PB07-I91G55
Design, Construction, and Maintenance of:
Cover Systems foe Hazardous Wiste
An Engineering Guidance Docur.er.t
(U.Su) Army Engineer Waterways Experiment
Station, Vicksbucg, KS
Prapared for
Environmental Protection Agency, Cincinnati, OH
May 87
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EPA/GCO/2-87/039
May 1987
DESIGN, CONSTRUCTION. AND MAINTENANCE OF COVER SYSTEMS
FOR HAZARDOUS WASTE
AN ENGINEERING GUIDANCE DOCUMENT
by
R. J. Lutton
US Army Engineer Watervays Experiment Station
Vicksburg, Mississippi 39180-0631
Interagency Agreement No. DW21930681-01-1
Project Officer
Robert P. Hartley
Land Pollution Control Division
Hazardous Waste Engineering Research Laboratory
Cincinnati, Ohio 45268-0001
HAZARDOUS WASTE ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
US ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268-0001
REPRODUCED BY
U.S. OEPARTMEMTOF COMMERCE
NATIOMW. TECHNOl
SPRWGf!f.lO.VA?2i61
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TECHNICAL REPORT DATA
(Please rrad tntincnoni on lilt rucrst bt/ort complttinf)
1. REPORT NO.
EPA/600/2-87/Q39
•a. TITLE AND SUBTITLE
DESIGN, CONSTRUCTION, AND MAINTENANCE OF COVER SYSTEMS
FOR HAZARDOUS WASTE: An Engineering Guidance
Document
3. RECIPIENT'S ACCESSION NO.
FB87 191 H58/AS
5. REPORT DATE
Mav 1987
6. fi<\f DOMING ORGANIZATION CODE
Richard J. Lutton
a. PERFORMING ORGANISATION REPORT NC
9. PERFORMING ORGANIZATION NAME AND ADDRESS
U.S. Army Engineering Waterways Experiment
Station
P.O. Box 631
Vicksburg, MS 39180
)O. PROGRAM ELEMENT NO.
II. CONTRACT/CHANT NO.
D',,1 21930681-01-1
U. SPONSORING AGENCY NAME AND ADDRESS
Hazardous Waste Engineering Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COV&REO
l«. SPONSORING AGENCY CODE
EPA/600/12
IS. SUPPLEMENTARY NOTES
o. ABSTRACT
Engineering for cover over solid hazardous waste addresses complex
interactions anong many technical, environmental, and economical factors.
This document emphasizes the special characteristics of solid waste
managenent as they bear on the cover system while at the sane time
stressing the need for engineering experience to integrate the complex
factors into the traditional engineering approach.
Cover systems typically consist of two to four layers of soil and
other materials and resemble a highway pavement system in many respects.
This similarity facilitates the preparation and use of construction and
maintenance specifications, examples of which are provided.
Engineering analyses and design techniques are discussed for
percolation, erosion, stability, flooding, freezing, and settlement.
Finally, guidance is provided on methods of maintanance and repair over
the unusually long design life of a solid waste disposal facility.
17.
J.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIHEHS/O>>EN ENDED TERMS C. COSATl Field/Croup
19 SECURITY CLASS trim]
Unclassified
18. DISTRIBUTION STATEMENT
Release to Public
20. SECURITY CLASS (Tin
Unclassified
31. NO. Of PAOtS
198
:i. PRICE
•;PA Fp"n
(R... 4-77)
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DISCLAIMER
This document has been funded by the United States Environmental Protec-
tion Agency under Interagency Agreement No. DW21930681-01-i with the US Army
Engineer Waterways Experiment Station. The document has been subject to the
Agency's peer and administrative reviews, and it has been approved for publi-
cation as an EPA document. However, mention of trade names, commercial prod-
ucts, and commercial facilities docs not constitute endorsement or
recommendation for use.
ii
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FOREWORD
Today's rapidly developing and changing technologies and industrial prod-
ucts and practices frequently carry with them the increased generation of
solid and hazardous wastes. These materials, if improperly dealt with, can
threaten both public health and the environment. Abandoned waste sites and
accidental releases of toxic and hazardous substances to the environment also
have important environmental and public health implications. The Hazardous
Waste Engineering Research Laboratory assists in providing an authoritative
and defensible engineering basis for assessing and solving these problems.
Its products support the policies, programs and regulations of the Environmen-
tal Protection Agency, the permitting and other responsibilities of the State
and local governments, and the needs of both large and small businesses in
handling their wastes responsibly and economically.
The user 01 this document should carefully read the Introduction to
understand the approach and the strengths and limitations. Simply character-
ized, the guidance is designed primarily to be used in combination with
engineering expertise rather than for stand-alone use by any scientist or
technician. Therefore, the strengths of this document lie in its.marshaling
together appropriate engineering practice, methods, and standards already
familiar to the broadly trained and experienced construction engineer. Soaie-
vhat speculative phenomenology is carefully avoided. Nevertheless, the guid-
ance is recotraended for scientists and for inexperienced engineers provided
their participation in OT influence on actual design, construction, and main-
tenance is not overextended.
In preparation of this document, several experience bases were reviewed
for pertinence to hazardous waste disposal practices. Among these sources of
experience were highway construction, land reclamation, earth work construc-
tion, general geotechnica'. engineering, and low-level radioactive waste dis-
posal. Although radios-.ive waste is regulated by the Nuclear Regulatory
Commission rather than EPA, the somewhat similar potential threats of land-
disposed low-level waste make that experience of more than Incidental techni-
cal interest.
Thomas G. Mauser, Director
Hazardous Waste Engineering Research
Laboratory
iii
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ABSTRACT
Engineering for cover over solid hazardous waste addresses complex inter-
actions among many technical, environmental, and economical factors. However,
che engineering approach developed over t!ia years in general earthwork and in
highway construction provides a fraEework by which the special viewpoint of
solid waste management can be accommodated. Accordingly, this technical
resource document emphasizes the special characteristics of solid waste man-
agement as they bear on thf cover system while at the sa1.*. time stressing the
need for engineering experience to integrate the complex factors into the tra-
ditional engineering approach.
Cover systems typically consist of two to four layers of soil and other
materials and resemble a highway pavernant system in many respects. This simi-
larity facilitates the preparation and use of construction and maintenance
specifications. Example specifications are provided in the appendices.
Criteria *nd methods are available for engineering analyses of percola-
tion, erosion, r.rability, flooding, freezing, and settlement. Techniques are
available for compensation for each of these threats, again using recognized
design and construction methods. Finally, guidance is provided on methods of
maintenance and repair over the unusually long design life of n solid waste
dispose: iA.:llii.y.
iv
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age
CONTENTS
Foreword ill
Abstract iv
Figures ix
Tables xii
Metric Conversion Table xiv
1. Introduction 1
Purpose 1
Regulatory guidance 1
Previous engineering guidance 3
Scope of document 4
Users of document 5
Other applications 6
Legality 6
2. Basis of Technical Design 7
Site characterization 7
Topography 7
Geological media 8
Waste characterization 9
Voids within containers 9
Voids among containers 10
Chemical constitution . . • 13
Design life 13
Operational plan 16
Hydrology 19
3. Design Methods 23
Regulations and standards 23
General design concepts 24
Materials selection 24
Layering 29
Use of tests , 32
Specifications and plans 35
Example desi^.is 38
Engineering analyses 40
Percolation 40
Areal erosion 41
Flooding 4i
Slope stability 43
Freezing 45
Settlement 49
Cost 49
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CONTENTS (continued)
4. Layered Design Elements 50
Hydraulic barrier 50
Soil 50
Membrane 54
Vegetative layer 54
Resistant layer 55
Biobarrier 58
Drainage layer 59
Filter layer 59
Soil 60
Fabric 61
Buffer layer and foundation 62
Monolayer design 62
5. Configurational Design 64
Areal size 64
Slope stability 65
Drainage system 65
Erosion mitigar.ts 68
Settlement contingency 68
Boundaries 72
Special features and structures 76
Nontechnical considerations 79
6. Cover Construction 81
Equipment selection 81
Material preparation 66
Blending 86
Modification 87
Soil placement 88
Soil compaction 89
Test criteria 90
Water content 93
Number of passes •- 94
Lift thickness 97
Special methods * 97
Interface treatment 100
Surcharging 100
Membrane installation 102
Sequence , . 103
Test section 104
Interruptions 107
7. Construction Quality Management 109
Quality control 109
Quality assurance Ill
Acceptance control 113
vi
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CONTENTS (continued)
8. Vegetation Establishment .... 114
Special considerations 114
Manipulating soil factors 115
Grain size 115
pH level 116
Nifogen and organic matter 116
Phosphorus 117
Potassium 118
Other nutrients and toxic materials 118
Choice of vegetation 118
Species selection 118
Time of seeding 119
Seed and surface protection 119
Mulch in general 119
Crop residues 122
Wood residues and paper 123
Bituminous products 12';
Plastic films 124
Other techniques 124
9. Periodic Inspection 126
General 126
Surface inspection 128
Settlement monitoring 130
Aerial inspection 130
Condition mapping 131
Sampling and testing 131
Ground-water monitoring - . . . 132
10. Maintenance and Repair 133
Periodic grooming 133
Maintenance of vegetation 134
Reconditioning of soil 134
Repairs 134
General 135
Problems and solutions 135
Reconstruction 140
Contingency plan 140
References 142
Appendices
A. Specifications for Construction of Cover Systems 147
-Plans and drawings 147
Organization of specifications 147
Specifications for cover design I 148
Specifications for cover design II 164
vii
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CONTENTS (continued)
Specifications for cover design III
Specifications for cover design IV
Specifications for cover design V .
Related Specifications
Mixing soils
Quality control and acceptance . .
Proof rolling
Grass maintenance
viii
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FIGURES
Number
1
2
3
4
5
6
7
8
9
10
li
12
13
14
15
16
17
18
Cohered waste cell at CECOS facility
Burial trenches at Oak Ridge area 6
Nonsysteiratic disposal of waste at Beatty LLRW
Systematic stacking of waste at Richland LLRW facility
Storage facility for radioactive waste at
Hanford reservation
Waste emplaced in single and multiple lifts
Waste emplaced above and below original ground surface
General hydrological system
Hydrological system impacting on cover design
Selective retardation of radionuclides leaked from waste
crib at Hanford
Schematic layered cover systems
Sicilarity between highway embankment and cover system
Example cover designs
Ten-year, 1-hour rainfall in inches
Modified Swedish method of finite slice procedure
with no water forces
Conceptual cross section and symbols for wedge analysis ....
Design freezing inrfex values for the conterminous
United States
Pag
2
3
8
11
12
16
17
18
20
20
21
30
31
39
42
44
45
47
ix
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FIGURES (continued)
Number
19
20
21
22
.73
24
25
26
27
28
29
30
31
32
33
34
31
36
37
38
39
Depth of f?eezing penetration into soils with
bare or covered surfaces
Plasticity criterion for impervious, erosion-resistant
compacted canal linings
Effect of bentonite additions on permeability
of granular soil
Fitted blocks for surface paving or armor
Confining embankment at CECOS facility
Trunk and lateicil channels in surface drainage
Cement-filled mat for erosion protection at
Hamilton landfill
Thickened cover layer for tolerance of settlement dazage ....
Extreme contrasting conditions possible within
cover foundation (waste cells) . . .
Subsidence holes at Sheffield LLRW facility
Clay wall connecting cover into low-permeability stratum ....
Design for overlap of membrane at edge of waste cell
Boundary feature between two cover sections
Filter feature separating riprap from adjacenc material ....
Gas venting trench
French drain for controlling seepage at Oak Ridge
Cutoff wall and dike for excluding ser-page
Construction equipment for waste disposal
Pagi
48
52
53
56
57
60
66
67
69
;o
71
73
73
74
74
75
75
77
78
79
82
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FIGURES (continued)
Number Page
40 Crane operating as a dragline 85
41 Construction of cover in areal increments versus all
at one tJine 89
42 Similarity between compaction in lab and field 91
43 Results of standard compaction tests on sand
and other soils 92
44 Effects of nuiber of passes by sheepsfoot roller 95
45 Effects of number of coverages by tire roller 96
46 Stress concentration in compaction 96
47 Density variation under surface loads such as tire rollers ... 98
48 Compacting constraints on sloping layer 99
49 Boundary strip vulnerable to poor coapaction 100
50 Poor bonding between compacted lifts 101
51 Temporary drainage during disposal operation 103
52 Possible procedures for areal construction 105
53 Possible variation in placement in warm versus
cold weather 106
54 Plan for test section to explore parameters of design ..... 107
55 Contingency placement of frozen soil in noncritical
areas in highway construction 108
56 Example inspection report for Sheffield LLRW facility 127
57 Inspection traverse at covered waste site 129
58 Erosiori gullies on recently completed cover system
at Ft. Drum 137 .
59 Erosion gullies on regular slope on Kin-Buc landfill 138
xi
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TABLES
mber
W^V^^B^*
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
Key Parties; in Contracting for Construction of Cover
Wastes with Potential for Affecting Cover
Design Life for Various Structures and Facilities
Durabilities of Canal Linings
Ground-water Parameters Important at Disposal Facilities ....
Factors in Design of Cover Systems
Technical Requirements from 40 CFR 264
Ranking of USCS Soil Types According to Performance of
Cover Functions
Some Low-cost Substitute Materials for Cover
Laboratory Soil Test Methods for Analysis and Design
Technical Provisions of Contracts Suggested for
Cover Construction
Plans of Contracts Suggested for Cover Construction
Analytical Comparison of Cover Designs Against Percolation . . .
Estimates of Repose and Friction Angles of
Cohesionless Soils
Approximate Average Permeability and Capillary
Head of Soils
Special Features in Cover Designs
Compaction Equipment and Methods for General Earthwork
Construction Test Methods
Page
5
13
14
!5
17
22
23
25
26
29
33
36
37
41
46
51
76
84
90
xii
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TABLES (concluded)
Number ' ' * Page
20 Important Aspects of QC Programs 110
21 Plant Vitality Levels in Terras of Organic Matter
and Major Nutrients in Soils 115
22 Important Characteristics of Grasses and Legumes 120
23 Grasses Commonly Used for Revegetation 121
24 Lcguces Commonly Used for Revegetation 122
25 Possible Future Problems 133
xiii
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METRIC CONVERSION TABLE
Multiply
By
To Obtain
acres
cubic feet per second
degrees (angle)
degrees (Fahrenheit)
feet
gallons (US liquid)
inches
mils
pounds (mass)
pounds (mass) per acre
pounds (mass) per square
pounds (force) per cubic
square feet
tons (short, mass)
tons (mass) per acre
ir.ch
foot
4046.856
0.02831685
0.01745329
5/9*
0.3048
0.003785412
0.0254
.0000254
0.4535924
0.1120851
16.01846
6894.757
0.09290304
907.1847
0.2241702
square meiers
cubic meters per second
radians
degrees Celsius or Kelvins*
meters
cubic meters
meters
meters '
kilograms
grams per square meter
kilograms per cubic meter
pascals
square meters
kilograms
kilograms per square meter
* 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.
xiv
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SECTION 1
INTRODUCTION
This introduction briefly explains the general tone and direction of
this engineering guidance document and its strongest recommendations — away
fron phenomenology and toward strict engineering with accountability in value
and long-term service.
Regulations for the management of hazardous waste disposal facilities
have now been promulgated by the Environmental Protection Agency (EPA) as
directed by Congress in the Solid Waste Disposal Act as amended by the
Resource Conservation and Recovery Act (RCRA). New hazardous waste disposal
facilities must meet the requirements of Title 40, Code of Federal Regula-
tions, Part 264 (40 CFR 264) in order to receive a permit. RCRA also dictates
actions for correcting old sites presenting endangerment. As a part of its
response to SCRA, the EPA has issued technical documents such as this one to
assist in the complex and important task of planning technically adequate dis-
posal facilities.
PURPOSE
This document provides technical guidance o;i design, construction, and
maintenance of cover for hazardous waste facilities (Figure 1) based largely
on waste management practice, concepts in soil construction, and innovations
from research for EPA and others. However, Che technical content is organized
to encourage new designs and practice developed by creative and competent
engineers within the limits of RCRA regulations. Suitable designs arc ulti-
mately translated into construction through plans and specifications, and
therefore sorct of the guidance is formulated directly as specifications.
REGULATORY GUIDANCE
EPA has'Issued basic technical gujdance to assist the permit writers and
others In regulating the disposal of hazardous waste as intended in RCRA. 7The
guidance document for cover was prepared and distributed in draft form (l)~ by
the Office of Solid Waste. In case of any contradiction or conflict in
design, that Office of Solid Waste guidance as well as the underlying statute
and regulations take precedence over the engineering guidance in the present
In the context of 40 CFR 264 this cover guidance is applicable to many
surface Impoundments (Subpart K) as well as all landfills (Subpart«N).
Number in parenthesis stands for citation listed under REFERENCES.
1
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Monitoring System
Undisturbed Soil ?«;'*> ;:;::>:
EXPLANATION
ii11111 n
Containers o( Waste
Hlgh-den»lty
Polyethylene Membrane
Soil Fill
Compacted Clay
Figure 1. Covered waste cell at CECOS facility.
i /.
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docuaent. A minimal cover system for new facilities satisfying these govern-
ing RCRA sources is illustrated in Figure 2. It should be expected that
thicker and more complex cover systems will often be required.
PREVIOUS ENGINEERING GUIDANCE
Engineering guidance offered in the past on solid waste management has
sometimes presented a mixture of descriptive phenomenology or research conclu-
sions in place of straightforward engineering practices, and, some past cover
design has been accomplished by other than experienced engineers. Descrip-
tions of processes or results of specific tests are often helpful conceptually
but seldom substitute for quantitative solutions and the systematic approach
of engineers. Disposal engineering has occasionally been made additionally
confusing by the failure to use engineering terminology and other language
recognizable as authoritative and workable to those expected to construct the
facilities. Solid waste disposal is not a simple technical task, and a versa-
tile, experienced engineering staff is one of the most important ingredients
in construction, operation, and closure.
FILTER OR FILTER SOIL LAYER
rv7"X"Xiv.* •i^^OL,*v^s~£orvv^bOkiji^b>^Lri'\*
30-cm DRAINAGE LAYER (k §10 3cm/sec)
20-mfl SYNTHETIC MEMBRANE
-I-I-I- (with soil bedding above and below)
-I-I-SO-cm LOW-PERMEABILITY LAYER (k S 10"7cm/sec)
Sx&X*: BACKFILL '•&#£•#&'#&#&$•&&•&
Figure 2. Minimal cover components as described
in RCRA guidance.
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A previous technical resource document and its backup report by Lucton
and others (2,3) attempted to discourage shallow conceptual "engineering" by
discussing the many interrelated factors impacting on performance of cover
systems. It was emphasized that the uniqueness of each site often dictates a
unique design. It was also emphasized that an engineer's creative interest is
a resource that should be used to the fullest. These criteria continue to be
applicable to design, construction, and maintenance of cover systems.
SCOPE OF DOCUMENT
With tht advance of research ar.d development, changes in regulatory
requirements, and growing experience gained in the operation of previous dis-
posal works, guidance has advanced to a more definitive form from the earlier
emphasis on general physical principles and possible mechanisms impacting
cover design. Therefore, the present document should be regarded as supersed-
ing the two previous documents (2,3) wherever there is an apparent conflict or
contradiction. Portions of those previous docutcents of a qualitative nature
and more descriptive of possible processes remain valid in that context, and
accordingly those documents are still useful for supplementary guidance.
A primary function of cover at moat hazardous waste facilities is to
exclude from the waste cells most water percolating downward from the ground
surface. Although this function is not alweys the main concern, e.g. in arid
regions, it always ranks high and clearly deserves concentrated attention in
the design stage. Analysis of cover designs for impedance of percolation is
explained herein and emphasized as a necessary step with possible quantitative
feedback in design nodificaticns.
This document also places high priority on realizing long design life for
the cover. Natural, near-surface processes will begin to attack the cover
Immediately after construction since the cover is more or less out of equilib-
rium with the natural environment. Guidance is provided on designs to mini-
mize erosion and on maintenance practices for what may prove tc be the
inevitable. Comparable deterioration localized in the subsurface must also be
given sufficient forethought and taken care of in the design to avoid a moi's
subtle, but persistent, damaging process.
After a discussion of useful preliminaries in Section 2, the main sub-
jects are covered in three broad parts of the document: design, construction,
and maintenance. Sections 3-5 together address design concepts in sufficient
detail to encourage the creative engineer to review workable options and inte-
grate them into a suitable design. Section 3 presents design methods; Sec-
tion 4 addresses cover stratification (in the vertical dimension); and
Section 5 presents design factors that must be considered along the horizontal
dimensions of the facility.
Cover construction is detailed in Sections 6-8. Section 6 reviews the
concepts 'and methods of soil construction as well as those for membrane and
filter fabric installation. Section 7 addresses quality control, quality
assurance, and acceptance testing. Section 8 review's general vegetation prac-
tices by drawing heavily from a previous report for details.
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Post-construction monitoring and inspection a/e included in Section 9 and
maintenance and repair in Section 10.
Specifications including*several for vertical cover designs recognized as-
effective are presented ir. Appendices A and B.
USERS OF DOCUMENT
This document is intended to be useful to all technical and nontechnical
persons concerned with the construction, operation, and closure of hazardous
waste disposal facilities. Users may be allied with the federal or state gov-
ernment, the facility owner, the facility operator, or an independent contrac-
tor. The specific viewpoint may be that of a design engineer, the applicant
for a pernit, a permit reviewer, a construction engineer, or the site manager
as well as others with related interests in hazardous waste management. Con-
struction and monitoring inspectors should be among the leading beneficiaries
since they can find in the document summaries of good practice in construction
and monitoring using the latest concepts and techniques set in the context of
the overall operation from planning to post-closure care. Despite the diver-
sity of viewpoint and allegiance, the main parties are linked frequently
through a formal contract (Table 1), and their interrelationships one to
another deserve clear definition.
TABLE 1. KEY PARTIES IN CONTRACTING FOR CONSTRUCTION OF COVER
Owner
Contractor
Engineer
Regulator
For whom the work is performed; prepares or authorizes
plans and specifications and pays for the work.
Agrees to perform the work according to plans and speci-
fications at established price or price forcula
Owner's representative formally identified in the
contract
Outside party exerting influence through regulations and
in a review capacity
Notes: The terms Owner, Contractor, and Engineer are frequently capitalized
in contracts, emphasizing their specificity and importance.
Ths Engineer is frequently, but not necessarily, within the Owner's
organization. .
The user should find the sample specifications and the other guidance
presented in the language of construction contracts to be helpful in making
quantitative evaluations of existing documents or in preparing new documents.
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Wich maturation of the hazardous waste management industry, the convenience of
descriptions and specifications in qualitative or semiquantitative terms has
disappeared. Although performance standards are advantageous at higher lev-
els, there is a point in the chain of responsibility for well-engineered con-
struction where prescriptive specifications are essential. This need may
arise in regard to portions of the facility, e.g. in directions to a contrac-
tor responsible only for satisfactory placement of the cover.
OTHER APPLICATIONS
The guidance is also applicable to other than covering new hazardous
waste facilities as follows:
a. Design and construction of cover systems suitable for r.o~h2zardous
waste, e.g. municipal waste.
b. Design, construction, and maintenance of cover systems for remediat-
ing uncontrolled waste sites as under RCRA or under the Comprehensive
Environmental Response, Compensation and Liability Act (CERCLA).
c. General conceptual guidance for expanding or tightening specifica-
tions for hazardous waste disposal facility features other than
cover, particularly specifications for liner systems, impoundment
dikes, and drainage arid for waste emplacement.
Expanding on b above, it should be pointed out that a separate report on cov-
ering uncontrolled sites has been prepared recently (4). However, it should
also be emphasized in engineering for cover systems, that the distinctions
between new facilities and uncontrolled old sites are minor ac most. Engi-
neering objectives and methods are essentially the same.
LEGALITY
This document in itself does not constitute forr.al EPA regulatory policy
and in no way relieves owners and other parties of their respective responsi-
bilities in construction and in hazardous waste management. The user should
be aware that the use of guidance from this document in permits, specifica-
tions, and other binding legal documents is not tantamount to approval by any
other than the signatories of the legal documents.
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SECTION 2
BASIS OF TECHNICAL DESIGN
This section summarizes Che considerations that must be carefully
reviewed before beginning to design the cover. The factors discussed below
will affect the composition, dimensions, and interrelationships of components
in the cover system. The first step in the design process, therefore, is to
assemble appropriate documentation or prepare a synopsis of each factor and
its impact.
SITE CHARACTERIZATION
The physical characteristics of the site and the configuration of its
surface are among the most important factors upon which cover design is based.
Sometimes the influence of site characteristics on cover design follows a more
direct influence on design of the entire disposal unit or the assemblage of
disposal units.
Topography
The importance of topography can be brought out by considering two dif-
ferent but typical cases: one site located on flat terrain and another on
hilly terrain with an average slope of 5 to 10 percent. It will almost cer-
tainly be necessary to Unit the size of disposal units or waste cells in the
hilly terrain, and their orientation and arrangement may also be restricted by
operational considerations. Broad flat sites present fewer restrictions on
size, orientation, and arrangement of the disposal units, one to another.
Siting in a canyon or at the head of a hollow Is one option favored in
some hilly terrains. An engineered embankment acror.s the canyon encloses the
lined fill area on the downstream side. Drainage of surface water may con-
verge on a central ditch superimposed on the waste cells generally abov-j the
original stream bed. This system contrasts with the usual arrangement of
drainage ditches carrying runoff outward to the nearest edge of the fill area.
i
The constraining influence of topography is illustrated in the extreme at
Oak Ridge National Laboratory (Figure 3). Unlined disposal trenches for low-
level radioactive waste (LLRW) are arranged to take advantage of relatively
flat topography on ridge tops and spurs. The orientations of trenches show a
relationship to topography, partly for ease of operations. Even the small
size of the trenches has been determined to some extent by topography; trench
length was reduced during the evolution of burial pract4-ce -to reduce seepage
fron the lower ends of trenches flooded by so-called bathtubblr.g. Although
short, narrow trenches are seldom If ever used in commercial RCRA facilities
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.• •
\ I
•
— • ' .--_....•-
Figure 3. Burial trenches at Oak Ridge area 6.
and the bathtubbing phenomenon is similarly precluded by liners and leachate
collectors, a systematic consideration of such factors should suggest useful
redundancies in design.
The geomorphological consequences of topography must be considered. Can-
yon fills may be expected to experience erosion and related effects increased
in proportion to the area of the upstream watershed. On mounded landfills
that area is less than the fill area itself. Finally, the questions of flood-
ing and floodplaina deserve attention. RCRA regulations are briefly explicit
in regard to disposal and disposal practices there (40 CFR 264.18). Normal
flow and storage must remain unobstructed and there must be no erosion of the
landfill.
Geological Media
Geologic media have rather subordinate status in disposal of hazardous
waste according to 40 CFR 264 because of the usual requirement of a liner
below and around the waste. However, media of low hydraulic conductivity can
provide capacity for retarding migration of some pollutants in ground water,
and thus an extra measure of protection In case of unexpected leakage or
8
-------
malfunction. Disposal sites are often selected at least partly on this basis.
Obviously, the best sites are those capable of transmitting ground water only
slowly if at all. A rate cf 1 ft/year has been suggested as a sufficiently
conservative upper limit. In contrast, any waste disposal unit situated in a
pervious setting, such as a gravel pit, over an unconfined aquifer would ordi-
narily deserve very conservative cover and liner designs with redundancies and
other special features for an extra factor of safety.
Geological media may also have importance to the extent that on-slte
soils are used to construct the cover and its supporting backfill or temporary
cover. Presumably some sites will be chosen partly on the basis of the avail-
ability of Bufficient soil for backfilling and cover construction. Once this
strategy is adopted, the physical characteristics and quantities of the soils
available at the site may serve to constrain the cover design to some extent.
In-place density and condition of soil as well as its availability can be
important in satisfying soil volume requirements. Experienced engineers (5)
have suggested that most soils have natural densities short by 10 to 30 per-
cent of the soil's naximum density by standard compaction tests (See Test
Criteria, SECTION 6). Since that maximum density is the target of good con-
struction compaction, It may frequently be that required volusfis will have to
be adjusted upward to compensate for the shortfall resulting from compaction.
It should be mentioned, however, that experience (2) also suggests that some
overconsolidated geological strata exhibit the opposite behavior, i.e., a
swelling upon excavation and compaction in a cover system.
WASTE CHARACTERIZATION
The character of the waste can have long-term impacts on the cover and
its performance in regard to problems of subsidence, differential offset, and
soil particle migration. It is even helpful conceptually to regard the dis-
posal unit as the lower component or foundation of the cover uith a transition
to the backfill soil within the waste cells. Influences follow either froE
the voids and other physical condition of the waste at the time of burial or
from chemical-related changes that take place over a long period. It is
Important to characterize the waste to focus attention on unfavorable eventu-
alities that In some cases may actually be avoidable. It would be advanta-
geous to evaluate the character of the waste before the waste is emplaced.
Certain worthwhile limitations on waste character and form as well' as place-
ment procedures may be suggested and then incorporated In the plan of
operations.
Voids Within Containers
The approximate void space within disposal packages or containers should
be estimated carefully for various categories of waste anticipated. It will
also be possible to make at least a rough estimate of the participation of
these void spaces in long-term general settlement. Void space left at the top .
of a sealed steel drum will presumably remain inaccessible to processes of
deterioration until the steel drum has begun to break down through corrosion.
Similarly, It can be expected that the small voids dispersed through compacted
-------
baled waste will remain inactive and largely inaccessible to processes of
deterioration for many years. Small evenly dispersed voids in absorptive
waste may serve to draw in and retain moisture over a long period and undergo
very little other physical change. Prediction of subtle changes that may be
taking place 50 or more years in the future will be accompanied by consider-
able uncertainty but nevertheless ueserves serious consideration and probably
will be useful.
Voids Among C
In comparison to void space within containers, the void space between or
among containers in the disposal unit is easier to describe and mo^e directly
relatable to cover deterioration. Four aspects of space among containers are
clearly important and need description: total volume, approximate continuity,
portion occupied by backfill soil, and distribution of backfill soil.
The importance of totn! space among containers can be brought into focus
by considering first the contrast in volume between extreme categories such as
barrels disposed randomly and boxes or bales stacked in closely packed,
orderly array (Figures 4 and 5). The comparison is pertinent to the extent
that cylindrical barrels and rectangular packages are common container forms.
However, it should be emphasized that space-wasteful random disposal is usu-
ally avoided at coat-conscious commercial disposal facilities. Space among
barrels dumped more or less randomly would approach 40 percent of total volume
in the disposal unit. Space among uniform boxes carefully stacked in a rec-
tangular pattern ordinarily constitutes less than 5 percent of total volume.
However, even here a few percent of such space, when concentrated in its dis-
tribution, may eventually affect the cover integrity.
The distribution and linkage of space among containers becomes important
in the arrangements with the least volume between containers, e.g. the stacked
box array. Chains of voids between boxes may project downward from the cover
through two or more layers of boxes and may present a serious threat of cover
disruption, primarily because they can be overlooked until the damage is
uiijerway. Piping (migration) of backfill soil originally occupying these
voids eventually undermines the cover and can cause disruption.
Where open space is relatively high, e.g. among disorderly arranged bar-
rels, long pathways for piping are numerous, and the potential for cover dete-
rioration should be obvious. Clearly, a disordered array of barrels may
persist as a threat of cover deterioration for many years. Figure 4 shows a
nonsystematic accumulation of barrels at one old LLRW facility. The long-term
threat of settlement t9" 'e&rewffiJgSB&ed h$r juse -of dry sand backfill which fills
voids better at the start.
Obviously one way of reducing the long-term threat to cover by piping
along voids in the waste is by the careful backfilling of the voids with soil.
In characterizing the waste, it is necessary to estimate the percentage of
space actually filled with backfill soil. Where the percentage is
Baled waste nay be considered as contained by the bale straps.
10
-------
'....''...••i''L.'f' • "'
Figure 4. Nonsystematlc disposal of waste at Beatty LLRW
facility (atypical practice).
-------
Figure 5. Systematic stacking of waste at Richland LLRW facility.
12
-------
substantially less than 100 percent, it is also helpful to describe the dis-
tribution, of the backfill. Such a description or characterization should be
useful ir. specification of the backfilling procedure or the result to be
obtained, i.e., by prescriptive or performance specification, respectively.
Chemical Constitution
The chemical constitution and the reactivity of bulk and containerized
waste always deserve careful consideration. A listing of wastes to go into
each cell is already required in Subpart B, 40 CFR 270. In large disposal
facilities, this undertaking may be complicated or simplified by any opera-
tional plan to segregate wastes into subcells according to waste type. The
eventual deterioration and breakdown of initially rigid elemerfts such as steel
barrels, bale straps, and boxes will have to be evaluated as to their expected
histories and the ultimate effects. Although it is frequently found that met-
als and sometimes even paper are little affected by burial in the short tern
(e.g. at the Savannah River Plant), the long-term effects over tens of years
and to the design life of the facility must be addressed to the highest degree
available with state-of-the-art knowledge and practice.
The potential for generation of gases or liberation of volatiles should
also be considered. It may be necessary to provide diversions and vents for
gases blocked from their upward pathways by the cover. Vents to the atmo-
sphere nay be adequate for toxic components of low concentration that wtll be
quickly dispersed in the air to acceptable levels. In extreme cases where the
gas or volatile component may reach a harmful concentration, it may be neces-
sary to provide on line or contingency features for absorption filters or
other n-.eacs of reducing concentration of toxic components. General categories
of reactive wastes that can conceivably affect the performance of cover are
provided in Table 2.
TABLE 2. WASTES WITH POTENTIAL FOR AFFECTING COVER
Volatile organic chemicals
Inorganic acids
Materials capable of reacting with others in the waste cell*
Materials capable of undergoing volume change
Saturated materials
*See lists of potentially reactive wastes in Appendix V of
40 CFR 264.
DESIGN LITE
Certainly one of the most important considerations impacting on cover
design and construction is the design life or service life of the facility.
13
-------
By this we mean how long the waste is expected to remain secure—not the
shorter period of active operation. The cover situated at the ground surface
Is exposed and subjected to complex near-surface conditions and processes.
Where the effectiveness of the cover system is required over hundreds of years
by a long design life for the facility, the system is subjected to an unusual
demand not found in most other types of construction. Table 3 contrasts the
design life for several waste facilities with shorter design lives in the more
usual types of construction such as for highways and dams. Such a design life
has not been defined for RCRA facilities. Without sufficient care In estima-
tion, the ultimate cost of a facility may greatly exceed estimates at the time
of construction as maintenance and repair costs accumulate.
TABLE 3. DESIGN LIFE FOR VARIOUS STRUCTURES AND FACILITIES
Facility or Feature
Expected
Service Life
(yrs)
Specifics and Remarks
Railroad subgrade CO
(repairs)
Soil retaining structure 50
(with fabric)
Roads 20
English Channel tunnel >120
(future)
Intermediate-level radio- 20
active waste storage
Uranium mill tailings 1,000
control
High-level radioactive 10,000
waste disposal
Low-level radioactive. 500
.'aste burial facility
Fly ash disposal area 1000
Repairs against pumping of soil (6)
Reference 7
Reference 8
Suggestion o* Anglo-French Working
Group
Temporary
40 CFTl 192
EPA standard of 1985
Scientific scenario (9) rather than
conservative engineering analysis
The dramatic impact of long design life can be brought into sharper focus
by considering previous experience with the expectable life for similar
-------
engineered features. Table 4 summarizes experience with various types of lin-
ing for irrigation canals, an engineered feature having requirements of low
permeability and erosion resistance similar to those of cover systems. Even
with these relatively short service lives frequent maintenance is required.
TABLE 4. DURABILITY OF CANAL LININGS*
Lining Type
Service.Life
(yrs)
Remarks
Cement concrete 50
Cer.ent-brick 20
Buried concrete pipe 50
Soil-cement
Asphalt-clay plaster 5
Mud plaster 2
Exposed membrane (thin)
Compacted soil (in situ)
Asphaltic concrete 20
Compacted earth 20
?**
Some to 60 year.'
Annual maintenance
Low maintenance
Some to 23 years
10 percent/ann. maintenance
25 percent/ann. maintenance
Temporary
Repeat compaction annually
Susceptible to weather effects
*Data iron Reference 10.
**Recent experience indicates that life of exposed resistant membrane
material can exceed 25 vears.
Certain strategies nay be adopted to reduce the long-term cost and neces-
sity for continuing maintenance. Where pertinent factors are carefully summa-
rized and evaluated as a preliainary to design of cover, this analysis cay
lead to modifications of design at the planning stage that can be incorporated
into specifications not only for the cover but also for other parts of the
disposal facility as well. An exaaple of one strategy is to target vegetation
plans on native species of grass that will be most hardy in the environment
and conditions characteristic of the site. This strategy is based on the
assumption that hardy, native species will be more likely to succeed and per-
sist v.'irh minimum care and maintenance.
Consideration of design life logically leads to consideration of storing
hazardous .waste. RCRA regulations are already in place as Subparts K and L of
40 CFR 264 to address impoundments and waste piles as approved methods of
storage. Neither type of storage area requires a cover except as might be
needed to prevent wind dispersal, and accumulation of wcstf usually continues.
15
-------
. V/' fJLYWOOO
V." PLYWOOD
2"PVC PIPE
55 G*L. DRUMS
BACK-FILL
Figure 6. Storage facility for radioactive waste at
Hanford reservation (11).
An acceptable impoundment may be converted from storage to permanent landfill
by appropriate stabilization and solidification of the waste and installation
of fin.al cover. A waste pile can be closed ac a permanent landfill only pro-
vided that it meets all requirements of Subpart N for landfills.
Outside of RCRA, the experience with engineered storage facilities has
been confined largely to radioactive waste. Figure 6 illustrates one :juch
storage unit. The waste is stacked on an asphalt pad, then covered with a
synthetic membrane and buried with a thick soil cover. A minimum of 20 years
is specified in which the waste packages can be retrieved for permanent dis-
posal elsewhere. Of some, though not overwhelming, imoortance is the fact
that part of the most threatening radioactivity of short-lived isotopes will
have decayed during this storage period.
OPERATIONAL PLAN
The operational plan for a disposal facility can be expected to affect
cover construction and even cover design to some extent. Procedures will have
been established on the basis of previous experience or in accordance with
regulations and local requirements. For example, it may have been previously
established that the facility will consist of trenches of given depth
(Table 5). Certain combinations of equipment may be favored by a contractor
so that the disposal operation is heavily influenced in turn. The anticipated
volume of waste and the anticipated rate at which that wasto reaches the site
will certainly have major impacts on operational plans. It is sometimes
advantageous to fill disposal units on a yearly basis so that the best season
of the year can be used for closing and covering the disposal unit and estab-
lishing a vergetated cover. Ongoing operations will determine to somn extent
the placement of cover in increments or at one time.
16
-------
TABLE 5. SOME TYPES OF DISPOSAL OPERATIONS
Method
Narrow trench
Wide trench
Mound
Simple area! fill
Layered areal fill
Composite*
Typical
Dinensions (n) Remarks
3 x 3 x dO Seldom
7 x 30 x 150 Common
3 x 30 x 150 Seldom
7 x 150 x 150 Conaron
20 x 150 x 150 Common
— Common
used
used
*rtethods ate commonly combined where site topography
-------
OVER SYSTEM
GROUND SURFACE
CONFINED UNIT
(ALSO SEE FIGURE 1)
LINER SYSTEM
COVER
SYSTEM
ORIGINAL i
*\ GROUND SURFACEt
TRENCH CELL
-LINER
SYS'
-------
Many commercial RCRA facilities fill in lifts across large areas and rise
lift by lift from a base below original ground to a final level well above
original ground. This popular plan has evolved as the most cost effective and
is used even in canydn-fill and head-of-hoilow operations. Intermediate cover
(Figure 7) sometimes includes bulk waste compacted like or with soil.
HYDROLOGY
The hydrologlcal system constitutes the most influential combination of
related external factors in cover design and maintenance. Figure 9 shows the
hydrologlcal system In Its broadest sense and Figure 10 In the more restricted
sense where attention is concentrated on cover performance. The several
aspects of climate, particularly the precipitation regime, have direct impacts
on the perfon-ance of the cover in blocking percolation into the waste cell.
Besides being foremost among general constraints to cover design, the climate
enters into detailed analysis and evaluation of proposed cover designs as
explained in Section 3. The importance of the hydrologlcal system can be
illustrated by considering two cxtrece cases.
It is believed that most of the low rainfall of a typical year at the
arid Hanford and Richland, Washington LLRW disposal facilities penetrates no
more than a fev meters of depth. Since the ground water is at much greater
depth, most radionuclides carried downward by percolating water stop well
above the water table (Figure 11). Thus, these facilities and another hazard-
ous waste facility to the south near Arlington, Oregon benefit directly froa
the dry regime. On the other hand, uncontrolled waste sites in the relatively
damp midwestern and eastern United States frequently exhibit ground-water con-
tamination- plumes of serious dimensions and concentrations despite the pres-
ence of cover over the waste in some cases. Major storm events must also be
considered since even an arid region can be subjected to infrequent but major
storms that cause anomalous ground saturation and percolation to depths ordi-
narily not reached. According/./, a rather complete review of expectable storm
events and their frequencies should be required in preparing the background on
the hydrological system.
Other aspects of the hydrologlcal system that need to be reviewed are the
evapotranspiration history, the water-retention characteristics of the near-
surface soil, and surface runoff parameters as well as available measurements
at gaging stations. In the broader sense of hydrology (Figure 9) the ground-
water system constitutes an important part. Characteristics of the ground-
water system are summarized In Table 6. Familiarization with ground-water
configuration, flow directions, and velocities Is essential, if for no other
reason than for background to planning and contingencies for unexpected per-
formance or even failure of the containment system.
19
-------
PRECIPITATION
DISCHARGE
AREA
LIMESTONE SOLUTION WIDEfED JOINTS
ii/Vi PERMEABLE SANDSTONE
S^-TZ-^ IMPERMEABLE SHALE
GRAVEL ACUIFES
AQUICLUCE
Figure 9. General hydrological system.
PRECIPITATION EVAPOTRANSPlRATION
r- VEGETATION j RUNOFF
{INFILTRATION
(D VEGETATIVE LAYER
DRAINAGE LAYER
BARRIER LAYER
LATERAL DRAINAGE
(FROM COVER)
L- SLOPE
PERCOLATION
(FROM BASE OF COVER)
O
O
Figure 10. Hydrological system impacting on cover design.
20
-------
•1C"4 .Cl/,
m
f
a*.
%
\
t
\
""•
*
1
\ i
i i
t
i
1
""
i
i — '
j I
3 1
» *
i
I
i 1
3
".I^'-r- :"•••*
~-~^-:
*
^^^ * — ^ _• u
,-r««
i
1
i
I
i f
'TmaffBrn"
t-*
•»:", *v-*
1
i i
i
l-y'
r ,-''
, ,
•«:* '
1 '
V-
il >
U
1
!
! ,Jn(J Jnd tr - „
'•'"•'" •>••><. .1 in Sill _= *
i ° •"
1 ~ «
1 tm
1 3
^~V I "»• <
t.- . tna Silt ^
Sine 4x4 Gr. Z
Witrr Ttble 12C6 '
j Wtter Ttc>l( li&t ^
[JSCt!
KetL-r
— f'
- i:
— Ic,
*•
- 30
- 36
12
/! S
— C *
- 60
1956 Field C»«lu4t1an
'\
u
10
18
-^&-H3-(--
ll
t-n»
reltn
0 10 ZO
1 1 I
Plint of Section
IS
Sand «nd Stlt — «.
!" I II!
,. . rr-r-'Jt-r^
*^ — — -*—'—— — — I* • *r~:~~ji-r,-
"il ul lifVlil"
r . «nd !. i 1 t
-------
TABLE 6. GROUND-WATER PARAMETERS IMPORTANT
AT DISPOSAL FACILITIES (12)
i • •
General ground-water system and boundaries
Recharge and discharge areas
Water zone boundaries
Hydraulic conductivities
Heads, potentials, or pressures
Seepage velocity or apparent velocity
Flow direction
Water-holding parameters
Ground-water chemistry
22
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SECTION 3
DESIGN METHODS
This section is purposely restrained in its discussion of rigorous design
methods since guidance on design of cover should be left sufficiently open to
benefit from the skill of the design engineer. Certain aspects of design are
emphasized however as usually necessary in the formulation of suitable plans
and specifications. Table 7 presents some of the factors influencing broad
design concepts and practice, of adequate thickness and effective layering.
TABLE 7. FACTORS IN DESIGN OF COVER SYSTEMS (11)
General site characteristics Daily evapotranspiration
General waste characteristics Thickness of waste
Operational plan Cell size
General geological setting Rate of disposal
Design life Intermediate cover distribution
General hydrology and meteorology Anticipated settlement
Regulations Anticipated erosion
Availability of cover materials Anticipated soil change (weathering)
Population distribution Bottom liner system
Water supply Leachate collection features
Daily precipitation Absorptive capacity of formations
REGULATIONS AND STANDARDS
Designing a cover for hazardous waste logically starts with the applica-
ble regulations or standards and regulatory guidance (1). These requirements
not only indicate much about the expected performance but also sometimes pre-
scribe specific technicalities that are regarded through experience as being
appropriate (Figure 2). Thus, a soil component of the barrier element of the
cover may be required to have a coefficient of permeability k = 10 centime-
ters/second or Itss as measured in the laboratory. A technical challenge
23
-------
comes in both design and construction to ensure that this requirement is net
and maintained, especially in view of rlie common disparity between permeabili-
ties at laboratory versus field scales. Summaries fr^ra 40 CFR 264 are given
in Table 8 for technical standards and requirements in- covers at new RCRA
facilities. Regulations are .also available for covering existing facilities
and uncontrolled sites.
GENERAL DESIGN CONCEPTS
Once the functions of the rover have been established or constrained by
regulation or standard or by clearcut technical objectives such as reduction
of percolation to insignificant levels, the various aspects and elements of
the design are defined and integrated using conventional design methods.
Materials Selection
A key task of cover design is the selection of suitable materials. The
cover usually will include a synthetic membrane and large volume of soil or
soil-like material, but other materials are sometimes included also: Portland
cecent concrete, bituminous concrete, seal coats, and geotextiles. Consider-
able flexibility is available in choice of materials beyond the requirements
spelled out in regulations and standards. Guidance on suitability of various
types of soil for performing cover functions and for general long-term service
has been reviewed elsewhere and is summarized in Table 9. The ranking of
soils for various engineering functions is a technique that has also been
developed on the basis of considerable experience in the Bureau of Reclama-
tion, Corps of Engineers, and other construction and engineering organiza-
tions. Classification is according to the Unified Soil Class.tfication
System (USCS).
Emphasis on the best soil for the cover will occasionally be unfeasible
since the soils available at or near the site will be the chosen material for
reasons of economy. The strategy of cover design then targets on the most
effective use of those available materials, usually in a layered construction.
The availability of material may extend off-site, sometimes including sources
of surplus material otherwise classified as waste. Fly ash available in the
near vicinity continues to be an attractive possibility for use. Fly ash has
a relatively fine grain size and, by careful compaction or addition of reac-
tive chemicals, can be brought to a strength and permeability that may be
suitable for fulfilling cover functions. Other substitutes for native soil
are discussed elsewhere (2).
Selection of soil and soil-like materials is based partly on the content
of various grain-size components. In designing and in procurement for con-
struction, particular attention is needed to define the grain-size classes
unequivocally and avoid misunderstanding and difficulties in obtaining desired
results. The grain-size classes can be defined quantitatively by reference to
standards such as the American Association of State Highway and Transportation
Officials (AASIiTO) designations for grout sand and cement sand (13). Grain
size can be defined more loosely using terms such as "sand," "granular," and
"clayey," but such generalizations are prefp-.-ably avoided. The sample speci-
fication for topsoil in Appendix A gives the size ranges and weight
-------
TABLE 8. TECHNICAL REQUIREMENTS FROM 40 CFR 264*
Paragraph Requirements
264.15 Follow a written schedule of Inspection for problems during dis-
posal operations and maintain a written record (this requirement
overlaps timewise on some aspects of closure cover emplacement
and should be applied to the extent that it does). Problems co
be remedied expeditiously.
264.111 Cover so as to minimize need for further maintenance and to con-
trol, minimize, or eliminate escape of hazardous constituent,
leachate, etc.
264.112 Written closure plan to be submitted with application for pernit.
264.113 Close within 90 or 180 days after receiving final waste volume.
264.115 Independent certificacion of closure in accordance with
specifications.
264.118 Written plan of post-closure care, normally for 30 years, to
Include monitoring, reporting, and maintenance.
264.142 Up-to-date written estimate of cost of closure.
264. 144 Up-to-date written estimate of cost of post-closure monitoring
and caintenance.
264.301 Systems for controlling run-on and run-off equivalent to 1-day,
25-year storm.
264.303 Inspection during and after construction of synthetic- or soil-
based cover for uniformity, cacage, and imperfections (e.g.,
holes, cracks, thin spots, or foreign matter). Inspection of
surface drainage system.
264.310 Cover finally to minimize migration of liquids, to function with
min.tsnum maintenance, to promote drainage and minimize erosion and
abrasion, to accommodate settling and subsidence without losing
integrity, and to have permeability no greater than the bottOE
liner or natural subsoils. Maintain the integrity and effective-
ness of the final cover, including the making of repairs.
*Similar technical requirements can be listed fron CERCLA regulations.
25
-------
TABLE 9. RANKING OF USCS TYPES ACCORDING TO PERFORMANCE OF COVER FUNCTIONS
UCCa
Jlyr.lol 7/picnl Sollo
*V*i We 11 -gra.lr J pmvels, gravsl-sand
fixtures, little or no fines
GP Poorly ^raJej grnvcls, gravel-
sar.d r.lxtarcs, llrtle or no
flues
CM Silty gravels, gravel-GfViJ-ollt.
slxtures
CC Clayey grovels, gravel -oand-c lay
S'J Well-graced sands, gravelly
oanSu, little or no flnrn
C? Poorly graded sands, gravelly
sanls, little or no fines
TM Hllty sar.dB, cajid-ain. (Matures
CC Clu/'.-y sar.ilfl, ft'ifnt-clay cUtures
ML Tnorginic ollts and very fine
snn-ln, ,-OCA flour, silty or
cliy*y fin'? siflH, or cliyy
ell tii vltli tllght pla>tli:li.y
Ci Ir.'-.rgiuili: clays of low to r.edlun
p'.ar.tl'.'lty, gravelly c.'nys,
iiiiivjy cliys, silty cluyc, lean
.cluyr.
Oi. Orginlc r.llts and organic allty
cloys of lou plasticity
.'•'H Inorganic silts, nicaceous or
dla'.osac-cous fine sanily or silty
stlls, elastic silts
CH Inorganic clays of high
plasticity, fn*. clays
CM Cr/a/llc rlayo of r.»i1i'in to high
plasticity. oixo/.iT silts
Co-llo Co
(PCI Value)*
I
I
<>200)
II!
(177)
V
(150)
I
I
II
(179)
IV
(157)
IX
do'-)
VII
(nil
r.
VIII
(107)
VI
XI
(6.-M
TrTrTn^bFTT
SllcXlncsi
(Civ, «)
1
(0-5)
I
III
(0-JO)
VI
(10-50)
II
(0-10)
II
(0-10)
:v
VII
(10-50)
V
VIII
(10-50)
V
(0-20)
IX
(50-100)
X
(50-100)
...
ty Water Percolation «Jns Mi^rst lor.
31 IppcrtncLS Ir.pcde Assist InpeJe Assist
(Sand-flravel, J) (k, cn/s)* (k , c=/s)" (H,, cc)« (n , c=)*
1 *, III X '
(9-;-ioo) no-1) (0)
i xii i ix n
(95-100) do" )
III VII VI VII- IV
(60-95) (5 x 10' ) (68)
V V, VIII IV VII
(50-90) do" )
' g
II IX, IV VIII III -
(95-100) do"3) (CO)
II XI „ II VII IV
(95-100) (5 « ID'') — j
IV VIII, V VI V
(60-95) (10"-1) (112) \
VI VI , VI 1 . V VI
(50-93) (?. i 10"^)
vii iv ix in vii :
(o-oo) (10°) deo)
e
vni n „ xi *" ii ix *'
<0-55) (3 i 10"°) * (180) J
ii .1
u)
VII ...
(0-60!
IX III X —
(0-50) do"1)
y. I. xn i x
(0-50) dO" ) (MO-WOO
— —
Pm1. an 1 oM.rr highly
ftfll!)
XII
(cont.lr.-JcJ)
-------
TABLE 9. (continued)
Kft[||lon ^m
H-lve >rcr;' >c-.l-,n
USC3 Flrf Wntcr vi, i.i t>j»t Fost fictic Salur«llon
Symbol R'lloKuice (K-Kactor)" (r>nn<)-Giavei, 1) Control (II . rn)> (llcnvc. t-3/day)
CW I I
(< .05) '95-100)
CP I 1
(95-100)
CM IV III
(60-95)
CO III V o
(50-90) £
n
o
sw ii n u
(.05) (95-100) §
SP II II g
(95-100) "
•0
n
SM VI I1/ »
(-12-. 27) (60-95) u
O
SC VII VI n
(.H-.27) (50-90) "
ML . XIII VI! 2,
(.60) (0-60) 5
CL g xii vin S
w (.28-. 1.8) (0-55) w
c
OL XI VII c
(.21-. 29) (0-60) S
V
KH . X IX S
(.25) (0-50) "'
CH IX X
(.13-- 29) (0-50)
OH VIII
Ft V
(.13)
X
1
(O.L3)
IX
(0.1
VII
I
-3)
IV
CracK
( Ka [ in c I on , It )
I
(0)
I
(0)
III
(o.i-M
IV
(i
VIII
VII
-«)
II
(0.2-?)
VII
(0.2
V!
II
-2)
V
V
- —
I
(0)
I
(0)
II
(0.2-7) —
V
VI
IV
(1-7)
III
X
V.
(2-27)
II v
III
(1-6)
VIII
-
- I
(0
—
—
IX
—
Ill
.8)
—
VIII
(1-10)
VII
—
IX
X
(>10)
IX
(continued)
-------
TABLE U. (continued)
UCC3
!*t«M)ll/
M ocou
V'.-ctvr
niscourngc
MrJn
Future U»r
dt lun
Ntl. j
)'u in Itl I .n
ro
00
r,w
CP
CM
CC
OL
CH
OH
vni
V
IX
IX
VII
IV
VI
III
VI
II
VI
IX
IX
II
I
III
VII
IV
IV
VIII
VIII
III
• PCI Is ruling cone Imlen, i li coefficient of p-rra'aM 11 ly, II. la ciplllnry h-od. «n>l K-Fnclor li tlw soil «ro'llbl I Ity factor.
The rntlnct I to XIII «r« for belt through pjorcot In ptrforalnfi the i^crlflrd cover function.
-------
percentages for sand, silt, and clay as used In classification. A better
option sometimes is to relate to a recognized size classification system (2).
Table 10 lists some materials other than soil which may also be consid-
ered for use in cover systems. Most have been discussed previously (2). Note
again that several of these materials are wastes and under certain circum-
stances have been regarded as potentially hazardous. Even the few question-
able materials present much less risk in the context of use in a cover system
as compared to their massive.disposal elsewhere as the principal waste. Nev-
ertheless, a prior shewing of safety is usually required unless all risk is
circumvented by using the waste as barrier or foundation below and effectively
enclosed by the synthetic membrane (Figure 2).
TABLE 10. SOME LOW-COST SUBSTITUTE MATERIALS FOR COVER
Materials*Remarks
Fly ash Alone or blended
Bottom ash
Slag In place of gravel
Mine waste and tailings Large variety
Incinerator residue
Processing plant sludge High water content
Dredged material Soil
Sewage sludge Composted preferred
Foundry sand May contain tar residue
Manufactured sand Crushed stone byproduct .
Demolition debris For riprap
*Use of waste material depends on a cost advantage.
Layering
A second opportunity for design creativity comes in the arranging of lay-
ers to combine effects beneficially. Layering is perhaps the most promising
yet underutilized technique for designing cover systems. By combining two or
three distinct materials in layers, the designer may mobilize favorable char-
acteristics of each together at little extra expense. The actual designing
using soils available at specific sites will test the ingenuity of the engi-
neer but again the effort deserves strong emphasis. Figure 12 schematically
illustrates the layered system. Figure 13 compares a waste cover system to a
29
-------
highway pavement structure — an analogy whose value is manifested in Appen-
dix A on preparing specifications.
A few of the specific layer combinations that can be developed in layered
designs are:
a. A clay hydraulic barrier underlain by a granular capillary buffer.
b. A synthetic membrane overlain by a coarsely granular drainage layer.
c. A resistant cap on a thick cover of nonselect soil.
Additional explanations of layered cover options are found under EXAMPLE
DESIGNS.
Water flows through unsaturated soil (including cover systems) according
to a modified form of Darcy's law in which k is a nonlinear function of
water content 0 , i.e., k(9). An important (and not immediately obvious)
LOAM:
[Iliilllllll
SILT (FILTER!
.:..:;••:: SAND (BUFFER) :/•::.:'•;.;;;
Note: Neither system satisfies RCKA
MEMBRANE
LOAM o OOCOOOOOOCOOCOOO
Figure 12. Schematic layered cover systems.
30
-------
FLEXIBLE
PAVEMENT
(TYPICAL)
SHOULDER
| TREATMENT
PAVEMENT
STRUCTURE
EMBANKMENT
SIDE SLOPE AREA
V/////////////77//////. j
y:-
.*." I tt • ".*• ".'.•__• ".* *
• """• ".*• •"•* *****
*."* •"."•• *•."»".
""""" :".'•!•;
;•":'•'•".';•
.*."•• • .* •*•
•.'•"•" i-'.
'•'".'•"•'•'
".*• *.*•*
• • . .*.\
- V." - J
COURSE 2-
b. WASTE COVER SYSTEM
Figure 13. Similarity between highway embankment and cover system.
31
-------
manifestation of the effect of k and its dependency on 0 occurs in layered
systems of contrasting soil types (15). 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 pres-
sure existing at the wetting front is reduced. Before the wetting front can
advance, the suction pressure in the upper layer must decrease until it is low
enough to alloy the pores to fill with water. This delay continues until the
upper layer approaches saturation at which time the water is believed to
descend along localized channels rather than as a planar wetting front. Where
the coarsely pored soil overlies the finer layer, a similar process Impedes
flow to the evaporation surface above.
Use of Tests
The designer of cover should strive to formulate the required character-
istics of cover materials In terms of the results of standard tests. Without
this quantitative characterization, the cuver design is difficult to evaluate,
and construction is difficult to specify and control. Table 11 presents a
summary of widely recognized or standard laboratory tests of soils and related
material suggested for use in quantifying or evaluating cover designs. Soac
tests are for index properties while others define basic characteristics.
Notice the preference for the standards of the American Society for Testing
end Materials (16). Methods of the American Association of State Highway and
Transportation Officials (AASHTO) are aleo available (17).
Attention has been focused elsewhere upon the complexities of choosing
and conducting the tests suited to engineering waste facilities — most criti-
cally those fcr the permeability of soil barrier layers. Any test can be mis-
leading when its idiosyncracios are not fully appreciated. This probler: helps
reerphasize the importance explained in Section 1 (PREVIOUS ENGINEERING GUID-
ANCE) of experienced engineers, I.e., the need for the perspective of techni-
cians who recognize the unfavorable consequences cf carelessness in testing or
in application of test results.
Results of standard tests can be translated into design criteria. It is
generally recognized, although not alwaya appreciated, that soil properties
have a considerable variability in comparison to those of other construction
materials such as steel and concrete. The variability partly results from the
fact that soils are natural whereas most other construction materials are man-
made. Accordingly, it is connnon practice in soil construction to use supple-
mentally index properties based on relatively inexpensive and rapid testing
procedures or methods of estimation. Numerous tests can be made and the soil
can be approximately characterized for its variability as well as average
properties (23). Widely recognized index properties of soils are used In
classifying according to the USCS. Discussions of thac system and its basis
are found in many sources and, therefore, a summary is not repeated here.
See -SOIL COMPACTION (SECTION 6) for a discussion cf how the important
compaction or relative density tests enter into design and into construction
to achieve design.
32
-------
TABLE 11. LABORATORY SOIL TEST METHODS FOR
ANALYSIS AND DESIGN
Name of Test
Standard or
Preferred
Method*
Properties or
Parameters
Determined
Remarks/Special
Equipment
Requirements
Gradation Analvsis
Index and Classification Tests
ASTM D421
DA22
D2217
Particle size
distribution
Percent Fines
ASTM D1140
Percent of weight of
material finer than
No. 200 sieve
Atterberg Limits
Specific Gravity
Soil Description
ASTM D4318
D427
ASTM D854
ASTM D2488
Plastic limit, liquid
limit, plasticity
index, shrinkage
factors
Specific gravity or
apparent specific
gravity of soil
solids
Deacription of soil
from visual-manual
examination
Can usually be
estimated closely
Soil Classification ASTM D2487
Unified soil classi-
fication
Moisture-Density Relations
Dry Unit Weight
Water Content
Relative Density
ASTM D2937
D698
ASTM D22I6
D2974
ASTM D4253
D4254
Dry unit weight
(dry density)
Water content as
percent of dry weight
Maximum and minimum
density of cohesion-
less soils
Either rndisturbed
or remolded samples
Modified test may
be substituted
for test with
vibratory table
Compaction
ASTM D698
(or 5- to
15-blow mod-
ification)
Optimum water and
maximum density
(continued)
33
Method for earth
and rock mixtures
Is given In
Reference 18
-------
TABLE 11 (continued)
Name of Test
Standard or
Preferred
Method*
Properties or
Parameters
Determined
Remarks/Special
Equipment
Requirements
Consolidation**
Permeability
Mineralogy
Organic Content
Soluble Salts**
Dispersivity
Unconfined
Compression**
Consolidation and Permeability
ASTM D2435 One-dimensional .
compressibility,
permeability of
cohesive soil
ASTM D2434
Reference 18
Constant head
permeability
Falling head
permeability
Physical and Chemical Properties
Reference 19
Identification of
minerals
Reference 20
ASTM D2974
Reference 21
ASTM D4221
Reference 22
For granular soils
Pressure chamber
optional
Requires X-ray
diffraction
apparatus. Dif-
ferential thermal
analysis apperatuu
soy also ba used
Where organic
matter content
is critical,
02974 results
should be
verified by wet
conbjstion tests
(Reference 20)
Concentration of
soluble salts in soil
pore water •
Dispersion tendency in Significant In
Organic and
inorganic carbon
content as percent
of dry weight
cohesive soils
Shear Strength and DeformaMlity
ASTM D2166
Undrained-
strength
evaluation of
potential erosion
of piping
Applicable to.
cohesive soil only
(continued)
34
-------
TABLE I! (continued)
Name of Test
Direct Shear,
Consolidated-
Drained**
Standard or
Preferred
Method*
ASTM D3080
Properties or
Parameters
Determined
Effective shear
strength parameters,
cohesion and angle of
internal friction
Remarks /Special
Equipment
Requirements
Triaxial Compres-
sion, Unconsoli-
dated-Undrained**
Triaxial Compres-
sion, Consolidated-
Undrained**
ASTM 1)2650
Reference 18
Undrained shear
strength parameters,
cohesion and angle of
internal friction
Undrained shear
strength parameters,
cohesion and angle of
Internal friction
Effective shear
strength param-
eters obtained if
pore pressure is
measured
*ASTM: American Society for Testing and Materials.
**3pecialized test assigned only to obtain input for special engineering
analysis and design.
Specifications and Plans
Construction and operation specifications are the vehicles for carrying
cover design to fruition. Specifications nay emphasize construction methods
or end results but most commonly use a combination of both. Strong emphasis
needs to be placed on performance standards, but at some poiTit or some level
between the legislature or regulating agency and the constructor of the cover,
specific directions on cover construction and maintenance oust be provided.
This step has often been ignored or shortcut in the past so that many ''plans"
have been little more than conceptual in nature. Therein lies the cause of
many of today^s problem sites. Plans and specifications not only clarify the
actual construction of the cover, but also they force the cover designer to
quantify the design and face head-on any weaknesses, e.g. details of inter-
faces within the layered system. .
Table 12 provides a partial list of technical provisions for cover con-
struction. The organization is adapted from that offered as guidance by the
AASHTO (13).for highway construction. The similarity of cover sys-t€ms to
highway systems (Figure 13) justifies this adaptation. Other sets of techni-
cal provisions may be used, or entirely new provisions may be developed.
Table 13 presents items that are frequently Included in a set of plans. Each
35
-------
TABLE 12. TECHNICAL PROVISIONS OK CONTRACTS SUGGESTED
FOB COVER CONSTRUCTION
PART 200 - EARTHWORK • •
SECTION 201 - CLEARING ANT) CRtlBBISC
202 - REMOVAL OF STRUCTURES AND OBSTR'JCTIONS
11 203 - EXCAVATION
" 204 - BACKFILL AMD EMBANKMENT*
" 205 - SUBCRADE PREPARATION*
" 206 - PREWATERINC OF EXCAVATION
207 - STRUCTURAL EXCAVATION
" 208 - TEMPORARY EROSION AND WATER POLLUTION CONTROL
PART 300 - PRIMARY COIIRSE(S)
SECTION 301 .- CLAY BARRIER*
" 302 - CLAY-MOn7FIEn BARRIKR
" 303 - SYNTHETIC MEMBRANE BARRIER*
" 304 - BLO>:k BARRIER*
305 - PAVEMENT
PART 400 - SECONDARY COURSERS)
SECTION 401 - BUFFER LAYER
4^2 - STONE PROTECTION*
403 - FILTER LAYER*
404 - FILTER FABRIC (IN PLACE)*
405 - DRAINAGE LAYER*
11 406 - VEGETATIVE LAYER*
11 40? - SPECIAL FOUNDATION
PART 600 - MISCELLANEOUS CONSTRUCTION
SECTION 6(11 - CONCRETE FOR MINOR STRl'CTt'RES AN7> INCIDENTAL
CONSTRUCTION
602 - REINFORCING STEEL
" 603 - Cl'I.VKRTS AND STORM DRAINS
604 - MANHOLES. INLETS. AND CATCH HAS INS
" 605 - 1INDERDHAINS
606 - CAS VF.KTS
607 - FENCES
609 - CURB. CtiKB AND GUTTER. PAVED DITCHES, AND PAVED FLUMES
610 - TURF ESTABLISHMENT*
611 - FURNISH AND PLANT TRF.F.S, SHRUBS. VINtS. AW
CROUNDCOVEKS
612 - MOBILIZATION
" 613 - SLOPE PROTECTION
615 - EROSION CHECKS
" 616 - RIPRAP . •
617 - REFERENCE MASTERS
11 618 - TRAFFIC CONTROL
PART 700 - MATERIALS DETAILS
SECTION 701 - HYDRAULIC CEMENT
" 702 - BITUMINOUS MATERIALS*
" 703 - AGGREGATES'
" -704 - SPECIAL SOIL HATE'llALS*
705 - STOSE BLANKET PROTECTION AND FILTER BLANKET*
706 - MASONRY UNITS
" 707 - JOINT MATERIALS
708 - CONCRETE. CLAY. AN!) FIBER PIPE . ...
709 - METAL PIPE
" 710 - SHEETING*
711 - GROUND COVER MATERIALS*
713 - CONCRETE CURING MATERIALS AW ADMIXTURES
714 - MISCELLAHE'IL'S
*Sectton or snhs»l(:tjon Is Riven In example specif Jc.it Ion In Appendix A.
36
-------
TA3LE 13. PLANS OF CONTRACTS SUGGESTED FOR COVER CONSTRUCTION
Item* Description
1 Site location, large and small scale
2 Existing topography with elevations, monuments, roads, and grid
lines or points
3 Soils data including boring logs, classification data, and soil
properties
4 Locations of underground obstructions and existing utilities
5 Waste cells in plan and profile at scale suitable for measuring
area and volume
6 Planned final topography (or profile lines)
7 Stockpile and storage areas and access
8 Vertical design(s) and extent of applicability
9 Methods of stabilizing weak foundation materials
10 Hydrological data and site drainage including runon
11 Cover drainage system including structures
12 Special features, such as gas venting system with construction
details
13 Areas to receive topsoil and to be seeded
14 Vegetation or surfacing plan
*0ther items to be added as needed.
item deserves one or more separate sheets, air? tetrplex system frequently need
numerous detailed drawings to explain all aspects and variations.
Specifications and .jians also provide the necessary basis for evaluating
proposed designs ana for evaluating the construction procedures. It is
relatively easy to foresee poor construction where clear specifications arc
not beirg followed. Conversely, clear documents prevent the contractor from
being unfairly penalized when modifications in design and construction are
required. Appendix A presents guidance on preparing specifications.
Well-conceived, formal plans and specifications can have value even where
not directly applicable rs part of a contract. Owners or operators accomplish-
ing construction in-hous>j rather than on contract should find that such concise
37
-------
directionr, simplify their construction program and associated interactions
within the organization. They may choose to prepare operational plans that
resemble contract plans and specifications.
EXAMPLE DESIGNS
The stratification of five example cover systems and a method for cover
designation are shown in Figure 14. Four designs are relatively simple and
their technical usefulness is expected on the basis of past experience at dis-
posal facilities or according to well established principles of soil mechanics
and soil physics. Flexibility remains to ihe extent that the thickness and
details of material types may be manipulated according to site and waste char-
acteristics. The fifth example design in Figure 14 is taken fren Figure 2 and
is reflective of RCRA requirements.
Appendix A provides guidance on preparing specifications for four of
these example designs. The preparation of plans and specifications demands
careful attention to detail, and sometimes the choice of wording can have
costly legal ramifications. Therefore, the specifications in the appendix as
well as the designs themselves should be regarded as intended for guidance
rather than for direct application at any facility.
As can be seen in Figure 14, design I consists of layers of loam, clay,
and sand from top down to the foundation of backfill soil and intermediate
cover. The compacted clay layer constitutes the main, barrier component
rejecting a large percentage of infiltrating water. The loam layer at the top
supports vegetation and protects the clay Ij.yer. The sand layer below che
clay barrier forms a supplemental capillary barrier and also protects from
long-term deterioration by downward migration of clay particles. This design
is more applicable to flat cover systems.
Design II is similar in makeup to design I but is made more refined by
the inclusion of a synthetic fabric at the base of the clay layer. This fab-
ric allows the use of a coarser, more effective capillary barrier in place of
sand in design I. Without the fabric between the clay and coarse sand layers,
clay particles may migrate downward with infiltrating water. The fabric also
imparts some tensile and shear strength to the clay layer, and therefore the
system may have advantages on gentle slopes.
Design III consists primarily of an impermeable membrane on the backfill
soil foundation. The membrane is overlain by sand, which provides protection
to the membrane and pathways for lateral drainage of infiltrating vat*r. The
surface layer consists of clean gravel or washed stone for protection against
erosion. Soil below the membrane should be free of pebbles and larger pieces
that might damage the membrane. This cap with its synthetic membrane would
satisfy at least some requirements of RCRA regulations.
Design IV consists primarily of a hard ca.p on layers of gr -.nular soil and
clayey soil. The clayey soil, which might be a glacial till such as Js common
in the northern United States, serves as tn'j barrlt-r layer. T'ie granular soil
layer provides an avenue of escape for water blocked by the barrier layer
below. The hard cap, composed of blocks cf concrete, asphalt, or ether
38
-------
Y//
:-CLAY
FABRIC •
I
(S/C/L-1)
''• '•
II-_-lHI--2 CLAY-_-_--_-
n
(S/F/C/L-1)
MEMBRANE-
SAND
m
IM/S/G-1]
BLOCKS
-_-_-_-_ - CLAY "
-XX v'BACKFILL
:'•'.• :::'-i''•::'--V-V••'•''••VVVV-'Vs A N p
/FABRIC
nrr-c LAY ^^riririririr^irir_™r~
J J s J J
RCRA Guidance (minimal)
DESICIUTION
KEY
B Blocks
C Clay
F Fabric
G Gravel
L Loam
M Membrane
P Pavement
S Sand
(C/S/R-1)
(C/M/S/F/L)
Figure 14. Example cover designs.
-------
resist.nnt material, is intended to protect against erosion and to reject cost
rainfall as rapid runoff. The discontinuous (blocky) nature gives design Iv a
decided advantage over other hard caps considered in the past which are inflex-
ible or adjust to settlements in an unpredictable manner.
Design V designated C/M/S/F/L is the only one in Figure 14 that explic-
itly addresses RCRA guidance (1). No specifications are given for this cover
in Appendix A in order to prevent direct application with insufficient techni-
cal analysis.
ENGINEERING ANALYSES
Cover designs arc checked and refined or revised to site s,- -.cities by the
use of engineering analyses. The principal concern is for percolation charac-
terization, but processes that nay degrade t'-e cover also deserve attention.
Percolation
Increments of water entering and leaving the cover systen during incre-
ments of time can be balanced or partially balanced by changes in stored
water. This process of water balancing has been mathematically modeled. the
HELP model, designed specifically for the analysis of waste disposal units and
their covers, is recommended as the best analytical tool to date. The HZL?
model culminated the modeling work started in the first of the two previously
cited EPA reports (2). The HELP nodel and its application hsve been described
thoroughly in a users' manual and program documentation (24,25). These
descriptions are not repeated here.
Although f:he HELP model has been promoted for use in predicting water
movement through cover and waste together, it is preferred here that use be
limited for the present to the cover only. Accordingly, the prediction of
percolation passing through the cover and into waste disposal units are suffi-
cient for evaluating the cover. Conditions in the hydrological system below
the cover cannot be observed directly. Clearly the more of the hydrological
system that is included and analyzed, the greater will be the involvement of
complex factors and in turn the less confidence can be put in results.
The accuracy of the HELP model has not been verified hy comparison with
actual measurements in comparable increments. Portions of the Department cf
Agriculture CREAMS tr.odel, through which the HELP model evolved, have compared
favorably with field measurements for runoff. Also, the subtraction for
cvapotranspiration on a daily basis is accomplished with a physically well
based model.
It is suggested that one effective way of osing the KEL? model in cover
design i§ to prepare a chart or tabulation giving monthly or annual totsls of
percolation for several cover designs or variations under consideration. This
analysis can be repeated for wet and dry years as well as being used for aver-
age conditions. Table 14 shows an example of this sort of comparison actually
used in RC.RA enforcement proceedings to compare the effectiveness of three
remedial cover designs.
-------
TABLE 14. ANALYTICAL COMPARISON OF COVER DESIGNS
AGAINST PERCOLATION*
„ . . Calculated Annual Percolation and (Runoff) (in.)
Precipitation — 7 j=
Period (in.) K = 1 x 10 ° " 1 x 10 I x 10 (cra/s)
1974-78 38.19 4.95 3.38 0.89
(1.78) (2.13) (2.35)
1979 66.46 15.84 8.02 1.14
(12.23) (17.38) (20.15)
*Cover design consists of 12-in. loan layer or. 12-in. compacted clay layer
(K as specified) on 24-in. sandy clay over waste. Good grass facilitates
evaporation to 12-in. depth. Location is in southeastern US. Calculated by
HELP model.
Areal Erosion
An empirical analysis of erosion potential has bean developed (26) for
predicting soil loss frora certain ground configurations and soil types. The
method uses the so-called universal soil loss equation. Application to cover
design has been described elsewhere (2) and "Is still recoirjnended. The use of
this analysis, however, should be tempered by the realization that a designer
wants erosion tc stabilize st negligible levels in only a few years. Erosicr.
of many tons of sediment from a waste disposal facility is unacceptably exces-
sive; therefore application of analyses primarily intended for use on eroding
croplands may be somewhat misleading and should be interpreted with care.
Flooding
Hydraulic analyses are usually needed to quantify possible flooding and
Co predict erosion along channels, adequacy of ponds sr.d structures, and over-
flow onto unprotected areas of the cover. Measures against severe gullying
may also come from this analysis. Analyses are first accomplished for the
site in general (HYDROLOGY, SECTION 2) but deserve careful review in the nar-
rower context of cover survivability and performance.
A hydraulic analysis combines the hydrological background, especially
infrequent heavy storm events, with watershed characteristics to model the
probable extreme flooding at the site in the future. Temperatures may need tc
be factored in since freezing can reduce percolation a~d exaggerate otherwise
minor runoff events. The principal aspects of the cover system in question
are usually the drainage network and the capacity of its structures and chan-
nels. Vulnerability may also be manifested in low resistance of cover materi-
als to erosion by high-velocity f loodw.-»cer.
41
-------
Design storm data are readily available for any location, and it is rea-
sonable to expect site documentation to include several extreme rainfalls for
recurrer.ee intervals of possible interest. For an average size landfill a
l-hour storm and storms of longer duration are of typical interest. One
recurrence interval would likely be 10 or 20 years, but the reasons should be
presented for choosing specific intervals and storm durations. Figure 15 is
an example of summary information available for checking design storm amour.ts.
Design life discussed in Section 2 may impact directly; e.g., a 200-year,
2-hour storm may be appropriate for analyzing a facility intended to function
for 200 years. Where contingencies for repairs are adequate, a 20-year storm
rasy be sufficient.
The sequel to the assembling of design storm data is the calculation of
flood discharges for ditches and other elements of the drainage system. The
calculation in simplest form utilizes the rational equation:
where
"RO
CR01A
peak discharge, cubic feet/second
runoff coefficient
rainfall intensity, inches/hour
area of basin, acres
Figure 15. Ten-year, 1-hour rainfall in inches (US Weather Bureau).
-------
The formula above incorporates the approximation that 1 inch/hour/
acre = 1 cubic foot/second. Roughly approximated, the C values for veg-
etated clayey soil on flats and slopes art about 0.5 and 0.7, respectively,
and for vegetated sandy soils on flats and slopes are about 0.2 and 0.4.
Where an upstream watershed area greatly exceeds the disposal area and
the concern is for flooding in a channel passing alongside a disposal unit,
analysis may produce a hydrographic history including a flood crest. Analyses
of this type are also fairly straightforward, but it will be essential that
the analysis be conducted by an engineer with experience in its conduct and
application ir-.luding both large and small watershe's.
The conclusions of the analysis should be such as to suggest the poten-
tial threats from flooding. Modifications in design may become evident that
will help avoid intolerable immersion or erosion of portions of the cover sys-
tem during the design life.
Slope Stability
Engineering analyses of slope stability are based on the concept that a
slope fails, unless the resultant resistance to shear on every possible sur-
face traversing 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 lo driving forces. Stability analysis is a sophis-
ticated technique requiring geotechnical engineers, often using soil test and
other field-sampled data as input. Mosc analytical and test work should be
accomplished by such specialists. However, it is sometimes also imperative
that an engineer closer to the design and construction of the cover system
contribute to the analyses to keep then; fror. being expensive with useless
embellishments.
Determination of the location of the critical surface usually requir s
successive trial analyses of likely candidates. Each trial evaluates a sur-
face having one of the following shapes:
a. Circular arc (Figure 16) within the foundation and/or the embankment.
b. Composite of a long horizontal plane in a foundation stratum connect-
ir)g with diagonal planes up through the foundation and embankment to
the ground sirface.
c. Plane paralleling the ground surface at shallow depth.
Analyses assuming a circular arc failure surface may be made using either
the modified Swedish method that considers forces on the sides of vertical
slices within the TOSS (Figure 16). -or the simpler Swedish method of slices
that assumes that side forces are equal in tragnitude and parallel to the base
of each .slice. The wedge method for planar sliding surfaces (Figure 17) is
appropriate for weak foundations requiring flat slopes or for an otherwise
strong foundation containing a thin weak stratum. Appropriate forces for
ground water are incorporated below the water table. Water forces tend to
-------
3. EXAMPLE EMBANKMENT SECTION
(II THROUGH IS)
ARE STEPS IN
CONSTRUCTION
ALL E FORCES ARE
PARALLEL TO AVER-
AGE OUTER SLOPE
BEING ANALYZED.
b. SLICES
WITH FORCES
.EGEND
I T1U
in
O
_J
u. -
O
K
O
^ -10
'
!
v/*^
^o
,7 ^CS FOR
\ CLOSURE:
i
»
1
w
5
1
w»
c '
£ 1.2 1.4 1.6 :.3 -••'-
TRIAL F S W7
W = WEIGHT OF SLICE
E = EARTH FORCE ON SIDE OF SLICE
N = MO°MAL "C BASE OF SLIC1
^L - LENGT" ACROSS BASE OF SLICE
C_ = DEVELOPED COHESION FORCE
(J. TRIAL FS VERSUS
ERRO?i OF CLOSURE
= RESULTANT OF MORMAL ANO OE-
VELOPEO FRICTION FORCE
- DEVELOPED ANGLE OF
FRICTION OF SOIL
TAN 6
ERROR OF CLOSURE
C. COMPOSITE
FOPCE POLYGON
FOR ONE TRIAL Fi
F S
Figure 16. Modified Swedish method of finite slice procedure with
no water forces (27).
-------
fOil riVE SLOPE
NEGATIVE JI.OOE UTITH RESPECT TO
OPPOSITE e»i8AN-*£MT SLOPE
COHESIONLESS EUBAN4MENT
(SYMMETRICAL, ABOUT CEKTFSLIMEI
__
D
t
CLAY FOUNDATION
H = HEIGHT Cr CMDA'I-'MCNT
O = THICKNESS OF CLAY FOUNDATION LAYER
K^ = HATIO Or HORIZONTAL TO VERTICAL
EARTH nBE«Sl/«LS. ACTIVE CASE
S - COTANGENT OF OLO^E ANCLE, ft
y - HEIGHT OF EMBANKMf NT ANS FOUWOATiON
MATERIAL "ER UNI i OF VOLUME
c -COHESION PER UNIT AHEA OF FOUNDATION SOIL
Figure 17. Conceptual cross section and symbols
for wedge analysis
reduce stability by increasing the driving forces and decreasing the resisting
forces due to uplift. 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.
A special, simple analysis is available for cohesionless soil embank-
ments. The infinite slope procedure (27) addresses rather shallow sliding and
may be appropriate for relatively thin granular cover over sloping waste where
shallow sliding can be serious. For dry conditions, the safety factor reduces
to
FS
tan
tan 6
where & is slope inclinatior. and i is material friction angle. The equiv-
alence of the 4> and 6 at the threshold of failure is reflected in the gen-
eral correspondence of the observed angle of repose and measured <> in
cohesionless soils (Table 15).
Freezing
The most serious freezing effects are cracking or buckling of layers,
sliding after thawing, and blocking of vents and drains. Also see Flooding
for effects of freezing on runoff. Since these problems are all limited to
the near-surface zone actually subject to freezing, a key characteristic to be
-------
TABLE 15. ESTIMATES OF REPOSE AND FRICTION
ANGLES OF COHESIONLESS SOILS
Friction Angle,
Soil Description
Silt
Uniform sand
Well-graded sand
Sand and gravel
Angle of Repose*
deg
26 - 30
26 - 30
30 - 34
32 - 36
At
Ultimate
26
26
30
32
Strength
- 30
- 30
- 34
- 36
deg
At
Peak Strength
28 - 34
30 - 36
34 - 46
36 - 48
*Lower values generally for soft or well-rounded particles at dense packing
or at high normal stresses.
factored into design is the depth of freezing. As long as vulnerable elements
of the cover system are not placed above the depth of freezing, the effects
are not serious.
Numerous weather stations record soil temperature profiles routinely.
The analysis for freezing depth has also been developed empirically using past
climate records much the same as storm data have been used in flooding analy-
ses. An essential intermediate parameter is the freezing index. 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 between
mean air temperature and freezing temperature (32°F) .
Figure 18 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 4CO US Weather bureau stations that were used for
basic data are spotted in the figure. A site-specific design freezing index
r-hould be used in preference to those in the figure wherever nearby stations
are available because differences In elevation and topographic position and
nearness to cities, bodies of water, or other sources of heat produce consid-
erable variations in the index over short distances. These variations are
particularly important to design in areas of indices of less than 1000, i.e.,
in much of the United States.
The maximum depth of frost penetration can be predicted in a general way
on the basis of the freezing index. For example, Figure 19 shows generalized
curves for a direct relationship at various soil conditions. This information
should be helpful in choosing thickness for various final cover soils.
It is also appropriate to consider applying the freezing index for peri-
ods of one or a few days rather than an entire cold season. For example, an
unfrozen silty sand placed on solid waste may be expected to freeze to a depth
-------
-. Us if
l^\
Figure 18. Design freezing index values in degree-days for the conterminous
United States.
-------
TURF-3O CM SHOW COVER
I~~T-I—i—:—\—' i • i ' i
0 2JO «OO 600 BOO IOOO :ZOO
DEGREE D»rs if}
TURF - SNOW FREE
i ' i ' ; ' i ' i ' i
7.00 40C 600 BOO 'OOO I20O
OE GR1C 04VS (Fl
BARE GROUND OR PAVEMENT — SNOW FREE
I
200
«oo eoo GCO
OEGBEE DAYS (f)
i I
(000 1200
NOTE: CHOOSE ABSCISSA ACCORDING TO
CME OF THREE GROUND SURFACE
CONDITIONS
140
Figure 19. Depth of freezing penetration into soils with
bare or covered surfaces.
-------
of 20 centimeters during 10 days in which the mean daily temperature is 22°F
(Figure 19). The index applies on a daily basis also in a very approximate
way.
Settlement
Despite the extreme complexity of the settlement processes, displacements
accumulating in the cover above a waste cell can be est'.mated with some confi-
dence over the very short term and the very long terra. Displacements ranging
from areally uniform to abruptly discontinuous will d<
-------
SECTION' 4
LAYERED DESIGN ELEMENTS
• ' This section reviews the several layer types that have been used in cover
or that have been proposed for such use. Layer types are discussed in no par-
ticular order. There is no implication of relative importance of layers, nor
is it implied that all types are needed in sn effective cover. Emphasis is
placed (Figure 14) on the use of no more layers than can be justified on the
basis of experience, physical principles, and expected benefit-to-cost ratio.
One should look with increasing skepticism upon designs of five, six, and more
layers.
HYDRAULIC BARRIER
• The hydraulic barrier layer is usually the most important element of the
cover in other than arid regions. A coefficient of permeability k «= 10 cen-
timeters/second or less by laboratory testing has been prescribed as necessary
for soil barriers, but analytical tools are available to allow a refined pre-
scription fitting the specifics of site climate and material types (See Perco-
lation, SECTION 3). Barrier layers of soil are almost always composed of
clayey soils that inherently have low permeability. USCS types CH, CL, and SC
are generally recommended; also see Table 9. RCRA regulations are interpreted
as requiring a synthetic membrane in the cover. Guidance (I) calls for both a
membrane and a low-permeability soil layer, with the membrane as the primary
barrier.
Soil
Tables 9 and 16 should be useful as guides in determining the relative
effectiveness of various soils in impeding or passing wafer, but other factors
such as shrinking and cracking characteristics or root-system development may
complicate the choice. Well-graded granular soils have lower k values than
poorly graded granular soils of the same median grain size. It has been sug-
gested that in continuously graded gravel for highways (28) k is directly
reflective of the nature of the fines passing the No. 200 sieve when they
exceed 15 percent. For graded gravels with less than 15 percent passing
No. 200, the effect of the fines is less direct.
Special attention and control are needed. The selection and use of clay
material have tended to be loose or poorly controlled, and materials other
than straight clay have been substituted frequently, e.g., till. This prac-
tice is sometimes even preferred since the combination of permeability and
other physical properties of some of these substituted soils may be well
suited to the cover system. Nevertheless, there is a clear need to be
50
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TABLE 16. APPROXIMATE AVERAGE PERMEABILITY* AND
CAPILLARY HEAD OF SOILS
General USCS Coefficient of Capillary
Soil Type Soil Type Permeability, cm/s Head, cm
Gravel
GP
GW
GM
GC
-1
_2
10
5 x 10~A
io~A
— — —
6
68
_ — _
Sand
Silt
Clay
SP
sw
SH
SC
ML
MH
CL
CH
5 x 10
10
10
2 x 10
10
10"
3 x 10
10
-2
-3
-3
-A
-5
r8
-9
60
112
180
180
200 - 400+
*Compaction reduces permeability ir. general.
especially thorough in testing and other documentation of prospective clayey
materials so that all parties know the facts. Considerations that deserve
special attention are the geology, mineralogy, uniformity, and total available
volume of the clay source.
Working design criteria for fine-grained, impervious, erosion-resistant
linings such as lean clay (CL) for canals are presented in Figure 20.
Although this confirmed guidance is recoinnended for consideration in cover
design, the differenr.es in function of an exposed canal lining from the buried
barrier should be carefully investigated. The developers of the criteria (29)
actually prefer gravelly soils in their added need for erosion resistance. In
order, they prefer GM-GC ard then GC, SW-SC, and SC. This practical experi-
ence indicates that gravelly or sandy soils will have sufficiently low k for
barriers, again, provided the clay and Intermediate size fractions are
adequate.
If well-graded fine soil is not available nearhy but coarse- and fine-
grained soils are, blending should be considered. Properly blended soils are
effective for Increasing impedance to water movement since the grain-size dis-
tribution is broadened as compared with distributions of the component soils.
51
-------
3D
c
2
10
* Although o Pi of 10 percent is
occeptobie. o value cf >2 oercent
is preferred. I I
I I
Maiiaium liquid limit = « 5
Sctisfoctory for ccrth lining- f
I
I i
£ Mmirr.-jm PI = 10
"i" line from
chart
?o jo «o
LIOUIO LIMIT -PERCEMT
Figure 20. Plasticity criterion for impervious, erosion-resistant
compacted canal linings (29).
Blending is usually an expensive operation, and a thorough review of other
options may be advisable before proceeding en a large scale. Where a barrier
layer of very low permeability is warranted, it may be necessary to modify the
soil available at the site by addition of special material. The addition of
bentonite to sandy cover soil substantially reduces k (Figure 21). A lesser
reduction has been obtained in fly ash (31).
All soil barrier layers should be compacted to reduce permeability.;
90-95 percent of standard compaction is a reasonable target for high-pr5ority
covers and careful construction control is needed. The porosity is decreased
.".r.c! some strengthening may also result. At municipal waste landfills, an
effort of more than two passes of the spreading or compacting equipment may be
Impractical to monitor and regulate on daily cover. Higher compactive effort
seems appropriate for intermediate and final covers except as it will Inter-
fere with establishing vegetation. Care should be taken to assure that the
water content during compaction does not greatly exceed the optimum percent-
age. See Section 6 for practices in soil compaction and Appendix A for
detailed specifications such as night be used at RCRA facilities.
The fine-grained soils that are suitable for blocking percolation are
also characterized by susceptibility to cracking. The cracking accompanies
large shrinkage brought about by a reduction in the high water content. High
daytime ter.peratures at the ground surface are the most common cause, but
freezing and thawing can bring about a redistribution of moisture also. It is
usually effective to pair the soil barrier with an overlying buffer or other
soil layer sufficient to dampen out the most severe movement of moisture
52
-------
FINE SAND - SiS-?i
NOTCS ! - SAND • UNTREATED VOLCLAY
? - SA\D • UMTHE-VTgU VOLCLAY (LABORA-
TORY TESTSI
3 - Fi£LO TESTS WIF.I VOLCLAY SLS-71 IN
GRADED SAND. IN FINE SAND OR i.M
G3ADED GRAVEL
-s' FIELD TESTS WITH SILT • VOLCLAY
Si.S-70
b - SCRTSD SAND • VOLCLAY SLS-71
ILABCR.'.TOHY 1ESTSI
6 • el.\t SA.\O • VOLCLAY SLS-71
ESTEi
Figure 21. Effect of bentonite additions on permeability
of granular soil (30).
(particularly drying) which otherwise culminates in cracking. The clay layer
in a RCRA system such as in Figure 2 is shielded from surficial drying effects
by the overlying synthetic membrane.
Some soils recover from cracking, e.g., when dry clay regains noisture,
swells, and closes cracks. This behavior is sometimes popularized as "self-
healing" in an exaggeration of what may actually be a very complex and partly
unconfirmed process. Any infilling of foreign soil along cracks will tend to
impede the recovery.
Damage to the barrier layer can also corr.e ?bout through differential set-
tlement. One technique for protecting the barrier from effects of differen-
tial settlement consists of providing an adequate layer thickness to
cocpensate for displacements which may possibly occur. This technique relies
53
-------
on the plasticity and swelling characteristics of the clay barrier to heal
immediately any opening starting to develop along shears.
Membrane
Synthetic membranes are often used as the primary barrier layer and, in
fact, are required for most RCRA covers. Guidance in the designation of mem-
brane type by its attributes is beyond the scope of this document. Selection
Is a major task for technical analysis and deserves careful consideration by
specialists familiar with properties of membranes as well as the needs at the
disposal site. See the technical resource document SW-870 (32) for a review
of membranes in liners also applicable to barrier layers In cover systems.
It is appropriate to mention some major technical concerns when using
synthetic membranes: volatile stability, freezing effects, heating effects,
temperature cycling, and tensile strength. The overall service life expected
of the cover system reflects a complex summation of the individual effects. A
facility design life of hundreds of years may exceed a reasonably expectable
life for a membrane based on past experience and projections which are conser-
vative in the engineering sense. However, current expectation is that longer
service will be obtained as new, improved materials are developed. In any
case, careful planning for maintenance and future repair is needed (SEC-
TION 10). A list of detailed c.ecbrane requirements, even when partly in qual-
itative terms, will be very useful since these service requirements lead
logically to a focusing of attention on the consequences of a gradual or rapid
deterioration uT the iiembrane.
VEGETATIVE LAYER
A preliminary step in establishing vegetation often is to plan measures
to stockpile and then reuse the original topsoil. The less fertile underlying
soil will be available for near-tern use. As the operation nears completion,
the stockpiled topsoil can be used in the final cover to facilitate rapid
growth of grasses and shrubbery. The original topsoil must be significantly
more fertile than underlying soil strata; otherwise, stockpiling is not prac-
tical or economical. It may be critical to protect stockpiled topsoil froc
excessive exposure that may dacage essential nicrobial components. In fact,
the stripping of topsoil is sometimes coordinated with placement in the cover
system during a short intei-val in spring or fall to avoid this detrimental
effect of stockpiling altogether.
Untreated subsoils are seldoa suitable directly, so it Is necessary fre-
quently to supplement subsoil when it must be used with fertilizers, condi-
tioners, etc. Loams or b'SCS types CM, GC, SM, SC, ML, and CL are reconcnenc'ed,
but agronomic considerations usually prevail. The upper lift should be placed
in a loose condition and not ccr.pacted. Other beneficial characteristics of
vegetative soil are Identified in Section 8 to which reference should be made
in designing the layer.
At least 18 to 24 inches of plant growth r.edlum is regarded as necessary
to provide a reservoir of moisture at field capacity. Intermittent deficien-
cies or excesses of water need tc be considered in designing the vegetative
54
-------
layer. Vegetation can exhaust moisture from a thin well-drained soil layer in
a short time ancl then be severely stressed during droughty conditions. Cer-
tain configurations of soil, particularly over barrier layers, may experience
localized saturation for extended periods. Under this circumstance roots may'
be killed quickly. Some relief from these extreme detrimental conditions may
be found in features such as drainagevays and in surface shaping.
Where experience is insuf.icient for presuming the survival of vegeta-
tion, a contingency may be needed in the plan for restoration or upgrading of
stressed Vcgetaticr.. Such a contingency might conceivably involve increasing
the layer thickness (at substantial cost).
RESISTANT LAYER
The placement of a resistant cap at the ground surface is another tech-
nique for protecting against severe erosion damage. The wide variety of
resistant materials offers broad ranges of performance and service life.
Air-entrained concrete can be expected to survive as a material for hundreds
of years in mild climates. Asphalt surface seals suffer relatively short-term
deterioration by oxidation and loss of volatiles and traditionally need sup-
plemental maintenance. Most man-made resistant layers placed in a continuous
sheet will be subjected to at least some flexural and thermal stress and will
sustain crack damage over a period of years. Crack sealing and other mainte-
nance can constitute £ substantial part of the. overall cost of such layers
even exceeding the cost of original installation.
Resistant layers composed of fitted blocks of durable material offer a
possible compromise. Figure 22 is adapted from investigations on use for
pavement (33). Blocks tend to be less susceptible to thermal stress damage
and are self adjusting to flexure that may accompany subsidence of the waste
below. A layer of fitted blocks provides an abundance of thin channels for
infiltration of water. However, these channels constitute no more than a few
percent of the total surface area and therefore are quite limited in their
capacity to admit water. Most heavy rain falling on hard surfaces is rejected
quickly as runoff. Nevertheless, a combination of surface and even subsurface
drainage features will usually be necessary.
One of the most attractive resistant materials is gravel (Figure 23).
Gravel is a highly durable, natural material that resists freezing disturbance
and also serves to dampen other temperature- and moisture-related processes
tending to degrade the cover system. Gravel is well established as construc-
tion material, and costs for stone protection can be estimated closely. Cost
advantages are also present in maintenance since repair largely amounts to
patching with more gravel. A commonly used specification for such gravel or
crushed stone is as follows:
Sieve Designation Weight Percent Passing
2 1/2 inches " 100
2 inches 95-100
1 inch 35-70
1/2 Inch 10-30
No. A 0-5
55
-------
CONCRETE BLOC?*. SURFACE
SUBCRAOE
Surctclicr bond
Herringbone
n_.
1
1
i
—
Figure 22. Fitted blocks for surface paving or ariaor.
Specifications for another material as well as construction methods are given
in Appendix A for design III (M/S/G-1).
Gravel and stone tailings from processing of sandy gravel are particu-
larly attractive for protection of slopes, and it may be reasonable to use
this material as a supplement to the more usual grass cover. Ordinarily
gravel slopes inclined between 5 and 25 percent resist erosion indefinitely;
56
-------
.
.
Figure 23. Washed gravel or slope at Wlndham landfill.
-------
whereas tiat areas under 5 percent should endure as well with the less expen-
sive vsgetative layer at the surface.
RIGBARRIER ...
Blobarrler is the terra popularized for a layer intended to block penetra-
tion by animals or plants. The perceived threat is only occasionally serious
and even then difficult to address quantitatively in ilosign. Animals invade
for access to food, protection, or favorable temperature. Plant roots descend
to tap moisture needed for continued growth. Animal tunnels and plant root
holes would seriously degrade the cover system if they penetrated the barrier
layer. There may be special cases In which the penetration of the disposal
unit and subsequent removal of moisture through evapotransplration is a favor-
able condition, but for the present, the consensus is largely to the contrary.
Other threats from animal and plant activity through the cover arise In possi-
bilities for physical transport of hazardous waste to the surface by the ani-
nals and uptake cf pollutants by the plants.
Materials suitable for resisting penetration by animals should have low
cohesive strength, e.g., like sand. Dry sand is cohesionless and therefore
tends to slough and collapse during or soon after penetration by tunneling.
Soils with low water-holding capacity are best against penetrstlon by plant
roots. Roots are discourage.'? from further downward intrusion upon encounter-
Ing a layer that is not only initially dry but also incapable of storing much
water, even on a temporary basis. Free-draining, ccarse granular colls are
most effective.
Gravel has the combined characteristics of very low water-holding capac-
ity and low cohesive strength and is often ideal as a biobarrier against
plants and most animals. However, the large voids present in narrowly graded
gravel provide no resistance to penetration by insects. Also, these open
voids facilitate piping and, therefore, a buried gravel layer needs to be pro-
tected by a filter layer located above (See FILTER LAYER). Fortunately,
insect activity seems to be restricted to a depth of no more than about
2 meters, and therefore protection from insect activity may be achieved by
manipulation of the depth of the barrier layer or thickness of the total
cover. Depths substantially less than 2 meters may be adequate In sone areas.
A gravel layer situated at the ground surface is capable of serving a
dual role as biobarrier and as surface armor (See RESISTANT LAYER). Other
resistant layers should similarly deter animals and plants. In contrast, the
hydraulic barrier is seldom effective doubling as biobarrier also. Roots may
preferentially tap the moisture of a fine-grained hydraulic barrier and in the
process, disrupt it. Burrowing animals may also degrade the barrier by tun-
neling since the moist fine-grained soil is supportive of small tunnels.
Occasional, serious penetrations are suspected with synthetic membranes but
the experience base is sketchy and Inconclusive.
The most attractive alternative to using a biobarrier in the cover system
Is through repairs and maintenance incorporated in long-term care. Damage to
the cover and exposure of the hazardous waste by invaders needs separate
58
-------
attention in the maintenance program. Provisions for repairs nay assume
greater importance when the cover system Includes no biobsrrler.
DRAINAGE LAYER
The function of a drainage layer is to convey water or gas laterally and
the layer must have a high permeability. This basic requirement usually dic-
tates that the drainage layer be composed of narrowly graded granular soil
such as sand. Suitable sand is almost always readily available. Drainage
layers should generally satisfy filter criteria (See FILTER LAYER) to avoid
susceptibility to plugging. Actually, drainage layers; and filter layers are
quite similar, and the specifications offered in Appendix A differ only in the
details.
Ground freezing temporarily blocks the effectiveness of drainage layers.
This phenomenon can be very serious in highway systems, and drainage in sub-
bases may need to be positioned near the ground surface to minimize delays in
drainage (34) during thaw. Fortunately, the resultant high pore pressure and
pumping from traffic is minor at most in cover systems, and the drainage layer
is usually positioned high anyway In order to remove water blocked by the bar-
rier layer (Designs III and IV in Figure U).
Drainage layers are occasionally supplemented with features such as pipes
to facilitate the lateral movement and removal of water or gas. Clearly, the
lateral movement is n-.ore efficiently accomplished where the average flow path
is measured in feet rather than tens of feet. Supplecentary features for
improving the drainage function are idei.:ified and discussed in Section 5.
FILTER LAYER
A filter layer of soil or synthetic fabric serves to prevent downward
migration of fine particles with percolating water. Migration of particles is
to be expected in soils containing or having access to appreciable open void
space. Thus, just about any soil layer, highly porous or not, situated over a
porous disposal unit is potentially vulnerable to this process. Drainage lay-
ers and biobarriers with their characteristic large and abundant voids are
particularly susceptible to participating in the migration process in combina-
tion with a finer soil layer above. Where movement is concentrated in dis-
crete pathways such as along fractures, the process is known as piping.
The filter with its intermediate pore sizes provides a framework for
favorable bridging action. The water continues downward, but the particles
are retained in the small pores of the filter. The process eventually stops
as the accumulated particles bridge across the miniature pathways. A filter
as thin as 2.5 centimeters can be effective in road beds (6), but constraints
of cover construction probably dictate a thickness at least 10 centimeters and
probably more. The use of a filter layer in a cover system was first proposed
seven years ago (2). Subsequent experience is insufficient to confirm effec-
tiveness, but it can be said confidently that any effect should mostly be on
the beneficial side, i.e., a filter layer offers extra assurance and should
not introduce new problems into the system. One possible exception, however,
comes In capillary effects. A soil filter interposed between coarse- and
59
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fine-grained soils may decrease the boundary's effectiveness as a capillary
barrier. Filter fabrics may circumvent this possible problem.
Soil
Criteria for granular filter soil are generally recognized, although
there is sone variability in detail (35). These criteria are also applicable
to designing filters around buried drainage ;>lpes. A key Corps of Engineers
criterion for stability is
15-percent size of filter soil f
85-percent Oi finer sail
A modifying criterion applicable to CL and CH soils only permits the 15-per-
cent size of the first filter soil to be as great as 0.4 millimeter
(Figure 24).
Figure 24. Illustration of the design of a graded (double) filter.
Gap-graded soils require special attention. For gap grad'ng in the finer
(protected) soil, the filter design considers the finer components only. Cap
grading should be avoided in the filter soil itself, i.e., .the grain-size
curve should resemble those in Figure 24 in shape. Also, note in that figure
the implications of dealing with ranges of sizes represented by a band rather
than a single curve.
60
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Fabric
The use of synthetic fabrics in solid waste management has been reviewed
elsewhere (36) . Fabrics ar*e increasingly being substituted for granular soil
layers in earthwork construction despite the disadvantage of high cost and
disagreements about cost effectiveness (6). Unfortunately, the limited past
experience still leaves open the question of service life which is a major
concern in waste management. The effectiveness of fabric filters as well as
soil filters may be decreased over a long period of time by physical deterio-
ration or by plugging from biological and chemical deposits. This problem is
probably nuch more serious where the filter surrounds a drainage pipe than in
the case where the filter is a layer expending across the entire cover system,
since percolation and reactants and products are more concentrated in the
first instance.
Synthetic fabrics are vulnerable to damage by large subsidence, but they
may serve to bridge across small subsidence holes and preserve cover integrity
for a long period. The consequence of the preservation of voids beneath an
apparently intact cover is one of the many aspects that need careful consider-
ation during design. Such bridging can conceivably be favorable in some
cases, but since the condition is only quasistable, it may only postpone and
Intensify a long-term problem.
Corps of Engineers criteria for filter cloth are based on the equivalent
opening size (EOS) and percent open area. Woven filter cloths generally are
available in the range of sizes between the No. 100 and No. 30 sieves. Non-
woven cloths range smaller than the No. 40 with coefficients of permeability
ranging from about 0.01 to 0.9 centimeters/second. The following selection
criteria are most useful with v/oven cloth:
a. Filter cloth adjacent to granular soil containing 50 percent or less
by weight of minus No. 200 materials should have a ratio of
85-percent size of soil >
opening size of EOS sieve
and should have an open area not to exceed 36 percent.
b. Filter cloths adjacent to all other types of soil should have an EOS
no larger than the openings in the No. 70 sieve (0.0083 inch), and an
open area not to exceed 10 percent.
c. To reduce the chance of clogging, no cloth should be specified with
an open area less than A percent and/of an EOS of less than the
No. 100 sieve (0.0059 inch). It is preferable to specify a cloth
with openings as large as allowable to permit drainage and prevent
clogging.
ASTK D4491, "Test Method for Water Permeability of Geotextiles by Permittiv-
ity" was approved by ASTM in 1985.
61
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BUFFER LAYER AND FOUNDATION
A buffer layer in this document is any layer not functioning in one of
thp specific ways above. Among the several miscellaneous functions of buffer
layers are the following:
a. Protect another layer during construction.
b. Serve as a foundation or base for construction.
c. Merge downward into backfill soil.
d. Distribute load.
e. Distribute deformation (such as settlement).
Each function may have its own requirements, but most requirements for a buf-
fer layer are much less stringent than for those layers discussed above.
Nonselect soil •* s usually adequate and often present on site. For the
protection of syntlic-ic membranes less than 30 mils in thickness, it is essen-
tial that the soil be fine and free of pebbles and clods exceeding 3/8 inch in
diameter that would threaten to puncture the membrane (37) . Thick membranes
uiay be able to sustain grain indentations without damage, but the risks should
be carefully evaluated in consultation with the manufacturer or authority
familiar with the characteristics of the membrane. Finally, the extra effort
to achieve uniformity in material is worth while in providing stability to the
layers above. More discussion on confirming uniformity and firmness is found
under Proof Rolling (Special Methods, SECTION 6).
It is usually appropriate to distinguish the foundation apart from other
buffer Jayer types. Cover systems are vulnerable to settlement and other pro-
cesses originating in the waste cell below. Accordingly, the foundation is a
key transitional zone between the cover system and the waste cell acting to
dampen out or distribute the more seriously adverse effects. One should dis-
tinguish this specific usage of the term "foundation" from a more general
usage found in the specifications in Appendix A. There, it has been necessary
to describe also other "foundation" conditions immediately below a course or
lift to be constructed and in some cases above the subgrade of the cover sys-
tem. Thus, in Figure 13, Course 1 is part of the foundation of Course 2, and
Course 2 is part of Course 3's foundation; yet the foundation of the cover
system as a whole lies immediately below the indicated subgrade.
MONOLAYER DESIGN
A cover composed of a single layer is an option that might be considered
under special conditions of material type and climate, particularly in arid •
regions where the downward penetration of water from the surface may be
limited to only a fev meters (See HYDROLOGY, SECTION 2). Very little water
reaches the disposal unit, and the small amount that does has little adverse
impact. A single-layer, thick cover will be sufficient for this situation.
The other conraon condition favoring a single-layer cover is an abundant supply
62
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of clay-rich soil from which to construct the cap. Again, the soil cover will
need to be of sufficiently great thickness. Note however that such a design
would not sacisfy RCRA requirements for new sites.
An important attribute of a single-layer cover besides low initial cost
is its relatively simple maintenance. Subsider.ee holes or erosion gullies can
be patched by the addition of more of the same soil. Ordinarily, however,
some consideration would be given to modifications that would prevent a recur
rence. A special application of a single-layer cover might be in its use at
waste storage facilities such as described under DESIGN LIFE (SECTION 2)
wherein requirements of longevity are largely relaxed.
-
-------
SECTION 5
CONFIGL'RATIONAL DESIGN
Configurational design is intended to encompass all aspects of design of
cover ether than the stratification of a typical increment, i.e., the areal
design factors as opposed to the vertical design (SECTION A) in the vertical- -
dimension alone. The average slope, topographic details, and drainage system
probably constitute the most important among such areal factors.
In a large measure the same design methods and attitudes suggested in
Sections 3 and U apply here also. However, the importance of testing and test
results is less in regard to configurational design. The emphasis is on modi-
fications and additions to the simple vertical design appropriate for the
anticipated complexities of surface topography and size and geometrical
arrangement of disposal units. Expected consequences of the character of the
solid waste must also be anticipated and incorporated at this stage.
AREAL SIZE
The size of the cover is determined by the size and arrangement of dis-
posal units. Covers for areal landfills may be quite extensive. Some flexi-
bility may be available in trench burial where the disposal units are
separated by partitions of undisturbed ground. The options are to cover indi-
vidual disposal units separately or to cover the assemblage of disposal units
in its entirety. The second option will require that an intermediate cover be
placed as each disposal unit is filled. Otherwise, hazardous waste would be
exposed or insufficiently covered over a period of years between the first
unit and the last unit of the facility. It is also feasible to proceed in a
stepwise manner wherein the final cover is completed over individual units or
cells with subsequent steps following in which Intervening areas are com-
pleted. This construction of the cover in several steps is probably not fea-
sible for systems of more than two layers since It would be difficult to mesh
the layers of the cover system from area to area.
The designer must also establish the amount of overlap beyond the outer
edge of the disposal unit. Some sort of protective fringe will be necessary
to block infiltration around the edge of the. disposal unit or assemblage of
disposal units. A reasonable rule of thumb night be sufficient guidance; for
example the cover might be prescribed to extend at least ten feet beyond the
outer edge of the cell liner. Ordinarily it would be preferable to have a
width based on specific considerations of the site such as the vulnerability
at the edge to water infiltration into particularly permeable layers in the
site media near the ground surface. A feature addressing this concern is
-------
illustrated generally In Figure 25, but note that the unlined cell was for
LLRW and is not suitable for RCRA needs.
SLOPE STABILITY
Inclined portions of the cover may be susceptible to instability from
lateral movement. Areal landfills raised well above adjacent ground are most
vulnerable. Vertical movement may also occur and be manifested as damaging
differential settlement. This deterioration is separate from erosion, though
also concentrated on the slope. Frequently erosion and Instability occur
together, and costly repairs and modifications are needed. Careful analysis
of conditions usually reveals potential problems, which can be avoided by mod-
ification of the design. Generally and as a rough rule cf thumb, any slope
over 25 percent and height over 50 feet deserves careful consideration for
analysis of stability.
To prevent instability, the cover designer usually concentrate^ on drain-
age of water and strengthening of the system (See Slope Stability, SECTION 3).
Instability Is often localized, particularly on steep slopes, and therefore
the stabilizing features should also be localized. One of the most effective
ways of improving stability In a questionable slope Is by construction of a
strong embankment for retaining any weak materials (Figure 8). Such an
embankment can constitute part of the cover or be part of a retaining system.
The CECOS hazardous waste facility In Niagara Falls, New York, makes use of
such a stable embankment for lateral support and as a foundation for the syn-
thetic liner (Figure 26). The stable embankment circumvents the problem of
unstable cover; however, some disposal space is sacrificed.
Both surface and subsurface drainage features are used to remove water
from soil and stabilize a threatening saturated condition. Transient satura-
tion nay follow thawing of frozen sell or may result from accumulation of
Infiltrating water Impeded by a hydraulic barrier. Buried pipe drains and toe
drains In the form of French drains arc optional supplemental features. A
major consideration in using subsurface drainage features Is the extent of
long-termed deterioration such as from piping or plugging. Surface drainage
ditches have the advantage of being directly observable during long-term ser-
vice, and maintenance is simple and inexpensive.
An option for strengthening slopes is the addition of a berm to give
additional mass resistance against sliding or flowing. Berms may also provide
favorable drainage where composed of coarse, granular material, particularly
riprap. Such a berm with large open voids keeps the level of transient satu-
ration at a depressed position where it will not threaten stability.
DRAINAGE SYSTEM
The cover system must be augmented with a well-conceived drainage system
to facilitate rapid conveyance of rainwater and meltwater to basins or chan-
nels located off the cover. This emphasis follows from the general axiom that
it is best to remove as much water as possible before It can infiltrate.
Accordingly the topography and the ditch and channel designs are high-priority
items ir. ti::j IDICI svsten. f'mrt direct channels have a decided advantage in
65
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-REMOVE S^WO FROM PROPOSED TRENCH
PERIMETER FOR CARRIER WALLS
10 ft
WIN
ORIGINAL GRACE
SAND
1
10 (t
Mir;
I—I
J
CLAY ;_:..---
*-
PHASE I TRENCH PREPARATION
-REPLACE SAND WITH CLAY AND
COMPACT BARRIER WALLS
ORIGINAL GRADE -v
SAND -
A-
JL
V-CLAY
PHASE II TRENCH PREPARATION
ORIGINAL
1ft M1N.— 1
WALL SLOPE 025:1 (WIN.)
-CLAY SUMP a FRENCH DRAIN-
PHASE III TRENCH EXCAVAT'ON
ORIGINAL GRACE-
CLAY-* SUMP A
PHASE IV ADDITION OF SAND BUFFER
Figure 25. Edge feature in LLRW trenches at Barnwell
L'.RW facility (38).
66
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FlRure 26. Confining embankment at CECOS facility.
-------
conveying water off stte. Similarly steep slopes are also the most expedi-
tious routes, but the sacrifice made in greater erosion has to be carefully
weighed.
Certain strategics nay be Available early in design where flexibility
renains in the choice of type of disposal unit. In Figure 27 one arrangement
of disposal trenches provides the opportunity to develop short direct paths
for runoff to trunk channels located on undisturbed ground between trenches.
Experience at Sheffield, Illinois, indicates that even the undisturbed ground
admits infiltration from low spots (40). The same general pattern of direct
runoff channels to a system of trunk channels can be considered for large
arcal fills; however, the trunk channels may be vulnerable to long-term dete-
rioration, particularly from settlement. It may also be necessary to provide
liners for the runoff channels to prevent infiltration from the channels them-
selves. A criterion for liner clay is given in Figure 20 and the explanatory
text. Liners are also discussed along vith other structures and features of
drainage under SPECIAL FEATURES AND STRUCTURES.
EROSION MITIGAN'TS
The designer usually faces a dilenma In choosing measures to minimize
erosion. The best techniques against field erosion promote infiltration and
thus may create an even more serious problem for the cover ovei hazardous
waste. A carefully designed and effective layered cover system addresses both
problems together by limiting most infiltration to the upper layers only (see
SECTION A).
Establishment of durable vegetation is often the most effective method of
erosion control despite the dilemma noted above. Details of vegetating a
cover are provided in Section 8. Conservation techniques such as terracing
should be considered also. Ridges are created to serve as obstructions for
reducing flow velocity and erosion. Application of gravel surfacing along
gullies in cover systems has been used as a repair procedure (4(1). Similarly
gravel can be placed along potential erosion lines to resist development of
gullies before the fact.
More elaborate protection against erosion Is justified where major runoff
channels are present, particularly along the edge of the cover system. Possi-
ble infringement of channels of this nature is generally avoided in siting or
designing the 'disposal units. Occasionally, the channel may be diverted.
Wherever the problem exists or wherever extra protection is wanted, the
designer may opt for a layer of cobbly, washed st.oiie or riprap. Stone mate-
rial aust meet criteria of weight and sir.p gradation adequate to resist the
velocity surge of design storm runoff. Other techniques of armoring may also
be considered (Figure 28).
SETTLEMENT CONTINGENCY
Provisions should be made for handling settlement on the basis of a vent-
careful appraisal of the arncunt: anJ nuLurc of evtr.t-jsl cumulative settlereent:
(see Settlement. SECTION 3). Understanding the process centered within the
disposal unit allows the rate and total seti-Jcment to be estimated and
68
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RunoC f
Interceptor
Ditches
Aftivo
Trer.ch
Arrows lnilir;iLC Direction of Runoff
Figure 27. Trunk and lateral channels in surface drainage (39),
69
-------
:>*£3§?^E
. . v . ' . • 'yZ's*?,>t
l^Mmm
Figure 28. Cement-filled mnt for erosion protection at Hamilton landfill.
-------
facilitates the plans for long-term monitoring and the planning fcr mainte-
nance and possible repair.
The appropriate design provisions may amount to thic'.ening the cover or
its important elements such as the soil hydraulic barrier. Thickening pro-
vides a tolerance for preservation of the continuity of the barrier or cover
as illustrated in Figure 29. Settlement may " -en more serious for a syn-
thetic me=br£ne since the thin sheet may tear or be punctured and become
ineffective.
Evenly distributed settlement may b« accommodated in advance by increas-
ing the inclination on the ground surface so that ground slope after settle-
ment is still properly directed and adequate to achieve runoff as planned.
SPCRCfNTSLOPf
a. BEFORE SETTLEMENT
b. AFTER SETTLEMENT
c. THICKEJ^EDCOVEP BEFORE
AND AFTER SETTLCMf NT
Figure 29. Thickened cover for tolerance of settlement damage.
71
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The problems of anticipating settlement and counteracting its effect are
cost conplex where the cover crosses an assemblage of separate disposal cells
with undisturbed soil or embankments between (Figure 30). The contrasting
behaviors of such disparate -materials, especially where superimposed as in the
figure, will accentuate the differential settlement. Unmanageable combina-
tions should be anticipated and avoided ir. order to head off serious problems.
Cover at the boundary of trenches or distinct waste cells is vulnerable to
damage. Not only is differential settlement concentrated at that interface,
but also there is a tendency for voids to be left there during the backfilling
operation. This vulnerability of trench boundaries can be observed from expe-
rience ac Sheffield. Figure 31 illustrates the preferential concentration of
subsidence holes along the side of a covered trench.
BOUNDARIES
The lateral boundaries of the cover system should be distinguished as a
separate part or feature so that they do not become a liability through
neglect. The importance of the outer edge of the cover system can be made
more understandable when the edge is viewed as a feature keying the cover sys-
tem into the liner or some important part of the site media. This viewpoint
is superior to considering the boundary of the cover system as a safe place to
terminate it. Figure 32 shows one simple edge feature, a vertical clay bar-
rier wall connecting the hydraulic barrier in the cover to a clay stratum in
the site oedia. An overlapping or welding of cover membrane across liner mem-
brane is ~ore typical of the edge of RCRA facilities; Figure 33 is an actual
design for a RCRA facility in the midwest. Also note the fabric serving to
drain water blocked by the cover membrane.
A bcur.dary will also be necessary where two or more cover systems are
used or. £ single hazardous waste facility. Attention ir.vist be focused then on
the interface between systens. The problem is clarified by considering one
promising combination of two cover systems (Figure 34). The designer may
choose to supplement his use of a vegetated soil on flat areas by using gravel
at the surface on slopes. One would anticipate some long-term deterioration
of the lateral boundary between these two cover systems, particularly where
the vegetated cover lies upslope of the graveled cover. Fine-grained parti-
cles in the vegetated soil will continue to be washed i.nto the relatively open
space of the gravel. Both cover systems will suffer a diminution of their
effectiveness along the boundary.
Careful attention by a knowledgeable engineer should produce options for
reducing long-term deterioration. Figure 35 shows a feature that has been
used upslcpe of riprap. Another option recommended for consideration is the
placement of an inexpensive fabric along the interface to block the migration
of fines (Figure 34). The ultimate deterioration of the fabric should be suf-
ficiently delayed (over a period of tens of years) to pernit a degree of self-
stabilisation, as by the establishment of permanent vegetation. Even in a
dereriorated condition, the fabric should continue to function favorably for
an indefinite period.
72
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COVER SYSTEM (PROJECTED)
SOIL DIKES
Figure 30. Extreme contrae*'ng conditions possible within
cover foundation (waste cells).
Figure 31. Subsidence holes (solid symbols) at Sheffield
LLRW facility (AO).
73
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CUTOFF
Figure 32. Clay wall connecting cover into low-permeability stratum.
10 Feet
SYNTHETIC MEMBRANE
SYNTHETIC FABRIC
PERIMETER
DITCH
-:-:-x-:-:-_-:-NA"fORAL GRAY AND BROWN
Figure 33. Design for overlap of membrane at edge of waste cell.
-------
FILTER FABRIC
v^i&^tttWW^&S SAND ;£;%%£
Figure 34. Boundary feature between two cover sections.
BACKflLL
CL I743i
06m RIPRAP
0 15 'a COAHiE FlL TER
\— 0 /5»> FINE fltrf-R
Figure 35. Filter feature separating riprap from adjacent material
upslope and at depth (Welland Channel Relocation,
St. Lawrence Seaway Authority, Canada).
75
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SPECIAL FEATURES AND STRUCTURES
It Is sotetlmes advantageous to consider special features as a separate
part of the design. Some redundancies may arise since special features may
also be considered more directly in addressing certain cover functions such as
drainage. Corsideration of special features listed in Table 17 is recommended
regardless of redundancy.
Surface drainage channels function to maximize runoff without appreciable
erosion. Infiltration is most effectively reduced or prevented by a channel
lining of concrete, clay, asphalt, or synthetic material. Grassed waterways
and channels are much less effective sometimes because the appreciable infil-
tration which they facilitate works contrary to the overall design. A major
problem with all surface runoff channels comes in assuring that longitudinal
continuity and gradient are maintained. General or differential settlements
discussed under SETTLEMENT CONTINGENCY can disrupt a channel and make it
ineffective.
TABLE 17. SPECIAL FEATURES IN COVER DESIGNS
Culverts Gas vents
Grnde stabilizers: Subdrains (e.g., plastic pipe)
Chute spillways Sump and collectors
Drop spillways
Pipe spillways Slurry walls
Drop Ir.lets
French drains
Liners:
Monitoring ports or access
Grassed waterway
Clay liner Pads
Gravel liner
Hard liner Tree wells and islands
Floodvays and diversions Sediment ponds
Subsurface water drainage features can serve in a capacity similar to
surface drainage features. In fact, the areal pattern or layout of one system
may partly superimpose on the other. In both cases, gravity drainage to lin-
ear depressions Is the essential process. Subsurface drainage features may
consist of linear gravel bodies filling trenches. Perforated drain pipes may
facilitate the drainage process. Such subdralns are routinely Installed along
highway bases vhere drainage problems are anticipated (^2). Subsurface drain-
age features usually require a filter wrap to prevent clogging, which other-
wise may abnrr a long service life. Vhnre a choice is necessary, a surface
-------
drain" ;e system is usually preferable to a subsurface drainage systen.
features are easier to monitor, evaluate, and repair.
Kev
Gas vents and drains are somewhat similar to water drains (Figure 36) but
tend to drain upward rather than downward and may be situated relatively high.
A feature preventing access of surface water must be included. Most RCRA
facilities generate very little gas.
DITCH SLOPED
TO DHAIN--
'GAS VENT
SLOPE
SAND OR GRAVEL
DRAIN SLOPED TO DISCHARGE'
ITREA TED IF HECESSARY!
Figure 36. Gas venting trench (43).
French drains and cutoff walls are special large features that are avail-
able for consideration in modifying a pattern of subsurface flow. French
drains are commonly used as toe drains to facilitate drainage of subsurface
water and improve slope stability. A major French drain has been used effec-
tively at Oak Ridge (Figure 37). Cutoff walir of soil of low permeability can
block and divert percolating water as a part of the drainage systen. Subsur-
face water might be blocked by such a feature and diverted to a subsurface
drain (Figure 38). Walls may be constructed using slurry (44) or by compact-
ing soil in a trench or by construction as an Increment of the overall system
at the time of cover placement. Another possible form of cutoff wall i«; shown
In Figure 25 where the wall keys the cover system into a suitable stratum in
the site media.
Other special features that conceivably will be needed at hazardous waste
facilities are two-dimensional pads for vents, shelters, and shrubs or trees.
The cover designer will have to anticipate these eventual needs and provide
the necessary technical details for proper integration Into the cover system.
Emplacement after construction of the cover may be acceptable or maybe even
77
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^~y&*yM
=<^\i' \; '
--X\. j-A ' i _ v '',
' ,^ >\ ^
\ *^^~ ' ,
,\*•'/<•' ;
CONTOUR 'f:T-:-.
Figure 37. French drain for controlling seepage at Oak
(fron Oak Ridge National Laboratory).
preferable in some cases, but elsewhere, and probably more commonly, such
retrofitting will introduce discontinuities and weaknesses into the system.
It is common practice in establishing monitoring holes in undisturbed media to
proviu= a concrete collar with wide flange at the ground surface to prevent
leakage of surface water down the borehole. The installation of such a roni-
toring feature through a cover and into the waste disposal unit will be con-
siderably more conplex if much settlement is possible. Sone sort of
telescoping collar might be necessary to accommodate the ultimate settlesent.
78
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190
180
17U
1 fil)
' ••><>
1 40
no
Uil
- I
oc
LU
Q
o
cc
a.
ac
Lil
2/VO HIGHEST RECORDED
FLOOD LEVEL I93G
EL 172
--INTEKGFDDED RIVL-R
SIL rS AND SAND
FINE TO MEDIUM SILTY SAND
. HIGHEST KECORJED
FLOOD LEVEL-ISO^
EL 176
BACKFILL WITH EXCA VA TED
ORGANIC SOIL AND SAND
TOP OF INNER DIKE
EL 17.1
/- FINAL
/ COVER
I '////. CELLS Of BURIED
i^v/ ;'• /'.,; n E F USE ;, -:
>/,W>£/? VIOUS BEN TON ITE '-'/'//// ''•''/''.•
& SOIL WALL & DlKE^y///.''////,-
VARVED SILTY CLAY •
Figure 38. Cutoff wall and dike for excluding seepage
(uicJlfi<-J from Rjferciici. 45).
NONTECHNICAL CONSIDERATIONS
Nontechnical aspects that may affect the design of the cover system are
concerned with aesthetics, convenience, work safeguards, snd the eventual use
of the cohered area. Careful consideration should be directed to the mid-term
and ultimate conditions at the site. If the site is to be returned to a
natural-like condition, there may be a benefit in contouring to a natural con-
figuration. On the other hand, it may be advantageous to form the surface in
an orderly and unnatural configuration attracting attention perpetually into
the future.
Where some beneficial use of the land is anticipated, that use should be
manifested in the cover design. Conceivably a disposal facility should serve
another purpose after closure and termination of license, e.g., for storage of
equipment and goods. The requirements and use of a storage area then would
have to be generally compatible with the cover design and its expected opera- .
tion, and vice versa. The need for large flat areas for parking vehicles or
for storing pallets would substantially affect the design of the c" -/r.
Again, the focusing on future use and continued serviceability of the cover
79
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should head off problems otherwise resulting from uncertainty about require-
ments decades in the future.
Final considerations falling between technical and nontechnical come in
the ever-present concerns for. job safety and for general environmental
safeguards.
80
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SECTION 6
COVER CONSTRUCTION
Workable cover designs must be implemented through appropriate construc-
tion techniques. Important tasks in construction are excavation or borrow,
material preparation, placement, compaction, and installation of special fea-
tures. Guidance on accomplishing these and other tasks ia provided in the
following paragraphs.
EQUIPMENT SELECTION
The choice of equipment for construction of the cover system is sometimes
intentionally limited to units readily available on site and therefore appear-
ing to be most cost effective. Otherwise, the contractor may select or adapt
equipment for each task fron a great variety. Major construction tas'.cs with
corrasponding equipment are as follows (Figure 39):
Tesk Equipaent
Materiel exccvctlon, nixing, and loeding scraper, loader, dozer
Material transportation truck, scraper, front
loader
Layer placenent grader, scraper, crane,
dozer, front loader
Layer compaction compactor, dozer
In selection of equipment for various jobs or combinations of Jobs, heavy
reliance is occasionally placed on descriptions from equipment manufacturers.
It thus remains for the designer as well as reviewing officials to recognize
and separate intrinsic characteristics among promotional clains.
Where the covering is accomplished by the site operator, there will be a
strong Inclination to use equipment already available. For some routine oper-
ations, these basic units often Include medium-size dozer, front loader, fork
lift, and crane. A major task then becomes the utilization of these units in
th/3 most effective manner.
The excavating, mixing, and loading operations in the schedule of con-
structing a cover are usually conducted on a small scale in comparison to
81
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•i
en
ro
FRONT SHOVEL
BACKHOE
TOWED SCRAPER
WHEEL LOADER
m
TRACK-TYPE LOADER
MOTOR GRADER
TRACK-TYPE TRACTOR
LANDFILL COMPACTOR
v.
;4
WHEEL-TYPE TRACTOR
EARTH COMPACTOR
Flguie 39. Construction equipment for waste disposal.
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operations for large earthwork such as highways or dam embankments. This
scale constraint tends to affect the selection and use of the equipment in
turn. Specialized equipment for large-scale excavation such as large power
shovels is not feasible on a cost-benefit basis. Versatile meclum-size front
loaders, can be used to excavate, tcir, load, and even transport materials.
The skillful contractor considers power, bucket slr.e. and similar characteris-
tics In determining the proper equipment.
Front loaders are particularly efficient on stockpiled material. An ini-
tial rough mixing nay be achieved by alternating increments from component
stockpiles in the process of loading. Mixing may also be accomplished by com-
bining the component stockpiles with a dozer prior to lending. Mixing accom-
plished at the loading site, however, should be followed by additional mixing
during placement of the soil in the cover system. A routine procedure will
have to be established early in the initial operations or on a test section to
ensure that components of a blended soil have not remained segregated here and
there in the cover.
Transportation of soil from the scurce to the site of construction is
accomplished by trucks or scrapers. Where public roads are Involved, trucks
will be the only reasonable means. Frequently, a stockpile adjacent to tha
disposal units will be established, so that the vehicle from offsite is not
necessarily the sair.e one that carries the naCerial to final placen?nt. One
advantage of an intermediate stockpile is the opportunity for additional
mixing.
A najor criterion for proper placeaent of a layer is preservation of the
condition of the Icyer below. This r.ay dictate that the equipment has light
contact pressure such as achieved with wide dor.er tracks. Wheeled vehicles
tend to rut. A technique that helps to protect the layer balow is utilization
of a front loader or other extendable unit to minimize crossings on the com-
pleted layer by limiting the equipment to the area well back on the incomplete
layer.
A crane (Figure 40) is ideal for remotely depositing soil in a position
for spreading. Then only the spreading equipment and laborers traverse the
cover. Cranes are probably limited by their reach to trench operations, but
they may already be available for utility in handling waste and in backfill-
ing. Backfilling around waste is very effectively accomplished with a crane,
and where this backfill merges upward to a foundation for the cover systea,
placement with the crane nxay be a key task of the construction of a cover sys-
tem. Dozers are ideal for spreading and are commonly preferred.
Equipment available for compacting is diverse but generally falls into
categories of smooth rollers, tamping rollers, impact rollers, and vibratory
rollers (Table 18). The sheepsfoot roller is a tamping roller that has
received extensive use and universal acceptance 'tn enbanknent construction,
but its use in cover compaction needs to be preceded by an evaluation of
effects on layers. The steel feet produce kneading action in the compacted
layer and may disturb the layer below as well. Obviously, a thin barrier
layer or membrane may be damaged by excessive disturbance. Sheepsfoot rollers
may be ideal for compacting the backfill and foundation below the subgrade
83
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TABLE 18. COMPACTION EQUIPMENT AND MF.THODS FOR GENERAL EARTHWORK
Equipment
type
Sheepsfoot
rollers
Applicability
Fine-grained soils
or dirty coarse-
grained soils
Compacted
thickness,
in.
6
Passes* Dimensions and weight*
4-8 Foot contact area 5 to
14 in. Foot contact
pressures 50 to
500 psi
Rubber tire
rollers
Smooth
wheel
rollers
Vibrating
baseplate
compactors
Crawler
tractor
Clean, coarse-
grained soils
Fine-grained soils
or well-graded,
dirty coarse-
grained soils
Wp.ll graded sand-
gravel mixtures
Fine-grained
soils other than
embankments
Coarse-grained
soils
Coarse-grained
soils
10 3-5 Inflation pressures
of 60 to 80 psi.
Wheel load 18,000
to 25,000 Ib
6-8 4-6 Inflation pressures
exceeding 65 psi for
fine-grained soils of
high plasticity. For
uniform clean sands or
silty fine sands, use
large tires at 40 to
50 psi
8-12 4 Tandem-type rollers
for base course or sub-
grade. 10 to 15 ton
weight; 300 Co 500 Ib
per lineal ir.ch of
width of rear roller
6-8 5 3-wheel roller weigh-
ing 5 to 6 tons for
soils of low plasticity
to 10 tons for soils of
high plasticity
8-10 3 Single pads dr.d plates
should weigh no less
than 200 Ib
10-12 3-4 No smaller than D8
tractor with blade,
34,500 Ib weight, for
high compaction
*For compaction to 95 to 100Z Standard Proctor maximum density.
84
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Figure 40. Crane operating as a dragline.
(Figure 13). It is recommended that compactors designed for compacting vaste
be avoided unless careful consideration and validation by test section demon-
stration have been accomplished.
Smooth rollers and tire rollers appear to have advantages in construction
of layered covers because they cause less disturbance other than densifica-
tion. -The simplest rollers are towed by tractor; more advanced models are
self-propelled. Weight is increased or decreased with ballast. Smooth-wheel
vibratory rollers are preferred in general earthwork for cohesionless (granu-
lar) soils.
85
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Numerous types of tractor-drawn equipment are available for scarifying
the surface to improve bonding with the next lift or layer above. Methods are
discussed under Interface Treatment. Rakes with short teeth may be custom-
made, or a type of farm harrow may be purchased. The depth of penetration
should receive considerable attention to ensure that the benefits of previous
compaction are not lost.
Water spreaders ere needed for increasing the water content in the pro-
cess of compaction. A tank truck with distributors for spreading water evenly
may already be available on the site for dust control. Alternatively, a con-
tractor eight have or be able to lease one.
Special tools and machines are available for establishing vegetation on a
cover. By contracting the vegetation work, the operator circumvents the ques-
tion of equipment needs, and this option will be favored by some. Harrows
loosen soils at the ground surface. Fertilizer and other additives are incor-
porated by disking or tilling or can be spread as a liquid. Kydroseeders
accomplish the fertilizing, seeding, and mulching at one time, and this equip-
ment is preferred by many contractors specializing In vegetation of disturbed
lands. However, some specialists feel that better results are achieved where
seeding is accomplished separately with drill seeders. Similarly, equipment
for crimping or punching straw mulch into soil gives a more durable surface
protection in the usual application. The thickness of the vegetative soil
layer and sensitivity of underlying courses may constrain the choice of soae
equipment.
MATERIAL PREPARATION
Blending
In circumstances where two or more materials must be blended, several
options are available. When the materials occur as strata one above the
other in the same borrow pit, excavation by shovel can sometimes blend them
together with little extra effort or expense. Construction control in this
case will.require maintaining the height of cut to obtain the necessary pro-
portions of each type of material and to assure that the two materials are
intermixed. Satisfactory mixing can be accomplished with dragline excavation,
but greater attention must be given to this operation since the tendency will
be to remove material in horizontal cuts. Several special types of excavating
equipment have been developed such as wheel excavators and belt loaders, which
have excellent capabilities for blending from vertical cuts.
When scraper excavation is used, the difficulty of securing a satisfac-
tory mixture is increased, and It is often necessary to provide supplemental
mixing on the fill by disking or blading. Excavation is performed by making a
slanting cut across the different types of soil, and care must be exercised to
secure the proper proportions of each t>pe in each scraper lo£d.
This discussion on blending Is in part from the Bureau of Reclamation (29)
and the Department of the Navy.
86
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Considerations of cost limit the procedure for blending soils from sepa-
rate sources. One of the soils may be stockpiled upon the other so that
loader cuts cs- he made across the two. Soils may be placed in thin layers on
the fill and tr .. .aixed by blading or similar manipulation before being com-
pacted. The correct proportion in terms of depth of the fine soil is usually
placed first, then the correct depth of coarse soil. The blending then fol-
lows. In this way, any remnant of the lower soil unaffected by blending con-
sists of the finer material rather than being coarse material more vulnerable
to percolation. Mixing plants are the ultimate though most expensive option
to obtain an intimate mixture.
The specifications for placing soil included in Appendix B illustrate how
three methods of mixing have been described in contracts, in this case for
construction of granular subbase for flexible road pavement.
Modification
Soil may also be modified with relatively minor amounts of additives
such as lime, cement, asphalt, and salts. Bentonite is coccconly considered
for improving the effectiveness of hydraulic barriers. Generally, the use of
modified soils may be considered in lieu of replacing poor soil*) with selected
material from a distant source. For example, the use of lime to moderate the
expansive characteristics of a clay soil from immediately available borrow may
be satisfactory and more economical than importing special material.
Conventional methods are usually used to place and coepact modified soil,
but special equipment and procedures are sometimes needed for mixing the addi-
tive. Special tests of the nodifled soil may be required to verify the amount
of additive, and visual observations should be made to ensure thac the addi-
tive is uniformly distributed. Construction control testing of placement
water and density is alao usually required (SECTION 7). After initial cali-
bration, periodic checks during construction will ensure satisfactory results.
For soil-cement and soil-bentonite mixtures, a stationary mixing plant
-------
SOIL PLACEMENT
The primary objective of placement operations is to distribute the soil
evenly and to the prop?"; thickness. .A relationship between the bulk thickness
as placed initially and the final thickness after compaction should be estab-
lished early in the operation so that compacted thickness will not be found
later to be deficient. This relationship is ideally determined in a test sec-
tion (See TEST SECTION).
Secondary objectives of a carefully managed placement operation are to
preserve the integrity of the layers situated below and to complete the homog-
enization or nixing process initiated in the borrow pit or at the stockpile
(Also see Blending). Preservation of the integrity of the layer situated
immediately below la especially critical. A relatively thin hydraulic barrier
can be seriously damaged by cracking or shearing if traversed excessively by
equipment constructing the layer above. It has been stated that placement of
soil to protect a membrane, a related procedure frota general earthwork con-
struction, requires hand manual labor (5). A fine mesh geogrid placed on the
vulnerable layer and removed later msy alleviate come traffic disturbance and
prevent contamination with debris (6).
One basic method of soil placement is by dozing from a pile at the edge
of the cover or in incremental piles across the cover. Tht sequence for such-
an operation starts with placement in piles distributed linearly along the
edge. The soil is then spread invard normal to the edge to form the proper
bulked (precosipactlon) thickness. Then the next linear pile is deposited at
the edge of the portion of the cover that is yet uncovered. Vehicles with
broad wheel or track surfaces are most suitable in traversing the newly spread
cover layer since they exert less ground pressure and are less likely to rut.
Upon obs«?tvstion of rutting of sufficient depth to defonn critical cover lay-
ers or foundation, a change in vehicle may be necessary.- By careful planning,
supervision, and inspection, the equipment passes across any portion rf the
cover can be kept to a minimum and reasonably uniform. Alternatively; these
traverses taay serve as a part of the compaction routine.
Where a crane is available, the layer material can be distributed in
piles across the area. The approximate volumes needed to achieve the desired
bulked thickness are distributed accordingly. This might facilitate the final
spreading, which then would amount simply to smoothing out a hummocky surface
of many separate piles.
It is anticipated that most cover systems will be completed in layer
increments, and guidance above is so directed. However, the cover may also be
completed in areal increments (Figure 41). Such area! subdivision nay be
necessitated by long tine intervals of exposure between increcants, or the
plan may provide more efficient use of the equipment, personnel, and material
flov. For example, a cover eight be completo-d in long strips flanked on one
side by the foundation of backfill r.ud on the other side by the completed and
seeded cover somewhat like strip mining of shallow coal. Such a procedure of
construction in strips would usually present substantial difficulties in
attaining layer continuity across the temporary boundaries of the strips. For
covers of only one or two layers, this interfacing problem might be
88
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a. AREALINCREMENTS
1 .
r
\
A
CO«Tff ir^lf ft COtfltfluCffON
SI AGE 3-5 (NEXT)
b. DELAYED PLACEMENT
Figure 41. Construction of cov<;r in areal increments versus
all at one tine.
subordinate when compared with advantages of cost or efficiency inherent in
the areal increment plan. A demonstration of feasibility in a test section
would probably be essential (See TEST SECTIOH).
SOIL COMPACTION
Depending on design requirements, SDil layers are constructed to one of
the following conditions:
a. No special compaction—as for the vegetative layer.
b. Equipment-traversed—emphasis on routing the haulage and spreading
equipment evenly.
c. Compacted—emphasis on special rolling to achieve compaction.
This section mostly describes the methods for c above. Note throughout the
marked distinction between procedures for fine-grained soils and those for
granular soils.
Compaction is usually described in terms of compacting equipment, water
content, load applications, and density results. General equipment types are
discussed under EQUIPMENT SELECTION'. Because the compaction process involves
a physical manipulation of a variable natural material, engineers depend heav-
ily upon widely accepted procedures based on past experience.
89
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Test Criteria
It is explained in this section and in Section 7 how tests are essential
for predicting conpaction results as well as for comparing field density
achieved to that desired. Tables 11 and 19 list compaction tests along with
other tests used in design and construction. Notice the distinction between
the tables: design tests versus construction tests.
TABLE 19.
CONSTRUCTION TEST
METHODS
Name of Test
Water Content
Unit Weight
Standard or
Preferred
Method*
ASTM D2216
ASTM D3017
AASHTO T217
ASTM D1556
ASTM D2167
ASTM D2922
ASTM D2937
Properties or
Parameters
Determined
(Oven dry)
(Nuclear)
(Calcium carbide)
(Sand cone)
(Rubber balloon)
(Nuclear)
(Drive cylinder)
Remarks /Special
Equipment
Requirements
Thickness
Surface and
Layer
Seam Integrity
Resistance
Permeability
ASTM D1558
ASTM D3385
Desig. £-36
Linear measurement
Visual examination
(Air lance)
(Vacuua box)
Needle penetration
Infiltration rate
Shallow well
permeability
Direct visual
Important; with or
without proof
rolling
Direct visual
Also for water
content
Approximates
permeability
Reference 29
Note: Design-oriented tests in Table 11 are sometimes needed also.
* ASTM: American Society for Testing and Materials
AASHTO: American Association of State Highway and Transportation
OfficiaTs
Compaction decreases permeability and increases strength of soil as a
result of the densification. The field compaction is planned from the results
90
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of laboratory compaction tests. In critical layers such as hydraulic barri-
ers, the coefficient of permeability may be addressed directly, and accord-
ingly, the density necessary to achieve the desired permeability can be
explored and established by a'series of permeability tests on specimens COE- •
pacted to different densities.
The laboratory compaction procedure is intended to simulate the compac-
tlve effort anticipated in field construction (Figure 42). A standard 25-blow
compaction test (Table 11) is used to simulate field compaction of fine-
grained soils in routine foundations and embankments (Figure A3). Another
"standard" compaction test may be prefetred but, once selected, should remain
the same for subsequent comparisons. Laboratory compaction is also reflective
of sone solid waste cover compaction, or it may be appropriate to adjust for
lower compactive efforts. Five- and fifteen-blow tests are similar to compac-
tion on municipal solid waste. Compaction tests are made on the soil at vari-
ous water contents to establish a relation between water content and dry unit
weight after compaction. Generally, five specimens should completely define
the compaction relation.
Numerous procedural details are potentially inportant, making it essen-
tial that testing be conducted by experienced technicians or in certified lab-
oratories. For example, it is sometimes impovtant to store the prepared soil
in an airtight container for a sufficient length of time to permit absorption
of water (Also refer to ASTM D 698).
The results of compaction tests are presented in the forra of a coiapaccioc
curve on a plot of dry densities (dry unit weights) versus the corresponding
water contents (Figure A3). The plotted points arc represented with a smooth
curve; for moist fine-grained soils, the curve approaches a parabolic form.
fc. 130,
«J
a.
o
_J
COMPACTED AT A WATER CONTENT OF 8 PERCENT
\-.
O 100
t. 1^1?
u
-------
no
10 15 20 25 30 35
MOISTURE CONTENT
IN PER CENT DRY WEIGHT
Figure A3. Results of standard compaction tests on sand and other soils.
The water content at the peak of the compaction curve Is designated the opti-
mum water content. The dry density of the soil at the optimum water content
is the maximum dry density. The zero air void curve represents the dr> dens-
ity and water content o* the soil when completely saturated with water.
Sand has a different response to compaction over a range of water con-
tents (Figure 43). The degree of compactness of such coheslonless (granular)
soils 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 measuring container. The upper
limit at 100 percent relative density is reached by tamping and shaking down
to a minimum volune. Refer to Table 11 for the standard procedure.
Some geological materials respond to compaction atypically. Figure 43
shows that sand may exhibit no maximum on the conipaccior. curve. The anomalous
behaviois of some overconsolidated soils was mentioned under Geological Media
(SECTION 2). Materials previously subjected to large natural overburden loads
or to cementation have gained an a-idltional increment of cohesive strength,
but they may degrade and change during placement and compaction. Residual
soils including extreme types, such as laterltlc soils may also be strengthened
raetastably. In any case, the testing for these soils should realistically
92
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reflect the planned compaction process in order to avoid misleading test
results. It is partly fori this r-eason tthat a different soil specimen is used
for each compaction test point in standard practice rather than varying the
water content on a repeat which may have degraded.
Water Content
Natural water content of soil often approaches the optimum for compac-
tion; therefore, it may be unnecessary to nodify the water content. Where
compaction tests indicate, however, that the natural water content is not
appropriate to satisfactory 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 ac appropriate later when used.
For fine-grained soils, field compaction sometimes achieves maximum dens-
ity at a water content somewhat greater than optimum indicated by a comparable
laboratory compaction test, and it is sometimes specified that departures from
optimum water content be on the wet side. This departure has been shown to
reduce permeability in the laboratory. Compaction on the dry side may he
appropriate with swelling soils since the water imbibed later should promote
further swelling and work aealnst the formation of cracks (px'-ept at the
ground surface). Field tests as described under TEST SECTION are suited to
exploring such construction details. However, since the appropriate water
content impacts on design, it would be best to resolve any question well
before the start of construction.
One may estimate optimum water content by wetting fine-grained 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. For pervi-
ous granular soil the conventional practice is to add water in abundance, but
for cover layers positioned directly on the waste and below a synthetic mem-
brane, a modification may be necessary to avoid wetting the waste cell below.
When large amounts of water are required, it nay be more efficient to add
most of it at the point of.excavation with only supplemental sprinkling after
the layer has been spread. Mixing and curing after sprinkling may be
required to produce a unifort. water condition throughout the layer before com-
paction can proceed. Inspection of uniformity should be made by sampling the
loose layer frequently just prior to compaction. Unless otherwise specified,
optimum water requirements should be enforced even though the required density
is obtained at other water conditions also. Adverse permeability properties
may result if the placement water is too low, and adverse shear properties may
result if too high. Thornfore, the inspector should be prepared and author-
ized to require application or removal of water. Control of pervious granular
soils includes visual inspection for free-draining characteristics and
uniformity.
The discussion on inspection control in this and the next two paragraphs Is
largely from the Bureau of Reclamation (29).
93
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The adequacy of the compaction and watar additions is monitored by field
density tests In conjunction with compaction control tests for clayey and
silty soils, or relative density tests for pervious sand and gravel soils
(Tables 11 and 19). Unless otherwise specified, the minimum acceptable dens-
ity is 90 percent maximum density (by standard test) for the minus No. 4 frac-
tion of clayey and silty soils and 70 percent relative density for the minus
3-inch fraction of pervious sand and gravel soils. With soils which are bor-
derline, between fine-grained soils controlled by the compaction test and
granular soils controlled by the relative density test, control may be based
on the criterion which produces the higher unit weight.
Number QJ Passes
The energy input which determines the density achieved by the compacting
process is increased by the number of passes of the equipment. Thus, while
the soil density actually achieved is the determining criterion, the number of
passes or coverages can be used as another parameter for estimating appropri-
ate compaction provided water content is right. Figure 44 shows how a family
of field compaction curves can be developed to quantify the effect of number
of passes in terns of dry density. The strengthening effect of compaction, in
farms of the California Bearing Ratio (CBR), is also illustrated. The compac-
tor was a sheepefcot roller, but similar compaction curves have been developed
for dozers (2) and for a tire roller (Figure 45).
Table 18 shows the approximate number of passes for intermediate sizes of
five types of compactors, i.e. appropriate for achieving 95 percent of naxicum
density as rspresented in a laboratory compaction test. The tabulated esti-
mates may be viewed as a consensus among construction organizations in a very
general way, but they should not he regarded as more than useful first approx-
imations. Better estimates can be obtained from equipment manufacturers, past
experience, or field tests.
The similarity in the number of passes necessary with a sheepsfoot roller
and with a tire roller may be surprising in view of the fact that the two.
types are quite different from one another. A tire roller covers an area com-
pletely in one pass. On the other hand, the sheepsfoot roller creates con-
centrations of stress only on the increments of area beneath the feet
(Figure 46). Accordingly, numerous passes of a sheepsfoot roller are needed
for a full coverage of an area. This contrast deserves little further consid-
eration in view of the fact that the two types of rollers compact in different
ways. The difference is illustrated dramatically in the next section where
attention is focused on lift thickness.
The designer should always have an appreciation of the effect of Increas-
ing the number of passes cince it is common in earthwork to specify a minimum
number of passes within the specifications. Such prescivptive directions may
It is recommended that "pass" or any comparable term such as "coverage" be
defined carefully, since meaning has varied in the past. Such past ambiguity
has occasionally resulted in contract disputes in general earthwork.
94
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WATEH COKTEMT IN PEB CENT OUT WEIGHT
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WATER CONTENT IN PER CENT DRY WEIC«T
I3O-PSI TIRE PRESSURE
Figure 45. Effects of number of coverages by tire roller.
HIGH STRESS
VOLUME
SHEEPSFOOT ROLLER
MODERATE STRESS-
VOLUME
SMOOTH ROLLER
Figure 46. Stress concentration in compaction.
96
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even be added to specifications otherwise emphasizing performance. In consid-
ering the guidance in Table 18, the designer may want co make adjustments for
differences in soil type. More passes may be necessary In poorly graded soils
in comparison to well-graded soils. However, it has been observed that sand
sometimes responds adversely to increased compaction by becoming less dense
beyond a certain point. Vibratory compactors overcome this problem, but their
suitability for solid waste management is not generally established.
Lift Thickness
Cover layers or courses exceeding about 6 inches thick should be con-
structed in lifts or increments to achieve the intended design. Certain sim-
ple guidance based on experience can be used in regard to appropriate lift
thickness. It has been found that loose lift thickness should not exceed the
length of the feet when compacting with a shecpsfoot roller. Otherwise, there
is the likelihood that the feet will fail to reach the lower portion of the
lift, and lew densities will remain there. In marginally thick lifts there
may be a tendency for local bridging to take place leaving small pockets of
low density at the base. In a highly simplified explanation, not universally
accepted, a sheepsfoot roller compacts from the bottom up so that eventually
the entire thickneso reaches a high density. The roller tends to "walk out"
as the compaction zone moves upward in the lift, and ultimately, only a thin
surface layer remains uncompacted.
A major disadvantage of a sheepsfoot roller 5.n cover construction comes
in its potential for damaging the layer being compacted or even affecting the
layer below. If the underlying layer is a relatively thin hydraulic barrier,
serious damage may result from the punching action of the feet. As long as
this threat is not overlooked but instead is carefully addressed, no problems
are anticipated. Of course, careful consideration may lead to the choice of
another type of roller.
The effect of lift thickness in compaction with a tire roller is substan-
tially different in that the densificatlon is concentrated at the ground sur-
face. This effect is illustrated in Figure 47 based upon tests specifically
to clarify this phenomenon. The curves represent conditions at four depth
intervals in 24-inch lifts. The top curve is for densities developed in the
top 6 inches. The high density at the surface results from the concentration
of stress there as is the case for any surface loading. In contrast, the
sheepsfoot roller punches to depth and achieves a stress concentration there
and for a given stress on the ground surface and other factors constant the
same density results regardless of lift thickness. Lift thicknesses of 6, 12,
and 24 inches have been studied. The decrease in density with depth in the
thick lift shows clearly that individual lifts must be fairly thin in order to
approach high density throughout a cover layer.
Special Methods
Slope compaction--
Compaction on a slope constitutes a special procedure that deserves spe-
cial attention. Such compaction is routinely done, e.g. in constructing clay
97
-------
3
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LU
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Z
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90
LIFT
24 IN.
90-PSl RUSBER-TIRED ROLLER
8 COVERAGES
I
0-6"-
^ A
/
/
XI
*'"•"
10 15 20 25
WATER CONTENT IN PER CENT DRY WEIGHT
NOTE: FIGURES ON CURVES INDICATE
DEPTH BELOW TOP OF LIKT.
Figure 47. Density variation under surface loads such as tire rollers.
liners for-irrrigation canals, but certain problems may arise when the contrac-
tor is inexperienced. Compaction can be accomplished by rolling either paral-
lel or perpendicular to contours. Figure 48 illustrates how a relatively wide
compactor can be used by inclining the lifts obliquely across the layer.
Alternatively 'the lifts may be kept horizontal and tha layer overconstructed
to be trimaod back at a later tine. Elsewhere, slopes are rolled up and down
the incline. On steep slopes a supplemental power source may be effective,
such as a winch and cable (5), and may even be necessary to avoid damage where
traction is difficult.
Proof rolling—
Proof rolling is sometimes used to test a road subgrade and accordingly,
might be considered also for checking the adequacy of the foundation below a
cover system (BUFFER LAYER OR FOUNDATION, SECTION 4). As applied in highway
and airfield runway construction, a roller traverses back and forth over the
98
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»r>r«pfoo< rolltr
Figure 48. Compacting constraints on sloping layer
from experience in canal construction.
compacted soil, and an inspector follows closely to watch for soft spots.
With packaged waste and other irregularities lying at shallow depth below a
waste cover system, proof rolling would help in giving much-needed assurance
that the foundation is reasonably sound. Weaknesses appear in the form of
concentrated rutting or evidence of wet spots or weaving plastic soils. The
presence of differentially settled areas or patches of wet or plastic soils
will necessitate careful consideration of the need for replacement or for
addition of a buffer of select soil.
Example specifications for proof rolling highway subgrades are shown in
Appendix B. Of course, proof rolling procedures for highway construction ara
not fully applicable to construction of cover systetus. Some sinplifIcatior.
will probably be warranted, especially in choice and use of the roller unit.
Soil-cenent compaction—
Compaction of soil-cement is usually required to he completed within
60 minutes after spreading and no more than 30 minutes between operations.
Compaction for embankments with 6-inch compacted lifts is accomplished in at
least six passes of a sheepsfoot roller folloved by at least four of a tire
roller. A separate procedure would be needed in the construction appropriate
for cover systems. The roller should have provision for ballast loading so
that the weights can be adjusted to provide the best compaction. After com-
paction, the compacted layer or lift is cured by keeping the exposed surfaces
continually moist using a fog spray until the overlying or adjacent layer is
placed or for a minimum of 7 days. A blanket of moist soil may be used for
permanently exposed surfaces. The surface of the completed layer may require
brushing just before initial set and just prior to constructing an overlying
layer.
Small-space compaction—
Special methods are required for compacting in small spaces where the
usual compaction equipment cannot operate. When accomplished systematically,
as when distinguished as a separate contract Item or unit of work, small-space
99
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compaction reduces potential deficiencies In vulnerable areas — most promi-
nently, zones of high permeability with added susceptibility to piping and
settlecent. An especially vulnerable location is a narrow band above the
sides and ends of trenches (Figure 49). Vibrating tampers are among effective
devices used in such small spaces.
COVER/MEDIA
COVER- INTERFACE,
UNDISTURBED MEDIA
Figure 49. Boundary strip vulnerable to poor compaction.
Interface Treatment
The horizontal interface between layers or courses of the systea or
between lifts within each layer should be carefully reviewed for intended
function and for potential problems (Figure 50). In nost cases, lift inter-
faces are scarified or otherwise minimized to achieve a blending of the two
lifts. Each layer is designed to be homogeneous and uniform, and any horizon-
tal partings or material discontinuities between lifts within the layer simply
Introduce departures of uncertain significance. Interfaces between layers, on
the other hand, are ordinarily to be preserved as nuch as possible since they
separate layers having different functions. Soae very specific provisions
usually need to be included in specifications so that each interface is either
largely removed or largely preserved. Appendix A presents some example speci-
fications regarding scarification prior to placement of another lift.
Surcharging
The technique of surcharging can sometimes be used to circumvent the need
for mechanical compaction ii. preparing the foundation for the cover. Sur-
charging is seldom feasible however on the cover itself. The procedure is to
pile teaporarily on the backfill, embankment, or cover foundation enough soil
to accomplish a densification. As little as 5 feet of soil will have a sub-
stantial effect, and most of the effect remains after unloading. The tech-
nique is especially suited to trench disposal operations where soil removed in
trenching can be placed on an adjacent filled trench. That surcharge pile is
later trimmed down as the new trench requires backfilling.
100
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•:
••""3?
,
'
:•
I
a
.:'*
Figure 50. Poor bonding between compacCed lifts.
101
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MEMBRANE INSTALLATION
Guidance is available elsewhere (32) on design and construction of poly-
meric aembrane liners. Most of that technical guidance is adaptable to
installation of a membrane in a cover* application. A unique hierarchy of
steps contributes to Installation of polyneric membranes: production of raw
polymer components, manufacture of sheeting or roll goods, assembly of panels,
and installation of the complete membrane. These four steps may even be
accomplished by four separate organizations.
Production of the raw components and combination of those components witn
scrim and other Ingredients into sheeting are carefully controlled manufactur-
ing processes, and applicable requirements or standards can be very specifi-
cally formulated and met. Placement and seaming of sheeting after receipt
from the manufacturer are not so amenable to quantification and therefore
deserve extra attention in the preparation of specifications. Common problems
in the past use of membranes for liners and for cover are concerned with seam
failure and with puncture or abrasion during installation.
Installation of membranes proceeds in steps that can be summarized as
follows:
a. Choose suitable installation equipment. Emphasize obtaining units
for routine and special needs. Special needs are determined by bulk
form of panels (rolled or folded), membrane thickness, seaming
requirements, and bedding requirements.
b. Assemble materials and equipment on site. Give special attention to
minimizing deterioration of panels while handled and exposed in
storage.
c. Assemble and instruct work crews. Much of the placement of the huge
panels is accomplished by large coordinated crews.
d. Place the panels on smoothed soil foundation (buffer or bedding
layer). Lay strip panels up and down rather than parallel to con-
tours. Allow prescribed overlap and remove wrinkles along seam.
e. Seam with appropriate bonding or heat treatment according to recom-
mendations of manufacturer. Keep surfaces clean and dry. Most seam-
ing is completed by application of pressure over a firm base.
f. Follow manufacturer'9 instructions in sealing around penetrations
such as monitoring holes, risers, and gas venta; similarly with fit-
ted boots.
Detailed information on liners and dteps In liner Installation Is available
in technical resource document SW-870 (32).
102
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Weather conditions affect installation through-substantial effects on
material and surfaces as well as effects on productiviry of the crew. Warn
weather is most favorable. It is generally recommended th.it seaming not be
attempted during rainy periods. These adverse effects of harsh weather dic-
tate that an additional step could be interposed ahead of a-f above:
Schedule installation in the warm dry season to the extent feasible, and
make provisions for minimizing disruption of schedule by unpredictable
individual storms.
Since the installed membrane may experience considerable shear or ten-
slonal stress on slopes, a trench or other anchorage may be placed at the top
of the slope as is done with liners. Temporary anchor points (e.g. with num-
erous sand bags) are usually necessary also during installation to prevent
disturbance by wind gusts.
SEQUENCE
Flexibility in placing the cover construction within the sequence of
operations ranges be'--»een extremes. Disposal units can be covered permanently
at the earliest convenient time after filling of the disposal units. Another
option is to emplace a temporary or intermediate cover and postpone the
emplacement of a permanent cover system until the last disposal unit at the
facility has been filled and some stabilization has occurred. A third option
is to enplace the complete cover in several areal increments. In any case,
the sequence of construction must follow a well-conceived plan. The conse-
quences of leaving all or a portion of a disposal unit open to receiving water
for an appreciable period must be balanced against higher cost and other con-
sequences of covering a disposal unit in increments. Clearly, an effective
system for water collection and removal is needed in either case. Socctimec
the leachate collection systen. is used, while elsewhere sump pumps are
installed in appropriate low points. Elsewhere, most runoff can be channeled
away froti the waste cell face (Figure 51). The interrelationship of the
sequence of cover construction with other factors complicates the planning,
e.g. there nay be other reasons for covering disposal units quickly with
intermediate cover.
DIVERSION DIKE OfJ COVER-
WORKING
FACE
2 PERCENT
Figure 51. Temporary drainage during disposal operation.
103
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The main possibilities for saving cost in planning the s&quence are often
contingent upon an early formulation in the planning process while there is
still flexibility in dimensioning, positioning, and orienting-the disposal
units. Lesser opportunities for Improvement come in lesser details and may
not appear until construction is underway. Ordinarily those details of
sequence formulated at a preliminary stage by a designer or reviewer condi-
tioned to value engineering are preferred. Since a contractor building a
cover system is usually motivated primarily by profit, he may prefer and
choose an expedient sequence of construction, conceivably to £*••> detriment of
the cover system. Therefore, the sequence of construction should receive
careful consideration by a separate reviewer such as a representative of the
regulating office. Figure 41 presents a hypothetical example of effective
planning in the sequence of operations on a cover completed in increments
along the cell. The channels developed to divert water away from active dis-
posal faces may be constructed as part of the permanent surface runoff system.
This sequence avoids the necessity for superimposing a drainage system at a
later tijie by making use of operational diversion ditches.
Sequencing must also be planned in regard to day-to-day construction,
e.g., layer by layer over a unit area. Possible procedures are presented in
Figure 52. The usual method is to construct each layer of the cover over the
entire unit area. This method is optimal for layer continuity, but its large
exposed surface may be vulnerable to deterioration by water evaporation or. the
one hand, or soaking by storm events on the other. The activity of construc-
tion equipment may also adversely affect the layer condition. Careful timing
should alleviate some of these problems. It may be possible to place the
upper lift of one layer and the lower lift of the next layer above in one day
and thereby minimize deterioration along a critical interface (Also see INTER-
RUPTIONS) . The size of the unit of cover under construction also can be
manipulated to minimize interference. Figure 53 shows how the area undergoing
compaction can sometimes be kept to a minimum in cold regions (34) , in this
case to guard against damaging freezes.
TEST SECTION
Field-scale testing has proven to be among the ciost valuable aids to
earthwork construction and can be applied as well to cover construction. The
achievement of desired construction results is demonstrated usir.g the
material, equipment, and procedures previously proposed as appropriate. The
factors that may be explored include the following:
/
a. Selection of soils in the borrow area.
b. Distribution of soils on the cover to obtain uniformity.
c. Water content at placement, and its uniformity throughout the soil.
d. Water content of borrow soil.
e. Methods for correcting borrow soil water content if too wet or too
dry.
104
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CELLS 1-5
(FILLEO AND BACKFILLED)
FINAL COVER
CELL 6
I ACTIVE)
-/xxxxxl Y/xxxxl Ixxxxxxj
l/XXXXXI f'XXXXX, iXXXXXXj
vxxxxxl IxxxxxxJ Ixxxxxx)
KXXXXXI l/XXXXXi tXXXXXX
I /xxxxx! xxxxxx' 'xxxxxxf
' f'xxxxxl kxxxxxl (xxxxxxl
[-XXXXXJ f XXXXXj fXXXXXXj
f-XX/Xx! KXXXXXi VXXXXX
-xxxxxl xxxxxxl fxxxxxl
^xxxxx< ^xxxxx| ^-xxxxxj
(-xxxxx.1 KXXXXXI Ixxxxxx
I-xxxxxJ xxxxxx! k'xxxxxl
^xxxx.) Vxxxxxl jxxxxxxj
BEFORE
AFTER
a. ONETIME COVER CONTRACT
-FINAL COVER
-FINAL COVER
ixxxxx/l Ixxxxx/j
(xxxxxx!
- CF/./. J
(ACTIVE}
EARLY STAGE
/ / s S / ft ssssstY'sss* |
Ixxxxxx1 Ixx.-xxJ/xxxxx.
l/'XXXXXl |XXXXX|l/XXXXXJ
*. - - -*— *f*4J*-*fSJSJSl
XXXXX, IXXXX/ J
XXXXXJ VXXXX-I
IXXXXXXi [XXXXX4
^XX.'XX1 XX'//''1
Vxxxxxi y'/"\
C'XXX/X1 l/XXXX/l
l/xxxxxl
LATE STAGE
b. INCREMENTAL COVERING
- C£ii 6
IACTIVE)
Figure 52. Possible procedures for areal construction.
f. Compactor characteristics.
g. Number of compactor passes.
h. Thickness of lift either loose or compacted.
i. Maximum size and quantity of rock or pebbles in the material.
j. Condition of the surface after compacting.
105
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FINISHED GRADE
L*VRGE AREA EXPOSED TO FREEZING
LIFTS AS PLACED IN
'WARM-WEATHER ROLLED FILL'
VX/x\X ORIGINAL GROUND
3. IN NORMAL WEATHER
FINISHED GRADE
SMALLER AREA
EXPOSED TO FREEZING
LIFTS AS PLACED IN
COLD-WEATHER HOLLED FILL
Figure 53.
ORIGINALGROUND
b. IN COLD WEATHER
Possible variation in embankment placement in
warn versus cold weather.
k. Effectiveness of tamping in small places inaccessible or undesirable
for roller operation.
1. Vulnerability of system, e.g.. to vehicle traffic.
Though initially costly, the full-scale field demonstration is generally
considered to be highly cost-effective in the long run. The sample of the
cover system constructed in this manner can be examined and sampled and then
tested In detail. Observations made in test pits within the test fill are the
only advanced information available about complex Interactions between the
relatively thin layers of the cover system during leading by construction
equipment. In situ tests of permeability can be made here as nowhere else to
evaluate preliminarily the hydraulic characteristics of the system. The test
section also provides the engineer a chance to verify the general plan and
timing of operations. A need for subtle charges "In sequence or timing may
become evident. Finally, the results of field density tests made on the test
section will provide the necessary information for establishing construction
control procedures consistent with design requirements.
A test section (Figure 54) may be broadened from the objective of demon-
strating suitability of chosen plans to a comparison of more than one option.
In this case, the test section includes several panels where one or a few
106
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TEST AREA 1
Figure 54. Plan for test section to explore parameters of design.
parameters are considered. For example, the effect of thickness nay be
explored in panels among which the thickness is varied but other factors are
kept constant. After construction and after careful dissection, observation,
or sampling and testing, a decision can be made on the best thickness for the
cover layer. For example, it may then be evident that layers less than a cer-
tain thickness experience disruption by the compacting equipment chosen for
use. Such a finding might necessitate a modification of what had been the
tentative design in regard to thickness or equipment constraints.
INTERRUPTIONS
Construction progress can be delayed by interruptions for weather and for
labor, logistical, and administrative reasons. Anticipating the importance of
favorable weather, the contractor should organize the job to coincide with the
construction season and make special efforts and plans to avoid extensions of
work into unfavorable seasons. Workable contingency plans must also be in
place to -ninimize unexpected delays and their effects from other causes as
well as weather.'
i Among possible interruptions are labor strikes on site or within ancil-
lary industry; e.g. strikes by truckers can conceivably affect the delivery of
necessary materials. Administrative interruptions night develop fron unex-
pected difficulty in attaining the required standards of construction, e.g.
the specified degree of compaction of soil. Delays might also cotne from an
office acting in a regulatory capacity.
Rain presents problems in working with clay and silt, and the preferred
construction season may be limited to a few months. Cover can be constructed
beyond the summer time window, but the prudent planner or contractor carefully
addresses possible consequences. The -following contingency measures may
partly alleviate problems from rain during placement and compaction (5):
107
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a. Blade and smooth-roll the unfinished surface to facilitate runoff.
b. Provide operational drainage to facilitate runoff.
c. Cover the system with temporary polyvinyl chloride sheeting anchored
with sandbags.
d. Add lime and scarify to absorb ooisture and restore workability.
e. Switch borrow area or stockpile to avoid excessive watering of soil
material.
Incorporation of frozen soil into compacted .layers is generally consid-
ered to be unsatisfactory practice and should not be allowed. Cold weather
can also stiffen membranes and fabrics and interfere with proper placement.
Construction should be scheduled to avoid cold conditions and In extreme con-
ditions interrupted temporarily or terminated for the season.
When unseasonal cold snaps occur, certain steps may help In getting
through short interruptions. A blanket of str^w or soil may temporarily pro-
tect those layers of the system already in plaoe. Otherwise the near-surface
portions eventually may have to be bladed down to unaffected soil with atten-
dant risk of damage. Possible techniques worth considering to minimize inter-
ruptions for unexpected rain or freezing in cold regions are illustrated in
Figures 53 and 55.
FROZEN SOIL IF NECESSARY
v
FILL COMPACTED AS PER
NORMAL SPECIFICATIONS
\X\7-\
^— ORIGINAL GROUKD SURFACE
Figure 55. Contingency placement of frozen soil in noncrltical
areas in highway construction.
108
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SECTION' 7
CONSTRUCTION QUALITY MANAGEMENT
Basic objectives of quality management are the minimization of and com-
pensation for unacceptable construction and materials. Necessary actions are
often difficult, unpleasant, and costly. By prescribing unambiguously the
general duties and perspectives of inspectors and others participating in
quality oanageaent, such undesirable circumstances are also minimized. One
may distinguish three similar and closely related engineering control Casks
undertaken during cover system construction. The tasks of quality control,
quality assurance, and acceptance inspection or testing can have important
separate roles in the construction effort, or they can be combined.
Where RCRA requirements are to be satisfied, the planning and implementa-
tion of construction quality management should be in agreement with guidance
issued in 1986 by Office of Solid Waste and Emergency Response (46).
QUALITY CONTROL
Quality control (QC) is the contractor's way of observing, measuring,
sampling, and testing for the purpose of establishing conformance or noncon-
formance to the plans and specifications in his daily operations. QC ir.
earthwork contends with the complexity and variability of the soil materials
and site conditions, and therefore is dissimilar from QC on a product assembly
line. QC is commonly accomplished by an independent element within the con-
tractor's organization, i.e., the contractor monitors the quality of his own
work through his QC program and can adjust quickly for necessary improvements.
Thorough documentation including test results is necessary to provide the
findings of the program to other interested parties.
Table 20 lists important efforts in a QC program for cover construction.
The QC prograa is built around a selection froa this list. As one important
example one should consider the control of soil compaction.
The contractor is usually responsible for taking or arranging for the
taking of sufficient tests to e-nsure the adequacy of compaction. At the start
of compaction many tests are required to ensure that the construction opera-
tions are producing the required results. After safJ sfact ion has been
The distinctions made in this section reflect long-standing construction
practice in the Corps of Engineers but are not universally established.
Therefore, each application should be carefully defined.
10'.
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TABLE 20. IMPORTANT ASPECTS OF QC PROGRAMS
i • •
Assessment of foundation for supporting the cover system
Confirmation of soil composition, especially particle-size distribution,
including any blending
Assessment of soil placement,, including equipment operation
Assessment of buffer or other layers immediately below and above a barrier
layer, for smoothness and fineness
Assessment of compaction equipment and procedure for compatibility virh mate-
rial and design
Confirmation of moisture control
Assessment of compaction results largely as manifested in unit weight
Assessment of synthetics placement with emphasis on defects, damage, and
overlaps
Confirmation of synthetics seaming
Tracking of retrofitting work for drainage control and other special
features
Confirmation of seaas, boots, and other seals around vents and access holes
penetrating the cover system
Assessment of vegetation plan and schedule
established, the number of tests required are only those necessary to ensure
that specifications requirements continue to be met. The number of field den-
sity tests required for adequate control cannot be stated generally. Testing
requirements should be based on area as well as on volume and should be devel-
oped site-specifically. Some guidance can be found below with test require-
ments for more general construction of the Bureau of Reclamation.
a. For all types of earthwork, one test for each shift.
b. For canal embankments, one test for each 2,000 cubic yards.
c. For compacted canal linings, one test for each 1,000 cubic yards.
d. For compacted backfill or for refill beneath structures: hand tamped
(mechanical tamping), one test for each 200 cubic yards; roller or
tractor tamped, one test for each 1,000 cubic yards.
e. For soil-cement earthwork, one test per 500 cubic yards or at least
two tests for each shift.
110
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When field density tests are taken ir. relatively narrow areas where
equipment travel is essentially along one route, care should be taken to avoid
sampling these paths. The density may be anomalously high there.
Horizontal and vertical survey control must be available so that the
inspector can adequately locate each field density test. Locations are usu-
ally defined in terras of station, offset from centerllne, and elevation above
bottom grade. The inspector is responsible for locating these tests so that a
complete representative record of the finished work is available.
Compaction testc for clayey and silty soils and relative density tests
for free-draining sand and gravel soils should be made. These companion tests
are required for each control field density test to compute the percent com-
paction or relative density, respectively.
QUALITY ASSURANCE
A quality assurance (QA) program obtains extra confidence for the owner
or regulator in the quality of construction and conformance to plans and spec-
ifications through documentation similar to QC. Such programs play a key part
in the extensive earthwork construction of Che Corps of Engineers. The QA is
conducted by or for the engineer (in government parlance the contracting
officer) and amounts to inspection and testing to confirm the adequacy and
results of the contractor's QC program.
QA has previously been assigned widely divergent importances in solid
waste disposal. Occasionally, a QA program was established but more commonly
there was none. Elsewhere, iliere has been a locre combination of QA with QC,
e.g. in disposal of low-level radioactive waste (47). A QA program is now
required for new RCRA facilities.
In a preliminary stage, the QA personnel mubt have a clear understanding
of construction QC requirements before their first examination of the contrac-
tor's QC or discussions with the contractor. The personnel should study all
contract QC provisions- that establish the contractor's requirements as well as
the parameters for QA personnel participation. The QC plan and Its relation
to QA and QA personnel should be reviewed next.
2
Specifically, the engineer should:
a. Assign QA responsibilities to his staff and assure that their duties
and authority to act are clearly understood. Assign one individual
as the coordinator for QC.
As envisioned by EPA in the pertinent RCRA guidance document (46), QA is
-responsible to but functions apart from the facility owner/operator.
The distinctions made in this section reflect long-standing construction
practice in the Corps of Engineers but are not universally established.
Therefore, each application should be carefully defined.
Ill
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b. Ascertain that his staff understands the contract requirements, knows
the inspection and test techniques to be used, and realizes the need
for timely inspections and tests.
c. Establish standards for daily QA reports and ascertain that the
reports are pertinent, factual, and complete.
d. Establish with QA nersonnel and laboratory personnel a clear under-
standing of the actions to be taken in the handling and correction of
deficiencies observed.
During construction, QC and QA should interact as follows:
a. The QA and QC representatives should have jobsite discussions on the
interrelationship of their activities during the preparatory phase.
Discussions should emphasize controls necessary to eliminate routine
construction deficiencies.
b. The QA supervisor should be knowledgeable of contract requirements
for each phase of work; participate in preparatory, initial, and
follow-up-phases; make joint inspections with QC personnel to evalu-
ate their effectiveness; review QC reports for completeness and accu-
racy; note and report deficiencies and direct contract compliance;
and check to see that QC is producing prompt corrections of defi-
ciencies and control problems.
c. The contractor should not be permitted to build upon or conceal any
feature of the work containing uncorrected defects. Payment for
deficient items will be withheld until they are satisfactorily cor-
rected or other action is taken according to any general provision
clause concerning inspection and acceptance.
d. The engineer should test to assure acceptability of the completed
work and to verify QC test procedures and results. QA testing should
be concentrated on completed work at unannounced intervals. The
engineer should verify the accuracy and calibration of equipment,
assure correct application of specified test standards, and verify
the coverage and accuracy of required QC tests. Test reports, which
should be submitted as attachments to the contractor's control
leporr.s, should be reviewed by the engineer, engineering or labora-
tory personnel, and/or the QA personnel assigned to the work, depend-
ii.g upon the type of test.
e. The plan of contractor submittals should be carefully checked to
assure that a.ll items of material and equipment needing documentation
are included. The reasonableness of the schedule dates should be
ex-inlned and the contractor informed of any found to be unrealistic.
The contractor's certified submittals should be checked in a timely
manner to ensure that installation details, materials, and equipment
comply with contract requirements. The contractor should be notified
of any deficiencies.
112
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f. Some QA testing in the case of critical earthwork must be conducted
continuously. During the stages of material processing, placement,
and compaction a comprehensive control and assurance testing program
is necessary.
ACCEPTANCE CONTROL
Acceptance testing and reports are sometimes considered a part of quality
assurance programs but elsewhere are a separate type of quality management.
Confirmation of the quality of incoming materials is one aspect detailed in
Appendix B through the example of bituminous concrete. Another viewpoint in
construction of hazardous waste facilities comes through a potential need for
quality management at a high level, e.g., a state or federal regulatory
agency. Clearly, the term acceptance implies the adequacy of a portion of the
constructed system. Accordingly, the term probably should never be used in
another, less definite context. Under the circumstances where the owner or a
regulatory office conducts or contracts for acceptance tesr.3, it would be
expected that the parameter being tested would be a fundamental and signifi-
cant one rather than an index property of only secondary importance or indefi-
nite significance. Accordingly, the coefficient of permeability is potenti-
ally an important acceptance test parameter, whereas compacted earth density
is usually not.
The specifications for bituminous concrete in Appendix B illustrate
acceptance testing and methods in construction by example from highway pave-
nent construction. Tha example of bituminous concrete material is not
directly applicable to typical cover construction but is intended to be useful
to experienced engineers by indicating generally the sophistication that has
been incorporated into similar construction.
Table 19 presents several construction tests and inspection procedures
also useful in determining the acceptability of portions of a cover system.
Also see Table 11. Of course, some criterion, standard, or cutoff value usu-
ally must accompany such procedures to develop their full value. Setting such
limits is no small task, but a first cut can be accomplished by an experienced
engineer adapting guidance in this document to the specifics of the project.
113
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SECTION 8
VEGETATION ESTABLISHMENT1
The role of vegetation in the cover system is to protect surflcial soil
against erosion and disruption. Although there Is an urgency in establishing
protection over the vulnerable, npwly constructed cover system, the long-term
health of vegetation is of even greater importance. Accordingly, the guidance
in this Section should be intermeshed with recommendation in Section 10 on
maintaining /in effective condition into the long term.
SPECIAL CONSIDERATIONS
Sound, vigorous vegetation on the cover system is highly cost-effective.
Primary benefits are often identified as decreases in erosion by wind and
water. Vegetation reduces raindrop 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 detrimentally Increased so that considerable
water enters. The increased infiltration is offset at least partly by tran-
spiration fvom vegetation, but the relative importance of these offsetting
processes is a complicated question approachable only on a site-specific
basis.
Rapid establishment and maintenance of perennial vegetatior. or self-
reseeding annual vegetation cen be accomplished on a cover system only by
carefully addressing soil type, nutrient and pH levels, climate, species
selection, mulching, and seeding time. Fertile soils, if available at all,
are sometimes cost-prohibitive so that soils or subsoils that are nonproduc-
tive alone often have to be used. The veget?tlve layer of a cover system
tends to be relatively shallow.
These shortcomings of the vegetative soil layer are compounded where the
cover system has been designed to impede percolation. A clay or membrane bar-
rier layer makes the plant-root zone above It susceptible to swamping after
rains since vertical drainage is impeded or blocked. Upon saturation, the
soil becomes anaerobic, a condition which, depending upon the duration, may
kill progressively larger roots. Short periods of swamping weaken the vegeta-
tion; longer periods may cause a complete loss.
This section is a modification of the corresponding sections in the previous
reports (2,3).
-------
At the other extreme, a thin vegetative layer dries excessively during
dry periods. No deep-soil moisture is available to tide the plants over even
moderate droughts. Plants that nave been weakened by prior waterlogging or
that are not dioup'ut-tolerant are especially vulnerable. Irrigation will help
during prolonged dry spells to prevent deterioration of plant cover, but one
prefers to avoid costly maintenance, even on an irregular basis.
Some disposal ur:lts have the potential to produce gases and soluble
organic decomposition products years after closure, and vegetation can be dan-
aged. Fine-grained soil layers help shield shallow plane roots from gases and
leachate. On the other hand, shrubs and trees may penetrate the cover with
long roots and cause leaks of water into and gases from the disposal unit.
Inspection of damaged vegetation on regional landfills and disturbed lands can
help identify vulnerabilities and disadvantages of plant species.
MANIPULATING 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 to be used (depths and areas) since the cover will usually
consif--: of a mixture. Table 21 Indicates typical rengee of organic matter and
nutrients in soils for various levels of plant vitality.
TABLE 21. PLANT VITALITY LEVELS IN TERMS OF ORGANIC MATTER
AND MAJOR NUTRIENTS IN SOILS (48)
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 Loan
<1.6
1.6-3.0
3.1-U. 5
U.S-5.5
>5.5
percent
Clay Loa.Ti,
Sandy Clay,
Clay
<2.6
2. 6-1*. 5
U.6-6.5
6.6-7.5
>7.5
Nitrogen
Ib/acre
<20
20-50
50-85
85-125
>12S
Phosphorus
Ib/acre
<6
6-10
11-20
21-30
>30
Potass iua
Ib/acre
<6C
60-90
91-220
221-260
>2SO
Medium level is typical of agricultural loani soil. Low levels need supple-
mental fertilization; high levels need no fertilization under normal
circumstances.
Grain Size
A rating of USCS soil types for the support of vegetation Is given in
Table 9. A loara is generally overall best soil type as it is easily kept in
115
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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 proper-
ties of clay and the grittiress of sand, are water retentive, and usually are
easily kept in good condition. Soils made up largely of sand can be produc-
tive if sufficient organic natter is present intarnally or as a surface mulch
to hold nutrients and moisture; sandy soils tend to dry out very rapidly and
lose nutrients by leaching. Although classification can be estimated by vis-
ual inspection, soil typing by an appropriate soil testing laboratory is pre-
ferred. Rather minor differences in soil type can Influence selections of
vegetation and mulch.
Flexibility for improving the chosen cover soil may be found In carefully
considering some inert wastes as additives. Fly ash has locally been mixed
with cover soil to provide good soil texture with enhanced water retention
capacity. The alkalinity of fly ash may also provide an advantageous comple-
ment to acidic soils.
pH Level
The pK of the soil is an inportant factor to be considered. If the pH io
greater than about 8, the solubilities of phosphorus, iron, zinc, and manga-
nese are so low that the plant cannot take up thece nutrients even though they
are pr-esen: in sufficient quantities. If the soil pH is below 5, the concen-
trations of soluble manganese and aluminum often are high enough to be toxic
and the availability of molybdenum and phosphorus is limiting.
The amount of lime necessary to neutralize a given soil depends upon soil
pore vater pH and reserve acidity. The reserve acidity, or buffering capac-
ity, Is a single factor that incorporates several variables; soils with high
levels of orp.anic matter and/or clay requirs higher amounts of line for pH
adjustment. The usual way of characterizing the buffering capacity is as tons
per acre of lime necessary to adjust the soil pH to about 6.5.
The pH of borrowed subsoil eay be particularly critical to lime require-
ments. Sooe vegetative layers on cover systems are mixtures of soil and sub-
soil, in rone cases from more than one locality. Subsoil is used in abundance
for barrier layer and other components below the topsoil, and these layers may
ultimately interact with the topsoll and vegetation. Acidic subsoils need
larger anounts and repetitive applications of lime. Burled wastes may act
much like acidic subsoils, so that lime applications may be beneficial in the
Backfill and intermediate cover vhere they merge as foundation immediately
below the cover system. However, line can alter properties of clayey soil
(2), sc the agronomical benefits may possibly be at the expense of desired
physical properties.
Nitrogen and Organic Matter
Nitrogen is of special importance in establishing vegetation because it
is needed in relatively large amounts (Table 21) during vigorous growth, is
easily lost from the sell, and is th«» most expensive nutrient to supply. All
116
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but a small part of soil nitrogen exists in organic forms, both in decaying
plant material and in the microorganisms decomposing the organic matter. Mea-
surements of the nitrogen content of soil and its organic content are inti-
mately related. Nitrogen accumulates in soil microorganisms where it is used
over and over again as old cells die and new ones are formed. The nitrogen
contained in the inicrobial cells is unavailable for use of plants growing on
the soil until the organisms die. The rate at which nitrogen is released by
breakdown of organic natter 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.
Since many cover soils consist largely of subsoils or mixtures of subsoil
and topsoil, they can be assumed to be low in organic matter content. The
most cost-effective method of adding organic matter is by mulching with straw,
cellulose, etc. Once vegetation becomes established, the plants themselves
will add organic matter.
The amount of nitrogen fertilizer required by a given soil depends uprr\
the amount of organic matter present (Table 21), the soil texture (more is
required on sandy soils) , the seed mixture chosen (more is required for
grasses than legumes), the cr^.tlcalness of the area (potential for erosion
damage), and economic factors (nitrogen fertilizer is the most expensive).
Generally 50 to 85 pounds/acre of nitrogen are recommended (Table 21) for
cover seeded with grass. Prior to the second growing season may be a partic-
ularly effective time for nitrogen additions in grass. It is usually most
effective, however, to include nitrogen-fixing species as major components of
the vegetation community.
Phosphorus
Much less phosphorus than nitrogen is held in the organic portion of the
soil, and subsoils are conspicuously deficient. Accordingly, phosphorus is
sometimes the key to vegetating subsoils (49). Results of phosphorus tests
are commonly expressed as pounds of readily extracted phosphorus per acre-
furrow slice (6-inch depth). Representative levels are shown in Table 21.
Unlike nitrogen, phosphorus is not mobile in the soil and thus Is lost very
slowly to leaching. One application of phosphorus usually will last several
growing seasons, but elsewhere legumes have benefited especially from addi-
tions before the second growing season.
Generally, at least 15 pounds/acre of phosphorus (35 pounds/acre ^'"'s^ ^s
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 pounds/
acre (115 pounds/acre P 0 ) are usually adequate; at pH values below 6.2 or
between 6.9 and 7.5, about 80 pounds/acre (184 pounds/acre p?0c) are needed
for optimum growth. Under very alkaline conditions (pH greater than 7.5),
phosphorus levels of 110 pounds/acre (253 pounds/acre P^^ are
Note, however, in Table 21 that texture and organic content tend to be inter-
related also.
117
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These recommendations are for raw subsoils or for sandy or high clay soils of
low organic material content.
Potassium
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 pounds/
acre of potassium (32 pounds/acre K-0) as a starter is recommended under any
circumstances. Applications can run as high as 230 pounds/acre of potassium
(277 pounds/acre K_0) on impoverished soils where legumes are to be seeded.
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 ir> 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. Toxicity may also need to be
considered where usste materials such as fly ash, phosphogypsum, manure, etc.
are added to the topsoil, but this is not anticipated as a major problem. If
these soils must be used, salection 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 in the cover systes.
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. State highway agencies are also very knowledgeable on the
subject.
Species Selection
/
Jiach" 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 for a particular site depends upon knowl-
edge of plants that have the desired characteristics. Table 22 gives the
major parameters usually important to species selection and examples of
grasses and legumes exhibiting these parameters. Particularly important char-
acteristics are low growing and spreading from rhizomes or stolons; rapid ger-
mination and development; and resistance to fire, insects, and disease.
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Plants that are poisonous or are likely to spread and ?;ecome noxious should be
avoided.
A very large nunber of species of grasses and legumes are available for
reclamation use. Species that find wide and frequent application are
described in Tables 23 and 24. It is usually advantageous to favor regional
vegetation for its adaptability as well as for hanaonious aesthetics. Consid-
eration should also be given to future use of the site, supplexental to waste
management. Where swampy or droughty conditions are anticipated because of
climate, cover configuration, or soil type, special consideration should be
given to swamp-tolerant or drought-resistant species.
Time of Seeding
Probably the most critical of all factors in the successful establishment
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 23
and 24 recommend times for certain grasses and legumes based on local
conditions.
Most perennials require, a period of cool, moist weather to become estab-
lished to the extent that they can withotand a cold winter freeze or hot sum-
mer 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 bpfore any hot summer drought. Early fall planting makes germina-
tion and early grovth possible in warm weather, despite 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 Tor 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-conipete the perennials. Annuals csn, however, be planted for quick vege-
tative cover any time the soil is damp and warm.
SEED ANT) SURFACE PROTECTION
Bare soil as a seeding medium suffers from large temperature and moisture
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,
increasing rain infiltration, and controlling wind and water erosion. Mulches
also help to overcome deficiencies in organic matter typically found in
119
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TABLE 22. IMPORTANT CHARACTERISTICS OF GRASSES AND LEGUMES
terlntlc
Ccsrion Exnnnles
Texture
Grovth height
Grovth habit
Repro
-------
TABLE 23. GRASSES COMMONLY USED FOR REVECETATION*
Vsrietv
Redtop ber.trrass
Szooth bro=eg.-ass
Field brc-eprass
Kentu;y,y bluefiress
Tall fescue
Meadcv fescue
Orchard grass
oest
Seeding
Tine
Fall
Spring
Spring
Fall
Fall
Fall
Spring
'Seed Der.s'ixy-t
seeds 'f:?
1J
2.9
6.i
50
5-5
5.3
12
t
Ir.aortai-.t Characterise ics
Strong, rhi:o=atous roots,
percnni al
Lon^-lived perennial
Annual, fibrous roots,
winter rapid growth
Alkaline sells, rapid grower,
perennial
Slow to establish, long-lived
perennial, ^ood seeder
Snallcr tha-i tall, susceptible
to leaf rust
.'lore heat tolerant b'jt less
Areas/ Conditions
of Adaotat ij.-.
l-'et, acid soils, warn
season
Da=p, cool su=r.ers,
drought resistant
Combelt eastward
North, hunid U.S.
south to Tennessee
Widely adapted, danp
soils
Cool to warn regions,
widely adapted
Tesperatt; U.S.
Ticcthy
Reed
Fall
Fall
U-.e
sunr.er
20
13
cold resistant thun smooth
bronor.rass or Kentuclr/ uiuegrass
Not winter hordy, poor dry
Innd priiss
Shallow roots, bunch
?nll coarse, STd forner,
percn.-.inl , resists flooiins
ond uro
.'toist southern U.S.
.'•'orthern U.S., cocl,
hunid areas
Northern 'J.S. , wet,
co;I areas
n
Taken from nany sources, but especially References 48 and 50.
Number of seeds per square foot when applied at 1 pound/acre.
landfill cover soils. Almost any material spread, fomed, or simply left on
the soil surface will act as a mulch. A wide variety of materials is used
commonly 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 chexical properties of the soil, the land-forming or cultural
practices, species to be seeded, and the characteristics of the raulch itself
such as its color, roughnessi 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 th° 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 westher
before, during, and after mulch application. Selection depends upon charac-
teristics of the area to be stabilized and the availability, cost, and proper-
ties of the sulch material. Several of the more common and effective mulches
and their applications are described below.
12!
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TABLE 2ft. LEGUMES COMMONLY USED FOR REVEGETATION*
Vnrietv
Alfalfa (nany varieties)
Blrdsfoot trefoil
Sweet clover
Fed clover
Alsike clover
Korean lespedeza
Sericea lespedeza
Hairy vetch .
White clover
Croviivevh
flcr.l
SccJ'.nc,
Tlr.c
Late
surfer
5prlr.fi
SprinR
Early
spring
Early
sprir.R
Early
sprlr-.g
Early
sprir.g
Fall
Sarly
f«ai
Early
fall
Seed D«.-ns:v.-t
serdr. / :'••
5.?
9.6
6.0
6.3
16
5^
8.0
0.5
13
2.7
Invor'.irt Cliar'ict >-ri::'.l cr.
Hood on alkaline lonn, re-
quires Rood nannp.er.ent
food on infertile soils,
tolerant to acid soils
fVjod pioneer on non-acid coils
Not drought resistant,
tolerant to acid soils.
Cinilar to »ed clover
Annual, videly uitaptcd
Perennial, tall erect plant,
widely adapted
Winter annual, survives belov
0°F, widely adapted
World-vide, nany varieties,
does well or. no'.st, acid soils
Perennial, creeping sterns ar.d
rhi:or:es, acid tolerant
Arenr./Condltl-jna
of Mnr.\n:'.r.n
Widely adapted
"olst, ter.peratc
U.S.
•'idely adapt eri
Cool , T.olst ar«as
Cool, raoist areas
Southern U.E.
Southern U.S.
All of L'.S.
All of U.S.
Northern U.S.
Taken from many sources, but mainly from References 48 and 50.
Number of seeds per square foot when applied at 1 pound/acre.
Jrop 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 Stages. Straw's fibrous texture is excellent for erosion con-
trcl, and the low nutrient value retards rotting so that straw normally lasts
a full season. Straw reflects much sunlight and thus may have the disadvan-
tage 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 ot 1.5 tons/acre is recom-
mended. On 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 spreaders work well on level areas, but blower types arc better
for steep slopes. Baled material tends to fall in bunches unless cut or
shredded and scattered or blown. Wheat straw is generally preferred over oat
straw since oat straw decays more rapidly and usually contains seeds that com-
pete with the perennials for space and water. Hay, in comparison to straw, is
difficult to spread, and it decomposes rapidly. However, hay possesses some
122
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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 it. Even running over the spread straw
with a dozer is useful. Asphalt or resins can be used as a binder or to
anchor, but while they greatly increase effectiveness, they aldo 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 sunsser annual crop
acts as a natural mulch for fall or spring seeding of the permanent seed mix-
ture. Rapiu 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 seed-
ing of perennials to fail. On the other hand, in wet areas, the soil under
the cover crop dries very slowly and often reaains 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 aro easy to apply, long lasting, and less
susceptible to blowing and fire than crcp residues. Disadvantages Include
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 aer-
ation 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 pnste 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 nixed
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.
123
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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 warm the
soil to advance the seeding date. The film clings to but does not penetrate
deeply into the soil; it is not readily removed by wind and rain and remains
effective from 4 to 10 weeks. Application rates of 1,000-1,200 gallons/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 ha 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^UI*.-.**-.water-
Resin is usually applied at a rate of 600-800 gallons/acre, and costs are
equivalent to those of asphalt emulsion.
Black asphalt absorbs solar energy and greatly increases the warming of
soils at all times of the year. Germination and development are assisted in
late fall and early spring, but in summer the absorbed heat car. 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
under other high-erosion conditions. The film is expensive, difficult to
place, and very susceptible to wind damage. Seedling emergence must be moni-
tored closely and the film ventilated or removed at the right tine. Even 1 or
2 days of temperatures ever 80°F is enough to kill most seedings. Often when
the film nust be removed, the seedling cover is not complete and serious ero-
sion results.
Other Techniques
Other techniques can be useful under special circumstances or availabil-
ity. Gravel and crushed rock have the advantage'since they are permanent. A
1- to 2-lnch layer of gravel will control surface erosion and vegetation
development in the driest of areas. Gravel with a minimum diameter of
1/2 inch will resist winds to 85 miles/hour.
Manure is a mulch iomecluics available at local feed lots. Manure acts as
both a mulch and a slow-release fertilizer of fair quality but is not reliable
in sustained erosion control as it tends to decompose rapidly.
-------
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-nrulch; however,
both are expensive and difficult to place, requiring insertion of several
thousand wire staples per acre as anchors. Synthetic fabrics and netting
designed to minimize erosion are becoming more ard taore popular for all high-
priority applications (36).
Wattling is one of numerous special techniques that may be used to estab-
lish vegetation 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
such as willow that taice ^oot easily, the wattle itself becomes a part of the
semipermanent or permanent stabilization system.
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SECTION 9
PERIODIC INSPECTION
Provisions should be made in the plan of operation for periodic inspec-
tions and irregular visits usually continuing years beyond closure of the
facility. Surface inspections and sampling, aerial photography, condition
mapping, and subsurface monitoring are all forms of primary or supplemental
inspection. Among key ingredients are provisions for assuring suitably expe-
rienced or trained inspectors.
GENERAL1
It is recommended that considerable time be spent on outlining appropri-
ate weekly, monthly, and less frequent Inspections. Emphasis should be placed
on collecting data as well as being consistent and punctual. Field inspec-
tions are highly cost-effective and on that basis should appeal to and receive
the enthusiastic support of the facility operator. Each inspection should be
documented by written or graphical record. Figure 56 is an example. Monu-
ments should be installed for survey control and point reference.
Observational parameters will be site-specific and nay be distinct
according to the combination of topography, climate, and ground-water condi-
tions. Each site deserves its own inspection plan tailored to its particular
characteristics. Among data that may be collected are those documenting the
following:
a. Precipitates on ground surface.
b. Odors.
c. Intermittent seeps or soft spots as from shallow interflow.
d. Erosional effects.
e. Depressions and puddles.
f. Subsidence areas.
g. Vegetation stress.
These generalizations have also been discussed in the context of overall site
monitoring (51).
126
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HONTHLY TKCNCH INSPECTION
/z
/JyfcTfc
F/
78
r-Jf
r-f
cz
p^====*
r-at
T-l ]
1) Kunbcr and cj'rcJc the Jocation of holes and
2) Describe belov the size and cause of
^^4
^s^J^
Figure 56. Example inspection report for Sheffield LLRW facility.
h. Undesirable species of vegetation.
i. Animal burrows and mounds.
Among these, a through c directly monitor for migrating pollutants or their
precursors, and d through i have peripheral functions in combination with site
maintenance.
Other monitoring tasks such as sampling can he combined with the field
Inspection to provide continuity. The degree of success depends upon the
ability of the inspector co interpret the situation and the amount of time
127
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available for the study. Ample time must be provided. lining may also be
critical as for locating seeps after a heavy rainstorm.
The inspector should have a detailed map or aerial photograph of the
entire site including sufficient markers and survey monuments to facilitate
location of ground positions. For convenience, the base map may be in several
sheets. While traversing the immediate site and the surrounding acreage, the
inspector should record findings on the sap and give an overall picture that
can be easily interpreted. Provided the inspections are made frequently, they
may allow the quickest response to developing problems.
Seeps can be useful sources of information or sampling points; however,
according to good engineering practice, seeps will be rare at waste sites.
Also, experience with landfill leachate has shown that seeps are often highly
variable in activity in rela:ion to location and the period of time (52).
When there are substantial changes in seep locations or flow rates or when new
seeps suddenly appear, a chang.- in the flow system may be indicated. The
nature and cause of the change, however, may have to be explained by a subsur-
face investigation.
Contamination of ground water or generation of gas may result in stress
and possible destruction of vegetation. Such stresses affect agricultural
crops, stands of trees, and marsh or meadow vegetation. In marsh enviroraaents
the condition of vegetation can serve as a monitoring device observable
directly or by remote sensing; however, new waste facilities will seldom if
ever be sited in or adjacent to marshes.
Crops dnd trees generally grov in areas with a water table at intermedi-
ate depth and are occasionally stressed by gases or through contaminant
uptake. Some agricultural crops, including fruit orchards, have been
destroyed by migrating gases generated within a nearby landfill and subtle
stresses placed upon these species may be detectable by field inspections.
While identifying the precise cause and mechanism of stress can be pro-
hibitively costly, it may be possible to relate the stress to a general cause
which may in turn be related to the presence of tht disposal facility. Hap-
ping the extent of stressed vegetation may provide an indication of the extent
of the total impact on the surrounding environment.
SURFACE INSPECTION
The cover systera should be inspected ac an appropriate interval by tra-
versing the cover on foot and making appropriate notes and photographic
records. The traverse may be established and continued in several ways. A
different path may be followed each visit or the same permanently established
route may be repeated. Inspections along variable traverses provide a total
picture but are not so conducive to recording subtle changes in individual
features on the cover.
Figure 57 shows an inspection traverse for one actual cover system. This
traverse was developed as appropriate in discussions between regulators and
the owner of the previously uncontrolled hazardous waste site. Or.c of the
128
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wJ Ol1'"'-11 |OtS .
_/ -> T,,«rciV.r J («•«' ••*•«) U^L] (.nrtifnct)
_// f 1 HfpitltyZ
N)
VO
® s*s8$&&
Figure 57. Inspection traverse at covered waste site.
-------
last modifications to the inspection plan concerned the position of major
turning points along the traverse. It was recommended that appropriate points
be surveyed and marked permanently for ease of relocation even in high grass.
By zigzagging across the traverse line, the inspector can observe and document
a representative strip'perhaps 100 feet wide.
Provisions may need to be made for regular examination of specific fea-
tures along a traverse. Features such as eroded banks, patches of dead vege-
tation, and exposed membranes should be reexatrlned during each inspection.
The position of such a feature can be located by triangulation provided there
are permanent surveyed points nearby. Representative vertical aerial photo-
graphs or detailed topographic maps, where available, will facilitate location
of points.
SETTLEMENT MONITORING
Settlement plates should be established on the completed cover and'moni-
tored by surveying periodically. The points may be concentrated along one or
a few profiles representative of the cover. Preferred orientations and super-
imposed positions of waste cells should be considered carefully to avoid miss-
Ing differential settlements developing over short distances. For example, In
Figure 30 one would expect any differential settlement to be concentrated
beside the superimposed soil dikes. Accordingly, settlement plates should be
placed over the superimposed dikes as well as over the adjacent superimposed
waste cells. Plates should be installed for permanence and with appropriate
protection from vandalism and accidental disturbance. Concrete bases 2 feet
or more in diameter are suggested.
Surveys should be repeated every few years until settlement behavior is
established. An interval of 10 years should be sufficient subsequently to
recognize any deterioration beginning sometime in the distant future.
AERIAL INSPECTION
Aerial photographs are particularly cost-effective for documenting the
condition of the surface of a cover system. There are no other reasonable
raeans of recording the details and extent of a developing eiosion system fron
ubiquitous rivelets converging downslope to trunk gullies. A set of such pho-
tographs over a period of time documents the rate at which the system Is
developing and Indicates the ultimate effect on the cover system. Oblique
aerial photographs may adequately reveal and document the condition of the
cover for substantially less cost than vertical photographs. With that cost
advantage, it may be possible to photograph the cover more frequently.
It is necessary to obtain more than one oblique view at each visit so
that information is not missed in blind spots. Color photographs are usually
preferred over black and white. It is particularly important to coordinate
the site visit and photography s;o as to minimize apparent differences result-
ing primarily from different stages of growth of the vegetation. With color
photography, one night choose to photograph the cover annually a certain num-
ber of days or weeks after emergence of new growth in the spring. This would
130
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tend to provide a contrast between healthy green areas and lagging or
unhealthy areas still colored brown.
CONDITION MAPPING
One of the most sophisticated plans for periodic inspection of the cover
consists of a complete mapping of one or more important characteristics over
the entire surface area. This procedure requires an aerial photograph or
detailed base map upon which to plot the observations. Variations in vegeta-
tion may already be evident in aerial photographs, and an examination on the
ground provides the opportunity to verify inferred conditions and to fill in
any questionable areas. Points or linear features can be located and areas of
uniform characteristics outlined directly on the map or photographs or on
overlay sheets. This information can be transferred to a clean office map;
but in any case, the field sheets should remain as a part of the file of post-
closure history.
SAMPLING AND TESTING
The cover inspection techniques described above concentrate on conditions
visible on the surface or from the air. To evaluate the condition of the
cover system belov the ground surface, test pits and other means of sampling
or observing the subsurface condition are needed. An experienced engineer
should supervise pit excavation and sampling. Provisions in the maintenance
plan or contract should specify frequency and approximate locations for sam-
pling and observation of the subsurface. It is possible to retain consider-
able flexibility in these specifics by presenting guidance in general terms.
If inspection pits are needed and are not in violation of RCRA regulations, it
might be reasonable to require annual inspection through the cover (or to the
impermeable membrane) at points determined randomly or according to possible
problems visible at the surface. For example, one test pit might explore the
subsurface where sparsity of vegetation indicates droughty or otherwise anoma-
lous conditions.
Very specific directions should be included on effective backfilling of
any test pits or borings. For relatively small borings, the procedure might
consist of backfilling with clay from the full depth of penetration. Appro-
priate backfilling for test pits and other large excavations through the cover
deserve careful attention to assure that the backfill or its interface with
the undisturbed cover system has not created a new problem. Conceivably a
plug formed by backfilling a test pit located in a topographic depression can
leak surface water through the cover system if the plug soil is permeable and
the barrier element is not properly restored.
One of the best methods of neutralizing this potential problem is by
backfilling the test pit with the original material types layer by layer.
This procedure tends to preclude the introduction of any anomalies of flow
paths caused by anomalies in hydraulic head or coefficient of permeability.
Possibly, excessive costs of such a backfilling procedure would need to be
weighed against expected effectiveness and overall results.
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The number of penetrations for observation or sampling should be held to
a reasonable minimum. This constraint throws an additional burden on the sam-
pling plan to obtain conplete and accurate information at the relatively few
points sampled. Sample disturbance should be avoided, and the in situ condi-
tion should be preserved or observed quickly. Jar samples from progressively
deeper levels provide a moisture profile at the time of sampling. Where the
primary purpose is for observation of the condition of the cover, the pit must
be of such dimensions to allow the observer an approp.iate view and working
space. Observations should be recorded in such a way as to show clearly the
important characteristics of each layer or increment thereof. A graphical
portrayal of the profile usually constitutes an important part. A plan map of
abrasions, seams, and deformations in a membrane is also important documenta-
tion. Where samples are to be recovered, the taetnod should be prescribed and
preferably will come from a widely recognized source such as the collectTori of
ASTM standards and recommended procedures. In the case of recovery of block
soil samples from pits, the emphasis should be placed on rapid recovery and
preservation of in situ water content by an appropriate method such as waxing.
GROUKD-WATER MONITORING
The effectiveness of the cover system is sometimes reflected in a subtle
way in the results of ground-water monitoring. A monitoring program will be
operational at ciany sites, particularly aa required of RCRA facilities (Sub-
part F of 40 CF.; 264), and will provide an available source of information
supplementing the inspection program specific to the cover. It is recommended
that measures for utilizing the ground-water monitoring program be specifi-
cally outlined as a part of inspection of the cover system. Without a formal
coordination in the inspection plan, tha subtle interrelationship is easily
overlooked.
The importance of the ground-water monitoring system Is highly influenced
by specific site and hydrogeological conditions. A site located well above
the water table and in which most of the potential water flow is directly
downward froa the ground surface ic ir.ost likely to show a direct • correspon-
dence between leachato migration and cover leakage. The most direct monitor-
ing in this case is in the leachate collection system. Any increase in the
volume of leachate not clearly correlated with a previously established back-
ground or seasonal cycle would suggest a deterioration in cover performance.
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SECTION 10
MAINTENANCE AND REPAIR
Maintenance of cover integrity and effectiveness is required by
40 CFR 264 (Table 8). A. maintenance program can accumulate substantial costs
over the intermediate term yet still continue to be burdensome where inade-
quate provisions are made for finding and correcting problems (Table 25).
Therefore, it is recommended that the program be scheduled with a concentra-
tion of effort on the front end, so that problems can be recognized soon and
adjustments can be made. As improvements are made and the understanding of
the facility and its environaent grows, the cover system should become stabi-
lized, and the maintenance expenditures should become moderate. Conversely,
cost may escalate if important processes are overlooked.
PERIODIC GROOMING
A category of maintenance (53) needs to be recognized short of cover
repair. There will be certain types of work to be accomplished on the cover
periodically and generally, particularly for the first few years after
closure.
TABLE 25. POSSIBLE FUTURE PROBLEMS
Chronic erosion
Erosion event
Inadequate drainage system
Slope creeping
Slope sliding
Subsidence
Differential settlement
Flooding
Chronic vegetation failure
Vegetation failure event
Frost disturbance
Wind erosion
Cracking
Plugging of porous soil
Deterioration of synthetics
Loss of locations and monuments
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Maintenance of Vegetation
Where vegetation is established on the cover system, at least a minimum
amount of maintenance is necessary. Judicious twice-yearly mowing will sup-
press weed and brush species. Annual fertilization (and lining 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 desiraui"
species, lest more harm than beneflc will result in the long run. In rare
circumstances, large insect populations may threaten the stand of vegetation
so that insecticide application becomes desirable.
Provisions should be made for the eventuality of. a favorable transition
from the originally established plant community to another of greater compat-
ibility with the site environment. Such a change may even be part of a long-
range strategy for vegetating the cover system. This strategy is a logical
extension of that according to which ryegrass is planted for rapid stabiliza-
tion with the intention that the ryegrass be only temporary, and perennial
grass will ultimately prevail. The planning of a long-term succession of
plants and the proper maintenance for accomplishment of the objective could
profitably occupy the designer in considerable effort. Often the plants that
are native to the region are targeted as ultimate occupants, but even then
problems may arise. For example, native tumbleweed has been a problem at dry
disposal sites since its roots can descend as far as 20 feet and into disposal.
units.
Reconditioning of Soil
Chronically weak and vulnerable vegetation sometimes signals a need for a
revitalization of a vegetative soil layer. The characteristics of possible
concern are:
a. Texture.
b. Water-holding properties and drainage.
c. Nutrient content.
d. Accumulations of gases.
e. Accumulations of toxic salts.
The guidance under HANIPULATIXG SOIL FACTORS (SECTION 8) is directly
applicable.
REPAIRS
Cc-'er repairs may be defined for purposes of this document as any work
undertaken after completion and acceptance of .the cover system for the purpose
of returning a defective portion of the system to an acceptable condition.
Major repairs can be distinguished from minor repairs as a matter of degree.
-------
Provisions should be made for both categories since both can reasonably be
expected over the life of the facility.
i • t
General
Minor repairs, which may be thought of as patching, categorically include
inexpensive repairs that can be accomplished in a short time by operational or
caretaker staff. Repairs of this nature are simply to return the cover to its
original condition. Minor patching repairs are probably most commonly needed
to take care of damage accumulating slowly over a long period of time.
There is usually a need for a category of repairs involving some modifi-
cation of the original cover system. These major repairs often incur greater
costs, although their tendency to be concentrated or highly localized helps to
moderate the total cost. A very cosnaon type of major repair addresses a
developing erosion problem as it arises unexpectedly during infrequent exces-
sively heavy storras.
Ordinarily it would be difficult to anticipate the problems and have a
repair work unit ready for a solution. The design of the cover system was
originally targeted on that combination of layering, surface configuration,
and other characteristics promising longevity and a minimum of problems.
Accordingly, the maintenance plans should provide contingencies for possible
future problems of a large variety. Certain generalized provisions can be in
place for accomplishing repairs that might conceivably be needed. It is also
important that the assignment of responsibility for repairs and the identifi-
cation of funding source or sources be given. Beyond this, it is appropriate
to be aware of the possible scope and timing of future problems and their
solutions. Information of this nature is given in the next subsection.
Maintenance contracts should be carefully prepared for both large and
small repair needs. The maintenance contract at one old corrected site con-
tained minimums on payment which encouraged the contractor to accumulate main-
tenance and repair needs before acting. Excavation and replacement of a small
volume of contaminated surface soil as a means of monitoring leachate was
delayed.
Problems and Solutions
On the basis of the problems observed on cover systems to date, it is
anticipated that a relatively few broad types will encompass most problems
developing in the future. In turn, it has also been observed that required
repairs are usually localized. Therefore, it should be possible to foresee
the possible repair work at the design stage and to make some provisions in
planning for deterioration that is nost likely to occur over a long period of
time.
Gully development—
The most cormon problem on portions of cover systems with slope exceeding
five percent is n development of large or small gullies early in an erosion
cycle. The cover system is especially susceptible to gullying when it has no
vegetation, s :> gully erosion processes have an advantage in the
135
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before vegetation has first been established. Gullying continues to threaten,
however, into the long term. Even such subtleties as the ruts from mainte-
nance vehicles are capable of starting the gullying process.
A dendritic pattern of tributary gullies converging on the deepest stem
gully can develop on waste cover surfaces that are irregularly configured in
harmony with the natural terrain (Figure 58). The cover in the figure
includes a synthetic membrane below soil. On Lhe other hand a planar slope,
as Is commonly established along the side of a cover system, will be more
likely to have a linear arrangement of gullies trending parallel down Che
slope with only a minimum of convergence inco larger channels (Figure 59).
Gully erosion can Involve subsurface water flow as well as surface ero-
sion. The contribution of subsurface flow is most dramatic where an imperme-
able membrane has been emplaced at relatively shallow depth, as in many RCRA
covers. Clearly the quantity of water that infiltrates can soon reach the
storage capacity of the soil. Within a granular soil of relatively high per-
meability, the perched water flows relatively -apidly along any elevation gra-
dients. Shallow laterally flowing water can emerge as seeps and substantially
aggravate the surface erosion condition.
Gullies can be removed by grading to a smoother V-shaped cross section
followed by establishment of turf. One potentially serious drawback of this
remedy is that the grading operation may detrimentally affect the original
cover design. For example, blading the sides of a gully to a V cross section
will substantially reduce the thickness of the top layer, particularly along
the gully axis. Operation of equipment along the gully may also have adverse
effects on the system through flexure and cracking and by rutting and offset
under tue wheels.
One method of gully repair that is recommended for consideration is back-
filling to the original grade with stone of narrow size rsnge (41.). The same
gradation as reconaiended for drainage layers may be considered. Optim-.im
results would probably be obtained with stone of the following ccarse charac-
teristics:
Sieve Size, in. Weight Percent Pcssing
5 95
3 75
1 0
This cobbly material has a very high coefficient of permeability, yet its
voids are sufficiently small to prevent turbulent water flow.
!U- filling Kviilies with free-draining stone, one mr-.y be able to convert a
detr.'rcental condition into an asset. The well' developed system of converging
gullies is highly efficient in drainage and in its response to c'nar.ges in the
site cr.vl ror.n-.er.t, but whan stabilized with free draining gravel, :he filled
gullies become a permanent system for expedient drainage of the slopes.
136
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Fifiure 58. Erosion gullies on recently completed cover system at Ft Drum.
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Figure 59. Erosion gullies on regular slope on Kln-Buc landfill.
A fabric or some other boundary feature acting as a filter will probably
be a necessary supplement to the gravel filling. The fabric serves to exclude
the fine particles of the surrounding soil, which otherwise would tend to wash
into and accumulate in the openwork gravel, eventually reducing its
effectiveness.
Subsidence—
Cover systems over porous types i»f waste continue to be vulnerable to
deterioration by the formation of subsidence holes during the long term. Sub-
sidence ssay be manifested as a stepwlse dropping of a roughly circular or
elliptic*:] area generally no more than a few meters across or nay be mani-
fested as & more subtle low spot where puddling tends to occur. To some
extent, which of these toras is found depends upon the nature of the cover
/ system. A cover including dense and therefore strong cohesive soils will
sometimes temporarily bridge across a void forming below. This style of sub-
sidence usually culminates in sudden formation of a deep offset. The less
dramatic, gradual type of settlement is sometimes more serious because it
tends to affect a larger area. Stall but significant lows facilitating infil-
tration of water can even form as ruts from operation of maintenance vehicles
(40).
'
;
Procedures for repairing settlement or subsidence depressions are fairly
straightforward. The hole is usually filled with additional cover soil from
the stockpile, but some rather extensive repairs and reconstructions may be
needed for deformed or torn synthetic membranes. It is reconnended that tech-
niques of keying, material matching, patching, and mending of aged synthetics
138
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be used in repairing depressed cover areas. These recommendations are not
based on past experience, but instead are anticipated to be cost-effective for
achieving the simple objective of restored layer continuity.
Slope instability —
On side slopes, particularly where they exceed 25 percent Inclination,
there Is usually a potential for slippage of entire sections of material lat-
erally or down the slope. Sometimes the process is combined with gully ero-
sion and manifested as mud flowage. Aggravating conditions include a high
degree of saturation stich as might arise from concentration of subsurface
seepage or from thawing of frozen ground.
Since the disruption caused by slope Instability Is at least locally
quite serious, a partial reconstruction of the cover is usually needed.
Reconstruction is discussed In the next subsection. Addition of a berm along
the base of the slope is one option that Is frequently effective.
Defective drainage system —
Occasionally a cover system will be constructed with defective drainage.
Some likely deficiencies evident in past experience are lack of diversion from
the crest of the slope and vulnerable bends or knickpolnts along the channels.
Also the lined portions of drainage channels are sotnetines found to be vulner-
able to erosion or insufficient in capacity. Elsewhere a need may become
apparer.t for such special drainage features as culverts, drop inlets, and
catch basins.
A number of techniques are available for repairing deficient dralr.age
systems. The possibilities for unexpected erosion can certainly be antici-
pated, and therefore, provisions for repairing erosion damage along the chan-
nels are deperving of considerable attention. Straightforward techniques that
are available include modification of channel alignment and installation of a
lining feature or control structure.
Placement of stone armor in channels is an effective technique for reduc-
ing erosion since the stone disrupts water flow as well as covering the vul-
nerable soil. Long-term remedies are usually preferable so the choice of
maintenance personnel has frequently been to manipulate the vegetation plan
for beneficial effects.
Upward or lateral leakage of gases and capillary water from the disposal
unit into the cover system has occasionally aroused serious concern in the
past. Although cover systems can be designed to control migrating gas and
many hazardous wastes present no gas-generation potential, a contingency for
such a problem should be incorporated in the overall facility plan. Simi-
larly, the capillary rise of contaminated water to the ground surface with
deposition of salts at or near the surface is not a very likely threat, par- .
tlcularly for RCRA covers, but neverthelesa deserves careful consideration.
Plans for replacing and repairing contaminated areas of the cover system
should be formulated at least in general terr:s. Unlike the repairs undertaken
for other types cf problems, repairs for chemical damage to the cover system
139
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may have to be preceded by a careful delineation of the problem area based on
field testing. Such preliminary work adds an increment of cost.
Leakage problems may be corrected by an upgrading of a gas drainage sys-
tem where one exists already. Where a drainage system is not ir. place
already, gravel drains and buried pipes may be retrofitted, but special care
will be needed to ensure that they are compatible with th° rest of the cover
system. For example, a French drain or gravel drain for conveying gas can
also convey water downward through the cover if not properly capped with
impermeable clay.
RECONSTRUCTION
All or a portion of the cover system may need to be reconstructed where
damaged by environmental processes such as slope instability or where shown to
be ineffective in performing its prinary function. Since the necessity for
reconstruction indicates a serious proMem and therefore a deficiency in the
original design, a new design is frequently necessary. Accordingly, new plans
and specifications may be developed for entering into another contract.
A cover may be reconstructed to correct sone of the following
deficiencies:
a. Drainage channels persistently susceptible to erosion.
b. Side slopes experiencing instability.
c. Barrier layer or other critical element of the cover system showing
signs of deterioration.
Deterioration of the barrier layer, e.g., by cracking or long-term and perva-
sive penetration by roots, is especially threatening. Such, effects can cone
about through a relatively subtle nisjudgment in cover design, e^g., an insuf-
ficient burial depth. Swampy or droughty areas of substantial size may war-
rant reconstruction, whereas correction of the same problem on a smaller scale
is considered only repair work and accomplished on a less formal basis.
CONTINGENCY PLAN1
Problems likely to develop in the distant future are difficult, cc. antici-
pate at a preliminary stage or even vhen.the cover system is designed and the
contract documents prepared. Confidence in the cover system is implicit in
the design. The whole purpose of the design process is to plan a cover system
that will be effective over a long period of time. On the other hand, the
expectation that any cover system will serve effectively through a design life
as long as hundreds of years is speculative. With that frame of mind, the
designer should be motivated to outline contingencies for repairing specific
Contingency plan here refers generally to a technical plan, not necessarily a
part of the contingency plan required in Subpart D of 40 CFR 264.
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future problems. Table 25 preser.ts a list of possible future problems, but
the specifics of an individual site and Its environment nay suggest others as
well. Visits should be made _to existing sites of similarly disturbed land to
observe conditions and* problems.
Once the general types of problems are recognized, it should be possible
to pinpoint the areas in the cover system deserving extra attention. Erosion
and instability are more common on steep slopes, and the gradient there serves
as a rough index of the degree of vulnerability. Accordingly, contingencies
there should place emphasis on the steep portions of slopes.
The next step in developing a contingency plan involves the examination
of the degrading process itself. The designer may want to review the exten-
sive literature on erosion and Instability processes from the viewpoint of
empiricism more than theory. At the minimum, the designer will need expertise
or documentation on geoinorphic processes at the relatively small scale of a
cover system. In the past there has been a serious tendency to ignore long-
tern deterioration of landfills and to assume that once vegetation has been
established, a landfill is satisfactorily closed.
Where the review of geomorphic processes suggests that specific small
areas may deteriorate in the future, a rough plen of action should be devel-
oped. The plan should be accompanied by an estimate of cost in terms of unit
costs in the present year. There is at present one ochool of opinion that a
clear understanding of the large total cost of waste disposal Including indi-
rect costs from the impact on the environment will eventually reduce the vol-
ume of wastes by forcing improvements in industrial processes. It can hardly
be argued that reasonable change in industrial processes and in product demand
among die public is not a ,-osltive change, and therefore the designer of the
cover system can exert a positive influence even beyond his icnnediate objec-
tive through a careful and thorough estimation of the costs of future
reconstruction.
A plan for possible future cover reconstruction cannot extend much beyond
the generalizations on vulnerable locations, deterioration processes, and
future COSLS. Other than including a provision for funding all reasonably
expectable work needs, there is little tangible to be said. The actual plan
of work will be formulated as the need arises and will be accomplished, more
or less, as a new job in site restoration. The big advantages will lie in the
immense amount, of useful technical background data on the site if the site has
been designed, constructed, and maintained according to guidance in this
document.
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No. 6, 1984. pp. 684-700.
36. Horz, R. C., "Geotextlles for Drainage and Erosion Control at Hazardous
Waste Landfills," L'S Environmental Protection Agency, Cincinnati, Ohio,
1985.
144
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37. Carr, G. L., and Gunkel, R. C. , "Laboratory Studies of Soil Bedding
Requirements for Flexible Membrane Liners," US Environmental Protection
Agency, EPA-600/S2-84-C21, Cincinnati, Ohio, 1984.
33. US Nuclear Regulatory Commission, "Environmental Assessment for the Barn--
well Low-Level Waste Disposal Facility," NUREG-0879, Washington, DC,
1982.
39. Tucker, P. C., "Trench Design and Construction Techniques for Lou-Level
Radioactive Waste Disposal," US Nuclear Regulatory Commission, NUREC/C.1.-
3144, Washington, DC, 1983.
40. Kahle, R., and Rowlands, J., "Evaluation of Trench Subsidence and Stabi-
lization at Sheffield Low-Level Radioactive Waste Disposal Facility,"
US Nuclear Regulatory Comalsslon, NUREG/CR-2 101, Washington, DC. 1981.
177 pp.
41. Luttcn, R. J., Torrey III, V. H., and Fowler, J., "Case Study of Repair-
Ing Eroded Landfill Cover," US Environmental Protection Agency, EPA-600/
9-82-002, Cincinnati, Ohio, 1982. pp. 486-494.
42. MacMaster, J. B., Wrong, C. A., and Phang, W. A., "Pavement Drainage in
Seasonal Frost Area, Ontario," Transportation Research Record 849, Wash-
ington, DC, 1982. pp. 18-24.
43. Salvato, J. A., Wilkie, W. G., and Mead, B. E., "Sanitary Landfill-
Leaching Prevention and Control," Water Pollution Control Federation,
Journal, Vol. 43, 1971. pp. 2084-2100.
44. JRB Associates, "Slurry Trench Construction for Pollution Migration Con-
trol," US Environmental Protection Agency, EPA-540/2-84-001, Cincinnati,
Ohio, 1984.
45. Mutch, R. D., and Siok, W. J., "Remedial Actions at'Solid Waste Land-
fills," Environment and Solid Waste, Butterworrh Publ., 1983.
46. US Environmental Protection Agency, "Technical Guidance Document: Con-
struction Quality Assurance for Hazardous Waste Land Disposal Facili-
ties," Office of Solid Waste and Emergency Response, Washington, DC, July
1986.
47. Johnson, H. V., Spigolon, S. J., and Lutton, R. J., "Geotechnical Quality
Control: Low-Level Radioactive Waste and Uraniun Mill Tailings Disposal
Facilities," US Nuclear Regulatory Commission, NTREG/CR-3356, Washington,
DC. 1983. 151 pp.
4.8. Bennett, F. W., and Donahue, R. L., "Methods of Quickly Vegetating Soils
of Low Productivity," US Environaental Protection Agency, EPA-440/3-75-
006, Washington, DC, 1975.
145
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49. Moldenhauer, W. C., Holmberg, G., and Schrader, W. D., "Establishing Veg-
etation on Exposed Subsoil in the Monona-Ida-Haniburg Soil Association
Area of Kansas, Iowa, Missouri, and Nebraska," US Department of Agricul-
ture, Agriculture Information Bulletin No. 251, Washington, DC, 1962.
14 pp.
50. US Department of Agriculture, "Grass, the Yearbook of Agriculture," House
Docuaent No. 480, 80th Congres?, Washington, DC, 1948.
51. Lutton, R. J., Strohm, Jr., W. E., and Strong, A. B., "Subsurface Moni-
toring Programs at Sites for Disposal of Low-Level Radioactive Waste,"
US Nuclear Regulatory Commission, NUREG/CR-3164, Washington, DC, 1983.
52. Fenn, D., Cocozza, E., Isblster, J., Braids, 0., Yare, B., and Roux, P.,
"Procedures Manual for Ground Water Monitoring at Solid Waste Disposal
Facilities," US Environmental Protection Agency, EPA-530/SW-611, Cincin-
nati, Ohio, 1977. 269 pp.
53. Conover, H. S., Grounds Maintenance Handbook, 3d ed., McGraw-Hill,
New York, 1977. 631 pp.
146
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1 ' 'APPENDIX A
SPECIFICATIONS FOR CONSTRUCTION OF COVER SYSTEMS
This appendix presents specifications that are generally suitable for
construction of cover systems. The specifications and the four cover designs
to which the specifications are applied should not be regarded as having offi-
cial status with EP.4. In fact, rome of the features do not satisfy RCRA as of
1986. These specifications should, however, illustrate to writers and review-
ers of specifications the state of the art, with its characteristic language
and necessary thoroughness.
Only technical provisions are considered here. The general provisions
and other parts and sections of the contract primarily prescribing legal, reg-
ulatory, and financial arrangements are not included.
PLANS AND DRAWINGS
Plans prepared by the owner as a part of the contract are almost always a
necessary adjunct to specifications for representing dimensions, positions,
and areal configurations as well as requirements amenable to tabulation. One
snould think i.i terns of "Plans and Specifications." Plans are unique to each
job and therefore are not addressed in this appendix, but a brief review of
the content of a set of plans is given in Table 12- and accompanying text of
Section 3 on pages 35 and 38. Frequent references no plans are found in the
specifications, reaffirming their primary importance.
Working drav/ings are commonly required of construction contractors.
Working drawings show structures or features necessary for adequate control of
the work. Examples are working drawings showing the sequence of construction
and the access routes for haulage and placement of cover materials. Possible
problems or problem locations are sometimes foreseen from such drawings.
ORGANIZATION OF SPECIFICATIONS
Specifications are organized for clarity in achievement of the intended
design. This organization includes the addressing of each major construction
task in a separate part (Table 12 on page 36). Materials and equipment are
sometimes addressed in separate parts, but elsewhere are addressed under each
construction task. Some versions of specifications leave the choice of equip-
ment and seme r.aterials with the contractor and largely excluded from the
specifications.
The example outline of technical provisions for covers in Table 12 is
organized much like that developed for use of state highway departments (13).
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The similarity between a cover system on backfilled solid waste and a paveaent
system on an embankment subgrade is sufficient to suggest that highway speci-
fications are usable models needing only careful modification. Also, the vast
experience available in highway departments in every state is potentially use-
ful. To apply the highway model, a few parameters are equated as Indicated in
Figure 13 on page 31.
It should be understood that some parts or sections will not always be
needed. The outline in the table is quite broad and even suited to contracts
for remedial cover at problem waste sites. For remedial work Section 201 OP.
clearing and grubbing and 202 on removing obstructions might need careful
detailing. Similarly, the preparation of the subgrade may amount to modifying
and supplementing the existing surface soil and be detailed sufficiently under
Section 205 (Table 12). Elsewhere, the subgrade .nay be entirely new and
deserving of elevated status in the design and construction effort and, there-
fore, might be allotted a lengthy Section 204 in the jpecificetlons, e.g.,
when a covering contract follows closely after filling of the waste cell.
Where the covering work is one portion of a contract for the whole dis-
posal operation, the parts and sections applying to cover will be integrated
into a more comprehensive set of specifications. Advantages and disadvantages
of contracting the cover system alone constitute a separate subject, beyond
the scope of this appendix. The size of the contract is, nevertheless, alwrya
deserving of careful consideration.
Details of Sections 204 and 205 and selected sections of Parts 300
through 700 art given below as applied to specific cover designs. Other parts
ar.d sections ran be similarly modified fron existing t .ts of specifications,
e.g., from AASHTO (13).
SPECIFICATIONS FOR COVER DESIGN I
The following selected guide specifications might be suitable for con-
tracting for construction of Design I identified as S/C/L-l under EXAMPLE
DESIGNS (See page 38). Section numbering is conformable to the organization
of technical provisions in Table 12 on page 36.
* * • C.'otc)
?oi BACKITI.L ASH rM!!ANK>:r.::T
-Oi.OI Pescrlpclon. Thin work sh.i i! conr.isc of constructing ctTib.nnV.rent s .
Including prcpnrfltlon of the t'ound.it ton .ire.i: conr.r rueclns: <)ikes vKMn rr
outside the rflscos.il cell aroa; pl.iclnr. .-.nii cocioncllnc nnprovcd m.iterlji
Note: The triple asterisk symbol (***) indicates omission of portions of the
specifications concerning other than cover construction.
Note: Where the cover system is to be placed on preexistent foundations such
as old backfill and intermediate cover, 205 SUBGRADE PREPARATION' may be
substituted for section 204. (See BUFFER LAYER AND FOUNDATION,
page 62).
148
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within vaste cell areas where unsuitable material has been reaoved; and
placinc. ac>£ conpactlnn raterlil Is gullies, pit?, and other depressions belov
Che
204.0? yjrerlals. Only materials Identified en the plnns or otherwise
approve* b« the Engineer shall be used in the construction of embankment and
backfill. "
204.03 Keying Methods. I'r.less £hovn otherwise on the plans or special pro-
visions. all sod and vegetable natter shall b« reaoved from the surface upon
which ecbaakxent is to be placed, and the cleared surface shall be completely
broken br plowing, scartfyinfi. ir stepping to a nlnlaun depth of 6 Inches.
This area shall then be compacted to the sar:e density required for the embank-
ment. Sec not to be removed shall be thoroughly disked before construction of
embantawct.'
Vhez: embankment is to be alaced on 'an existing hillside that is steeper
than 6 horizontal on I verclr . the slope shall be continuously benched in
not le*s than 12-inch rises .-s the work is brought up in lifts. Each bench
shall becia at the intersection o: the ground line and the vertical side of
the previous bench and shall he of sufficient vfdth to permit placing and
cc-pac:i-l operations. Exist lie slopes shall also be stepped to prevent any
wedcir.R action of the cnbankirent aeainst structures. No direct payment will
be =«<:* for the material thus cut out nor for it.- compaction alon? with the
new e>rKir.isent naterial.
Oa r.evly constructed slc-r-vs. the bench- kevlng shall be accomplished only.
where irtcicated on the plans.
20-. Ci Sjckfilline Arnur.d Structures. If cmSankcent can be deposited on one
side only; of abutments, win? «ai!s. or culvert heacwalls, care shall be taken
that rccrairir.E leaedlatelv adlaccnt to the structure will not cause ovcrturn-
Inc of ?r etccsslve pressure .•'sasr.st the stmrtcrc. When prbanksent is to be
places cr both sides of a rrrcr*te wall, canhoie. or box-type structure, oper-
ations shall be so conducted th.it the cichankr^r.: !s always at approxlcately
the srra* elevation on both s:-ies »^t" the structure.
201. PS ?:acir.E and Coopnct !r.c. Enbanknen: ..» tnr.iiieor irav allrv c.reater lift
thickr.-«< provldlr.c proper Jor.. .-.ssure uniforra density. V&ter-
shall be added or renotreu ii ^cc*ssary to !.-..-! Mtate compaction to the
requires density. Construction equipment shal! be routed uniformly over the
entire s-jriacc of each lift.
r the material const s:» fredonlnant iv of rock fr.icncnts of such size iNote)
that the material cannot be pl.ired in lifts of the thicknprn prescribcrt
without crcshlnK, pulvcrt;in«, or further hrr.ifctni; down the pieces resulting
froa excavation methods, such cuiterial. ii-av h< placed in the embankment in
lifts aot exceeding in thickneRS the approxja.n« nveraRe size of the larcer
rorks. bet not gre.ater than ...... [2 feut suc^ested I . Each lift shall be (Note)
leveled jrd smoothed with suitable level inc «;uipnent and by distribution of
ppnlls an«l finer frawrents or soil. Wncrc end dumping is employed, direct end
duirdin^ ujon the previously constructed lift, of cnbankment will not be permit-
ted. Soci' shall be dumped on tr-.e lift bi-ini; constructed and do:ed ahead Into
place. =i^k..- lifts shall not fc« constructed .ibove an elevation I feet below
the finished subgradc.
Note: .This paragraph should be removed in the common case where rock frag-
ments constitute no more than a minor component.
Note: The dot underline symbol ( ) indicates the need for a decision on
dimensions, etc. A suggested value may be given in parentheses [__].
1-19
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204.06 Moisture and Density Control. The plans show the areas In vhlch
enbankment shall be constructed with oolsture and density control, and the
Distance be low iuburaJe to vhlch su«:!i methods shall be applied. All ecbonk-
nenc down to 2 .feet below su^rad* shall be Included. Construction lifts
shall be no thicker than 6 Inches after coxpactlrn.
Each lift shall be'cocpactoJ to not leai than |95 percent sug-
gt^ceJJ of the maxlauo density. The material shall be dried or moistened
uniforely before coapactlon, as necessary to bring cotsture content to that
appropriate for achieving required density.
Maximum densities shall be determined In accordance vlth ASTX E698. (Note)
In-place field density shall be Jetorilned nccordlns to ASTM D1556. D2I67,
D29J7, or D2922. The Contractor is responsible for testing but nay use an
approved conmerclal testing laboratory. All costs of sacpllng and testing
shall be borne by the Contractor.
Density requirements vill not apply to portions of embankments con-
structed of materials which cannot be rccred In accordance ulth approved
netho.1s.
20-1.07 Compacting Without Moisture, and Density Control. Embankment caterials
not designated for moisture ar.i density control final! be deposited in lifts
nnt exceedtnq 8 Inches In thickness before compaction, unless otherwise speci-
fied bv the Engineer. The acceptable r.vpcs and application of compaction
equipment are stipulated In the plans, however, other approved equip-c.it cav
be used.
DinplnK and rolling areas sh.il! be kept .it-par.He, and no lift shall be
covered by another until cocp'iccli-'n complying with the reculrements of this
subsection is secured. Hauli~c ard IcvollnK cqulpncnt shall be routed and
distributed over each lift of the rill in such a canner-js to nakc use of con-
pact Jon effort afforded thercbv.
:Oi.O.S (Reserved)
-------
(b) Measureoent of Special Excavation. Measurements will he made for
unsuitable existing materials actually excavated and removed to
obtain proper compaction in the foundation for backfill and embank-
menc. No measurement will be cade of the suitable material tempo-
rarily removed and replaced to facilitate compaction of the material
for the full depth shcun on the plans.
Where It is Impractical to measure excavated material by the
cross-section method due to the erratic location of isolated depos-
it:,, acceptable cethoJs Involving three-dimensional measurements may
be used.
(c) Measurement of Szbankments. When specified !n tho contract, embank-
ments will be measured and paid for In accordance vith the terms set
forth.
When payment for embankircnt constructed vtth eoisture and dens-
ity control is specified as a separate bid Itec, the volume so con-
structed will be computed in cubic yards by the tr.cinetr from the
• dimensions of the embankment cross section and. the depth belov the
completed subcrade to vhlch this r.cthod of construction apples.
(d) Measurement of Subcrade Treatment. The vork of stnMllr.lne, subtsrade
treatment areas vill be measured bv the square vard from the limits
'of the areas so created. Correction of subqrade deficiencies,
including those "srnblishcd bv proof rolline, shall be incidental to
embankment construction and not a pay item.
(e) Measurement of Vater. When pavmenr for water Is specified In the
contract, the water uspd In the work will he rcasurod r-y the
1,000 pal Ion*: <".C.) bv nc.inn of calibrated tanks or distributors or
by ncans of accurate water meters.
When wattr is not specif i»*d .is a fav itra In the contract, the
wnter used till not he reasured or paid fcr imt vill be lnc!i!c:itnl
to the work.
20A.10 Basis of Fav~e:-t. The accepted qu.int It ics <"f (rah.inkrvnt (or nnck- (N'ntc)
fill) will be paid ac die contract price for each of the r.iv ttcr.s listed
below that Is included In the bid Kchedulc.
Fav '.tern I'.iv '.'nit
F.nbankaent with .Votstiire Control ruble v.ird
Fabiinkment without Moisture- Control Ctibic vard
Special Excavation Cub!c vaid yr Ton
Water M.ci (l.OOa callous)
205 SUBCRADE PREPARATION' (Note)
205.01 Description. This work shall consist of shaping and cocpactinc the
subftrade pi lor to placir.E the lovcsr cover course thereon.
205.02 Construction Requirements. This work shall be done after any unstable
sections of the subgrade have been repaired and after any existing nateri.il
required to be removed has been removed.
Note: Lump-sum bidding and payment is often preferred over bidding and pay-
ment-baaed on unit prices. A lump-sum price so bid is paid as full
compensation for the estimated.quantities shown iu the contract.
Note: This section may be used in place of section 204 where existing back-
fill and embankment is largely adequate as a foundation for the cover
system.
151
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The Contractor shall compact and shape the s^bgrade for Its full area as
nay be necessary to produce, at the tlse the lowest course Is placed, the
required density and stability,In the top 6 Inches of the bubgrade ano the
required grade and cross section. The Contractor will be required to scarify,
dry the ciaterlal, or apply water as nay be necessary to obtain the required
density and stability. Unless otherwise provided in the contract, the
"required density" shall be (95 percent suggested] of oaxlcuo density.
The "required stability" shall be such that when any oatertal for cover
layers above Is distributed on the subgrade, no rutting or displacement will
o*cur. Rutt!**£ deformation traceable bel: * th«. subgrade from any layer above
shall be considered as indicating subgrade instability.
The "required grade and cross section" shall consist of a smooth subcrade
surface conforming to the prescribed elevations for the particular subgrade
being prepared, prior to constructing an additional course thereon. The pre-
scribed elevation for any point on the subgrade surface where measurement is
made shall be as determined from the rrndes staked by the Engineer and the
typical sections shown in the plans.
In conlunction with the operations of subgrade preparation, the Contrac-
tor rhall produce, load, and haul material of the sane type as that used In
the subgrade or in the course to be constructed where and In such anounts as
the Engineer directs and Incorporate such material Into the subcradc. This
work shall be at the appropriate contract prices for (he material In place or,
in the absence of such prices, regarded ;s extra work.
205.03 Method of Measurement. Suhgrade prep.irntion wll i be measurcu on an
nreal basis. locations wlierc Rr-.dli.i; cir subgradn correrrlri is rcqui-cd"will
not be Included In these measurements but Instead wll! be measured as extra
work on a volume basis.
205.04 Basis of Payment. If the backfill, er.banktnent. or intermediate cover-
being prepared was constructed under the sane contract, the Contractor shall
perform ali vor^ required herein at his own expense and without nnv direct
compensation being aadc ihercfor. Pavcent for subcrade preparation as a seo-
arate item will be nade only when the backfill, embankment, or inrerredlate
cover being prepared was constructed under a previous contract.
' Payment for Subgrade Preparation will be compensation in full for all
coses of preparing the subgrade as specified, except that anv expenses
incurred in correcting unstable conditions below the top 6 Inches will be
compensated separately as extra work or at the contract prices for the equip-
ment used 1f so provided in the contract.
Payment will be cade under:
Pay I tee Pay Knit
Scbgradc Preparation Square yard
Subgrade Correction Cubic yard
301 CLAY HARRIER :
301.01 Description. This work jhall consist of furnishing and placing a clay
course on a prepared surface in accordance with these_specificatlons. in rea-
sonably close coTforoity vith the lines, grades, thicknesses, and typical
cross sections shown on the plans. ,'
t
301.02 Materials. The clav catcrl.il in place in the course shall be-hcaese-
necur. pnd shall aeet the requirements of subsection 704.05. Either or both of
two material categories may be utilized from the material sources:
(a) Homogeneous ciny BMtprfnl, defined as clavev r.acerlal havlTic unl-
•' foroity of grain slr.e .1:..! faineraicclcal cccposltipn at the source
. deposit or in the cntjrlal as delivered.
152
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ne'^r r\av material, defined as clayey material from a
source ti>.>U or !n r':c L.arrr'.tl as dell.ered having Indications of
stratification, weathering 01 sol', fo-r.IOR eff^.'s. or other physi-
cal characteristics which will result in a coabi..dti3n of tvo it
BOIO soil types. Shortfall in estimated total volume of lioaoKT.^aas
el.iy oatcrial available it-"- cue source will be another basis for
classifying material as nonhomogenenus.
. The Contractor shall mix all nonhnaopeneous clay material according to
subsection 301.04 to achieve the requirements of the clay course. l'ce of both
homogeneous and nnnhonor.eneous clav naterlals will be pe rait ted. but their
usage shall be separated by restriction to separate arear of the clay course
approved in advance by the Engineer.
Homogeneous clay material will be accepted based on testing of samples
representative of loads excavated at the source or delivered at the Job site.
Nonhor.ogeneaus clny material mixed in a plant or *»y road-mix method will be
accepted based on samples of the plant output or ot combined windrows.
301.03 Preparation of Course Foundation. Before placing operations are (Note)
begun, the area of the suberade or course upon which the clay course Is to be
placed shall be cleaned and checked for condition and for confonaance with the
grades, lines, thicknesses, and tvpical sections shown on the plans or as
ordered by the Engineer. When the clav course is superimposed within
(10 days suggested) upon subgrade or another course constructed under theit
specifications and that previous work has been accepted by the Engineer, the
checking activity may be waived.
The subgrade and any preceding course sh.il! be compact and suitable to
support the construction and compaction equipment without settlement or dis-
placement. Soft ,or yielding areas shall be corrected and eade stable before
the clay course is placed.
The foundation shall be tested for r.oisture condition and where fo >nd tc
be dry or wet of optln-in coistiire curing original compaction by (2 per-
centage points suggested vhcre the foundation Is sard] or more, it o'hali be
examined for cracks, soft s;jots, and other delects and then shall be adjusted
into the acceptable range by audition of water or by drvinz. The presence of
defects nay be cause for recuirl-.fi replacement or repair of the foundation.
301.0' Mixing. The clay rourse shall be brought to a homogeneous condition
rior to compaction. I'nless otherwise j^ecifled. the Contractor shall olv
nonhoz&geneous clay material by one of the following aethods:
(a) Stationary PJ.int Method. Before placement, nonhomogeneous clay
material shall be mixed in an approved mixer. Addition of water
shall be restricted to prevent balling and other proble=s preserving
or Increasing segregation of material components. Air pollution
through the peneration of dust shall be kept at levels permitted bv
State and Federal regulations. After nixing, the drv material shall
be placed according to subsection 301.OS.
(b) Travel Plant Method. After nonhoxogeneou.-. clay material for each (Note)
lift of the clav course has been placed with a spreader or in win-
drows, the material shall be nixed uniformly bv an approved travcl-
irg nlxlne plant. Vatei may be added to the extent that the
addition docs not result in balling or other interference with the
mixing process.
(c) Koad Mix Method. Aftet nonhor.ogeneous clny material Cor each lift fNote)
of the clav course has heen placed with a spreader or in wtnrircws.
the material shall be mixed uniformly by motor grader or other
Note: In the case of Design I the foundation of the clay course consists of a
sand course and underlying subgrade.
Note: Mixing in place may be unacceptable for Design I because of disrupting
effects on the capillary barrier immediately below.
153
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uqulpoent approved by the Engineer u-.ril the olxture Is inlfora
throughout. Water cay be added Co the extent that the addition does
not result In balllnc or other Interference with the nixing process.
In all cases of nixing and addition of water, the formation cr preserva-
tion of balls.or granules of unalxed components lamer than (1/4 inch
'uggestedj across as spread and ready for compaction shall be avoided. The
Contractnr shall understand that such granules vlll be a basis for rejecting
part or all of. the clay course.
301.05 Placing and Spreading. Clav oaterlal foi each life of th.. clav course
chill he placed and spread in such vavs as to avaid daoage to the previous
lift or the course fcuncatlon. The Ccntractor shall understand that cracks,
ruts, offsets, punctures, and other indicatlcr.: of daa*.ge to ucderlylng nato-
rlal by equipment or procedures will constitute valid criteria fot rejection
and will necessitate replacement of imaged eieocats at the expense of the
Contractor.
Where mixing Is aceoopllshed using travel plant or road oil methods
according to subsection 301.04, such nixing shall be considered a part of
placing and spreading.
The thickness of the loose lift shall be such as will ceet the required
compacted thickness specified In subsection 301.06.
301.06 Coapactlne. Loose lifts of clav cateriai shall be compacted by equip-
ment and procedures capable of attaining the prescribed density vithout danage
to the lift being compacted or to underlying courses or lifts. Cocpactors
that icpart a kneadlr.E action cr penetrate the tea surface of the lift shall
not be used unless approved by the Engineer. As appropriately sized tire
roller compnctor will usually be acceptable. The course shall be constructed
in lifts not exceeding (6 Inches suggested), and lift thicknesses In
eultlple-lift courses shall be approxtnatelv ecua^.
The Contractor shall dc=onstrate the suitability of his proposed coispac-
tor.unit'for the materiel and icursc desiin by ccttstruetlr.p a life under sial-
lar conditions. This demonstration will norraiiy be performed at the Job
site, but closely sisllar experience elsewhere =£y b; substituted when
approved by the Engineer. The ta?cs for evaluating results vlll be the
required in-plnce density And the indications o: damage .such as cracks,
depressions, and shear surfaces.
The required density shall be {90 3«rccnt succcstcd! of maxir.ua
densiiv determined in accordance with ASTX Dt-Sfl. Cecpactlon shall continue
until a density not less than the required density has been achieved to the
full depth of the lift.
The surface of each lift shall be oaintair.ed during the cr=?action opera-
tions in .such n ir.-inncr that a uniform texture is produced and ..nv coarse '.'Cia-
ponent allowed under subsection 301,0? Is flr=iv ceycH. Water <:hnll be
uniforcly applied over the cateriuls during c^r^actton in the .irour.t necessary
for proper compaction.
In-plnce field density shall be determined In accordance with ASTM DISSn,
D2I67. D2937, or D293I. Modification of testinc rjv be reonire
-------
301.08 Protection and Maintenance. The Contractor shall be required, within
the Holts of his contract, to maintain and protect the clay barrier In good
condition and In a manner satisfactory to the Engineer froo the start of work
until all work hat been completed and accept-'. Maintenance by the Ccr.rraccor
shall Include immediate repairs of any defects, regardless of cause, that day
occur. This work shall be done by the Contractor at his ovn expense, and
repeated ac often as Day be necessary to keep the course continuously intact.
Repairs are to be tudc in a manner to ensure restoration of a uniforn surface
and durability and Integrity of the part repaired. ' Faulty and damaged work
shall be replaced for the full depth of the course by the Contractor at his
own expense.
301.09 Method of Measurement. Clay course vill be measured by the cubic (Note)
yard in accordance wltb 109 MEASUREMENT AND PAYMENT. When specified as pay
Item, water added to the materials will be ceasured by the 1.000 callous by
eeans of calibrated tanks or distributors or by Beans of accurate water
oeters.
301.10 Basis of Payee.-.t. The accepted quantities of Clay Barrier, of the
type specified, will be paid for at the contract price as follows:
Pav Ire^ Pav Unit
Clay Barrier Course Cubic yard
Hater for Clay Harriet '.'nurse M.C. or Incidental to clay
* * *
403 FILTER LAYER
£03.01 Description. This work shall consist of furnishing and placing a fil-
ter course on a prepared surface In accordance with these specifications. In
reasonably close conformity with the lines, grades, thicknesses, and typical
cross section* i>:.own or. the plans.
(03.02 Materials. The filter materials shall be homogeneous sand and shall
cect the reouirements of subsections 703.19 and 703.01. Material will be
accepted based on test reports of sarples representative of loads delivered.
(03.03 Preparation t :' Course Foundation.' Before placing operations are
begun, the area of the subgrade or course upon vhlch the sand course is to be
placed shall be cleaned and checked for condition and for confonrance with the
grades, lines, thicknesses, and typical sections shown on the plans or as
ordered by the Engineer. 1»*here the sand course is superlraposed within
[10.days suggested| upon subgrade or another course constructed under these
specifications and that previous work has been accepted by the Engineer, the
checking activity cny be waived.
The subgrade and any preceding course shall be compact and suitable to
.support the construction and compaction equipment without settlement or dis-
placement. Soft or yielding areas shall be corrected and made stable before'
the sand course is placed.
The foundation shall be tested for moisture condition and where found to
be dry or wet of opticun roisture by [4 percentage points suggested
where foundation Is clayey] or more. It shall'be examined for cracks, soft
spots, and other defects and then shall be adjusted into the acceptable range
by addition of water or by drying. The presence 01' defects may be caure fcr
requiring replacement or repair of the foundation.
\
403.04', Placing and Spreading. Sand material for each lift of the course
shall be placed and spread in such ways as to avoid material segregation and
nixing with or damage to the previous lift or the course foundation. The
Contractor shall understand that segregations, mixtures, or cracks, ruts,
offsets; punctures, and other indications of damage to underlying material by
equipment or procedures will constitute valid criteria for rejection and ulll
necessitate replacement of rejected elements at the expense of the Contractor.
Note: Section 109 MEASUREMENT AND PAYMENT Is not included In this appendix.
155
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The loose thickness of v&ch li.'t shall be such as will ciect the required
compacted thickness spec if led tn subsection 403.05.
403.05 Compactlr.c. Loose lifts of sand catcrlal shall be conpacted bv equip-
ment and procedures capable of attaining the prescribed density without damage
to the lift he Ing compacted or to the underlying material. Compactors that
impart a kneading action or penetrate the top surface of the lift shall not be
usdd unless approved by the tnpineer. An appropriately sized tire-roller coa-
pactor will usually be acceptable.
The required density for cocpact ion shall he (85 percent sug-
gested) of nuixlrtma relative Jensl r v. The Contractor shall provide the naxltrua
and minimum density paraneters for the chosen sand ru-rertal .ilonp with the
calculated relative density required by this contract at least tv»» upeks prior
tc plnclni* snnd oatorlal In the course. Details of the test etc thuds i.hnl! be
provided al so. A net hod vising a vibratory table Is ur.ua 1 !y preferred for
determination of mnxtoun relative density.
The course sha 11 he constructed Ir. lifts not exceeding [6 Incites
suggested) and lift thicknesses In multiple lift courses shall be approxi-
mate !v equal. Compact ion shall continue until a density not l«:ss than the
required density has been achieved to the full depth of the lift. Water shall
be .'.pplled unlfomlv over the catcrlals during compaction In the aoount neces-
sary for proper compaction.
In-plncc field Jensily shall be determined In accordance with ASTX D155&.
r-2'67. 02937. or D2922. Th* Contractor is responsible tor testing but nay use
an approved concr.erc ial ~est inc laboratory. All ccsts of samp I in?, and testing
shall be borne by the Cot tractor,
£03.06 Construction Joints and Surfaces. At t^.e end of each day of construc-
tion a Lateral construction joir.t shall be icark**d if not clear!-.' cvidt-r.:..
Ter.por.irv covering cay be required by the Knpj neer to preserve the as-
conscructed condition Intended. Lpoti resurpt Ion o:' work the joint shall he
uncovered and mcLstcned os reoded co assure interlock alcr.$ the joint when the
lift is extended.
Course surfaces shall similarly be protected by teoporary cover, to be
reioved completely upon rtpunptlon of work with addition cf the course above.
iC3.C7 Protection and Maintenance. The Contractor shall be rcculred to iraln-
tain and protect the filter layer in good condition and in a tcanner satlsfac-
torv to the Fnr.lr.eer froci the ct=c he first starts, vork unril all work has
been cotr.pleted and accepred. Vointenance by the Contractor shall include
innudlGte repairs of any defects, regardless of cause, that nay occur. This
vork shall bo done bv the Contractor at his ovn expense and repeated as often
as cay be uecessarv to keep the courso centInuousIv intact. Repa Irs are to be
rade In a manner to ensure restoration of a uniform surface' and durability and
Integrity of the part repaired. Faultv and daaaeed work shall be replaced for
the full depth ol Che course by the Contractor at his own expanse.
603.03 Method of Measurement. Sand course will he nea^ured bv the cubic yard
Jr. accordance, with :09 XEASr?.FXE%T AND PAYMENT. When specified as pay Item.
water added to the raterlnls *.-j II be ncasured by the 1,000 rallons by neans of
calibrated tanks or distributers rr by =eans o;" accurate water ceters.
i03.09 B-i si s of Pnvnifrnc. The ace opted ^uanciLles of Filter Layer. 01 the
type specified, will be paid for at the contract price as follows:
P.iv Tt«*n P.TV Tnit
Filtor L.'tver Course . Cubic yard
Water for Filter Laver Course M.C. O" Ir.ciJ«r.ril lo snnd
156
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406 VECETATIVF LAYER
£06.01 Description. This work shall consist of furnishing and placing i
vegetative soil layer on a prepared surface In accordance with these specifi-
cations in reasonably close conformity with the lines, grades, thicknesses,
.and typical cross sections shovn on the plans. The vegetative layer does not
include vegetation.
406.02 Materials. Vegetative soil types shall be:
(a) Torroil meeting the requlrecents of subsection 704.01.
(b) Loamy soil as defined by the US Department of Agriculture on the
basis of grain size components and free of stones, roots, and debris
over ...... [2 inches suggested) in greatest dlcenslon. Up to
[8 percent suggested) gravel oav be included and such gravel
may be excluded as a grain-size component for purposes of calculat-
ing soil grain-size content.
Material vlll be accepted based on test reports on saoples representative of
loads delivered.
406.03 Preparation of Course Foundation. Before placing operations are
„..„..:•. the area of the subgrade or course upon which the vegetative course is
to be placed shall be cleaned and checked for condition and for conforaance
with the grades, lines, thicknesses, and typical sections shovn on the plans
or as ordered by the Engineer. Where the soil.course Is superimposed -Ithln
[10 days suggested! upon subgrade or another course constructed under
these specifications and that previous work has been accepted by the Engineer,
the checking activity cay be waived.
The foundation shall be cocpact and suitable to support the construction
ar.d cocpaccion equipment without settlement or displacement. Soft or yielding
foundation areas shall be corrected and made stable before the -curse is
placed.
The foundation shall be tested for noisture condition and where found to
b* dry or wee of optlnuo noisture by |i percentage points suggested
where foundation is clayev] or nure. it shall be examined for cracks, soft
spots, and other defects and then shall be adjusted into the acceptable range
by addition of water or by drying. The presence of defects day be cause for
requiring replacement or repair of the foundation.
606.04 Placing and Compacting Other Tnan Topsoll. Soil material for each
lift of the vegetative course other than topsoil shall be placed and spread in
such wavs as to avoid material segregation and mixing with or damage' to the
previous lift or the course fou;:d.itlon. The '.'untractor shall understand that
segregation;-, or mixtures or eracr..-:. ruts, offsets, punctures, and other
indications of dam.nre to underlying material by equipment or procedures will
constitute valid criteria of damage aid will necessitate replacement of
damaged elements at the expense of the Contractor.
Loose lifts of soil material shall be compacted using a dozer or similar
low-pressure unlr and procedures capable of attaining the prescribed density
without damage to the lift being compacted or to underlying material. The
density after compaction shall i.e [82-86 percent suggested) of maximum
density determined In accordance with ASTM D698. tn-olace field density shall
be determined in accordance with ASTM DJ556, DIM67, D2937. or D2922. The Con-
tractor is responsible for testing but may use an approved commercial testing
laboratory. All costs of sampling and testing shall be borne by the
Contractor.
•The course shall be constructed in lifts not exceeding ...... [8 inches
suggested], and lift thicknesses in multiple lift courses shall be approxi-
mately equal.
406.05 Placing Topsoil. After being stripped from the source, the topsoil
shall be placed Immediately or stockpiled. Stockpiles shall contain not less
than 200 cubic yards, shall have a height of *t least 4 feet, and shall be
triaaed to uniform surfaces and slopes. The Contractor shall be responsible
157
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for preserving the vitality of stockpiled topsoll. Leaching, drying, or heat-
Ing will be considered CO Indicate deterioration of topsoll and the Engineer
will evaluate the acceptability of stockpiled topsoil material on the basis of
these or other Indications. Where evaluation Indicates that topsoll no longer
neets the requirements of subsection 406.02. the topsoll aaterial shnll be
replaced- at the Contractor's expense.
Where specified or directed, the Contractor shall scarify the surface of
the underlying course before the topsoll Is placed to loprove bonding. Scari-
fying shall be accomplished In such a canrer that depressions and ridges so
forned shall be parallel to the contours and no deeper than [3 inches
suggested! total relief.
Topsoll in an unworkable condition due to excessive moisture, frost, or
other conditions shall not be placed until it Is suitable for spreading. Top-
soil shall be placed on the designated areas and spread to the specified
thickness above the tops of any rldees forced by scarification. After the
topsoll is spread, all large stiff clods, rocks, roots, or other foreign nat-
ter shall be ivnoved fron the surface.
406.06 Protection and Ma'ntenance. The Contractor shall be required, within
the Hairs of his contract, to ralntain and protect the vegetative layer in
good condition and in a r.anner satisfactory to the Engineer Iron the tine he
first starts work until ill work has heen completed and accepted. Maintenance
by the Contractor shall Include irr-.cdlate repairs of any defects, regardless
of cause, that ray occur. This work shall be- done by the Contractor at his
own expense and repeated as often as =ay be necessary ro keep the course con-
tinuously Intart. Repairs arc to be radc In a manner to ensure restoration of
a unlforn surface and durability ard Incep.rilv of the p.-.rt r»patred. Faulty
and cian.med work shall bi- replaced for Chi- full depth of the ccvjr.-;<- hv the
CiintI'.TCtor at iil.s own expense.
406.07 Method of Measurement. Vegetative courses will he measured by ti,v
cubic yard In accordance with 109 hLASL'R!-"r<-T AND PAVMKNT. Topsoil chlcrncs£
sh.-.il be as sjasured above the tops of scarification ridges. Ulien .specified (N
as pay item, water added to the rj:crlald vlll he ceasured by th-' 1,000 pai-
lons bv ™tans of calibrated tanks or distr1butors or by menus of accurate
water meters.
406.08 Basis of Pavmenl. Tlie accepted quantities or Vegetative Laver of t!i«
types speciflud vlll be paid for at the contract prices for ioas course and
topsoll course and per 1,000 gallcr.s for'water complete in place -is follows:
Pav !ten Fav I'n i t
Loan Course Cubic yard
Topsoll Course Cubic yard
Water for Vegetative Course M.G. or Incidental to loac or topsoll
610 1T8F ESTABLISHMENT
610.01 Description. This work shall consist of soil preparation, seeding.
fertilizing, lining if required, and mulching on all areas designated for
turf establIshrent as shown on the plans or where directed by the Engineer.
610.0- Materials. Materials shall r.ect the requirements specified in the
following subsections nl '00 MATEK:ALS DETAILS:
Agricultural Ltcestone 711.02
Fertiliser 711.03
Seed 711.04
Mulch 711.05
Eaulsified Asphalt 702.04
Note: Where its costliness Is considered critical, topsoil may need to be
measured froa the half-height cf scarification ridges in order to
reduce cost. This detail is typical of the many dlleomas requiring
resolution in preparing specifications.
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610.03 Scheduling and Seasons. The Contractor shall establish turf as soon
as he has satisfactorily completed a unit or portion of the project for par-
tial acceptance as provided under 103 PROSECUTION* AND PROGRESS or Indicated (Note)
on the plans. Discrete units ray be the cover systea over an Individual waste
cell; or the portion nay be an arbitrarily delineated area which can be
protected frcn further traffic and other disturbance.
The noma 1 seasonal dates for seed Inn shall be:
Spring seeding [Established locnllyl
Fail seedlnR (Established locally)
However, the vork Day be performed at anv season of the year when a mulct) Is
used unless otherwise specified. The Contractor shall ROC 1fv the Engineer at
least iH hours In advance ot" the time fie Intends to hc-tjln sowin3 seed and
shall noc proceed with such work unrll pernlsblon to do so li;:s Seen obtained.
When delays in operations carrv the work beyond the noraal seasonal dates, or
vht'ti conditions of hlp.h winds, excessive moisture, or Ice are sncr that satis-
factory result? are not likely to be obtained for nnv stap.e of the work, the
Engineer will stop the work. The work shall be resumed with the Engineer'»
approval when the desirtd results are llkelv to be obtained or when approved
corrective measures and procedures are adopted.
610.04 Soil Preparation. All areas to be seeded shall be cultivated to pro-
vide a reasonably firm, but friable seedbed. Depth of cultivation shall be as
shown on the plans unless otherwise directed bv the Engineer. On slopes
steeper th?n 3 horizontal on I vertical, depth of cultivation *ay be reduced
as directed. All areas to be seeded shall neet the specified finish p.radcs,
be free of anv weed or plant growth, stonea of |2 Inches suggested] it>
dtareter or larger, or other dtbris. Licestone. If required, shall he applied
unifomlv either prior to or during noil preparation, and shall be incorpo-
rated into the soil surface to the depth shown on the plans. The a&pllcatlon
of 1 ir.eFtone after boil preparation has been cottp leteri shall be only on
approval of :he t'nc*. ine^r. All eechanlcal ecul oment for soil preparation shall
be a? approved and s'na 1 ! j.aps pjr.iHe! to the contours unless otherwise
approved.
610.05 Test Ine, Yixlnc, and Inoculat ing Seeds. Provisional acceptance of the
seeds nusc he ohrair.ei1 !,c;ore the seedy are r.lxed. Each let of seed sh.? 11 be
subject to sarplir.^ and rest Ins before cixlnc. Sowing seed shall not be
delayed pending reporzs of those recis. Sanplini? and testing shall bo accoa-
p1Ished by an approved cept Ing laboratory at nc additional expense to the
Ovp.er. Seeds of Che kinds specified shall be cilxed on the job In the f ornul a
sr"ci:led unless otherwise approved. 5«:e-J mixed prior to deliverv nav be
approved on che basis of J certification by the vendor statinc the olni^ur.
percentage rf gemination and purity of each kind ot seed and the quantity of
each kind of seed in the mixture. All seed of lenuair.ous plants shall be
Inoculated with approved ccltt:re^ prior ro alxlr.ij or snvlnq unless oiher*'iae
specified or approved or unless accccpanied by a certificate of prei nocula-
tlor.. '-lien seed is to be sown dry and is to be inoculated, the culture phnil
be applied as directed hy the canufacturer and the soed allowed to dry suf-
flcier.tlv to be in thp proper condition for aiixfne or sowing. Seed oust be
bown within 30 hours after this tre.itcenr. Where seed Is t^ be distributed
hydrau 1 Ic.n lly, the proper proport Ion of inoculant may be added to the water
and see;] mixture, tccerher with anv Hirestcne or fertilizer specified, pro-
viding the alkalinity of the solution does not exceed S pH.
610.06 Application Met hods. Seed, fertilizer, liaestone, and rulch naierlal
nay be placed by the fol lovlnc n-.CLhods:
(c) Fivdr.iuHc r.pthod. The seed and fertilizer, or the ceed. ferclllrer,
and ru Ich sha I I be c.ixeJ In t '.ie spec i fled amount of w.itor to produce
a slurry and then uniforoly applied under pressure at the rates and
on the areas Indicated on the plans. Wood cell ti lose r.u Icli Incorpo-
rated as an Integral p^rt of the s lurry mix shall bc> added after the
seed and fertilizer, nn^ c round ) I nest one If rec-ui red, KJV-.' heen
Note: Section 108 PROSECUTION AND PROGRESS Is not included in this appendix.
159
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thoroughly mixed. Mixtures shall be const.intly agitated from the
tine they are aixed until chey are applied co the seedbed. Such
niictures shall be applied ulthln . [8 hours suggested I from the
time of mixing. Any area Inadequately covered shall be retreated as
directed by the Engineer.
Ulicn seed, fertilizer, and nulch are applied hydraulically,
compact icn or rolling will not be req-slred.
(b) Dry method. Drills, cultipackers, fertilizer spreaders, or other
approved mechanical seeding equipment cay be used to apply seed and
fertilizer in dry font.
Fertilizer in dry fora, and ground lti:scone If required, shall
be spread separately at the rates Indicated on the plans and incor-
porated in one operation to the required depth on those areas Indi-
cated on the plans. Seeded areas shall be compacted ulthln
[1 day suggested) after seeding has been completed.
Hand-operated seeding devices nay be used when seed, fertil-
izer, and ground licestone are applied In dry fora. Generally,
hand-operated seeders shall be used only on areas which are Inacces-
sible to cechanical seeders.
610.07 Application of Mulch. Straw, hay, or other =ulch, uhen specified,
shall be spread unifonaly over seeded areas at the race of ..... [1.5 tons/
acre suggested). The nulch may be anchored vith the rulch tiller, asphalt
enulslon. cvinc, netting, or other approved tledoun or adhesive oaterlals.
When asphalt emulsion Is used as a ciedovn or adhesive. Type SS-I or approved ~
equal shall be applied either simultaneously vlth the scrau or hay or in a
separate operation.
When immediate protection of nevly eraded slopes is r.eccssarv at other
than the normal seeding season, hay or scrav ?.ulch shall be applied before the
seeding with actual seeding conpleted later during the specified seeding
season.
610.08 Grub Prooflnc. Grub procfir.c uhen specified shall be perforced on
those areas and with materials and rates of application thereof as shown on
the plans.
610.09 Liability. Final acceptance of the seed &av be subject to the results
of of tidal sampling and testing. The velcht of seed sovn Is based on ITS
labeled purity and gemination. Tolerances provided by the testing laboratory
and approved by the Engineer for the various seed species shall be used in the
determination of whether seed conforms to the labeled purity and germination
statements and neets the nlnlnum specified. When, after the application of
the appropriate tolerances, the purity and K.enr.lnatlon of any kin-i of seed
except cereal grain and legumes are shown bv the rests to be less than that
shnun en the 1-ibel but the gerninaticn reets the irinic.ua specified with the
appropriate tolerance applied and the specified weight of pure live seed has
not been .sovn, the deticlency shall be sovn.
When the germination of any Vine of seed except cereal grains nnd legumes
is shown by the tests to be less than the mlnlmua specified, after the appro-
priate tolerances have been applied. It will be considered n total deficiency.
Such deficiency shall require coirplete reseedirg of the kind of seed which was
deficient;.
Rese'edlng together vith necessary grading and tricnlnK shall be done at
the expense of the Contractor by spreading the seed by an approved nethod and
during an approved season.
When, in the judgment of the Engineer, at any ti=e prior to the accep-
tance of the contract any area which has been seeded fails for any re'ason to
produce a satisfactory grouch of grass, the Contractor shall rcseed and refer-
tllize such areas In the same manner 39 specified in the contract and. If
deemed necessary by the Engineer, also r.ulch such areas at the rate specified
In the contract.
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610.10 Care During Construction. The Contractor shall care for the seeded
and eulched areas until final acceptance of the ptoject. Such care shall con-
sist of providing protection against traffic by approved warning signs or bar-
ricades and repairing areas damaged following the seeding or mulcl.lug
operations by wind, water, fire,,or other causes. Such damaged areas shall be
repaired to reestablish the condition and grade of the area prior to seeding
and shall then be refertlllzed, reseeded, and reculched as specified herein.
The Contractor shall keep seeded areas moved until acceptance of the contract
by catting to a height of 3 inches when growth reaches 6 Inches or when the
growth tends to smother seedlings or as directed.
610.11 Method oC Measurement. Measurement shall be based upon the number of
acres, measured to the nearest 0.01 acre, of ground surface actually covered
by seed, linestone if required, fertilizer, and mulch of the type specified,
completed and accepted.
610.12 Basis of Payment. The accepted quantities of Turf Establishment will
be paid for at the contract unit price, which payoent shall be full com-
pensation for furnishing and placing all materials, labor, tools, and Inciden-
tals necessary thereto except Topsoll Course which ulll be paid for separately
under section '.06.
Paytrent vlll be made under:
Pav I ton
Turf Establishment, Hydraulic method
without nvilch
Turf Establishment. Hydraulic eel hod
with r.ulch
Turf Establishment, Dry method
without xulch
Turf Establishment. Dry sethnd
vlth aulch
702.04 Emulsified Asph.ilt. Emulsified .isphalt shall conforn to the require-
ments 01 AASHTO M 140 or M 208 or comparable standard.
703.01 Fine Aggregate for Concrete. Fine aggregate for concrete shall con-
fora to the requirements of AASIITO .16.
703.19 Ferceable Material. Permeable material for drainage layers or for use
In backfilling trenches, under, around, ano over undcrdralns-and for other
subdralease purposes shall consist of hard, durable, clean sand, grave I, or
crushed stone, and shall be free iron organic material, clay balls, or other
deleterious substances.
\- . ' ,
\
704,01 Topsoll. Topsoll to be furnished by the Contractor shall consist of
loose, friable, sandy loam free of admixture of subsoil, refuse, stuaps,
roots, rocks, brush, weeds. Or other material which would be detrimental to
the proper development of vegetative growth. The term used herein shall mean
that portion of the soli profile defined technically as the "A" horizon by the
Soil Science Society of Aaerlca. The minimum and maximum pH value shal! be
..... [6 and 7 suggested). Topsoll shall be tested In confortnancc vlth the
standards of the Association of Offici.il Agricultural Chemists.
Toj-soil shall cortaln a nlnlnua of ..'... f5 percent suggested) and a oax-
Inun of, (IS percent suggested) organic matter. Topsoll shall have a
grading analysts as follows: •
161
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Sieve Ceslgnntton Veli-ht Percent Passive
I Inch 100
1/4 Inch 97-100
So. 10 80-100
Particle Sl;es
Sand 0200 sieve to 010 sieve
Silt 0.00" m to 0200 r.lcve
Clay 0.002 r^z or less
Minicuci Percent Maxim™ Percent
Sand 20
Silt ' 10 (.(!
c.lav 5 30
Topsoll shall not contain stones 2 Inctu-s and over in dlaaetcr.
Prior to stripping at the source, topsull shill have demonstrated hy the
occurrence upon It of healthy crops, grass, or other plant growth, that It is
01' pood quality and rcnsci.ibly free dralnlne. All testlr.j1 shall he at the
expense of the Contractor, The Contractor will be relaiburstd tt-, materials
provided to loprove the pH, organic ratter, or c'.her qualltl--^ of the topsail
tros lhe levels required when such Improvements are ordered by the Engineer.
70i.OS Clfly for Barrier. Clav to he furnished l»v the Contractor Khali con-
sist or" clay sotl free of refuse, vev.et.ition, and rocks. Clav shall have a
Uradtr.e annlvsti> as obtained nccordlny; to test :;:ethods In A SIX Di?2 and as
define J In the L'nlfied So 11 Classification s;. stes.
Sieve Deslcnatlon
1 inch
1/4 Inch
::o . : o
MI., it
.^ar.d
S1H
Clav
'-elKht
ruz. ferc'/nt
0
iO
iO
Percent PA?.sln^
ICO
95-100
80-100
.V.iKl-nun Ferctr.t
20
60
70
'••'here ere source rectorial Is clny shnlti or verv 'Jtlff cl.^y. Pi22 testirc s:;j 1!
bo codified to being icnJucted or. ur.iirled. slaked caterlnl wlcl-.o-.it 'Note)
blender i.-at ton.
Clav cvicerial shall h.ive the -fol loulr.^ phvslc.il characteristics:
(a) Dry enough to spread vlthout revork!r.«.
(b) No reactive cocpunents such as flne-cralned Iron sulflde or carbon
vhlch Js or r.ay becone unstable.
(c) i.lquld Unit !n the ran>;c 125-i1) suRKestecl nnd ?:asliclty
Ir.dex In the- rar.i;e |IO-t'5 su.-.^esfd 1.
(d) J.'ond 1 ::pers i ve
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711.02 Agricultural I. Iocs tone. Agricultural llrcstone shall be ground lice-
stone containing not less than [88 percent suggested) calclus and mau-
eeslun carbonates, Limestone shall, conforn to the standards 01 the
Association of Official Agricultural Chemists .md shall comply vlth all exist-
ing State and Voderal regulations. Rates of application shall he shovr. on the
plans.
Limestone shall meet the following sieve analysis: at least 40 percent
passing the No. 100 sieve and .it least 95 percent passing the No. 8 sieve.
7M.03 Fertilizer. Fertilizer shall he a standard coirmerclal prade and shall
cor.foro co all State and Fcdcr.il regulations and to the standards of the Asso-
ciation of Official Agricultur.il Chemists. Cosaercl.il fertiliser ^hzll pro-
vide the nlnlmuo percentage of available nutrients as specified. The
Contractor shall furnish an affidavit from the vendor or a testing laboratory
as to the available-nutrients contained therein.
Fertilizer shall be furnished in bulk or In new. clean, sealed and prop-
erly labeled hags. Fertilizer failing to ueet the specified analysis may be
used ns determined by Che Engineer providing sufficient uaterlols are applied
to comply with the nutrient requirements indicated on the plans without addi-
tional cost to Che Owner.
A liquid form of fertilizer containing the nlnlnum percentage of avail-
able nutrients nay he used when approved by the Engineer.
711.04 Seed. The seed shall be furnished separately or in cixcures according
fi the plans In standard sealed containers, labeled am! delivered to the job
prior to use for sampling and testing by the Engineer. .'. certifying ^tatement
:rca the vendor shall be furnished by the Contractor in duplicate verifying
seed test and results within 6 ncnths of date ci delivery. Seed and labels
shall conform to all current St.itt: and Feder.-il regulations and will be subject
to the testing provisions of the Association of Official Seed Analysts.
Types of seed or seed mixtures shall be as shovn on the plans, including
the percentage or puriry, perairation, [Owner cav prefer to require "pure live
seed"] and weed seed concent.
[The vise of a forn affidavit on the official stationery ft the supplier
shoving all pefc'inenr data for each lot of seed :.hnii l>e jt the discretion of
the O-mer.] Legume seed when specified in the =ir.ture rhall be inoculated .
vith approved cultures Jn accordance with instructions of the vendor.
:il.05 Kulch.
(a) Wood chips. Wood chips shall be obtained froa disease-free preen
hardwood, shall be 1/6 Inch noclral thickness, with 50 rtrccnt hav-
ing an area not less than one square inch, nor Dor.*! than f* square
Inches. All wood chip sulch shall.be free frcrn leaves, tviqj, shav*
Inqs, bark, or c-aterials injurlnus to plant growth.
(b) Straw. Straw for ir.ulcHni; shall be from rnts, wheat, ry'i or ether
approved p.r.iin crops which are free from noxious weeds, mold, or
•other objectionable material. Straw mulch shall be in an air-dry
'condition and suitable for placing with taulch blover equipr.c:it.
fc) Itiy. Hay shall be of approved herbaceous rowings, free iron (Note)
n'pxirms weeds, asold, or rther objectionable material. Hoy shall be
In an .ilr-
-------
SPECIFICATIONS FOR COVER DESIGN II
The following selected guide specifications might be suitable for con-
tracting for construction of Design II identified as S/F/C/L-"! under EXAMPLE
DESIGNS (See page 38). Section numbering below is conformable to the organ-
ization of technical provisions in Table 12 on page 36.
. AXD EMBANKMENT*
jtil CI AY BARRIER
(Sa=e as previous 301 CLAY 'EA23IES* except a cross reference Is needed
to the restrictions under subscctit-a iO^.04 on placement of the bottota lilt.)
4M rlLTES LAYER
(Sane as previous 403 Ft
subs
(Sane as previous 403 FtLTiTv LAVES* except ir.itcrlal requlrcncncs are In
ection 703.21 Fine Aggregate for L'noerdraln. }
40i FILTI-v FABRIC (IN PL'.CE)
iOi.Ol Description. This work sia?l consist of furnishing and placing a
filter fabric on a prepared sur:"?^e !r. accordance with these specifications.
in reasonably close com'oraltv -*tb the lines, g rules, and typical cross
sections shovn an the pU.is.
iOi.02 Materials. Requirement? :>r filter fabric ihall he accordl: g to sub-
section 71C.11. A file shall h* =.sir.t.Tined by the Contractor for each r.hlp-
.enr, rcll, or other convcnier.t, iifo-t ifiable let shoving the dates received,
transferred, ar.d stockpiled aiorc v::h certification ai.d test doctccntatlon.
Th!s liltf vill fom a Lasls for «valuatlne the acceptability of che zsterial
at any ti^e up to covering ir p2jce. Lent; storage and excessive exposure will
be unacceptable and sh.ill necess:;c.!v replacement of affected raterlals,
10^.03 Preparation of Fabric Fcur.^.jtli>n. The sani course serving aa founda-
tion shall be cleared and shall re cleared of sharp objects which cicht danaee
the fabric during installation. Ar.v condition of surface looseness such as
fron cryini; shall necessitate E?rin'tHr.R and rolling or taaplnc to restore
fircness.
iOi.Cl Placing. The filter fabric shall be unrolled directly on the founda-
tion, overlapping all fabric secct-rs by ..... |3 feet suggested] . Unless
approved otherwise by the Enslnetr in advance, the overlap shall tc stapled.
bonded, or sevcd or otherwise fastened. On ground sloping nore than ...fc.-
(5 percent siiKK-'5ted I , the Ensir.ter aay require that fabric be unrolled across
contours. .
Should the fabric be d.ir.icoj di-rinv .inv step of the installation, the
torn or punctured section shall Ve repaired hv pl.iclnR n pifcc of fabric larce
enouch to cover the damnited area arsi to provide overlap directly on top of nnd
extending 3 feet beyond the riarjcexj arc.i.
Vehicles and equipment such as loaders and defers shall he prevented free
operating directly on the fabric. The
-------
wide cracks or extra wheels exerting ground pressures sufficiently low as to
avoid rutting or clearing to acre than (1/3 suggested) the thickness of
the lift. Dozer blades, etc. shall not cake direct contact with the fabric;
however. If tears, punctures, or damaging abrasions occur In the fabric during
the spreading operation; the cuterial above shall be cleared from the fabric
and the damaged area repaired as previously described.
Overlying soil material shall be spread In the direction of fabric over-
lap. I.e. such that soil does not cove beneath the top half of the overlap.
Large fabric 'wrinkles which ray develop during spreading operations shall be
folded and flattened in the direction of the spreading. Occasionally, large
folds oay tend to reduce the fabric overlap width. Special care shall be
given co maintain proper overlap and fabric continuity.
404.05 Construction Joints and Surfaces. The work shall be scheduled and
temporary or permanent covering shall be provided to preserve the original
properties of the filter fabric. Overlap Interfaces shall be free of soil and
debris. Seaming accomplished In the field shall be according to recbmcenda-
ticns of the aanufacturer of the fabric. Such recommendations shall be pro-
vided to the Engineer for review at least 2 weeks prior to the start of
seaaing.
40*.OS Protection and Maintenance. The Contractor shall maintain the filter
fabric in good condition and In a canner satisfactory to the Engineer frQD the
start of work until all work has beer, completed and accepted. Maintenance
shall include icznediate repair of any defects regardless of the cause. This
work shall be done by the Contractor at his cvn expense and repeated as often
. as cay be necessary to keep the fabric continuously, intact. Repair:; are to be
cade In a manner to ensure restoration of .1 unifom surface and durability and
Integrity of the pnrt repaired. Faulty and dasaccd work shall be replaced by
the Contractor at his own expense.
iOi.07 Method of Measurement. Kilter fabric will be measured In place by the
square ynrd of coverage ordered placed. Overlaps shall not count extra.
40i.C3 Basis of Pavnent. The accepted Quantities of Filter Fabric (In Place)
o: the type specified will Se paid a: the cortr.-.ec price and vlll Include all
material, equlpr.ent. tools, labor, and Incldc.-tais necessary to complete this
itec of work.
Payment will he made under:
Pav Ft en P.iv L'nit
Filter Fabric (In Place) Square yard
* * •
406 VEGETATIVE LAYER"
* * *
610 TCRF
702.04 Emu'ijlfled Asphalt.'
7.03.19 Permeable Material.*
* See undar Design I ' .'
165
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703.21 Fine Aggregate for I'nderdrain. The fine aggregate shall neet Che
requirements of AASHTO H 6. [Alternative gradation specifications may be
supplied by the Owner.)
704.01 Topsoil.*
704.05 Clav for Barrier.*
710.11 Filter Fabric. The filter fabric shall be ccnposed of strong rotproof
polyrterlc fibers forced into a fabric of either the vovcn or nonuoven type.
Both type fabrics shall be free of any treatcent or coating vhich night stR-
niflcantly alter ptn-sical properties. Fabric shall eeec the requirements of
Table 710.1IA or 710.1 IB. (Note)
A ccnpetent laboratory sli.ill be cainrained or retained by the producer of
the fabric at the point or sanufbttute to ensure cuallty control. Intermedi-
ate processors such as those seam Irs rolled sheeting into larger pleres shall
be Included in this requlrenent to the extent that their procesnlns and han-
dling affect the fabric. •
During all periods of shipment .ind steracc. the l'.?brtc shall be protected
In a heavy-duty cover InR- from direct sunlight* ultraviolet rays*, li-aperafures
greater than 140*F.. mud* dirt. dust, .ir.c debris.
The Contractor shall furnish certified test reports with onch
material attesting that the fabric reets the rpquirrronLS of this
tlon. A sample *>: .5 square y.irds of J.ibrlc iron edcl: sl.iprent shnlj be
furnished the Owner for verification testing. SaTpli-s ih.ill be provided at no
cost to the Owner.
711.02 Agricultural Llcestone.*
711.03 Fertlllier.*
711.04 Seed.*
711.05 Mulch. *
\
* See under Design:I
Note: Tables for example only; methods and requirements are not confirmed.
166
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TABLE 710.11A. REQUIREMENTS FPR WOVEN FI1.TFR FABRIC
Test
Method
' Requirements
Tensile Strength
(imaged cloth)*
Bursting Strength
(imaged cloth)*
Puncture Strength
(unaged cloth)*
Abrasion Resistance
Breaking
St renpth
Peroeabllity
AST?! 0 1682 Crob Test Method
I square Inch .(nws; rate of
12 inches/minute.
AST>t D 751 Diaphragm
Bursting Tester
ASTM D 751 Tension TesLlnR
Machine with King Clamp;
steel ball replaced with a
5/16 Inch diaceter solid
steel cylinder centered
within the ring clanp.
ASTM D I6R? .is above, after
abraded as in ASTM f> 1175
Rotnry Pl.itform. Double
Head Method; rubber-hat.e
abrasive vhcels equal to
CS-17 "Callbrase"; 1 kllo-
prna load per vhccl;
1;OCO revolutions.
ASTM D lfiH3, I square lr.cn
Jqvs; rate of 12 Inches/
clmite.
ASTM D 4491 Permittivity
Htnlcum ?00 pounds in
any principal direc-
tion. . Apparent eIon-
gat Ion at failure
between 10 and
35 percent.
Minlsuo 500 psl
Minidun 120 pounds
55 pounds In
any principal
direction
HinlcuD 180 pounds
3.3
ir./sc
3.8
rm/scc.
x 10~
1s the condition as received from the manufacturer or distributor.
TABLE 710.1 IB. RFQUIRFMrNTS FOR KONVHVF.N FILTER FABRIC
Test
Crab Strength*
Crab Elongation*
^Perceablllty*
Method
ASTM n 1682**
ASTM D 16B2«*
ASTM 0 4491
Requirement
Mlnlc.um 90 pounds
Mlninun 50 percent
Minimum 2 x 10 . cm/sec.
Fabric Toughness
(Crab Strength x
Crab Elongation)
Kaxltr.um 3 x 10 CD/sec.
Mlnlmin-fiOOO (Ib-percent)
*Tests run on wct'SAtrples so-ked 24 hours at arhlent room tcsperntiire.
•'Tensile strength de rmlnrd by tlie method stated In Table 710.1IA.
167
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SPECIFICATIONS FOR COVER DESIGN III
The following selected guide specifications might be suitable for con-
tracting for construction of Design III identified as M/S/G-1 under EXAMPLE
DESIGNS (See page 38). Section number below is conformable to the organiza-
tion of technical provisions in Table 12 on page 35. A separate filter blan-
ket is included with STONE PROTECTION but may be omitted when the sand-gravel
interface is expected to remain stable.
204 BACKFILL AND EXBAXKflENT*
303 SYNTHETIC MEMBRANE BARRIER
303.01 Description. This work shall consist of furnishing and placing a syn-
thetic eeebraae barrier on a prepared surface In accordar.ee vlth these speci-
fications, in reasonably cJcse conformity vith the lines, grades, and typical
cross sec ions shown or. the plans or established by the Engineer.
303.02 Materials. Recuirerents for membrane caterial shall be according to
subscctlca iiO.10. Meabrane thickness shall be at least (-0 ells sug-
gested). A tile shall be caintalncd by the Contractor for each shipaent,
roll, or other convenient, identifiable lot, shpving the dates received,
transferred, and stockpiled alone with certification and test documentation.
This file v:ll fora a basis for evaluating the .icce: t ability ol the aaterlal
at onv tire uo to covering in place. Long storage jr.d excessive exposure will
be unacceptable and shall necessitate replacement of affected materials.
303.03 Preparation of Venbrane foundation. The sand course or other soil
servfn: as fc-jniji'Ion for [he net brane shall be cleaned and shall be cleared
of sh.ir? cbtecrs ^--ich r.ir.ht v the oanufacturcr of the rccnbrane
sheeting. Such nethods shall be confonrnble to the desired results. Including
irnerneabllity and durability.
On ground sloping core tlian |S percent succesrei^I, the fabric shall
he. unrolled across ci.ntours. An anchor trench shall he provided at the top.
Should the ccKhnnc he damaged during ar.v step of the installation, che
torn or punctured section shall be rrp^lred by placing a piece of meobranc
large enruch to cover the daoaged areo and to provide overlap directly on top
of and extending I f>oc beyond the dacaged area. The manufacturer's rccoroen-
datlons shall be followed for bonding the patch to the sheet and In other
repairs cf similar consequence.
Vehicles and erjulprent such as loaders and dozers shall be prevented from
operative directly on the cetr.br.inc. These units may operate on the first lift
of the. overlying cou.-sc provided that lift Is at least [6 Inches sug-
gested;) la thickness and free of stones and other hard objects greater than
[1/S Inch surge-Jtedl in largest di«=eter nnd provided the units have
vide traces, or extra wheels exerting ground pressures -sufficiently low as to
avoid rutting or denting to more than |l/5 suggested] the tnlckness of
the lift. Do:er blade?, etc. shall not nake direct contact vith the nenbrane;
* See under Design I .
16S
-------
however. If tears, punctures, or damaging abrasions occur In the cembrane dur-
ing the spreading operation, the material above shall be cleared froa the mec-
brane and the damaged area repaired as specified above.
303.05 [Reserved! (Note)
I • •
303.06 Construction Joints and Surfaces. The work shall be scheduled and
temporary or permanent covering shall be provided to preserve the original
properties of the cesbrnne material. Overlap Interlaces shall be free of soil
and debris. Seining accooplished In the field shall be according to recom-
mendations of the manufacturer of the cerbrane. Such recco&endations shall be
provided to the Engineer for review at least two weeks prior to the start of
seaming.
303.07 Protection md Maintenance. The Contractor shall aalntaln the cen-
Irane In good condition and In a eanner satisfactory to the Engineer fron the
tla.e he first starts work until all work has been correlated and accepted.
y.a Intenance shall include Immediate repair of any defects, regardless of the
cause. This work shall be done by the Contractor at his ovn expense and
repented as often as :r.av be necessary to Keep the nembrane continuously
Intact. Repairs arc to be made In a nan:ier to ensure restoration of a unl/orn
surface and durability and integrity of t!ic part repaired. Faulty and danaged
work shall be replaced bv the Contractor at his own expense.
303.OS Method of Mt-'usureren t. Svnchetlc nembr.ine will he measured In place
by the sauare VHM! o:' covtrage ordered placed. Ovi-rlaps ihall not count
ext ra.
303. O1' ri.isl<; of Paviiu-nl . The accepted <;u.i:'.t 11 les of Synthetic "embrane Har-
rier of th<: type r:pecl!:i:d will be paid :or at tl-o contract price and wl r I
Include .ill natertal. t-eu: pnent, tools, labor, and Incidentals necessary to
crncpletr this Iron of work.
Payrr.ci'.r will br rade under:
Pav It en Pav L'nlt
Synthetic Xenbrane Barrier Square yard
iO: STONK PROTECTION
403. Ul Description. This wori- shall consist of placins protective stone cov-
erlr.g atiri Mlt^r blanket as shewn on the plans or directed by Che Engineer.
It further Includes the preparation of the foundations, the construction of
the toe ditch, and the disposal of excess 51:1 and excavr.ted materials.
402.02 Materials. All naterlals shall be gravel or crushed stone neetint; the
requlrexcnts of the fr.llowinp specifications:
Protection Stone 705.01
Filter Stone 705.02
except where broken f'-ncrerc is permitted as a substitute for stone by the
402.03 P-sparatlon of Foundations. The ground surface upon which the stone
and filter .lankets are ro be placed shall be brought i.-.to reasonably close
confcrc.ltv to the correct lines, gr.ides, and density before placement Is
cocnenced. On slope.-,. ;he stone blanket shall he'^in in a toe ditch. TIP toe
ditch shall he ..... [2 feet suggested) d?ep and the side next to the til!
shall have the sane slope. After the stone blanket is placed, the toe ditch
ch.ill he backfilled.
Note: A subsection on cold-weather construction and restrictions may be
neeaed in regions subject to cold weather.
169
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40?.04 Stone Blanket. Store blankec shall be placed Co the thickness and
Units shown and to a thickness toler.inre of plus or ainus M/* Inch
«upvt>>ted |. The stone shall be handled into place to forn a neat, ur.ifom,
reasonably compact liver in which the scalier stones arc not sei^rer.ated but
remain evenly distributed within the blar.ket.
402.05 Filter Blanket. Filter blanket material shall be uniformly placed to
the thickness and Halts shovn and to a thickness tolerance of plus or oinus
[1/2 inch sucgested]. It shall be corrected to the extent necessary to
hold It In place while the store blanket Is placed upon it. The filler bl;m-
V.»;t shall he placed af tor the stone blanket Is placed in the toe ditch and
before the utone blanket Is placed upon the slopes.
602.0'> Method of Me.inureneni . This work will be measured for pavneni In
cub Ic yard:; of accepted rratcr ia i. No separate rertsur«-'cient will be cade for
excavat ion and dlsposa 1.
£02.07 Basis nf Payment. This work will be paid for at the contract price
complete In place as follovs:
P.iv I ton Pav L'nl t
Scene Blanket Protect ion Cubic yard
Filter Blanket Cubic vard
405 DRAINAGE LAYER
405.0! Description. This work snail consist nf furnishing and placir.r, a sand
drainage course on a prepared surface In accordance with these specifications,
in rpa.icr.ahlv close confers icy with the lines » tirades , thicknesses , ar.d cypl-
cal cross seer ions shown on ihe plans or established by the Engineer .
405.02 Materials. The drainage material shall be ho:r.of;er.eous sand ;nc shal 1
teet the requirements nf subsections 703.1^ -*nd 703.01. Material will be
accepted based cr. testing of samples representative or lends delivered.
405.03 (Reserved] (Note)
405.04 Placing and Spre^dlr.c. Sard racarfal for each lift c: the
course snail h* placed and fpread in r.uch way; ns ro avoid c-itcrial segrega-
tion and nilxinc with or d-axa^c to the previous lift or the crursp fc;:r.d.^ticn.
The Contra ctor sSall understand that segregations, or alxtures, or cracks,
ruts, offsets, puncture0, ar.d other i:id-icatiur.s cf darni^e to underlyir.7, nate-
r In 1 by equip- *r.i or procedures v i 1 1 ccnstiti:;o valid criteria for reiecilon
and will necessitate replacement of rejected vlenencs at the erpenrr of the
Contractor .
The thicVness cf the loose lift shall be such as will ceet the reouired
compacted thickness specified In subsection 405. OS.
405.05 Cor.poct trur. Loose lifts of snnri material shall he ccr.pacted by equip-
o.ent and procedures capable of nttalninc the prescribed density wit!-.CTi; darcacu
to the lift being r.-r-uacrerf or to the underlying r.aterial. Ccapactors that
i^p.irt a knradlr.?, action or penetrate the top surface of the lift shall not be
uood ijnU-ss approved by the rln^tncer. An appropriate ly sized tlrc-roiler com-
pactor will usually be acceptable.
The required densltv for compact 'n ^hnll be ...... (fiS percenr PUP,-
gcstei!| of r.^.rlr=um dcnsirv. The Contractor shall provide rhe daxlau= and
cln.lmua dcnsitv pflrnmetcrs for the chosen snr.d r.«iterial nlonp with the cal-
culated relative density required by this contract nt least tvo weeks prior to
pinclnr, sand c-ater In I in the course . De tai 1 s 'of the ter, t ret^ods shal 1 be
prov Iced n I so. A method tic ire a vibrator v table is iisun 11 y prt frrrcd for
determination of oaxlmtim relative densitv.
Note: Specifications on preparation and checking of condition of membrane
immediately below may be needed'here for Design 111.
- 170
-------
The course sha II be const rucccd tn lifts r.oc exceeding ...... [6 Inches
suggested), and lite thicknesses In ecu It lp If- 1 1 f t courses shall be
2pprox Inately equal. Compaction shall continue until n denslrv not less than
the required density has been achieved to the 1'ull depth of the lift. -ater
shall be applftd unlfomly over the tt.iterlals during; compaction in the acount
ceces'ary for proper conp.ict Ion .
In-place field density nhall be determined in accordance wtth ASTM ri556,
D1M67, 02937. or D2922. Die Contractor Is responsible for testing but pay use
an Approved cooserclal testing laboratorv. All costs of sampling and testing
sha 11 be borne by the Contractor.
iOS.Cfa Construction Joints and Surfaces. At the end of each day's construc-
tion a lateral construct Ion Joint shnll be narked if not clearly evident.
Tecpor.iry cover inc cay be required to preserve the as-constructed condition
intended. f'pon resunpt Ion of work the joint sha 1 1 be uncovered ar*l aois".ned
as needed to assure Interlock along; the joint uhcn the lift Is extended.
Course surfaces shall slr.Ilarlv be protected by tecporary cover, to be
rer.nvpd coa?letely upon resumption of work with addition of the course aLove.
-05.0? Protection and Maintenance . The Contractor shall be required to cain-
tain ar.d protect die drainage lay;r In s;ocd condition and In a nanntr satis-
factory to tl:e Engineer f roc. the t ice he first starts work ur.i i 1 nil vork has
tieen completed ar.d accepted . Ma Intcnancc bv the Contractor shall Ir.c lude
immediate repairs of anv defects, regardless of the cause. This vork shall be
done by the Contractor at his o-ti expense and repeated as often as ray be
necessary :e * eep the coarse conclnuoiiclv Incccr. Repairs are to be c.ade in a
tanner en ensure restoration of a uni fora stir face and. durnbi 1 1 ty and integrity
: f the part repa 1 red . Fau I cv and dnxdv.fd woi k ph.'i 1 ! b*- rep laced for the !"u J 1
depth of the course by the Cor. tractor at his ovr. exrense .
-C ; .OR Me I hoc of wensur'--ienc . San'! cot:: se vi ! ! be neas»jre«i bv the- cubic vard
in accordance vl th 109 KEAS'JKL*!?::"" AND PA^.KNT. Wnen sreclfled as pav Itca.
-•j: T addec to t he rat or *a J q will he rn'risurod bv tl.c- 1 ,('00 railnns by nenns o:
d tanks or distributors cr bv rre.ins of accurate vacer ce
-05 . OV B.'is 1 «; oi Pnyn:ent . ~-~Yf ncct'Pt (\c qu.inr 1 1 1 e* of lira I ~.ace Lay- r , of the
t vpe spec i i f tid , vi M ht pa id for Jt the co::c rnc t pr : c-.1 as : o: love :
ct; I.ave r Cour^*; C\-l J c yard
'-.it cr for Pra i naj;e I.*TV«T C our si; X .c. or Inc :d*-ntnl to
KJne AcKr«ri:.ite for ''nncrclc . *
j. I 9 PP rroab 1 e -°.a i e r 1 ;i! .
Protection Stone. In addition to r.eeMn;; ;::e quality r^qui ri-Ecnts of
.•: BO. pro: ect lor. ^tone tr.;i t ** r 1 n ! r.ha 1 1 be In accordnnce with
/-ASIITO X i3. No. 1'7.
705.02 Filter St»">no. In .dJItlon to reeiinr. the qu.nlily requi rcm^nt s of
A^\SHTO M 80, filter bl.inV-et material y:hall conform co the cradntlon require-
=ent: -f -\ASSiTO M ^3. No. 4f-7.
* See under Design I
171
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riO.Ci Manufacturer's Inscrucrions. Instructions certified as suitable for
the purpose by the nanufac:urer of the sheeting shall he supplied for place-
cer.c, seamlnc. bonding, and ojher procedures anticipated In cu=pletlnz the
barrier. The Instructions shall be appropriate for the chosen cembranc
l-.cludinK Its specific thickness or pause. The Instructions shall be provided
to the Enair.cer no less than one veek prior to first delivery of membrane
material to the job site.
710.10 Polyvlnyl Chloride. Polyvtnyl chloride sheetlr.e shall neet the
requirements o: Table 710. !0 and shall !>e free of treatment or coating vhl.-h (Note)
eight significantly alter physical properties. A competent laboratory shall
be maintained or retained bv the producer or" the sheetinc at the point of
manufacture to ensure cuality control. Intcrr.cd late processors such as those
seaslng rolled sheetinc into larger pieces shall be Included In this recuire-
r.enc to the extent that their processing and handling affect the mecbrane.
During all periods or" shipment and storase, the trembranp shall he pro-
tected la a heavy-duty covering froci direct sunlight, ultraviolet rays, tem-
peratures ereacer than 140**'.. rud, dirt, dust, and debris.
The vendor shall Mirnish certified test reports wirh each shipment of
rarerial attesting that the r.Iotn neein c^.e requirements of thl:: specifica-
tion. A sarspie of S square yards shall be furnished the Ovr.or iron each
f.h:pni;nt f-r verification tcstirs. F.icplts ^h.il! be at no cost to the Ovncr.
SPECIFICATIONS FOR COVF.K DKSICN IV
The following sclecCcd puldc spec! f JcationE mip,hc be siiitahle for con-
tractJn^ for conscruction of Dcr.lKn IV Identified as C/S/B-1 under F.X/\MPJ.F.
DESIGNS (See par,<^ 38). Sccrion numbering below is conforntible to the organ-
ization of technical provisions in Table 12 on
ir-v :i<; pri:v!cns >!il ('LAV Ei'r'Ki i'K' e».c<-pt rnterlal .rcrui rer.ent ? arc
to allov use 01 tlii nr ctrer mtive soil).
3f!i Fl.CCK BAHRltR
701.01 Doscrlpt ion. This worl. shall i-onsf«t of ror.si riirt I n>; a blouk suri'.ire
ct'ursi- in accordance with t!i.?sc spec f 1 icar ions .ind in confrrriliy vltti the
l!r.es. r.raiii"., thlckr.csscs, and f-rlcal secticns siiovn on the planr.. The vork
inclu^ci; the furnlshlnr of p^jnt , ljbc?r, i";ui pr.ent . anii materials to place rhc
course. A course of cushion sand shall be required vhcre the uncM-rlyinp.
course Is not suitable for enbcddin^ the blocks.
Note: This table is preliminary and subject to change. See the original
source SW-870 (32)
* See under Design I
-------
TABLE 710.10. MATERIAL PROPERTIES OF UNSUPPORTED POLYVINYI, CHLORIDE (PVC)
Property
Thickness
Specific Gravity
(mlnlc.-jc)
Hinloua Tensile Properties
leach direct Ion)
1 . fire-king Factor
(pounds/Inch width)
2. Elong.itlon at Break
Test Method
ASTM DI593
Para 8.1.3
ASTM D792
Method A
ASTM DS82
Method A or '8
(I Inch wide)
Method A or B
Gauce
20
±51
1.20
46
300
(nominal )
30 45
s» ,s:
1.20 1.20
69 104
?00 300
(percent)
3. Modulus (force) at 1001
Elongation (pounds/inch
wld'.h)
Tear Resistance (pounds,
ralnlcua)
Low Temperature
Inicenslonal Stability
(each direction, percent
change caxlnim)
Water Extraction
Volatile Los:,
Resttftar.ee to Sol! Burial*
(percent change eaxlc'jn
In original value)
1. Breaking Factor
2. Elongation al break
3. Modulus at I00: Elongation
Bonded Sean Strength**
(factory seao, breaking
fdctur. ppl width)
Hydrostatic Resistance
(pounds/sq In. ctnicur.)
Method A or 3
ASTM 01004
ASTM n| 7<)CI
ASTM Di:04
212°F, IS Din.
ASTM UI235
ASTM U30S)J
120 day sol!
burial
ASTM D3083
ASTM U751
Method A
18
36.3
60
27
6 8 11
-15°F -20T -20T
±5 :5 .'5
-.33: -.35; -.is:
max. cax. uax.
0. ?:
-5
62
100
•Test value of "after exposu-e" sample lb based on precut sair.pl r i! icens l«r..
120-day tesc Is required for Initial certification.
**Factory bonded seam strength Is the responsibility of Che fabricator.
173
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304.02 Materials. The concrete block shall cosply with itie requlreoents for
concrete block for slope paving in subsection 705.04. The block shall have
the following nominal dinensions: (Note)
Length [!2 Inches suggested]
Thickness ( 4 inches su?^estiic! I
Width • [ 8 Inches suggested!
The standard dicenstons of the block shall be the specified nocir.al d I^ens tc*n
ninus 3/8 inch. The maxicua permissible variation in dleenslons of individual
units fron standard dimensions shall be not more than i/fl Inch. The size of
block used shall be consistent throughout any continuously paved area. All
units shall be sound and free from cracks or other defects that vould Inter-
fere with the proper placing of the blocks or Inpalr the strength, peraanence,
and appearance of the construct Ion.
Cushion sand shall conform to the requircaenis r.ct forth !n subsec-
tion 703.0ft. Crcut, where used, shall consist or one part r.nscnry recent
conforming to the requirecents of subsection 7C1.01, and two parts oortar
sand, conforcing to the requirements of subsection 703.03.
304.03 Placement. Blocks shall he laid on o 3-inch bed of cushion sand or
cateriJ1 acceptable to the £rt;ineer as ccislvaient to cushion sand. An under-
lyi" course composed of sand free of pebbles and larcer pieces will serve QS
cushion '-'here approved as such hy the Rm;incur and provided such substitution
dees not result in o thlc-r.css deficiency.
Placement shall he in running bond with the loni> dimension transverse to
the slope and all joints tl^ht. Blocks shall ho thoroughly r armed ir. p lace to
provide a uniformly even surface jnd solid b^dJini under each block.
C.Tp*: in the block course over i rrcsu lar tppocr.iphv. ( nt1;. r'r J lovi ni*. the lav 1 rr of b lc"-r i,, in t !ie if.- to he
^rnutci!. ru: :" ic lent nor car «and sh.n 11 be :;pr i-.'id nv*»r t In- r-uri ace ."inci .-•••••p:
: :uo the jo ::.c-.t tc III! cl.e I.i t ter t« I 3 1 ncho*; rui;>;cstfd ' :' re- th»-
sur • .TCI: . The Mork shall be wetted rn rhe snt, t±: 1 act Ion of the Kncl ~^*er ^erorc
.my r.rou; is p 1.iced. The Jointr. sha 11 be f M 1 erf wi th r.r&ut f ro= the ^r: r^n
flush with the top of the bioct.
After f.rcct ln« hnr. N-en COTD 1 et t-d .ind rlu1 i-.rout has -;uf:" !c l»*rt Iv li.nr^-
enod. l he blocks sha 11 he vetted and covered. nnti n I It ••-•»• t! to cure :-*r the
first ••ever: days alter Rrou: Inp.. Grout siia 11 not be ;»our*rtJ uur lr,»*. : r»-x :ru:
veat ^icr.
30i.05 Method of Measurement. The rjnantttv to he p.i 1 d ur.Jt-r this Uei shall
Lc the number of sqn,i r«> y.irris coraputed from the pavraent 11 n«*s shovn rr. thr
pl.ins. or as directed by the Engineer.
3di.06 Pasis of Pnycent. The untc price bid for this Iten shall !rciu^.: rhe
costs "f furnishing all r.aterinls, labor, flr.d equipment r.efessary tci ccrpicte
the fork sat is factor!1y.
Parent vl 1 1 be made under:
PJV Ttea Pnv t'nlt
Concrete Block Paving *•*;•!a re
Note: A substantial cost savings may come from using brick or other available
commercial blocks provided that ground moisture is not detrimental to
durability.
-------
405 DRAINAGE LAYER
(Sace as previous 403 FILTER LAYER* ex.-epr sand eaterfal described under
subsection 703.15 Is required In place of sand under subsection 703.01).
701.01 Portland Cerent. Portland cecent shall conform to the requirements of
the following cited specifications for the type specified or permitted:
_ Tvpg _ Sgeclf ieatlcn
Portland Ctrcnt AASKTO X 85
Blended (Hydraulic Cecent AASHTl- M 240
Masonry Cement AASKT3 K 150
L'nlsss otherwise perr-lttcd by the Engineer. the product of only or.« =111
of anv nr.e brand and tvpe of Portland ceaent shall be used nr. the project,
except for reduction of any excessive air vhere al r-ent ralni r.R cccicnt Is used.
T!ie l^cntractor shall provide suitable reans for Etorlnn and ^r
the cogent ap.alnst dacpness. rcir.ent thich. lor any rcasnn. has becone par-
tiallv set or vhlcr. contains lucos of caked cer.ent shdll bo rejected. Cen:nt
salvaged i'ron disc.irOrt ir used t;a;-.s shall not be used.
703.(13 Mortnr Sand, ''orrar r.anrf shall cnr.slsc of clean, hard, durable.
uncc.iii-i! par t IcltfS. fr»-e fron Innps of clay and all deleterious subdtar.ces.
Vhcn dry the nortar sand shall c.eet the following r.radatlon requ 1 remenrs :
5fpv«* f'erlcnatlon '-'eight Percent Pnrslna
»i 100
*B 95-100
1150 10- 40
.-,rt Ic les, free frm lunps of clay and all deleterious substances.
Vh'jn drv, the cushion sand <;hail r.eet the following Rradatlon
requ lrcs;ents:
Flcve nc-;l;na;ion Wglrht Percent Passing
1/i Ir.ch ICO
:.o. JN 0-35
So. iO'J C-10
The s.ird Tiiy be deter-.lred to be unacceptable for cushion sand If it contain."
nor» than '.U percent bv velght of loazi or silt.
703.iS A?;r<-rate fcr Vasonry Xor:ar. Ajcregate for rasonrv cortar shall neet
the rcoulrccer.es ol AAS'.iT" M 45.
* See under Design I
175
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703.19 Permeable Material.*
705.04 Concrete Block for Slope Pnvlnp:. The shape and dimensions of the
units shall be shown in the plnns or speclficatluns. The cilninum averase
compress ive si re net h ol" cor.cret tr p.ivlni: block sha 11 be 2 , 500 pounds /.--qua re
Inch. This it renfitli slu 1 1 he rfer*- mijitfd by lo.id .ippl Icat J on In a dl rerc ion
para J !e 1 to the y lope upon which the b lock Is to be p I need . The compress ive
strt-nrth of anv Inrilv i;ht .
All test procedures Hha!l he In accordance vllh ASTM CKO.
SPECIFICATIONS PC?. CJVER DESIGN V
Cover Design V under EXAMPLE DESIGNS (See pa«e 38) reflects current KCRA
guidance. No specifications are offered for this design in order to avoid
direct application of such specifications without the benefit of thorough and
detailed engineering analyses to addrt's-3 the specifics of any new *f aci li ty .
* See under Design I
176
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APPENDIX B
RELATED SPECIFICATIONS
The following specifications are taken directly from outside sources
without modification to illustrate special method or details. The excerpts
are not necessarily directly applicable to cover construction and maintenance.
The examples illustrate indirectly the detailed consideration sometimes
regarded as necessary in similar construction.
MIXING SOILS
The following excerpt is from a set of specifications for constructing
subbasc for flexible pavements using soils needing additional mixing during
pl&cenent. The source Is the Department of the Navy. Note that the paragraph
numbers do not mesh with those suggested elsewhere in this document (Table 12
on page 36).
3.1 PLACING: Clean underlying surface of all foreign substances
and inspect for proper compaction and smoothness before placement
of subbasc course. When Che temperature falls belov 35*F, project
ell areas of completed subbaoe course against freezing.
3.1.1 Read Mix Method: Haul materials to area to be paved And
spread unifornly fro= spreader boxus. covlriR vehicles, or by other
approved cethods. Coarse material »ay be placed li, a unifora layer
on the ur.derlvlng course fol loved by spreading a uniforc layer of
fine material, or materials taay be placed in wlndrovs on the under-
lying, course. Place course and fine materials In proportions such
that, vhen ulended. they shall conform to the requirements speci-
fied. Six. ulndrowed cacerlal using blade graders, harrovs, disks.
or other suitable equipnent. Mixing shall not disturb the under-
lying course. Continue initial cixing until the Dixturu is unifcro
throughout Its depth Adding water as necessary to prevent secrega-
tlon during nixing operations. Sprinkle additional water, as
required, to facilitate satisfactory Bixing. Continue cixinit until
the water Is unlforalv distributed throughout the cLxture. Add
fine or coarse material, or both, ro the clxturc, as required, to
secure compaction and density specified. After caterials arc
thoroughly rUcd and compacted, the tcs-.iJttnR 'aver shall confora
to the indicated thlcknenn,
3.1.^! Hl*ed-ln-Place Kethod: Lonsen( pulverize, and blade to a
unifora depth the existing suher.^dr r.ateriol which is suitable for
use for the ;:ubbjsr course vhcn blrndrd with the required
proportlo-i» of other aazreenteB or blndlnp. material. Spread segre-
gates or blndlna frnrcrial, or horn, in unifora layers of such depth
that vhen the raterlals are thorouahly mixed and compacted the
resulting laver shall conforn to the indicated thlcWrrso and cross
section. Continue Initial uixing until mixture la uniform through-
out. Rvsove portions of any layer in which cep.rec.ation of eaterial
occurs and replace with satisfactory oateriol , or add suitable
material and olx with the negrei;ated naterial.
177
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J.I.3 Windrow Traveling-Plane Kcchod: Blend and deposit haul
materials in vlndrcvs on the underlying course In &uch proportions
that the ipeclfled gradation shall b« net. Site of windrow shall
not excceJ the mixing capacity of the traveling plant. Hake
adjustncnte In the mounts of the various oatertalt being blended
when ao directed. Mixing cperatloj shall produce a satisfactory.
unlforo, blended aaterlal vhen deposited on underlying course in
windrows of unlforo cross section. Spread wlndrowed nixed Mterlal
to required contour and uniform thickness and to the depth that
when coapacted. the resulting layer shall conforn to the indicated
thickness and crose section.
QUALITY CONTROL AND ACCEPTAN',L
The Virginia Highvay Department developed and uses the following con-
struction specifications for quality of bituminous concrete for pavements.
Note that the section numbers do not correlate with those suggested elsewhere
in this document (Table 12 on page 36). Substantial differences In scale and
cost In cover construction may dictate a much smaller effort and reduced scope
in such specifications used there.
Section 21?.T9: Acceptance - Sacpling for determination of Rrada-
tlon and asphalt content will be performed at the plant, and no
further sacpllng will be performed for these properties. However.
should visual examination reveal that the material in any batch or
load is obviously concanln.ited. deficient In asphalt content or net
thoroughly olxod, that batch or load will be rejected without addi-
tional sacpllng or testing of the lo'.. In the cve = : It is neces-
sary to determine, quantltatIvelv, the quality of the uaterinl In
an Individual batch or load, one sasple (taken frrs the batch or
load) will be tested end the results compared ro the "process tol-
erance for one test" as described her«lnbelow. The results
cbCiir.ed In the testing of a specific Individual botch Oi- lond will
apply only to the batch or load in question. Gradation and asplialc
concent determinations will be performed in the pl^nt laboratory
furnished by the Contractor; however, the Pepnrtr.ent reserves the
rlRht to discontinue the use of the plant laboratory for acceptance
testing In the event of raechaMcal aaIfunction? !n the laboratory
equlpnent and In cases of errereencv Involving plant Inspection
personnel. In the event of sjch calfunctlons or emergencies,
acceptance testing will be prr;orned at the District or Centra!
Office laboratory until the r:a 1 function or emergency han been
satisfactorily corrected or resolved.
Acceptance for gradation and asphalt content will be based upon
a tr.ean of th; results of four t<:stn performed r>n sanples ta^cn In a
stratified randoa manner fron each 2.000 ton lot (4,000-to;i lot
when the contract Itea Is in excess of 30,000 tons). A lot will be
considered to be acceptable for gradation and asphalt content if
the nean ot the results obtained froa the four tests fall within
the following process tolerances allowed for deviation froti the
Job-alx fffncula:
178
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Process Tolerance
Sleva (percent paaglng)
Top sire 10.0
1 1/2" 5.5
3/4" 5.5
m- • 5.5
3/8" 5.5
«* 4.5
*8 4.5
'30 4,5
*SO 3.0
*200 1.5
Asphalc content* 0.5
•Asphalt content will be measured fa.
extractable asphalt.
In the event asphalt Input is monitored by automated recorda-
tion, the above process tolerance for asphalt will not apply.
Variability ccr.trol for asphalt content will be evaluated based
upon extractable asphalt. At any time the aaphalt content, as
evidenced by at-tomated recordatlnn, deviates acre than ±0.2 percent
frooi that shovn In the job-calx foncula, the production shall be
halted and corrective action taken to bring the aaphalt content to
within this tolerance.
The temperature of the mixture at the plant sliall not vury nore
than tiO'F fron the approved Job-mix temperature. The temperature
of the mixture at the tire of placement in the road shall not be
more than 30*F below che approved Job-nix temperature. Loads which
do not conforn to these temperature tolerances will he rejected.
In the event thnt the job requires less than 2,000 tons of mate-
rial; or that the amount of material necessary to complete the job
Is less than 2,000 tons (4.000 tons for contract Itees in excess of
50,000 tons); or th.nt the Job-mix formula Is rod if led within a lot,
tho nenn resulrs of samples taken will be compared to a new process
tolerance, computed as follows:
Process tolerance for one test - process tolerance for ce.in of
four tests/0.5
Proceca tolerance for mean of two tests - process tolerance
for mean of four
tents/0.7
Process tolerance for oesn of three tests •• process-tolerance
for dean of four
tests/0.9
Individual teat results and lot averages obtained from accep-
tance testing will be plotted on control ctiarts as the information
is obtained. Standard deviations, when computed, will be mndo
avollsble to the Contractor. However, the Inspector will in no way
atter.pt to Interpret test results, lot averages or atandard devia-
tions for the Contractor 1'a terms of needful plcnt or process
adjustments.
Section 217.30: Adjustoent System - An adjustment of tha unit bid (Note)
price will not be made for the value of one teet result or the v*an
value of two or three test results, unless clrcur.stnncen as stated
In Section 212.29 require that the lot sire be less than 7.000 tons .
(4.000 tons for contract item* In excess to 50,000 tons). Should
Note: Substandard materials or construction may be determined to be unaccept-
able at wacte disposal facilities, regardless of penalties, as a matter
of policy.
179
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the value of one tent result or the »ean value of tvc or sore test
f-'ilti. «fl required by Section 212.29 fall outside th« allovable
prater*- tolnnacc, an adjustment will be applied to the unit bid
price aa
Sieve
2"
1 1/2"
I"
3/i"
1/2"
3/8"
It.
tS
no
»50
»200
Adjustcent points for each I
percent that the pradation Is
out of process tolerance
A one-point adjtsticent will be oppllod for each 0.1 percent that
the aaterial is out of the prjccss tolerance for asphalt content.
In the <;vent the total adlustient for a lot is greater than
«!5 points, the felling material shall be removed fray- the road. In
the event the total adjusccent is 25 points or less <>nd the
Contractor does not elect to recove and replace the larerl.i) , the
unit price paid for the material will be reduced 1 percent of the
unit price bid for each adjustment point. The odjus:c*nr will he
applied to the tonnage represented by the sample or samples.
The Contractor anal! control Ihe varJntlllry of his product in
order ta fumli.h the project vlth a unjfora jslx. VTnen the contract
iteo is greater than 't^GOO tons flnd an adjustment Is n^ceosary as
indicated in the followina t£ble, it shall be for the entire quan-
tity of thnt type caterlal on the project based upon its variabil-
ity as measured by the standard deviation.
Sieve
Size and
Asphalt
Content
Standard Deviation
1 Adjustment
Point
4.5-5.5
4.6-5.5
4.6-5.5
4.6-5.5
4.6-5.5
4.1-5.0
4.1-5.0
3.1-4.0
2.1-3.0
0.33-0.42
2 Adjustment
Points
5.6-6.5
5.6-6.5
5.6-6.5
5.6-6.5
5.6-6.5
5.1-6.0
5.1-6.0
4.1-5.0
3.1-4.0
0.43-0.52
3 Adjustment
Points
6.6-7.5
6. 6-?. 5
6.6-7.5
6.6-7.5
6.6-7.5
6.1-7.0
6.1-7.0
5.1-6.0
4.1-5.0
0.53-0.62
1 1/2"
3/4"
1/2"
3/8"
(4
fa
no
050
»200
Asphalt content
The unit bid price shall be reduced by 0.5 percent for each
adjustcent point applied.
The disposition of natcrlal having standard deviation!) larger
than those shovn in the table, shall be determined by the Engineer.
180
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PROOF ROLLING
The following specifications detail the procedures cf proof rolling
sometimes required by the New York Department of Transportation. The major
differences in finar.eas of foundations for cover systems as compared to those
for highway pavement systems should be considered carefully. Differences will
affect equipment selection as well as procedures. Ncte that the paragraph and
table numbers do not mesh with those suggested elsewhere in this document
(Table 12 on page 36).
203-3.13 Proof Rolling in Embankment Sections. Immediately
prior 10 final triminirii: of lli- subirrndv surface and placement
of sub-bast- materials in embankment sections, all areas of the
subirnide surface within roadway limits .-hall !«• proof rolled ac-
cording In the reqmremcir.s of this article.
A. Purtwsf. Tl'e purpose of proof rollint: embankment*"- is to
ascertain the \ip.lfor.Tiity of compaction Ivnrulh the subprade
surface. In locate deficiencies requiring correction, and to es-
tablish that corrective work has l*«?ii cffectivp, all prior to
placement of the subba-sc.
/?. Efjitijywfiit. The proof roller shall consist of a chariot type
ri^id steel fnunc n'ilii a l>ox lw«ly suitable for hallast loading
up to fifty ("»(') tons cros> wi.'icht. ar.il nioun'.{-c
jul.iu-^i-'d t'i the hi-jhest -Ires> li-\-el shown lit Fif,rr.re 20^-4
i'as,-.(l on:
1. The Entiutcr's tenerai ,!"^cri| '-on of the sub.urniir soils.
2. The KiiiriiiPi'r'- i-stimatio:i of t. • iclntiv sniicrartc sup-
port \viihin tin.- . Prnrrriiirf. After an acc'-ptable stress level i= established.
two complete jia>se* of tin- roller shall l-o applied over n!l ele-
ments i.f the nrea to b«- proof ridled. Any 'lefiriciirics dis.:loscii
i iluriui: the |>ro(»f rollini: operation shall lie corrected. Subsi-
dence depressions shall b»- fillcil with material similar to the
su'.nrrado ^«>il and then eornnaeted in a normal manner. After
compaction, thc.-c r.rens sholl l»e prt-of rollctl airain. Corrective
work shall l>e judged complete arM accepted by the Kni:inecr
wlien all (jlement« fif the sul,crude surfare over a riven em-
banfcnent shmv a snlUfartorv uniform re.-ponse to the proof
181
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Fioum 203-4 GUIDE FOR SELECTING THE INITIAL STRESS LEVEL
* FOR PROOF ROLLING EMBANKMENT SECTIONS
JuJfONT*
W
O
vt
stuns;
LCVtL
CROSS ion;
not PSI
«t
«•«.
so
foe
G.-U.
so
.L
oco
Li
.
ft
I
I
1
1
1
|
IR
cooo
CKCELlCftT
1 I "l!!l fl " li'»*
[
n
(BiVEL SA*0 • SILT -CL** I
JVJ-.CS o» GIU VCIL* SANL'S
1 IIH 0" "C ( "»t
AND • SILT a tT U.« .
^•1 . n.flhr plo»',C'!T
N'J{ »i ^AN?- I
wftt.ll ptoitiCi'f |
"H him «•*?!-«!
»*t» 1 SAMO • 5»Li -Ci*r u.tv.«t o,
Li '•-•
|$!ll'> OM A'f f.nt 'jANOS
ILEAl* CL«WS . 5 ilTV Cu** i .
llo'Jraac«3M SILTS ^ ]_
r«T CLAY* . SILTI CI.ATS |
1
MINI HUI/
30
40
1
34
SO
2
ie
CO
3
4Z
TO
• )A»O -StLT U-itcr*t |
1
I i
I CRAbTUiand irfAvtt,' • \ _ I
L&ANOM.II I.ITI« >-Pc'.«*r*
4
44
• 0
3
30
00
MAX MUM
30
ISO
E. Ezrcplinnf. Proof rollini: of thp sulirrndc surface in fm-
Imikincnt sections will not be required in any aroa whore:
1. duo to restriction'^ in availnlik- «cccs> nnd/or mnneuvcr-
injj spncc. use of tbe firoof roller may tlamni;e iiHjacont
work;
2. (lie proof roller will npproncli :i culvert, pipe or olher con-
duit closer than ."> fer-t in anv direction.
GRASS MAINTENANCE
Maintenance work can also be contracted and the following excerpt on
maintaining grass illustrates the format of suitable specificatiois for all
ground maintenance. The example applies to upkeep at active Department of the
Navy bases rnd thus has sone major differences from long-term maintenance of
covered waste cells. The frequency of maintenance activity is much less at a
closed waste cell or site. Note that the paragraph numbers do not correlate
with those suggested elsewhere in this document (Table 12 on page 36). The
tabulation included midway in the excerpt can alternatively be included with
plans that would ordinarily accompany these specifications.
b. CRASS MAINTENANCE
6.1 Lawn Aeration: Crass In aree shnll be aerated during
the period through . A uchl.ie which reroven 1/2-inch
cores or which has renovating cpoona to penetrate the soil at least
2 Inches on a spacing of not norc than ft Inches by 8 Inches sholl
be used. If a coring machine to used, o drau oat shall be used to
break up loose cores and cpre&l soil. This work shall not be done
when soil IB extremely wet or ei.treaely dry.
6.2 (FertUlier)(/ind)(llce) shall be delivered to the olte l.i
the original, unopened containers bearing the manufacturer "a
182
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guannteod chcaicel annlyals, naie, trade naae. or trademark and In
conforaance to state and federal lav. In lieu of container*.
fertilizer and Hoc Day be furnished In bulk and a certificate
Indicating th« above Information shall accoapany e-.ch delivery.
The fertilizer shall be applied when blades of grass are dry.
TIME OF TYPE OF METHOD-OR-KATE TOTAL AMOUNT
ARF.A ACRES APPLICATION FERTILIZER OF APPLICATION REQUIRED
6.3 Renovation: Cr-.'ss In areas shown on plan shall have thatch
removed by vert i-cuit Ing during the period _ through _ .
Apply fertilizer at the rate of _ pounds per 1,000 square feet
and overseed, If desired, with _ seed applied at the rate of
_ pounds per I ,UOO square feet. Irrigation shall be done
6.4 Irrigation of Craso: Crass In areas _ and _ shall
be irrigated with a unlfois application of __ Inches of voter
when less than that amount of rain has b^en received the previous
ceven davn. Water shall be applied at a rate which will not cause
runoff. The Contractor shall provide and nain'aln a slnplc ralr.
faKV which has the approval of the Contracting Officer. The sntlre
axount of water shnll not he provljecj In crie application. The
Contractor shall provide Information to the Contracting Officer on
the application rate and degree of overlap required for uniforn
application. for each type of Irrigation cqulprccn: to be used. If
Irrigation Kysten Is electrically controlled, watering shall be
done at night; otherwise, watering shall be don-: during earliest
possible aorning hours.
6.5 Weed Control: In grassed nreas the Contractor shall cor.-
trol vegetation such as noxious wee<1s, vinea, brush. or grass. If
control is required, EPA-approved chealcalc according to label
directions will be used. Materials proposed for such uee r.ust hove
the prior approval of the station Navy-ctrtif led Pest Control
Inspector or the Special Assistant for Applied Biolo.'.y,
_ . Extreme caution shall be exercised to prevent
spray drift from adversely affecting nesrty desirable shrubs,
trees, and ernes. All such uork shall be monitored under the
direct and continuing supervision of a Knvy-certlf led Pest Control
Inspector. All pesticide usage unrter ':hls contract shall be
reported to the Contracting OCllcer on n oonthly basis and provide
all information which is required to be submitted on DD Form 133?.
fi.d Flower Dodo: Flower beds In areas _ shall be treated
with an EPA-approved herbicide at the tlee of planting to control
weed pulling.
6.7 Insect and Dlseauc Control: Th° retractor will not have
the responsibility for Inaect and disease control but Is requested
to report infestations procptly to the Contracting Officer.
183
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