Research and Development
sxEPA
Design and
Construction of
Covers for Solid
Waste Landfills

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                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.

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                                             ' 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

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                                 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

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                                  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

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                                  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

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                                  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

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                            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

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                             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

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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

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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

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                              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 USDAHL—lh mainline	   Ill*

  56    Disruption of surface slope by excessive settlement  	   118

  57    Combined buried pipe drain and gravel or sand drain with
          cover	   119

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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

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                              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

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                             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

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                                   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

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                              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

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                     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

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                    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

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 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

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                    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

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                   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

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                    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

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                               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

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                                  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

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 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

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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

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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)

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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)

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                                      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.

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                                                  LEGEND
                                                 yt

                                               •'LOAM\  US DA TYPE
                        PER CENT SAND
Figure k.  USCS soils superimposed on  the USDA textural
           classification chart."  (Correlations are
           only approximate.)

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      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.

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     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«

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                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

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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

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                                  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

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         (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

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 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

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       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

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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

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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

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              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

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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

-------
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UUUUUU'UlJUULlutf J,

                              ASSEMBLY

                                               MOTf FINISHED LENGTH TO PRODUCE A DROP
            © ROD
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^TAPfft j *£R rr






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   (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










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/
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/


» '
/ /
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~/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.

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                                          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.

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            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

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                      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

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 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

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     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

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                    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

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 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

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                                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

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                                           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

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                                   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

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                                            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

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                                          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.
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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.
(








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        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

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                                  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

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           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

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 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

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 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

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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

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 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

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     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

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 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

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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 sizes—clay 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

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                                                                           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

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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

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                                  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*

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         (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

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     (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

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         (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.

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                                      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

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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

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                                      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

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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

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                      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

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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

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 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

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               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:  good—dense vegetal cover of high-
quality grass having extensive root systems, properly managed in grass for
several years; medium—30-80 percent of "good" vegetal quality and density,
well managed in grass for at least 2 years; poor—less than 30 percent of
"good" vegetal density, low-quality grass and poor management.


                                      95

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 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

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                                                                          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

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   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

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                   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

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                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

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                   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

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           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

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                                                         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

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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

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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

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 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

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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

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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.

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     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

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                   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

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  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

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                 MAINLINE
                                               INITIALIZE ACCUMU-
                                               LATIONS FOR ONE
                                               DELTA TIME
                                              CONVERT BREAK-
                                              POINT TIME VALUES
                                              TO ROUTING INTER-
                                              VALS
Figure 55.   Flow chart  of USDAHL—Ik 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

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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

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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

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                                            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

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                  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

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                                  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

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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

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     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

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           -  (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*

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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

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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

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                                 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

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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

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     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

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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

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                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

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                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

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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

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                  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

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                              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

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     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

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                  (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

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                                           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

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1

1

i -»_
i V
PUEBLO
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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
process—wind 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

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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

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                 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

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              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

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     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

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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

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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

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                                 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

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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

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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

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                                 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

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     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

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                  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

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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

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                                                           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*

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                  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

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                                                            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

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      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

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                                  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

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               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

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     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

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 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

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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

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                               •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

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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

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                                 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

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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

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    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

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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

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                                                                                                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."

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         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

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              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

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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.

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              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

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     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

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                                  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

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                                 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

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  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

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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

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           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

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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

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     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

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                                 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

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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

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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

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                                 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

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         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

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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

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                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

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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

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                                 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

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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

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 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

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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.


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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.


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        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.
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                                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.

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                                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.

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     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.

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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


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 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

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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


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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+

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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.
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                                 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

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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.
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                                 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.
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                                 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

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      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.
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     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

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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

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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

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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

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           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

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                                 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

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                   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

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"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

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                                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

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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.

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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.

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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

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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.

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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.,

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  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

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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

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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

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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

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                                  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 Laboratory—Cin, 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

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