Research and Development
sxEPA
Design and
Construction of
Covers for Solid
Waste Landfills
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution-sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
-------
' EPA-600/2-79-165
August 1979
DESIGN AND CONSTRUCTION OF COVERS FOR SOLID WASTE LANDFILLS
by
R. J. Lutton, G. L. Regan, and L. W. Jones
U.S. Army Engineer Waterways Experiment Station
Vicksburg, Mississippi 39180
Interagency Agreement No. EPA-IAG-D7-01097
Project Officer
Robert E. Landreth
Solid and Hazardous Waste Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 1+5268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 1*5268
-------
DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U. S. Environmental Protection Agency, and approved for publica-
tion. Approval does not signify that the contents necessarily reflect the
views and policies of the U. S. Environmental Protection Agency, nor does men-
tion of trade names or commercial products constitute endorsement or recom-
mendation for use.
11
-------
FOREWORD
The Environmental Protection Agency (EPA) was created because of in-
creasing public and government 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 environ-
ment. The complexity of that environment and the interplay between its com-
ponents require a concentrated and integrated attack on the problem.
Research and development is that necessary first step in problem solution
and it involves defining the problem, measuring its impact, and searching for
solutions. The Municipal Environmental Research Laboratory develops new and
improved technology and systems for the prevention, treatment, and management
of wastewater and solid and hazardous waste pollution discharges from munici-
pal and community sources, for the preservation and treatment of public drink-
ing water supplies and to minimize the adverse economic, social, health, and
aesthetic effects of pollution. This publication is one of the products of
that research, a most vital communication's link between the researcher and
the user community.
This report is a result of research supported by the EPA to obtain
engineering information essential to the design of cover materials for land-
fills. Proper selection and placement of these materials will aid in the
prevention of leachate generation.
Francis T. Mayo, Director
Municipal Environmental Research
Laboratory
111
-------
ABSTRACT
Selection and design of cover for solid/hazardous waste landfills
usually require engineering planning for efficient accommodation of the
volume of incoming waste within certain moderate to severe constraints.
The foremost constraints are usually the amount and characteristics of
cover material available in the immediate vicinity. Local soils available
in adequate amounts seldom have the best characteristics for the several
cover functions, e.g., they are too clayey or sandy.
Several steps are recommended for effective planning of cover.
First, identify the primary and secondary functions to be served by the
cover and establish relative importances, e.g., impeding water percolation
is more important than supporting vegetation, etc. Second, use data on
soil properties in terms of the Unified Soil Classification or the U. S.
Department of Agriculture systems to rate available soil for effectiveness
in the various functions. Third, specify certain design procedures in
the disposal operation for circumventing the deficiencies of the selected
cover soil. Placement procedures, such as compaction, will improve the
soil for certain functions. Elsewhere, the soil properties favorable
for one function are unfavorable for another, e.g., a clayey cover soil
impeding water percolation will prevent leakage of decomposition gases
that may also be desired. Fourth, where a single soil cannot serve
contrasting cover functions, the designer may incorporate features, such
as layering, or can resort to the use of special non-soil materials and
additives.
This report was submitted in fulfillment of Phases I and II of
Interagency Agreement No. EPA-IAG-D7-01097 between the U. S. Environmental
Protection Agency and the U. S. Army Engineer Waterways Experiment
Station (WES). Work for this manual was conducted during the period
March 1977 to December 1978, and work was completed in December 1978.
Dr. R. J. Lutton, Geotechnical Laboratory, WES, was principal investigator
and author. Mr. G. L. Regan, WES, coauthored an interim report, and
Dr. L. W. Jones, University of Tennessee, prepared most of Section 19.
Director of WES during the work period was COL John L. Cannon, CE.
Technical Director was Mr. F, R. Brown.
IV
-------
CONTENTS
Foreword iii
Abstract iv
Figures viii
Tables xiv
Abbreviations and Symbols xvi
Metric Conversion Table xxii
Acknowledgment xxiv
1. Introduction 1
Purpose of study 1
Scope of manual 1
Background 2
Soil classification system 2
Nature of solid waste 3
2. Requirements of Cover on Solid Waste 12
Cover functions 12
Functional priorities lU
Satisfying requirements and using this manual lU
3. Soil Properties and Testing l6
General relations l6
Grain-size analysis IT
Engineering indices 19
Agricultural indices 20
Compaction tests 22
Permeability tests 25
Strength tests 26
Consolidation test 31
Swell tests 31
Soil suction tests 32
Dispersion tests 3^
Mineralogical analysis 3^
k. Selection of Soil for Cover 35
Determination of cover functions 35
Explanation of soil rating 35
5. Placement and Treatment of Soil ^1
Cover compaction Ul
Soil blending 50
Additives and cements 51
Layering 60
6. Nonsoil Cover Materials 69
Commercial materials 69
Waste materials 77
v
-------
CONTENTS (continued)
7. Summary of Considerations for Operations Plan or
Specifications Qh
General outline , Qh
Recommendations for specific design elements 85
8. Control of Infiltration/Percolation 88
Factors affecting infiltration/percolation rates 88
Determining infiltration 92
Determining evapotranspiration 100
Determining water storage capacity IQk
Water balance analysis of percolation for design 106
Criteria for allowable percolation 109
Designing for infiltration/percolation control 115
9. Control of Gas 121
Gas production in solid vaste 121
Gas flow through cover soil 121
Designing for control of gas flow 12^
10. Water Erosion Control 127
The universal soil loss equation 127
Cover construction factors 133
Use of USLE for design 138
Designing for water erosion control
11. Wind Erosion Control
Erosion in the solid waste/soil system ikk
The wind erosion equation 1^6
Use of WEE for design 153
Designing for wind erosion control 15^
12. Dust Control 157
Causes and sources of dust 157
Design features for dust minimization 158
13. Stability of Side Slopes 160
Slope stability in the solid waste/soil system 160
Evaluating stability l6l
Stability analysis 165
Designing for slope stability 172
ih. Trafficability 176
Trafficability on the solid waste/soil system 176
Evaluating soil trafficability 177
Use of RCI and VCI for design l8l
Designing for trafficability 186
15. Dewatering and Consolidating Saturated Waste 190
Sludge/slurry consolidation 190
Designing for dewatering and consolidating 192
16. Cold Climate Operations
Phenomena of cold climates
Winter problems at landfills 196
Designing for cold climate 200
17. Minimization of Fire Hazard
Conditions for fire hazard
Designing against fire hazard 20U
18. Crack Resistance 207
Phenomenon of cracking at landfills 207
vi
-------
CONTENTS (continued)
Indices of expansive behavior 208
Designing against cover cracking 209
19- Establishment and Support of Vegetation 212
Considerations unique to landfills 212
Soil factors 213
Choice of vegetation 216
Seed and surface preparation 220
Maintenance of vegetation 223
Designing for vegetation 223
20. Animal and Vector Control 226
Minimizing attractiveness to birds 226
Discouraging burrowing animals 226
Minimizing vector access 227
21. Aesthetic Considerations 228
22. Future Construction and Land Use 229
Disposal areas as sites for construction 229
Designing for future use 231
23. Summary Example 236
References 239
VI1
-------
Number
1
2
3
U
5
6
T
8
9
10
11
12
13
1U
15
16
IT
18
19
FIGURES
Summary of the USC system
USDA textural classification chart
Comparison of USCS and USDA particle-size scales
USCS soils superimposed on the USDA textural classification
chart
Manual section organization and use
Fundamental relations in soil
Gradation curves of some sanitary landfill cover soils
States of consistency of soil
Water-holding characteristics of USDA soils
Typical ^-in.-diam compaction mold and sliding-weight ,
fixed-head rammer for standard compaction test
Standard compaction test results with landfill cover soil . . .
Flow of water through saturated soil
Principle of falling-head test
Graphical criterion of shear strength of soil
Schematic diagram of direct shear "box
Schematic diagram showing stresses during triaxial compression
test
Schematic diagrams of fixed-ring and floating-ring
consolidometers
Time-consolidation curve
Void ratio-pressure curve
Page
I*
6
6
7
15
16
18
19
21
23
21+
26
27
29
30
30
32
33
33
viii
-------
Number FIGURES (continued)
20 Relation of effective angle of internal friction to dry unit
weight Ul
21 Coefficient of permeability of materials as affected by
degree of compaction k2
22 Cover compaction on municipal solid waste as compared to
laboratory test results kk
23 Schematic guidance for predicting cover compaction results
with intermediate-size dozers on municipal solid waste
using laboratory test results ^5
2k Example standard compaction curves for various soil types ... ^6
25 Points of maximum dry density and optimum water content by
standard compaction test for soils used as cover on
sanitary landfills ^7
26 Effect of compaction lift thickness on soil density for
27
28
29
30
31
32
33
3k
35
36
37
38
39
eight coverages of a 90-psi roller
Cracking from flexing of cover on spongy base of solid waste . .
Effect of gravel additions to silt
Example of freeze-thaw and wet-dry durability test data and
soil-cement design criterion
Permeability of some cement -treated soils
Erosion rates for cement-stabilized sandy soil
Typical layered cover systems
Two types of gas vents for layered cover systems
Fly ash sources east of the Rocky Mountains
Grain-size distributions for fly ash
Grain-size distributions for bottom ash and boiler slag ....
Grain-size distribution for typical inclinerator residue from
municipal solid waste
Types of dredged material, by region, as sampled in
Reference 50
Frequency of USCS types among kOO samples of dredged soils . . .
kQ
k9
50
53
5^
55
66
68
77
78
79
80
82
82
IX
-------
FIGURES (continued)
Number Page
1*0 Factors affecting the infiltration rate into unfrozen soil ... 88
1*1 General infiltration rate function 89
1*2 Relationship of rainfall, runoff, and infiltration during a
rainfall event 90
1*3 Effect of mulches on infiltration rate 91
1*1* Relationship between hydraulic conductivity and volumetric
water content for a clay soil 92
1*5 Infiltration as measured by field infiltrometers 93
1*6 Estimation of direct runoff amounts from storm rainfall .... 96
1*7 Relative growth (GI) graphs for alfalfa modified by cutting and
for corn as modified by tillage 101
1*8 Average annual lake evaporation in inches, according to the
National Weather Service 102
1*9 Potential evapotranspiration curves calculated on a monthly
basis 103
50 Generalized flow chart for Program SCSRO with percolation
option Ill
51 Mean annual percolation in inches below a l*-ft root zone
(Hydrologic Soil Group A). Four inches available
water-holding capacity 112
52 Mean annual percolation in inches below a l*-ft root zone
(Hydrologic Soil Group B). Eight inches available
water-holding capacity 112
53 Mean annual percolation in inches below a l*-ft root zone
(Hydrologic Soil Group C). Eight inches available
water-holding capacity 113
5!* Mean annual percolation in inches below a U-ft root zone
(Hydrologic Soil Group D). Six inches available
water-holding capacity 113
55 Flow chart of USDAHLlh mainline Ill*
56 Disruption of surface slope by excessive settlement 118
57 Combined buried pipe drain and gravel or sand drain with
cover 119
-------
w , FIGURES (continued)
Number
58 Gas collecting and venting system of laterals in gravel
trenches above waste cell 125
59 Average annual values of rainfall-erosivity factor R 128
60 Nomograph for determining soil-erodibility factor K for
U. S. Mainland 130
6l Effect of unit weight on erosion rate at three different
slopes. Soil is classified ML 135
62 Effect of plant-residue mulch on soil loss. Mulch factor is
soil loss with mulch divided by soil loss without mulch . . . 137
63 Influence of mulch types on rates of soil loss from 5H on IV
construction slope 138
6^ Surface and interceptor ditches 139
65 Embankment protection structures
66 Effect of drainage ditch shape on velocity and erosivity ....
67 Prevailing wind erosion direction in the Great Plains showing
degrees from north or south and percentage of all erosion
occurring along that direction 1^5
68 Wind erosion climatic factor C1 in percent for March and
October 1^8
69 Wind erosion versus percent coarse fraction
70 Knoll adjustment (a) from top of knoll and (b) from upper
third of slope 1^9
71 Soil ridge roughness factor T' from actual soil ridge
roughness 150
72 Chart for determining soil loss A/ from A' A' and L' 151
73 Relationship of factor V to quantity and type of vegetative
cover. For example, 800-lb/acre actual flat residue has
equivalent V = 2500 Ib/acre 152
7U Chart for determining soil loss A' 153
75 Cover configurations at sloping sides of disposal areas .... l60
76 Idealized shear surface cutting landfill mass of waste and
cover soil 162
XI
-------
FIGURES (continued)
Number Page
77
78
79
80
81
82
83
8k
85
86
87
88
89
90
91
92
93
9U
95
96
97
98
Behavior of loose and dense specimen of medium-fine sand
during triaxial compression
Three cases of groundwater conditions in a landfill
Need for thick soil cover in thawing landfill slopes
Modified Swedish method of finite slice procedure with no
water forces
Forces acting on typical slices
Example design envelope for Cases II and III
Cross section and symbols for stability chart
Stability chart for cohesionless embankment on plastic
foundation
Construction of solid waste retaining dikes and slopes
RCI means and ranges for various soil types
Profile of a typical area showing various topography-moisture
conditions during the year
SI for two vehicle classes
Soil trafficability in USCS terms
Soil trafficability in USDA terms
Example load-depth diagram
Effect of thickness on consolidation of dredged material ....
Dike and sludge cross section
Design freezing index values for the conterminous
United States
Depth of freezing penetration into soils with bare or covered
surfaces
Regional depth of frost penetration
Mean annual total snowfall
Rates of heave as related to silt-clay content
163
I6k
165
166
168
169
170
171
Ilk
178
180
182
183
18U
191
192
193
195
197
198
199
201
Xll
-------
FIGURES (continued)
Number^ Page
99 Estimated occurrence of expansive soils by physiographic
unit 208
100 Plasticity index as related to swelling potential at 1-psi
surcharge 210
101 Settlements predicted and observed from loading 10-ft-thick
section of old municipal landfill 230
102 Foundation design for building at old sanitary landfill .... 231
103 Settlement of solid waste beneath and around building founded
on piers 235
Xlll
-------
TABLES
Number Page
1 USDA Textural Types Corresponding to USCS Soil Designations ... 8
2 USCS Soil Types Corresponding to USDA Soil Terminology 9
3 Approximate Composition of Municipal Solid Waste 10
h Test Compaction Energy 22
5 Approximate Average Permeability and Capillary Head of Soils . . 28
6 Ranking of USCS Soil Types According to Performance of Cover
Functions 36
7 Landfill Equipment Needs 1+2
8 Guidance for Selecting Soil Stabilizer 52
9 Example Effects of TSPP and NaCl on Compaction and Permeability . 58
10 Chemical Additives for Cover Soil 6l
11 Products Recommended for High-Priority Cover 70
12 Estimated Unit Costs for Some Cover Layers 73
13 Empirical Values for Obtaining Runoff Coefficient 9k
l*t Typical f Values for Bare Soils 95
15 Vegetation Cover Factor for Estimating Infiltration Capacity . . 95
16 Hydrologic Soil Groups Used by the Soil Conservation Service . . 97
17 Runoff Curve Numbers for Soil-Cover Complexes at AMC II 98
18 Seasonal Rainfall Limits for Antecedent Moisture Conditions ... 99
19 Curve Numbers for Antecedent Moisture Conditions I and III ... 99
20 Tentative Estimates of Vegetation Parameter "a"-for
Infiltration Equation 100
XIV
-------
TABLES (continued)
Number Page
21 Examples of Consumptive Use in Western United States ...... 10U
22 Hydrologic Capacities of Texture Classes ............ 105
23 Monthly Water Balance Analysis in Inches for Chippewa Falls,
Wisconsin ........................... 108
2k Monthly Water Balance Analysis in Inches with Thick Cover .... 110
25 The Relation of Tile Spacing to the Hydraulic Conductivity of
Soils ............................. 120
26 Approximate Averaging Porosity of Loose and Compacted Soils . . . 122
27 Approximate Values of Factor K for USDA Textural Classes .... 131
28 Values of the Factor LS for Specific Combinations of Slope
Length and Steepness ..................... 132
29 Generalized Values of Factor C for States East of the
Rocky Mountains ........................
30 Values of Factor P ....................... 135
31 Example of Monthly Wind Characteristics Available for U. S.
Stations ........................... 1^6
32 Estimates of Repose and Friction Angles of Cohesionless Soils . . 170
33 Categories and VCI of Vehicles ................. 185
3k Effects of Slipperiness and Stickiness of Soils in Low-
Topography, Wet-Season Condition ............... 187
35 Relative Volume Change as Indicated by PI and Other
Parameters .......................... 209
36 Volume Change as Indicated by LL and Grain Size ......... 209
37 Relative Levels of Organic Matter and Major Nutrients in
Soils ............................. 213
38 Characteristics of Grasses and Legumes ............. 217
39 Grasses Commonly Used for Revegetation ............. 218
kd Legumes Commonly Used for Revegetation ............. 219
xv
-------
LIST OF ABBREVIATIONS AND SYMBOLS*
ABBREVIATIONS
AASHTO
AET
AMC
Ann.
ASTM
°C
CI
CN
CU
cfs
cm
cm/hr
cm/ra
cm/s
cm/sec
deg
diam
El
EPA
ERG I
FS
°F
ft
American Association of State Highway and Transportation
Officials
actual evapotranspiration
antecedent moisture condition
annual
American Society for Testing and Materials
degrees Celsius
cone index
curve number (for calculating runoff)
consumptive use
cubic feet per second
centimeter
centimeters per hour
centimeters per meter
centimeters per second
centimeters per second
degrees
diameter
erosion index
Environmental Protection Agency
effective rating cone index
factor of safety
degrees Fahrenheit
foot
* Abbreviations and symbols explained on tables and figures and not used
in text are not repeated here.
xvi
-------
ABBREVIATIONS AND SYiffiOLS (continued)
ft /min cubic feet per minute
gal gallon
2
gal/yd gallons per square yard
gm gram
gm/cm grams per square centimeter
gm/min grams per minute
H horizontal
I infiltration
in. inch
in./ft inches per foot
in./hr inches per hour
kg kilogram
ksf kips per square foot
lb pound
2
It/ft pounds per square foot
Ib/ft pounds per cubic foot
lb per cu ft pounds per cubic foot
2
Ib/yd pounds per square yard
Ib/yd pounds per cubic yard
LGP low ground pressure (vehicle)
LL liquid limit
Mth. monthly
m meter
mil mil
mm millimeter
mm/hr millimeters per hour
mph miles per hour
P precipitation
PET potential evapotranspiration
PI plasticity index
PL plastic limit
PRO percolation
pcf pounds per cubic foot
pH hydrogen ion concentration
xvii
-------
psf
psi
Q
R
RCI
RI
RO
RPM
S
SCS
SI
SL
ST
AST
use
uses
LISDA
USLE
V
VCI
WEE
yd
#/ft3
SYMBOLS
A
A'
Ai
A2
A5
a
b
C
ABBREVIATIONS AND SYMBOLS (continued)
pounds per square foot
pounds per square inch
- unconsolidated-undrained triaxial compression (test)
- consoliciated-undrained triaxial compression (test)
rating cone index
remolding index
runoff
revolutions per minute
consolidated-drained triaxial compression (test)
Soil Conservation Service
slope index
shrinkage limit
storage
change in storage
unified soil classification
Unified Soil Classification System
United States Department of Agriculture
universal soil loss equation
vertical
vehicle cone index
wind erosion equation
yard
pounds per cubic foot
area; average water erosion soil loss
average wind erosion soil loss
erodibility increment for dry aggregate
erodibility increment for T'
erodibility increment for C'
erodibility increment for L'
erodibility increment for V
subscript in chemical formula; factor in infiltration equation
subscript in chemical formula; slope vertical to horizontal
carbon; cover/management factor; watershed/storm coefficient
XVlll
-------
ABBREVIATIONS AND SYMBOLS (continued)
C compression index
c
C gas concentration
o
C' climatic factor
CH, methane gas
CO carbon dioxide gas
c rate of infiltration decrease; subscript in chemical formula;
soil cohesion
cn developed soil cohesion
c coefficient of consolidation
v
c' effective soil cohesion
D foundation layer thickness
D free space gas diffusivity
o
D gas diffusivity of porous media
P
D soil grain size vhere 15 percent by weight is finer
Dn soil grain size where 85 percent by weight is finer
d subscript in chemical formula; day
E rainfall kinetic energy
e void ratio; Napierian base; subscript in chemical formula
e initial void ratio
o
F force
f infiltration rate; infiltration capacity
f final infiltration rate
c
f initial infiltration rate
o
f soil infiltration rate after 1 hour continuous rainfall
f infiltration rate of vegetated soil
f(-) function of (-)
G specific gravity of solids
s
GI growth index of vegetation
H hydrogen; height; drainage length
AH change in height
H capillary head
H, total initial thickness
T/
HpS hydrogen sulfide gas
I maximum 30-minute rainfall intensity
i average rainfall intensity; hydraulic gradient
xix
-------
ABBREVIATIONS AND SYMBOLS (continued)
K soil erodibility factor; potassium
K1 soil credibility index
K coefficient of active earth pressure
K 0 potassium oxide
k coefficient of permeability; hydraulic conductivity
L cover thickness; slope-length factor
L' length in prevailing wind direction
LS topographic factor combining length and steepness effects
N empirical vegetation cover factor; nitrogen
NIA stability number
t\.
NH ammonia gas
n porosity
0 oxygen
P practice factor; phosphorus
p pressure
AP total load
P1 average initial effective stress
PpCL phosphorus pentoxide
Q quantity of water; gas production rate
q rate of flow; rate of discharge
R rainfall and runoff erosivity index
S sulfur; degree of saturation; slope-steepness factor; soil
shear strength
S available storage of water
a
T1 soil ridge roughness factor
T consolidation time factor
v
t time
u pore water pressure
V equivalent vegetative cover
v wind velocity
W weight force
w weight water content; coefficient in chemical formula
x coefficient in chemical formula
y coefficient in chemical formula
z coefficient in chemical formula; depth
xx
-------
ABBREVIATIONS AND SYMBOLS (continued)
6 slope inclination
y unit weight of soil
v dry unit weight (or dry density)
d
Y wet unit weight (or wet density)
m
Y unit weight of water
w
8 volumetric water content
a normal stress on shear surface
a major principal stress
c minor principal stress (chamber pressure)
<{> angle of internal friction
4>' effective angle of internal friction
greater than
< less than
» much greater than
xxi
-------
METRIC CONVERSION TABLE
Multiply
By
To Obtain
acres
atmospheres
cubic feet per second
cubic yards
degrees (angle)
Fahrenheit degrees
feet
gallons (U. S. liquid)
gallons (U. S. liquid)
per square yard
inches
inches per hour
kips (force)
miles (U. S. statute)
miles (U. S. statute)
per hour
mils
pounds (force) per
square foot
pounds (force) per
square inch
pounds (mass)
pounds (mass) per acre
pounds (mass) per
cubic foot
1+OU6.856
101.325
0.02831685
0.761455^9
0.017^5329
5/9
0.30U8
0.003785^12
1^.5273
0. 025^
0.02514
14.14148222
1. 6093^14
0.025^
1+7.88026
689*4
.757
0.145359214
0.1120851
16.018U6
square meters
kilopascals
cubic meters per second
cubic meters
radians
Celsius degrees or Kelvins*
meters
cubic meters
cubic decimeters per square
meter
meters
meters per hour
kilonewtons
kilometers
kilometers per hour
millimeters
pascals
pascals
kilograms
grams per square meter
kilograms per cubic meter
(Continued)
* To obtain Celsius (c) temperature readings from Fahrenheit (F) readings, use
the following formula: C = (5/9) (F - 32). To obtain Kelvin (K) readings,
use: K = (5/9) (F - 32) + 273.15-
xxi i
-------
METRIC CONVERSION TABLE (Continued)
Multiply By To Obtain
pounds (mass) per 0.593276 kilograms per cubic meter
cubic yard
square feet 0.0929030^ square meters
square inches 6.1+516 square centimeters
square miles 2.589988 square kilometers
tons (force) per 95.76052 kilopascals
square foot
tons (short, mass) 907.181+7 kilograms
tons (mass) per acre 0.22U1702 kilograms per square meter
yards 0.91^ meters
xxni
-------
ACKNOWLEDGMENTS
The following individuals were among those contributing constructive sug-
gestions for preparation of this manual:
R. G. Ahlvin, WES - executive reviews of report
D. C. Banks, WES - technical review and discussions
F. Bopp, WES - review of interim report
E. T. Engman, USDA - discussion of hydrologic modeling
H. D. Holtan, University of Maryland - discussion of hydrologic modeling
M. Yaramanoglu, University of Maryland - discussion of hydrologic modeling
R. C. Horz, Jr., WES - soil testing
L. D. Johnson, WES - revisions to Section 8
P. G. Malone, WES - discussion and review of interim report
J. M McMillan, State of Mississippi - sampling sites and background
E. B. Perry, WES - discussion and review on erosion
D. E. Ross, SCS Engineers - review of interim report
N. B. Schomaker, EPA - cover soil test data
W. C. Sherman, Jr., WES - technical reviews
H. E. Westerdahl, WES - discussion of hydrologic modeling
W. E. Willoughby, WES - discussion of trafficability
G. B. Willson, USDA - discussion of composting
D. A. Woolhiser, USDA - discussion of hydrologic modeling
R. E. Smith, USDA - discussion of hydrologic modeling
XXiV
-------
SECTION 1
INTRODUCTION
Each year in the United States, approximately three billion tons of
solid vastes are generatedl as follows:
Mining 1,890,000,000 tons 63 percent
Agricultural 660,000,000 tons 22 percent
Industrial 270,000,000 tons 9 percent
Municipal " 150,000,000 tons 5 percent
Sewage 30,000,000 tons 1 percent
Industrial and municipal wastes constitute a small proportion on a relative
basis, but the annual tonnages are staggering when the pollution potential is
considered.
Much solid waste is disposed on land behind dikes or by land burial, in
conflict with growing limitations on land availability. Economical use of
land space and growing concern for the preservation of a healthful environ-
ment and our future were important factors in the enactment of Public Law
9^-580,2 "Resource Conservation and Recovery Act of 1976" (21 October 1976).
The act provides for "promulgation of guidelines for solid waste collection,
transport, separation, recovery, and disposal practices and systems...," and
calls for development and publication of guidelines for solid waste management.
PURPOSE OF STUDY
This study was intended to provide a basis for development of guidelines
in selection, design, and construction of cover for management of municipal,
industrial, and hazardous solid wastes (with the exception of radioactive
waste). The manual describes and evaluates various cover materials and pre-
sents cover design procedures relative to specific functional requirements and
controlling physical phenomena to aid permit writers, designers, and others
seeking the most effective solutions to problems of burial of solid waste.
SCOPE OF MANUAL
Natural soils as cover are the principal subject; however, synthetic
membranes, chemicals, and waste products are also discussed in detail since
their relative importance should grow in the future. Each of the important
functions of cover is considered in the context of selecting and designing
cover but with cognizance of the effects of conflicts that may arise, e.g.,
between water infiltration and gas venting. A scheme is proposed for estab-
lishing functional priorities and in turn for weighting the importance of soil
-------
characteristics to allow for most effective selection. Allowance is made for
functional conflicts through design features. Procedures are presented for
designing soil cover systems to meet the'requirements based on principles of
soil mechanics and the state of the art in soil construction. Accordingly,
this manual is not so much a review of current methods as it is a guide to
potentially the best practice.
BACKGROUND
Preliminary investigations for solid waste disposal operations are sum-
marized briefly here, whereas a review of all aspects of solid waste disposal
in sanitary landfills is available elsewhere.3»4 During preliminary investi-
gations the potential sites are chosen and the local geology is determined.
The subsurface may be explored at two or three most likely sites. Subsurface
exploration is accomplished by trenching or boring, and soil samples are
usually obtained for laboratory testing. Preliminary investigations can be
particularly important to hazardous waste disposal in view of the serious con-
sequences of leakage.
One purpose of preliminary site investigations is to ascertain the sub-
surface conditions of each potential site. The geology should be favorable to
minimizing the environmental impact of the disposal project on surrounding
water supplies, i.e., not significantly altering water quality. Another pur-
pose locally is to evaluate supportive qualities of the foundation soil where
the cover side slope constitutes a dike retaining potentially unstable waste.
Subsurface exploration should provide soil samples representative of the soil
types and stratification. Final site selection is ordinarily based on the
type of waste disposal area (e.g., landfill versus trench operation), favor-
able topography, favorable geological and groundwater conditions, public ac-
ceptance, and availability of adequate amounts of cover materials with neces-
sary properties for minimizing objectionable environmental effects.
Geologic and subsurface sampling and exploration may also be conducted on
potential off-site borrow areas, which might provide suitable soil for cover.
Investigations should be sufficient to define the soil types and quantities
and natural water contents. Laboratory testing may also include classifica-
tion and compaction tests and, if necessary, tests for permeability and
strength properties in compacted samples.
SOIL CLASSIFICATION SYSTEM
A soil classification system categorizes soil according to general, but
somewhat arbitrary, groups possessing similar properties. These properties
may be from an engineering or an agricultural point of view.
Currently, soils used in solid waste disposal design and construction are
classified5 according to either the Unified Soil Classification System (USCS)
or the U. S. Department of Agriculture (USDA) Classification System. The USCS
(Figure l) is engineering oriented; soils are grouped according to gradation
of particle sizes; to percentages of gravel, sand, and fines; and to plas-
ticity characteristics. The USDA system (Figure 2) classifies on the basis of
texture only, i.e., percentages of gravel, sand, silt, and clay. Figure 3
-------
emphasizes the grain-size differences between the USDA and USC systems. Fig-
ure k presents relationships between the two systems based on laboratory tests
on hundreds of soil samples. Simplified listings of classification inter-
changeability are given in Tables 1 and 2.
A nationwide study5 of soils being used for covering solid waste obtained
a sample that clearly suggests their diversity. Sixty-three cover soils (or
sets of samples) from sanitary landfills were collected and tested in the
laboratory. The objective of sampling was to develop a nationwide cross sec-
tion of usable soil, but no statistical representation of relative importances
was intended. The frequency of occurrence in this study was as follows:
Soil Type
GP
GM
SW
SW-SM
SP
SP-SM
SM
Occurrences
1
2
5
5
1
1
16
Soil Type
SM-SC
SC
ML
CL
OL
MH
CH
Occurrences
1
2
5
15
1
2
k
Two other soils not classified are probably CL by description.
Twenty of the 3^ coarse-grained soils were gravelly though this component
was not always explicitly included in the USCS designation. The scarcity of
soils designated GC and SC is considered to be misleading since these soils
are usable and fairly common.
Adding to the complexity is the occurrence of more than one soil type at
a site, with attendant complexities from mixtures or heterogeneity. Also,
some variability in important characteristics within one type may be expected.
Refer to COVER COMPACTION in Section 5 for further discussion of variability
of soil manifested in variable compaction test results.
NATURE OF SOLID WASTE
Solid wastes range over a considerable spectrum; and a manual such as
this, applicable to all types, is necessarily lengthy and complicated. For-
tunately, the designer of a cover for a specific site can usually narrow his
range of interest to one of several solid waste types and can gloss over cer-
tain other parts of this manual that obviously are inapplicable. Four logical
classes of solid waste from an engineering viewpoint are solid municipal,
high-solids industrial, saturated industrial, and rubble wastes. Hazardous
waste in barrels or other rigid containers constitutes a fifth class with
special problems requiring special attention.
Solid municipal waste (excluding sewage sludge) comes directly from home
and business collections and consists of a mixture of materials of great di-
versity. Table 3 shows approximate makeup of typical municipal waste. In
greater detail one might find tree branches, auto tires, partially filled
-------
Major Divisions
1
Fine-gnilned Soils Coarse -grained Soils
Itorc than half of material Is smaller than No. 200 sieve size.) More than half of material la larger than Ko. 200 sieve size.
smallest particle visible to the naked eye.
s
4J
a
S
a
t
V
i
s.
£
2
Gravels
tore than half of coarse fraction
is larger than Ho. b sieve size.
-la. elce nay be used as equivalent
slews size)
SandB
More than h^f of coarse fraction
la saaller than Ro. U sieve sire.
(For visual classification, the I/1*
to the Ho. 4
5S
S»T
w
s,is«
^ r* t> 5 *<
n'»
ih~.
l°s
fal
lag
o<^
3 1«I
»! u||
l^i^
11
A ~Z
0 m a
* -1
; i.
8 3»
R. S3,
a ~ a
i'!.
. ss
.3 &*
S 31.
Highly Organic Soils
Group
Symbol a
3
CW
OP
OX
OC
sv
SP
m
sc
ML
CL
OL
m
CH
OB
Pt
Typical Names
l>
Well -graded gravels, gmrel-aand mixtures,
little or no floe«.
Poorly graded grmvela or gravel-mand mlxtureB
little or DO fines.
Silly gravels, gravel-eand-sllt mixture.
Clayey gravela, gravel -eaM -clay mixtures.
Hell-graded sands, grove lly sands, little or
no fines.
Poorly graded sands or gravelly sands, little
or no flail.
Sllty aanda, sand-silt mixtures.
Clayey aands, sand-clay mixtures.
iDorgaolc eilts and very flue amnda, rock
flour, sllty or clayey fine aanda or
clayey silts vltb alight plasticity.
Inorganic clays of lov to uedlua plasticity,
gravelly clays, aaady clays, allty clays,
lean elaya.
Organic allta and organic allty claya of lov
plasticity.
Inorganic elite, mieaeeou. or dlatomeeoua
fine sandy or allty soils, elastic silts.
Inorganic claya of high plasticity, fat claya.
Organic clays of medium to nigh plasticity,
organic allta.
Peat and other highly organic soils.
Field Identification Procedural
(Excluding particles larger than 3 in.
and basing fractions on estimated wights)
5
Wide range In grain slice and substantial
aaounta of all Intermediate particle sizes.
Predominantly one size or a range of alzes with
sane Intermediate sizes missing.
nonplastic fines or flnea with lov plasticity
(for* ideotlflcatlon procedures see ML belov).
Plastic flnas (for Identification procedures
see CL belov] .
Wide range In grain size and substantial amounts
of all Intermediate particle sizes.
Predominantly on site or a range of alias
vltb some Intermediate alias missing.
RonplABtln flnaa or floea vltb lev plasticity
(for IdeDtlfloatlon procedures see ML belov).
Plastic fines (for identification procedurea
see CL belov) .
Identification Procedures
on Traction Smaller than Bo. liO Sieve Size
Dry Strength
(Cruahlng
characteristics)
Rone to alight
Medium to high
Slight to
medlua
Slight to
medium
High to very
high
Helium to high
Dllatancy
(Reaction
to abating)
Quick to alov
Rone to very
slcv
Slav
Slov to none
Rone
Rone to very
alov
Toughness
(Consistency
near PL)
Hone
Medium
Slight
Slight to
medium
High
Slight to
medium
Readily Identified by color, . odor, spongy feel
and frequently by fibrous texture.
(1) SollB possession characteristics of tvo groups are designated by coabinatlons of group symbols. For einsple Gtf-CC, veil-
graded gravel-sand aUture vlth clay binder. (2) All sieve sizes on this chart are'U. S. standard.
FIELD IDENTIFICATION PROCEDURES FOR FIUE-GRAIKED SOILS OR FRACTIONS (MINUS KO. Uo SIEVE)
Screening la not Intended; aimply remove by hand the coarse particles that Interfere with tests.
Dilatancy ^reaction to shaking). After removing particles larger than NQ. bQ sieve size, prepare a pat of moist soil vlth 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 pals of one hand and shake horizontally, striking vigorously against the other hand several times. A
positive reaction consists of the appearance of vater on the surface of the pat vhlcb 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 voter 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. ' ^
Dry Strength (crushing characteristics). After removing particles larger than No. 1*0 sieve sUe, mold a pat of soil to the consis-
tency of putty, adding water if necessary. Allow the pat to dry coapletely by oven, cun, or air-drying, and then test its
Figure 1. Summary of the USC system.
(continued)
-------
Information Required for
Describing Soils
6
For undisturbed soils add info nut Ion
on stratification, degree of compact*
nets, cenentation. moisture conditions,
and drainage characteristics*
Give typical naae; Indicate approximate
percentages of eand and gravel, oaxl-
otuB size; angularity, urface condi-
tion, and hardness of the coarse
grains; local or geologic naate and
other pertinent descriptive informa-
tion; and syibol ID parentheses.
Kxaaple:
Sllty sand, grawlly; about £00 hard,
angular gravel particles 1/2 -In.
latin site; rounded and aubangular
and grains, coarse to fine; about 15$
nonplastic flnea with low dry strength;
well compacted and volat In place; al-
luvial sand; (SIl).
for undisturbed soils add inforoation
on structure, stratification, con-
sistency In undisturbed and re-
olded states, aolsture and drain'
agt conditions.
Give typical nane; indicate degree and
character of plasticity; aaount and
MTlsna size of coaree grains; color
in vet condition; odorr If any; local
or geologic oaoe and other pertinent
descriptive Inforaatlon; and ayabol
In parentheses.
Example;
Clayey silt, brown; slightly plastic;
snail percentage of fine aand;
numerous vertical root holes; fira
and dry in place; loess j (ML).
laboratory Classification
Criteria
7
tions ao given under field Identification.
I
?
a
a
a
I
1
Determine percentages of gravel and sand from graln-slie -curve.
Depending on percentage of fines (fraction nailer than Ho. 2OO
sieve size) coarse-grained soils are classified as follows:
Less than 5* - CV, OP, SV, SP,
Ibre than 12* - CM, X, SM, SC.
50 to 12% Borderline eases requiring
use of dual symbols
Dfio
Cu ° ^ Greater than U
^\. cc " fa ^° P Between 1 and 3
Rot oeetlng all gradation requirements for Ctf
Atterberg llalts below "A" line Above "A" line vlth
or PI less than k PI between U and 7
are borderline cases
requiring use of dual
Atterberg llalts above "A" line syabolc.
vlth PI greater than T
cu
Dfio
~ Creator than 6
B10
Hot neetlng all gradation requlreoenta for SW
Atterberg limits below "A" line Above "A" lire- vlth
or PI less than fc W butvuui fc and 7
are borderline cases
requiring uae of dual
svabols.
Atterberg llalts above "A" line
vlth PI greater than 7
60 i 1 1 1 1
r-
~ Coopa
Toug
5O vlt
£ 30
1 1 1
ring Soils at Equal
iness and Dry Strenc
n Increasing Plastic
«j 20
£ " n,
10 7^-
1
I.fljlllrt Mult J^"
'th Increase >
1 CB- 7^- 1
S A Kn.
7^- OH
'- . i
0 10 ' 20 30 UO 50 60708090100
ii«nx LOOT
pusncmr CHART
Pbr laboratory classification of fine-grained aolla
strength by breaking and crunbltog betveen the fingers. This strength Is a ceaoure of the character and quality of the colloi-
dal fraction contained In the ooil. The dry strength Increases vlth increasing plasticity.
High dry strength ID character!otic of claya of the CH group. A typical Inorganic ollt poaaeoaeo only very slight dry strength.
Sllty fine ouida and silte have about the saoe slight dry strength, but can be dlstinguiohed by the feel when powdering the
dried opedj&en. Fine o&nd feels gritty vhereao a typical ollt has t.he nrjaoth feel of flour.
Toughneoa (consiotency near plastic Halt). After partlcleo larger than the no. &0 oleve aize are renoved, a opecioen of ooll
about one-half Inch cube In olze lo molded to the conslotency of putty. If too dry, voter ouot be added and if sticky, th?
specimen should be spread out In a thin layer and alloved, to looe oorae noloture by evaporation. Then the specimen lo rolled
out by hand on a ooooth ourface or between the pa-lno into a thread about one-eighth Inch In diaceter. The thread ig then
folded and rerolled repeatedly. During this manipulation the moisture content is gradually reduced and the specimen otiffeno.
finally looeo ito plaoticlty, and crunbleg when the plaotic llnlt lo reached.
After the thread cru&bleo, the pieceo ohould be lintped together and A slight kneading action continued until the lunp crunbleo.
The tougher the thread near the plastic Unit and the otlffer the lunp vhen it finally crunbleo, the core potent io the colloi-
dal clay fraction in the soil. Weakness of the thread ut the plastic limit and quick loss of coherence of the lump belov the
plaotic Unit indicate either Inorganic clay of low plasticity, or aaterialo ouch aa Kaolin-type claya and organic clays which
occur btlow the A-lin*.
Highly organic clayo have a very weak and opongy feel at the plastic limit.
Figure 1. (continued)
-------
100
9
St-nid 7.0 lo 0.05 mm, diameter
Silt 0.05 to 0 002 mm diameter
Cloy smaller than 0002 mm. diameter
100 VO 80 70 60 50 40 30 20 10
100
Figure 2. USDA textural classification chart.
Sieve openings in inches
3 2 l'/2 1 % Yz
10
U.S. Standard Sieve Numbers
20 40 60 200
1 1 1 1 1 1 1 1
USDA
uses
uu
GRAVEL
II 1 1 1 II 1 1 1
SAND
Very! I 1 Very
coarseF00"6! We 1 fine
SILT CLAY
GRAVEL
Coarse Fine
SAND
Coarse
Medium Fine
SILT OR CLAY
1 1 1 1 1 MINI 1 1 1 1 1 II
III II
100 50
10
1 T 0.42 0.25 0.1 / 0.05 0.02 0.01 0.005
0.5 0.074
Grain size in Millimeters
0.001
Figure 3. Comparison of USCS and USDA particle-size scales.
-------
LEGEND
yt
'LOAM\ US DA TYPE
PER CENT SAND
Figure k. USCS soils superimposed on the USDA textural
classification chart." (Correlations are
only approximate.)
-------
TABLE 1. USDA TEXTURAL TYPES CORRESPONDING TO USCS SOIL DESIGNATIONS
USCS Soil TypeUSDA Soil Types~
GW Same as GP (except well graded in grain sizes)
GP Gravel, very gravelly sand (less than 5 percent
silt and clay)
GM Very gravelly sandy loam, very gravelly loamy
sand, very gravelly silt loam, very gravelly
loam
GC Very gravelly clay loam, very gravelly sandy
clay loam, very gravelly silty clay loam, very
gravelly silty clay, very gravelly clay
SW Same as SP (except well graded in grain sizes)
SP Sand, gravelly sand (less than 20 percent very
fine sand)
SM Loamy sand, sandy loam; sand; gravelly loamy
sand and gravelly sandy loam
SC Sandy clay loam, sandy clay; gravelly sandy
clay loam and gravelly sandy clay
ML Silt, silt loam, loam, sandy loam
CL Silty clay loam, clay loam, sandy clay
OL Mucky silt loam, mucky loam, mucky silty clay
loam, mucky clay loam
MH Silt, silt loam (highly elastic, micaceous or
diatomaceous)
CH Silty clay, clay
OH Mucky silty clay
PT Muck, peat
Note: Modified from Reference 5; see Figure 1 for additional descriptive
information.
-------
TABLE 2. USCS SOIL TYPES CORRESPONDING TO USDA SOIL TERMINOLOGY
USDA Soil TypeUSCS Soil Type
Gravel, very gravelly loam sand GP, GW, GM
Sand SP, SW
Loamy gravel, very gravelly sandy GM
loam, very gravelly loam
Loamy sand, gravelly loamy sand, sand SM
Gravelly loam, gravelly sandy clay GM, GC
loam
Sandy loam, gravelly sandy loam SM
Silt loam, sandy clay loam (with fine- ML
grained sand)
Loam, sandy clay loam ML, SC
Silty clay loam, clay loam CL
Sandy clay, gravelly clay loam, SC, GC
gravelly clay
Very gravelly clay loam, very gravelly GC
sandy clay loam, very gravelly silty
clay loam, very gravelly silty clay
Silty clay, clay CH
Muck, peat PT
Note: Modified from Reference 5«
-------
TABLE 3. APPROXIMATE COMPOSITION OF MUNICIPAL
SOLID WASTE
Description
Paper (including cardboard)
Garbage
Glass /ceramics
Grass/dirt
Metal
Plast ic /rubber /leather
Wood
Plastic film
Cloth
Total
Weight Percent
ko
20
10
10
5
5
5
3
2
100
plastic and paper bags, and garbage beginning rapid decomposition. The mix-
ture is very poorly amenable to description in quantitative terms except that
it commonly arrives on site at a low unit weight and is changed in one or more
of the following steps:
Unit Weight
Ib/yd3
From noncompacting garbage trucks 500
From compactor garbage trucks 600-700
7
After average compaction on dump 750-850
After extra compaction 1000
Maximum likely on dump (before
long-term settlement) 1200
Obviously, the ultimate settlement can be large although 90 percent oc-
curs within 2 to 5 years." In special cases, the waste may be milled or
shredded to achieve ultimately densities0-510 of 1^00 to 1600 Ib/yd3 and reduce
differential settlement. Baling (after compacting) is another special pro-
cedure achieving uniform, high initial density.
Disposal of bulk industrial solid wastes presents engineering problems of
a more conventional nature. Solids are usually uniform and fine in texture,
10
-------
and properties can "be determined by laboratory testing. The extent of
engineering studies will be governed by the pollution potential, with toxic
materials receiving high priority. Special effort may be needed for designing
retaining dikes, a part of the cover in this manual. Problems with differen-
tial settlement of industrial waste with consequent disruption of the cover
will not be major ordinarily.
Saturated industrial solid wastes often settle mechanically like con-
solidating soil, and their behavior is predictable.H Likewise, drainage and
settlement can be hastened by certain construction techniques. However, some
industrial slurries have poor qualities, besides an enduring potential for
serious pollution and, by virtue of a colloidal nature, may remain for years
in a saturated condition with a very high water content.
11
-------
SECTION 2
REQUIREMENTS OF COVER ON SOLID WASTE
A common requirement in sanitary landfilling has been that a layer of
earth "be placed over the compacted solid waste after each day's operation.
Most solid waste disposal operations also employ a final, thick soil layer for
long-range cover after completion of the operation. A membrane or other syn-
thetic material is sometimes used in place of soil. Intermediate covers are
also distinguished for surfaces exposed for long periods "but eventually buried
by subsequent solid waste lifts. The cover (soil or other material) serves
important functions under the general classification of health, aesthetics,
and site usage.
COVER FUNCTIONS
The specific functions of cover on solid and hazardous waste sites as
determined by the Office of Solid Waste, U. S. Environment Protection Agency
(EPA) are outlined below:
a. Health considerations.
(l) Minimize vector breeding areas and animal attraction by
controlling:
(a) Fly and other insect emergence and entrance.
(b) Rodent burrowing for food and harborage.
(c) Bird and animal attractiveness.
(2) Control water movement to:
(a) Minimize moisture infiltration, or
(b) Maximize moisture infiltration.
(c) Minimize final cover erosion.
(3) Control potentially harmful gas movement by:
(a) Minimizing gas movement, or
(b) Maximizing gas movement.
12
-------
(M Minimize fire hazard potential by:
(a) Controlling movement of atmospheric oxygen.
(b) Providing barrier cell walls.
b. Aesthetic considerations.
(l) Minimize blowing paper.
(2) Control noxious odors.
(3) Provide sightly appearance to the landfill operation.
c. Site usage considerations.
(l) Minimize settlement and maximize compaction to:
(a) Assist vehicle support and movement.
(b) Insure equipment workability under all weather conditions.
(c) Provide for future construction.
(2) Provide for vegetative growth.
Several other functions can be added and will logically fall under the head-
ing, "Health considerations" or "Site usage considerations," as follows:
a. Minimize wind erosion and dust generation.
b. Resist cold climate deterioration and operational difficulties.
c. Preserve slope stability.
d. Resist cracking.
e. Dewater solid waste.
Within the complete list, a few functions stand out as primary, while the
others are usually secondary. Primary functions are more or less independent
of others and concern such landfill processes as movement of water and gas and
susceptibility to erosion. Secondary functions are considered here to restate
primary functions but viewed in a different sense. An example of a secondary
cover function is fire resistance; resistance to fire is contingent upon
satisfactorily impeding air or gas migration, a primary function. Similarly,
slope drainage (and side slope stability) is a secondary or somewhat different
way of looking at the primary function, assisting water percolation
(infiltration).
The physical characteristics of the cover that are basic to the primary
cover functions and are also involved in most of the secondary functions are
13
-------
the conductivity to vater, conductivity to gas, shear strength, and tensile
strength (or capillary potential).
FUNCTIONAL PRIORITIES
The functions as listed above are straightforward, but in actuality cover
functions are complexly interrelated; for this reason, it should "be understood
that designing solid waste cover involves considerable subjective judgment. A
ranking of priorities is necessary in arriving at a determination of which
functions are most important at the specific site and in designing features to
compensate for adverse side effects on other cover functions. For example, a
cover that functions to impede infiltration and percolation of water from the
surface will also impede upward movement of decomposition gases. If gases are
to be moved through the cover to minimize lateral movement, a gas vent system
may be required. A brief hypothetical scenario illustrates the problem of
conflicting functions and suggests the priorities approach recommended here.
Suppose that it has been determined that cover for a disposal area re-
ceiving hazardous chemical wastes must not only serve all of the usual func-
tions but have special effectiveness in preventing the generation of dust in a
region prone to high wind velocity. Suppose that the powdery waste is damp
upon arrival at the area but that it dries quickly in the semiarid climate.
Finally, suppose that the area is usually subjected to a two-month rainy sea-
son in which much of the 15-in. annual precipitation is concentrated.
First priorities for most of the year would be wind erosion resistance
and dust control with water infiltration control and other functions following
in progressively lower rankings; this is assuming that there are no other par-
ticular hazards such as flammability or generation of toxic gas. Control of
animals and aesthetic considerations usually fall low in the ranking because
they are insensitive to particulars on the choice of soil type. The problem
of air pollution by toxic dust particles is solved by specifying that the
daily cover shall consist of sand, which by its coarse grain size will resist
wind erosion and shall be at least 12 in. in thickness, extra thickness assur-
ing complete shielding of an irregular surface of waste. The infiltration of
rainwater largely takes place in the short rainy season; therefore, specifica-
tions should require that all intermediate cover exposed during the rainy
period shall include, if practical, a 6-in. layer of compacted clay below
6 in. of sand. Finally, it may be specified that certain dust palliatives or
water be applied during disposal operations to prevent drying and dust genera-
tion by traffic erosion.
SATISFYING REQUIREMENTS AND USING THIS MANUAL
Thi-s manual (Figure 5) provides guidance on satisfying the functional
requirements of cover on solid/hazardous waste. In Section U, the general
procedure for selecting soil for cover is presented with heavy reliance on a
summary tabulation of soil ratings for the various functions. Section 5 re-
views all aspects of placement and treatment of cover soil. Section 6 pro-
vides information on nonsoil cover materials available for special conditions
or especially stringent requirements (particularly to impede water or gas
lU
-------
INTRODUCTORY GENERAL DETAILS AND
SECTIONS RECOMMENDATIONS EXPLANATIONS
22
Figure 5- Manual section organization and use.
movement). Section J summarizes the overall plan for developing a solid waste
cover system.
Sections 8-22 (Figure 5) present the details of each cover function,
review pertinent characteristics of soils and other materials, and propose
specific design methods taken from the present state of the art of waste dis-
posal or adapted from general soils construction. It may be necessary to con-
sult the appropriate section, 8-22, for clarification of generalizations and
terminology used in Sections k and 7 . This introduction of the summary and
recommended methods before the exposition and details is considered to be the
more effective organization of the manual. Alternately, it is equally appro-
priate to consider details function by function before Sections 3-7 « In this
way, the reader becomes familiar with the important characteristics of soil
before they are used for ranking cover effectiveness.
A third way in which this manual can be used is to improve or make more
specific the covering procedures already in practice. In this instance, the
user will likely find Sections 3-7 to constitute a useful summary, but he may
then proceed (Figure 5) to the section or sections dealing with his specific
cover problems. Specific needs may be precipitated by economic considera-
tions. For instance, it may be that the soil type usually required by local
regulations is not available except at great expense; therefore, assistance is
needed in determining an adequate substitute, e.g., in assuring that noxious
or flammable gases are controlled until the landfill is stabilized. In such a
case, the reader would find guidance on substitute soils and design features
in Sections 9 and 17 and on other covers in Section 6.
-------
SECTION 3
SOIL PROPERTIES AND TESTING
This section summarizes concepts and testing procedures of soil mechanics
and geology sufficiently to understand and describe the use of soil for cover-
ing solid waste. Much of the presentation has been adapted from Reference 12,
but numerous other references on soil mechanics also provide the detailed in-
formation for close study. Designations prefixed ASTM refer to standard pro-
cedures of the American Society for Testing and Materials to which the reader
may also refer; ASTM and Reference 12 procedures are not necessarily
identical.
Information is applicable to disturbed or undisturbed natural soil in the
foundation or in the borrow area and to soil in place as cover on solid waste.
As in all soil engineering, it is important that the designer have his objec-
tive clearly in mind when he assigns specific tests, e.g., for general index-
ing or for water content as placed in cover, etc.
GENERAL RELATIONS
A soil mass is considered to consist of solid particles between which are
voids of various sizes, which are filled with gas (air) and water. The funda-
mental relations of weights and volumes of the components of a soil mass can
be derived using the schematic sketches shown in Figure 6. Some of the more
important relations used in soil engineering calculations are unit weights
(densities), void ratio, porosity, and degree of saturation. The quantities
WOOHT
VOLUME
W
AIM
WATCH
'QUO
fj***j
MOIST SOIL
WOOHT
W
WATCH
TT
Vw Vv
WATER CONTENT
W =
vw
0=
V
ws
V DRY UNIT WEIGHT (DRY DENSITY) yd =
Vt
SATURATED SOIL
VOID RATIO
POROSITY
NOTE: UNIT WEIGHT OF WATER, y = 62.4LB/FT. DEGREE OF SATURATION
e =
n =
v
v.
s =
_e
+ e
Figure 6. Fundamental relations in soil.
16
-------
that must be known to compute these relations are the weight and volume of the
wet specimen, the weight of the same specimen after oven-drying, and the spe-
cific gravity of the solids. 12 The weights of the specimens usually can be
obtained without difficulty. The volume of the wet specimen is determined by
linear measurement (volumetric method), or by measurement of the volume or
weight of water displaced by the specimen (displacement method). See Refer-
ence 12 for laboratory procedures. ASTM D 85^ prescribes a method for deter-
mining specific gravity. Definitions are as follows (also see Figure 6):
a. Dry unit weight Yd or dry density is the weight of oven-dried soil
solids per unit of total volume of soil mass and is usually expressed
in pounds per cubic foot.
b. Wet unit weight Ym or we"t density is the weight (solids plus water)
per unit of total volume of soil mass, irrespective of the degree of
saturation (see below). The wet unit weight is usually expressed in
pounds per cubic foot.
c. Void ratio e is the ratio of the volume of voids to the volume of
solid particles in a given soil mass.
d. Porosity n is the ratio (usually expressed as a percentage) of the
volume of voids of a given soil mass to the total volume of the soil
mass.
e. Degree of saturation S is the ratio (usually expressed as a per-
centage) of the volume of water in a given soil mass to the total
volume of voids.
An important component of soil is its water content, which in soil
mechanics is designated w and defined as the ratio (usually expressed as a
percentage) of the weight of water in a given soil mass to the weight of solid
particles. Water content is also quantified as 0 the ratio of volume of
water to the total volume of the given soil mass; in fact this definition is
preferred in some fields other than soil mechanics. Water content is rou-
tinely determined in the laboratory by weighing the soil specimen before and
after drying in an oven to constant weight at 110 +_ 5°C (ASTM D 22l6) Rela-
tions in Figure 6 indicate that volumetric water content may be expressed as
0 = nS (1)
Other relationships among the measured quantities-^ allow Equation 1 to be
extended to the following useful expression in the nonpercentage form
wy
where YW ^s unit weight of water.
GRAIN-SIZE ANALYSIS
Grain-size analysis is a process in which the proportion of each grain
IT
-------
size present in a given soil (grain-size distribution) is determined. Fig-
ure T displays in the usual way the distributions of grain sizes for seven
representative soils . Grain-size distribution of coarse-grained soils is
determined directly by sieve analysis, while that of fine-grained soils is
determined indirectly by hydrometer analysis. Sieve and hydrometer analyses
(ASTM D 422) are used in combination for mixed soils.
Sieve Analysis
A sieve analysis consists of passing a dried sample through a set of
sieves and weighing the amount of material retained on each sieve. Sieves are
U S. STANDARD SIEVE OPENMG IN INCHES U. S. STANDARD SIEVE NUMBERS
432 I 3 4 6 « 10 1416 JO 30 40 50 70 IOC 140 200
HYDROMETER
0.5
GRAIN SIZE IN MH.UMETERS
GRAVEL
CCMKI | not
SAND
co« 1
KOMI 1
me
SH.TORCLAY
SAMPLE NO.
1
2
3
4
5
6
7
ELEVATION
OR DEPTH
MISSION CANYON,
CALIFORNIA
TACOMA, WA
HAZLEHURST, MS
CENTRA LIA.WA
VICKSBURG, MS
KENT HIGH LANDS,
WASHINGTON
DALLAS, TEXAS
(WALNUT HILLS)
CLASSIFICATION
SANDY GRAVEL (GP)
GRAVELLY SAND (SW)
CLAYEY SAND (SC)
SANDY SILTY CLAY (CL)
SILT (ML)
CLAYEY SILT (ML)
FAT CLAY (CH)
NATW%
10.8
3.0
12.0
30.5
18.0
27.3
34.9
LL
PL
NON-PLASTIC
NON-PLASTIC
21.0
40.0
30.0
33.1
68.0
12.0
21.0
26.0
24.7
27.0
PI
9.0
19.0
4.0
8.4
41.0
Figure T. Gradation curves of some sanitary landfill cover soils
(from Reference 5 and this study)
18
-------
constructed of wire screens with square openings of standard sizes. The sieve
analysis is performed on material retained on a U. S. Standard No. 200 sieve.
The sieve analysis, in itself, is applicable to soils containing a small por-
tion passing the No. 200 sieve provided the grain-size distribution of that
portion is not of interest. The percentage of material "by weight retained on
the various sieves is computed as follows:
Percent retained =
weight retained on a sieve
total weight of oven-dried sample
x 100
Hydrometer Analysis
The hydrometer method of analysis is based on Stokes1 law, which relates
the terminal velocity of a sphere falling freely through a fluid to the diam-
eter. It is assumed that Stokes1 law can be applied to a mass of dispersed
soil particles of various shapes and sizes. The hydrometer is used to deter-
mine the percentage of dispersed soil particles remaining in suspension at a
given time. The maximum grain size equivalent to a spherical particle is
computed for each hydrometer reading using Stokes1 law. The hydrometer
analysis is applicable to soils passing the No. 10 sieve for routine classi-
fication purposes; when greater accuracy is required (such as in the study of
frost-susceptible soils), the hydrometer analysis should be performed on only
the fraction passing the No. 200 sieve.
ENGINEERING INDICES
The Atterberg limits are standardized index water contents used to define
the various states of consistency for fine-grained soils. Important states
from a geotechnical standpoint are shown in Figure 8. For testing procedures,
see Reference 12 or ASTM D 1*23 and D 1*2U.
INCREASING MOISTURE CONTENT ^-
SOLID
SEMISOLID
PLASTIC
SEMILIQUID '
SHRINKAGE
LIMIT
PLASTIC
LIMIT
LIQUID
LIMIT
Figure 8. States of consistency of soil.
Liquid Limit
The liquid limit (LL) of a soil is the water content, expressed as a
percentage of the weight of oven-dried soil, at which two halves of a soil pat
separated by a groove of standard dimensions will close at the bottom of the
groove along a distance of 1/2 in. under the impact of 25 blows in a standard
LL device. The LL represents the boundary between plastic and semiliquid
conditions.
The LL device holds the soil pat in a brass cup, which is raised and then
dropped (10 mm) by a crank and cam onto a block of resilient material. The
19
-------
cam must be shaped so that the height of the cup is maintained constant for a
short section at the end of the turn rather than rising continuously to the
point of release. The LL is determined from four tests at different water
contents by plotting water content versus number of blows to closure (semi-
logarithmic). The intersection of a straight line through the test points and
the 25-blow line on the graph gives the LL.
Plastic Limit
The plastic limit (PL) of a soil is the water content, expressed as a
percentage of the weight of oven-dried soil, at which the soil begins to
crumble when rolled into a thread 1/8 in. in diameter. The PL represents the
boundary between plastic and semisolid conditions.
In the test procedure take 2 to 5 gm of the same material used for the LL
test at any stage of drying at which the mass becomes plastic enough to "be
shaped without sticking. Shape into an ellipsoidal mass and roll into a
thread carefully. When the diameter of the thread becomes 1/8 in. without
crumbling, fold and knead the thread into a ball again and repeat the rolling
process. When this process has dried the soil to the point where the thread
will break into numerous pieces having a diameter of 1/8 in. and about 1/8- to
3/8-in. length, determine the w to obtain PL.
Plasticity Index
The difference between LL and PL is the plasticity index (Pi). The PI
indicates the range of plasticity of the given soil, and generally, the higher
the PI, the greater the plasticity.
Shrinkage Limit
The shrinkage limit (-SL) of a soil (remolded) is the water content, ex-
pressed as a percentage of the weight of the oven-dried soil, at which further
loss in moisture will not cause a decrease in its volume. In determining SL,
accurate measurements of volume are critical. Reference 12 describes the
recommended mercury displacement technique. The SL represents the boundary
between semisolid and solid conditions.
AGRICULTURAL INDICES
Soil chemistry and water storage are important considerations in planning
for support of vegetation.
Water Storage
The availability states of water in soil have fundamental importance in
agriculture, and an understanding of the concept is helpful in selecting and
designing solid waste cover. One can distinguish bound water, available
water, and gravitational water for a given soil according to availability for
use by plants (Figure 9) Boundaries of these simplistic states of water are
defined by two quantities that can be determined using apparatus for measuring
soil suction pressure (negative or tension pore pressure), but such tests are
20
-------
GRAVITATIONAL
WATER
SAND
FINE SANDY
SAND LOAM
FINE
SANDY
LOAM
LOAM SILT CLAY HEAVY
LOAM LOAM CLAY
LIGHT LOAM
CLAY
LOAM
CLAY
Figure 9- Water-holding characteristics of USDA soils.
not undertaken ordinarily for cover design. Actually, the conditions will
probably change as vegetation becomes established. Estimations based on soil
type are used instead (Figure 9)-
Field capacity. Field capacity is the maximum water content retained in
soil without draining "by gravity, i.e., the storage capacity for capillary
water. In order to standardize this somewhat arbitrary point, agronomists use
the soil suction pressure of 0.33 atmospheres.
Wilting point. Wilting point is the lower limit of plant utilization of
capillary water. The soil suction pressure at this point is 15 atmospheres by
definition.
Soil Chemistry
A review of soil characteristics that are important to the support of
vegetation is given under SOIL FACTORS in Section 19. These characteristics
mainly concern soil chemistry and particularly the contents of nutrients and
the pH of pore water.
21
-------
COMPACTION TESTS
The laboratory compaction procedure is intended, to simulate the com-
pactive effort anticipated in field construction. A standard, 25-blow compac-
tion test (also called the standard Proctor test) is used to simulate field
compaction for most routine foundation and embankment design. To simulate
solid waste cover placement, it is appropriate to use lower compactive ef-
forts. Five- and fifteen-blow compaction tests are recommended here for
municipal solid waste. Compaction tests are made on a soil at various water
contents to establish a relation between water content and unit weight of the
compacted soil.
Standard (25-Blow) Compaction
The standard method apparatus consists of a cylindrical metal mold (Fig-
ure 10), with detachable collar approximately 2-1/2 in. high, that can be
fastened firmly to a detachable baseplate. A U-in.-diam mold is used for com-
pacting samples composed entirely of material passing a No. k sieve. A 6-in.
mold is used for compacting samples containing material retained on the No. k
sieve and passing the 3/^-in. sieve.
The metal hand rammer (Figure 10) is of the sliding-weight, fixed-head
type having a 2.0 +^ 0.005-in.-diam circular face and a free-falling weight of
5-5 +. 0.02 Ib. The rammer is equipped with a guide for controlling the height
of fall of the sliding weight to the prescribed 12.0 +_ 0.06 in.
Sufficient amounts of the prepared sample are placed in the U-in. mold in
three equal layers to give a total compacted depth of approximately 5 in.
Each layer is compacted by 25 uniformly distributed blows from the rammer; the
energy input during compaction is given in Table k in comparison to other
tests. The standard procedure for soils containing material retained on the
No. h sieve is the same except that the diameter of the test mold is 6 in. and
TABLE k. TEST COMPACTION ENERGY
Compaction
Test
Standard
15-blow
5-blow
Modifiedt
Approximate
ASTM
D 698
-
-
D 1557
Equivalent*
AASHTO
T-99
-
-
T-180
Compaction Input
ft-lb/ft3
12,375
7,^25
2,1*75
56,750
* Other approximately equivalent procedures for standard and modified
compaction tests.
t Not recommended for most solid waste cover testing.
22
-------
r[LD AND AHfVCAL
"
\ /
1.
T
CXACTLY- 'wHfH DffOP IKIGffr
f
'
f
-'
=
_
\ ?
\
UUUUUU'UlJUULlutf J,
ASSEMBLY
MOTf FINISHED LENGTH TO PRODUCE A DROP
© ROD
(?) DROP WEIGHT
'
L
?
\
^TAPfft j *£R rr
st-""
I ' \
' ."
/ ~^
1 J
At
(3) HANDLE
PLAN
ELEVATION
Figure 10. Typical it-in.-diam. compaction mold and sliding-weight
fixed-head rammer for standard compaction test.12
23
-------
the number of blows of the compaction rammer is 56 per soil layer instead of
25. This results in equal compactive efforts for the two molds (Table h).
A sufficient number of test specimens are compacted over a range of water
contents to establish definitely the optimum water content and maximum
density. Generally, five specimens should completely define a compaction
curve. It is sometimes important to store the prepared soil in an airtight
container for a sufficient length of time to permit absorption of moisture
(also refer to ASTM D 698).
Five- and Fifteen-Blow Compaction
The 5- and 15-blow compaction tests differ from the standard compaction
test in that lesser compactive efforts are used (Table k), resulting in lower
maximum densities and higher optimum water contents. The apparatus, prepara-
tion of sample, and procedure are the same as those used in the standard com-
paction test (5-5-lb weight with a 12.0-in. free drop), except that only the
U-in. mold is used and the number of blows per layer is reduced. These tests
appear to give results more like those achieved in compacting cover on munici-
pal solid waste (see Section 5).
Presentation of Test Results
The results of compaction tests are presented in the form of a compaction
curve on a plot of dry densities (dry unit weights) versus the corresponding
water contents (Figure ll). The plotted points are connected with a smooth
too
98
I-
U.
1 96
y.
a
95
94
93
I I I I
SANDY SILTY CLAY (CD
CENTRALIA, WASHINGTON
(SEE FIGURE 7)
ZERO AIR
VOID CURVE
-------
curve; for most soils, the curve approaches a para"bolic form. The water con-
tent at the peak of the compaction curve is designated the optimum water con-
tent. The dry density of the soil at the optimum water content is the maximum
dry density. The zero air void curve (Figure 11) represents the dry density
and water content of the soil completely saturated with water. The curve of
zero air voids should be shown with the compaction curve.
Relative Density
The degree of compactness of a cohesionless (granular) soil is sometimes
expressed in simplified, different terms as percent relative density. The
lower limit corresponding to 0 percent relative density is obtained by pouring
the soil loosely into the container. The upper limit at 100 percent relative
density is reached by tamping and shaking down to a minimum volume. Refer to
ASTM D 2049 for procedures.
PERMEABILITY TESTS
The flow of water through saturated soil is assumed to follow Darcy's law
for laminar flow:
q. = kiA (3)
where q = rate of discharge through a soil of cross-sectional area A at 20°C
k = coefficient of permeability (also called hydraulic conductivity)
i = hydraulic gradient: the loss of hydraulic head per unit distance
of flow
The application of Darcy's law to a specimen of soil in the laboratory is il-
lustrated in Figure 12. The k has the dimensions of a velocity and is
usually expressed in centimeters per second. Permeability depends primarily
on the size and shape of the soil grains, the void ratio of the soil (compac-
tion), the shape and arrangement of the voids, and the degree of saturation.
See Section 8 regarding complications introduced by unsaturated conditions.
Constant-head Test
The simplest method for determining k is the constant-head type of test
illustrated in Figure 12. This test is performed by measuring the quantity
of water Q and the elapsed time t . The head of water is kept constant
throughout the test. For fine-grained soils, Q is small and may be diffi-
cult to measure accurately. Therefore, the constant-head test is used prin-
cipally for coarse-grained soils (clean sands and gravels) with k values
greater than about 10~3 cm/sec.
Falling-head Test
The principle of the falling-head test is illustrated in Figure 13. This
test is conducted in the same manner as the constant-head test, except that
the head of water is not maintained constant but is permitted to fall within
the upper part of the specimen container or in a standpipe directly connected
to the specimen. The quantity of water flowing through the specimen is
25
-------
WATER SUPPLY
OVERFLOW
TO MAINTAIN
CONSTANT HEAD
SCREEN
q = = kiA
WHERE q = RATE OF DISCHARGE
= QUANTITY OF FLOW, Q,
PER UNIT OF TIME, t
k = COEFFICIENT OF
PERMEABILITY
i = HYDRAULIC GRADIENT
= h/L
A = CROSS-SECTIONAL AREA
OF SPECIMEN
GRADUATE
Figure 12. Flow of water through saturated soil.
12
determined indirectly by computation. The falling-head test is generally used
for less pervious soils (fine sands to clays) with k values less than
10~3 cm/sec.
Estimating k
Reliable determination of k in the laboratory requires facilities and
experience not ordinarily expected in organizations charged with designing
cover. Accordingly, the value of k may be estimated. Table 5 provides use-
ful estimates, but some caution should be exercised here since soil structure
and compaction have major effects on k . Generally, agricultural top soils
preserving vestiges of natural aggregate structure and root holes are much
more permeable than freshly reworked or compacted subsoils. By the same
token, some allowance may have to be made for increasing permeability with
time as the cover soil becomes naturalized with vegetation and sod.
STRENGTH TESTS
Site-specific strength data are usually not needed for designing cover;
therefore, the following tests for determining strength under various condi-
tions are not often assigned. Important exceptions are in cases where cover
soil is to provide support to the sloping side of the disposal area (see Sec-
tion 13). Testing may be even more important in evaluating the strength of
the foundation of such retaining covers or dikes. The value of simple
strength indices is shown for predicting operational trafficability in Sec-
tion lU.
26
-------
hc
STANDPIPE
OVERFLOW
'." A '
(a)
(b)
USING SETUP SHOWN IN O), THE COEFFICIENT OF PERMEABILITY IS
DETERMINED AS FOLLOWS:
L, I I
k = TT In;-- = 2.303 7- login-r
At h
At
USING SETUP SHOWN IN (b), THE COEFFICIENT OF PERMEABILITY IS
DETERMINED AS FOLLOWS:
WHERE: h£ = HEIGHT OF CAPILLARY RISE
O = INSIDE AREA OF STANDPIPE
A = CROSS-SECTIONAL AREA OF SPECIMEN
L = LENGTH OF SPECIMEN
h = HEIGHT OF WATER IN STANDPIPE ABOVE
DISCHARGE LEVEL MINUS h AT TIME, t
L CO
h. = HEIGHT OF WATER IN STANDPIPE ABOVE
DISCHARGE LEVEL MINUS h£ AT TIME, t,
t = ELAPSED TIME, t, - t
i O
Figure 13. Principle of falling-head test.
12
-------
FABLE 5. APPROXIMATE AVERAGE PERMEABILITY* AND
Soil Type
Gravel
Sand
Silt
Clay
uses
Soil Type
GP
GW
GM
GC
SP
SW
SM
SC
ML
MH
CL
CH
Coefficient of
Permeability , cm/s
-^- .
ID'1
ID"2
5 x ID'1*
10"^
5 x 10"2
10-3
ID'3
_L \J
2 x W~k
10-5
10"7
3 x 10-8
10~9
1
Capillary
Head , cm
.
6
68
60
112
180
18 0
200 - UOO+
* See effect of compaction in Section"
strength of soil i:
S = c + a tan
(M
where c = cohesion
o = normal stress on the shear surface, and
4> = angle of internal friction (Figure Ik)
By definition, c = 0 for cohesionless soils, such as sand, and intrinsic
strength is entirely reflected in * . With the pore water pressure u taken
into consideration, the criterion becomes
S = c' + (a - u) tan '
(5)
where c' and $' are comparable to c and $ except for being under ef-
fective stress conditions.
Cone Index and Remoulding Index
Relative shear strength of an undisturbed, fine-grained soil can be
evaluated with a cone penetrometer. This instrument employs a 30-deg cone
with 1/2-in. base-end area. The force necessary to push the cone slowly
through the soil is indicated by a dial that ranges from 0 to 300. The value
300 occurs under a force of 150 lb. The measured value, termed cone index
28
-------
S-C+a TANcf>-
in
UJ
Of.
i-
Ul
I
NORMAL STRESS
Figure lU. Graphical criterion of shear strength of soil.
(Cl), is useful as a dimensionless index of strength.
As traffic and other loads act on moist or wet soil, the soil is remolded
further and its strength usually is changed. Remolding index (Rl) procedures,
one for fine-grained soils and another for poorly drained, coarse-grained
soils with fines, have "been devised to quantify this strength change." For
fine-grained soils, an undisturbed sample is taken with a sampler and extruded
into a cylinder mounted on a base. The CI values for the undisturbed soil are
read at the surface and at 1-in. increments to a depth of U in. with the cone
penetrometer. One hundred blows of a 2.5-lb hammer, dropped 12 in., are then
applied, and CI values are obtained in the remolded soil. The RI is deter-
mined by dividing the sum of the five CI readings made after remolding by the
sum of the five readings made before remolding. Coarse-grained soils with
fines are indexed similarly except a different cone size and remolding pro-
cedure are used.
Drained Direct Shear
The direct shear test is used commonly to measure the shear strength of
fine-grained soil^ under drained (effective stress) conditions. A relatively
thin, square block of soil is placed in a rigid box (Figure 15) that is di-
vided horizontally into two frames, the block is confined under a vertical
(normal) stress, and a horizontal force is applied so as to fail the block
along a horizontal plane at its midheight. Generally, a minimum of three
specimens, each under a different normal stress, are tested to establish the
relation (Figure lk) between shear strength and normal stress in terms of ef-
fective cohesion c1 and effective friction angle ' . The magnitudes of
the normal stresses used depend on the range of stresses anticipated for de-
sign. Because of the difficulties involved in controlling soil drainage dur-
ing direct shear, only the S-test procedure12 in which complete consolidation
29
-------
NORMAL FORCE
SHEARING
FORCE
*UPPER
FRAME
.".-.'.. :'. POR.OUS. STONE .' ...'.-.'
;':'..''. -POROUS-: STONE-
Figure 15- Schematic diagram of direct shear "box.
12
is permitted under each increment of normal and shear stress is recommended.
Triaxial Compression
In the triaxial compression test, a cylindrical specimen of soil encased
in a rubber membrane is placed in a chamber, subjected to a confining fluid
pressure (Figure l6), and then loaded axially to failure.12 Controlled drain-
age of pore water may be permitted. Three specimens are usually run under
different confining pressures to establish the relation between shear strength
and normal stress. Prior to shear, the three principal stresses are equal to
= DEVIATOR STRESS
= cr, - a.
"'1 »
' '. p-
I ».
' I »
9>
cr* »
*
»~
-~
HUH
'//////
SOIL
SPECIMEN
CROSS
SECTIONAL
AREA OF
SPECIMEN = A
///////
~* ^3
*
~*
-^- -
-^
Figure l6. Schematic diagram showing
stresses during triaxial
compression test.12
30
-------
the chamber fluid pressure. During shear, the major principal stress o-j_ is
equal to the applied axial (deviator) stress plus the minor principal stress
(chamber pressure) a (Figure l6).
Three basic triaxial compression test procedures are unconsolidated-
undrained, consolidated-undrained, and consolidated-drained, the Q, R, and S
tests, respectively. The procedure is selected to simulate closely, or to
bracket, the conditions anticipated in the field. In the Q test, the water
content of the specimen is not permitted to change during the application of
the confining pressure or during the axial loading of the specimen to failure.
The Q test usually is not applicable to soils that are free-draining, i.e., to
soils having a permeability greater than 10~3 cm/sec. In the R test, complete
consolidation of the specimen is permitted under the prescribed confining
pressure. Then, with the water content held constant (no further consolida-
tion), the specimen is axially loaded to failure. Specimens must as a general
rule be completely saturated before application of the deviator stress. The
S-test procedure allows complete consolidation of the test specimen under the
confining pressure and during the axial loading to failure. Consequently, no
excess pore pressure exists at the time of failure. Also see S test under
Drained Direct Shear.
CONSOLIDATION TEST
When a saturated soil is loaded, consolidation occurs by a slow drainage
of pore water. Consolidation behavior is insignificant in cover soil but can
assume importance occasionally in foundations of retaining slopes and embank-
ments and in the solid waste itself (when saturated). Where either material
is clayey or otherwise drains especially slowly, pore pressure may rise under
the new loading and lead to slope instability or bearing capacity problems
(see Equation 5).
The routine test-^ to quantify consolidation behavior consists of incre-
mentally loading a soil specimen in one dimension in a consolidometer (Fig-
ure 1?) and measuring for each increment the displacement at various elapsed
times up to 2^ hours. Figure 18 shows a record of one increment of loading.
Only the so-called primary consolidation is related to expulsion of water.
Free drainage is necessarily permitted, of course (refer to ASTM D 2^35).
From each displacement-time plot for all load increments, the total dis-
placement at the end of a selected time interval (commonly 2k hours) is ob-
tained. Next, the displacement data are converted to void ratio changes and
related to pressure as in Figure 19. The compression index Cc can then be
obtained for direct use in settlement prediction (see Section 15) a-s indicated
in the figure. Where the e-p plot is curved at the pressure of interest in-
stead of linear, C is the slope of the tangent.
SWELL TESTS
The shrink/swell behavior of fine, clay-rich soils can be excessive in
some regions of the United States, and testing may occasionally be necessary
to evaluate the need for special requirements of design or construction.
31
-------
LOADING PLATE
o POROUS STONE' ' a / *:
»:,«. .'.: ; t '.>. :<;-, '..;.. .a :...'.*'.«. .-'.
SOIL SPECIMEN
. : .-..«: . .»....:. vr- ..».. ;.-..-. ..<
v / . POROUS STONE .-'.to ..:*.-.
" > *. : .:>..,'.:<=. '. .:«....'^yf:; .'*.'; ./' '<>' :'* .
;': .«';: POROUS STONE »-<7'f' ' ,
P; «.*.:. .»-.;«-..-;:.-.v.1.-»:. ..»'....<.'..'.. :'*' '
SOIL SPECIMEN
4 ''.'. '?':' .-'.«'..<. VI-:- . .<7.'-.--»: .<*.. y.:
.'«;'': POROUS STONE. o -.-:.
> : <.«.". ».'.*../: :':«'. ;;4 ''.*.: 4 :?.
i
^*-
BASE
-/7.C
/9W
AT ING
G
b. FLOATING-RING CONSOLIDOMETER
Figure !? Schematic diagrams of fixed-ring and floating-ring
consolidometers.12
Engineering indices are usually very useful for predicting 'such behavior as
explained in Section 18.
In rare cases, swell testing may be deemed necessary by the importance or
size of the covering operation. The swell test is a simple, routine labora-
tory testl5 that provides quantitative information on swell pressure or linear
swell of the soil. Standard consolidometer and loading bar device^^ are used
in one of two modes.
a. Hold the loading bar constant (constant specimen volume) and measure
maximum uplift pressure resulting from saturation.
b. Hold the load constant and measure the vertical movement (specimen
volume change) resulting from saturation.
Swell tests have provided useful guidance for field compaction of swell-
prone soil; however, the essence, as applied to cover soils over solid waste,
often lies in the generalizations that have come from previous studies.
SOIL SUCTION TESTS
Soil suction pressure is used in some theoretical analyses of water
32
-------
1200
2400
O.I >
SO 100
Figure l8. Time-consolidation curve.
c " log, 10- logini
PRESSURE, p , TONS/SQ FT
0.6
Figure 19. Void ratio -pressure curve.
33
-------
movement in unsaturated soils. Such analyses are beyond the scope of this
manual, and suction pressure is not routinely used in designing cover. Test
methods are available but not reviewed here.
Capillary head Hc can be considered a property of the soil determining
the tenacity for holding vater. Active Hc marks the height above the water
table to which water will rise by capillary action in the given soil. Passive
HC is the height above the water table to which capillary water will drain
from a transient condition of saturation. Though conceptually simple, Hc is
not routinely determined in most geotechnical laboratories. The designer can
use estimates of relative capillarity such as in Table 5-
DISPERSION TESTS
Dispersion tests are another special group of tests for characterizing
fine-grained soils suspected of having a tendency to erode rapidly. The so-
called dispersion and pinhole tests are reviewed in the ASTM volume that in-
cludes Reference l6. In almost all cases, the designer should rely on experi-
ence of soil conservation specialists and engineers familiar with local
conditions rather than attempting a testing program. It should be sufficient
to know that a dispersive tendency exists or does not exist.
MINERALOGIGAL ANALYSIS
Information on the clay mineralogy of a soil is useful background in site
investigations and for designing cover. An X-ray diffraction analysis obtains
a semiquantitative estimate of abundances of montmorillonite, illite, kaolin-
ite, etc., in the finest fraction that, in combination with data from a
hydrometer grain-size analysis, reveals much of the engineering behavior to be
expected. However, clay mineralogy can be immensely complicated by the common
occurrence of interlayered combinations of the basic clay minerals. Even
within the important montmorillonite group the exchangeable cation position in
the mineral structure determines the degree of swelling behavior.
Ordinarily, the consideration of mineralogical aspects of cover at a site
should be assigned to a geologically oriented office or laboratory. It will
often be found that sufficient mineralogical background already exists and new
analyses are unnecessary.
-------
SECTION k
SELECTION OF SOIL FOR COVER
Details in Sections 8-22 are summarized in the following paragraphs and
brought to bear on the task of selecting the most suitable soil for cover.
The functions of solid waste cover are considered in Table 6 and the various
soil types are ranked according to suitability.
DETERMINATION OF COVER FUNCTIONS
The numerous functions of cover identified in Section 2 and listed in
Table 6 must first be ranked by importance. This ranking process is a key
part of the selection procedure, but it can only be accomplished site specifi-
cally. For example, at many landfills the rate of percolation of surface
water may be of utmost importance; elsewhere, for instance in arid regions,
this function is entirely subordinate. Long- and short-term functions should
be separated and given some absolute ranking. For example, it is difficult to
distinguish the relative importance of reduction in dust during the operation
of a landfill as opposed to the reduction of potential for fires, where the
latter suggests covering and enclosing cells in clay-rich, but dust-prone,
soil. These decisions are made at the design stage. Only at this point in
the development of the project can the actual conditions, such as climate,
soil availability, transportation costs, and population proximity, be evalu-
ated in the context of the generalizations made in this manual.
For each function judged to be significant, soils should be ranked from
best to worst. This step has already been accomplished in Table 6. Next, it
will be necessary to flag those soils that are actually available for use at
the site. These may include materials brought in from a distance to upgrade
indigenous soil or soil brought in where indigenous soils are insufficient in
quantity. Allowance may be needed for the high cost of importing materials.
EXPLANATION OF SOIL RATING
The rating of soils accomplished in Table 6 is based on the following
discussions. Functional ratings of soil are from I (best) to as many as XIII
(poorest). Quantitative parameters are also provided wherever available, so
that the reader can see the absolute position of a particular soil rating.
The first column in Table 6 concerns the go/no go aspect of traffica-
bility. The ratings of I to XII from coarse granular to fine peaty soils are
based on a complete set of rating cone index (RCI) values as discussed in Sec-
tion iH. In column 2 the stickiness trafficability based on the weight per-
cent of clay is given. A complete set of values for this parameter is
35
-------
TABLE 6. RANKING OF USCS SOIL TYPES ACCORDING TO PERFORMANCE OF COVER FUNCTIONS
to
Trafficability Water Percolation
USCS
Symbol
GW
typical Soils
Well-graded gravels, gravel-sand
mixtures, little or no fines
GP
Poorly graded
gravels, gravel-
sand mixtures, little or no
CM
QC
SW
SP
SM
SC
ML
fines
Silty gravels
mixtures
, gravel-sand-silt
Clayey gravels, gravel-sand-clay
mixtures
Well-graded sands, gravelly
sands, little
Poorly graded
sands, little
Silty sands,
Clayey sands,
or no fines
sands, gravelly
or no fines
sand-silt mixtures
sand-clay mixtures
Inorganic silts and very fine
sands, rock flour, silty or
Go-No Go
(RCI Value)*
I
(>200)
I
(>200)
III
(177)
V
(150)
I
(>200)
I
(>200)
II
(179)
IV
(157)
IX
(10U)
Stickiness
(Clay, %)
I
(0-5)
I
(0-5)
III
(0-20)
VI
(10-50)
II
(0-10)
II
(0-10)
IV
(0-20)
VII
(10-50)
V
(0-20)
clayey fine sands, or clayey
silts with slight plasticity
CL
Inorganic clays of low to medium
plasticity, gravelly clays,
OL
MH
sandy clays,
clays
silty clays, lean
Organic silts and organic silty
clays of low
plasticity
Inorganic silts, micaceous or
diatomaceous
fine sandy or silty
VII
(111)
X
(61.)
VIII
(107)
VIII
(10-50)
V
(0-20)
IX
(50-100)
Gas Migration
Slipperiness Impede Assist Impede Assist
(Sand-Gravel, J) (k, cm/s)* (k, cm/s)« (HC, cm)* (HC> cm)*
1 X- in
(95-100) (lO"2)
I XII I
(95-100) do"1)
III VII , VI
(60-95) (5 x 10" )
V V, VIII
(50-90) (10'U) §
H
II IX IV £
(95-100) (10"J) g
II XI II 8.
(95-100) (5 x 10) J
as
IV VIII V »
(60-95) (10"J) v
I
VI VI , VII ja
(50-90) (2 x 10' ) ^
<2
VII IV IX M
(0-60) (10 ) o
CO
4)
3
H
flj
X I
(6)
IX II
VII IV
(68)
IV VII
c
VIII III °
(60) |
vii iv 2
CO
0)
^
VI V to
( 112 ) g
s
V VI
a
a
III VIII d
(180) £
3
d
VIII II XI " II IX 3='
(0-55) (3 x 10"B) * (180) g
|
to
VII
(0-60)
IX III X
(0-50) do ')
a
to
soils, elastic silts
CH
Inorganic clays of high
plasticity, fat clays
OH
Organic clays of medium to high
plasticity, organic silts
Ft
Peat and other highly organic
soils
VI
(11*5)
XI
(62)
XII
(1*6)
X
(50-100)
X I. XII
(0-50) (10~y)
I X
(200-UOO+)
(continued)
-------
TABLE 6 (continued)
Erosion Control
Reduce Freeze Action
USCS Fire Water Wind Dust Fast Freeze Saturation
Symbol Resistance (K-Factor)* (Sand-Gravel, %) Control (H , cm)* (Heave, mm/day)
GW
GP
GM
GC
SW
SP o
S
f_
SM g
0)
:
a
s
E
Mli "
01
a
CL §
m
OL
MH
CH
OH
Ft
I I
(< .05) (95-100)
I I
(95-100)
IV III
(60-95)
III V o
(50-90) i
c
c
II II u
(.05) (95-100) |
W
ii ii 8
(95-100) w
vi iv 3
(.12-. 27) (60-95) t.
o
VII VI M
(.11.-. 27) (50-90) *
XIII VII 2
(.60) (0-60) ?
XII VIII I
(.28-. US) (0-55) to
c
XI VII c
(.21-. 29) (0-60) *
B
x ix a
(.25) (0-50)
IX X
(.13-. 29) (0-50)
VIII
V
(-13)
X I
(0.1-3)
IX I
(0.1-3)
VII IV
(0.14-1.)
IV VII
(1-8)
VIII II
(0.2-2)
VII II
(0.2-2)
VI V
(0.2-7)
V VI
(1-7)
III X
(2-2?)
II VIII
(1-6)
VIII
IX
I III
(0.8)
Crack
Resistance
(Expansion, % )
I
(0)
I
(0)
III
V
I
(0)
I
(0)
II
IV
VI
VIII
(1-10)
VII
IX
X
!>io)
IX
(continued)
-------
TABLE 6 (
,ed)
to
Co
'JSCS Side Slope
Impede
Discourage Vector Discourage Support Future Use
Symbo.L Stability Seepage Drainage Burrowing Emergence Birds Vegetation Natural
GW
GP
GM
§ §
GC 3 3
0 0
o a
SW c a> a>
H a, a.
W L, t-,
o 4) m
SP a) a)
£*
O U V
-p T3 W
03 U "-*
SM £ g S
B " "*
: a £
ID W
>
CL c a q
-rH 33
a; c c
OL t 33
§ §
t< i.
MH eg
§ 3
LO O
CH
OK
Pt
X X
X X
viii vi
H
H Y V
X3 » V
U
H
C-
CH TV TV
nj -l-A 1A o
PH -P
a)
K -P
" IX IX So
c u u
-H H >
tn X)
g VII £ II g
-H 3 &
^H W P.
CO 3
0) CO
^ IV fe In
CH O
W 4-t
M <
o VI g III *
0} bO
3-1 C
H 1 -rH
> III VII g
1 U
g" VI IV |
Jf!
S
03
fc II IV
i
CD
I VIII
VIII
III
Foundation
>,
--i
_^
,0
oi
u
H
C-<
oS
V-
0
O
O
K;
0
.2
CO
0)
i
-H
03
^
i
c
i
*-
01
en
SCI is rating ;one index, K is coefficient of permeability, H is capillary head, and K-Factor is the soil credibility factor.
The ratings I to XIII are for best through pc^rest in performing the specified cover function.
-------
provided, but considerable subjectivity has been required in estimating ranges
since the grain size (i.e., clay content) is not an essential part of the
USCS, the system used in the table.
Ranking for slipperiness trafficability in column 3 is similar to ranking
in the previous column though based on a different parameter, sand and gravel
percentage. Sand and gravel components decrease the slipperiness, i.e., im-
prove the quality of soil from that functional point of view, by increasing
frictional resistance. Attention is called to the fact that all three
trafficability functions provide approximately the same soil ranking.
Water percolation is addressed in columns k and 5. The best parameter
for judging relative effectiveness for water percolation is the coefficient of
permeability k , although it specifically reflects water movement in a satu-
rated condition. The rankings in columns k and 5 are diametrically opposed,
since one reflects impeded percolation and the other assisted percolation.
Gas migration is addressed in columns 6 and 7 from contrasting viewpoints
of impeded and assisted flow. The parameter on which the ranking is partly
based is the capillary head Hc of the soil. This parameter reflects the
tenacity with which the soil holds water. The relationship between contained
water and the ability of gas to move through the soil is discussed in Sec-
tion 9- Column 8 shows the fire resistance ranking of soils. The ranking is
the same as that for impeded gas migration in column 6, since fire resistance
is increased if gas movement is impeded (see Section 17).
Two types of erosion control are considered in columns 9 and 10. Soils
are rated for resistance to water erosion on the basis of values of the USDA
soil erodibility K-factor. For wind erosion resistance, soils are rated ac-
cording to the sand and gravel content. The basis for the ranking and choice
of quantitative parameters is made clear by discussions in Sections 10 and 11.
Column 11 is concerned with dust control. Fine-grained particles are essen-
tial for dust, so that the appropriate quantitative rating parameter is con-
sidered to "be the sand and gravel content. The ranking, therefore, is the
same as for wind erosion control.
Columns 12 and 13 concern cover functions of reducing freeze action. The
fast freezing/fast thawing aspects, which also involve the tendency to freeze
to greater depths, give soil ratings I to X based on Hc . The Hc values
are the same as used in column 7 for assist gas migration. For the heaving
aspect of freeze action, laboratory measurements are available. The quanti-
tative parameters on which the ranking in column 13 is based are discussed and
illustrated more fully in Section 16.
Ranking for crack resistance involves considerable judgment, since only a
few general ranges of expansion (and contraction) percent have been estimated
in the literature (see Section 18). It is, however, well known that the ex-
treme cracking is almost restricted to soils with high clay content, and only
those soils rated VIII or worse should cause much concern.
Important aspects of the side slope cover are stability, seepage, and
drainage. The seepage and drainage aspects in columns 16 and 17 have rankings
39
-------
and rating values identical to those for impede water percolation and assist
water percolation, respectively. The stability of side slopes may in some
cases be a very important function of the cover. In such cases, the choice of
soil should be carefully considered and based on laboratory strength tests.
As indicated in Section 20, the effectiveness of soils for discouraging
burrowing animals is believed to increase with the percentage of sand content.
Accordingly, the same ranking is used in column l8 as was used for slipperi-
ness trafficability, since in both cases the important parameter is sand and
gravel content. In order to impede vector emergence, a soil with a high clay
content or a well-graded combination of clay and silt, with or without
sand, is preferred. This quantitative parameter is approximately the same as
for stickiness trafficability; therefore, the same ranking is used in col-
umn 19- Soil type is apparently not a pertinent consideration in discouraging
birds, so no preference is given in Table 6.
Loamy soils are somewhat more suitable for supporting vegetation than
soils at the sand, silt, and clay extremes of grain-size distribution. Thus,
a ranking of cover soil for supporting vegetation in column 21 gives the high
positions, somewhat subjectively, to loam and other well-graded mixtures. For
the long-range future use of a landfill site for natural or parklike settings,
the ranking should be the same as for supporting vegetation. Where the future
use of the landfill will be to support pavement or light structures, a major
concern is for high modulus. This aspect of cover soil is adequately re-
flected in RCI values as for go/no go trafficability (see Section lU). It
should be remembered, however, that the supportive capability of the underly-
ing solid waste is commonly the critical factor.
1*0
-------
SECTION 5
PLACEMENT AND TREATMENT OF SOIL
After selection of the soil for covering solid waste, efforts should "be
directed to the most effective placement and treatment. Soil cover can be
improved in several ways as it is constructed. Materials may be added for
better gradation, hauling and spreading equipment can be operated benefi-
cially, and the base or internal structure of the cover system may be
improved.
COVER COMPACTION
Some compaction is almost always accomplished during the spreading of
cover soil; and this densification is highly effective in producing benefits,
principally increasing strength and reducing permeability. Figures 20 and 21
illustrate these effects. Various aspects of the compacting procedure are
oc
U
O
y
K
J
ee
u
O
u
GWJ^xrwMt rr«
j'otTttHCO FKOH
sr*ess
H4TCKIAL3 tITHOVT
^s
at
VOIP HAT 10. ' (fOU
L2 I.I t.O 03
30
25
20
75
Figure 20.
100 MO 120
DRY UNIT WEIGHT (yD), PCF
Relation of effective angle of internal
friction to dry unit weight.IT
-------
10 * 10"' 10
PERMEABILITY. CM/SEC
Figure 21. Coefficient of permeability of materials as affected
"by degree of compaction.
identified and explained below. Also see Dispersants under ADDITIVES AND
CEMENTS for a means of improving compaction results.
Compacting Equipment and Passes
Special equipment for compacting is available in a variety of types,
weights, and costs (Table 7). Rubber-tired rollers, sheepsfoot rollers, and
TABLE 7. LANDFILL EQUIPMENT NEEDS
Solid
waste handled
(tons/8 hr)
0-20
20-50
50-130
130-250
250-500
500-plus
Crawler loader
Flywheel
horsepower
<70
70
to
100
100
to
130
150
to
190
Weight'
(Ib)
< 20,000
20,000
to
25,000
25,000
to
32,500
32,500
to
45,000
combination of
machines
COM
Crawler
Flywheel
horsepower
<80
80
to
110
110
to
130
150
to
180
250
to
280
B 1 N A T 1 0 N
dozer
Weight*
(Ib)
< 15,000
15,000
to
20,000
20,000
to
25,000
30,000
to
35,000
47,500
to
52,000
0 F M A C
Rubber-tired loader
Flywheel Weight*
horsepower (Ib)
<100
100
to
120
120
to
150
150
to
190
MINES
< 20,000
20,000
to
22,500
22,500
to
27,500
27,500
to
35,000
combination of
machines
Note: Compiled from assorted promotional material from equipment manufacturers and based on ability of one machine
in stated class to spread, compact, and cover within 300 ft of working face.
" Basic weight without bucket, blade, or other accessories.
-------
vibratory rollers for highway construction may be directly useful in opera-
tions disposing of industrial and utility wastes. High priority, well-
regulated operations covering physically uniform solid waste may achieve
high-quality results similar to those in highway embankments and structural
foundations. Elaborate and expensive compactors are not usually so practical
on municipal waste landfills, and instead special lightweight, multipurpose
compactors have "been developed.
Actually, the simple track-type tractor is probably most popular for
covering solid waste, with tamping rollers and tired vehicles having much
less popularity. A 2-yd bucket is a more or less standard accessory often
preferred to the s*oil or garbage blade. Economics and versatility usually
dictate this choice of compacting equipment. As far as the technical basis
for the selection, the effectiveness in handling and compacting the solid
waste is usually most important, and a compactor is seldom acquired princi-
pally for its effectiveness on cover alone.
The number of passes by the spreading and compacting equipment across
the soil is a separate aspect of compaction, but closely related to the type
of equipment. The equipment weight (transmitted as pressure through tracks
or wheels) and the number of passes largely determine the energy of the com-
pacting process. Unfortunately, an effort of more than two passes may be
impractical to monitor and regulate at municipal landfills.
The validity of laboratory compaction tests for predicting field compac-
tion hinges on the similarity of energy input in the two different ways.
Compaction results are also affected by the soil type, but the following
approximations can be made regarding field techniques for achieving about
95 percent of the standard maximum density on a solid base.
Compacted
Lift thickness
Equipment
Sheepsfoot rollers
Rubber-tired rollers
Crawler tractors
in.
6
10
10-12
Passes
l*-8
6-12
6-8
Figure 22 based on new data for this manual indicates that soil compacted
routinely over municipal waste falls below standard compaction curves. How-
ever, much of this difference results from the sponginess of solid waste below
(see Base Density and Resilience) and the lesser number of passes nomlally
undertaken. The anomalously high field compaction at the Byram landfill ap-
parently reflects the original high density of the geological formation used
as cover here.
General guidance (Figure 23) has been derived from these results regard-
ing the field compaction effort necessary in 6-12 in. of soil cover at solid
waste operations. Field dry density can be predicted from measured placement
water content by using laboratory compaction curves at total blow counts
-------
130
125
120
IIS
I 10
105
100
95
3 SINGLE PASSES
ALLIS-CHALMERS HD 11 SERIES B
CLAYEY SAND SOIL
HAZLEHURST, MS
10
15
20
25
j
30
130
125
120
115
1 10
105
100
95
2 SINGLE PASSES
ALLIS-CHALMERS 12 G SERIES B
SANDY CLAY SOIL
MENDENHALL, MS
10
15
20
25
30
UJ
0
a: 110
D
105
100
95
90
85
eo
75 -
70 -
65
5 SINGLE PASSES
ALLIS-CHALMERS 12 G SERIES B
SILT SOIL (LOESS)
VICKSBURG. MS
\
\
COMPACTION TEST RESULT
HAND-PACKED RESULT
FIELD COMPACTION RESULT
I
I
J
I 10
105
1OO
95
90
85
80
75
70
65 -
to
15
20
60
3-4 SINGLE PASSES
CATERPILLAR 983
TERTIARY CLAY FORMATION
BYRAM,MS
\
I
I
25 30 35 "10 15 20
WATER CONTENT, 70 OF DRY WEIGHT
25
30
35
40
Figure 22. Cover compaction on municipal solid waste as compared
to laboratory test results.
-------
105
80
Figure 23.
10
15 20 25
WATER CONTENT, % OF DRY WEIGHT
30
Schematic guidance for predicting cover compaction
results with intermediate-size dozers on municipal
solid waste using laboratory test results.
corresponding to the expected number of equipment passes. For example, at a
site where the dozer makes four passes on the average, a 5-blow compaction
curve should be determined by laboratory testing and be used for predictions.
The curves shown in Figure 23 appear generally valid, but relations between
field compaction and laboratory curves should be determined site specifically
if cover density data are deemed necessary.
Soil Type
For a given compaction effort and method, the soil type largely deter-
mines maximum dry density and optimum water content. Maximum dry densities
for standard compaction range from approximately 50 to 130 Ib/ft3, usually in-
creasing as the grain-size distribution becomes more well graded. Optimum
water content tends to increase as percentage of silt or clay increases.
Figure 2k presents conceptually useful generalizations, but such generalized
compaction curves should never be used in design as a substitute for testing
the actual soil.
Figure 25 shows how variable individual landfill sites^ can be. Nineteen
distinct groups of soil samples from landfill sites (see Section l) are
-------
130
120
no
100
90
o
Q_
X
13
LU
o:
o
SP
..v
80
0
5 10 15 20 25 30
MOISTURE CONTENT, PERCENT OF DRY WEIGHT
Figure 2k. Example standard compaction curves
for various soil types.5
plotted according to standard laboratory compaction test results. Full com-
paction curves were determined, but only points of maximum density/optimum
water (the top of each individual compaction curve) are shown on the
figure.
The salient features of this presentation are:
a. At individual landfills two or more USCS types may be present, e.g.,
Reed Road (Houston), Texas, has separate and distinct CL and CH
soils.
b. USCS types overlap considerably, e.g., all CL soils together range
from 96 to 117 Ib/ft3 in maximum dry density.
c. Within a single USCS type from a single landfill site a range of
values commonly occurs, e.g., the SM samples from Lexington, Massa-
chusetts, vary from 100 to 2.0k Ib/ft^ in maximum dry density.
Where information on compacted density is needed, the tests should be
run. Five- and fifteen-blow compaction tests are usually most appropriate
since they more closely simulate a few passes of a tractor across soil on
waste as discussed above.
-------
140
130
U.
O
Q.
H
I
O
U
z
D
90
80
5 10 IS 20 25 30
WATER CONTENT, PERCENT OF DRY WEIGHT
LEGEND
10
1. SC/WAUNUT HILLS 11.
2. SM/SOUTH LOOP (DALLAS), TEXAS
3 . CL/REED ROAD (HOUSTON), 12.
TEXAS
CL/LOWERY ST 13.
SM/LEXINGTON, MASSACHUSETTS 14.
ML/CENTRALIA, WASHINGTON 15.
CL/CENTRALIA
CH/WAUNUT HILLS (DALLAS), ' 6-
TEXAS
CH/LOWERY ST (DENVER), 17'
COLORADO 18.
GRAVELLY SILTY SAND/TACOMA, 19.
WASHINGTON
GRAVELLY CLAYEY SAND/
WALNUT HILLS
SM/CEDAR HILLS (SEATTLE),
WASHINGTON
SC/MURFF (DALLAS), TEXAS
SC/KENT HIGHLANDS, WASHINGTON
SM, SP-SM.SW-SM/48TH ST (DENVER)
COLORADO
CL/NORTHEAST (FT WORTH),
TEXAS
CL/SOUTHEAST (FT WORTH)
ML.CL/KENT HIGHLANDS
CH/REED ROAD
Figure 25. Points of maximum dry density and optimum water content
by standard compaction test for soils used as cover on
sanitary landfills.
Lift Thickness
The overall degree of compaction is markedly influenced "by the lift
thickness, i.e., placed and compacted in one operation. Figure 26 reveals the
characteristic decrease in unit weight with depth. Accordingly, relatively
-------
DRY DENSITY IN LB PER CU FT
95 100 IOS 110 lift
ft
5 $
z
5 IO
S
o
ft.
2 '*
**
j
kl
* ?0
hi
O
25
/
/
/
& '
/ ^
*/
/
» '
/ /
/
Z*
/
'' */
^
;'/
"^or'-«
' /
^ //
/.'
$'/>?
1 /
/ '
/
/
/
xy NOTE
/ /' '
(Lo+#w L
IP \ 1 1
f 1 v
^ v/
/' '
//
/
/
/
~/7%
' LECCNO
/ O 6" LIFTS
/ 12" LIFTS
24* LIFTS
FI6URES ON
WATER CONT
CURVES ARC
ENTS.
Figure 26. Effect of compaction lift thickness
on soil density for eight coverages
of a 90-psi roller.13
thin-lift construction is recommended for cover in order to achieve relatively
high overall density with its "beneficial effects. Ordinarily, lifts should
be 1 ft or less in loose thickness.
Compaction in thin-lifts on a spongy waste, however, can lead to exces-
sive cracking (Figure 27) Commonly, the passing equipment causes wavelike
deformation in adjacent parts of the cover. Daily cover cracked in this way
is not so effective. Percolation of rainwater will "be high, at least ini-
tially, since the water can move directly into large open cracks that pass
through the cover. Addition of a second lift on an as-needed basis should be
considered to rectify this situation whenever weather conditions threaten a
period of high potential percolation.
Water Content
Natural water content of soil often approaches the optimum for compac-
tion; therefore, it may be unnecessary to modify the water content. Where
compaction tests indicate, however, that the natural water content is not
appropriate to high-density compaction, water may be added by sprinkling or
subtracted by spreading to dry before using. Spreading and drying are expen-
sive, and it may be advantageous to excavate and stockpile in fair weather
and add water as appropriate later when used.
U8
-------
FLEXURAL
CRACKING
FLEXURAL
CRACKING
Figure 27. Cracking from flexing of cover on spongy
base of solid vaste.
Field compaction sometimes achieves maximum density at a water content
somewhat greater than optimum indicated by a comparable compaction test, and
it is sometimes specified that departures from optimum water content be on
the wet side. However, compaction on the dry side often achieves somewhat
greater strength.19 Also, compaction on the dry side may be best with swell-
ing soils since the water imbibed later will promote further swelling and work
against the formation of cracks (except at the surface).
Lacking compaction test data, one may estimate standard optimum water by
wetting soil until a compact ball can be formed manually. No water should be
squeezed out, and the soil should retain its dense structure after opening the
fist.20
Base Density and Resilience
A solid base on which to compact each lift is essential for ordinary soil
construction. Municipal and some industrial wastes are deficient in compari-
son, and the designer must settle for the best compaction of waste within
reason. He must also allow for the consequences of a spongy base and the
settlements that inevitably will follow. Where these effects are to be mini-
mized, the designer should specify either the actual compactive effort (equip-
ment and number of passes) or some indicator of satisfactory results being
achieved, e.g., compacted density of 850 Ib/yd3 for waste running 500 Ib/ydJ
loose.'
-------
At the present state of the art, specifying a conservative compactive
effort is most logical since field tests for determining bulk density of waste
are not routinely conducted. One might specify four passes of equipment as a
first cut until experience indicates a change is warranted. Additional reduc-
tion in sponginess and settlement can be achieved by mixing soil or granular
waste into the soft waste during spreading. Reducing the thickness of each
soft waste lift should also help. Baling of solid waste might be considered
for even better results.
SOIL BLENDING
Soil blending increases expense of covering waste and, therefore, has
usually not been duly considered previously. The benefits derived from blend-
ing, however, are sometimes dramatic through the alteration of grain-size
distribution or average grain size.
Well-graded soils, i.e., with a wide range of grain sizes, have rela-
tively low k values and are generally desirable for the purpose of mini-
mizing infiltration. If well-graded soils are not available nearby, but
coarse- and fine-grained soils are, blending may provide an acceptable product
besides an increased source supply. The procedure is effective only for in-
creasing impedance to water movement since a broadening of the grain-size
distribution almost always results. Of course, a thorough review of other
options should be made before proceeding on a large scale. Blending may be
accomplished in place using a blade or harrow.
Gravel Additions
Figure 28 shows by example the effect on maximum compacted density of
adding gravel to a finer soil; similar effects can be expected from other
coarse materials, such as waste crushed slag. Density is increased by any
150
UJ 140
-I 130
t-
o
>- 120
u.
o
m
O
J
10O
>-
O SO
90 1
\
T
T
T
T
T
I
r
LARGE SCALE TESTS
ON TOTAL MATERIAL
PROCTOR TESTS ON
3/4-INCH FRACTION OF
TOTAL MATERIAL
10
20
30 40 SO 60 70
PERCENTAGE OF GRAVEL BY WEIGHT
80
90
100
Figure 28. Effect of gravel additions to silt.21
-------
addition except for mixtures with more than 95 percent gravel. These results
were produced in a large compaction mold to accommodate gravel sizes, but the
tests involved about the same input energy as standard compaction (see Sec-
tion 3) and, therefore, are comparable to testing procedures outlined in this
manual.
Effects of gravel additions on permeability have been measured in the
laboratory also.22 Tests reveal that k drops with addition of gravel to
sand to about one-seventh the value of the sand alone. This effect remains
about the same over the range of gravel contents of 20 to 65 percent. For
mixtures containing more than 65 percent gravel, the k increases again "be-
cause sand is insufficient to fill space "between pebbles.
Sand- and Silt-size Additions
Additions of sand or silt should prove beneficial to cover where the
grain size effectively supplements the distributions of natural soils, espe-
cially where reduced percolation is desirable. Strength is also enhanced upon
compaction. Other benefits from additions of sand are potential savings in
spreading and compacting costs where the original soil is clay-rich and there-
fore sticky or slippery when wet. Granular materials may also serve to con-
dition certain soils to support vegetation.
The use of sandy and silty material locally may offer a convenient way
of disposing of certain granular wastes. Foundry sand, washed gravel tail-
ings, incinerator waste, and coarse tailings from mine mills are all pro-
spective additions provided they have minimal pollution potential. Large
amounts of silt-size fly ash and other furnace products are generated through-
out the United States, and their use as additions to cover should be consid-
ered (also see ADDITIVES AND CEMENTS).
Clay Additions
The addition of clayey soils produces particularly dramatic reduction
of k . Certain operational difficulties should be expected with clayey soils
that tend to contain considerable water and therefore may be difficult to
handle. It may be appropriate to excavate blending clays through relatively
dry spells, store, and then incorporate during favored times of the year.
Harrowing will usually be necessary. Elsewhere, it may be advantageous to use
commercially available clay. Sacked bentonite should be available at modest
cost in dry form suitable for rapid and inexpensive incorporation. Each case
will have to be evaluated for cost and desired beneficial effect.
ADDITIVES AND CEMENTS
In distinction from nonsoil systems described in Section 6, additives and
cements are defined as synthetic materials added in relatively small amounts
to soil to achieve beneficial effects. One may distinguish strengthening
cements or stabilizers, dispersants, freeze-point suppressants, water repel-
lants, and dust palliatives. Factors that enter into determining the cost
effectiveness of additives and cements are their relatively high unit cost,
manner of addition or incorporation, and duration of effect. A major concern
51
-------
in using any cover system with increased strength is the remaining suscepti-
bility to cracking as a result of differential settlement or environmental
deterioration, such as freeze-thaw; plans for patching repairs are essential.
Table 0 provides some guidance in choosing among three popular stabilizing
additives/cements.
TABLE 8. GUIDANCE FOR SELECTING SOIL STABILIZER
23
OILS
CLASS
TWC STABILIZING
HCSTHICTION ON LL.
*i. »NO HI or SOILS
MCSTHICTION
ON I-IOO MATLI
HOHSH
ill BITUMINOUS
III HORTLANO CCMCNT
«-» OK III ITUMINOUS HI NOT TO tXCl'.D 10
SH-SM OH III HOHTLANO CCMCMT ft NOT TO t*CttO SO
SW-SC OH ICI LIMB PI NOT LeU THAN It
SH-JC
IM OH »C III BITUMINOUS
onsu-sc
»i HOT TO exceeo 10 MOT TO cxcteo
III HOHTLAND CCMCNT HI NOT TO CXCCCO
NO. INOBYCQ
to.J
O* OH GH III BITUMINOUS
(b »O*TLAND CCWCNT
GK-OMOH (II BITUMINOUS
GH-GM OH ill HOHTLANO CCMCNT
am-GC on
(Cl LMC
01 NOT LCSS THAN It
»i NOT TO exceeo to
»i NOT TO exceeo JO
»l NOT LCSi THAN It
MATL SHOULD CONTAIN AT
LCAST 4St aV WT OF MATL
»ASSINS NO < neve
CLL-OMAOCa MATL ONLV
MATL SHOULD CONTAIN AT
LCAST U\ IV WT Of MATL
PASSING NO 4 sieve
OM OH OC III BITUMINOUS HI NOT TO CXCCCO 10 NOT TO CXCCCO CLL-GHAOCO MATL ONLY
OH GM-GC »» "r «T
IM HOHTLANO CCMCNT HI NOT TO exeeco MATL SHOULD CONTAIN AT
NO. mo BY eo LCAST m BY »T OF MATL
so Fines CONT HASSING NO 4 sieve
tO * "* ^T -"
4
1C) UIMC »*l NOT LCSI THAN 12
CH OR CL
OH MM OH
ML OH OH
OROL OR
ML-CL
III HORTLANO CCMCNT
III LIMC
LL LCSS THAN 40 AND
HI LeSS THAN tO
ORGANIC AND STHONGLV AGIO
SOILS FALLING NITHIN THIS
ARCA ARC NOT SUSCtHTIBLC
OF STABILIZATION BV ORDI-
NARY MCANS
Cemented Soil
Cemented soil systems have been developed for lining canals, surfacing
roads, and strengthening embankments and subgrades, and they presumably can
perform as well locally for covering solid waste (Figures 29 and 30).
Soil-cement. Soil-cement is composed of sandy soil, portland cement, and
water that have reacted and hardened. About 8 percent of dry cement is incor-
porated in place and compacted after water is added to about optimum content.
Premixing and placement wet is another method that seems less amenable to
covering waste because of extra costs, except possibly on steep slopes. Some-
what higher cement content is needed in poorly graded soils or where fines are
lacking, but correspondingly less for well-graded mixtures. Figure 29 shows
by example how a U. S. Bureau of Reclamation criterion of 6 percent weight
loss is applied to freeze-thaw and wet-dry testing results to establish cement
content for lining jobs where the environment is severely cold or alternately
wet and dry.
-------
MAXIMUM ALLOWABLE
WEIGHT LOSS 6%
9 11 13
CEMENT CONTENT, PERCENT BY VOLUME
Figure 29- Example of freeze-thaw and
vet-dry durability test
data and soil-cement de-
sign criterion.2^
While mixing and incorporating with rotary hoe or tiller, the operator
should add water to the desired amount; then compact within about 1 hr.
Sprinkling intermittently helps during a curing period of several days, and a
cover of wet soil achieves further curing. The last step may be combined with
preparation and seeding for vegetation with sufficient planning. Soil-cement
may be vulnerable to deterioration where organic and sulfurous products of the
waste can gain access.
Soil-bitumen. Bitumen stabilizes sandy soils by cementing and water-
proofing. An optimum content increases the cohesion of the soil, yet does not
separate grains enough to reduce frictional strength. From U to 8 percent
bitumen (soil dry weight basis) is recommended as a first cut for sandy loam
to be refined subsequently by testing mixtures of various contents. Sand
should require somewhat less bitumen.
The mixing procedure should be developed site-specifically. Water is
added as needed to the soil for desired compaction; then add cutback or emul-
sified asphalt or tar. Further mixing, spreading, and compacting should be
accomplished in relatively short time. It may be expeditious to spread before
adding the bitumen (and disking). The critical time from final mixing to com-
paction is thereby reduced to as little as a few minutes.
-------
1,000
0.01
A 6 8 10
CEMENT CONTENT BY VOLUME, PERCENT
14
Figure 30. Permeability of some cement-treated soils.'
The longevity of effectiveness of soil-bitumen is a. factor that deserves
careful consideration. Volatiles eventually leak away and leave the system in
an altered, sometimes degraded, condition. Cracking will also reduce integ-
rity, and patching may eventually become necessary.
Modified Soils
Cement-treated soil. Incorporation of as little as 1 percent of Portland
cement has been shown to have stabilizing effects on granular soil, and
cement-stabilized soils are used occasionally for lining embankments and
drainage ditches. The effect in laboratory tests is illustrated in Figure 31.
However, other environment influences, such as freeze-thaw, can reduce the
practicability of the technique (see Soil-cement ) .
Lime-treated soil. Lime (calcium oxide or hydroxide) is principally
-------
0.65
SHEAR STRESS (GM/CM2)
1.0 1.32
T
1.65
r
800
Figure 31.
1000
1200 1400
SPEED (RPM)
1600
2.0
1800
Erosion rates for cement-stabilized sandy soil. 5
(Reproduced by permission of Transportation
Research Board.)
mixed into clayey soils for its effects as a flocculant or base exchanger
(see Swell Reducers). However, lime also promotes some beneficial pozzolanic
reaction in fine, cohesive soils,2° and strengthening may continue for many
weeks of curing. See Table 8 for applicability of lime versus other stabi-
lizers. The following approximate lime percentages have been suggested as a
rough guide for selecting lime contents.
Soil Type
Approximate Percentage
Hydrated Lime
Quicklime
Clayey gravels (GC,
GM-GC)
Silty clays (CL)
Clays (CH)
2-U
5-10
3-8
2-3
3-8
3-6
These percentages may amount to overdesign in some solid waste applications,
so the designer should consider smaller additions and evaluate test trials on
the basis of measured high pH.27
Fly ash-lime (or cement)-treated soil. Fly ash is attractive as an addi-
tive to soil because of its pozzolanic properties,28 i.e., though not a cement
55
-------
in itself, fly ash develops cementitious properties with lime or cement and
water. Accordingly, a. small amount of lime or portland cement should be in-
cluded unless self-hardening has been confirmed by test or previous experience
with the particular fly ash (see Fly ash-treated soil).
Proportioning of soil, lime, and fly ash is dictated by economy and
desired properties in normal soil stabilization. In solid waste disposal,
a scarcity of cover soil and a growing surplus of fly ash nearby may obviate
such normal concerns and lead to the practice of using as much fly ash as can
be tolerated (see Section 6). Thus, a normal mix for stabilization with the
common lime to fly ash ratio of I:k may contain about 20 percent fly ash,
5 percent lime, and 75 percent soil, but mixtures placed over waste may be
just as effective at 60 percent fly ash, 5 percent lime, and 35 percent sand.
Any accompanying sacrifice in strength should not be critical in landfill
covering.
Sands and gravels are more suitable for lime-fly ash stabilization than
are fine-grained, plastic soils. The resulting broadened grain-size gradation
should be conducive to dense compaction and best reaction, although the forma-
tion of cementitious products works against attainment of densities otherwise
possible. Water content often should be slightly below optimum for maximum
density. Mixing is important as with other additions, and a rotary tiller
may be very effective. Preferably, water should be added only after mixing
dry ingredients, and compaction should follow as soon as possible. Traffic
should be prohibited on the cover for several weeks if maximum curing is
desired.
Fly ash-treated soil.* Some fly ashes possess moderate self-hardening
characteristics when moistened and compacted29 and, therefore, offer promise
alone as major additions to cover over waste. This phenomenon is partly due
to the free lime content of the ash itself. Laboratory tests or field trials
will be necessary to establish such useful peculiarities of specific fly ash
sources where previous experience is lacking. Tests also establish optimum
mixtures for strength, durability, etc.
Fly ash from western, low-sulfur coal often contains high calcium.3°
Such material,31 (mixed with clay or with sand) may heat in reaction upon
wetting and cause major increase in strength and decrease in k . Reduction
in k of as much as a thousand fold31 for treated sand is probably partly due
to altered grain size and distribution as explained under SOIL BLENDING rather
than to development of cementation.
Fly ash-lime (or cement)-sulfate-treated soil. This mixture is proposed
here as a locally viable option for covering waste following research on the
uses of fly ash-lime-sulfate (or sulfite).32 See Modified Fly Ash under WASTE
MATERIALS for additional information.
* The pollution potential of fly ash has not been entirely defined, and
its use in cover at a landfill should be prefaced on favorable conclusions of
environmental impact studies.
56
-------
Other treated soil systems. As witnessed by the proposed beneficial use
of waste sulfates and sulfite, new developments in treating soil will continue
to appear for consideration. Materials that deserve serious consideration and
trial should possess most of the following attributes:
a. Replace scarce soil.
b. Improve physical properties of soil; or at least develop no adverse
properties.
c. Have low pollution potential.
d. Are wastes themselves.
e. Reduce expenses.
Dispersants
Several soluble salts act as dispersing agents and are recommended for
improving soil compaction and reducing k . The treatment is primarily for
fine-grained soils containing clay minerals. Better compaction can be
achieved on coarse-grained soils by other means, such as blending in fine
material (see SOIL BLENDING)
Dispersion (deflocculation) involves the breakdown of clayey aggregates
into the individual mineral particles. The effect is to increase dry unit
weight, to lower permeability, and incidently, to facilitate compaction.
Dispersing agents are evaluated qualitatively by adding a small amount to a
ball of moist soil and noticing whether the soil becomes wetter. Soil should
be at least 15 percent finer than 0.002 mm and 50 percent finer than 0.07^ mm
to be significantly affected by dispersing agents.33 It has also been found
that montmorillonite is much more susceptible than kaolinite or illite, and
treatment of many soils in the northeastern and midwestern United States would
be questionable. Testing should be undertaken prior to specifying the use of
dispersants in these regions.
3-3
Three dispersing agents have been found notably effective. Common
sodium chloride produces satisfactory results in many cases and is inexpen-
sive. Tetrasodium pyrophosphate and sodium polyphosphate appear to have
slight advantages in many cases over sodium chloride.33 Sodium carbonate or
bicarbonate is also effective. Applications are approximately 0.20 to
0.33 lb/ft2 for salt and 0.05 It/ft2 for sodium polyphosphate. The applica-
tion for sodium chloride amounts to about 0.1 percent of dry soil weight for
a 6-in. compacted layer. Costs of such chemically sealed soil linings for
ponds were estimated to range 300-3000 dollars/acre in 1963.33 For a solid
waste cover, cost would be considerably less since extra spreading and com-
pacting would be insignificant and lesser additions should be adequate.
Table 9 shows the effectiveness of treatments as far as reducing perme-
ability. Disadvantages of the use of dispersing agents are increased suscep-
tibility to erosion and to cracking due to the enhanced shrink/swell behavior.
It follows from these known characteristics that dispersed (treated) silt and
57
-------
TABLE 9. EXAMPLE EFFECTS OF TSPP AND NaCl* ON COMPACTION AND PERMEABILITY33
Co
Coefficient of Permeability, ft/day
Soil
Class
ML
SC-SM
SM-ML
CL
CL
CL-ML
CL
CL
CL
CH
CL
CL
Percent Finer Than
Location
New York
Virginia
Pennsylvania
New Jersey
Virginia
Virginia
Virginia
Pennsylvania
Texas
Texas
Texas
Colorado
0.002 mm
16
IT
lU
28
H5
20
33
22
30
IK)
27
32
200 mesh
50
U8
50
80
90
90
85
70
70
85
55
75
85 Percent
Standard
Density
no chemical
0.1
0.137
0.06
1.19
0.50
0.02
0.01
0.05
0.03
0.1*4
0.95
85 Percent
Standard
Density
+ TSPP
0.001
0.028
o.ocA
0.112
0.136
0.001
0.001
90 Percent 85 Percent
Standard Standard
Density Density
+ TSPP + NaCl
0.00001
0.0001
0.0002
0.0001
0.0001
0.0003
0.00001
0.01
0.005
0.002
0.002
0.072
90 Percent
Standard
Density
+ NaCl
0.0013
0.00001
0.0008
0.0001
0.001+
TSPP is tetrasodium pyrophosphate, and NaCl is sodium chloride.
-------
clay may tend to erode and migrate downward into waste cells and leave the
cover in a degraded condition. Therefore, the specification of use of dis-
persants should be preceded by on-site experimentation or trial revealing any
consequences besides densification. Both erosion and shrink-swell can be
reduced by covering the treated soil with a protective layer that will support
vegetation. Conversely, the placement of a sand or silt layer before (below)
the dispersed clay layer should largely eliminate the problem by slowing in-
ternal erosion and allowing the clay layer to deform and reseal itself. Such
a combination of filter layer (see LAYERING) with overlying dispersed clay
layer has been used to seal a leaky irrigation canal.1°
Swell Reducers
Lime is the principal additive for reducing shrink/swell behavior in
clay-rich soils. About 5 percent is optimum for effecting ion exchange (cal-
cium for sodium), flocculation, and cementation. Quicklime contains more
calcium and, therefore, is preferred to hydrated lime by some users provided
a mellowing period is allowed for homogenization. See Modified Soils for more
specific guidance on requirements.
A recommended procedure begins with restriction of the work area to a
unit small enough to allow completion in a convenient work period. If cemen-
tation reaction is expected, the time period should be short, i.e., a few
hours. Avoid crossing units already completed and in a curing state. Place
sacks of lime on the work area at spacing to meet designed mix ratio. Open
sacks and distribute: then mix dry with a harrow. Add water in increments of
about 0.5-1.0 gal/yd^, followed by more harrowing. Bring water to or slightly
above optimum and hold during compaction that follows. Lift thickness ordi-
narily should not exceed 1 ft.
Other consequences of lime treatment that should be considered are that
it reduces PI, improves the agricultural grade, and increases k of the
soil. The reduced PI may benefit trafficability (Section lU), but the in-
crease in k is usually not desirable.
Freeze-point Suppressant
Poor compaction can result when soil pore water is frozen during cold
weather operations. Ordinarily soils construction for roads, etc., is cur-
tailed in the winter to avoid the poor results. Some improvements can be
achieved by adding a freeze-point suppressant and may be advisable where
covering operations are expected to continue during cold spells. Calcium
chloride has been recommended^1* as effective, either in solution or in dry,
flaked form. Treatment of the borrow area should be considered also.
Other Additives*
Hundreds of other chemicals have been proposed for their beneficial
* The pollution potential of additives should be given special consider-
ation prior to usage.
59
-------
effects on soil. Some are proported to impart water repellancy and strength;
others have more obscure attributes. Many of these compounds are proprietary
developments and their properties and characteristics are difficult to evalu-
ate. Table 10 provides preliminary guidance by listing chemical additives,
along with some probable characteristics and applications.
Some previous experience or assistance from authoritative sources will
often be necessary for the designer to make a choice among these products;
state highway departments are one possibility. Consider the following in
selecting an additive: cost, ease of application, and duration of effective-
ness. Many additives work for only a short period, so that rapid follow-up
treatment, such as establishment of vegetation, will usually be necessary to
sustain the benefits.
LAYERING
Layering is perhaps the most promising, yet presently underutilized,
technique for designing final solid waste cover. By combining two or three
distinct materials in layers, the designer may mobilize favorable character-
istics of each together at little extra expense. The systematics are briefly
set forth here. The actual designing using materials available at specific
sites will test the ingenuity of the responsible engineer; therefore, high
priority may be warranted. Figure 32 schematically illustrates the system.
Topsoil
A topsoil or a subsoil made amenable to supporting vegetation frequently
forms the top of a layered cover system. Untreated subsoils are seldom suit-
able directly, so it has been necessary frequently to supplement subsoil with
fertilizers, conditioners, etc., as explained in Section 19 to obtain the
desired result. Loams or USCS types GM, GC, SM, SC, ML, and CL are recom-
mended, but agronomic considerations usually prevail. The upper lift should
be placed in a loose condition and not compacted.
Barrier Layer or Membrane
The primary feature in many layered systems is the barrier. This layer
functions to restrict passage of water or gas. Barrier layers are almost
always composed of clayey soil that has inherently low permeability; USCS
types CH, CL, and SC are recommended. Soil barriers are susceptible to dete-
rioration by cracking when exposed at the surface, so that a buffer layer is
recommended to protect the clay from excessive drying.
Synthetic membranes may be used in place of soil barriers. Costs are
generally high in comparison to available soils, and problems in placement or
with deterioration may arise. Nevertheless, membranes are a viable option
that should be considered for some special jobs. See Section 6 for a review
of available membranes. Membranes should be spread carefully over the smooth
buffer soil to lie in a relaxed state; about 5 percent slack is necessary with
polyethylene. Manufacturer's recommendations for field splicing should be
followed. Provide a trench (8 in. deep) or other anchorage at the top of any
slope.
60
-------
TABLE 10. CHEMICAL ADDITIVES FOR COVER SOIL
Category and Agent
Attribute*
Strength Water Du3t/Wind
Comments**
Inorganic chemicals
Calcium chloride
Lime
Phosphoric acid
Potassium silicate
Sodium carbonate
Sodium chloride
Sodium silicate
Sodium silicate N
Sodium silicate No. 9
Soil lok
Resinous materials
Aerospray 52
Aerospray 70
AM-9
Amoco A
Amoco B
Aniline-furfural
Aniline bydrochloride
furfural
Aroplaz 6065
Aropol 7110
Aropol 7720 M
Arothane 156
Yes
Yes
Yes
Yes
Yes Yes Maintains moisture content. Easily
leached out by water.
See discussion in text.
Cementing agent. Mixes easily with soil.
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
See discussion in text.
Easily leached out by water.
Effective in well-graded, compacted sand.
Forms hard crust after 1-hour cure.
Effective in sands.
Effective when sprayed on. Approximate
cost $0.60/gal.
Combination sodium silicate and calcium
chloride. Effective in fine-grained soils.
Forms hard surface.
Yes Alkyd resin emulsion that forms a hard
crust. Approximate cost $2.85/gal.
Yes Polyvinyl acetate resin emulsion. Effec-
tive in sand. Approximate cost $2.50/gal.
Yes Blend of water-soluble acrylamide and
diacrylamide. Provides flexible surface
after long curing.
Requires moisture and temperatures above
1»0°F (U°C) to cure. Effective mixed with
sand.
Fast curing resin. Effective mixed with
sand.
Yes Yes Provides tough surface for dry silt and
clay. Soil moisture reduces final strength
Toxic.
Nontoxic resin. Effective in highly acid
or neutral soils with Pi's of 3 to 20.
Yes
Yes Unsaturated polyester resin. Significantly
increases soil strength of sand, silt, or
clay.
Yes Unsaturated polyester resin. Effective in
sand, silt, or clay.
Yes Polyurethane elastomer with rapid curing.
(Continued)
6l
-------
TABLE 10 (continued)
Attribute*
Category and Agent
Strength Water Dust/Wind
Comments**
Resinous materials (continued)
Arothane 160
Arothane 170
Ashland CR 726
Base 792-D
Base 792-L
Celanese 13-67-5
Celaneae 510+872
Celanese 16-78-16
Celanese 16-78-1
Celanese 16-77-1
Chem-Rez 200
Chrome lignin
CIBA 509+X8157/136
CIBA 6010+X8157/136
CIBA 6010+X8157/157
DCA-70
DCA-1295
Dow CX-7
Dow derakene 11H
Dresinate DS-60W-80F
Edoco X-2111-1
Emlon E-200
Yes Yes Yes Polyurethane elastomer with rapid curing.
Effective in clay.
Yes Yes Yes Similar to Arothane 160.
Yes Blend of resorcinol and an accelerator.
Effective mixed with clay.
Yes Blend of polyvinyl resins and modifiers.
Yes Similar to Base 792-D.
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Blend of EpiRez ,510 arid EpiCure 872.
Effective mixed with sand.
Blend of EpiRez 510, S1^, and EpiCure
8701. Requires moisture to cure. Effec-
tive mixed with sand.
Blend of EpiRez 510, 856, and EpiCure 87.
Effective mixed with sand or clay.
Yes Furfural based rapid setting resin.
Effective in sand or clay.
Yes Risinous alkali waste and a hexavalent
chromium compound in gel form.
Blend of Araldite 509 and X8157/136.
Effective mixed with clay.
Blend of Araldite 6010 and X8157/136.
Effective with sand or clay of variable
moisture content.
Yes
Yes Yes Emulsion of polyvinyl acetate and chemical
modifiers. Cures in 2 to k hours. Can be
reinforced with fiberglass filaments.
Yes Yes Improved DCA-70. Fiberglass reinforcement
may be harmful if inhaled or blown into
eyes.
Yes Blend of vinyl ester resin, benzoyl peroxide,
and N. N. dimethylanitine. Fast curing.
Effective mixed with sand.
Yes Blend of vinyl ester resin, benzoyl peroxide,
and N. N. dinethylanitine. Requires moisture
to cure. Effective mixed with sand or clay.
Yes Thermoplastic resin. Effective in spray
applications. Approximate cost $0.3Vgal.
Yes Effective in sand or clay.
Yes Yes Yes Water soluble resin that cures within 2 hours
in combination with diethylene triamine.
Effective in sand or clay.
(Continued)
62
-------
TABLE 10 (continued)
Attribute*
Category and Agent
Dust/Wind
Comments**
Resinous materials (continued)
Epon 828 Yes Yes
Epon 828+VltO Yes
General latex-vultex Yes
General Mills TSX-lt29+TSX-U28 Yes
HK-1 Yes
HK-2 Yes Yes
Jones-Dabney No. 6 Yes
Jones-Dabney No. 7 Yes
Lignin liquor Yes
Ligno sulfonates Yes Yes Yes
Lino-cure C Yes
Norlig 111 Yes Yes Yes
Orzan Yes Yes Yes
Paracol TCl81t2 Yes
Paracol Sllt6l Yes
Petroset RB Yes Yes Yes
Petroset 3B Yes Yes Yes
R 20 Yes
Resinox 9673 Yes
Resin 321 Yes
Epoxy resin with slow curing time. Pene-
trates sand or clay and forms a hard
crust.
Blend of Epon 828 and Vl*0. Effective in
sand or clay.
Blend of an epoxy resin and a catalyst .
Causes low strength gain.
Blend of a resin and a coreactive resin.
Causes low strength gain.
1:1 mix of Base 792-D and 792-L.
3:1 mix of Base 792-D and 792-L. Forms
tough resilient film but curing can take
more than 7 hours with loose sand in
humid conditions.
Blend of EpiRez 5159, SOM, and Epicure
8714. Effective in sand or clay.
Resinous alkali waste and compounds.
See Horlig 1»1,
Foundry resin that forms a hard, water-
proof surface when applied with ethylene
glycol.
Ligno sulfonate. Approximate cost
$0.27/gol.
Mixture of ligno sulfonate and chemicals.
Forms shrinkage cracks when cured. May be
leached out by water. I
Resin emulsion. Good results with mine
tailings.
Blend of wax and resin. Effective with
mine tailings. Approximate cost $0.39/gal.
Emulsion of resins, elastomer, and volatile
solvents. Effective in gravel and rock.
Approximate cost $2/gal.
Emulsion of resins, elastomer, oils, sol-
vents, and water. Effective in particles
below gravel size. Approximate cost
$1.60/gal.
Sodium methyl silanolate. Nonbiogradable.
Approximate cost $0.05/yd2 treated.
Finely powdered resinous substance. Effec-
tive in acid soils (silty clay and clayey
silt).
(Continued)
63
-------
TABLE 10 (continued)
Attribute*
Category and Agent
Strength Water Dust/Wind
Comments**
Resinous materials (continued)
Soil seal
Vinaol
Vistron siljaar S-3840
Whitesides 69-1-1
Polymeric materials
Compound SP 301
Curasol AE
Curasol AH
Neoprene 750
Petroset RB
Petroset SB
Petroset AX
Petroset AT
Polyco 2U60
Surfaseal
Terra-krete
Ucar 130
Vultex l-V-10
White soil stabilizer
Bituminous materials
APSE (Asphalt penetrative
soil binder)
Yes Emulsion of material copolymers in the
plastic resin range. Effective in fine-
grained sand.
Yes Powdered resinous substance. Effective
in sandy silt, silty sand, clayey silt,
and clayey sand. Susceptible to micro-
bial attack,
Yes Modified polyester resin. Requires mois-
ture to cure. Causes low strength gains.
Yes Emulsified epoxy resin. Effective mixed
with clay.
Yes Latex copolymer emulsion. Effective in
spray application. Approximate cost
$1.30/gal.
Yes Polyvinyl acetate latex dispersion. Form*
a hard crust. Cleanup is difficult.
Approximate cost $2.60/gal.
Yes Polyvinyl acetate latex. Forms a flexible
crust.
See Resinous materials.
See Resinous materials.
Emulsion of elastomer, asphalt, solvents,
and water.
Emulsion of elastomer, oils, and water.
Styrene/butadiene latex. Effective in
spray applications. Approximate cost
$0.87/gal.
Yes Viscous plastic material. May require
several applications, allowing drying time
prior to each additional application.
Approximate cost $l4.1(0/gal.
Yes Chemicals in latex base. Forms hard
surface.
Yes Polyvinyl acetate.
Yes Prevulcanized rubber latex.
Yes Latex polymer, effective mixed with soil.
Approximate cost $U.31/gal.
Yes Low penetration grade asphalt, kerosene,
and naptha. Good penetration in impervious
or tight soils. Cures in 6 to 12 hours.
Flammable.
Yes
Yes
Yes
Yes
Yea
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
(Continued)
-------
TABLE 10 (continued)
Attribute*
Category and Agent
Strength Water Dust/Wind
Comments**
Bituminous materials (continued)
Liquid shale tar (shale oil) Yes
Peneprime
Petroset AX Yes Yea
Miscellaneous materials
Admex 710
Aggrecote 600
Aquatin Yes
Bio-binder Yes
Bisphenol A
Calcium acrylate Yes Yes
Calcium sulfonate Yes
Cyanaloc 62 Yes
Dust bond 100 Yes
Dustrol Yes
ELO
Formula 125 Yes
Gelatin 1JXPF Yes
Goodyear X335
Heavetex P1396 Yea
Heavetex P1397 Yes
Hysol Yes
K-aton 101
Landlock
Lemac Uo
Orzan GL-50 yes
Pacific N 7^8 S yes
Yes
Yes
Yea
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Effective in sand or clay.
Same as APSB.
See Polymeric materials.
Concentrate of chemicals and pectin.
Forms fragile crust. Stains skin, cloth-
ing, and equipment. Approximate cost
$2.30/gal.
For spray applications. Approximate
cost $2.JT/gal.
Organic salt that forms strong bonds
in wet, fine-grained soils.
Approximate cost $0.36/gal.
Medium grade road oil. Flammable.
Organic cementing agent and a sodium
methyl siliconate base. Effective in
gravel to clay. Caustic in concentrated
form. Approximate cost $10/gal.
Good penetration in sand. Forms hard,
brittle surface.
Cementing material that can be sprayed
or mixed with soil. Approximate cost
$0.30/gal.
(Continued)
65
-------
TABLE 10 (continued)
Attribute*
Category and Agent
Miscellaneous materials (continued)
Stabinol
Sulfite liquor
Terra-krete No. 2
Strength Water Dust/Wind
Yes
Yes
Yes
Comments**
3=1 mix of Portland cement and Resin 321
or a complex salt. Deteriorates after
long storage.
Effective sprayed on sand and gravel.
Easily leached out by water.
Inorganic and organic materials with a
synthetic binder. Approximate cost
$2.50/gal.
Tung oil
Waste oil
Yes
Yes Yes Yes
* Attributes are marked yes where addition to soil is claimed (not necessarily substantiated) to stabilize
generally, to repell water or resist water erosion, or to resist dusting or wind erosion. Dispersants
are another group of additives used primarily to aid in the compacting process; they are not included in
this table but are discussed in the text.
** The pollution potential of additives should be given special consideration prior to usage.
LOAM (FOR VEGETATION)
ggoooooouuuuuuuUU»»6uOt/uJui)UtlUtJUm>ueB6o86g8f68ooooooooooooo6c_
oooooooooooooooooo 700000000000000000
OOOOOOOOOOOOOOOOOO GRAVEL
OOOOOOOOOOOOOOOOOO vrrnvtu.
OOOOOOOOOOOOOOOOOO w w v\f v«/w\sww«/www w www wOOOOOOOOOOOOOOOOOO
OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOQAMMaaDOOOOOOOOOOOOO
ii I Ii i nun |»il III lii'MKII IIIMII'^^ i HII11 ii i r mV
nnnnnnnnnnnnnnnnnnnrT^ i 1 ^^^innng
-------
Buffer Layer
A buffer layer may be described as a random layer having a subordinate
covering function and characteristics in comparison with the adjacent layer.
The principal service of a buffer is to protect a barrier layer or membrane
located above or below. The buffer shields a vulnerable, thinner barrier or
sheet from tears, cracks, offsets, and punctures. Below a barrier, the buffer
layer also provides a smooth, regular base. Any soil type will serve as a
buffer ordinarily, but it should be free of clods. A properly placed buffer
filling voids around barrels of waste serves to prevent settlement and dis-
ruption of the final capping cover.
Water Drainage Layer or Channel
A water drainage layer, blanket, or channel may be designed into the
cover in numerous ways to provide a path for water to exit rapidly. Poorly
graded sand and gravel are recommended as effective drainage materials, i.e.,
soils classified GP and SP. Drainage channels and layers may be associated
with a system of buried pipe drains, but the expense of this combined system
ordinarily limits its applicability to high-priority disposal areas. Some
experience has suggested that biological buildups or icing can seriously
interfere with operation of drainage layers.
Filter
Where layers with grossly discordant grain sizes are joined, there may be
a tendency for fine particles to penetrate the coarser layer. As a result,
the effectiveness of the coarse layer for water drainage may be reduced by
clogging of pores. Removals from the fine layer may promote additional bad
effects, such as internal erosion and settlement (see Dispersants). Similar
problems can develop around pipe drains buried in the cover system.
Such problems are commonly confronted in construction and agriculture,
and procedures have been established for choosing grain size for a filter. A
widely used criterion35 is written
D1C (filter)
< it. to 5 (6)
Dg (base)
where 015 and D85 refer to the grain sizes for which 15 and 85 percent by
weight of the soils are finer, respectively. A review of filter construction
is available elsewhere.36 Less rigorously, filters might ordinarily be spec-
ified as SP, SM, ML, and MH soils depending on the classification of soil to
be protected. A filter fabric or cloth with k comparable to that of sand
may be considered in place of a filter layer to protect sand and gravel.
Gas Drainage Layer and Vents
A gas drainage layer has consistency and configuration similar to those
of the water drainage layer or channel. Both layer types function to transmit
preferentially. The position in the cover system is the main distinction.
67
-------
The gas drainage layer is placed on the lower side to intercept gases rising
from vaste cells, whereas the drain for water is positioned on the upper side
to intercept water percolating from the surface.
Gas vents are a proven tool in the present state of the art in municipal
waste landfilling. It has been found that dangerous concentrations of flam-
mable gases can accumulate if not vented properly to the atmosphere. Fig-
ure 33 illustrates two recommended gas vents. The designer should be aware
of the fact that occasionally a biological or ice buildup can interfere with
proper channeling or venting.
(
'////////(
1OOOOOO OOOOOOO
too ooooooo ooooi
>
0
> c
)
^///y//s/ss//s/s
ooooooooooooooooooooooooo
ooooooooooooooooooooooo oo
O O O O 0
000
OOOOOOO
OOOOOOO
OOOOOOO
OOOOOOO
OOOOOOO
OOOOOO
OOOOOOO
ooooooo
OOOOOOO
OOOOOOO
OOOOOOO
OOOOOOO
OOOOOOO
OOOOOOO
OOOOOOO
,o o o o o o 01 ooooooooooooooooooo
oo oo ooo oo ooo/' -^oooooooo ooo ooooo oooo oooo
ooooooooooool loooooooooooooooooooooooo
ooooooooooo oV ^6000000000000000000000000
oooooooooooo oTWlS o oooooooooooooooooooooooo
ftflOOOOOOOOOOOOOOOOOOOOOOQOOOg0^00000000^
PIPE VENT
,.00000001
*'2 ° 2 2 2 o °"ooooooooooooooooooo
>|ooooooo|0000000000000000000
o'oo o oo oooooooooOOOOOOOOOOO°
3 JD^Q p O O^O QJ OOOOOOOOOOOOOOOOO OO
OOOOOOO
OOOOOOO
oo o oo oo
ooooooojo o o oo oo)oooooo°
ooooooo"
OOOOOOO OOOOOOOOOOOO OOOOOOOOOOOOOOOO
ooooooooooooooooooooooo ooo o o o o o o o o^
o oo
000
GRAVEL TRENCH
Figure 33. Two types of gas vents for layered cover systems.
Construction Techniques
Some general recommendations for layering the final or closure cover from
the bottom up are as follows:
a. Make buffer layer below barrier thick and dense enough to provide a
smooth, stable base for compacting in c below.
b. Compact all layers except topsoil and top lift of upper buffer.
c. In barrier layer, strive for 90 percent of maximum density according
to 5- or 15-blow compaction test.
d. Cover barrier layer soon enough to prevent much drying.
e. Provide sufficient design thickness to assure performance of layer
function; specifying a 6- to 12-in. minimum should prevent exces-
sively thin spots resulting from poor spreading techniques.
f. Construct in units small enough to allow rapid completion.
g. Consider seeding topsoil at time of spreading.
68
-------
SECTION 6
NONSOIL COVER MATERIALS
Tvo broad, contrasting classes of nonsoil cover materials are described
in this section. Commercially available capping materials or membranes may be
preferable to soil-based systems over industrial wastes that pose a high risk
of serious pollution (where not properly shielded). In contrast elsewhere, an
economic advantage may accrue from using inexpensive, locally generated wastes
in place of scarce, indigenous soil.
COMMERCIAL MATERIALS
For high assurance or factor of safety for performing specific functions,
available commercial materials should also be considered. For example, bitu-
minous and portland cement concrete barriers and membranes of various types
function alone or in conjunction with soil or granular waste layers to exclude
water. A summary of materials and their characteristics is presented in
Table 11. Of course, the cost of buying and installing these special systems
is prohibitive for most solid waste covering (Table 12).
General Considerations
Important characteristics of flexible membranes and rigid barriers in-
clude vulnerability to tearing or cracking, respectively. A smooth buffer of
sand should reduce membrane puncture during construction, but extra long-term
planning will be necessary against stressing effects of differential settle-
ment. The rigid barriers sometimes have an advantage because cracks can be
exposed, cleaned, and repaired (sealed with tar) with relative ease.
Deterioration is another major problem for serious consideration. Con-
crete barriers are susceptible to chemical deterioration in harsh environments
such as those rich in sulfates. Sunlight, burrowing animals, and plant roots
increase the deterioration of membranes. Twenty years is about the extent of
experience with membranes.37 Longer design service life may be somewhat risky
in adverse environments .and conditions.
The cost of commercial coverings will often be the overriding considera-
tion. Table 12 provides figures that the designer may use as first approxima-
tions of installed cost. These data are from a few summary sources, mostly
concerned with irrigation canal linings, and no assurance is offered that all
figures are mutually concordant and directly applicable to relatively small
waste covering operations. The designer will need to analyze the cost effec-
tiveness based on specific needs and local material and labor costs.
-------
TABLE 11. PRODUCTS RECOMMENDED FOR HIGH-PHIORTTY
Material and Description
Advantages^
Bitumen cements or concretes
(AC-iiO and AC-20 viscosity
grades.)
Portland cements or concretes
(3000 psi and 5000 psi)
a. Provide tight, impervious barriers
covering municipal/hazardous waste.
b. Good availability.
c. May be used as thick waterproofing
layers in flat areas or on slopes.
a. Good availability.
b. Provides good highly impermeable
containers or covers for hazardous
waste disposal. Very low water
permeability.
a. Expensive
b. Special heating and storage equip-
ment required for handling.
c . Vulnerabl r- to break i np.
May crack during curing, allowing
po*,ential paths for esi'-apir,^, ('a:^e^
or infiltrating water.
Leakage from hazardous wastes in
liquid form may weaken concrete
with time.
Liquid and emulsified asphalts
(RC and EC 30, 70, 250, 800,
and 3000 liquid asphalts.
R3'3 and CRS's 1 and 2, MS's
and CMS's 2, and SSI
emulsion.)
Tars
{RT 1, 2, 3, li,
RTCB 5 and 6).
7, 8, and 9.
Bituminous fabrics
Comraerc i al polyme ri c memb rane s
(Butyl rubber)
a. Can be sprayed on soil covers to
decrease water and gas permeability.
b. Can be mixed with soil to form
waterproof layer.
c. Penetrate open surfaces, plug voids,
then cure.
d. Penetrate tight surfaces, plug
voids, then cure.
e. Provide hard, tight, stable
membrane (RC and MC 800 and 3000).
a. Can be sprayed on soil surfaces or
mixed with particles. Tars mix well
with wet aggregate.
b. Penetrate tightly bonded soil
surfaces and plug voids (RT 1 and 2).
c. Penetrate loosely bonded fine
aggregate surfaces and plug voids
(RT 2, 3, and M.
d. Penetrate loosely bonded coarse
aggregate surfaces and plug voids
(RT 3 a:id U).
e. Low spray on temperatures 60° to
150°F (15° to 65°C) for RT 1, 2, 3,
and k and RTCB 5 and 6.
f. Provide hard, tight, stable surface
membrane (RT 7, 8, and 9). May be
used in flat areas or on slopes.
g. Provide good penetration, then cure
to form hard surface (ItTCB 5 and 6).
a. Require minimal special equipment
and nkill.
b. Resist tearing.
a. Available in various size sheets.
b. Can be reinforced with fibers for
added strength.
c. Can be Joined at seams to cover
large areas.
d. Good availability .
e. Good heat resistance.
f. Very low water permeability.
g. Low vapor transmissivity.
a. Must leave sprayed surface exposed
until,it either cures (EC's,
or sets (SSf:0 .
b. Must be covered for protection.
c. Require additional equipment to
handle and apply the asphalts.
Spraying temperatures range from
75° to 270°F (25° to 130°C).
d. Use of RC and MC 800 and 3000 in
thick membrane construction may
require numerous applications.
a. Tar may be removed by traffic i f
not covered with a protective
soil layer.
b. Tars are more susceptible to
weathering effects than asphalts.
Must be protected from weathering.
c. Require special equipment for
handling and application.
d. RT 7, 8, and 9 require application
temperatures of 150° to 2?5°F
(65° to 105° C).
a. Expensive.
b. Lap.: should be sealed.
a. Poor resistance to weathering
and abrasion.
b. May be damaged by gnawing/burrowing
animals if not protected with .^i.;.
c. May be damaged by heavy equipment
operating directly on surface and
may be punctured by large stones or
sharp edges in direct contact.
(continued)
70
-------
TABLE 11 (continued)
Material and Description
Advantage?.
Disadvantage
Commercial polymeric membranes
(continued)
(ileoprerie rubber
(chloroprene rubber))
(Hypalon (chlorinated
chlorosulfinated
polyethylene})
(Poiyolefin (polyethylene
and chlorinated
polyethylene))
(Elasticized polyolefin
(3110))
a. Good resistance *-.,' oils, ,;rt'n?.e,
gasoline, acids, and alkalies.
b. Good resistance to abrasion,
weathering, and flexing.
c. Can be Joined at seams to cover
large areas.
d. Can be reinforced with fibers for
added strength.
e. Very low water permeability.
a. Outstanding resistance to abrasion
and weathering.
b. Available in various size sheets.
c. Can be fiber reinforced for added
strength.
d. Can be Joined at seams to cover
large areas. This can be done
onsite or at factory.
e. Very low water permeability.
a. Available in various sizes.
b. Can be Joined at seams to cover
large areas.
c. Can be fiber reinforced.
d. Chlorinated polyethylene has
excellent outdoor durability.
e. Very low water permeability.
a. Can be joined at seams to cover
large areas. Field bonding of
individual sheets is done using
a heat seaming technique.
b. Excellent resistance to soil micro-
organisms, extremes of weather, and
ozone attack.
c. Very low water permeability.
a. More expensive than other natural
and synthetic rubbers.
b. Use is limited to special applica-
tions because of a_ above.
c. May be damaged by gnawing/burrowing
animals if not protected with a
soil layer.
d. May be damaged by heavy equipment
operating directly on surface and
may be punctured by large stones or
sharp edges in direct contact.
a. May be damaged by gnawing/burrowing
animals if not protected with a
soil layer.
b. Does not perform satisfactorily
when exposed to amyl acetate,
benzene, carbon tetrachloride,
cresote oil, ovc ! oi^'X^:^', dioctyl
phthalate, ethyl acetate, lacquer
methylene chloride, napthalene,
nitrobenezene, oleum, toluene,
tributyl phosphate, trichloroethy-
lene, turpentine, and xylene.
c. For good seam quality, the weather
must be at least 50°F (10°C) and
sunny. If not, heat has to be
applied to seams to develop full
early strength.
d. May be damaged by heavy equipment
operating directly on membrane.
e. May be punctured by large r.tor.ts 1:1
sharp edges in direct contact.
a. May be damaged by gnawing/burrowing
animals if not protected with a soil
layer.
b. May be damaged by heavy equipment
operating directly on membrane.
c. May be punctured by large stones
or sharp edges in direct contact.
d. Polyethylene has poor durability
when exposed.
a. May be damaged by gnawing/burrowing
animals if not protected with a
soil layer.
b. May be damaged by heavy equipment
operating directly on membrane.
c. May be punctured by large stones
or sharp edges in direct contact
with membrane.
(continued)
-------
TABLE 11 (continued)
Material and Description
Advantages
Disadvantages
Commercial polymeric membranes
(continued)
(PVC (polyvinyl chloride))
(EPDM (ethylene-propylene
unsaturated diene
terpolymer))
Surfur (thermoplastic
coating) (Molten sulfur)
Bentonite
a. Fair outdoor durability.
b. Available in sheets of various sizes.
Factory seaming available.
c. Seams can be bonded in the field
with vinyl to vinyl adhesive.
d. Generally used without reinforcement,
however, can be fiber reinforced
for special applications.
e. Very low water permeability.
Less permeable to gas than
polyethylene.
a. Good outdoor durability. Ozone and
oxidation resistant.
b. Sheets may be bonded to cover large
areas.
c. Very low water permeability.
a. Can be formulated for a wide range
of viscosities.
b. Can be sprayed on various materials
to act as a bonding agent.
c. Reduces permeability.
d. Resistant to weather extremes
(subfreezing to very hot).
e. Resistant to acids and salts.
f . Can be mixed with fine aggregate to
form a type of concrete .
a. No special equipment needed.
b. Can be mixed with soil,
a. May be damaged by gnawing/burrowing
animals if not protected vith a soil
layer.
b. For extended life, this membrane
must be covered with soil or other
material.
c. May be damaged by heavy equipment
operating directly on surface and
may be punctured by large stones or
sharp edges in direct contact.
d. Not as durable as hypalon or
chlorinated polyethylene.
e. Becomes stiff in cold weather.
a. May be damaged by gnawing/burrowing
animals if not protected with a
soil layer.
b. May be damaged by heavy equipment
operating directly on surface and
may be punctured by large stones or
sharp edges in direct contact.
a. Requires high temperatures for
workability, 250°-300°F
(20°-150°C).
b. Requires special equipment for
handling and application.
c. May not tolerate much shear
deformation.
d. If applied to hazardous waste
containers prior to land disposal,
heat absorption by volatile wastes
may cause gas expansion and
possible explosion hazards.
a. Difficult to handle and
spread after wetting.
b. Susceptible to shrink-swell.
72
-------
TABLE 12. ESTIMATED UNIT COSTS* FOR SOME COVER LAYERS
Layer Type and Thickness
Installed Cost
dollars /yd2
Loose soil (2 ft)
Compacted soil (2 ft)
Cement concrete (i* in.)
Asphalt concrete (U in.)
Soil-cement (7 in.)
Soil-asphalt
Polyethylene membrane (10 mil)t
Polyvinyl chloride membrane (20 mil)
Chlorinated polyethylene membrane (20-30 mil)
Hypalon membrane (20 mil)
Neoprene membrane
Ethylene propylene rubber membrane
Butyl rubber membrane
Paving asphalt (2 in.)
Sprayed asphalt membrane (lA in.) and soil cover
Reinforced asphalt membrane (lOO mil) and soil cover
Bentonite layer (2 in.)
p
Bentonite admixture (9 Ib/yd ) in soil
0.35
0.70
9.00
2.50-3-50
1.50
1.50
1.00-1.50
1.30-2.00
2.UO-3.20
2.50
5-00
2.70-3-50
2.70-3.80
1.20-1.70
1.25-1.75
1.50-2.00
l.UO
0.75
* Based on data assembled in References 20, 37, 38, 39, and hO with
qualitative adjustments to present.
t Not recommended because of thinness.
Portland Cement Concrete or Mortar
Portland cement concrete or mortar ordinarily should be placed on a well-
compacted base. This requirement and the high cost (Table 12) make concrete
(and mortar to a lesser degree) unattractive for use over municipal and other
soft solid waste that will settle subsequently. Reinforcing steel bars do not
materially improve the integrity except to reduce separation after cracking,
and steel increases cost by about 15 percent. 3o
The water-cement mixing ratio should not exceed 0.65 in mild climates.
This limit should be reduced to 0.5 in severe climates where freeze-thaw is
frequent, but as a general rule, placement of cement concrete or mortar should
be restricted to the warm season. Portland cement, sand, and gravel should
be proportioned approximately 17, 39, and kh weight percent, respectively, in
73
-------
concrete. In large operations consideration might "be directed to applying
cement mortar pneumatically as shotcrete; unit cost should be about half that
for concrete. Concreting plans and specifications should include a paragraph
on curing, since curing greatly improves durability and water tightness.
Ordinarily, keep the concrete or mortar saturated for at least 5 days; a wet
soil cover will prolong curing advantageously. A design life of 50 years
would be reasonable except for the early development of fractures from dif-
ferential settlement.
Bituminous Concrete or Mortar
Besides its rather substantial advantage in unit cost (Table 12), bitu-
minous concrete or mortar can be placed in freezing weather and can use
somewhat poorer quality aggregate than cement concrete. Asphalt usually con-
stitutes about 7-10 percent of the mixture. Solids should be well graded from
gravel down to about 10 percent passing the No. 200 sieve'for concrete.
Asphalt mortar uses only sand and is sometimes applied pneumatically. Special
hot-mixing equipment may be available on contract or from road agencies,
especially in the off season. Compaction is essential, yet flexing in the
process (see Lift Thickness under COMPACTION) can easily cause unacceptable
cracking. Thickening the buffer soil below helps reduce the cracking problem.
A soil sterilant will discourage vegetation from penetrating the concrete at
a later time.
Bituminous materials are considered potentially useful for encapsulating
radioactive wastes,37 where the design life should exceed ^0 years. Experi-
ence with more conventional uses of bituminous concrete (as in canal linings)
suggests that the soil covering is almost essential as protection and will
extend the life well beyond the 10-20 years expected^O otherwise. Unfortu-
nately, soil cover complicates maintenance, and it may be prudent to consider
delaying the final cover application until most settlement has taken place.
A particularly attractive dual usage of an asphalt concrete barrier is where
it serves also as a surface pavement, e.g., a parking lot.
Bitumen-sulfur Concrete
Substitution of sulfur for asphalt in bituminous concrete offers promise
for reasons of economy and environmental responsiveness. Sulfur can replace
25-50 percent of the asphalt with little sacrifice of desired properties. 1
The usual equipment for preparation and handling of asphaltic concrete works
as well on the sulfur-extended material.
Sprayed Bituminous Membranes
Membranes formed in place with cutback, emulsified, or airblown asphalt
are common for canal lining and show promise for special solid waste covering.
A high-softening-point asphalt blown hot with a phosphoric catalyst is best.^0
Membrane thickness should be about 1/h in. Special equipment needed for
spraying the membrane may be available from highway or street maintenance
shops in the off-season. Soil buffers above and below are necessary to re-
duce vulnerability to puncture or deterioration; the lower should be sprayed
with water to prevent excessive dust and attendant pinholes, etc. A soil
-------
sterilant discourages vegetation from germinating and penetrating the
membrane.
With special equipment, one part of shredded rubber can "be mixed with
three parts of asphalt and spread to form a membrane with superior flexibility
and tensile strength, besides consuming large quantities of solid waste scrap
tires.^2 The rubber reacts with the resin portion of the asphalt with atten-
dant swelling. Thus, the membrane is especially effective for sealing.
Reinforced Bituminous Membrane
The sprayed in-place technique can be extended by incorporation of a fab-
ric for added strength; polypropylene has been used.39 After the fabric has
been joined into a continuous sheet, the sealant of anionic asphalt emulsion
with fibers, water, and wetting agent is sprayed on.
Sprayed Sulfur Membrane
Sprayed sulfur membranes appear to offer promise in place of asphalt or
cement in chemically severe environments. Summary information on this rela-
tively new development is given in Table 11 and Reference 1*3.
Polyurethane Foam
The use of polyurethane foam for both lining and covering landfills has
been promoted.^ A final soil cover is applied over the foam.
Prefabricated Bituminous Membrane
This category of membranes comprises all thin bitumen-coated felts or
fiber-mats, similar to those used in the roofing industry.20 Reinforcing ma-
terials used are jute, hemp, and glass fiber. The membranes have a thickness
of approximately 1/U in. and are supplied in rolls.
Construction procedures similar to those used for hot sprayed membranes
should be followed in preparing the subgrade and placing the membrane. All
joints of the membrane are usually lapped at least 2 in. and bonded with hot
asphalt cement, cold mastic, or special cutback.
Plastic and Rubber Membranes
Extensive use is being made of plastic and synthetic rubber membranes for
lining ponds and pits but, as yet, only sparse use in solid waste cover
systems.^»^5 The most common are plasticized polyvinyl chloride, polyeth-
ylene, and butyl rubber. Considering both performance and cost, polyethylene
may be the most economical.20
Membranes are supplied in pieces up to 100 ft wide to minimize the amount
of field joining required, but joining does not require highly trained labor.
Polyethylene and butyl are supplied in folded rolls while polyvinyl chloride
is generally accordion-folded in both directions so that the sheet can be
opened lengthwise from the back of a truck. Adjacent sheets need to be
75
-------
sealed, not just overlapped, to produce watertightness. Strips 10 by 1000 ft
were unrolled in one case^5 in Delaware to cover 10 acres of landfill;
shingled overlaps were left unsealed.
Polyvinyl chloride sheets can "be joined and sealed by injecting a small
amount of adhesive along a ^-in. overlap, then gently smoothing the adhesive-
covered area to effect a bond. A few minutes later the large sheets can be
opened. Special adhesives that develop strength more slowly are used with
polyethylene and butyl. Tape can be used to join panels of polyethylene also.
Plastic and synthetic rubber membranes should be covered with soil as
soon as possible to prevent early deterioration by mechanical damage (particu-
larly wind damage) and sun exposure. To prevent excessive softening and
dimensional changes in hot climates, placement may have to be limited to
nighttime (for polyethylene and polyvinyl chloride).
Bentonite
Bentonite is a versatile material that warrants serious consideration
on special waste-covering jobs. The primary constituent is the clay mineral
montmorillonite. Bentonite is distinguished from other clays by its extreme
fineness, high absorbency, and property of swelling in water. High-quality
bentonite contains up to 90 percent colloidal-size particles. The best
quality bentonite comes from Wyoming, but local bentonite may be a satisfac-
tory, cheaper substitute.
Bentonites exhibit high swelling or low swelling according to whether the
principal cation is sodium or calcium. High-swelling sodium bentonite, when
unconfined, absorbs nearly 5 times its weight of water and at full saturation
is nearly 15 times its dry bulk. On drying, it shrinks to its original vol-
ume. The swelling-shrinking cycle can be repeated over and over, and this
behavior gives bentonite its water-sealing power. Low-swelling calcium ben-
tonite free-swells 1.5 to 7 times in water.
The Soil Conservation Service (SCS) standards for sealing farm ponds
with bentonite39 approximate the requirements for soil cover over solid waste
as follows:
Application Rate
Soil Application Method Ib/ft^
Clay Pure membrane or mixed layer 1.0-1.5
Sandy silt Mixed layer 1.0-1.5
Silty sand Mixed layer 1.5-2.0
Clean sand Mixed layer 2.0-2.5
Open rock or gravel Clay or sand mixed layer 2.5-3.0
76
-------
WASTE MATERIALS
The other category of nonsoil materials that is available for covering
solid waste ranges through a long and diverse list of granular wastes (some
are in fact soils). The designer should review those presented below for
direct applicability and to suggest other possibilities in his vicinity.
Fly Ash*
The idea of effectively covering waste with another waste makes fly ash
a promising candidate for consideration. In a few places (e.g., West Vir-
ginia), fly ash is already being used as intermediate cover. Sources circled
in Figure 3^ account for much of nearly ^0 million tons of fly ash produced
FLY ASH SOURCE
WITH 50 Ml. RADIUS
Figure 3^. Fly ash sources east of the Rocky Mountains.
28
* The pollution potential of fly ash has not been entirely defined, and
its use in cover at a landfill should be prefaced on favorable conclusions of
environmental impact studies.
77
-------
annually in the United States (more than 85 percent east of the Mississippi
River). Other generalities and the use of fly ash in combination with soil
are discussed under ADDITIVES AND CEMENTS in Section 5.
Fly ash is essentially a silt with active or latent pozzolanic quality.
Figure 35 summarizes grain-size distribution. Coefficient of permeability is
about 10~^ cm/sec when loose (Figure 21); compaction and cementation can re-
duce k to as little as 10~" cm/sec, provided no cracks develop. Fly ash
SIEVE ANALYSIS
U OPENINGS US. STANDARD SERIES
3" |!£'W*4 10 *20*40 *BQ*200
toon
100
10
1.0 O.I 0.01
PARTICLE DIAMETER IN mm
0.001
0.0001
COBBLES
GRAVEL
COARSE! FINE
SAND
caseiMEDiuMi FINE
SILT AND CLAY
CLAY
Figure 35. Grain-size distributions for fly ash.
is largely nonplastic according to Atterberg limits. The pollution potential
from soluble calcium, sulfur, and trace element constituents should be held
relatively immobile by the inherently low permeability of properly compacted
and reacted fly ash. Fly ash is susceptible to wind and water erosion so
that special stabilization, such as with water or waterborne additives, may
be necessary.
Modified Fly Ash
The principal modification of fly ash is the addition of lime to enhance
cementation. The increase in strength should be twofold or more. Where the
free lime content of the fly ash is low (as from many eastern coals30)9 lime
additions may be necessary to achieve any cementation at all. However, both
quicklime and hydrated lime are expensive commercial chemicals, and the need
should be clearly established by testing. Hydrated lime is preferred to
quicklime for its finer grain size for better distribution. The common mix
ratio is I:k lime to fly ash, but much less lime should'suffice over solid
waste where high strength is not usually needed.
78
-------
The addition of calcium sulfates or calcium sulfite to the fly ash-lime
combination serves three purposes. The sulfate speeds up the strengthening/
curing process, and its usage provides an outlet for stocks accumulating as
waste from gas scrubbers and numerous industrial processes.32 Additionally,
the lime requirements are reduced, typically to about 5 percent in combination
with about 15 percent sulfate waste and 85 percent fly ash. Permeability
tends to be around 5 x 10~° cm/sec after proper compaction.
Bottom Ash and Slag
Ash and slag at the bottom of the boiler are the counterparts of fly ash
carried up the stack. As such, these wastes accumulate to the extent of
about 18 million tons annually in the United States and form a significant
source of solid waste cover. The source locations are about the same as those
in Figure 3^. Grain size (Figure 36) is noticably coarser than for fly ash.
SIEVE ANALYSIS
CLE6^N^"E
3" I'/aW
lOOn*&ywvz>
US STANDARD SERIES
4 «0 <20«40 '80*200
100
10 01 0 01
PARTICLE DIAMETER IN mm
0001
00001
COBBLES
GRAVEL
SAND
SOARSB FINE IcRSElMEDIUMl PW
SILT AND CLAY
CLAY
Figure 36. Grain-size distributions for bottom
ash and boiler slag.^6
Permeability (Figure 21) is correspondingly higher (5 x io~3 cm/sec), and
these wastes alone are most suitable for granular drainage layers of layered
covers. Blending may be required for general suitability as cover.
Furnace Slag
More than 50 million tons of furnace slag are generated each year in the
United States in producing iron and steel. These materials are used exten-
sively for road fill and base near sources in the eastern Midwest and else-
where. The grain size is gravelly and coarser so that the ordinary function
79
-------
for reducing infiltration is totally out. Slag should be considered for
aggregate or to blend with other cover materials or for local slope erosion
protection. Another possibility is as a thick buffer base which, by its high
density, surcharges the waste below and hastens the long-term compaction.
Furnace slag is a glass that is sometimes unstable; therefore, the pollution
potential of slag deserves special attention. Considerable experience on the
pollution potential should be available in slag-producing regions.
Incinerator Residue
Approximately 20 percent of solid waste input volume remains as residue
after incineration*^ and should be considered as a possible cover material,
particularly in large urban areas. Certain soluble constituents might make
this sandy (permeable) waste susceptible to leaching and unsatisfactory as
cover where subjected to much percolation. The grain size of one example is
given in Figure 37 for comparison with bottom ash/boiler slag in Figure 36.
SIEVE ANALYSIS
CLEAR SQUARE
OPENINGS US. STANDARD SERIES
3" I'/j'V V*4 <40 *2O*4O
100
90
I80
gro
£,
a
UJ
*>
20
10
100
10
1.0 O.I 0.01
PARTICLE DIAMETER IN mm
0001
0.0001
rAPRt re
GRAVEL
COARSE! FINE
SAND
CRSEiMEDIUMl FINE
SILT AND CLAY
CLAY
Figure 37. Grain-size distribution for typical
incinerator residue from municipal
solid waste.
Foundry Sand
Foundry sand is an example of miscellaneous, granular wastes locally
available in small tonnages.
Mine and Pit Wastes
Wastes from mining (including overburden at quarries and gravel pits) are
in a sense complementary to fly ash as cover material since many mine wastes
80
-------
are preferentially situated avay from large ur"ban areas where fly ash is
usually abundant. The immense tonnages (see Section l) of these wastes sug-
gest great potential locally as cover in place of indigenous soil. Disposal
sites for neighboring communities can be located near the source mines to
reduce cover transportation costs to a minimum. However, siting within the
mined-out area is receiving critical scrutiny presently because of the risk
of embedment in the permanent water zone. The grain size of mine waste varies
widely; rock pieces are usually abundant, but clay may be scarce in fresh mine
waste. Such mine waste is ideal for mixing into municipal waste for increased
density. On the other hand, mine waste may not serve well as a water barrier
and will probably require final covering eventually itself. A review of ma-
terials and sources is available in Reference hd.
Mine Mill Tailings
The wastes remaining after hydraulic processing of mined rocks and soils
accumulate along with the mine and pit wastes, but at fewer sources. Grain
size is in contrast since the distribution is much narrower. Processing of
phosphate rock leaves a clay slurry, while many metalliferous ores produce
silt-size tailings. Coal-washing plants release a slurry with particle sizes
reflective of the original rock grain sizesclay from shale, sand from sand-
stone. The pollution potential of slurries retaining traces of organic and
inorganic chemicals, such as flotation agents from the separation process,
should be considered. A comparison should be made of costs and logistics of
handling partially dry slurry versus drying apart and then handling.
Plant Sludges
A precedent is said to have been established already for using innoxious
industrial sludge (e.g., paper-mill sludge11) over municipal waste. Ordi-
narily, however, these sludges contain high water contents, and an intermedi-
ate drying stage may be necessary before application.
Reservoir and Channel Silt
Water storage reservoirs on rivers and streams begin accumulating sand,
silt, and clay even before the impoundment structure is completed. Since
these accumulations eventually shorten the effective life of the reservoir,
removal for use in covering waste will be doubly beneficial. Similarly, silt
is sometimes conveniently available during cleanup of flood protection chan-
nels. This potential source has the advantage of providing material in a damp
condition rather than a mud. Silt from the Bonne Carre spillway is used ex-
tensively around New Orleans for fill, including cover over solid waste.
Dredged Material
The material dredged each year (about 300 million yd3) by the Corps of
Engineers1*? in maintaining waterways and harbors constitutes another large
potential stock of cover material. The geographical distribution of avail-
able dredged materials favors areas along coasts (Figure 38) and flanking
navigable rivers exclusively; but in fact, these favored areas encompass a
significantly large part of our solid waste sources also. Besides, these
8l
-------
TOTAL NUMBER
OF SAMPLES
(ALL REGIONS]
Inorganic Fine-grained
Material of High Plaiticity'
NOTE Samples asugned to groups on
bosu of fir«t letter of USCS cloMification
TOTAL 400 SAMPLES
Figure 38. Types of dredged material, "by region, as sampled in Reference 50.
areas tend to provide fev other soil sources.
Dredged materials vary greatly in character (Figure 38) from site to
site.50 Figure 39 reveals this variability in terms of USCS types among
50
LU
J
a.
40
j
< 30
O
h
U. 20
O
h
z
UJ 10
u
K
UJ
°- 0
-SM-SM-ML
CH OH
Figure 39- Frequency of USCS types among
1*00 samples of dredged soils.50
82
-------
1+00 samples from throughout the conterminous United States. However, there
are concentrations in SP and CH types.
One concept considered feasible and perhaps even best for handling
dredged material is to reuse the primary disposal site as a holding basin
over and over. Accordingly, the dredged material is allowed to consolidate
and dry but then is loaded out on trucks and moved to places where it can be
put to most productive use. Such a handling system should be ideal for sup-
plying abundant cover material to solid waste disposal sites situated nearby.
Unfortunately, drainage of thick accumulations may not lower water content
sufficiently,^1 and evaporative drying in thin lifts may be necessary at
greater costs.
Composted Sewage Sludge
Sewage becomes a valuable special cover material when the sludge is con-
verted to a convenient, safe form by composting. Several composting processes
and combinations are available; one involves forced aeration of piles of
digested sludge and bulking material like wood chips.52 Composting can elimi-
nate malodors and human pathogens and produces a stable, humuslike organic
material that is convenient to store and spread. The value of compost is as
a source of nutrients for nonfood-chain plants and as an organic amendment
to improve the physical properties of soil (i.e., a topsoil conditioner).
Advances in this developing field will be prompted by a demand for the compost
product; the designer of covers should review periodically his needs in view
of changing costs/benefits of compost versus other, more conventional mate-
rials for topsoil.
Shale, Soft Rock, and Stiff Clay
Shale, soft rock, and stiff clay are not wastes per se, but in some
regions are so abundant as to be the primary prospective sources of fill and
waste cover. Large portions of the Great Plains are underlain by shale (see
Section 18). These sources are particularly important where the waste burial
technique is by trenching, and shale or soft rock is removed in required exca-
vation. Weathered rock usually may be classified as clayey soil, from CH to
ML. Relatively unweathered shale is commonly hard and requires ripping (with
a special dozer accessory) for excavation. The resultant blocky material is
coarse and often has to be spread, trafficked, and dried to reduce adequately
the block size. The high field density of the cover of stiff Tertiary clay
in Figure 22 reflects the original, high density of lumps and chunks not
broken down during cover spreading and compaction.
83
-------
SECTION 7
SUMMARY OF CONSIDERATIONS FOR OPERATIONS PLAN OR SPECIFICATIONS
The following plan is suggested for development of cover at waste dis-
posal areas and operations according to the aims of Public Law 9^-580. The
plan is based on the current state of the art (reviewed in Section l) and the
consideration of numerous cover functions (Sections 2 and 8-22).
GENERAL OUTLINE
For the most effective development of a solid waste cover system, the
following general steps are considered to be basic. Some leeway may be avail-
able in the soil testing program, but the importance of tests should not be
underestimated since they provide quantitative characterization of the mate-
rials available.
a. Establish cover functions (based on accurate review and projection
of waste type, climate, population, hazards, etc* Follow generally
the guidance of Section 2).
b. Inventory available cover systems.
(l) Establish cover soil sources (along with general types and
quantities available).
(2) Classify soils from all significant soil sources (by testing
representative samples. Bulk samples should represent mixed
material after handling. Assign tests, such as grain-size
gradation and Atterberg limits, to classify according to USC and
USDA systems).
(3) Obtain special testing (for strength, compaction, permeability,
capillary head, clay mineralogy, etc., according to cover func-
tion requirements).
(k) Review nonsoil options.
c. Choose best cover systems.
(l) Rank functions by importance.
(2) Rank available cover for effectiveness in each function.
81*
-------
(3) Make choice.
d. Design cover system.
(l) Design basic placement and configuration for choice c(3).
(2) Design for other functions not fulfilled "by d(l).
e. Plan operation and prepare specifications.
f. Establish quality control-assurance.
RECOMMENDATIONS FOR SPECIFIC DESIGN ELEMENTS
The following paragraphs summarize choice of material and design for
specific functions:
a. Impede infiltration/percolation by:
(l) Increasing surface slope and developing ditch system.
(2) Mixing well to avoid permeable zones.
(3) Blending other soils for better gradation.
(U) Using additives.
(5) Increasing cover thickness.
(6) Using barrier membranes.
(7) Compacting (with special compacting equipment).
(8) Using a layered system.
b. Assist infiltration/percolation by:
(l) Reducing surface slope.
(2) Using permeable soil.
(3) Eliminating compaction requirements.
c. Impede gas movement by:
(l) Using very fine soil, such as clay.
(2) Maintaining high degree of saturation.
d. Assist gas movement by:
(l) Using coarse granular cover soil, or
85
-------
(2) Incorporating venting system.
e. Control vater erosion by:
(l) Using favorable soil (according to the universal soil loss
equation (USLE)).
(2) Specifying coverages and compactive effort.
(3) Reducing surface slope.
(H) Providing surface drainage and perimeter ditch.
(5) Establishing vegetation quickly.
(6) Providing mulch and other temporary slope protection.
(7) Using additives.
f. Reduce wind erosion by:
(l) Choosing coarse soil (according to the wind erosion equation
(WEE)).
(2) Minimizing knoll-like configurations on surface.
(3) Choosing favorable length, width, and orientation designs.
(k) Establishing vegetation quickly.
(5) Using additives.
(6) Using wind barriers.
g. Minimize dust by:
(l) Centralizing haul road systems.
(2) Maintaining haul roads.
(3) Applying dust palliatives.
(lj) Starting vegetation early.
h. Hold slope stability by:
(l) Designing according to stability analyses.
(2) Keeping inclination at 1:U or less.
(3) Providing toe drains and slope protection.'
86
-------
(k) Using the trench method in special cases.
(5) Incorporating slope berms.
(6) Using zone construction.
(7) Compacting to prescribed standards.
(8) Providing features for seepage control or drainage.
i. Reduce cold climate effects by:
(l) Using coarse granular soil for cover.
(2) Reserving supply of unfrozen cover material.
(3) Scheduling operations on a seasonal basis.
Some other functions of cover are of a secondary nature, and they are
addressed in the outline above by way of the more primary functions. Thus,
steps taken to control gas movement will effectively minimize fire hazard.
Other functions are largely considered in a qualitative manner in the present
state of the art. For example, the controls of animal burrowing and vector
emergence have not been studied in detail but are rather confidently addressed
in general terms.
The question of steps and provisions in design to be taken in anticipa-
tion of future use of the landfill cannot be brought into sharp focus until
those future uses are established. Section 22 provides guidance of a general
nature. In any case, documentation of the operation and a plan for long-
range maintenance and emergency repair seem essential in view of the growing
list of forgotten dumps reappearing as serious, expensive problems of
restoration.
-------
SECTION 8
CONTROL OF INFILTRATION/PERCOLATION
Percolation is the process whereby water passes through a soil zone or
profile such as solid waste cover. Percolation is closely related to but not
synonymous with infiltration, which relates to the entry of water into the
soil through pores and cracks in the surface. Large openings within the soil
allow relatively rapid gravitational infiltration and percolation while
smaller pores restrict movement to slower capillary and adsorptive actions.
Most water enters a waste disposal area either as rainfall (or snowmelt)
or "by man-induced surface circulation. Natural precipitation is addressed in
this section although recirculation of leachate may become commonplace in the
future as a means of hastening "biochemical stabilization.
FACTORS AFFECTING INFILTRATION/PERCOLATION RATES
Figure UO outlines the factors affecting infiltration;53 selected factors
are discussed below.
Infiltration
Rate
Capillary or
Hydraulic
Conductivity
Gradient of
Total Potential
Fluid
Properties
Porous Medium
_Properties
_|De
]Vi
Density
Viscosity
Moisture Content
Pore Size, Shape,
Distribution and
Continuity
Surface Conditions -_
Pressure Gradient
Gravitational
Gradient
Pressure at
Soil Surface
Pressure at
Wet Front
Depth to
Wet Front
Particle Size Distribution
Porosity
Layering (Homogeneity)
Colloid Content
Colloid Swelling
Salt Content
Organic Matter
Shrinkage Cracks
Root & Animal Activity
Tillage
Packing
Inwash of Particles
Hydrostatic Head
Barometric Pressure
Moisture Content
Surface Tension
Contact Angle
Pressure of Confined Air
Moisture Content
Volume Infiltrated
Figure 1*0. Factors affecting the infiltration rate
into unfrozen soil.
88
-------
Idealization of Infiltration Process
Numerous models of the infiltration process have been proposed over the
last 50 years. The Horton model is described briefly here as one example of
a general infiltration rate-time relationship.5^ The curve in Figure kl
shows the infiltration capacity function during a rainstorm and represents the
u
a.
U
o
<
= fc+(f0-fc)e
,-ct
INFILTRATION
CAPACITY CURVE
Figure kl.
TIME
General infiltration
rate function.
limit for water entering a soil cover. The maximum infiltration rate occurs
at the beginning, and the rate decreases first rapidly and then more slowly
before reaching a stable minimum. The minimum infiltration rate usually ap-
proaches the percolation rate of the soil.
Refer to Figure 1*2 for an illustration of the relationship between rain-
fall intensity and infiltration capacity. Rainfall of intensity (units
length/time) below the infiltration capacity penetrates the surface and either
contributes to groundwater flow or becomes part of the capillary water content
of the soil. Some of this groundwater returns to the atmosphere as vapor
through evaporation and transpiration. When the rainfall intensity exceeds
the infiltration capacity, water accumulates on the surface and runoff occurs.
Therefore, during a rain, as the infiltration capacity of the soil decreases,
the amount of runoff increases.
Soil Moisture Content
The most important factor affecting infiltration is usually the moisture
content of the soil. The infiltration process is driven53 "by the combined
gravity and capillary forces acting downward. Capillary force also diverts
water laterally (and even upward) from large pores to capillary pores, which
may be very numerous. As the process continues, capillary pores become
filled; and with percolation to greater depth, the gravitationally driven
water encounters increased resistance due to reduction in large-pore space
and sometimes also to a barrier, such as clay. A rapid reduction of
89
-------
TIME
Figure k2.
Relationship of rainfall, run-
off, and infiltration during
a rainfall event.55
infiltration rate occurs in the first few hours of a storm (Figure 1*2). High
and low intensities, even within one storm, may be directly reflected in the
rates of infiltration and runoff. Periods of low intensity permit recovery,
either wholly or partially, of high infiltration rates "by providing time for
elimination of surface water accumulations and for internal drainage of
gravitational water within the soil.
Soil Surface Factors
Falling water drops and overriding traffic may disrupt the structure of
bare soil and cause crusting, particularly in natural soils. The crust56 is
the top few millimeters of soil, which differs considerably from that below,
and is characterized by few large pores, high bulk density, and platiness
and stratification. The crust usually has a low coefficient of permeability,
and in effect impedes infiltration.
Susceptibility to crusting is directly related to low organic matter,
high exchangeable sodium, and high silt. These components all affect the
structural stability of soil aggregates against breakdown by the slaking
action of water. Soils high in silt apparently have sufficient particle-to-
particle contact to form bonds when the soil dries. Silt also has low shrink-
age potential, so that the hard crust does not crack or disintegrate by
itself.
90
-------
Vegetation Factors
Vegetation or other surface cover has considerable influence on infiltra-
tion by attenuating rainfall kinetic energy and reducing crusting. Such
mulches as straw, burlap, or dead grass are effective attenuators; Figure U3
shows how straw and burlap act to maintain a high infiltration rate. Natural
cover of grass, trees, or crops also increases the infiltration rate by pro-
viding large root passages for water and "by breaching crusts that have formed.
An effect of vegetation should always be included in calculating the infiltra-
tion rate (see DETERMINING INFILTRATION).
Burlap ^Removed
20 40 60 80 0 20 40 60 80 100
Time in Minutes
Figure k$. Effect of mulches on infiltration
rate (from Miller and Gifford in
Reference 56).
Frozen Condition
Freezing of pore water can reduce infiltration severely (see discussion
under DETERMINING INFILTRATION).
Flow in Unsaturated Soils
The processes of infiltration and percolation in solid waste cover soil
seldom involve full saturation such as discussed under PERMEABILITY TESTS in
Section 3. Partial saturation complicates flow (Figure hk), but the funda-
mental concepts remain valid. Various investigators^? have shown that water
flows through unsaturated soil according to a modified form of Darcy's law in
which k is a nonlinear function of water content, i.e., k(0).
An important (and not immediately obvious) manifestation of the effect
of k and its dependency on 0 occurs in layered systems of contrasting soil
types.58,59 When a wetting front, moving downward in an unsaturated soil of
relatively fine pore sizes, contacts a predominantly large-pore soil, the pore
volume capable of holding water at the suction pressure existing at the wet-
ting front is reduced. Before the wetting front can advance, the suction
pressure in the upper layer must decrease until it is low enough to allow the
pores to fill with water.
91
-------
12 r
10
u
o
o
y
3
on
o
0.1 0.2 0.3
WATER CONTENT
0.4
0.5
Figure HU. Relationship between hydraulic
conductivity and volumetric
water content for a clay
soil.57
This hang-up or delay continues until the upper layer approaches sat-
uration, at which time the water is believed to descend along localized
channels5° rather than as a planar wetting front. Where the coarsely pored
soil overlies the finer layer, a similar process reduces the rate of flow to
an evaporation surface above.59
DETERMINING INFILTRATION
Numerous methods have been proposed for obtaining infiltration and in-
filtration rate. Theoretically based methods5T tend to be highly simplified
and require special determinations of properties and are not reviewed here.
Infiltration is important as direct input into analysis of percolation as
explained under WATER BALANCE ANALYSIS OF PERCOLATION FOR DESIGN.
Infiltrometer Measurement
The obvious and often preferred method of determining infiltration rate
is by the use of an infiltrometer. In simplest form, the infiltrometer is a
metal tube forced into the soil through a test section of the solid waste
cover. The tube projects above the surface, and within this space a reservoir
of water is maintained. Careful monitoring of the amount of water added to
-------
hold a constant reservoir depth is used to develop the infiltration curve.
A preferred infiltrometer also includes an outer concentric ring within
which a second reservoir is maintained (Figure ^5). This outside reservoir
produces a buffer to minimize the lateral spreading of water below the inner
OUTER
CYLINDER
SOIL
SURFACE-,
INNER
CYLINDER
\
INFILTRATION
DIRECTION
\ /
LESS LATERAL
E/
/
\
SATURATION FRONT
Figure i*5- Infiltration as measured by
field infiltrometers.
tube. Realistically simulating the cover-solid waste interface in a test
section of cover may require special care. Where the solid waste is coarse
textured and porous, a reasonable degree of similarity may be obtained by
using a gravel drainage layer below the test cover. However, see complica-
tions discussed under Flow in Unsaturated Soil.
Surface Measurement
Infiltration can also be calculated as a by-product of determination of
the runoff coefficient by surface measurements. The runoff coefficient is the
percentage of total precipitation that flows off the surface; infiltration
accounts for the remainder. Actual runoff measurements may be obtained by
carefully fencing a test plot of the landfill or a test section of the pro-
posed cover system. Representative vegetation should be included since
vegetation is important in separation of runoff and infiltration. A rain
gage should be located nearby to record the precipitation day to day or for
even closer increments of time. Important factors in establishing a runoff
plot are an adequate system for collecting and storing runoff, a barrier fence
that does not intercept rainfall from beyond the immediate plot, and contin-
gencies for high precipitation rates.
Available Runoff Coefficients
Infiltration can be estimated easily where reliable runoff coefficients
93
-------
are available. Considerable work has been done in developing more or less
standard runoff coefficients for various agricultural and engineering situa-
tions (Table 13).
TABLE 13. EMPIRICAL VALUES FOR OBTAINING RUNOFF COEFFICIENT
Value
Site Description v'
Topography
Flat land, with average slopes of 1 to 3 ft/mile 0.30
Rolling land, with average slopes of 15 to 20 ft/mile 0.20
Hilly land, with average slopes of 150 to 250 ft/mile 0.10
Soil
Tight impervious clay 0.10
Medium combinations of clay and loam 0.20
Open sandy loam O.HO
Cover
Cultivated lands 0.10
Woodland 0.20
* Add values vr for topography, soil, and cover, and subtract from unity to
obtain runoff coefficient (adapted from M. M. Bernard (Transactions,
American Society of Civil Engineers, 1935)).
Occasionally, it may be appropriate to choose two or more runoff coef-
ficients to be used according to different antecedent water conditions.55
This conclusion follows from the phenomenon previously described in which the
infiltration rate decreases during a rainstorm. A somewhat higher runoff
coefficient should be used after a period of heavy rainfall or perhaps to
represent the entire wet season.
ASCE Method
Infiltration capacity values for bare soil of three broad classes are
provided (Table lU) as the basis of the ASCE empirical method. ° These values
have been developed for semiloose soil wetted 2k hours previously in condi-
tions equivalent to July in the central United States. Soils classified
"High" in the table include, besides sand, the open-structured soils of other
textures, particularly the most friable silt loams. The higher values of f-|_
in the range indicated are ordinarily associated with relatively loose and
porous sandy soils. The central values of fj for "Intermediate" soils are
associated with the loams typical of the better agricultural regions. These
loams contain considerable clay and much silt but are friable at ordinary
water contents. The "Low" soil class includes not only most clays and clay
loams but also other soils that are dense in structure. The higher values of
f± are ordinarily associated with heavy loams characterized by high clay
content, dense structure, and excessive swell/shrink behavior. "Low" soils
-------
TABLE Ik, TYPICAL f VALUES FOR BABE SOILS60
Soil Classf!* (in./hr)
High (sandy soil) 0.50 - 1.00
Intermediate (loam, clay, silt) 0.10 - 0.50
Low (clay, clay loam) 0.01 - 0.10
* fj is the infiltration capacity after 1 hr of
continuous rainfall.
are commonly deeply cracked, and the initial infiltration rate may be high;
however, soon after wetting, the cracks are closed and f-j_ decreases rapidly
to a more characteristic, low rate.
Table lU should be supplemented with Table 15, which provides a
TABLE 15. VEGETATION COVER FACTOR,. FOR
ESTIMATING INFILTRATION CAPACI]
Vegetation
Permanent forest and grass
Close-growing crops
Row crops
Cover
Good
Medium
Poor
Good
Medium
Poor
Good
Medium
Poor
Cover Factor, N
3.0 -
2.0 -
1.2 -
2.5 -
1.2 -
1.1 -
1.3 -
1.1 -
1.0 -
7.5
3.0
l.U
3.0
2.0
1.3
1.5
1.3
1.1
vegetation factor N for the relationship for the infiltration capacity of
vegetated soil,
fn = Nf, (7)
Iv 1
Grass cover classes are as follows: gooddense vegetal cover of high-
quality grass having extensive root systems, properly managed in grass for
several years; medium30-80 percent of "good" vegetal quality and density,
well managed in grass for at least 2 years; poorless than 30 percent of
"good" vegetal density, low-quality grass and poor management.
95
-------
Curve Number Method
The SCS curve number (CN) method55 is videly used for predicting direct
runoff (and in turn infiltration) from rainfall. Total daily rainfall is the
usual basis and rainfall intensity is largely ignored. Graphical solutions
for the runoff are given in Figure U6. In Table 16 the four hydrologic soil
567
RAINFALL IP) IN INCHES
Figure k6. Estimation of direct runoff amounts from storm rainfall
(modified from Reference 55).
groups distinguished in the method are briefly described and correlated with
types of cover for solid vaste.
Vegetation is also important, and curve numbers for several combinations
of hydrologic soil group and land use or vegetation are given in Table 1?.
These curve numbers are for the intermediate antecedent moisture condition
(AMC II). Where conditions of greater or lesser antecedent rainfall
(Table 18) prevail (AMC I or AMC III), the curve number is adjusted downward
or upward, respectively (Table 19)-
A major problem for the designer of cover over solid waste arises in
anticipating and designating the condition and health of the vegetation.
Consider the common case where the designer preliminarily estimates that a
vegetated sanitary landfill cover will be similar to a pasture/range or a
-------
61
TABLE 16. HYDROLOGIC SOIL GROUPS USED BY THE SOIL CONSERVATION SERVICE
Final Constant
Infiltration
Rate, fc
in./hr
Hydrologic
Soil Group
Soils Included*
0.15 - 0.30
A (Low runoff potential) Soils having high 0.30 -
infiltration rates even when thoroughly
wetted, consisting chiefly of sands or
gravel that are deep and well to
excessively drained. These soils have a
high rate of water transmission.
B Soils having moderate infiltration rates
when thoroughly wetted, chiefly moderately
deep to deep, moderately well to well drained,
with moderately fine to moderately coarse
textures. These soils have a moderate rate
of water transmission.
C Soils having slow infiltration rates when
thoroughly wetted, chiefly with a layer
that impedes the downward movement of
water or of moderately fine to fine texture
and a slow infiltration rate. These soils
have a slow rate of water transmission.
D (High runoff potential) Soils having very 0 to 0.05
slow infiltration.rates when thoroughly
wetted, chiefly clay soils with a high
swelling potential; soils with a high perma-
nent water table; soils with a clay pan or
clay layer at or near the surface; and
shallow soils over nearly impervious materials.
These soils have a very slow rate of water
transmission.
0.05 - 0.15
* Soils are classed in the next lowest category when a high percentage of
stones is present.
meadow. In Table IT, there still remains a large range of choices of curve
numbers. In fact, the pasture/range category approaches the full range of the
table. In the extreme case of hydrologic soil group A, the curve number
ranges from 6 for a contoured pasture or range in good condition to as much as
68 for a pasture or range in poor condition without contouring.
Holtan Equation
In the Holtan equation,"3 infiltration capacity is a function of the vol-
ume of available soil water storage and of the permeability of the confining
horizon. The computation proceeds according to the empirical relation
97
-------
TABLE 17. RUNOFF CURVE NUMBERS
FOR SOIL-COVER COMPLEXES AT AMC II
55, 62
Cover
Land use Treatment or practice
Fallow Straight row
Row crops
Contoured
"
" and terraced
Small grain Straight row
"
Contoured
11
" and terraced
It tl H
Close-seeded legumes* Straight row
or rotation meadow
Contoured
"
" and terraced
n H H
Pasture or range
Contoured
"
Meadow
Woods
Farmsteads
Roads (dirt)**
(hard surface)**
Hydrologic condition
A
Poor
Good
Poor
Good
Poor
Good
Poor
Good
Poor
Good
Poor
Good
Poor
Good
Poor
Good
Poor
Good
Poor
Fair
Good
Poor
Fair
Good
Good
Poor
Fair
Good
....
77
72
67
70
65
66
62
65
63
63
61
61
59
66
58
64
55
63
51
68
49
39
47
25
6
30
45
36
25
59
72
74
Hydrologic soil group
B
86
81
78
79
75
74
71
76
75
74
73
72
70
77
72
75
69
73
67
79
69
61
67
59
35
58
66
60
55
74
82
84
C
91
88
85
84
82
80
78
84
83
82
81
79
78
85
81
83
78
80
76
86
79
74
81
75
70
71
77
73
70
82
87
90
D
94
91
89
88
86
82
81
88
87
85
84
82
81
89
85
85
83
83
80
89
84
80
88
83
79
78
83
79
77
86
89
92
Close-drilled or broadcast.
f = GlaS + f
a c
(8)
where f = infiltration capacity in inches per hour
GI = growth index of vegetation in percent of maturity
a = infiltration capacity in inches per hour per
storage
Sa = available storage in equivalent inches of water
f_ = constant rate of infiltration
of available
-------
TABLE 18. SEASONAL RAINFALL LIMITS FOR
ANTECEDENT MOISTURE CONDITIONS 5 5
Total 3-day Antecedent Rainfall
Dormant Season Growing Season
AMC Group
I
II
III
in.
<0.5
0.5-1.1
>1.1
in.
<1.U
l.it-2.1
>2.1
TABLE 19. CURVE NUMBERS FOR ANTECEDENT MOISTURE CONDITIONS I AMD
CN for
Condition
II
99
90
80
70
60
CN for
Conditions
I
97
78
63
5.1
ko
III
100
96
91
85
78
CN for
Condition
II
50
hO
30
20
10
5
CN for
Conditions
I
31
22
15
9
1+
2
III
70
60
50
37
22
13
The vegetative factor a , estimated from Table 20, is an index of surface-
connected porosity and a function of plant root density. The growth index GI
is calculated from relations between air temperature and the range of tem-
peratures needed for growth of the particular crop.63 Figure U7 illustrates
an example of annual distribution of weekly GI values. For a landfill cover
vegetated with grass, the discontinuities for harvesting would be absent, and
the overall distribution is similar to potential evapotranspiration as calcu-
lated by Holtan.63 Values of fc most commonly used in Equation 8 are those
listed in Table 16.
Frozen Soil Conditions
Moisture content at the time of freezing is highly important to infiltra-
tion, though other factors, such as vegetated versus bare surface, are capable
of exerting strong modifying effects. The following summation on soil freez-
ing and effects on infiltration capacity has been offered.53 The effect is
basically a manifestation of the blockage of pores and storage space by ice.
99
-------
TABLE 20. TENTATIVE ESTIMATES OF VEGETATION
PARAMETER "a" FOR INFILTRATION EQUATION*^
Basal Area Rating a
Vegetation
Fallow
Rov crops
Small grains
Hay:
Legumes
Sod
Pasture:
Bunchgrass
Temporary (sod)
Permanent (sod)
Woods and forests
Poor
Condition
0.10
0.10
0.20
0.20
0.1*0
0.20
0.1*0
0.80
0.80
Good
Condition
0.30
0.20
0.30
o.Uo
0.60
0.1*0
0.60
1.00
1.00
* For Equation 8.
a. If soil is frozen (late in the fall) while at a high moisture content
or an impervious layer develops at the surface due to refreezing of
meltwater at the time of the thaw, intake rate is very low and re-
mains reasonably constant.
b. If soil is at a low moisture content, but its temperature is below
freezing, meltwater entering the soil is frozen in the pores and
intake rate decreases very rapidly to near zero.
c. Occasionally, soil is frozen at moderately high moisture content
(70-80 percent field capacity), yet some of the meltwater is able to
penetrate and transfer heat and in turn to melt the ice in pores. As
the soil warms and more ice melts, the infiltration rate increases as
much as six to eight times its initial rate.
DETERMINING EVAPOTRANSPIRATION
Evapotranspiration is usually the main process by which a cover soil
loses water, so it is a major factor in determining percolation (see WATER
BALANCE ANALYSIS OF PERCOLATION FOR DESIGN). The methods below are available
for estimating potential or actual evapotranspiration. Actual evapotranspira-
tion is a closer estimate of real losses, taking into account on a periodic
basis the water actually available for plant use. During a period of sub-
normal or no precipitation, actual evapotranspiration falls below potential
evapotranspiration of the crop.
Lysimeter Measurements
A lysimeter for measuring actual evapotranspiration consists of an
100
-------
Figure kl. Relative growth (Gl) graphs
for alfalfa modified by
cutting and for corn as
modified by tillage.°3
upright vegetation-soil cell so designed that input water and water percolat-
ing out the bottom can be accurately measured; the difference is evapotrans-
piration. Direct measurements of evapotranspiration will usually only be
feasible where the designer has access to the special skills of agricultural
engineers. Such talent is found in universities and agricultural agencies.
Pan Evaporation Adjusted
A considerable background has been developed in measuring or estimating
evaporation from free water surfaces (Figure k&). Most commonly, an evapora-
tion pan is used so that water loss can be accurately measured. Since evapo-
ration from a typical pan, k ft in diameter and 10 in. deep, differs from free
water evaporation, a pan coefficient is applied to the pan evaporation value.
The range of pan coefficients spans the value 0.7,
appr ox imat ion.
6k
which is an adequate
It has been suggested that the rate of transpiration is about the same
as the rate of evaporation from a free water surface provided the availability
101
-------
Figure U8. Average annual lake evaporation in inches,
according to the National Weather Service.
of water to the plants is not restricted. Therefore, where vegetation remains
all year long and prevents essentially all evaporation from soil, the esti-
mated free water evaporation may be assumed to approximate potential
evapotranspiration. To obtain the annual distribution of potential evapo-
transpiration by this method, simply multiply pan evaporation, month by month
or at shorter intervals, by an approximate factor, e.g., 0.7. Obviously,
estimations of evapotranspiration based on pan evaporation values lack sensi-
tivity to differences from crop to crop.
Thornthwaite Method
An empirical calculation that has remained popular since introduced many
years ago is the Thornthwaite method."5 in order to determine potential
evapotranspiration, mean monthly (or closer interval) values of temperature
are used; adequate records are available from the National Climatic Center or
local sources. Three steps are involved. A heat index is obtained for each
of the 12 months and summed for the annual index. Daily potential evapo-
transpiration is obtained from the heat index by use of tables. Finally, the
potential evapotranspiration is adjusted for month and day lengths with cor-
rection factors also provided in tables.
Figure U9 presents the potential evapotranspiration curves for Seabrook,
New Jersey, and Berkeley, California, calculated on a monthly basis, in rela-
tion to precipitation and changes in soil moisture. A minor obstacle to using
102
-------
nches
nches
NOTE: ANNUAL MARCH OF PRECIPITATION (1), POTENTIAL EVAPOTRAN-
SPIRATION (2), ACTUAL EVAPOTRANSPIRATION (3), PERIODS OF
WATER SURPLUS (4), WATER DEFICIT (5), SOIL MOISTURE UTILIZA-
TION (6), AND SOIL WATER RECHARGE (7).
Figure Up. Potential evapotranspiration curves
calculated on a monthly "basis.
66
103
-------
the Thornthwaite method is the necessity of access to the appropriate refer-
ence and tables.°5 The library of a university or technical organization or
agency may solve this problem.
Consumptive Use
The basic importance of water to crop success has led to an accumulation
of information on specific crop requirements. In the vestern United States,
the consumptive use facilitates prediction of the amount of irrigation needed
to supplement relatively low natural precipitation. Consumptive use is often
lumped on an annual basis for a given crop in a given area, but its distribu-
tion over a growing season can be estimated rather well. This estimation may
be accomplished on the basis of agricultural experience with the crop or with
the aid of another evapotranspiration model. Table 21 provides some example
values of consumptive use from the literature.
TABLE 21. EXAMPLES OF CONSUMPTIVE USE IN WESTERN UNITED STATES
Crop
Alfalfa
Alfalfa
Alfalfa
Pasture
Wild Hay
Grass /Weeds
Small Grain
Oats
Wheat
Wheat
Location
Los Angeles , CA
Bonners Perry, ID
Mesa, AZ
Los Angeles, CA
Grays Lake, ID
San Bernardino, CA
Los Angeles, CA
Scottsbluff, NB
Bonners Perry, ID
San Luis Valley, CO
Consumptive Use
ft /year
3.1, 3.5
2.8
1«.3
3.5
2.6
1.8
1.6
1.2
1.5
1.2
DETERMINING WATER STORAGE CAPACITY
Two factors largely determine the water-holding capacity of a soil cover
over solid waste, pore characteristics and thickness of the layer. Water
storage capacity is basic to percolation analysis as explained under WATER
BALANCE ANALYSIS OF PERCOLATION FOR DESIGN.
Soil Characteristics
The water-holding capacity of soil can be described in several ways de-
pending upon the specific interest. Total water capacity has significance in
freshly compacted soils (Figure 11). However, with the introduction and
development of vegetation, some degree of aggregation develops, and the total
10k
-------
soil water content no longer represents a simple component. One may then
distinguish gravitational water, available water, and unavailable water (Fig-
ure 9) as discussed under AGRICULTURAL INDICES in Section 3-
Water content above field capacity is by definition at best only detained
in the soil. When free to do so, it will drain by gravity. That portion of
contained water below the wilting point percentage is tightly bound in the
soil and not extractable by plants. The most important water to healthy
vegetation is that percentage available between the wilting point and field
capacity. Figure 9 and Table 22 summarize percentages of the three states of
TABLE 22. HYDROLOGIC CAPACITIES OF TEXTURE CLASSES61
Texture Class
Coarse sand
Coarse sandy loam
Sand
Loamy sand
Loamy fine sand
Sandy loam
Fine sandy loam
Very fine sandy loam
Loam
Silt loam
Sandy clay loam
Clay loam
Silty clay loam
Sandy clay
Silty clay
Clay
Storage
Capacity
percent
2ll.ll
2H.5
32.3
37.0
32.6
30.9
36.6
32. T
30.0
31.3
25.3
25.7
23.3
19. ^
21.1+
18.8
Large Pores
percent
17.7
15.8
19.0
26.9
27.2
18.6
23.5
21.0
llt.U
11.1+
13.1+
13.0
8.1+
11.6
9.1
7.3
Plant-available
Porosity
percent
6.7
8.7
13.3
10.1
5.U
12.3
13.1
11.7
15.6
19.9
11.9
12.7
11+.9
<7 Q
7.0
12.3
11.5
soil water through the range of USDA soil types. Other estimates are avail-
able also.67,68 rphe designer should establish a basis for selection among
these data or for choosing from another source instead after consultation
with experts or careful consideration of conditions at the specific site.
Remember to consider conditions expected once the vegetation has been
established.
Root Layer Deptji
The thicker the cover soil, the greater will be the water storage capac-
ity. Actually, the storage capacity of most concern is that of water avail-
able to plant use, i.e., in the root zone, since water above field capacity
is assumed to drain away quickly vertically or laterally. In agricultural
situations, the root zone is on the order of 1+ ft thick, but at a solid waste
disposal site, it will be limited by the thickness of cover, i.e., the solid
waste cell itself is presumed inhospitable to vegetation root systems.
105
-------
Storage Calculation
The calculation of storage capacity reduces to obtaining the best esti-
mate of available water content, based largely on soil type, and to adjusting
the estimate for the thickness of the root zone. For example, consider a 2-ft
cover of silty loam over solid waste. Figure 9 for agriculture soils shows
that this cover should hold approximately 2 in. of water per foot of soil
since the wilting point is approximately l.U in. and the field capacity
3.^ in. Accordingly, the storage capacity for the 2-ft root zone, i.e., the
full thickness of solid waste cover, is estimated to be k in. of water.
WATER BALANCE ANALYSIS OF PERCOLATION FOR DESIGN
The water balance analysis can be conducted on several levels of detail
according to the needs of the designer. Gross estimates of percolation may be
made in a preliminary manner, or details can be developed using a more elabo-
rate accounting method, such as monthly balancing. Results of analysis
using mathematical models and computers are summarized at the end of this
subsection.
Disadvantages of water balance analysis are that an empirical runoff
coefficient and other parameters requiring experience and engineering judgment
for estimation are used and that the various forms of output including
percolation are not usually checked by field measurement. Therefore, an over-
estimation of another output quantity nay lead to a serious underestimation of
percolation, which is the primary interest. Several terms are abbreviated:
percolation (PRC), precipitation (P), runoff (RO), consumptive use (CU),
infiltration (l), potential evapotranspiration (PET), actual evapotranspira-
tion (AET), and change in storage (AST).
Gross Estimate
The amount of percolation can be grossly predicted on the basis of either
of the following annual (Ann.) water balance equations:
Ann. PRC = Ann. P - Ann. RO - CU (9)
Ann. PRC = Ann. P - Ann. RO - 0.7 Ann. pan evaporation (10)
For example, assume that the 20-year average annual P (ignoring snow) at
Chippewa Falls, Wisconsin, is 2^.5 in. Assume that a reasonable runoff coef-
ficient for this site is 0.065^9 and that annual CU for grass is 20 in. of
water. For the continuity dictated by Equation 9, the annual PRC is grossly
estimated to be 3-0 in.
Monthly Balance
The water balance method using a monthly increment of time has recently
been demonstrated to be a useful tool for assessing cover at waste disposal
sites.°7 Monthly hydrologic and climatologic data are used to compute monthly
106
-------
infiltration (P - RO); then soil water storage and evapotranspiration esti-
mates are incorporated to obtain average monthly (Mth.) percolation into the
waste, i.e. ,
Mth. PRC = Mth. P - Mth. RO - Mth. AET - AST (ll)
A thorough review can "be found in Reference 67» but the necessary tables and
details of procedure and calculations are only available in Reference 65.
An example of monthly water balance analysis is provided here as a review
of the procedure. Consider again the hypothetical site at Chippewa Falls,
Wisconsin. This location represents a region where appreciable snow and ice
accumulate during the winter; it supplements the three sites considered
previously^ having little snow (Cincinnati, Orlando, and Los Angeles). The
selection of Chippewa Falls also allows for direct comparison with an analysis
performed on an actual site nearby using a somewhat abbreviated procedure.°9
A tabulation is arranged in columns of months with a summary column for
annual totals (Table 23). On the first line, monthly amounts of P are
distinguished as snow or rain according to the season. All precipitation in
December, January, and February is considered to be snow that runs off during
the spring melt. An average rainfall runoff coefficient was back-calculated
for this area°9 by applying the SCS curve number method to actual rainfall
events for a 20-year period. Subtracting line RO from line P provides
I , the moisture available for infiltration. The PET was obtained°9 by
distributing the CU of a grasslike crop over the growing season in a
Thornthwait e di stribution.
The remainder of the accounting is like that in Reference 67. The quan-
tity (l - PET) pinpoints periods of moisture excess and deficiency in the
soil. A negative value indicates the amount by which I fails to supply the
potential water need of the cover vegetation. A positive value indicates the
excess water that is available for recharge or percolation.
Soil moisture storage (ST) is obtained following the concepts described
under DETERMINING WATER STORAGE CAPACITY. The value 1.05 in. at capacity
is assigned in humid areas to the last month having a positive value of
(I - PET), i.e., end of the wet season, in June at Chippewa Falls (Table 23).
To determine the soil moisture retained in subsequent months of water defi-
ciency, consult tables of soil moisture retention in Reference 65. '
After finding storage for each month with negative value of (I - PET),
add each positive value of (I - PET) representing an addition of moisture to
the soil to the previous month's ST value. The value of ST cannot exceed
field capacity, and any excess of (I - PET) above this maximum becomes perco-
lation. In the Chippewa Falls example, percolation occurs in the two periods
between the summer and winter when (I - PET) is positive and ST is at
1.05 in. On the other hand, as soil moisture is depleted, AET decreases
below PET by the difference between (I - PET) and AST . Where (I - PET)
is positive, the rate of evapotranspiration is not limited by moisture avail-
ability and AET equals PET .
107
-------
o
OO
TABLE 23- MONTHLY WATER BALANCE ANALYSIS
IN INCHES FOR CHIPPEWA FALLS. WISCONSIN*
Parameter Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann.
Average Precipitation 0.89t O.Tlt 0.77* 0.67* l.OOt h.Qk
(P) 0.77* 2.55 3.73 U.19 3.65 3.56 3.37 2.0^ 0.67* 21+.53
Runoff (RO) 0.05 0.17 0.2U 0.27 0.2U 0.23 0.22 0.13 O.OU 1.59
Moisture available forQ>00 Q^Q Q^2 2^Q ^ ^^ ^ ^^ 3^ ^^ Q^3 Q^Q 22>gl|
inliltration (L)
JTUOCIiUJ-CXX CVOJ.HJ U.L CUIS
piration (PET)
(I - PET)
(E neg (I - PET))
Soil moisture
storage (ST)
(AST)
Actual evapotrans-
piration (AET)
Percolation (PRC)
0.00
0.00
1.05
0.00
0.00
0.00
0.00
0.00
1.05
0.00
0.00
0.00
0.00
0.72
1.05§
0.00
0.00
0.72
1.10
1.28
1.05
0.00
1.10
1.28
2.50
0.99
1.05
0.00
2.50
0.99
3.90 i*.6o U.oo
0.02 -1.19-0.67
(0) -1.19-1.86
1.05 0.27 0.13
0.00 -0.78-0.ll4
3.90 1*.19 3.U7
0.02 0.00 0.00
2.70
0.1*5
0.58
+0.1*5
2.70
0.00
1.20
0.71
1.05
+O.U7
1.20
0.2l*
0.00
0.63
1.05
0.00
0.00
0.63
0.00
0.00
0.05
0.00
0.00
0.00
20.00
19.06
3.88
~*Analysis is modified slightly from that by Dass et alb9 based on a 30-year climate record and a
2-ft silty sand cover with grass.
t Precipitation between November l6 and March 15 is listed as snow but is changed to runoff at
spring thaw.
* Precipitation in November and March is divided into half rain, half snow.
§ Water-holding capacity is assumed to be at maximum in March when snow melts.
-------
The example water balance analysis was expanded to explore the effects of
a much thicker soil cover on percolation (Table 2U). A storage capacity of
8 in. was substituted for the soil storage of 1.05 in. from Reference 69»
again starting in March. The overall effect on cumulative percolation vras
small, with a reduction by only about 20 percent. This analysis indicates
that increasing cover thickness is not an efficient way of reducing perco-
lation, at least in the northern Midwest.
Woolhiser Plots
A useful group of illustrations has been assembled as a product of a
simulation study (Figure 50) of potential percolation from crpplands.^^
Woolhiser was able to calculate average annual PRC for a given crop at
52 sites east of the Rocky Mountains using the SCS curve number procedure for
RO and subroutines for calculating AET and PRC . The model incorporates
sophistication for changing root depth during the growing season. The result-
ing large collection of data was sufficient for contouring, and maps were
prepared that are directly useful for roughly estimating percolation in four
soil types (Figures 51 through 5M
Dr. D. A. Woolhiser, USDA Science and Education Administration and
Mr. R. J. Montgomery at Colorado State University modified the SCSRO model and
computer program for the present study and analyzed the four hydrologic soil
groups in a simple, waste cover configuration. Data were generated on average
annual percolation through 2 ft of soil with meadow vegetation. When their
data are plotted and contoured, it is found that the predictions of annual
percolation through U ft of type A soil supporting straight-row corn (Fig-
ure 51) are about the same as predictions for 2 ft of comparable soil with
meadow vegetation. The predictions for B and C soils are less conformable;
and, in the extreme, the predictions of annual percolation through 2 ft of
type D cover soil in the humid Southeast appear to be as much as 50 percent
greater than shown for k ft of cropland soil in Figure 5^.
USDAHL Program
An empirical mathematical model of hydrologic systems has evolved from
work at the USDA Hydrograph Laboratory (HL). Portions of the research have
been published previously, but a summary is available^ along with a listing
of the computer program. The model (Figure 55) incorporates in the water
balance continuity equation the Holtan equation (Equation 8) for infiltration
capacity and an evapotranspiration model based on pan evaporation and an ad-
justment for growth index (Figure Vf).
The USDAHL program, like most other hydrologic models, was primarily de-
signed for predicting surface runoff. Volumes running off the surface exceed
those percolating to depth usually, so that the sensitivity of this model for
predicting percolation should be considered critically. In fact, an esti-
mation of groundwater recharge (deep percolation) is required as model input.
CRITERIA FOR ALLOWABLE PERCOLATION
Perhaps the greatest challenge in designing a cover for a humid area is
109
-------
TABLE 2k. MONTHLY WATER BALANCE ANALYSIS IN INCHES WITH THICK COVER*
Parameter
Average Precipitation 0
(P)
Runoff (RO)
Moisture available for-
infiltration (l)
Potential evapotrans-
piration (PET)
(I - PET) 0,
(Z neg (I - PET))
Soil moisture Q
storage (ST)
(AST) 0.
Actual evapotrans-
piration (AET)
Percolation (PRC) 0.
Jan
.89t
.00
.00
.00
00
00
00
00
Feb
O.Tlt
0.00
0.00
0.00
8.00
0.00
0.00
0.00
Mar
0.77*
0.77*
0.05
0.72
0.00
0.72
8.00§
0.00
0.00
0.72
Apr
2.55
0.17
2.38
1.10
1.28
8.00
0.00
1.10
1.28
May
3.73
0.21;
3.1»9
2.50
0.99
8.00
0.00
2.50
0.99
Jun
^4.19
0.27
3.92
3.90
0.02
(0)
8.00
0.00
3.90
0.02
Jul
3.65 3
0.2k 0
3.1+1 3
U.60 It,
-1.19-0.
-1.19-1.
6.89 6.
-1.11-0.
14.52 3.
0.00 0.
Aug
.56
.23
.33
.00
.67
86
33
56
89
00
Sep
3.37
0.22
3.15
2.70
0.1^5
6.78
+0.1*5
2.70
0.00
Oct
2.0l4
0.13
1.91
1.20
0.71
7.1*9
+0.71
1.20
0.00
Nov Dec
0.67* i.oot
0.67*
0.014
0.63 o.oo
0.00 0.00
0.63 o.oo
8.00 8.00
+0.51 o.oo
0.00 0.00
0.12 0.00
Ann.
k.ok
2k. 53
1.59
22.9*4
20.00
19.81
3.13
* Compare with Table 23.
t .Precipitation between November l6 and March 15 is listed as snow but is changed to runoff at
spring thaw.
* Precipitation in November and March is divided into half rain, half snow.
§ Water-holding capacity is assumed to be at maximum in March when snow melts.
-------
Read
Field
Characteristics
Read evaporation
and crop coeffi.
series parameters
CO
cc
DC
LU
CD
o
uu
QC
CO
UJ
a
QC
a
Call TPREAD
i
r
Call SNOW
Call AMCF
Call
SRO
t
Call
STEMP
i
Call ETRANS
Subroutine CN computes
an average curve number for
each day of the year.
Subroutine TPREAD reads in
1 year of daily precipita-
tion and temperature data.
Subroutine SNOW determines
which daily values of precipi-
tation are snow, accumulates
it and converts it to snowmelt
on the appropriate days.
Subroutine AMCF computes the
antecedent precipitation
index for each day.
Subroutine SRO computes daily
surface runoff using the SCS
curve number procedure.
Subroutine STEMP computes a
5-day moving average temperature
for use in the nitrification
calculations.
Subroutine ETRANS computes evapo-
ration, transpiration, percolation
nitrification and nitrate move-
ment on a daily basis for 1 year.
Compute rainfall,
runoff, percolation
evapotranspiration
and N loss
statistics.
Write
Output
Summary
Figure 50.
Generalized flow chart for Program SCSRO
vith percolation option.62
Ill
-------
NOTES: 1. FOR STRAIGHT-ROW CORN
2. APPLICABLE EAST OF ROCKY
MOUNTAINS ONLY
*0
Figure 51 Mean annual percolation in inches belov a l*-ft root zone
(Hydrologic Soil Group A). Four inches available water-
holding capacity.°2
V-4-JLL
NOTES: 1. FOR STRAIGHT-ROW CORN
2. APPLICABLE EAST OF ROCKY
MOUNTAINS ONLY
Figure 52. Mean annual percolation in inches below a k-ft root zone
(Hydrologic Soil Group B). Eight inches available
water-holding capacity.62
112
-------
NOTES:
FOR STRAIGHT-ROW CORN
APPLICABLE EAST OF ROCKY'
MOUNTAINS ONLY
Figure 53. Mean annual percolation in inches below a U-ft root
(Hydrologic Soil Group C), Eight inches available
water-holding capacity.62
zone
NOTES: 1. FOR STRAIGHT-ROW CORN
2. APPLICABLE EAST OF ROCKY
MOUNTAINS ONLY
Figure 5^. Mean annual percolation in inches below a it-ft root zone
(Hydrologic Soil Group D) Six inches available water-
holding capacity.°2
113
-------
MAINLINE
INITIALIZE ACCUMU-
LATIONS FOR ONE
DELTA TIME
CONVERT BREAK-
POINT TIME VALUES
TO ROUTING INTER-
VALS
Figure 55. Flow chart of USDAHLIk mainline (see Reference 63
for explanation of subroutines).
-------
in establishing what are tolerable limits of percolation. Attempts at solving
this problem have been made previously.67S69 Annual percolation is estimated
and used along with an assumed field capacity67,70,71 (l-h in./ft) of the
waste to estimate the time to field capacity of the waste cell. Upon reaching
field capacity, the leachate will be generated at the annual percolation rate.
This criterion is valuable in that it offers a starting point, albeit an over-
simplified one. Experience shows that a leaking solid waste disposal site
becomes a problem before field capacity. Water percolating through the cover
usually becomes channelized, especially in heterogeneous solid waste such as
from municipal sources.
A more realistic criterion for allowable percolation may be on the basis
of what is the tolerable leachate rate. If a system is designed capable of
collecting and retaining X in. of leachate (distributed over the landfill
area), then that X value will dictate the allowable percolation rate through
the cover. Accordingly, the designer may be advised to analyze, besides the
average condition, a daily or hourly water balance for the 20-year storm, etc.
In this way, extreme throughflows will be incorporated in the design and will
not surprise and overwhelm a system designed only for average percolation.
DESIGNING FOR INFILTRATION/PERCOLATION CONTROL
Several of the parameters influencing infiltration and percolation can
be manipulated during design and construction. The principal techniques
are soil selection or blending, compaction, and layering. Presently, the
usual intention is to impede the percolation of water, and the following
guidance is oriented in that direction. For cases where the cover is intended
to pass water freely, the appropriate procedure should also be apparent in
contrast.
Selection of Soil
It was emphasized under Flow in Unsaturated Soils that permeability is a
direct indicator of a soil's tendency to allow percolation of water. Accord-
ingly, one of the most useful means of designing a cover to impede the passage
of water into solid waste cells is by use of fine-grained soil with inherently
low k . Conversely, where relatively free passage of water is needed, the
choice of cover soil should be among those with predominantly coarse grain
sizes (and high k ). Well-graded granular soils have lower k values than
poorly graded granular soils (Table 6) provided the median grain size is the
same. Table 5 should be useful as a guide in determining the relative effec-
tiveness of various soils in impeding or passing water, but other factors,
such as shrinking and cracking characteristics, and root-system development
may complicate the choice.
Blending
If well-graded fine soil is not available nearby but coarse- and fine-
grained soils are, blending should be considered. As explained in Section 5
soil blending is effective for increasing impedance to water movement, since
the grain-size distribution is broadened as compared with distributions of
the component soils. Blending is usually an expensive operation, and a
115
-------
thorough review of other options should be made before proceeding on a large
scale.
Compaction
As a general rule, the cover should be compacted at all solid waste dis-
posal areas. Compaction is effective in reducing infiltration and percola-
tion; the porosity is decreased and k values sharply reduced. At municipal
waste landfills, an effort of more than two passes of the spreading or com-
pacting equipment may be impractical to monitor and regulate. Higher compac-
tive efforts seem appropriate for intermediate and final covers, except as
it will interfere with seeding grass. Care should be taken to assure that
the water content during compaction does not greatly exceed the optimum
percentage.
Layering
Layering achieves effects not obtainable with a single material. A two-
layer system should be sufficient for most covers and, in order to impede
percolation, might consist of a layer of compacted clay of very low k value
beneath a layer of silty sand to support vegetation, to provide erosion pro-
tection, and to help retain capillary water in the clay layer. Layering
offers promise for significant improvements in cover design, but the geometry
and layer composition should be incorporated in the design on a site-specific
basis after other options have been considered.
Membranes and Barriers
Numerous impermeable membranes and barriers are available to stop perco-
lation where such a need has been established. The costs are high, and cover
systems incorporating such features are ordinarily only specified over hazard-
ous wastes. Section 6 provides a review of such commercial cover materials.
Locally, infiltration barriers will serve beneficially as gas barriers also,
but elsewhere the two functions are in conflict (see Gas Barriers in Sec-
tion 9).
Increased Thickness
The principal effects of increasing cover thickness are to increase the
water storage capacity, to extend percolation time, and to reduce effects of
cracks and settlements. Contrasting effects can develop; the increased
storage capacity and root zone may result in more efficient evapotranspira-
tion, but then more water can be stored in the cover for subsequent slow
drainage and percolation. Departures from the more or less standard 2-ft
thickness should be backed up by an appropriate water balance analysis. Note
that increasing thickness and storage is apparently not an efficient design
tool (Tables 23 and 2U) for reducing percolation (see Discontinuities).
Discontinuities
An otherwise well-designed cover system may be compromised in time if
deep cracks or offsets develop. Such discontinuities commonly form in
116
-------
association with differential settlement and, therefore, are aggravated by
formation of depressions detaining some runoff. The first step to avoiding
discontinuities conies in placement and compaction of the solid waste that
forms the base. Heterogeneity should be reduced as much as possible; bulky
objects, such as hard frames or elastic tires, should be kept from the upper
part of the waste cell. A second beneficial procedure is to increase cover
thickness sufficiently so that anticipated differential settlement will not
expose the waste cell to direct percolation. Ponding in associated depres-
sions can be avoided by providing sufficient slope.
Surface Slope
Rainfall runoff increases with an increasing slope of the surface; hence
infiltration decreases. Since erosion also increases with an increasing slope
(see Section 10), the design of the slope should balance opposing considera-
tions (where percolation is undesirable). On slopes of less than 3 percent,
the irregularities of the surface and vegetation commonly act as traps for
detention of runoff. The value 5 percent has been suggested and used in
grounds maintenance^^ as a first approximation of a slope sufficient to pro-
mote runoff without risking excessive erosion.
Figure 56 illustrates one detail of slope design peculiar to cover sur-
faces over spongy solid waste (municipal waste). Allowance should be made for
anticipated compaction after placement of solid waste, remembering that set-
tlement will be proportional to waste thickness. Otherwise, pockets of solid
waste of anomalously great thicknesses may settle sufficiently in time to com-
promise the design of surface slopes and drains. Designing slopes much
greater than 5 percent may be necessary where such anomalous waste thicknesses
are present.
The common circumstance of deposition of solid waste on hillsides will
lead to the opposite effect. Settlement of the greater thickness at the out-
side edge (Figure 56) will cause surface slope to increase in time. Fore-
thought in designing may be necessary here also to avoid increased erosion
with increasing slope.
Winter Grass
In mild climates, as in the southeastern United States, consideration
should be given to growing both summer and winter grass to protect the cover
from erosion and to extend the range of evapotranspiration to a year-round
basis.
Ditching and Drainage
The first rule of surface drainage design for solid waste sites is to
intercept and direct all water from outside the immediate area. Interception
is accomplished by constructing a ditch or system of ditches on the uphill
sides. The ditch is designed to accommodate anticipated discharge, e.g., a
10-year storm, according to an appropriate hydraulic formula such as the
following one intended for flatlands.3°
117
-------
5 PERCENT SLOPE
COVER
a. BEFORE SETTLEMENT
POTENTIAL
CRACKS
b. AFTER SETTLEMENT
Figure 56. Disruption of surface slope by
excessive settlement.
Q = CA5/6
where Q = required discharge in cubic feet per second
C - watershed/storm coefficient
A = drainage area in square miles
and
to
(12)
On the cover itself discharge volumes are small, and the main concern is
removxng water quickly with minimal damage by erosion. A ditch slope o?
2 percent xs recommended. 72 Dltches should ^ ed and f £
maxntenance, side slopes should not exceed 1 vertical (V) on 3 horizontal
or xn cases of V-shaped channels, IV on
-------
Subsurface Drainage
Removal of cover soil water through buried drains offers promise for ef-
fective reduction of percolation into waste cells, since such drains have been
proven viable in engineering and agriculture. Buried pipe drains are conduits
of fired clay, concrete, metal, etc., with open joints or perforations that
collect and convey drainage water.3° Fired clay has "better resistance than
metal to corrosive conditions that may arise at solid waste disposal sites.
Drains require little maintenance and leave the surface in a natural and
aesthetically pleasing condition. A herringbone pattern of drains can be
adapted easily to minor topographic irregularities as they are developed in
landfilling. Each main drain ordinarily follows a topographic low, and the
lateral drains intersect at appropriate intervals. Combinations of buried
pipe drains with gravel or sand drains (Figure 57) are even more efficient.
ijP/PE DRAIN
iiAND GRA VEL
liOR SAND
[^FILTER
COVER
Figure 57 Combined buried pipe drain
and gravel or sand drain
with cover.
Table 25 should be helpful in estimating adequate spacing of pipe drains.
Maintenance
The overall plan for development and eventual closure of a solid waste
disposal site should be supplemented by contingency plans for long-range
maintenance and repair to counteract unexpected changes in soil structure,
vegetation, slope, and drainage that will in turn affect percolation.
119
-------
TABLE 25. THE RELATION OF TILE SPACING
TO THE HYDRAULIC CONDUCTIVITY OF SOILS
Hydraulic
Conductivity Tile Spacing, in feet, for Tile Placed at Depth of
in./hr 3 ft It ft5 ft
o.o - 0.05
0.05- 0.20
0.20- 0.80
0.80- 2.50
2.50- 5.0
5.0 -10.0
0 to 15
15 to 30
30 to 60
60 to 110
110 to 155
155 to 220
0 to 20
20 to HO
Uo to 80
80 to lU5
lU5 to 205
205 to 290
0 to 25
25 to 50
50 to 100
100 to 180
180 to 255
255 to 360
120
-------
SECTION 9
CONTROL OF GAS
Cover commonly serves the function of limiting gas flow paths from solid
waste. Elsewhere, control may be passive, e.g., in the case of granular soil
cover that allows escape of gas over the large landfill surface area. Since
municipal wastes generally produce large quantities of gases, emphasis will be
placed on covering municipal wastes in the following discussions.
GAS PRODUCTION IN SOLID WASTE
Organic materials in municipal waste undergo decomposition that gradually
changes from aerobic to anaerobic after covering. Carbohydrates, fats, and
proteins in the waste are broken down by microbial fermentation and converted
to gases and organic residues. The chemical reaction can be represented as
follows: 73
Anaerobic
WW.
Carbon dioxide (009) and methane ( City) comprise as much as 90 percent of
the gases produced. It has been suggested?*4- that C02 concentrations are
highest shortly after waste placement and covering. As the fill ages and de-
composition progresses, COg concentrations decrease and level off, whereas City
concentrations tend to increase and level off. Water added to the waste by
percolation through the cover accumulates in the waste and at least initially
increases the rates of decomposition and gas production.
Alone, CHI). is not explosive, but when it accumulates at concentrations of
5 to 15 percent in air, it is highly explosive. ?5 Since oxygen is virtually
void in a densely compacted and sealed landfill when CK\± is produced, there is
no danger of the fill exploding. However, if City moves through the soil and
accumulates in structures, it may cause explosive conditions.
Methane migrating through the sides or top of landfills may adversely
affect plant life. Where disposal sites are located next to planted areas,
or where parks and recreational areas are planned after disposal operations
cease, the effect of CH> on plant health is of particular concern.
GAS FLOW THROUGH COVER SOIL
Gases produced in waste cells move in all directions through cover layers
and surrounding soil to the atmosphere or adjacent substrata. Flowage takes
121
-------
place either by diffusion or in response to a gradient of total pressure.7°
The total pressure gradient mechanism is usually subordinate in solid waste
except in those cases vhere it is feasible to pump gases into or from waste
cells. Flow of gases is dependent on several physical parameters, particu-
larly porosity, degree of saturation, and free space gas diffusivity.
The rate of diffusion through a porous medium, such as soil, is less than
through air. The relationship"^ 7** for a dry material is
D = 0.66nD (13)
P °
2
where Dp = diffusivity (units of length /time) of the porous medium
n = porosity
D0 = free space diffusivity at 20°C
Equation 13 assumes no water present in the pores. In soils, the degree of
saturation S , or fraction of void space occupied by water, enters and the
relationship becomes
D = 0.66n(l - S)D (lU)
P °
In Equation ll*, the constant Do has values of 15 and 21 ft2/day for C02
and CHjj, respectively. As explained in Section 5j n is dependent on the
state of compaction of the soil. Table 26 compares n values of several
soils in loose and dense conditions, but overall, n varies only within the
range of about 30 to 50 percent. Thus, the effect of n on Dp seldom
varies by more than a factor of 2. The effect on Dp of variations in S
from saturation (100 percent) down to realistic dry conditions of perhaps as
little as 2 percent ranges to as much as a factor of 50. This prominent in-
fluence of S on the diffusivity of gas through waste covering soil has been
demonstrated in a study of vaporization and flux of hazardous chemical
waste.77
TABLE 26. APPROXIMATE AVERAGE POROSITY
OF LOOSE AND COMPACTED SOILS
Average Porosity, %
Soil Type Loose Dense
Gravel
Uniform sand
Silty sand
Clayey sand
Silt
Clay
37
1*6
1*1*
1*1*
1*1*
1*5
28
31*
37
31*
37
122
-------
Gas diffusion through a soil cover has "been calculated1 according to the
relationship
-»(M
- ML )
(15)
where q = discharge velocity (units length/time)
C = gas concentration fraction by volume on the confined side of the
cover*
L = cover thickness
Gas transfer and effects of changing design features, such as cover thickness
and soil type, can be examined using the concepts incorporated in the
equation.
Consider for example the following conditions offered as reasonably
representing a municipal sanitary Iandfill75 covered largely with clay:
Temperature = 68°F
Do(C02) = 15 ft2/day
Do(CH^) = 20.7 ft2/day
n = 60 percent**
S = 50 percent
L = 3 ft
CQ(C02) = 30 percent
C (CH, ) = 35 percent
From Equation lU
D
j& = 0.66(0.60)(1 - 0.50) = 0.198
o
Equation 15 predicts the following discharge velocities for City and C02, again
according to Reference 75:
n - (0.30)(15 ft2/day)(0.198)
^C02 ~ 3 ft
= (°-35)(20.7 ft2/day)(0.198) = 0^7Q ft/day
t
For 1 acre, the discharges are:
* C0 is actually the difference in concentration on opposite sides of
the cover.
** The porosity n = 60 percent is probably estimated too high in this
example (see Table 26).
123
-------
- (0.297 ft/day)(U3.560 ft2/acre)(l acre) _ ft3/min
WC02 ~ (1 day/2U hr)(l hr/60 min)'^ '
- (0.^78 ft/day)(U3,560 ft2/acre)(l acre) = , ,g
^CH, (1 day/2^ hr)(l hr/60 min)
DESIGNING FOR CONTROL OF GAS FLOW
The discussions above have summarized the parameters influencing gas flow
through cover. The following procedures instituted during the design/
construction phase make use of the various factors to help control the flow.
Soil Selection
A cover soil that will maintain a high degree of saturation is most ef-
fective in reducing gas flow. A fine-grained soil, such as clay, has more
tenacity for capillary water than a coarse granular soil; in other words, the
capillary head Hc is greater. Table 5 presents some typical values of Hc
for various soils. Figure 9 provides another view of the same concept; over
half the water in clay is bound tightly, in contrast to sand with less than
5 percent. In selecting a cover soil to minimize gas movement, the finest
grained soil available in adequate quantity will ordinarily be best. Ob-
viously, a sand or gravel is the preferred soil for facilitating gas flow, as
in venting systems.
Special Compaction
Decreasing porosity of the soil by specifying appropriate compactive
effort is desirable and recommended for intermediate and final cover in order
to reduce gas migration. A scheme of quality control should usually be speci-
fied to confirm the effectiveness of the compaction.
Increased Cover Thickness
Thickening the cover is a direct and effective procedure for reducing q
as indicated by Equation 15. The technique is especially useful for inter-
mediate and final soil covers and in subsequent maintenance work after the
disposal operation has ceased.
Gas Barriers
Barriers to gas may be considered where adverse consequences of excessive
gas leakage justify their extra cost. Also, they may constitute an important
part of systems designed to recover CH^ as a source of energy. A suitable
barrier may be incorporated in a layered cover system, e.g., as a highly com-
pacted layer of damp clay a few inches thick. Impermeable membranes are other
possibilities, but overlaps or seams between strips or sheets may be vulner-
able to leakage. In all cases, the consequences of effectively restricting
the flow of gas should be evaluated. It has been suggested that membranes may
even balloon and rupture.^ It may be necessary to install numerous vents to
121*
-------
prevent the forcing of lateral movement to dangerous concentrations in base-
ments and other adjacent spaces.
Layered Cover
Layered soil cover can "be effective in blocking and channeling gas move-
ment while providing for support of vegetation and for other cover functions.
Figure 32 shows three basic components in one recommended system. The clay
layer is the barrier, serving mainly to restrict infiltration of rainwater.
The gravel layer below is intended to convey (to vents) the rising gases
blocked by the barrier; a secondary value is the level base on which the bar-
rier is founded. The topsoil supports vegetation and helps retain moisture in
the clay as explained in Section 5 under LAYERING.
Gas Vents and Channels
Gas channels and vents are used in conjunction with barriers to convey
freely the gases along special paths and through the cover to the atmosphere.
Figure 58 shows a simple design for venting gases. The access channels may
consist of parallel strips of gravel spaced at regular intervals and incorpo-
rated at the base of final covering. The strips should be thick enough
and wide enough to avoid disruption of their continuity by careless construc-
tion or subsequent settlement. Where coarse granular material is plentiful,
a continuous blanket is preferred. Pipe drains in the gravel increase effec-
tiveness but do add to expense.
Vertical, gravel-filled trenches about 3 ft wide and 10 ft deep have been
used as a remedial feature providing venting through cover on landfills with
gas problems.7" These filled slot vents are effective as long as the backfill
Riser
,V^i
Vented gas 1
Vegetation
Final cover material
Perforated lateral
Grav.l
Cell
Figure 58- Gas collecting and venting system
of laterals in gravel trenches
above waste cell.3
125
-------
remains open; clogging along the waste/backfill interface can occur from
activity of microorganisms. One disadvantage of granular slots is that rain-
water is imbibed directly. Therefore, the slots should be designed to occupy
topographic highs to avoid even greater vater infiltration from concentration
of runoff.
Forced Draft Venting
Forced draft vents offer promise for alleviating difficult gas migration
problems. Although powered pumps may be feasible in the future, "attic" tur-
bines are adequate to provide small total pressure differences that can draw
gas through wells and vents. Cost is minimal and maintenance insignificant
except for vandalism.
Plant Kills
Certain steps can be taken to preserve vegetation as a necessary part of
the cover in the face of potential gas problems.TO Shallow-rooted species
adapt better over anaerobic conditions. Special efforts should be directed to
liming, fertilizing, amending, and mulching as described generally in Sec-
tion 19. Barriers, slots, and vents should also be considered.
Maintenance/Contingency Plan
Some sort of contingency plan for controlling unexpected gas flowage is
recommended in view of the associated risk. Such a plan can be adapted from
standard plans recommended elsewhere, provided they are modified as appro-
priate for local soils and conditions. Periodic inspection should be pre-
scribed as a part of the plan; gas concentration measurements within and below
the cover are suggested.
Discontinuities
See the discussion in Section 8 on this topic. Breaks in the cover will
provide unplanned exits for gas.
126
-------
SECTION 10
WATER EROSION CONTROL
When raindrops strike bare soil cover 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
stress. Consequently, rill erosion increases with increasing slope and chan-
nel length, while sheet erosion continues more uniformly between the rills;
relative contributions to total soil loss differ with soil and surface
conditions.
THE UNIVERSAL SOIL LOSS EQUATION
The most accurate soil loss prediction tool that is now field-operational
is the USDA universal soil loss equation (USLE).^2 This equation has been
used for agricultural erosion-control planning for more than a decade in the
eastern states and is now also used to a limited extent in the western states,
Hawaii, and several foreign countries. Development of the equation has in-
volved the analysis of the records from more than 10,000 plot-years of erosion
studies at k2 research stations. The USLE is applicable to soil cover over
solid waste with limitations as discussed under USE OF USLE FOR DESIGN.
The USLE provides average soil loss as the product of two quantitative
factors (soil-erodibility and rainfall-erosivity) and four qualitative factors.
The equation is
A = RKLSCP (16)
where A = average soil loss, in tons per acre, for the time period used for
factor R (e.g., annual)
R = rainfall and runoff erosivity index
K = soil erodibility factor
L = slope-length factor
S = slope-steepness factor
C = cover/management factor
P = practice factor
Rainfall and Runoff Erosivity Factor R
Factor R in the USLE usually equals the pertinent rainfall erosion
index El and is predictable from meteorological data. For average annual soil
127
-------
loss, R can be obtained from Figure 59; for shorter specific time periods,
it is the actual local El for that period. El is specifically the product of
the maximum 30-minute rainfall intensity I in inches per hour and the rain-
fall kinetic energy E . The E term has been empirically approximated as
E = 916 + 331 log Q i (ft-tons/acre-in.)
(IT:
vhere i is intensity in inches per hour. A tabulation of values from the
equation is also available.
80
The E of an individual rainstorm can be obtained by dividing the storm
into successive increments of essentially uniform intensity, using the equa-
tion to compute E of each increment, and then summing. The relation of soil
loss to El is linear; therefore, individual-storm values of El can be summed
to obtain seasonal or refined annual values more representative than the
generalizations presented in Figure 59- Nevertheless, the R values in the
figure are useful approximations, being computed from 22-year rainfall records
(1937-1958) for about 2000 locations fairly uniformly distributed over the
states east of the Rocky Mountains. For computation of average annual El
values, continuous records of 20 years or more help to avoid bias from cycli-
cal variations in the rainfall pattern.
The computed El must be modified to evaluate
two special cases:
R for the following
35 -^ 50
Figure 59- Average annual values of rainfall-erosivity factor R .
79
128
-------
a. Where snowmelt runoff on moderate to steep slopes is significant
(adjust El upward).
"b. On the Coastal Plains of the Southeast (adjust El downward). A maxi-
mum of 350 has been used temporarily, pending research.
Soil ErodiMlity Factor K
The average increase in soil loss with increase in El differs from soil
to soil even when rainfall, topography, cover, and management remain the same.
The factor K is used to distinguish such differences and is the average soil
loss in tons per acre, per unit of R , for a given soil on a "unit plot" (de-
fined as 72.6 ft long with 9 percent slope, continuous fallow, and tilled
parallel to the land slope). Long-term plot studies under natural rainfall
produced K values ranging from 0.03 to 0.69.
Generally, it has been found that K is affected by particle-size dis-
tribution (percent sand, silt, and clay), organic-matter content, soil struc-
ture, and permeability. In regard to the grain sizes, very fine sand (0.05-
0.10 mm) content is more effectively included with or classified as silt. The
nomograph in Figure 60 has "been developed from empirical relationships"1 in
order to predict K for any soil.
The nomograph solution may be improved in accuracy for some special con-
ditions. Separate K values can be obtained for clays in dry and wet seasons
by using, along with normal ratings, increased permeability ratings appropri-
ate for dry, cracked clays in the dry season. Occasionally, one can improve
accuracy by regarding loose gravel or rock fragments on the surface as partial
mulch cover and reducing the calculated K accordingly. The nomograph has
been evaluated as inadequate for distinguishing erodibility of high-clay sub-
soil (such as excavated and used as solid waste cover); chemical properties of
the soil become important here.82 Standard textural classes (Table 27) are
too broad to be accurate indicators of K for in situ agricultural soils but
may be useful for first approximations of remolded waste-cover soils.
Topographic Features Factors L and S
The USLE incorporates effects of ground length and steepness in the com-
bined topographic factor LS . The separate factors L and S are the
ratios of soil loss in comparison with that from the "unit plot" with length
72.6 ft and slope 9 percent, other conditions remaining constant. The length
of concern (Table 28) is from the entry of flow to an exit into a well-defined
channel or to a slope decrease sufficient to initiate deposition. The effect
of increased length is primarily toward greater accumulation and more channel-
ization of runoff and, in turn, increased erosional capability. Also, runoff
tends to increase linearly or greater with increases in steepness, and soil
losses increase even more rapidly.
The research data used to derive LS factors in Table 28 were from field
plots not longer than 270 ft nor steeper than 18 percent. LS values for
greater dimensions and slopes are speculative, being based on extrapolations.
129
-------
bO
o
- vary fin* granular
2-tino granular
3- m«« or coarta granular
4-blocky, ploty, «r mottivo
SOIL STRUCTURE
RATING
PERMEABILITY
RATING
PERCENT SAND
(OIO-2.0mm)
vary tlo«
5- si on
4- slam ta mad.
3- modarata
2- mod 10 rapid
I- rapid
: MUK tpcroprlttt 01U. tnur lull it left «ml prvcMO to point!
th« toll's I UM (0.10-2.0 ). I or9«nlc Mtttr. itructurt. >nd ptrwjbll 1ty, Iji lh«t snutnce
Interpolate bttMvcn plotted curves. The dotted line Illustrates procedure for a soil having:
sKvfs 65*. »M SI. OM 2.8%. structure 2. penmbllltir 4. Solution: K 0.11.
Figtire 60. Nomograph for determining soil-erodibility factor K for U. S. Mainland.
79
-------
TABLE 27. APPROXIMATE VALUES OF FACTOR K FOR
USDA TEXTURAL CLASSES?9
Texture class
Sand
Fine sand
Very fine sand
Loamy sand
Loamy fine sand
Loamy very fine sand
Sandy loam
Fine sandy loam
Very fine sandy loam
Loam
Silt loam
Silt
Sandy clay loam
Clay loam
Silty clay loam
Sandy clay
Silty clay
Clay
Organic
0.5$
K
0.05
.16
.te
.12
.2U
M
.27
.35
.^7
.38
.U8
.60
.27
.28
.37
.1H
.25
matter
2%
K
0.03
.lH
.36
.10
.20
.38
.2U
.30
.Hi
.&
.1*2
.52
.25
.25
.32
.13
.23
0.13-0.
content
k%
K
0.02
.10
.28
.08
.16
.30
.19
,2k
.33
.29
.33
.k2
.21
.21
.26
.12
.19
29
The values shown are estimated averages of broad
ranges of specific-soil values. When a texture is
near the borderline of two texture classes, use
the average of the two K values.
Soil loss estimates for slopes steeper than about 30 percent are potentially
subject to considerable error.
Shape of the slope is also important. An irregular slope can be evalu-
ated as a series of segments with uniform gradients. For engineered land-
fills, two or three segments should be sufficient. Provided the segments are
selected so that they are also of equal length, Table 28 can be used with
certain adjustments that have been found62 to be appropriate. Enter Table 28
with the total slope length for LS values corresponding to the percent slope
of each segment. For three segments, multiply the chart LS values for the
upper, middle, and lower segments by 0.58, 1.06, and 1.37» respectively. The
average of the three products is a good estimate of the overall effective LS
value. If two segments are sufficient, use the multiples 0.71 and 1.29.
131
-------
TABLE 28. VALUES OF THE FACTOR LS FOR SPECIFIC
COMBINATIONS OF SLOPE LENGTH AMD STEEPNESS 79
% Slope
0.5
1
2
3
4
5
6
8
10
12
14
16
18
20
25
30
40
50
60
Slope length (feel)
25
0.07
0.09
0.13
0.19
0.23
0.27
0.34
0.50
0.69
0.90
1.2
1.4
1.7
2.0
3.0
4.0
6.3
8.9
12.0
50
0.08
0.10
0.16
0.23
0.30
0.38
0.48
0.70
0.97
1.3
1.6
2.0
2.4
2.9
4.2
5.6
9.0
13.0
16.0
75
0.09
0.12
0.19
0.26
0.36
0.46
0.58
0.86
1.2
1.6
2.0
2.5
3.0
3.5
5.1
6.9
11.0
15.0
20.0
100
0.10
0.13
0.20
0.29
0.40
0.54
0.67
0.99
1.4
1.8
2.3
2.8
3.4
4.1
5.9
8.0
13.0
18.0
23.0
150
0.11
0.15
0.23
0.33
0.47
0.66
0.82
1.2
1.7
2.2
2.8
3.5
4.2
5.0
7.2
9.7
16.0
22.0
28.0
200
0.12
0.16
0.25
0.35
0.53
0.76
0.95
1.4
1.9
2.6
3.3
4.0
4.9
5.8
8.3
11.0
18.0
25.0
--
300
0.14
0.18
0.28
0.40
0.62
0.93
1.2
1.7
2.4
3.1
4.0
4.9
6.0
7.1
10.0
14.0
22.0
31.0
--
400
0.15
0.20
0.31
0.44
0.70
1.1
1.4
2.0
2.7
3.6
4.6
5.7
6.9
8.2
12.0
16.0
25.0
--
500
0.16
0.21
0.33
0.47
0.76
1.2
1.5
2.2
3.1
4.0
5.1
6.4
7.7
9.1
13.0
18.0
28.0
--
--
600
0.17
0.22
0.34
0.49
0.82
1.3
1.7
2.4
3.4
4.4
5.6
7.0
8.4
10.0
14.0
20.0
31.0
--
800
0.19
0.24
0.38
0.54
0.92
1.5
1.9
2.8
3.9
5.1
6.5
8.0
9.7
12.0
17.0
23.0
--
--
1000
0.20
0.26
0.40
0.57
1.0
1.7
2.1
3.1
4.3
5.7
7.3
9.0
11.0
13.0
19.0
25.0
--
--
Values given for slopes longer than 300 teet or steeper than 18% are extrapolations beyond the range of the research data and,
therefore, less certain than the others.
Cover/Management Factor C
Factor C in the USLE is the ratio of soil loss from land cropped under
specified conditions to that from clean-tilled, continuous fallow.&2 There-
fore, C combines effects of vegetation, crop sequence, management, and agri-
cultural (as opposed to engineering) erosion-control practices. On landfills,
freshly covered and without vegetation or special erosion-reducing procedures
of cover placement, C will usually be about unity. Where there is vegeta-
tive cover or significant amounts of gravel, roots, or plant residues or where
cultural practices increase infiltration and reduce runoff-velocity, C is
much less than unity. C ranges from about 0.6o to less than 0.01 on cropped
land and, therefore, is important to planning erosion control on landfill.
A field-tested routine adaptable to landfill planning modifies C to re-
flect the net effect of interrelated crop and management variables and local
rainfall patterns or seasons. The first-year procedure amounts to distin-
guishing five crop stages: cover placement (rough fallow), seedling, estab-
lishment, developing-maturing crop, and sometimes residue-stubble. Probable
calendar dates for successive periods are selected. The fraction of the local
132
-------
annual El that normally occurs during each crop stage is next estimated.
These fractions are multiplied "by estimated corresponding C values
(Table 29), and the resulting products are summed to obtain the overall C .
In the second and subsequent years, the cover placement, seedling, and
establishment stages are not normally repeated, and C values should be
summed from developing-maturing and possibly residual-stubble stages only.
Computed C values are in many cases available upon request from local SCS
offices.
Supporting Practices Factor P
Factor P in the USLE is similar to C , except that it accounts for ad-
ditional effects of practices that are superimposed on the cultural practices,
e.g., contouring, terracing, and contour stripcropping. Approximate values of
P , related only to slope steepness, are listed in Table 30. These values are
based on rather limited field data, but P has a narrower range of possible
values than the other five factors. Influences of the type of vegetation,
residue management, rainstorm characteristics, and soil properties on the
value of P have not been evaluated to the point of predictability.
COVER CONSTRUCTION FACTORS
Several construction factors complicate the picture developed by the USLE
as follows.
Compaction Effects
The effect of compaction on soil erodibility is not well understood.
Numerous researchers have considered the question83-85 -5^ seem to have pro-
duced conflicting results. One study, unfortunately of limited scope, ob-
tained the results presented in Figure 6l. The dry unit weight at which a
cohesive soil is most susceptible to erosive breakdown was indicated to vary
with variation in slope, other factors remaining constant. For the ML soil at
IV on 1H, the greatest erosion occurred when the soil was heavily compacted;
but at slopes of only IV on 3H, the greatest erosion occurred when the soil
was lightly compacted. At intermediate slopes, the critical unit weight was
suggested to lie somewhere between. This study taken alone seems to indicate
that on solid waste sites where long slopes seldom exceed IV on 3H, the more
the compaction, the less the erosion, within practical limits.
Blending Effects
Composite soils are seldom prepared primarily for erosion resistance;
nevertheless, several conclusions are considered pertinent on the assumption1
that mixing of separate soil components is a viable cover option in special
cases. The following are generalizations^ On composition effects of com-
pacted soils. Erodibility generally increases with:
a. Increasing silt content.
b. Decreasing clay content.
133
-------
TABLE 29. GENERALIZED VALUES OF FACTOR C FOR STATES
EAST OF THE ROCKY MOUNTAINS ^
Crop, rotation, and management
Base value: continuous fallow, tilled up and down slope
CORN
C, RdR, tall TP, conv
C, RdR, spring TP, conv
C, RdL, fall TP, conv
C, RdR, we seeding, spring TP, conv
C, RdL, standing, spring TP, conv
C-W-M-M, RdL, TP for C, disk lor W
C-W-M-M-M, RdL, TP for C, disk tor W
C, no-till pi in c-k sod, 95-80% re
COTTON
Cot, conv (Western Plains)
Cot, conv (South)
MtADOW
Grass & Legume mix
Alfalfa, lespcdeza or Ser/cia
Sweet clover
SORGHUM, GRAIN (Western Plains)
RdL, spring TP, conv
No-till pi in shredded 70-50% re
SOYBEANS
B, RdL, spring TP, conv
C-B, TP annually, conv
B, no-till pi
C-B, no-till pi, fall shred C stalks
WHKAT
W-F, fall TP after W
W-I , stubble mulch, 500 Ibs re
W-F, stubble mulch, 1000 Ibs re
Productivity level
High
Mod.
C value
1.00
0.54
.50
.42
.40
.38
.039
.032
.017
0.42
.34
0.004
.020
.025
0.43
.11
0.48
.43
.22
.18
0.38
.32
.21
1.00
0.62
.59
.52
.49
.48
.074
.061
.053
0.49
.40
0.01
0.53
.18
0.54
.51
.28
.22
Abbreviations defined:
B soybeans
C - corn
c-k - chemically killed
conv - conventional
cot - cotton
F - fallow
M - grass & legume hay
pi - plant
W -wheat
we- winter cover
Ibs re - pounds of crop residue per acre remaining on surface after new crop seeding
% re - percentage of soil surface covered by residue mulch after new crop seeding
70-50% re - ~IQ'7i cover for C values in first column; 50% for second column
RdR - residues (corn stover, straw, etc.) removed or burned
RdL - all residues left on field (on surface or incorporated)
TP - turn plowed (upper 5 or more inches of soil inverted, covering residues)
13U
-------
TABLE "30. VALUES OF FACTOR P
Practice
Contouring (Pt.)
Contour strip cropping (Psc-)
R-R-M-M1
R-VV-M-M
R-R-W-M
R-W
R-O
Contour listing or ridge planting
(Pel)
Contour terracing (Pt)2
No support practice
Land slope (percent)
1.1-2
2.1-7 1 7.1-12
12.1-18
18.1-24
(1 actor P)
0.60
0.30
0.30
0.45
0.52
0.60
0.30
3 0.6/Vr7
1.0
0.50
0.25
0.25
0.3K
0.44
0.50
0.25
0.5/v/n"
1.0
0.60
0.30
0.30
0.45
0.52
0.60
0.30
0.6/VrT
1.0
0.80
0.40
0.40
0.60
0.70
0.80
0.40
0.8/VrT
1.0
0.90
0.45
0.45
0.68
0.90
0.90
0.45
0.9/VrT
1.0
R = rowcrop, W = fall-seeded grain, O = spring-seeded grain. M = meadow. The crops are grown in rotation and so arranged on
tlie field that rowcrop strips are always separated by a meadow or winter-grain strip.
2 These P| values estimate the amount of soil eroded to the terrace channels and are used for conservation planning. I or prediction
of off-field sediment, the Pt values are multiplied by 0.2.
3 n = number of approximately equal-length intervals into which the field slope is divided by the terraces. Tillage operations must
be parallel to the terraces.
80
Unit
(a)
85 90 95
Weight («/ft s )
Slope Ratio 31
80 85 90
Unit Weight (»/ft
(b) Slope Ratio 2\
134-
12
I II
9
U/-
L
80 85 9O
Unit Weight (*/ft
(c) Slope Ratio I
95
')
I
Figure 6l. Effect of unit weight on erosion rate at three
different slopes.83 Soil is classified ML.
(Reproduced by permission of American Society
of Civil Engineers.)
135
-------
c. Increasing amount of organic material in sandy soils.
d. Decreasing amount of organic material in clayey soils.
e. Decreasing plasticity index.
The overall effect of sand content is less definite, since sand grains are
easily detached by splash erosion but are transported with relatively greater
difficulty than fines.
Stabilization with Additives and Cements*
Numerous agents for general stabilization and against water erosion are
listed in Table 10.* Cement-stabilized soils are used occasionally for lining
embankments and drainage ditches. Oil-in-water emulsions have been used on a
large scale, despite limited water resistance of some, since their resinous
petroleum fractions have strong affinity to soils. One study°7 has indicated
the following order of decreasing effectiveness of selected additives: water
soluble urethane, vinyl acetate emulsion, synthetic rubber latex, and acrylic
ester emulsion. Erosion resistance tests of several petrochemical additives,
using water jet erosion,°8 showed the most effective were Peneprime, Airflex
720, Dowell Ml 1*5, Aerospray 52 and TO, Geotech stabilizer EA-11-00^, and 1:1
mixture of Geotech stabilizer SA-117-58 and Surface stabilizer. In another
study,"9 spray-on chemicals effective in controlling erosion of uncemented
sand were Soilbond, Landlock, Curasol AH, and Aerospray 70, but the tradi-
tional method of rolled-in straw and sprayed-on fiber was, in general, the
most effective and least expensive method of erosion control.
Aerospray 70 and Curasol AH performed best on highly erodible Piedmont
regional soils^O t^t did not perform as well as the straw-emulsion method.
In the moderately erodible soils of the Ridge and Valley region, Petroset SB
and Soilgard were best. The Atlantic Coastal Plain's slightly erodible soils
performed well with Petroset SB and asphalt emulsion. None of the chemicals
tested were as cost-effective as the conventional mixture of straw and
asphalt-emulsion (see Section 19).
From laboratory tests to evaluate 70 chemicals used in erosion control on
tailings ponds,91 effective additives were ranked in order of decreasing cost-
effectiveness as lignosulfonates, Compound SP-HOO, Soilgard, DCA-70, cement
and lime, sodium silicates, Paracol TC-18U2, Pamak WTP, Petroset SB-1,
PB-1*601, Rezosol, Dresinol TC-18U3, Coherex, and potassium silicate.
Mulching Effects
Mulch or crop residue effectively protects cropland during the approxi-
mately 8 months from harvest until the next crop develops. A similar effect
is expected where mulch is placed on solid waste cover. Figure 62 shows the
average relation of soil loss to variations in mulch coverage, as observed on
* The additives and cements listed in Table 10 and those discussed here
are from separate sources and have not been interrelated.
136
-------
(E
O
1.0
as
0.6
i
<> a4
02
O 20 40 60 80 100
% OF SURFACE COVERED BY MULCH
Figure 62. Effect of plant-residue mulch
on soil loss.62 Mulch factor
is soil loss with mulch divided
by soil loss without mulch.
35-ft cropland slopes subjected to 5 in. of simulated rain in two 1-hour
storms. The mulch factor approximates the ratio of loss with mulch to loss
without. How much the slope length or steepness could be increased before
unanchored mulch would be undercut or transported by the flowing water has,
however, not been fully determined. The relative effectiveness of several
types of mulch and related surface additions is indicated in Figure 63 for a
rain intensity of 2.5 in./hr to a total of 5 in.92 gee Section 19 for dis-
cussion of various mulch types.
Special Drainage Features
Surface drainage helps to remove water as surface runoff before it can
infiltrate the cover and enter the solid waste cells in an uncontrolled man-
ner. A well-organized system of ditches and laterals is often essential, and
a source, such as Reference 36, may be needed for particulars. The design of
the system, however, must also incorporate accessories that assure an ac-
ceptably low level of erosion during fast runoff. Some drainage accessories
are illustrated in Figures 6U and 65 for consideration in reducing erosion in
ditches; berms and ditch linings for direct protection; check dams for reduc-
ing velocity and in turn scouring; and spillways to carry concentrated flow
off the steep edges of a disposal area. Another option is to adjust design to
wider and shallower channel cross sections in order to reduce velocity (Fig-
ure 66). A flat-bottomed channel is considered best.
137
-------
NO MULCH
2 T/A WOODCHIPS
15 T/A STONE
70 T/A GRAVEL
2.3 T/A STRAW
60 T/A STONE
4 T/A WOODCHIPS
7 T/A WOODCHIPS
135 T/A STONE
240 & 375 T/A STONE
12 & 25 T/A WOODCHIPS
0 10 20 30 40
SOIL LOSS (tons/acre)
Figure 63. Influence of mulch types on
rates of soil loss from 5E
on IV construction slope.92
USE OF USLE FOR DESIGN
Considerable design control can be exerted on erosion of cover at a solid
waste disposal area on the "basis of the USLE. Specific controls may take the
form of restrictions on the choice of cover soil, or on the various design
features for drainage, top and side slopes, and surface treatment or vegeta-
tion. A particularly useful technique in selecting appropriate soil is with
the credibility factor K . The only precaution here is that site selection
studies should be adequate to quantify the characteristics needed for analysis
of remolded soil mixtures for the landfill cover as distinct from tilled crop-
land soils. It is also critical in using the USLE, which was developed for
agricultural purposes, that allowance be made for distinctions of landfill
cover/management practices.
The USLE is useful for comparing effectiveness of optional cover soils or
for evaluating proposed cover against specific allowable erosion soil loss.
Where a limiting loss, e.g., in tons per acre per unit time, is specified, a
proposed cover type and configuration, rainfall pattern, and cover management
and practice can be quickly evaluated for acceptability using Equation 16.
This approach should prove useful in many cases, if not in most, since the
climate is fixed, the choice of soil type may be rather inflexible, and con-
sequently, the equation is simplified considerably.
Elsewhere, the designing of cover for small landfills may reduce to
choosing among a few established standard configurations rather than being a
result of engineering analysis. The USLE, in this circumstance, can quickly
rank the optional designs according to effectiveness in erosion control.
138
-------
vo
Slope Interceptor Ditch
Turfed Areo
In Soils That Erode Rapidly
This Slope Should Be
Flattened And Protected.
Sod Lining
SURFACE 8 INTERCEPTOR DITCHES
Sodded Ditch
Interceptor Ditch
Types of Linings
Sod Riprap
Cloy Concrete
Lumber Asphalt
SURFACE DITCH LININGS
2nd Ditch,Where
Needed On Long
Back Slopes.
Rock Rii
Riprapped Ditch
Construct Check Dam When
Velocity Is Great Enough To
Cause Scouring.
SURFACE 8 INTERCEPTOR DITCHES
Figure 6U. Surface and interceptor ditches.
-------
SECTION A-A
Q.«L.hopg» To Moin
~ Coll«e.tir»0 OUch Or
H
*r-
O
SECTION 0-0
PLAN
VERTICAL DROP INLET
SPILLWAYS ft BERM ORAINACE STRUCTURES
Figiore 65. Embankment protection structures
-------
I.OO'
1.87'
18.0'
V=1.00*
10.0'
15.0'
21.0'
10.5'
V=1.37
7.0'
= RELATIVE VELOCITY
Figure 66. Effect of drainage ditch shape on
velocity and erosivity.
DESIGNING FOR WATER EROSION CONTROL
Several approaches are available to the designer of landfill cover for
minimizing water erosion. Also, see Reference 72 for useful details on
erosion control in grounds maintenance.
Selection of Erosion-resistant Soils
The nomograph of Figure 60 provides the direct means of ranking specific
available soils for erosion-resistance and providing K- values for quantifica-
tion. In this selection process, the other major USLE factors are independent
of variations in K and need not be considered. For purposes of covering
solid waste, the variables in the nomograph are probably reduced from their
original importance in agriculture by virtue of the remolding and mixing dur-
ing cover-soil excavation and placement. Therefore, the K values in
Table 27, based largely on grain size, are probably representative, and the
table may be considered as a simple alternate or for checking Figure 60
values.
-------
Dispersive Clay and Dispersants
Soils in a dispersed condition as a result of intrinsic nature or chemi-
cal treatments are usually susceptible to excessive erosion. Such materials
should be avoided where erosion is of importance. The SCS has considerable
experience with recognizing and handling local, dispersive clay and may be
able to give advice on potential problems.
Overall Landfill Configuration
The two factors, L and S in the USLE, dominate the erosion aspect of
runoff. For relatively small to intermediate size disposal areas (<500 ft
across), L is ordinarily subordinate to S , and a favorable configuration
is largely determined by suitably gentle slopes. Table 28 indicates that
can be held below 0.2 (an arbitrary limit for example) only on nearly flat
slopes. As a rule of thumb, try to hold overall top slope to 5 percent or
less.
Drainage Features
Ditches may be stabilized with vegetation, additives, linings, or berms.
Also consider using special features as shown in Figures 6U and 65. Channel
bottom width can be increased to reduce velocity.
External Runoff Diversion
It is generally essential to divert natural drainage from outside the
immediate site from overflowing the solid waste cover. This diversion can be
accomplished easily by maintaining throughout construction an adequate ditch
along the hillside near the intermittently changing boundary of cut or origi-
nal ground surface to landfill surface. The landfill, being located on the
vulnerable, downhill side, may require a soil berm as erosion protection where
heavy natural flow is anticipated.
Any cut more than 5 ft high with higher ground above should be provided
with a cutoff ditch several feet back of the top-of-cut line to intercept sur-
face water flowing down from the higher ground. Placing a ditch at the base
of the cut is also good practice. The cut slope may be protected further by
riprap, sod, or temporary mulch.
Side Slope Protection
Important final fill slopes more than 5 ft high should be protected from
erosion by building berms and gutters along the top of the slope. The surface
water, thus intercepted, may be disposed of by spillways and vertical drop in-
lets or other suitable conduits to proper outfall ditches. Methods of pro-
tecting fill slope berms include shooting with light asphaltic material, pav-
ing with sod, or providing paved gutters.
Favorable Cropping Practices
The importance of vegetation in reducing erosion was emphasized under
-------
Cover/Management Factor G. Vegetation should be started as soon as possible
on final cover, in some cases cell by cell. It may even be feasible to seed
intermediate cover soils for the benefits the roots and canopy will bring over
a single season. Tables 29 and 30 summarize the relative effectiveness of
various vegetation-based agricultural practices in reducing erosion.
Application of Mulch
The use of mulch or inert materials is often specified to minimize ex-
posure and protect otherwise bare soil at construction sites. Figures 62
and 63 provide guidance on the various types of mulch. Applications should
always be encouraged for the interval before vegetation emerges.
Smoothing and Compaction
The principal reason for smoothing and compacting cover soil is for the
desired effects on control of water and gas movement (Section 8). However,
the compaction also has effects on erosion (see COVER CONSTRUCTION FACTORS),
and this aspect should be considered, too. It appears that special compactive
effort is beneficial in reducing erosion (except on steep slopes) and at the
same time helps control infiltration. Therefore, a program of compaction of
final and sometimes intermediate and daily cover is recommended as explained
in Section 5-
Additives
According to the experiences cited under Stabilization with Additives
and Cements, cement and several chemical stabilizers are effective against
soil erosion. However, generally the most cost-effective method of erosion
control, until natural grass cover is established, is the straw-mulch treat-
ment, either rolled into the soil or sprayed with asphalt emulsion.
Maintenance
The need for considering long-term maintenance to avoid erosion problems
is discussed in DESIGNING FOR FUTURE USE in Section 22.
-------
SECTION 11
WIND EROSION CONTROL
Wind erosion of agricultural lands is a serious problem in arid and semi-
arid regions and elsewhere on sandy soils as witnessed by the Dust Bowl of the
southern Great Plains (Figure 67). Published information on wind forces that
can be used for predicting wind erosion and for designing control practices is
not abundant. However, sufficient data have been assembled within the past
35 years to allow characterization of wind forces at specific stations
(Table 31) and generalization of these characteristics to encompassing regions
for use in design.
This section follows a procedure93 for using wind characteristics along
with soil and vegetation factors found to be important in the erosion process
to predict soil loss and as a basis for designing erosion control measures.
An earlier, simpler exponential equation9^ expressed the amount of soil loss
as a function of soil cloddiness or grain size, amount of surface vegetation
residue, and degree of surface roughness.
EROSION IN THE SOLID WASTE/SOIL SYSTEM
The majority of studies on wind erosion and measures for its reduction
have been conducted in the interest of agriculture. The seriousness of wind
erosion is obvious on this scale where plowed fields may be thousands of feet
across and extending together over large regions. Correspondingly, the ero-
sion potential at landfills is of much lesser magnitude. Another aspect of
erosion may arise on landfills (particularly inactive landfills) where the
cover of soil is actually breached by erosion to expose the waste to potential
wind dispersion. Such small, localized instances of wind erosion are of po-
tentially widespread concern.
Besides having the obvious advantage in small size and, in turn, reduced
problem magnitude, the landfill is distinct in other basic ways. The landfill
is subject to design, wherein overall configuration, orientation, and composi-
tion of the cover can be manipulated to reduce erosion potential. One problem
to be faced in covering solid waste is the thoroughly remolded condition of
the soil and its reduced erosion resistance after excavation. Also, landfill
equipment tends to be heavy (in comparison with farm equipment) and to make
numerous traverses, and the grain or clod size is reduced further in this ad-
ditional intense reworking. In the process of effective grain-size reduction,
the cover soil becomes more credible. This aspect is not covered in the fol-
lowing prediction equation and should be carefully considered separately.
Ikk
-------
INTERNATIONAL FALLS
62* 24%
\\OMAHA \ ***22X X
\ 2I«.33X A
\ ___--^->
u«K"T
C*YWNE
XSCOTTSBLUF*
,X"'.Z2»\
^X. ' NORTH PLATtk
_J>_ i IfVJZX At
i
1
1
i -»_
i V
PUEBLO
1
]
1
DENVER
" /^
\ ' \ ' \t7»
v . _ -*?
V TOPEKA ',
\OOOOLAMO \ ^ KANSAS CITY
\ "*» ^^ %
T. |t,08OGE27C,TY 1
I
|
'AL»UOUCROUE
M
'.25 X
/WHART
/ "'.5'X OKLAHOMA
/ / 1 CITY
AMARILLD 0".*"l
I IT',28iX
\ tMlf
SALINA t \ 5*. 25 X
Z'.32X\
I
WICHITA ',
4*,44X
~\
TULSA \
5', 42X,
,1
1
LJITk CAT 1 ' '
ROSWEUL /LUBBOCK
3-.2«t / 22-.IBX
J.HOMS
/l'T*f«
J /MIDLAND
EL PASO /W.27X
n; 2ox
10*. 36X
(DALLAS
T'.STX
'PORT ARTHUR
14-, 23X
GALVCSTON
I4-.28X
Figure 67.
Prevailing wind erosion direction in the Great Plains
showing degrees from north or south and percentage of
all erosion occurring along that direction.95
(Reproduced by permission of Soil Science Society of
America.)
-------
TABLE 31. EXAMPLE OF MONTHLY WIND CHARACTERISTICS*
AVAILABLE FOR U. S. STATIONS93
Item
Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sept.
Oct.
Nov.
Dec.
Laredo, Tex.
(Jan. 1943- Feb. 1945; Sept. 1946- Aug. 1955)
Magnitude
Direction. . _ .
Preponderance-
175
115
1. 9
222
135
1. 8
320
135
1. 7
409
135
2. 4
437
135
2. 9
496
135
3. 5
433
135
3.8
357
135
3.2
240
135
1.7
228
135
2. 2
196
113
1. 8
169
113
2. 0
Lubbock, Tex.
(Aug. 1942- Dec. 1945; Jan. 1950- Dec. 1956)
Magnitude
Direction
Preponderance
308
43
1 3
438
23
1 2
640
22
1. 5
546
45
1. 1
456
68
1. 3
428
90
1. 9
178
90
2. 0
145
90
1. 5
209
68
2. 0
204
67
1. 6
293
56
1 2
385
22
1 2
Midland, Tex.
(Apr. 1940- Oct. 1946)
Magnitude
Direction _
Preponderance - -
141
23
1. 6
262
180
1. 1
346
45
1. 2
455
157
1. 1
289
90
1. 5
245
90
1. 8
118
90
1. 7
95
90
1. 5
149
90
1. 8
150
90
1. 9
143
45
1 4
166
90
1 i
Port Arthur, Tex.
(May 1950 - Apr. 1955)
Magnitude
Direction
Preponderance ._ _ __
t
359
135
1. 5
393
90
1. 6
386
90
2. 2
379
112
2. 1
265
112
2. 3
149
90
1.6
171
90
1. 2
76
68
1.3
97
67
1. 3
149
112
1. 3
252
112
1. 4
320
112
1 4
* Characteristics are defined as follows: Magnitude - sum of the products of
the cube of mean windspeed greater than 12 mph times wind duration for all
l6 principal compass directions; direction - angle in degrees parallel to
maximum wind erosion direction, measured counterclockwise with east 0 ,
north 90 , west l80°, and south 270 ; preponderance - ratio of wind erosion
forces, parallel force: perpendicular force.
THE WIND EROSION EQUATION
Soil loss depends on cloddiness, surface roughness, and surface moisture
of the soil; on amount, kind, and orientation of the vegetation; on wind ve-
locity or force; and on the windward distance across the field. The wind
erosion equation (WEE) expresses functionally the amount of erosion, in tons
per acre per annum, from a given soil surface as
A1 = f(K', C1, L1
(18)
* To avoid confusion with other symbols in this report, it has been
necessary to change some symbols from the source references, e.g., K' in
place of the original I' .
-------
where K' = a soil erodibility index
T' = a soil ridge roughness factor
C1 = a climatic factor
L' = the field length along the prevailing wind erosion direction
V = an equivalent quantity of vegetative cover
Climatic Factor C'
The climatic factor C' combines two important aspects of the erosion
processwind velocity v and near-surface water content w . An empirical
relation95 indicates that C' is approximately proportional to v3/w2 . C'
in percent has "been calculated93 for most regions of the United States on an
average monthly basis (e.g., Figure 68). Wind speeds below 13 mph are indi-
cated by experimentation to be nonerosive.
The WEE was originally set up in terms of C' averaged annually to
account for annual soil loss. As subsequently expanded93 to obtain monthly
erosion losses using monthly C' (Figure 68), the equation may require con-
siderable judgment as to what climatic conditions (which months) account for
most erosion. Until clarified by further research, it seems best to use the
monthly C' factor and procedure93 outlined "below to estimate monthly erosion
loss and to regard these estimates as highly conservative (excessively large
amount s).
Soil Erodibility K'
Soil erodibility K1 includes the second most important aspect of the
erosion process, the nature of the soil, and also an adjustment for knoll or
hill configuration. K' is equal to the product of the soil erodibility fac-
tor from Figure 69 and the knoll adjustment available in Figure TO. The
important effect of soil grain or clod size is clearly evident in the figure.
Soil Ridge Roughness Factor T'
Soil ridge roughness is a measure of the surface roughness other than
caused by clods or vegetation.95 it is determined from direct observations
and given in terms of the actual amplitude measurement from crest to trough
in the ground microtopography. The effect of the roughness on wind erosion
is incorporated as a percentage factor T' obtained from Figure 71 The
figure shows that roughness of about 3- to i|-in. depth has the maximum reduc-
ing effect on erosion.
Field Length Factor L*
The equivalent field length L' is defined as the unsheltered distance
along the direction of prevailing wind erosion (Figure 67). L' is obtained
by measuring the distance across the landfill exposure and subtracting lengths
protected by barriers, such as hedges and thick fences. Barrier protection is
usually estimated at 10 times the barrier height where a better length deter-
mination is lacking. L' is not applied directly in the WEE but is instead
used in a graphical procedure (Figure 72) as explained under USE OF WEE FOR
DESIGN. V
-------
MARCH
OCTOBER
so,*)
Figure 68. Wind erosion climatic factor Cf in percent
for March and October."^
-------
300
Ul
oc
3
W
OC
o
>-
CO
5
O
CC
200
100
0 20 40 60 80
FRACTION >0.84 mm (PERCENT)
Figure 69. Wind erosion versus percent
coarse fraction.93
70O
600
Ul
o
(/>
OT
250
2OO
8
IOO
I-5 2 25 3 '
WINDWARD KNOLL SLOPE
5 6
(PERCENT)
10
Figure TO. Knoll adjustment (a) from top of
knoll and (b) from upper third
of slope.95 (Reproduced by per-
mission of Soil Science Society
of America.)
-------
1.0
0.4
234567
SOIL RIDGE ROUGHNESS (INCHES)
IO
Figure 71. Soil ridge roughness factor T" from
actual soil ridge roughness.93
Vegetative Cover Quantity V
The vegetative cover quantity V combines type and orientation effects
with the actual tons per acre of vegetative cover or residue. Values of V
have "been computed for various kinds of vegetation or residue and are pre-
sented in Figure 73. The basic measurement of tonnage is made "by actually
weighing samples of the vegetation according to a standard procedure.95 A
graphical solution (Figure 7*0 is used to incorporate V as the final step
in the determination of A' , as explained below.
Seasonal Aspects of Wind Erosion
The WEE is based on a monthly period, and K' and modifying factors are
not in a form suitable for determining A' season by season, or otherwise.
It is emphasized,93 however, that a great variation in wind force occurs
through the year. Generally, wind erosion forces are greatest in the spring
and least in the summer, but exceptions to this generalization are not uncom-
mon. Reference 93 cites greatest forces in the summer at Laredo, Texas, and
Riverside, California, as two examples of exceptional cases.
Tabulations of the best available monthly statistics (Table 31) for nu-
merous stations around the United States are available93 an<} provide a useful
basis for estimating the seasons of maximum and minimum vind activity. These
data can be used for judging seasonal aspects and for scheduling landfill
operations as explained under DESIGNING FOR WIND EROSION CONTROL.
150
-------
LLJ
or
o
c/5
O
00
HERE
SCA
PLACE MOVABLE
10,000 1,000 100 10
EQUIVALENT FIELD LENGTH L1 (FEET)
PROCEDURE:
FOR UNSHELTERED AREA OF APPROXIMATELY EQUAL LENGTH AND
WIDTH, FOLLOW THIS EXAMPLE WHERE A^ - 86 TONS/ACRE/YEAR,
A'3 = 55 TONS/ACRE/YEAR, AND L' = eoo FT, COPY MOVABLE
AND PLACE THE COPY ALONG LEFT SIDE OF CHART.. MOVE UP TO MATCH
55 (A^l ON MOVABLE SCALE TO 86 (AJ) ON CHART. FOLLOW CURVE
FOR 86 TO RIGHT TO INTERSECTION WITH 600 (L'l. RETURN HORIZONTALLY
LEFT TO MOVABLE SCALE AND READ A^ = 42 TONS/ACRE/Y EAR.. FOR
SOLVING THE MORE COMPLICATED CASE WHERE AREA LENGTH GREATLY
EXCEEDS WIDTH, CONSULT THE ORIGINAL REFERENCE.93
u
Y.
U
c
D
J
2
Z
<(
>-
3
ND
i '. Qr
440-
420-
400-
380-
360-
340-
320-
300-
280-
260-
-240-
D 220-
^ 200:
^ 180-
0 I6CT
co 140-
0 120-
-~ 100-
*^-
o so-
il 60-
<* 50-
ir 40-
O
-^ 25-
V 20-
."« I5~
CO
00
3 5-
1 2-
1-
Al F
Figure 72. Chart for determining soil loss
from A^ , A' and L' .93
151
-------
STANDING AND FLAT GRAIN SORGHUM STUBBLE
-OF AVERAGE STALK THICKNESS, LEAFINESS, AND\
QUANTITY OF TOPS ON GROUND.
i_L._L_LLi_
02 46 8 10 12 14 16 18 20 22 24 26 28 30 32
V1 (THOUSANDS OF EQUIVALENT POUNDS PER ACRE)
ACTUAL COVER (THOUSANDS OF POUNDS PER ACRE)
O ro ro o
_O wi O 0< & oi c
/
I
/
/
! /
X
\
i
i
/
x
/
X
/
/
x
/^
/
/
/
/
/
r - -
/
X
X
X
x"
x
X
X
STANDING AND FLAT ANCHORED SMALL GRAIN
STUBBLE WITH ANY ROW WIDTH UP TO 10 INCHES
INCLUDING STOVER.
Ill 1 1 1 1 1
) 2 4 6 8 10 12 14 16 18 20 22 24 26 21
V' (THOUSANDS OF EQUIVALENT POUNDS PER ACRE)
Figure 73. Relationship of factor V to quantity and
type of vegetative cover.93 For example,
800-lb/acre actual flat residue has
equivalent V = 2500 Ib/acre.
152
-------
OS 08 I 2 3 4 5 6 6 10 2O 30 40 6O 8OIOO
fi,'4 = T'K'c'f(L') TONS/ACRE/ANNUM)
200 3OO
Figure 7^. Chart for determining soil loss
USE OF WEE FOR DESIGN
L5 ''
93
The WEE was developed for agricultural use in assessing susceptibility
of specific sites to wind erosion and designing control practices to combat
erosion. Against landfill erosion, the equation's utility is broadened con-
siderably, since some of the factors that are inflexible in the agricultural
situation, and can only be assessed, can be manipulated in the design stage of
a landfill.
The five incremental steps in solving Equation 18 are as follows :"->
Step 1. Determine (Figure 69) an credibility increment A{ = K that
would occur from a wide, isolated, smooth, unsheltered, bare
field having a calculated percentage of dry aggregates greater
than 0.8U mm in diameter (under climatic conditions as at
Garden City, Kansas, where the measurements for the table were
made). Adjust K1 for knoll configuration where appropriate
(Figure 70).
Step 2. Account for the effect of roughness T1 (Figure Jl), and find
the erodibility increment A 2 = A{ T1 .
153
-------
Step 3. Account for the effect of local wind velocity and surface soil
moisture C' , from Figure 68, and find the erodibility incre-
ment A^ = A£ C' .
Step U. Account for the effect of length of field L' , and determine
A]^ = Ao f(L') . Calculation of A^ is not a simple multi-
plication because L' , A 3 , and Ap are interrelated. A
graphical solution of this portion of the equation is given in
Figure 72.
Step 5. Account for the effect of vegetative cover in V (Figure 73),
and determine the actual annual erosion for a specific landfill
surface A£ = A1 = A^ f(V) . Here again, the relationships
among AjJ. , A1 , and V are not simple. A graphical solu-
tion is given in Figure 7^.
The WEE is potentially useful for determining acceptability or unac-
ceptability of a landfill design where coupled with a criterion for acceptable
levels of annual wind erosion. Ways of reducing high erosion should become
apparent when each factor in the equation is carefully considered separately;
thus, a manipulation of the orientation of the landfill might reduce L1 and,
in turn, erosion loss. This and other methods of design modification are dis-
cussed below.
DESIGNING FOR WIND EROSION CONTROL
Design for wind erosion control on landfills has considerable flexibility
in comparison with control measures available for application to agricultural
fields (see EROSION IN THE SOLID WASTE/SOIL SYSTEM). Each factor of the WEE
including even C1 concerns one or more variables that are at least locally
subject to manipulation. The principal techniques for designing new landfills
or modifying existing ones are briefly explained below.
Soil Composition
The susceptibility of soils to wind erosion is directly reflected in the
K1 value, which is a function of the coarse soil fraction. Figure 69 gives
the values corresponding to measured percentages of grains over 0.8U ran in
diameter. The figure is a basic tool to be used in design for selecting or
modifying cover soil type on the basis of sieve analyses of those soils
available.
Knoll and Side Slope Configuration
The vulnerability of knoll-like configurations on landfills can be eval-
uated by the use of Figure 70. An adjustment factor is obtained as an erosion
loss percentage of 100 or more in comparison with erosion loss from a similar
flat surface. This factor should be used to estimate the effects of sides of
landfills that may present a knoll-like configuration toward the prevailing
winds. It is apparent from Figure 70 that even gentle windward slopes may
cause major erosion concentrations and, therefore, are places in need of sta-
bilization or protection (see Wind Barriers) when exposed to highly erosive
-------
winds. It may even be reasonable to arrange side slopes in protected orienta-
tion and leeside positions.
Trench Method
Use of the trench method rather than disposing waste in the more common
embankment type landfill is highly effective in reducing erosion. Most land
burial in the Great Plains has been accomplished by trench method or by
filling old excavations.
Length-width and Orientation Configuration
L' is an important variable in the wind erosion process, as indicated
previously. On an eroding surface, the rate of soil movement is zero on the
windward edge and increases with distance to Ieeward95 until, on a large sur-
face, the flow reaches a maximum. At least three approaches are available
during the designing of a landfill to reduce L1 and soil loss:
a. Orient short dimension parallel to prevailing wind.
b. Use barriers at strategic locations.
c. Use only a small segment of landfill at one time, keeping the re-
mainder protected by vegetation or other means.
Vegetation Cover
The importance of vegetation in reducing wind erosion can hardly be over-
emphasized. Figure 73 indicates that even the relatively sparse cover pro-
vided by crop stubble gives a large equivalent cover for use in the WEE .
The effectiveness of vegetation in reducing wind erosion is increased when the
growth is erect and tall. Timely seeding and emergence of vegetation are
important in reducing bare soil exposure time. However, timing may not be a
straightforward matter since coordination with the growing season, windy sea-
son, and landfill operations plan must also be assured.
Stabilization with Mulch
The procedure for temporary stabilization of soils with hauled-in vegeta-
tive mulches generally consists of: preparing the seedbed, seeding grasses
and legumes, choosing and applying a vegetative mulch, and anchoring the
mulch.96
Wind Barriers
A system of wind barriers may be effective in reducing L1 and, in turn,
the erosion (according to the WEE). In preparing the barriers, two critical
factors are the height that determines sheltered length and the sturdiness to
resist overturning. Barriers may consist of slat or brush fences and board
walls. For example, slat snow fences cause beneficial eddy effects on the
leeward side.
155
-------
Additives
Since the need for wind erosion protection at landfills is often short-
term and may be urgent, emergency methods should be such as can be applied
when the need arises and will be instantaneously beneficial. The application
of chemicals to stabilize soil cover is one of the most effective quick-
response methods (Table 10). The popular procedure of sprinkling with water
is temporarily quite effective. Unfortunately, wind erosion is most common
in water-deficient areas where, in addition, evaporation rates are usually
high.
Special Area
A special area with surface configuration or trench orientation arranged
for unusual or severe wind conditions may be reserved. Some areas may expe-
rience more than one prevailing wind during a season so that the precautions
under Length-width and Orientation Configuration may need to be considered
for an oblique, standby area also.
156
-------
SECTION 12
DUST CONTROL
The generation and dispersion of dust ranks high among problems associ-
ated with day-to-day landfilling and waste disposal. Dusty conditions are
unsightly and highly irritating to workers. Any dust dispersed beyond the
site is bound to cause widespread complaints in the community. Dust from
a hazardous waste disposal area carries the added stigma of a health hazard
of considerable magnitude. Regardless of whether there is a basis in fact, a
nearby neighborhood may suspect that dust coming from an industrial plant
waste area contains hazardous waste. This section reviews briefly the tech-
niques for designing against the problem, whether it "be a potential health
hazard or only a nuisance.
CAUSES AND SOURCES OF DUST
About the only soils that are not capable of producing significant dust
are sand or gravel, from which erosional processes of wind and water already
have removed the fine material. On just about any construction site, includ-
ing landfills or hazardous waste disposal areas, some dust inevitably will be
generated from the soil on or adjacent to the activity. Cover soil will be
the primary source of dust particles, but additional components may be added
from the waste material itself, as demolition wastes of plaster, concrete, and
wood. Such waste may be dry and partially deteriorated and, therefore, es-
pecially susceptible to dust generation.
The causes of dust are usually a combination of the following four sepa-
rate processes:
a. Breakdown of soil structure.
b. Drying.
c. Vehicle wind eddies.
d. Gusty winds.
Of these factors, gusty winds are not subject to control within economic con-
straints. Almost as uncontrollable is the creation of vehicle wind eddies;
slower vehicle speed might help slightly. The other two aspects, however,
are controllable to whatever degree necessitated by the seriousness of the
problem and the economics of the landfilling operation. Therefore, the re-
mainder of this section concerns preventing or minimizing a dust problem by
taking measures to strengthen the soil structure and to retain soil moisture.
157
-------
DESIGN FEATURES FOR DUST MINIMIZATION
Several options are available in the design stage for reducing the po-
tential for dust generation. Formulas such as exist for water erosion and
wind erosion are not available to quantify or to predict the amount of dust
from certain conditions; therefore, design adjustments are somewhat qualita-
tive. Thus, a considerable degree of judgment must be exercised. Also, the
trade-off among the various design aspects or cover functions requires that
the designer weigh each choice for minimizing dust against the possibly ad-
verse effects to other cover functions.
Haul Roads Limitation
The haul roads for daily operation should be so organized as to concen-
trate traffic on one or a few routes. This organization reduces to a minimum
the length of road or tracks that is subject to producing dust. This pro-
cedure follows closely with procedures for maintaining haul roads in a condi-
tion for minimization of dust.
Haul Roads Maintenance
One or more of the following maintenance techniques may be appropriate
for haul roads:
a. Use clay-poor soils, such as river sand.
b. Surface the road with gravel.
c. Sprinkle with water as needed throughout the day.
d. Spray on or mix in chemical additives.
Selection of Soils
The dust problem can be largely eliminated where it is reasonable to use
a granular soil to cover the waste. Soils become progressively less suitable
as cover from the point of view of dust in the rank order of increasing clay
and silt sizes. The determination of grain size in this case should be based
on a standard procedure involving complete breakdown of the soil structure,
since this pulverization closely simulates the history of the soil in the
field undergoing heavy traffic.
Additives or Waste Oil
To be effective a dust palliative should strengthen bonds between soil
particles and hold this strengthened condition for an appreciable period.97
The additives in Table 10 are grouped according to five general types but are
not ranked according to effectiveness; all have shown some promise in labora-
tory and field testing. Some operators will opt for calcium chloride or
waste oil as recommended elsewhere^ for dust control. Waste oil has some air
pollution potential,9o t>ut when restricted to relatively small landfilling
operations, use of waste oil is predominantly beneficial. Otherwise, it seems
158
-------
that some experimentation should, be undertaken to develop experience in se-
lecting and using palliatives at landfills. Factors that will have to be
considered in making a choice are additive toxicity, duration of effective-
ness, cost, stability, and so forth. The designer should not expect or plan
to rely on dust palliatives for more than a few months. Beyond this time a
vegetative cover should be developed, and the causes of dust may even have
been removed from the particular section of the landfill.
Vegetation
The importance and urgency of a vegetative cover for dust control is
parallel to the importance of vegetation in controlling wind erosion. Further
details are found in Section 11.
159
-------
SECTION 13
STABILITY OF SIDE SLOPES
Some specific consequences of slope instability can be disruption of
transportation, blockage of runoff ditches, or disturbance of building founda-
tions. Hovever, the effect upon an aware and sensitive population can be even
more serious, since such an unexpected and unplanned occurrence as a slope
failure often implies accompanying pollution of the environment and infers
inability of the operator or municipality to handle its engineering problems.
SLOPE STABILITY IN THE SOLID WASTE/SOIL SYSTEM
The special nature of waste-retaining slopes (Figure 75) that makes them
somewhat more critical than ordinary fill slopes is the fact that they confine
potentially harmful waste. Any failure of the side cover may release con-
taminants directly into the environment. The specific slope stability and
related problems are as follows:
a. Slope failure opening waste cells.
Figure 75- Cover configurations at sloping sides of disposal
areas.
160
-------
b. Slope deformation opening cracks and leading to other problems.
c. Unanticipated lateral seepage of leachate or water.
d. Uncontrolled lateral seepage of leachate or water.
The last two problems are somewhat separate from slope stability yet fre-
quently are involved in a contributory role.
Design for stable slopes usually incorporates features for controlling
subsurface drainage and developing adequate shear strength. Features will
ordinarily be selected and designed within the constraint of cover material
availability. Where inferior soils must be used, it may be necessary to ad-
just the design accordingly; but adjustments are seldom prohibitively expen-
sive, since slopes are usually not high. Three basic configurations are used
for the side or sloping cover at solid waste disposal areas (Figure 75)-
EVALUATING STABILITY
The accuracy and results of analyses depend mainly on the accuracy with
which shearing strength and slope conditions can be quantified.
Strength of Waste and Soil
Fill slopes in general soil engineering are designed with cognizance of
the shear strength of the soil as determined in standard tests. Section 3
reviews tests for soil strength; the same tests apply to soillike wastes.
Strength of municipal refuse has not been adequately studied, in part because
of the difficulty in obtaining representative samples for testing. Refuse
compositions of paper, food, hard plastics, metal, etc., change from day to
day, and other changes in properties take place with time due to decomposition
and to absorption of water.
A conservative stance can "be taken in extreme cases by assuming that the
waste itself has no strength and that the strength of the mass behind the side
slope is related to the strength of the cover soil in the same ratio as the
volume proportion of cover soil (Figure 76). Thus, shearing along any in-
clined surface involves one or more cover soil layers. For example, if the
volume ratio of soil cover to waste is 1:3, the solid waste mass could be con-
sidered to have an overall strength of approximately one-fourth that of soil.
Compaction of Soil
Compaction decreases porosity n of a given soil and, in turn, produces
a higher $ . The following effect has been observed99 for medium-fine sand:
n , % <() , deg
h3.0 32
38.5 3U
36.0 37
3l*.0 1*0
161
-------
v»^i**^."»\L'i.i«*^.*c\*_':/r»N*'s^*'V«^*r«\i*\'"!
Figure 76. Idealized shear surface cutting
landfill mass of waste and
cover soil.
Also, see Figure 20 for similar results from a range of granular soils. The
effect has been explained10^ to be related to the degree of interlocking of
the grains, i.e., the greater the degree of interlocking, the greater the
overall shear resistance. Figure 77 illustrates this same phenomenon from a
slightly different viewpoint. Specific results are plotted for triaxial com-
pression tests on another medium-fine sand compacted to two different density
conditions (in terms of initial void ratio e0). The material compacted to
low e0 had extra strength manifested as a peak on the plot. Beyond this
peak, the stress dropped away to a value consistent with the loosely packed
specimen as expansion destroyed the interlock.
Foundation
Most of the failures that occur in soil embankments originate in weak
foundation soils. Accordingly, it is essential that strength and consolida-
tion characteristics be evaluated even though the foundation is not part of
the cover per se. A preliminary evaluation should be made routinely. Where
there is evidence that the foundation is weaker than the soil to be used as
cover, it is prudent to undertake a stability analysis, if necessary, with as-
sistance from an experienced agency. It will be shown in STABILITY ANALYSIS
how methods of analysis are organized to include the foundation in the search
for the potential failure surface.
Groundwater
Groundwater can have an important effect on the stability of a slope.
Where the phreatic surface lies below the mass of potential instability, the
effect is insignificant or possibly even beneficial by virtue of capillarity.
The importance of groundwater increases with depth below the phreatic surface
162
-------
Figure 11. Behavior of loose and
dense specimen of
medium-fine sand dur-
ing triaxial compres-
sion. 101 (Reproduced
"by permission of John
Wiley and Sons.)
3.
1
/
1 ^
(
1
/
/
/
x\
/
X
I
1
X
1
/
^
f
/
K
Fort Peck
TestFP
Dense;
Test FP
In both te
Sample
Sample
Speed
1.8 per
Sample
^
Sand
4-2-6
ea = 0.605
4-2-2
0 = 0.834
5tS
diameter >
length - 2
Ib per sq i
Df axial stra
cent per rr
saturated
r^3
X X
= 1.40*
99*
in>
in
-o
5 10
Axial strain
15 20
in per cent
25
"because of increasing pore pressure and corresponding reduction in S
(Equation 5)
Three cases of various degrees of importance of groundwater are idealized
in Figure 78. The preferred condition in the present state of the art of
landfill operation and maintenance is Case I where the phreatic surface is
located below the original ground surface and "below the landfill waste cells
and side slope. Here, the cover soil excludes so much rainwater as to prevent
a rise of the level of saturation into the landfill. The effect of the
groundwater on the side slope is negligible and can be ignored.
Case II in Figure 1& represents the extreme where the waste and part of
the impounding slope or dike are saturated. Actual instances of Case II are
abundant in the mining industry where plant tailings are dumped and remain in
a saturated condition. Industrial sludges and slurries are similarly im-
pounded in a saturated condition. Water soon seeps to an equilibrium (steady)
seepage configuration so that a flow net-^l Can be used to estimate pore pres-
sures for the stability analysis.
Case III is an intermediate condition between Cases I and II. Water
percolating through the cover establishes a phreatic surface that may fluctu-
ate within the solid waste mass according to climatic conditions, particularly
163
-------
7\
CASE I
CASE
CASEIH
Figure lQ. Three cases of groundwater conditions
in a landfill.
in humid regions. Conditions expected to occur over the design life of the
fill must be predicted and used to estimate the extreme phreatic surface posi-
tion. For sustained high water levels, Case III might approach Case II as far
as transient pore pressure effects on stability. A temporary rise might only
impose a weight surcharge if short in duration.
Changing Conditions
Changes of conditions that influence slope stability mostly involve the
groundwater regime. Freeze/thaw change is usually seasonal, whereas dry/soak
change is seasonal or in association with short, drastic climate episodes.
The third change, a rise of the groundwater table into the solid waste cell,
marks flow to a new water table equilibrium after disturbance of the old one
by deposition of the solid waste.
In effect, the freeze/thaw and dry/soak phenomena impose temporary
perched-water conditions on the cover soil. Soils frozen early in the season
thaw in the spring from the top down. Thaw water may be trapped over frozen
soil to form a shallow, saturated zone (Figure 79) that is susceptible to
sliding (see Section l6). Similarly, experience indicates that shallow
sliding sometimes occurs in clay embankments after heavy rainfall.l02 This
161*
-------
ZONE OF POTENTIAL
SATURATION AND IN-
STABILITY DURING THAW
DEPTH OF FREEZING
Figure 79- Need for thick soil cover in thawing
landfill slopes.
instability presumably results from rapid saturation of a shallow zone previ-
ously made permeable, porous, and weak by formation of drying cracks.
STABILITY ANALYSIS
Engineering analyses of slope stability are based on the concept that a
slope fails, unless the resultant resistance to shear on every surface tra-
versing the fill is greater than the resultant of all shearing forces exerted
on that surface by the mass above. The surface that is most likely to fail is
called the critical surface. The factor of safety (FS) quantifies the ratio
of resisting forces to driving forces.
Analytical Procedures
Determination of the location of the critical surface usually requires
successive trial analyses of likely candidates. Each trial evaluates a sur-
face having the shape of a circular arc within the foundation and/or the em-
bankment or a composite of a long horizontal plane in a foundation stratum
connecting with diagonal planes up through the foundation and embankment to
the ground surface. ^02
Analyses assuming a circular arc failure surface are made using either
the modified Swedish method-^ that considers forces on the sides of slices
within the mass, or the simpler Swedish method of slices that assumes that
side forces are equal in magnitude and parallel to the base of each slice.
The wedge method for planar sliding surfaces-^ is appropriate for weak founda-
tions requiring flat slopes or for an otherwise strong foundation containing
a thin weak stratum. Computer programs are available for the trial analyses;
a vector solution of the modified Swedish method is given here to illustrate
the general concept.
The sliding mass is divided into a number of slices of convenient width
as shown in Figure 80. Where the failure arc passes through more than one
type of soil, applicable values of shear strength are used for each slice.
Slice 6 with forces acting on it is shown in detail below as an example. The
force Wg is the total weight of the slice. The resisting cohesive force
is assumed to act parallel to chord AB and is equal to chord AB times
165
-------
ASSUMED TRIAL
FAILURE ARC
SLICE 6
b. SLICES
WITH FORCES
d. EXAMPLE EMBANKMENT SECTION
(1) W
(2)C0,=C0.AL,
W
ALL E FORCES ARE
PARALLEL TO AVER-
AGE OUTER SLOPE
BEING ANALYZED.
UI
K
3
o
K
O
u
(1) THROUGH (9)
ARE STEPS IN
CONSTRUCTION
LEGEND
W = WEIGHT OF SLICE
E = EARTH FORCE ON SIDE OF SLICE
N = NORMAL TO BASE OF SLICE
AL e LENGTH ACROSS BASE OF SLICE
CD = DEVELOPED COHESION FORCE
FO = RESULTANT OF NORMAL AND DE-
VELOPED FRICTION FORCE
<£ = DEVELOPED ANGLE OF INTERNAL
/
f
ceo.
-*
fOR
FURfi
.2 1.4 1.6 1.
TRIAL f S
d. TRIAL FS VERSUS
ERROR OF CLOSURE
CAROft OF CLOSURE
C. COMPOSITE
FORCE POLYGON
FOR ONE TRIAL FS
FRICTION OF SOIL
~, d>n = ARC TAN
TAN <;
__^_«i
F S
Figure 80. Modified Swedish method of finite slice procedure with
no water forces.-^
166
-------
the developed unit cohesion CD . The force Fpg acting at an angle cf>D
with N6 the normal to AB is the resultant of the normal force at the base
and the developed frictional force.
Assuming a trial FS, the forces acting on each slice are combined into
the composite force polygon (Figure 80). Use a convenient force scale and
follow steps I through 5 on each slice in sequence; start at the uppermost
(Slice l).
Step 1. Draw the W vector.
Step 2. Draw the CL vector parallel to the base of the slice.
Step 3. Draw a line normal to the base of the slice from the upper end
of the W vector.
Step k. Construct a line at $£, from the normal line to establish the
direction of vector resultant of the normal and frictional
forces on the base of the slice (e.g.,
Step 5. From the head of the CD vector, draw the side earth force
vector E parallel to the average embankment slope to inter-
sect the resultant vector, thereby closing the force polygon.
This establishes the magnitude of the resultant vector (FDI)
The forces on each subsequent slice are then constructed using
the E vector of the previous slice as a base. The composite
force polygons must be drawn to a large scale to ensure accurate
results, since they are cumulative -type diagrams in which small
errors can have a large effect on the error of closure. To ob-
tain the FS of balanced external forces, composite force poly-
gons for different trial FS are constructed to determine which
one results in closure. The errors of closure for each trial
composite force polygon are plotted versus the trial FS as shown
in Figure 80. A smooth curve drawn through the plotted points
establishes the FS corresponding to zero error of closure.
Steady Seepage Analysis
Seepage through the side slope tends to reduce stability by increasing
the driving forces and decreasing the resisting forces due to uplift (Equa-
tion 5)- In the case of steady seepage, the water force acting on each slice
is determined from flow nets or assumed to vary linearly below the saturation
line. The forces on typical slices are shown in Figure 8l. To simplify con-
struction of the composite force polygon, the resultant of the weight and
water forces for each slice having a sloping water surface is determined (Fig-
ure 8l). The procedure for determining the FS for zero error of closure is
the same as that shown in Figure 80.
Analysis for steady seepage Cases II and III (Figure 78) may warrant the
use of composite strength envelopes (Figure 82). The applicable shear
strength depends on the developed normal force, which is influenced by the
side earth forces. Consequently, the applicable shear strength should be
167
-------
TRIAL
FA/LURE ARC
3. EMBANKMENT SECTION
WS(EFFI
b. SLICE WITH SLOPING
WATER SURFACE
C. SLICE WITH HORIZONTAL
WATER SURFACE
(TOTAL)
U83
d. RESULTANT
OF WEIGHT AND
WATER FORCES
UL = WATER FORCE ON LEFT SIDE OF SLICE
UB = WATER FORCE ON BASE OF SLICE
Figure 8l. Forces acting on typical slices."
168
-------
2 3
NORMAL STRESS, O. TONS/SOFT
Figure 82. Example design envelope for Cases II and III.
checked by trial and error as the composite force polygon is constructed.
The S strength is assumed as a basis for D in the first portion of the
composite force polygon, and the resulting developed normal force divided by
AL is compared with normal stress at the intercept of the S and R enve-
lopes to determine when the (R + S)/2 strength or the S strength governs
(Figure 82).
Expedient Methods
Infinite slope. A special, simple analysis is available for cohesionless
soil embankments. The infinite slope procedure!^ represents rather shallow
sliding and seems particularly appropriate for relatively thin cover over
sloping waste, where shallow sliding can be serious. For dry conditions, the
safety factor reduces to
FS =
tan
(19)
where B is slope inclination. The equivalence of the friction angle and
inclination at the threshold of failure is reflected in the general corre-
spondence of the observed angle of repose and measured friction angle in co-
hesionless soils (Table 32).
Design charts. Numerous design charts have been prepared for rapidly
designing slope inclination on the basis of soil c and .li+5103 One chart
procedure is reviewed here as an example intended for embankments of cohesion-
less soil resting on shallow clay foundations (Figure 83). The method (Fig-
ure 8k) utilizes an active earth pressure coefficient KA corresponding to
169
-------
TABLE 32. ESTIMATES OF REPOSE AND FRICTION
ANGLES OF COHESIONLESS SOILS
Friction Angles, deg
Angle of Repose *
Soil Description deg
Silt
Uniform sand
Well-graded sand
Sand and gravel
26 - 30
26 - 30
30 - 31*
32 - 36
At
Ultimate Strength
26 -
26 -
30 -
32 -
30
30
3H
36
At
Peak Strength
28 - 3U
30 - 36
3U - H6
36 - hQ
* Lower values generally for soft or well-rounded particles, at dense
packing, or at high normal stresses.
POSITIVE SLOPE
NEGATIVE SLOPE WITH RESPECT TO
OPPOSITE EMBANKMENT SLOPE
COHESIONLCSS EMBANKMENT
(SYMMETRICAL ABOUT CENTERLINE)
RIGID BASE
M = HEIGHT OF EMBANKMENT
O = THICKNESS Of CLAY FOUNDATION LAYER
KA = RATIO OP HORIZONTAL TO VERTICAL
EARTH PRESSURES. ACTIVE CASE
b = COTANGENT OF SLOPE ANGLE ft
Y = WEIGHT OF EMBANKMENT AND FOUNDATION
MATERIAL PER UNIT OF VOLUME
C = COHESION PER UNIT AREA OF FOUNDATION SOIL
Figure 83. Cross section and symbols for stability chart.
170
-------
o.s
z
X
K
ttl
4
h
(rt
0.2
O.OS 0.10 0.1S
O _ DEPTH OF FOUNDATION
H HEIGHT OF EMBANKMENT
t
a. N., VERSUS K,
0.20
0.2t
Figure Bk. Stability chart for cohesionless emlDankment on
plastic foundation.1^
171
-------
the ratio of the horizontal to vertical earth pressures at the center of the
embankment.1^ Chart 2 in Figure Qk gives values of KA for a horizontal
ground surface and for negative slopes (i.e., reverse slope on opposite side
of embankment). First try a value of KA for an assumed embankment slope to
obtain a value of the stability number N-^ and a corresponding slope. This
slope can then be used to determine a second trial value of KA , if neces-
sary, a revised stability number and slope, and so forth.
Consider as an example a homogeneous retaining dike kO ft high, having a
shear strength corresponding to <(> of 28 deg and a unit weight of 120 Ib/ft3
to be constructed on a layer of clay, k ft thick, having a Q-test shear
strength of 1200 lb/ft2. Use a FS of 1.3. The developed angle of internal
friction D of the dike soil is 22 deg (tan 4>D = 0.532/1.3 = 0.1+09). The
developed cohesion CD of the foundation soil is 1200/1.3 = 923 lb/ft2. The
ratio of D/H is k to kO or 0.1. The first trial value of KA from Chart 2
(Figure 8k) is 0.35, assuming a slope b of IV on 2H. For D/H = 0.1 and
KA = 0.35 , the stability number 1% is 0.285 in Chart 1. Solving for b ,
v NKYH _ 0.285 x 120 x i+Q
b = - ^3 =
Additional trials of KA appear unnecessary, and this foundation should re-
main stable at a higher inclination than allowed by Equation 19 of the in-
finite slope analysis.
DESIGNING FOR SLOPE STABILITY
Foundation Evaluation
Examine foundation conditions, sampling and testing if necessary, to
assure that the foundation is not weak and likely to participate in displace-
ment of embankment or cover above. S tests characterize long-term strength
and stability.
Stability Analysis
A stability analysis should be required for Case II in Figure 78, for
weak foundations, and for slopes exceeding a certain height found to be limit-
ing by experience. Other bases for requiring analysis are implicit, serious
consequences of slope failure by virtue of toxicity or fluidity of solid
waste.
Soil Selection
Selection of soil for embankments should be influenced by estimates or
tests for shear strength of available soils. Allowance should be made for the
compaction and corresponding strengthening effect (see Compaction of Soil).
The most appropriate test is usually the S test in which drainage is per-
mitted and pore pressure not allowed to develop. The Q strength is appli-
cable to end of construction loading while the S strength is applicable to
long-term loading conditions.
172
-------
Slope Inclination
Decreasing the design inclination is directly effective in increasing
stability of soil slopes. In fact, a simple rule of thumb of not exceeding
IV on kR (or other inclination shown by experience or analysis to be rela-
tively stable) would assure satisfactory slope performance in most cases.
Seepage Control
The subsurface conditions with respect to saturation and location of the
phreatic surface should be established during the design stage. If an unsatu-
rated condition cannot be assured by design or cannot be confidently predicted
otherwise, it may be necessary to assure conservatism in designing for
strength, i.e., by assuming a particularly weak material. In so doing, it
will be possible to accommodate transient saturation conditions. Several de-
sign features for keeping the phreatic surface below a certain level within
the slope or dike retaining structure are described below. Remember that
seepage usually releases leachate; therefore, a plan for collection, storage,
treatment, and disposal may be needed.
Underdrains. The purpose of an underdrain or drainage blanket (Fig-
ure 85) is to keep the top flow or phreatic surface well within the dike where
pore pressure can cause no undesirable action (see Toe drains). Thickness of
the blanket should be at least 18 in.11-12 Poorly graded sand and gravel are
recommended as under LAYERING in Section 5- The possibility of clogging by
biological or slime buildup should be considered.
Toe drains. A toe drain is a prism of relatively coarse material, such
as sand or gravel, placed at the base of the slope. This coarse prism tends
to concentrate seepage passing through the slope along the toe and thereby
prevents formation of a wet slope. A toe drain also adds strength to dike or
landfill cover, since the coarse material, when compacted, tends to have a
higher friction angle than the finer soil above. A toe drain should be de-
signed on the basis of a realistic seepage flow pattern, but it can be esti-
mated roughly in proportions as shown in Figure 85.
Cutoffs. Cutoffs are impervious walls incorporated below the side slope
or dike to block seepage through foundation soils. Cutoffs are not a part of
the cover, but they are related in function. A cutoff reduces seepage to
levels where no significant effect on slope stability can develop.
Allowance for Freeze/Thaw and Dry/Soak
A design for stability of slopes that are susceptible to freeze/thaw or
dry/soak activity provides sufficient side slope soil thickness. Thus, in
Figure 79, the soil may thaw to a mushy consistency of little or no strength
to an appreciable depth, yet the slope will remain stable by virtue of the
strength of soil remaining below for any conceivable, critical shear surface.
Special Compaction
Specifications can be particularly stringent on compaction to be obtained
173
-------
COARSE TOE DRAIN
RIPRAP
DIKES
BERM
Figure 85. Construction of solid waste retaining
dikes and slopes.
in retaining slope cover, since these soils are not based on spongy waste.
These specifications should require that the soil "be compacted with reference
to standard testing procedures. Such requirements usually necessitate field
tests for quality control or quality assurance. Alternately, a certain system
of compaction field equipment can "be specified on the basis of approximate
correlation of certain compactive effort with this equipment to desired in-
place density (see COVER COMPACTION in Section 5). Lift thickness should also
be prescribed and, as a first approximation, might be 1 ft for soils.
Zone Construction
Zone construction refers to the rather sophisticated procedure of dike or
dam construction where separate materials are used in zones for strength or
seepage effects. The simplest zoning involves the incorporation of an
-------
impervious wall along the waste side or within a cover or dike to impede the
flow of water. Zone construction might also toe undertaken where insufficient
amounts of a single type of soil are available.
Toe Protection
Cover slopes extending into a surface drainage channel might, under
flooding conditions, be severely eroded, oversteepened, and weakened to the
point of failure. Where such a vulnerability is indicated "by preliminary
study, riprap or other slope protection should be incorporated in the design
to absorb the energy of the flowing water. Incorporating berms might also
be considered.
Berms
Another design for increasing stability uses a berm or system of berms
(Figure 85) rather than having a single unbroken inclination. Berms reduce
the overall inclination and thereby lower the driving force in the stability
analysis; berms also reduce slope erosion. Level-by-level construction pro-
vides ready-made berms, and the berms may actually facilitate the operation
by providing working space for construction of the final side slope cover on
the lift above.
Reinforcement
Consider incorporating brush and similar wastes in the form of thin
horizontal mats at intervals in the waste slope where problems are antici-
pated. As these mats are exposed by erosion, they help slow the water and re-
duce its eroding potential.72 Flat mats of scrap tire sidewalls have been
suggestedlCW to strengthen embankments and simultaneously to use another
troublesome solid waste. With sufficient strengthening, a landfill side slope
inclination and height can be increased to achieve more efficient use of the
site.
Trench Burial
The trench method of waste disposal circumvents slope stability problems,
since the trench provides containment on all sides of the waste material. The
effectiveness of the trench method is highly dependent, however, on the nature
of soil, rock, or liner material below; other criteria for choosing this
method of disposal are beyond the scope of this manual.
175
-------
SECTION Ik
TRAFFICABILITY
Trafficability of landfill cover is defined as the capacity of the soil
or other material to support vehicle traffic. Factors influencing traffic-
ability of cover soils include not only the many variables that combine to
determine the strength but also the slope, condition of underlying solid
waste, and geometrical obstacles, such as drainage ditches.
TRAFFICABILITY ON THE SOLID WASTE/SOIL SYSTEM
Trafficability problems generally involve bearing capacity, traction
capacity, slipperiness, or stickiness. Bearing and traction capacities" are
primarily functions of soil strength (or shearing resistance). Trafficability
bearing capacity concerns the ability to support a vehicle without undue
sinkage; traction capacity concerns the ability to develop sufficient resis-
tance between the vehicle wheels or tracks and the soil for the necessary
forward thrust. Trafficability of a soil is considered adequate for a given
vehicle if the soil has sufficient bearing capacity to support the vehicle and
sufficient traction capacity to enable the vehicle to develop the forward
thrust necessary to overcome its rolling resistance. Obviously, the poorer
bearing capacity of underlying solid waste can dominate trafficability on some
landfills.
The two other characteristics, slipperiness and stickiness, also affect
the operation of a vehicle. Slipperiness is a deficiency of traction capacity
in a thin, surficial layer of a soil, which is otherwise trafficable. A ve-
hicle immobilized solely because of slipperiness spins its wheels or tracks
and no longer moves forward, yet does not sink excessively. Stickiness is
the characteristic of a soil to cling and accumulate on the running gear of
vehicles. Rolling resistance of the vehicle is then increased, and steering
becomes difficult. In extreme cases, stickiness can "freeze" the running gear
of a vehicle. Finally, there is the problem of tracking sticky mud from a
landfill to the adjacent public roads.
The concept of trafficability0 used in this manual has been developed
primarily for military purposes and has required two modifications for adapta-
tion to use in solid waste coverage. First, cover soil is always placed in a
remolded condition, and generalizations from published soil test data must be
used selectively to avoid undisturbed, original strength characterization.
This restriction does not appear serious, since undisturbed soil strength is
essentially canceled out of the soil rating discussed below. The second
modification is that most existing vehicle ratings are for military vehicles,
176
-------
and. some judgment and selectivity are necessary in applying established vehi-
cle ratings to landfill equipment. Construction-type vehicles are emphasized
for their similarity to those used in landfill operations.
EVALUATING SOIL TRAFFICABILITY
It has been demonstrated that the performance of vehicles in terms of
"go"* and "no go," slope-climbing ability, drawbar pull, and force required
to tow can be predicted with reasonable accuracy for given soils in the
absence of a thin, soft surface layer. The basic indices are the cone index
(Cl) and the remolding index (Rl) as explained under STRENGTH TESTS in Sec-
tion 3.
Rating Cone Index
The rating cone index, defined
RCI = CI x RI
expresses the probable strength of the specific soil under repeated traffic.
In the relationships for RI and RCI , the CI for more or less undisturbed
soil cancels, and the RCI largely represents the trafficability strength of
remolded soil. Accordingly, the RCI is directly applicable to solid waste
cover where the soil is always in a remolded condition.
Vehicle Cone Index
The minimum RCI , just sufficient for 50 passes of a specific vehicle,
is called the vehicle cone index (VCl). If the RCI is higher than the VCI
of a particular vehicle, at least 50 successful passes can be expected along
the same straight path, or one such vehicle can be expected to execute severe
maneuvers without becoming immobilized. Correlations of VCI with RCI are
most consistent for a critical layer, which is 6-12 in. deep in a normal soil
profile, i.e., where CI increases or remains constant with depth. The traf-
ficability classification scheme described herein is based on soils data
(e.g., see Figure 86) from this 6- to 12-in. layer.
Fine-grained Soils
In general, the soil layer between 6- and 12-in. depths is most critical
for fine-grained soils and sand with fines (poorly drained). However, the
critical depth can vary with the strength profile of the soil and the vehicle
type and weight.105 The "go" ability of a given vehicle in fine-grained soils
is assured if the RCI in the critical layer is equal to or greater than the
VCI assigned to that vehicle. In general, an RCI equal to 50 percent of
VCI indicates sufficient strength to permit one or two straight passes.
If RCI is greater than VCI , additional traction is available to
* In trafficability,6 "go" means 50 passes of a given type vehicle along
a line or severe maneuvers by one vehicle without immobilization.
ITT
-------
SP-SM
USCS SOIL TYPES
LS
SC
SCL
SL SiCL CL
USDA SOIL TYPES
SiC
SiL
Si
Pt
LEGEND
NUMBER OF SAMPLES
USED IN ANALYSIS
PLUS ONE STANDARD
DEVIATION FROM MEAN
MEAN
MINUS ONE STANDARD
DEVIATION FROM MEAN
HIGH TOPOGRAPHY,
WET-SEASON CONDITION
ALL SITES,
WET-SEASON CONDITION
LOW TOPOGRAPHY,
WET-SEASON CONDITION
LOW TOPOGRAPHY.
HICH-UOISTURE CONDITION
Figure 86. RCI means and ranges for various soil types.
178
-------
accelerate, negotiate slopes, or tow extra load. VCI's for numerous military
vehicles are available1^7 along with relationships for computing mobility in-
dexes and relating these indexes to drawbar pull, slope, and required towing
force.
Coarse-grained Soils
For coarse-grained soils or clean sands, CI measurements alone are
adequate to quantify trafficability. Usually, the strength is not altered
significantly by changes in water content. Clean sands possess adequate
strength to support many types of vehicles without excessive sinkage. In
clean sands, the first pass is the most critical, and subsequent passes are
usually made with less difficulty. The 0- to 6-in. depth is considered the
critical layer for coarse soils.
Tracked vehicles experience little or no difficulty traversing level,
clean sand. The effect of soil strength on performance of a given tracked
vehicle is small; however, a significant difference in performance exists
among vehicles having other types of track systems. A wide range in wheeled-
vehicle performance occurs as a result of changes in tire pressure, number of
tires, and tire size.
Soil Moisture Categories
A principal factor influencing the trafficability of a soil is its water
content. Accordingly, consideration must be given to conditions of cover soil
drainage and climate, both of which affect trafficability through their effect
on soil moisture. Two topography-drainage site classes and three moisture-
season site classes are distinguished separately or in combinations (Fig-
ure 87).
a. Low topography. Low topography is defined^ as that at which a water
table exists within k ft of the surface, permanently or intermit-
tently during the year. Such sites usually occur as bottomlands,
lower terraces, or occasionally as upland flats associated with im-
pervious pans. They are generally characterized by poor to fair ]
external drainage and moderately poor to very poor internal drainage.
b. High topography. Sites of high topography have water tables at
depths greater than U ft at all times. These sites are characterized
by pervious soils and moderate to good internal and external drain-
age. They are usually located on ridges or upper slopes.
c. Wet-season condition. The wet-season condition is intended to rep-
resent the average moisture condition prevailing in soils during the
wet season. Exclusion of some of the drier sites from the data base
used in trafficability studies tended to bias averages toward wetter-
than-average conditions.
d. High-moisture condition. The high-moisture condition represents the
worst trafficability condition; marshes and other perennially wet,
soft areas are examples. Low-lying areas with fluctuating water
179
-------
HIGH TOPOGRAPHY AREA
OD
O
SEASON CONDITION
RAINFALL
MOISTURE
CONTENT !
HIGH-
+-HOISTUHC
CONDITION
MOISTURE
CONTENT I
OHV SEASON WET SEASON
isrunc CONDITION
VUHSQWET-SCASON CONDITION
PERIOD OF OTO4' WATER TABLE
RAINFALL
DRY SEASON WET SEASON
TIME
Figure 87. Profile of a typical area showing various topography-moisture
conditions during the year."
-------
ta~bles and upland areas with seasonal, perched vater tables are ex
amples of low topography where a high-moisture condition occurs
intermittently. Low- and high-topography areas that have been sub-
jected to moderate or heavy rainfall are normally under a high-
moisture condition during and immediately following rain periods, but,
a combination of high moisture and high topography has not been in-
cluded in the data base. A high-moisture condition is considered
to prevail at any low-topography site where the water table is known
to have been within the top 18 in. This l8-in. criterion is based
on studies showing that the decrease in soil strength with the de-
crease in depth to the water table becomes critical anywhere above a
depth of 18 in.
e. Dry-season condition. The dry-season condition has not been dis-
tinguished, since it ordinarily presents favorable trafficability.
(An exception is that dry sand may immobilize wheeled vehicles with
standard tires.) It will suffice to say that landfill cover that
performs satisfactorily in wet-season conditions will usually perform
even more satisfactorily in dry-season conditions. Accordingly,
designing for wet-season trafficability will also cover dry-season
trafficability with a degree of conservatism.
Slope Index
Vehicles that can traverse horizontal surfaces often become immobilized
when climbing, other things being equal. The immobilizing force is a function
of the vehicle weight and the angle of slope. Accordingly, an index for slope
is useful as an adjustment in VCI above that for level ground." These ex-
cess index points, called slope index (Si), help determine "go" or "no go"
when a comparison is made between adjusted VCI and measured RCI of soil.
Procedures are available for determining slope effects and are summarized in
Figure 88. SI values for tracked and wheeled vehicles can be obtained for a
given slope from the curves. If, for example, the slope is 30 percent, SI
for the two vehicle classes would be 1^ and 20, respectively.
Conversely, an effective rating cone index (ERCl) may be used for rating
the trafficability of a sloping soil. The ERCI is computed by subtracting
SI from RCI . For example, if the RCI of a soil is 50 and the slope is
30 percent, the ERCI would be 38 (50 minus lU) for tracked vehicles.
USE OF RCI AND VCI FOR DESIGN
The soil trafficability scheme discussed above is directly useful for
design purposes. As summarized in Figures 89 and 90, the scheme evaluates
soil types in descending order of their median RCI under three conditions
of moisture: high topography and low topography under wet-season conditions
and low topography under high-moisture condition. Soil types according to
both the USCS and the USDA are employed.
Vehicle Categories
A soil that is easily trafficable for one vehicle nay be impassable for
181
-------
1O
2O
30
4O 5O 6O
SLOPE INDEX
70
BO
90 100
Figure 88. SI "or two vehicle classes.
another, and each vehicle has its own minimum soil strength for operation.
Therefore, it has been necessary to incorporate vehicle requirements into the
scheme for estimating vehicle trafficability. The VCI for individual ve-
hicles within seven broad categories are given in Table 33. Categories 2
through 7 include vehicles commonly used in waste disposal operations.
Soil Trafficability, Level Terrain
Soil trafficability for level terrain is presented in USCS terms for the
three moisture-topography conditions in Figure 89. A similar presentation in
USDA terms is made in Figure 90- Information for each soil type takes the
form of approximations of the probability of "go" on level terrain for various
vehicle categories. The percent probabilities of vehicle "go" have been
arbitrarily classified as:
Excellent greater than 90 percent probability of "go"
Good 76 to 90 percent probability of "go"
Fair 50 to 75 percent probability of "go"
Poor 0 to U9 percent probability of "go"
182
-------
u>
Soil
Type
Symbol
GW, GPl
SW, SPJ
SP-SM
OM
SM
CH
GC
SC
MH
CL
SM-SC
ML
CL-ML
Strength Measurements
I 1 1
131 It- I 51
Vehicle Category
6 I
GW, GPl
SW, SPJ
SP-SM
CH
GC
SC
SM-SC
MH
GM
SM
CL
ML
CL-ML
OL
OH
Pt
GW, GPl
SW, SPJ
CH
GC
SC
SM-SC
MB
CL
SP-SM
GM
SM
ML
CL-ML
OL
OH
Pt
Probable Range*
Mean
RCI
125-21*1 1.19-2.17 196-316
130-224
167-217
127-231
151-211tt
123-211
147-185
118-224
111-209
300
98-191*
97-257tt
I60-2l6tt
94-170
109-217
90-188
102-200
85-165
95-135
64-164
76-90tt
0.77-1.83
0.84-1.10
0.72-0.98
0.32-1.oott
0.59-0.95
0.47-1.13
0.46-1.02
0.44-0.72
0.94
0.74-1.14
0.59-1.21tt
0.45-l.3ltt
0.51-0.99
0.29-1.03
0.46-0.88
0.27-0.81
0.31-0.69
0.38-0.74
0.32-0.78
0.45-0.67tt
69-167 0.64-1.02
150-l82tt
83-151
71-165
81-183
81-171
71-155
87tt
42-132
76-90tt
0.45-0.63tt
0.46-0.92
0.42-0.80
0.15-0.87
0.26-0.60
0.27-0.53
0.56tt
0.26-0.66
0.45-o.6ltt
137-287
158-210
104-208
64-l60tt
82-180
65-211
67-189
54-136
282
81-193
6l-255tt
72-208tt
48-162
34-188
46-146
34-134
34-96
41-89
14-110
4l-51tt
48-146
66-98tt
43-123
39-117
12-126
22-88
26-66
4gtt
21-49
4l-51tt
20
40
60
80
Vehicle Cone Index
100 120
140
160
180
200
I I I I I
High Topography, Wet-Season Condition
Low Topography, Wet-Season Condition
Low Topography, High-Moisture Condition
PROBABILITY OF "GO" ON LEVEL TERRAIN
I I Excellent Greater than 90%
111 Good 76 to
Fair 50 to
Poor Less than
* Based on +1 and -1 standard deviation
t Estimated from properties of soil
tt Based on less than five samples.
Figure 89. Soil trafficability in USCS terms.
-------
00
Soil
Type
Symbol
Strength
Probable
CI Rl
Measurements
Range*
RCI
Mean
FCI
f
1 l 1
20
1 1
2
1*0
1
1 3 1 >* 1
60
I T 1
Vehicle Category
51 6 1
Vehicle Cone Index
80 100 120
1 1 1 1 1
lUo
1 I
7
160
I i
180
i i
£00
1 1
LS
S(fn)
C
SC
SCL
SIC
SiCL
SL
CL
SiL
L
Si
S(fn)
SC
SCL
CL
SiC
SiCL
C
SL
l£
L
SiL
Si
Ft
SC
SCL
CL
SiC
C
SiCL
S(fn)
SL
SiL
L
LS
Si
Pt
High Topography, Wet-Season Condition
135-249
130-218
167-227
137-229
125-l63tt
156-208
122-204
114-180
126-222
106-190
202tt
1.16-1.80
1.18-2.12
0.80-1.lit
0.74-0.96
0.23-1.17tt
0.66-0.91*
0.1*2-1.1*6
0.77-0.97
0.54-0.88
0.51-0.87
0.5l*tt
£01-300
190-300
159-219
110-202
23-l87tt
108-188
81-215
86-172
76-172
63-11*7
108tt
66-201*
71-209
60-176
66-138
70-164
87-177
78-166
68-150
87-177
59-133tt
76-90tt
0.60-0.90
0.5l*-0.96
0.66-0.98
0.64-1.12
0.54-0.86
0.19-0.85
0.33-0.67
0.3U-0.72
0.22-0.68
0.38-0.50tt
0.1*5-0.67tt
1*4-172
51-159
44-152
50-126
1*4-120
24-110
36-100
28-86
12-110
30-52tt
l*l-51tt
212-300tt
113-237
95-211
85-197
100-196
80-180
111-195
111-241
89-181
96-190
49-237tt
76-90tt
0.79-1
0.60-0
0.57-1
0.67-1
0.59-0
,8ltt
98
.01
.07
99
0.72-1.20
0.32-1
0.24-0
o.4o-o
o . 38-0
0.40-0
0.45-0
.10
,84
.90
,76
,48tt
.67tt
278-300tt
92-180
69-175
66-184
62-180
68-176
46-168
20-188
37-143
41-125
27-101tt
4l-5ltt
29ltt
150t
136
122
125
121
122
107
104
90
83
64tt
46tt
Low Topography, Wet-Season Condition
A vehicle with a vehicle cone index of 60 would
have a 5O-75# chance of "go" on ar. ML soil of low
, wet-season condition.
Low Topography, High-Moisture Condition
PROBABILITlf OF "GC
OH LEVEL TH3RAIH
Greater than 90)6
76 to
50 to
Less than
Figure 90. Soil trafficability in USDA terms.
-------
TABLE 33.
UP VCI OF VEHICLES.
108-111
Category
VCI
Range
Vehicle Types
Low 29 or Tractors designed for very low ground pressure.
ground less Examples: VCI of DUD LGP, D5 LGP, and D6C LGP
pressure all = 17 approximately.
2 30-1+9 Tractors with comparatively wide tracks and low contact
pressures. Examples: VCI of D7 tractor = 38, Dl*
tractor = 1*9, IH model TD 20-200 tractor = 36.
3 50-59 Tractors with average contact pressures and some
trailed vehicles with very low contact pressures.
Example: VCI of D8 tractor (old model) = 50.
U 60-69 Most tractors with high contact pressures, and all-
wheel-drive trucks and trailed vehicles with low con-
tact pressures. Example: VCI of 2-1/2-ton, 6 by 6
dump truck = 62.
5 70-79 Most all-wheel-drive trucks and many trailed vehicles.
Example: VCI of 1-1/2-ton, k by k dump truck = 73.
6 80-99 Many all-wheel-drive and rear-wheel-drive trucks and
trailed vehicles intended primarily for highway use.
Example: VCI of 1/2-ton, It by 2 pickup truck = 88.
7 100 or Rear-wheel-drive vehicles and others that generally
greater are not expected to operate off roads, especially in
wet soils. Example: VCI of 5-ton, h by 2 dump
truck = 119.
Figures 89 and 90 are based on a comprehensive program of trafficability
testing^ with cone penetrometer data from 767 sites in 1+1 states, generally
located in the humid, temperate regions of the United States. A few sites
were located in subhumid or arid climatic areas wherein water contents were
similar to wet-season water contents in the humid, temperate regions. The
study established sample statistics of strength indexes (e.g., see Figure 86
for RCI).
The VCI's corresponding to 50, 75, and 90 percent probabilities of "go"
were derived from cumulative frequency graphs of the RCI data (not shown;
see Reference 6). For example, from a frequency graph for CL soil at low-
topography, high-moisture condition, RCI's at 50, 75, and 90 percent cumula-
tive frequencies were found to be 7^, 50, and 39, respectively. Lines delin-
eating the vehicle probability of "go" on the bar graphs in Figures 89 and 90
are solid where based on five or more samples and judged to be most reliable.
Broken lines indicate that less than five samples were used or the data were
otherwise questionable.
185
-------
The figures may be used to estimate the probability of "go" (or "no go")
given a specific USCS or USDA soil and a specific piece of solid waste and/or
soil handling equipment. The example in Figure 89 indicates that a vehicle
with VCI of 60 has probability of about 60 percent (within 50 to 75 percent)
of "go" on a ML soil (RCI averaging Qk ) at low-topography, wet-season con-
dition. If this probability is considered unacceptable, contingency pre-
cautions should be outlined or a more trafficable soil should be used for the
cover.
Design Adjustment for Slope
The design procedure outlined under Soil Trafficability, Level Terrain
above will need to be adjusted where slopes are involved. The procedure for
reducing ECI to ERCI or for increasing VCI has been described under
Slope Index above.
Soil Slipperiness and Stickiness Effects
Guidance in predicting slipperiness and stickiness of available soil
types on the basis of experience" is presented in Table 3^. Severe slipperi-
ness will often immobilize wheeled vehicles that are not equipped with special
traction devices and, in combination with relatively low RCI (a few points
above VCI), will often cause even chain-equipped wheeled vehicles to become
immobilized. Slipperiness may reduce control of tracked vehicles but will
seldom immobilize them. Soils designated as having moderate to severe sticki-
ness (Table 3M will, when wet, cling to a vehicle's running gear and may
accumulate detrimentally. Soil slipperiness and stickiness, best considered
as subordinate factors in designing for cover trafficability, are involved in
choosing soil (Table 3*0 or special procedures only when other considerations
are about equal.
DESIGNING FOR TRAFFICABILITY
The foregoing discussion provides guidance for analyzing cover for ade-
quate trafficability. However, trafficability will seldom be primary in cover
design, nor will manipulation of soil type be cost-effective. Special designs
and operational procedures are usually the better approach.
Soil Selection
Figure 86 provides a useful summary of relative effectiveness of soil
types based on RCI . In rare cases, it may be reasonable to consider im-
porting soil where the figure predicts poor performance from the intended
cover soil. Supplies of best material, such as sand, where limited, can be
saved for selected use, e.g., along haulage routes.
Site Configuration
The designer has latitude to arrange the site in such a way as to facili-
tate trafficability. Choosing high ground certainly helps. Most landfills
with relief greater than a few feet can be sloped to promote runoff and keep
soil moisture relatively low.
186
-------
TABLE 31*. EFFECTS OF SLIPPERINESS AND STICKINESg OF SOILS IN
LOW-TOPOGRAPHY. WET-SEASON CONDITION6
uses
Soil
Type
GW, GP,
SW, SP
SP-SM
CH
GC
SC
SM-SC
MH
GM
SM
CL
ML
CL-ML
OL
OH
Pt
Effects
Slipperiness
None
None
Severe
Moderate
Moderate
Slight
Severe
Slight
Slight
Moderate
Moderate
Moderate
Moderate
Moderate
Moderate
of
Stickiness
None
None
Severe
Moderate
Moderate
None
Moderate
None
None
Moderate
Slight
Slight
Slight
Slight
Slight
USDA
Soil
Type*
S(fn)
SC
SCL
CL
SiC
SiCL
C
SL
LS
L
SiL
Si
Pt
Effects
Slipperiness
None
Moderate
Moderate
Moderate
Severe
Moderate
Severe
Slight
Slight
Moderate
Moderate
Moderate
Moderate
of
Stickiness
None
Moderate
Moderate
Moderate
Severe
Moderate
Severe
Slight
None
Moderate
Moderate
Slight
Slight
* Abbreviations for USDA types are S sand, C clay, L loam, and Si silt.
Drainage Ditches
Ditches serve the same purposes as manipulation of site layout, i.e.,
they remove water quickly and reduce infiltration. Traffic routes deserve
high priority.
Equipment Changes
Use RCI in design to choose other equipment of relatively lower VCI
during wet seasons or periods. Such substitution may even be possible on an
unscheduled basis. Elsewhere, supplement wheel traction by adding chains or
by switching to tracks.
Flatter Slopes
Another operational procedure for periods of inclement weather and poor
trafficability is to arrange routing so as to eliminate slope climbing for
haulage vehicles. The operator may reroute the traffic temporarily so that
187
-------
all but a short dumping segment moves downgrade. A level traverse may also
be effective.
Stabilized Soil
Fly ash, lime, or cement can be used to increase strength and reduce
permeability of the traffic-carrying cover soil. It is recommended that
special attention be directed to testing fly ash for acceptability where
available as waste in the region.
Lime Additions
Add lime during wet conditions to haul roads and to facilitate cover
manipulation. Lime is superior to cement for this purpose, and about 2 per-
cent might be tried as a first cut. In effect the PI is reduced by an in-
crease in PL , and the soil condition should change beneficially from plastic
to semisolid.
Semipermanent Distribution Routes
The on-site handling and covering operation should be arranged so that
vehicles with potential trafficability problems are confined to limited paths
designed and maintained for trafficability. Indigenous or imported granular
soils, base courses, and/or inexpensive pavements should be considered to
prepare a distribution route for use during the operations at one level, for
example.
Daily Maintenance
Daily maintenance may be established and equipment made available to
assure that deterioration in cover trafficability is rectified before becoming
disruptive. As a first approach, it may be effective to assign municipal or
other road grading equipment and a crew to half-day maintenance periods at
intervals of 2 to 5 days to add supplemental soil, then sprinkle, smooth, and
compact. The on-site equipment should be sufficient to take care of rutting
and other trafficability problems that arise during daily operation. Stock-
piles of suitable additive material (granular, clayey, etc.) should be kept
on hand or be readily available.
Special Wet-season Area
The disposal area should be organized in such a way as to have a standby
section available for use during periods of inclement weather. This section
might be laid out on well-drained sandy terrain near arterial access and "be
composed of single-height waste cells where likelihood of trafficability
problems is minimal.
Special Waste Compaction
It is anticipated that cover trafficability may become a problem where
high degrees of compaction of solid waste are not achieved. Deep, immobi-
lizing ruts may develop as a consequence of spongy waste "subgrade" rather
188
-------
than deficiencies of the cover soil. Attempts to reduce this problem may "be
made by increasing the waste compaction effort. One might also consider in-
creasing the ratio of soil to waste in the covering operation.
Reduced Thickness
Some experienced operators find that reducing the soil cover thickness
improves trafficability in wet conditions. Presumably, the solid waste pro-
vides better traction here.
189
-------
SECTION 15
DEWATERING AND CONSOLIDATING SATURATED WASTE
Certain solid wastes from treatment of industrial and municipal waste-
water are disposed in a saturated condition as sludges and slurries. It will
often be advantageous to speed up the removal of contained water in a con-
trolled manner, and certain cover materials can function effectively here.
Particularly troublesome solid wastes are those that tenaciously hold
the included water and tend to remain in a plastic or liquid state indefi-
nitely. Examples are paper-mill sludges^! and clay slurries from phosphate
mining. A pollution potential of the interstitial water compounds the
problem.
SLUDGE/SLURRY CONSOLIDATION
Sludges and slurries ordinarily are fully saturated, yet most of the
water is not bound strongly to the solids. Therefore, consolidation prop-
erties are like those of saturated fine-grained soils. A useful reference11
has been abstracted in the following.
Formulation of Consolidation Process
If saturated material is loaded one-dimensionally (see CONSOLIDATION
TEST in Section 3), the decrease in volume is accomplished by water being
squeezed from the voids at a rate controlled by the sludge permeability. The
change in height AH , per unit of original height, equals the change in vol-
ume per unit of original volume. When volume change is expressed in terms of
void ratio, AH becomes
Secondary compression occurs after this primary compression and may be
related to plastic creep and compression of the constituent particles; it is
not considered pertinent here. The rate of consolidation can also be calcu-
lated, though accuracy is reduced by changing consolidation parameters,
secondary compression, and construction rate (increasing load rate).
Vertical Stresses
The vertical stress acting on a horizontal plane at depth z is equal to
190
-------
the weight of all matter that rests above the plane. A load-depth diagram is
usually constructed by plotting stress versus depth as in the example in
Figure 91- As a result of the hydrostatic pressure, the effective contact
1 FT SAND. 100 PCF
10 FT SLUDGE
J) H
1 FT SAND, 100 PCF
TOTAL VERTICAL
STRESS
HYDROSTATIC
PRESSURE
Figure 91. Example load-depth diagram.
11
EFFECTIVE STRESS
in SLUDGE
100
PSF
stress between sludge particles is reduced by the magnitude of u (Fig-
ure 91). The average vertical stress within a layer may be taken at the mid-
depth point with negligible error (about 10 percent). The average effective
stress in the sludge layer is Po = 138 Ib/ft2 in the example.
Primary Settlement Calculation
Settlement of a slurry/sludge landfill can be predicted once consolida-
tion test results (see Section 3) are available.H Wet unit weight is avail-
able by testing, and the average initial P0 for each sludge layer can be
calculated (Figure 9l)- The total load AP above each layer is the wet
weight of all sludge, sand, and surcharge layers above the one being consid-
ered. The primary settlement for a layer is computed as
AH =
C H,
c t
1 + e
log
10
P' + AP
o
P1
o
(21)
where Cc = compression index determined at P' (see Section 3)
Ht = total initial thickness of the sludge layer. In Figure 91»
Ht = 2H
eo = initial void ratio existing at P'
Consolidation Time
According to the widely accepted calculation of Terzaghi, the time re-
quired to reach a given percent consolidation is
t =
T H
v
v
(22)
where H = thickness or length of one-way drainage
191
-------
Tv = a time factor varying with degree of consolidation
Cy = coefficient of consolidation
Tv is determined from existing charts. H The cv is considered a soil
property although it depends also upon effective stress. A laboratory test is
needed to establish a specific value of cv as explained in Reference 12.
The effects of t and H and the degree of consolidation achieved are
illustrated in Figure 92 for a clay with very low cv . If the soil is under-
lain by impervious material and escaping water must flow to the surface, H
NOTE: TIME It) REQUIRED TO REACH A
GIVEN PERCENT CONSOLIDATION IS:
WHERE Tv IS A CONSTANT FOR EACH
PERCENTAGE OF CONSOLIDATION.
H IS LENGTH OF ONE -WAV DRAINAGE
PATH. AND Cv IS THE COEFFICIENT OF
CONSOLIDATION.
Cv =0.01 SO FT /DAY
TIME, YR
Figure 92. Effect of thickness on consolidation of
dredged material.51 (Specific example
is for H = 10 ft.)
is the total thickness of sludge/slurry. Alternatively, if drainage layers
intervene as would be the case where sand is placed intermittently as cover,
the thickness H is one-half their vertical interval. Obviously, H has a
great effect on time to desired consolidation.
DESIGNING FOR DEWATERING AND CONSOLIDATING
From principles above and in Section 3, it is a logical step to consider
designing rapid stabilization of a landfill of sludge or slurry by choice of
cover or incorporation of features for increasing rate of drainage (Fig-
ure 93). Several techniques are recommended.
192
-------
-LIMI r SURCHARGE TO
APPROXIMATELY HERE
M/N OF 8 FT OR AS NEEDED FOR
CONSTRUCTION EQUIPMENT
-E AS7~H SDHCHARGi
EXTEND TO PREVENT
DISCHARGE ON SLOPE
FACE
EARTH DIKE
PEA GRAVEL POCKET
DRAIN PIPE
AS CONSTRL/CTED-
PEA GRAVEL POCKET
.
^^ UPPER DRAINAGE RL ASK !
JPPER 5LUDGF. LAVE'. R
,-MlDPLE DRAINAGE fl
0 LOAER SLUDGE LAYER
J
DRAIN PIPE
AS CONSTRUCTED-
Figure 93. Dike and sludge cross section.
11
Glean Sand
Clean sand with its inherently high k is an obvious material for cover
intended ultimately to drain sludge and slurry solid wastes. The USCS type
recommended first is SP . Granular wastes may be substituted locally.
Reduced H Value
The most effective way of speeding the dewatering and stabilization of
sludge/slurry is to reduce H , e.g., by incorporating intermediate drainage
layers. Design H on the basis of cv from consolidation testing and the t
value specified for the project.
Collector Pipes
Drainage layers normally develop large pore pressures that render them
ineffective unless collector pipes are provided.51 Gravity drainage to the
surface through side slopes (Figure 93) is especially effective. Such gravity
drains are complicated by the necessity to have sufficient inclination to
account for anticipated settlement.
Special Equipment
Application and spreading of cover over sludge or slurry will usually en-
counter extreme problems of bearing capacity. Special LGP equipment exerting
only low ground pressure may be necessary (see Section lit and Reference 111).
193
-------
SECTION 16
COLD CLIMATE OPERATIONS
In Alaska, the northern tier of states, and the mountainous regions,
daily mean air temperatures fall below freezing frequently or for extended
periods of days or even weeks during the winter. The ground freezes to
depths of several inches or a few feet, and measures to counteract or reduce
freezing/thawing disturbance and other effects on cover soils may be
necessary.
PHENOMENA OF COLD CLIMATES
The phase change from water to ice results in an increase in volume of
about 9 percent. If water occupies all pores in a granular (nonfrost suscep-
tible) soil, the overall volume increase upon freezing depends on the relative
volumes of water and soil particles, but it will be considerably less than
9 percent. Frost heave that occurs under these circumstances is minor in the
overall problem of severe frost action.
The phenomena involve the migration of water to a freezing front from
the unfrozen soil or waste to form distinctive layers, lenses, or veins of
ice, which may add significantly to the original water content of the cover
soil. Fortunately, the potential for serious damage requiring costly repairs
in a landfill operation are relatively minor. Careful selection of cover
soil and incorporation of design features and orderly operating procedure
should reduce the seriousness of frost action.
Freezing Index
A widely used method of quantifying the severity of cold climate is with
the freezing index.112 The index is computed in degree-day units by summing
cumulatively the values for each day over a freezing season. The daily values
are simply the differences in mean air temperature and freezing temperature
(32°F).
Figure 9^ shows freezing indices for the conterminous United States for
the coldest year in a 10-year cycle or the average of the three coldest in a
30-year cycle. The nearly UOO U. S. Weather Bureau stations that were used
for basic data are spotted in the figure. A site-specific design freezing
index should be used in preference to those in the figure wherever nearby
stations are available because differences in elevation and topographic posi-
tion and nearness to cities, bodies of water, or other sources of heat, pro-
duce considerable variations in the index over short distances. These
194
-------
V/T
Figure 9k. Design freezing index values for the conterminous
United States.
-------
variations are particularly important to design in areas of indices of less
than 1000, i.e., in much of the United States.
Frost Depth
The maximum depth of frost penetration can be predicted in a general way
on the basis of the freezing index. For example, Figure 95 shows generalized
curves for a direct relationship at various soil conditions. Figure 96 shows
a recent map of mean depth of frost penetration. This information should be
helpful in choosing thickness for various final cover soils and in choosing
other design measures outlined at the end of this section.
Since much of the importance of frost action at solid waste operations
concerns daily cover, it is appropriate to consider applying the freezing
index for periods of one or a few days rather than an entire cold season. The
index applies on a daily basis also, in a very approximate way. For example,
an unfrozen silty sand placed on solid waste may be expected to freeze to a
depth of 20 cm during 10 days in which the mean daily temperature is 22°F
(Figure 95).
Snow Depth
Provisions should be made in planning and design for expected heavy ac-
cumulations of snow (Figure 97). Total snowfall data are available for the
numerous U. S. Weather Bureau stations. Values from nearby stations are
sufficiently site-specific except in mountainous areas where large changes in
elevation over a short horizontal distance may result in large differences in
snowfall. Accordingly, local adjustments in the predictions of snowfall
should be made in mountainous areas.
WINTER PROBLEMS AT LANDFILLS
Several problems may develop as a direct consequence of cold climate
during the operation and life of a waste disposal area. A careful review of
general winter practices in the region, along with consideration of soil
availability, economic limitations, and environmental restraints should help
rank potential problems and aid in selecting the best materials available.
Frozen Waste
Garbage wastes tend to resist freezing as decomposition takes place.
However, inert solid wastes that are rich in water may freeze after exposure
of only a few hours on the ground surface. Further distribution and compact-
ing will be accomplished with difficulty, if at all, and such material will
be buried in a frozen condition. The subsequent thawing of frozen waste may
have an indirect, disrupting effect on cover and may even compromise its
general function of sealing the waste.
Snow Interference
The daily operation at a landfill may be interrupted occasionally by
heavy snowfall. Also, it may be unreasonable to clear accumulations of snow,
196
-------
TURF-30 CM SNOW COVER
r~T~i > i i i ' i ' i r~~\
O 200 400 600 800 1000 I2OO
DEGREE DAYS (F)
TURF-SNOW FREE
I ' I ' I ' I
0 ZOO 400 600
DEGREE
T
600 IOOO
DAYS (M
1200
BARE GROUND OR PAVEMENT SNOW FREE
I
200
I
400
I
600
DEGREE
DAYS
800
(F)
IOOO
1200
140
Figure 95. Depth of freezing penetration
into soils with bare or
covered surfaces .-
197
-------
vo
Fig-ore 96. Regional depth of frost penetration (in inches).
79
-------
S»0» IN HIGH
WDUNTAIKS, RAKELV
_, AS L0» AS 6000 FT
"|-ELEVATION
HAWAII
Figure 97. Mean annual total snowfall (in inches).
-------
and as a result, snow and ice may "be incorporated in the cover and waste.
Allowance should be made for this additional moisture in the landfill. In
extreme cases where rapid covering of frozen material provides insulation, a
frozen stratum may remain for months into warmer weather when thawing may
cause unexpected subsidence.
Apparently, a more common occurrence than snow "burial and preservation,
however, is the melting of snow on the surface of garbage waste as a result
of heat of decomposition.''' The exothermic effects are most pronounced in the
first year. The potential for unwanted infiltration can be serious.
Frozen Cover Soil
Supplying unfrozen cover soil may be difficult during severely cold
weather. Cover soils that are frozen when removed from the borrow source may
not be compactible to the extent desired by design. If the soil is available
only in frozen, solid or blocky form, it may be unreasonable and uneconomical
to reduce grain size sufficiently for effective covering.
Three factors determine whether a source of cover soil will be suscep-
tible to hard freezing and the formation of blocky lumps: soil grain size,
conditions of drainage, and exposure and insulation. Figure 95 indicates that
fine-grained clay and damp topsoil freeze to only about half the depth that
gravel and sand do under similar conditions.
Frost Heave
In the context of landfilling, frost heave has a short-term effect in
seasonal disruption of the cover and a long-term effect arising at such time
as the landfill is used as a foundation for pavements or light structures.
The severity of frost heave damage in Arctic climates has led to efforts to
establish indicators of frost heave susceptibility.H^ Actual tests on nu-
merous soils have provided information on heave rate according to the percent-
age of silt and clay size material.^-5 Figure 98 indicates that heave rate
increases conspicuously from gravel to sand to silt. A less severe heave rate
apparently characterizes come clays in comparison with silt.
Slope Sliding
Frozen ground conditions may be detrimental to the stability of landfill
slopes during periods of 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 (see Sec-
tion 13).
DESIGNING FOR COLD CLIMATE
Several landfill design recommendations follow from the operations prob-
lems identified above.
200
-------
VERY HIGH
HIGH
MEDIUM
LOW
VERY LOW
NEGLIGIBLE
Croiftlly and
sandy CLAYS
(CL,,CL-OL)
I I .
(lOOecf) 0.24mm/doy"
3 4 9 6 7 f 10 20 30 40 SO 10 70 K> 90100
PERCENTAGE 8V WEIGHT FINER THAN 0.02 mm
SUMMARY OF ENVELOPES FOR THE VARIOUS SOIL GROUPS
NOTES! Standard tuft ptrformtd by Arctic Conttructian and Ftott ffftcti Laboratory, tpaclmani 6 in. die
ty Sin high, fro tin at ponotration ran of appro*imalaly 0.15 in oar day, »ith fru malir at 38'f can-
tinuoui/jr arailt*!* at bait of ipteimon. Sp*cimtnt campaclta' la 93% or batlir of applicabli ttonfaro',
*e»pl unfjtturta* cj»y$. Sa'urt/ieni btfora tratiing g»f»rally t5%or bittar.
* Indicant1 titan rail du» la tiptniian in rolumi, if all anginal vottr in 100% tottiratad tpacimin tnrt
fro ton, with rota at trait panatration O.IS inch ptr day.
Figure 98. Rates of heave as related to silt-clay content.
(Reproduced by permission of Transportation
Research Board. )
115
Selection of Soil
Soils available as cover should be carefully evaluated in regard to sus-
ceptibility to undesirable frost actions. Figure 98 serves as a criterion for
selection where the primary concern is for frost heaving. Gravels and sands
201
-------
are obviously the best material for resisting heave. Where problems are an-
ticipated with poor workability during winter operations, coarse-grained soils
should be preferred provided they are well drained. Coarse soils drain freely
and should retain less water to act as a cementing agent when frozen. The
only disadvantage of coarse soils is their tendency to freeze quicker and to
greater depths than fine-grained soils; to avoid freezing to great depth,
finer soils should be chosen.
Unfrozen Soil Supply
A supply of unfrozen cover material is advantageous, but stockpiling
under cover may not be feasible. A more economical way of reserving unfrozen
soil is in a relatively thick borrow area. At such a source, a layer of snow
and/or frozen soil may be used as insulation, to be removed only as the cover
material is needed. Also, a special source of suitable texture and config-
uration might be reserved for use during especially cold periods or in the
middle of the freezing season.
Drainage
Drainage of borrow areas will help to reduce the problem of freezing and
formation of blocky and unmanageable cover soil. Surface grading to slope
and excavation of ditches or trenches should be sufficient in most cases, but
these drainage features should be constructed well before the freezing season
begins.
Additives
Additives for reducing frost action (particularly frost heave) fall into
four groups:11" void pluggers and cements, flocculants, dispersants, and
waterproofers. Well-graded soils with coarse particles respond best to addi-
tive treatment. The most promising application of chemical treatment and
additives appears to be on soils exhibiting only modest frost susceptibility.
Dispersants are effective, but their permanence and durability are uncertain.
Calcium chloride has been used for preventing frost heave in highway subgrade
soilsH2 ancj for improving compaction^ results (see Section 5); its principal
effect is a lowering of the freezing temperature of the soil water. Lignin
and chrome lignin (see Section 11) have been successful in reducing ice seg-
regation. The liquor changes capillary properties of soil and prevents soil
water from migrating to form ice lenses. Sodium sulfate has been recommended
as effective against heave in cemented soil.H' Other additives have been
used but generally at considerable expense.
Seasonal Scheduling
A practical way of achieving successful landfilling in a severely cold
climate is by careful scheduling, e.g., by reserving more sheltered areas for
winter operations and protecting soil borrow sources (see Unfrozen Soil
Supply). In areas containing a variety of soils, gravels may be expected to
freeze early and thaw early, whereas fine soils freeze late and thaw late;
accordingly, a preference may develop for changing cover soil type during
progression of the cold season.
202
-------
Another scheduling option is to construct dikes and side retaining slopes
requiring large volumes of soil during the summer and fall and to handle only
waste and thin cover during the freezing season. It may even be reasonable to
dispense with cover requirements during severely cold spells when the frozen
water content helps keep the waste firmly in place and relatively free of
pollution potential.
Trench Method
Not only does the trench method facilitate cold climate operations by
providing a measure of shelter from the weather, but it also tends to protect
the cover soil that remains partly buried until needed.
Snow Removal
It may be feasible at least locally to remove snow during slack periods
of operation. Removing snow from flats reduces the amount possibly becoming
available for infiltration upon thawing. Generally, try to avoid incorpo-
rating snow on daily cover into the next higher waste cell.
Snow Fences
Snow fences can provide some control on where drifting snow is deposited
and thus may reduce the amount of snow that needs to be removed from the
cover later.
Rapid Covering
Where percolation into waste cells is of particular concern, it may be
advisable to incorporate in the operations plan contingency instructions for
quick coverage before or during heavy snowfall. Coverage at this time might
ordinarily be relaxed because of severe working conditions. However, covering
may be most effective then, since snow falling on uncovered irregular, open
waste surfaces may not be removable later before it melts and infiltrates (see
Snow Interference).
Gas Vents
Gas vents and channels can be blocked detrimentally by icing, and the
designer should evaluate depth of freezing in this context.
203
-------
SECTION 17
MINIMIZATION OF FIRE HAZARD
The burning of waste is prohibited at sanitary landfills and industrial
disposal sites. This restriction does not assure, however, that a fire will
not be accidently ignited during operations, to smolder and break out, perhaps
even after covering.
CONDITIONS FOR FIRE HAZARD
The most likely and direct cause of fire is in the unsuspected introduc-
tion of previously smoldering waste brought in trucks from the waste col-
lection route. Possibilities for exothermic chemical reactions in some
decomposing waste produce conditions favorable for supporting combustion,
also. It is, therefore, essential that a fire potential is recognized and
that suitable measures for preventing initiation and spread are incorporated
in design.
Two conditions are required for a fire hazard to exist or develop. There
must be flammable material in the landfill and sufficiently free access of
air for oxidation. Where air can leak through relatively coarse cover or
along void-rich waste layers from cracks or other openings along the side,
there may be sufficient oxygen to sustain the process.
Large accumulations of coal mine wastes are beyond the scope of this
manual; however, they serve as a good example of fire hazard potential. The
solid waste of interest in this case is fine-grained rock and raw coal wasted
as slurries from the crushing and washing plants. A survey of refuse banks in
13 coal-producing states revealed 292 burning banks.118
DESIGNING AGAINST FIRE HAZARD
Only one of the conditions mentioned above is usually susceptible to
manipulation and design. This is a limitation of the access of air to dis-
courage combustion. It is assumed that the type of solid waste delivered to
the site is not subject to manipulation, and this aspect is not considered
further. The following methods may be used to restrict the necessary oxygen
supply.
Rapid Covering
The covering of smoldering or burning waste with damp soil will often be
adequate to smother the fire completely. In view of the rarity but urgency
204
-------
of the problem, a liberal thickness of cover is recommended.
Selection of Soil
Selecting a fine-grained soil for cover is an effective vay of reducing
fire hazard. As explained in Section 9, clayey soils hold water better than
coarse soils that drain freely, and the degree of saturation is a dominant
factor in impeding gas flow.
Peat and other organic soils (Figure l) constitute a special group that
should "be avoided as cover because of a susceptibility to burning.
Removal and Backfilling
Occasionally, it may be advisably expeditious to remove smoldering waste
and backfill with patches of clay or other soil of low k value. Caution
should be exercised in this remedy to avoid an explosive intermixing of meth-
ane, air, and heat.
High Water Content
High water content w , near saturation, is temporarily effective in ex-
tinguishing an existing fire or for stabilizing a landfill susceptible to
combustion. Maintaining high w in the cover soil will probably not be fea-
sible in the long range, where regular additions of water will increase
percolation.
Trench Method
An effective method of reducing the surface area for potential air leak-
age is to use the trench method of disposal. This method works best in clayey
soils3 where an effective barrier to gas movement is supplied by the
sidewalls.
Valley Filling Method
In the area method of solid waste disposal, the use of valleys as sites
for fill may have advantage in controlling fire hazard. In this way the
flanks of the landfill are naturally sealed by the valley slopes.29 Active
and abandoned strip mine pits can provide the same geometrical advantage, if
the boundaries do not open into highly permeable soil or rock.
Compaction
Despite the difficulty of achieving good compaction on a spongy base of
solid waste, extra compaction should be specified for cover over potentially
combustible materials (see Section 9).
Cell Construction
Cell construction, a standard procedure for disposal of solid and haz-
ardous waste, is thought to be effective in confining internal fires. The
205
-------
daily soil cover, which in a multiple-lift landfill constitutes the floor,
sidewalls, and top of a cell, tends to contain any fire within the individual
cell.
Separate Site
Wastes that are regarded as highly flammable should be excluded from the
usual landfill and disposed in a separate area.3 Special cover materials and
procedures can be used there.
206
-------
SECTION 18
CRACK RESISTANCE
To be effective in containing gases and excluding surface water, a cover
soil should resist cracking. Otherwise, certain design features or construc-
tion procedures may be needed.
PHENOMENON OF CRACKING AT LANDFILLS
Detrimental effects of cracking in cover involve uncontrolled leakage
of gas upward or percolate downward and easy access for burrowing animals and
vectors. Cracks are ideal places for animals to enter in search of food and
warmth in the waste below. By nature, cracks are well distributed and closely
spaced in a drying soil layer, and correction is difficult, short of a com-
plete renovation of the cover involving soil additions and recompaction. This
is not to say that a crack-prone soil cannot be used as a daily cover. The
process of cracking involves shrinkage upon loss of water by evaporation.
Therefore, the relatively short exposure of a daily cover may not allow
serious cracks to develop before the addition of more waste. The final cover
deserves the most concern.
The phenomenon of crack formation is closely related to the clay miner-
alogy of the soil. Certain clay minerals are much more prone to shrinking and
causing cracks. Montmorillonite clay is the most notorious, and soil engi-
neers in vast areas of the central United States, particularly the Great
Plains and Gulf states, face problems with these clay soils continually in
road construction and building foundations (Figure 99). Likewise, operators
of solid waste sites should be alert to potential problems locally.
Expansive behavior is at the opposite extreme of the spectrum of volume
change phenomena from cracking, i.e., clay-rich soils may be prone to major
problems of expansion when subjected to additions of water, then cracking upon
drying. A common construction procedure, therefore, is to preserve the water
content as close to natural content as possible.
The problem of volume changes in cover soils at landfills is considera-
bly simpler than similar problems faced in highways and building foundations
where most of the soil is in an undisturbed condition. Guidance provided
below applies only to expansive soils in a remolded condition.
Fills containing appreciable percentages of expansive clay are sensitive
to treatment during placement. It has been found that compaction density is
sometimes critical, and expansive soil may undergo greater expansion if it is
207
-------
LEGEND
[ j NONEXISTEN
NONEXISTENT TO LIMITED
LIMITED TO MEDIUM
MEDIUM TO WIDESPREAD
VERY WIDESPREAD
Figure 99- Estimated occurrence of expansive soils by
physiographic unit (from Witczak).-
compacted to a higher density. This characteristic follows from the fact
that there are more clay particles per unit volume in the dense condition.
For a loosely compacted expansive soil, some of the expansion upon wetting
effectively reduces the high porosity. Actually, this effect is less critical
in landfill cover soil, since the concern is not so much for the expansion
that takes place during wetting as for the shrinkage and cracking that takes
place during drying. Therefore, high compactive effort should be beneficial
since the densification might retard the loss of water, which leads to
cracking.
INDICES OF EXPANSIVE BEHAVIOR
Methods of classifying expansiveness with convenient indices, such as
Atterberg limits, have been developed in the last 30 years.120,121 Qne of
the most frequently cited!' -1 considers the colloid content, PI, and SL.
Another useful index is the clay content and specifically the particular
clay mineral. Montmorillonite clays swell notoriously when the water content
is increased. This behavior depends on the particular cation at specific
positions in the crystal structure. Sodium montmorillonite (Wyoming benton-
ite) is the most expansive of all and can hold great volumes of water within
its expanded crystal structure. Illite and kaolinite have limited or insig-
nificant expansive behavior except in cases where the illite crystal struc-
ture has degraded to a mixed-layer condition of illite alternating with other
208
-------
clay minerals, such as chlorite or montomorillonite. This simplified ex-
planation is intended only to emphasize that mineralogical analysis of a pos-
sible clayey cover can "be useful in predicting the tendency for cracking.
The indexing summaries presented here (Tables 35 and 36) have resulted
from extensive experience^,120 vith expansive clays, mostly in the Great
Plains and Rocky Mountain regions. Swelling potential was measured as ex-
pansion at dead-load stresses of about 1000 psf. Indices found to be useful
for predicting expansive (and cracking) behavior were the LL and the weight
TABLE 35. RELATIVE VOLUME CHANGE AS INDICATED BY
PI AND OTHER PARAMETERS
Likelihood of Volume
Change with Changes
in Moisture
Little
Little to moderate
Moderate to severe
Plasticity Index
Arid
0
15
30
Regions
- 15
- 30
or more
Humid Regions
0-30
30 - 50
50 or more
Shrinkage Limit
12 or more
10 - 12
10 and less
TABLE 36. VOLUME CHANGE AS INDICATED BY
LL AND GRAIN SIZE
Passing No. 200
Sieve, percent
60
30
> 95
- 95
- 60
< 30
Liquid Limit
percent
> 60
ko - 60
30 - 1*0
< 30
Probable Expansion
percent
> 10
3-10
1-5
< 1
percent passing the No. 200 sieve (Table 35). The same source1^ has provided
the correlation between PI and swelling potential shown in Figure 100.
DESIGNING AGAINST COVER CRACKING
The following methods of design and operation are recommended to allevi-
ate or avoid entirely the cracking problem.
Selection of Soil
Criteria based on LL and PI should be used to choose a soil with low-
cracking potential (Tables 35 and 36).
209
-------
h
Z
HI
u
IT
LJ
Q. 6
o
1
ID
z
J
J
UJ
r
i
PLASTICITY INDEX
Figure 100. Plasticity index as related to
swelling potential at 1-psi
surcharge.
Moisture Preservation
High moisture within the cover soil may be maintained by frequent
sprinkling to compensate for water loss by evaporation. There is a self-
healing mechanism working to advantage. Sprinkled water or natural precipi-
tation may migrate preferentially along the developing cracks but will quickly
cause expansion of the crack walls with resultant crack closing.
Compaction
Compaction is probably always a beneficial procedure. Any detrimental
expansive behavior at the surface is probably negligible compared with the
benefits in reduced permeability and impeded drying. Compaction on the dry
side of optimum water content should be at least temporarily beneficial since
the tendency is for water to be imbibed and the clay to swell.^9 This action
works against the cracking behavior.
Layered System
A layered cover system may solve the cracking problem by sufficiently
210
-------
reducing evaporation from the clay layer. Such a system should consist of a
compacted clay layer with a layer of free draining sandy soil above to im-
pede evaporation. The surcharging effect of the upper layer on the clay will
also help suppress expansion and subsequent cracking.
Increased Cover Thickness
Increasing the thickness of cover insulates buried portions from the
heat of the sun and reduces evaporation and cracking. Thickening that is
undertaken to remedy a developing problem of cracking should be preceded by
sprinkling, sufficient to expand the soil and close cracks.
Lime Treatment
The usual additive for-reducing swell is lime; therefore, it is recom-
mended for use on troublesome clay soil covers. Preferably work the lime in
mechanically for best results. See Section 5 for additional explanation.
211
-------
SECTION 19
ESTABLISHMENT AND SUPPORT OF VEGETATION
Sound, vigorous vegetation on soil cover over solid vaste is highly
cost-effective.122 Primary benefits are often identified as decreases in
erosion by wind and water (see Sections 10 and 11). Vegetation reduces rain-
drop impact and runoff velocity and strengthens the soil mass with root and
leaf fibers. At the same time, however, the soil's infiltration capacity is
increased so that considerable water enters. The increased infiltration is
offset at least partly by transpiration from vegetation, but the relative im-
portance of these offsetting processes is a complicated question that has not
been conclusively answered.123-125 See Section 8 for discussion of the im-
portant effects of vegetation upon infiltration and percolation.
CONSIDERATIONS UNIQUE TO LANDFILLS
Rapid establishment and maintenance of perennial vegetation or self-
reseeding annual vegetation can be accomplished on soil covering solid waste
only by carefully addressing soil type, nutrient and pH levels, climate,
species selection, mulching, and seeding time.126 Fertile soils, if avail-
able at all for landfill cover, are usually cost-prohibitive, so that non-
productive soils or subsoils often have to be used. Landfill cover is also
usually shallow.
These shortcomings of the soil cover are compounded where the cover has
been designed to impede percolation. A clay or plastic barrier makes the
plant-root zone susceptible to swamping after rains since no vertical drain-
age occurs. Upon saturation, the soil becomes anaerobic, a condition which,
depending upon the duration, may kill progressively larger roots. Short pe-
riods of swamping weaken the vegetation; longer periods may cause a complete
loss.
At the other extreme, thin cover soil dries excessively during dry pe-
riods. No deep-soil moisture is available to tide the plants over even mod-
erate droughts. Plants that have been weakened by prior waterlogging or
that are not drought-tolerant are especially vulnerable. Irrigation may be
necessary during prolonged dry spells to prevent complete loss of plant
cover.
Landfills may continue to produce gases and soluble organic decomposi-
tion products for years after closure, and vegetation can be damaged.^-^7,12o
Fine-grained soil cover over decomposing waste helps shield shallow plant
roots from gases and leachate. On the other hand, shrubs and trees may
212
-------
penetrate the cover with long roots and cause leaks of water into and
from the landfill. Inspection of damaged vegetation on landfills can help
identify vulneraMlities and disadvantages of plant species, since no system-
atic study has yet been undertaken.
SOIL FACTORS
Major factors determining effectiveness of the soil for supporting vege-
tation are grain size, pH level, and nutrient content. Laboratories capable
of evaluating soil for these factors are located throughout the United States
and most county agents can provide guidance. Sampling should be representa-
tive of all soils (depths and areas) to be used since the cover will usually
consist of a mixture. Table 37 indicates typical ranges of organic matter
and nutrients in soils for various levels of plant vitality.
Grain Size
Two common soil classification systems are described in Section 1, and a
rating of soil types (based on grain size) for the support of vegetation is
given in Table 6. In the USDA system, a soil composed of a mixture of clay,
silt, and sand such that none of the components dominate is called a loam.
The stickiness of the clay and the floury nature of the silt are balanced by
the nonsticky and gritty characteristics contributed by sand component. A
loam is rated overall best soil type as it is easily kept in good physical
condition and is conducive to good seed germination and easy penetration "by
roots.
Clay-rich soils may be productive when in good physical condition, but
they require special management methods to prevent puddling or breaking down
of the clay granules. Silt-rich soils lack the cohesive properties of clay
and the grittiness of sand, are water retentive, and usually are easily kept
in good condition. Soils made up largely of sand can be productive if
TABLE 37. RELATIVE LEVELS OF ORGANIC MATTER AND MAJOR NUTRIENTS IN SOILS
126
Organic Matter,
Relative
Level*
Very low
Low
Medium
High
Very
high
Sand,
Loamy
Sand
<0.6
0.6-1.5
1.6-2.5
2.6-3.5
>3.5
Sandy Loam,
Loam,
Silt Loam
<1.6
1.6-3.0
3.1-U.5
U.6-5.5
>5.5
percent
Clay Loam,
Sandy Clay,
Clav
<2.6
2.6-U.5
U.6-6.5
6.6-7.5
>7.5
Nitrogen
Ib/acre
<20
20-50
50-85
85-125
>125
Phosphorus
Ib/acre
<6
6-10
11-20
21-30
>30
Potassium
Ib/acre
<60
60-90
°1-220
221-260
>26o
* Medium level is typical of agricultural loam soil. Low levels need supple-
mental fertilization; high levels need no fertilization under normal
circumstances.
213
-------
sufficient organic matter is present internally or as a surface mulch to hold
nutrients and moisture; sandy soils tend to dry out very rapidly and lose
nutrients by leaching.
The general classification of a soil can usually be estimated by visual
inspection; however, soil typing by an appropriate soil testing laboratory is
preferred. Rather minor differences in soil type can influence selection of
species or mulch.
pH Level
Soil used to cover solid waste is usually composed of a mixture of soil
and subsoil, in some cases from more than one locality. The pH of the soil
is an important factor to be considered. The amount of lime necessary to
neutralize a given soil depends upon soil pore water pH and reserve acidity.
The reserve acidity, or buffering capacity, is a single factor that incor-
porates several variables; soils with high levels of organic matter and/or
clay require higher amounts of lime for pH adjustment. The usual way of
characterizing the buffering capacity is as tons/acre of lime necessary to
adjust the soil pH to about 6.5.
The pH of the subsoil (where appreciable in the cover) may be particu-
larly critical to lime requirements. Acidic subsoils need larger amounts and
repetitive applications of lime. Buried landfill wastes may act much like
acid subsoils, so that large lime applications or frequent liming intervals
may be necessary.
If the soil pH is greater than about 8, the solubilities of phosphorus,
iron, zinc, and manganese are so low that the plant cannot take up these
nutrients even though they are present in sufficient quantities. If the soil
pH is below 5, the concentrations of soluble manganese and aluminum often are
high enough to be toxic and the availability of molybdenum and phosphorus is
limiting.
Nitrogen and Organic Matter
Nitrogen is of special importance in establishing vegetation, because it
is needed in relatively large amounts (Table 37) during vigorous growth, is
easily lost from the soil, and is the most expensive nutrient to supply. All
but a small part of soil nitrogen exists in organic forms, both in decaying
plant material and in the microorganism decomposing the organic matter.
Measurements of the nitrogen content of soil and its organic content are
intimately related. Nitrogen accumulates in soil microorganisms where it is
used over and over again as old cells die and new ones are formed. The nitro-
gen contained in the microbial cells is unavailable for use of plants growing
on the soil until the organisms die. The rate at which nitrogen is released
by organic matter breakdown depends upon the moisture and temperature condi-
tions in the soil. High or low moisture retards release; high temperature
and moderate moisture levels produce maximum release rates. Most landfill
cover soils consist largely of subsoils or mixtures of subsoil and topsoil,
so that they can be assumed to be low in organic matter content. The most
cost-effective method of adding organic matter is by mulching with straw
-------
cellulose, etc. Once vegetation becomes established, the plants themselves
will add organic matter.
The amount of nitrogen fertilizer required by a given soil depends upon
the amount of organic matter present (higher organic matter levels requiring
higher application rates), the soil texture (more is required on sandy soils),
the seed mixture chosen (more is required for grasses than legumes), the
criticalness of the area (potential for erosion damage), and economic factors
(nitrogen fertilizer is the most expensive). Generally 50 to 85 Ib/acre of
nitrogen are recommended (Table 37) for landfill cover seeded vith grass.
Fertilizers are rated by the amount of nitrogen they contain per weight of
fertilizer (e.g., 6 percent nitrogen). To calculate the required amount of
fertilizer, simply divide the recommended nitrogen application by the frac-
tional amount of nitrogen in the fertilizer. For example, to apply 50 Ib/acre
of nitrogen using fertilizer that is 6 percent nitrogen, simply divide 50 by
0.06 to get 833 Ib/acre of fertilizer.
Phosphorus
Much less phosphorus than nitrogen is held in the organic portion of the
soil. Results of phosphorus tests are usually expressed as pounds of readily
extracted phosphorus per acre-furrow slice (6-in. depth). Representative
levels are shown in Table 37. Unlike nitrogen, phosphorus is not mobile in
the soil and thus is lost very slowly to leaching. One application of phos-
phorus usually will last several growing seasons.
Phosphorus content is expressed either as percent phosphorus pentoxide
(P205) or, as is now the trend in industry, percent elemental phosphorus.
Care should be taken regarding the basis of characterization since percent
P205 is 2.3 times an equivalent percent phosphorus. Generally, at least
15 Ib/acre of phosphorus is recommended as a starter. The availability of
phosphorus to the plant is quite dependent on pH. At optimum pH values
(6.2-6.8), amounts of 50 Ib/acre are usually adequate; at pH values below
6.2 or between 6.9 and 7-5, about 80 Ib/acre are needed for optimum growth.
Under very alkaline conditions (pH greater than 7-5), phosphorus levels of
110 Ib/acre are required. These recommendations are for raw subsoils or for
sandy or high clay soils of low organic material content.
Potassium
The potassium soil tests are generally based upon pounds of exchangeable
K per acre. Fertilizer analyses are often provided in terms of percent K^O,
which is greater than an equivalent percent potassium by a factor 1.2. The
industry is now changing over to the elemental potassium basis, and care must
be taken in calculations.
Potassium is much less important in grass establishment than in legume
establishment and maintenance; thus, the rate of application depends upon
both test results and species to be seeded. A minimum application of
26 Ib/acre of potassium (32 Ib/acre K20) as a starter is recommended under
any circumstances. Applications can run as high as 230 Ib/acre of potassium
(277 Ib/acre KgO) on impoverished soils where legumes are to be seeded.
215
-------
Potassium is moderately mobile in the soil and is slowly leached out, but one
heavy application should be adequate for several growing seasons.
Other Nutrients and Toxic Materials
Other mineral nutrients needed in small amounts by all plants for ade-
quate growth are usually present in most soils, or as impurities in typical
fertilizers, and thus are not determined in typical soil tests. Deficiencies
rarely limit plant growth and should be suspected only under unusual
circumstances.
Soils with toxic levels of heavy metals or with high levels of salts
present special problems, and their use as final cover material should be
avoided unless no other soils are available. If these soils must be used,
selection of tolerant plant species is usually the most effective way to
overcome the associated problems. In general, soils that support an adequate
or reasonable level of vegetation in their native state will not present
toxicity problems when used for landfill cover.
CHOICE OF VEGETATION
General guidance in selection of plants and time of seeding is provided
below. More specific supplemental data may be available from county agents
or seed companies.
Species Selection
Each species of grass, legume, shrub, or tree has its climatic, physio-
graphic, and biological strengths and limitations. Moisture, light, tempera-
ture, elevation, aspect, balance and level of nutrients, and competitive
cohabitants are all parameters that favor or restrict plant species. The
selection of the best plant species!29 for a particular site depends upon
knowledge of plants that have the desired characteristics. Table 38 gives the
major parameters usually important to species selection and examples of
grasses and legumes exhibiting these parameters. Particularly important
characteristics are low growing and spreading from rhizomes or stolons; rapid
germination and development; and resistance to fire, insects, and disease.
Plants that are poisonous or are likely to spread and become noxious should be
avoided.
A very large number of species of grasses and legumes are available for
reclamation use. Species that find wide and frequent application are de-
scribed in Tables 39 and kO. A local agronomist should be consulted for
recommendation of locally adapted or newly introduced plant varieties.
Time of Seeding
Probably the most critical of all decisions in the successful establish-
ment of vegetative cover on poor soils is the time of seeding. The optimum
time of seeding depends on the species selected and the local climate.
Tables 39 and Uo recommend times for certain grasses and legumes based on
local conditions.
216
-------
TABLE 38. IMPORTANT CHARACTERISTICS OF GRASSES AMP LEGUMES*
Characteristic
Degree
Common Examples
Texture Fine Kentucky bluegrass, bentgrass, red fescue
Coarse Smooth bromegrass, reed canarygrass,
timothy
Growth height Short Kentucky bluegrass, buffalograss, red fescue
Medium Redtop, perennial ryegrass
Tall Smooth bromegrass, timothy, switchgrass
Growth habit Bunch Timothy, big bluestero, sand dropseed,
perennial ryegrass
Sod former Quacksrass, smooth bromegrass, Kentucky
bluegrass, switch* grass
Reproduction Seed Red and alsike clover, sand dropseed, rye,
perennial ryegrass, field bromegrass
Vegetative Prairie cordgrass, some bentgrasses
Seed and White clover, crownvetch, quackgrass,
vegetative Kentucky bluegrass, smooth bromegrass
Annual Summer Rabbit clover, oats, soybeans, corn,
sorghum
Winter Rye, hairy vetch, field bromegrass
Perennials Short-lived Timothy, perennial ryegrass, red and
white clover
Long-lived Birdsfoot trefoil, crownvetch, Kentucky
bluegrass, smooth bromegrass
Maintenance Difficult Tall fescue, reed canarygrass, timothy,
alfalfa
Moderate Kentucky bluegrass, smooth bromegrass
Easy Crownvetch, white clover, birdsfoot
trefoil, big bluestem
Shallow rooted Weak Sand dropseed, crab grass, foxtail, white
clover
Strong Timothy, Kentucky bluegrass
Deep rooted Weak Many weeds
Strong Big bluestem, switchgrass, alfalfa, reed
canarygrass
Moisture Dry Sheep fescue, sand dropseed, smooth
bromegrass
Moderate Crested wheatgrass, red clover
Wet Reed canarygrass, bentgrass
Temperature Hot Lehman lovegrass, fourwing saltbush,
ryegrass
Moderate Orchard grass, Kentucky bluegrass, white
clover
Cold Alfalfa, hairy vetch, smooth bromegrass,
slender wheatgrass
* Adapted from Reference 130.
217
-------
PABLE 39. GRASSES COMMONLY USED FOR REVEGETATION*
ro
H
Co
Variety
Redtop "bentgrass
Smooth bromegrass
Field bromegrass
Kentucky bluegrass
Tall fescue
Meadow fescue
Orchard grass
Annual ryegrass
Timothy
Reed canary grass
Best
Seeding
Time
Fall
Spring
Spring
Fall
Fall
Fall
Spring
Fall
Fall
Late
summer
Seed Densityt
seeds /ft2
lU
2.9
6.U
50
5.5
5.3
12
5.6
30
13
Important Characteristics
Strong, rhizomatous roots,
perennial
Long-lived perennial
Annual, fibrous roots,
winter rapid growth
Alkaline soils, rapid grower,
perennial
Slow to establish, long-lived
perennial, good seeder
Smaller than tall, susceptible
to leaf rust
More heat tolerant but less
cold resistant than smooth
bromegrass or Kentucky bluegrass
Not winter hardy, poor dry
land grass
Shallow roots, bunch grass
Tall coarse, sod former,
perennial, resists flooding
and drought
Areas /Conditions
of Adaptation
Wet, acid soils, warm
season
Damp, cool summers,
drought resistant
Cornbelt eastward
North, humid, U.S.
south to Tennessee
Widely adapted, damp
soils
Cool to warm regions ,
widely adapted
Temperate U.S.
Moist southern U.S.
Northern U.S., cool,
humid areas
Northern U.S., wet,
cool areas
* Taken from many sources, but especially 126 and 129-
t Number of seeds per square foot when applied at 1 Ib/acre.
-------
TABLE kO. LEGUMES COMMONLY USED FOR REVEGETATION*
ro
H
vo
Variety
Alfalfa (many varieties)
Birds foot trefoil
Sweet clover
Red clover
Alsike clover
Korean lespedeza
Sericea lespedeza
Hairy vetch
White clover
Crownvetch
Best
Seeding
Time
Late
summer
Spring
Spring
Early
spring
Early
spring
Early
spring
Early
spring
Fall
Early
fall
Early
fall
Seed Densityt
seeds/ft2
5.2
9.6
6.0
6.3
16
5.2
8.0
0.5
18
2.7
Important Characteristics
Good on alkaline loam, re-
quires good management
Good on infertile soils,
tolerant to acid soils
Good pioneer on non-acid soils
Not drought resistant,
tolerant to acid soils.
Similar to red clover
Annual, widely adapted
Perennial, tall erect plant,
widely adapted
Winter annual, survives below
0°F, widely adapted
World-wide, many varieties,
does well on moist, acid soils
Perennial, creeping stems and
rhizomes, acid tolerant
Areas /Conditions
of Adaptation
Widely adapted
Moist, temperate
U.S.
Widely adapted
Cool, moist areas
Cool, moist areas
Southern, U.S.
Southern, U.S.
All of U.S.
All of U.S.
Northern U.S.
* Taken from many sources but mainly 126 and 129.
t Number of seeds per square foot when applied at 1 Ib/acre.
-------
Most perennials require a period of cool, moist weather to become estab-
lished to the extent that they can withstand a cold winter freeze or hot
summer drought. For most species in most localities, early fall seeding
(late August in the north through early October in the south) allows enough
time for the plants to develop to the stage that they can withstand a hard
winter. Plants then have a good start for early spring growth and can reach
full development before any hot summer drought. Early fall planting makes
germination and early growth possible in warm weather, the weather growing
cooler as the plants develop. Spring planting is usually second choice for
all but a few of the more rapidly developing perennials. Germination and
early development are slowed due to the cool early spring weather. Late
frosts often severely damage the young plants. Late spring planting does not
allow enough time for most perennials to mature before summer, and annual
weeds will usually out-compete the preferred perennial species.
Annuals generally are best seeded in spring and early summer. They com-
plete their growth quickly before the summer heat arrives and the soil mois-
ture is depleted. Thus, in late spring and in summer, the annuals easily
out-compete the perennials. Annuals can, however, be planted for quick vege-
tative cover any time the soil is damp and warm.
SEED AND SURFACE PREPARATION
Bare soil as a seeding medium suffers from large temperature and mois-
ture fluctuations and from rapid degeneration due to wind and water erosion.
Mulch in General
Mulches make the establishment of suitable plant cover more efficient by
reducing evaporation, moderating soil temperatures, preventing crusting, in-
creasing rain infiltration, and controlling wind and water erosion. Mulches
also help to overcome deficiencies in organic matter typically found in land-
fill cover soils. Almost any material spread, formed, or simply left on the
soil surface will act as a mulch. A wide variety of materials are used com-
monly or under special circumstances: straw and other crop residues, saw-
dust, wood chips, wood fiber, bark, manure, brush, jute or burlap, gravel,
stones, peat, paper, leaves, plastic film, and various organic and inorganic
liquids.
The effectiveness of any mulch depends upon many factors including the
physical and chemical properties of the soil, the land-forming or cultural
practices, species to be seeded, and the characteristics of the mulch itself,
such as its color, roughness, and manner of application. The effect of color
and roughness are directly related to the radiation balance at the soil sur-
face and, consequently, the heat transfer into and out of the soil. Slope,
aspect, and orientation of the soil surface also influence the solar energy
input. Other factors determining mulch efficacy are steepness and length of
slope, soil texture and depth, rate of application of mulch, and the weather
before, during, and after mulch application. Selection depends upon charac-
teristics of the area to be stabilized and the availability, cost, and prop-
erties of the mulch material. Several of the more common and effective
mulches and their applications are described below.
220
-------
Crop Residues
Crop residues, such as straw and hay, are readily available and are
widely used mulches; and of these, straw is by far the most common mulch in
all parts of the United States. Straw's long and fibrous texture is excellent
for erosion control, and its low nutrient value retards rotting so that it
normally lasts a full season. Straw reflects much sunlight and thus may have
the disadvantage of keeping the soil cool early in the spring or late in the
fall, when warmth would facilitate germination and early growth.
Where erosion is not a problem, an application of 1.5 tons/acre is rec-
ommended. On higher slopes or where erosion is expected to be a problem,
2 tons/acre produces better results. Application rates over 2.5 tons/acre
often result in reduced germination and emergence, and such high rates should
be avoided. Beater-type mulch spreaders work well on level areas, but a
blower type is better for steep slopes. Baled material tends to fall in
bunches unless cut or shredded and scattered or blown. Wheat straw is gener-
ally preferred over oat straw since oat straw decays more rapidly and usually
contains seeds that compete with the perennials for space and water. Hay, in
comparison to straw, is difficult to spread, and it decomposes rapidly. How-
ever, hay possesses some nutritive value and reflects less solar radiation.
Overall, however, the best plant residue mulch is the one most available and
nearest.
Straw should be anchored, if possible, so that it does not blow or wash,
making piles and leaving bare spots. A disk harrow (with disks set straight)
that is run over the mulch across the slope is effective at anchoring.
Notched disks work best. Running over the mulch with a special punch roller
or a cultipacker also helps to anchor the mulch. Even running over the spread
straw with a bulldozer helps keep the straw in place. Asphalt or resins can
be used as a "binder or to anchor, but while they greatly increase effective-
ness, they also increase cost.
Crop residues produced in place can be effective in special circum-
stances. Rapidly growing crops are especially useful as temporary cover when
placed in late spring or early summer, since chances of successfully seeding
perennial grass-legume then are low. Subsequently, the summer annual crop
acts as a natural mulch for fall or spring seeding of the permanent seed mix-
ture. Rapid-growing, coarse grasses, such as Sudan grass or a local equiva-
lent, are good choices as they are widely adaptable and the tall stiff stalks
are effective as a mulch. One disadvantage of the summer cover crop regime
is that the crop depletes available soil moisture in dry areas, causing the
seeding of perennials to fail. On the other hand, in wet areas, the soil
under the cover crop dries very slowly and often remains too wet to fertilize
and work into a good seed bed even into the next spring.
Wood Residues and Paper
Wood residues, such as sawdust, wood chips, bark, and shavings, are used
extensively in many areas. Wood residues are a concentrated source of organic
matter, and supplementary nitrogen should be applied with the mulch. Advan-
tages of wood residues are that they are easy to apply, long lasting, and
221
-------
less susceptible to blowing and fire than crop residues. Disadvantages in-
clude their competition for available nitrogen, their lowering of the pH, and
the frequent packing of the finer materials. Chips, shavings, and millrun
sawdust make good mulch, but the finer resaw sawdust packs tightly and may
retard aeration and infiltration. Microorganisms carrying on decomposition
of the highly cellulosic mulches (most are less than 0.2 percent nitrogen)
compete with plant roots for available nitrogen.
Wood cellulose fiber and shredded paper are available commercially for
use in several designs of hydroseeders and/or hydromulchers. The products
are furnished in bales that are mixed with water to form a sticky paste and
sprayed directly in place with specialized equipment. The dried slurry sticks
together and forms an effective mulch at much lower application rates than
required of nonslurried materials. Usually, seed and fertilizer are mixed
directly into the same slurry so that seeding, fertilizing, and mulching are
accomplished in a single operation. The low labor requirement and speed of
hydroseeding makes it the method of choice in many, large-area projects.
Bituminous Products
Petroleum-based products, such as asphalt and resins, are often suitable
and are frequently used as mulching materials. Specially formulated emulsions
of asphalt under various trade names have been used throughout the world to
prevent erosion, reduce evaporation, promote seed germination, and varm the
soil to advance the seeding date. The film clings to but does not penetrate
deeply into the soil; it is not readily destroyed by wind and rain and remains
effective from k to 10 weeks. Application rates of 1000-1200 gal/acre are
usually required to control erosion. Asphalt mulches cost about twice the
applied cost of a straw mulch.
Asphalt emulsions are often used in conjunction with straw mulches to
increase resistance to wind and water damage. Application rates are low so
that the straw is merely cemented together without complete coverage by the
asphalt.
Resin-in-water emulsions are often as effective as well-anchored straw
as mulching materials. Resin emulsions are stable and can be diluted with
large amounts of water without breaking the emulsion. The resins resist
weathering by wind, rain, or soil bacteria and leave the soil surface perme-
able to water. Resin is usually applied at a rate of 600-800 gal/acre, and
costs are equivalent to the asphalt emulsion.
Black asphalt absorbs solar energy and greatly increases the warming of
soils at all times of the year. Germination and development are greatly ac-
celerated in late fall and early spring, but in summer, the absorbed heat can
be lethal to young seedlings. Aluminized asphalt and white-pigmented resins
have been developed to overcome these problems but have not found wide
application.
Plastic Films
Plastic films are sometimes effectively used on very steep slopes or
222
-------
under high-erosion conditions. The film is expensive, difficult to put down,
and very susceptible to wind damage. Seedling emergence must be monitored
closely, and the film ventilated or removed at the right time. Even 1 or
2 days of temperatures over 80°F is enough to kill most seedings. Often when
the film must he removed, the seedling cover is not nearly complete and seri-
ous erosion results.
Other Techniques
Other techniques can be useful under special circumstances or avail-
ability. Gravel and crushed rock have the advantage since they are permanent.
A 1- to 2-in. layer of gravel will control surface erosion and vegetation
development in the driest of areas. Gravel with a minimum diameter of 1/2 in.
will resist winds to 85 mph.
Manure is an excellent mulch, which can often be found at local feed
lots. Manure acts as both a mulch and a slow-release fertilizer of fair
quality but is not reliable in erosion control as it tends to decompose
rapidly and is hard to spread evenly. Jute netting and woven thread-and-paper
fabric are available commercially for stabilizing very steep or critical
areas. These products are especially effective when used in conjunction with
a straw or hay under-mulch; however, both are expensive and difficult to put
down, requiring insertion of several thousand wire staples per acre to anchor
them.
Wattling is another technique-LSI that may be used to help establish veg-
etation on vulnerable slopes. Tied bundles of flexible twigs are laid in
furrows or trenches along contours, staked down, and partially covered with
soil. Rows of wattles act to trap soil moving down the slope, to dissipate
energy of soil and water movement, and to reduce effectively the slope of
small areas immediately upslope. The areas between wattle rows are thus made
favorable for establishment of vegetation. If the wattle is made of twigs
that take root easily, such as willow, the wattle itself becomes a part of
the semipermanent or permanent stabilization system.
MAINTENANCE OF VEGETATION
Once- the selected vegetation is established on the landfill, at least a
minimum amount of maintenance is necessary to keep less desirable, native
species from taking over and weak areas in the cover from developing. In
most areas judicious, twice yearly mowing will keep down weed and brush
species. Annual fertilization (and liming if necessary) will generally allow
desirable species to out-compete the lower quality weedy species. Occasional
use of selective herbicides usually controls noxious invaders, but care must
be taken to avoid injuring or weakening the desirable species, lest more harm
than benefit results in the long run. In rare circumstances, large insect
populations may threaten the stand of vegetation so that insecticide applica-
tion becomes desirable.
DESIGNING FOR VEGETATION
The role of vegetation over solid waste is to protect, as quickly as
223
-------
possible, the exposed final cover soil against erosion and disruption.
Therefore, it is vitally important that the soil support and hold healthy
vegetation. The following recommendations are set forth on the basis of dis-
cussions in this and previous sections.
Topsoil
A preliminary step in establishing vegetation is to stockpile and then
reuse the original topsoil. The less fertile underlying soil will be avail-
able as daily or intermediate cover. As the operation nears completion, the
stockpiled topsoil can be used in the final cover to facilitate rapid growth
of grasses and/or shrubbery. The original topsoil must be significantly more
fertile than underlying soil strata; otherwise, stockpiling is not practical
or economical.
Suitable Seed Mix
Regional vegetation should be considered for planting at the disposal
site. This continuity with existing vegetation is important from the aesthe-
tic point of view. Consideration should also be given to future use of the
site. For example, if a golf course is planned for construction on a munici-
pal waste disposal area, appropriate species of trees and grasses should be
selected and planted toward the close of disposal operations. Tables 39 and
HO recommend numerous grasses and legumes for consideration.
Swamping or Droughty Conditions
Where swamping or droughty conditions are anticipated because of cli-
mate, cover configuration, or soil type, special consideration should be
given to swamping-tolerant or drought-resistant vegetation.
Maximum Slopes
A general rule of thumb1-^ provides that IV on 2H is the maximum slope
on which vegetation can be established and maintained, assuming ideal soil
with low erodibility and adequate moisture-holding capacity. In soils less
than ideal, maximum vegetative stability cannot be attained on slopes steeper
than about IV on 3H. Optimum vegetative stability generally requires slopes
of IV on ItH or flatter.
Conditioning and Fertilizing
Where soil is deficient, fertilize to reach adequate levels of nutrients
and pH. Guidance is provided under SOIL FACTORS. Flexibility for improving
available cover soil may be found in carefully considering some inert wastes
as additives. Fly ash has locally been mixed29 with cover soil to provide
good soil texture with enhanced water retention capacity. The alkalinity of
fly ash may also provide an advantageous compliment to acid soils.
Mulching
Mulch application is a cost-effective method of erosion control. Mulch
221+
-------
applied to both flat and steep slopes attenuates the energy transfer and
splash action of raindrops. This attenuation minimizes water erosion until
vegetation has a chance to establish a stable root system. Often a tacking
material is applied to reinforce straw/hay mulch. Asphalt cements, chemical
stabilizers, and netting are used for this purpose, but these materials may
also be used alone as mulches.
Netting and Wattling
Freshly seeded cover may be protected with netting of jute, paper yarn,
plastic netting, fiberglass scrim, and filter cloth. The netting is placed
over the seeded soil, so that the vegetation penetrates as it grows. Areas
of slow growth remain protected by the netting until vegetation is estab-
lished. This technique is suitable for use in flat areas and on slopes.
Also consider wattling on erosion-prone slopes.
Partitioning of Area
Partitioning of the disposal area may prove effective toward early
achievement of stable vegetation growth. Accordingly, a relatively small
part of the site can be filled, covered, seeded, and mulched in a short
period of time before proceeding to the next. Exposure to erosion and other
adversities is reduced to a minimum. With some overlap of closure of one
subarea on the opening of another, the regular personnel and equipment on
site may be used efficiently for vegetation preparation during disposal
downtime.
Maintenance
Waste disposal areas have long lives, and permanent vegetative cover
should be maintained. Once a cover of vegetation is started and a stable,
extensive root system develops, organic matter and decomposition processes
develop a layer of humus capable of perpetuating the cover vegetation. Hov-
ever, erosion forces, burrowing animals, etc., may damage parts of this cover
of soil and vegetation. Provisions should be made for maintenance, specifi-
cally for transplanting grass sods, planting new seeds or shrubs, and re-
placing eroded soil during the inactive life of the area.
225
-------
SECTION 20
ANIMAL AND VECTOR CONTROL
Soil covering municipal solid waste should function to minimize animal
attraction and vector "breeding. This requirement is normally not so important
in land disposal of industrial and hazardous wastes because potential food and
breeding conveniences are much less than in municipal wastes. This section
suggests procedures and soils to minimize two basic animal nuisances, birds
and burrowing animals.
MINIMIZING ATTRACTIVENESS TO BIRDS
Birds are attracted by the availability of food (and perhaps of warmth)
and they have occasionally become a serious problem, e.g., near airports.133
In order to reduce the attraction of large colonies, municipal waste should be
covered quickly. The type of soil is not important as long as the cover:
a. Forms a thick layer over the waste.
b. Is strong enough to discourage digging by birds.
c. Is first placed early in the daily disposal operation.
DISCOURAGING BURROWING ANIMALS
When a disposal area is properly designed and constructed for primary
functions, such as erosion control, burrowing animals will automatically be
deterred. However, control of burrowing animals is occasionally a primary
cover function, and related experiences are pertinent. In rolled earth
dams,13^-136 animals create passageways for water to penetrate and damage the
structural integrity. A similar damage can be expected in sanitary landfills
where such holes may lead to increased water percolation.
Burrowing animals, such as rats, dig tunnels into municipal waste for
shelter and waste food scraps. To make waste areas unattractive to burrowing
animals, wastes should be covered daily with a soil that will not easily stand
open to provide passageways. Since animal tunnels depend on the arching
phenomenon to remain open, a soil possessing low arching potential should be
used.
Arching is a process of ground stress transfer where overburden load is
carried around a weak zone or opening by the mobilization of shearing
strength. Use of a cover soil with low shear and tensile strengths should
favor burrow instability and discourage burrowing animals. Generally, as
226
-------
percentages of silt-clay size particles are increased, in mixtures (remolded)
of sand, silt, and clay, strength increases. Accordingly, dry, loose, clean
granular soils, such as sand and well-graded gravel, should be effective in
deterring burrowing animals. When these soils are unavailable, mixtures of
creosote and soil may serve as substitutes.134,136
MINIMIZING VECTOR ACCESS
Municipal waste generally attracts flies and mosquitoes that are capable
of transmitting disease. Flies are attracted by the availability of food and
breeding areas in the wastes, and mosquitoes by the water-filled containers
that serve as hatcheries for eggs.
Soil cover should be added over municipal waste early in the daily dis-
posal operations. A strong,.dense, well-graded soil will impede vector larvae
emergence. This type of soil includes gravel, sand, silt, and clay provided
large voids are not developed. Clays and clay-rich soils are particularly
effective provided they are not cracked. Where flexural cracks (Figure 26)
tend to develop, a cohesionless soil may be best.
227
-------
SECTION 21
AESTHETIC CONSIDERATIONS
Municipal/industrial waste disposal areas should be inoffensive and ac-
ceptable. The role of cover for aesthetics is simply:
a. To minimize blowing paper during daily operations.
b. To aid in the control of odors.
c. To reduce quickly the harsh appearance of exposed solid waste.
Any soil type should serve adequately. Attention to these considerations will
help maintain good public relations in the vicinity of a waste disposal site.
Aesthetics may not be primary functional requirements of cover soils but are
interrelated with other requirements and should be kept in mind always during
design/construction phases.
228
-------
SECTION 22
FUTURE CONSTRUCTION AND LAND USE
This section is concerned with the measures that can be taken during de-
sign and construction to facilitate and improve future land use. Specifically,
those aspects concerning the composition and configuration of the cover are
emphasized. Efficient use of landfill after the primary vaste disposal pur-
pose has been achieved requires long-range planning. Planning is particularly
important where construction of a building is anticipated. The consequences
of changing plans for the landfill will usually require costly modifications,
such as the removal of settlement-prone cover-waste layers.
DISPOSAL AREAS AS SITES FOR CONSTRUCTION
A conservative viewpoint has prevailed for many years in the state of the
art of using landfills. The tendency is to think of landfills for use as
parks and the like rather than to support structures. Actually, a spectrum of
uses can be opened through proper planning. Thus, it may be possible to pro-
vide for light structure foundations by doubling or tripling the ratio of soil
cover to waste material in the top lifts below the proposed foundation grade.
Such increase in the proportion of soil would, of course, reduce the primary
function of the landfill, i.e., to hold solid waste. The short-range and
long-range objectives must be balanced in reaching a decision on such a de-
sign modification.
Supportive Characteristics of Waste
The conservative attitude about future construction on landfills centers
around the poor supportive qualities of most solid waste. Table 3 shows an
average composition of municipal refuse. The composition clearly indicates an
inherent resistance to compaction and a latent ability to absorb water as it
becomes available. Both characteristics tend to delay the sanitary landfill
from the trend toward increasing stability with time expected in fills of soil
or rock. Figure 101 confirms the severity of the problem but suggests that
predictions of settlement may be adequate for engineering design. At the
present time, little can be done by manipulation of cover soil composition
and placement to counteract unfavorable characteristics. There is some leeway
for manipulation of the configuration of the cover, however, as mentioned
above.
Industrial sludges and slurries may have even poorer qualities, besides
an enduring potential for serious pollution; they are however more uniform and
predictable (see NATURE OF SOLID WASTE in Section l). Some sludges by virtue
of a colloidal nature can remain for years in a saturated condition with a
229
-------
0.0
Gibson ft Lo's theory
Terzaghi's theory
Observed resull
Extension of
Terzaghi's theory
150 200
Time (days)
250
300
350
Figure 101. Settlements predicted and observed from loading 10-ft-
thick section of old municipal landfill.137
very high water content. Relatively thin cover interstratified with such
slimes, sludges, or slurries may do little to improve the condition as a
foundation and, in fact, may actually cover up, obscure, and preserve sub-
strata that are entirely unsuitable as foundation; however, see Section 15.
Use Options Available
Several potential uses for sanitary landfills and industrial waste sites
involve little consideration of the integrity of the mass. These uses fall
into the following general categories:
a. Nature park.
b. Recreation park.
c. Tree farm.
d. Wild area.
e. Animal refuge.
Landfill uses that will require some planning of cover soil composition and
configuration include the following:
a. Paved parking area.
230
-------
b. Tennis court, etc.
c. Vehicular track or strip.
d. Ski or toboggan hill.
Future uses that vill require considerable planning and may sacrifice part of
the waste disposal purpose are all those concerning roads and utilities and
those involving the foundation of structures (Figure 102). The following
foundation types are generally required for increasingly heavier structures:
a. Mat foundation.
b. Spread footings.
c. Pile foundation.
d. Piers or caissons.
The reader is referred elsewhere ' ' for recommendations on mats, deep
foundations, utilities, and other structural aspects since these subjects
exceed the scope of this manual.
DESIGNING FOR FUTURE USE
Perhaps the best cover design measure in preparation for the future use
Proposed Construction Drain
NATURAL SOIL
Proposed Construction Drain
Q_) 3 Ft. »ini«u» Clay barrier recommended. 10 Ft. barrier constructed
(?) Temporary drain installed after building pad fill completed
(T) Perimeter Gas Vent with periodic riser vents
Figure 102. Foundation design for building at old sanitary landfill.
231
138
-------
of a landfill of solid or hazardous waste is to know before the operation be-
gins what the eventual use will be. Ideally, this information would include
surveyed locations of structures requiring significant support, recreational
facilities requiring specific topography, and such details as the load antici-
pated on parking lots. Where such preparations have not been made, the site
may require extensive renovation before it can be used.
Increased Cap Thickness
The low bearing capacity of a sanitary landfill can be circumvented by
increasing the soil thickness above waste.139 In this way, the strong soil
resists both punching and rotational shear. The thickness of soil should be
at least 1.5 times the width of structural footings.
Increased Cover/Waste Ratio
Reduction in the overall amount of spongy waste (versus daily cover) in a
landfill will also improve the supportive capability as a foundation.3 At
some ratio not much below the common 3:1 waste to soil, the efficiency of the
landfill for disposal of solid waste becomes unacceptably low. This conflict
is one reason for recommending careful planning. It may be that sacrifice of
disposal space is only needed immediately below the intended foundation as
discussed below.
Compaction
Beneficial effects of compaction on strength, permeability, and secondary
characteristics, such as erodibility, have been discussed elsewhere. Field
compaction should be planned and incorporated into specifications for the
landfilling operation. It will also be advisable to have such quality control
during construction that the design compaction conditions are achieved.
Additives and Cements
Another technique worth consideration is the incorporation of stabilizers
into the soil during cover placement. Common chemicals mixed with soil in-
clude lime, portland cement, and numerous organic chemicals. The desired
effect may be strengthening by cementation, waterproofing, or dispersion for
greater density and lower permeability. Wetting, mixing, compacting, and cur-
ing are all critical stepsl^O and achieving a homogeneous and uniform mixture
is not so simple.
Selective Disposal
Consider placing and compacting waste suitable for foundations in areas
(pads) to support planned buildings. For example, fly ash and bottom ash may
be compacted in 1-ft lifts in assigned areas while other solid waste is dis-
tributed elsewhere in adjacent areas. This method is the extreme case of
Increased Cover/Waste Ratio.
232
-------
Undisturbed Structural Pads
Leaving pedestals of undisturbed ground as structural pads solves the
problem of providing foundations for future buildings in sanitary land-
filling operations.
Devatering Layers
Drainage layers placed originally as cover may facilitate and hasten the
consolidation of saturated solid waste. Such a system might consist of 1-ft
sand layers connected to gravity drains as discussed in Section 15.
The settlement process may be accelerated under certain conditions of
groundwater circulation and solid waste degradation. It was observed in one
full-scale field test2? that settlement increased with removal and recircula-
tion of leachate through the waste cells. Faster settlement apparently re-
sulted from the increase in decomposition rate.
Preloading
Preloading involves densification by placing a temporary surcharge of
soil. Preloading might be a useful landfill preparation when:
a. Soil or other material is readily available for use as preload.
b. Time for stabilization is short.
c. Only minor additional decomposition is anticipated.
A program of careful monitoring of the settlement under the preload is essen-
tial. Only after a satisfactory decrease in the settling rate is established
would it be feasible to remove the preload and build the structure. Even
then, settlement may continue if waste decomposition continues.3
Backfilling^ and Replacement
Where the future use of a landfill is not specifically identified, a more
practical approach may be to postpone foundation improvement until plans for
usage are firmed up. At such time, the landfill can be excavated immediately
at the planned foundation and backfilled with suitable granular material that
drains well and is low in frost susceptibility. Pipe drains at the perimeter
of the foundation should also be provided.
The extra cost of granular materials from outside the site may necessi-
tate the use of some of the excavated waste in fills for roadways-1-^ and light
structure foundations. In such case one should blend soil into aged waste to
50 percent or more. No layer of the refuse/soil mixture should be within h ft
of finished grade.
Excavation and backfilling may require safeguards against disturbing a
stabilized condition or exposing the buried solid waste as a health hazard.
It may be necessary, for instance, to line the backfill area with impervious
233
-------
clay to prevent an inflow of leachate or gas into the granular foundation. In
any case, initial excavation should proceed with due concern for R^S and CH^.
Gas Channels and Vents
A common difficulty is keeping landfill gases from accumulating in the
structure. Even "buildings erected on undisturbed soil pads must be specially
designed to prevent such accumulation. A layer of sand can be laid over the
proposed structural area and then be covered by two or more membranes. 139 An
additional layer of sand above protects the membranes. Gas is thus blocked
from the structure and can migrate laterally to vents at convenient locations.
Utility connections must be made gas-proof if they enter a structure
below grade. If the building is surrounded by filled land, utility and sewage
lines that traverse the fill must be flexible, and slack should be provided
so that the lines can adjust to settlement without breaks or low spots.
Remedial Grouting
Occasionally, additives should be considered to stabilize the foundation
portion of the landfill and improve its supportive qualities. Additives may
be spread, worked into the cover soil, or injected into the cover and waste
cells below. The labor cost for injection may be quite high; it was estimated
several years ago that labor and material cost ranged between 25 and
100 dollars/yd3 of treated
A grout composed of soil, cement, and water is sometimes used to fill
voids in dumped stone deposits and, by analogy, may be suitable for filling
voids in inter layered solid waste and cover soil. Various types of chemical
grouts are available. Those chemical grouts with relatively low viscosity may
be capable of penetrating the soil pore structure to provide cementation.
Sodium silicate is used for this purpose, but its permanence is questionable.
On aging, the silicic gel shrinks and cracks and may be dissolved under
alkaline conditions. Certain fixative chemicals or physical stabilizers con-
vert sludge waste to nontoxic, load-bearing material. 29
Pile and Pier Foundations
Where other means of achieving a supportive foundation on a solid waste
landfill are unsuccessful, a system of piles or piers can be used to support
important structures. Even with these extreme measures, problems may not be
entirely eliminated. The landfill may continue to settle around and away from
the stable structure and incidentally cause the piling to take additional, un-
anticipated loads through mobilization of negative skin friction. Figure 103
shows schematically the surface settlement observed in one landfill-related
problem; incidently, methane generation and migration had compounded the
problem.
Documentation
The most cost-effective technique for future use may be to build a perma-
nent file of information on the configuration, content, and history of the
-------
WOODEN SCREEN
APARTMENT BUILDING
NATURAL SOIL
Figure 103-
Settlement of solid waste beneath and
around building founded on piers.
landfill. Accurate topography for the base of waste alone will, in combina-
tion with ultimate surface topography, provide invaluable engineering back-
ground and may make expensive borings unnecessary. Information on settlement,
erosion, and concentrations and timing of leachate will also be useful later.
The planner should consider requiring such a record from the operator with
provisions for placing a short description (with accurate location map) on
public record.
Maintenance
Provisions for maintenance after site closure should follow a logical
plan according to future use. Some cover deterioration like erosion can be
tolerated where the future use plan has inherent provisions for repair mainte-
nance, e.g., at a landfill converted to a golf course. On the other hand,
maintenance of cover may not be practical where the site is remote and no
further active use is planned. In such cases, it is necessary to design the
cover more conservatively to avoid serious deterioration in the future.
235
-------
SECTION 23
SUMMARY EXAMPLE
This manual provides guidance on covering solid waste by reviewing the
various factors affecting the satisfactory performance of cover and by making
numerous recommendations for effective selection and placement. The follow-
ing hypothetical example should serve to illustrate how the manual may be
used on a specific site problem.
The hypothetical example is a municipally owned and operated sanitary
landfill in a small city. Household and commerical waste will form the bulk
of the incoming solid waste, but small amounts of industrial waste will be
accepted. The location of the landfill has been established by preliminary
investigation. The landfill will eventually be converted to a nature strip
and park serving subdivisions that are anticipated to develop on both sides
of the fill in the future.
The only materials available in abundance in this region have been found
previously to be the natural silty soil that reaches thicknesses of 20 ft and
sand and silt mixtures available as a by-product of washed gravel operations
in the vicinity. A third material, available in lesser quantity, is rela-
tively stiff clay exposed in active gravel pits at the base of the gravel-
bearing stratum. This clay is not used otherwise and would have to be
excavated.
On the basis of existing test results or the results of new tests for
the study, the three possible cover materials are determined to be of USCS
types SP, ML, and CH. The water content for the SP varies considerably since
this soil drains well. The ML contains about 20 percent water as excavated,
and the CH soil commonly contains about 25 percent water.
The preliminary investigations are completed, and a preliminary design
is prepared for the final topographic configuration. Various constraints are
imposed, e.g., at least a 5-ft buffer of undisturbed soil must intervene
between the base of solid waste and the highest position of the phreatic
surface. As a first step in designing a cover and choosing appropriate ma-
terial, the city engineer in cooperation with the city planner establishes
the priorities of functions of the cover.
The city engineer prepares the following tabulation for displaying
effectiveness of the three soils in the six most important cover functions
(in order of priority). Other cover functions are considered subordinate in
this example.
236
-------
Cover Function SP ML CH
Impede infiltration of water IX IV I
Control "bird population by
reducing attractiveness to birds
Control wind erosion of soil II VII X
Limit gas migration* VII III I
Control water erosion of soil II XIII IX
Assure trafficability I IX VI
All other functions (approximately
equally important)
The most favorable rating is I. Clearly, the SP and CH soils have distinct
advantages in certain functions. The SP soil is rated I for trafficability
and II for water and wind erosion control. The CH soil has its advantages in
impeding water percolation and gas migration. The ML soil is rated between
the other two in all functions except trafficability, where it is rated
poorer than both.
As a next step, a cost analysis is performed, and it is quantitatively
determined that considerable expense will be incurred in importing SP and CH.
Existing equipment can accomplish all excavation and transportation of indig-
enous ML soil, and therefore, cost of using this soil (beyond the on-site
costs comparable to using stockpiled SP or CH) will be negligible. This large
advantage convinces the city that the ML soil on the site should be used.
After the decision is made to use ML soil, certain operational proce-
dures must be established to improve somewhat marginal soil qualities. The
ML soil, though rated a modest IV, has a permeability of approximately
10~5 cm/sec that should adequately impede percolation and gas leakage during
the relatively short exposure of daily and intermediate covers. For the
final cover, however, a 6-in. layer of compacted CH should be incorporated at
the bottom for added resistance to percolation and gas migration. A system of
gravel-filled trenches will safely vent to the atmosphere.
To hold water erosion to an acceptably low level, an operational plan of
compacting cover is recommended even for daily cover. Arrangements should
also be made to use large stockpiles of gravel and SP soils as additions to
daily cover whenever rainfall threatens to reach an amount established pre-
viously as excessive. Long-range measures for protecting the final cover from
* A rating of I indicates that gas will not tend to move through the soil
but will tend to seek an alternative direction of travel.
237
-------
"both wind and -water erosion are a program of rapid topsoil restoration and
seeding for vegetation. A stabilizing additive and/or a thin covering of SP
soil from the stockpile can "be specified as needed to prevent excessive vind
erosion in the short range.
The remaining cover function given special consideration is traffica-
"bility. The ML soil has deficiencies in this function, so two operational
procedures are recommended. First, the main access should be routed on
permanent, all-weather gravel roads along both boundaries with short branches
as needed to the working area. Second, a special area should be reserved for
wet-period operations. These detailed considerations having beneficial ef-
fects on trafficability and the other principal functions discussed above
are finally formalized in specifications or in plans for operation, closure,
and maintenance. The development of the disposal area (in regard to cover)
will then proceed in an orderly, efficient manner.
238
-------
REFERENCES
1. Ellison, R. D. , "Presentation - Session III Environmental Problems,"
Specialty Conference of the Geotechnical Engineering Division, American
Society of Civil Engineers, 13-15 June 1977, Ann Arbor, Michigan.
2. 9^th Congress of the United States of America, "Resource Conservation and
Recovery Act of 1976," Public Law 9U-580, 21 October 1976.
3. Brunner, D. R. and Keller, D. J., "Sanitary Landfill Design and Opera-
tion," U. S. Environmental Protection Agency, Report SW-65ts, 1972,
Washington, D. C., 59 PP.
U. Noble, G., Sanitary Landfill Design Handbook, Technomic, Westport, Con-
necticut, 1976, 285 pp.
5. Schomaker, N. B. and Murdock, R. F. , "Selection and Placement of Soil
Cover Material in a Sanitary Landfill," U. S. Public Health Service, Open
File Report UD-03-68-20, Cincinnati, Ohio, 1969.
6. Meyer, M. P. and Knight, S. J. , "Traff icability of Soils, Soil Classifi-
cation," U. S. Army Engineer Waterways Experiment Station, Technical
Memorandum 3-2kO, Supplement 16, Vicksburg, Mississippi, 1961.
7. Salvato, J. A., Wilkie, W. G. , and Mead, B. E. , "Sanitary Landfill -
Leaching Prevention and Control," Journal of the Water Pollution Control
Federation, Vol 1*3, 1971, PP 208U-2100.
8. American Public Works Association, Municipal Refuse Disposal, 2nd ed.,
Public Administration Service, Chicago, Illinois, 1966, 528 pp.
9. Wayne, D. D. , "Waste Use in Highway Construction," Transportation Re-
search Board, Transportation Research Record 593, Washington, D. C.,
1976, pp 9-12.
10. Reinhardt, J. J. and Ham, R. K. , "Solid Waste Milling and Disposal on
Land Without Cover, Vol I. Summary and Major Findings," U. S. Environ-
mental Protection Agency, Report EPA/530/SW-62d.l, Washington, D. C. ,
11. Ledbetter, R. H., "Design Considerations for Pulp and Paper-mill
Sludge Landfills," U. S. Environmental Protection Agency, Report
EPA-600/3-76-111, Cincinnati, Ohio, 1976, 137 pp.
239
-------
12. U. S. Army Corps of Engineers, "Laboratory Soils Testing," Engineer
Manual 1110-2-1906, Washington, D. C., 1970.
13. Jumikis, A. R., Soil Mechanics, Van Nostrand, Princeton, New Jersey,
1962, 791 pp.
14. U. S. Army Corps of Engineers, "Stability of Earth and Rock-fill Dams,"
Engineer Manual 1110-2-1902, Washington, D. C., 1970.
15. Chen, F. H., Foundations on Expansive Soils, Elsevier, New York, 1975,
280 pp.
16. Decker, R. S. and Dunnigan, L. P., "Development and Use of the Soil Con-
servation Service Dispersion Test," in Dispersive Clays, Related Piping,
and Erosion in Geotechnical Projects, American Society for Testing and
Materials, Special Technical Publication 623, 1977, PP 9U-109.
17. U. S. Naval Facilities Engineering Command, "Soil Mechanics, Foundations,
and Earth Structures," Design Manual-7, Alexandria, Virginia, 1971 (with
changes to 197^)-
18. U. S. Army Engineer Waterways Experiment Station, "Soil Compaction In-
vestigation," Technical Memorandum 3-271, Vicksburg, Mississippi,
19^9-1957.
19. Lambe, T. W. and Whitman, R. V., Soil Mechanics, John Wiley, New York,
1969, 553 pp.
20. Kraatz, D. B., "Irrigation Canal Lining," Irrigation and Drainage
Paper 2, Food and Agriculture Organization, United Nations, Rome, 1971,
171 PP-
21. Holtz, W. G. and Lowitz, C. A., "Compaction Characteristics of Gravelly
Soils," U. S. Bureau of Reclamation, Earth Laboratory Report EM-509,
Denver, Colorado, 1957.
22. Jones, C. W., "The Permeability and Settlement of Laboratory Specimens of
Sand and Sand-Gravel Mixtures," in Symposium on Permeability of Soils,
American Society for Testing Materials, Special Technical Publication 163,
1955, PP 68-78.
23. U. S. Army Corps of Engineers, "Soil Stabilization Emergency Construc-
tion," Technical Manual 5-887-5, Washington, D. C., 1966.
2h. Rogers, E. H., "Soil-cement Linings for Water-containing Structures,"
Proceedings of Second Seepage Symposium, U. S. Department of Agriculture,
Report ARS 1+1-11*7, 1969, PP 9^-105.
25. Akky, M. R. and Shen, C. K., "Erodibility of a Cement-Stabilized Sandy
Soil," in Soil Erosion: Causes and Mechanisms Prevention and Control,
Highway Research Board, Special Report 135, Washington, D. C., 1973,
pp 30-1+1.
-------
26. Moh, Z. C., "Soil Stabilization with Cement and Sodium Additives,"
Journal of the Soil Mechanics and Foundation Division, American Society
of Civil Engineers, Vol 88, 1962.
27. Eades, J. L. and Grim, R. E., "A Quick Test to Determine Lime Require-
ments for Lime Stabilization," Highway Research Board Record, No. 3, 1966.
28. Capp, J. P. and Spencer, J. D., "Fly Ash Utilization," U. S. Bureau of
Mines, Information Circular 8U83, Washington, D. C., 1970, 72 pp.
29. Phillips, N. P. and Wells, R. M., "Solid Waste Disposal," U. S. Environ-
mental Protection Agency, Report 650/2-7^-033, 1971*, 268 pp.
30. Rosner, J. C., "Soil Stabilization Utilizing Lime and Fly Ash," Proceed-
ings of l^th Paving Conference, University of New Mexico, Albuquerque,
1978, pp 20-35.
31. Parker, D. G., Thornton, S. I., and Cheng, C. W., "Permeability of Fly
Ash Stabilized Soils," in Geotechnical Practice for Disposal of Solid
Waste Materials, American Society of Civil Engineers, 1977, PP 63-70.
32. Smith, L. M. and Larew, H. G., "User's Manual for Sulfate Waste in Road
Construction," U. S. Department of Transportation, Report FHWA-RD-76-11,
Washington, D. C., 1975, 27 pp.
33. Decker, R. S., "Sealing Small Reservoirs with Chemical Soil Dispersants,"
Proceedings of 1963 Seepage Symposium, U. S. Department of Agriculture,
Report ARS Ul-90, 1965, PP 112-129.
3^. Haas, W. M. et al., "Using Additives to Improve Cold Weather Compaction,"
Transportation Research Record 560, Washington, D. C., 1976, pp 57-68.
35- U. S. Army Engineer Waterways Experiment Station, "Investigation of
Filter Requirements for Underdrains (revised)," Technical Memorandum
183-1, Vicksburg, Mississippi, 19Ul.
36. Soil Conservation Service, "Drainage of Agricultural Land," SCS National
Engineering Handbook, Section l6, U. S. Department of Agriculture, 1971
(reprinted by Water Information Center, Inc., Port Washington, New York,
1973).
37- SCS Engineers, "Study of Engineering and Water Management Practices that
Will Minimize the Infiltration of Precipitation into Trenches Containing
Radioactive Waste," U. S. Environmental Protection Agency, Report
ORP LV-78-5, Las Vegas, Nevada, 1978, 85 pp.
38. Willson, R. J., "A Lower Cost Canal Lining Program," Proceedings of 1963
Seapage Symposium, U. S. Department of Agriculture, Report ARS Ul-90,
1965, PP 85-93.
39- Geswein, A. J., "Liners for Land Disposal Sites," U. S. Environmental
Protection Agency, Report EPA/530/SW-137, Cincinnati, Ohio, 1975.
2Ul
-------
1*0. Haxo, H. E. , Jr., "Assessing Synthetic and Admixed Materials for Lining
Landfills," in Gas and Leachate from Landfills , U. S. Environmental Pro-
tection Agency, Report EPA-600/9-76-OQ1* , Cincinnati, Ohio, 1976,
pp 130-158.
1*1. McBee, W. C. and Sullivan, T. A., "Direct Substitution of Sulfur for
Asphalt in Paving Materials," U. S. Bureau of Mines, Report of Investiga-
tions 8303, Washington, D. C. , 1978, 23 pp.
1*2. Lansdon, H. G., "Construction Techniques of Placement of Asphalt-Rubber
Membranes," Proceedings of 13th Paving Conference, University of New Mex-
ico, Albuquerque, 1976, pp 96-108.
1+3. Saylak, D., "Research Activities of the Texas Transportation Institute on
Sulfur -Asphalt and Recycled Pavement Systems," Proceedings of lUth Paving
Conference, University of New Mexico, Albuquerque , 1977 > pp 60-87
1*1*. Fields, T., Jr., and Lindsey, A. W., "Landfill Disposal of Hazardous
Wastes: A Review of Literature and Known Approaches," U. S. Environ-
mental Protection Agency, Report EPA/530/SW-165, Cincinnati, Ohio, 1975.
1*5. Farb, D. G. , "Upgrading Hazardous Waste Disposal Sites," U. S. Environ-
mental Protection Agency, Report EPA/500/SW-677, Washington, D. C., 1977.
1*6. Faber, J. H. and DiGioia, A. M. , "Use of Ash in Embankment Construction,"
Transportation Research Record 593, Washington, D. C., 1976, pp 13-19.
1*7- Pavoni , J. L. , Heer, J. E. , Jr., and Hagerty, D. J. , Handbook of Solid
Waste Disposal, Van Nostrand Reinhold, New York, 1975, 5^9 PP.
1*8. Collins, R. J. and Miller, R. H., "Availability of Mining Wastes and
Their Potential for Use as Highway Materials: Vol 1, Classification and
Technical and Environmental Analysis," U. S. Department of Transporta-
tion, Report FHWA-RD-76-106, Washington, D. C., 1976.
1*9. Reikenis, R., Elias, V., and Drabkowski, E. P., "Regional Landfill and
Construction Material Needs in Terms of Dredged Material Characteristics
and Availability," U. S. Army Engineer Waterways Experiment Station, Con-
tract Report D-7^-2, Vicksburg, Mississippi,
50. Bartos, M. J., Jr., "Classification and Engineering Properties of Dredged
Materials," U. S. Army Engineer Waterways Experiment Station, Technical
Report D-77-18, Vicksburg, Mississippi, 1977.
51. Johnson, S. J. et al. , "State-of-the-Art Applicability of Conventional
Densification Techniques to Increase Disposal Area Storage Capacity,"
U. S. Army Engineer Waterways Experiment Station, Technical Report D-77-H,
Vicksburg, Mississippi, 1977-
52. Colacicco, D. et al, "Cost of Sludge Composting," U. S. Department of
Agriculture, Report ARS-NE-79, Belt svi lie, Maryland, 1977.
-------
53. Gray, D. M. and Norum, D. I., "The Effect of Soil Moisture on Infiltra-
tion as Related to Runoff and Recharge," in Soil Moisture, Proceedings of
Hydrology Symposium, No. 6, National Research Council of Canada, 1968,
pp 133-150.
5!+. Viessman, W., Jr., Harbaugh, T. E., and Knapp, J. W. , Introduction to
Hydrology, Intext Educational, New York, 1972, ^15 pp.
55. Soil Conservation Service, "Hydrology," SCS national Engineering Handbook,
Section U, U. S. Department of Agriculture, Washington, D. C., 1972.
56. Gary, J. W. and Evans, D. D., eds., "Soil Crusts," University of Arizona,
Agricultural Experiment Station, Technical Bulletin 2lU, Tucson, 197^.
57. Philip, J. R., "Theory' of Infiltration," in Advances in Hydroscience,
Vol 5, V. T. Chow, ed., Academic Press, New York, 1969, PP 215-296.
58. Miller, D. E. and Gardner, W. H., "Water Infiltration into Stratified
Soil," Soil Science Society of America, Proceedings, Vol 26, 1962,
pp 115-119.
59. Hillel, D., "Computer Simulation of Soil-Water Dynamics: a Compendium of
Recent Work," International Development Research Centre, Monograph
IDRC-082e, Ottawa, 1977, 2lU pp.
60. Jens, S. W. et al., "infiltration," in Hydrology Handbook, Manual of
Engineering Practice No. 28, American Society of Civil Engineers, New
York, 191+9, PP 33-63.
6l. England, C. B., "Land Capability: a Hydrologic Response Unit in Agri-
cultural Watersheds," U. S. Department of Agriculture, Report ARS Ul-172,
Washington, D. C., 1970, 12 pp.
62. Stewart, B. A. et al., "Control of Water Pollution fron Cropland:
Vol II - An Overview," U. S. Department of Agriculture, Report ARS-H-^-2,
Hyattsville, Maryland, 1976, 187 pp.
63. Holtan, H. N. et al., "USDAHL-71* Revised Model of Watershed Hydrology,"
U. S. Department of Agriculture, Technical Bulletin (ARS) 151*8, Washing-
ton, D. C., 1975-
6^4. Linsley, R. K. and Franzini, J. B. , Water-Resources Engineering, 2d ed.,
McGraw-Hill, New York, 1972, 690 pp.
65. Thornthwaite, C. W. and Mather, J. R., "instructions and Tables for Com-
puting Potential Evapotranspiration and the Water Balance," Publications
in Climatology, Vol X, No. 3, Drexel Institute, New Jersey, 1957,
pp 185-311.
66. Thornthwaite, C. W. and Mather, J. R., "The Water Balance," Publications
in Climatology, Vol VIII, No. 1, Drexel Institute, New Jersey, 1955,
86 pp.
2U3
-------
67. Fenn, D. G., Hanley, K. J., and DeGeare, T. V., "Use of the Water Balance
Method for Predicting Leachate Generation from Solid Waste Disposal
Sites," U. S. Environmental Protection Agency, Report SW-168, Cincinnati,
Ohio, 1975.
68. Baver, L. D., Soil Physics, 3d ed., Wiley, New York, 1959, ^89 pp.
69. Dass, P. et al., "Leachate Production at Sanitary Landfill Sites,"
Journal of the Environmental Engineering Division, American Society of
Civil Engineers, Vol 103, 1977, pp 981-988.
70. Fungaroli, A. A., "Pollution of Subsurface Water by Sanitary Landfills -
Volume I," U. S. Environmental Protection Agency, Report SW-12 rg, Wash-
ington, D. C., 1971.
71. Fenn, D. G. et al., "Procedures Manual for Ground Water Monitoring at
Solid Waste Disposal Facilities," U. S. Environmental Protection Agency,
Report EPA/530/SW-611, Cincinnati, Ohio, 1977.
72. Conover, H. S., Grounds Maintenance Handbook, 3d ed., McGraw-Hill, New
York, 1977, 631 pp.
73. Esmaili, H., "Control of Gas Flow from Sanitary Landfills," Journal of
the Environmental Engineering Division, American Society of Civil Engi-
neers, Vol 101, 1975, PP 555-566.
7^. Engineering-Science, Inc., "Final Report - In-situ Investigation of Move-
ments of Gases Produced from Decomposing Refuse," California State Water
Quality Control Board, Publication 35, Sacramento, April 1967.
75. Carlson, J. A., "Recovery of Landfill Gas at Mountain View, Engineering
Site Study," U. S. Environmental Protection Agency, Report EPA/530/SW-
587 d, Cincinnati, Ohio, 1977, 63 pp.
76. Moore, C. A., "Theoretical Approach to Gas Movement Through Soil," in
Gas and Leachate from Landfills, U. S. Environmental Protection Agency,
Report EPA-600/9-76-OOU, Cincinnati, Ohio, 1976, pp 33-^3-
77. Farmer, W. J. et al., "Problems Associated with the Land Disposal
of an Organic Industrial Hazardous Waste Containing HCB," in Re_sidual
Management by Land Disposal, U. S. Environmental Protection Agency, Re-
port EPA-600/9-76-015 , Cincinnati, Ohio, 1976, pp 177-185.
78. Flowers, F. B. et al., "Vegetation Kills in Landfill Environs," in Man-
agement of Gas and Leachate in Landfills, U. S. Environmental Protection
Agency, Report EPA-600/9-77-026, 1977, Cincinnati, Ohio, pp 218-236.
79. Stewart, B. A. et al., "Control of Water Pollution from Cropland:
Vol I - A Manual for Guideline Development," U. S. Department of Agri-
culture, Report ARS-H-5-1, Hyattsville, Maryland, 1975, HI pp.
-------
80. Wischmeier, W. H. and Smith, D. D., "Rainfall Energy and Its Relationship
to Soil Loss," American Geophysical Union, Transactions, Vol 39> 1958,
pp 285-291.
81. Wischmeier, V. H. and Mannering, J. V., "Relation of Soil Properties to
Its Erodibility," Soil Science Society of America, Proceedings, Vol 33,
1969, PP 131-137.
82. Roth, C. B., Nelson, D. W., and Romkens, M. J. M., "Prediction of Subsoil
Erodibility Using Chemical, Mineralogical, and Physical Parameters,"
U. S. Environmental Protection Agency, Report EPA-660/2-71*-OU3, Washing-
ton, D. C., 1971*, 111 PP.
83. Foster, R. L. and Martin, G. L., "Effect of Unit Weight and Slope on
Erosion," Journal of the Irrigation and Drainage Division, American
Society of Civil Engineers, Vol 95, 1969, pp 551-561.
Qk. Meyer, L. D., Wischmeier, W. H., and Daniel, W. H., "Erosion, Runoff and
Revegetation of Denuded Construction Sites," American Society of Agri-
cultural Engineers, Transactions, Vol lU, 1971, pp 138-lUl.
85. Christensen, R. W. and Das, B. M., "Hydraulic Erosion of Remolded Co-
hesive Soils," in Soil Erosion: Causes and Mechanisms Prevention and
Control, Highway Research Board, Special Report 135, Washington, D. C.,
1973, pp 8-19.
86. El-Rousstom, A., "Rain Erodibility of Compacted Soils," University of
Arizona, Doctoral Dissertation, Tucson, 1973.
87. Kobashi, S., "Erosion and Surface Stratum Failure of Steep Slopes and
Their Prevention Methods," Proceedings of the Fourth Asian Regional
Conferences on Soil Mechanics and Foundation Engineering, Vol 1, 1971,
PP ^33-1*36.^
88. Morrison, W. R. and Kuehn, V. L., "Laboratory Evaluation of Petrochemi-
cals for Erosion Control," U. S. Bureau of Reclamation, Memorandum Ap-
plied Sciences 73-1-6, Denver, Colorado, 1973.
89. Forsyth, R. A., Mearns, R., and Hoover, T., "Erosion Control of Unce-
mented Sand," California Division of Highvays, Research Report CA-DOT-TL
1139A-1^2-73-2U, Sacramento, September 1973.
90. Wyant, D. C., Sherwood, W. C., and Walker, H. N., "Erosion Prevention
During Highway Construction by the Use of Sprayed on Chemicals," Virgini
Highway Research Council, Report VHRC-72-R1, Charlottesville, July 1972.
91. Dean, K. C., Havens, R., and Glantz, M. W., "Methods and Cost for Stabi-
lizing Fine-Sized Mineral Wastes," U. S. Bureau of Mines, Report of In-
vestigation 7876, Washington, D. C.,
-------
92. Meyer, L. D., Johnson, C. B., and Foster, G. R., "Stone and Woodchip
Mulches for Erosion Control on Construction Sites," Journal of Soil ami
Water Conservation, Vol 27, 1972, pp 26^-269.
93. Skidmore, E. L. and Woodruff, I,'. P., "Wind Erosion Forces in the United
States and Their Use in Predicting Soil Loss," U. S. Department of Agri-
culture, Handbook 31*6, Washington, D. C., 1968, 1*2 pp.
9l*. Chepil, W. S., "Soil Conditions that Influence Wind Erosion," U. S.
Department of Agriculture, Technical Bulletin 1185, Washington, D. C.,
1958, 1*0 pp.
95. Woodruff, N. P. and Siddoway, F. H., "A Wind Erosion Equation," Soil
Science Society of America, Proceedings, Vol 29, 1965, pp 602-608.
96. Chepil, W. S. et al., "Mulches for Wind and Water Erosion Control,"
U. S. Department of Agriculture, Report ARS 1*1-81*, Washington, D. C.,
1963, 23 pp.
97. Sultan, H. A., "Soil Erosion and Dust Control on Arizona Highways,
Part I, State-of-the-Art Review," Arizona Department of Transportation,
Report RS-10-ll*l-l, Phoenix, October 197**, 132 pp.
98. Office of Solid Waste Management Programs, "Decision-makers Guide in
Solid Waste Management," 2nd Edition, U. S. Environmental Protection
Agency, Report SW-500, Washington, D. C., 1976.
99. Rowe, P. W., "The Stress - Dilatancy Relation for Static Equilibrium of
an Assembly of Particles in Contact," Proceedings, Royal Society,
London (A269), 1962, pp 500-527.
100. Hough, B. K., Basic Soils Engineering, 2d ed., Ronald Press, 1969, New
York, 63l* pp.
101. Taylor, D. W. , Fundamentals of Soil Mechanics, Wiley, 191*8, TOO pp.
102. U. S. Army Corps of Engineers, "Design and Construction of Levees," En-
gineer Manual 1110-2-1913, Washington, D. C., 1978.
103. Scott, R. F. , Principles of Soil Mechanics, Addison-Wesley, Reading,
Massachusetts, 1963.
IQl*. Forsyth, R. A. and Egan, J. R., Jr., "Use of Waste Materials in Embank-
ment Construction," Transportation Research Record 593, Washington,
D. C., 1976, pp 3-8.
105. U. S. Department of the Army, "Soils Trafficability," Technical Bulletin
ENG 37, Washington, D. C., 1959-
106. Nuttall, C. J., Jr., Wilson, C. W., and Werner, R. A., "One-Pass Perfor-
mance of Vehicles on Fine-Grained Soils," U. S. Array Engineer Waterways
Experiment Station, Contract Report 3-152, Vicksburg, Mississippi, 1966.
21*6
-------
107. Knight, S. J., "Trafficability of Soils; A Summary of Trafficability_
Studies Through 1955," U. S. Army Engineer Waterways Experiment Station,
Technical Memorandum 3-2UO, Supplement lH, Vicksburg, Mississippi, 1956.
108. Meyer, M. P., "Trafficability Classification of Thailand Soils," U. S.
Army Engineer Waterways Experiment Station, Technical Report 3-753,
Vicksburg, Mississippi, 1967
109. U. S. Army Engineer Waterways Experiment Station, "Trafficability of
Soils; Vehicle Classification," Technical Memorandum 3-2UO, Supplement 9,
Vicksburg, Mississippi, 1951.
110. U. S. Department of the Army, "Soils Trafficability," Chapter 9 in Tech-
nical Manual 5-330, (draft in preparation, Mobility and Environmental
Systems Laboratory, USAE Waterways Experiment Station), 1977.
111. Willoughby, W. E., "Assessment of Low Ground-Pressure Equipment for Use
in Containment Area Operation and Maintenance," U. S. Army Engineer
Waterways Experiment Station, Technical Report DS-78-9, Vicksburg,
Mississippi, 1978.
112. Corte, A. E., "Geocryology and Engineering," in Reviews in Engineering
Geology, Vol II, Geological Society of America, 1969, pp 119-185.
113. U. S. Army Corps of Engineers, "Pavement Design for Frost Conditions,"
Engineer Manual 1110-1-306, Washington, D. C., 1962, 33 pp.
lilt. Casagrande, A., "Discussion on Frost Heaving," Highway Research Board,
Proceedings, Vol 11, Part 1, 1932, pp 168-172.
115. Linell, K. A. and Kaplar, C. W., "The Factor of Soil and Material Type
in Frost Action," Highway Research Board, Bulletin 225, 1959, PP 81-126.
116. Lambe, T. W., "Modification of Frost Heave of Soils with Additives,"
Highway Research Board, Bulletin 135, 1956, pp 1-23.
117. Glenn, J. H., "Relationship of Water Quality and Soil Properties to
Seepage Problems," Proceedings of Second Seepage Symposium, U. S. De-
partment of Agriculture, Report ARS Ul-lU7, 1969, pp 1-7.
118. McNay, L. M., "Coal Refuse Fires, an Environmental Hazard," U. S. Bureau
of Mines, Information Circular 8515, Washington, D. C., 1971.
119. Witczak, M. W., "Relationships Between Physiographic Units and Highway
Design Factors," Highway Research Board, National Cooperative Highway
Research Program, Report 132, Washington, D, C., 1972.
120. Holtz, G. W. and Gibbs, H. J., "Engineering Properties of Expansive
Clays," American Society of Civil Engineers. Transactions, Vol 121,
1956, pp 6U1-663.
2U7
-------
121. Sowers, G. P., "Shallow Foundations," in Foundation Engineering, McGraw-
Hill, New York, 1962, pp 525-632.
122. Tolman, A. L. et al, "Guidance Manual for Minimizing Pollution from
Waste Disposal Sites," U. S. Environmental Protection Agency, Contract
Report 68-03-2519, Cincinnati, Ohio (draft in preparation).
123. Molz, F. J. et al, "Transpiration Drying of Sanitary Landfills,"
Groundwater, Vol 12, 197k, PP 39^-398.
12k. Rovers, F. A. and Faquhar, G. J., "Infiltration and Landfill Behavior,"
Journal of the Environmental Engineering Division, American Society of
Civil Engineers, 1973, pp 671-688.
125. American Society of Agricultural Engineers, Evapotranspiration and Its
Role in Water Resource Management, Conference Proceedings, St. Joseph,
Michigan, 1966.
126. Bennett, F. W. and Donahue, R. L., "Methods of Quickly Vegetating Soils
of Low Productivity," U. S. Environmental Protection Agency, Report
EPA-l»UO/9-75-006, Washington, D. C., 1975-
127. Duggan, J. C. and Scanlon, D. H., "Effects of Decomposition Gases on
Landfill Revegetation at TVA's Land Between the Lakes," in Management
of Gas and Leachate in Landfills, U. S. Environmental Protection Agency,
Report EPA-600/9-77-026, Cincinnati, Ohio, 1977.
128. Flower, F. B. et al., "Vegetation Kills in Landfill Environs," U. S.
Environmental Protection Agency, Report EPA-600/9-77-026, Cincinnati,
Ohio, 1977.
129. U. S. Department of Agriculture, "Grass, the Yearbook of Agriculture,"
House Document #1*80, 80th Congress, Washington, D. C., 19^8.
130. Foot, L. E., Kill, D. L., and Bolland, A. H., Erosion Prevention and
Turf Establishment Manual, Minnesota Department of Highways, Minneapolis,
1970.
131. Leiser, A. T. et al., "Revegetation of Disturbed Soils in the Tahoe
Basin," California Department of Transportation, Report CA-DOT-TL-7036-
1-75-2U, Sacramento, June 197k.
132. Becker, B. C. and Mills, T. R., "Guidelines for Erosion and Sediment
Control Planning and Implementation," U. S. Environmental Protection
Agency, Report EPA-R2-72-015, Washington, D. C., 1972.
133. Davidson, G. R. et al., "Bird/Aircraft Hazards," U. S. Environmental
Protection Agency, Report SW-116, Washington, D. C., 1974.
13k. Dawson, J. P., "Control of Damage by Muskrats to Earth Structures,"
University of Saskatchewan, Thesis, 1950.
2U8
-------
135. Creager, W. P., Justin, J. D., and Hinds, J., Engineering for Dams,
Vol III, Wiley, New York, 19^6, pp 619-929.
136. Sherard, J. L. et al., "Failures and Damages," in Earth and Earth-Rock
Dams, Wiley, New York, 1963, PP 113-199.
137. Rao, S. K., Moulton, L. K., and Seals, R. K., "Settlement of Refuse
Landfills," in Geotechnical Practice for Disposal of Solid Waste
Materials. American Society of Civil Engineers, 1977, PP 57^-598.
138. Mabry, R. E., "Building Development on a Municipal Refuse Fill," in
Geotechnical Practice for Disposal of Solid Waste Materials» American
Society of Civil Engineers, 1977, pp 793-809.
139. Sowers, G. F., "Foundation Problems in Sanitary Landfills," Journal of
the Sanitary Engineering Division, American Society of Civil Engineers,
Vol 91*, 1968, pp 103-116.
Lambe, T. W., "Soil Stabilization," in Foundation Engineering. McGraw-
Hill, New York, 1962, pp 351-^37.
2U9
-------
TECHNICAL REPORT DATA
(Please read Inunctions on the reverse before completing)
fU PORT NO.
EPV600/2-79-165
2.
3. RECIPIENT'S ACCESSION NO.
TI "LE AND SUBTITLE
DESIGN AND CONSTRUCTION OF COVERS
SOLID WASTE LANDFILLS
5. REPORT DATE
August 1979 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
A. THOR(S)
R. ). Lutton, G.L. Regan, L.W. Jones
8. PERFORMING ORGANIZATION REPORT NO.
9. P£ ^FORMING ORGANIZATION NAME AND ADDRESS
U.i. Army Engineer
Waterways Experiment Station
P.O. Box 631
Vicksburg, Mississippi 39180
10. PROGRAM ELEMENT NO.
1DC818. SOS 1, Task 23.A
11. CONTRACT/GRANT NO.
EPA-IAG-D7-01097
12 SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research LaboratoryCin, OH
Office of Research and Development
U.!). Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
March 1977-December 1978
14. SPONSORING AGENCY CODE
EPA/600/14
15. S JPPLEMENTARY NOTES
Project Officer: Robert E. Landreth(513) 684-7876
16. ABSTRACT
Selection and design of cover for solid/hazardous waste usually require engineering
planning for efficient accommodation of the volume of incoming waste within certain
moderate to severe constraints. The foremost constraints are usually the amount and
characteristics of cover material available in the immediate vicinity. Local soils
available in adequate amounts seldom have the best characteristics for the several
cover functions, e.g., they are too clayey or sandy. Several steps are recommended
for effective planning of cover. First, identify the primary and secondary functions
to be served by the cover and establish relative importances, e.g., impeding water per-
colation is more important than supporting vegetation, etc. Second, use data on soil
properties in terms of the Unified Soil Classification or the U.S. Department of Agri-
culture systems to rate available soil for effectiveness in the various functions.'
Third, specify certain design procedures in the disposal operation for circumventing
the deficiencies of the selected cover soil. Placement procedures, such as compaction
will improve the soil for certain functions. Elsewhere, the soil properties favorable
for one function are unfavorable for another, e.g., a clayey cover soil impeding water
percolation will prevent leakage of decomposition gases that may also be desired.
Fourth, where a single soil cannot serve contrasting cover functions, the designer may
incorporate features, such as layering, or can resort to the use of special non-soil
materials and additives.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COS AT I Field/Group
Industrial Wastes
Attenuation
Soils
Waste Disposal
Soil Mechanics
Solid Waste Management
Pollutant Migration
Groundwater Pollution
Leachate
Landfills
13B
18. U STRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
274
20. SECURITY CLASS (This page/
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
250
us wwimannmawcofnci «ra -657-060/5399
------- |