennsylvania Department of Environmental Resources.
Test fluid was one part oil-contaminated soil to four parts water.
GSamples under backpressure during initial permeability tests.
Control sample—tested after 30-day exposure to 0.01 N CaS04.
4-87
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The waste tested—one part oil contaminated soil and four parts water—
was not characterized further. Neither the extent of the oil contamination
nor the characteristics of the contaminated oil were reported. It may be
assumed that either tap water or deionized water was used to prepare the
waste fluid. The extent to which the oil or its contaminants would be
extracted by the water is unknown but probably very small. Although it is
not discussed in the report, the waste material in contact with the clay
liner sample may have involved three phases, with oil being the lightest
phase.
No indication of the length of the permeability testing procedure or
pore volumes displaced is given. The hydraulic heads used in the tests
also are not reported. These details may be stated in a letter that is
referenced in the report. Soil characterization data were not included.
Report B describes the results of a similar investigation in which
liner samples from a disposal site were tested with four different wastes.
The permeabilities are reported in Table 4-16. All samples showed slight
(twofold) increases in permeability after a 30-day exposure to the wastes.
It is notable that "control sets" exposed for 30 days to 0.01 N CaS04
showed similar increases.
Soil properties are listed below:
Cation exchange capacity: 11.1 meq/100 g soil
Predominant exchangeable cation: Calcium
Major mineral fraction: Alpha quartz
Other minerals (trace to minor): Microcline, Adularia, Muscovite,
Kaolinite
Percent clay size ( 0.002 mm): 13
Percent silt size (0.002 mm -0.05 mm): 30
Percent sand size (0.05 mm -2.0 mm): 22
Percent larger than 2.0 mm: 35
Liquid limit (percent water): 31
Plastic limit (percent water): 22
Wastes used in the tests were not characterized beyond the description
given in the table. Presumably, they were diluted with water as was done
in Case A, but this is not stated in the report. The duration of the
tests, pore volumes replaced, and hydraulic head are not provided in the
report.
Report C provides permeability data on a soil sample tested with
chrome ore leachate. The leachate (pH = 13.0) contained 1,400 mg/L total
chromium and 1,200 mg/L hexavalent chromium. A constant head test, con-
ducted at a pressure of 20 psi, gave a permeability of 1..2 x 10 8 cm/s.
With the falling head method, a permeability of 2.2 x 10 8 cm/s was measured.
Soil characterization and details of the test method were not provided
in the brief report.
-------
TABLE 4-16. PERMEABILITY TEST RESULTS3
(Pennsylvania Case 8)
Sample
A
B
C
D
Coefficient of permeability (cm/s)
Before exposure After exposure
to waste to waste Waste
1.4 x io"8 2.0 x 10~8 Electric furnace
baghouse dust
-0 _0
1.4 x 10 2.1 x 10 Tar decanter sludge
(high in organics)
-ft -ft
1.8 x 10 ° 3.0 x 10 ° Neutralized pickle
liquor rinse water
sludge
-8 -8
1.8 x 10 3.0 x 10 Hot strip mill recycle
system sludge (high
in oil)
aTest data reported to Pennsylvania Department of Environmental Resources.
4-89
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4.5.22.3 Studies Sponsored by Waste Management, Inc.—
Waste Management, Inc., has sponsored a series of studies to determine
compatibility between landfill leachate and in situ clay soil, which func-
tions as the landfill liner. (Weaver and Brissette, Canonie Environmental
Services Corporation, 1982). Permeability data were obtained in triaxial
devices. Each report includes details of the sampling effort, soil charac-
terization data, and the permeability test results. One important conclu-
sion by Canonie is as follows:
... It has been our experience that in concentrations of less
than 1 percent organics have no significant impact on soil permea-
bility.
The laboratory permeability results presented in each of the reports
indicate that no appreciable change in permeability will occur on soils at
the specific sites due to contact with the waste leachate obtained from the
facility.
4.5.22.4 Test Data from D'Appolonia Consulting Engineers, Inc.--
D'Appolonia Consulting Engineers, Inc. (D'Appolonia), has performed
numerous permeability studies involving site-specific soil samples and
leachates. Projects have involved slurry trench walls as well as liners
for landfills. In 1983 D'Appolonia compiled their permeability test data
from 14 projects (D'Appolonia Consulting Engineers, Inc., 1983). Leachates
tested in the D'Appolonia projects were frequently high in salts, and some
were highly acidic. All data were obtained from triaxial tests. Permeabil-
ity data from the various projects are summarized below.
Project A—No significant changes were observed in long-term permeability
tests on soil samples containing 2 percent or 3 percent commercial bentonite
when they were subjected to an aqueous waste fluid of pH 7. The fluid,
collected during dredging operations and shipped to D'Appolonia by the
client, contained minor concentrations of a number of inorganic salts
(sulfate, chloride, fluoride). Specific conductance was reported as 1,710
umho/cm.
The permeability tests involved the exchange of up to 4.7 pore volumes
with test times of 24 to 76 days. The hydraulic gradients used varied from
36 to 168; cell pressures were 1.0 to 1.5 kg/cm2.
Project B—Extensive permeability tests were performed on reddish-brown
clay samples (undisturbed Shelby tube samples) using a stabilized pH 4
fluid. The fluid was prepared in the laboratory using pond water and waste
from the site. The most significant characteristic of the stabilized pH 4
fluid was the specific conductance at 94,000 umho/cm at 25 °C; pH was 3.88.
It should be noted that Shelby tube samples may not always be compacted to
exactly the same density so that slight deviations in measured permeability
are not considered to be significant.
Although all permeabilities measured were below 1 x 10 7 cm/s, a trend
toward increased permeability was apparent as more pore volumes were ex-
changed. Changes in soil chracterization were also in evidence as more
4-90
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pore volumes of test permeant fluid were passed through the samples.
Elevated hydraulic gradients 110 and 450 were used for the tests, and cell
pressures were 2.5 and 4.5 kg/cm2. Test times ranged from 100 to 350 days.
In three of the samples, more than 12 pore volumes were exchanged.
Project C—A waste fluid characterized by high salt concentration and
high total organic carbon was tested in four soil samples. The samples
contained varying proportions of two soils—a fine-to-coarse sand, and a
sandy clay with 1 to 3 percent commercial bentonite.
Permeability tests were run at a hydraulic gradient of 20. After
initial permeability increases in some samples, the permeabilities decreased.
Samples were tested for 692 days. For each sample, between 2 and 13 pore
volumes were exchanged. The permeability decrease noted was approximately
1 order of magnitude for a cement bentonite sample. For the other three
soil mixtures, permeability decreased by a factor of 2 to 4.
The constituents present in the permeant are not known precisely.
Available chemical analysis data indicate that the chemical concentrations
in the waste material vary considerably from year to year.
Project D—Slight decreases in permeability were reported for clay-soil
samples (with bentonite) exposed to contaminated groundwater samples taken
from piezometers. Soil samples were 25 percent flyash, 25 percent uncontam-
inated clay, 25 percent contaminated clay, and 25 percent silt. Bentonite
(1 percent) was added.
Two permeant fluids were tested; pH values were 10.57 (Sample A) and
8.8 (Sample B). Specific conductance was reported at 35,300 and 13,200
umho/cm at 25 °C.
Samples were tested at a gradient of 190 with cell pressure at 1.5
kg/cm2. Test duration was 90 days with more than three pore volumes ex-
changed. Final permeabilities were determined to be below 1 x 10 8 cm/s.
Project E—Permeability tests were run on a silty clay soil from a
proposed facility with four waste leachates as the permeant fluid. Soil
samples were compacted in the laboratory (95 percent of standard Proctor
density). Chemical characteristics of the waste fluids tested are shown in
Table 4-17.
Permeability tests were performed at a hydraulic gradient of 47 and
cell pressure of 0.75 kg/cm2. Total test time was 40 to 50 days. The
resuTts of the permeability tests are given in Table 4-18. All samples
were saturated with 0.01 N calcium sulfate solution prior to introduction
of the waste fluid.
Project F—Permeability data on undisturbed Shelby tube samples tested
with tap water showed permeability values ranging from 6.1 x 10 8 to 2.0 x
10 9 cm/s with an average of 1.0 x 10 8 cm/s. Fifty-seven samples were
tested with total test time varying from 6 to 10 days. Hydraulic gradient
was 25 to 50, and cell pressure was 3.5 to 5.5 kg/cm2.
4-91
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TABLE 4-17. CHEMICAL CHARACTERISTICS OF WASTE PERMEANTS, PROJECT Ee
Waste leachate permeant fluid
Parameter
Column test designation
Ph
Specific conductance
Filterable residue at
180 °C
Acidity
Alkalinity
Phenolpthalein
alkalinity
Chloride
Sulfate
Dissolved metals:
Cadmium
Calcium
Chromium (hexavalent)
Chromium (total)
Iron
Lead
Magnesium
Manganese
Nickel
Selenium
Sodi urn
Zinc
Units
pH units
umho/cm
at 25° C
mg/L
mg/L CaC03
mg/L CaC03
mg/L CaC03
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
No. 3
P-l
12.63
20,500
12,100
0
4,140
2,660
1,600
50
0.02
610
450
880
<0. 1
0.49
<0. 1
0.07
0.23
1.86
945
3.82
No. 4
P-2
11.23
11,900
8,620
0
130
90
2,300
2,550
<0.01
170
14
16
<0. 1
0.32
0.4
0.04
0.10
0.196
1,860
0.12
Sludge
P-3
8.37
10,100
8,720
0
20
2
570
500
<0.01
1,800
0.06
0.08
<0. 1
<0.01
135
0.14
0.46
<0.001
12
0.02
Composite
leachate
P-4
11.23
11,000
8,380
0
224
143
1,800
2,250
<0.01
505
21
52
<0. 1
0.01
2.8
0.06
0.10
0.342
1,350
0.03
Data from D'Appolonia Consulting Engineers, 1983.
Leacnates were generated from various wastes by 1:4 shake extraction of
solid waste with water.
cComposite leachate obtained by mixing four waste leachates in the following
proportion:
No. 3 leachate - 5 percent
No. 4 leachate - 75 percent
No. 5 leachate - 5 percent (composition not specified)
Sludge leachate - 15 percent.
4-92
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TABLE 4-18. RESULTS OF PERMEABILITY TESTS, PROJECT Ea
Sample
fluid
P-l
P-2
P-3
P-4
Permeant
0.01 N CaS04
No. 3 leachate
0.01 N CaS04
No. 4 leachate
0.01 N CaS04
Sludge leachate
0.01 N CaS04
Composite leachate
Pore volumes
exchanged
0
3.2
0
0
4.7
13.5
0
0.8
_
- 3.2
- 12.7
-
- 8.8
.
-4.7
- 13.5
- 17.2
-
- 0.8
-.5.6
Permeability
(cm/s)
1.6 x io"7
1.7 x io"7
11 4 x io"7
1.1 x io"7
1.3 x io"7
1.4 x IO"7
1.5 x io"7
2.4 x io"7
4.2 x io"7
1.1 x IO"7
1.2 x io"7
8.1 x io"7
aData from D'Appolonia Consulting Engineers, Inc., 1983.
4-93
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Project G—Slurry wall test data were provided for two different
leachates identified as low pH or high pH. A commercial bentonite product
was added to a clay-sand mix. Sixty-day tests at hydraulic gradients of
170 to 205 and cell pressure at 1.5 kg/cm2 gave permeability values below 7
x 10 8 cm/s. Between 19 and 47 pore volumes were exchanged in the tests.
Project H—Potential clay liner materials were tested with a permeant
fluid generated in the laboratory by leaching a young slag from a pilot
plant. The pH of the leachate was 4.90; specific conductance was 2.70
umho/cm at 25 °C.
Hydraulic gradients of 25 and 100 and cell pressures of 0.75 and 1.5
kg/cm2 were used in the permeability tests. Distilled water was used to
saturate the samples. Small permeability decreases were observed in tests
with the slag leachate. Total testing time was approximately 2 to 3 months.
Project I—Groundwater spiked with several chlorinated hydrocarbons
was used as the permeant fluid in tests on undisturbed Shelby tubes samples.
The total concentration of chlorinated ethanes was 500 ppm. The soil
samples tested were comprised of smectite (50 to 75 percent), kaolinite (10
to 25 percent), vermiculite (10 to 25 percent), mica (10 to 25 percent),
and quartz (10 to 25 percent).
Permeability tests were conducted at a hydraulic gradient of 150 and a
cell pressure of 1.5 kg/cm2. Four samples were tested for up to 140 days
with a maximum of 24 pore volumes exchanged. Distilled water was used as
the initial permeant fluid. Slight decreases in permeability were observed
with the spiked groundwater as permeant fluid.
Project J—Two soil samples were tested with a highly acidic waste
fluid (pH = 1.5) that was collected from waste ponds. Other significant
characteristics of the fluid were specific conductance = 22,200 umho/cm at
25 °C and sulfate = 15,000 ppm.
Slight decreases in permeability were observed after exchange of more
than 10 pore volumes. Hydraulic gradients of 20 to 100 were used with cell
pressures of 0.7 to 2.0 kg/cm2.
Project K—Three waste fluids were tested with a sandy soil mixed with
a commerical bentonite product. Significant characteristics of the waste
fluids are shown below.
Parameter
pH
°K
Specific conductance
(umho/cm at 25 °C)
Sulfate (ppm) 470 460 180
4-94
Waste fluids
8
6.65
920
9
7.65
1,000
10
5.00
430
-------
No significant change in permeability occurred when the pH 9 fluid was
tested with the sandy clay soil. The test involved exchange of 7.4 pore
volumes. A slight increase in permeability was noted with the pH 8 fluid
tested with the sandy clay soil after 4.7 pore volumes were exchanged.
Waste fluid at pH 10 tested with the sandy clay soil mixed with bentonite
decreased permeability after exchange of 4.2 pore volumes.
A hydraulic gradient of 22 was used for the tests involving the waste
fluids and soil. A hydraulic gradient of 100 was imposed on the soil
bentonite tested with pH 10 fluid. Cell pressure was 1.1 kg/cm2. The pH 8
and 9 samples were tested at a hydraulic gradient of 22 and a cell pressure
of 1.0 kg/cm2.
Project I—Two waste fluids with neutral pH were used in tests with
soil mixed with approximately 1 percent treated bentonite'from three vendors.
The only notable characteristic of the waste fluids was specific conductance.
The permeability data are summarized in Table 4-19. The hydraulic gradient
used in the tests was 80 to 90; cell pressure was 1.0 kg/cm2.
Project M—Permeability tests were performed on 20 soil samples to
determine the effect of a permeant fluid of pH 1.5. The fluid, collected
from waste ponds at a disposal site, had a high salt concentration (specific
conductance = 22,200 umho cm at 25 °C; sulfate = 15,000 ppm).
The only permeability increases noted were for a soil characterized as
silt stone and one characterized as sand stone. For these samples, permea-
bility increases were just less than 1 order of magnitude after passage of
approximately 12 pore volumes. Hydraulic gradients used in the tests were
15 to 285; cell pressures were 0.75 to 4.00 kg/cm2.
Project N--Permeability studies on three composite soil samples were
conducted. Three waste leachates used as the permeant fluid were prepared
in the laboratory by extracting tailings from a pilot plant. Fluids tested
were characterized by pH (3, 6, or 9).
Initial permeabilities were determined with groundwater from the
proposed site. The results of the permeability tests are shown in Table
4-20. Permeability increases of approximately 1 order of magnitude were
observed in the glacial till samples tested with permeant fluids of pH 6
and 9.
4.5.23 Tests Reported by Bentonite Companies
4.5.23.1 American Colloid Company—
The American Colloid Company produces Volclay soil sealants. These
products are a special type of high swelling sodium montmorillonite that
has been treated by a proprietary process to render the material unreactive
toward most chemical materials. American Colloid Saline Seal 100 is a
patented product intended for use in containing wastes with high levels of
dissolved salts, acids, or alkali.
4-95
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TABLE 4-19. RESULTS OF PERMEABILITY TESTS, PROJECT Lc
Waste fluid A
(1.900 umho/cm at 25 °C
Pore volumes
K /K
max7 initial
Waste fluid B
(3.800 umho/cm at 25 °C)
Pore volumes
K /K. ... , replaced
max initial K
Cement
bentonite
Aqua gel
Saline seal
1.0
2.2
1.6
6
8
7
1.0
6.9
3.9
13
7
13
Data from D'Appolonia Consulting Engineers, Inc., 1983.
TABLE 4-20. INITIAL AND FINAL PERMEABILITIES DETERMINED IN
TRIAXIAL CELL TESTS WITH LEACHATES, PROJECT Na
Sediment sample
Glacial till
(Composite No. 1)
Stratified drife
(Composite No. 2)
4% Bentonite/till
Admixture
Leachate
permeant
PH
3
6
9
9
3
6
9
9
3
9
Laboratory permeabil
(cm/s)
ity @ 20 °b
Initial with Final with
site groundwater waste leachates
5.5 x lo"8
3.8 x io"8
5.7 x io"8
3.6 x io"7
1.8 x IO"5
1.5 x io"5
1.3 x 10~5
2.1 x io"5
1.0 x io"10
l.OxlQ-10
1.4 x io"7
3.4 x IO"7
5.6 x IO"7
5.7 x io"7
1.3 x IO"5
1.2 x 10°5
1.3 x io"5
2.1 x io"5
1. 5 x lO10'
l.SxiO-10"
aData from D'Appolonia Consulting Engineers, Inc., 1983.
Permeability calculations based on final column sample dimensions.
C0etermined as 83.1 percent saturation based upon final moisture content
measurements.
Determined as 83.4 percent saturation based upon final moisture content
measurements.
4-96
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American Colloid has conducted permeability tests of Saline Seal 100
with gasoline, kerosene, and 1,1,2-trichloroethane. The trichloroethane
tested was waste solvent that had been contaminated with other uncharacter-
ized materials. It was said to be predominantly trichloroethane (Jepsen,
1983).
The American Colloid tests were conducted with a fixed-wall compaction
permeameter. Inside walls of the cylinder were coated with a thin film of
slurry to provide a barrier against capillary effects along the wall.
Samples were compacted to at least 90 percent Proctor. Soil samples were
either 5.1 or 10.2 cm (2- or 4-inch) -thick cores and consisted of a uniform
standard silica sand mixed with between 6 and 15 percent bentonite (dry
weight). Test samples were prehydrated with deionized water for at least
48 hours, and provision was made for deairing. After the test fluid was
added to the permeameter, head loss was recorded periodically until stable
readings were established. The results of these permeability tests are
shown in Table 4-21.
4.5.23.2 Federal Bentonite—
Another major bentonite company, Federal Bentonite, produces, among
other bentonite products, petroleum tank farm sealants. The products are
made by treating sodium-bentonite with specific polymers in order to obtain
the desired sealing characteristics. PPS-21 is a free-flowing granular
bentonite product designed to promote an impermeable barrier in the event
of failure or leak in petroleum tank farms.
Permeability tests with water and with kerosene were performed on
5.1 cm (2-inch) samples of test soil consisting of PPS-21 mixed with washed
beach sand. Samples were prehydrated with deionized water under a 136-cm
head prior to introduction of the kerosene. Tests results are summarized
in Table 4-22.
4.5.23.3 Discussion--
The behavior of polymer-treated bentonites over a long time period is
not demonstrated in the test results presented here. Although the duration
of the American Colloid tests exceeded 40 days, only a fraction of a pore
volume of fluid was displaced during the tests. The number of pore volumes
was not expressed in the data presented by Federal Bentonite.
Suggestions that the polymers in the treated bentonites will degrade
after 3 to 4 years have been made, and at least two laboratories claim to
have data in support of this time-degradation behavior (Beattie, 1983;
Zlamal, 1983). Many applications for the treated bentonites involve short-
term performance requirements. In long-term applications, such as barriers
for landfills, the time-degradation issue could have serious implications.
The long-term viability of treated bentonite seals needs to be verified.
4-97
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TABLE 4-21. EFFECT OF CONCENTRATED ORGANICS ON A
TREATED BENTONITE SEAL
Test duration
Organic permeant (days)
Gasoline 68
Kerosene 40.2
1,1,2-Trichloroethane 71
(waste)
Pore volumes Permeability
displaced (cm/s)
0.6 4.7 x 10"7
0.16 4.7 x 10"8
-7C
0.58 4.2 x 10 '
Unpublished data on Saline Seal 100 from American Colloid Company, personal
communication, January 23, 1983.
All tests conducted using a hydraulic head of 76.2 cm (2.5 feet).
c —7
Permeability of prehydrated soil was 1.5 x 10 cm/s prior to addition of
organic permeant.
TABLE 4-22. PERMEABILITY (cm/s) OF A TREATED BENTONITE SEAL
TO KEROSENE3>D
After exposure After exposure
to kerosene to kerosene
Sample of kerosene for 7 days for 42 days
Prior to
addition
of kerosene
Sample 1:
(Prehydrated for 24 h)
Sample 2:
(Prehydrated for 48 h)
Sample 3:
(Prehydrated for 72 h)
Sample 4:
(Prehydrated for 96 h)
5.1 x 10
-8
3.4 x 10
•8
2.5 x 10
-8
3.2 x 10
-8
2.2 x 20
-8
1.5 x 10
-8
2.0 x 10
-8
1.3 x 10
-8
1.6 x 10
-8
1.3 x 10
-8
1.1 x 10
-8
9.6 x 10
-9
Data from Federal Bentonite (1983) on tank farm sealant PPS-21.
""Tests conducted under a standard 136-cm head using a falling head
permeameter.
4-98
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4.6 REFERENCES
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Anderson, D. C 1982. Does Landfill Leachate Make Clay Liners More Perme-
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Anderson, D. C., K. W. Brown, and J. Green. 1981. Organic Leachate Effects
on the Permeability of Clay Liners. National Conference on Management
of Uncontrolled Hazardous Waste Sites, Washington, D.C. pp. 223-229.
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Sites, Washington, D.C., October 31-November 2, 1983.
Anderson, D. C., and S. G. Jones. 1984. Fate of Organic Liquids Spilled
on Soil. National Conference on Management of Hazardous Wastes and
Environmental Emergencies, Houston, Texas, March 1984. pp. 1-22.
ASTM. 1985. American Society of Testing Materials. Annual Book of ASTM
-Standards. Vol. 04.08.
Seattle, B. 1983. Federal Bentonite, Montgomery, Illinois, personal
communication with Research Triangle Institute.
Brown, K. W., and D. C. Anderson. 1980. Effect of Organic Chemicals on
Clay Liner Permeability: A Review of the Literature. In: Disposal
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Brown, K. W., and D. C. Anderson. 1982. Effects of Organic Solvents on
the Permeability of Clay Soils. EPA 600/S2-83-016. Texas A&M Univer-
sity, College Station, Texas.
Brown, K. W., and J. C. Thomas. 1984. Conductivity of Three Commercially
Available Clays to Petroleum Products and Organic Solvents. Hazardous
Waste. 1(4):545-553.
Brown, K. W., J. Green, and J. Thomas. 1983. The influence of Selected
Organic Liquids on the Permeability of Clay Liners. Land Disposal of
Hazardous Waste: Proceedings of the Ninth Annual Research Symposium
at Ft. Mitchell, Kentucky, May 2-4, 1983. EPA-600/9-83-018.
Brown, K. W., J. C. Thomas, and J. W. Green. 1984. Permeability of Com-
pacted Soils to Solvents Mixtures and Petroleum Products. In: Land
Disposal of Hazardous Waste: Proceedings of the Tenth Annual Research
Symposium at Ft. Mitchell, Kentucky, April 3-5, 1984. EPA-600/9-84-007.
Buchanan, P. N. 1964. Effect of Temperature and Adsorbed Water on Permea-
bility and Consolidation Characteristics of Sodium and Calcium Mont-
morillonite. Ph.D. Dissertation, Texas A&M University, College Station,
Texas.
Buelt, J. L., and S. Barnes. 1981. A Comparative Evaluation of Liner
Materials for Inactive Uranium-Mi 11-Tailings Piles. Prepared for the
U.S. Department of Energy under Contract No. DE-AC06-76RLO 1830.
Buettner, W., and M. D. Haug. 1983. Permeability Testing of Fine Grained
Soils. In: Potash Technology Mining, Processing, Maintenance, Trans-
portation, Occupational Health and Safety, Environment: Proceedings
of the First International Potash Technology Conference, October 3-5,
1983. Saskatoon, Saskatchewan, R. M. McKercher, ed. Pergamon Press,
Toronto, Canada.
Chapman, D. L. 1913. A Contribution to the Theory of Electrocapillarity.
Philosophical Magazine. 25(6):475-481.
Coia, M. F. 1981. The Effect of Electroplating Wastes Upon Clay as an
Impermeable Boundary to Leaching. M.S. Thesis, Department of Civil
and Environmental Engineering, Duke University, Durham, North Carolina.
Daniel, D. E. 1982. Effects of Hydraulic Gradient and Field Testing on
Hydraulic Conductivity of Soil. U.S. EPA Cooperative Agreement
CR 810165 to the University of Texas, Austin.
Daniel, D. E. 1983. Third Quarterly Progress Report to the U.S. EPA for
the Project: Effects of Hydraulic Gradient and Field Testing on
Hydraulic Conductivity of Soil. U.S. EPA Cooperative Agreement
CR 810165 to the University of Texas, Austin. For the period February
1983 to May 1983.
4-100
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Daniel, D. E., and H. M. Liljestrand. 1984. Effects of Landfill Leachates
on Natural Liner Systems. A Report to Chemical Manufacturers Associa-
tion by Department of Civil Engineering, University of Texas, Austin.
D'Appolonia Consulting Engineers. 1983. Data Compilation and Presentation
for Column Testing Associated with Hazardous Waste Isolation. Prepared
for Research Triangle Institute by D'Appolonia Consulting Engineers,
Inc., Pittsburgh, Pennsylvania.
Dunn, R. J. 1983. Hydraulic Conductivity of Soils in Relation to Subsur-
face Movement of Hazardous Wastes. Ph.D. Dissertation, Department of
Civil Enginering, University of California, Berkeley.
Evans, J. C. , R. C. Chaney, and H. Fang. 1981. Influence of Pore Fluid on
Clay Behavior. Department of Civil Engineering, Lehigh University,
Bethlehem, PA. Sponsored by Woodward-Clyde Consultants, Plymouth
Meeting, PA. Fritz Engineering Laboratory Report No. 384.14, December 4,
1981.
Everett, E. E. 1977. Suitability of the Lacustrine Clays in Bay County,
Michigan for Land Disposal of Hazardous Waste. M.S. Thesis, The
University of Toledo, Toledo, Ohio.
Foreman, D. E., and D. E. Daniel. 1984. Effects of Hydraulic Gradient and
Method of Testing on the Hydraulic Conductivity of Compacted Clay to
Water, Methanol, and Heptane. In: Land Disposal of Hazardous Waste:
Proceedings of the Tenth Annual Research Symposium at Ft. Mitchell,
Kentucky, April 3-5, 1984. EPA-600/9-84-007.
Fuller, W. H. 1974. The "State of the Art" of Migration and Attenuation
of Some Potentially Hazardous Polluting Trace and Heavy Metals, Asbestos
and Cyanide in Soil. University of Arizona, Tuscon, Arizona.
Gouy, G. 1910. Sur La Constitution de la Charge Electrique a la Surface
d'un Electrolyte. Anniue Physique (Paris). 4(9):457-468.
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Green, J., G. Lee, R. Jones, and Ted Palit. 1983. Interaction of Clay
Soils with Water and Organic Solvents: Implications for the Disposal
of Hazardous Wastes. Environmental Science and Technology. 17:278-282.
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on the Integrity of Clay Liners for Industrial Waste Disposal Pits—
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Griffin, R. A., and W. R. Roy. 1985. Interaction of Organic Solvents with
Saturated Soil-Water Systems. Report prepared for the Environmental
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Mitchell, J. K., and J. S. Younger. 1967. Abnormalities in Hydraulic Flow
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Clays Exposed to Selected Electroplating Wastes. M.S. Thesis, Duke
University, Durham, North Carolina.
Olivieri, I. 1984. The Effect of Organic Fluids on the Fabric of Compacted
Clay. M.S. Thesis, Department of Civil Engineering, Louisiana State
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Peirce, J. J. 1984. Effects of Inorganic Leachates on Clay Liner Permeabil-
ity. Final Report. U.S. EPA Contract No. 68-03-3149, 24-1. Department
of Civil and Environmental Engineering, Duke University. September 28,
1984.
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4-104
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CHAPTER 5
CURRENT PRACTICES: CLAY LINER DESIGN AND INSTALLATION
This chapter describes the state-of-the-art knowledge and techniques
currently used for clay liner design and installation. Information in this
chapter was compiled from a variety of sources, including a review of
existing literature on design and installation for various applications and
interviews with key personnel from selected engineering firms, waste management
companies, government agencies, professional associations, and contractors,
all of whom are experienced in various aspects of clay liner installation
and construction. The number of clay-lined facilities designed specifically
for hazardous waste containment and information on these sites are somewhat
limited. In addition, the design and installation practices for clay
liners for other applications are similar to those for hazardous waste
facilities (though possibly not as rigorous in design and installation
procedures). For these reasons, information from these applications is
included as well.
Clay liner construction utilizes equipment and techniques similar to
those used in other earthwork construction projects. However, the soil
compaction practices used to achieve low permeability employed in clay
liner construction differ from compaction practices used for strength ana"
stability, as used in foundations and roadbeds. For cohesive soils (i.e.,
clays), maximum strength is achieved when soil is compacted at dry of
optimum moisture content (see Chapter 3 for a discussion of compaction
parameters), but the lowest permeability is achieved 2 to 3 percent wet of
optimum moisture content. Therefore, when clay liners are compacted, it is
necessary to specify and control carefully compactive effort, density, and
moisture content to ensure that the desired permeability is achieved.
The first two sections of this chapter describe current practices for
designing and constructing clay liners. Literature reviews and interviews
with design engineers and contractors indicate that construction quality
assurance (CQA) and construction quality control (CQC) are considered among
the most important elements of successful facility construction, with clay
liner failures often attributed to deficiencies in these areas. Because of
the importance of CQA and CQC activities during the construction of clay
liners, this subject is covered separately in the third section of this
chapter, including a description of the element of a CQA plan. Common
problems encountered during clay liner construction and solutions to these
problems are tabulated in the final section of this chapter.
5-1
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5.1 DESIGN
The fundamental aspects that must be considered during the design of a
clay liner are:
Stability of the liner against major earth movements such as
slope failure, settlement, and bottom heave
Resistance of the liner to fluid flow (i.e., permeability)
Compatibility of the liner material with the wastes it is
meant to contain
Long-term durability of the liner.
The design effort applies standard geotechnical engineering practices to
address these considerations and thus to meet the special performance
requirements of clay liners.
Clay liner design is very site and material specific. Waste volume
requirements and waste characteristics must be considered during the design
effort, and facility designs must be tailored to the site-specific conditions.
The design effort may be divided into the following activities:
Site investigation
Liner material selection and characterization
Facility design
Preparation of construction specifications and the quality
assurance (QA) plan.
Site investigation, liner material selection, and liner material characteri-
zation are done prior to facility design. Preparation of construction
specifications and the QA plan follow facility design. Most of the design
engineers interviewed during the course of this project emphasized that
design activities usually continue through the construction of the clay
liner because unexpected situations often arise that necessitate modifica-
tions in the original plans.
5.1.1 Site Investigation
As with any earthwork project, a clay-lined hazardous waste containment
facility must be designed to be compatible with the geological conditions
at the specific site. For this reason, the first step in the design effort
is a comprehensive evaluation of the site. Ideally, sites should be selected
according to the suitability of the in situ earth materials for containing
hazardous wastes. However, in actual practice this is not always possible.
Constraints such as land use, zoning laws, land ownership, and distance to
waste generators often result in sites being selected for reasons other
5-2
-------
than their technical suitability for containing wastes. This fact, combined
with the subsurface heterogeneity and spatial variability that is the rule
in most geologic environments, makes adequate site investigation a critical
part of facility design.
5.1.1.1 Purpose—
Site investigations are conducted to delineate a site's topography,
subsurface geology, and hydrogeology. Topography influences facility
configuration and drainage system design (runon/runoff control). Subsur-
face site investigations are necessary to determine whether soils suitable
for liner material are available at the facility site or whether it is
necessary to identify and investigate borrow sources. In addition, knowledge
of in situ soil properties is important for foundation design. Soil charac-
teristics influence selection of the method of slope stability analysis
appropriate for facility design, are a necessary input to stability analyses,
and determine the necessity for special design measures to control settlement
or to ensure maximum protection against contaminant migration.
Hydrogeologic information about the site is important for the proper
monitoring of well placement. From a design standpoint, it is important to
determine the depth to water table for the site, including seasonal varia-
bility. Some States require a specific thickness of unsaturated soil
between the facility base and the water table. For sites with high water
tables, this can necessitate aboveground facility design. In States where
facilities can extend below the water table, high groundwater levels can
necessitate special intergradient (below water table) designs. Groundwater
elevations are necessary for assessing liquefaction potential for in situ
soils where significant seismic ground motion can occur. Hydrogeologic
investigations also are necessary to locate, identify, and delineate hydro-
logic pathways (e.g., fractures and sand seams) at the site so that provi-
sions for sealing them can be incorporated into the facility design. These
pathways can contribute to rapid migration of wastes from the facility if a
liner leak occurs. In addition, when liners constructed below the ground-
water table intersect these pathways, hydraulic pressures can build against
the outside of the liner. In unfilled facilities this can result in heaving,
slope failure, and liner rupture.
5.1.1.2 Approach and Methodology—
The investigation of a facility site should address the following:
Regional and site-specific investigations to relate the site
geology to the regional geological picture.
Topography, including drainage patterns.
Analyses of representative soil samples. Important tests
can include Atterberg limits, particle size distribution,
shrink/swell potential, cation exchange capacity, total
organic carbon, mineralogy, shear strength, dispersivity,
compressibility, consolidation properties, density and
moisture content, Proctor density, laboratory (compacted)
permeability, and chemical compatibility.
5-3
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In-place soil characteristics including depth to bedrock,
in-place permeability, and the presence of features that can
act as failure planes or hydrologic pathways (e.g., slicken-
sides, fractures, faults, silt and sand lenses and seams,
and root holes).
Bedrock characteristics including type, form, fractures,
solution cavities, and joints.
Hydrogeologic site characteristics including depth of the
water table, horizontal and vertical flow components, hydro-
geologic pathways, seasonal variability, and location and
use of aquifers.
Land use and ownership.
Climate.
This information is necessary for facility design and, to some extent, for
planning efficient borrow site development.
5.1.1.2.1 Indirect Methods—Indirect investigative methods include
collection of existing site information and remote sensing techniques.
These methods do not require drilling or excavation and are appropriate for
the initial stages of site investigation.
Site investigations usually begin with compilation and review of
existing information pertinent to the site. Sources of information include
Soil Conservation Service County Soil Surveys, U.S. Geological Survey
topographic and surficial geology maps, published literature, State geo-
logical survey information, and county records of geotechnical tests asso-
ciated with previous construction projects. This information can be very
useful for planning the scope and approach of further site investigation
activities.
Geophysical remote sensing techniques that can be applied during site
investigation include electrical survey methods, ground-penetrating radar,
and seismic refraction. All of these techniques are conducted on the
surface but provide information about the subsurface. The selection of
geophysical techniques depends to a large degree on the geologic setting
(White and Brandwein, 1982).
.Electrical resistivity surveying can be used to delineate the depth of
the water table as well as the presence of subsurface layers or lenses of
different permeability that have contrasting resistivities (e.g., clay and
sand layers). However, electrical resistivity methods cannot be applied in
certain geologic settings where general subsurface resistivity is relatively
high and are best used in areas (e.g., the Atlantic Coastal Plain) where
electrical resistivities of subsurface materials contrast strongly (White
and Brandwein, 1982). Further information on electrical surveying may be
found in the U.S. Environmental Protection Agency (1978) and Freeze and
Cherry (1979).
5-4
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Seismic refraction surveys can give valuable information about the
depth to bedrock, the subsurface bedrock topography, and the condition
(fracturing) of the bedrock (Cichowicz et al., 1981). In addition, the
seismic velocity of a geologic material is altered by the degree of weather-
ing and water saturation and therefore can provide information about the
variability of these parameters in the subsurface. However, because of the
multitude of variables that can affect a material's characteristic seismic
velocity, seismic results can be difficult to interpret, especially in
areas with complex subsurface geology or in areas where there is little
contrast in seismic propagation velocities in the subsurface. For this
reason, limited exploratory drilling will usually be necessary in conjunction
with seismic surveys to confirm interpretations based on this technique
(Cichowicz et al., 1981). More detailed information on seismic refraction
surveying may be found in Oobrin (1960).
Ground-penetrating radar also has some utility to site investigations
for locating buried structures and pipes and for indicating depth to shallow
bedrock. However, it is limited by a shallow depth of penetration when
compared to other techniques (White and Brandwein, 1982).
The advantage of indirect techniques during the early stages of site
investigation is that their use can reduce drilling costs and costs associ-
ated with laboratory tests and analysis. Much information about a site,
including an indication of its technical suitability as a containment
facility site, can be gained at a relatively low cost. In addition, the
information gathered indirectly can be used to plan direct site investiga-
tions, ensuring that these are'carried out as efficiently and economically
as possible.
5.1.1.2.2 Direct Methods--Direct methods of site investigation include
drilling boreholes and wells and excavating pits and trenches. The purpose
of these methods is to expose subsurface material so that the physical
conditions can be observed and measured (e.g., faults, slickensides, sand
seams, depth to bedrock and to the water table, penetration tests, and
in situ permeability) and to obtain samples of subsurface material for
laboratory testing of engineering properties.
Direct investigations are conducted during the final stages of site
investigation and must provide sufficient information for input to the
facility design. The scope of investigation necessary to accomplish this
goal will vary from site to site according to the complexity of the subsur-
face geology, the potential for seasonal variability in site conditions,
and the amount of information about the site that is already available.
Regulatory personnel from the Wisconsin Department of Natural Resources
have recently published the following recommendations for site investiga-
tions for clay-lined landfills (Gordon et al., 1984):
Drill an adequate number of soil borings across the site to
characterize the soil deposits within and beneath the site.
The borings should extend a minimum of 25 feet below the
5-5
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anticipated site base grade or to the water table, whichever
is deeper.
Install a sufficient number of water table observation wells
and piezometers to define both the horizontal and vertical
groundwater flow directions.
Excavate backhoe pits on a grid pattern across potential
clay borrow sources to characterize their depth, area!
extent, and uniformity and to obtain samples of the clay
material for testing.
Perform appropriate laboratory tests on samples from the
potential clay borrow sources to determine if they will meet
the design specifications.
These recommendations are presented as examples; detailed exploration needs
are site and facility specific.
Subsurface heterogeneities can lead to increased permeability (seepage)
or loss in strength in the foundation. Where these are suspected, it may
be appropriate to dig test pits and trenches to identify and determine the
prevalence of these features. Downhole television monitors also can be
used in boreholes to identify important subsurface features such as faults,
fractures, slickensides, and zones of permeable material.
Accessible (pits, trenches, and large boreholes) and inaccessible
(boreholes and wells) methods of site investigation are summarized in
Tables 5-1 and 5-2. These methods are discussed in more detail in U.S.
Department of Interior (1974). Methods of obtaining disturbed and undisturbed
samples during both accessible and inaccessible site exploration are discussed
in U.S. Department of Interior (1974) and ASTM (vol. 04.08, 1985). Methods of
conducting laboratory tests of engineering properties on these samples are
discussed in Chapter 3 and Appendix A of this document. Detailed discussions
of general geotechnical site investigation techniques may be found in
Winterkorn and Fang (1975).
Hydrogeologic site investigations are necessary for planning the
groundwater monitoring system and for estimating hydraulic stresses that
may act on the facility so that they may be properly considered during
facility design. Further information on conducting hydrogeologic investi-
gations and on installing monitoring wells and piezometers may be found in
U.S. Environmental Protection Agency (1983), Fenn et al. (1977), Johnson
Division (1975), and Lutton et al. (1983).
5.1.2 Liner Material Selection and Characterization
Soil liner materials are selected based on their ability to meet
specific performance standards and the costs to bring the material onsite.
Requirements that must be met for a soil to perform properly as a liner
material include:
5-6
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TABLE 5-1. ACCESSIBLE METHODS OF SUBSURFACE EXPLORATION
Methods
Trenching
Cuts
Test pits
en
I
Accessible boring
Procedure
Type of soil and
in-place condition
limitations
Use
Accessible caissons
Tunnels and drifts
Blasting
Excavate 3 ft Bin. width
by hand, dragline, power
shovel, bulldozer prefer-
able; explosives if neces-
sary; min. bracing or
slope unstable soils.
Same as trenching,
performed on gentle to
fairly steep slopes;
steps up slope may be
necessary.
Excavate rectangular hole,
3 ft by 5 ft min. at
working level, by hand or
hand-operated power tools;
explosives if necessary.
Cribbing required over
5 ft depth. Log and
sample as excavation
progresses when sheeting,
inclined poling, or
notched-box cribbing is
required in unstable
soils and for ground-
water control.
Drill 28 in. nin. dia.
hole, using heavy power-
operated disc, bucket,
helical augers, single
tube or core barrels in
stable soils; log and
sample as excavation
progresses; casing required
for protection during sam-
pling and inspection.
Same as accessible borings;
casing and air pressure
required in unstable soils.
Excavate accessible holes,
5 by 7 ft min., using hand
or hand-operated power
tools, lagging required.
Expose strata using ex-
plosives and hand or
power tools.
Coarse-grained soils,
including those con-
taining large quan-
tities of gravel and
cobbles, and soft
weathered rock; and
all fine-grained
soils, dense consol-
idated, wet or satur-
ated or dry and hard;
loose unconsol(dated,
wet or saturated and
soft or dry and
granular.
Same as above but
primarily for con-
solidated dry soils
and bedrock.
Depth about 20 ft
or to groundwater
or unstable mater-
ial.
Depth to SO ft,
infrequently 80
ft, or ground-
water if pervious
strata and high
flow.
Depth of 100 ft in
soil, 150 ft in
rock. Requires
heavy drill rig.
Same as above, used
only when caisson
is part of construc-
tion.
Expensive, used only
under special con-
ditions.
Limited to exposed
faces or outcrops.
Access for logging and disturbed sampling for laboratory
test, for reconnaissance and feasibility design stage;
and for hand-cut undisturbed sampling for final design
or for field tests such as field density, permeability,
full-sized bearing capacity tests Unsatisfactory in
unstable coheslonless soils. Economical and best
method for shallow explorations of borrow, foundation,
and aggregate deposits.
Use same as above, except is more expensive and used in
areas of limited access by heavy equipment and for
greater depths. Best method for "hand cut" undisturbed
sampling except in unstable soils or below groundwater.
Nonaccessible methods. Table 5-2, recommended for undis-
turbed sampling of fine-grained unstable soils below
water table.
Use same as above for stable soils in place of test
pits; very economical if equipment is available and
area is accessible.
Limited use, used primarily in establishing footing
grade during construction for individual caissons,
under very poor foundation conditions and/or under
water.
Limited use, for final exploration of dam-site abutments
when other methods have disclosed questionable condi-
tions that cannot be resolved otherwise.
Use to expose rock faces and outcrops for rip-rap and
crushed aggregate sources and to indicate size and shape
of particles that may be expected during quarrying.
Source: U.S Department of Interior, 1974.
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TABLE 5-2. NONACCESSIBLE METHODS OF SUBSURFACE EXPLORATION
Methods
Procedure
Type of soil and
in-place condition
Limitations
Use
Auger boring (hand)
Auger boring
(power)
Oi
I
oo
Drive-tube boring
Percussion (churn)
drilling
Wash boring
Rotate and force auger
bit into soil, withdraw
and empty when full.
Auger bits, 2 to 8 in. ,
helical or post hole.
Same as above, using
powered drill rigs.
auger bits, 4 to 24 in.,
helical, disc, or buck-
et. Over 28 in. consid-
ered to be accessible.
Force open pipe or tube,
with sharpened edges,
without rotation, into
soil; withdraw and
remove soil. Thin- or
thick-wall tubing or
pipe, 2 to 8 in. dia.
Chopping and cutting
action by impact of
heavy chisel-edged bit.
Water added and cuttings
form slurry that is re-
moved intermittently by
pump or bailer. For holes
larger than 4 in.
Chopping and cutting by
impact and twisting action
of lightweight bit, and
jetting action of circulat-
ing water to remove cut-
tings For holes from 2 in.
to over 8 in. dia.
Fine-grained cohesive. About 20 ft, 80 ft (1) Advance hole. (2) Data for logging. (3) Represen-
fairly hard to soft
or fine-grained, non-
cohesive, dense to
loose, weakly cemented,
or dry or moist; with
particles k in. to IS
in. depending upon
size of auger.
Fine-grained as
above, and coarse-
grained soils with
particles as large
as 3 in. depending
upon auger.
Fine-grained cohesive
and slightly cohesive
soils such as loess,
firm to soft clays,
and silts.
Coarse-grained soil
containing cobbles
and boulders, and
hard, dense, fine-
grained soiIs and
rock.
Fine- or coarse-
grained soils, with
small amounts of
gravel and few
cobbles; fairly hard
to soft; weakly ce-
mented to loose;
above or below water
table.
with tripod; unsa-
tisfactory in un-
stable cohesionless
soils below ground-
water; slow in hard
soils.
tative disturbed samples for classification, index
tests, and standard properties tests. (4) Access for
field penetration and permeability tests. (5) Access
for undisturbed sampling.
Same as above.
Economical depth
about 40 ft, over
100 ft with special
equipment; unsatis-
factory In unstable
cohesionless soils
below groundwater;
slow in hard, dense
soil.
About 80 ft depend- Same as above.
Ing upon equipment.
Not satisfactory in
coarser fine-grained
soils, clean sands, or
cohesionless soils
below water table.
Unsatisfactory in Used with other methods to advance hole through hard,
unstable soil or cemented strata, coarse gravel, boulders, or other
fractured rock; no obstructions.
information for log-
ging or samples for
classification.
No information for
logging or samples
for classification;
slow in hard or ce-
mented layers.
(1) Used with other methods to advance hole particularly
through unstable soils requiring casing. (2) Penetrate
fine-grained soils to establish depth to bedrock. (3)
Drill holes for groundwater observation. (4) Provide
access for sampling and penetration testing of impervi-
ous soils above groundwater or pervious or impervious
soiIs below.
(continued)
-------
TABLE 5-2 (continued)
Methods
Procedure
Type of soil and
in-place condition
Limitations
Use
Jetting
Rotary drilling
Rotary drilling
en
10
Continuous sampling
High-velocity water jet
directed downward from
pipe raised and lowered
in short strokes; erodes
soil, which is carried
upward by water. For
holes 2 in. to over 10 in.
dia.
Power rotation of bit;
cuttings removed by cir-
culation of drilling mud
or water; holes IS In. to
over 10 In. dia.
Power rotation of bit;
cuttings removed by cir-
culation of air. Holes
2 in. to over 10 in. dia.
Drive-tube boring or ro-
tary drilling (core bor-
ing) that provides samples
as a result of advancing
the hole.
Fine- or coarse-
grained soils; weak-
ly cemented nonco-
hesive or cohesive;
above or below water
table.
Fine- or coarse-
grained, compact or
cemented soils, and
rock.
Fine- or coarse-
grained, compact or
cemented soils and
rock.
No Information for
logging or samples
for classification;
slow in hard cohe-
sive soils.
No information for
logging or samples
for classification;
difficult In loose,
coarse-grained soil
with cobbles and
boulders.
Information for
logging and samples
for classification;
unsatisfactory in
loose coarse-grained
soil with cobbles
and boulders.
Depends upon the
method selected.
Same as (1), (2), and (3) for wash boring.
(1) Advance hole. (2) Access for field penetration test
(not suitable for well permeameter test or groundwater
observation If drilling mud used). (3) Access for dis-
turbed or undisturbed sampling.
(1) Advance hole. (2) Access for field penetration
test. (3) Well permeameter test. (4) Groundwater
observation. (5) Access for disturbed and undisturbed
sampling. (6) Advance hole to install casing for nu-
clear moisture-density probes.
Source: U.S. Department of Interior, 1974.
-------
Low permeability (usually < 1 x 10 7 cm/s) when compacted
Sufficient strength to support itself and the overlying
facility components without failure when compacted to the
required permeability and thickness
Compatibility with waste or waste leachate to be contained
(i.e., no significant loss in permeability or strength when
exposed to waste or waste leachate).
Cost considerations also enter into material selection when liner material
must be brought from offsite.
The in-place, native soil at the facility site is the ideal liner
material from the standpoint of cost and convenience; this material will be
excavated during foundation preparation and therefore does not need to be
transported to the site. If the native soil is not suitable as a liner
material, a suitable soil from a nearby borrow source can be utilized.
Most engineers interviewed reported an economic haul distance of 8 to 10
miles for borrow clay, although haul distances of up to 25 miles were
reported in some instances. When suitable soils are not available at
economic distances from the facility, it may be necessary to blend an
additive, such as bentonite, with the native soil to improve its perform-
ance as a liner material or to blend together local soils to achieve the
proper material properties. These solutions are used in areas where suitable
clay is scarce.
5.1.2.1 Native Soils-
Native soils include those obtained onsite and those obtained from
nearby borrow areas. Design engineers' opinions differed over suitable
soil types for a clay liner. These differences are, to some extent, due to
regional variability in soil types. However, the differences are also due
to the fact that soil selection based on the desirable characteristics for
liner soils (low permeability, high strength, self-healing capacity, chemical
compatibility, and low settlement and shrink/swell potential) involves some
compromise between these characteristics. The soils with the lowest permea-
bility and the highest flexibility and self-healing capacity (CH or fat
clays, see Section 3.4 of this document, unified soil classification system)
have the lowest strength and highest shrink/swell potential and are more
affected by chemicals than other soils. Gravelly or sandy clays have high
strength and a relatively low potential for settlement. However, they also
tend to be brittle and crack when stressed, and they may be more likely to
contain sandy or gravelly inclusions that could locally raise permeability.
Opinions differ on the suitability of fat (CH) clays for liners. Some
consider that their tendency to wick moisture; to dry, shrink, and crack;
and to expand upon moistening, combined with a higher likelihood of permea-
bility changes when exposed to certain chemicals, makes them inherently
unsuitable as liner materials. Others consider that the^'r low permeability
and high self-healing capacity makes them the preferred "iner material as
5-10
-------
long as provisions are made to prevent moisture change in the liner during
construction and operation and after closure. Interestingly, the location
of the persons interviewed seemed to affect their opinion on the use of fat
clays in liners. Engineers in regions where these clays were common were
more positive about their use than engineers in regions where these clays
are not common and other clay types are more readily available. However,
all engineers agreed that the major factors influencing soil selection were
its cost and its ability to be compacted to the required permeability.
If sufficient quantities of soil suitable for use as a liner material
are not available at the facility site, a borrow source must be identified.
When a borrow source is selected, routine testing procedures are used to
screen various potential sites. The time and expense involved in permea-
bility testing discourage its use for this routine screening. Design firms
often estimate clay suitability (i.e., permeability and strength) based on
quicker, more easily performed tests, including Atterberg limits, gradation
(particle size distribution), and compaction tests (standard Proctor).
Once a potential borrow source has been identified, the site should be
investigated, with the methods described in Section 5.1.1, to determine the
amount of suitable soil present at the site and the degree of spatial
variability of soil properties in the soil deposits and to confirm that the
soil is sufficiently impermeable to serve as a liner material. Borrow
source investigation results then can be used to plan an efficient extrac-
tion procedure for the liner material.
Prior to facility design, representative samples of the liner material
are subjected to laboratory compaction and permeability tests to establish
the relationship among moisture content, density, compactive effort, and
permeability*. This information is needed for preparation of the facility
design and the construction specifications. Although both standard and
modified Proctor compaction tests are used, standard Proctor is preferred
by most engineers because it results in a wetter optimum moisture content
for a given soil. Fixed-wall, flexible-wall, and consolidation cell permea-
meters are used to measure laboratory permeabilities and to establish the
moisture content and compactive effort at which minimum permeabilities may
be achieved (for further discussion of these techniques, see Chapter 3).
Strength of the liner and foundation soils also must be measured for
input to the design. The triaxial compression strength test (ASTM D2850-82)
is generally preferred for measuring soil strength. However, the direct
shear test (ASTM 03080-72, 02573-72) or vane shear test may also be used.
The shear test chosen should mimic the type of failure most likely to occur
in the soil liner.
The results of compaction, permeability, and strength tests are used
to establish an envelope of acceptable values for parameters that will be
used during design to establish material and compaction specifications.
Sufficient testing should be conducted to determine the range of vari-
ability in these soil properties and to determine the suitability of all
soil types that may be encountered at the soil source. Correlating these
5-11
-------
test results with soil index properties, appearance, and feel enables
ranges of acceptable values of these properties to be established and
specified for routine screening of liner material as it leaves the borrow
source (see Section 5.3.4).
Most design engineers interviewed also recommended that compatibility
studies of liner soils with wastes or waste leachates be conducted as a
part of the material selection, especially when the soils are comprised of
fat clays. However, no cases were uncovered (by the authors) where compat-
ibility problems with a natural soil resulted in rejection of that soil as
a liner material. One of the biggest problems with compatibility testing
is the selection of a representative waste or leachate composition. Another
is deciding how much of a change in soil properties (e.g., permeability) on
exposure to the waste or waste leachate constitutes incompatibility. More
discussion on the techniques and the problems associated with compatibility
testing may be found in Chapter 4 of this document.
5.1.2.2 Admixed Soils—
When the in situ native soil is not suitable as a clay liner and
nearby borrow sources of suitable soils do not exist, it may be economical
to use bentonite or other clay materials as a soil additive to decrease the
permeability of the native soil. Bentonite is a clay material composed of
mostly sodium-montmori11onite (with minor amounts of calcium-montmori11onite
and other clay minerals) and is, as a result, highly expansive with the
addition of water. Bentonite1s expansive nature enables relatively small
amounts (5 to 10 percent) to be added to a noncohesive soil and makes it
cohesive and behave similarly to a soil containing 50 percent nonbentonite
clay (Kozicki and Heenan, 1983). Blending two native soils can also be
used to produce a soil with the desired material characteristics.
Important parameters to consider in the design of bentonite liners
include aggregate particle size of the dry bentonite, mineralogy (as reflected
by swelling potential), and the required bentonite application rate. Both
granular and milled (powdered) bentonite are currently used as admixed
liner material. However, a Canadian firm with extensive experience in
designing bentonite liners recommends that only powdered bentonite be used
in liners (Kozicki, Ground Engineering, Ltd., Regina, Saskatchewan, personal
communication, 1984) because powdered bentonite mixes uniformly throughout
the soil mass, making intimate contact with the soil grains. Granular
bentonite cannot be as intimately mixed with the soil. A failure of one
bentonite/sand admixed liner has been attributed to the use of granular
bentonite (Diamond, 1979).
The type of exchangeable cations present in a bentonite influences its
ability to lower the permeability of a native soil and is an important
property to control. Sodium is the predominant cation in high-swelling
bentonite; its high-swelling capacity minimizes the amount that must be
used to lower the permeability of a soil. Other bentonites can contain
significant amounts of exchangeable calcium, resulting in a clay that has a
lower swelling capacity. Thus, it is important to select and specify a
bentonite that has the degree of swelling desired. This can be done easily
with a simple test (Rollins, 1969).
5-12
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The amount of bentonite to admix with the native soil to achieve a
specified compacted permeability varies according to soil conditions. In
general, 3 to 8 percent bentonite will lower the permeability of most
granular material to between 1 x 10~7 cm/s to 1 x 10 9 cm/s (Kozicki and
Heenan, 1983). However, it is necessary to determine the optimum application
rate and moisture content for the specific soil/bentonite admixture.
Usually this is accomplished by conducting a series of compacted permeability
tests on admixtures with different percentages of bentonite. Alternatively,
one design engineer determines the proper percentage by the amount necessary
to bring the liquid limit of the soil to 45 or to produce a CL classified
soil (Pacey, Emcon Associates, Inc., San Jose, California, personal communi-
cation, 1984). Once the proper percentage of bentonite is determined,
density, moisture content, compactive effort, and permeability relationships
need to be established for facility design purposes. Proper soil percentages
for blended soil liners can also be determined through the above procedures.
All personnel experienced with bentonite additives agree that compat-
ibility tests are especially critical for admixed liners. The high-swelling
clay minerals are generally more affected by chemicals than other clay
minerals. As an example, sodium-montmorinonite is easily changed to
calcium-montmorillonite when it undergoes ion exchange with solutions high
in calcium salts. This change will seriously reduce the swelling potential
of bentonite and thereby increase the permeability of the admixture.
One approach to dealing with the compatibility problem is to pretreat
the admixed bentonite with the waste liquid it is to contact. This method
is currently being used for bentonite admixed linings for brine ponds.
When brine is used to wet the bentonite admixtures, all chemical effects
take place during installation, precluding any change once the brine pond
is filled (Kozicki, Ground Engineering, Ltd., Regina, Saskatchewan, personal
communication, 1984). Although it may not be reasonable to pretreat bento-
nite with hazardous wastes or waste leachate, it may be possible to pretreat
admixtures with a nonhazardous material that will have a similar effect on
the bentonite.
5.1.3 Facility Design
Once the site and liner material have been selected and characterized,
the design of the hazardous waste containment facility can begin. Facility
design is accomplished through standard geotechnical practices but must be
tailored to the individual site geology and facility operational require-
ments. The following text summarizes some important points about the
design of clay liners gathered through our interviews and review of the
literature. Other facility components (e.g., leachate collection systems
and caps) necessary for proper facility performance are not covered by this
document. More detailed discussions of earthwork design engineering may be
found in references such as Winterkorn and Fang (1975), U.S. Department of
the Navy (1982), and U.S. Department of the Interior (1974).
5-13
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5.1.3.1 Configuration—
The configuration of the clay liner is determined by the configuration
of the containment facility, which is determined by topography, geology,
hydrogeology, land ownership, existing structures, and waste volume require-
ments. Generally, facilities are rectangular, but topographic constraints
or land availability can result in irregular shapes. Facility size is
usually determined by projected waste volume requirements and planned modes
of facility operation. However, facility size also can be limited by
technical considerations, such as seismic design criteria.
Facilities may be excavated below ground, built above ground and
contained by dikes, or built partially above and below ground. Generally
the designs of clay liners for these types of facilities are similar,
except that dike design is required for aboveground facilities and ground-
water control measures are usually required for facilities sited below the
water table (intergradient design).
5.1.3.2 Foundation Design—
Foundations for clay liners are designed to control settlement and
seepage and to provide structural support for the liner. The natural
foundation should provide satisfactory contact with the overlying liner,
minimize differential settlements and thereby prevent cracking of the
liner, and provide an additional barrier to leachate migration from the
facility.
5.1.3.2.1 Settlement—Settlement is usually not a problem for clay
liner foundations. Most clay liners are sufficiently thick to withstand
some differential settlement of the foundation soils. As long as the
topography is fairly uniform and significant soil heterogeneities are not
present, differential settlement should be minimal. However, several
design engineers recommend excavating and recompacting the upper 1 to 2
feet of foundation soil to control local settlement and seepage prior to
liner installation. Several engineers also recommend that foundation
settlement analysis based on the site's soil properties (determined during
site investigation) be conducted during the design of the facility. These
analyses should take into account the weight of all facility components on
the foundations, especially footings for pile-type structures such as
leachate collection risers, which, if improperly designed, can be forced
into or through the liner. Compensated foundation, which implies that the
weight of soil extracted from the site balances the weight of fill material,
also can be used to minimize subgrade settlement (Vesilind et al., 1983).
Techniques for conducting settlement analyses are given in any standard
soil mechanics text.
Haxo (1980) notes that differential settlement is a localized structural
stress phenomenon; therefore, the greater the liner's thickness and elasticity,
the greater the tolerance range for differential settlement. A suffi-
ciently thick liner can engage in self-healing if the subgrade settles
nonuniformly.
5-14
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The ability to predict the extent of settlement depends upon the type
of process anticipated to cause settlement. Primary consolidation, which
is a reduction in void ratio due to removal of pore fluids by mechanical
loading, generally occurs according to the consolidation theory developed
for soil. Basically, the theory states that the rate and amount of compres-
sion is equal to the rate and amount of pore fluids squeezed out of the
soil (Anderson, 1982).
Secondary consolidation (densification) depends upon the applied load
and the chemical and physical nature of the solid particles and the waste.
Therefore, secondary consolidation is more irregular and less predictable
than primary consolidation and may be significant in settlement of plastic
clay soils, heterogeneous fill materials, organic materials, and other
compressible materials.
Tertiary consolidation (densification) occurs when the volume of
solids is reduced. The effect of tertiary consolidation on mineral soils
is minimal; however, it may be a major concern with organic soils, organic
waste, soluble materials, and materials subject to chemical attack. Tertiary
consolidation is highly irregular and is influenced by a number of environ-
mental factors that make it difficult, if not impossible, to predict (Anderson,
1982).
5.1.3.2.2 Seepage—Seepage both into and out of the facility must be
controlled during construction and site operation. Although the clay and
flexible membrane liners are designed to accomplish this goal, for their .
optimum performance and because it may function as a backup liner, the
foundation also should be designed to control seepage. For intergradient
facilities, seepage can reactivate slickensides in the foundation soil. If
these features are present near the toe of sidewall slopes, slope failures
can result (Boutwell, Soil Testing Engineers, Inc., Baton Rouge, Louisiana,
personal communication, 1984). Opening of slickensides or joints can occur
from stress removal by excavation and when soils heave in response to
unbalanced water pressures in underlying permeable strata (Boutwell and
Donald, 1982).
Heterogeneities such as large cracks, sand lenses, or sand seams in
the foundation offer pathways for leachate migration and could cause piping
failures. Soft spots in the foundation can cause differential settlement,
possibly causing cracks in the liner and damage to the leachate collection
and leak detection system. Cracks and sand lenses or seams also can cause
problems during liner construction if the facility penetrates the water
table. An illustration of this problem was provided by a design engineer
during one of the interviews. In the case he cited, a 2-foot clay liner
was installed without adequate site investigation or foundation preparation.
A small fracture in the foundation base was connected to an artesian (geo-
pressured) aquifer 30 feet below the landfill bottom. The overburden that
was removed during construction originally provided confining pressure on
the fracture. After the liner was installed, hydrostatic pressure in the
crack exceeded the confining pressure provided by the liner, causing a
rupture of the liner. The expense of excavating the ruptured liner and
5-15
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crack, grouting the crack, and pumping the aquifer to reduce the hydraulic
head could have been avoided or minimized if adequate site investigation
and foundation preparation had been practiced prior to liner installation.
Solutions to these problems include the various dewatering systems
(e.g., pumping wells, slurry walls, trenching, and pumping) to lower the
hydraulic gradient on the facility (Boutwell et al., 1980). Further discus-
sion on dewatering methods may be found in Cashman and Haws (1970), and
Section 5.1.3.4.7 describes intergradient facility design in more detail.
Other methods to control foundation seepage include properly keying dikes
into the foundation subsoil, selecting impermeable materials for dike
cores, grouting cracks and fissures in the foundation soil with bentonite
or other grouting material, and designing compacted clay cutoff seals to be
emplaced in areas of the foundation where lenses or seams of permeable soil
occur. Figure 5-1 illustrates typical clay cutoff seal designs.
5.1.3.2.3 Dike Design—Containment facilities built above ground or
partially above ground require dikes to support the aboveground portion.
Hazardous waste containment facilities may be designed to be above ground
for several reasons. Regulations may require a certain distance between
the facility bottom and the nearest underlying aquifer or, in some cases,
the water table. Aboveground design may be necessary to achieve this
separation. In regions with high water tables, limits placed on excavation
depth in order to prevent bottom heaving or rupture may necessitate a
partial aboveground design (see Section 5.3.4.1.7). In addition, low-cost,
suitable dike construction material may be readily available at or near the
facility site, making aboveground construction more economical than excavated
facilities.
A containment facility dike serves as a retaining wall to resist the
lateral forces imposed by the stored wastes. Design for retaining charac-
teristics requires slope stability analysis, which is normally accomplished
by using the Bishop method of slices (Boutwell et al., 1980). As the waste
produces much of the outward force on the dike, the geotechnical properties
of the wastes must be defined. In addition, time-related changes in the
properties of both the waste and the dike material resulting from consolida-
tion, settlement, changes in saturation, or chemical interactions must also
be evaluated (Boutwell et al., 1980). Figure 5-2 illustrates typical dike
configurations.
Erosion resistance and control of desiccation must also be considered
during the design of dikes. Berms and vegetation may be used to control
erosion. In arid regions special designs incorporating gravel-filled
troughs in the dike crest have been used to provide a method to prevent
desiccation cracking. If the trough is kept filled with water, the exposed
upper portion of the dike can be kept moist. For further information on
dike design, the reader is referred to Sherard et al. (1963), U.S. Bureau of
Reclamation (1973), Winterkorn and Fang (1975), U.S. Department of the Army
(1977), and U.S. Department of the Navy (1982).
5-16
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• Interior Side Slope
Cut required to overexcavate
permeable seam or zone and
replace with compacted seal.
Permeable
Seam or Zone
Clay compacted in lifts not exceeding
9" in loose thickness to a minimum of 95%
of the standard proctor density (ASTM D-698)
Side
•Interior Side Slope
Cut required to overexcavate
permeable seam or zone and
replace with compacted seal.
Permeable
Seam or Zone
Clay compacted in lifts not exceeding
9" in loose thickness to a minimum of 95%
of the standard proctor density (ASTM D-698)
• Base Grade
Comer
Clay compacted in lifts not exceeding
9" in loose thickness to a minimum of 95%
of the standard proctor density (ASTM D-698)
Cut required to overexcavate
•permeable seam or zone and
replace with compacted seal.
Base Grade
Bottom
Permeable
Seam or Zone
After Waste Management, Inc.
Figure 5-1. Compacted clay cutoff seal.
5-17
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Cover Soil
Berm
Toe Drain
Homogeneous Dike
and Soil Liner
Synthetic Membrane
Liners
Leachate Collection
System
HOMOGENEOUS DIKE
Toe Drain
Synthetic Membrane
Liners
Leachate Collection
System
Low-Permeability
Soil Liner
ZONED DIKE
Figure 5-2. Dike components and typical configurations.
5-18
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5.1.3.2.4 Sidewall Design—Sidewall slopes of the hazardous waste
containment facilities identified during this project ranged from 4 to 1
(horizontal to vertical) to vertical. Factors that influenced the selec-
tion of sidewall slopes included waste volume/landfill area considerations,
foundation and liner soil stability, equipment operation constraints, and
stability of other facility components.
One factor that influences the choice of sidewall slope is whether the
sidewall liner is to be compacted in horizontal lifts or in continuous
lifts parallel to the liner surface (Figure 5-3). Generally, the continuous
lift method cannot be used for side slopes steeper than around 2.5 to 1
because of operational limitations of compaction equipment. However, this
limitation varies according to soil characteristics and equipment type. In
one case, described during an interview, continous lifts were compacted on
slopes as steep as 2 to 1 with a sheepsfoot roller. However, the facility
was small, the slopes were short, and the roller had to be both pushed and
towed to negotiate the slope. In soils common to Louisiana, a bulldozer
can operate on slopes as steep as 2 to 1 but tends to tear the liner mater-
ial. A slope of 2.5 to 1 is recommended for bulldozer operation, and a
slope of 2.8 to 1 is recommended when sheepsfoot rollers are used (Boutwell
and Donald, 1982).
Some design engineers interviewed preferred horizontally compacted
side slopes to those with continuous lifts because the former are more
stable and they allow steeper slopes and hence greater facility waste
capacity. However, most engineers interviewed believe that, for horizontal
sidewall lifts, the orientation of lift boundaries and the compacted clay
fabric perpendicular to the liner surface increase the likelihood of seepage
through the liner, limiting the desirability of horizontally compacted
sidewall slopes. Thus, most engineers consider it especially critical to
ensure that lifts are adequately tied together in horizontally compacted
side slopes. However, no case studies were found during this investigation,
which demonstrated increased seepage due to horizontal sidewall lift compaction.
Other sidewall slope considerations collected during our interviews
and literature review include:
Flexible membrane liner (FML) manufacturers generally recommend
that, when an FML is part of the liner system, sidewalls
should not be steeper than 3 to 1. Tracked vehicles placing
earth materials on FMLs tend to stall, spin their tracks
through the loose earth, and damage the FML on steeper
slopes (Morrison et al., 1982). However, FML-lined facili-
ties with side slopes of 1 to 1 were encountered during our
survey. Opinions differed among design engineers on this
subject.
For admixed bentonite liners, slopes of 3 (H) to I (V) are
generally preferred. Mechanical spreading methods can be
used on 2.5-to-l slopes, but this is the marginal case.
Hand placement can be used on slopes of 2 to 1, with mixing
and compaction performed by towing equipment up and down the
slope (Kozicki and Heenan, 1983).
5-19
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Overbuild and
Cut to Slope
JL
Horizontal Lifts
Continuous Lifts
Rgure 5-3. Methods of liner sidewall compaction.
5-20
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The angle of repose of sand corresponds to approximately a
2-to-l slope. Thus, if a granular leachate collection
system is designed to extend up the slopes, sidewall slopes
cannot exceed 2 to 1.
Although steep sidewalls with horizontal lifts maximize
volume and provide greater stability, construction costs can
be greater than with continuous lifts because of logistic
and scheduling requirements and the extra liner material
that must be used and then trimmed away.
With thinner linings (2 to 3 feet), extra width to accom-
modate equipment may result in the sidewall lining being
thicker than the'bottom lining for horizontally compacted
sidewalls.
One engineering firm preferred horizontally compacted side-
walls for thick linings (^5 feet) and continous sidewall
liner lifts for thin linings (<2 feet).
One engineer recommended that 4-inch lifts (versus 6-inch
bottom lifts) be used in horizontally compacted liner side-
walls.
Slopes of 3 to 1 or less tend to collect water if not properly
smoothed.
Maximum sidewall slopes of 2 to 1 are advisable for liners
composed of highly plastic soils because of the loss of
stability of these soils when they are saturated (Day,
1970). Highly plastic soils contain high amounts of smectite
clay minerals. The high dispersivity of these minerals
results in a loss of strength upon wetting.
Slope stability analysis must be conducted for both foundation and
liner soils to ensure that shearing stresses developing within sidewall
slopes following excavation or dike construction will not exceed the avail-
able shear strength of the soil and cause a failure of the slope. The
shear strength (or cohesion) of the soil and its variability in the soil
mass, degree of saturation of the soil (or pore water pressure), slope
height and inclination, heterogeneities in the soil mass, and expected
stresses on the slope are all important inputs to slope stability analyses.
Applicable strength tests for the waste and soil include a measure of
relative shear strength by a cone penetrometer, vane shear tests, remolding
index, drained direct shear, triaxial compression, and consolidation tests.
Strength tests should be selected to mimic the expected mode of failure in
the soil (Haxo, 1983).
Several methods of slope stability analysis are currently used.
Classic limit equilibrium methods are generally used for earthwork design.
5-21
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These methods take a free body from the slope and, using estimates of the
forces acting on the body, calculate the equilibrium shear resistance of
the soil and compare it to the shear strength of the soil to indicate the
factor of safety (Fang, 1975). Regardless of the specific procedure used
for carrying out the computations, the following principles are common to
all limit equilibrium methods: a potential failure surface is postulated;
the shearing resistance required to equilibrate the assumed failure mechanism
(i.e., the shear stresses required along the failure surface to balance the
driving forces of the unsupported slope) is calculated by means of statics;
the calculated shearing resistance required to maintain equilibrium is
compared to the available shear strength of the soil along the assumed
failure plane (the ratio of the existing strength to induced shear stress
is one definition of a factor of safety); and the mechanism with the lowest
factor of safety is found by iteration.
Choosing the method depends to some extent on the properties and
hydrologic conditions of the soils to be evaluated. For homogeneous soils
with equal pore pressure distributions, methods that consider the whole
free body are appropriate, such as the friction circle method (Taylor,
1948). If soil properties vary through the soil mass, the method of slices,
which divides the free body into several vertical slices, is appropriate
(Bishop, 1955; Fellenius, 1927). If straight line failure planes can be
identified in the soil mass, the wedge method can be used (Lambe and Whitman,
1969). The wedge method has been recommended for evaluating the stability
of clay liners placed on side slopes (Boutwell and Donald, 1982). For
facilities below the water table it is necessary to consider pore water
pressure, and the effective stress (total stress minus pore water pressure)
should be used instead of total stress (Fang, 1975). Methods of stability
analysis that consider these factors include the Bishop and Morgenstern
method (Bishop and Morgenstern, 1960) and the Spencer method (Spencer,
1967). Factors that must be considered when slope stability is calculated
in special problem soils are presented in Table 5-3.
Essentially two types of slope stability problems occur in clay:
short-term stability (end-of-construction case) and long-term stability
(steady-seepage case). The short-term case applies just after the excava-
tion is completed and assumes that time has been insufficient for any water
to move in or out of any representative soil element within the soil profile.
When a soil profile is believed to be relatively homogeneous and without
discontinuities, this is a reasonable assumption and has been used with
much success. Should the clay have substantial joints and fissures, drainage
may occur so quickly along these discontinuities that the problem may not
be adequately represented by the assumption (Esu, 1966). In general, only
short-term stability analysis is necessary for interior containment facil-
ity slopes if the facility is to be filled shortly after construction;
long-term slope stability should be considered for the outer slopes of
aboveground facilities (Boutwell and Donald, 1982).
A factor of safety is customarily calculated during slope stability
analysis. The factor of safety is calculated as a ratio of terms reflect-
ing conditions that impact a slope's stability. Terms that are used for
5-22
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TABLE 5-3. FACTORS CONTROLLING STABILITY OF SLOPED
CUT IN SOME PROBLEM SOILS
SOIL TYPE
PRIMARY CONSIDERATIONS FOR SLOPE DESIGN
Stiff-fissured Clays
and Shales
Field shear resistance may be less than suggested by
laboratory tests. Slope failures may occur progres-
sively and shear strengths reduced to residual values
compatible with relatively large deformations* Some
case histories suggest that the long-tern performance
is controlled by the residual friction angle which for
some shales may be as low as 12°. The most reliable
design procedure would involve the use of local
experience and recorded observations.
Loess and Other
Collapsible Soils
Strong potential for collapse and erosion of relative-
ly dry material upon wetting. Slopes in loess are
frequently more stable when cut vertical to prevent
infiltration. Benches" at intervals can be used to
reduce effective slope angles. Evaluate potential for
collapse as described in DM 7.1, Chapter 1* (See
DM-7.3, Chapter 3 for further guidance.)
Residual Soils
Significant local variations in properties can be
expected depending on the weathering profile from
parent rock. Guidance based on recorded observation
provides prudent basis for design.
Sensitive days
Considerable loss of strength upon remolding generated
by natural or man-made disturbance. Use analyses
based on unconsolidated undrained tests or field vane
tests.
Talus
Talus is characterized by loose aggregation of rock
that accumulates at the foot of rock cliffs. Stable
slopes are commonly between 1-1/4 to 1-3/4 horizontal
to 1 vertical. Instability is associated with abun-
dance of water, mostly when snow is melting.
Loose Sands
May settle under blasting vibration, or liquify,
settle, and lose strength if saturated. Also prone to
erosion and piping.
.Source: U.S. Department of the Navy, 1982.
5-23
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these calculations include available shear strength versus required shear
strength, required soil cohesion versus available cohesion, actual friction
angle versus stable friction angle, actual height versus stable height, and
resisting moments versus moments tending to cause failure. Probabilistic
statistical methods also have been developed for factor of safety calcula-
tions (Fang, 1975).
A factor of safety of 1.0 means that if the slope is constructed
perfectly as designed, it will not fail. However, because actual construc-
tion is rarely perfect, a larger safety factor is usually used to design
slopes for critical facilities. For public earth works projects (e.g.,
dams) in California, a safety factor of 2.0 is used. One design engineer
considered a safety factor of 1.7 to be the minimum acceptable for use on
outer slopes of hazardous waste facilities (Reynolds, California Department
of Health Services, Sacramento, California, personal communication, 1984).
Static slope stability analysis is appropriate in areas with little or
no seismic risk. Dynamic slope stability must be considered in areas where
significant ground motion can occur (Fang, 1975; also see Section 5.1.3.4.6),
In summary, the following guidance should be applied to the design of
slopes (Lutton et a!., 1979):
Examine, sample, and test foundation conditions to ensure that it
is not weak and likely to participate in. displacement.
Conduct detailed engineering stability analyses for any site
where the consequences of slope failure are serious. Estimate
changes in hydrology, seismic stability, identify average and
worst case patterns, and integrate all information into a factor
of safety.
When selecting soils, consider soil shear strength, allowing for
compaction and the corresponding strengthening effect.
Specify slope inclination; decreasing the design inclination
effectively increases the stability of soil slopes.
Use underdrains, toe drains, cutoffs, and leachate collection and
disposal systems for seepage control.
Allow for freeze/thaw and dry/soak conditions in the selection of
a sufficiently thick side slope soil.
Compact soil as specified, using field tests for quality control
or quality assurance. Prescribe lift thickness.
Consider other miscellaneous factors including toe protection
(e.g., from flooding conditions) the use of berms or systems of
berms rather than having a single unbroken inclination, and the
use of reinforcement to strengthen embankments.
5-24
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5.1.3.2.5 Bottom Design—The bottom of the containment facility must
be shaped to facilitate leachate collection in landfills and drainage in
surface impoundments and to prevent puddling and ponding on the liner
during construction. Most design engineers use a 1- to 2-percent slope for
the facility base, with 2 percent being preferred.
Kmet et al. (1981) used an analytical model of landfill leakage devel-
oped by Wong (1977) to evaluate several landfill design parameters, includ-
ing clay liner bottom slope. In general, increasing the bottom slope
decreased the liner leakage by providing more rapid movement of leachate to
the collection sump. Leakage rapidly increased when bottom slopes decreased
to below 2 percent. Bottom slope increase to 5 percent provided additional
reduction in leakage, with little additional benefit for steeper slopes.
The configuration of the bottom slope depends on the facility configur-
ation and the leachate collection system design. Most designs incorporate
a sand/gravel drainage layer with a system of pipes, with the liner bottom
sloping to the pipes and the pipes and underlying liner sloping to a collec-
tion sump. Based on the analytical model described previously (Wong,
1977), Gordon et al. (1984) recommend a maximum leachate flow distance to
the pipe network of 150 feet, and 50 feet has been stated as the reasonable
minimum due to construction practicalities (Kmet et al., 1981). Small
facilities may have a pipeless collection system, and one design engineer
interviewed preferred a properly designed granular drainage layer without
pipes to a piped system because it precludes the necessity of cleaning out
pipes.
5.1.3.3 Liner Design—
Clay liners are constructed of compacted clay soils installed in a
series of lifts of specified thickness. The liner must be sufficiently
thick and impermeable to retard leachate flow and to provide structural
support to overlying facility components. For clay liners, a permeability
of 1 x 10 7 cm/s is required by Federal regulations. One design engineer
recommended that a permeability of 1 x 10 8 cm/s be specified to provide a
factor of safety.
Liner thicknesses of I to 12 feet of native clay were encountered
during the course of this study, although most design engineers recommended
5 to 10 feet of clay. State regulations usually determine liner thickness,
with 2 feet (as recommended by EPA guidance) as the minimum. Transit time
prediction methods (described in Chapter 8 of this document) also have been
used to specify liner thickness.
In general, the liner is designed to be uniformly thick over the
entire facility except for thicker areas that will be excavated for the
leachate collection sump and for any leachate collection pipes recessed
into the landfill bottom. This is necessary so that, following excavation,
the liner will have the uniform, specified thickness over the entire landfill
bottom as illustrated in Figure 5-4. In addition to this, engineers working
for the Department of Natural Resources, State of Wisconsin, recommend an
extra foot of liner under leachate collection lines (Gordon et al., 1984).
5-25
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en
I
(X)
cr>
Drainage
Layer
Recess for Pipe
iiiLillSS?^^^
•-"'•vV'-^.-
Leachate Collection Pipe
Figure 5-4. Liner design for collection system pipes and sump.
-------
Extra liner thickness and compact!ve effort have been recommended for the
toes of sidewall slopes to combat seepage and to ensure that the bottom and
sidewall liners are adequately tied together.
Lift thickness is selected by the design engineers and the contractors
depending upon soil characteristics, the compaction equipment to be used,
and the required compactive effort. Lift thickness is usually specified in
the construction specifications. The liner lifts must be thin enough so
that adequate compactive effort reaches the lower portion of the lift.
Emplacement of thin lifts ensures that the entire lift is adequately compacted
and because more additional compactive effort is transferred to lifts below
the lift being installed. However, these advantages must be balanced with
the added construction expenses associated with thinner lifts since more
lifts must be compacted to achieve the specified liner thickness. Interviews
with design engineers indicate a general preference for loose lift thickness
of 6 to 9 inches. However, loose lift thicknesses of up to 15 inches have
been encountered during our survey, and a 2-foot lift was used over a sand
drainage layer at one facility (see Section 5.1.3.3). Some engineers think
that adequate compaction can be achieved with thick lifts if heavy enough
compaction equipment is used. Four-inch lifts were recommended by one
engineer for horizontally compacted sidewalls.
Clay liners may be designed to be installed over the entire facility
(small facilities) or in segments (large facilities and continuous-operation
facilities). If the liner is installed in segments, a beveled or step-cut
joint between segments (Figure 5-5) should be specified to ensure that they
are properly tied together. A bevel with an 8 to 1 slope was specified for
a large facility where the liner was installed in wide transverse strips
(Boutwell, Soil Testing Engineers, Baton Rouge, Louisiana, personal communi-
cation, 1984).
Most admixed bentonite liners are only 4 to 6 inches thick. Bentonite
company literature indicates that liner thickness can be as small as 4 to 6
inches because of the low permeability (10 9) that can be achieved with
bentonite (IMC, 1982). However, Federal guidance recommends a 2-foot clay
liner, and many States require liners up to 10 feet thick. Regulatory
personnel in some of these States did not think that thin bentonite linings
satisfy the regulations. Besides failing to meet the thickness requirements,
thin liners may not provide adequate structural stability for the overlying
facility components such as leachate collection risers and may be hard to
construct to uniform thickness. In general, clay liner thickness and
permeability requirements must be independently satisfied; the use of a
clay with a lower permeability than required does not justify a thinner
liner (Boutwell and Donald, 1982).
Two facilities with bentonite liners are included in the case studies
section of Chapter 7. At Site 0, local soils were augmented with 3 percent
bentonite to achieve the required permeability. The actual permeability
achieved was 8.3 x 10 8; however, a 4-foot liner was still used at the
site. In addition, 3 percent lime was added to stabilize the bentonite by
reducing its swelling capacity (by replacing sodium with calcium in the
5-27
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Bevel Cut
Step Cut
Figure 5-5. Methods of keying-in liner segments.
5-28
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bentonite). The same effect and permeability could have been achieved
without lime addition by using lower cost bentonite already with a high-
calcium-montmorillonite content.
Site P presents an approach to achieving both low permeability and
high strength while minimizing the addition of bentonite. In this double-
clay-lined site, the upper liner consists of a 1-foot compacted layer of
admixed polymer bentonite and native soil (5 x 10 8 cm/s) sandwiched between
two layers (3 ft above and 1 ft below) of recompacted native soil of a
higher permeability (10 6 cm/s). The lower liner is composed of 6 inches
of compacted admixed liner underlain by 5 feet of recompacted or in situ
native soil. The sides are single lined with 18 inches of compacted native
soil overlying 6 inches of compacted admixed soil. The designers of the
site used the recompacted native soil to provide structural strength and
protection to the admixed liner with the admixed liner providing lower
permeability. It is not certain whether this liner design would satisfy
current regulatory requirements, especially in States requiring thick
liners.
Liner system configuration differs according to the type of contain-
ment facility. In landfills, the clay liner usually lies below a synthetic
liner that lies below the leachate collection system. In some cases, the
clay liner may be sandwiched between two synthetic liners or vice versa.
Leak detection systems may be installed between the liners or under the
liner system. A leak detection system may consist of a sand, gravel,
and/or geotextile layer underlying the entire facility (continuous cov-
erage) or individual lysimeters or other instruments at specific points
under or between liners (discrete coverage). Collection lines from the
leak detection system either pass through the clay liner or pass under the
liner to exit at the landfill periphery. The latter design is preferred by
many engineers because objects penetrating a liner offer potential pathways
for leakage through the liner.
The relationship of the clay liner to other system components for a
waste pile is the same as for a hazardous waste landfill, except that a
primary synthetic liner is not required and thus may not be present in a
waste pile. The leachate collection system will rest directly on a clay
liner when it is the primary liner.
The major difference between the liner system in an impoundment and
that of a landfill or waste pile is that because impoundments by definition
are designed for holding bulk liquids, leachate collection systems are not
installed on top of the liner. Surface impoundment liner system designs
incorporating clay liners can consist of a single clay liner or may consist
of a system of redundant liners (all clay or clay and synthetic) with leak
detection or collection between or under the liners. If the wastes are to
remain in the impoundment after closure, synthetic linings are required.
Outlet pipes from leak detection/collection systems (below the primary
liner) may pass through the primary liner or may run under it to the peri-
phery of the facility.
5-29
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A rip-rap layer on the upper side slopes of surface impoundments may
be necessary to protect against wave erosion (Section 5.1.3.4.2). A dis-
charge structure for loading wastes into the pond will prevent scouring of
the liner surface (Section 5.1.3.4.2). Adequate free board (sidewalls
above the liquid surface) to contain runoff from large rain storms should
be included in surface impoundment designs (U.S. Environmental Protection
Agency, 1982b).
When clay liners are installed over granular leak detection layers,
the granular layer often does not provide enough stability for compacting
the first lift of liner material. Techniques that allow equipment to
'bridge1 over sand layers without causing rearrangement and damage include:
The use of a geotextile over the drainage layer (this also
prevents piping)
The use of lighter compaction equipment that can 'bridge1
the sand
The specification of thicker lower lifts.
At one large facility, this problem was solved by using a loose lift thick-
ness of 2 feet for the first lift over the sand layer. The normal lift
thickness at this site was 15 inches; the use of large compaction equipment
enabled thick lifts to be specified.
5.1.3.4. Special Design Considerations--
This section describes some special design practices that are needed
to prevent specific causes of clay liner failure. A full discussion of
each of these failure mechanisms, along with illustrative case studies, may
be found in Chapter 6 of this document.
5.1.3.4.1 Control of Erosion—Erosion can be a problem during liner
construction and on dikes and freeboard areas in completed facilities. The
most accurate soil loss prediction tool that is now field-operational is
the U.S. Department of Agriculture's Universal Soil Loss Equation (USLE)
(Wischmeier and Smith, 1978). This equation has been used for agricultural
erosion control planning for more than a decade. The maximum erosion rate
should not exceed 2 tons per acre using the USLE (U.S. Environmental Protec-
tion Agency, 1982b). Important design considerations for erosion control
are listed below (Lutton et al., 1979):
Erosion-resistant soils (erosion resistance is quantified by
the soil credibility factor, K, in the USLE) should be
selected.
Dispersive clays and soils in a dispersed condition should
be protected from erosion or avoided in facility areas where
' erosion can occur.
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The overall landfill configuration is important. The two
factors, L (slope-length factor) and S (slope-steepness
factor), in the USLE dominate the erosion aspects of runoff.
It is generally essential to divert natural drainage from
outside the immediate site (through external runoff diversion)
to prevent erosion in the facility excavation.
Final dike slopes more than 5 feet high should be protected
from erosion by building berms and gutters along the top and
sides of the slope.
Vegetation should be started as soon as possible on exterior
dike walls and be well maintained throughout the life of the
site.
The use of soil covers is often specified to minimize exposure
and to protect otherwise bare soil at the construction site.
Applications should always be encouraged for intervals when
construction is interrupted.
A program of long-term maintenance can be used to avoid
erosion problems after closure of the landfill site. This
is especially important for flood-retaining structures for
facilities sited in the 100-year flood plain.
5.1.3.4.2 Control of Scouring—Scouring is the erosion of the liner
or sidewalls of a containment facility by the force of moving water. Sur-
face impoundments often need to be protected from wave erosion on their
upper side slopes. Rip-rap (loose rock) is the most widely used material
for this purpose. Concrete aprons can be used, but studies by the U.S.
Department of Interior have shown that rip-rap is generally more effective
and easily placed (Small, 1981). Rip-rap must be properly sized and placed
to result in a stable protective blanket (U.S. Department of Interior,
1974). One design engineer recommends that a wind rose for the site and
the pond fetch should be used to determine maximum wave height. The rip-rap
layer can then be designed, based on wave height and expected fluctuations
of liquid levels in the pond. Rip-rap generally is uniform in size, and
dumped rip-rap performs better than hand-placed rip-rap. More information
on the design of rip-rap layers may be found in U.S. Department of the
Interior (1974) and U.S. Environmental Protection Agency (1982b).
Clay liners in surface impoundments must also be protected from ero-
sion by discharge of waste into the impoundment. At least one clay liner
failure identified during this study was attributed to erosion from dis-
charging wastes into the pond. Discharge structures used to reduce this
erosion include concrete or rip-rap aprons, discharge tubes with upward
facing outlets, and various weirs, such as a reverse duckbill weir (Day,
1970).
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Johnson and Cole (1976) reported that a bentonite liner in a papermill
lagoon was protected from scouring by covering with coarse-grained material.
First the liner was covered with 3 to 4 inches of till, and then a 6-inch
gravel cover was placed over the till in the most susceptible areas (e.g.,
at the base of the aerators). Sidewalls with 3-to-l slopes were protected
from scour by 6 inches of crushed stone that was covered with rip-rap. No
problems have resulted in this facility. Johnson and Geisel (1979) reported
that a clay liner used in a municipal wastewater treatment lagoon was
protected by covering with gravel.
Voigts and Savage (1974) described a wastewater treatment lagoon lined
with natural clay. Rip-rap was added to the slopes to protect against wave
action and erosion, and a concrete scour pad was placed under the aerators
to prevent scouring the liner. Stone was added around the scour pad out to
35 feet as an additional safety factor to prevent erosion. The aerator
supports, which penetrated the clay liner, were sealed with neoprone water
stops in the middle of the compacted clay.
5.1.3.4.3 Cold Climate Design—Failures from operations in cold
climates are minimized by following design considerations outlined by
Lutton (1979). Although these considerations were developed for covers,
the following are relevant to liners as well:
Evaluate soil susceptibility to undesirable frost actions
and locate the earth barrier below the frost zone.
Maintain an unfrozen soil supply.
Consider seasonal scheduling and alternating the choice of •
liner soils depending on the availability of unfrozen materials.
In addition, temporary liner covers of soil or organic mulch have been used
for protection from freezing temperatures.
5.1.3.4.4 Control of Piping—Piping is a form of internal soil erosion
that occurs below the ground surface (see Section 6.4). It occurs when
fine particles migrate away from a cohesive soil layer and may result from
physical causes (discordant grain size) or chemical dissolution.
Compatibility testing of the liquid waste or leachate and the liner
material (see Chapter 4) is a prerequisite to minimizing piping from chemical
dissolution. The compatibility testing can document the chemicals' effect
on permeability. During the permeability test, observations for signs of
migrating soil particles should be made and recorded. Dissolution effects
(e.g., observation of an unusual color of effluent) and obvious structural
changes in the soil material should also be noted. The waste and liner
would be considered compatible and piping from dissolution would be consid-
ered unlikely if the test showed no permeability increases, no migrating
soil particles, and no other dissolution effects.
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Four laboratory tests to determine soil susceptibility to dispersive
erosion have been developed by the U.S. Soil Conservation Service (SCS).
Dispersion tests are a specialized group of tests for characterizing fine-
grained soils suspected of having a tendency to erode rapidly. A major
conclusion of a recent symposium on soil piping was that these four tests
should be performed on soils where piping would cause unacceptable damage
(Sherard and Decker, 1977). The four tests are the pinhole test, a test of
dissolved salts in the pore water, the SCS dispersion test, and the crumb
test. The test methods and extensive test data are available in ASTM
Special Technical Publication No. 623.
When a clay liner overlies a granular drainage layer, control of
piping can be accomplished by the incorporation of a filter layer below the
clay layer. A filter layer will have a grain size slightly larger than the
clay and will capture the migrating clay particles. For example, clay over
gravel represents the joining of discordant grain sizes such that the clay
particles can penetrate to the voids of the gravel. When a filter is
placed under the clay, internal erosion is largely eliminated. In addition,
the filter would help to minimize drainage problems in the sand or gravel
layer (or the leachate collection system) that occur from clogging by the
fine clay particles.
Filter layers may be composed of geotextiles or a layer of graded
material. Resource Conservation and Recovery Act (RCRA) guidance documents
have been developed by EPA, and these documents contain criteria for selec-
ting filter layers to stop migrating particles and to avoid plugging of
drainage layers (U.S. Environmental Protection Agency, 1982b). The criteria
were developed by the U.S. Army Corps of Engineers and are based on grain-
size ratios for the adjacent layers.
5.1.3.4.5 Control of Desiccation—Desiccation cracks are prevented by
several testing, design, and construction procedures. Waste compatibility
with the liner should be confirmed to avoid cracking from chemical attack.
If the waste leachate creates cracks or channels in the liner material,
alternative liner materials should be evaluated. The liner material should
be tested to determine the liquid, plastic, and shrinkage limits. These
criteria may be used to evaluate a soil's cracking potential (Lutton et a!.,
1979). Tables 5-4 and 5-5 show the expected volume changes associated with
these indices. Soils with high volume changes have a greater tendency to
crack with decreased moisture.
Clay liners may be subject to developing desiccation cracks during and
immediately after installation. The clay may be protected from desiccation
after construction by installing a synthetic membrane; by installing 1 to
2 feet of soil; or for surface impoundments, by putting liquids into the
impoundment immediately after construction.
5.1.3.4.6 Seismic Design—Earthquakes occur across the United States.
Although they are less frequent in eastern States, geological conditions
are such that damage from ground motion is more widespread in the East than
in California when earthquakes do occur (see Section 6.8). If a facility
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TABLE 5-4. RELATIVE VOLUME CHANGE OF A SOIL AS INDICATED BY
PLASTICITY INDEX AND OTHER PARAMETERS
Likelihood of volume
change with changes
in moisture
Little
Little to moderate
Moderate to severe
Plasticity index
Arid regions Humid regions
0 to 15 0 to 30
15 to 30 30 to 50
30 or more 50 or more
Shrinkage limit
12 or more
10 to 12
10 and less
TABLE 5-5. SOIL VOLUME CHANGE AS INDICATED BY
LIQUID LIMIT AND GRAIN SIZE
Passing No. 200
sieve (%)
>95
60 to 95
<30
Liquid limit
>60
40 to 60
<30
Probable expansion
>10
3 to 10
-------
is located in an area likely to experience ground motion from seismic
events, it should be designed to withstand this ground motion. The most
likely types of damage from seismic events include (LARG, 1982):
Failure of structures from ground shaking
Failure of facility components due to soil liquefaction,
liquefaction-induced settlement and landsTiding, and soil
slope failure in foundations and embankments
Failure of facility components due to fault rupture
Lands!iding and collapse of surrounding structures.
Of these failures, current Federal locational standards protect only against
fault rupture by requiring a 200-foot setback from active faults. The
other three types of failure are caused by earthquake-induced ground motion.
LARG (1982) found that ground motion is much more important as a
failure mechanism than fault rupture. More sites are impacted by ground
motion than by surface faulting for a given seismic event because the only
sites impacted by faulting are those actually located on a surface fault
trace. LARG's study of six hazardous waste facilities in California also
found that ground-motion-induced failure of tanks and poorly designed
surface impoundments were potentially the most significant contributors to
hazardous waste release during earthquakes.
The process of designing earthquake-resistant structures may be divided
into four steps. They are:
Determining the maximum credible or maximum probable earth-
quake for the site
Determining the expected peak ground acceleration at the
site from the maximum earthquake, based on regional and
site-specific geologic factors
Determining site-specific seismic hazards, such as potential
for soil liquefaction, slope failure, and landslides
Designing the facility to withstand peak ground acceleration.
The current California Water Resources Control Board hazardous waste
regulations encompass these steps in addition to requiring a 200-foot
setback from active Holocene faults. Specifically, the California Adminis-
trative Code (CAC) requires the following for new hazardous waste facilities
or expansion of existing facilities:
A determination of the expected peak ground acceleration at the
waste management unit associated with maximum credible earthquake
(CAC Article 9, Section 2595)
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Consideration of regional and local seismic conditions and fault-
ing and site-specific surface and subsurface conditions in the
above determination (CAC Article 9, Section 2595)
Use of the peak ground acceleration to determine the stability of
and safety factors for all embankments, cut slopes, and associated
fills during the design life of the unit (CAC Article 9, Section
2595)
Design of the waste management unit to withstand the maximum
credible earthquake without damage to the structures that control
leachate, surface drainage, erosion, and gas (CAC Article 4,
'Section 2547).
Determining the maximum expected seismic event and the resultant
seismic loading at the site are the key elements in seismic risk analysis.
The two approaches to this determination are deterministic and probabilistic
(Bernreuter and Chung, 1984). The first step in both methods is to delineate
regional (tectonic province) and local (fault) sources. For the deterministic
method, the next step is to select the governing earthquake or maximum
credible earthquake, usually the most damaging historical earthquake associ-
ated with the site. Attenuation of the seismic energy with distance from
the source is then determined based on regional and local subsurface condi-
tions. The maximum (peak) ground acceleration at the site is then determined
based on surface and subsurface site characteristics.
The probabilistic approach involves developing an earthquake recurrence
model for each source that could impact the site. The ground motion at the
site from different earthquakes at different distances is calculated (based
on local and site-specific subsurface geology), and this information is
used to calculate the probability that a given level of ground motion will
not be exceeded within a specified time period. One weakness of the proba-
bilistic approach is that it results in the same probability of occurrence
of a large earthquake for any time period. In the real world, the longer
the time period since the last earthquake, the more likely it is that
another earthquake will occur (Bernreuter and Chung, 1984). In California,
the deterministic approach is considered to be the conservative or worst
case approach and is required for determining peak ground acceleration at
hazardous waste facilities and for large public work projects, e.g., dams
(Reynolds, California Department of Health Services, Sacramento, California,
personal communication, 1984).
In order to adequately estimate peak ground acceleration associated
with the maximum credible or maximum probable earthquake at a site, it is
very important to conduct comprehensive assessments of the regional geology
and adequate site-specific subsurface investigations. Site-specific sub-
surface geology determines the magnitude and direction of propagation of
seismic energy to such an extent that it is impossible to generalize attenua-
tion of seismic energy with distance for seismic events. In addition,
determining a site's geology is necessary for identifying features that are
vulnerable to seismic ground motion such as unstable soil or rock slopes
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prone to landslides and unconsolidated, saturated deposits prone to liquefac-
tion-induced settlement and failure. Liquefaction is primarily controlled
by the character of ground motion, soil type, soil moisture content, and in
situ soil stress conditions. Slopes most vulnerable to earthquake shocks
are:
Very steep slopes of weak, fractured, and brittle rocks or
unsaturated loess that are vulnerable to transient shocks
due to the opening of tension cracks
Loose, saturated sand that may be liquefied by shocks with
sudden collapse of structure and flow slides
Sensitive cohesive soils with natural moisture exceeding the
liquid limit
Dry, cohesionless material on a slope at the angle of repose
that will respond to seismic shock by shallow sloughing and
slight flattening of the slope (U.S. Department of the Navy,
1983).
Estimates of ground motion are derived from peak bedrock acceleration
at a site. The methodology used to determine peak bedrock acceleration
should take into account regional and local seismicity, surface and subsur-
face geology, seismotectonic features, faulting mechanisms (e.g., thrust
and strike-slip) and regional attenuation. This peak bedrock acceleration
is then modified for site-specific surface and subsurface conditions that
focus or attenuate seismic energy or that are sensitive to ground motion.
These conditions include type, thickness, and density of materials overlying
the bedrock, surface topography, and depth to groundwater (for liquefaction
assessment). The goal of this approach is to define peak ground accelera-
tion and ground motion response spectra at a site (Reynolds, California
Department of Health Services, Sacramento, California, personal communication,
1984). Peak ground acceleration is then'used for the seismic design of the
facility. Methods for estimating earthquake ground motions may be found in
Hays (1980).
Dynamic side-slope stability may be calculated through standard methods
such as those described by Makdisi and Seed (1978), Sherard (1967), and
Seed (1975). Computer programs are also available for designing earthworks
to withstand seismic events (EERC, 1984). The risk of densification and
settlement in response to ground shaking can be reduced by compacting soils
to densities high enough to prevent further settlement. The potential for
liquefaction can be reduced by removing and replacing sensitive (granular)
soils or by lowering the water table (Eagling, 1983).
In general, seismic design of earthworks involves building structures
with more strength, density, mass, and thickness. Deeper foundations,
greater cross-sectional area, and better materials are specified for seismic-
resistant designs. Size and configuration are also important; generally,
smaller facilities are more resistant to damage from ground shaking. A
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safety factor (Section 5.1.2.3.4) also must be incorporated into the design
(Reynolds, California Department of Health Services, Sacramento, California,
personal communication, 1984).
5.1.3.4.7 Intergradient Facility Design—The construction of sites
below the water table (intergradient facilities) presents problems due to
seepage and hydraulic forces on the compacted clay liner. Excavations
below the water table can experience hydraulically induced side-slope
slippage and heave or rupture of the foundation base. In addition, a
buildup of water pressure behind a recompacted clay liner can threaten the
structural integrity of the liner. Although not allowed in some States
(e.g., New York), intergradient facilities are constructed in other States
(e.g., Louisiana) where sites with low-permeability soils above the water
table are rare.
When the excavation extends below the groundwater table, it is necessary
to consider the long-term or steady-seepage case for slope stability analysis.
For this case, pore pressures are assumed to be in equilibrium and are
determined from considerations of steady seepage (generally from the construc-
tion of a flow net or finite element analysis); the excess pore pressures
generated due to the total stress changes in the slope during the excavation
are assumed to have dissipated. This case is analogous to the drained-shear
test, and effective stress parameters should be used. A number of analytical
techniques are available that are appropriate for intergradient design.
Summaries of the available total stress and effective stress methods that
describe the particular assumptions on which the methods are based are
presented in a number of foundation engineering texts and technical publica-
tions (e.g., Winterkorn and Fang, 1975; Schuster and Krizek, 1978).
If the clay soil in which the containment facility is excavated is
located above an underlying permeable stratum (aquifer), there is potential
for heave or rupture of the floor of the excavation. To prevent this from
occurring, the downward pressure at the interface of the clay soil layer
and the aquifer must exceed the upward hydrostatic pressure. Where the
width of the excavation floor is narrow compared to the thickness of the
clay soil layer over the aquifer, the shear strength of the soil can add
substantially to the calculated stability of the soil layer. However, for
large floor dimensions with respect to clay layer thickness or for long-
term considerations, the overburden weight should exceed the upward hydro-
static force.
A related but distinctly different problem involves the stability of
the compacted soil liner. Assuming it is properly designed and installed,
the liner may be expected to have a nearly uniform low permeability. Water
pressure can build up behind the clay liner sidewalls or under the clay
liner on the excavation floor, cause it to separate from the parent soil,
and cause it to heave or rupture. Whether a liner heaves or ruptures
depends on the plasticity of the soil, with more plastic soils tending to
heave and stiffer soils tending to rupture. The analysis of this problem
involves, again, a comparison between the "uplift" water pressure and total
overburden stress due to the weight of the liner (soil density and liner
thickness) and any waste material in place.
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Control of these problems may be achieved by at least three methods:
(1) decrease the depth of excavation into the clay layer, (2) decrease the
hydrostatic pressure acting on the bottom of the clay layer, or (3) increase
the overburden pressure. Assuming the design depth is an economically
based decision, the best permanent solution is the added weight of the
waste material. However, in the short term the use of some type of dewater-
ing system or soil grouting may be necessary if the desired depth is too
deep and results in excessive uplift pressures. If the imbalance of forces
is small and it is estimated that the time period between excavation of the
overburden and replacement by the waste material is short, a method for
evaluating the rate of heave proposed by Boutwell and Donald (1982) can be
applied. They note that the uplift of the bottom of the excavation must be
small with respect to the effective diameter of the excavation and that the
worst case occurs when the underlying permeable stratum is very thick. The
authors indicate that in some cases the analysis may show additional dewater-
ing measures to be unnecessary.
Dewatering methods that can be used to reduce hydraulic head on the
liner include dewatering wells, slurry wall cutoffs, and sump pumping.
Further information on the design and applications of these dewatering
processes may be found in Cashman and Haws (1970).
5.1.4 Construction Specifications and CQA Plan
These documents establish the lines of communication among the contractor,
design engineer, owner-operator, and regulatory personnel and are critical
to the proper construction of a clay liner. Both specifications and the
CQA plan must be proposed prior to the construction. These documents
usually must be approved by the permitting agency prior to construction and
must be complete and detailed enough to assure them that the liner will be
properly constructed.
5.1.4.1 Construction Specifications—
The two types of construction specifications are:
Performance, which specifies a required level of performance
for the completed facility components (e.g., the liner will
have a permeability of 1 x 10 8 cm/s).
Method, which specifies methodology and equipment to be used
in constructing the liner.
In general, engineers designing clay liners for hazardous waste facilities
prefer a combination of method and performance specifications. The perform-
ance must be specified to ensure that the liner performs as required. Most
designers consider some method specifications necessary, especially if the
contractor is not experienced in constructing clay liners for hazardous
waste facilities and may not be aware of the importance of operational
methodology in constructing clay liners so that they will not fail. In
addition, moisture content, density, and compactive effort must be controlled
in the field if the specified permeability is to be achieved; specification
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of these parameters helps ensure that it is achieved. Combination method
and performance specifications must be very carefully drawn to solve the
problem of the specified method that does not yield the specified performance.
Equipment (e.g., sheepsfoot rollers for compaction) and lift thickness
are usually specified, and maximum clod size and scarification between lifts
is sometimes specified. Prior to liner construction most design engineers
specify the construction of a test fill with the same materials, equipment,
and methodology that is to be used for the liner construction. Test fills
can give the constructor valuable experience with the equipment, method-
ology, and soil to be used during construction and can help convince the
constructor of the necessity of using certain equipment or methodology.
Test fills are also necessary to ensure that the permeability measured in
the laboratory can be achieved in the field with the equipment to be used
in constructing the liner. Test fills are further discussed in
Section 5.3.4.1.
Design tolerances are usually present in the specifications and/or the
QA plan. Although statistical methods are available for determining design
tolerances, most engineers use a 'rule of thumb1 method based on their
experience. A safety factor approach (e.g., specifying an order of magnitude
lower permeability than required) is one approach. Another is to allow a
certain percentage of test failures based on experience during quality
control (QC) activities. Specifications usually include design drawings
and text and for clay liners often include the following:
Facility configuration and size
Foundation preparation
Liner material characteristics (e.g., index properties)
Liner thickness and permeability
Sidewall slope
Bottom slope and configuration
Lift orientation on sidewalls
Lift thickness
Maximum clod size
Percent Proctor density
Percent wet of optimum moisture content
Scarification between lifts
Compaction equipment and number of passes
Test-fill compaction.
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5.1.4.2 CQA Plan—
The design effort does not end with the start of construction but
continues until the facility is completed. The CQA plan is prepared prior
to construction and establishes the lines of communication and the testing
program necessary to inform the designers, owner-operator, and regulatory
agencies about whether the construction process is producing a liner that
performs as required by regulation. The design engineer uses the CQA and
CQC results to identify unexpected problems encountered during liner con-
struction that can necessitate changes in the original design. The CQA
program also informs the designers and/or owner-operator whether the con-
struction specifications are being followed by the contractor. Further
discussion of CQA and of the CQA plan may be found in Section 5.3 of this
document.
5.1.5 Design Case Studies
This section presents, as examples of current practices, important
design features of some of the clay-lined hazardous waste facilities identi-
fied during the course of this study. These examples are presented to
illustrate the variability in clay liner design and construction practices.
Further information on these facilities, including diagrams of the facilities,
may be found in Chapter 7 of this report.
5.1.5.1 Site D—
This site, a secure landfill in the Southeastern United States, has a
clay liner constructed of compacted clay from a nearby borrow area (about 3
miles away) with a maximum compacted permeability of I x 10 7.* The liner
is 10 feet thick and lies on a low-permeability deposit of opaline clay-
stone or Fuller's earth. The facility is constructed below the water
table, and a French drain system was installed around the site prior to
excavation to drain the overlying red sand material. Side slopes are 3 to
1. A 17-foot-wide bench with a 3-foot-wide drainage trench was constructed
at the top of the opal claystone. This bench enabled a thicker liner to be
installed above the claystone unit. Below the bench, a minimum of 10 feet
of the claystone was left as a foundation, except for the leachate collec-
tion sump, which is underlain by 4.5 feet of claystone. A test fill was
specified for this facility prior to construction to check equipment per-
formance. The clay liner was compacted in 6- to 8-inch lifts, with a
sheepsfoot roller or a smooth drum vibratory roller. The clay liner is
overlain by a flexible membrane liner (FML). Each landfill cell is com-
pleted prior to its operation.
5.1.5.2 Site F—
This site is a series of five clay-lined landfill cells each lined
with 10 feet of recompacted clay, an FML, and a 1- to 2-foot overlying
compacted clay layer to protect the FML. The clay liner was constructed of
material obtained from a borrow area about 15 miles from the site. This
facility was constructed above the ground with dikes to contain the wastes.
The high water table at the site, regulatory considerations, and ready
*A11 permeabilities in this section are laboratory measurements unless
otherwise specified.
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availability of suitable dike material (industrial slag) at the site con-
tributed to the selection of an aboveground design. Foundation preparation
included removal of industrial slag and organic silt material previously
disposed on the site.
A test fill was specified prior to construction. The liner was
constructed in 6-inch lifts with a sheepsfoot roller. The sidewall slope
is 2 to 1, and the sidewalls were compacted in horizontal lifts. The
bottom slope of the liner ranged from 1 to 2 percent. The entire liner was
installed prior to waste placement.
5.1.5.3 Site H--
This facility is a rectangular 9-acre cell used as a sanitary land-
fill. It is lined with a 4-foot clay liner. Prior to clay liner installa-
tion, the fill area was rough-graded. Clay was brought to the facility
from a nearby borrow area. The variable nature of the borrow area required
a soil's technician to be present during all removal operations to ensure
that the material met the project specifications. A technician present at
the landfill rechecked the material by performing the required soil tests
as the clay was emplaced. The liner was compacted in 12-inch lifts with
either a rubber-tired or sheepsfoot roller.
This clay liner is underlain by two 12-foot x 100-foot lysimeters for
leak detection.
5.1.5.4 Site I—
This facility consists of three clay-lined surface impoundments that
cover approximately 8 acres in a semiarid region of the United States. The
impoundments,are lined with two 5-foot compacted clay liners separated by a
15-inch granular leak detection layer. The impoundments are partly above
ground and partly below ground and are contained by dikes. The dikes are
12 feet wide on top.
The interior dike sidewall slopes are 3 to 1. The soil excavated for
the facility was used as the liner material. The liners were compacted in
8-inch lifts with a sheepsfoot roller. A 2-foot layer of sandy soil was
placed on top of the liner for protection. Troughs for loading wastes into
the impoundment were lined with rip-rap. This facility experienced failure
from desiccation cracking of the liner because it was left exposed for 7
months prior to waste emplacement.
5.1.5.5 Site J--
This facility consists of six ponds and a landfill. The ponds range
in size from h to 4 acres. The bottom liners at this facility consist of
two recompacted clay layers separated by a leak detection system. The
lower clay liner is 1 foot thick and the upper clay liner is a minimum of 5
feet thick. The sidewalls are constructed partially underground and par-
tially above ground. The aboveground sections are built upon dikes. The
leak-detection system is a 6-inch drainage blanket that slopes to a trench
containing a 2-inch slotted polyvinyl chloride (PVC) collection pipe (Fig-
ure 7-15). The dikes around the ponds are topped with a gravel-filled
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trench. This trench is filled with water to help prevent desiccation of
the dikes during dry months.
5.1.5.6 Site K—
This site in the Western United States consists of six double-lined
ponds ranging from 1.2 to 2 acres. The pond liners were constructed of the
local excavated claystone material. The liner system consists of a 1-foot
recompacted basal liner. Sump and collection trenches are excavated into
this bottom liner. A 1-foot sand layer covers the lower clay liner. The
sand layer is overlain with 3 feet of compacted clay. The liner was com-
pacted with a segmented smooth-wheeled roller. The facility is constructed
partially in ground and partially above ground with dikes to contain the
wastes.
5.1.5.7 Site L--
The landfill consists of a flat double clay liner on top of which a
dike was placed to contain the wastes. The liner extends beyond the dike
to form the liner for a 12-foot-wide drainage ditch that encircles the
site.
The liner system at this facility consists of six layers listed below
from the top down:
An 8- to 12-inch drainage layer (sand or gravel)
An 18- to 25-inch compacted clay layer
A 12-inch sand leak-detection layer
•
A 12-inch compacted clay layer
A 6- to 18-inch compacted soil layer
A bidim type C34 (synthetic soil stabilization geotextile)
layer.
5.1.5.8 Site M—
This 12-acre site is designed to consist of three cells of approximately
equal size. The facility is lined with 1 foot of recompacted clay. A
leachate collection system is above the clay liner, and a leak detection
system lies 2 feet below the clay liner. The first cell was excavated to a
maximum depth of 6 feet. This provides a minimum of 5 feet of separation
between the lowest layer of waste and the highest seasonal groundwater
elevation. The sidewalls were excavated to a maximum slope of 3 to 1. The
bottom slopes 1 percent to the center of the landfill.
The clay for the liner was obtained from a nearby borrow area. Prior
to the placement of the clay liner, all large rocks, roots, and other
foreign matter were removed from the foundation. The foundation was then
graded to a 1-percent slope and scarified to permit better bonding between
the foundation and the first clay lift. Uncompacted liner material was
5-43
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placed in 12-inch lifts and moistened as necessary. The clay was then
compacted with "approved" equipment. Documentation of the specific types
of equipment used was not available.
5.1.5.9 Site P—
The facility consists of one double-lined hazardous waste cell. The
bottom liner is composed of leachate collection and detection systems as
well as a series of natural soil and bentonite/soil liners. The side liner
and dike containment system includes a soil and a bentonite/soil liner.
The bottom liner extends over the entire bottom and 6 feet up the
sides. It is a layered system containing two drainage or collection layers
and two soil liners. Proceeding from the top layer downward, the bottom
liner components are as follows:
Leachate collection system—1 foot of No. 78 gravel and sand
with 4-inch perforated PVC pipes
Upper soil barriei—5 feet of compacted soil further subdivided
into three layers:
3 feet of compacted native soil. Permeability = 1 x
10~4 cm/s.
1 foot of enchanced soil, i.e., native soil blended
with 9- to 12-percent polymer-treated bentonite. Permea-
bility on the order of 5 x io"8 cm/s.
1 foot of compacted native soil. Permeability = 1 x
IO"4 cm/s.
Leak detection layer—A 1-foot sand/gravel layer with perfor-
ated pipe to detect leaks and/or to control seepage through
the upper barrier. The pipes are connected to several
independent monitoring stations to determine the approximate
location of any leaking that might occur.
Lower soil barrier—A 6-inch layer of enhanced soil, i.e.,
native soil blended with 9 to 12 percent polymer-treated
bentonite. Permeability on the order of 5 x 10 8 cm/s.
Buffer zone—5 feet of either in situ or recompacted native
soil. Permeability = 1 x 10 4 cm/s.
The side liner system extends from a point 6 feet above the cell
bottom to the top of the cell. This section will not have liquid impounded
against it; therefore, the liner system is not as extensive as the bottom
liner. Proceeding from the top layer downward, the side liner components
are as follows:
5-44
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1 foot of No. 78 gravel
18 inches of compacted native soil; permeability = 1 x 10 4
cm/s
6 inches of enhanced soil, i.e., native soil blended with 9-
to 12-percent polymer-treated bentom'te; permeability on the
order of 5 x lo"8 cm/s.
5.1.5.10 Site Q--
The landfill consists of a single containment cell covering an area of
approximately 3 acres. It is located in a former sand and gravel pit. The
cell has a double liner consisting of two 4-inch layers of a bentonite/soil
mixture on the bottom and side slopes up to a vertical elevation of 20 feet
above the cell bottom. The bentonite/soil layers are separated by a 12-inch
layer of sand on the bottom of the cell and a 6-inch layer of sand on the
side slopes. The side slopes above the 20-foot vertical level are covered
with a single 6-inch layer of the bentonite/soil mixture. All bottom and
side slope bentonite/soil surfaces are covered with a 12-inch protective
layer of gravel. The slope of the cell sidewalls varies from 2.5 to 1 to 3
to 1.
The central-piant (pugmill) mixing method was used to blend the bento-
m'te. It was spread with a dump truck, grader, screened boards, and hand
labor. A backhoe-mounted hydraulic tamper was used to compact the liner.
5.2 CLAY LINER CONSTRUCTION: METHODOLOGY AND EQUIPMENT
This section describes the methodology and the equipment that are
presently used for constructing clay liners. For clarity and convenience,
the discussion is broken down into preinstallation, installation, and
postinstallation construction phases.
5.2.1 Preinstallation Activities
Before the liner is installed, the foundation is prepared, groundwater
control measures are initiated for sites below the water table, leak detec-
tion systems may be installed, and the groundwater monitoring program is
implemented.
5.2.1.1 Foundation Preparation—
The foundation of a clay-lined hazardous waste containment facility is
the native soil substrate either unaltered or recompacted. For aboveground
facilities, dikes constitute part of the foundation. Operations during the
construction of foundations should include the following to accomplish
these goals (U.S. Department of the Army, 1977):
Stripping and excavating to remove all soft, organic, perme-
able, and otherwise undesirable materials. Proof-rolling
with heavy equipment such as rubber-tired rollers or dozers
should be done to detect soft areas likely to cause settle-
ment.
5-45
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Filling of rock joints, clay fractures, depressions, and any
areas where undesirable material has been removed. Fill
material should be engineered backfill compacted to the
required specifications or grouting material.
These items are important to ensure secondary containment and to ensure
that the liner retains its integrity during and after construction.
Foundation construction will essentially determine the configuration
of the clay liner. Whether the foundation is excavated or built above
ground, the sidewall slope and bottom slope must be properly controlled and
shaped. Excavation and shaping are accomplished with standard earth-moving
equipment such as dozers, scraper-pans, and road graders. Slope control is
achieved through traditional instrument surveying or through electronic
(laser surveying) devices. Trenches are cut for the collection sump and
for leachate-collection pipes if they are to be recessed into the liner.
Removal of soft spots and permeable areas in the foundation is accom-
plished with standard excavating equipment. Once these are removed, the
resulting holes and irregularities are backfilled and compacted in a manner
similar to clay liner construction. At some facilities, the entire founda-
tion surface is disked or tilled to a depth of 1 to 2 feet and recompacted
in one or two lifts. At other facilites, the foundation is left unaltered.
At the end of foundation construction, the entire landfill base can be
seal-rolled (rolled smooth) to seal the soil and to ensure that precipi-
tation that may fall on the site prior to liner placement will run off
properly and will not puddle or pond on the foundation surface. Final
proof rolling also can be used to ensure the integrity of the finished
foundation.
If the facility is constructed entirely or partially aboveground,
dikes are constructed around the periphery of the excavation to serve as
retaining walls for the liner (see Chapter 7 for examples of diked facili-
ties). Dikes are generally earth or rockfill embankments and are con-
structed with the same techniques and equipment used to construct earth or
rockfill dams. Foundations for dikes are prepared to control underseepage,
to provide satisfactory contact with the overlying compacted fill, and to
minimize differential settlement (U.S. Department of the Army, 1977). Dike
foundation preparation operations are generally the same as described for
the clay liner foundation. Dikes may be constructed in horizontal compacted
lifts in a manner similar to clay liners. For further information on dike
construction, the reader is referred to Sherard et al. (1963), U.S. Depart-
ment of the Interior, 1974; Winterkorn and Fang, 1975; U.S. Department of
the Army, 1977; and U.S. Department of the Navy, 1982.
5.2.1.2 Groundwater Control —
When a foundation excavation extends below the water table, unbalanced
hydrostatic pressures from groundwater can develop in the foundation bottom
and sidewalls. These pressures can cause seepage, sidewall failure and
collapse, and bottom heave or rupture during subsequent facility construc-
tion and operation. Groundwater control measures can reduce this hydraulic
pressure and thus reduce the likelihood that these failures will occur.
The most common methods of reducing hydrostatic head around a facility are:
5-46
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Construction of a slurry cutoff wall
Trenching and pumping
Installation of dewatering wells for lowering the water
table by pumping.
Slurry cutoff walls can be constructed by excavating a trench with a
back hoe (or similar equipment) and backfilling with bentonite, asphalt,
cement grout, or other suitable material. Alternately, slurry walls can be
installed with the vibrating-beam technique, in which bentonite is injected
along vibrating beams driven into the ground. Trench and pump methods
involve digging trenches and installing sump pumps to remove infiltration.
Dewatering wells are constructed by standard well-drilling techniques
(Johnson Division, 1975) and are pumped to lower the water table, thereby
reducing hydrostatic pressure on the facility sides and bottom.
A complete discussion of these techniques is beyond the scope of this
document. For more information, the reader is referred to D'Appolonia,
1980; U.S. Environmental Protection Agency, 1984; Schmednecht and Harmston,
1980; U.S. Environmental Protection Agency, 1982a; and Cashman and Haws,
1970.
Groundwater control to preserve liner integrity is necessary only
during construction and operation of the facility. Once the facility is
filled, the weight of the waste will balance the inward hydrostatic forces
on the liner, eliminating the need for groundwater control measures.
5.2.1.3 Leak Detection System Installation—
If a leak detection system is part of the facility design, it is
necessary to install this prior to liner emplacement. This involves laying
granular drainage layers and pipes over part or all of the foundation.
Following its installation, the system can be covered with a properly
graded soil blanket or a geotextile to prevent damage during subsequent
construction activities, to provide a stable base for placement of the
basal-liner lifts, and to prevent piping of clay liner material into the
porous drainage layer. For further information on leak detection system
design and installation, the reader is referred to the TRD on leachate
collection and leak detection.
5.2.2 Clay Liner Installation
-Clay liners are constructed by compacting clay soil. Clay liner
materials covered in this document include natural, untreated soil and soil
mixed with bentonite additives to achieve a lower permeability. Installa-
tion procedures differ for these materials, and they will be addressed
separately in this document.
5.2.2.1 Natural Soil Liners--
Natural soil liner material may be excavated from the site during
foundation preparation or may be transported to the site from a nearby
5-47
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borrow source if soil material at the facility is insufficient or if the
in situ soil is not a suitable liner material. QC measures are necessary
at the borrow site and/or at the facility to ensure that the liner material
meets design specifications (see Section 5.3.4). Excavation at the borrow
site is usually accomplished with backhoes, front-end loaders, or other
standard excavating equipment. One engineer recommended a side-cut excavator
for use at the borrow site. This equipment is apparently very productive
and produces material with a uniform, small clod size.
Prior to emplacement, a borrow pile or storage pile of the liner
material usually is established at the site. Depending on climatic con-
ditions and the condition of the clay, the borrow pile may have to be
protected from moisture loss and erosion. If the clay is wet when orig-
inally placed in the pile, protection from moisture loss will reduce the
amount of water that must be added to the clay prior to compaction. This
is especially important in arid climates. In areas of heavy rainfall,
erosion prevention may be necessary to prevent loss of liner material.
Plastic or soil covers may be installed to control borrow pile moisture
content and erosion. Alternatively, the pile may be graded and seal-rolled
with motor graders, bulldozers, and smooth-wheeled rollers.
5.2.2.1.1 Liner Material Emplacement—Thickness requirements for clay
liners for hazardous waste facilities (usually 2 to 12 feet) necessitate
installing the clay in a series of lifts (layers) to ensure uniform compac-
tion throughout the liner. For each liner lift, material from the borrow
pile is emplaced into the facility with scraper-pans or trucks and uni-
formly distributed over the site with dozers or graders (Figure 5-6). Lift
thickness is controlled during emplacement by using measuring staffs,
shovel blades, or instrument surveys. Figure 5-7 shows liner material
being emplaced in the area of a collection pipe. The foundation was excavated
for the pipe, and, as a result, the lowest liner lift was thicker in this
area. (This is also illustrated in Figures 5-4 and 7-11.)
Liner emplacement methods vary with the size of the facility and the
method of facility operation. For small facilities, individual liner lifts
are often installed over the entire excavation, and the liner is constructed
as a single unit. For larger facilities and for continuous operation
facilities, where the wastes are emplaced in the facility as parts of the
liner are built, the liner is installed in segments. After each liner
segment is installed, it is beveled or step-cut with grading equipment so
that the next segment may be tied into the previously installed segment,
eliminating a potential pathway for seepage through the liner along the
boundary (see Section 5.1.3.3, Figure 5-5).
5.2.2.1.2 Clod Size Reduction—Following placement, the liner material
for each lift is broken up for homogenization and clod size reduction
(clods are unbroken aggregates of liner material). The clod size of the
liner material affects moisture control and compaction operations. Reduc-
tion in clod size increases the surface-volume ratio and decreases the time
it takes for moisture to become evenly distributed within the clod (curing
time), thereby facilitating moisture control operations. In addition, clod
5-48
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Note: Photo courtesy of Wisconsin Oept. of Natural Resources
Rgure 5-6. Liner material emplacement.
5-49
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Note: Photo courtesy of Wisconsin Dept. of Natural Resources
Figure 5-7. Emplacement of liner material over foundation excavation
underneath a collection pipe.
5-50
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size reduction allows more effective and homogeneous distribution of compac-
tive energy through the lift than would be achieved in lifts with clods of
greater size (Withiam, D'Appolonia Consulting Engineers, personal communica-
tion, 1984; Pacey, EMCON Associates, San Jose, California, personal com-
munication, 1984). Homogeneous compaction helps ensure homogeneous permea-
bility.
Opinions differ among design engineers on optimum clod size for clay
liner construction. Clod size recommendations gathered through interviews
include 1 inch, 2 to 3 inches, no larger than one-half the lift thickness,
and no larger than the lift thickness (see Table 5-8, Section 5.3.3.4).
Clod size reduction is especially important in restricted areas where hand
compactors must be used (e.g., around penetrating objects and in the corners
of some facilities). Specifications obtained from the U.S. Department of
the Navy (1982) and from the nuclear industry require that clod size be
reduced to 1 to 3 inches in areas that are to be compacted by hand. Con-
struction specifications sometimes specify maximum clod size, but not in
most cases. In actual practice, clod size may not be carefully controlled.
Clods with horizontal dimensions exceeding the lift thickness have been
observed by the authors at some facilities under construction.
There is no documented information on the effect of clod size on the
achievement of specified liner permeability in the field. However, in a
laboratory study of compacted clay, Daniel (1981) demonstrated that clod
size can significantly affect permeability. Table 5-6 presents the results
of this experiment. Daniel (1984) has also described a field case study
where large clods and inadequate curing have resulted in nonuniform moisture
distribution in compacted clay liners.
The importance of clod size control depends, to some extent, on how
much moisture must be removed or added to meet the specified compaction
moisture content. If moisture must be added, large clods may necessitate
long curing times and repeated moisture applications to ensure uniform
moisture content across the clods, resulting in delays in construction
schedules. Thus, efficient clod size reduction can save construction time
and money.
Clod size reduction is usually accomplished using disk harrows or
rotary tillers with various shaped tilling blades. Availability usually
determines equipment selection. High-speed pulvi-mixers (e.g., BOMAG MPH
100), designed for breaking up soil and old asphalt pavement, have proven
to be superior to tillers or disks for blending bentonite with soil (Kozicki
and Heenan, 1983) and may be very good for breaking up soil clumps for
untreated soil liners (Figure 5-8). The manufacturer claims that these
machines are capable of reducing clod size of cohesive soils to 2 inches in
a single pass and 80 percent of the clods to less than 1.5 inches after two
passes.
5.2.2.1.3 Moisture Control—Moisture control includes the addition or
removal of water from the liner soil to achieve the specified compaction
moisture content (molding water content). Correct and uniform moisture
5-51
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TABLE 5-6. EFFECT OF CLOD SIZE ON PERMEABILITY OF
LABORATORY COMPACTED CLAY
Maximum size Permeability
of clods (in.) (cm/s)
3/8 2.5 x io"7
3/16 1.7 x IO"8
1/16 8.5 x 10°9
Source: Daniel, 1981.
5-52
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Note: Photo courtesy of Bomag, Inc.
Figure 5-8. Use of puivi-mixer for clod size reduction.
5-53
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content is essential for compacting to the specified permeability. Minimum
permeability can be obtained only if the molding water content is within
several percentage points on the "wet side of optimum." (This is fully
explained in Chapter 3.) For this reason, it is important to control the
moisture content of the liner material carefully prior to and during liner
construction to ensure that the moisture is uniformly applied and distributed
throughout the soil of each lift. Nonuniform moisture distribution in clay
liners has been attributed to inadequate breakup of large clods prior to
compaction; uneven water distribution by sprinkling devices, especially on
slopes; and inadequate curing time allowed for the water to penetrate the
soil (Ghassemi et al., 1983).
Moisture is added to liner material prior to placement. Often it is
most convenient to do this at the borrow area, although it may be necessary
to add moisture during liner material emplacement if the soil has dried
during handling and transport (Figure 5-9). Moisture addition is accomplished
with sprinkler trucks, sprinkling systems, or other sprinkling devices
during spreading and mixing operations. Added moisture must be thoroughly
mixed into the soil with mixing devices such as disk harrows, rotary culti-
vators, or pulvi-mixers, to ensure that moisture is uniformly distributed
throughout the soil mass.
Adequate equilibration time after moisture addition is critical to
ensure that moisture is uniformly distributed throughout the soil. Clod
size reduction reduces penetration time and helps achieve uniform moisture
content across all clods within reasonable time. Equilibration times may
reach days or weeks if soil material is very dry or if soils with a high
montmorillom'te content are used in the liner. Moisture addition in the
borrow area may be necessary in these cases to avoid construction delays
that would result if the material were moistened in place prior to compaction
and then allowed to equilibrate. In dry areas or during dry periods of the
year, it may be necessary to cover the soil during equilibration to prevent
additional moisture loss from evaporation.
If the liner material becomes too wet to work during construction,
moisture reduction may be accomplished through a combination of mechanical
agitation, aeration, and solar drying.
Moisture content may be maintained during inactive periods by sloping
and seal-rolling the liner to ensure proper runoff or by covering the liner
with plastic or a layer of moist soil to prevent drying or overwetting of
the liner material. Prevention of drying is important because desiccation
can cause cracking of the liner, which can greatly increase its permeability.
Moisture content measurement is a QC activity; techniques for measuring
soil moisture content are discussed in Chapter 3, and techniques for estimat-
ing soil moisture during construction are discussed in Section 5.4.3.2.3.
5.2.2.1.4 Compaction—The important theoretical aspects of compaction
of fine-grained soils to achieve low permeability are discussed in Chap-
ters 2 and 3. Compaction quality control and quality assurance are discussed
5-54
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Figure 5-9. Moisture addition to liner material prior to compaction.
5-55
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in Section 5.3.4. The discussion below is limited to the practical aspects
of compaction in the field.
Compaction of a clay liner is accomplished through standard compaction
practices as used in other earthwork construction. The following variables
exist for compaction operations:
Lift thickness and number
Equipment type and size
Number of equipment passes
Soil quality
Soil moisture content.
Because of their interrelated nature, it is necessary to control all of
these variables to achieve adequate compaction in the field. Compaction of
clay soils to obtain low permeability differs from compaction of earth to
obtain structural stability in that compaction is performed at a higher
moisture content (usually 2 to 3 percent wet of optimum). Thus, moisture
content is one of the most critical factors to control when clay liners are
compacted.
A critical aspect of the compaction of clay liners is to tie (join)
together adjacent lifts properly. Improperly tied lifts can result in
greatly increased horizontal permeability along the lift interface, an
especially serious problem when sidewall lifts are compacted in a horizontal
manner (see Section 5.1.3.2.4). Figure 5-10 illustrates joints and seepage
along lift boundaries in sections of two experimental liners. These liners
were compacted with a small self-propelled sheepsfoot roller (first figure)
and a vibratory plate hand compactor (second figure). Two measures recom-
mended by the interviewed design engineers for tying together liner lifts
are (1) scarification of the surface of the last installed lift, through a
disk harrow or other device, before the next lift is installed and (2) control
of the moisture content of the adjacent lifts so that they are equivalent
and as specified. Haxo (1983) recommended the use of compaction equipment
with feet that are at least 50 percent longer than the height of the com-
pacted lift. However, most sheepsfoot rollers have feet that are 7 to 10
inches long (HiIf, 1975), which could hamper implementing Haxo's recommenda-
tion.
Johnson and Sallberg (1960) reported on several studies of the devel-
opment of "compaction planes" or laminations between lifts. The results of
these studies indicate the following:
For all types of rollers, laminations or lift partings are
much more likely to occur in soils compacted wet of optimum
than in those compacted dry of optimum.
5-56
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Joints Between Linerlifts
Note: Photo courtesy of Richard Warner, University of Kentucky
Joints Between Lifts Coated with Seepage
Note: Photo courtesy of Kirk Brown and Assoc., Austin, TX
Figure 5-10. Joints and seepage along lift boundaries.
5-57
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Laminations in a compacted soil are produced primarily from
"springing" of the lift under compactive equipment.
Tamping feet tend to mesh the boundary between successive
layers.
Because clay liners must be compacted wet of optimum to achieve minimum
permeability, this information suggests that a great deal of attention must
be paid to ensure proper bonding of clay liner lifts.
Two methods of sidewall compaction are used for clay-lined hazardous
waste facilities. Depending on soil conditions, if sidewall slopes are
less than around 2.5 (H) to I (V), it may be feasible to compact the sidewalls
in lifts that are continuous with the bottom liner lifts. This ensures
continuity between the liner bottom and sidewalls and also orients the lift
boundaries and compacted clay fabric parallel to the liner surface. However,
if the sidewall slope is to be steeper than 2.5 to 1, the sidewalls may
have to be compacted in horizontal lifts because most compaction equipment
cannot operate on such steep slopes. When sidewalls are compacted in a
horizontal manner, they are overbuilt and trimmed back to the final slope
with a motor grader or excavator.
Compaction equipment is usually selected based on technical performance
and availability. Some of the technical factors to be considered are
whether side slopes or bottom slopes are to be compacted, lift thickness,
and liner material. In some cases technical considerations are not weighed
as heavily as they should be, and the choice is made based on what equipment
is available that can "do the job." The following is a list of the kinds
of equipment currently used for compacting clay liners: .
Sheepsfoot or clubfoot roller—self-propelled and towed
Padfoot (pegfoot or wedgefoot) roller—self-propelled and
towed
Vibratory sheepsfoot rolles—self-propelled and towed
Rubber-tired roller
Wobble-wheel, rubber-tired roller
Smooth-wheeled roller
Vibratory smooth-wheeled roller
Vibratory plate compactor (for compaction around penetrating
objects—hand operated)
Bulldozers
Tractors.
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Table 5-7 describes the types and typical uses of compaction equipment
(U.S. Department of the Navy, 1982). This table covers all types of earth-
work compaction operations and is not limited to clay liner construction;
only that equipment suitable for cohesive soils at wet-of-optimum moisture
levels should be used for clay liners. Geotechnical textbooks and most
experts interviewed recommend the use of sheepsfoot or tamping foot rollers
for compacting cohesive (clay) soils to achieve low permeability. The dif-
ferent types of roller feet are illustrated in Figure 5-11. All of these
tamping rollers are often referred to ge.nerically as sheepsfoot rollers.
The general consensus is that the kneading action of these devices affects
the soil fabric in a beneficial way (see Chapter 3 for a discussion of soil
fabric and permeability). However, this opinion is derived from laboratory
studies of impact versus kneading compaction, which show that lower perme-
abilities can be achieved with the latter. We know of no field studies
that demonstrate the superiority of tamping or sheepsfoot rollers over
other types of rollers in reducing the permeability of cohesive soils.
This is an important point because laboratory kneading compactors use a
tamping foot of about 0.5 inch in diameter, and the test procedure ensures
that its impacts cover the entire surface area of the test soil. In con-
trast, the feet on a sheepsfoot roller are several inches across and are
separated on the roller by a space of several inches (Figure 5-12). Thus,
they do not induce shear strains as intensely or as uniformly through the
soil mass as the laboratory technique does.
One engineer interviewed related a case in which the required compacted
density for a clay liner could not be achieved with a sheepsfoot roller but
was achieved with a vibratory smooth-wheeled roller. The differences
between permeabilities for the two types of rollers were not determined in
this case. An interview with another design engineer revealed that at
another site (South Central United States) adequate compaction in near-
saturated clays was being achieved with several passes of a bulldozer. One
major engineering firm interviewed requires by specification that for
cohesive soil compaction at nuclear power plants a variety of equipment
(including a towed sheepsfoot roller, a self-propelled static wedgefoot
roller, and a towed static wedgefoot roller) be evaluated with several
different lift thicknesses in a test fill prior to construction. This
facilitates selection of the most suitable equipment and lift thickness for
each soil type to be compacted (see section 5.3.3.1).
Hi If (1975) mentions that sheepsfoot or clubfoot rollers are prefer-
able to other roller types because their mixing action produces a more
homogeneous liner with respect to moisture content and physical charac-
teristics. Hi If (1975) also states that pad-type tamping foot rollers,
because of larger foot end areas, do not blend and mix embankment materials
as effectively as conventional sheepsfoot rollers. Figures 5-11 and 5-12
illustrate the difference between sheepsfoot and padfoot (or pegfoot)
rollers.
The size and configuration of a facility may place some limits on
equipment selection. Large compaction equipment (necessary for thick lift
compaction) may not be usable at small sites because of large turning
5-59
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TABLE 5-7. CO.a-MLflON EQUIPMENT AND METHODS
Equipment
Type
Applicability
Requirements for Compaction of 95 to 100 Percent Standard Proctor
Maximum Penalty
Compacted
Lift
Thlckneas,
in.
Paaaea or
Coverage*
Dimensions and Weight of Equipment
Poaalble Variations in
Equipment
Sheepafoot
Rollers
CT)
O
For fine-grained solla or
dirty coarse-grained aoili
with more than 20 percent
passing No. 200 sieve. Not
aultable for clean coarse-
grained soils. Particularly
appropriate for compaction of
impervious sane for earth dam
or linings where bonding of
lifts is important.
Soil Type
Foot Foot
Contact Contact
Area Pressures
sq. ft. psi
4 to 6 paases
for fine-
grained soil.
6 tp 8 passes
for coarse-
grained soil.
5 to 12 250 to 500
7 to 14 200 to 400
Pine-grained
soil PI>30
Pine-grained
soil PIOO
Cosrse-gralned 10 to 14 ISO to 2SO
soil
Efficient compaction of soils wet of
optimum requires less contact pres-
sure than the same tolls at lower
moisture contents.
For earth dam, highway and
airfield work, articulated
self propelled rollers are
commonly used. For smaller
projects, towed 40 to 60
inch drums are uaed. Foot
contact pressure should be
regulated so as to avoid
•hearing the soil on the
third or fourth pass.
'Rubber Tire
Roller
Do.
For clean, coarse-grained
soils with 4 to 8 percent
paaalng the No. 200 sieve.
For fine-grained a.oila or well
graded, dirty coarse-grained
noils with more than 8.
percent passing the No. 200
10
6 to 8
3 to 5
coverage*
4 to 6
coverages
Tire Inflation preaaures of 35 to 130
pal for clean granular material or
base course and subgrade compac-
tion. Wheel load 18,000 to 25,000
Ibs.
Tire inflation pressures in exceas of
65 psl, for ftne-gralned soils of
high plaatlclty. For uniform clean
sands or ailty fine sands, use
large size tires with pressure* of
40 to 50 psl.
Wide variety of rubber tire
compaction equipment la
available. For cohealve
soils, light-wheel loads,
such as provided by wobble-
wheel equipment, may be
substituted for heavy-wheel
load if lift thickness Is
decreased. For granular
soils, large-site tlrea are
desirable to avoid shear
and rutting.
Smooth Wheel
Rollers
Do....
Appropriate for aubgrade or
base course compaction of
well-graded sand-gravel
mixtures,
Hay be used for fine-grained
soils other than in earth
dams. Not aultable for
clean well-graded sands or
• tlty uniform sands.
a to 12
6 to 3
4 coverages
6 coverages
Tanden type rollers for bsse course
or aubgrade compaction 10 to IS ton
weight, 300 to SOO Iba per lineal
in. of width of rear.roller*
3-wheel roller for compaction of.
fine-grained soil; weights from 3
to 6 tons for materials of low .
plasticity to 10 tons for Materials
of high plasticity.
3-wheel rollers obtainable
in wide range of sizes.
2-wbeel tandem rollers are
avallab« in the range of 1
to 20 ton weight. 3-Axle
tandem rollers are gener-
ally used in the range of
10 to 20 tons weight. Very
heavy rollers are used for
proof rolling of aubgrade
or base course*
-------
TABLE 5-7 (continued)
1
1
Equipment
Type
Vibrating
Sheet s foot
Rollers
Vibrating
Smooth Drum
Roller*
Vibrating
Baseplate
Compactors
Crawler
Tractor
Power Tamper
or Rammer
Applicability
For coarse-grained Bolls
sand-gravel mixtures
For coarse-grained soils
aand-gravel Mixtures - rock
fills
For coarse-grained soils with
less than about 12 percent
passing Ho. 200 sieve* Best
suited for materials with 4 to
8 percent pausing No. 200 sieve,
placed thoroughly uct.
Beat suited for coarse-grained
soils with less than 4 to 8
percent panning No, 200 sieve,
placed thoroughly wet.
For difficult access, trench
backfill. Suitable for all
Inorganic soils.
Requirements for Compaction of 95 to 100 Percent Standard Proctor
Maximum Density
Compacted
Lift
Thickness.
In.
8 to 12
6 to 12
(soil)
to
36 (rock)
8 to 10
6 to 10
4 to 6 In.
for silt
or clay, 6
In. for
coarse-
grained
ublltti
Panes or
Coverages
3 to 5
3 to 5
4 to 6
3 coverages
3 to 4
coverages
2 coverages
Dimensions and Weight of Equipment
1 to 20 tone ballasted weight.
Dynamic force up to 20 tons.
- do -
Single pads or plates should weigh
no less than 200 Ibs. Hay be used in
tandem where working space Is avail-
able. For clean coarse-grained soil,
vibration frequency should be no less
than 1,600 cyclua par minute.
Vehicle with "Standard" tracks having
contact pressure not less than 10
pat.
30-lb minimum weight. Considerable
range Is tolerable, depending on
materials and conditions.
Possible Variations in
Equipment
Hay have either fixed or
variable cyclic frequency.
- do -
Vibrating pads or plates
are available, hand-
propelled, single or in
gangs, with width of cover-
age from 1-1/2 to IS ft.
Various typed of vlbrat Ing-
drum equipment should be
considered for compaction
In large areas.
Tractor weight up to 65 Ions.
Weights up to 250 Ibs.,
foot diameter 4 to 10 in.
i
en
Soured: U.S. Department of the Navy. 1982.
-------
Foot
Tapered or
Wedge Foot
Cross Section
of Tapered Foot
Clubfoot
Pegfoot
Sheepsfoot
Not drawn to scale.
After Johnson and Sallberg, 1960
Figure 5-11. Sketches of different types of roller feet.
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Padfoot Roller
'*•'* ^'j^y^^^tSSLJit
Vibratory Smooth-Wheeled Roller
Rgure 5-12. Various compacting rollers.
5-63
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en
i
cr>
Sheepsfoot Roller
Figure 5-12. Various compacting rollers (continued).
-------
radii. If sidewalls are steep, some equipment may not be able to negotiate
the slope. Sidewall slopes of 2.8 to 1 or less have been recommended for
sheepsfoot rollers (Boutwell and Donald, 1982). Figure 5-13 shows the
compaction of a 2-to-l slope with a sheepsfoot roller. In this case it was
necessary to both push and tow the roller to negotiate the slope. If
sidewalls are compacted in horizontal lifts, lift width may restrict the
size of the compaction equipment.
The number of passes necessary to achieve the specified compactive
effort depends upon the size, weight, and configuration of the equipment.
In general, small equipment requires more passes than large equipment.
Compactive effort can be estimated from the towing force required to tow
the equipment per unit distance multiplied by the number of equipment
passes. It is usually expressed on a per unit volume of fill basis (e.g.,
foot pounds per cubic foot) (Selig, 1982; Johnson and Sallberg, 1960) as
follows:
(W) (T) (L) = comPactive effort per unit volume of fill (ft lb/ft3),
where:
F = draw bar pull (Ib)
N = number of passes
L = length of each pass (ft)
W = roller width (ft)
T = lift thickness (ft).
For each soil/moisture content/equipment combination, a different
numbers of passes are required to achieve a specified permeability and
density. Thus, it is extremely important to determine the compactive
effort necessary to achieve the design permeability with each type of
compaction equipment to be used in a test fill prior to construction
(Section 5.3.3.1.1). Mitchell et al. (1965) demonstrated that, with some
clays, increasing compactive effort can decrease permeability hundredfold
without changing density or moisture content by additional shearing that
breaks down soil structure. Compaction should be controlled in the field
by measuring density, moisture, and compactive effort. The specified
values are based on the relationship, previously derived in the laboratory
and confirmed in the field test fill, among these variables and the permea-
bility for the specific soil and the specific compaction equipment to be
used.
Moisture content, density, and compactive effort measurements are
necessary for controlling compaction to ensure that the specified permeabil-
ity is achieved in the field. Visual observations of construction operations
are also critical to compaction quality control. A full discussion of
compaction quality control is found in Section 5.3.
5-65
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Note: Photo
5-66
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5.2.2.2 Admixed Bentonite Liners--
In areas where suitable soils for clay liners are not available or
cannot be economically delivered to the construction site, bentonite addi-
tives may be blended into the unsuitable native soils to enable them to be
compacted to the required permeability. Selection of the type and the
proper percentage of bentonite additive is described in Section 5.1.2. The
difference between installation of natural soil liners and bentonite admix-
tures mainly lies in the liner emplacement methods. When bentonite is
stored onsite, it is critical to keep it covered and protected from precipi-
tation as it cannot be worked in the wet state.
5.2.2.2.1 Bentonite Mixing and Spreading—When bentonite soil addi-
tives are used, they must be thoroughly and uniformly mixed with the native
soil. This is most easily done when the native soil is relatively dry.
Mixing can be accomplished in place with the additive applied evenly over
the site and then mixed into the native soil, or mixing can be done in a
central plant where the additives and soil are blended in a mixing device
and the final mixture is spread over the site.
Central plant mixing is the preferred method of several design engineers
interviewed and in a study by Lundgren (1981) has been shown to be more
effective than tilling in place. In this method, the bentonite and the
soil are mixed in a pugmill, cement mixer, or other device where moisture
is added during the mixing process. Moisture content, particle size, and
bentonite content must be monitored and controlled during this mixing
process. Central plant mixing is illustrated in Figure 5-14. Laboratory
tests of central plant mixing of bentonite and soil yielded the following
results (Lundgren, 1981):
More than 10 minutes mixing time is preferable.
The soil may be dry, naturally conditioned (drained), or
saturated when the bentonite is added.
Water should be introduced into the mixer after the bentonite
and after a couple of minutes of homogenizing.
All investigated bentonites (five types) were homogenized to
the same degree.
Following central plant mixing, spreading may be accomplished as with
natural soil liners (using trucks or pans and graders or dozers) or with a
continuous asphalt paving machine (Geo-Con, 1984).
Currently, central plant mixers are commercially available that are
specifically designed for bentom'te/soil admixtures. These mixers are
capable of producing 1,000 ydVday of admixed material. Computer controls
for these devices are capable of achieving an accuracy of ±0.5 percent
moisture in the admixture throughout the project (Geo-Con, 1984).
5-67
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en
cr>
oo
Note: Photo courtesy of Geo-Con, Inc., Pittsburgh, PA
Figure 5-14. Central plant mixing of bentonite and soil.
-------
In-place spreading and mixing is a commonly practiced construction
method for bentonite/soil liners. Locally available liner material is
first spread uniformly over the prepared foundation. The bentonite is then
spread uniformly over the native liner material. If the side slopes are
steep (2.5 to 1 or greater) or the liner is small, bags of bentonite can be
placed on the site in a predetermined pattern and then the bentonite is
manually raked over the liner material. Bag placement must be determined
carefully so that the specified quantity of bentonite per cubic foot of
liner is maintained uniformly throughout the fill. This is frequently
accomplished by placing the bags of bentonite in a grid pattern over the
facility site. Close visual scrutiny is necessary during manual mixing to
ensure that the spreading is adequate. Alternatively, for larger sites
with sidewall slopes of 2.5 to 1 or less, mechanical or pneumatic spreaders
can be used. A belt-feed cement spreader has been found to be particularly
suitable for bentonite. This spreader, pictured in Figure 5-15, requires
only two men and provides uniform spreading rates at up to 25 ton/hr (Kozicki
and Heenan, 1983). The spreader can be operated with feed from dump trucks
or, when modified with a cyclone, fed pneumatically in bulk from tank
trucks (Figure 5-16).
Following in-place spreading, the bentonite must be mixed into the
soil along with enough water to bring the mixture to the proper moisture
content. This step activates (swell) and disperses the bentonite. Mixing
can be accomplished with disk harrows, rototillers, tined rotovators, or a
high-speed pulvi-mixer (soil stabilizer). Disks (Figure 5-17) and tillers
should make several passes in a crisscross pattern to help break up clods
and ensure more complete mixing (Ghassemi et al., 1983). Water may be
added from sprinklers attached to the mixer or by sprinkling between passes.
Rototillers have been demonstrated to be more efficient at mixing than disk
harrows (Ghassemi et al., 1983), and larger wheeled rototillers are more
effective than the wheelless types (Lundgren, 1981). Six or eight passes
are generally required for adequate mixing.
At several Canadian installations, a high-speed pulvi-mixer (soil
stabilizer) achieved very good mixing to a depth of 200 mm in the first
pass and to a depth of 300 to 350 mm on subsequent passes (Figure 5-18).
Water can be added after the first dry-mix pass (Kozicki and Heenan, 1983)
or, as illustrated (Figure 5-18), it can be added during mixing. Two
passes are generally sufficient to mix the bentonite thoroughly and reduce
all clods to less than 1 inch. Although this equipment is considerably
more expensive than conventionally used mixing devices, the reduced number
of passes and ensurance of better mixing make it cost competitive (Kozicki,
1983, Ground Engineering Ltd., Regina, Saskatchewan, Canada, personal
communication).
In-place spreading and mixing are generally recommended only for
single-lift (4- to 6-inch) liners; for thicker liners, the central plant
method is preferred. One contractor with admixed liner installation experi-
ence has stated that because of the difficulty of conducting stringent
quality assurance/quality control for in-place spreading mixing, central
plant mixing is the preferred method for hazardous waste containment facility
liners (Ryan, 1984).
5-69
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tn
i
Note: Photo courtesy of Ground Engineering, Ltd., Regina, Saskatchewan
Figure 5-15. Truck-loaded bentonite spreader.
-------
CJ1
I
Note: Photo courtesy of Ground Engineering. Ltd., Regina, Saskatchewan
Figure 5-15. Truck-loaded bentonite spreader (continued).
-------
en
i
ro
Note: Photo courtesy of Ground Engineering, Ltd., Regina, Saskatchewan
Figure 5-16. Pneumatically fed bentonite spreader.
-------
en
i
-vj
CO
Note: Pho.o courtesy of Ground Endearing, Ltd, Reflina,
Figure 5-16. Pneumatically fed bentonite spreader (continued).
-------
Figure 5-17. Blending bentonite with soil using a disk harrow.
5-74
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/s'./
Figure 5-18. Soil stabilizer mixing bentonite in place.
-------
5.2.2.2.2 Compaction—Following spreading and mixing, the bentonite
admixture is compacted. Vibratory smooth-wheeled rollers or vibratory-plate
compactors are preferred for this operation, for two reasons. First,
because admixed liners are often thin (4 to 6 inches), tamping-foot or
sheepsfoot rollers can penetrate the liner. However, this may not be an
issue for hazardous waste facility liners because most regulations require
liners 2 feet thick or greater. The second reason stated for this preference
is that the native soils used at these sites often have a high sand content
and are most effectively compacted with smooth vibratory rollers (Kozicki,
Ground Engineering, Ltd., Regina, Saskatchewan, Canada, personal communi-
cation, 1984).
5.2.2.3 Climatic Effects—
The following section is a discussion of climatic influences on clay
liner construction activities and the measures to avoid problems resulting
from climatic stresses.
5.2.2.3.1 Precipitation and Desiccation—Precipitation can interfere
with construction operations by eroding or flooding the site or by over-
moistening the liner material. Provisions for protecting a borrow pile
from erosion or overwetting have already been discussed. For liner instal-
lation, when construction is interrupted at night or by rain, the compacted
lift is usually seal-rolled (rolled smooth with a smooth drum or wheeled
roller). If the site is properly graded, this ensures that water will run
to the lowest point of the site and not puddle or pond on the liner surface.
Two hazardous waste management companies have used or suggested inflat-
able domes over secure landfills for protection from the elements during
construction and operation (Figure 5-19). These domes enable construction
activities to proceed despite inclement weather. In addition, for facilities
with continuous operation where wastes are emplaced in the landfill while
other parts of the liner are still being constructed, the dome prevents
rainwater from falling on the site, thus eliminating the need to collect
and treat leachate generated during operation. Upon closure of the facility,
the dome is deflated and moved to another location.
Plastic covers may be used during inactive periods to prevent drying
or wetting of the liner material. Soil covers are sometimes used to pre-
vent desiccation and erosion. It is important to protect the liner against
desiccation, especially if high-swelling soils have been used, because des-
iccation cracks can seriously increase the liner's permeability. In certain
areas, 6- to 8-inch dessication cracks can develop in 1 day (Ghassemi et al.,
1983). If desiccation cracks occur, it is necessary to disk and recompact
the portion of the liner that has been affected. A liner failure documented
in Chapter 7 (Site I) illustrates the importance of controlling desiccation.
5.2.2.3.2 Freezing—Liners should not be constructed of frozen soils.
From the standpoint of compaction, frozen soils are difficult to work and
the compactive effort needed to achieve a specified density and permeability
increases with decreasing temperature, often to the point that the required
permeability and density cannot be achieved. Thus, in colder climates,
liners cannot be properly constructed during the winter months.
5-76
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Note: Photo courtesy of Waste Management, Inc., Oakbrook, IL
Rgure 5-19. Inflatable dome over a hazardous waste landfill.
5-77
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Freezing of a liner can cause surface cracking and degradation of the
liner soil fabric, resulting in increased permeability (Mercuric, Ebasco
Services, Inc., New York, New York, personal communications, 1984). At the
end of a construction season, as well as at night in the fall and spring
when temperatures drop below freezing, the liner should be protected from
freezing. Liners can be protected from freezing with a blanket of soil or
organic mulch.
5.2.3 Postinstall ation Activities
Upon completion, the liner is rolled smooth to seal the surface so
that precipitation and/or leachate can run freely to the leachate collec-
tion sump. The completed liner is surveyed to ensure that thickness,
slope, and surface topography are as required by the design specifications.
Seals around objects penetrating the liner (e.g., antiseep collars around
leak detection system pipes) should be checked for integrity. The liner
can be covered with plastic or a soil cover to prevent desiccation if any
time will pass before the next liner system component (e.g., FML or leachate
collection system) is installed or before the liner is covered with waste.
This is especially important for bentonite liners or for liners composed of
highly swelling native soils where desiccation cracking can occur very
quickly.
For surface impoundments, rip-rap can be placed on the upper sidewall
slopes to protect them from wave erosion. Experience in dam construction
has shown that in most cases rip-rap is best placed by dumping. A U.S.
Army Corps of Engineers' survey cited by Small (1981) found that dumped
rip-rap failed only 5 percent of the time, whereas the failure rate for
hand-placed rip-rap was 30 percent. The failure rate for concrete pavement
used as a substitute for rip-rap was 36 percent. Proper sizing of dumped
rip-rap is critical to its performance. Rip-rap slopes also must be main-
tained to provide reliable liner protection. Erosion-resistant structures
for channeling or loading liquid wastes into surface impoundments also may
be constructed after liner installation.
5.3 QUALITY ASSURANCE AND QUALITY CONTROL
A recent survey of hazardous waste surface impoundment technology
revealed that rigorous CQA and CQC are necessary to achieve good site
performance (Ghassemi et al., 1983). Liner failures at several impoundments
were attributed to various factors including "failure to execute proper
quality assurance and control." The success of surveyed facilities that
have performed very well is attributed to many factors including "the use
of competent design, construction and inspection contractors, close scrutiny
of all phases of design, construction, and CQA inspection by the owner/
operator, excellent CQA and CQC and recordkeeping during all phases of the
project, and good communications between all parties involved in establish-
ing the sites" (Ghassemi et al., 1983).
Potential causes of clay liner failure that can be avoided with careful
CQA and CQC include:
5-78
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Use of materials that do not meet the design specifications
Inadequate foundation preparation
Inclusions of roots and other organic matter, large rocks,
pockets of permeable materials, and other foreign objects in
the liner material
Inadequate moisture control both prior to and after compac-
tion
Inadequate clod size reduction, mixing, and spreading of
liner materials
Emplacement of inadequate amounts of liner materials (espe-
cially important with bentonite/soil liners)
Failure to follow installation procedures specified in the
design
Use of improper or inadequate construction equipment
Specification or application of inadequate compactive effort
Failure to tie lifts together properly
Inadequate control of soil moisture content and density
during compaction and poor maintenance after construction.
This section specifically addresses quality assurance and quality
control for the construction of clay liners for hazardous waste landfills,
waste piles, and surface impoundments. It addresses liners constructed of
both recompacted soil and bentonite/soil admixtures and includes QA activities
that are necessary to ensure that the liner material is as specified and
that installation procedures will result in a liner that will perform as
specified in the facility design. This text is a compilation of information
on current CQA and CQC practices obtained in the course of this study
through interviews with design engineers and through literature reviews.
The section on current practices (Section 5.3.4.4) tabulates much of the
information obtained during this effort.
Proper installation of all of the components of a hazardous waste
storage or disposal unit (i.e., clay liners, synthetic liners, leachate
collecting system, dikes, and cover systems) is necessary to ensure the
specified performance of the clay liner and the total containment system.
As with clay liners, an adequate CQA and CQC program is necessary during
installation of these components to ensure that they will perform as speci-
fied; however, a discussion of CQA and CQC for these components is beyond
the scope of this document.
5-79
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5.3.1 Key Terms
The following concepts and terms are used throughout this section.
Construction Quality Management—The process whereby scien-
tific and engineering principles and practices are used to
ensure that a land-based hazardous waste facility is con-
structed in conformance with its design. The emphasis on
construction quality management must begin as early as
possible in the design of the facility, must be stressed
throughout the actual construction of the facility, and
ceases upon closure of the facility. Managing construction
quality is the responsibility of the permit applicant, the
construction contractor, and the design engineering firm.
It consists of two components, CQC and CQA.
CQA—A planned series of overview activities, the purpose of
which is to provide assurance that CQC is being implemented
effectively. The system involves a continuing evaluation of
the adequacy and effectiveness of CQC, the inspections
performed, the data collected, and the interpretation of the
data made in response to the CQC activities. For hazardous
waste land disposal facilities, this series of overview
activities may involve verifications, audits, and evaluations
of the factors that affect the installation, inspection, and
performance of a hazardous waste land disposal facility to
ensure that the facility meets the design specifications.
CQC—Planned and unplanned inspection activities, the purpose
of which is to help provide the level of construction quality
that will result in a facility that meets the design specifi-
cations. The overall system involves integrating several
related factors including: (1) proper selection of specified
materials, (2) installation to meet the full intent of the
specification, and (3) inspection to determine whether the
resulting product is according to the specification.
CQA Plan—The CQA plan that is discussed in this chapter is
a written approach that may be followed to attain and main-
tain consistent high quality in the construction of hazardous
waste storage and disposal facilities. The purpose of a CQA
plan is to ensure that a completed facility meets or exceeds
all design criteria. The CQA plan is tailored to the specific
facility to be constructed and documents the permit appli-
cant's commitment to CQA.
The CQA plan is prepared as part of the facility design
activities. It is usually prepared by the design engineers
but in some cases may be prepared by an independent third
party responsible for CQA for the facility. The CQA plan
indicates what tests and observations will be made during
construction to ensure that design criteria are met, as well
5-80
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as test frequency and test spacing requirements for CQC.
Acceptance/rejection criteria for specific tests are speci-
fied in the plan and reflect the precision of the specific
test methods used and the specified values, design tolerances,
and expected field variability of the tested parameters.
Also specified in the CQA plan are corrective actions to be
implemented if some part of the work is substandard and
consequently rejected.
While the overall content of the CQA plan will depend on the site-specific
nature of the proposed hazardous waste land disposal facility, as a minimum,
several specific elements should be included in the plan. These elements
are summarized briefly below.
Responsibility and Authority—The responsibility and authority
of all organizations involved in permitting, designing, and
constructing the hazardous waste land disposal facility
should be discussed fully in the CQA plan.
CQA and CQC Personnel Qualifications—The CQA officer, CQC
inspector(s), and all other CQA and CQC personnel should
possess the training and experience necessary to fulfill
their identified responsibilities, and their qualifications
should be presented in the CQA plan.
CQC Activities (Observations and Tests)—The specific obser-
vations and tests that will be used to control or monitor
the installation of the hazardous waste land disposal facility
components should be summarized in the CQA plan.
Construction Quality Evaluation—The sampling activities,
sample size, sample location, frequency of testing, acceptance
and rejection criteria, and plans for implementing corrective
measures, all as contained in the project specifications,
should be presented in the CQA plan.
Documentation—The QCA plan should include a discussion of
the reporting requirements for the project. This should
include such items as daily summary reports, observation and
testing data sheets, problem identification and corrective
measures reports, block evaluation reports, design acceptance
reports, and final.documentation. Provisions for the final
storage of all records should also be discussed in the CQA
plan.
The following is a more detailed list of important items to be included
in a CQA plan to address the above elements properly. These items have
been largely adapted from the proven and effective "Contractor Quality
Control Plan" of ER 1180-1-6 (U.S. Department of the Army, 1978). They are
presented here only as an example and should not be considered an obligatory
or complete or exclusive outline. These items are:
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A planned QA organization
An education plan to ensure that the workmen, construction
management, and inspectors are aware of the various quality
requirements of the project and the reasoning behind the
requirements
Proposed methods for performing CQC inspections, both for
construction process control and for acceptance sampling and
testing (quality evaluation); this includes inspections of
subcontractors' work
Delineation of areas of authority and responsibility for
each individual in the CQC/CQA group
Name and qualifications of each individual assigned a CQA or
CQC function; method of establishing and verifying personnel
qualifications to perform specific tests and/or tasks
Discussion of how CQC inspections will be performed:
by inspectors employed by the permit holder designated
by name, their qualifications, and the specific tests
and observations to be made
by subcontract inspectors designated by name, their
qualifications, and the tests and observations to be
made subject to approval of the regulatory agency
The test and/or observation method to be used for each
specification quality requirement; whether it is a standard
or alternative method; the reference standard or literature
reference for each; the method for establishing size of the
unit of construction for acceptance testing; the method for
establishing sample sizes and sampling locations; acceptance/
rejection criteria for each test; and the method for dealing
with outlying observations
Location, availability, applicability, and calibration of
test facilities and equipment
Procedures for advance notice and coordination of special
inspections when and where required
Procedures for reviewing all drawings, samples, certificates,
or other documents for compliance with permit requirements
and for certification of their acceptability to the regulatory
agency; qualifications required of the individual performing
the reviews
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Procedures for reviewing inspection test results and observa-
tion records; qualifications required of individuals perform-
ing the reviews
Procedures for observing and testing fresh exposures of the
site media (soil profile) and for comparing the results with
evaluations made during site characterization studies;
qualifications required of individuals performing the observa-
tions and tests
Action to be taken by inspectors and reviewers (re: 10, 11,
and 12 above) when deficiencies are identified and/or reported,
including who is to be notified and in what manner
Reporting procedures, providing for submittal and/or storage
of all test and observation reports, at specified intervals,
and reporting of all actions taken under item 13 above;
report formats to be used
Definition of responsibility and authority of all persons
and groups involved in the CQA and CQC effort; definition of
who has the authority to reject either materials or workman-
ship and to require removal and/or replacement
A copy of a letter of direction to the permit holder's
inspection representative responsible for CQA, setting forth
duties and responsibilities and signed by a responsible
official of the permit holder's organization.
5.3.2 Personnel
The individuals or groups of individuals who may be involved in the
preparation, approval, and use of a CQA plan include permit applicants
(e.g., site owners/operators), permitting agencies, design engineers,
construction contractors, CQA officers, and CQC inspectors. The responsi-
bilities and authorities of each of these groups must be well defined and
understood by all prior to facility design and construction.
Successful CQA and CQC requires clarity in written and oral communica-
tions among all the parties, especially in defining key terms and in deline-
ating areas and lines of authority and responsibility in scope of work and
other contractual arrangements. For example, "inspector," "inspection,"
"certification," and "verification" are terms that are used ubiquitously
and frequently without regard to precise definition. The definitions of
these terms should be understood and accepted by all parties involved in
the clay liner project and clearly documented in a CQA plan.
5.3.2.1 Responsibility and Authority—
The overall responsibility of the CQA and CQC personnel is to execute
activities specified under the CQA plan. As a minimum, CQA personnel
includes a CQA officer and a CQC inspector. Specific responsibilities and
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authority of each of these persons are defined in the CQA plan and associated
contractual arrangements with the owner. For the CQA officer, specific
responsibilities and areas of authority may include:
Reviewing and fully understanding all aspects of the speci-
fied landfill design and proposed construction techniques
Serving as the owner's or design engineer's liaison with the
contractor in interpreting and clarifying contract documents
Providing CQA reports to the owner on the results of inspec-
tions and testing
Advising the owner or design engineer of work that the CQA
officer believes should be corrected, rejected, or uncovered
for inspection and of work that may require special testing,
inspection, or approval
Reviewing inspection and test results and rejecting defective
work when authorized to do so by the owner or design engineer
Directing the CQC inspector in performing site inspections
and testing
Stopping construction site activities in cases where devia-
tions from design plans and specifications are detected and
implementing corrective actions.
For the CQC inspector, specific responsibilities may include:
Conducting onsite observations and tests of the work in
progress to assess compliance by the contractor with the
plans, specifications, and construction-related contractual
provisions for the project
Reporting to the CQA officer results of all inspections
including work that does not meet the specifications or
fails to meet contract requirements
Monitoring reviews and tests conducted by the contractor as
required by the specifications and contract
Verifying that tests, equipment, and system startups are
conducted by qualified personnel and proceed according to
standardized procedures defined by contract documents.
5.3.2.2 Qualifications of CQA Personnel--
Inspectors and CQA officers should be trained in the proper use of all
test methods and equipment. They should have the ability to calibrate
equipment, administer the required tests, record and interpret data, and
make pertinent observations. The training that is required to obtain these
skills may come from the classroom or through field experience. However,
emphasis is generally placed on first-hand (field) testing experience.
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In addition to the above requirements, CQA officers should be regis-
tered professionals who thoroughly understand the theory and application of
all physical and observational tests, the overall site design, the proper
use of the various types of construction equipment, and project management
and who have sufficient practical experience in landfill construction.
5.3.3 Observations and Tests
This section describes the observations and tests that should be
specified in a CQA plan for clay liner construction. The following section
is divided according to the CQA and CQC activities that will take place
during preconstruction, construction, and postconstruction periods of clay
liner installation activities. All ASTM test methods referenced in this
chapter may be found in ASTM (1985).
5.3.3.1 Preconstruction--
The first activity under preconstruction CQA is to review the design
drawings and construction specifications for the clay liner that is to be
installed with emphasis on CQA and CQC. The design drawings and construction
specifications need to be clear and understandable from the standpoint of
both the onsite CQC inspectors and the contractor. If the design is deemed
inadequate or unclear by the CQA officer, it should be returned to the
design engineer for clarification and/or modification.
Prior to construction, the CQA officer must also assess the capa-
bilities of the construction contractor's personnel so that he can determine
the type and amount of training, instruction, and supervision that will be
needed during construction operations. The contractor's prior performance
in general earthwork activities, experience in construction of hazardous
waste facilities, and experience in working the specific type of soil and
equipment to be used in constructing the facility in question need to be
addressed in this assessment.
A preconstruction training plan should be included in the CQA plan.
as stated by the U.S. Department of the Army's Construction Control Manual
(1977):
Preconstruction instructions and training should be given to
field inspection personnel to acquaint them with design concepts
and to provide them with a clear understanding of expected
conditions, methods of construction, and the scope of plans and
specifications. This may be done by training sessions, preferably
,with design personnel present, using a manual of written instruc-
tions prepared especially for field personnel, to discuss engineer-
ing considerations involved and to explain control procedures and
required results.
If significant quantities of the soil liner material are to be stored
at the construction site, the CQA officer should make provisions to ensure
that storage facilities are adequate to prevent alteration of the liner
material. For natural clay soils, this could include seal-rolling, grading,
or covering the storage pile to encourage runoff and to reduce erosion. If
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bentonite/soil admixtures are to be used as liner material, it is critical
that bentonite material stored onsite is sheltered from precipitation
because this material cannot be worked except when in a dry state.
The CQA plan must provide assurance that any liner material brought
onto the site is as specified. Soil material screening begins as a precon-
struction activity and continues during construction as long as material is
being brought onsite or excavated from the site. This activity can be
accomplished in several ways, depending on the source of the liner material
and site conditions. If the liner material is obtained onsite, the inspec-
tion can be accomplished as it is placed in the borrow pile for storage.
If the excavated soils are heterogeneous, it may be necessary to segregate
the soil material as it is excavated, with suitable soil placed in a borrow
pile for future use and soil that does not meet specifications discarded.
The CQC inspector observes the segregation operations carefully to ensure
that only suitable material is retained for liner construction.
Similarly, if the liner soil is obtained from a nearby borrow area,
the soil material may be inspected at the borrow site or as the material
arrives at the construction site. Borrow site inspection is more desirable,
especially if the soil is heterogeneous, because this will ensure that only
suitable material is transported to the site, saving transportation costs.
Subsurface characterization of the borrow site may expedite this effort for
heterogeneous borrow sources. The U.S. Department of the Navy (1982)
recommends that during initial exploration of the borrow pit area, borings
or test pits be made on a 200-foot grid. If variable conditions are found
during this initial exploration, intermediate borings or test pits should
be made. Borrow pit exploration should produce the following information:
A reasonably accurate subsurface profile down to the antic-
ipated excavation depth
Engineering properties of each material considered for use
Approximate volume of each material considered for use
Water level
Presence of sands, gypsum, or other undesirable materials
Extent of organic or contaminated soils, if encountered.
For extremely heterogeneous borrow areas, it may be necessary for the
inspector to guide the excavating equipment to avoid substandard soil
material.
Inspection of the soil can be largely visual; however, CQC personnel
conducting this inspection must be experienced with visual-manual soil
classification techniques (ASTM D 2488). Changes in color or texture may
indicate a change in soil type or soil moisture content. The soil also may
be inspected for roots, stumps, and large rocks. In addition, as a check
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of visual observations, samples of the soil usually are taken and tested to
ensure that the soil's index properties are within the range stated in the
specifications; tests of moisture/density characteristics (ASTM D 698) also
should be conducted to ensure that these relationships do not change. The
number of tests to be conducted depends on site-specific conditions (i.e.,
soil type and heterogeneity) and the experience of the CQC personnel.
Usually a minimum number of tests per cubic yard of material is specified,
with additional tests required by the inspector if visual observations
suggest a change in soil type.
Soil index properties are simplified tests that provide indirect
information about the engineering properties of soils beyond what can be
gained from visual observations. Although the correlation between index
properties and engineering properties is not perfect, it is generally
adequate for CQC purposes. Index property tests commonly used to screen
soils are described below.
Atterberg limits include the liquid limit and the plastic limit (ASTM
D 4318). These tests are commonly used along with grain size distribution
for monitoring changes in soil type. A significant change in Atterberg
limits usually reflects a change in important engineering properties, such
as the relationship among moisture content, density, compactive effort, and
permeability.
Grain size analysis is another important screening test for changes in
soil composition. The percentage of clay-size particles and the overall
particle size distribution of a soil affects its engineering properties,
especially permeability and strength. Rough estimates of grain size may be
obtained through manual estimates (ASTM D 2488) and may be sufficient for
screening. A 200-mesh sieve may be used to separate coarse (sand and
gravel) and fine (silt and clay) particles. More detailed grain size
distributions may be obtained by sieving the coarse fraction and by using
several settling methods (hydrometer, decantation, or pipette) for the fine
fraction (ASTM D 422). Cases where samples of incoming or installed liner
materials contain inadequate quantities of the necessary soil particle size
may be referred to the CQA officer for evaluation. Moisture content and
consistency tests are also needed for screening soils. Again, it is impor-
tant to monitor carefully for soil type changes as long as liner material
is being placed. A change in soil type requires the compaction of another
test fill as described in the following text.
When bentonite/soil liners are specified, incoming bentonite should be
inspected to ensure that its quality is as specified. For all bentonite
shipments, certification of compliance with material specifications should
be obtained from the manufacturer or supplier. In addition, the quality of
the arriving bentonite should be tested frequently for dry fineness, pH,
and viscosity and fluid loss of a slurry made from the bentonite. Dry
fineness is the percentage passing a 200-mesh sieve. It is necessary to
control dry fineness to ensure proper mixing of the bentonite. Slurry
viscosity, slurry fluid loss, and pH are standard tests specified by the
American Petroleum Institute (API, 1982). These tests are necessary to
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ensure the quality of the bentonite in terms of its swelling potential.
Electric pH meters should be used for pH measurements; pH papers are usually
not reliable (Xanthakos, 1979). If bentonite additives are specified, the
manufacturer's certificate contained with each shipment should state compli-
ance with the specified characteristics. More information on testing
bentonite quality may be found in Xanthakos (1979).
5.3.3.1.1 Test Fill—An important preconstruction CQA activity is to
determine the suitability of the equipment and methodology to be used to
compact the liner. To accomplish this, most design engineers recommend
that a representative test fill of liner material be compacted with the
designated equipment to see if the specified density/moisture content/
permeability relationships determined in the laboratory can be achieved in
the field with the compaction equipment to be used and at the specified
lift thickness. Test fill dimensions must be sufficient to accommodate the
compaction equipment. Several lifts are usually compacted in the test fill
to check the methodology to be used to tie lifts together. The test fill
also is used to determine the number of equipment passes (or amount of
compactive effort) needed to achieve the specified permeability and to
determine the ability of mixing equipment to break up large clods of uncom-
pacted liner soil.
Field permeability tests can be conducted on the compacted test fill
material. Field compactive effort is different from the compactive effort
applied in the laboratory. Although densities may be the same for different
types of compactive efforts, the fabric and the permeability of soil com-
pacted by different methods can differ significantly (Mitchell, 1976).
These permeability tests, therefore, are necessary to ensure that the
compactive effort that is applied in the field will result in the same or
lower permeability than was demonstrated in the laboratory tests of the
liner material. Additionally, the test fill is useful in establishing a
relationship between field permeability and laboratory permeability measure-
ments on undisturbed samples of compacted liner material, which can vary by
as much as 3 orders of magnitude (Day and Daniel, 1985). The long time
necessary for field permeability measurements often limits their use during
construction operations because of scheduling problems. However, field
permeability measurements can be scheduled conveniently during test fill
compaction.
In addition to the number of passes necessary to achieve the specified
permeability, equipment type, size, and compatibility with the soil type
are evaluated and recorded during test fill compaction. Equipment items to
be checked and recorded include:
For sheepsfoot rollers—drum diameter and length, empty and
ballasted weight, length and face area of feet, and the
yoking arrangement
For rubber-tired rollers--the tire inflation pressure,
spacing of tires, and empty and ballasted wheel loads
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For vibratory rollers—the static weight, imparted dynamic
force, operating frequency of vibration, and the drum diameter
and length (U.S. Department of the Army, 1977).
This information is necessary to estimate the compact!ve effort and compac-
tive force applied in the field.
Compacting the test fill is also valuable in that it gives the CQA
officer, CQC inspector, and construction personnel some experience with the
behavior of the specific soils, equipment, and methodology to be used at
the site during compaction. This is a very useful base of knowledge to
apply when observing compaction of the actual containment facility liner.
The test fill compaction thus serves to calibrate the inspectors' and
contractors' observations to the conditions that will be encountered during
the compaction of the liner.
The successful use of density and moisture content measurements for
CQC of clay liner compaction depends upon the relationship established
among density, moisture content, compactive effort, and permeability for
the specific soil and for the specific compaction equipment and methodology
used during test fill compaction. If a change in soil characteristics or a
change of compaction equipment or methodology occurs during liner construc-
tion, another test fill should be compacted with the new soil, equipment,
and/or methodology because the original relationships may no longer apply.
If this is not done, there is no assurance that CQC using density/moisture
content/compact!ve effort measurements will result in a liner with the
specified permeability.
5.3.3.2 Construction—
An important CQC activity during clay liner installation is observation
of the construction process, including personnel performance, by the inspec-
tors. Observations by an experienced inspector, coupled with a soundly
developed and implemented CQC testing plan, will ensure that the liner is
installed as specified, that any potential problems are identified in a
timely manner, and that proper corrective actions are implemented.
5.3.3.2.1 Foundation Base Preparation—CQC for excavation and con-
struction of foundations is not fully addressed in this document. Standard
methods for controlling the quality of foundation preparations and earthen
embankments may be found elsewhere (e.g., Spigolon and Kelley, 1984; U.S.
Department of Interior, 1974; U.S. Department of the Army, 1977). The
foundation base must be adequately prepared before the clay liner is con-
structed. The natural foundation should provide satisfactory contact with
the overlying compacted liner, minimize differential settlements and thereby
prevent cracking of the liner, and provide an additional barrier to leachate
migration from the facility. To ensure that these goals are met, observa-
tions during the construction of foundations should include the following
(U.S. Department of the Army, 1977):
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Observations of stripping and excavation to ensure that all
soft, organic, and otherwise undesirable materials are
removed. Proof-rolling with heavy equipment can be used to
detect soft areas likely to cause settlement. Consistency
of the foundation soil may be checked with a hand penetrome-
ter, field vane shear test, or similar device.
Inspection of soil and rock surfaces for adequate filling of
rock joints, clay fractures, or depressions and removal and
filling of sand seams.
Inspection of the depth and slope of the excavation to
ensure that it meets design requirements.
Observations to ensure proper placement of any recessed
areas for collection or detection pipes and sumps.
Tests and observations to ensure the quality of compacted
fill.
Visual observation of the construction process is the major means of
ensuring that the foundation is constructed as designed. Some instrument
surveying may be necessary to ensure that facility dimensions, side slopes,
and bottom slopes are as specified. Visual-manual soil identification
techniques (ASTM D 2488) and index property tests (ASTM D 422; D 4318) may
be used to monitor foundation soil composition.
Soil consistency may be checked with a cone penetrometer (ASTM D 3411).
This method is widely used to determine the consistency of cohesive soils
for classification and is more accurate than the visual-manual method. It
is less accurate than the laboratory method (ASTM D 2166), but can be used
to give broad consistency classifications for cohesive soils. Shear strength
of foundation soils can be checked in the field with a field vane shear
device (ASTM D 2573) or a torvane device (Lanz, 1968). The ASTM D 2573
method is standardized and, although it is less accurate, can be correlated
with the standard laboratory method for unconfirmed compressive strength
(ASTM D 2166). Although all of these field expedient methods give only
approximate values, they are usually sufficient for construction. Compac-
tion is controlled as described in Section 3.3.3.2.3.
Further information on quality control of foundations may be found in
Spigolon and Kelley (1984), U.S. Department of the Interior (1974), and
U.S. -Department of the Army (1977).
5.3.3.2.2 Liner Lift Placement—Liner lift placement includes the
operation of spreading the liner material(s) over the floor of the facility;
breaking and homogenizing clods of soil; and, for blended clay liners and
admixed liners, uniformly blending the mixed materials.
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During placement of soil materials, the soil is spread uniformly as
specified. The loose lift thickness of the soil should be measured systema-
tically over the entire site, with a marked staff or shovel blade, and
survey levels should be made every few lifts for verification and documenta-
tion of liner thickness. Following spreading, the liner material is disked
or tilled to break up large soil aggregates and to homogenize the material.
All large clods of liner material should be reduced in size as much as
possible to facilitate moisture penetration and to ensure uniform compaction
through the lift. Opinions differ on the acceptable maximum clod size; in
a series of interviews with design engineers, recommendations ranged from 1
inch to no greater than the lift thickness (see Table 5-8 in Section 5.3.3.4).
Close observation by the onsite CQC inspector is critical to ensure that
this is properly accomplished.
If bentonite additives are to be admixed with the natural soil, the
proper percentage of the additive must be controlled. For spreading and
in-place mixing, this is accomplished by visual observations of the addi-
tive as it is spread over the site by hand or by a suitable spreading
device. In addition, a spreader can be roughly calibrated by using it to
spread the additive over a plastic sheet or pan of given dimensions and
then weighing the collected material. Visual observations also should be
made to ensure that additives are uniformly distributed in each liner lift.
To ensure the proper bentonite percentage in admixtures, the methylene blue
test (see Appendix A) can be carried out on representative samples of the
admixed material. The soil mixture's liquid limit or plasticity index has
also been used to ensure proper bentonite percentage.
If bentonite additives are to be blended with the native soil prior to
emplacement, proper bentonite percentage can be ensured by using the
methylene blue test on samples of the mixed material. CQC personnel also
can inspect the mixing operations to ensure that the proper amounts of
bentonite and soil are placed into the mixing device and that mixing time
and force are sufficient.
5.3.3.2.3 Moisture Control—Moisture content of the liner soil should
be measured and controlled both before and after lift placement to ensure
that the soil moisture content is as specified and for activating bentonite
additives. Nuclear probes (ASTM D317-78) and/or manual moisture content
measurements are generally used to control moisture in the field (see
Chapter 3). The following description of manual moisture estimation is
adapted from Johnson et al. (1983).
In order for quality control personnel to satisfactorily estimate
fill water contents, they must become thoroughly familiar with
the fill material prior to the start of fill operations. Prefer-
ably, they should spend some time in the field laboratory, per-
forming several compaction tests to become familiar with the
differences in appearance and behavior of the various fill materi-
als, to recognize when they are too dry or too wet, as well as
when they are at the specified water content. Inspection personnel
should also run several Atterberg limits on fine-grained soils so
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they can compare the appearance and feel of the soils when they
are at the plastic limit with that at proper water content for
compaction.
Trained personnel should then be able to pick up a handful of
soil and make a reasonable estimate of the relation of its water
content to its optimum water content by feel and appearance
(experienced technicians often can estimate deviation of water
content from optimum within ±1 percent). Occasional moisture
tests should be made to confirm these manual estimates.
A few reference bags of liner material at known moisture contents stored at
the site can be very helpful for calibration of manual moisture content
estimates.
Many design engineers recommend that oven moisture content measure-
ments by the appropriate test method (ASTM 02216-80) be taken at intervals
to ensure that nuclear measurements and manual estimates are accurate.
Proper moisture content is achieved and maintained with sprinkling devices
(if too dry) or by a combination of mechanical agitation, aeration, and
solar drying (if too wet).
If the liner is to be left exposed between the installation of succes-
sive lifts or after completion, the QC personnel make sure that it is
protected from moisture content change by ensuring that seal-rolling is
uniformly performed over the site and that cover material, if used, is
properly emplaced. If desiccation does occur, the QC inspector reports
this to the QA officer, who notes this and specifies remedial actions, such
as disking and recompaction of the affected portion of the liner.
5.3.3.2.4 Compaction—Soil selection based on laboratory compaction
and permeability tests is made on samples of the liner material during
design of the facility. A relationship among moisture contents, densities,
and permeabilities is established based on test results. Design specifi-
cations usually require achievement of a minimum percentage of the maximum
density (Proctor or modified Proctor) at a specified range of water contents,
based on these results. The specified density/water content corresponds to
the density/water content at which the specified permeability can be achieved
as established by the laboratory and test fill compaction tests. This
density/water content is then tested during quality control of clay liner
installation.
Additionally, during compaction of each lift, compact!ve effort and
uniformity of compaction are observed and recorded. Compactive effort is
estimated by the number of passes of equipment of a known size and weight.
It is important to make coverage uniform, especially at fill edges and in
equipment turnaround areas and at the top and bottom of slopes (Spigolon
and Kelley, 1984). In addition, permeability tests often are conducted
periodically on the compacted liner material as a check on the moisture/
density/permeability relationship. It is generally agreed that all of the
above measurements are necessary to ensure that the specified permeability
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is being achieved in the field. Density measurement should never be used
alone for quality control of clay liner installation.
The relationship among moisture content, density, compactive effort,
and permeability is unique for a specific soil or soil mixture and specific
type of equipment. Laboratory compaction tests to establish density/moisture
curves are determined regularly on field samples of the clay liner to
determine changes in optimum water contents. If these tests or field
inspection of the incoming liner materials indicate a significant change,
laboratory permeability tests and a test fill compaction must be conducted
to establish the density, moisture, and permeability relationship for the
new soil. Otherwise, attainment of the moisture/density relationship that
was specified for the original soil may result in an unacceptable permeabil-
ity with the new soil. Similarly, if different compaction equipment or
methodology is used, another test fill should be compacted with the new
equipment because the type of compactive effort applied affects the final
permeability.
The design engineers interviewed during this investigation stressed
the importance of visual and manual observations by a qualified inspector
for liner compaction quality control. Some consider specific tests only a
backup documentation to observations by the qualified CQC inspector. All
professionals interviewed agreed that observation of the construction
process is the primary and most effective approach to GQC. Testing is
secondary; beyond the minimum test frequency and spacing, visual observa-
tions are used to identify problem areas and to call for more intensive
testing to document and delineate any substandard liner areas. Remedial
actions (e.g., removal and reconstruction) are then ordered for the sub-
standard areas so delineated. All engineers stressed the importance of
having a qualified inspector on the site at all times during construction.
An experienced observer can determine how compaction is proceeding
(e.g., moisture content and density) by observing how the equipment moves
across the area to be compacted, how the soil contacts or sticks to the
compaction equipment, how the soil heaves during compaction, how deep the
compaction equipment sinks into the soil, and how the roller walks out of
the soil (sheepsfoot rollers only) (Johnson et al., 1983). In addition, it
is important to observe uniformity of coverage by compaction equipment,
especially at fill edges, in equipment turnaround areas, and at the top and
bottom of slopes (Spigolon and Kelley, 1984).
5.3.3.2.5 Specific Tests—Testing and sampling of the liner are
necessary to ensure compliance with the design requirements and to document
the as-built conditions of the clay liner. Specific tests to ensure that
compaction results in the specified liner permeability include field density
tests (nuclear, sand-cone, and others), field moisture content measurements,
laboratory compaction tests, and both field and laboratory permeability
tests. The methods and QC measures for conducting these tests may be found
in several documents (AASHTO, 1978; ASTM, 1985; U.S. Department of the
Army, 1970; and U.S. Department of the Interior, 1974) and are briefly
discussed in Appendix A. The main tools used for controlling the quality
of compaction are field density and moisture content measurements, with
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supplementary laboratory compaction tests to monitor changes in soil mater-
ial. A laboratory compaction test should be conducted for every 10 to 20
field density/moisture determinations, depending on soil variability (U.S.
Department of the Navy, 1982). Presently, nuclear probes are often used to
measure field density and moisture content because of ease and quickness of
testing (see Chapter 3). However, nuclear devices must be calibrated for
each soil that is to be tested. In addition, if nuclear devices are used,
other field density and moisture content measurements, such as sand cones
and oven drying, should be made periodically to confirm nuclear results.
Again, it is necessary to measure density, moisture, and compactive effort
in the field to ensure that the required permeability is achieved during
clay liner compaction.
In addition to density and moisture measurements and estimates of
compactive effort, permeability tests should be made regularly to confirm
that the measured moisture/density levels correspond to these required for
the specified permeabilities. Shelby tube or block samples may be taken
for laboratory permeability tests (ASTM D 1587-74; ASTM, 1983), or field
permeability tests may be performed with a double-ring infiltrometer (ASTM
D 3385-75; ASTM, 1983) or similar field permeability device (Appendix A).
Laboratory permeability tests are easier to conduct, do not consume valuable
construction time, and are quicker than field permeability tests. However,
they can underestimate field permeability by as much as 3 orders of magnitude
(Day and Daniel, 1985). Field permeability tests more accurately represent
actual permeabilities, but they can take days to complete, seriously inter-
rupting construction activities. Field permeability tests should be con-
ducted on the test fill prior to construction. Field permeability tests
can be accommodated easily during this phase because they will not interrupt
construction activities. (For further discussion of field versus laboratory
permeability measurements and for a discussion of test methods, see Daniel,
1981; Olson and Daniel, 1981; and Rogowski and Richie, 1984; also see
Chapter 3 of this document.)
Several design engineers recommended that moisture/density measurements
and Shelby tube samples for laboratory permeability tests be obtained from
the lift underlying the lift that has just been compacted. These engineers
believe that during compaction of a lift, significant compactive effort is
being applied to the underlying lift. A more accurate representation of
the degree of compaction across the liner is achieved by testing the under-
lying lift.
Following Shelby tube sampling or nuclear density measurements, the
resulting hole is filled with liner material and hand tamped or is grouted
with bentonite. Over excavation of the hole with a shovel to slope the
sides of the hole prior to backfilling may further facilitate sealing.
Test locations should be staggered from lift to lift so that the testing or
sampling holes do not line up. This also gives better test coverage of the
liner.
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Index property tests (e.g., grain size, clay content, and Atterberg
limits) are used to evaluate liner soils prior to emplacement in order to
monitor changes in soil type. These test methods are well established and
are described in Chapter 3 and in Appendix A.
Minimum test frequency and test spacing should be specified for all
tests in the test plan. Test spacing practices and frequency are discussed
in Section 5.3.3.4 of this report.
5.3.3.3 Completion Tests—
Upon completion of the liner, CQA personnel should check that it is
rolled smooth to seal the surface so that precipitation and/or leachate can
run freely to the leachate collection sump. The completed liner should be
surveyed to ensure that thickness, slope, and surface topography are as
required by the design specifications. Seals around objects penetrating
the liner (e.g., leak detection system stand pipes) also should be checked
for integrity.
Field permeability tests should be conducted on the completed liner as
a final QA check. It appears that field measurement of permeability is
preferable to laboratory measurement because it subjects a larger portion
of the liner to permeability testing. Recent work has shown that field
permeability measurements yield an average hydraulic conductivity close to
a liner's actual hydraulic conductivity. Laboratory tests, even on undis-
turbed samples, gave a hydraulic conductivity 1,000 times less than the
actual value, measured by collecting seepage through the liner (Day and
Daniel, 1985). Several field permeameters can be set up over the site, or
if the site is not too large or is a surface impoundment the facility can
be filled with water and seepage from the site can be measured after account-
ing for evaporation. The latter method, when feasible, is the best way to
ensure that the entire site will function according to specifications once
it is filled, assuming that no waste/liner compatibility problems occur.
If the completed liner is to be left exposed prior to installation of
the overlying facility components, CQC inspectors should ensure that the
liner is covered adequately with soil or plastic sheeting to prevent desica-
tion and wind erosion or that it is maintained at suitable moisture content
by managed water application.
5.3.3.4 Current Sampling Program Design Practices—
Current CQC practice relies on the inspector's observations and judgment
for accepting most of the work, with actual sampling and testing of the
material serving only to document compliance and to help guide the inspec-
tor's judgment. Table 5-8 is a summary of information on current CQC
practices obtained during interviews with design engineers active in design-
ing and controlling the construction quality of clay liners. Also included
in this table is information from earthwork construction manuals of the
U.S. Department of the Interior and the U.S. Department of the Navy.
Tables 5-9 and 5-10 list recommendations for construction documentation
recently published by the Wisconsin Department of Natural Resources per-
sonnel .
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TABLE 5-8 CURRENT QA PRACTICES FOR CLAY LINER CONSTRUCTION
cn
t
CT>
Source of
Information
A
B
C
0
E
F
G
H
Minimum frequency of
In-place moisture or
density tests
1 per 1.000 yd3 of fill
Moisture tests only (used
with permeability tests
and compact! ve effort to
control compaction)
Frequency per unit volume
of fill based on experience
1 per 2,500 ft2 of lift
Frequency, per unit volume
of fill, based on experi-
ence and liner material
homogeneity
Statistical approach
9 per acre of lift
1 per 2,000 ft2 or at least
1 per lift
Sample or
test hole
Permeability testing filling method
Occasional lab test
Triaxial and some field tests Benlonite
Lab tests
Triaxial--! per 3 acre feet Liner material
with minimum of 1 per acre hand-tamped
Modified triaxial, fixed-wall,
and consolidation lab tests —
per unit volume of fill.
based on experience
Lab tests — 5 to 6 per acre
Falling head field test at
density test location--! per
acre of lift
Lab test--! per 10,000 to Liner material
20,000 ft2 or every third or bentonite
lift hand- tamped
Test fill Maximum clod size
recommended allowed
Not usually % lift thickness; none
greater than lift
thickness
Yes 2 inches
•j lift thickness
Yes
-------
TABLE 5-8 (continued)
cn
I
Source of
information
Minimum frequency of
in-place moisture or
density tests
Permeability testing
Sample or
test hole
filling method
Test fill
recommended
Maximum clod size
allowed
Maximum rock or
root size allowed
I per 2,500 ft2-minlmum
of 4 per lift or 1 per
day—more as needed
1 per 10,000 ft* or 1 per
lift
Site specific, based on
experience
1 per 1,000 yd3 or 1 per
day
1 per 1,000 yd3 or 1 per
day
1 per 1,000 yd3--! per 200
yd3 if hand tamped
1 per 500 to 1,000 yd3
1 per 2,000 yd3
Laboratory test--l per 2,000
yd3 or 2 per lift—occasional
field test
Lab and field
Lab triaxial
Lab constant head--l per 25,000
yd3 or 1 per week
Lab falling head--l per
25,000 yd5
Bentonite
Bentonite
Yes
Yes
Sometimes,
especially
for admix-
tures
Yes
No
Yes
Lab—1 per 16,000 yd3, field -
1 per 40,000 yd3
H lift thickness
-------
TABLE 5-9. RECOMMENDATIONS FOR CONSTRUCTION DOCUMENTATION OF CLAY-LINED
LANDFILLS BY THE WISCONSIN DEPARTMENT OF NATURAL RESOURCES
1.
Item
Clay borrow source
testing
Testing
Grain size
Moisture content
Atterberg limits
Frequency
1,000 yd3
1,000 yd3
5,000 yd3
2. Clay liner testing
during construction
3. Granular drainage
blanket testing
(liquid limit and
plasticity index)
Moisture-density curve
Lab permeability
(remolded samples)
Density
(nuclear or sand cone)
Moisture content
Undisturbed permeability
Dry density
(undisturbed sample)
Moisture content
(undisturbed sample)
Atterberg limits
(liquid limit and
plasticity index)
Grain size
(to the 2-micron
particle size)
Moisture-density curve
(as per clay borrow
requirements)
Grain size
(to the No. 200 sieve)
Permeability
5,000 yd3 and all
changes in material
10,000 yd3
5 tests/acre/lift
(250 yd3)
5 tests/acre/lift
(250 yd3)
1 test/acre/lift
(1,500 yd3)
1 test/acre/lift
(1,500 yd3)
1 test/acre/lift
(1,500 yd3)
1 test/acre/lift
(1,500 yd3)
1 test/acre/lift
(1,500 yd3)
5,000 yd3 and all
changes in material
1,500 yd3
3,000 yd3
Source: Gordon et al., 1984.
5-98
-------
TABLE 5-10. ELEMENTS OF A CONSTRUCTION DOCUMENTATION REPORT
Major elements
Components
A. Engineering plans
8 Engineering cross-sections
C. Comprehensive narrative
0. Series of 35-mm color prints
E. Construction certification
Completed sub-base elevations.
Final clay liner grades.
Top of drainage blanket grades.
Leachate collection lines, cleanouts,
and manholes with spot elevation
every 100 feet along the lines and
at all manhole entrances and exits.
Drainage features.
All monitoring devices.
Spot elevations at all breaks in
slope and on approximate 100-foot
centers.
Document testing locations.
Other site information as appro-
priate.
Minimum of one east-west and one
north-south through the completed
area.
Explaining how construction of the
project was accomplished along with
an analysis of the soil-testing
data obtained in 1 through 3 above.
This report should also include an
appendix containing all the raw
data from the field and laboratory
testing.
Documenting all major aspects of
site construction.
Should be certified by a registered
professional engineer to have been
completed according to the approved
plans. Any deviations from the
plans should be noted and
explained.
Source: Gordon et al., 1984-.
5-99
-------
Statistical sampling methods for earthwork quality control (geostatis-
tics) have been developed by the U.S. Department of the Interior and the
U.S. Army Corps of Engineers (U.S. Department of the Interior, 1974; U.S.
Department of the Army, 1977; Davis, 1966; Turnbull et al., 1966; Willenbrock,
1976). These documents include statistical methodology to establish degree
of confidence for a testing program. Other discussions of statistical
methods may be found in Winterkorn and Fang (1975), Selig (1982), Wahls et
al. (1968), Jorgenson (1971), and Kotzias and Stamatapoulous (1975).
Figures 5-20 and 5-21 illustrate a simple, concise method of documen-
tation of clay liner CQC statistics developed by Soil Testing Engineers of
Baton Rouge, Louisiana. Figure 5-20 illustrates the sampling locations for
QC tests of a clay-lined landfill cell. Figure 5-21 is a graphic presenta-
tion of the moisture/density/permeability data and clearly illustrates the
statistical analyses performed on these data. These figures are presented
as examples of good CQC documentation and statistical analysis.
5.3.4 Documentation
An effective CQA plan depends heavily on recognizing all construction
activities that should be inspected and assigning responsibilities to CQA
and CQC personnel for inspecting each activity. This is most effectively
accomplished by documenting CQA and CQC activities and should be addressed
as the fifth element of the CQA plan. CQC personnel will be reminded of
the factors to be inspected and will note by signing required descriptive
remarks, data sheets, and checklists that the inspection activity has been
accomplished.
5.3.4.1 Daily Recordkeeping—
Standard daily reporting procedures should include preparation of a
summary report with data sheets for supporting observation and testing and,
when appropriate, for problem identification and corrective measures.
5..3.4.1.1 Daily Summary Report—A summary report, or project inspec-
tion diary, should be prepared daily by the CQA officer. This report
provides the chronologic framework for identifying and recording all other
reports. At a minimum, the summary reports should include the following
information (Spigolon and Kelley, 1984):
Unique identifying sheet number for cross-referencing and
document control
Date, project name, location, and other identification
Data on weather conditions
Reports on any meetings held and their results
Unit processes, and locations, of construction underway
during the time frame of the report
5-100
-------
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-------
Equipment and personnel in each unit process, including
subcontractors
Descriptions of areas or units of work (blocks) tested
and/or observed and documented
Description of offsite materials received, including any
quality verification (vendor certification) documentation
Calibrations, or recalibrations, of test equipment, including
actions taken as a result of recalibration
Decisions made regarding approval of units of material or of
work (blocks) and/or corrective actions to be taken in
instances of substandard quality
Unique identifying sheet numbers of observation and testing
data sheets and/or problem reporting and corrective measures
data sheets used to substantiate decisions described in the
preceding item
Signature of the CQC inspector and concurrence by the CQA
officer.
Items above may be formulated into site-specific checklists and data
sheets so that details are not overlooked.
5.3.4.1.2 Observation and Testing Data Sheets—All observations and
field and/or laboratory tests should be recorded on appropriate data sheets.
Required data to be included in a test report (data sheet) for most of the
standardized test methods are included in the pertinent ASSHTO (1983) and
ASTM (1985) standards. Examples of field and/or laboratory test data
sheets are given in U.S. Department of the Army (1970, 1978) manuals and in
Spigolon and Kelley (1984).
Due to their nonspecific nature, no standard format can be given for
data sheets to record observations. Recorded observations may take the
form of notes, charts, sketches, photographs, or any combination of these.
Where possible, a checklist may be useful to ensure that no pertinent
factors of a task-specific observation are overlooked.
Observation and testing data sheets should include at least the follow-
ing information (Spigolon and Kelly, 1984):
Unique identifying sheet number for cross-referencing and
document control
Description or title of the observation/test
Location of the observation/test or location from which the
sample increment was obtained
5-103
-------
Type of observation/test; procedure used (reference to
standard method when appropriate)
Recorded observations or test data, with all necessary
calculations
Results of the observation/test; comparison with specifica-
tion requirements
Personnel involved in the observation/test
Signature of the CQC inspector and concurrence by the CQA
officer.
Items above may be formulated into site-specific checklists and data sheets
so that details are not overlooked.
5.3.4.1.3 Problem Identification and Corrective Measures Data Sheets--
Problem reporting and corrective measures data sheets should be cross-
referenced to specific observation or testing data sheets where the problem
was identified. They should, at a minimum,, include the following informa-
tion:
Unique identifying sheet number for cross-referencing and
document control
Detailed description of the problem
Location of the problem
Probable cause
Method and time frame of locating the problem (reference to
data sheets)
Estimated duration of the problem
Suggested corrective action
Documentation of correction (reference to data sheet)
Final results
Suggested methods to prevent similar problems
Signature of the CQC inspector and concurrence by the CQA
officer.
In some cases, not all of the above information will be available or obtain-
able. However, when available, such efforts to document problems could
help to avoid similar future problems.
5-104
-------
The CQA officer should be made aware of any significant recurring
nonconformances. The CQA officer will then determine the cause of any
problems and recommend appropriate changes to prevent future recurrence.
When this type of evaluation is made, the results should be documented.
Upon receiving the CQA officer's written concurrence, copies of the
report(s) should be sent to the design engineer and the facility owner/
operator for their comments and/or acceptance. These reports should not be
submitted to the permitting agency unless they have been specifically
requested. However, a summary of the data sheets along with final testing
results and inspector certification of the facility may be required by the
permitting agency upon completion of construction.
5.3.4.2 Photographic Reporting Data Sheets--
Photographic reporting data sheets may also prove useful. Such data
sheets should be cross-referenced with observations or testing data sheets
and/or problem identification and corrective measures data sheets. Photo-
graphic reporting data sheets should include the following minimum informa-
tion:
A unique identifying number for cross-referencing and document
control
The date, location, and weather conditions for the photograph
Location and description of the work or work product
Purpose of the photograph
Signature of the photographer and CQC inspector.
These photographs will serve as a pictorial record of work progress, problems,
and mitigation activities. They should be kept in plastic file sheets in
the chronological order in which they were taken. The basic file should
contain color prints; negatives should be stored in a separate file in
chronological order.
A video recording of problem areas and/or conditions and of the com-
pleted installation of each soil component may also prove useful.
5.3.4.3 Block Evaluation Reports--
Each inspection block may have several quality characteristics, or
parameters, that are specified to be observed or tested, each by a different
observation or test, with the observations and/or tests recorded on different
data sheets. At the completion of each block, these data sheets should be
organized into a block evaluation report. These block evaluation reports
may then be used to summarize all of the site construction activities.
Block evaluation reports should be prepared by the CQA officer and, at
a minimum, should include the following information (Spigolon and Kelley,
1984):
5-105
-------
Unique identifying sheet number for cross-referencing and
document control
Description of block (use project coordinate system to
identify areas and appropriate identifiers for other units
of materials or work)
Quality characteristic being evaluated; references to sections
of specifications
Sampling method; how it was established
Sample increment locations (describe by project coordinates
or by a location sketch on the reverse of the sheet)
Tests and/or observations made (define procedure by name or
other identifier; give unique identifying sheet number for
observation test data sheets)
Summary of test data (give block average and, if available,
the standard deviation for each quality characteristic)
Define acceptance criteria (compare block observation/test
data with design specificatin requirements; indicate compli-
ance or noncompliance; in the event of noncompliance, identify
documentation that gives reasons for acceptance without
specification compliance)
Signature of the CQA officer.
•
5.3.4.4 Design Engineer's Acceptance of Completed Components—
All daily inspection summary reports, observation and testing data
sheets, problem identification and corrective measures sheets, and block
evaluation reports should be reviewed by the CQA officer and then submitted
to the design engineer. The reports should be evaluated and analyzed for
internal consistency and for consistency with similar work. Timely submission
of these documents will permit errors, inconsistencies, and other problems
to be detected and corrected as they occur, when corrective measures are
easiest.
The design engineer should assemble and summarize the above information
into a periodic design acceptance report. The reports should indicate that
the materials and workmanship comply with design specifications and permit
requirements. These reports should be included in project records and, if
requested, submitted to the permitting agency.
5.3.4.5 Final Documentation--
At the completion of the project, the facility owner/operator should
submit a final documentation report to the permitting agency. This report
should include all of the design engineer's acceptance reports (i.e.,
periodic summaries of all daily inspection summary reports, observation and
5-106
-------
test data sheets, problem identification and corrective measures data
.sheets, and block evaluation reports), deviations from design and material
specifications (with justfying documentation), and as-built drawings. This
document should be prepared by the CQA officer and included as part of the
CQA plan documentation.
5.3.4.5.1 Responsibility and Authority—The final documentation
should reemphasize that areas of responsibility and lines of authority were
clearly defined, understood, and accepted by all parties involved in the
project. Signatures of the facility owner/operator, design engineer, CQA
officer, CQC inspector, and construction contractor should be included as
confirmation that each party understood and accepted the areas of responsi-
bility and lines of authority and performed their function(s) according to
the CQA plan.
5.3.4.5.2 Relationship to Permitting Agencies—Final documentation
submitted to the permitting agency as part of the CQA plan documentation
does not sanction the CQA plan as a guarantee of facility construction and
performance. Rather, the primary purpose of the final documentation is to
improve confidence in the constructed facility through written evidence
that the CQA plan was implemented as proposed and that the construction
proceeded according to design plans and specifications.
5.3.4.6 Storage of Records—
During the construction of a hazardous waste land disposal facility,
the CQA officer should be responsible for the facility records, including
the originals of all the data sheets, summary reports, and block evaluation
reports; the design engineer's acceptance of completed components reports;
and facility drawings. With the CQA officer in charge of the facility
construction records, any documentation problems should be noted and there-
fore remediated quickly. Once the facility construction is complete, the
document originals should be stored by the owner/operator in a manner that
will allow for easy access. An additional copy should also be kept at the
facility if this is in a different location from the owner/operator's
files. A final copy should be kept by the permitting agency in a publicly
acknowledged repository.
5.4 CLAY LINER DESIGN AND CONSTRUCTION: PROBLEMS AND PREVENTIVE MEASURES
Table 5-11 lists common problems encountered during clay liner design
and construction, their probable causes, and suggested solutions. This
table was compiled from information assembled from a wide variety of sources,
including literature surveys, case studies, and interviews with experts in
the field. This table summarizes information presented in this chapter.
5-107
-------
TABLE 5-11. POTENTIAL CLAY LINER DESIGN AND INSTALLATION PROBLEMS AND PREVENTIVE MEASURES
Problems
Cause
Preventive measures
Sidewall slump and collapse
Improper characterization
of soil strength profile
that results in improper
sidewall design.
High inward hydraulic
pressure on sidewalls
(sites below water table).
Bottom heave or rupture
Accumulation of water in
landfill during construction
High inward hydraulic
pressure on bottom
(sites below water table).
Rainfall
Seepage into site
(sites below water table)
Drying and cracking of clay
liner, greatly increasing
permeability
Desiccation
Properly characterize subsurface condi-
tions.
Design a more gentle sidewall slope
(depending on shear strength
of foundation soil).
Reduce hydraulic head by:
— Installing slurry wall around site
perimeter to cut off groundwater.
— Trenching and pumping around site
to cut off groundwater.
~ Pumping from wells to lower local
groundwater table.
Control depth of excavation to
lower head potential.
Reduce hydraulic head by slurry
wall, pumping, or other technique.
Fill landfill before heaving occurs.
Cover site with inflatable dome (re-
duces leachate treatment requirements
for continuous operation facilities).
Seal roll liner at end of construc-
tion day to ensure proper runoff of
precipitation into sump.
Reduce hydraulic head in surrounding soil.
For all infiltration:
— Operate leachate collection
system to remove water.
— Design leachate collection system
or detection system (between liners)
to handle extra water input.
Do not construct during extremely
hot, dry periods.
Wet down liner during dry periods.
Cover liner with plastic sheet or
soil layer if liner construction is
interrupted.
Do not leave liner exposed prior to
waste emplacement or leachate collection
system installation.
(continued)
5-108
-------
TABLE 5-11 (continued)
Problems
Cause
Preventive measures
Loss in liner density
(increased permeability)
Reduction in clay workability
Erosion of upper liner after
construction
(liquid impoundments)
Visible partings between
liner lifts and increased
permeability parallel to
lifts
Pockets of high-permeability
material (e.g., sand and
gravel) in liner material
Leakage around designed
liner penetrations
Leachate collection
system clogging
Leachate collection system
damage during waste
emplacement
Areas of high permeability
Freeze/thaw
Low temperatures
Wave erosion
Liner lifts not properly
tied together
Heterogeneous clay liner
material
Improper sealing around
penetrating objects
Sediment entering into
systems
Inadequate management
of personnel
Substandard compaction
Do not construct during winter in
cold climates
Cover liner with soil blanket or other
insulation material when cold weather is
anticipated.
Increase compactive effort.
Cease construction till spring.
Place rip-rap on lagoon sidewalls
extending from below liquid level into
the freeboard area.
Scarify or disk lower lift prior to
installing next lift.
Ensure moisture content of last lift
and lift being installed are the same.
Closely inspect liner material at
borrow site or as it is being
installed and reject coarse-grained
material.
Avoid liner penetrations in design.
Seal properly around penetrating objects.
Cover system with geotextile or
graded soil layer.
Initiate personnel training program.
Cover system with geotextile or soil
cover prior to waste management.
Design system to minimize protrusions
(manholes, etc.) in waste emplacement
areas.
Conduct proper CQA and CQC, including:
- Monitoring for material variability
- Observation of compaction operations
- Moisture/density/permeability tests.
5-109
-------
5.5 REFERENCES
AASHTO: The American Association of State Highway and Transportation
Officials. 1978. Standard Specifications for Transportation Materials
and Methods of Sampling and Testing, Part 2, Methods of Sampling and
Testing, 12th edition. Washington, D.C.
Anderson, D. 1982. Inplace Closure of Hazardous Waste Surface Impoundments
(draft), Chapter 5--Evaluating Stabilized Waste Residuals. EPA-68-83-
2943.
API. 1982. American Petroleum Institute. API Recommended Practice:
Standard Procedure for Testing Drilling Fluids. API RP13B. American
Petroleum Institute, Dallas, Texas.
ASTM. 1985. The American Society for Testing and Materials. 1985 Annual
Book of ASTM Standards, Volume 4.08, Soil and Rock; Building Stones.
Philadelphia, Pennsylvania.
Bernreuter, D. L., and D. H. Chung. 1984. Earthquake Hazard Analysis for
Nuclear Power Plants, Energy and Technology Review, Lawrence Livermore
National Laboratory, Livermore, California.
Bishop, A. W. 1955. The Use of the Slip Circle in the Stability Analysis
of Slopes. Geotechnique. 5(1):1-17.
Bishop, A. W., and N. R. Morgenstern. 1960. Stability, Coefficients for
Earth Slopes. Geotechnique. 10(4):129-150.
Boutwell, G. P., Jr., R. B. Adams, and D. A. Brown. 1980. Hazardous Waste
Disposal in Louisiana. Geotechnical Aspects of Waste Disposal.
American Society of Chemical Engineers, A Two-Day Seminar.
Boutwell, G. P., Jr., and V. R. Donald. 1982. Compacted Clay Liners for
Industrial Waste Disposal. American Society of Civil Engineers,
National Meeting, Las Vegas, Nevada.
Cashman, P. M., and E. T. Haws. 1970. Control of Groundwater by Water
Lowering. Chapter 3 in: Ground Engineering, Institution of Civil
Engineers, London.
Cichowicz, N. L., R. W. Pease, Jr., P. J. Stoller, and H. J. Yaffe. 1981.
Use of Remote Sensing Techniques in a Systematic Investigation of an
Uncontrolled Hazardous Waste Site. EPA 600/2-81-187, U.S. Environmen-
tal Protection Agency, Cincinnati, Ohio.
Daniel, D. E. 1981. Problems in Predicting the Permeability of Compacted
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CHAPTER 6
FAILURE MECHANISMS
This chapter discusses failure mechanisms that can affect performance
of clay liners at waste disposal facilities. The failure mechanisms described
include:
Desiccation cracking
Slope instability
Settlement
Piping
Penetration
Erosion
Freeze/thaw cycling
Earthquakes
Scouring
Design or construction errors.
When available, laboratory and field studies of these failure mechanisms
are presented along with actual site data. Special design considerations
that may help to control these types of failure mechanisms are discussed in
Section 5.1.3.4 of this document.
6.1 DESICCATION CRACKING
6.1.1 Description
Cracking, a characteristic of clay-rich soils, results from volume
changes in the clay structure or from stresses imparted to the soil mass.
Desiccation cracks result from wet/dry cycling, which can disrupt the
cohesive structure of the clay. Syneresis cracks result from a chemical
reaction that causes shrinkage and dewatering of the colloidal clay material
due to aggregation of particles by physicochemical attraction. Clay minerals
that expand in water can undergo expansion or shrinkage caused by (1) replace-
ment or removal of water by other solvents, (2) cation exchange, or (3) in-
creasing ionic strength at the clay/liquid interface (Griffin et al.,
1984). The amount of volume change depends upon the clay mineral type, the
arrangement of the clay particles, the size and surface area of the clay
particles, and the kind and proportion of cations adsorbed on the clay
(Brown and Anderson, 1980). Stress cracks result from stress applied to
clay soils through seismic activity, subsidence, or human action (e.g.,
compaction).
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The phenomenon of crack formation is closely related to clay mineralogy.
Certain clay minerals are much more prone to shrinking and crack formation.
Montmorillonite (bentonite) clay is the most notorious for shrinking and
cracking, and soil engineers in the Great Plains and Gulf States continually
face problems with these clay soils in road construction and building
foundations (Lutton et al., 1979). For example, montmorillonite can have a
200-percent difference in volume between the hydrated and dehydrated state.
When water is removed the clay undergoes three-dimensional shrinkage and,
when the water removal rate is not uniform, cracks form in the wetter
portion. Disruption of clay barriers also may occur during swelling or
uptake of water. A barrier that has swelled and heaved may lose its inte-
grity upon heaving or it may shrink or crack later when the water is removed
(Brown and Anderson, 1980).
Volume changes also may occur by chemical desiccation when interlayer
water is extracted or displaced by an organic fluid. Extraction or displace-
ment of water changes the interlayer spacing, which may result in a volume
change. If the fluid lacks a large dipole moment or cannot form a hydrogen
bond, interlayer spacing may decrease since fewer layers of organic molecules
are retained. If the intruding fluid has a higher affinity than water for
the clay's surface, interlayer spacing may decrease greatly since some of
the more tightly bound water is removed.
6.1.2 Studies of Cracking
Chemical desiccation (i.e., the extraction or displacement of interlayer
water by chemical species) is discussed in detail in Chapter 4. This
section discusses studies of cracking from wet/dry cycling (thermal desicca-
tion) in sites where the cracking phenomenon has been observed.
Hawkins and Norton (1967) investigated the necessary soil cover and
optimum thickness to protect a bentonite layer that had been placed as a
protective cover for buried radioactive waste. The bentonite layers pro-
tected (covered) by 2 feet of soil did not crack. Layers protected by less
topsoil formed cracks that were resealed by swelling, but some of the
overlying soil became entrapped in the cracks. After various shrink/swell
cycles, it is possible that permeable channels may develop through a ben-
tonite layer. Kays (1977) also noted that desiccation cracks in reservoir
linings made of bentonite may not reseal entirely upon rewetting.
Roll in and Dylla (1970) investigated the effectiveness of bentonite
seals for water retention in the arid West. One seal was constructed as a
3-inch layer (12.5 percent bentonite in sand) covered with 6 inches of
earth. A second seal was a pure layer of bentonite 0.5 inch thick covered
with 6 inches of earth. The seals were exposed to a series of wet/dry
cycles over 6 years. The seals retained their initial effectiveness during
the first 3 years, but their effectiveness decreased by roughly 10 percent
per year for the last 3 years of the study. Roll in and Dylla estimate a
seal life under extreme conditions of 8 to 12 years; however, they do not
indicate the percentage loss of effectiveness they assume will terminate
the life of the seal. Note that the burial depth was 6 inches, which is
inadequate based on the previously cited study.
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Drying tests were performed on a polymer-treated bentonite, Void ay
SLS , by its manufacturer (Hughes, 1975). The bentonite was packed into a
fixed-wall permeameter and covered with several inches of soil. The perme-
ability to leachate (composition unknown) was found to be 1.5 * 10 cm/s.
The material was then subjected to drying cycles with surface temperatures
of 150 °F (in the cover soil) for 1 month and again exposed to leachate.
After a drying cycle, cracks extended 0.25 to 1 inch into the cover soil.
The permeability after three drying cycles was 1.0 x 10 cm/s, which was
essentially the same as the start of the experiment.
Permeabilities were measured after the leachate had contacted the
dried-out soil cover for 4 hours to allow the soil time to absorb water to
compensate for the natural moisture loss. The manufacturer claimed that it
was not visually obvious that the leachate had penetrated the seal. However,
it may have been more meaningful to start measuring the permeability when
the leachate was introduced because the critical period in the field occurs
when the cracks are still open (Pertusa, 1980).
Desiccation cracks were observed in the cover system of the West
Valley, New York, disposal site for low-level radioactive waste (Prudic and
Randall, 1979). These cracks propagated downward, and subsidence cracks
were found that propagated upward. The cracks increased the cover permea-
bility and resulted in the overflow of leachate, or the "bathtub" effect.
Climate records were examined, revealing that crack formation correlated
with the two driest periods at the site.
Daniel (1983) analyzed data on several leaking clay liners in Texas.
He concluded that desiccation of the clay liner between completion of
construction and commencement of operations allows the clay to become
severely cracked and results in higher permeabilities. Daniel (1983) also
concluded that higher permeabilities may result from nonuniform moisture
distribution in the clay, resulting in clods with wet surfaces and dry,
cracked interiors. This problem is caused in part by (1) inadequate breakup
of large clods during compaction, (2) uneven distribution of water by large
water trucks, and (3) inadequate time for water to penetrate the soil.
A case study of a failed liner system caused by thermal desiccation
(case study I) is presented in Chapter 7 of this document. A summary of
this case study is presented below.
Problems that occurred at site I resulted from desiccation cracks in
the facility's clay liner. Liner construction was completed in the fall of
1980; however, it was left unprotected and unfilled until late the follow-
ing spring. During this time, desiccation cracks formed in the liner,
increasing its permeability. When the pond was finally filled, waste
migration into the leak detection system occurred.
6-3
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6.2 SLOPE INSTABILITY
Some landfills and impoundments are constructed above or partially
above ground with retaining walls to prevent the lateral spread of poten-
tially harmful wastes. Failure of the sidewall liner may release contami-
nants directly into the environment or allow contaminant movement into
surrounding zones of permeable soil.
6.2.1 Description
The soil in a sloping liner has an internal shear stress. If site
configuration is such that the overburden forces due to gravity become too
large compared to the shear strength of the liner, the slope is no longer
stable and a slide occurs. The site configuration and the shear strength
of the soil are the key for determining the safety factor for design of
stable slopes.
6.2.2 Discussion of Slope Instability
The mechanisms involved in slope instability and slides vary greatly
with soil type and strength. Only a few of the more important mechanisms
for slides are discussed here. For example, shallow slides involve only
the upper few feet of the slope and can occur when flakes are pushed out by
water or bonding is weak between two soil types. Local slides occur when
the shear strength is insufficient for a limited part of the site. Local
slides usually do not spread and can be avoided with use of a slightly
flatter slope. Large slides include several different phenomena where a
whole valley or parts of it are involved and are usually considered natural
disasters. Failure of a clay liner sidewall can occur as slippage of the
whole compacted layer over the undisturbed soil or bedrock. Another mechanism
is the creep of very cohesive saturated clays; by this mechanism, tension
can be generated in a sidewall slope and cracks perpendicular to the slope
can enhance failure. Waste consolidation can uncover sidewall slopes,
relieve lateral pressures, and create an unstable condition (U.S. EPA,
1980). For sites with an earth barrier over a synthetic membrane, a slide
may develop if the clay slips over the membrane's smooth surface.
The probability of a local slide is greatest during construction if
the excavation is deep and the sidewall slopes are not designed properly.
Compaction of the liner on the sides can be difficult and may be insufficient.
If the soil in the sidewall slope is saturated, the compacted layer may
slide. Once the waste is put in place, the slope stability may improve and
the possibility of shallow slides decrease.
If the landfill is large and placed on a slope, loading of the landfill
can increase the weight considerably, which might be a major factor in
triggering a large slide. However, waste placed at the foot of the slope
increases the stability of that slope once the fill is completed.
Changes in soil moisture conditions also must be considered. For
example, frozen soils thaw from the top, and thaw water trapped over frozen
6-4
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soil may form a shallow, saturated zone that is susceptible to sliding.
Similarly, experience indicates that shallow sliding sometimes occurs in
clay embankments after heavy rainfall. This instability presumably results
from rapid saturation of a shallow zone previously made porous and weak by
formation of drying cracks (Lutton et al., 1979). Compaction is necessary
because it reduces porosity and increases shear resistance by increasing
the interlocking of soil grains.
When landfills or impoundments are sited below the water table, sidewall
slope failure can result from inward hydraulic pressure on the liner. This
is a problem only during construction and early operation; once the landfill
or impoundment is filled with waste, outward pressure from the waste balances
the inward hydraulic pressure.
6.3 SETTLEMENT
6.3.1 Description
Differential settlement of the bottom liner may lead to cracks, increas-
ing the volume of leachate escaping the site. However, the problem should
be minor if the liner is compacted, sufficiently thick, and placed on a
uniform foundation. The subsoil will show some settlement, but no adverse
impacts are expected if the settlement is uniformly distributed and moderate.
If the subsoil settlement is large, tension cracks in the side slope of the
liner can result.
Extreme subsidence leading to a catastrophic collapse of landfill or
lagoon liner can occur through sinkhole formation in areas underlain by
Karst geology. The only way to control this type of failure is to avoid
siting facilities in regions of Karst terrain.
6.3.2 Studies of Settlement
A study was also made at the West Valley, New York, site that was used
in the 1960's for disposal of low-level radioactive waste similar to that
described for the Sheffield site (Prudic and Randall, 1980). The cover
material consisted of approximately 10 feet of glacial till that was composed
of 35 percent silt, 35 percent clay, and about 30 percent sand and stone.
This material was covered with 1 foot of topsoil and then vegetated.
Problems developed in the 1970's with the formation of cracks and a
rise in the water level in the trenches ("bathtub" effect). The study
identified two major causes of the cracks: (1) subsidence of the waste
causing cracks that propagated upward and (2) desiccation cracks that
propagated downward (Prudic and Randall, 1980). The usual disposal practice
for low-level radioactive waste sites is not to compact or cover the wastes
each day to avoid contaminating equipment and personnel. This practice was
followed at the West Valley site (Kelleher and Michael, 1973).
Buelt and Barnes (1981) performed a laboratory study of the effect of
subsidence on several liner materials that were candidates for lining waste
piles containing uranium mill tailings. The soil liners consisted of soil
6-5
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with ID percent clay in the form of sodium bentonite, Saline Seal
GSR-60 (American Colloid Company). The liners were compacted in'
100 , and
into a
cylinder, sand was placed on top to simulate the tailings, and a water-
filled bladder was placed under the liner to simulate subsidence. Accele-
rated aging was carried out by passing several pore volumes of high-calcium
leachate through the liner to accelerate the ion exchange rate of calcium
and sodium. After 50 days, a subsidence of 3.5 percent was induced by
emptying the bladder.
The soils with Saline Seal 100® and GSR-60® had high initial permeabil-
ities (10 to 10 cm/s) because (1) they were not wetted prior to compac-
tion, (2) their granular nature inhibited mixing into the smaller pores of
the soil, and (3) the subsidence bladder made it difficult to obtain the
desired compaction.
The permeability of the Saline Seal 100 liner decreased from its
originally high value and reached a plateau of 6 x 10 cm/s until the
subsidence test. When subsidence was induced, permeability increased as
the liner was disrupted. The permeability then slowly decreased, indi-
cating that this liner exhibits some self-healing characteristics.
The permeability of the GSR-60® liner remained constant at 3 x 10 cm/s
until subsidence was induced and then increased significantly. Again, the
clay demonstrated a tendency to seal the liner following a disruptive
incident by permeability reductions following the subsidence test.
The permeability of the sodium bentonite liner increased initially and
then decreased to about 10 cm/s. The increase may indicate Na-Ca ion
exchange early in the test. The permeability of this liner did not increase
when subsidence was induced. The authors observed that the sodium bentonite
was better distributed in the soil because of its small particle size and
thus produced a more stable liner. The sodium bentonite liner was judged
to be the most effective of the clay liners in this laboratory test. These
results may or may not be indicative of liner performance in a field environ-
ment.
6.4 PIPING
6.4.1 Description
Piping is a form of internal soil erosion that occurs below the ground
surface. Fine-grained soils such as clay contain small particles (1 to 2
microns in diameter) that are bound together within the soil matrix. As
water seeps through the soil matrix, some of the fine clay particles can be
detached from the soil matrix and can migrate into a coarser, more porous
layer below the clay. As smaller particles erode, resistance to flow
decreases and progressively larger particles can be removed from the soil
matrix. As these particles are removed, the internal erosion increases and
tends to form an underground flow channel or "pipe" that moves upstream;
i.e., the "pipes" progress and grow larger in the opposite direction of the
6-6
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seepage flow (Bowles, 1979). For a clay barrier with downward infiltration,
this means that the "pipes" initiate on the underside of the liner and
progress upward. Piping can be caused by excessive seepage into the clay
or by chemical dissolution of the clay by a reactive fluid.
6.4.2 Studies of Piping
A literature review on piping was performed by Brown and Anderson
(1980) and is summarized here to provide insight into the piping mechanism
and its effects.
Soil grains are dislodged and eroded away when the hydraulic gradient
at the exit of a percolating soil mass is large enough to overcome the
forces of interparticle bonding. Piping is more likely for soils with low
structural stability or dispersive soils where the soil-colloid bond strengths
are low compared to the energy of the water flowing through the soil. Some
of the other factors that affect piping include exchangeable sodium percentage,
soil cracks, low permeability, hydraulic gradients, chemical composition of
the eroding water, and water content at compaction (Brown and Anderson,
1980).
The early stages of piping are associated with vertical contrasts in
the structure and permeability of soils and with shifts in soil pore size
distribution toward macropores (Brown and Anderson, 1980). Piping is also
accelerated by the dissolution of the clay pore walls, and eventually the
matrix between pores, by a reactive fluid. Clays, which contain large
quantities of silica and alumina, are susceptible to dissolution by both
acids and bases. Acids solubilize alumina, iron, alkali metals, and alkaline
earths, while bases solubilize silica (Brown and Anderson, 1980).
Effects of piping have been observed on dams, where seepage of reservoir
waters has caused dispersive piping and eventual channeling all the way
through these earth structures. Although piping failures have occurred in
earthen dams, the dams often are exposed to very high hydraulic gradients
that are not expected in a properly constructed and operated disposal
facility. Failure usually occurs through collapse of the pipe roof, which
rapidly erodes as a result of the high water velocity. This mode of failure
may conceal the fact that piping was the real cause of the disaster (Bowles,
1979). Channeling occurred in soils with a local permeability of 1 x 10 5 cm/s.
Differential solution and subsequent leaching, especially with sediments
containing calcium carbonate, resulted in formation of channels, pot holes,
and cavities (Mitchell, 1976). In this respect, dissolution seems to be in
some circumstances a precondition for piping.
Cedergren (1977) reported that differential leaching of limestone,
gypsum, and other water-soluble mineral components can lead to development
of solution channels that get larger with time and substantially increase
permeability. He warned against underestimating the importance of minor
soil and geologic details on the permeability of soil formations because
they cause the majority of failures in dams, reservoirs, and other hydraulic
structures. Cedergren (1977) concluded that most failures caused by excess-
ive water seepage can be placed in two categories:
6-7
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Those that are caused by soil particles migrating to an
escape exit, causing piping and erosional failures
Those caused by uncontrolled seepage patterns that lead to
saturation, internal flooding, and excessive seepage.
In a study of the variables affecting piping, Landau and Altschaeffl
(1977) noted a strong interaction between the chemical composition of the
eroding water and compaction water content. Ion concentration seemed to
have little effect on soil piping susceptibility for mixed illitic and
kaolinitic clay loam compacted dry of optimum. Optimum refers to the water
content at maximum density as determined in the Proctor Density Test (see
Chapter 3). For the same soil compacted wet of optimum, soil piping suscept-
ibility was highly related to ion concentration in the eroding water. When
low-ion-concentration eroding water is combined with wet-of-optimum compac-
tion, Landau and Altshaeffl (1977) reported low resistance to internal
erosion. These results indicate that an evaluation of leachate/liner
interactions for liners compacted wet of optimum may be useful to predict
resistance to piping.
Some piping involves the slaking of soil particles. Slaking is defined
as the disintegration of unconfined soil samples when submerged in a fluid.
Moriwaki and Mitchell (1977) investigated the dispersive slaking of sodium-
and calcium-saturated kaolinite, illite, and montmorillonite. All the
clays slaked by dispersion when saturated with sodium, with the process
proceeding faster with sodium-kaolinite and sodium-illite. Sodium-illite
swelled slightly, while dispersion of sodium-montmorillonite was preceded
by extensive swelling. Sodium-kaolinite underwent no visible swelling
while dispersing. For the calcium-saturated clays, illite dispersed much
more slowly, while the dispersion rate increased for kaolinite and montmoril-
lonite. Calcium-kaolinite was thought to disperse faster because of its
higher permeability relative to sodium-kaolinite. Sodium-montmorillonite
was thought to disperse slowly because the large degree of swelling it
underwent would lower permeability, thus slowing water entry and retarding
dispersion.
Compaction decreases the electrolyte content of expelled interlayer
water (Rosenbaum, 1976). Such a lowering of fluid electrolyte concentrations
in sodium-saturated clays may cause substantial swelling and dispersion
(Hardcastle and Mitchell, 1974). This dispersion causes particle migrations.
If the fluid-conducting pores are large enough to transport these dispersed
clay particles, permeability increases and soil piping may result (Aitchison
and Wood, 1965).
Piping initiates on the underside of a clay liner, where clay particles
can migrate into a substrata with larger pore diameters. The soil pipe
then progresses upward through the clay liner until it finds an opening
into the waste impoundment. Clay particles have been shown to migrate
through porous media containing less than 15 percent clay (Hardcastle and
Mitchell, 1974). Consequently, clay liners underlain by soils containing
less than 15 percent clay may be susceptible to soil piping.
6-8
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6.5 PENETRATION
6.5.1 Description
Penetration of an earth barrier may result from operating equipment on
the barrier, burrowing animals, root penetration, or vandalism. Once waste
has been placed on the clay liner, the potential for damage due to one of
these mechanisms is reduced. Designed penetrations such as manholes and
leachate collection or detection system pipes, which are common at clay-
lined hazardous waste disposal facilities, provide another mechanism for
failure. Lack of adequate compaction or sealing around such penetrations
may provide a pathway for leachate migration. Improper operation of mechanical
equipment during waste placement operations may displace penetrating pipes,
which in turn may damage the clay liner.
In arid regions, the danger of root penetration appears to pose more
of a problem than does penetration by burrowing animals. Mammals in an
arid region generally do not burrow more than 2 to 3 feet, with 5 feet
being an overall maximum depth. Spade foot toads may penetrate to a depth
of 6 feet. Root penetration for mesquite and tamarisk, which typically are
found in arid regions, may range from 30 to 50 feet in alluvial soil to 2
to 3 feet on a rocky slope (Pertusa, 1980).
In rolled-earth dams, animals have created passageways for water to
penetrate, which has damaged structural integrity. Similar damage can be
expected in waste disposal facilities, where such holes may increase water
percolation (Lutton et a!., 1979).
6.5.2 Studies of Penetration
Rodents are a problem at some sites, particularly for municipal solid
waste, and are best controlled by professionals (Noble, 1976). An extermi-
nation program is most effective when coupled with measures to eliminate
sources of shelter and food.
A double-lined aeration lagoon recently was subjected to a hurricane.
The winds from the storm caused the areator, which penetrated the clay
liner, to sway. This movement resulted in the failure of the clay liner
surrounding the penetration. This failure was confirmed when liquid from
the pond was discovered in the leak detection system.
6.6 EROSION
6.6.1 Description
When raindrops strike bare soil at a high velocity, they shatter soil
granules and clods and detach particles. Sheet erosion follows where
detached soil particles are transported uniformly downslope. Rill erosion
develops in channels only inches in depth when soil particles are detached
by concentrated flow and by slumping of undercut sidewalls. The capability
of runoff to detach soil increases approximately as the square of the shear
6-9
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stress. Consequently, rill erosion increases with increasing slope and
channel length, while sheet erosion continues more uniformly between the
rills; relative contributions to total soil loss differ with soil and
surface conditions (Lutton et al., 1979).
6.7 COLD CLIMATE OPERATIONS (FREEZE/THAW CYCLING)
In Alaska, the northern tier of States, and in the mountainous regions,
daily mean air temperatures fall below freezing frequently for days or even
weeks during the winter. The extreme depth of frost penetration ranges
from 0 to 6 inches in the southern United States to 60 to 70 inches in the
northern United States. Average depths of frost penetration range from 0
to 3 inches to 20 to 60 inches for the same regions (Jones et al., 1982).
When air temperatures are below freezing, frost penetrates the ground
surface, causing the upward migration of soil moisture. When this moisture
contacts the frostline, ice may form. Various theories explain this phenomenon
by means of capillary flow, suction force, thermodynamics, or vapor transfer
(Young and Warkentin, 1966; Jumikis, 1962). The freezing effects upon soil
mainly depend on the soil's chemical and physical properties and moisture
conditions as well as on the freezing rate.
Two types of freezing phenomena occur in soils. Closed-system freezing
in a soil occurs when no source of water is available, beyond that originally
present in the soil voids, during the freezing process. This type of
freezing usually results in very thin or nonexistent ice lenses. Open-system
freezing, on the other hand, occurs when water in addition to the original
soil pore water is available close to the freezing zone. In this case, ice
lenses are formed in certain types of soils and heaving of the ground
surface occurs. Closed-system freezing has been considered less important
than open-system freezing because it generally does not result in frost
heave. However, closed-system freezing has important effects on some soil
liners for canals and reservoirs and on earth embankment dams (Jones,
1981).
Chamberlain and Gow (1978) studied the effects of freeze/thaw on the
permeability of four fine-grained soils. Freezing and thawing cause signif-
icant structural changes in consolidated clay slurries, which in turn cause
large increases in vertical permeability. The increase was greatest for
the soil with the largest plasticity index and, in general, the increase
was smaller at the highest applied stress levels. For soils where clay
particles predominate, the increased permeability occurs as a result of the
formation of vertical shrinkage cracks.
Wang and Roderick (1971) studied the freezing behavior of three different
samples of compacted, fine-grained soils during closed- and open-system
freezing. The soil samples ranged from 100 percent silt to a mixture of
33 percent silt, 57 percent clay, and 10 percent sand. The plasticity
indexes ranged from 4 for the former to 21 for the latter soil sample.
Other test variables included dry density and degree of saturation. Test
results indicated that frost heave for the closed-system samples was much
6-10
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less than for the open-system samples partially because ice lenses in the
open-system samples were much larger than in the closed-system samples.
The effect of closed-system freezing on canal and reservoir liners and
earth embankments was studied in both the field and laboratory by Jones
(1981). This study produced the following conclusions:
In compacted fine-grained soil susceptible to frost action,
closed-system freezing progresses inward from the soil
surface at a slow to moderate rate. Either in a laboratory
test specimen or in a field structure, the following takes
place: (1) moisture in the soil voids migrates toward the
cold surface, (2) soil density near the surface decreases,
(3) density in a zone at some depth in the soil increases,
(4) thin ice lenses may or may not form, and (5) under
certain soil and freezing conditions overall shrinkage of
the soil may occur.
For some compacted soils in canal linings, an increase in
density at depth, as well as a decrease near the surface of
the lining, can be attributed to closed-system freezing.
The closed-system type of freezing that occurs below the
surface of an earth embankment when construction is halted
by cold weather may significantly affect soil moisture and
density. This will require the removal and/or recompaction
of the upper zone of soil that has a density below the
specification limits.
The depth to which frost penetrates in soil with resulting
frost action is determined mainly by cumulative, below-freezing
temperatures; degree of shading; snow or other surface
cover; and thermal properties of the soil. Frost penetrates
deeper in soil with significant amounts of gravel because
the thermal conductivity of gravel is higher than that of
finer soil.
Because of the higher thermal conductivity of solid bedrock
compared to soil, it is possible that closed-system freezing
could occur in compacted embankment soil in contact with a
bedrock abutment at depths below those in the embankment and
to some distance from the abutment. This could cause a zone
of soil with higher moisture content and lower density near
the abutment contact that, if not corrected, might produce a
condition conducive to piping of the soil.
A loose soil cover effectively reduces frost action in a
compacted embankment.
6-11
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In certain soil and climatic conditions, closed-system
freezing can cause soil shrinkage and the formation of
cracks that might be detrimental to soil barriers for retain-
ing water.
Other winter problems at landfills may include frozen waste, snow
interference, frozen cover soil, and slope sliding. Frozen wastes are
difficult to distribute and compact, and subsequent thawing of frozen waste
may have an indirect, disruptive effect on the cover soil. Snow interference
may result in snow and ice being incorporated into the cover soil and
waste. Allowance should be made for this additional moisture in the disposal
facility. Unfrozen cover soil may be difficult to supply during severely
cold weather, so the cover may not be compacted to the extent desired by
the design. Frozen ground conditions may be detrimental to the stability
of landfill slopes during thawing. A layer of saturated soil with little
or no strength may develop to a depth of a few feet over a frozen base.
Such a development can create an unstable zone that may slide easily.
6.8 EARTHQUAKES
Except in California, current technology for the design and construc-
tion of waste disposal facilities has not addressed methods for increasing
the resistance to failure from earthquakes. In the eastern United States,
earthquakes, although much less frequent than in the western States (partic-
ularly California), are potentially damaging to a much larger area. This
is because the subsurface conditions in the East result in propagation of
ground motion over a much wider area. The location of past destruction
earthquakes in the United States is illustrated in Figure 6-1. In Figure 6-2
areas of comparable damage are compared for the 1811 New Madrid, Missouri,
earthquake and the 1906 San Francisco earthquake. Although the New Madrid
earthquake was lower in magnitude, it resulted in damage to a much larger
area of the country than the San Francisco event, because of differences in
subsurface geology in the two areas.
The probability of failure from earthquakes is relatively low in most
areas of the country and has received a low priority in design considera-
tions. However, a methodology exists for designing earthworks to withstand
earthquake-induced ground motion. This methodology originally was developed
for dams and public works projects in California. The Nuclear Regulatory
Commission (NRC) has considered seismic-resistant design for their low-level
radioactive waste facilities. Chapter 5 of this document further discusses
designing a facility for ground acceleration.
Three major earthquake-induced failure mechanisms exist for clay-lined
hazardous waste facilities. These are:
Rupture along faults
Soil instability (e.g., liquefaction, soil failure, and
large settlements)
Deformation.
6-12
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Of these, the latter two are much more important than rupture; only facil-
ities on faults experience rupture, whereas ground shaking, which can cause
soil instability and deformation, can affect a large number of facilities
in the region where the earthquake occurs (Chung and Bernreuter, 1984). In
addition, earthquakes are not always manifested by surface faulting.
Soil instability is a potentially serious failure mechanism. If a
facility is diked above ground, failure of these dikes due to liquefaction
can produce a catastrophic failure of the retaining wall and a large-scale
release of waste into the environment (especially for surface impoundments).
Large settlements, induced by ground motion under the facility, also can be
serious. If the settlement is great enough, the liner can rupture.
Deformation results from a facility response to ground movement.
Ground motion can distort the configuration of the facility. Although
deformation is not likely to cause slope failure or liner breachment,
damage to the leachate collection system or leak detection system can occur
through the bending and rupturing of collection pipes and collection risers.
A facility also may be damaged indirectly by earthquake failure in
nearby structures or geologic formations. For instance, a landfill or
surface impoundment may successfully withstand ground acceleration without
damage, only to be damaged by a nearby structure or slope that fails.
Evaluation of seismic hazards at a site must therefore include all structures
and geological features that could fail and damage the facility in question.
The degree of damage to a facility from an earthquake depends upon how
well the facility was designed to resist ground acceleration and how much
ground acceleration occurs at the site. Potential damage from ground
acceleration at a site is not necessarily reduced with distance from the
epicenter of the earthquake even though acceleration and amplitude are
higher closer to the fault. The response frequency of the structure is
critical; ground vibrations will have their greatest effect on structures
that vibrate harmonically in response to the vibrational frequency. Earth-
works are more sensitive to low-frequency vibrations than to high-frequency
vibrations. Because high-frequency vibrations occur in the near field
(close to the earthquake center) and low-frequency vibrations occur in the
far field, damage from seismic activity may be greater for facilities
farther from the active fault than for facilities sited nearby.
Delineation between near- and far-field effects from seismic events,
as well as the general propagation of seismic energy away from the source,
depends upon:
Source geometry (geology and structure)
Earthquake intensity
Destructive interference or magnification of seismic waves
by the medium of transportation (the geologic environment).
6-14
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The site geology is the critical factor influencing the potential impact of
a seismic event on a facility. Seismic energies can be dampened or magnified
and focused by different subsurface geological structures.
On May 2, 1983, a 6.5-magnitude earthquake occurred in Coalinga,
California, with its epicenter approximately 5.5 miles to the southeast of
a hazardous waste facility. Several hazardous waste surface impoundments
were in operation at the facility at the time of the quake. Following the
quake, the facility was inspected by an engineer for a report to the State
of California Regional Water Quality Control Board. The following is an
exerpt from his report:
Although the facility suffered no significant damage, subtle
evidences of strong ground shaking were observed across the site.
A distinctive sign of severe ground shaking was the disruption of
a thin surface veneer of dried soil. The drying of surface soil
moisture from recent rains has resulted in the formation of an
approximately 1/4-inch soil crust in many drainage swales.
During seismic shaking, this crust had been "shattered" and
underlying soil powder [has] been forced up through tiny cracks
forming a distinctive soil pattern.
Other observations of ground shaking included slumping of the
surface of small stockpiles of sand, movement of loose soil clods
on cut slopes, and small cracks in the surface layer of truck
compacted roadways. Several soil slumps were observed along
erosion cuts in an unused soil berm in the area of [a] future
pond. This berm has no function in site design or operation.
Wave action in containment ponds due to ground shaking was docu-
mented by a fresh oily residue approximately 6 to 8 inches above
the static fluid level. Severe ground shaking also resulted in
the displacement of two small gasoline storage tanks from their
elevated mounting stands.
Despite these signs of significant ground shaking, all perimeter
waste containment and drainage control facilities were found free
of any evidence of damage or signs of slope instability. All
structures were carefully examined for the presence of tension
cracks, soil sluffing, or unusual soil moisture or seeps. A
system was immediately installed to monitor any unusual fluctua-
tions of fluid levels in waste ponds and downgradient monitoring
wells.
The only observation of seismic impacts on waste impoundments was
confined to the presence of tension cracks in (1) perimeter
embankments of two interior oil recovery ponds that had been
scheduled for reconstruction, and (2) an internal levee between
[two] ponds. Both facilities located behind perimeter drainage
control structures were immediately taken out of service and the
fluids pumped to other containment areas.
6-15
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No significant damage was noted to any on- or off-site access
roads and the site remained accessible throughout the period
following the earthquake.
Another site, a landfill 5 miles from the quake, showed extensive
cracking of embankments and fill material. Portions of the tops of an
embankment slope had been displaced about I foot. However, no release of
material resulted from this damage.
At two other sites, 25 and 100 miles from the epicenter, no signs of
damage or shifting were observed during similar inspections.
6.9 SCOURING
Scouring is the erosion of the liner or sidewalls of a containment
structure by the force of moving water. As a failure mechanism, scouring
is of concern for surface impoundments, such as wastewater treatment lagoons,
which use mechanical aerators as part of the water treatment process.
Scouring can also occur due to wave erosion on the sides of a lagoon due to
wind or from improper waste placement techniques. Scouring can cause
failure of the liner with subsequent soil contamination and perhaps ground-
water contamination.
Covering susceptible areas in the impoundment with gravel or rock
(rip-rap) is one means to prevent scouring. Johnson and Cole (1976) reported
that a bentonite liner in a paper-mill lagoon was protected from scouring
by such covering. First the liner was covered with 3 to 4 inches of till,
and then a 6-inch gravel cover was placed over the till in the most suscept-
ible areas (e.g., at the base of the aerators). Sidewalls with 3:1 slopes-
were protected from scour by 6 inches of crushed stone that was covered
with rip-rap. No problems have resulted in this facility. Johnson and
Geisel (1979) reported that a clay liner used in a municipal wastewater
treatment lagoon was protected by covering with gravel.
Voigts and Savage (1974) described a wastewater treatment lagoon lined
with natural Michigan clay. Rip-rap was added to the slopes to protect
against wave action and erosion, and a concrete scour pad was placed under
the aerators to prevent scouring the liner. Stone was added around the
scour pad out to 35 feet as an additional safety factor to prevent eroding
the clay liner. The aerator supports, which penetrated the clay liner,
were sealed with neoprene water stops in the middle of the compacted clay.
A failure due to scouring has occurred at a clay-lined sludge impound-
ment. The facility was originally designed to contain solid wastes.
However, when put into service, the facility was instead used for the
disposal of a hazardous sludge containing approximately 70 percent moisture.
The sludge placement technique involved emptying the contents of a tank
truck through a single pipe and allowing the sludge to drop down directly
onto the liner. The force created by the sludge falling onto the liner has
scoured or eroded away a section of the 3-foot clay liner.
6-16
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6.10 FAILURES FROM DESIGN OR CONSTRUCTION ERRORS
The discussion of failure mechanisms has included the importance of
design and construction techniques to prevent or minimize failures. Obvi-
ously, a design or construction error can contribute to the occurrence of a
failure and in this sense could be considered a cause of failures. For
example, an error in the slope stability analysis in the design stage could
lead to construction of an unstable side slope. Construction problems are
addressed briefly here; a more complete discussion of construction may be
found in Chapter 5 of this document.
Daniel (1983) presented several conclusions based on case studies of
leaking clay pond liners. He concluded:
Desiccation of the clay liner between the completion of
construction and the commencement of operations allows the
clay to crack.
A nonuniform moisture distribution in the soil results in
clods with wet surfaces and dry, cracked interiors. This
problem is caused by inadequate breakup of large clods prior
to compaction, uneven water distribution by water trucks,
and inadequate time for water to penetrate the soil.
High permeabilities result from inadequate control of moisture,
density, and compactive effort during liner compaction.
Improper screening of incoming liner material can result in
small roots, rocks, and lenses, and in other heterogeneities
in the clay liner that can increase field permeability.
Examples of field installation problems can be found in the case study
data presented in Chapter 7. At Site B, the depth of liquid waste was as
great as 40 feet (bathtub) effect. This liquid entered an improperly
sealed sand seam on the upper portion of the facility sidewall and contami-
nated an aquifer. At Site 0, water eroded the area around a standpipe
because a poor seal was obtained during installation. At a site not included
in Chapter 7, excavation to depths that left an insufficiently thick layer
of natural clay is suspected to have resulted in leakage problems. Sites
where a steep slope has failed and required regrading and reconstruction
are not uncommon.
Montague (1982) described a landfill in New Jersey that was constructed
with an 18-inch primary clay layer and a 12-inch secondary clay layer with
a leak detector layer between the two. The site was designed to receive
chemical solids and dry chemical sludges from the manufacturer of organic
chemicals. Seven months after operations at the site commenced, liquid was
discovered flowing into the leak detector area between the two layers. The
company operating the site stated there were two possible causes: (1) impro-
per placement of the clay liner in the trench where the monitoring manhole
pipe was laid, or (2) a break in the clay caused by truck traffic in the
6-17
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solid waste area. Attempts to locate the Teak have been unsuccessful over
the past 2 years. The leak indicates a failure in the primary liner, but
there is no evidence of leakage through the secondary liner or of ground-
water contamination (Montague, 1982).
Potential installation problems underscore the need for strict quality
control and quality assurance in the design, construction, and operation of
hazardous waste disposal facilities. The operator must be assured that the
facility is constructed as designed with properties (as measured in the
field or from representative samples) that are uniform and within specifica-
tions. A discussion of construction quality control and quality assurance
may be found in Chapter 5 of this document.
6.11 REFERENCES
Aitchison, G. D., and C. C. Wood. 1965. Some Interactions of Compaction,
Permeability and Post-Construction Deflocculation Affecting the Probabil-
ity of Piping Failure in Small Dams. In: Proceedings of the 5th
International Conference on Soil Mechanics and Foundation Engineering.
pp. 442-446.
Bernreuter, D. L., and D. H. Chung. 1964. Earthquake-Hazard Analysis for
Nuclear Power Plants. Energy and Technology Review. Lawrence Liver-
more National Laboratory. Livermore, CA. Time.
Bowles, J. E. 1979. Physical and Geotechnical Properties of Soils.
McGraw-Hill Book Company, New York, New York. 478 pp.
Brown, K. W., and D. Anderson. 1980. Effect of Organic Chemicals on Clay
Liner Permeability, A Review of the Literature: Disposal of Hazardous
Wastes. In: Proceedings of the Sixth Annual Research Symposium at
Chicago, Illinois, pp. 123-134.
Buelt, J. L. , and S. M. Barnes. 1981. A Comparative Evaluation of Liner
Materials for Inactive Uranium-Mi 11-Tailings Piles. NTIS CONF 811049-7.
16 pp.
Cedergren, H. R. 1977. Seepage, Drainage and Flow Nets. 2nd ed. John
Wiley and Sons, Inc., New York, New York. 534 pp.
Chamberlain, E. J., and A. J. Gow. 1978. Effect of Freezing and Thawing
on the Permeability and Structure of Soils. In: International Symposium
on Ground Freezing, Ruhr-University, Bochum-Germany, pp. 31-43.
Chung, D. H., and D. L. Bernreuter. 1984. Seismic Design of Low-Level
Nuclear Waste Repositories and Toxic Waste Management Facilities.
UCRL-90766, Preprint, Lawrence Livermore National Laboratory, Livermore,
California.
Daniel, D. E. 1983. Selected Case Histories of Field Performance of
Compacted Clay Liners. Prepared for presentation at the Spring Meet-
ing, Texas Section of the American Society of Civil Engineers, Corpus
Christi, Texas, March.
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Griffin. 1984. Migration of Industrial Chemicals and Soil-Waste Interac-
tions at Wilsonville, IL. In: Proceedings of the 10th Annual Research
Symposium on the Land Disposal of Hazardous Waste, EPA-600/ 9-84-007,
U.S. Environmental Protection Agency, Cincinnati, Ohio.
Hardcastle, J. H., and J. K. Mitchell. 1974. Electrolyte concentration,
permeability relations in sodium illite-silt mixtures. Clays and Clay
Minerals. (2):143-154.
Hawkins, R. H., and J. H. Horton. 1967. Bentonite as a Protective Cover
for Buried Radioactive Waste. Savannah River Laboratory, E. I. du Pont
de Nemours and Company, Aiken, South Carolina.
Hays, W. W. 1980. Procedures for Estimating Earthquake Ground Motions.
U.S. Department of Interior Geological Survey. Washington, DC.
Hughes, J. 1975. Use of Bentonite as a Soil Sealant for Leachate Control
in Sanitary Landfills. Soil Lab Engineering Report Data 280-E, American
Colloid Company, Skokie, Illinois, 36 pp.
Johnson, J. J., and F. J. Geisel. 1979. Clay caps lagoon system. Water
and Sewage Works 126(11):30-31.
Johnson, P. E., and S. W. Cole. 1976. Bentonite glacial till, the right
mixture for lining Brown Co. cascade mill lagoons. Paper Trade Journal
160(16):36-38.
Jones, C. W. 1981. Closed-System Freezing of Soils in Linings and Earth
Embankment Dams. U.S. Department of Interior, Engineering and Research
Center, Denver, Colorado. 48 pp.
Jones, C. W. , D. G. Miedema, and J. S. Watkins. 1982. Frost Action in
Soil Foundations and Control of Surface Structure Heaving. U.S.
Department of the Interior, Engineering and Research Center, Denver,
Colorado. 13 pp.
Jumikis, A. R. 1962. Soil Mechanics. Von Nostrand, Princeton, New Jersey.
Kays,, W. B. 1977. Construction of Linings for Reservoirs, Tanks, and
Pollution Control Facilities. Wiley-Interscience, John Wiley and
Sons, Inc., New York, New York. 379 pp.
Kelleher, W. J., and E. J. Michael. 1973. Low-Level Radioactive Waste
Burial Site Inventory for the West Valley Site, Cattaraugus County,
New York. New York State Department of Environmental Conservation,
44 pp.
Landau, H. C. , and A. G. Altschaeffl. 1977. Conditions Causing Piping in
Compacted Clay. In: Dispersive Clays, Related Piping, and Erosion in
Geotechnical Projects. ASTM Special Technical Publication 623, American
Society of Testing Materials, pp. 240-259.
6-19
-------
Lutton, R. J. , G. L. Regan, and L. W. Jones. 1979. Design and Construction
of Covers for Solid Waste Landfills. EPA-600/2-79-165. Municipal
Environmental Research Laboratory, U.S. Environmental Protection
Agency, Cincinnati, Ohio. 250 pp.
Mitchell, J. K. 1976. Fundamentals of Soil Behavior.
Sons, Inc., New York, New York. 422 pp.
John Wiley and
Montague, P. 1982.
Jersey. Civil
Hazardous Waste Landfills: Some Lessons from New
Engineering, ASCE 52(9):53-56.
Moriwaki, Y. , and J. K. Mitchell. 1977. The Role of Dispersion in the
Slaking of Intact Clay. In: Dispersive Clays, Related Piping, and
Erosion in Geotechnical Projects. ASTM Special Technical Publication
623, American Society of Testing Materials.
Noble, G. 1976. Sanitary Landfill Design Handbook.
Co., Inc., Westport, Connecticut. 144 pp.
Technomic Publishing
Pertusa, M. 1980. Materials to Line or to Cap Disposal Pits for Low-Level
Radioactive Wastes. Geotechnical Engineering Report GR80-7, Department
of Civil Engineering, The University of Texas, Austin, Texas. 62 pp.
Prudic, D., and A. Randall. 1979. Ground-Water Hydrology and Subsurface
Migration of Radioisotopes at a Low-Level Radioactive Waste Disposal
Site, West Valley, New York. In: Management of Low-Level Radioactive
Waste, Vol. II. pp. 853-882.
Roll in, M. B., and
in the field.
96(IR2).
A. S. Dylla. 1970. Bentonite sealing methods compared
Journal of Irrigation and Drainage Division, ASCE
•Rosenbaum, M. S. 1976. Effect of compaction on the pore fluid chemistry
of montmorillonite. Clays and Clay Minerals 24:118-121.
Sherard, J. L. , and R. S. Decker. 1977. Summary Evaluation of Symposium
in Dispersive Clays. In: Dispersive Clays, Related Piping, and
Erosion in Geotechnical Projects. ASTM Special Technical Publication
623, American Society of Testing Materials, pp. 467-479.
U.S. Environmental Protection Agency. 1980. Lining of Waste Impoundment
and Disposal Facilities (SW-870). Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, Cincinnati, Ohio.
385 pp.
Voigts, D. L. , and E. S. Savage. 1974. Engineering Approach to a Secondary
Treatment System. Tappi Press Publications 57(6):96-100.
Wang, Mian-Chang, and G. L. Roderick. 1971. Frost Behavior of Compacted
Soils. In: Frost Action and Drainage, Highway Research Record No.
360.
6-20
-------
Wischmeier, W. H., and D. D. Smith. 1978. Predicting Rainfall Erosion
Losses, A Guide to Conservation Planning. USDA Agriculture Handbook
No. 537, U.S. Department of Agriculture.
Wyss, A. W., H. K. Willard, and R. M. Evans. 1980. Closure of Hazardous
Waste Surface Impoundments (SW-873). Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, Cincinnati, Ohio.
92 pp.
Young, R. N., and B. P. Warkentin. 1966. Introduction to Soil Behavior,
MacMillan, New York, New York.
6-21
-------
CHAPTER 7
CLAY LINER PERFORMANCE
7.1 INTRODUCTION
Knowledge of the performance of existing liner designs under field
conditions is an important factor for evaluating the adequacy and practical-
ity of various designs for compacted clay liners. As part of this project,
an attempt was made to gather clay liner field performance information. At
the onset of this effort, only clay-lined hazardous waste sites with lysim-
eters or leak detection systems were deemed suitable for our purposes. As
work progressed, however, it became apparent that additional sites without
lysimeters or leak detection systems that contained predominantly nonhazar-
dous wastes might also be useful. In addition, several facilities that are
unlined but located in deposits of low-permeability soil were included in
the case study section. The inclusion of such sites is generally for the
illustration of a specific performance problem.
The success or failure of a disposal site depends upon many factors,
most of which are unrelated to the type of waste contained within. Hazardous
and nonhazardous waste sites are probably equally susceptible to the physical
failure mechanisms discussed in previous chapters. This is not the case,
however, where chemical and clay interactions are important; in these
cases, industrial and chemical waste disposal sites have a greater proba-
bility of displaying these effects than do municipal or nonchemical waste
sites. Therefore, by including as many different types of sites (municipal,
industrial, and chemical) as possible, problems resulting from most types
of failure mechanisms can be "tested for" through the analysis of the site
data.
This chapter discusses the various factors affecting clay liner perform-
ance as well as the techniques and problems of clay liner performance
monitoring. Section 7.2 of this chapter is a detailed discussion of 17
facility case studies. This section includes such information as the age
of the facility, liner specifications, construction techniques, waste
types', local hydrology and geology, and facility performance. Section 7.3
contains a summary of the information presented in the case study discussions.
The relationship between the number of successes and failures of the three
facility types (lined with compacted soil, lined with admixed materials, or
unlined) is also presented. Sections 7.4 to 7.7 include discussions on
various factors that influence a facility's performance and methods for
monitoring that performance. The final section, Section 7.8, presents the
conclusions that can be drawn from the chapter.
7-1
-------
7.2 CASE STUDIES
This section contains descriptions of 17 clay-lined facilities listed
in Table 7-1. The data for these facilities were obtained from State and
Federal agencies, commercial waste disposers, clay liner design and construc-
tion firms, and the industrial sector. Information on approximately 50
other disposal facilities was also obtained during this effort and previous
data-gathering efforts. In most cases, either necessary information was
not available or the facility did not have any unique features worthy of
discussion.
7.2.1 Criteria for Site Selection
Several important sets of data are needed in order to evaluate the
effectiveness of a disposal site. These include:
Geologic and hydrogeologic site characteristics
Types of waste in the site
Geotechnical characterization of the clay
Leachate collection, leak detection, or groundwater monitor-
ing data
Physical description of the site
Liner description
Construction procedures.
Many times, while the files on specific sites were reviewed, it became
obvious that critical sets of data were either fragmentary or not available.
One reason for this is that many sites had been "grandfathered in" when the
States started permitting disposal facilities. In this circumstance,
important information, which is now required before a site can receive a
permit, was never developed or submitted to the States when these older
sites were started. For this reason, even though we know about the existence
of many old clay-lined sites, their incomplete documentation makes them
unsuitable for our purposes.
In some cases, when sites have been suspected of causing groundwater
pollution, the State or landfill operator has initiated a hydrogeological
study designed to evaluate the performance of the clay or soil leachate
barrier. Sites where these studies have been performed are among the best
documented and are included in our data base. However, the motivation for
performing these studies was the suspicion of poor performance, and their
inclusion here may distort our perception of the capabilities of clay
liners in general. We have no way of including the hundreds of undocumented
clay-lined sites that may be performing well.
7-2
-------
TABLE 7-1. CLAY-LINED FACILITY INFORMATION
Site
Startup date Waste type
Liner description
(liner components listed from
the top down)
Facility performance and comments
I
CO
1976
1971
1977 '
1979
late 19/0's
1976
1980
1980
1479
HWb
Nil and IIW
(including un-
solidified liquids)
IIW (including
organic solvents,
heavy metal
sludges and acids)
high-density poly-
ethylene
IIW
IIW
IIW
195b IIW
(eachate collec-
tion system
added in 1982.
75% MSWC
25% paper mi 11
sIudge
Liquid IIW
IIW (I {quids and
sol ids)
-Unrecompacted in situ-glacial till.
-Zone-of-saturation landfill.
-In situ glacial till. Sand or
grave) seams were excavated and
then backfilled with clay.
-Leachate collection system.
-In situ clay-shale soil contain-
ing calcium carbonate nodules
and seams. Sand or gravel
seams were excavated and then
backfilled with soil.
-Leachate collection system.
-80-mil (HOPE) liner.
-5-foot recomputed clay liner.
-French drain above liner in
each cell.
-Recompacted Demopolis Chalk.
-Leachate collection system
-Flexible membrane liner (FML)
(llypalonee or HOPE)
-10-foot recompacted clay
liner from borrow site.
-Leachate collection system.
-Unrecompacted glacial till.
-Leachate collection system.
-4-foot recompacted clay liner.
-Three lysfmeters
-5-fool recompactpil clay liner.
-Leak detection system.
-5-foot recompacted clay liner.
-5-fool recompacted clay liner.
-Leak detection system
-1-foot recoinp.K toil clay liner.
Original monitoring well installation
problem has been corrected. No
recent performance problems have been
reported.
Bathtub effect has caused inward
hydraulic gradient to reverse.
Severe groundwater contamination
has resulted.
Groundwater contamination has
occurred, possibly due to a
reaction between the low pH waste
and the calcium carbonate inclusions
in the local soil.
No performance problems.
Minor problems, including buildup
of leachate head, have been
corrected.
Leachate removed from collection
system is less contaminated than
the groundwater. Contamination
was caused by an adjacent facility
requiring remedial action.
Contamination in well is thought
to have come from an adjacent
abandoned drum storage facility by
way of a sand and gravel seam.
Initial collection of liquid in
lysimeters Uiuughl to be MM!
moisture release following canst ruc-
tion
Desiccation cracks formed in
unprotected liner prior to filling
with waste. When pond was filled,
waste migrated into the detection
system.
Chlorinated organic liquid placed
in pond caused liner failure.
fcontinued)
-------
TABLE 7-1 (continued)
Site
Startup date Waste type
Liner description
(liner components listed from
the top down)
Facility performance and comments
1981
Iiquid HW
1978
HW
1977
1974
19BO
1980
MW
HSW
HW
HW
1976
HW
Nil = Nonhazardous
HW - Hazardous waste
CMSW - Municipal solid waste
-3-foot recompacted clay liner.
-Leak detection system
-1-foot recompacted clay liner.
-Leachate collection system.
-Approximately 2-foot
reconpacted clay liner.
-Leak detection system.
-1-foot recompacted clay liner.
-Approximately 1-foot compacted
soil liner.
-Geotextile
-Leachate collection system.
-1-foot recompacted borrow clay
soil liner.
-Leak detection system.
-Leachate collection system.
-4-inch ben ton He (averaging
11 percent by weight) and
sand 1iner.
-Two lysimeters.
-Leachate collection system.
-4-foot-thick recompacted local
clay liner with 3 percent
bentonite and 3 percent lime
added.
-Leachate collection system.
-5-foot recompacted soil liner
including a 1-foot layer of
bentonite (9 to 12 percent) and
soil.
-Leak detection system.
-6-inch bentonite and soil layer
-5-fool in situ soil layer
-Leachate collection system
-4-inch hentonite/soiI liner.
-leak detection system.
-4-inch benlunile/soiI liner.
Liquid volumes collected in detection
system were used to calculate liner
permeability. Values ranged from
4 x 10"8 to 3 x 107 cm/s.
Recent major earthquake 100 miles
north of the facility caused no
damage.
Failure in upper liner has occurred.
Lower liner is still functioning.
No performance problems.
Groundwater contamination has been
detected at several monitoring points.
Cap failure caused increased leachate
volumes. Problem was corrected by
replacing section of cap.
Small amounts of liquid have been
collected in the leak detection
system. Monitoring wells have
shown no significant changes.
Liquid volumes collected in detection
system were used to calculate the
liner permeability. Values ranged
from 3 x 10~H to 6.5 x 10~" cm/s.
-------
As one might suspect, the best documented sites are those relatively
few that have been built after the institution of strict permitting require-
ments at the State and Federal level. In general, permit files contain
hydrogeological reports and engineering reports that document the installa-
tion of the facility and the characteristics of the clays used. Typically,
however, these sites are only a few years old and therefore do not supply
much data relevant to the prediction of the long-term performance of clay
liners.
The site data presented in the following sections include all of the
relevant information that was made available to the authors for each site.
As discussed in the previous paragraphs, the quality, quantity, and type of
these data were quite varied.
7.2.2 Site A
7.2.2.1 Physical Description—
This sanitary and hazardous waste landfill is located in an area of
glacial till soils. The liner at this facility consists of the unrecompacted
glacial till, which has a relatively low permeability. A plan view of the
facility is presented in Figure 7-1.
7.2.2.2 Startup Date—
This facility began operations in 1976.
7.2.2.3 Local Geology and Hydrology—
This facility is located in the midwestern United States. Average
annual precipitation at this site is 35 inches.
•
The soil in the vicinity of the landfill is described as a clay-loam
till. Soil borings indicate that it extends to depths of 150 feet. Under-
lying the till is a thick formation consisting of limestone, dolomite,
sandstone, and slate. Occasional gravel, silt, or sand lenses are present
in the upper till layers. It is not known if these areas were excavated
and backfilled with clay prior to waste placement.
There is very little information about the groundwater levels in this
area. However, it is known that the groundwater flows in a northeasterly
direction and that the facility is located in an area where the possibility
of groundwater contamination is low.
Monitoring wells are located both upgradient and downgradient of the
site.' Samples are analyzed quarterly for abnormalities in groundwater
conditions.
7.2.2.4 Waste Type--
Both sanitary and hazardous wastes (including drummed combustibles and
Teachable metals) are accepted at this facility.
7-5
-------
Hydraulic Gradient
Monitoring /
Wells \
Hazardous
Waste
. 1,000 feet
(approximate)
Figure 7-1. Plan view of site A.
7-6
-------
7.2.2.5 Liner Description—
The liner at this facility consists of unrecompacted in-situ glacial
till. This material has the following characteristics.
Permeability 3.0 x 10"6 to 5 x 10"8 on/s
(triaxial tests with
leachate and water)
Liquid limit 22 - 26%
Plasticity index 2 - 10%
Moisture content 12 - 22%
Amount passing No. 200 sieve 75 - 95%.
Compatibility testing performed by a private firm has indicated that
the leachate will not react with the surrounding liner soils in a way that
would significantly increase its hydraulic conductivity. The major organic
components of the test leachate were phenol, methylene chloride, 1,1,1-
trichloroethane, toluene, 1,1-dichloroethane, and diethylphthalate.
7.2.2.6 Liner System Installation—
This is an unlined facility. Methods used for the excavation were not
available.
7.2.2.7 Performance—
Analysis of groundwater samples taken from the present monitoring
wells has not revealed any leachate migration problems. However, the
original monitoring wells were improperly installed, having contained steel
mill slag where clean gravel should have been used. Samples taken from
these wells in 1976 had pH levels between 10.7 and 11.3. The analysis also
revealed a chemical oxygen demand (COD) of 3,193 ppm and a chloride level
of 1,028 ppm. These elevated levels were attributed to the steel-mill slag
in the well casings. Samples taken from newly constructed wells in 1981
had pH levels of around 7, COD levels ranging from less than 10 ppm to
approximately 60 ppm, and chloride levels ranging between 4 ppm and 12 ppm.
7.2.3 Site B
7.2.3.1 Physical Description—
This 166-acre facility contains an 80-acre zone-of-saturation, or
intergradient, landfill. A small section of the landfill has a recompacted
clay liner; the remainder of the landfill is unlined. A leachate collection
system (LCS) lies between the waste and the landfill bottom. A plan view
of the facility is presented in Figure 7-2.
7.2.3.2 Startup Date--
This landfill began accepting waste in 1971.
7-7
-------
Monitoring Wells
CO
Leachate
Seeps
Old Section
No Data
Figure 7-2. Plan view of site B.
-------
7.2.3.3 Local Geology and Hydrology—
This facility is located in the northern central portion of the United
States. Average annual precipitation at this facility is approximately
30 inches.
The site is located in a glacial till, which consists primarily of
clay and silt. Site investigations have shown that sand and gravel lenses
are present throughout the till. Underlying the glacial till is a layer of
moderately fractured dolomite up to 200 feet thick. A permeable aquifer
exists in this bedrock layer. The glacial till is saturated to within
10 feet of the ground surface. Groundwater flow was in a southeasterly
direction prior to the development of the disposal facility.
7.2.3.4 Waste Type—
This facility contains municipal solid waste, nonhazardous industrial
waste, and hazardous waste. Included in this are large amounts of plating
sludge and pickle liquor as well as smaller amounts of various solvents.
Liquid wastes were not solidified prior to their disposal.
7.2.3.5 Liner Description—
The liner at this facility is a minimum of 30 feet of in situ glacial
till. The glacial till has the following characteristics:
Soil Characteristics Average Value
Amount passing No. 200 sieve 68%
Clay 40%
Liquid limit 29%
Plastic index 14%
Field permeability 7.5 x 10-6 cm/s
Laboratory permeability 9 x 10-8 cm/s.
Lenses of sand or gravel that were encountered during site construction
were excavated and backfilled with a minimum of 5 feet of recompacted clay.
A leachate collection system is located on top of the landfill base.
Specifications for this system were not available.
7.2.3.6 Liner System Installation—
No information on the excavation and construction of this facility was
available.
7.2.3.7 Performance—
Recently, three major and numerous minor leachate leaks have been
observed in the western side of the final cover (see Figure 7-2). The
State geologists attribute these leaks to the 26-foot hydraulic head within
the landfill. One geologist estimated that, at times, the head is as great
as 40 feet. This high hydraulic head has caused the inward gradient of
this zone-of-saturation landfill to reverse.
7-9
-------
A second problem encountered at this site is the migration of leachate
into the groundwater in a very small area on the northern edge of the land-
fill (see Figure 7-2). Excavations in the problem area revealed that in
one spot a permeable deposit that had been improperly sealed with clay was
below the level of the waste material. Leachate entered this permeable
layer and was detected in a monitoring well. Remedial action consisting of
the installation of a clay cutoff wall and leachate removal has resulted in
some improvement in the groundwater quality; however, significant contamina-
tion is still present.
7.2.4 Site C
7.2.4.1 Physical Description—
The facility consists of 31 small drum disposal trenches, 4 treatment
ponds, and 2 evaporation ponds (see Figure 7-3). The total storage and
disposal area is approximately 16.5 acres.
The ponds and trenches were excavated in the local natural soil. If
sand seams or other potentially troublesome areas were located in the pond
bottoms, these areas were recompacted. No recompacting was done in the
disposal trenches. Several monitoring wells surround the facility.
7.2.4.2 Startup Date~
The facility was opened in 1977, but because of groundwater contamina-
tion it was forced to close in January 1982. Since that time, changes have
been made and parts of the facility are again in operation.
7.2.4.3 Local Geology and Hydrology--
This facility is located in the midwestern plains of the United States.
Average annual precipitation in this area is approximately 25 inches.
Investigations have indicated the presence of two water-bearing zones
beneath the facility at depths of approximately 40 and 50 feet below the
ground surface. Several springs and a creek are to the north of the facility.
The relationship between the groundwater zones and springs is unknown.
Soil borings indicate that approximately 3 feet of topsoil overlie 30
to 40 feet of weathered clay-shale. This weathered clay-shale is a plastic
silty to highly plastic clay (CL to CH) with calcium carbonate nodules and
seams throughout. Bedrock lies under the clay-shale layer. An example of
a typical soil boring is illustrated in Figure 7-4.
7.2.4'. 4 Waste Type-
Various hazardous wastes including organic solvents, heavy metal
sludges, and acids were held in the treatment and evaporation ponds and
disposed of in the drum storage area.
7.2.4.5 Liner Description—
While this facility is almost completely unlined, potential problem
areas uncovered by the pond excavations, such as sand seams, were recompacted.
7-10
-------
p
n
a
a
4
Evaporation
Ponds
•f
•i
*•
4-
D
A
"T
-du
n
n
n
4- 4- 1
Treatment
Ponds
4- 4-
4"0 H
^^
4-
t- / +
Disposal
Trenches
4-
^
4- D
*{p* Monitoring wells in the upper
water-bearing zone
O Monitoring wells in the lower
water-bearing zone
Y Approximate Scale
D
200 ft 400 ft
Figure 7-3. Plan view of site C.
-------
Evaporation
Pond
Treatment
Pond
Disposal
Trench
Upper Water-
Bear ing Zone
Lower Water-
Bearing Zone
40ft
10ft
1
Topsoil
Clay-shale
soil with
calcium carbonate
nodules and
seams
Bedrock
Figure 7-4. Cross-sectional view of site C (vertical dimensions are to scale).
-------
The local clay-shale soil was the only barrier to waste migration. A cross
section of the facility is presented in Figure 7-4.
7.2.4.6 Liner System Installation—
Information about the procedures used to excavate and recompact the
disposal areas was not available. Methods used to install the monitoring
wells were also not available.
7.2.4.7 Performance—
Analysis of groundwater samples indicates that contamination has
occurred. Elevated concentrations of chromium, arsenic, barium, cadmium,
lead, and mercury were detected near the disposal ponds and trenches.
However, except for chromium, none of the heavy metals were detected in
offsite monitoring wells. In addition to heavy metal contamination, several
volatile organics such as chloroform, trichloroethane, dichloroethane,
benzene, and methylene chloride were detected in both onsite and offsite
monitoring wells. The highest levels of volatile organics were found
onsite in the uppermost water-bearing zone in wells closest to the disposal
areas. Base-neutral-extractable organics and acid-extractable organics
were also detected in onsite and some offsite wells (see Table 7-2).
Investigations of the groundwater contamination at this facility
suggest that the treatment ponds are the major source of contamination in
the uppermost water-bearing zone. This conclusion is based on the fact
that the materials in the ponds were usually of low pH and would be reactive
with the carbonate seams and inclusions in the surrounding soil. Several
of the trenches were used for the disposal of highly acidic waste oil
reprocessing sludges. These sludges may have also attacked the surrounding
materials and allowed contamination to occur.
7.2.5 Site D
7.2.5.1 Physical Description—
This recompacted clay- and synthetic-lined hazardous waste disposal
facility consists of two large disposal sections, each of which is divided
into several smaller disposal cells. These in turn are divided into three
subcells each for the segregation of different waste types. Four of the
five disposal cells in Section I are closed, and the remaining cell is
currently active. The first of 10 proposed disposal cells in Section II is
under construction. This construction is scheduled to be completed in the
fall of 1984, at which time landfill ing operations will be initiated. A
pi an.view of the facility is presented in Figure 7-5.
7.2.5.2 Startup Date-
Construction of this facility was started in 1979.
7.2.5.3 Local Geology and Hydrology—
This facility is located in the southeastern United States. Average
annual precipitation at this site is approximately 47 inches.
7-13
-------
TABLE 7-2. GENERAL OCCURRENCE OF CHEMICAL PARAMETERS IN THE GROUNDWATER AT SITE C
No. parameters detected
No.
Parameter parameters
tested for tested for
Volatile organics-
No. found 31
Highest
concentration
Trace metals-
No, found 8
Highest
concentration
Ac id-extrac table
organics
No. found 11
Highest
concentration
Base-neutral-
extractable organics
No. found 46
Highest
concentration
Ons ite
Upper water-
bearing zone
20
370,000
8
20,000
6
24,000
"
11
410
and highest concentration (ppb)
Offsite
Lower water-
bearing zone
19
3,100
8
500
ND
ND
3
83
Upper water-
bearing zone
18
79,000
8
300
3
3,300
6
250
Lower water-
bearing zone
6
510
7
500
ND
ND
1
160
ND = No parameters of this type were detected.
-------
Section II
Direction of
Ground and
Surface Water
Flow
^/Claystone
^4, Processing
Facility
Drum Storage and
Waste Handling Facility
IN
Scale
400'
800*
Figure 7-5. Pfan view of site D.
-------
Information on the local geology and hydrology was obtained through
the use of 32 exploratory borings. These borings have confirmed that there
are several distinct soil layers. The lowest of these layers is the
Tuscaloosa Formation, which is overlain by the Black Mingo Formation, which
in turn is overlain by Quaternary deposits. The upper surface of the
Tuscaloosa Formation is located approximately 55 to 120 feet below the
ground surface. This material consists of clayey sands and clays. Lenses
or beds of coarse to fine sand are located in this formation. In situ
hydraulic conductivity testing of this_formation revealed that it has a
permeability in the range of 1.09 x 10 6 to 4.01 x 10 6 cm/s.
The Black Mingo Formation encountered at this site consists of four
subunits: the Basal Clay Unit, the Opal Claystone Unit, the Red Sand Unit,
and the Buhrstone Unit.
The Basal Clay Unit consists of very hard black clay with frequent
sand and silt lenses. The upper surface of this material is located approxi-
mately 60 to 115 feet below ground level and varies in thickness from 1.5
to 15.5 feet. In a few of the borings, this material was not present.
The Opal Claystone Unit, on the other hand, is either above the Tuscaloosa
or Basal Clay Formations over the entire site. This material consists of
low-permeability (exact value unknown) silt and clay with very few sand
inclusions. The thickness of this formation varies from 20 to 60 feet.
The Red Sand Unit, which is located above the Opal Claystone Unit,
consists of sand to clayey silts. The silts and clays are generally present
as 1/4-inch to 2-inch layers interbedded with the sand. The thickness of
this formation varies from 0 to 15 feet. In situ hydraulic conductivity
testing of this material revealed that its permeability ranges from 6.24 x
10"5 to 6.43 x 10"4 cm/s.
The final unit of the Black Mingo Formation, the Buhrstone Unit, is
found scattered over the entire area. When present, it ranges up to 14
feet thick. This material is described as clayey silt to silty clay.
The Quaternary deposits contain layers of variegated clay that were
originally thought to be a source of low-permeability liner material.
Further investigations revealed that the silt and sand content was much too
high for it to be used as a base liner.
An aquifer is present in both the Tuscaloosa and the Red Sand Forma-
tions. The Tuscaloosa aquifer is approximately 60 to 70 feet below the
ground surface. The Red Sand aquifer is roughly 40 feet above this aquifer.
The direction of flow in both cases, as well as the direction of surface-
water flow, is toward a lake located southwest of the facility.
7.2.5.4 Waste Type--
This facility accepts most types of hazardous wastes. These wastes
are classified as alkaline, acid, or organic and are disposed of with
7-16
-------
similar wastes only. This is accomplished through the use of three subcells
that are incorporated into all of the cells in Section II of the facility.
The size of each of the subcells was determined so that maximum separation
of potentially incompatible wastes was provided and based on past operating
experience.
7.2.5.5 Liner Description—
The liner at this faci1ity_consists of 5 feet of recompacted clay
(maximum permeability of 1 x 10 7 cm/s) brought to the facility from a
borrow pile located several miles away. Ten-foot sidewall liners are
present above the top of the Opal Claystone Unit (see Figure 7-6). An
80-mil high density linear polyethylene (HOPE) membrane liner lies on top
of the recompacted clay. This liner is protected with a soil layer that is
9 inches deep on the bottom and 24 inches deep on the sidewalls. A leachate
collection system is located on top of the protective soil layer (see
Figure 7-6).
The subcell separation berms are constructed of recompacted clay and
are built up in 5.5-foot-high sections as the landfill operations progress.
The side slopes of these berms are 1:1.
7.2.5.6 Liner System Installation--
Prior to excavation of the landfill cells, a channel to drain the
perched water table within the Red Sand Unit was constructed. After this
channel was completed and in operation, excavation of the landfill cells
was initiated. Side slopes were cut on a 3:1 (horizontal:verticle) slope
down to the top of the Opal Claystone Unit. At this location, a 17-foot-wide
"bench" with a 3-foot-wide trench was excavated into the top of the opal
claystone (see Figure 7-6). This area was excavated to provide room for a
thicker liner. Below the "bench," side slopes-were also 3:1. A minimum of
10 feet of the opal claystone was left as foundation material. At the
leachate collection system sump locations, approximately 4.5 feet of opal
claystone remained as the foundation.
After the sides and base of a cell were graded, clay was brought to
the site from the borrow area. Before the clay was placed in the excava-
tion, a "test fill" was constructed with borrow soil that was selected
based on the basis of laboratory screening procedures. The "test fill" was
constructed in the field with equipment and procedures that were to be
employed during liner construction. Undisturbed Shelby tube samples were
taken from the completed "test fill" and were tested in the laboratory for
density, moisture content, and permeability. The clay was compacted in 6-
to 8-inch lifts with either a sheepsfoot or smooth-drum vibratory roller.
The liner specifications required a permeability of 1 x 10 7 cm/s or less.
Testing results from the construction quality assurance (CQA) tests on the
installed liner were not available; however, results from tests performed
on Shelby tube samples taken from the "test fill" were as follows:
Density 114.9 - 120.0 lb/ft3
Water content 22.6 - 29.8%
Permeability 1.8 x 10"8 to 8.0 x 10"8 cm/s.
7-17
-------
10-ft Recompacted
Clay Liner
Side Wall
1 Slope
1
1—»
00
3ft-Wide
Key Trench
In Situ
Opal Claystone
24 in Protective
Soil Cover
80 mil HOPE
Liner
1 ft Drainage
Layer
Typical 5.5-ft-High
Section of a Cell
or Subcell Separation
Berm
9 in Protective
Soil Cover
5 ft Recompacted
Clay Liner
\\
\\
Filter Fabric
Figure 76. Cross-sectional view of site D liner.
-------
7.2.5.7 Performance—
Groundwater samples taken from upgradient and downgradient monitoring
wells have not been statistically different since the start of waste place-
ment.
7.2.6 Site E
7.2.6.1 Physical Description—
The facility presently occupies approximately 100 acres, with room for
expansion to 340 acres. There are over 20 disposal trenches at various
stages of operation as well as 4 active evaporation ponds (see Figure 7-7).
7.2.6.2 Startup Date—
This facility became active in the late 1970's.
7.2.6.3 Local Geology and Hydrology—
This facility is located in the southeastern United States. Average
annual precipitation at this facility is 50 inches.
It is located in a natural clay formation called the Demopolis Chalk
Formation. Testing of the Demopolis Chalk Formation has shown that it has
the following properties:
Average permeability 4.0 x 10 8 cm/s
Permeability to polychlorinated biphenyl (PCB) liquids:
- Light oils and PCB's, 9 x 10"9 cm/s
- Heavy oils and PCB's, 1.5 x 10"10 cm/s
88% of the material passes the No. 200 sieve
35% of the material is less than 0.001 mm in diameter
Liquid limit of 31%
Plastic limit of 20%.
Soil borings in the area have shown that the clay is a minimum of 500 feet
thick and in some places extends to depths of over 700 feet.
The closest usable groundwater is located below this clay formation.
However, a few locations of perched water are in the vicinity of the site.
In addition, the Demopolis Chalk Formation is saturated to within 10 to 30
feet of the ground surface.
The 100-year projected flood elevation for a creek, located 3,000 feet
north of the facility, is 125 feet above mean sea level. This should
present no problem to the facility because the disposal trenches are located
7-19
-------
-4-
Key
> Active Impoundment
^ or Trench
Completed Impoundment
or Trench
-•- Monitoring Weil
I 1 200 ft (approx.)
N
+
r~n r
4.-
-f -f
« u I Active
II I
3 S I
o
U
Active
01 I
o I Proposed j
* !L '
Evaporation
Ponds
Capped
Figure 7-7. Plan view of site E.
7-20
-------
at points that range from 180 to 220 feet above mean sea level. The lowest
elevation of the site is 148 feet above mean sea level.
7.2.6.4 Waste Type—
The site is designed to be a full-service facility that accepts all
types of hazardous wastes. The majority of the material received for dis-
posal consists of acidic and caustic industrial wastes, heavy metal sludges,
contaminated containers, sludge, and oil sludges. All wastes received by
the facility are handled separately, and only compatible materials are
placed within proximity of each other.
PCB wastes are handled separately and only PCB's and PCB-compatible
wastes will be located in the same disposal trench.
7.2.6.5 Liner Description—
Each disposal trench is lined with recompacted native soil. Construc-
tion information concerning the number and thickness of lifts was not
available. A calculated amount of absorptive material is placed on top of
the recompacted bottom of each trench. The wastes are then placed on top
of this material and covered with 6 to 8 inches of the natural clay. The
final trench covers are also constructed with natural clay.
The current monitoring system consists of the following:
A subsurface collection system and a secondary retention
dam. This system would collect any materials that might
migrate.
Several monitoring wells placed within proximity to active
trenches.
Observation wells surrounding the entire facility.
A French drain system is located at the lowest point in each trench.
In the event that liquid is collected in this drain, it would be pumped out
and treated as incoming waste.
7.2.6.6 Liner Installation—
No information was available.
7.2.6.7 Performance—
In general, this facility is operating as planned. There have, however,
been a few minor problems. Groundwater from a more permeable weathered
section of the Demopolis Chalk Formation has infiltrated the sidewalls of
trenches 15 and 19. At trench 15, this problem was remedied by installing
a cutoff wall on the south-southeast side of the trench. Recompaction of
the entire sidewall at trench 19 eliminated the groundwater flow into this
trench. More recently, large volumes of leachate (up to 50 feet deep) have
been accumulating in some of the trenches with interim final covers. These
large volumes of leachate are attributed to the infiltration of groundwater
7-21
-------
and precipitation. Frequent pumping of the leachate has helped to reduce
these volumes. Final covers consisting of 3 to 5 feet of recompacted
Demopolis Chalk and a HOPE liner are scheduled to be installed by the end
of 1986. In addition, the State monitoring well analysis has shown trace
levels (92 ppb maximum) of 12 organic compounds in groundwater samples. An
investigation of their source indicates that they may have come from the
well casing materials.
7.2.7 Site F
7.2.7.1 Physical Description—
The 380-acre facility consists of five secure land disposal cells with
a total area of 25 acres. Cells 1, 2, and 3 are closed; cell 4 is currently
being filled; and cell 5 is under construction. The remainder of the
facility is devoted to sanitary landfill ing, waste treatment operations;
and recovery of lime from the old slag disposal operation.
The five cells are lined with 10 feet of recompacted clay soils. On
top of the clay liner is a flexible membrane liner (FML), which in turn is
covered with a 1-foot layer of recompacted clay. A layer of geotextile
lies above the 1-foot clay liner. Finally, a 12-inch drainage blanket
containing slotted 4-inch corrugated HOPE pipe at a minimum of 100-foot
intervals is installed on top of the geotextile (see Figure 7-8).
7.2.7.2 Startup Date—
The facility is located at the site of a slag disposal operation that
has not been active for 90 years. The clay-lined facility as it currently
exists has been in operation since 1976.
7.2.7.3 Local Geology and Hydrology—
This facility is located in the northeastern United States. Average
annual precipitation in this area is approximately 36 inches.
Numerous onsite borings and test pits have revealed that the site is
an old disposal area covered with waste industrial slag ranging in depth
from approximately 7 feet to 45 or 50 feet. The disposed slag fill ranged
in size from silt-sized particles to boulders. Beneath the slag was a
layer of marsh silt that ranged in thickness from a few inches to as much
as 5 feet.
Below the slag and marsh silt materials covering the entire site was a
6-foot layer of lacustrine clays. These clays contained lenses of gray
nonpTastic silts and clay with minor amounts of fine sand. The presence of
these lenses throughout'the lacustrine clay eliminated it from considera-
tion as an in situ liner material. Laboratory analysis of the lacustrine
clay indicated that it had the following properties:
Natural water content 26.5 - 42.8%
Liquid limit 50%
7-22
-------
^J
ro
Flexible
Membrane
Liner
(Not to scale)
Interior
Clay Dike
1-ft Drainage Layer
Slotted 4-inch
Geotextile Wrapped
Leachate Collection Pipes
1 to 2 ft Compacted Cover Soil
10 ft Compacted Clay Liner
\\
\\ // \\ // \\ // \\ // \\
\\
Figure 7-8. Cross-sectional view of site F.
-------
Plastic limit 22%
Dry unit weight 99 lb/ft3
Permeability (laboratory 1 x 10 8 to 6 x 10 8 cm/s
compacted)
Amount passing No. 200 99%
sieve
Amount passing 2 microns 54 - 63%.
Underlying the lacustrine clay was a 5-foot layer of glacial till
consisting of brown to red-brown silts, clays, and sands with varying
amounts of gravel. Laboratory testing demonstrated that the permeability
of the till was 3 x 10 7 cm/s, making it unsuitable for use as a liner
material.
Groundwater under the facility occurs in three zones:
Unconfined water table above the lacustrine clays
Confined aquifer in the upper 10 feet of bedrock
Immobilized groundwater held within the impermeable confin-
ing beds.
Piezometers installed in the soil-boring holes indicated that the
groundwater elevations ranged from 0.5 to 6 feet below the ground surface.
7.2.7A Waste Type--
Each of the five disposal cells are, or will be, divided into four or
five subcells. The purpose of these subcells is to isolate the various
waste groups accepted at the facility, thereby preventing the interactions
of incompatible wastes. When five subcells are used, as in cells 1, 2, 3,
and 4, the waste categories are as follows:
General wastes. These wastes represent approximately 44 per-
cent of the total waste volume. General wastes are defined
as materials of both an organic and inorganic nature that do
not contain a significant quantity of any of the other waste
categories.
The hazardous acidic or acid-generating materials are
covered with lime to ensure that any acid that is generated
will be neutralized.
Pseudo metals. This type of material represents approximately
6 percent of the total waste volume. Pseudo metals are arsenic,
antimony, bismuth, and phosphorous. Chalcogens, beryllium,
7-24
-------
and any of their compounds as well as alkaline-sensitive
materials are also disposed in this subcell.
This subcell has a pH buffer system that maintains pH
levels between 6 and 8.
Heavy metals. These wastes represent approximately 15 percent
of the total waste volume. This group is comprised of all
heavy metals and asbestos. This subcell contains the smallest
amount of organic materials, which helps to reduce fire hazards
caused by the reaction of strong oxidizing agents with organics.
Highly flammable wastes. This type of material represents
approximately 12 percent of the total waste volume. These
materials generally exhibit a flash point between 80 and
100 °F. These materials are kept apart from powerful oxidiz-
ing agents, materials that are prone to spontaneous heating,
or materials that react with air or moisture to evolve heat.
Toxic materials. These wastes represent approximately 23
percent of the total waste volume. Included in this category
are all highly toxic organic compounds, carcinogens, RGB's,
and other halogenated wastes. No sol vent-type wastes were
permitted in this subcell.
If only four subcells are used, the psuedo-metals subcell is eliminated.
7.2.7.5 Liner Description—
The liners at the five secure land disposal cells are very similar.
Minor design changes have been made as each cell was constructed. The com-
ponents of the liners include:
A minimum of 10 feet of local and borrow soil placed above
the in situ glacial till. The soil is compacted so that the
permeability is no greater than 1 x 107 cm/s.
An FML. Both Hypalon and HOPE ranging from 30 to 80 mils
have been used.
Cover soil of 12 to 24 inches compacted to a permeability of
1 x 10 7 cm/s or less.
In some of the cells, an 8-inch layer of slag material
placed over the cover soil. This layer is to provide a firm
base for equipment movement.
A leachate collection system located on top of the liner
system. This system consists of a 12-inch drainage blanket,
slotted 4-inch geotextile wrapped pipes located 100 feet
apart (maximum), and standpipes or manholes to enable collec-
tion and removal of the leachate.
7-25
-------
7.2.7.6 Liner System Installation—
Prior to liner installation, all of the industrial slag material and
the organic marsh silt were removed. The lacustrine clays were not excavated
because of the high water table. Dewatering was conducted as necessary.
Borrow liner material was transported to the facility. Prior to liner
compaction a test patch was required. This patch enabled the construction
contractor to determine the compactive effort necessary to achieve the
required permeability. Density, moisture content, and permeability measure-
ments were conducted on the test patch to establish the ability of the
equipment to compact the liner to the design specifications.
It was determined that the liner should be compacted in 6-inch lifts
with a sheepsfoot roller. The finished clay liner thickness was 10 feet.
The sidewalls were installed in horizontal lifts and cut back to a final
slope of 2:1. The slope of the bottom liner ranged from 1 to 2 percent.
The clay liner was protected by the FML. The entire liner was installed
before waste placement was initiated.
A system of dikes was used to separate the large cell into the various
subcells. The interior dikes were constructed in 4^-foot-high sections.
New sections of the interior dikes were constructed by keying into the top
of the previous dike (see Figure 7-8).
CQA consisted of soil density and moisture content measurements (nuclear
gauge) and laboratory permeability tests on undisturbed Shelby tube samples
of the liner.
7.2.7.7 Performance—
The performance of this facility is very difficult to determine at
this time. A potential Superfund site located next to this facility has
caused extensive groundwater contamination in the area. For this reason,
baseline groundwater data have not been obtained. However, it is known
that the leachate removed from the collection system of the newly constructed
facility is less contaminated than the local groundwater.
7.2.8 Site G
7.2.8.1 Physical Description—
The facility consists of several disposal areas covering 80 acres. A
100-acre section is planned for future development. Some sections of the
landfill are active, while others are capped (see Figure 7-9). Each disposal
area is lined and/or capped with unrecompacted local soil. A leachate
collection system was installed in 1982. Several monitoring wells are
located within the area.
7.2.8.2 Startup Date—
This site was first used as a dump in 1955. Sanitary landfilling
operations began in 1967. A leachate collection system was added in 1982.
7-26
-------
r>o
Intermittent Creek
Leachate Collection System
Storage Area
I
(Access Road)
Hydraulic
Gradient
Leachate Collection Tank
if
-m~ Monitoring Well
N
Figure 7-9. Plan view of site G.
-------
7.2.8.3 Local Geology and Hydrology—
This facility is located in the midwestern United States. Average
annual precipitation at this facility is approximately 35 inches.
The soil in the vicinity of the landfill is described as silty clay to
clayey silt, which extends to a depth of 200 feet. A layer of shale under-
lies the till material. Discontinuous sand and gravel seams are located
throughout the area. When encountered, they have been removed prior to
landfill ing.
Groundwater is known to occur in sand and gravel seams within 6 feet
of the surface. The static water level in the clay soil is not known.
7.2.8.4 Waste Type—
The facility has accepted various types of hazardous wastes including
organics, heavy metals, and pesticides.
7.2.8.5 Liner Description—
The local soil (unrecompacted) used to line the site has the follow-
ing physical properties:
Permeability I x 10-7 to 1 x 10-9 cm/s
Natural moisture content 9 to 12%
Plastic limit 20 to 21%
Liquid limit 11 to 13%
Plasticity index 8 to 10%
Cation exchange capacity 1.2 to 2.0 (milleq./lOO g sample).
7.2.8.6 Liner System Installation—
This information was not available.
7.2.8.7 Performance—
Analysis of groundwater samples from well No. 1 (see Figure 7-9) has
indicated high levels of lead, chloride, COD, total dissolved solids, chlo-
roform, and various chlorinated organics.
This contamination is thought to come from an old drum disposal site
previously owned by another company located adjacent to the landfill. The
drum disposal site is located on a sand and gravel seam that extends upward
near the ground surface. Contaminants from this site can reach this per-
meable area and travel southward to Site G's monitoring well No. 1. There-
fore, indications are that the contamination in well No. 1 has not come
from Site G.
7-28
-------
7.2.9 Site H
7.2.9.1 Physical Description—
This site has a rectangular 9-acre cell lined with 4 feet of locally
obtained clay that was put down in four lifts. A leachate collection
system composed of 8-inch perforated polyvinyl chloride (PVC) pipe is on
top of the clay liner. Directly below the clay liner are two lysimeters.
A third lysimeter is located under the leachate storage basin (see Figure
7-10). The present cell is filled to near capacity, and a new cell is
being constructed in such a manner that the bottom clay liners will be tied
together to form one large cell with no vertical wall dividing the old and
new disposal areas. The presence of lysimeters almost directly below the
leachate collection drain pipes presents a unique opportunity to evaluate
the performance of the intervening layer of clay.
7.2.9.2 Startup Date--
Operation began in December 1980.
7.2.9.3 Local Geology and Hydrology—
The facility is located in the northern central United States. Average
annual precipitation in this area is 30 inches.
The site is underlain by approximately 50 to 100 feet of dense silty
sand. This material contains boulders, cobbles, and pockets of sandy
material. The permeability of this glacial till ranges from 1 x 10 4 to
9 x 10 7 cm/5. Bedrock is encountered beneath this layer. The water table
is at a depth of 50 to 80 feet in the silty sand or bedrock. Groundwater
flow is primarily in the southeast direction.
7.2.9.4 Waste Type-
Wastes accepted at this facility consist of approximately 75 percent
municipal and 25 percent paper-mill sludge. Small quantities of other
industrial wastes are also disposed of at this facility.
7.2.9.5 Liner Description—
The liner system consists of 4 feet of recompacted clay underlain by
two collection lysimeters. The clay for the liner was obtained from a
nearby borrow area. It consists of a reddish-brown to reddish-gray silty
clay. The specifications for the material used were as follows:
Liquid limit >30%
Plasticity index >15%
P-200 >50%
Permeability <1 x 10 7 cm/s.
A leachate collection system is present above the clay liner (see Figure
7-11).
7-29
-------
•$-
a
L1
Under
Construction
N
Leachate
Storage
Basins
Single Monitoring Weil
Monitoring Well Nest
Lysimeter Sump
Piezometer
Lysimeter Area
Figure 7-10. Plan view of site H.
7-30
-------
Silty Sand
Protective
Layer
\
8" Perforated Pipe Leachate Drain
Crushed Rock
20 mil PVC Sheeting
4" Perforated Pipe
Figure 7-11. Cross-sectional view of site H liner showing details
of leachate collection system and lysimeter construction.
7-31
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The leachate collection system consists of a 1-foot trench excavated
into 5-foot-thick sections- of the clay liner. Eight-inch perforated PVC
pipe is positioned in the trench, which is backfilled with 3/4-inch crushed
rock. The entire trench is overlain by a 2-foot-high mound of sand. A
1-foot-thick layer of silty sand covering the entire bottom of the landfill
serves as a protective layer for the clay liner (see Figure 7-11).
The lysimeters located under the clay liner are approximately 12 feet
by 100 feet. They are lined with 20-mil PVC sheeting and filled with
medium to coarse sand. Four-inch perforated PVC pipe positioned in the
bottom of each lysimeter (see Figure 7-11) connects them to a manhole, thus
enabling leachate detection and collection.
7.2.9.6 Liner System Installation--
Prior to clay liner installation, the fill area was rough graded.
Clay was brought to the facility from a nearby borrow area. The variable
nature of the borrow area required a soils technician to be present during
all removal operations to ensure that the material met the project specifi-
cations. The technician rechecked the material by performing the required
soil tests as the clay was emplaced. The liner was compacted in 12-inch
lifts with either a rubber-tired or sheepsfoot roller.
The construction quality control (CQC) program called for 29 Shelby
tube samples taken at various locations in each of the four 1-foot-thick
clay lifts. These samples were tested for various parameters. The results
of these tests were:
Permeability 7 x 10"8 cm/s, 5 x 10"10 cm/s
Liquid limit 39 - 82%
Plastic limit 20 - 37%
Plasticity index 16 - 54%
P-200 >50%
Density 92 - 102.8% of maximum dry density
(nuclear guage)
95 - 110.8% of maximum dry density
(sand cone).
7.2.9.7 Performance—
Quarterly sampling of all monitoring points began in December 1980.
This sampling included determining leachate volumes and composition, lysi-
meter liquid volumes and composition, and groundwater composition. The
liquid volumes collected from both the lysimeters and the leachate collec-
tion system are shown in Table 7-3.
7-32
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TABLE 7-3. LYSIMETER (L) AND LEACHATE COLLECTION SYSTEM (LCS)
LIQUID VOLUMES (GAL) AT SITE H
Date
Lla
L2
L3
LCSb
12/80
38
66
Dry
3/81
24
9.4
1
NA
6/81
1.9
0.6
Dry
NA
9/81
0.03
0.03
1
89,603
12/81
Dry
Dry
0.75
NA
3/82
Dry
Dry
Dry
NA
6/82
Dry
Dry
Dry
32,995
9/82
Dry
Dry
Dry
63,321
12/82
Dry
Dry
Dry
89,678
12/83
Dry
Dry
Dry
NA
aLysimeter 1 is located below the leachate holding pond.
The numbers indicate the total monthly volume of leachate that was pumped from the collection system at
-jj irregular intervals.
u> NA = Data not available.
-------
As Table 7-3 indicates, the volume of liquid collected in lysimeters
has declined steadily over time. The liquid that was initially collected
in the lysimeters may be soil moisture released after site construction.
Analysis of leachate and groundwater samples is presented in Table 7-4.
To date, there is no apparent difference in water quality between the base-
line groundwater samples and the more recently taken samples from upgradient
and downgradient monitoring wells.
7.2.10 Site I
7.2.10.1 Physical Description—
This facility consists of three clay-lined surface impoundments as
well as a landfill. The ponds that cover approximately 8 acres are lined
with two compacted clay liners that are separated by a leak detection
system.
7.2.10.2 Startup Date-
Construction of the three ponds at this facility was completed in the
fall of 1980. Waste was placed in two of the ponds that fall but was not
placed in the third pond until the following spring.
7.2.10.3 Local Geology and Hydrology—
This facility is located in a semi arid section of the western United
States. Average annual precipitation at the facility is approximately
15 inches.
Approximately 75 percent of the site area was used for the land appli-
cation of sewage sludge. This material was disked into the top layer of
soil to form a 2-foot layer of highly organic topsoil. Below this layer
lies 5 to 7 feet of residual clay soil underlain by 5 to 20 feet of sandstone,
which overlays 10 to 20 feet of clay stone bedrock. The residual clay soil
has the following properties:
Liquid limit 36 to 57 (average - 45) %
Plasticity index 16 to 27 (average - 21) %
Natural water content 14.6 - 26.1 (average - 23) %
Dry density 80.9 (1 sample) lb/ft3
pH 7.5-7.7 (average - 7.6)
Unified Soil Classification CH, CL, and CL-CH
System designation
The groundwater at the site ranges from 100 to 200 feet below the
surface. Drainage across the site is to the east.
7-34
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TABLE 7-4. MONITORING DATA FOR SITE H
CO
en
Parameter
Sample date
Chloride (mg/L)
COD (mg/L)
PH
Alkalinity, total
(mg/L)
Conductivity
(micro/cm)
Total hardness
CaC03 (mg/L)
Iron, dissolved
Baseline
groundwater
analysis
6/80
1.5 -
4.0 -
7.2 -
120 -
300 -
122 -
0.49 -
5.4
21.0
7.6
240
385
228
2.65
Upgradient
well
9/81
2.5
11
7.4
206
405
222
0.06
Range for
all other
wells
9/81
1 -
4 -
7.2 -
150 -
320 -
162 -
0.01 -
3
50
7.4
168
350
182
0.09
Leachate
6/81
230
5,315
6.1
960
5,000
3,650
161
: :
Range for all
lysimeters
6/81
16 -
40 -
7.1 -
291 -
625 -
344 -
0.06 -
19
57
7.2
445
840
480
0.20
-------
7.2.10.4 Waste Type—
The three ponds have received most types of hazardous waste, except
pesticides, herbicides, PCB's, dioxin, reactive materials, and any material
containing more than 5 percent solvents. Pond No. 1 was the only pond to
receive oily wastes.
Wastes were placed in the ponds through a trough leading to the base
of each pond.
7.2.10.5 Liner Description—
The liner at this facility consists of two 5-foot layers of recom-
pacted local clay soil that are separated by a 15-inch leak detection
layer. The three ponds are separated by dikes that are 12 feet wide at the
top (see Figure 7-12). The interior slopes of the dikes (sidewalls) are
3:1. A cross-sectional diagram of the liner system is illustrated in
Figure 7-13.
Properties of the local clay soil that was used as the liner material
are listed in Section 7.2.10.3. Additional laboratory testing of_this
material_indicated that it had a permeability ranging from 2 x 10 9 to
4.8 x 10 8 cm/s. The value for the permeability of the claystone material
ranged from 3 x 10 9 to 1 x 10 8 cm/s.
7.2.10.6 Liner System Installation—
The local soil was excavated with dozers and scrapers. Excavated
clayey materials were placed on a stockpile. Here the material was spread
in 8-inch lifts and then watered to achieve a moisture content between
optimum and 3 percent above optimum. After the excavation was complete,
the pond bottoms were graded according to design specifications. This
included the additional excavation of a 10-foot-wide trench area beneath
the leak detection system collection pipes.
The stockpiled liner material was disked and then placed in the pond
excavations in horizontal lifts (which, before compaction, were 8 inches
thick). The lifts were compacted to 95 percent standard Proctor density
with a sheepsfoot roller.
A backhoe was used to excavate a shallow trench into the bottom liner
for the leak detection drain and sump. Perforated pipe was placed in the
trench and then covered with gravel. The entire bottom liner was then
covered with a sand drainage layer.
The final 5-foot (minimum) clay liner was constructed through the same
procedure as previously discussed. A 2-foot protective layer of sandy soil
was placed on top of the finished clay liner. Waste unloading troughs were
protected at the bottom with rip-rap.
7.2.10.7 Performance—
The construction of the liners of these ponds was completed in the
fall of 1980. Ponds No. 1 and 3 were filled with waste shortly thereafter.
Pond No. 2, however, was left unfilled and uncovered until the following
7-36
-------
OJ
Leak
Detection
Sump
Figure 7-12. Plan view of site 1.
-------
OJ
00
Truck Maneuvering Area
•18-in Gravel Layer
3-ft Freeboard
Waste
2 ft Liner Protection Layer
10 ft (max.)
Liquid
Depth
5-ft (min.)
18 in Leak Detection Layer Compacted Clay Liner
5-ft (min.)
Compacted Clay Liner
Leak Detection Pipe
\\
\\ // \\
\\
\\
10ft
Figure 7-13. Cross section of liner at site I.
-------
spring. Approximately 3 months later, liquid started accumulating in the
leak detection system. This liquid had elevated levels of chloride, ammon-
ium, and total dissolved solids as well as increased conductivity. Liquid
was not detected in the sumps of ponds No. 1 and 3.
The most probable cause of the failure at pond No. 2 was waste migra-
tion through desiccation cracks in the upper liner. Cracks ranging from 2
to 10 mm wide were observed on the upper portion of the sidewalls. In most
cases, these cracks could not be traced for any more than a few feet along
the surface. An exception to this was in the corners of the liner, where
the cracks appeared to be up to 20 feet long.
7.2.11 Site J
7.2.11.1 Physical Description—
This facility consists of a drum disposal pit, a solvent recovery
facility, and seven ponds, one of which is used for landfill ing. The ponds
range from approximately 1/2 to 4 acres. All of these areas are lined with
two layers of compacted clay separated by a leak detection system. A
10-foot-high retention dike located northeast of the disposal areas prevents
any overflowing liquid, such as may occur during a 100-year storm, from
leaving the facility. Several groundwater monitoring wells are installed
around the facility (see Figure 7-14).
7.2.11.2 Startup Date--
Ponds No. 1 through 4 and the drum pit went into service in June of
1979. The remaining ponds (No. 5 and 6) started operation in May of 1981.
Pond No. 7 was used as a landfill starting in May of 1981.
7.2.11.3 Local Geology and Hydro!ogy--
This facility is located in the southern central United States. The
average annual precipitation at the facility is approximately 26 inches.
The top layer of soil at this site consists of red silty clay. Thin
sandstone and gypsum lenses are present at depths ranging from 8 to 18 feet
below the ground surface. A layer of gray siltstone encountered at depths
ranging from 14 to 27 feet underlies the silty clay. The physical properties
of the silty clay are as follows:
Soil type Very fine silts or clays
Liquid limit 31.0 - 46.0%
Plastic limit 22.3 - 29.5%
Plasticity index 7.4 - 20.1%
Optimum moisture content 18.0 - 23.7%
7-39
-------
Groundwater
Flow
o
Solvent
Recovery
Facility
Figure 7-14. Plan view of site 3.
-------
Maximum dry density 99.3 - 110.4 lb/ft3
_q _o
Laboratory permeability 2.0 x 10 - 2.9 x 10 cm/s.
Six borings were dug in an attempt to determine the location of the
water table. At the time of exploration, water was encountered in two of
the borings at depths of 7 and approximately 27 feet below the ground
surface. Ten days later, water was standing in all six borings at depths
ranging from 5 feet 8 inches to 23 feet below the ground surface. Surface
drainage from the site is in two directions—north and east.
7.2.11.4 Waste Type—
This facility receives most types of hazardous liquids and sludges.
7.2.11.5 Liner Description—
The bottom liners at this facility consist of two recompacted clay
layers separated by a leak detection system. The lower clay liner is
I foot thick and the upper clay liner is a minimum of 5 feet thick. The
sidewalls are constructed partially underground and partially above ground.
The aboveground sections are built upon dikes. The leak detection system
is a 6-inch drainage blanket that slopes to a trench containing a 2-inch
slotted PVC collection pipe (See Figure 7-15). Quality assurance test
results of the completed liners are as follows:
• Dry density 94.2 - 115.8 lb/ft3
• Moisture content 15.8 - 31.0%
-9 -8
• Permeability 5.3 x 10 - 2.8 x 10 cm/s
• Liquid limit 35.6 - 63.0%
• Plastic limit 16.1 - 31.6%
Plasticity index 6.7 - 36.6%.
7.2.11.6 Liner System Installation—
No specific information on the liner construction or the equipment
used was available. However, it is known that construction of the second
phase (ponds No. 5, 6, and 7) took place during the winter. Problems due
to frozen and unworkable liner materials caused many construction slowdowns.
Quality control (QC) and quality assurance (QA) inspectors were present
at the facility during construction operations. They conducted tests, made
observations, and prepared a project diary and final documentation report.
7.2.11.7 Performance—
Liquid, presumed to be construction water, was being collected and
removed from all of the detection systems by early 1982. This liquid was
periodically analyzed and found to be "clean" until Febrtary 1982. At this
7-41
-------
Dike
Sidewall Slope
ro
2 in Slotted PVC
Leak Detection Pipe
5 ft (min.)
Compacted Clay
Liner
6 in Drainage Blanket
(Leak Detection System)
1-ft Compacted Clay Liner
6 in (min.)
Figure 7-15. Cross-sectional view of site J liner.
-------
time, samples removed from the pond No. 5 detection system contained a
yellow-brown oily liquid with an organic-solvent odor. A small water phase
was present in the sample. Analysis of this sample showed that it contained
over 11.2 percent perch!oroethylene (perc) plus small amounts of other
chlorinated and nonchlorinated organics. The facility was allegedly not
accepting wastes with more than a trace of "perc."
An investigation of the problem revealed that aqueous wastes coming
from one of the disposal facility's customers contained approximately
5 percent degreasing fluid waste, which contained perch!oroethylene. This
waste was to have been stored in a separate tank at the originator's plant.
Evidently, it was not made clear to the workers where to put the "perc"
waste, and it was placed in an aqueous waste storage tank. Being insoluble
and heavier than water, it sank to the bottom. When a tank truck from the
disposal facility would collect a load of aqueous waste, it would also
receive a few hundred gallons of the "perc" waste. The waste sampling
method used by the disposal facility on all loads of incoming waste was not
able to sample the bottom few inches of each load. In addition, the parking
area where all truckloads of waste were sampled was slightly sloped; this
sloping caused the relatively small amount of "perc" waste in the bottom of
the tanker to flow to the back of the truck, where it could not be reached
by the sampling device.
Over approximately 9 months, the aqueous waste containing the "perc"
was placed in one of the clay-lined ponds and went unnoticed until the
liner failure occurred. The apparent incompatibility is consistent with
current research on the effects of chlorinated solvents on clays.
Presently, the leak in the pond No. 5 liner has slowed down considerably.
Perchloroethylene concentrations in the detection system liquid are less
than 100 ppm. It is estimated that several thousand gallons of the "perc"
waste are adsorbed into the clay liner and the sludges in the pond's bottom
and will present minor problems for many years.
7.2.12 Site K
7.2.12.1 Physical Description—
This facility consists of six double-lined ponds ranging in size from
1.2 to 2 acres. The liners are composed of a 3-foot recompacted clay
layer, below which lies a leak detection system and a 1-foot layer of
recompacted clay. A typical cross-section of the pond and liner system is
illustrated in Figure 7-16. The design depth of all six ponds is 10 feet.
7.2.12.2 Startup Date—
The construction of the first pond at this facility was completed in
December 1981. Five additional ponds have been constructed since then.
7.2.12.3 Local Geology and Hydrology--
This facility is located in the western United States. Average annual
precipitation at this facility is approximately 6 inches, while the average
annual evaporation is 63 inches.
7-43
-------
•--I
I
Dike
3 ft (min.)
Recompacted
Clay Liner
1-ft (min.)
Recompacted Clay Liner
// \\
1 ft (min.)
Sand Basket
(Leak Detection
System)
4 in Slotted PVC Pipe
Figure 7-16. Cross-sectional view of site K liner.
-------
A total of 10 trenches and 12 borings ranging from 8 to 100 feet in
depth were used to investigate the geology at this facility. This investi-
gation, combined with prior knowledge, revealed three distinct layers of
silty claystone, siltstone to sandstone, and silty claystone. The uppermost
layer caps a flat ridge at the facility. Here the silty claystone is up to
80 feet thick. The next layer ranges up to 120 feet thick. The lower
layer is in excess of 80 feet thick across the entire site.
The uppermost claystone layer was characterized most extensively. It
has the following properties:
Liquid limit 56 - 84%
Plasticity index 36 - 55%
P200 83 - 99%
Laboratory permeability 5.0 x 10~7 - 2.8 x 10~8 cm/s
(remolded)
Laboratory permeability 3.7 x 10 7 -6.1 x 10 8 cm/s
(undisturbed)
Investigations also revealed the presence of occasional gypsum veins through-
out the claystone material. These veins ranged in thickness from less than
1/10 inch to about 3 inches and had an average permeability of 2.4 x 10-3 cm/s.
A review of published data indicated that several seismic faults exist
in the region of the disposal facility. However, within 4 miles of the
site no seismic faults show evidence of recent creep. The two seismic
faults within 1/2 mile of the facility are both inactive.
State investigations indicate that groundwater is scarce in the vicinity
of the site. This fact was confirmed by drilling 12 borings on the site
property. Of the 12, only 1 encountered water at a depth of 32 feet perched
on claystone bedrock.
The scarcity of groundwater is due to low rainfall, high evaporation,
and the fine-grained nature of the sediments.
7.2.12.4 Waste Type—
The facility accepts liquid-scrubber wastes that are generated while
stack gases are cleared from oil-refining facilities. The wastes are
highly saline with pH values in the wide range of 3.5 to 9.0. The waste is
temporarily stored in the evaporation ponds. When it has been reduced to a
semisolid, it is removed and disposed of onsite.
7.2.12.5 Liner Description—
The pond liners were constructed of the local excavated claystone
material. The liner system consists of a 1-foot recompacted basal liner.
Sump and collection trenches are excavated into this bottom liner. A
7-45
-------
1-foot sand layer covers the lower clay liner. The sand layer is overlain
with 3 feet of clay.
Four undisturbed samples were taken from one of the constructed liners
and tested for their Atterberg limits, percent passing the No. 200 sieve,
moisture content, and dry density. The results of these tests are presented
below.
Atterberg limits
-Liquid limit (%) 70 87 84 93
-Plasticity index (%) 49 67 64 69
Amount passing No. 200 86.9 88.1 88.3 87.2
sieve (%)
Moisture content (%) 24.9 21.5 20.8 23.0
Dry density (lb/ft3) 94.6 103.0 104.4 99.8
Permeability tests were conducted in which remolded liner samples were
subjected first to water and then to typical wastes. The permeability of
the liner material to both water and the scrubber waste ranged from 2 x 10-7
to 1 x 10-8 cm/s. The design specifications called for the liner permeabil-
ity to be no greater than 1 x 10-6 cm/s.
7.2.12.6 Liner System Installation--
The leak detection system was constructed by first excavating and
subsequently recompacting the clay soil to provide a 3-foot foundation
beneath the collection drains and sump. A 1-foot clay liner was then
placed over the base and side slopes of the excavated area. The sump and
drain-pipe trenches were then excavated over the 3-foot foundations. After
the installation of the drainage system, a 1-foot layer of sand was placed
over the entire clay liner. Finally, a 3-foot recompacted clay liner was
placed on top of the sand layer. A segmented steel-wheel compactor was
used for liner compaction.
Construction activities were inspected by the design firm. Included
in these inspections were numerous density, moisture content, and permeabil-
ity tests. At the completion of construction, the design firm certified
that the facility was constructed according to design specifications and
would therefore perform as designed.
7.2.12.7 Performance--
Liquid volumes collected in the leak detection system were used to
determine the installed liner permeability. The permeabilities for five of
the six ponds were calculated based on Darcy's Law, the collected leachate
volumes, and the impounded liquid depth and pond area. The value for
pond No. 4 was not available. These values are as follows:
7-46
-------
Pond Average Permeability (cm/s)
1 2.95 x 10-7
2 1.8 x 10-7
3 4.1 x 10-8
4 Data not available
5 1.4 x 10-7
6 1.4 x 10-7
The permeability of the installed liner system is less than the specified
value of 1 x 10 6 cm/s.
This facility is located approximately 100 miles south of the epicenter
of a recent major earthquake. After the quake, the excavation, slopes, and
berms were examined carefully, but no indications of seismic damage were
noted. Careful monitoring of the ponds since the quake has not revealed
any unusual changes in fluid levels or leachate collection volumes.
7.2.13 Site L
7.2.13.1 Physical Description—
The landfill consists of a flat double-clay liner on top of which a
dike has been placed to contain the wastes. The liner extends beyond the
dike to form the liner for a 12-foot-wide drainage ditch that encircles the
site (see Figure 7-17).
The landfill is divided into two separate sections, one for each of
two types of waste. The largest area is designed to contain dewatered
sludge pumped from settling tanks. It has a 5-foot-high perimeter dike and
a drainage blanket on top of the liner composed of 1 foot of graded clean
sand with drain pipes installed to collect and remove leachate. Sludge is
transferred to this portion of the landfill through a pipeline from offsite
settling tanks.
The smaller section of the landfill is designed to hold chemical
wastes from the plant manufacturing units and QC laboratory. It has a
gravel bottom over its liner. The working area was developed in sections
across the width of the landfill with the waste layer maintained at approxi-
mately 3 feet in depth. Each lift of waste was covered with river sediment
material previously deposited on the site.
7.2.13.2 Startup Date—
The site became active in 1978.
7-47
-------
CO
Waste
Dike
Drainage Layer
Leachate Collection Pipe
Leak
Detection
Layer
Figure 7-17. Cross-section of containment system at site L.
-------
7.2.13.3 Local Geology and Hydrology—
The facility is located in the northeastern United States. Average
annual precipitation at this facility is approximately 40 inches.
The facility is located in an area where there is approximately 3 feet
of topsoil over a subsoil varying from silt to sand to fine gravel and
sandy clay. Groundwater is located in the subsoil layer at depths ranging
from 4.5 to 14.5 feet below the ground surface.
7.2.13.4 Waste Type—
The landfilled waste material can be defined as either sewage treatment
plant sludge or chemicals. The sewage treatment plant sludge consists of
dewatered (12 to 15 percent solids) sludge removed from settling tanks and
transferred to the landfill. The chemical waste consists of inert material
from lime slaker operations (inert rocks and insoluble calcium and magnesium
salts), hard-pitch residue that is only slightly water soluble and that
crystallizes at 180 °C, filter aid (dicalite) wetted with phosphate esters,
filter paper wetted with phthalate esters, and residue from the manufacture
of tetrachlorophthalic anhydride.
7.2.13.5 Liner Description—
The liner system at this facility consists of the six layers listed
below from the top down:
8- to 12-in. drainage layer (sand or gravel)
18- to 25-in. compacted clay
12-in. sand leak detection layer
12-in. compacted clay
6- to 18-in. compacted soil
Bidim type C34 (synthetic soil stabilization geotextile).
The physical properties of the clay used for the liner are as follows:
Soil classification - grey silty clay
Particle size distribution: Gravel - 1%
Sand - 29%
Clay and colloids - 70%
Liquid limit 45%
Plastic limit 17%
Plasticity index 18
Liquidity index 0.1
7-49
-------
Specific gravity 2.67
Moisture content 28.5%
Dry unit weight 95.0 1b/ft3
Maximum dry density 101.5
Optimum moisture content 19.5%
Permeability 6.6 x 10"8 to 3.8 x 10"9 cm/s.
7.2.13.6 Liner System Installation--
No information was available on installation procedures.
7.2.13.7 Performance—
Within the first year of operation, problems developed in the upper
clay liner. Evidence of this was the appearance of contaminated water in
the leachate monitoring layer manhole. Slight contamination in local
groundwater monitoring wells was also discovered. A study conducted to
determine the source of the groundwater contamination revealed that the
source of contamination was not the double-lined pond.
7.2.14 Site M
7.2.14.1 Physical Description--
This 12-acre site is designed to consist of three cells of approximately
equal size. At the time of this writing, the first cell was still in use
and construction had not yet started on either of the remaining two cells.
The facility is lined with 1 foot of recompacted clay. A leachate
collection system is above the clay liner and a leak detection system lies
2 feet below the clay liner. In addition to the leachate collection and
subsurface monitoring (leak detection) systems, three groundwater monitor-
ing wells are situated around the facility as well as drainage ditches to
prevent surface runoff from entering the landfill (see Figures 7-18 and
7-19).
7.2.14.2 Startup Date--
Construction was initiated in 1977. The first wastes were accepted in
1978.
7.2.14.3 Local Geology and Hydrology--
This facility is located in the northern central portion of the United
States. Average annual precipitation in the vicinity of this facility is
approximately 26 inches.
A total of five borings were used to investigate the subsurface condi-
tions at the proposed landfill site. The borings indicated a uniform
geologic profile over the entire facility. The top 1 to 2 feet of soil
consists of a silty sand underlain by approximately 25 feet of fine- to
medium-grained sandy alluvium.
7-50
-------
I
en
Original Ground Contour
Actual
Sidewall
Slope
1 ft
Coarse
Sand or
Fine Gravel
Subsurface Monitoring
System Pipe
(Leak Detection)
Historial High
Water Table
Subsurface
Monitoring
(Leak Detection)
System Sump
and Manhole
Leachate
Collection
System Sump
and Manhole
Leachate
Collection
System Pipes
1 ft Compacted
Clay Liner
Figure 7-18. Cross-section of site M.
-------
Location of borings
Location of monitoring wells
Manhole
Area for
Future Development
Direction of
Groundwater
Flow
Leachate Collection System
Perforated Pipes
Subsurface
Monitoring
System (Leak
Detection)
W-3
Figure 7-19. Plan view of site M leachate collection and leak detection systems.
7-52
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Groundwater was encountered in all five borings at depths ranging from
approximately 10.5 to 15 feet below the original ground surface. Groundwater
flow was toward a marshy area located east of the proposed facility. Other
information indicates that in a second deep aquifer groundwater flow is in
a southeasterly direction.
7.2.14.4 Waste Type and Placement—
The landfill is used for the disposal of inorganic lime sludge.
Samples of the sludge have been analyzed for heavy metals content and
percent solids. The results of these analysis are presented in Table 7-5.
Due to the high moisture content of the waste material, a special pro-
cedure for waste placement was developed. This procedure involved mixing a
thin layer of the sandy soil obtained from the site excavation with a thin
layer of the waste in order to reduce the overall moisture content and to
give the material structural stability. The range of soil to waste ratios
varied from 0.5:1 to 1.5:1. Exact mixing proportions were determined in
the field and judged sufficient when the landfill equipment was able to
drive over the mixture. Due to the great amount of soil mixed with the
waste and the waste's inorganic nature, no daily cover was used at this
facility. The proposed final cover will consist of a 6-inch compacted clay
cap, 2 feet of topsoil, and a vegetative cover. No gas venting or collec-
tion will be necessary.
7.2.14.5 Clay Liner Description—
The clay for the liner was obtained from a nearby borrow area. The
specifications for the clay are as follows:
Liquid limit 50 - 70%
Plasticity index >28%
P200 >75% (by weight)
Permeability <1 x 10 7 cm/s
(recompacted)
No documentation was available on the as-built liner material characteristics.
7.2.14.6 Liner System Installation—
7.2.14.6.1 Excavation—The first cell was excavated to a maximum
depth of 6 feet. This provides a minimum of 5 feet separation between the
lowest layer of waste and the highest seasonal groundwater elevation. The
sidewalls were excavated to a maximum slope of 3:1. The bottom has a
1-percent slope to the center of the landfill.
The earthen material removed during excavation was segregated and
stockpiled for future use as cover material and waste stabilizer.
7-53
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TABLE 7-5. HEAVY METAL CONTENT AND PERCENT SOLIDS OF LIME SLUDGE
DISPOSED AT SITE M
Sample date
7/79
7/80
10/81
7/82
Cadmium
(rag/kg)
6.6
1.6
3.3
0.89
Chromium
(rag/kg)
200
110
1,300
170
Copper
(mg/kg)
4,500
5,300
3,800
520
Cyanide
(mg/kg)
750
140
2
52
Iron
(mg/kg)
5,400
10,000
11,000
880
Lead
(mg/kg)
5,200
5,100
4,800
520
Nickel
(mg/kg)
1.300
1,100
340
64
Zinc
(mg/kg)
5,700
4,900
5,200
640
PH
7.8
8.6
7.9
8.5
Total
solids
(%)
--
11.1
28.7
12.1
I
en
-------
7.2.14.6.2 Subsurface Monitoring System—Four trenches were excavated
in the landfill base to a depth of 2 feet. Four-inch perforated PVC pipes
and coarse sand and gravel were placed in these trenches to serve as the
subsurface monitoring system.
7.2.14.6.3 Clay Liner—Prior to the placement of the clay liner, all
large rocks, roots, and other foreign matter were removed from the foundation.
The foundation was then graded to a 1-percent slope and scarified to permit
better bonding between the foundation and the first clay lift. Uncompacted
liner material was placed in loose 12-inch lifts and moistened as necessary.
The clay was then compacted with "approved" equipment. Documentation of
the specific types of equipment used was not available.
7.2.14.6.4 Leachate Collection System—The leachate collection system
consists of 4-inch perforated PVC pipes placed in a 12-inch layer of sand
on top of the clay liner. The 4-inch pipes run into a 6-inch pipe in the
center of the landfill, which leads to a 1,000-gallon concrete tank and
manhole system. Documentation of the construction procedures used to
install the leachate collection system was not available.
7.2.14.7 Performance--
Samples from the monitoring wells have been analyzed on a quarterly
basis since 1978. Examples of these data are presented in Table 7-6.
These data indicate that the groundwater quality has not changed significantly
since the commencement of the landfill operation.
The leachate from the landfill has also been sampled and analyzed
since 1978. Examples of these data appear in Table 7-7. Table 7-8 contains
leachate volume data.
The subsurface monitoring system tank also has been checked on a quar-
terly basis. There has been no indication of leachate entering this system.
The above facts confirm that the landfill has performed as designed
since its construction and initial waste placement in 1977 and 1978.
7.2.15 Site N
7.2.15.1 Physical Description—
The site is located in an old sand and gravel pit and covers approx-
imately 160 acres. The eight cells range in size from 9 acres to 25 acres
with 20 acres being the average cell size. At the time of writing, the
liner covers 108 acres.
The facility bottom is lined with a 4-inch bentonite and sand layer.
The sides of the landfill are unlined. Two 1,000-ft2 PVC-lined lysimeters
are below the liner as well as a system of 24-inch perforated pipe, which
lowers the groundwater table. A leachate collection system is above the
liner. In addition to these systems, several monitoring wells and surface-
water monitoring points are around the facility (see Figures 7-20 and
7-21).
7-55
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TABLE 7-6. GROUNDWATER MONITORING WELL SAMPLE ANALYSIS AT SITE M
en
en
Well Sample Cadmium Chromium Copper Cyanide Iron
number date (mg/kg) (rog/kg) (nig/kg) (mg/kg) (nig/kg)
1 7-79 <0.01 <0.05 <0.05
1 7-82 <0.01 <0.05 <0.05
2 7-79 <0.01 <0.05 <0.05
2 /-82 <0.01 <0.05 <0.05
3 7-79 <0.01 <0.05 <0.05
3 7-82 <0.01 <0.05 <0.05
<0.01
<0.02
<0.01
<0.02
<0.01
<0.02
TABLE 7-7. LEACHATE ANALYSIS AT SITE
Cadmium Chromium Copper Cyanide
Sample date (mg/L) (mg/L) (mg/L) (mg/L)
7/79 <0.01 <0.05 0.15 0.02
7/80 <0.01 <0.05 0.20 0.03
10/81 <0.01 <0.05 0.30 0.09
7/82 0.02 0.05 0.35 <0.02
Iron
(mg/L)
3.5
4.0
3.0
3.5
0.30
0.10
0.25
0.4
0.1
0.05
M
Lead
(mg/L)
<0.1
<0.1
0.1
<0.2
Lead
(mg/kg)
<0.1
<0.2
<0.1
<0.2
<0.1
<0.2
Nickel
(mg/L)
0.10
0.05
0.35
0.15
Nickel Zinc
(mg/kg) (mg/kg)
<0.05 0.01
<0.05 0.5
<0.05 0.15
<0.05 0.10
<0.05 <0.01
<0.05 0.02
Zinc
(mg/L) pll
0.13 7.4
0.10 7.5
0.10 6.9
<0.10 7.2
pll
8.0
7.5
7.9
7.2
7.9
7.3
-------
TABLE 7-8. LEACHATE VOLUMES AT SITE M
Date Volume
1/82 31,000
4/82 150,500
7/82 124,520
10/82 66,925
7-57
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I
en
CO
Groundwater '—
Pumping Station
Figure 7-20. Plan view of site N.
-------
Gruundwater
Pumping Lysimeter
Station Manhole
Leachate
Pumping
Station
en
1C
%* - ' ' • ' i'w
6 in Sand Layer
(Collection System)
in Bentonite-Sand Liner
Lysimeter
20 mil PVC Membrane
Lysimeter Drain Pipe
Perforated Groundwater
Drain
Compacted
Native Sand
18 in (min.)
Figure 7 21. Cross-sectional view of site N liner and leachate management systems.
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7.2.15.2 Startup Date-
Construction of cell 1 was initiated in 1974. Since then, seven addi-
tional cells have been installed.
7.2.15.3 Local Geology and Hydrology—
This facility is located in southeastern Canada. The average annual
precipitation in the vicinity of the landfill is approximately 35 inches.
Very little information was available concerning the local geology and
hydrology. As previously mentioned, however, the facility is located in an
old sand and gravel pit. The local soil is very sandy and, for this reason,
a bentonite liner was chosen.
Because natural groundwater elevations at the facility are very near
the surface, a drainage system was installed to lower the groundwater
table. The final groundwater elevation is maintained at 5 feet below the
liner bottom.
7.2.15.4 Waste Type—
The facility accepts municipal solid waste only. At the time of this
writing, the facility contained approximately 25 million yd3 of waste
material.
7.2.15.5 Liner Description—
Laboratory studies have shown that 6 percent by weight of bentonite
(sodium montmorillonite with 55 to 75 percent by weight pas-sing the #70
mesh sieve) in a 6-inch sand layer would produce a liner with the specific
permeability of 1 x 10-8 cm/s. During liner installation, a 4-inch layer
produced a more uniform mix. Therefore, a 4-inch liner was installed with
an additional 3 percent by weight of bentonite as a safety margin. The
liner was compacted to a minimum 90 percent standard Proctor density.
7.2.15.6 Liner System Installation—
7.2.15.6.1 Excavation—Little additional excavation was necessary due
to the location of the facility in an old sand and gravel pit. Areas that
were to be lined were excavated to bottom contours and graded to a 1-percent
slope with large-capacity self-loading scrapers. A 7-ton, self-propelled,
vibratory, smooth-drum roller was used to compact the basal sand and to
complete the grading of the cell bottom into a relatively smooth surface.
7.2.15.6.2 Liner—The following methods were used to construct the
1 i ner.
Bentonite was spread to a 5/8-inch thickness with three to five passes
of a large scraper. Next, a tractor-mounted rotatiller was used to mix the
bentonite into the sand to a depth of approximately 4 inches. The liner
material was allowed to hydrate naturally. Additional water was added as
necessary to achieve the required moisture content. The liner was compacted
with a vibratory smooth-drum roller a minimum of four passes.
7-60
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The leachate collection system was then installed on the liner and
covered with clean pea gravel. A 6- to 8-inch layer of loose sand was
placed over the finished liner. No traffic was allowed on the completed
area before refuse was spread over the liner from the top.
QA testing of the constructed liner indicated that the bentonite
content ranged from 8.5 to 15 percent by weight and averaged about 11.2
percent by weight. Greater than 90 percent compaction was achieved in all
areas with variations from 93 to 100+ percent standard Proctor density.
The moisture content varied from 3 to 12 percent.
7.2.15.6.3 Monitoring Systems—Methods used to install the various
monitoring systems were not available.
7.2.15.7 Performance—
Analysis of water samples collected from lysimeter 1, surface-water
monitoring points, and groundwater monitoring wells indicates that leachate
has passed through the liner and entered the groundwater. Liquids have
also been detected but not analyzed in lysimeter 2. Table 7-9 contains the
results of the analysis for biochemical oxygen demand (BOD), COD, total
coliform, and fecal coliform at several of the monitoring points.
7.2.16 Site 0
7.2.16.1 Physical Description--
This landfill is approximately 2 acres in size. It is lined with a
mixture of local soil combined with a 1:1 mix of bentonite and lime. The
lime was added to reduce the swelling potential of the bentonite. A leachate
collection system is on top of the clay liner. Several groundwater monitor-
ing wells are located adjacent to the landfill. The landfill has been
capped and covered with asphalt pavement.
The leachate collection system consists of a stone-packed sump (drywell)
with a casing pipe extending to the surface that is used for observation
and leachate withdrawal.
7.2.16.2 Startup Date--
Construction of this facility began in June of 1980. It was filled
and capped by September 1980.
7.2.16.3 Local Geology and Hydrology—
This facility is located in the southeastern United States. Average
annual precipitation at the facility is approximately 50 inches.
The soil in the vicinity of the landfill is composed of a mixture of
clay, silt, and sand. Soil borings of the site indicate that this soil
mixture extends to a minimum of 10 feet. Analysis of the native soil gave
the following results:
7-61
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TABLE 7-9. WATER SAMPLE ANALYSES: BOD, COD, TOTAL COLIFORM,
AND FECAL COLIFORM
Samp!
(see
ing location
Figure 7-20)
Lla
SW lb
SW 2b
SW 3b
SW 4b
MWlb
MW 2b
MW 3b
MW 4b
BOD
(mg/L)
336
<1
<1
1
260
>800
16
13
2
COD
(mg/L)
1,560
3.9
5.8
19
400
1,870
45
100
10
Total col i form
100 mL
14,000
500
1,900
500
0
0
190
0
0
Fecal col i form
100 mL
14,000
140
320
90
0
0
0
0
0
aSample date - 12/5/83.
bSample date - 10/11/83.
7-62
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Average permeability 8.7 x 10 s cm/s
Plasticity index 7.1%
Liquid limit 27.1%
Plastic limit 20.0%
Amount passing No. 200 sieve 31.3%.
Monitoring wells have indicated that groundwater is well below the
bottom of the site and poses no potential problem. Water samples from the
monitoring wells are taken monthly and analyzed for PCB's, pH, specific
conductance, and chlorinated organics.
7.2.16.4 Waste Type—
The major material disposed at this site was PCB's. The facility also
contains solvents, waxes, and oils, all of which were solidified with
sawdust prior to their disposal.
7.2.16.5 Liner Description—
The 4-foot-thick liner consists of a homogeneous mixture of 3 percent
bentonite, 3 percent lime, and 94 percent native soil.
The physical properties.of the liner material are:
Liquid limit 27.8%
Plastic limit 20.7%
Plasticity index 7.1%
Permeability 8.3 x 10"8 cm/s
Amount passing No. 200 sieve 35.4.
The leachate collection system consists of a stone-packed sump (drywell)
with a casing pipe extending to the surface that is used for observation
and leachate withdrawal.
7.2.16.6 Liner Installation—
The liner at this facility was installed in 8-inch lifts and compacted
to at least 95 percent of maximum Proctor density. The bottom of the
facility slopes at a rate of 2 percent to the leachate collection system.
The sidewall slopes are 3:1 maximum. The 3-foot-thick cap constructed of
the same mixture was compacted to 90 percent of maximum density. No informa-
tion on the installation of the asphalt cover was available.
7.2.16.7 Performance—
Due to a poor seal around the leachate collection system casing pipe
(standpipe), surface water eroded through this area and was collected in
7-63
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the sump. This problem was solved by removing a 12-foot-diameter section
of the cap surrounding the pipe. The area was then filled with tightly
compacted pure bentonite. A concrete dome was placed on top of the ben-
tonite to direct the flow of water away from the casing pipe. Because
additional liquids were still being collected in the collection system, the
entire cap was paved with asphalt. No information was available on the
performance of the facility after the asphalt was installed.
7.2.17 Site P
7.2.17.1 Physical Description—
The facility consists of one double-lined hazardous waste cell. The
bottom liner is composed of leachate collection and detection systems as
well as a series of natural soil and bentonite/soil liners. The side liner
and dike-containment system include a soil and a bentonite/soil liner (see
Figures 7-22 and 7-23).
7.2.17.2 Startup Date—
The facility was constructed and began accepting waste in 1980.
7.2.17.3 Local Geology and Hydrology—
This facility is located in the southeastern United States. The
average annual precipitation in the vicinity of this facility is approxi-
mately 52 inches. No information on the local geology was available.
Groundwater at this site occurs in soil and fractured rock. The
maximum groundwater table is located approximately 14 to 15 feet below the
liner bottom. Groundwater levels at the site fluctuate with precipitation,
tending to be high in winter and spring and low in the remainder of the
year.
7.2.17.4 Waste Type-
Approximately 80 percent of the disposed waste is brine purification
mud. This material has the consistency and appearance of fine, wet sand.
The remaining 20 percent of the wastes are all mercury-contaminated substances
including sulfide treatment filter cake, retort ash, Reductone filters,
decomposer packing, and contaminated earth.
7.2.17.5 Liner Description—
The liner at this facility is composed of two sections: a bottom
liner and a side (dike) liner. Each of these sections has its own specifica-
tions.
The bottom liner extends over the entire bottom and 6 feet up the
sides. It is a layered system containing two drainage or collection layers
and two soil liners. From the top layer downward, the bottom liner compon-
ents are as follows:
Leachate collection system—1 foot of #78 gravel and sand with
4-inch perforated PVC pipes.
7-64
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I
CTl
cn
//
Side Liner System.
(see Figure 7-23
for details)
Waste
6ft
Bottom Liner System
(see Figure 7-23 for details)
// \\
\\
\\
\\
\\
Native Soil
Figure 7 22. Cross section of site P showing relationship of liner and dikes.
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I
cr>
en
• 6 in Bentonite/Soil Liner
18 in Recompacted Clay Liner
1-ft Drainage Layer
1-ft Leachate
'•.'•'••'•.;-: Collection Layer
3 ft Recompacted
Clay Liner
t Bentonite/Soil Liner
1-ft Recompacted Clay Liner
^M^i::^;^^H^?^t^-1-ft Leak Detection Layer
in Bentonite/Soil Liner
5-ft Recompacted
Clay Liner
Figure 7-23. Detailed cross section of site P liner.
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Upper soil barrier--5 feet of compacted soil further subdivided into
three layers:
3 feet of compacted native soil; permeability =
I x 10-4 cm/s.
1 foot of enhanced soil, i.e., native soil blended with
9 to 12 percent polymer-treated bentonite; permeability on
the order of 5 x 10-8 cm/s.
1 foot of compacted native soil; permeability =
1 x 10-4 cm/s.
Leak detection layer. A 1-foot sand/gravel layer with perforated
pipe, to detect leaks and/or to control seepage through the upper
barrier. The pipes are connected to several independent monitoring
stations to allow the determination of the approximate location of
any leaking that might occur.
Lower soil barrier. A 6-inch layer of enhanced soil, i.e., native
soil blended with 9 to 12 percent polymer-treated bentonite; permea-
bility on the order of 5 x 10-8 cm/s.
Buffer zone. 5 feet of either in situ or recompacted native soil.
Permeability = 1 x 10-4 cm/s.
The side liner system extends from a point 6 feet above the cell
bottom to the top of the cell. This section will not have liquid impounded
against it; therefore, the liner system is not as extensive as the bottom
liner. From the top layer downward, the side liner components are as
follows:
I foot of #78 gravel
18 inches of compacted native soil; Permeability = 1 x 10-4 cm/s
6 inches of enhanced soil, i.e., native soil blended with 9 to
12 percent polymer-treated bentonite.
Liner-waste compatability tests were conducted from June through
December 1980 with a percolation column. In it was placed a compacted
blend of 1,600 g native soil and 360 g bentonite (i.e., 18.4 percent ben-
tonite). The column was filled with actual facility liquids, with analysis
as follows:
1.87 ppm mercury
154,036 ppm chlorides
pH 6.1.
7-67
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Short-term permeability results are as follows:
Permeability (cm/s)*
2.23 x 10"7
2.92 x 10"7
3.71 x 10"7
4.05 x 10"7
4.81 x 10"7
5.88 x 10~7
Approximately 0
7.2.17.6 Liner System Installation--
The construction methods used are as follows:
Soil spreading. All soils and gravel were placed with scrapers
and spread with bulldozers.
Soil compaction. All soils were compacted to 95 percent Standard
Proctor density. This was done by repeated front-end loader or
scraper passes (rubber-tired). An independent soils laboratory
took samples as the work progressed, and any fill not meeting the
minimum 95 percent compaction was upgraded accordingly.
Mixing of soils and bentonite. The bottom 6-inch layer of "en-
hanced" soil was constructed by first spreading two lifts of
approximately 4.5 to 5 inches of loose native soil. Likewise,
the top 12-inch layer of "enhanced" soil was constructed by first
spreading four such lifts. Scrapers were used to spread the
soil. After placement of loose soil for each layer, the bentonite
product was hand-placed at an application rate of 50 lb/40 ft2.
Mixing was accomplished with a rotivator until the color of the
bentonite became unnoticeable.
"Enhanced" soil compaction was done by repeated passes of a
front-end loader or rubber-tired scraper until a minimum of
95 percent Proctor was achieved.
Quality assurance. Soil layers were sampled as the work pro-
gressed to ensure 95 percent standard Proctor density. During
construction of the "enhanced" soil layers, a minimum of one
^Calculated values based on leachate absorbed into test specimen. All
data supplied by American Colloid Company.
7-68
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field density test was performed per 2,500 ft2 of lift. Tests
for moisture, permeability, grain-size distribution, and liquid
and plastic limits were also performed by qualified soils per-
sonnel on an "as-needed" basis.
Results from the quality assurance of the constructed liner indicate
that the wet unit weight ranged from 101 lb/ft3 to 115 lb/ft3, the moisture
content ranged from 23 to 28 percent, and the laboratory permeability
ranged from 2 x 108 cm/s to 7 x 108 cm/s.
7.2.17.7 Performance—
Leachate collected in the leachate collection layer was analyzed and
found to contain high levels of chlorides and measurable levels of mercury.
Small amounts of liquid have also been collected from the leak detection
system. This liquid does not contain high levels of either chlorides or
mercury. The monitoring wells have not shown any significant changes.
The performance of this facility is very difficult to determine at
this time. A complete analysis of the liquid collected in the leak detec-
tion system is being performed. Attempts are being made to correlate these
results with changes in precipitation, waste type, and water table level.
The complete analysis was not available at the time of this writing.
7.2.18 Site Q
7.2.18.1 Physical Description—
The landfill consists of a single containment cell covering an area
of approximately 3 acres. It is located in a former sand and gravel pit.
The facility has a double liner consisting of two 4-inch bentonite/soil
layers. These layers are separated by a leak detection system.
7.2.18.2 Startup Date--
This facility was placed in operation in October 1976.
7.2.18.3 Local Geology and Hydrology—
This facility is located in the northeastern United States. Average
annual precipitation at this facility is approximately 35 inches.
The immediate area around the facility is mostly sand and gravel. The
facility is located above the 100-year flood plain.
7.2.18.4 Waste Type—
•The sludge deposited in the landfill is a black, semisolid, relatively
odorless material, which will support the weight of small grading equipment.
The sludge is nonvolatile and noncombustible. It consists primarily of
metal hydroxides and waste pigments. Typical sludge composition is as
follows:
7-69
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Metal Percentage
Iron 10 - 24
Lead 5-20
Chromium 6-12
Barium 2-12
Calcium 4-48
Aluminum 1-3
Copper 1-2
Cadmium 1-2
Zinc 0-1
Carbon 2-10
7.2.18.5 Liner Description—
The cell has a double liner consisting of two 4-inch layers of a
bentonite/soil mixture on the bottom and side slopes up to a vertical
elevation of 20 feet above the cell bottom. The bentonite/soil layers are
separated by a 12-inch layer of sand on the bottom of the cell and a 6-inch
layer of sand on the side slopes. The side slopes above the 20-foot vertical
level are covered with a single 6-inch layer of the bentonite/soil mixture.
All bottom and side slope bentonite/soil surfaces are covered with a 12-inch
protective layer of gravel. The slope of the cell sidewalls varies from
2.5:1 to 3:1. A typical cross section of this facility is illustrated in
Figure 7-24.
7.2.18.6 Liner System Installation—
Most of the bentonite/soil mixture used for the liner was premixed in
a pug mill to predetermined proportions by closely controlling the feed
rate of each material. Soil was fed from a hopper onto a conveyer belt at
a constant rate. Dry bentonite was fed from a hopper onto the conveyor
belt on top of the soil through a variable-rate vibratory feeder. . The feed
rate of the bentonite was periodically checked and adjusted as necessary by
weighing timed samples. The two materials were discharged into the pug
mill -where water was added at a controlled rate to produce a thoroughly
mixed product at desired moisture content (specific value unknown). The
mixture was discharged from the pug mill into dump trucks and was placed in
position at a predetermined thickness with a grader, screened boards, and
hand labor. The mixture was then compacted to the specifications with a
backhoe-mounted hydraulic tamper.
During all construction phases, CQA and CQC required full-time super-
vision by qualified personnel and a soils consultant as required.
7-70
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12 in Gravel Layer (Leachate Collection)
6 in Bentonite/
Soil Layer
12-in Sand Layer (Leak Detection)
o o o
6 in Sand Layer
4-in Bentonite/
Soil Layers
4-in Perforated
Pipes
Figure 7-24. Cross section of site Q liner.
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7.2.18.7 Performance--
This facility is presently active and uncapped. As a result, a great
deal of leachate is being collected. Liquid has also been collected in the
leak detection system. Analysis of this liquid shows that it has slightly
elevated levels of cadmium, lead, zinc, iron, copper, cyanide, and COD.
The permeability of the upper bentonite/soil liner has been determined from
the volume of liquid pumped from the sump, the waste head, and the facility
area. This value, as reported by the site owner, varies from 3 x 10 8 cm/s
to 6.5 x 10"8 cm/s.
Analysis of the groundwater from the facility monitoring wells has
shown no significant changes since construction of the facility and is well
within drinking water standards.
7.3 LINER TYPES
The feasibility of using a clay liner at a waste disposal facility
depends on several factors, the most important being availability of suit-
able liner material. The location of a facility in a deposit of low-
permeability soil lowers the facility cost by greatly reducing or eliminat-
ing liner material transportation costs. The cost incurred by transporting
suitable borrow soils a short distance (e.g., 5 miles or less) may allow
this to be a viable liner option. Another type of soil liner consists of a
relatively high-permeability soil that has been augmented with certain
natural or treated bentonite additives. The addition of bentonite to a
highly permeable material greatly reduces the material's permeability.
These three types of facilities (i.e., unlined, recompacted soil lined, and
bentonite/soil lined) were included in this study.
*
Two of the four unlined facilities discussed have had groundwater
contamination problems. One facility had a problem due to a faulty well
installation. No other problems have been reported at this facility. The
fourth unlined facility has had contamination detected in one of its moni-
toring wells. A study of this contamination indicated that its source was
an adjacent drum disposal facility.
Nine facilities with recompacted soil liners are discussed in this
chapter. Three of these nine facilities have had some type of performance
problem. These three facilities all have leak detection systems that were
responsible for quickly detecting and providing the information necessary
for determining the cause of the failures.
-Four facilities with admixed (bentonite/soil) liners are discussed in
this chapter. Two of these facilities have had small amounts of liquid
detected in between their double liners. However, overall they appear to
be functioning according to their design specifications. One facility had
a cap problem that was rapidly detected and corrected. The liner at this
facility has had no detected problems. The final facility with a ben-
tonite/soil liner that is discussed in this section has had'performance
problems. Leachate has migrated through the 4-inch liner and has resulted
in extensive groundwater contamination.
7-72
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7.3.1 Unlined Facilities
Although the purpose of this document is to discuss clay liners, in
some cases information relating to waste disposal and clay liners may be
obtained from the case histories of unlined disposal sites. Generally
speaking, unlined sites are located in soil formations that are relatively
low in permeability. However, such soil formations are rarely homogeneous.
They generally contain sand or gravel seams, varying amounts of organic
matter, and cracks or fissures. In some cases, they may also contain
lenses of gypsum, limestone, or other soluble material. Discontinuities
such as these are often excavated and then backfilled with recompacted clay
prior to waste disposal. When this is not specified or when highly perme-
able areas are unnoticed during facility construction, the siting of an
unlined hazardous waste disposal facility in a heterogeneous, soil may cause
severe performance problems.
Examples of unlined waste disposal facilities are sites A, B, C,
and G. These four facilities are 8 to 30 years old. Extensive groundwater
contamination has occurred at two of these facilities: a slight problem due
to poor well installation procedures occurred at one facility, and contamina-
tion in a well at the fourth facility is thought to have come from an adja-
cent abandoned drum disposal operation.
Facility 8, a zone-of-saturation or intergradient landfill, has had
severe groundwater contamination problems. This facility is located in-a
low-permeability glacial till deposit. Lenses of sand or gravel that were
encountered during the site construction were excavated and backfilled with
a minimum of 5 feet of recompacted clay. A buildup of leachate in the
landfill due to the disposal of unsolidified liquids, precipitation, and
seepage caused waste to enter a permeable deposit that had been improperly
sealed with clay. This resulted in leachate migration and groundwater
contamination.
Facility C is also unlined. Geological investigations revealed that
calcium carbonate seams and nodules were present throughout the entire
area. The design specifications called for the excavations of such seams
and then required the excavated areas to be backfilled with the local
clay-shale soil. Groundwater contamination at this facility can be attrib-
uted to inadequate excavation of the calcium carbonate deposits, inadequate
recompaction of the excavated areas, or lack of sufficient waste/liner
material compatibility testing.
'Initial groundwater samples taken from a monitoring well at site A had
pH values between 10.7 and 11.3. An investigation into the problem revealed
that waste migration from the unlined facility was not the cause. Instead,
the contamination was traced to some steel-mi 11 slag that was used as well
packing instead of the specified clean gravel. This problem was remedied,
and since that time no other problems have been reported.
Facility G is an old, unlined hazardous waste disposal facility.
Samples from a groundwater monitoring well at this facility have contained
7-73
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high levels of various pollutants. A study of this contamination indicated
that its source was an old drum disposal s-ite (previously owned by another
company) located adjacent to the landfill. This drum disposal site is
located on a sand and gravel seam. This permeable seam was determined to
be the mechanism by which the contaminants were transported to the moni-
toring well at Site G.
7.3.2 Recompacted Soil Liners
Recompacted soil liners are the most common type of soil liner in
current use. This category consists of both recompacted in situ soil
liners and liners constructed of material that has been transported to the
facility from a nearby borrow area. Sites D, E, F, H, I, J, K, L, and M
are all in this category. Some of these facilities have a double liner
system (in the case of sites D and F, one of the liners is a synthetic).
When this is the case, the drainage layer separating the clay liners is
called a leak detection layer or system. All of these facilities have
either a leachate collection or a leak detection system (in some cases,
both). These facilities are 4 to 9 years old. The performance at these
facilities is quite varied. Six of the facilities (sites D, E, F, H, K,
and M) appear to be functioning as planned with only a few minor problems.
In the case of site K, the liquid volumes removed from the detection system
were used to calculate the liner permeability. The calculated values were
all lower than the design specifications required.
The remaining three facilities (sites I, J, and L) have all had per-
formance problems. For example, the clay liner for a pond at site I was
left empty and unprotected for several months. During this time desicca-
tion cracks formed in the liner. Failure to repair the liner prior to
waste placement resulted in waste migration into the leak detection layer.
Waste migration into the leak detection system also occurred at site L
shortly after waste placement. An investigation was unsuccessful in
determining the location of the leak. However, it was determined that the
lower compacted clay liner was not leaking. The other recompacted clay-
lined facility with performance problems, site J, also has a leak detection
system. In this case, perch!oroethylene was mistakenly placed into a pond.
Approximately 6 to 9 months later, and literally overnight, the "perc"
penetrated the liner and was detected in the leak detection system. The
apparent incompatibility of the "perc" and the liner material is consistent
with current research on the effect of chlorinated solvents on clays.
7.3.3 Admixed Liners
Admixed liners are those composed of permeable soil and an additive
designed to decrease its permeability. Commonly used additives include,
asphalt, fly ash, soil cement, and polymer-treated or natural bentonite.
Bentonite, a natural clay mineral, is the only additive discussed in this
document.
The addition of bentonite (generally 3 to 15 percent is used) to a
highly permeable soil can decrease its permeability so that it can be used
7-74
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as a liner material. A discussion of the physical and chemical properties
of bentonite as well as its advantages and disadvantages as a liner material
may be found in Chapters 2 and 5 of this document.
Facilities N, 0, P, and Q are all lined with bentonite/soil admixtures.
These facilities are 5 to 11 years old. The liner configurations at these
facilities are quite varied. Site 0 has a 4-foot-thick native soil liner
containing 3 percent bentonite and 3 percent lime. The lime was added to
reduce the swelling potential of the bentonite. Sites P and Q are lined
with a layered system containing bentonite/soil liners ranging from 4 to 12
inches thick and leak detection systems. Site P has the additional protec-
tion of a series of compacted native soil liners. Facility N is lined with
a 4-inch bentonite/sand liner. Two lysimeters and a groundwater pumping
system are located below the liner, and a leachate collection system is on
top of the liner.
Just as the liner systems at these four facilities are varied, so are
their performances. Both sites P and Q have had small amounts of liquid
detected in their leak detection layers; however, overall they seem to be
functioning according to specifications. In the case of site Q, the liquid
volumes collected were used to calculate the as-built liner permeability.
This value ranged from 3 x 10 8 cm/s to 6.5 x 10 8 cm/s, which is less than
the specifications required. The source and quality of the liquid being
collected from the detection system at site P are currently being investi-
gated by the site owner.
Site 0 had a problem with liquid eroding the cap and infiltrating
through the eroded section. This problem was corrected by repairing the
eroded portion and then paving the entire cap with asphalt. The liner at
this facility has not had any detectable problems.
Finally, facility N, a very large municipal waste disposal facility
located in an abandoned sand and gravel pit, has produced extensive contam-
ination that has been detected in the subsurface monitoring layer, the
lysimeters, and several groundwater monitoring wells. Analysis of the con-
tamination indicates that the leachate is passing through the 4-inch liner
and entering the groundwater.
7.4 SITE CHARACTERIZATION
The location of a clay-lined hazardous waste disposal facility may
have a significant effect on its performance. The site-specific geology,
hydrology, and climate must be evaluated thoroughly prior to the facility
design and construction. Some of the geological factors that must be
investigated include the local soil type, permeability, and nature of the
soil deposit (e.g., whether it contains continuous or discontinuous sand or
gravel seams, gypsum, or other reactive material seams and the depth of the
deposits).
Hydrological factors that must be investigated include location of the
water table, location of any perched water tables above the main water
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table, and the groundwater and surface-water flow patterns. Problems
associated with high water tables include excessive pressure on the side or
bottom liners. This hydraulic pressure may cause sidewall slumping or
collapse or bottom heaving. High water tables may also result in the
unwanted infiltration of groundwater. For a facility under construction,
this may make compaction and other liner installation procedures difficult
or impossible without continuous groundwater pumping. For a closed facil-
ity, groundwater infiltration may result in overloading the leachate collec-
tion system, causing high leachate levels in the facility.
Site-specific climate data such as average temperature and amount of
precipitation also must be known. Locations that have below-freezing
temperatures for long periods of time have the potential for freeze/thaw
cycling of unprotected liners. This may result in increased liner permea-
bility and poor liner performance. Hot climates, on the other hand, may
affect clay liners by causing excessive evaporation and possibly desicca-
tion of the liner. Clay liners located in hot, arid climates are even more
susceptible to desiccation and cracking. On the other hand, excessive
precipitation at an open clay-lined facility may cause a buildup of hy-
draulic head on the liner, thus increasing the flow of liquid through it.
Excessive precipitation may also cause a rise in the groundwater table and
the previously discussed problems associated with this phenomenon.
A complete discussion of these site-specific factors, their associated
problems, and the potential failure mechanisms involved may be found in the
preceding chapters of this document.
7.4.1 Case Studies
Several performance problems or liner failures that may have been
partially caused by inadequate site characterization are illustrated by
case studies B, G, and I.
Site B, a zone-of-saturation or intergradient facility, is located in
a low-permeability soil formation. Sand or gravel seams that were en-
countered during excavation were to be removed and replaced with recom-
pacted clay. No additional recompaction was specified. A buildup of
leachate within the liner due to precipitation, the disposal of free liquids,
and seepage caused the gradient to reverse. Within the site, apparently a
sand seam was either not discovered or not properly sealed during construc-
tion. The leachate flowed through this sand seam and caused severe ground-
water contamination in a limited area of the property.
Another problem caused by a sand seam was discovered at site G.
Contamination in one of the facility monitoring wells was initially attrib-
uted to waste migration from within the site. However, an investigation
into the problem revealed that the source of contamination was an adjacent
abandoned drum disposal facility. Leachate from this facility entered a
water-bearing sand seam that encountered one of the wells at site G.
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Site I is located in a semiarid climate. Three ponds with double clay
liners were installed in the fall of 1980. Two of the ponds were filled
shortly after construction, while the third pond was not filled until the
following spring. During this time, the unprotected clay liner developed
severe desiccation cracks. These were not repaired prior to filling;
consequently, contaminated liquid passed through the liner and began accum-
ulating in the leak detection system. This problem, which was caused by
the arid climate and the loss of water from the liner, could have been
avoided with adequate liner maintenance and a rigorous preservice inspec-
tion.
7.5 INSTALLATION OF CLAY LINERS
This section presents a very brief discussion of clay liner installa-
tion methodology and procedures. Only one case study is included for
discussion because it is very difficult to attribute a liner failure
to poor construction techniques. For a complete discussion of this topic,
see Chapter 5.
7.5.1 Installation Methods
It is widely believed that the performance of clay liners is affected
by the equipment and procedures used to install them. Conclusive field
data to support this belief, however, are not available. Specific items
that need to be controlled during clay liner construction are discussed in
the following sections.
7.5.1.1 Excavating, Grading, and Foundation Preparation—
The excavation and grading of the bottom and side slopes of the liner
foundation should be conducted according to design specifications. This
generally requires the use of construction equipment such as dozers, back-
hoes, scrapers, and graders. For unlined facilities constructed in low-
permeability soil, special care must be taken to locate and fully excavate
all permeable zones that may allow for leachate migration. For facilities
that are to be lined with recompacted local soil or admixed materials,
suitable liner materials are generally excavated, stockpiled, and used as
required. In all cases, the specified slopes and elevations of sidewalls
and bottoms as well as those of collection system pipes and manholes must
be carefully controlled. This will help ensure that the liner is properly
located regarding the water table and local geological features. Specified
side and bottom slopes are also necessary so that leachate will flow to the
collection system pipes and sump, thus preventing the "bathtub" effect.
7.5.1.2 Liner Materials—
Native soil liner material may be excavated from the site during
foundation preparation or may be brought to the site from a nearby borrow
area. Admixture materials may be shipped to the facility in bags or bulk
form. In all cases, the use of materials that are specified in the facil-
ity design is extremely important. As previously discussed, materials such
as sand, rocks, roots, or other organic matter, if included in the liner,
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will greatly affect its permeability and ultimate performance. When materi-
als such as bentonite are to be added to in situ materials to form'a liner,
the bentonite content must be carefully controlled. The use of inadequate
quantities of bentonite will produce a liner with higher than required
permeability and lower than specified performance.
7.5.1.3 Moisture Content/Density/Compactive Effort--
The relationship among moisture content, density, and compactive
effort is discussed in Chapter 2. Careful control of these parameters is
necessary throughout all phases of liner construction. The final liner
permeability and performance depend on proper moisture control and distri-
bution, mixing, and compaction techniques. Too little or too much water
added to the liner material will make it difficult to compact to the speci-
fied density, thus affecting permeability. Inadequate mixing of materials
may result in a heterogeneous liner. Insufficient compactive effort may
result in a liner that is more permeable than required.
7.5.2 Quality Assurance/Quality Control For Clay Liners
A survey of hazardous waste surface impoundment technology has found
that rigorous quality assurance is necessary to achieve good site perform-
ance (Ghassemi et al., 1984). Liner failures at several impoundments
included in the survey were attributed to various factors including "fail-
ure to execute proper quality assurance and control." The success of
surveyed facilities that have performed very well is attributed to many
factors including "the use of competent design, construction and inspection
contractors, close scrutiny of all phases of design, construction and QA
inspection by the owner/operator, excellent CQA/CQC and recordkeeping
during all phases of the project, and good communications between all
parties involved in establishing the sites."
Specific problems that may result in clay liner failure and that can
be avoided with careful CQA include:
Use of materials with specifications other than the ones in the
approved design
Lack of careful screening and testing of incoming materials to
remove roots and other organic matter, rocks, pockets of permeable
materials, and other foreign objects prior to placement
Lack of adequate moisture control both prior to and after compac-
tion
Improper size reduction, mixing, and spreading of liner materials
Use of inadequate liner materials (especially important with
bentonite/soil liners)
Failure to follow installation procedures specified in the design
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Use of improper construction equipment
Application or specification of inadequate compact!ve effort.
The following case study is of a surface impoundment that has had
performance problems. Due to insufficient information, this case study is
not included in Section 7.2. The problems at this facility may have
resulted from a combination of factors, one being the lack of adequate CQA.
A sewage-treatment lagoon was to be lined with 3.7 pounds of polymer-
treated bentonite per square foot of liner mixed with the native soil to a
depth of 4 inches. The particle size of the bentonite that was supplied
did not meet the original specifications, making it very difficult to
spread and mix the material adequately. Problems were also encountered in
achieving proper moisture content. After the bentom'te/soil layer was
compacted, the final permeability of the liner was to be determined by
filling the lagoon with water to a depth of 15 feet. The decrease in
liquid head and the evaporation rate were then to be used to determine the
as-built liner permeability. Unfortunately, the as-built liner permeability
was much greater than expected. Actual as-built permeabilities were never
determined, however, because the water flowed through the liner faster than
it could be pumped into the lagoon. Examinations of the liner profile
revealed large discontinuities in the liner materials (see Figure 7-25),
which explains the high permeability.
A second attempt to construct the liner to the same specifications was
successful. All phases of liner installation (by a different contractor)
were carefully monitored by the site owner. Final permeability testing
confirmed that the liner exceeded the required specifications. A cross-
section of this liner revealed uniform thickness and material content (see
Figure 7-26).
A complete discussion of CQA/CQC may be found in Chapter 5 of this
document.
7.6 WASTE TYPES
Prior to recent Federal regulations (Federal Register, 1982), unsolidi-
fied liquid wastes either containerized or in bulk form were often disposed
of in landfills. Since these recent regulations, free-standing liquid
wastes are required to be removed from drums and solidified prior to final
disposal. While the option still exists to store liquids in surface impound-
ments or evaporation ponds, free liquids must be removed prior to final
facility closure.
7.6.1 Free Liquids
Many performance problems have resulted from the practice of placing
containerized or bulk free liquids in waste disposal facilities. With bulk
liquids, a liquid head is imposed on the liner. If the head becomes too
great or if the waste material is incompatible with the liner material, the
waste has a much greater chance of infiltrating into or through the liner.
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Figure 7-25. Bentonite/soil liner constructed without adequate CQA.
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'-J*.
Figure 7-26. Bentonite/soil liner installed with extensive CQA.
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Fifty-five-gall on drums, which are often used to contain free liquids,
have the potential to degrade with time. This can result in leaky drums,
which, in turn, may cause leachate levels to build and the performance
problems associated with this phenomenon to occur. Several problems are
also associated with the waste placement and closure operations of a facil-
ity that contains drums. Drums are usually stacked upright in several
layers or lifts. Absorptive material such as soil is then placed between
the drums and compacted to fill all voids. It is difficult to determine
when all of the lower voids are filled and when the material has been
compacted properly. If the spaces are not completely filled, piping into
the spaces between the drums may occur. This can result in differential
settlement and cap failure, which may lead to increased liquid infiltration
and hydraulic gradient on the liner, thus affecting its performance.
An example of a facility where a performance problem has resulted, at
least in part, from free liquid disposal is site B. This facility is
approximately 13 years old. It is a zone-of-saturation (intergradient)
facility where liquids were not solidified prior to disposal. These
unsolidified liquids along with the accumulated precipitation and seepage
resulted in a "bathtub" with leachate seeps penetrating the cap/liner
interface.
Present landfill regulations require that leachate collection and
removal systems must be installed immediately above the liner. These
systems must be designed to ensure that the leachate depth does not exceed
30 cm. Properly functioning leachate collection systems along with the
regulation preventing free liquids from being disposed of in landfills
should prevent similar future performance problems from occurring.
7.6.2 Stabilized or Solidified Liquids
As previously mentioned, Federal regulations require that free liquids
not be placed in landfills. In response, free liquids are now removed,
solidified, or stabilized prior to their final disposal. Removed liquids
may be recycled, impounded, used as fuel, or in some way treated and then
placed in a landfill either in drums or bulk. The solidification process
may be accomplished by mixing the liquid with absorptive material such as
lime, cement kiln dust, fly ash, or some other substance. Stabilization of
wastes may include processes such as neutralizing acidic or basic wastes or
precipitating heavy metals. These processes generally decrease the toxic
or hazardous nature of the waste and are currently practiced at many of the
case study sites in Section 7.2.
A procedure that provides protection from leaking drums is practiced
at site E. Here, a "calculated amount" of "absorptive material" is placed
beneath each lift of waste. This material will theoretically absorb any
liquids that might leak from the drums. The success of this method is not
proven at this time as site E has had large volumes of leachate accumulating
in some of its waste trenches.
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7.6.3 Sludges and Solid Wastes
7.6.3.1 Sludges-
Depending on the water content, sludges may be either landfilled or
placed in evaporation ponds. However, in both cases, it is important that
most of the moisture be removed prior to final facility closure. Case
studies M, P, and Q are all landfills that contain various types of sludges.
All of these facilities contain both leachate collection systems and some
form of leak detection system.
Site M uses a special procedure for waste placement. This procedure
involves mixing a thin layer (approximately 2 feet) of locally available
soil with a thin layer of the inorganic lime sludge, thereby reducing the
overall moisture content of the material and giving it structural stability.
The range of the soil-to-waste ratio varies from 0.5:1 to 1.5:1. Exact
mixing proportions are determined in the field and judged sufficient when
the landfill equipment is able to drive over the mixture.
Facilities P and Q contain brine purification mud and metal hydroxide
and waste pigment sludge, respectively. These facilities are both lined
with bentonite/soil admixtures. The bottom and lower side liners at both
of these facilities are thicker than the upper side liners to provide extra
protection in areas where a liquid head may be present.
The following case study is not included in Section 7.2 due to insuf-
ficient information. Enough information is available, however, to allow a
failure that occurred at this facility to be attributed to improper waste
placement procedures. This double-lined facility was originally designed
for the disposal of solid wastes. A change in the parent company's waste
disposal needs resulted in this facility accepting high-liquid-content
sludges. The sludges were transported to the site in tank trucks that
would back up to the facility and dump their load through a pipe whose
outlet was well above the base of the liner. The impact of the sludge on
the liner caused severe liner erosion and groundwater contamination probably
as a result of an erosional breach in the liner.
7.6.3.2 Solid Waste-
Solid wastes may be landfilled in containers such as 55-gallon drums
or in bulk form. When wastes are landfilled in drums, all free liquids
must be removed or solidified prior to final disposal. Care must be exer-
cised to make certain that the voids between adjacent drums are filled with
wel1-compacted soil or other material. Problems that may result from the
disposal of drums are discussed in Section 7.6.1.
Solid wastes such as contaminated soil or other fine uniform material
may be emplaced and compacted in lifts. When this method is used, the void
volume in the landfill is reduced; thus, future problems due to settlement
or piping are less likely to occur. Solid wastes that are not uniform,
such as unshredded tires, scrap metal, and municipal solid wastes, on the
other hand, are more difficult to compact thoroughly and therefore have the
potential to settle differentially. This can be minimized by crushing or
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shredding the waste, thereby reducing its void spaces and overall volume.
The use of a landfill compactor will also help to prevent future problems
due to piping and settling.
7.6.4 Waste Compatibility
7.6.4.1 Waste/Liner Compatibility—
Laboratory tests suggest that dilute aqueous leachates will not affect
the permeability of clay liner materials if the moisture at compaction is
uniform and close to optimum and if compaction is uniform. However, data
from several studies suggest that drastic increases in permeability can
result from certain clay-chemical interactions. Examples of organic chemi-
cals that have been demonstrated to increase clay soil permeability are:
aliphatic and aromatic hydrocarbons (e.g., cyclohexane, heptane, kerosene,
naphtha, benzene, and xylene), alcohols (e.g., methanoi and ethylene glycol),
ketones (e.g., acetone and dioxane), amines (e.g., aniline and pyridine),
carbon tetrachloride, and nitrobenzene. Changes in permeability have also
been noted with strongly acidic permeant fluids.
Bentonite is sometimes given a polymer treatment to improve its resis-
tance to the effects of normally incompatible fluids. The long-term viabil-
ity of polymer-treated products needs to be verified.
The enormous variability in clay soil from different locations compli-
cates the task of predicting clay-chemical compatibility. Data from several
laboratory studies suggest the possibility of drastic increases in permea-
bility as a result of certain clay-chemical interactions. It should be
emphasized, however, that many aqueous leachates have been tested and
produced no significant increases in permeability. For a detailed discus-
sion of clay-chemical interactions, see Chapter 4 of this document.
Facilities C and J have both had liner failures that have been attri-
buted to liner/waste incompatibility. In the case of site C, an investiga-
tion of groundwater contamination identified the facility's treatment ponds
as the probable source of the pollution. This conclusion was based on the
fact that the materials in the treatment ponds were usually of low pH and
would have reacted with carbonate seams and inclusions in the surrounding
soil. Several of the disposal trenches at this facility were also used for
the disposal of highly acidic waste, in this case oil reprocessing sludges.
These acidic sludges may have also reacted with the carbonate inclusions,
creating paths for leachate seepage and groundwater contamination.
The liner failure at site J occurred almost overnight. Samples of
liquid removed from the leak detection system at one of the ponds on one
day were reported to be "clean." Samples taken the following day contained
over 11.2 percent perchloroethylene plus small amounts of other chlorinated
and nonchlorinated organics. The facility was allegedly not accepting
wastes with more than a trace of perchloroethylene.
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An investigation into the problem revealed that aqueous wastes coming
from one of the disposal facility customers contained approximately 5 per-
cent degreasing fluid waste that contained perchloroethylene. This waste
was to have been stored in a separate tank at the originator's plant.
Evidently, it was not made clear to the workers where to put the "perc"
waste, and it was placed in an aqueous waste storage tank. Being insoluble
and heavier than water, it sank to the bottom. When a tank truck from the
disposal facility would collect a load of aqueous waste, it would also
receive a few hundred gallons of the "perc" waste. The waste sampling
method used by the disposal facility on all loads of incoming waste was not
able to sample the bottom few inches of each load. In addition, the parking
area where all incoming truckloads of waste were sampled was slightly
sloped, causing the relatively small amount of "perc" waste in the bottom
of the tanker to flow to the back of the truck where it could not be reached
by the sampling device.
Over a period of approximately 9 months, the aqueous waste containing
"perc" was placed into one of the clay-lined ponds and went unnoticed until
the liner failure occurred. The apparent incompatibility is consistent
with current research on the effects of chlorinated solvents on clays.
7.6.4.2 Waste/Waste Compatibility-
Large disposal facilities that accept most types of wastes, such as
sites E and F, generally have a waste placement plan. Such a plan is used
to separate incompatible or reactive materials and in some cases to place
together materials that produce "favorable reactions."
Most cells at site F are divided into five subcells. The purpose of
these subcells is to isolate the various waste groups accepted at the
facility, thereby preventing the interactions of incompatible wastes. The
waste categories, percentage of total wastes, and separation rationale at
site F are as follows:
General wastes. These wastes represent approximately 44 percent
of the total waste volume accepted at site F. General wastes are
defined as materials of both an organic and inorganic nature that
do not contain a significant quantity of any of the other waste
categories.
The hazardous acidic or acid-generating materials are covered
with lime to ensure that any acid that is generated will be neu-
tralized.
Pseudo metals. This type of material represents approximately 6
percent of the total waste volume accepted at site F. Pseudo
metals are arsenic, antimony, bismuth, and phosphorous. Chalco-
gens, beryllium, and any of their compounds as well as alkaline-
sensitive materials are also disposed of in this subcell.
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This subcell has a pH buffer system that maintains pH levels
between 6 and 8.
Heavy metals. These wastes represent approximately 15 percent of
the total waste volume accepted at site F. This group is com-
prised of all heavy metals and asbestos. This subcell contains
the smallest amount of organic materials, which helps to reduce
fire hazards caused by the reaction of strong oxidizing agents
with organics.
Highly flammable wastes. This type of material represents approx-
imately 12 percent of the total waste volume accepted at site F.
These materials generally exhibit a flash point between 80 and
100 °F. These materials are kept apart from powerful oxidizing
agents, materials that are prone to spontaneous heating, or
materials that react with air or moisture to evolve heat.
Toxic materials. These wastes represent approximately 23 percent
of the total waste volume accepted at site F. Included in this
category are all waste materials containing more than 5 percent by
weight of highly toxic organic compounds, carcinogens, PCB's, and
other halogenated wastes. No solvent-type wastes are permitted in
thi.s subcell.
7.7 PERFORMANCE MONITORING
Several methods can be used to monitor the performance of clay-lined
landfills. These methods generally involve groundwater monitoring or
monitoring of the unsaturated zone directly beneath the clay liner. Moni-
toring the quantity and quality of the leachate above the liner may also
give some indication of the facility performance. This type of monitoring
program for a facility should be able to detect performance problems, such
as leachate migration, soon after they occur. This will enable the rapid
remediation of any problems and prevent serious groundwater contamination.
7.7.1 Unsaturated Zone Monitoring
Two systems that are commonly used to monitor the unsaturated zone
beneath a clay liner are lysimeters and continuous-coverage leak detection
systems. A continuous-coverage leak detection system generally consists of
a flexible membrane overlain by a porous layer that contains perforated
collection pipes. Just as with a leachate collection system, the porous
layer is usually sloped so that any detected fluid will drain to a sump.
Here the liquid may be sampled and analyzed for hazardous constituents.
Total liquid volumes removed from a detection layer may also be used to
estimate the liner permeability.
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The advantages of a continuous-coverage leak detection system include
its ability to provide early indications of the liner performance and its
ability to detect and collect all liquids that appear in the detection
system. The disadvantages of a continuous-coverage detection system include
its relatively high cost and the possibility that the leachate, if a chemical
compatibility failure should occur, might spread out upon and damage a
large portion of the lower clay liner or foundation soil.
Another approach to unsaturated zone monitoring involves the use of
either pressure-vacuum lysimeters or collection lysimeters. Pressure-vacuum
lysimeters consist of a porous cup, placed in a bore hole, that a vacuum
may be applied to. This vacuum causes pore liquids to collect in the
porous cup. The liquid is then removed and analyzed for hazardous constit-
uents. A collection lysimeter, on the other hand, is a lined gravel or
sand-filled basin or trench beneath the primary liner. A collection pipe
located at the low point of the lysimeter leads to a sump from which any
detected liquids can be sampled and analyzed.
The following discussion on the advantages and disadvantages of col-
lection and pressure-vacuum lysimeters is taken from Kmet and Lindorff
(1983).
Both pressure-vacuum lysimeters and collection lysimeters can be used
to monitor the unsaturated zone beneath a landfill and provide an early
indication of landfill performance. Each has its own advantages and
disadvantages.
The major advantage of a collection lysimeter is that it provides a
method of monitoring the quantity as well as the quality of leakage
from the base of a landfill. If one assumes that the leakage reaching
the lysimeter is representative of leakage over the entire base of the
site, it is possible to calculate the volume of leakage from the entire
landfill and thus assess the effectiveness of the liner in attenuating
the leachate and in limiting the rate of leachate movement.
Also, collection lysimeters do not require the special equipment or the
care necessary to sample pressure-vacuum lysimeters properly. Samples
can be taken from a manhole or riser by a bailer rather than a vacuum
pump. In addition, collection lysimeters do not require that a vacuum
be placed on the system at least several days prior to sampling, as is
the case with pressure-vacuum lysimeters. When the monitoring results
from a landfill indicate that one or more pressure-vacuum lysimeters
•are dry, one is never sure whether there was insufficient soil moisture
or whether improper sampling techniques were used. With collection
lysimeters, one is reasonably certain that if liquid is present in the
subsurface, it will be collected. Collection lysimeters also eliminate
the problem of frozen lines in cold weather that can occur with pressure-
vacuum lysimeters.
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Research, including work done by Apgar and Langmuir (1971); Johnson and
Cartwright (1980), has suggested that some chemical constituents may be
filtered out by the porous membrane of the pressure-vacuum lysimeter,
thereby producing inaccurate water quality data. This is not a concern
with collection lysimeters since no membrane is present.
The major disadvantage of a collection lysimeter in comparison with a
pressure-vacuum lysimeter is the lower cost and shorter time required
for pressure-vacuum lysimeter installation. Whereas a pressure-vacuum
lysimeter is installed in a bored hole, construction of a collection
lysimeter necessitates excavation of sufficient area to appropriate
grade to install the basin, collection pipe, and manhole. A substan-
tial number of pressure-vacuum lysimeters could be installed in the
time and for the cost of one collection lysimeter. A pressure-vacuum
lysimeter can be installed for less than $100 plus drilling costs.
Although data is [sic] limited, the cost of collection lysimeter
installation, including excavation, materials, and construction costs,
is expected to be several thousand dollars and can approach $10,000 for
the larger lysimeters.
Another disadvantage is that only one collection lysimeter can be in-
stalled at a given location. Therefore, data is [sic] generated for
only one depth in the unsaturated zone, typically just below the clay
liner. In contrast, pressure-vacuum lysimeters are frequently installed
in a nest at different depths to monitor changes in water quality with
depth.
Several of the facilities discussed in Section 7.2 of this document
have some type of unsaturated zone monitoring system. Six of these "facili-
ties—sites H, L, M, N, P, and Q—are landfills and three—sites I, J, and
K—are ponds. Sites H and N both have lysimeters beneath their clay liners.
Facility H has two 1,200-ft2 lysimeters directly beneath the 4-foot-thick
recompacted clay liner. An additional lysimeter is located under the
leachate storage basin. For approximately 9 months after the start of
landfill ing operations, small quantities of liquid were removed from the
lysimeters under the landfill liner. These liquid volumes declined steadily
over time and were reduced to zero 1 year after the start of landfill oper-
ations. The liquid that was initially collected in the lysimeters is most
likely soil moisture that was released after liner construction.
Facility N also has two lysimeters beneath the liner. This facility
also has a groundwater drain that is used to lower the groundwater table.
An interesting fact about this facility is that although highly contaminated
liquids have recently been removed from the lysimeters, contaminated liquids
were first discovered in the groundwater drain manhole. This has continued
to be the location where the majority of contamination has been detected.
The three ponds with unsaturated zone monitoring all have continuous-
coverage leak detection systems between two recompacted clay liners. At
two of the ponds, facilities I and J, major performance problems have
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developed in the upper clay liners. In both cases, the problems were
quickly detected (overnight at site J) and corrected, thus preventing any
contamination from penetrating the lower liner. The third double-lined
pond, site K, has had small quantities of liquid accumulating in its leak
detection system. These volumes were used to calculate_the overall liner
permeability, which ranged from 4 x 10 8 cm/s to 3 x 10 7 cm/s, demonstrat-
ing that the original specifications of 1 x 10 6 cm/s had been met.
Four of the six landfills, facilities L, M, P, and Q, have continuous-
coverage leak detection systems. Liquids have been detected in the leak
detection layers of sites L, P, and Q. However, only one, site L, is con-
sidered a failure. Here, slightly contaminated liquids were removed from
the detection system manhole less than 1 year after the start of operation.
Facility Q also had slightly contaminated liquids removed from its detection
system. The volume of liquid removed was used by the facility owner_to
calculate the admixed liner's permeability, which ranged from 3 x 10 8 cm/s
to 6.5 x 10 8 cm/s, indicating that the liner met the original permeability
specification of 1 x 10 7 cm/s. The as-built liner permeability at facility
P has not been determined. The source of small amounts of uncontaminated
liquids in the detection system at this facility was being investigated by
the site owner. The results of this investigation were not available at
this writing.
7.7.2 Groundwater Monitoring
Information on Federal groundwater monitoring requirements may be
found in "Groundwater Monitoring Guidance for Owners and Operators of
Interim Status Facilities" (U.S. EPA, 1983).
Groundwater monitoring wells are the-most commonly used type of per-
formance monitoring systems. They are relatively inexpensive to install
and maintain, and samples are easily obtained from them. They may be
placed in areas where contamination is estimated to be most likely to
occur. They may also be placed in groups or clusters with each well being
at a different depth and therefore monitoring the vertical as well as
lateral movement of any contamination. Generally, wells are placed both
upgradient and downgradient from a facility prior to the start of opera-
tions. This enables baseline data for both upgradient and downgradient
wells to be obtained. Future groundwater samples may then be compared with
the baseline data and facility performance can be estimated.
Two major problems with relying solely on monitoring wells to determine
facility performance are that leachate plumes may be missed and that the
monitoring data are only qualitative. If an adequate number of wells at
varying depths are used, the possibility of missing a contaminant plume is
greatly decreased.
An additional problem that may occur with monitoring wells is poor
construction procedures such as the use of inappropriate materials. This
can often lead to well-water contamination that is incorrectly attributed
7-89
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to the waste disposal facility. Examples of such problems occurred at
sites A and E. Groundwater samples taken from the wells at site A in 1976
had pH levels between 10.7 and 11.3, COD's of more than 3,000 ppm, and
chloride levels greater than 1,000 ppm. Originally, it was thought that
this contamination originated in the disposal facility. A complete analysis
of the problem, however, revealed that the monitoring wells were improperly
installed and contained steel-mill slag where clean gravel should have been
used. Analysis of samples taken from new wells, constructed according to
the specifications, has not indicated elevated levels of any hazardous con-
stituents.
Monitoring well analysis at site E has shown trace levels (92 ppb
maximum) of 12 organic compounds in the groundwater. An investigation of
their source indicated that the organics most probably came from the plastic
well casing materials. This case study points out the importance of testing
the compatibility of all materials with the local groundwater as well as
the expected leachate.
7.7.3 Leachate Level and Quality Monitoring
Leachate collection systems are designed to remove leachate that would
otherwise accumulate in the liner. By doing this, they prevent the buildup
of leachate head, thus keeping liquid infiltration into the liner to a
minimum and therefore contributing to the overall performance of the liner.
Some facilities incorporate leachate level and leachate quality moni-
toring into their overall monitoring program. These parameters serve as
indices of the efficiency of treatment methods that they may have been used
on waste materials and the leachate collection system. Analysis of the
leachate may be used to predict the quality of the liquid, if any, that may
be passing through the liner. Leachate and liner samples can be subjected
to laboratory compatibility tests to indicate the facility performance.
7.8 CONCLUSIONS
The sites included in our study and a brief description of their clay
liners and performance are presented in Table 7-1 and are fully described
in Section 7.2. The 17 sites included in this section were chosen because
they illustrate a specific performance problem or facility characteristic.
While conducting our information search, we encountered many facilities
both with and without failures that were not included here because they
would not have provided any additional information.
Comparing the data from successful sites with the data from leaking
sites does not reveal any significant differences in clay or liner charac-
teristics that might explain the differences in performance. Similarly,
performance does not seem to be related to the use of recompacted borrow
clay versus recompacted native clay or admixed materials. The performance
of facilities without recompacted liners is, however, generally poorer than
the performance of facilities with a recompacted clay or admixed liner.
7-90
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Also note that many of the sites discussed in this section are relatively
new (after 1975). It is therefore difficult to state whether the facilities
without detection systems are performing well or poorly as sufficient time
for leaching chemicals to reach monitoring wells may not have elapsed.
Performance of the facilities that have detection systems, on the other
hand, is much more quickly determined than is the case with facilities I, J,
L, N, and Q. Sites I, J, L, and N have reported performance problems. In
all cases, the leak detection system was instrumental in the rapid detection
of the performance problems. Site Q has had small amounts of liquid detected
in its leak detection system. The volume of liquid removed was used to
determine the permeability of site Q's upper liner. This value was lower
than the design specification, indicating good performance. Of the 17
facilities discussed in Section 7.2, 6 have had major liner failures. Of
these six, the cause of four of the failures is known and the cause of the
failure of the remaining two is unknown. Generally, the cause of a failure
in a clay-lined landfill is very difficult to determine because this would
require removing the waste and other overburden, which may in itself cause
liner damage and impose further hazards. Determining the cause of a liner
failure in a lagoon or evaporation pond is somewhat less difficult because
the waste is more easily removed.
The four facilities with explained failures include three lagoons or
ponds and a landfill that accepted unsolidified liquids. Two of these
facilities had leak detection systems; the others did not. The failures at
the facilities with detection systems were noticed soon after they occurred,
thus preventing groundwater contamination. The other two failures were not
detected until groundwater contamination was found in a monitoring well.
Two of the failures were due to chemical compatibility problems, one to
leachate migration through an improperly sealed sand seam, and the other to
desiccation cracks that formed in an unprotected liner.
Sites with a single layer of clay or those relying on in situ clay
formations are less secure since a leak cannot be detected until pollutants
are found in groundwater samples. The security of a landfill would be
greatly increased if it were constructed with a continuous-coverage leak
detection system installed between two layers of clay. If the inner layer
failed, the leak detection layer would serve as a buffer zone that might
preserve the integrity of the outer layer. The use of lysimeters as a
method for determining liner performance also may provide an early indica-
tion of leachate migration. However, these devices are not foolproof
because they are only able to detect leaks in the section of the liner
directly above them.
7.9 REFERENCES
Apgar, M., and D. Langmuir. 1971. Groundwater pollution potential of a
landfill above the water table. Groundwater 9(6):76-96.
CECOS International, Inc. 1980. Chemical Management Facility Number 4,
Pine Avenue Site, Engineering Report, Vol. 1. Prepared by Wehran
Engineering, Middletown, New York.
7-91
-------
Federal Register, Monday, July 26, 1982, Vol. 47, No. 143.
Ghassemi, M., M. Haro, and L. Fargo. 1984. Assessment of Hazardous Waste
Surface Impoundment Technology (Case Studies and Perspectives of
Experts). Draft. Prepared for the U.S. Environmental Protection
Agency, Contract No. 68-02-3174, Work Assignments 97 and 123. Multi-
disciplinary Energy and Environmental Systems and Applications,
Torrance, California.
Johnson, T. M., and K. Cartwright. 1980. Monitoring of Leachate Migration
in the Unsaturated Zone in the Vicinity of Sanitary Landfills.
Circular 514, Illinois State Geological Survey, Champaign, Illinois,
82 pp.
Kmet, P., and D. W. Lindorff. 1983. Use of Collection Lysimeters in
Monitoring Sanitary Landfill Performance. Paper presented at the
National Water Well Association Conference on the Characterization and
Monitoring of the Vadose (Unsaturated) Zone, Las Vegas, Nevada,
December 8-10.
U.S. Environmental Protection Agency. 1983. Ground-water Monitoring
Guidance for Owners and Operators of Interim Status Facilities.
Office of Solid Waste and Emergency Response, Washington, DC. pp.
7-92
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CHAPTER 8
CLAY LINER TRANSIT TIME PREDICTION METHODS
8.1 INTRODUCTION
Although recompacted clays may have low hydraulic conductivity, they
are, nonetheless, permeable porous media. If a finite depth of liquid
waste or leachate is maintained indefinitely over a clay liner, the liquid
and leachate chemicals will eventually seep through. The goal of transit
time prediction methods is to determine both the rate of seepage with time
and the time it will take for liquids to seep through a liner.
Generally, the transit time prediction methods discussed in this
chapter may be used in two ways. First, these methods may be used to
facilitate the design of new clay liner systems. In fact, the U.S. Environ-
mental Protection Agency (U.S. EPA) has considered using a transit time
equation to provide a method for estimating necessary bottom liner thickness
as a function of the design facility life. Second, these methods may be
used to predict the performance of existing clay liner systems and to
determine the potential for groundwater contamination from leachate or
liquid wastes.
This chapter examines seven transit time prediction methods and compares
their strengths, weaknesses, and applicability to various clay liner condi-
tions. Section 8.2 reviews the assumptions and basic equations that underlie
the use of all these methods. Section 8.3, which comprises the bulk of the
chapter, discusses the derivation and use of each method. Section 8.4
compares the consequences—i.e., the predicted transit time, in years—of
using each method. The methods are compared under two different performance
criteria and assuming three different initial moisture contents of the clay
liner. The prediction of transit times generated by various models cannot
be compared with any actual liner data because no data regarding liner
infiltration and breakthrough under certain conditions are currently avail-
able. Section 8.5 offers a summary and some conclusions regarding the use
of the different methods.
Many of the terms used in this chapter have specific technical meanings,
and Section 8.6 provides a list of these terms along with their definitions.
References are contained in Section 8.7.
8.2 BACKGROUND CONSIDERATIONS
8.2.1 Performance Criteria
It is necessary to establish specific performance criteria that will
provide a definition for "transit time" to design or evaluate a liner
8-1
-------
system. These performance criteria should be designed so that if they are
satisfied, the liner system will ensure safe operation over the intended
life of the facility or up to a certain time after closure. Performance
criteria may be expressed in terms of seepage flux, contaminant flux (indi-
cated by the concentration of a chemical that is present in the leachate),
or the time taken to reach a specified flow rate or chemical concentration
at the bottom of the liner. The following are five examples of possible
specific liner performance criteria:
Specified seepage flux at the liner bottom
Specified contaminant flux for a particular leachate component
at the liner bottom
Time taken to reach a specified seepage flux at the liner
bottom
Time taken to reach a specified leachate chemical flux at
the liner bottom
Time taken for the concentration of a specific leachate
component to reach a specified value at the liner bottom.
Selection of specific performance criteria is very important in predict-
ing corresponding "transit times," and it can also influence the applicability
of a given method. A wide variation in the predicted transit times was
observed in the present work (as shown in Table 8.2 in Section 8.4.1) based
on performance criteria selected and models used.
Recommendations regarding the use of specific performance criteria are
beyond the scope of this work. However, examples of the consequences of
different performance criteria will be considered in the evaluation of
transit time prediction methods.
8.2.2 Clay Liner System
The equations and boundary conditions used in transit time prediction
methods are based on a specific site geometry or flow domain. This flow
domain describes the path of waste leachate through a clay liner system.
For the sake of this discussion it consists of, in a vertically downward
direction, saturated solid waste; a sand/gravel bed on top of the clay
liner (leachate collection system); a clay liner; a sand/gravel leak detec-
tion-system; underlying local soil; and an underlying saturated aquifer
zone. Current regulations (40 CFR 264.301(a)(2)) require a leachate collec-
tion system on top of a clay liner to maintain a leachate head of less than
1 foot. This makes it unnecessary to include the saturated solid waste
zone and the leachate collection system zone in the flow domain. The
sand/gravel leak detection layer may not be present in some designs. A
schematic of the flow domain that is used to illustrate the transit time
equations discussed below is shown in Figure 8-1.
8-2
-------
Impounded Liquid Head
in Leachate Collection Zone
Clay Liner
Leak Detection System
Local Site
Soil
Saturated
Aquifer
Figure 8-1. Flow domain for leachate flow.
8-3
-------
Because the hydraulic conductivity of the clay liner material is much
lower than the underlying site soil, the rate of leachate flow is predomi-
nantly controlled by the clay liner with the underlying soil influencing
only the boundary conditions at the bottom of the clay layer. Some of the
transit time methods are thus based on leachate flow through the clay liner
alone. Due to the large ratio of liner width to liner depth, it is adequate
to consider vertical flow alone to describe the leachate flow.
Any attenuation capacity of the clay or temporary immobilization of
some contaminants tends to slow the leachate migration. Failure to account
for such factors will result in underestimates of transit time.
Note that throughout this section only aqueous leachate systems are
considered; i.e., we are considering only the flow of water and dissolved
species through the flow domain. Although some organic-solvent-based
leachates may be immiscible with water, analysis of such a three-phase
system (two immiscible liquid phases + air) is extremely complex and none
of the transit time prediction methods discussed below (except numerical
methods) apply to this situation.
8.2.3 General Equations
8.2.3.1 Flow Equation—
A general one-dimensional equation to describe the vertical flow of
fluid through the saturated/unsaturated flow domain at a given position z,
but ignoring the specific storage terms, may be written as follows (Bear,
1979; Huyakorn and Pinder, 1983):
where
z = vertical coordinate, expressed as positive downward
distance
K = saturated hydraulic conductivity
k = relative hydraulic conductivity with respect to K
¥ = pressure head
<|> = porosity
S = fractional saturation and is equal to 1 for saturated media
W
t = time.
8-4
-------
The moisture content, 6, is given by (S ). The saturated hydraulic
W
conductivity depends upon the porous media (clay, soil, etc.) and the
composition of the leachate solution. (Clays may have substantially higher
permeabilities to some organic solvents or inorganic chemicals than to
water. See Chapter 4.) The relative conductivity, k , is predominantly a
function of moisture content and depends upon soil type. The pressure
head, f, is also predominantly a function of moisture content and soil
type; in addition, it includes the effect of the liquid head on top of the
liner. Porosity, <|>, depends upon the soil type and is related to the pores
open to the fluid flow.
Equation (8.1), the generalized flow equation, describes moisture
movement in the flow domain. For saturated environments, the equation
transforms into a steady state formulation and one can determine the steady
state flux. For unsaturated conditions, this equation describes the advance-
ment of the saturated wetting front and also the unsteady state fluid flux
as a function of position. Fluid source and sink terms have not been
included in the above formulation because they are not likely to be important.
8.2.3.2 Solute Transport Equation —
Equation (8.1) does not consider the transport of soluble chemicals in
the leachate. A general equation to describe the vertical transport of a
nonradioactive solute species may be written as follows (Bear, 1979; Huyakorn
and Pinder, 1983):
3_ 8_(vC) (8.2)
at az az
where
D = dispersion coefficient that includes both molecular
diffusion and mechanical dispersion
C = solute concentration in liquid phase
z = vertical coordinate, expressed as positive downward
distance
v = Darcian velocity in z direction
-R = retardation factor to account for attenuation capacity of
the clay or soil .
The source and sink terms are not included because they are not expected
to be significant. For a conservative species, the retardation factor
equals 1. The Darcian velocity, v (cm/s), is obtained from the flow equation
and is given by:
8-5
-------
8.2.3.3 Parameters Involved in General Equations—
The preceding governing equations involve several physicochemical
properties of porous media that must either be determined experimentally or
estimated from available data for similar soils. The transit time prediction
methods discussed here make certain assumptions to simplify these equations.
As a result, a certain method may require only a few of these parameters.
Table 8-1 identifies the different methods presented here and the physicochem-
ical properties required for each. It also includes several references
that offer additional information regarding each parameter.
The saturated hydraulic conductivity, K , and porosity (effective), <|>,
of different layers of homogeneous porous media in the flow domain are
required by all methods. Several methods, such as fixed- and flexible-wall
permeameters, are available for measuring the saturated hydraulic conductivity
of a soil, although no standardized American Society of Testing Materials
(ASTM) method exists to date. A review of available methods is given in
Section 3.8 of this Technical Resource Document (TRD) and in another draft
TRD entitled "Soil Properties, Classifications, and Hydraulic Conductivity
Testing" (in preparation). Due to clay-chemical interactions and their
effect on clay-permeability (see Section 4), it is recommended that hydraulic
conductivity be measured with a representative leachate solution.
Methods like the gas expansion method and mercury porosimetry are
available to determine total porosity; however, it is the effective porosity
that is important for flow dynamics. Methods to determine effective porosity
are still at research-tool levels, and are discussed in the above-mentioned
draft TRD. Transit time prediction methods dealing with the unsaturated
flow dynamics in the clay liner use the term "saturation moisture content"
rather than porosity of the medium.
ASTM standard methods are available for measurement of moisture suction
potential, *(9), of soil media. Method No. D-2325 refers to coarse- and
medium-grained soil materials, whereas No. D-3152 refers to fine-grained
materials such as clay (ASTM, 1985).
Like the suction potential, H'(e), the relative hydraulic conductivity,
K , with respect to saturated hydraulic conductivity, is also a function of
moisture content and soil type. Measurement of relative hydraulic conductiv-
ity is more difficult and involved than that of saturated hydraulic conduc-
tivity and, to date, there are no standardized ASTM methods to measure K .
A review of currently available techniques is presented in "Soil Properties,
Classifications, and Hydraulic Conductivity Testing."
The solute transport equation involves two additional parameters:
retardation factor, R, and the axial dispersion coefficient, D. Retardation
factor is dependent upon the attenuation capacity (e.g., adsorption) of the
8-6
-------
TABLE 8-1. PARAMETERS REQUIRED IN DIFFERENT TRANSIT TIME PREDICTION METHODS
oo
Transit
time prediction
method
Simple transit
time equation
Modified transit
time equation
Green- Ampt
wetting front
model
Transient linear-
ized infiltration
model
Modified transit
Saturated
hydraulic
conductivity,
Ks
V
V
V
V
V
Effective
porosity,
V
V
V
V
V
Parameter
Moisture Relative
suction hydraulic Dispersion Retardation
potential, conductivity, coefficient, factor,
ty (6) Kp (6)i D R
V
V V
V V
time equation
with diffusion
Numerical methods:
Flow equation
Solute transport
equation
References
V
Section 3.8
a.b.c.d
V
a.b.c.d
V
ASTM method
No. D-2325
D-3152
Vol. 04.08
V
a,b,c,d
V
b,c,d
V
Section 4
b,c,d
aU.S. EPA (1985, draft).
bBear (1972).
cGreenkorn (1983).
dFreeze and Cherry (1979).
6ASTM (1985).
-------
soil medium and needs to be .determined experimentally. Note also that the
attenuation capacity of soil is time dependent and it is reduced as the
soil approaches saturation with respect to adsorbed species. For conserva-
tive liner thickness predictions, it is probably best to assume retardation
factor of unity (no attenuation).
The dispersion coefficient consists of two parts: hydrodynamic disper-
sion and molecular diffusion. The hydrodynamic dispersion coefficient is
dependent upon flow velocity, whereas the molecular diffusion coefficient
is not. The molecular diffusion coefficient should be readily available
from the literature, whereas measurement of the hydrodynamic dispersion
coefficient is tedious and time consuming, and no standardized methods are
available for this purpose.
8.3 TRANSIT TIME PREDICTION METHODS
Equations (8.1) and (8.2) describe leachate flow and solute transport
in the flow domain shown in Figure 8-1. Solving these equations will give
the seepage flux, leachate flux, moisture profiles, and concentration
profiles as a function of time. Together with the appropriate performance
criteria, these equations may be used to assess the performance of an
existing facility or to design an effective new facility. These equations
are complex, and in this form they can only be solved numerically; but with
certain assumptions it is possible to simplify the equations and allow
analytic solutions. Each of the different transit time prediction methods
discussed below uses some form of simplification to achieve this end. In a
report attached as Appendix A to U.S. EPA (1984), Cogley et al. reviewed
several transit time equations and developed the groundwork for the discussion
that follows.
8.3.1 Simple Transit Time Equation
A simple transit time equation is under consideration by EPA as a
method to estimate the necessary bottom liner thickness as a function of
the design impoundment life (U.S. EPA, 1984, Appendix A). This equation
assumes a flow domain that includes only a saturated clay liner. Figure 8-2a
shows a schematic of the modified flow domain, and Figure 8-2b graphically
shows the assumed pressure potential profile. The vertical axis in Figure
8-2b corresponds to a location in the liner flow domain shown on the left.
Due to saturated conditions, Equation (8.1) is transformed into a steady
state equation, and the steady state Darcian velocity (cm/s) or flux
(cm3/cm2s) is given by Equation (8.3). At the top of the 1-iner (z = 0),
the 1-iquid pressure head is equal to the impoundment liquid head (H* = h);
at the liner bottom, z is equal to liner thickness (z = d). Because the
liner is saturated, the pressure head is taken as zero (M* = 0) at the liner
bottom, assuming free drainage. Thus, the steady state Darcian velocity
and flux, assuming linear potential gradient, are given by:
v = Ks (jj + 1) . (8.4)
8-8
-------
oo
i
z = 0
Impounded Liquid
0
Pressure Head
a) Schematic of Liner
b) Steady State Pressure Head
Profile
Figure 8-2. Schematic of flow domain and assumed steady state pressure head
profile: Simple Transit Time Equation.
-------
Because the liner is assumed to be saturated, the seepage flux is
established as soon as the impoundment liquid head is established. The
time taken by the leachate chemicals at the top of the liner to arrive at
the liner bottom under steady state saturated conditions, due to advection
only, may be obtained by solving Equation (8.2). Assuming D = 0 and R = 1,
Equation (8.2) gives the required transit time, t, as:
t =
v KS (h+d) '
(8.5)
The liner thickness that is required to achieve a given transit time
may then be obtained based on Equations (8.4) and (8.5):
d = 0.5
(8.6)
Because only the advective transport of solute is considered when the
solute transport equation is solved, the leachate concentration at the
bottom of the liner after the transit time would be the same as that of
waste leachate on top of the liner. Before this transit time, the leachate
chemical concentration in the seepage at the liner bottom would be zero.
The leachate chemical flux at the liner bottom after the transit time can
be obtained simply by multiplying the seepage flux (cm3/cm2s) by the leachate
concentration (ppm).
The key assumptions in this approach are:
Steady state saturated Darcian flow
Pore fluid pressure at the bottom of the liner is equal to
atmospheric pressure; i.e., the bottom layer of the liner
remains saturated indefinitely
Solute transport is by advection only; i.e., there is no
diffusion or dispersion
Attenuation capacity of the clay is ignored.
Most clay liners are only partially saturated at the time of placement
and become saturated due to the flow of leachate through them. Thus,
unsteady state, unsaturated flow equations would be appropriate to describe
moisture movement during the initial wetting stage. When unsaturated, the
clay has lower hydraulic conductivity than when saturated (conductivity is
a function of moisture content). However, suction forces induced by capil-
lary tension in unsaturated soils may dominate over gravitational forces.
This was pointed out by Moore (1980):
During early stages of wetting of a compacted clay liner,
capillary attraction forces will predominate over gravitational
forces. As the clay liner becomes wetter, the capillary forces
decrease in importance; and, when the liner is saturated, these
forces become negligible in comparison to gravitational forces.
8-10
-------
The importance of capillary forces depends upon the initial moisture
content of the compacted clay before it is covered by waste material. If
the higher hydraulic conductivity under saturated conditions can offset
higher potential gradients but lower hydraulic conductivity under unsaturated
conditions, the simple transit time equation may give satisfactory results.
If, with reduced moisture content, the increase in capillary forces is
greater than the corresponding reduction in hydraulic conductivity, this
approach will underpredict the required liner thickness.
The simple transit time equation assumes that the pressure head at the
liner bottom is zero. However, actual soil underlying the clay liner is
likely to influence the conditions at the liner bottom. If a saturated
clay liner is placed on an unsaturated soil bed, the soil may exert a
suction potential to initiate seepage within the clay liner. Thus, the
bottom layers of the liner will not remain saturated, and this suction
potential will add to the overall potential gradient and reduce the transit
time.
A limiting assumption in this approach is that molecular diffusion or
dispersion is not significant compared to convective flux. In view of the
low permeability of clays and the corresponding low fluid velocity, the
molecular diffusion process may be a significant factor. Diffusion may
allow the dissolved chemicals to migrate faster in a liner compared to
advective flow and will thus reduce the transit time of the chemical species.
Originally, Equation (8.2) was solved based on total porosity instead
of effective porosity (U.S. EPA, 1984, Appendix A). However, effective
porosity is more appropriate because it accounts for closed pores and
considers only the pores that are open to the fluid flow. This is a rela-
tively simple modification as it does not alter Equations (8.5) and (8.6)
but substitutes another value for .
The simple transit time equation is very easy to use. One needs to
know only the saturated hydraulic conductivity of the liner material, its
total (or effective) porosity, and the leachate head at the top of the
liner. Because these parameters should be readily available, this equation
provides a method to obtain quick estimates of liner performance or required
liner thickness.
8.3.2 Modified Transit Time Equation
Cogley et al. (in U.S. EPA, 1984, Appendix A) modified the simple
trans.it time equation to account for effective porosity and the suction
potential at the liner bottom. However, other assumptions regarding steady
state conditions, saturated Darcian flow in a homogeneous liner, and advec-
tive solute transport were made as before. The flow domain and the pressure
potential profiles for the modified transit time equation are shown in
Figures 8-3a and 8-3b. These are similar to those in Figures 8-2a and 8-2b
except for the boundary condition at the liner bottom. Due to the steady
state saturated conditions, Darcian velocity and flux are again given by
8-11
-------
00
Impounded Liquid
2 = 0
-hd 0
Pressure Head
a) Schematic of Liner
b) Steady State Pressure Head Profile
Figure 8-3. Schematic of flow domain and assumed steady state pressure head profile:
Modified Transit Time Equation.
-------
Equation (8.3). At the top of the liner (z = 0), the pressure head is
given by impoundment height (V = h), and at the bottom of the liner (z = d)
the pressure head is negative due to suction (¥ = - h,). When these boundary
conditions are incorporated and a linear potential gradient assumed, the
Darcian velocity and flux are given by:
h+h
1) .
(8.7)
Equation (8.2), the solute transport equation, may then be solved as
before—assuming saturated steady state conditions and ignoring dispersion
and attenuation processes (D = 0 and R = 1). The resulting transit time
for a solute species -for a given liner thickness is given by:
(h+hd+d)
(8.8)
The required liner thickness for a specified leachate transit time is
then obtained as:
d = 0.5
Kst
Kst (h+hd)
(8.9)
Equations (8.8) and (8.9) are similar to Equations (8.5) and (8.6)
except for the h. term and the use of effective porosity instead of total
porosity.
Since only advective transport is considered for solving the solute
transport equation, the leachate concentration at the bottom of the liner
(after transit time) would be the same as the concentration of waste leachate
on top of the liner. Before this transit time, the leachate concentration
in the seepage at the liner bottom would be zero. The leachate chemical
flux at the liner bottom after the transit time is given simply by multiply-
ing the seepage flux by the leachate concentration.
Like the simple transit time equation, the modified equation assumes
saturated steady state conditions and negligible diffusion processes in
solute transport. The incorporation of suction potential at the liner
bottom is actually somewhat inconsistent with the assumption of saturated
flow since the negative pressure would induce unsaturated conditions in
lower sections of the liner. Although the suction potential at the bottom
is included, the higher hydraulic conductivity value corresponding to
saturated conditions is used in this equation. As a result, for a specified
transit time, this modified equation yields greater values for liner thick-
ness compared with the simple transit time equation.
8-13
-------
In addition to the information required to use the simple transit time
equation, the capillary suction at the bottom of the liner (~h.) must be
specified. The suction pressure or capillary pressure head depends upon
the clay liner material, its particle size distribution, and the underlying
site soil dynamics (McWhorter and Nelson, 1979). The underlying site soil,
for example, may be assumed to be in stable equilibrium with respect to the
water table, in which case the required suction potential will be given by
the depth of the site soil above the water table. Depending upon the value
of the capillary suction potential, different values of the required liner
thickness are obtained.
8.3.3 Green-Ampt Wetting Front Model
The transit time equations discussed above ignore both the initial,
unsaturated nature of the liner and infiltration dynamics. Green and Ampt
(1911) derived a simple model to describe the infiltration process that has
been proposed as a method to assess liner reliability (U.S. EPA, 1984,
Appendix A). A similar approach was also analyzed by McWhorter and Nelson
(1979) and discussed by EPA (U.S. EPA, 1983).
The Green-Ampt model (1911) describes moisture movement in unsaturated
soil during ponded infiltration by assuming a sharp, saturated wetting
front moving down the soil column as a square wave. The model is schemat-
ically shown in Figures 8-4a and 8-4b. Figure 8-4a shows a schematic of
the liner flow domain and also indicates the variation of moisture content
with depth in the liner. Figure 8-4b graphically shows the corresponding
pressure potential profile. Above the wetting front, the soil is fully
saturated, with a moisture content, 9 , while below the wetting front the
moisture content is equal to its initial value, 9.. At a given time, t,
following establishment of the ponded leachate head on top of the liner,
the wetting front will have moved down a certain distance, L. Saturated
flow analysis may be applied to the saturated zone above the wetting front
to determine the Darcian velocity or flux as given by Equation (8.3). The
pressure head or capillary suction potential below the wetting front is
-Y , due to the partial, initial saturation of the clay liner. At the top
of the liner (z = 0), the pressure is given by the impoundment height
(H* = h); at the wetting front (z = L), the potential is given by the suction
QV = -¥ ). Thus, when these boundary conditions across the saturated zone
are incSrporated, the Darcian velocity or flux (q) is given by assuming a
linear potential gradient:
v = q = K
+ 1) .
(8.10)
In Equation (8.10) the wetted depth, L, is variable with time and is
related to the flux, q, by conservation of pore fluid volume:
(8.11)
8-14
-------
o
to
£
Liner
c»
i
Impounded Liquid
Green-Ampt Moisture
/Profile
Moisture Content 0
Pressure Head
a) Moisture Content Profile
in Liner
b) Pressure Potential Profile
Figure 8-4. Green-Ampt infiltration model.
-------
The time required for the wetting front to reach a depth of L is
obtained by combining Equations (8.10) and (8.11) and integrating:
(8.12)
Thus, Equation (8.12) predicts the time required for an unsaturated
clay liner to become saturated to a depth of L. When the liner thickness,
d, is substituted for the wetted depth, L, the time required for the wetting
front to reach the liner bottom is obtained. The required liner thickness
for a certain specified transit time, t, can also be calculated. The
seepage flux at the liner bottom is zero before the wetting front reaches
the bottom. The seepage flux when the wetting front reaches the bottom may
be obtained by substituting the liner thickness, d, for the wetted depth,
L, in Equation (8.10). This seepage flux relationship is identical with
that in the modified transit time equation, provided the same values are
used for the capillary suction potentials, - h. and - f .
The "transit time" predicted by the Green-Ampt model is not necessarily
a true transit time. The solute transport equation is not solved in this
approach, and the time given by Equation (8.12), after d is substituted for
L, is only the time required for the liner to become saturated. If the clay
liner is initially saturated, this equation would predict zero transit
time. However, for a liner that is initially unsaturated, the saturation
time will be equivalent to the leachate transit time.
Because this approach gives the seepage flux after liner saturation
and the time required to achieve saturation, it can be used only with
performance criteria prescribing the seepage flux and the saturation time.
This model does not determine the leachate chemical flux or concentration
at the liner bottom, so it cannot be used to predict performance with
criteria based on leachate chemicals.
To use Equation (8.12), one needs to know the saturated hydraulic
conductivity of the liner material, initial liner moisture content, satura-
tion moisture content, liquid head on the liner, and the capillary suction
potential below the wetting front due to the unsaturated clay. Capillary
potential depends upon initial moisture content and must be determined for
each clay liner material.
This model handles the dynamics of infiltration in an approximate
manner. It determines the time required for saturation and would be appli-
cable to clay liners that are initially unsaturated. Because it does not
consider solute transport, it cannot determine the leachate concentrations
and leachate transit times. For a partially saturated liner, the time
required to achieve saturation may not represent the leachate transit time.
8-16
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8.3.4 Transient Linearized Infiltration Equation
The general equation for flow through an unsaturated media is highly
nonlinear because the hydraulic conductivity and capillary suction potential
depend on the moisture content of the soil. Because the top boundary
condition for this equation is expressed as a positive pressure (due to the
ponded liquid) and the bottom boundary and initial liner conditions are
given by initial pressure head, it is convenient to write Equation (8.1) in
terms of pressure head (ijj) (Bear, 1979):
.
diji * at
3z
.
dtj/ ' 82
(8.13)
where
K = effective hydraulic conductivity, depends upon »ji, and is
equal to K k
0 = moisture content and also depends on fy
z = vertical coordinate expressed positive downward
When both sides are multiplied by (di|j/dG):
dijj dK aj)
de di|> 3z •
at de 3z
(8.14)
(14)
Defining D* = K (di|>/d0) and K* = dK/d0 and substituting in Equation
(Richards, 1931; Philips, 1957) obtains:
§4 =
at
8z
(8.15)
Equation (8.15) is the linearized form of the nonlinear infiltration
equation, and its analytical solution may be obtained by assuming D* and K*
to be constant for a given clay liner. Moore (1980) has previously recom-
mended this technique for impoundment liner evaluation. To obtain the
analytical solution, one must assume the clay liner to be a semi-infinite
medium; i.e., one must assume that the liner extends to an infinite depth
and that its pressure head at the infinite boundary remains unchanged from
its initial value. At the top of the liner (z = 0), pressure head is equal
to the depth of ponded liquid (<|* = h); initial (t = 0) pressure head through-
out the liner is equal to »{».; and at the bottom of the liner (z = »),
pressure head remains at its initial value (i}» = ij».). When these boundary
and initial conditions are applied, the analytical solution may be obtained
as follows (Bear, 1979):
8-17
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erfc () + exp () erfc
(8.16)
I «- C-y LJ \* \J C.\ U U
where
erfc = complementary error function.
Solutions to Equation (8.16) are presented graphically in Figure 8-5
with the liner thickness, d, replacing z. Unlike the transit time equations
and the Green-Ampt model, the transient linearized solution results in a
continuous profile of soil moisture that is physically more accurate.
There is no sudden increase in moisture content or reduction in the suction
potential at the liner bottom. Rather, moisture content gradually increases
from the initial value to saturation as the wetting front advances. Due to
the semi-infinite boundary condition employed, the solution is accurate
until the time when the moisture content at the liner bottom begins to
rise.
A model based on the transient linearized infiltration equation solves
the flow equation but does not consider the solute transport equation.
Like the Green-Ampt model, this approach is most suitable when the clay
liner is initially unsaturated. The transit time calculated with Equa-
tion (8.16) is the time required to saturate the clay liner. When the
initial moisture content is high, the wetting front advances faster than
the corresponding leachate front; in such situations, the transit time
predicted by Equation (8.16) does not reflect the actual leachate chemical
transit time.
For initially unsaturated clay liners, the leachate transit time may
be approximated by the time required to achieve liner saturation. Because
the moisture content as predicted by this linearized model increases gradu-
ally, there is no sudden or well-defined breakthrough of the saturation
front. Therefore, it is necessary to define the breakthrough of the front
in terms of relative changes in moisture content or pressure. For example,
a common choice is the point where suction potential is reduced by 50 per-
cent; but significant amounts of liquid may have seeped through before the
capillary suction potential is reduced by 50 percent. A conservative value
for the quantity (ijj - .; the depth of impounded liquid on top of the liner, h;
and the parameters D* and K*. The variation of hydraulic conductivity, K,
and pressure potential, \\i, with clay moisture content, 0, must be known to
determine the last two parameters. These relationships are usually nonlinear;
8-18
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0.999
0.8
-3-
i
0.1
0.001
D*/K*z
0.05 0.1
0.5 1.0
K*t/d
5.0 10 50
Figure 8-5. Graphical solution to equation (8.16)—linearized infiltration model.
8-19
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therefore, it is difficult to assign reasonable values to D* and K* as
defined in Equation (8.15), even after these relationships are obtained
from laboratory measurements.
This model determines the time required for the clay liner to become
saturated, and it accounts for the dynamics of infiltration processes. The
seepage flux, before the moisture content at the bottom of liner begins to
rise, is negligible. After liner saturation, the steady state seepage flux
may be obtained by an equation similar to (8.10) or (8.7). Like the Green-
Ampt wetting front model, this approach does not determine the leachate
chemical flux or concentration and therefore cannot be used with perform-
ance criteria based on leachate chemicals.
8.3.5 Modified Transit Time Equation with Diffusion
The modified transit time equation may be improved by including a
diffusion term and seeking an analytical solution to the solute transport
equation. The assumption of saturated steady state Darcian flow in a
homogeneous liner may be made as before. The steady state Darcian velocity
or flux, v, after the negative pressure at the liner bottom, -h, is con-
sidered, is given by Equation (8.7):
(8.7)
The solute transport equation for a saturated clay liner with a constant
dispersion coefficient, D, and steady state velocity, v, may be rewritten
for a noninteracting (R = 1) species as follows:
9C _ D 32C _ v 3C
3t <)> 82? 3z
(8.17)
Equation (8.17) is very similar to Equation (8.15). To obtain an
analytical solution to Equation (8.17), one must again assume that the clay
liner extends to an infinite depth and its concentration at the infinite
boundary remains unchanged from its initial value. The initial and boundary
conditions are as follows: at the top of the liner (z = 0), the leachate
concentration is C , (C = C ); initially (t = 0), concentration throughout
the liner is zero (C = 0); and at the bottom of the liner (z = »), concen-
tration remains unchanged (C = 0). The analytical solution for Equation
(8.17) may be written similarly to Equation (8.16) (Bear, 1979; Ogata and
Banks, 1961; Cleary and Ungs, 1978):
= -| erfc
t
exp () erfc
z+4
(8.18)
8-20
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.Equation (8.18) describes concentration profiles of the leachate
chemical species with time. At a given location, the concentration rises
gradually from zero to the leachate concentration at the top of liner.
Because there is no explicit or sudden breakthrough of the leachate front
at the liner bottom, it is necessary to define leachate breakthrough in
terms of a relative change in concentration (C/C ) at the liner bottom.
For example, an average value of 0.5 may be chosen; however, significant
amounts of chemicals may escape the liner before the relative concentration
at the liner bottom reaches a value of 0.5. A conservative value of C/C =0.1
may be used arbitrarily to represent the leachate chemical breakthrough.0
Figure 8-6 shows a graphical solution to Equation (8.18).
An iterative technique similar to that discussed in Section 8.3.4
above may be used to obtain the required liner thickness for a specified
leachate transit time. Equation (8.18) predicts the leachate concentration
at the liner bottom with time. The steady state seepage flux is given by
Equation (8.7). Again, the leachate chemical flux is obtained by multiply-
ing the seepage flux by the leachate concentration. The leachate chemical
flux at the liner bottom is negligible before the concentration there
begins to rise.
To use the modified transit time equation with diffusion, one must
know the saturated hydraulic conductivity and effective porosity of the
liner material; the depth of impounded liquid; the capillary suction poten-
tial at the liner bottom; and the effective dispersion coefficient for the
leachate chemical species. For low-permeability clays, the dispersion
coefficient may be approximated by the molecular diffusion coefficient of
the leachate species in water. This equation is simple to use. It assumes
a saturated liner medium but accounts for the effect of suction potential
at the liner bottom and the contributions of both advection and molecular
diffusion to the solute transport process.
8.3.6 Numerical Solutions
The various models discussed in previous sections attempt to obtain
simplified solutions to Equations (8.1) and/or (8.2), which describe flow
and solute transport in saturated and unsaturated media. Section 8.3.4
represents an attempt to linearize the flow equation for unsaturated media
by introducing simplifying assumptions. Although the flow equation is
relatively independent of the transport equation, the solute transport
equation is coupled with the flow equation due to the advective contribution
of flow to solute transport. For th-is reason, linearization of the solute
transport equation is especially difficult. Section 8.3.5 describes an
analytical solution for flow and solute transport in saturated media. Such
a solution is not possible for unsaturated media due to nonlinearities
involved in the governing equations.
Numerical methods can be used to describe accurately the movement of
the saturation front and solute transport in unsaturated clays. Computer
programs are available to solve the generalized unsaturated flow and solute
transport problem in one or two dimensions. They generally employ finite
8-21
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0.999
0.8
o
o
0.1
0.001
0.05 0.1
0.5 1.0
vt/0d
5.0 10 50
Figure 8-6. Graphical solution to equation (8.18)—transit time equation with diffusion.
8-22
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difference or finite element numerical techniques and require data regarding
the variation of hydraulic conductivity and moisture potential with moisture
content in clay and underlying site soil. To use the numerical methods,
one should be familiar with both the numerical techniques and the require-
ments and limitations of the specific program used.
Numerical methods reduce governing Equations (8.1) and (8.2) to approxi-
mating algebraic equations that are then solved through implicit linear
algebra techniques. Finite difference techniques approximate the partial
derivatives in the governing equations by using finite difference equations
(Pinder and Bredehoeft, 1968; Mercer and Faust, 1980). The finite difference
equations are solved for each node on an arbitrary grid through an iterative
procedure. Compared to finite element codes, finite difference codes are
simple, are relatively easy to program, and require less computer time for
data manipulation. Finite element approximations incorporate a finite
series of basis (or shape) functions and associated time-dependent coef-
ficients to describe the dependent variables. The series are then input to
the governing equations and the resulting error or residual is minimized
(Pinder, 1973; van Genuchten, 1978). Finite element codes are more complex,
require more input data, and are more expensive to execute. However, the
finite element codes are more flexible and can handle irregular flow geometries
and boundary conditions. Because no irregular flow geometries or boundary
conditions are involved, simple one-dimensional finite difference codes may
be adequate to describe the vertical flow and solute transport through a
clay liner system.
Several computer codes are available to solve the unsaturated flow
and/or solute transport problem in one or two dimensions. A complete list
may be obtained from a computerized data base called the Model Annotation
Retrieval System, maintained by the International Groundwater Modeling
Center at the Holcomb Research Institute of Butler University. A partial
list of some of the models and their characteristics is given in Appendix B.
A comprehensive list is also given by Bachmat et al. (1980).
8.3.6.1 Numerical Solution of the Flow Equation—
The solution to Equation (8.1), the general flow equation, for an
unsaturated clay liner yields moisture content profiles in a clay liner
with time and also the rate of seepage flux through the liner at different
locations as a function of time. Notable among the available programs to
solve the unsaturated flow equation in a liner system is a finite difference
program, "SOILINER," developed by Goode and Smith (in U.S. EPA, 1984).
This program was specifically written for a clay liner system and is described
in detail in their report. This program considers vertical one-dimensional
flow in the flow domain shown in Figure 8-1 and solves the equation in the
form given in Equation (8.13), which incorporates suction potential (¥).
The following sections describe the input data required by the SOILINER
program.
8.3.6.1.2 Grid Specifications—The vertical linear flow domain may be
divided by a certain number of node points. The number of node points and
spacing between the node points (element length) must be specified. The
8-23
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spacing may be uniform or graded. Alternatively, the coordinate for each
node point may be specified for maximum flexibility in node spacing.
8.3.6.1.3 Clay and Soil Properties—Saturated hydraulic conductivity
and porosity for each element in the flow domain may be specified. This
allows maximum flexibility to account for heterogeneous layers in the flow
domain. Typically, two or three layers may be included to represent the
clay liner, underlying site soil, and intermediate (optional) leak detection
zone. In addition, functional relationships for each different type of
material must be provided to determine the relative hydraulic conductivity
(k ), moisture content (0), and soil-specific moisture capacity (d0/cW) as
a function of capillary suction potential (¥). These relationships are
obtained by least square fitting the experimental data by a continuous
functional form. The program has included functional relationships for
three different soil types (clay and two different sandy soils), and more
relationships can easily be included.
8.3.6.1.4 Initial Conditions—Because the program solves an unsteady
state equation, initial conditions must be specified. For example, initial
distribution of the pressure head for the flow domain may be specified.
The clay liner may be assumed to have a constant initial moisture content
and corresponding uniform initial suction potential. The underlying site
soil may be assumed to be at static equilibrium with respect to the water
table.
8.3.6.1.5 Boundary Conditions—Also needed are the boundary conditions
at the top and bottom of the flow domain. The boundary condition at the
top is due to the impounded liquid depth on top of the liner. The pressure
head at the top is thus equal to the depth of the free liquid. The boundary
condition at the bottom is critical because it contributes to the overall
potential gradient across the liner and flow domain. If the underlying
site soil above the water table is included in the flow domain, the bottom
boundary potential will be zero, corresponding to the free liquid surface
of the water table. If only the clay liner is considered in the flow
domain, the suction potential at the bottom of the liner due to the underly-
ing site soil needs to be estimated. If it is assumed that the liner
bottom is ventilated and open to the atmospheric air, the suction potential
at the liner bottom will remain at the initial level until the moisture
content at the bottom begins to rise or the saturation front reaches the
bottom.
Similar input data will be required by all the numerical codes solving
the unsaturated flow equation. To run such a program, a user often also
needs to specify the maximum time step the program should use and the final
end time. In addition, those times must be specified to obtain moisture
profiles and flux at intermediate times. The output from such a flow
problem typically includes distribution of suction potential, moisture
content, flow velocity, and seepage flux at each node (or specified output
nodes) in the flow domain.
8-24
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Most of the programs for unsaturated flow were developed for a general-
ized unsaturated flow situation (typically infiltration into soil) and thus
may require some effort to be adapted to the present clay liner problem.
However, the SOILINER program is written specifically for flow through an
unsaturated clay liner.
The solution of the unsaturated flow equation describes the variation
of moisture profiles and seepage flux in the liner with time. Like the
linearized flow model, the numerical solution predicts a gradual increase
in the moisture content and reduction in the suction potential. Thus,
there is no sudden or explicit breakthrough of the saturation front at the
liner bottom. As before, such a concept may be defined on the basis of the
relative reduction in the suction potential at the liner bottom. A conserva-
tive value for the relative reduction [OP-M*.VCh-H*.)], such as 0.1, may be
used to represent the saturation breakthrough. Thus, the user can predict
the time required for the liner to become saturated or for the saturation
front to reach the bottom.
However, the numerical solution to the flow equation does not address
the transport of leachate chemicals. It does not determine the leachate
chemical concentration profiles and the flux with time; therefore, it
cannot predict the true leachate transit time. By arguments similar to
those presented for the Green-Ampt model and the linearized flow model,
this approach is suitable for clay liners that initially are predominantly
unsaturated. Where the clay's initial moisture content is high, the satu-
rated wetting front may advance faster than the front representing the
leachate chemicals. Where the liner is initially saturated, the unsaturated
flow equation is not applicable.
8.3.6.2 Numerical Solution of the Solute Transport Equation—
It is necessary to solve Equation (8.2), the solute transport equa-
tion, to describe the transport of leachate chemicals in an unsaturated
clay liner system. As discussed previously, the unsaturated solute transport
equation is coupled with the unsaturated flow equation due to advective
contribution of the seepage flux to the solute transport (the term involving
Darcian velocity, v, in Equation (8.2)) as well as due to the variation of
moisture content with time that is determined from the flow equation. For
this reason, the solute transport equation and the flow equation must be
solved simultaneously. Alternatively, the variation of velocity and moisture
content at each node with time may be stored in a separate data file while
the flow equation is solved. This data file may then be used as an input
to the solute transport program, in addition to other input parameters for
the solute transport program, to obtain solute concentration profiles and
solute fluxes with time.
Almost all of the available computer programs for solving the unsatu-
rated solute transport problem require the solution of the flow problem
first because they do not solve both equations simultaneously. Thus, it is
necessary to store the velocity and moisture content values at each node
for all time steps in a separate file. Solute transport usually includes
diffusional as well as convective elements. The dispersion coefficient
8-25
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includes the effect of both molecular diffusion and hydrodynamic dispersion.
For clay liners with very low permeability, the molecular diffusion may be
expected to dominate the dispersion process. Since different chemical
species in the leachate may have differing dispersion and attenuation
properties, they may migrate differently in the flow domain. Therefore,
the solute transport equation must be solved specifically for the chemical
species of interest. Different solute transport equations may be written
for specific chemicals by using respective dispersion and retardation
coefficients; these equations may be solved simultaneously to obtain concen-
tration profiles and chemical fluxes for each chemical. Since the bulk
flow velocity and the moisture content profiles would be the same for any
number of chemicals in the leachate, the flow problem needs to be solved
only once, irrespective of the number of chemical species in the leachate.
The input data required to solve the solute transport problem are
described below:
8.3.6.2.1 Grid Specif ications--These are the same data required for
the flow problem (Section 8.3.6.1).
8.3.6.2.2 Clay and Soil Properties — Since the flow equation must be
solved along with the solute transport, all the above-mentioned physical
data are needed for the companion flow problem program. In addition, for
the solute transport problem the dispersion coefficient, D, must be specified
for all elements. If the hydrodynamic dispersion is ignored, the dispersion
coefficient would simply be the molecular diffusion coefficient of the
chemical species of interest in water and would be reasonably constant for
the entire flow domain. If the hydrodynamic dispersion coefficient is
included, the functional relationship between the hydrodyrfami c dispersion
coefficient, D. , and Darcian flow velocity must be specified as in:
Dh=v (8.19)
where
a. = longitudinal dispersivity.
Since the flow is considered to be one-dimensional, the transverse
dispersivity values are not required and may be taken as zero. The longi-
tudinal dispersivity, or., depends upon the type of flow medium and may have
different values for each heterogeneous layer in the flow domain such as
clay and underlying site soil. Since the hydrodynamic dispersion coefficient
depends upon flow velocity, it needs to be evaluated for each time step for
all elements. The overall dispersion coefficient, D, is obtained by adding
together the molecular diffusion coefficient and the hydrodynamic dispersion
coefficient.
Also needed is the retardation coefficient, R, for all elements, to
account for the leachate attenuation capacity of the clay and soil. The
8-26
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retardation coefficient is specific for a leachate chemical/soil combination
and must be determined experimentally. Thus, the clay and the underlying
site soil may have different attenuation capacities for a given chemical.
The attenuation capacity usually slows down the migration of a chemical,
therefore ignoring that the attenuation is likely to yield a conservative
estimate of the required liner thickness. If the attenuation capacity of
the soil/clay is ignored, the value of the retardation coefficient, R, is
set to 1.
The flow equation is usually considered independent of the solute
transport equation. One way in which leachate chemicals can affect the
solution of the flow equation is by altering the permeability of clays and
soils. Many pure organic solvents and inorganic acids and bases have a
strong effect on the properties of the flow medium. Such effects, if
known, need to be taken into account to solve the flow equation.
8.3.6.2.3 Initial Conditions—To solve the unsteady state solute
transport equation, initial concentration values of the chemical species in
the flow domain must be specified. Usually, the initial solute concentra-
tions may be assumed to be zero.
8.3.2.6.4 Boundary Conditions—Like the flow problem, the boundary
conditions at the top and bottom of the flow domain need to be specified.
The concentration of chemical species at the top is the concentration in
the impounded liquid, C . The concentration at the bottom is difficult to.
designate. Ideally, theYe is a matching chemical flux condition at the
bottom to represent inflow and outflow. If the underlying site soil is
included, the matching condition may be described by the dilution of the
leachate seepage due to the aquifer flow rate. If this dilution is con-
sidered to be large enough, the concentration at the bottom boundary may be
taken to be zero. This boundary condition is difficult to specify if the
underlying site soil is not included in the flow domain. One alternative
is to assume that the underlying site soil does not influence the leachate
chemical flux; mathematically, the leachate chemical flux may be assumed to
be the same in the bottom two elements:
/,_ \
- vC (8.20)
/ n-1
where
n = bottom element.
8.3.6.2.5 Darcian Velocity and Moisture Content Profiles—These
parameters are obtained by solving the flow equation first. The moisture
content and flux values at each node need to be saved for all time steps in
an input file that is later recalled from the solute transport program. If
the flow and solute transport equations are solved simultaneously, such
saving of data will not be needed.
8-27
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Similar data are needed for all codes solving the solute transport
equation. The user also needs to specify the maximum allowable time step
and the end time. For stability, it may be necessary to have smaller time
steps than those used in the flow problem. If this is the case, a particular
flow time step at a certain time may need to be subdivided for the solute
transport problem. The velocity and moisture content values will then
remain the same until the time is advanced by the flow step.
The typical output from a solute transport code will indicate the
solute chemical concentrations and fluxes at all nodes for all times or for
specified output times. Solving both the flow and the solute transport
equations determines the moisture content profiles as well as the chemical
concentration profiles with time along with the seepage fluxes and the
chemical fluxes. At a given location, the concentration rises gradually
from zero to the leachate concentration at the liner top. Thus, there is
no sudden or explicit breakthrough of the leachate at the liner bottom.
Therefore, breakthrough must be defined in terms of the relative change in
concentration (C/C ) at the liner bottom. As discussed before, a conserva-
tive value of C/C °= 0.1 may be arbitrarily used to represent the leachate
chemical breakthrSugh. Such a definition may be used to determine the time
required for leachate chemical breakthrough.
Compared to other prediction methods, the numerical solutions of the
flow and solute transport equations for unsaturated media provide a great
deal of information. The numerical solutions provide an accurate descrip-
tion of the leachate migration, and they can be used with any set of per-
formance criteria. However, numerical techniques are expensive to run and
require expertise in the use of the computer models. Available programs to
solve the flow equation outnumber those available for the solute transport
problem. Although some of the programs are proprietary, two available flow
programs in the public domain are SOILINER, which was developed by GCA and
is written specifically for clay liners, and FEMWATER, which was developed
by Oak Ridge National Laboratory (ORNL). ORNL also has a solute transport
program, FEMWASTE, available in the public domain. In the present work,
SOILINER was modified by incorporating a subroutine CONCAL to solve the
solute transport equation simultaneously with the flow equation. A simple
forward-time centered space difference scheme was used to solve the solute
transport equation. Details of this modified program, LINERSOL, are given
in Appendix C. In LINERSOL, the flow solution is first advanced by a flow
time step. The current moisture content and velocity profiles are then
used to advance the solute transport equation by the same flow time step.
For stability and accuracy, it is often necessary to divide a flow time
step into a smaller solute transport time step. The program LINERSOL can
thus solve both the flow and solute transport equation simultaneously for a
liner system.
8.4 COMPARISON OF DIFFERENT APPROACHES
This section compares each of the transit time prediction methods
discussed above. To compare the methods under equal concitions, we first
describe a "basic liner scenario" that specifies assumptions concerning
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initial site conditions and the leachate flow domain. Because the methods
make different assumptions, different transit time predictions may be
expected both where the initial moisture content of the liner varies and
under different performance criteria. Three different initial moisture
contents and two different performance criteria are considered in the
following analysis.
8.4.1 Basic Assumptions
The leachate flow domain is assumed to consist of 2 m of compacted
clay liner placed on top of underlying site soil. The depth of this site
soil is assumed to be 5 m above the water table. The water table is assumed
to be stable with time and the leachate head on top of the liner is assumed
to be 30 cm (this is the maximum allowed by current regulations).
The clay liner is assumed to have an effective porosity of 0.495 and a
saturated hydraulic conductivity of 1 x 10 7 cm/s. The underlying site
soil is considered to have an effective porosity of 0.287 and a saturated
hydraulic conductivity of 1 x 10 2 cm/s. The relationships among the
moisture content, hydraulic conductivity, and capillary suction potential
for the clay and site soil are assumed to be those given by Figure 8-7
(U.S. EPA, 1984). For a leachate chemical species, it is assumed that the
dispersion coefficient is dominated by molecular diffusion and that the
molecular diffusion coefficient, D, in water is 1 x 10 6 cm2/s. The attenua-
tion capacity of the clay soil for this chemical species is assumed to be
negligible by setting the attenuation coefficient, R, equal to 1.
The site soil is initially assumed to be in static equilibrium with
the water table. Thus, the initial suction potential varies linearly with
the depth, and at the top of the site soil the suction potential is -500 cm.
Because the site soil has a very high permeability relative to the clay
liner, the flow through the liner may be expected to have only a small
effect on the suction potential profile in the site soil.
The liner simulations with each of the prediction methods are carried
out based on three different values for the initial moisture content of the
clay liner: 50 percent, 80 percent, and 95 percent of saturation. The
initial suction potential at the time of placement is assumed to be constant
throughout the clay liner and is determined by the initial moisture content
as illustrated in Figure 8-7. The following suction potentials are associ-
ated with the three values of initial moisture content:
Saturation
50 percent
80 percent
95 percent
Suction potential
-500 cm
-57.38 cm
-14.82 cm
The clay liner is assumed to be exposed to a constant leachate head of
30 cm on top of the liner immediately after placement in the field.
8-29
-------
a) -1
-2
-3
-4
-5
1 -6
5 -7
-8
-9
-10
-11
b) 3.0
— Clay
Sand
0.0 0.5 1.0 1.5 2.0 2.5 3.0
0.0 0.5 .10 .15 .20 .25 .30 .35 .40 .45 .50
Moisture Content (volumetric)
Figure 8-7. Soil properties of hypothetical clay (solid line)
and sand (dashed line) for liner design.
a) Unsaturated hydraulic conductivity (cm/s)
as a function of capillary pressure (pF = log(-
-------
Based on the scenario described, two different performance criteria
were applied to determine the breakthrough time predicted by each method.
One performance criterion is based on the flow equation and the advancement
of the saturation front. The second criterion is based on solute transport
in the liner and the advancement of the leachate chemical front. Table 8-2
summarizes the results of the liner simulations for each method under the
two performance criteria. The following sections present the assumptions
and calculations for each simulation.
8.4.2 Comparison With Performance Criteria Based on Saturation Front
Performance criteria based on movement of the saturation front may be
defined in several ways. For example, transit time may be defined as the
time taken for the liner to become saturated to achieve a steady state
moisture content profile, or for the relative reduction in the suction at
the liner bottom to be equal to or greater than 0.1 (i.e., (H'-4'.)/(h-*f.) > 0.1).
Where applicable, each of the methods discussed in previous sections was
used to determine the transit time based on the saturation front criteria.
8.4.2.1 Simple Transit Time Equation—
This approach assumes a saturated liner and thus cannot be used with
the above criteria. With this approach, the time required for saturation
equals zero.
8.4.2.2 Modified Transit Time Equation—
This approach also assumes a saturated liner so the time required to
saturate the liner is zero.
8.4.2.3 Green-Ampt Wetting Front Model —
Equation (8.12) is used to obtain the required time to saturate the
liner. The depth of saturation of the liner, L, is replaced by the liner
thickness, 200 cm. The suction potential in front of the wetting front,
-¥, depends upon the initial moisture content in clay liner. The saturated
hydraulic conductivity of the clay liner is 1 x 10 7 cm/s, and the leachate
head on top of the liner is 30 cm. Table 8-3 shows the parameters and the
predicted transit times assuming three values for initial moisture content
of the liner.
Under actual conditions, the time required to saturate the liner
should decrease with increasing initial moisture content. However, due to
the use of approximate nonlinear suction potential characteristics and also
the arbitrary nature of specifying the suction potential in front of the
wetting front, the calculated results are different than expected. This
indicates that a good choice of the suction potential is necessary to
obtain consistent results.
8.4.2.4 Transient Linearized Infiltration Model —
With this method, transit time is obtained from Equation (8.16) or
Figure 8-5, with the liner thickness, d, which is 200 cm, substituted for
z. The parameters D* and K* are determined at an average liner moisture
8-31
-------
TABLE 8-2. RESULTS OF COMPARING TRANSIT TIME PREDICTION METHODS
00
I
Transit time prediction (yr)
Performance criteria based
on the saturation front
Initial liner saturation
Transit time prediction method 50% 80% 95%
1 Simple transit time 000
equation
2 Modified transit time 000
equation
3 Green-Ampt wetting front model 2.4 3.01 1.0
4 Transient linearized 19.7 4.69 2.0
infiltration model
5 Modified transit time 000
equation with diffusion3
6 Numerical solution 10 5 2.5
of the flow equation
7 Numerical solution NA NA NA
of the solute transport
equation
Performance criteria based
on solute transport
Initial
50%
27.3
8.6
NA
NA
6.0
NA
11.5
liner saturation
80% 95%
27.3 27.3
8.6 8.6
NA NA
NA NA
6.0 6.0
NA NA
16.0 17.5
NA = not applicable.
This approach assumes a saturated liner; thus, initial moisture content does not affect the transit
time prediction.
-------
TABLE 8-3. TRANSIT TIME ESTIMATION USING THE GREEN-AMPT
WETTING FRONT MODEL
Parameters for Green-Ampt model
Moisture
Initial liner content Suction potential Transit time
saturation (%) by volume -4* (cm) (yr)
50 0.248 -500.00 2.38
80 0.396 -57.38 3.01
95 0.47 -14.82 0.97
8-33
-------
content, (0. + Q )/2. Table 8-4 shows the parameters and the predicted
transit times assuming three values for the liner's initial moisture content.
Unlike the Green-Ampt model, the linearized flow model consistently
predicts longer transit times as the initial liner moisture content is
decreased. This indicates that the model describes the dynamics of infiltra-
tion better than the Green-Ampt equation. The predicted transit times are
consistently longer than the corresponding Green-Ampt values.
8.4.2.5 Modified Transit Time Equation With Diffusion--
This approach considers the liner to be saturated, so the time required
for saturation is zero.
8.4.2.6 Numerical Solution of the Flow Equation--
The computer program SOILINER was used to determine the transit time
based on the saturation front. Since the site soil was included in the
simulation, which provided a suction potential of about -500 cm at the
liner bottom, the moisture content profiles in the liner tend to achieve
steady state distribution after a certain time period. Thus, where the
initial moisture content was higher (80 percent and 90 percent), some
drainage in the lower portion of the liner was predicted. The seepage flux
also achieves a steady state value. Before the steady state moisture
profile is achieved, the seepage flux is low and reaches a higher steady
state value while the moisture profile is established. Therefore, the time
required to achieve this steady state moisture content profile was considered
to be the transit time in these numerical solutions. Table 8-5 shows the
predicted transit times for the three values of initial moisture content.
The numerical results correctly indicate that the time required to
achieve saturation decreases as the liner moisture content increases. This
time would approach zero if the initial moisture content increased to the
saturation value. The linearized flow model shows better agreement with
numerical results at higher initial moisture content because the assumption
of constant D* and K* is more realistic when the change in moisture content
of the liner is smaller.
8.4.2.7 Numerical Solution of the Solute Transport Equation—
This solution is not required for performance criteria based upon the
saturation front alone.
8.4.3 Comparison Using Performance Criteria Based on Solute Transport
Performance criteria based on solute transport may be chosen, for
example, to define transit time as the time required for the relative
concentration of a chemical species at the liner bottom to achieve a value
greater than or equal to 0.1 (C/C >0.1). The steady state concentration of
the leachate species throughout the liner after a sufficiently long time
will be equal to its concentration in the leachate on top of the liner.
This concentration, C , is assumed to be constant with time. Prediction
methods are compared for three initial liner moisture contents of 50 percent,
80 percent, and 95 percent of saturation based on the above-defined perform-
8-34
-------
TABLE 8-4. TRANSIT TIME ESTIMATION USING THE TRANSIENT LINEARIZED INFILTRATION MODEL
Initial
Initial liner Moisture suction
saturation content by potential
(%) volume (cm)
50 0.248 -500.00
80 0.396 -57.38
95 0.47 -14.82
Average
Average suction Average dt|» dK
moisture potential K 69 d8 0* K* D* K*t
content (cm) (cm/s) (cm) (cm/s) (cm/s) (cm/s) K*d d
0.3713 -80.22 5.041 x i(f9 -1,066.47 -1.126 x l(f7 5.376 x Ifl"6 1.126 x l(f7 0.2387 0.35
0.4455 -26.21 2.777 x l(f8 -498.85 -6.757 x l(f7 1.385 x l(fs 6.757 x l(f7 0.1025 0.5
0.483 -9.46 7.0 x lo"8 -444.33 -1.745 x Ifl"6 3.110 x lo"6 1.745 x l(f6 0.0891 0.55
Transit
time
(yr)
19.7
4.69
2.0
co
GO
en
-------
TABLE 8-5. TRANSIT TIME ESTIMATION USING A NUMERICAL SOLUTION TO THE
FLOW EQUATION
Initial liner Moisture content Transit time3
saturation (%) by volume (yr)
50 0.248 10.0
80 0.396 5.0
95 0.470 2.5
aTransit time equals the time required to achieve a steady state moisture
profile.
8-36
-------
ance criteria. The dispersion coefficient, D, of the chemical species is
assumed to be 1.0 x 10 6 cm2/s, and the attenuation coefficient, R, is
taken to be 1.
8.4.3.1 Simple Transit Time Equation--
The required time is given by Equation (8.5). Because this equation
assumes that the liner is saturated, the initial moisture content does not
affect the predicted transit time. When the following values are substituted
in Equation (8.5), the estimated transit time is 27.3 years:
Liner thickness: d = 200 cm
Liquid head: h = 30 cm
Saturated hydraulic conductivity: K = 1.0 * 10 cm/s
Porosity: = 0.495.
8.4.3.2 Modified Transit Time Equation—
The required time is given by Equation (8.8). This equation also
assumes the liner to be saturated, so the initial moisture content does not
affect the predicted transit time. Since the liner is considered to be
underlain by 5 m of site soil above the water table, the suction potential
at the liner bottom, -h., is considered to be -500 cm. When this value,
and other parameters as above, are substituted, the predicted transit time
is 8.6 years.
8.4.3.3 Green-Ampt Wetting Front Model--
This approach does not consider the solute transport equation and
hence cannot determine the time required for the above criteria. For
highly unsaturated liners, the required solute transport time may be approx-
imated by the saturation front transit time and may be calculated as in the
previous section.
8.4.3.4 Transient Linearized Infiltration Model —
Like the Green-Ampt model, this approach also does not consider the
solute transport equation and cannot determine the time required for the
above criteria. For highly unsaturated liners, the time required for the
solute transport may be approximated by that required by the saturation
front and may be determined as before.
8.4.3.5 Modified Transit Time Equation With Diffusion—
The required time for the solute chemical breakthrough may be obtained
from Equation (8.18) or Figure 8-6 by substituting liner thickness, d, for
z. This approach also assumes a saturated liner, so the initial moisture
content of the liner will not affect the predicted transit time. The
seepage flux or Darcian velocity is first obtained as given by Equation
(8.7). The following values are substituted:
Saturated hydraulic conductivity: K = 1.0 x 10 cm/s
8-37
-------
Liquid head: h = 30
Suction potential at the liner bottom: -h, = -500 cm.
Thus, v = 3.65 x 10 cm/s, and the parameter D/vd = 0.0137. From Fig-
ure 8-6, parameter vt/<)>d = 0.7 and the predicted transit time is 6 years.
8.4.3.6 Numerical Solution of the Flow Equation—
Since solute transport is not considered, the time required for solute
chemical breakthrough cannot be determined. For highly unsaturated liners,
the time required for the solute chemical breakthrough may be approximated
by that required for the saturation front breakthrough and may be determined
as above.
8.4.3.7 Numerical Solution of the Solute Transport Equation—
The computer program SOILINER, which was originally developed to solve
the flow equation, was modified to include the advective and diffusive
solute transport. Only molecular diffusion was considered to describe the
dispersion process. This modification solves the flow and solute transport
equations simultaneously. First the solution of the flow equation is
advanced by a flow time step. The computed values of the fluxes and moisture
contents are then used to advance the solution of the solute transport
equation. For stability and accuracy, it was often necessary to subdivide
the flow time steps into smaller solute transport time steps. The computa-
tions were carried out for the time period of 10 years for three initial
liner moisture contents of 50 percent, 80 percent, and 95 percent of satura-
tion. Solute breakthrough, as defined above, was not observed in any of
the cases during the 10-year period. The depth of the penetration corre-
sponding to C/C =0.1 was noted for various intermediate times, and the
time required f8r the solute breakthrough at the liner bottom was then
extrapolated (see Figure 8-8). These extrapolated breakthrough times are
as shown in Table 8-6.
As the results indicate, the transit time decreases as the initial
liner moisture content decreases. This contrasts with the flow equation,
where transit time (based on advancement of the saturation front) decreases
as liner moisture content increases. As the initial liner moisture content
increases, the time required for liner saturation decreases as indicated by
the flow equation. However, the initial seepage is due to displacement of
liner moisture, and, therefore, the transit time based on leachate chemicals
is longer with greater initial liner moisture content. Also, it is interest-
ing that for the case of 50 percent saturation the transit time based on
both -the flow and solute transport equations are close together. Therefore,
it appears that where the initial saturation is 50 percent or lower, it may
be sufficient to use the flow equation alone to predict the breakthrough
times. But for higher saturations, use of the flow equation alone is
likely to underpredict the transit time required for solute breakthrough.
8.5 SUMMARY AND CONCLUSIONS
Transit time and associated performance criteria may be defined in two
ways: on the basis of the movement of moisture in the liner, or on the
8-38
-------
20
17.5
16
11.5
10
9
8
V
0)
E
95%
50%
80%
40 80 120
Depth of Penetration (cm)
160
200
Figure 8-8. Extrapolation of transit times for solute transport, for initial
liner saturations of 50%, 80% and 95%.
8-39
-------
TABLE 8-6. TRANSIT TIME ESTIMATION USING A
NUMERICAL SOLUTION TO THE SOLUTE TRANSPORT EQUATION
Initial liner Moisture content Transit time
saturation (%) by volume (yr)
50 0.2475 11.5
80 0.396 16.0
95 0.47 17.5
8-40
-------
basis of the movement of waste chemicals in the liner. Both of these
definitions are recognized in the methods discussed. For criteria based on
moisture movement, it is sufficient to consider an equation describing
moisture flow in the liner (flow equation); for criteria based on chemical
movement, it is also necessary to consider the equation(s) describing
transport of the chemical(s) in the aqueous phase (solute transport equation).
The methods discussed in this section are arranged in ascending order
of complexity. The simple transit time equation makes the most simplifying
assumptions, requires the least amount of data, and is easy to use. All
the analytical solutions are relatively easy to use compared to numerical
methods because a single final equation is used for transit time prediction.
Numerical solutions are expensive and time consuming but can also provide
accurate solutions, with the accuracy dependent upon the quality of required
data. Numerical solutions also require expertise in the available models
and hence may not be easily accessible.
One of the most important elements for selecting a transit time predic-
tion method is the initial degree of saturation of the liner. The simple
and modified transit time equation and the transit time equation with
diffusion assume a saturated liner and thus may be applicable where there
is a high initial degree of saturation. On the other hand, the Green-Ampt
model and the linearized infiltration equation are more applicable in
situations where the initial degree of saturation in a liner is low. The
performance criteria or the definition of "transit time" are also important
in the method selection process. If the transit time is based on liner
saturation, obviously the three transit time equations based on a saturated
liner will not be applicable since they will indicate zero transit time.
If the transit time is based on chemical transport, the Green-Ampt model
and the linearized infiltration equation may not be applicable because they
do not consider the solute transport equation. Numerical solutions of the
flow and solute transport equations together will of course be applicable
in all situations.
8.6 DEFINITION OF TERMS
This section provides an explanation of various terms frequently used
in the discussion of transit time prediction methods. Where a symbol is
associated with a term, it is listed. The abbreviations in parentheses
stand for dimensions of the unit and are defined as follows:
D = dimensionless
L = length
T = time
M = mass.
Capillary action (capillarity). The rise or movement of fluid in the
interstices of a soil due to capillary forces.
8-41
-------
Capillary suction potential, f (L). The potential expressed in head of
water that causes the water to flow by capillary action. The word
"suction" is used to emphasize the negative sign of this potential.
This term is generally used to indicate pressure head of water in the
unsaturated zone.
Chemical flux (M/L2 T). Rate of flow of a chemical species expressed as
mass per unit cross-sectional area per unit time. The chemical flux
may be obtained by multiplying total volumetric flux by chemical
concentration.
Concentration, C (M/L3). Concentration of a chemical species in the aqueous
phase expressed as mass per unit volume.
Darcian velocity, v (L/T). Velocity of aqueous phase based on total cross-
sectional area obtained by dividing volumetric flow rate by cross-
sectional area. The actual velocity of water in the soil is obtained
by dividing the Darcian velocity by soil porosity.
Degree of saturation (%). Percent of the void volume in soil that is
filled by water. Same as moisture content expressed in terms of
percent.
Dispersion coefficient, D (L2/T). Describes spreading of the dissolved
species, due to hydrodynamic or mechanical dispersion and molecular
diffusion. The first process is caused by mixing due to variations in
fluid velocities associated with distance from pore walls. Diffusion
occurs in response to concentration gradients and by random thermal
motion.
Flux (L/T or M/L2T). Flow rate per unit area. The first group of dimensions
apply when the flow rate is expressed as volumetric flow rate, whereas
the second group of dimensions apply when the flow rate is expressed
as mass flow rate.
Leachate. This term is used to emphasize the chemical species in an aqueous
medium. Leachate may have several chemical species in varying concen-
trations in an aqueous medium. Leachate may also be generated by
organic solvents; however, in this section we are primarily concerned
with aqueous medium.
Leachate flux (M/L2T). This is the same as chemical flux described above.
Moisture content (volumetric), 6 (D). Volume fraction of water in soil.
This is obtained by multiplying porosity with fractional degree of
saturation.
Moisture content (% v/v). Percentage of soil volume occupied by moisture.
Porosity, (D). Ratio of volume of voids in a soil mass to the total
volume of the soil mass. This is often referred to as total porosity.
8-42
-------
Only interconnected voids contribute to the water flow and when the
volume of such interconnected voids is used, this ratio gives
effective porosity.
Potential, ¥ (L). Expressed in head of water. Potential is a driving
force, and in this report it is always expressed relative to atmospheric
pressure; thus, this term is similar to pressure head.
Pressure head, V (L). Expressed in head of water. Water pressure head
defined relative to atmospheric pressure is given by:
where
P = water pressure
W
P = pressure in air phase taken as atmospheric pressure
3
p = density of water
W
g = gravitational acceleration.
From this definition it is clear that V is positive in the saturated
zone and negative in unsaturated zone. The negative pressure head in
the unsaturated zone arises due to the capillary suction.
Relative hydraulic conductivity, k (D). The ratio of hydraulic conductivity
of a given soil at a certain moisture content with the hydraulic
conductivity of the same soil in saturated condition.
Retardation factor, R (D). Accounts for linear first-order interactions
between a chemical species and soil (e.g., adsorption).
Saturated hydraulic conductivity, K (L/T). Hydraulic conductivity of a
saturated soil with respect to water.
Saturated medium. A porous medium in which all voids are filled with fluid
under pressure greater than atmospheric pressure.
Seepage. Movement of water (vertically downward). This term refers to the
total liquid flow through a porous medium; for example, a clay liner.
Seepage flux, q (L/T). Volumetric flow rate of seepage in a porous medium
per unit cross-sectional area. In a clay liner flow domain, the
seepage flux has the same value as the Darcian velocity.
Suction potential, V (L). Same as potential except that the word "suction"
is used to emphasize the negative sign of the potential or pressure
8-43
-------
head. In the case of an unsaturated medium the suction is due to
capillary forces, so in this case the suction potential is the same as
capillary suction potential.
Unsaturated medium. A porous medium in which only a fraction of the void
volume is filled with fluid under less than atmospheric pressure. The
term "partially saturated medium" means the same as "unsaturated
medium" except that the moisture content is greater than zero.
8.7 REFERENCES
ASTM. 1985. American Society of Testing Materials. Annual Book of ASTM
Standards. Vol. 04.08.
Bachmat, Y., et al. 1980. Groundwater Management: The Use of Numerical
Models. Water Resources Monograph No. 5, American Geophysical Union,
Washington, DC.
Bear, J. 1972. Dynamics of Fluids in Porous Media. Elsevier, New York.
Bear, J. 1979. Hydraulics of Groundwater. McGraw-Hill, New York, New
York.
Cleary, R., and M. Ungs. 1978. Groundwater Pollution and Hydrology:
Mathematical Models and Computer Programs. Reprint #78-WR-15, Water
Resources Program, Princeton University, Princeton, New Jersey.
Freeze, R. A., and Cherry, J. A. 1979. Groundwater. Prentice Hall,
Englewood Cliffs, NJ.
Green, W. H., and G. A. Ampt. 1911. Studies in soil physics I: The flow
of air and water through soils. J. Agricult. Sci. 4:1-24.
Greenkorn, R. A. 1983. Flow Phenomena in Porous Media. Marcel Dekker,
Inc., New York.
Huyakorn, P. S., and G. F. Pinder. 1983. Computational Methods in Subsurface
Flow. Academic Press, New York, New York.
McWhorter, D. B., and J. D. Nelson. 1979. Unsaturated flow beneath tailings
impoundments. ASCE J. Geotech. Eng. Div. 11:1317-1334.
Mercer, J., and C. Faust. 1980. Groundwater modeling: Mathematical
models. Groundwater 18:3.
Moore, C. A. 1980. Landfill and Surface Impoundment Performance Evaluation
Manual. Document SW-869, submitted to the U.S. Environmental Protection
Agency Office of Water and Waste Management by Geotechnics, Inc.
Ogata, A., and Banks, R. B. 1961. A Solution of the Differential Equation
of Longitudinal Dispersion in Porous Media. U.S. Geological Survey
Professional Paper 411-A.
8-44
-------
Philips, J. R. 1957. The theory of infiltration: 1. Soil Science 83:345-
357.
Pinder, G. 1973. A Galerkin finite element simulation of groundwater
contamination on Long Island, NY. Water Resources Res. 9(6):1657.
Pinder, G., and J. Bredehoeft. 1968. Application in digital computer for
aquifer evaluation. Water Resources Res. 4:1069.
Richards, L. A. 1931. Capillary conduction of liquid through porous
media. Physics 1:318-333.
van Genuchten, M. 1978. Simulation Models and Their Application to Landfill
Disposal Siting: A Review of Current Technology. In: Proceedings of
the Fourth Annual Hazardous Waste Management Symposium, San Antonio,
Texas.
U.S. EPA. 1983. U.S. Environmental Protection Agency. Lining of Waste
Impoundment and Disposal Facilities. Document SW-870. Prepared by
Matrecon, Inc., March.
U.S. EPA. 1984. U.S. Environmental Protection Agency. Procedures for
Modeling Flow through Clay Liners to Determine Required Liner Thickness.
EPA/530-84-001, EPA Technical Resource Document for Public Comment,
U.S. Environmental Protection Agency. April.
U.S. EPA. 1985. Environmental Protection Agency. Soil Properties, Classi-
fication, and Hydraulic Conductivity Testing. Technical Resource
Document. Draft report prepared by Research Triangle Institute for
Hazardous Waste Engineering Research Laboratory, Cincinnati, Ohio.
8-45
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-------
APPENDIX A
TEST METHOD DESCRIPTIONS
-------
A-2
-------
APPENDIX A
TEST METHOD DESCRIPTIONS
The descriptions presented in Table A-l are only intended to give the
reader general information about the specific test methods. These method
descriptions are taken directly from Geotechnical Quality Assurance of Con-
struction of Disposal Facilities (Spigolon and Kelly, 1984). More detailed
information can be obtained from the references noted for the various test
methods. Data sheets for some of the test methods are provided as illus-
trative examples. These data sheets are merely examples and their inclusion
here does not connote that the authors recommend that they specifically be
used.
A-3
-------
TABLE A-l. LIST OF TEST METHODS
Method Number
Parameter Measured: Water Content
Standard Oven-Dry 1
Standard Nuclear Moisture/Density Gage 2
Gas Burner 3
Alcohol Burning 4
Calcium Carbide (Speedy) 5
Microwave Oven 6
Infrared Oven 7
Parameter Measured: Unit Weight
Standard Laboratory Volumetric 8
Standard Laboratory Displacement 9
Standard Field Sand-Cone 10
Standard Field Rubber Balloon 11
Standard Field Drive-Cylinder 12
Standard Nuclear Moisture/Density Gage 13
Parameter Measured: Specific Gravity
Standard Laboratory 14
Parameter Measured: Grain-Size Distribution
Standard Sieve Analysis (+200 Fraction) 15
Amount of Soil Finer than No. 200 Screen (Wash) Standard 16
Standard Laboratory Hydrometer (-200 Fraction) 17
Pipette Method for Silt and Clay Fraction 18
Decantation Method for Silt and Clay Fraction 19
Parameter Measured: Liquid Limit
Standard Multipoint 20
Standard One Point 21
Parameter Measured: Plastic Limit
Standard Laboratory 22
Parameter Measured: Cohesive Soil Consistency
Standard Unconfined Compression 23
Field Expedient Unconfined Compression 24
Hand Penetrometer 25
Handheld Torvane 26
(continued)
A-4
-------
TABLE A-l (continued)
Method Number
Parameter Measured: Water Content/Density/Compactive Effort
25 Blow Standard Proctor Compaction 27
25 Blow Modified Proctor Compaction 28
Nonstandardized Proctor Compaction 29
Rapid, One Point Proctor Compaction 30
Rapid, Two Point Proctor Compaction 31
Hilf's Rapid 32
Ohio Highway Department Nest of Curves 33
Harvard Mi nature Compaction 34
A-5
-------
Method No. 1
Parameter Measured: Water Content
Title of Test Method: Standard Oven-Dry
Principle of Test Method: This method determines the water content of a soil
sample by first weighing it wet and then again after it has been dried in
an oven.
Test Method
(1) Apparatus: Drying oven (thermostatically controlled, preferably
of the force-draft type), balance sensitive to 0.01 g., specimen containers
(tares) with lids, and a desiccator.
(2) Procedure: The procedure for this method consists simply of taking
a specimen of known weight, placing it into an oven and drying it at a partic-
ular temperature and specified time. Upon drying the specimen is removed,
reweighed and the moisture content is calculated.
(3) Reference: ASTM D 2216.
Limitations: With many soils, close control of water content during field
compaction is necessary to develop a required density, strength and hydraulic
conductivity in the soil mass. Oven-drying is the standard test for deter-
mining water content of soils in the geotechnical engineering practice.
However, the method 'does not lend itself easily to field use. Although
temperature controlled ovens are currently available on some construction
sites, they require 4 to 12 hours for drying which may be excessive for the
close control of field compaction. All soils can be tested for moisture
content by oven-drying.
Status of the Method: Oven-drying of soil is the accepted laboratory method
among the geotechnical engineering profession for determination of water
content.
Calibration Procedure: N/A
Documentation of Test: Items to be recorded include the wet weight and the
dry weight. An example data sheet is provided.
A-6
-------
Name:.
Date:.
.Saapla Numbers..
. Sheet Number .
WATER, CONTEXT DETERMINATIONS
DATA AND COMPUTATION SHEET
NOTES: Tare la weight of container (watch glaaaea and clip, Petri diahea, can, etc.)
100*
Water Content = w= fft« of
Wt. of Dry Soil
Sample Number
Type of Teat
Container Nuaber
Wt. Sanple * Tare Wet
Wt. Sample + Tare Dry
Wt. of Water
Tare
Wt. of Dry Soil
Water Content
Sample Number
Type of Teat
Container Number
Wt. Sanple + Tare Wet
Wt. Sample +• Tare Dry
Wt. of Water
Tare
Wt. of Dry Soil
Water Content
,
Sample Number
Type of Teat
Container Number
Wt. Sample + Tare Wet
Wt. Sample * Tare Dry
Wt. of Water
Tare
Wt. of Dry Soil
Water Content
v
A-7
-------
Method No. 2
Parameter Measured: Water Content
Title of Test Method: Standard Nuclear Moisture/Density Gage
Principle of Test Method: This method measures in place water content by
directing fast neutrons of known intensity into the soil and measuring the
intensity of slow or moderated neutrons reflected back.
Test Method
(1) Apparatus: Fast neutron source, slow neutron detector (readout
device and housing) and reference standard and site preparation device.
(2) Procedure: This method allows the determination of water content of
soil and soil aggregate in place through the use of nuclear equipment. The
equipment is calibrated to determine water content, as weight of water per
unit volume of material. Water content as normally used is defined as the
ratio, expressed as a percentage, of the weight of water in a given soil mass
to the weight of solid particles. It is determined with this procedure by
dividing the water content by the dry unit weight of the soil. Therefore,
computation of water content using the nuclear equipment also requires the
determination of the dry unit weight of the material being tested. Most
available nuclear equipment has the provision for measuring both the water
content and the wet unit weight. The difference between these two measurements
gives the dry unit weight.
(3) Reference: ASTM D 3017.
Limitations: The method described is useful as a rapid, nondestructive
technique for the in-place determination of the water content of soil. The
fundamental assumptions inherent in the method are that the hydrogen present
is in the form of water as defined by ASTM D 2216, and that the material
under test is homogeneous. Test results may be affected by chemical composi-
tion, sample heterogeneity, and, to a lesser degree, material density and the
surface texture of the material being tested. The technique also exhibits
spatial bias in that the apparatus is more sensitive to certain regions of
the material under test. The nuclear method, which is applicable to a wide
range of soils, requires operation by an experienced technician in order to
obtain reliable measurements. A weakness in the nuclear method is that a
sample is not taken to determine the water content, and thus the test results
cannot be compared to the other water content methods, e.g. the oven-dry method.
In addition, this method requires equipment that utilizes radioactive materials
which themselves may be hazardous to the health of the operator. Effective
operator instructions together with routine safety procedures are essential
to the proper operation of this type of equipment.
Status of the Method: Nuclear gages offer a rapid and accurate means for
obtaining water content values for a wide variety of soils. Recent advances in
the design of nuclear equipment and a better understanding of the nuclear
principles involved have led to increasingly widespread use of nuclear gages in
earthwork construction control.
A-8
-------
Calibration Procedure: The apparatus must be calibrated against a reliable
direct method (e.g. oven-drying).
Documentation of Test: Items to be recorded include the water content and the
wet unit weight. An example data sheet is provided.
A-9
-------
DATA SHEET FOR FIELD DENSITY TEST
j NUCLEAR GAUGE MET SOD
I
A ; Moisture Standard Count
Gauge Type j Seri al
' Density Standard Count |
FOR
JOB 003 NO.
SOURCE O1 _.__
MATERIAL ' DATE
TEST LOCATION
ELEVATION
TEST NUMBER
C Moisture Count
D Moisture Count Ratio
E | Density Count
F Air-Gap Count {if used)
Density Count Ratio
Hj Density, Wet Wt., PCF
I • Moisture Content, PCF
0 : Density, Dry Ht. , PCF
KJ MOISTURE CONTENT, PERCENT
I \ OPTIMUM MOISTURE, PERCENT
— i ' - -
M i DENSITY, DRY WT., PCF
N j THEORETICAL DENSITY, PCF
0 | PERCENT COMPACTION
. i
P ! REQUIRED PERCEffT COMPAC.
Q j MODE 4 PROBE DEPTH, IN.
R 1 TYPE OF MATERIAL ' '
!
1
M
/ \
/ \
c
A"
E • E '
B °r r
From G
i Chart
From D
4 Chart
H - I
T
See Curve
From J
See Curve
£x 100
See Specs.
Laboratory !,'o.
«
i
i
r
!
[
I
Tcchnici an(s)
A- 10
i
i
i
-------
Method No. 3
Parameter Measured: Water Content
Title of Test Method: Gas Burner
Principle of Test Method: This method determines the water content of a soil
sample by first weighing it wet and then again after it has been dried.
Test Method
(1) Apparatus: Gas stove, frying pan, balance and stirring rods.
(2) Procedure: This method determines the approximate water content of
soils by means of a gas-burner stove. The gas burner method involves the
weighing of a moist sample, placing the sample in a pan on the stove and
drying it to a constant weight, with occasional stirring of the sample to
prevent burning. The dry sample, first permitted to cool, is then reweighed
and the water content is determined.
(3) Reference: N/A
Limitations: The gas-burner method is used extensively for testing gravelly
material. Two or more samples may be tested concurrently. When care is
exercised to prevent overheating or burning of the sample, the testing time is
usually about 1/2 hour. The method is inaccurate for organic soils or for
those soils containing particles with loosely bound water, unless the drying
time is accomplished at a temperature of not more than 140°F (60°C) for 1 hour
or longer.
Status of the Method: The gas-burner method is used extensively as a rapid
method for testing gravelly soils in the field control of earthwork.
Calibration Procedure: N/A
Documentation of Test: . Items to be recorded include the wet weight and the dry
weight. No example data sheet is provided.
A-ll
-------
Method No. 4
Parameter Measured: Water Content
Title of Test Method: Alcohol Burning
Principle of Test Method: This method determines the water content of a soil
sample by first weighing it wet and then again after it has been dried by
alcohol burning.
Test Method
(1) Apparatus: Metal pan, balance, denatured alcohol and stirring rods.
(2) Procedure: This method determines the approximate water content of
soil by burning alcohol that has been added to the soil. The general procedure
consists of placing a weighted quantity of moist soil in a pan, adding alcohol
to it and stirring the mixture, then igniting the alcohol. After ignition and
the complete removal of the moisture by burning, the sample is reweighed and
its water content is calculated.
(3) Reference: N/A
Limitations: The alcohol burning test is a rapid inexpensive method for deter-
mining the water content of soils. The method is usable with non-cohesive and
cohesive soils. The method should not be used if the soil contains a large
proportion of clay, gypsum, calcareous matter or organic matter. A large
quantity of alcohol is required for testing coarse gravelly material. For
multiple burnings, the testing time can be in excess of 1/2 hour. In terms of
safety, the alcohol burning test possesses the potential for fire. Care should
be exercised not to have alcohol on hand or in an open storage container near the
testing apparatus during the ignition phase of the test. The alcohol should be
stored in a safety container.
Status of the Method: The alcohol burning method of obtaining the water content
of soil in the field has provided satisfactory results. Its use in the field
has been well established.
Calibration Procedure: N/A
Documentation of Test: Items to be recorded include the wet weight and the
dry weight. No example data sheet is provided.
A-12
-------
Method No. 5
Parameter measured: Water Content
Title of Test Method: Calcium Carbide (Speedy)
Principle of Test Method: This method determines the water content of a soil
sample by measuring the pressure developed when measured quantities of the
soil sample and powdered calcium carbide are mixed.
Test Method
(1) Apparatus: Calcium carbide pressure moisture tester, tared scale,
two each 1-1/4 in. steel balls, brush, cloth and scoop.
(2) Procedure: The calcium carbide gas pressure method for determining
water content consists of mixing measured quantities of moist soil and powdered
calcium carbide in a closed chamber and measuring the pressure developed by
the formation of acetylene gas. The reaction of calcium carbide and water
forms acetylene gas and calcium hydroxide. The pressure developed is
directly related to the amount of water entering into the reaction.
(3) Reference: AASHTO T 217.
Limitations: Only two sizes of testers are commercially available to test
for water content using this method: (1) 26 gram capacity model and (2) a
six-gram capacity model. The small chamber capacities of these devices
control the soil sample size to be used. As a result, this method is unsuit-
able for representative samples of coarse granular material. AASHTO T 217
recommends that this method should not be used on granular material having
particles large enough to affect the accuracy of the test (i.e. a soil with a
grain-size distribution such that an appreciable amount would be retained on
4.75 mm sieves). If a six-gram sample is used (according to AASHTO T 217),
the sample should not contain any particles that will be retained on the
2.00 mm sieve. The testing of heavy clays with this method requires special
handling.
Status of the Method: The apparatus for this method is relatively inexpen-
sive and well adapted to field testing. Use in the United States is extensive.
In the field the calcium carbide method has been used extensively in the
control of embankment construction. Normal testing time is less than 10 min.
A moderate amount of operator training is required. The calcium carbide
method is a standard method for rapid water content determination referenced
under AASHTO.
Calibration Procedure: A calibration curve is required.
Documentation of Test: Items to be recorded include soil sample weight,
pox^dered calcium carbide weight and the resultant gas pressure. No example
data sheet is provided.
A-13
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Method No. 6
Parameter Measured: Water Content
Title of Test Method: Microwave Oven
Principle of Test Method: This method determines the water content of a soil
by first weighing it wet and then again after it has been dried in the oven.
Test Method
(1) Apparatus: Microwave oven suitable for drying, balance, specimen
containers.
(2) Procedure: The procedure for this method is the same as that for
the Standard Oven-Dry method. That is, a specimen is placed wet onto a.
balance and weighed. It is then placed in a microwave oven and dried
completely. It is then weighed again. The weight difference was the water
content.
(3) Reference: N/A
Limitations: Microwave ovens are not noted for their drying ability. There
are necessary safety precautions when using a microwave oven.
Status of the Method: This method is not commonly used. Although a microwave
oven heats much more rapidly than a conventional oven, it is an erratic dryer
at best. Thus this method should probably only be used to determine water
contents for soils which can be expected to have a low value, i.e. relatively
low water content.
Calibration Procedure: N/A
Documentation of Test: Items to be recorded include the wet weight and the
dry weight. No example data sheet is provided.
A-14
-------
Method No. 7
Parameter Measured: Water Content
Title of Test Method: Infrared Oven
Principle of Test Method: This method determines the water content of a soil
by first weighing it wet and then again after it has been dried in the oven.
Test Method
(1) Apparatus: Infrared oven suitable for drying, balance, specimen
containers.
(2) Procedure: The procedure for this method is the same as that for
the Standard Oven-Dry method. That is, a specimen is placed wet onto a
balance and weighed. It is then placed in an infrared oven and dried
completely. It is then weighed again. The weight difference was the water
content.
(3) Reference: N/A
Limitations: There are necessary safety precautions when using an infrared
oven. Infrared ovens are generally not widely available.
Status of the Method: This method is not commonly used. It can yield rapid
results, however. The method should be desirable to a large operation where
the benefits of rapid results outweigh the costs of the limitations above and
the initial investment.
Calibration Procedure: N/A
Documentation of Test: Items to be recorded include the wet weight and the
dry weight. No example data sheet is provided.
A-15
-------
Method No. 8
Parameter Measured: Unit Weight
Title of Test Method: Standard Laboratory Volumetric
Principle of Test Method: This method determines the unit weight of an
undisturbed soil sample by measuring its weight and volume.
Test Method
(1) Apparatus: Sampling tools, balance, water bath, volume measuring
device, oven and coating material (e.g. paraffin).
(2) Procedure: This method determines the density of cohesive soil in
its natural state, compacted cohesive soil, and stabilized soil by measuring
the weight and volume of undisturbed samples. The method briefly consists of
cutting out a block of soil, coating it with a known amount of paraffin,
weighing to obtain the net weight of the sample and immersing it in an over-
flow volumeter to determine the net volume of the sample, then dividing
through for the unit weight.
(3) Reference: AASHTO T 233.
Limitations: The method is suitable for any material that remains intact
during sampling. This metod is particularly adaptable to irregularly shaped
specimens and soil containing gravel shells, etc. Sample size is not limited;
large samples with coarse aggregate can be tested. This method'is time
consuming.
*
Status of the Method: This method is a nonstandard test when used in rela-
tion to compaction control. However, periodic record sampling on compacted
embankments for dams usually entails obtaining block samples. In addition,
if the sample is properly removed from the fill, this test provides for index
and engineering properties.
Calibration Procedure: N/A
Documentation of Test: Items to be recorded include the sample's net weight
and net volume. An example data sheet is provided.
A-16
-------
UNIT WEIGHTS
ORDER NO.
CLIENT'S NO.
OATC_____
PROJECT.
.LOCATION.
:TESTED BY.
SAMPLE NO.
ORIGINAL SAMPLE SIZE
WT. CONTAINER * VET SOU.. CRAMS (wl
WT. CONTAINS* * ORT SOIL. SRAM3 «w')
WT. MOISTURE. ORAU3 (W^iw-w'l
WT. CONTAINER * ORY SOIL, SRAUS (W*>
VT. CONTAINER, OftAMS
WT. CONTAINER * DRY SOIL. ORAM3
-------
Method No. 9
Parameter Measured: Unit Weight
Title of Test Method: Standard Laboratory Displacement
Principle of Test Method: This method determines the unit weight of a soil
sample by determining the weight of the sample and the volume of its hole.
Test Method
(1) Apparatus: Sampling tools, soil tray and pans, balances, measure,
drying equipment, two gallons of lubricating oil, and a gauge point.
(2) Procedure: This method determines the density of soil in-place by
finding the mass and water content of a disturbed sample and measuring the
volume occupied by the sample using an oil of a known density. The method
can be performed fairly fast, however a chief concern is the mess caused by
the oil. The general procedure consists of leveling the test site, digging a
hole in the compacted earthwork, weighing the material removed, measuring the
volume of the hole by placing a measured quantity of oil in it and calculating
the wet unit weight by dividing the weight of the moist soil by the volume of
the hole.
(3) Reference: AASHTO T 214.
Limitations: This method may be used in testing materials with both fine and
coarse particles; however, the test is best suited for soils and soil-
aggregate mixtures that are relatively impervious. The method may not be
suitable for testing materials having fissures, cracks, or large voids.
Status of the Method: The oil displacement method is a conventional test in
the control of earthwork construction. However, it often provides less
satisfactory results than the sand-cone method.
Calibration Procedure: N/A
Documentation of Test: Items to be recorded include the weight of the soil
sample and the volume of the oil. No example data sheet is provided.
A-18
-------
Method No. 10
Parameter Measured: Unit Weight
Title of Test Method: Standard Field Sand-Cone
Principle of Test Method: This method determines unit weight by determining
the weight of a soil sample and the volume of its hole.
Test Method
(1) Apparatus: One gallon jar, double cone assembly, base plate and
accessories.
(2) Procedure: The test consists of digging out a sample of the mate-
rial to be tested and weighing it. The volume of the hole is then determined
by using the sand-cone.
(3) Reference: ASTM D 1556.
Limitations: The sand-cone has features which limit its usefulness. The
method can be used satisfactorily, however, if these limitations are recog-
nized and proper precautions observed. The poured density of sand is affected
by atmospheric moisture and changes in relative humidity which means the sand
should be calibrated before use. Care should be exercised to avoid jarring
and densifying the sand during the filling procedure and the test should not
be conducted during vibration of the site such as occurs during the use of
heavy equipment. Sample size is limited by sand supply.
Status of the Method: The sand-cone test is a conventional test method for
earthwork control. The method is reliable and the most commonly used test to
determine the density of in-place soil. On Corps of Engineers earthwork
projects the test serves as the referee test for all other control tests
used. The sand-cone test is widely used in cohesive soils and can be also
used in soils that are of low plasticity as well as gravelly soils. The
test is not applicable in clean sands or gravel and loose granular material.
The method is applicable to large and small projects.
Calibration Procedure: N/A
Documentation of Test: Items to be recorded include the weight of the soil
sample and the volume of the sand. No example data sheet is provided.
A-19
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Method No. 11
Parameter Measured: Unit Weight
Title of Test Method: Standard Field Rubber Balloon
Principle of Test Method: This method determines unit weight by determining
the weight of a soil sample and the volume of its hole.
Test Method
(1) Apparatus: Calibrated vessel, elastic membrane, pressure control
device, baseplate and accessories.
(2) Procedure: This method determines the in-place density by removing
soil from a hole, weighing the excavated material, and measuring the volume of
the hole by a liquid-filled (water) balloon under constant pressure. Chief
advantages of this method are its operation simplicity and speed with which
tests can be conducted.
(3) Reference: ASTM D 2167.
Limitations: For general use in clays and consolidated sands, the rubber
balloon apparatus provides good results. The method is not suitable for
very soft soil which will deform under slight pressure or in which the
volume of the hole cannot be maintained constant. The method is not well
adapted to the measurement of volumes in loose granular material. However, of
all in-place density tests some soil engineers recommend the water balloon as
the preferred method for granular soils. The tests is well adapted to small
and large projects. Physical limitation of the apparatus restricts the size
of the test hole to approximately four or six inches in diameter and from six to
twelve inches in depth.
Status of the Method: The water balloon test is widely used for determining
in-place density for the control of earthwork. The method is used by the
Corps of Engineers and other agencies because of its application to a wide
range of materials and its past performance record.
Calibration Procedure: N/A
Documentation of Test: Items to be recorded include the weight of the soil
sample and the volume of water. No example data sheet is provided.
A-20
-------
Method No. 12
Prameter Measured: Unit Weight
Title of Test Method: Standard Field Drive-Cylinder
Principle of Test Method: This method determines the unit weight of a soil
sample by securing one in a known-volume tube and then weighing it.
Test Method
(1) Apparatus: Acceptable drive cylinder, drive head, straightedge,
shovel, weight, scales, drying oven and airtight containers.
(2) Procedure: The drive-cylinder method for determining in-place
density involves obtaining a relatively undisturbed soil sample by driving
a thin-walled cylinder into the soil with a special driving head. Two proce-
dures are described in ASTM D 2937 for performing this test, one for testing
at the surface or at very shallow depths, usually less than 3 ft (1 m), and
one for testing at greater depths. The general procedure for both depths
consists of driving a sampling tube into the soil, withdrawing the tube with
the sample, trimming the sample flush with the ends of the tube, weighing,
then calculating the unit weight of the soil by dividing the net weight of
the sample fay the volume of the tube.
(3) Reference: ASTM D 2937.
Limitations: The drive-cylinder method of determining in-place density can
be used satisfactorily in moist, cohesive, fine-grained soils and in many
sands which exhibit tendencies toward cohesiveness. The method is not
appropriate for sampling very hard soils which cannot be penetrated easily,
or for soils of low plasticity which are not readily retained in the cylinder.
The method sample size is limited by the sample tube. The chief disadvantage
of the test is that it is limited to fine-grained soils.
Status of the Method: The standard field drive-cylinder method is a conven-
tional test method in earthwork control. It is, however, less accurate
than the sand cone or water balloon methods.
Calibration Procedure: N/A
Documentation of Test: Items to be recorded include the soil sample's weight.
No example data sheet is provided.
A-21
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Method No. 13
Parameter Measured: Unit Weight
Title of Test Method: Standard Nuclear Moisture/Density Gage
Principle of Test Method: This method determines unit weight by a gamma
source and a gamma detector.
Test Method
(1) Apparatus: A nuclear source emitting gamma rays, a gamma ray detector
and a counter.
(2) Procedure: This method determines the density of soil and soil-
aggregate in place through the use of nuclear equipment. In general, the
total or wet density of the material under test is determined by placing a
gamma source and a gamma detector either on, into, or adjacent to the material
under test. These variations in test geometry are presented as the back-
scatter, direct transmission, or air gap approaches. The intensity of radiation
detected is dependent in part upon the density of the material under test.
The radiation intensity reading is converted to measured wet density by a
suitable calibration curve. Some commonly used sources of gamma rays are
radium, cobalt 60 and cesium 137.
(3) Reference: ASTM D 2922.
Limitations: The method described is useful as a rapid, nondestructive tech-
nique for the in-place determination of the wet 'density of soils and soil-
aggregates. The fundamental assumptions inherent in the method are that
Compton scattering is the.dominant interaction and that the material under
test is homogeneous. Test results may be affected by chemical composition,
sample heterogeneity, and the surface texture of the material being tested.
The technique also exhibits spatial bias in that the apparatus is more
sensitive to certain regions of the material under test. The nuclear method
is applicable to a wide range of soil. The nuclear method requires a con-
siderably experienced operator in order to obtain reliable measurements. A
weakness in the nuclear method is that a sample is not taken to determine the
water content, and thus the test results cannot be compared to another unit
weight method. In addition this method requires equipment that utilizes
radioactive materials which may be hazardous to the health of the operator.
Effective operator instructions together with routine safety procedures are
essential to the proper operation of this type of equipment.
Status of the Method: Nuclear gages offer a rapid and accurate means of
obtaining density values for a wide variety of materials. Recent advances in
the design of nuclear equipment and a better understanding of the nuclear
principles involved have led to increasingly widespread use of nuclear gages
in earthwork construction control.
Calibration Procedure: The apparatus must be calibrated against a reliable
direct method (e.g. standard field sand-cone).
A-22
-------
Documentation of Test: Items to be recorded include the counter's gamma ray
counts. No example data sheet is provided.
A-23
-------
Method No. 14
Parameter Measured: Specific Gravity
Title of Test Method: Standard Laboratory
Principle of Test Method: This method determines the specific gravity of a
soil sample by the use of a pycnometer.
Test Method
(1) Apparatus: A pycnometer and a balance.
(2) Procedure: The procedure for this method is to procure a soil
sample, weigh it with the balance, and then determines its specific gravity
by the use of the pycnometer.
(3) ASTM D 854.
Limitations: N/A
Status of the Method: This is the standard method. It is widely used.
Calibration Procedure: N/A
Documentation of Test: Items to be recorded include the sample weight and
the pycnometer reading. An example data sheet is provided.
A-24
-------
Name:
Sasple Nucbers
Date:
Sheet ituraber
SPECIFIC GRAVITY DETERMINATIONS
Sample Number
Pycnooeter Bottle Number:
Date:
Wt. Bottle + Water + Sample = Wa ••
Temperature of Suspension ~ T -
Wt. Bottle + Water at temp. T = WW:
Wo — .
Evap. Dleh No.
Wt. Ssmple •+• Dish
of Diah
s —'
W
- W
Remarks:.
Sample Nunber.
Date:
Pycnometer Bottle Nunber:
Wt. Bottle + Water + Sample
Temperature of Suspension
Wt. Bottle + Water at temp. T
= wa=.
= T =.
= Tlif=
w
Evap. Dish No.
Wt. Sample +•
Weight of Dish
Dry Wt. of Soil W
Dry =.
Remarks:
Sample Number,
Pycnoaeter Bottle Nunber:
Evap. Diah No.
Wt. Bottle •*• Water •»• Sample =• Wfl:
Temperature of Suspension = T -
Wt. Bottle + Water at terap. T = T7W-
8 = —ST "
Wt. Sample + Dish Dry
Weight of Dish
Dry Wt. of Soil Wn
ww -
A-25
-------
Method No. 15
Parameter Measured: Grain-Size Distribution
Title of Test Method: Standard Sieve Analysis (+200 Fraction)
Principle of Test Method: This method determines the +200 fraction of a
soil sample by the use of a No. 200 sieve.
Test Method
(1) Apparatus: A No. 200 sieve, that is a sieve with 200 openings per
square inch, and balance.
(2) Procedure: This is a method dependent test. A dried soil sample
is weighed and poured onto a No. 200 sieve and shook. That amount of soil
not passing through the sieve is the +200 fraction. The +200 fraction is
then weighed on the balance.
(3) Reference: ASTM D 422.
Limitations: The limitations of the method are its possible sources of
error. These include: (a) overloading the sieve; (b) inadequate or incorrect
shaking; and (c) broken or damaged sieves.
Status of the Method: This is the standard method. It is widely used.
Calibration Procedure: N/A
Documentation of Test: Items to be documented include the weight of the
dried soil sample and the weight of the +200 fraction. An example data sheet
is provided.
A-26
-------
ro
U. S. Sl|i>4l>< Slot Or«iln|> U luiliti U. t. Sl«i>
-------
Method No. 16
Parameter Measured: Grain-Size Distribution
Title of Test Method: Amount of Soil Finer than No. 200 Screen (Wash)
Standard
Principle of Test Method: This method determines the -200 fraction of a
soil sample by the use of a No. 200 sieve and washing.
Test Method
(1) Apparatus: A No. 200 sieve and a balance.
(2) Procedure: This method is similar to that described for determining
the +200 fraction. However if the soil sample to be tested contains plastic
fines, drying will cause them to adhere to the fine sand grains, and the test
will yield erroneous results. The solution is to weigh the dry sample
beforehand. Pour it on the No. 200 screen. Wash the sample to loosen the
fines and allow them to pass through the sieve. Dry that amount of soil
remaining on the No. 200 screen and weigh it. The two weight differences is
then the fines content.
(3) Reference: ASTM D 422.
Limitations: The significant limitation of this method is the extra time
required for washing and redrying.
Status of the Method: This is the standard method. It is widely used.
Calibration Procedure: N/A
Documentation of Test: Items to be documented include the dry weight of the
sample and the dry weight of the +200 fraction. No example data sheet is
provided.
A-28
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Method No. 17
Parameter Measured: Grain-Size Distribution
Title of Test Method: Standard Laboratory Hydrometer (-200 Fraction)
Principle of Test Method: This method determines the grain-size distribution
of the -200 fraction of a soil sample by the use of Stokes' Law and a standard-
ized hydrometer.
Test Method
(1) Apparatus: A No. 200 sieve, a standardized hydrometer, a sedimenta-
tion cylinder, a thermometer and a breaker.
(2) Procedure: This method determines the grain-size distribution of
that fraction of a soil sample passing the No. 200 sieve (the -200 fraction).
The method utilizes a deflocculating (dispersing) agent and Stokes' Law
to enable the different particle sizes to settle at different rates, thus
enabling the technician to determine their distribution.
(3) Reference: ASTM D 422.
Limitations: An experienced technician is required to perform this test
method. Considerable time is required for sample preparation. The test
itself requires several hours to perform.
Status of the Method: This is the standard method. As it is the only
"exact" method for determining the percent silt sizes and the percent clay
sizes, it is widely used.
Calibration Procedure: N/A
Documentation of Test: Items to be documented include the dry weight of the
sample and the dry weights of the settled fractions. Example data sheets
are provided.
A-29
-------
Name:.
Date:
.Sample and Test Number.
Sheet Number.
HYDROMETER ANALYSIS
)ATA AND COI4PUTATION SHEST
Evaporating Dish No.
Wt. Sample + Dish Dry =
Wt. Dlah =
Dry Wt. W0 =.
Hydrometer Number
^ 100
= 100
(R
.(R
m)
m)
Date
Time
Temp.
Elapsed
Time
R1
-
R=R'+c
Grain
Dlam
R •*• m
\1%
Remark a
A-30
-------
- - III.
lOu
9O
eo
H- 70
r
0
UJ
5 RA
•* 6O
V
£D
2 5O
iir
H
5 40
u
DC
U
0. --
3O
2O
10
°.o
TYLER STANDARD SIEVE NUMBERS
3 4 6 & 10 14 2O 26 35 46 65 IOO ISO ZOO
T
1
1
1
1 "1
/•
5 1
MEDIUM CWAVCU
PROJE(
DEPTH
FINC C
GRAVtL
t
1
1
05
OAHSC
SAND
MCDIUM
SAND
•f
VATIO
1
HYDROMETER
-
1
01 005 001 0-005 0.001 O.OOO5 U
G ft AIM SIZE IN MILLIMETEHS
riNE vi
SAHO
•SKI
CLAV
US BUREAU OF SOILS CLASSIFICATION
BORING NO
RC
c
.0001
I
SAMPir MO ,
-RAIN SIZE DISTRIBUTION DIAGRAM
-------
Method No. 18
Parameter Measured: Grain-Size Distribution
Title of Test Method: Pipette Method for Silt and Clay Fraction
Principle of Test Method: This method determines the silt and clay fractions
of a soil sample by the use of a dispersing agent, Stokes' Law and a Pipette.
Test Method
(1) Apparatus: A No. 200 sieve, a beaker and a pipette.
(2) Procedure: The soil sample is deflocculated in a dispersing
agent for one hour. The soil-water-agent mixture is then agitated and allowed
to sit. Theroretically all the sand and silt sizes will have settled by
then. The water, with the suspended clay sizes, is then drawn off by the
pipette. The settled fraction is the original soil sample minus the clay
fraction. The settled fraction is completely dried and passed through a
No. 200 sieve. The fraction passing is the silt fraction, the fraction
remaining is the sand fraction.
(3) Reference: Mills, 1970.
Limitations: The method is less exact than the standard laboratory hydrometer
method.
Status of the Method: The method lends itself well to field laboratory use
and is widely accepted.
Calibration Procedure: N/A
Documentation of Test: Items to be documented include the dry weight of the
sample, the dry weight of the settled fraction and the dry weight of the
silt fraction. No example sheet is provided.
A-32
-------
Method No. 19
Parameter Measured: Grain-Size Distribution
Title of Test Method: Decantation Method for Silt and Clay Fraction
Principle of Test Method: This method determines the silt and clay fractions
of a soil sample by the use of a dispersing agent, Stokes' Law and
decantation.
Test Method
(1) Apparatus: A No. 200 sieve and a beaker.
(2) Procedure: The.soil sample is deflocculated in a dispersing agent
for one hour. The soil-water-agent mixture is then agitated and allowed to
sit. Theoretically all the sand and silt sizes will have settled by then.
The water, with the suspended clay sizes, is then drawn off by decantation
(careful pouring). The settled fraction is the original sample minus the
clay fraction. The settled fraction is completely dried and passed through
a No. 200 sieve yielding the silt fraction.
(3) Reference: Mills, 1970.
Limitations: The method is less exact than the standard laboratory hydrom-
eter method. As is also more rudimentary than the pipette method, it can
be less accurate than this method in execution.
Status of the Method: The method lends itself well to field laboratory use
and is widely accepted.
Calibration Procedure: N/A
Documentation of Test: Items to be documented include the dry weights of
the sample, the settled fraction and the silt fraction. No example sheet
is provided.
A-33
-------
Method No. 20
Parameter Measured: Liquid Limit
Title of Test Method: Standard Multipoint
Principle of Test Method: This method determines the liquid limit of a soil
sample by the use of the liquid limit device and a minimum of three trials.
Test Method
(1) Apparatus: Evaporating dish, spatula, liquid limit device, grooving
tool and balance.
(2) Procedure: A soil sample is oven dried. Distilled water is added
and mixed thoroughly with the sample till it is ready to be tested. A sample
is placed in the liquid limit device and divided by the grooving tool. The
test is run till the soil halves meet. The result is plotted. A minimum of
three trials are performed.
(3) Reference: ASTM D 423.
Limitations: The method requires considerable time and a laboratory environ-
ment to be performed.
Status of the Method: For the purposes needed at a hazardous waste disposal
facility the standard one point method will yield reasonable data with less
effort and hence is more widely used.
.Calibration Procedure: N/A
Documentation of Test: Items to be recorded include the oven-dry weight of
the sample, the water content and the number of blows. An example data
sheet is provided.
A-34
-------
ATTERBERG LIMITS DETERMINATION
'RQJECr
IXCAVAMOH NU<48£R
OA(E
SAMPLE «UM3£S
LIQUID LIMIT, WL
IUN NUMBER
'ARE HUW8ER
I. WEIGHT OF WET SOIL *• TARE
1. WEIGHT OF DRY SOIL » TARE
.. WEIGHT OF WATER, W^ (4. -B.)
1. WEIGHT OF TARE
.. WEIGHT OF ORT SOI L.»SCS.-O.J
V
'*TER CONTENT, .9^, 108;
IUMJER OF 8LO<5
'L
*
t— —*
K 5
e tt
0 h
oc I
- -
3
"P
— 1
— 1
'p
(
J
L-
'l
r>
J
-
r
h
rnr^
fffr
rii'-rr
•• i ; • i •
•
1 t
mj
9 10
IS 20
NUMBER OF 3LOWS
2S
30
40
SO
UN NUU3ER
ARE NUM9ER
. «£I5«T OF »ET SOIL » TARE
. «EIG«T OF ORT SOIL » TARE
. WEIGHT OF WATER, w, (F.-G.)
. WEIGHT OF ORT SOIL. W5fC. -r.;
AT£R CONTENT, m^(~* 100)
t
PL1STI
*
: LIMIT. *o
MATUSAL
WATES
TOMTIT
(Sifnmlure)
3T
JT
A-35
90.1) 14*1
-------
Method No. 21
Parameter Measured: Liquid Limit
Title of Test Method: Standard One Point
Principle of Test Method: This method determines the liquid limit of a soil
sample by the use of the liquid limit device and one trial.
Test Method
(1) Apparatus: Evaporating dish, spatula, liquid limit device, grooving
tool and balance.
(2) Procedure: A soil sample is oven dried. Distilled water is added
and mixed thoroughly with the sample till it is ready to be tested. A sample
is placed in the liquid limit device and divided by the grooving Cool. The
test trial is then run till the soil halves meet. The data is then plotted.
(3) Reference: ASTM D 423.
Limitations: The method requires considerable time and a laboratory environ-
ment to be performed.
Status of the Method: The method is more widely used than the standard
multipoint method, but as it is a correlation test method and it is usually
used in soil identification, it is often less practical than the commonly
used visual-manual procedure (ASTM D 2488).
Calibration Procedure: N/A
Documentation of Test: Items to be recorded include the oven-dry weight of
the sample, the water content and the number of blows. No example data
sheet is provided.
A-36
-------
Method No. 22
Parameter Measured: Plastic Limit
Title of Test Method: Standard Laboratory
Principle of Test Method: This method determines the plastic limit of a soil
sample, that is the lowest water content at which the soil can be rolled into
1/8 in. threads without breaking.
Test Method
(1) Apparatus: Evaporating dish, spatula, suitable containers, and
balance.
(2) Procedure: For a given soil sample begin at a water content esti-
mated to be greater than that at the plastic limit. A good start point would
be the approximate liquid limit. Shape the soil into an ellipsoidal mass.
Roll the sample into 1/8 in. threads. Cut the threads into 6 to 8 pieces.
Repeat the process till the threads break at 1/8 in. An oven-dry moisture
content determination at that point will yield the plastic limit.
(3) Reference: ASTM D 424.
Limitations: The method is simple and straightforward.
Status of the Method: This is the standard method and is widely used.
Calibration Procedure: N/A
Documentation of Test: Items to be recorded include the oven-dry and wet
weight of the sample at the plastic limit. An example data sheet is
provided.
A-37
-------
ATTERBERG LIMITS
SAMPLE N2
PROJECT.
DATE.
SOURCE OF SAMPLE
SUMMARY
NATURAL
WATER CONTENT
LIQUID
LIMIT
PLASTIC
LIMIT
PLASTICITY
INDEX
SHRINKAGE
LIMIT
„
PLASTIC LIMIT
NATURAL WATER CONTENT
DETERMINATION N*
CONTAINER N*
CONTAINER 4- WET SOIL
CONTAINER + DRY SOIL
WEIGHT OF WATER
CONTAINER 4- DRY SOIL
WEIGHT OF CONTAINER
WEIGHT OF DRY SOIL
PERCENT WATE.R
1 .
2.
3
1
1
2
3
LIQUID LIMIT
DETERMINATION N*
NUMBER OF BLOWS
CONTAINER N*
CONTAINER 4- WET SOIL
CONTAINER 4- DRY SOIL
WEIGHT OF WATER
CONTAINER -4- DRY SOIL
WEIGHT OF CONTAINER
V/jrfGHT OF DRY SOIL
PERCENT WATER
1
Z
3
4
5
6
LJ
h-
O
O
hi
-------
Method No. 23
Parameter Measured: Cohesive Soil Consistency
Title of Test Method: Standard Unconfined Compression
Principle of Test Method: This method uses a compression device to determine
the unconfined compressive strength of a soil sample: that is the load per
unit area at which the specimen fails in simple compression.
Test Method
(1) Apparatus: Compression device, sample ejector, deformation indi-
cator, vernier caliper, timer, balance and oven.
(2) Procedure: An unidsturbed sample is secured and a specimen prepared
as per the reference. An estimate of the failure strength is made based on
experience with a similar material. The specimen is placed in compression by
uniformly progressive loads at 30 second intervals till failure or 20% strain
is reached. The results are plotted.
(3) Reference: ASTM D 2166.
Limitations: The method requires a laboratory environment, the securing of
an undisturbed sample (as described by ASTM Method D 1587) , considerable
specimen preparation, calculations and considerable time.
Status of the Method: The method is the standard means for unconfined com-
pressive strength determination. However because of its limitations it is
not commonly used in process control (because of more efficient methods) but
is widely used in acceptance testing.
Calibration Procedure: The deformation indicator must be zeroed at the
beginning of the test.
Documentation of Test: Items to be recorded include the water content of the
sample as well as the strain deformations at their respective loads. An
example data sheet is provided.
A-39
-------
UNCONF1NED COMPRESSION TEST - DATA SHEET
Soil Description .
Project.
laboratory .
Boring No.
U 7.
Surface Elev._
.7.
_5amp!e No
PI %
Sample Depth Interval.
Date Tested
Pocket Penetrometer, P.P.
.tsf Specific Gravity, G,.
Dry Unit Weight,
.. pel
Soil Specimen Measurements
Diameter , in. Initial Area, Ao: sf Initial Length, lo: .
Proving Ring Conversion Factor.
Corrected Area, A{ a
WATER CONTENT
Specimen Location
Container No.
Wt. Cont. +• Wet SoiUgmi.)
Wt. Cant. +• Dry SoiUgmi.)
Wt. Container (gmi.)
Wt. Dry SoiKgnn.)
Wt. Woter(gm».)
V/al.r Cont.nl(r.)
Top
Middle
Bottom
Entire Remolded Sample
COMPRESSION TSST
Elapsed Time
(Min.)
Load Dial
Reading
Load
(Ibt.)
' Vert. Dial
(inches)
Axial Strain
-------
Method No. 24
Parameter Measured: Cohesive Soil Consistency
Title of Test Method: Field Expedient Unconfined Compression
Principle of Test Method: This method uses a field expedient compression
device to determine the unconfined compressive strength of a soil sample.
Test Method
(1) Apparatus: Sample selector, compression device, stress and
deformation indicators, balance, oven and trimmer.
(2) Procedure: A sample is secured and prepared. An estimate of the
sample's failure strength is made based on experience with a similar material.
The specimen is then placed in compression by uniformly progressive loads
till failure or a predetermined percent strain is achieved. The results
are plotted.
(3) Reference: TM 5-530, 1971.
Limitations: The method involves a procedure virtually identical to that
called for in the standard laboratory method. However the apparatus used
in the field expedient method is less accurate, less-care is given to
sample preparation and the method itself is less accurate.
Status of the Method: The method lies between the standard laboratory
method and the hand device methods in terms of accuracy and resources
required. As the standard laboratory method is the accepted method for
laboratory needs and the hand devices are sufficient for field testing. This
method is not widely used.
Calibration Procedure: The stress and strain indicators must be zeroed at
the beginning of the test.
Documentation of Test: Items to be recorded include the sample's water
content as well as the stress and strain readings. No example data sheet
is provided.
A-41
-------
Method No. 25
Parameter Measured: Cohesive Soil Consistency
Title of Test Method: Hand Penetrometer
Principle of Test Method: This method uses the hand penetrometer to deter-
mine the unconfined compressive strength of a soil sample.
Test Method
(1) Apparatus: Hand penetrometer with stress and strain indicators,
trimming knife.
(2) Procedure: A sample is taken and trimmed by the hand penetrometer
and a trimming knife. The test is then run with the device. One man can run
the device and read the various stress and strain indicators. These values
can be plotted and the unconfined compressive strength determined.
(3) Reference: Hvorslev, 1943.
Limitations: The sampling operation may cause a slight disturbance and
decrease in strength of very brittle soils, a small downward deflection of
soft soils, and a slight compaction of loose and partially saturated soils.
Status of the Method: The determination of cohesive soil consistency classi-
fication by this method is widely used as it is more accurate than the
visual-manual method, and although it is less accurate than the standard
laboratory method it is quite sufficient given the broad classifications for
cohesive soil consistency.
*
Calibration Procedure: The stress and strain indicators must be zeroed at
the beginning of the test.
Documentation of Test: Items to be recorded include the stress and strain
readings during testing. An example data sheet is provided.
A-42
-------
UNCONFINED COMPRESSION TEST
Soi Deicript!
Boring N
LL
0-
f.
Pocket Penelron
Axial Strain Rate
i«ter.
•
Surface E!
*M
f
t-
P-
7.
ttf
PI
Spei
inch
>ample f>
>roj«
.aba
:!fic Gravity
Grain Size Distribution
7.Gr.
nc.s.
7.f.5
% Sill
r. Clay
tt
rato
7.
, e,
Remarks:
1
<,
ample C
Dote
•
)epth Interv
r.«i.rl
9I
Dry Unit Weight, J
)!agram of Failure:
pef
•
.
Unconfinaa1 Compriiiiv* Slionglh
«
-------
Method No. 26
Parameter Measured: Cohesive Soil Consistency
Title of Test Method: Handheld Torvane
Principle of Test Method: This method uses a handheld torvane to determine
the soil shear strength of the in situ soil.
Test Method
(1) Apparatus: Handheld torvane with gage.
(2) Procedure: The handheld torvane is pushed through the soil crust to
the desired depth. A rotary motion is then applied to the handle. The gage
values are read and the soil shear strength, values for cohesion and the
internal angle of friction, and consistency classification can be determined.
(3) Reference: Lanz, 1968.
Limitations: The method is standardized and the values gained from the method
can be correlated to the standard laboratory method for unconfined compres-
sive strength. However the method is somewhat less accurate than others.
Status of the Method: The torvane is the most widely accepted of the shear
vane devices. Since it yields in situ values rapidly it is widely used.
Calibration Procedure: The gage must be zeroed before testing.
Documentation of Test: Items to be recorded'include the gage readings. No
example data sheet is included.
A-44
-------
Method No. 27
Parameter Measured: Water Content/Density/Compactive Effort
Title of Test Method: 25 Blow Standard Proctor Compaction
Principle of Test Method: This method determines the optimum moisture content
and the maximum density of a soil sample by an impact compaction test. This
is the original Proctor test.
Test Method
(1) Apparatus: Molds, rammer, extruder, balance, drying oven, sieves.
(2) Procedure: The specimen is prepared and placed in a mold. Most
commonly the mold is the 4 inch mold. The soil is placed in three like
layers. Each layer is compacted. Most commonly the compaction is 25 blows
with a 5.5 pound hammer dropping 12 inches. Following compaction of all
three layers the specimen is removed from the mold and trimmed. The mass of
the sample is determined. This is divided by the volume of the mold and then
the wet density of the sample, in pcf, is determined. The water content of
the sample is then determined by oven drying. This entire procedure is
repeated for at least four specimens. The four specimens' water contents
should vary by about 1-1/2% between each sequential sample. The specimen
water contents should bracket the estimated optimum moisture content. The
values are plotted along with the "zero air voids curve." The optinum
moisture content and maximum density of the sample can then be determined.
(3) Reference: ASTM D 698.
Limitations: This method requires a laboratory environment, the considerable
time involved in sample drying and several hours to perform the test itself.
Status of the Method: This is the standard method. It is widely used. It
is suited for the lesser compactive effort as might be applied to trench
backfill. It may not be as suitable as the modified method for higher
compactive efforts such as that which might be applied to a trench floor.
Calibration Procedure: The rammer must be calibrated before initial use and
again after each 1,000 molds.
Documentation of Test: Items to be recorded include the mold volumes, speci-
men masses, and specimen water contents. An example data sheet is provided.
A-45
-------
SOILS LABORATORY COMPACTION TESTS PROCTOR METHOD . Sample No.
SITE
HOLE
AREA
DEPTH
RUN
NO.
1
2
3
4
5
6
7
8
9
10
11
12
13
WEIGHT OF
SAMPLE +
CYLINDER
KG.
WEIGHT
OF
CYLINDER
KG.
WEIGHT
OF
SAMPLE
KG.
TESTED BY: DAI
WEIGHT OF
SAMPLE
LBS./CU. FT.
rf
COMPUTED BY: DATE
WATER
ADDED
GRAMS
NUMBER OF BLOWS
PLASTIC LIMIT
SPECIFIC GRAVITY
DATE
WATCH
GLASS
NO.
WATER
CONTENT
%
DRY WT.
•
CYLINDER MO.
VOL. OF CYLINDER CU. FT,
UNIT WEIGHT FACTOR
REMARKS ,
•
CHECKED BY:
DATE
-------
Method No. 28
Parameter Measured: Water Content/Density/Compactive Effort
Title of Test Method: 25 Blow Modified Proctor Compaction
Principle of Test Method: This method determines the optimum moisture content
and the maximum density of a soil sample by an impact compaction test.
Test Method
(1) Apparatus: Molds, rammer, extruder, balance, drying oven, sieves.
(2) Procedure: The specimen is prepared and placed in a mold in three
like layers. The mold most commonly used is the four inch mold. Each layer
is compacted. The compaction used for the four inch mold is 25 blows with
a 10 pound hammer dropping 18 inches. Following compaction of all three
layers the specimen is removed from the mold and trimmed. The mass of the
sample is determined. This is divided by the volume of the mold and then the
wet density of the sample, in pcf, is determined. The water content of the
sample is then determined by oven drying. The entire procedure is repeated
for at least four specimens. The four specimens' water contents should vary
sequentially by about 1-1/2 percent. The specimen water contents should
bracket the estimated optimum moisture content. The values are plotted along
with the "zero air voids curve." The optimum moisture content and maximum
density of the sample can then be determined.
(3) Reference: ASTM D 1557.
Limitations: This method requires a laboratory environment, the considerable
time involved in sample drying and several hours to perform the test itself.
Status of the Method: This is also a standard method. It is widely used.
As it better represents greater compactive effort than does the original
Proctor test, it is more suitable for process control testing for trench
floors and the like.
Calibration Procedure: The rammer must be calibrated before initial use and
again after each 1,000 molds.
Documentation of Test: Items to be recorded include the mold volumes, speci-
men masses, and specimen water contents. No example data sheet is provided.
A-47
-------
Method No. 29
Parameter Measured: Water Content/Density/Compactive Effort
Title of Test Methods: Nonstandardized Proctor Compaction
Principle of Test Methods: These methods determine the optimum moisture
content and the maximum density of a soil sample by kneading compaction,
static compression or other devices.
Test Methods
(1) Apparatus: Molds, sieves, balance, drying oven, extruder, kneading
device or static compression device.
(2) Procedure: The procedures are method specific. (See the references.)
However the procedures are very similar to the standard laboratory methods.
Only the nature of the compactive effort and the specifics of the mold
size, etc., differ.
(3) Reference: Johnson and Sallberg, 1962; and Antrim, 1970.
Limitations: These methods require a laboratory environment, the considerable
time involved in sample drying and several hours to perform the tests
themselves.
Status of the Method: These are not standard laboratory methods. They were
developed for use in special situations. They are used by several state
highway departments. They are not widely used in the laboratory because of
the preference for the standard methods or in the field because of the ease
and sufficiency of other methods.
Calibration Procedure: See the references.
Documentation of Test: Items to be recorded include the mold volumes, speci-
men masses, and specimen water contents. No example data sheet is provided.
A-48
-------
Method No. 30
Parameter Measured: Water Content/Density/Compactive Effort
Title of Test Method: Rapid, One Point Proctor Compaction
Principle of Test Method: This method determines the optimum moisture content
and the maximum density of a soil sample by an impact compaction test and
estimation, given one specimen test and its derived value.
Test Method
(1) Apparatus: Molds, rammer, extruder, balance, drying oven, sieves.
(2) Procedure: The procedure is essentially the same as that for the
standard laboratory method. However, rather than running four or more
(usually the number is five) specimens through the test and deriving a like
number of points, only one test is run and one point is derived. The one
point is at a water content estimated to be on the dry side of the optimum.
From this point, and the well documented data on the soil, the optimum moisture
content and maximum density can be determined.
(3) Reference: EM 1110-2-1911, 1977.
Limitations: This method depends upon good and well documented data on the
local soils. The method also depends upon data which defines a relatively
good line of optimums.
Status of the Method: For suitable soils this method provides a much more
rapid means^of process control. It is widely used. It is probable that this
method could be sufficiently applied to the compaction of trench backfill.
Calibration Procedure: The rammer must be calibrated before initial use and
again after each 1,000 molds.
Documentation of Test: . Items to be recorded include the mold volumes, speci-
men masses, and specimen water contents. No example data sheet is provided.
A-49
-------
Method No. 31
Parameter Measured: Water Content/Density/Compactive Effort
Title of Test Method: Rapid, Two Point Proctor Compaction
Principle of Test Method: This method determines the optimum moisture content
and the maximum density of a soil sample fay an impact compaction test and
estimation, given two specimen tests and their derived values.
Test Method
(1) Apparatus: Molds, rammer, extruder, balance, drying oven, sieves.
(2) Procedure: The procedure is essentially the same as that for the
standard laboratory method. However, rather than running four or more
(usually the number is five) specimens through the test and deriving a like
number of points, only two tests are run and two points are derived. The
first test is with a specimen estimated to be at the optimum moisture content
or just on the dry side of the optimum. The second test is with a specimen 2
or 3 percentage points dry of the water content of the first specimen. From
these points, and the well documented data on the soil, the optimum moisture
content and maximum density can be determined.
(3) Reference: EM 1110-2-1911, 1977.
Limitations: This method depends upon good and well documented data on the
local soils. The method also depends upon data which defines a relatively
good line of optimums.
Status of the Method: In this method two curves are developed, as opposed
to one curve as in the one point method, thus this method can be expected to
yield a better estimated curve. As this method provides more accuracy than
the one point method, it is perhaps even more applicable to trench backfill
compaction process control.
Calibration Procedure: The rammer must be calibrated before initial use and
again after each 1,000 molds.
Documentation of Test: Items to be recorded include the mold volumes, speci-
men masses, and specimen water contents. No example data sheet is provided.
A-50
-------
Method No. 32
Parameter Measured: Water Content/Density/Compactive Effort
Title of Test Method: Hilf's Rapid
Principle of Test Method: This method determines the optimum moisture content
and the maximum density of a soil sample by the standard impact compaction
test of three samples, the use of standardized forms, and an estimate of the
optimum moisture content.
Test Method
(1) Apparatus: Molds, rammer, extruder, balance, drying oven, sieves.
(2) Procedure: The procedure utilizes the standard impact compaction
test. Three samples are tested. The first sample is that at field moisture,
a water content estimated to be on the dry side of optimum. The second
and third samples are tested at water contents two and four percent more
than the field moisture. The derived values are compared to standardized
forms and plotted. Without determination of water content, the maximum
density and difference of the field moisture from the optimum content can
then be determined. This is done fay connecting the plotted points, which
bracket the optimum moisture content, and thus yield its value.
(3) Reference: Hilf, 1970.
Limitations: This method is only suitable for low plasticity cohesive soils.
Status of the Method: When applicable this method yields sufficient data
in much less time than the standard impact tests. However, because it yields
only an approximation of the optimum moisture content its applicability is
limited.
Calibration Procedure: The rammer must be calibrated before initial use and
again after each 1,000 molds.
Documentation of Test: Items to be recorded include the mold volumes, speci-
men masses, and specimen water contents. No example data sheet is provided.
A-51
-------
Method No. 33
Parameter Measured: Water Content/Density/Compactive Effort
Title of Test Method: Ohio Highway Department Nest"of Curves
Principle of Test Method: This method determines the optimum moisture content
and the maximum density of a soil sample by the standard impact compaction
test yielding one point, and its placement on a nest of curves for like soils.
Test Method
(1) Apparatus: Molds, rammer, extruder, balance, drying oven, sieves,
circular slide rule.
(2) Procedure: A single test is performed as per one of the standard
impact compaction methods. The derived point is then matched to a nest of
curves. For field expedience this nest of curves is often contained on a
circular slide rule. The optimum moisture content and maximum density are
then estimated from the appropriate curve.
(3) Reference: Ohio Highway Department, 1958.
Limitations: This method depends upon good and well documented data on the
local soils.
Status of the Method: Where a nest of curves exists this method is a rapid
means of determining the optimum moisture content and maximum .density. It
has proven to be sufficient in a widespread history of usage.
Calibration Procedure: The rammer must be calibrated before initial use and
again after each 1,000 molds.
Documentation of Test: Items to be recorded include the mold volumes, speci-
men masses, and specimen water contents. No example data sheet is provided.
A-52
-------
Method No. 34
Parameter Measured: Water Content/Density/Compactive Effort
Title of Test Method: Harvard Miniature Compaction
Principle of Test Method: This method determines the optimum moisture content
and the maximum density of a soil sample by a kneading compaction test with
the Harvard Miniature device.
Test Method
(1) Apparatus: Molds, tamper, extruder, balance, drying oven, sieves.
(2) Procedure: The procedure utilizes different apparatus than does
the standard impact compaction test. Also this procedure utilizes kneading
as opposed to impact compaction. Other than that, with the exception of
specifics, the procedures are quite similar. This procedure is readily
adaptable to better represent the actual field compactive efforts to be
achieved.
(3) Reference: Wilson, 1970.
Limitations: This method is suitable only for soils passing the No. 4
screen. Thus it is applicable for usage at a hazardous waste disposal
facility.
Status of the Method: The method is small in terms of apparatus cost and
size, simple, adaptable to duplicate the compactive effort achieved by
larger equipment and ideal for field laboratory use. For better representing
the actual field compactive efforts to be achieved the kneading action of the
Harvard Miniature apparatus is superior to the impact action of the impact
devices.
Calibration Procedure: N/A
Documentation of Test: Items to be recorded include the mold volumes, speci-
men masses, and specimen water contents. No example data sheet is provided.
A-53
-------
-------
APPENDIX B
A PARTIAL LIST OF AVAILABLE NUMERICAL MODELS TO
DESCRIBE FLOW AND/OR SOLUTE TRANSPORT IN
PARTIALLY SATURATED POROUS MEDIA
-------
B-2
-------
APPENDIX B: A PARTIAL LIST OF AVAILABLE NUMERICAL MODELS
TO DESCRIBE FLOW AND/OR SOLUTE TRANSPORT IN
PARTIALLY SATURATED POROUS MEDIA
(Source: Model Annotation Retrieval System database, IGWMC,
Holcomb Research Institute, Butler University, Indianapolis, IN)
Ahlstrom, S. W., H. P. Foote, and R. J. Serne. 1976. (Washburn, J. F.)
Battelle Pacific Northwest Labs, P.O. Box 999, Richland, WA 99352,
MMT-DPRW, To predict the transient three-dimensional movement of
radionuclides and other contaminants in unsaturated/saturated aquifer
systems.
Baca, R. S. 1977. Rockwell Hanford Operations, P.O. Box 250, Richland, WA
99352, FECTRA, A two-dimensional vertical model to simulate steady or
unsteady transport for a given velocity field in a saturated or unsat-
urated porous media with complex or arbitrary geometry.
Brutsaert, W. 1971. Ingenieurburo Dr. -Ing. Gerhard Bjornsen, Beratender
Ingenieur Fur Wasserwirtschaft Und Wasserbau, 54 Koblenz—Kurfursten-
strasse 87A, Fed. Rep. of Germany, 2-D-INFILTRATION MODEL, To compute
the temporal and spatial variation of moisture content and water table
response in a vertical cross-section of a heterogeneous (layered)
anisotropic soil provile, as caused by precipitation, irrigation, and
artificial recharge.
Cooley, R. L. 1974. U.S. Geological Survey, Water Resources Division, Box
25406, M.S. 413, Federal Center, Denver, CO 80225, Prediction of
transient or steady-state hydraulic head distribution in unsaturated,
anisotropic, heterogeneous, two-dimensional, cross-sectional flow
systems.
Davis, L. A. 1980. Waste and Land Systems, Inc., 1501 Lemay Avenue,
Suite 207, Ft. Collins, CO 80524, SEEPV, A transient flow model to
simulate vertical seepage from a tailings impoundment, including
saturated/unsaturated modeling of impoundment with liner and under-
lying aquifer.
Dutt, G. R. , M. J. Shaffer, and W. J. Moore. 1976. Bureau of Reclamation,
U.S. Dept. of the Interior (Contact G. R. Dutt of Univ. of Arizona for
full address), SALT TRANSPORT IN IRRIGATED SOILS, A transient, one-
dimensional vertical simulation of solute transport in the unsaturated
zone, coupled with a chemical model.
B-3
-------
Elzy, E., and F. T. Lindstrom. 1974. Reichhold Chemicals, Inc., 2340
Taylor Way, P.O. Box 1382, Tacoma, WA 98401, SLM-1 (SANITARY LANDFILL
MODEL), A simplified contaminant mass balance model, based on one-
dimensional vertical routing of contaminant in unsaturated zone and
horizontal routing in saturated zone, corresponding to flow through a
series of stirred tanks and incorporating sorption, chemical reactions,
and biodegradation in each cell.
Gaudet, J. P., and R. Haverkamp. 1977. Institut De Mecanique De Grenoble,
B. P. 53, Centre De Tri, 38041 Grenoble—Cedex, France, WATSOL, Simu-
lation of transient, one-dimensional, vertical ground water flow and
solute transport in the unsaturated zone.
Green, D. W., H. Dabiri, C. F. Wienaug, and R. Prill. 1969. Kansas Water
Research Institute. University of Kansas, Manhattan, Kansas, TWO-PHASE
UNSATURATED FLOW, A one-dimension model for transient, vertical,
two-phases (air/water) flow in unsaturated heterogeneous porous media.
Gupta, S. K., and C. S. Simmons. 1981. Battelle Pacific NW Laboratories,
P.O. Box 999, Richland, WA 99352, UNSATID, One-dimensional simulation
of unsteady vertical unsaturated flow.
Havercamp, R., and M. Vauclin. 1982. Institut De Mecanique De Grenoble,
B.P. 53, Centre De Tri, 38041 Grenoble—Cedex, France, SIMTUS, Simula-
tion of one-dimensional, nonsteady flow in unsaturated, isotropic,
homogeneous soils.
Hoogmoed, W. 1981. Soil Tillage Laboratory, Agriculture University.
Diedenweg 20, Wageningen, The Netherlands, LONG TERM SIMULATION OF
UNSATURATED VERTICAL MOISTURE FLOW IN BARE SOILS, To simulate vertical
movement of water in the unsaturated zone of a soil profile.
Huyakorn, P.S. 1982. Geotrans, Inc., P.O. Box 2250, Reston, VA 22090,
SATURN 2, To study transient, two-dimensional variably saturated flow
and solute transport in anisotropic, heterogeneous porous media.
Intera Environmental Consultants, Inc. 1975. 11999 Katy Freeway, Suite 610,
Houston, Texas 77079, HYDROLOGIC CONTAMINANT TRANSPORT MODEL, A
transient three-dimensional model to simulate flow and solute trans-
port in a saturated/unsaturated anisotropic heterogeneous aquifer
system.
Kaszeta, F. E., C. S. Simmons, and C. R. Cole. 1980. Battelle Pacific NW
Laboratories, P.O. Box 999, Richland, WA 99352, MMT-1D, To simulate
transient, one-dimensional movement of radionuclides and other con-
taminants in saturated/unsaturated aquifer systems.
Khaleel, R., and D. L. Reddell. 1977. Texas A&M Univerisity, Department
of Agricultural Engineering, College Station, TX 77843, A two-
dimensional vertical model for the simulation of unsteady two-phase
flow and dispersion in saturated-unsaturated porous media.
B-4
-------
Kraeger-Rovey, C. E. 1975. Consulting Engineer. 297 W 36th Avenue,
Denver, CO 80211, LINKFLO, To simulate three-dimensional steady and
unsteady saturated and unsaturated flow in a stream-aquifer system.
Larson, N. M., and M. Reeves. 1977. National Energy Software Center
(NESC), Argonne National Laboratory, 9700 South Cass Avenue, Argonne,
IL 60439, ODMOD, Prediction of coupled one-dimensional, vertical
movement of water and trace contaminants through layered, unsaturated
soils.
Marino, M. A. 1981. Department of Land, Air, and Water Resources, Univer-
sity of California, Davis, CA 95616, DRAIN FEM, A two-dimensional
model to simulate the transient movement and distribution of a solute
in a saturated-unsaturated subsurface drainage system.
Marino, M. A. 1977. Department of Land, Air, and Water Resources, Univer-
sity of California, Davis, CA 95616, INFILTRATION FEM, To simulate
transient movement and distribution of a solute (introduced as a
constituent of artificial recharge) in a saturated-unsaturated porous
medium.
Narasimhan, T. N. 1981. (Cole, C.R.), Battelle Pacific NW Laboratory,
Water and Land Resources Division, P. 0. Box 999, Richland, WA 99352,
TRUST, to compute steady and nonsteady pressure head distribution in
multidimensional, heterogeneous, variably saturated, deformable porous
media with complex geometry.
Narasimhan, T. N., and S. P. Neuman. 1981. Lawrence Berkeley Laboratory,
Earth Sciences Division, University of California, Berkeley, CA 94720,
FLUMP, To compute steady and nonsteady pressure head distributions in
two-dimensional or axisymmetric, heterogeneous, anisotropic, variably
saturated porous media with complex geometry.
Neuman, S. P. 1979. Department of Hydrology and Water Resources, University
of Arizona, Tucson, Arizona 85721, UNSAT 11, Computes hydraulic
heads, pressure heads, water content, boundary fluxes and internal
sinks and sources in a saturated/unsaturated, nonuniform, antisotropic,
porous medium under nonsteady state conditions.
Pickens, J. F. 1979. GTC—Geologic Testing Consultants, Ltd., 785 Carling
Avenue, 4th Floor, Ottawa, Ontario, Canada KIS 5H4, UNFLOW, Simulation
of two-dimensional (cross-sectional) transient movement of water in
saturated-unsaturated nonuniform porous media.
Pickens, J. F. 1979. GTC Geologic Testing Consultants, Ltd., 785 Carling
Avenue, 4th Floor, Ottawa, Ontario, Canada KIS 5H7, TRANUSAT, Simula-
tion of two-dimensional (cross-sectional) transient movement of water
and solute in saturated-unsaturated nonuniform porous media.
Reeves, M., and J. 0. Duguid. 1975. Intera Environmental Consultants,
1201 Dairy-Ashford, Suite 200, Houston, TX 77079, Moisture Transport
Code, A two-dimensional transient model for flow through saturated/
unsaturated porous media.
B-5
-------
Sagar, B. 1982. Analytic and Computational Research, Inc., 3106 Inglewood
Boulevard, Los Angeles, CA 90066, VADOSE, Steady or transient, two-
dimensional, area!, cross-sectional or radial simulation of density-
dependent transport of moisture, heat and mass in variably saturated,
heterogeneous, anisotropic porous media.
Sagar, B. 1982. Analytic and Computational Research, Inc., 3106 Inglewood
Boulevard, Los Angeles, CA 90066, FLOTRA, Steady or transient, two-
dimensional, area!, cross-sectional or radial simulation of density-
dependent flow, heat, and mass transport in variably saturated, aniso-
tropic, heterogeneous deformable porous media.
Segol, G., and E. 0. Frind. 1976. Department of Earth Sciences, University
of Waterloo, Waterloo, Ontario, Canada N2L 3G1, 3-D SATURATED-UNSATURATED
TRANSPORT MODEL, Determination of concentration of conservative or
nonconservative solute in transient, 3-dimensional saturated-unsaturated
flow systems.
Serne, R. J. 1976. Battelle Pacific NW Laboratories, P.O. Box 999, Richland,
WA 99352, PERCOL, to calculate one-dimensional steady-state movement
of liquid waste in a heterogeneous, saturated-unsaturated porous
medium, including chemical reactions.
Skaggs, R. Wayne. 1980. P.O. Box 5906, Department of Biological and
Agricultural Engineering, North Carolina State University, Raleigh,
NC 27650, DRAINMOD, An unsteady, one-dimensional, horizontal/vertical
saturated/ unsaturated model to simulate watertable position and soil
water regime above water table for artificially drained soils.
Van Gemuchten and G. F. Pinder. 1976. Research Soil Scientist, U.S.
Salinity Laboratory, 4500 Glenwood Dr., Riverside, CA 92501, TRANSONE,
Simulation of one-dimensional vertical mass transport through unsat-
urated and saturated porous media.
Wesseling, J. W. 1982. Delft Hydraulics Laboratory, P.O. Box 152, 8300 Ad
Emmeloord. The Netherlands, SOMOF, Simulation of transient unsaturated
soil moisture flow in a vertical profile.
Wind, G. P., and W. Van Doorne. 1975. Institute for Land and Water Manage-
ment Research (ICW), P.O. Box 35, 6700 AA Wageningen, The Netherlands,
FLOW, Forecast of moisture conditions in partly unsaturated, partly
saturated soil.
Yeh, G. T., and D. S. Ward. 1981. Environmental Sciences Division, Oak
Ridge National Laboratory, Oak Ridge, TN 37830, FEMWASTE/FECWASTE, A
two-dimensional model for transient simulation of transport of dissolved
constituents through porous media.
Yeh, G. T. , and D. S. Ward. 1981. Environmental Sciences Division, Oak
Ridge National Laboratory, Oak Ridge, TN 37830, FEMWATER/FECWATER, A
two-dimensional model to simulate transient, cross-sectional flow in
saturated-unsaturated anisotropic, heterogeneous porous media.
B-6
-------
APPENDIX C
PROGRAM LINERSOL: MODIFIED VERSION OF PROGRAM SOILINER
-------
APPENDIX C
PROGRAM LINERSOL: MODIFIED VERSION OF PROGRAM SOILINER
The computer program SOILINER written by Dan Goode of GCA (.1983)
solves the equation of flow in an unsaturated media and describes the
infiltration in a partially saturated liner. The program determines the
infiltration rate and moisture content profiles with time and thus determines
the time taken by a liner system to achieve a steady-state moisture content
profile after establishment of a liquid head on top of the liner. It may
be necessary to solve the solute transport equation (C.2) to determine the
appropriate transit time. The program SOILINER was modified for this
purpose to include the solute transport equation by a simple finite differ-
ence formulation.
Several computer programs are available to solve the flow and solute
transport equations for a partially saturated porous media in general.
These programs, however, solve the equations separately; it is necessary to
solve the flow equation first and store the variable values required by the
transport equation at all flow time steps to obtain the solution to the
solute transport equation. A program that solves both equations simul-
taneously will be easier to use because there will be no need to save the
intermediate variables. The advantage of the program SOILINER is that it
is written specifically for a liner system and is thus easy to use, although
it solves only the flow equation. Therefore, in the present work, the
program SOILINER was modified to include a simultaneous solution of the
solute transport equation.
C.I METHODOLOGY
The vertical transport of a dissolved solute chemical species in
aqueous phase in a liner is described by the solute transport equation,
expressed by Equations C.I and C.2. In terms of moisture content, 0, and
effective hydraulic conductivity, K, Equations C.I and C.2 may be written
as:
8_ (R0C) _ §_ (U||) . 3 (vC) . fr .
at ~ al az aT • and (c-1)
v = -K(fi - 1) . (C.2)
C-3
-------
The dispersion coefficient D includes both the molecular diffusion
coefficient of the species of interest and the hydrodynamic dispersion
coefficient and may be expressed by (Huyakorn and Pinder, 1983):
a. v
(C.3)
where or. is the longitudinal dispersivity, v is the Darcian velocity given
by Equation (C.2), D is the molecular diffusion coefficient, and is
porosity.
Since the variables 0, v, or pressure head, ¥, depend upon the solu-
tion of flow equation, it is necessary to solve the flow equation first by
advancing its solution by a flow time step, Atf, . If the values of
moisture content, 6, and pressure head, ¥, are aisfumed to be constant
during the flow time step, Equation (C.I) may be rewritten as:
»s-
(C.4)
Equation (C.4) may now be expressed by a simple explicit forward time
space-centered finite difference scheme, denoting i for a nodal position z
in liner, j as time level, Az. as nodal increment at node i, and At as time
increment (the nodal grid system is shown in Figure C-l).
Riei
Di
(C.5)
K r
Kici
Az.
AZ. ,)
Equation (C.5) is explicitly formulated, so the stability of its
solution depends upon the time increment, At. When stability criteria are
applied, an upper limit on the time increment, At, may be set' as:
C-4
-------
Top of
Domain
Bottom
of Domain
Node 1
Node 2
Node 3
(Nodal increment)
Az,
Node i-1
Node i
Nodei+1 "
AzM
Az,
Node n-1 '
Node n
Figure C-1. Mesh-centered nodal grid system.
C-5
-------
At < 0.5 | —^ , (C.6)
(minimum
where Az. is nodal increment at node i, and 6. and D. are moisture content
and dispersion coefficient at node i, respectively. Since the right-hand
side depends upon the nodal position, a minimum possible value must be
determined. The maximum allowable time increment, At, as given by Equation
(C.6), may be smaller than the flow time step, in which case it will be
necessary to subdivide the flow time step in a number of smaller appro-
priate time increments for the solute transport equation. In such a case,
the variables 6. and ¥., derived from the flow equation, may be assumed to
be constant during all the smaller time increments until the solution of
the solute transport equation is advanced by the flow time step, At-, .
If the allowable time increment as given by Equation (C.6) is greater than
the flow time step, the time increment for the transport equation is set
the same as the flow time step.
Equation (C.5) may thus be solved with appropriate time increments,
At, to obtain the concentration profiles at the next time level. To obtain
the solution at a particular time level, j, the moisture content and pres-
sure head values must be specified. Since the flow equation is solved
first, two set values of 0. and 4». are available at time levels j and j+1,
respectively. Attempts to use mean or j-level values of 0. and ¥. were not
successful in simulations described earlier, however, stable solutions were
obtained through advanced (j+1) time level values.
C.2 SUBROUTINE CONCAL
The computational procedure to solve Equation (C.5) is outlined in
Figure C-2 showing the flow diagram. For clay materials of low saturated
hydraulic conductivities, the flow velocities are considerably smaller, and
the molecular diffusion may be expected to dominate the dispersion process.
In such a case, the contribution of hydrodynamic dispersion may be ignored
by assuming a constant value for the overall dispersion coefficient, 0.
The retardation factor, R, depends upon a specific chemical-liner material
combination and must be determined experimentally. A noninteractive species
(R=l) is assumed to obtain a conservative estimate of transit time. R=l
and a constant value of the overall dispersion coefficient were used to
write a subroutine CONCAL to solve Equation (C.5); its listing is given in
Figure C-3. This subroutine was added to the program SOILINER with additional
minor changes in the original program to accommodate the new subroutine.
The modified version is called LINERSOL.
C.3 PROGRAM LINERSOL SIMULATIONS
This program was used to carry out the solute transport simulations
described earlier. In all these numerical simulations, a liquid head of
30 cm of water was assumed to be established at the top of the liner. The
C-6
-------
From Main Program
Time T; and Last Flow Time Step DTP
Updated Values of d\, i>\. Ki
Old Values of Solute Concentrations, C,
U
Determine Maximum Time Increment,
TOLDT from Equation 23
if
Determine No. of Time Increments,
NT - INT (DTF/O.S5/TOLDT) -c 1
and time increment, DT = DTF/NT
If
T - T - DTP
IT-0
if
T - T + DT
IT»IT + 1
IF
Calculate New Concentration Values,
Cj from Equation 22
if
No .^^ ^^-^
M
Return to Main Program With Updated
Concentration Values, C,
Figure C-2. Computational flow diagram of subroutine CONCAL.
C-7
-------
11920 C*
11930
11940
11930 C*
11960 C
1' 9-70 C
11990 C
11990 C
12000
12010
12020 C
12030
12040
12050
12060
12070
12072
12080
12093
12090
12100
12110
12120
12130
12140
12130 C
12160
12170 C
12130
12190
12200
12210
12220
12230
12240
12230
12270
12230
12290
12300
12310
12320
12330
12340-
12330
123sO
12370
12330
12390
12400
12410
12-120
12430
12440
12430
12460
12470
124SO C
12 JC0
12300
•*•***
*
»***
10
15
17
20
23
30
35
40
*
30
100
120
130
SUBROUTINE CONCALCPSI>RMOISTrSTARK/DZ/CQNC/NUMEL,DT>ICON,DFUZVT,
TOLDT)
CALCULATES CONCENTRATION PROFILES OF LEACHATE SPECIES DUE
TO AOVECTION AND MOLECULAR DIFFUSION OF THE SPECIES
DIMENSION PSKD.RMOISTCl) »STARK( l).DZd).CONC(l) .CONCN<200)
DIMENSION AC200)>B<200)»CC200>
IFdCON.NE.O) GOTO 20
CONCd)»1.0
DO 10 I»2»NUMEL
10 CONCd)»0.0
CONC(NUMEL+1)=0.0
IF (DFUZVT.LE.0.0) GOTO 17
DZd>*DZd)*RMOISTd>
DO 13 I=2iNUMNP
PROD = DZd-l>*DZ( I-1)*R«OIST(I)
IF (PROD.LT.VMIN) VMIN=PROD
15 CONTINUE
TOLBT=0.423*VHIN/OFUZVT
ICON=1
RETURN
IFCDFUZVT.LE.0.0) GOTO 23
NT*INT
GOTO 30
DTN=DT
NT=1
DO 33 I*2>NUMEL
A( I)sSTARK( I-1)*(1.0-KFSI(I)
8( I)=STARK( DXd.O-KPSId-m-PSIdM/DZd))
C(I)=RMOIST( I>XASS(DZ(I)+DZd-l))/DTN/2.0
CONCN(I>=0.0
CONCN(NUM£L-H )=0.0
DO 130 IT=1/NT
DO 100 I*2.NUMEL
IF(CONCd-l) .LE.0.0) GOTO 100
CONCN(I)»«Ad>»CQNC(I-l)-B< I)*CONC( .
IF (DFUZVT.GT.0.0) GOTO 40
GOTO 50
D=DFUZVT*((CONCd)-CONC(I-1))/DZ.LE.O.0) GOTO 130
CQNC< NUMELM ) »CONC ; NUMEL ) *C3NC ( NL'MEL )/CQNC < NUMEL-I )
130 CONTINUE
Figure C-3. Listing of the subroutine COIMCAL in program LINERSOL.
C-8
-------
liner was assumed to be 200 cm thick with a saturated hydraulic conduc-
tivity of 1 x 10 7 cm/s. At the bottom of the liner a negative pressure
head of -500 cm was assumed to exist due to the influence of the underlying
permeable site soil of 5 m depth above the water table. Figures C-4 through
C-6 show the advancement of moisture content profiles as determined by
program SOILINER for three initial saturations (50 percent, 80 percent, and
95 percent) of liner. Figures C-7 through C-9 show the solute concentration
profiles in the liner at different times obtained by using only advective
transport mechanism (D=0) in program LINERSOL for the same three initial
liner saturations. Figures C-10 through C-12 show the advancement of
concentration profiles with time due to both advection and molecular diffu-
sion using program LINERSOL._ The dispersion coefficient was assumed to be
constant and equal to 1 x 10 6 cm2/s. These figures clearly show that the
transit times based on solute transport can differ from those based on
liner saturation and that transit times for given criteria depend upon
initial liner saturation.
C-9
-------
I
N"
_c
*-
a
20
40
60
8°
100
120
140
160
180
200 L
1 X
0.20 0.25 0.30 0.35 0,40
Moisture Content, 9
0.45 0.50
Figure C-4. Simulated moisture content profiles in a finer at different times,
for initial liner saturation of 50 percent.
C-10
-------
180 -
200
0.20
2.2 X 108 (Steady State)
I I
0.25
0.30
0.35 0.40
Moisture Content, i
0.45
0.50
Figure C-5. Simulated moisture content profiles in a liner at different times,
for initial liner saturation of 80 percent.
C-ll
-------
I
a
2
20 -
40 -
60 -
80 -
100
120
140
160
180
200
0.20
1 X 107
seconds
9.47 X 107
(Steady
State)
0.25
0.30
0.35 0.40
Moisture Content, (
0.45
0.50
Figure C-6. Simulated moisture content profiles in a liner at different times,
for initial liner saturation of 95 percent.
C-12
-------
20
40
60
80
u
N*
03
•J 100
_c
**
a
09
120
140
160
180 -
200
1 X 107 seconds
3.16 X 107
16 X 108
0.2 0.4 0.6 0.8
Solute Concentration, dimensionless
1.0
Figure C-7. Simulated solute concentration profiles in a liner at different times,
for initial liner saturation of 50 percent (advection only).
C-13
-------
20 s
40
60
80
u
N*
5 100
c
a
Q
120
140
160
180
200
1 X 107 seconds
3.16 X 107
1.58 X 10s
3.16 X 108
0.2 0.4 0.6 0.8
Solute Concentration, dimensionless
1.0
Figure C-8. Simulated solute concentration profiles in a liner at different times,
for initial liner saturation of 80 percent (advection only).
C-14
-------
200
°'2 0-4 0.6 0.8
Solute Concentration, dimensionless
1.0
Figure C-9.Sirnu.ajdI solute concentration profiles in a liner at different times
for ,n.t,al liner saturat.on of 95 percent (advection only).
C-15
-------
o
N*
l_"
C
160 -
180 -
200
0.2 0.4 0.6 0.8
Solute Concentration, dimension less
1.0
Figure C-10. Simulated solute concentration profiles in a liner at different times,
for initial liner saturation of 50 percent (advection and molecular diffusion).
C-16
-------
N
1"
a
<5
100
120 -
140 -
160
180
200
0.2 0.4 0.6 0.8
Solute Concentration, dimensionless
Figure C-11. Simulated solute concentration profiles in a liner at different times,
for initial liner saturation of 80 percent (advection and molecular diffusion).
C-17
-------
o
------- |