xvEPA
United States
Environmental Protection
Agency
Office of
Research and Development
Washington, DC 20460
Technology Transfer
CERI 90-50
Seminars-
Design and Construction of
RCRA/CERCLA
Final Covers
Presentations
July 17-18, 1990
Atlanta, GA
July 18-19, 1990
Philadelphia, PA
July 19-20, 1990
Boston, MA
July 24-25, 1990
Dallas, JX
July 25-26, 1990
Kansas City, MO
July 26-27, 1990
Denver, CO
August 13-14, 1990
Newark, NJ
August 14-15, 1990
Chicago, IL
August 15-16, 1990
Seattle, WA
August 16-17, 1990
Oakland, CA
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U.S. ENVIRONMENTAL PROTECTION AGENCY
SEMINAR ON DESIGN AND CONSTRUCTION
OF RCRA/CERCLA FINAL COVERS
July - August, 1990
AWBERC
ii ^ EPA
'
ii
26 w MARTIN 'LUTHER KING OR.
CINCINNATI, OHIO *&268
US EPA-AWBERC LIBRARY
30701 100593992
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Notice
The U.S. Environmental Protection Agency (EPA) strives to provide accurate, complete, and useful
information. However, neither EPA nor any person contributing to the preparation of this
document makes any warranty, expressed or implied, with respect to the usefulness or effectiveness
of any information, method, or process disclosed in this material. Nor does EPA assume any
liability for the use of, or for damages arising from the use of, any information, methods, or process
disclosed in this document.
Mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
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TABLE OF CONTENTS
Speakers [[[ iii
Introduction [[[ . , 1
Robert E. Landreth
Critical Factors in Soils Design for Covers .................................... ^
David E. Daniel
Geosynthetic Design for Landfill Covers ..................................... 35
Robert M. Koerner
Durability and Aging of Geosynthetics ....................................... 47
Robert M. Koerner
Alternative Cover Designs ................................................ 59
Robert E. Landreth
Construction Quality Assurance for Soils ..................................... 67
David E. Daniel
Construction Quality Assurance for FML's .................................... 91
Robert M. Koerner
Expert Systems [[[ 103
Robert E. Landreth
Hydrologic Evaluation of Landfill Performance (HELP) Model 111
for Design and Evaluation of Liquids Management Systems ......................
Paul R. Schroeder
Sensitivity of Cover Effectiveness to Design Parameters ..........................
Paul R. Schroeder
Gas Management Systems ................................................ 161
Paul R. Schroeder
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Appendix A A-l
Appendix B B-l
Appendix C C-l
Appendix D D-l
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SPEAKERS
David E. Daniel
David Daniel received a Ph.D. in Civil Engineering from the University of Texas. He has worked
as a geotechnical engineer with Woodward-Clyde Consultants in San Francisco, California.
Dr. Daniel is currently Associate Professor of Engineering at the University of Texas. He has taught
courses in Measurement of Soil Properties, Geotechnical Aspects of Waste Disposal, Consolidation
and Settlement of Soils, and Management of Hazardous Wastes, to name a few. He has worked as
a consultant in Permeability Testing, Specialized Testing of Unsaturated Soils, and Municipal Solid
Waste Landfills, among others. Dr. Daniel serves on numerous professional society committees.
Robert M. Koerner
Robert M. Koerner received his Ph.D. in Civil Engineering from Duke University. He is the H.L.
Bowman Professor of Civil Engineering at Drexel University in Philadelphia, Pennsylvania. Dr.
Koerner has been at Drexel for 20 years following 10 years of working for various consultants and
contractors. Since 1974, his research and development work has been focused in the geosynthetics
area and in 1986 he founded the Geosynthetic Research Institute (GRI). The focus of GRI activities
are on generic research in all aspects of polymer materials involved in the
environmental/geotechnical/transportation fields. Included in these studies are geomembranes,
geotextiles, geogrids, geocomposites and geopipe. The publication of test standards, conducting
continuing education courses and formation of various seminars are all ongoing activities of GRI.
Dr. Koerner has published over 100 technical papers and three books in the geosynthetics area, the
latest effort being the textbook "Designing with Geosynthetics" now in its second edition. He is
currently president of the North American Geosynthetics Society (NAGS).
Robert E. Landreth
Robert Landreth holds a M.S. degree in Civil Engineering. He is an Environmental Engineer at the
EPA Risk Reduction Engineering Laboratory (RREL). He directs technical and administrative
aspects of extramural research projects on solid and hazardous waste pollution, including multimedia
research to establish disposal guidelines and standards for flexible membrane liners in waste
managemnet facilities.
Mr. Landreth works closely with the land disposal division of EPA's Office of Solid Waste in
developing RCRA guidance. He assembled and guided a team in developing guidance on use of
double liners and technical resource documents related to RCRA both Subtitle C and D.
(over)
m
-------
Gregory N. Richardson
Gregory Richardson received both his M.S. in Civil Engineering and his Ph.D. in Geotechnical
Engineering from the University of California. He worked with other firms for 12 years before
joining Westinghouse Environmental and Geotechnical Services, Inc. where he is presently employed.
Dr. Richardson's fields of specialization include landfill design and geosynthetics. He is responsible
for design and quality control of both solid and hazardous waste landfills and is co-author of an EPA
manual on the use of geosynthetics in landfill and surface impoundment designs. He is also a
developer of test equipment for evaluating both mechanical and hydraulic properties of geosynthetics
and a consultant to geosynthetic manufacturers on product development and application.
Paul R. Schroeder
Paul R. Schroeder holds a Ph.D. in Environmental Engineering from The Ohio State University. He
is a Research Civil Engineer at the U.S. Army Engineer Waterways Experiment Station in Vicksburg,
Mississippi. He conducts research and computer software development on dredged material and
hazardous waste disposal.
Since 1983, Dr. Schroeder has been developing and verifying water balance models for landfills and
dredged material disposal facilities. He has received the Wesley W. Homer award from the American
Society of Civil Engineers (ASCE) for his work on verification of the Hydrologic Evaluation of
Landfill Performance (HELP) model.
IV
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INTRODUCTION AND REGULATORY OVERVIEW
Robert E. Landreth
I. Objective and Overview of Seminar
II. Current Regulations and Guidance
A. RCRA Subtitle C
B. CERCLA
C. RCRA - Subtitle D
III. Available Information and/or Technical Assistance
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Introduction
1. Introduction/Background of Speakers
2. Purpose of Seminar
3. Regulatory Guidance
4. Overview of Design
Speakers
Robert E. Landreth
David E. Daniel
Robert M. Koerner
Paul R. Schroeder
Gregory N. Richardson
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Purpose:
Overview of Design and Construction of
Cover Systems
Regulatory Concerns:
RCRA - Subtitle C
- Subtitle D
CERCLA
-------
Subtitle C
40 CFR 264 (Permitted) and 265 (Interim Status)
Subpart G - Closure and Post Closure
Subpart K - Surface Impoundments
Subpart N - Landfills
Guidance Manual
Guidance only - not regulations
Other final cover designs acceptable
site specific
adequacy
-------
Subpart K and N
264.303 - monitoring and inspection
265.303 - not required
Subpart K and N
264.310 - leachate collection and removal
265.310 - not required
-------
Subpart K and N
264.310(b)(1)(v) Cover permeability <: bottom liner
264.310(b)(1)(v) Cover could be almost any material
(assumes no engineered liner)
Note: Agency may impose 265.11 and require a more
impermeable cover.
General Closure Performance Standards
% must close in a manner
minimize need for maintenance
controls, minimizes, or eliminates
hazardous waste
hazardous constituents
leachate
runoff
decomposition products
-------
vegetation/soil
top layer
drainage layer
low-f
FML/soil laye'r
waste
\\// \1// \\// \\//
000
O
O
O O « O
O
60cm
30cm
60cm
filter layer
20-mii FML
cobbles/soil
top layer
biotic barrier
(cobbles)
drainage layer
low-permeability
FML/soii layer
gas vent layer
waste
«% * « o " « = = « « o o « «
- « « e« o o .« e * ^ «.«".««%
J.«««»«Je ««.« o / «
Ct'o'^''^0' O » ° « .
o o (?
o O> o
o o
o
60crn
30cm
30cm
geosynthetic filter
geosynthetic filter
20-mil FML
60cm
30cm
geosynthetic filter
-------
Construction Quality Assurance (CQA)
Written Plan for inspecting
quality of materials
quality of construction practice
Settlement and
-------
Interim Covers
Subtitle D
CERCLA
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CRITICAL FACTORS IN SOILS DESIGN FOR COVERS
David E. Daniel
I. Permeability
II. Composite Action with Geomembrane
El. Desication Problems
IV. Freeze/Thaw Problems
V. Settlement
VI. Thickness
VQ. Drainage Layer
Vm. Gas Collection Layer
IX. Top Soil
11
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Soils Design for Covers
Composite Action of Clay and FML
Low-Permeability Compacted Soil
Drainage Layer
Gas Collection Layer
Topsoil
Functions of Cover:
Raise Ground Elevation
Promote Good Surface Drainage
Separate Waste from Animals and
Insects
Separate Waste from Plant Roots
Minimize Infiltration of Water into
Waste
Restrict Gas Migration or Enhance Gas
Recovery (Some Sites)
Serve Other Site-Specific Functions
12
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EPA-Recommended Cover Design
for Hazardous Wastes
60 cm
30 cm
60 cm
Top Soil
Filter
Drainage Layer
FML
Low Permeability
Soil Layer
Waste
EPA-Recommended Cover Design
for Hazardous Wastes
(Includes Optional Layers for Arid Site)
60 cm
30 cm ,,
60 cm
Cobbles
Top Soil
Filter
Biobarrier
Drainage Layer
FML
Low Permeability
Soil Layer
Filter
Gas Vent Layer
Waste
13
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Minimize Infiltration of Water into Waste:
Good Surface Drainage Promotes Runoff
Topsoil Stores Water
Plants, through Evapotranspiration,
Transmit Water from Soil to the
Atmosphere
Drainage Layer (Surface Water
Collection and Removal System) Can
Drain Water to Low Point, Where the
Water Is Removed from the Cover
System (Be Careful of Drying Out
Topsoil Too Much)
Hydraulic Barrier Impedes Infiltration,
which Improves Efficiency of Overlying
Drainage System and Promotes Storage
of Water in Topsoil (which in Turn
Maximizes Evapotranspiration and
Runoff)
14
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Flow Rates Through Liners
I-
Hydraulic Conductivity "k
SOIL LINER
Area "a"
GEOMEMBRANE
COMPOSITE LINER
Flow Rate Through Soil Liner Alone
q =
q = flow rate (m3/s)
ks = hydraulic conductivity of soil (m/s)
i = hydraulic gradient
A = area(m2)
Example:
h = 1 ft; D- 3 ft
k = 1 x 10'7 cm/s
= 1 x 10-9 m/s
i =(1+3)/3 = 4/3 =
A = 1 acre = 43,560 ft2 = 4047 m2
q = ksiA
q = (1 x IO-9 m3/s)(1.33)(4047 m2)
= 5.38 x 10'6 m /s x 60 s/rnin x 60 min/hr x 24 hr/day
= 0.465 m3/day x (3.28 ft/m)3 (7.48 gal/ft3)
= 123 gal/acre/day
15
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Flow Rate Through Geomembrane Liner Alone
From Giroud & Bonaparte (1989):
q = flow rate (m3/s)
CB - 0.6 (flow coefficient)
a = area of hole (m2)
g = acceleration due to gravity ( m/s2)
h = head (m)
Example:
h = 1 ft = 0.305 m
a= 1cm2 = 1 x 10-4m2
For one hole in an acre:
q = (0.6)(1 x 10-4 m2)V2 x 9.8 m/s2 x .305 m
= 1.47 x IO-4 m3/s x 60 s/min x 60 min/hr x 24 hr/day
= 12.67 m3/day x (3.28 ft/m)3 (7.48 gal/ft3)
= 3,346 gal/acre/day
16
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Flow Rate Through Composite Liner
From Giroud et al. (1989):
Good Contact:
q = 0.21 hO-9a0.iks0.74 q = f|OW rate (m3/S)
h = depth of liquid (m)
Poor Contact: a = area of hole (m2)
q = 1.15hO-9aO-1kso.74 ks = hydraulic conductivity of
subsoil (m/s)
Example:
1 hole/acre poor contact
ks = 1 0-7 cm/s a = 1 cm2 h = 1
q = 1.15(.305 m)0-9(0.0001 m2)0.i(i x 1Q-9 m/s)0-74
= (1.15)(.343)(.398)(2.18 x 10'7) = 3.4 x 10-8 m3/s
= .0028 m3/day
= 0.8 gal/acre/day
References
Giroud, J. P., and R. Bonaparte (1989), "Leakage through Liners Constructed with
Geomembranes - Part I. Geomembranes Liners," Geotextiles and
Geomembranes. Vol. 8, pp.27-67.
Giroud, J. P., and R. Bonaparte (1989), "Leakage through Liners Constructed
with Geomembranes - Part II. Composite Liners," Geotextiles anrj
Geomembranes. Vol. 8, pp. 71 -111.
Giroud, J. P., Khatami, A., and K. Badu-Tweneboah (1989), "Evaluation of the
Rate of Leakage through Composite Liners," Geotextiles
Geomembranes. Vol. 8, pp. 337-340.
17
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Flow Rates if h = 1 ft:
Soil Liner Alone
Hydraulic Conductivity Flow Rate
(cm/s) (gal/acre/dav)
1x10-6 1,200
1x10-7 120
1x10-8 12
1x10-9 1
Geomembrane Liner Alone
Size of Hole Number of Flow Rate
(cm2) Holes per Acre (aal/ascre/day^
No holes 0.01
0.1 1 330
0.1 30 10,000
1.0 1 3,300
1-0 30 100,000
10 1 33,000
18
-------
Composite Liner
Hydraulic Conductivity Size of Hole Number of F'ow Rate
of Subsoil (cm/s^ (cmfl Holes per Acre
1 x 10-6
1 x 10-6
1 x10-6
1 x 10-6
1 x 10-6
1x10-7
1 X 10-7
1 X10-7
1x10-7
1 X 10-7
1 X 10-8
1 X10-8
1 X 10-8
1 X10-8
1 X10-8
1 X 10-9
1 X10-9
1 X 10-9
1 X10-9
1 X10-9
0.1
0.1
1.0
1.0
10
0.1
0.1
1.0
1.0
10
0.1
0.1
1.0
1.0
10
0.1
0.1
1.0
1.0
10
1
30
1
30
1
1
30
1
30
1
1
30
1
30
1
1
30
1
30
1
3
102
4
130
5
0.6
19
0.8
24
1.0
0.1
3
0.1
4
0.2
0.02
0.6
0.03
0.8
0.03
19
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Poor Liner
Soil Alone:
(ks = 1 x 10-6 cm/s)
Geomembrane Alone:
(30 holes/acre, a = o.1 cm2)
Composite:
(ks- 1 x10-6cm/s,
30 holes/acre, a = 0.1 cm2)
1,200 gal/acre/day
10,000 gal/acre/day
100 gal/acre/day
Good Liner
Soil Alone:
(ks-1 x10-7cm/s)
Geomembrane Alone:
(1 hole/acre, a = 1.0 cm2)
Composite:
(ks- 1 x10-7cm/s,
1 hole/acre, a = 1.0 cm2)
120 gal/acre/day
3,300 gal/acre/day
0.8 gal/acre/day
Great Liner
Soil Alone:
(ks = 1 x10-8 cm/s)
Geomembrane Alone:
(1 hole/acre, a = 0.1 cm2)
Composite:
(ks-1 x10-8 cm/s,
1 hole/acre, a- 0.1 cm2)
12 gal/acre/day
330 gal/acre/day
0.1 gal/acre/day
20
-------
Clav Liner
Composite Liner
Leachate
Leachate
FML
A = Area of Entire Area < Area of Entire
Liner Liner
Leachate
DO.
Leachate
Don't
21
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Natural Clav Soils:
T3
0
T3
C
03
E
E
o
o
03
CC
Fines Content > 20%
Plasticity Index > 10%
(But High PI a Problem)
Coarse Fragments < 10%
Almost No Particles > 1 in.
03
03
CC
[hydraulic Conductivity < 10 cm/s
CO
E
o^
_><
|>
"o
-o
C
o
o
3
03
k_
T3
>,
I
4-
2 4 6 8 1012
Percent Bentonite
22
-------
Important Compaction Variables:
Molding Water Content
Type of Compaction
Compactive Effort
Size of Clods
Bonding Between Lifts
Hydraulic
Conductivity
Dry Unit
Weight
Molding Water Content
23
-------
10-5
o
&
$ 10-6
o
c
o
0 10-7
.0
2
T 10-8
^ 116
108
I 100
92
Increasing
Effort
'Increasing
Effort
12 16 20
Molding Water Content (%)
24
24
-------
Influence of Clod Size:
Hydraulic Conductivity (em's)
Molding
W.C. (%} 0.2-in. Clods Q.75-in. Clods
12
16
18
20
2x10-3
2x10-9
1 X10-9
2x10-9
4x10^
1 X10-3
3x10-10
7x10-10
Bor«hol«
Lift 1
Lift 2
Lift 3
Lift 4
25
-------
E
o
O
O
10
10
-4
-5
10
10
10
-7
-8
10
-9
0
D Good Construction
A Excellent Construction
Thickness of Liner (ft)
26
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Before Freezing
After Thawing
Figure 6. Schematic diagram of collapse of clay
particles in clayey silt. (Chamberlain and Gow)
1000
2
8
,00
10
o
3
&
I'M i'M| r~-
Ellsworth Cloy
100
10
Efftctlvt Strtss
Figure 7. Increases in permeability as a function
of effective stress for some clays and silts.
(Chamberlain and Gow)
27
-------
^ 10
-7
o>
V)
£
^cj
>>
^
>
o
3
O
o
0
-8
x -9
10
(kPa)
50
100
Sample Containing
Desiccation
Cracks
"Sample Containing
No Desiccation
Cracks
04 8 12 16
Ef f ecHve Confln ing Pressure (psi)
Omega Hills Landffill Cover Study
Milwaukee, Wisconsin
Test Plot 1
Test Plot 2
Test Plot 3
6 in.
4ft
18 in.
4ft
6 in.
2ft
12 in. '
2ft
Other Details:
Test Plots Were Placed on a 3:1 Slope
Test Plots Measured 40 x 40 ft
28
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Test Plot 1
Omega Hills Cover Study
Year Precipitation Runoff Percolation
86-87
87-88
88-89
35.3
22.8
32.4
7.1
1.5
2.2
0.06
0.18
2.19
(Values in Inches)
Observations after 3 years:
- Upper 8 to 10 in. of Clay Was Weathered and Blocky
- Cracks up to 1/2 inch Wide Extended 35 to 40 inches
into the Clay
- Roots Penetrated 8 to 10 inches into Clay in a
Continuous Mat, and Some Roots Extended into
Crack Planes as Deep as 30 in. into the Clay
- The Base of Clay Layer Appeared Undamaged
- No Freezing below 3-ft Depth
29
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Omega Hills Cover Study
Test Plot 2
18 in.
Year Precipitation Runoff Percolation
86-87
87-88
88-89
35.3
22.8
32.4
4.3
1.5
2.0
0.27
1.19
3.85
(Values in Inches)
Observations after 3 years:
- Virtually the Same Observations Made for Test
Plot 1 Also Apply to Test Plot 2
- In 1988-89, Test Plot 1 Allowed 2.19 in. of
Percolation while Test Plot 2 Allow 3.85 in. of
Percolation. Surprisingly, the Greater Thickness of
Topsoil in Test Plot 2 Did Not Reduce Percolation
and Did Not Diminish the Damaging Effects of
Desiccation.
30
-------
C/3
W
£
55
Strain
Before Settlement
After Settlement
T
Distortion:
31
-------
1 10
Tensile Strain (%)
100
Recommendations:
Do Not Try to Put a Permanent, Low-
Permeability Cover on an Unstable
Waste that Will Undergo Large
Settlement; Stabilize the Waste before
Attempting to Place a Final Cover
Clay Soils Compacted at High Molding
Water Content Can Best Resist Strains
from Differential Settlement without
Cracking, but Such Soils Are Vulnerable
to Damage from Desiccation
Design for A/L < 0.05
An FML/Clay Composite Is Especially
Important for Covers Placed on Waste
that Will Undergo Settlement
32
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Interfacial
Friction
Cover Soil
FML
Interfacial
Friction
Angle, 6,
Compacted Soil
Two Design Concerns:
1. Slippage within Topsoil:
- Slope Angle (3 Must Be < <)> (Dry State)
- Slope Angle p Must Be < <|>/2 forSaturated
Soil and Downward Seepage Parrallel to
Slope
2. Slippage along Soil/FML Interface:
- Slope Angle p Must Be < 8 (Dry State)
- Slope Angle p Must Be < 8/2 for Saturated
Soil and Downward Seepage Parallel to
Slope
drainage layers
, - FML
FML anchors
(separate anchor trench for each geosynthetlc)
low-permeablllty soil
watte
FML
33
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Recommendations for Gas Vent Laver:
Use Granular Material (k > 1 cm/s) or
the Equivalent Geosynthetic (Geotextile,
Geonet, or Both)
Provide Adequate Filters Above and
Below the Vent Layer
Vent Pipes should Be Anchored to the
Barrier Materials, But in a Way that
Ensures that a Geomembrane is Not
Torn Should There Be Some Differential
Settlement Between the Pipe and the
Geomembrane (This Settlement Should
Be Minimized in the Design, e.g., Do Not
Extend the Vent Pipe Any Deeper than
Necessary)
May Have Horizontal Collection Pipes in
Gas Vent Layer
Vent Pipes Often Spaced about 200 ft
Apart (1 Pipe per Acre)
Surface Drainage:
Maintain an Adequate Slope and Drain
Runoff to Areas Where Flow Can Be
Controlled; May Require Benches on
Long Slopes
Control Erosion
Control Erosion
Bench in
Slope
Protect Against Erosion in Drainage
Areas that Might Have High Flow Rates
34
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GEOSYNTHETIC DESIGN FOR LANDFILL COVERS
Robert M. Koerner
I. FML Design Concepts
n. Geonet and Geocomposite Sheet Drain Design Concepts
m. Geopipe and Geocomposite Edge Drain Design Concepts
IV. Geotextile Filter Design Considerations
V. Geogrid Cover Soil Reinforcement
VI. Geotextile Methane Gas Vent
35
-------
Geosynthetic Design for Landfill Covers
by
Robert M. Koerner
Geosynthetic Research Institute
Drexel Univesity
Philadelphia, PA 19104
Geopipe
or
Geocomposite
Edge Drain
eotextile
Geonet or
Geocomposite
Sheet Drain
FML (Geomembrane)
Geotextile
36
-------
Types of Geosynthetics Used in Landfill Covers
1. FML's (geomembranes) -- surface water barriers
2. Geonets & Geocomposites -- surface water drains
3. "Geo" pipe & Geocomposites -- perimeter water drains
4. Geotextiles - filters for drainage and removal systems
5. Geogrids - cover soil reinforcement
6. Geotextiles - methane gas venting systems
Customary Primary Functions of Geosynthetics (GS) Used in
Landfill Cover Systems
Type
of
GS Separate
FML (GM)
GT V
GN
GP
GC
GG
Primary Function
Reinforce
V
V
Filter Drain
V V
V
V
V
Barrier
V
Design-bv-Function Concept
Allowable (Test) Value
Required (Design) Value
where
Test Values via ASTM, NSF, GRI, etc.
Design Values via Geotechnical, Hydraulic, Polymer,
Environmental Engineering Principles
- or Regulations -
Factor-of-Safety via site specific situation varying
from 2 to 100
37
-------
1. FML Design Concepts
(a) Compatibility
(b) Vapor Transmission (Water and Methane)
(c) Biaxial Stresses via Subsidence
(d) Planar Stresses via Friction
1(a) FML Compatibility
liquid is generally surface water
usually EPA 9090 is not necessary
dimensional stability test is ASTM D-1204
resistance to soil burial is ASTM D-3083
water extraction test is ASTM D-3083
volatile loss test is ASTM D-1203
biological resistance test is ASTM G-22
fungus resistance test is ASTM G-21
1(b) Vapor Transmission (Water and Methane)
Water vapor transmission test is ASTM E96
WVT rates for common FML's are:
PVC - 30 mil - 1.9 g/m2-day
CPE - 40 mil - 0.4 g/m2-day
CSPE - 40 mil - 0.4 g/m2-day
HOPE - 30 mil - 0.02 g/m2-day
HOPE - 96 mil - 0.006 g/m2-day
Methane vapor rates can be evaluated similarly
Test method to follow is ASTM D1434
See EPA-600 Sept., 1988 (TRD)
38
-------
1(c) Biaxial Stresses via Subsidence
FS =
allow
reqd
where
CTaiiow= 3'D Tension test via GRI GM-4
areqd = requires subsidence estimate
DC
H
co
Regarding the Allowable Strength via GM 4 Test
5000
4000-
3000-
2000-
1000
40 60
STRAIN (%)
80
100
Regarding the Required Strength
'req'd
reqd
4 L D t
where
Ycs = unit weight of cover soil
Hcs = height of cover soil
39
-------
1(d) Planar Stresses via Tension
FS =
allow
reqd
where
Taiiow= Wide Width Tensi|e Strength of GM's
ASTM D35.10.86.02 (in task committee)
Treqd = reclu'res friction calculations;
an outline follows
Regarding the Required Strenath
req'd
reqd
°au
L W
40
-------
2. Geonet and Geocomposite Sheet Drain
Design Concepts
(a) Compatibility
(b) Crush Strength
(c) Flow Capability
2(a) GN/GC Compatibility
liquid is generally surface water
usually EPA 9090 is not necessary
polymers are generally PE, PP or HIS
2(b) Crush Strength
FS =
allow
reqd
where
aaiiow = rib lay-down for GN's via GRI GN-1
= core collapse for GC's via GRI GC-4
(must include a creep consideration)
°reqd = cover soil dead load plus
construction equipment live load
Stress
Geocomposite
Strain
41
-------
2(c) Flow Capability
Callow
FS =
where
Callow = Transmissivity Test via ASTM D-4716
(note, it must simulate entire cross section)
q d = Site specific water balance model or HELP
ASTM D-4716 Flow Rate Test
Constant Load
Overflow
I
Screw Jack
Outlet Reservoir
5000
Overflow Weir
10000
Normal stress (Ib./ft?)
42
15000
-------
3. Geopipe and Geocomposite Edge Drain
Design Concepts
(a) Compatibility
(b) Crush Strength
(c) Flow Capability
3(a) GP/GC Compatibility
liquid is generally surface water
usually EPA 9090 is not necesssary
polymers are generally PE or PVC
3(b) Crush Strength
FS =
allow
reqd
where
°ailow = crusn strength for GP via ASTM D-2412
= core collapse for GC via GRI GC-4
areqd = cover soil dead load plus
construction equipment live load
Stress
3(c) Fiow Capability
FS =
'allow
^reqd
= for GP's use hydraulic theory
= for GC edge drains use ASTM D4716
qreqd = flow coming from surface water drain
(cumulative over its entire length)
43
-------
4. Geotextile Filter Design Considerations
(a) Compatibility
(b) Permeability (permittivity)
(c) Soil retention
(d) Clogging evaluation
4(a) Geotextile Compatibility
liquid is generally surface water
usually EPA 9090 is not necessary
polymers are generally PP or PET
4(b) Geotextile Permeability
_« _ Callow
where
= Water Permittivity of Geotextiles via
ASTM D4491
= Site specific water balance or HELP
4(c) Geotextile Soil Retention
FS = -r-
°95
where
d85 = 85% finer particle size of the
upstream soil
X = constant (2 to 4)
095 = 95% opening size of geotextile, via
ASTM D-4751
4(d) Geotextile Clogging Evaluation
Gradient rato test (GR)
Long-term flow test (LTF)
Hydraulic conductivity ratio test (HCR)
Fine fraction filtration test (F3)
44
-------
5. Geoarid Cover Soil Reinforcement
T [Required Geogrid (or GT) Strength]
Tension H (Covef Soj, Depth
.Crack / at Unit weight y)
Active Wedge
Passive Wedge
L (Slope Length)
r=(,
LH -
2H2
sin 2(3
)x Y
sin ( P - 5 )
cos5
H
where
S = Possible Seepage Force
E = Possible Earthquake Force
6. Geotextile Methane Gas Vent
sin
FS =
'allow
veqd
where
Callow =
Qreqd =
in-plane flow of gas via modified radial
permeability test
amount of methane generated in the
site-specific landfill
45
-------
DURABILITY AND AGING OF GEOSYNTHETICS
Robert M. Koerner
I. Common Polymers and Formulations
II. Mechanisms of Degradation
III. Synergistic Effects
IV. Accelerated Testing Methods
V. Summary and Conclusions
47
-------
Durability and Aging of Geosynthetics
by
Robert M. Koerner
Geosynthetic Research Institute
Drexel University
Philadelphia, PA 19104
1. Common Polymers and Formulations
2. Mechanisms of Degradation
3. Synergistic Effects
4. Accelerated Testing Methods
5. Summary and Conclusions
1. Polymers and Formulations
(a) Types of Geosynthetics
(b) Types of FML's
(c) Typical Formulations
48
-------
1(a) Types of Geosynthetics
FML's* (geomembranes)
Geotextiles
Geonets
Geogrids
Geocomposites
Geopipes
*focus for this presentation, but
applies to all polymeric materials
1(b) Types of FML's
Thermoset elastomers (rarely used)
- Thermoplastic*
flexible (PVC, CPE, CPE-R, CSPE-R, EIA-R)
semi-crystalline (VLDPE, HOPE)
Bituminous (rarely use)
*focus for this presentation
1(c) Typical Formulations of FML's
FML Resin Plasticizer Carbon Black Additive*
Type and/or Filler
PVC
CPE
CSPE
EIA
VLDPE
HOPE
45-50
60-75
45-50
70-80
96-98
97-98
35-40
10-15
2-5
10-25
0
0
10-15
20-30
45-50
5-10
2-3
2-2.5
3-5
3-5
2-4
2-5
1-2
0.5-1
*refers to antloxldant, processing aids and lubricants.
49
-------
2. Mechanisms of Degradation
(a) Ultraviolet
(b) Radiation
(c) Chemical
(d) Swelling
(e) Extraction
(f) Delamination
(g) Oxidation
(h) Biological
2(a) Ultraviolet Degradation
UV-B range is most sensitive
PE < 300 nm
PET < 325 nm
PP < 370 nm
Mechanism is well understood
Carbon black is screening agent
Chemical stabilizers are scavengers
Both preventative methods usually used
Cover with soil and maintain
Exposed FML's have limited lifetimes
2(b) Radiation Degradation
-y-rays and neutrons are problems
Mechanism is well understood
Non-problem unless waste is radioactive
Concern with high level and transuranic waste
Unknown with low level waste
Some laboratory studies are available
50
-------
2(c) Chemical Degradation
Good historic data base for many liquids
Mixed chemicals (e.g., leachate) require
EPA 9090 evaluation
Surface water should present no concern
2(d) Swelling Degradation
All polymers swell when exposed to moisture
General ordering is PVC (highest)-to-HDPE (lowest)
Process is largely reversible
May not lead to degradation
May, however, lead to secondary effects
2(e) Extraction Degradation
Leaching of plasticizers is well known
Movement of other compounds may be possible
Low molecular weight resin may be mobilized
Closest ASTM tests are:
water extraction D3083
volatile loss D1203
2(f) Delamination Degradation
Only applies to scrim reinforced or laminated liners
ASTM D413 is ply adhesion test
Requires factory sealed edges to prevent wicking
Flood coating is necessary in the field
51
-------
2(g) Oxidation Degradation
Essentially unavoidable
Reaction understood:
R* + 02 -» ROO
ROO* + RH -> ROOM + R
where
R* = free radical
ROO" = hydroperoxy free radial
RH = polymer chain
ROOM = oxidized polymer chain
Anti-oxidants must be added to
scavenge the free radicals
2(h) Biological Degradation
No documented case histories available
Bacteria cannot find chain endings
Resins are not food source
Plasticizers are under evaluation
Animals may dig holes, but this is
also un-documented
52
-------
3. Svneraistic Effects
(a) Elevated Temperatures
(b) Applied Stresses
(c) Long Exposure
3(a) Elevated Temperatures
Provides mobility to molecular structure
Accelerates all of the degradation processes
Cyclic temperature effects unknown
Can, however, be laboratory modeled
3(b) Applied Stresses
Compressive stresses always exist
Tensile stresses exist on slopes
Biaxial stresses result from bending
Complicated issue
Field monitoring is warranted
3(c) Long Exposure
Requires simulated laboratory modeling
Field Performance feed-back is necessary
Difficult issue with new materials
53
-------
4. Accelerated Testing Methods
(a) Stress limit testing
(b) RPM for pipes
(c) RPM for FML's
(d) Elevated temperature and Arrhenius modeling
(e) Multiparameter approach
STRESS LIMIT TESTING
100i
10 100 1000 10000 100000 1000000
Failure Time (hrs.)
RATE PROCESS METHOD FOR GEOPIPES
logo
(Mpa)
"allow
= 6.5
log'rime
50 yrs.
RATE PROCESS METHODS FOR GMs
100
CO
t/3
0)
CO
33
-------
ELEVATED TEMPERATURE TESTING
Hydraulic Load Device
Air (7)
Liquid Level
Sight Glass
-T^JPH
1 'Record
^-*.
~T^
HI
[T ._. .._..
o
c
0
o
o
o
0
er o
Liquid
1
^ «C
Sand
3
4
3
3
3
3
3-
3
3
= -
Leachate
Recirculation
Pump
-Heat Transfer
Coils
_Perforated
"Plate Press
-Thermocouples
Test Liner
Drain
_
ra
£
ro
tr
c
g
T5
ca
o>
CE
In A
Governing Equation:
In K = In A - (|)y
*
78 C 48°C
Inverse Temperature (1/T)
18 C
Graphical Method of Plotting Reaction Rate Values
for Change in a Specific Geomembrane Property.
ARRHENIUS MODELING
Example: Two identical tests for 18 weeks:
1st: 1#C = 29?K
2nd: 78°C = 351°K
Activation Energy @ 78° C, E =109,000 J/mol
Gas Constant, R = 8.314 J/mol- K
r = Ae RT (theArrheniusEquation)
Solution:
r@78
r@18
109,000 \ r 1 1 I
8.314 'l-351~ 291-1
Hence
@18
= 2254 x 18 wks
= 784 years
55
-------
MULTIPARAMETER PREDICTION METHOD
(Modified from Hoechst)
1. Establish constant stress behavior of the specific GM in NCLT or SCLT
2. Establish constant strain behavior of the specific GM via Stress
Relaxation Tests
3. Obtain field data of strain gauged GM over sufficient time to
establish trends and couple to constant strain curves
4. Superimpose the above three site specific curves in order to
extrapolate the lifetime of the GM
100
90
80
70
60
50
LU
>
C/3
CO
LU
DC
CONSTANT STRESS TESTS
(e.g., NCLT or SCLT)
OTILE REGION
0.9 0)
co"
0.8 §
LU
0.7 CO
CL
0.6 5]
0.5
p
o
0.3
0.25 9
LL
0.2 z
1 10 10 10
TIME (HOURS)
10 10 10 10
10
100 1000 10000
YEARS
CONSTANT STRAIN TESTS
(i.e., STRESS RELAXATION)
1 0 ' 1 10' 1 0" 1 0
TIME (HOURS)
100 1000 10000
YEARS
56
-------
100
90
80
70
.-. 50
03
CO
HI
IX
CO
HI
^
C/3
111
30
20
10
FIELD
DATA
10
COUPLE LAB AND FIELD
STRAIN GAUGE DATA
1 10 10 10.
TIME (HOURS)
10 10
10 10
10
10
100 1000 10000
YEARS
LL
o
co
co
LLJ
co
I
100
90
80
70
60
50
40
30
20
1 0
1 0
SUPERPOSITION OF SITE SPECIFIC
CONSTANT STRESS CURVE,
CONSTANT STRAIN CURVE, and
FIELD STRAIN CURVE
(a) no addl relax.
(b) intermed. relax.
(c) full relax.
I I I
IT* IT
-1
0.9
0.8
0.7
0.6
0.5
0.4
co~
CO
oJ
LL
a
Z
O
O
0.
3 E,
a:
g
25
* i
.15 £
O
1 10 10
TIME (HOURS)
1 o-
10 10
1 0
1 0
8
1 0
10
100 1000 10000
YEARS
5. Summary and Conclusions
Durability and Aging are important issues
Particularly beyond 30-yr. post closure period
Most degradation processes are eliminated, or
greatly reduced, by covering the FML
Predictive methods are emerging
Field feed-back is essential
57
-------
ALTERNATIVE COVER DESIGNS
Robert E. Landreth
I. Other Options Considered by EPA
II. Other Federal Agencies
HI. Selected States
59
-------
Alternative Cover Designs
1. RCRA Subtitle C
2. RCRA Subtitle D
3. CERCLA
Leachate Management Strategy
Recirculation
Mummify
60
-------
Considerations for Soils Only at Municipal Solid Waste Landfills
Health considerations
Aesthetic considerations
Site usage considerations
Health Considerations
Minimize vector breeding areas and animal attractiveness
Control water movement
Control gas movement
Minimize fire potential
61
-------
Aesthetic Considerations
Minimize blowing paper
Control odors
Provide sightly appearance
Site Usage Considerations
Minimize settlement/maximize compaction
Assist vehicle support and movement
Equipment workability under all weather conditions
Provide for vegetation
Future
62
-------
CERCLA Paragraph 121
If: State requirement more stringent than RCRA
TTien: ARAR
If: State has authorized RCRA program
Then: State requirements ARAR
CERCLA Paragraph (121UdU3)
All wastes offstte require RCRA permit
Consolidation of wastes into smaller
area does not require RCRA regs.
63
-------
If: RCRA waste present and waste treated, stored or disposed
after 11/19/80 then Subtitle C applicable
If: CERCLA activity involves treatment, storage or disposal
(even after date) then Subtitle C applicable
If: Removal of wastes potentially pose health threat
but not to groundwater and residual leachate <.
health based levels
Then: Alternate landfill closure
cover to prevent direct threat
long-term management
may also have land use restrictions
64
-------
If: Residual contamination _> health based levels
does not pose direct contact threat or impact
groundwater residual leachate .> health based
levels
Then: Alternate clean closure
fate and transport modelling
notice on deed
New Materials for Potential Use
65
-------
CONSTRUCTION QUALITY ASSURANCE FOR SOILS
David E. Daniel
I. Materials Control
n. Moisture Content
in. Density
IV. Compaction
V. Protection
VI. Certification
VII. Test Pads
67
-------
Construction Quality Control Tests:
Atterberg Limits
Grain Size Distribution
Compaction Curve
Hydraulic Conductivity of
Lab-Compacted Soil
Lift Thickness
Moisture Content
Dry Density
Hydraulic Conductivity of
"Undisturbed" Sample
Material
Tests
Tests on
Prepared and
Compacted
Soil
Methods of Testing:
- Loose Lift Thickness: Shovel
- Final Lift Thickness: Survey
- Atterberg Limits: ASTM D 4318
- Grain Size Distribution:
ASTM D 1140 (Fines Content)
ASTM D 422 (Sieve /
Hydrometer Analyses)
- Compaction Curve:
ASTM D 698 (Std. Proctor)
ASTM D 1557 (Mod. Proctor)
- Hydraulic Conductivity (Lab.
Compacted Soil): Rigid or
Flexible Wall Permeameter
(Draft ASTM Standards)
68
-------
- Field Water Content:
- Direct Oven Drying (ASTM
D 2216)
- Microwave Oven Drying
(ASTM 4643)
- Other Direct Drying
- Nuclear Methods (ASTM
D3017)
- Field Dry Density:
- Nuclear Methods (ASTM
D 2922)
- Sand Cone (ASTM D 1556)
- Drive Cylinder (ASTM
D 2937)
- Balloon (ASTM 2167)
- Lab. Hydraulic Conductivity
(Field Compacted Soil):
Flexible Wall Permeameter
69
-------
TABLE 5-9. RECOMMENDATIONS FOR CONSTRUCTION DOCUMENTATION OF CLAY-LINED
LANDFILLS BY THE WISCONSIN DEPARTMENT OF NATURAL RESOURCES
1.
Item
Clay borrow source
testing
Testing
Grain size
Moisture content
Atterberg limits
Frequency
1,000 yd3
1,000 yd3
5,000 yd3
2. Clay liner testing
during construction
3. Granular drainage
blanket testing
(liquid limit and
plasticity index)
Moisture-density curve
Lab permeability
(remolded samples)
Density
(nuclear or sand cone)
Moisture content
Undisturbed permeability
Dry density
(undisturbed sample)
Moisture content
(undisturbed sample)
Atterberg limits
(liquid limit and
plasticity index)
Grain size
(to the 2-micron
particle size)
Moisture-density curve
(as per clay borrow
requirements)
Grain size
(to the No. 200 sieve)
Perraeability
5,000 yd3 and all
changes in material
10,000 yd3
5 tests/acre/lift
(250 yd3)
5 tests/acre/lift
(250 yd3)
1 test/acre/lift
(1,500 yd3)
1 test/acre/lift
(1,500 yd3)
1 test/acre/!1 ft
(1,500 yd3)
1 test/acre/lift
(1,500 yd3)
1 test/acre/lift
(1,500 yd3)
5,000 yd3 and all
changes in material
1,500 yd3
3,000 yd3
Source: Gordon et al., 1984.
70
-------
0)
'CD
Yd.max
P Yd.max
Zero Air Voids
Acceptable Zone
Molding Water Content, w
co
o
o
O
10
10
10
-4
_>»
'>
'S 10
-5
-6
-7
10
10
-8
-9
(A)
10 15 20 25
Molding Water Content (%)
o
Q.
g>
'o
120
110
100
90
15
20
(B)
25
Molding Water Content (%)
71
-------
o
Q.
120
110h
100 h
10 15 20 25
Molding Water Content (%)
o
Q_
D)
Q
120
110
100
90
10-5
i
Mod.
Proctor
Curve
Acceptable Zone Based on
Typical Current Practice:
Tb > 0.9 >d,max and
w = 0 - 4% Wet of w0pt
_L
15 20 25
Molding Water Content (%)
72
-------
CO
E
O>
"(D
18
17
16
15
14
1 x 10'8 cm/s
Acceptable
Zone
Standard
Proctor
I- 1 x 10-7 crn/s /
U 5x10-7 cm/s
0 10 20 30
Molding Water Content (%)
O)
0)
(A)
k Modified Proclot
O Standard Ptoclor
D Reduced Proclot
Molding Water Content
>%
4-J
^>
o
3
o
O
O
o
"5
m
o
>.
x
Modified Proctor
O Standard Proctor
O Reduced Proctor
g>
'oj
O)
'o>
Acceptable Zone
Molding Water Content
(D)
Acceptable Zone
Modified to Account
for Other Factors
73
-------
o
Q.
O>
'
'o>
120
100
80
60
(B) .
Zero Air Voids
Line of Optimums
0 10 20 30 40
Molding Water Content (%)
74
-------
gj
I
«*-»
"c
ID
Q
Overall Acceptable
Zone
Acceptable Zone
Based on Hydraulic
Conductivity
Acceptable Zone
Based on Shear
Strength
£
Q
Molding Water Content
1UO
100
95
90
So
80
2
/*
0
\
"-A.
,-irf
---0
2
\
S*N
fS
jcf
5
X
XV
^s
l^4
]X0"
3
V
^S
^
2
0
zero A
\
"Si
o
3
tfVofcJS
X
N.
tJ
5
X
4(
East Borrow Area
Type A Soil
Q Red, Proctor
O Std. P'foctor
A Mod. Proctor
Molding Water Content (%)
75
-------
10
10
£,
>
o
I
J.
10
10
-3
-4
-5
-6
25 30 35
Molding Water Content (%)
East Borrow Area
Type A Soil
Q Red. Proctor
O Std. Proctor
A Mod. Proctor
40
O)
1
IUO
100
95
90
85
80
//
/ /
*-<,
A
//
/ /
s^^
^
East Borrow Area
Type A Soil
O Red. Proctor
O Std. Proctor
A Mod. Proctor
20 25 30 35 40
Molding Water Content (%)
76
-------
Soil-BentonitQ Mixes:
1. Mix batches of soil at different bentonite
contents, e.g., 0, 2%, 4%, 6%, "8%, and 10%
bentonite (dry weight basis).
2. Develop standard Proctor compaction
curves for each bentonite content.
3. Compact Samples with standard Proctor
procedures 2% wet of optimum water
content for each bentonite content.
4. Permeate the soils prepared in Step 3 and
develop a plot of hydraulic conductivity vs.
bentonite content.
5. Decide how much bentonite to used based on
data from Step 4, taking into account
construction variability (i.e., use more
bentonite that Step 4 indicates is required
because mixing in the field will not be as
thorough as in the laboratory).
6. For the average bentonite content expected
in the field, utilize the procedures described
earlier in which soils are compacted with 3
different compactive efforts.
Important Details:
- Sampling Pattern
- Bias in Some Tests
- Outliers
77
-------
Random Sampling
1. Establish a Grid with Approximately 10 Times More Grid Points than
Sampling Points.
8
37
110
J
119
y
128
^
i «
11
20
1
29
1
12
21
30
1
13
4
22
» 1
14
i
23
31 1 32
15
24
33
4
16
25
34
»
\7
26
35
38 39 40 41 42 43 44
18
27
36
45
2. Use a Random Number Generator to Generate Sampling Numbers.
Take Last Digit(s) of Generated Numbers and Ignore Numbers
that Are Outside of Range. Use a Computer to Generate the
Random Numbers, or Tables in Mathematical Handbooks, e.g.,
"A Table of 14,000 Random Units" in CRC Standard
Mathematical Tables.
3. Be Sure that Sampling Points Are Not atPrecisely the Same
Location in Adjacent Lifts.
4. Supplement Random Sampling with Additional Sampling in Any
Questionable Areas. Also, Take at Least One Sample for Each Day
of Construction Activity.
78
-------
Bias in Tests:
Density Tests (Nuclear and Drive Ring)
Water Content Tests (Nuclear and
Microwave Oven Drying)
Hydraulic Conductivity of "Undisturbed
Samples"
Outliers:
- Accept a Percentage of Outliers
- Repeat Test 2 to 5 Times; If All
Repeat Tests Pass, Test Results
Are Considered Acceptable
- If Area Is To Be Reworked; Define
Area To Be Repaired by
Additional Tests that Separate
Passing Area from Failing Area
- Rework Area As Needed; Retest
with One or (Usually) More
Tests
79
-------
CRITICAL VARIABLES TO CHECK FOR LOW-PERMEABILITY
COMPACTED SOIL USED IN A COVER SYSTEM
Material:
Minimum Liquid Limit =
Minimum Plasticity Index
Maximum Particle Size =
Maximum Percentage of Gravel =
Minimum Percentage of Fines =
Water Content/Density Defined (Y/N)
Maximum Clod Size =
Lifts:
Scarify Surface Before Placing (Y/N)
Maximum Loose Lift Thickness =
Maximum Completed Lift Thickness =
Compactor:
Minimum Weight =
Type of Roller Drum
Compaction:
Minimum Number of Passes
Protection:
Protection from Dessication & Freezing (Y/N)
80
-------
CRITICAL VARIABLES TO CHECK FOR LOW-PERMEABILITY
COMPACTED SOIL USED IN A COVER SYSTEM
(with Daniel's Recommendations)
Material:
Minimum Liquid Limit = 35%
Minimum Plasticity Index = 10%
Maximum Particle Size = 2 in.
Maximum Percentage of Gravel = 10%
Minimum Percentage of Fines = 30%
Water Content/Density Defined (Y/N) Yes
Maximum Clod Size = 2 in. during Processing
Lifts:
Scarify Surface Before Placing (Y/N) Yes
Maximum Loose Lift Thickness = 9 in.
Maximum Completed Lift Thickness = 6 in.
Compactor:
Minimum Weight = 30.000 Ibs Static Weight
Type of Roller Drum Footed. Length of Foot > 7.5 in.
Compaction:
Minimum Number of Passes = 6
Protection:
Protection from Dessication & Freezing (Y/N) Yes
81
-------
Check List for Low-Permeability Soil Layer Used in Cover System
(Recommended by D. E. Daniel)
General
Ask to see the Engineering Report or other documentation that describes the
design. [Read the appropriate section(s) concerning design of the low-
permeability soil layer.]
Ask to see the QA/QC Report. [Read the appropriate section(s) concerning
the low-permeability soil layer.]
Ask to see the Plans and Construction Specifications. [Read the parts that
deal with the low-permeability soil layer.]
Site Preparation
Is there any evidence of landsliding? [Look for large cracks in the ground
or other evidence of instability.]
Are there proper controls on ground elevations? [Ask how elevations were
determined and where the benchmark(s) is/are located.]
Have all grasses and tree roots been excavated in areas to receive
engineered barriers? [Visually inspect.]
Subgrade Inspection for Bottom Liner
Is the subgrade free of organic matter? [Visually inspect.]
Is the subgrade properly sloped as shown on plans? [Ask for details and be
sure that elevations are confirmed by survey and documented.]
Is the subgrade sufficiently strong to support equipment? [Check by
walking over the area; feet should not sink into soil more than 1 inch.
Bounce up and down on wet soil; ground should not visually deform or
quake.]
Has the subgrade been tested for density and moisture at the required
frequency? [Ask if tests were performed, if tests are required.]
Is the subgrade reasonably smooth? [Should be able to place a long stick or
rod onto surface at all locations and not see separation large enough to
accomodate your fist. If surface is uneven, it should be "proofed-rolled,"
e.g., with smooth steel-drum roller.]
82
-------
Low-Permeability Soil Layer
Materials
Material should be cohesive. [Check by rolling material into thread ~ 1/8
inch in diameter; if soil crumbles and cannot be rolled into a thread, it may
not have enough fines -- ask for quantitative assessment.]
Have Atterberg limits been measured? [Ask for this information and
compare the results with the minimum required values for Liquid Limit and
Plasticity Index. Ask how the samples were selected and look for: (1)
random sampling supplemented by additional tests on suspect material; (2)
at least one sample taken per day of operations; and (3) sampling any time
there is an obvious change in material or borrow source.]
For soil bentonite liners, has sufficient bentonite been added, and has the
blending been thorough? [Ask how weights are controlled and how bentonite
is blended,]
Check for frequency and size of gravel-sized particles (£4.76 mm or 3/16
inch) in diameter. [Do this visually. There is usually no problem if the
gravel-sized particles comprise < 10% of the material and the largest
particles are no larger than about 2 inches. If larger particles are present,
they should be removed. If more than 10% of the material is gravel, ask
for test data that demonstrates that the gravel does not raise the
permeability above the maximum allowable value.]
Have grain size analyses been performed? [Ask for this information and
compare the results with the minimum required value for percentage fines
and the maximum allowable value for percentage of gravel. Ask how the
samples were selected and look for: (1) random sampling supplemented by
additional tests on suspect material; (2) at least one sample taken per day
of operations; and (3) sampling any time there is an obvious change in
material or borrow source.]
Is there evidence of deleterious material? [Look for roots, sticks,
vegetation, and debris such as bricks,]
Visually check water content; the material should be placed in its final
location at a water content close (within 2-3 percentage points) to the
desired value. Small adjustments in water content can be made just prior
to compaction, but large adjustments should be made in a separate
conditioning area. [One learns mainly from experience what is a
satisfactory water content. Rolling the soil into a thread, as in a plastic
83
-------
limit test, can be helpful since the water content should almost always be
wet of the plastic limit.]
Check results of water content tests. [Determine whether the water content
of the material in the borrow pit is close (within 2-3 percentage points) to
the acceptable range of water content. If the water content is not close, the
material should be taken to a separate moisture adjustment area where the
soil is slowly wetted or dried, while being repeatedly mixed, over a period
of at least 48 hours to allow time for water to be evenly distributed in the
soil.]
Check to make sure that the soil is wetted or dried evenly. [If the soil is
dried, it should be spread in a layer no thicker than about 12 inches and
mixed with tilling equipment. If the soil is wetted, water should be evenly
distributed over a layer and the soil mixed with tilling equipment. If the
water content is changed by more than 2-3 percentage points, the moisture
adjustment should be made in a separate conditioning area.]
Placement
Check subgrade for roughness. [Except for the first lift, a new lift should
never be placed on a smooth surface. Visually observe the surface to
receive the new lift to be sure it is rough, either from foot prints of roller
or from scarification equipment. Scarification, if performed, should be to a
depth of approximately 1 in.]
Check subgrade for desiccation damage. [Visually inspect subgrade; look for
evidence that surface has dried out. If previously compacted lift has
desiccation cracks wider than 1/8 inch or is suspected of having desiccated
(e.g., because of change in color), require additional water content tests.
Compare water contents with values measured immediately after
compaction. If necessary, excavate damaged lift(s) and rebuild.]
Check loose lift thickness. [Loose lifts are normally < 9 in. thick. Inspect
visually from the edge of a lift or from grade stakes, or dig down through a
loose lift and measure its thickness.]
Check for repair of any grade stake holes and be sure that grade stakes are
recovered and not buried in the liner. [Ask how the grade stake holes are
repaired and request a demonstration. Ask what methods are used, e.g.,
inventory procedures, to ensure that all grade stakes are recovered and not
buried in the liner.]
84
-------
Compaction
Check that the compactor meets requirements. [Check weight, type of drum
(footed or smooth), length of feet on drum, and type of energy (static or
vibratory).]
Check that number of passes over an area is adequate. [Ask if there is a
minimum, and if so, what procedures are followed to spot check for
compliance. You can count the passes over a given area to confirm for at
least one location.]
For liners on slopes, check to be sure compactor is not shearing the liner.
[On sloping landfill covers compacted with heavy equipment, the compactor
tends to slip down the slope and may shear the low-permeability soil layer
if the slope is too steep and/or the compactor too heavy. Look for scarps or
shear surfaces.]
Check the water content and dry density of the compacted soil. [Ask for test
results and determine: (1) whether sampling was random, with additional
tests as required in suspect areas or to be sure that at least one test was
performed each day that soil was compacted; (2) how the tests were
performed; (3) whether the water content tests are periodically checked
with overnight oven drying, and if so, how the test results compare; (4)
whether nuclear density test results (if this type of test is used) are
periodically checked with the sand core, and if so, how the nuclear results
compare with sand core; (5) how holes made for the water content and
density tests are repaired (ask for a demonstration); and (6) how the
water content and density results compare with the specifications.]
Determine the protocol if a water content or dry density test fails. [Ask for
an explanation. Determine: (1) if a mechanism exists to overrule an
erroneous water content or density test (look for at least 3 passing tests
required to overrule a failing test); and (2) the procedures used to define
the extent of the area surrounding a failed test that requires repair.]
Surface Finishing
Check surface of final lift for proper contact with geomembrane [Make a
visual inspection and look for a smooth surface that is free of rocks or other
debris].
85
-------
Protection
Identify procedures used to protect each lift from desiccation and freezing.
[Be particularly inquisitive about procedures for weekends and other
extended periods and about contingency plans should the weather suddenly
and unexpectedly become very hot or cold.]
Final Grading
Check to be sure final surface is graded to drain to low points. [Confirm
that appropriate surveys were or will be made.]
Make sure that the as-compacted lifts are no thicker than the maximum
allowable value. [This check is made for elevations determined by
surveyors.]
Check surface of final lift for proper contact with geomembrane, if a
geomembrane will be placed on the compacted soil. [Make a visual
inspection and look for a smooth surface that is free of rocks or other
debris].
-------
Check List for Granular Drainage Layers in Cover Systems
(Recommended by D. E. Daniel)
Surface Preparation
Check to be sure that all testing of the underlying geomembrane or soil
liner has been completed prior to placing a drainage layer.
Material
Check percentage fines. [Check visually, and ask for quantification via
sieve analyses. Check grain size after compaction, if heavy equipment
operates on the surface of the material.]
Check the composition. [Look out for limestone, which normally does not
have adequate chemical resistance. Drainage material is normally a quartz
gravel.]
87
-------
Placement
Make sure that the material is placed in a way that (1) ensures that the
underlying geomembrane liner is not damaged, and (2) the material is not
crushed or ground into a finer material from the weight of the equipment.
[Inspect visually, and ask for grain-size analyses on as-compacted
material if there is any question about crushing effects. Be especially
concerned about the corners of blades of dozers puncturing the membrane as
the material is pushed at the "working face."]
Check for obvious stability problems on slopes. [Be particularly concerned
about slopes inclined at 3:1 (18°) or steeper. Ask for, or look for in the
engineering report, information concerning stability analyses if you have a
question.]
Protection
Check to be sure that fine material cannot wash into the drainage material.
[Look at surface contours and make sure surface erosion cannot wash soil
into the drainage material.]
88
-------
min. 3 - 4 lifts
///////
drainage material
-W
L = long enough for equipment to reach operating
speed in test area ( 50' - 100')
W = 4 equipments widths wide (35* - 50')
89
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CONSTRUCTION QUALITY ASSURANCE FOR FML'S
Robert M. Koerner
I. Preliminary Details
II. Subgrade Preparation
III. Deployment
TV. Field Seaming
V. Destructive Seam Tests
VI. Nondestructive Seam Tests
VII. Penetrations, Appurtenances, and Miscellaneous Details
91
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Construction Quality Assurance for FML's
by
Robert M. Koerner
Geosynthetic Research Institute
Drexel University
Philadelphia, PA 19104
1. Preliminary Details
2. Subgrade Preparation
3. Deployment
4. Field Seaming
5. Destructive Seam Tests
6. Nondestructive Seam Tests
7. Penetrations, Appurtenances
and Miscellaneous Details
92
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1. Preliminary Details
(a) Manufacture
(b) Fabrication
(c) Storage at Factory
(d) Shipment
(e) Storage on Site
1(a) Manufacture
Proper resin and type of resin
(virgin, reclaim, reprocessed)
Proper additives (carbon black,
additives, plasticizers, fillers, etc.)
Thickness, width and length
Windup core strength and diameter
Adequate protective covering
Proper marking and identification
1(b) Fabrication of Panels
Adequate fabrication facilities
Proper solvent, or bodied solvent
Adequate shear and peel of factory seams
Blocking strip added if necessary
Proper folding
Proper pallets and protective covering
Proper marking and identification
1(c) Storage and Facility
enclosed facility
elevated off ground
temperature considerations
implications of long-term storage
1(d) Shipment
method of loading
concern over stacking
method of unloading
1(e) Storage on Site
safe and secure area
shelter if long storage
temperature considerations
protection from ground moisture
93
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2. Subarade Preparation
removal of stones, construction debris,
grade stakes and sandbags
removal of ruts caused by placement
equipment
concerns over frozen ruts
concerns over saturated conditions
concerns over standing water (puddles)
3. Deployment
verification of panel layout
construction deployment equipment
FML spotting
proper shingling orientation
implications of shifting roll or panel
inspection of full roll or panel
proper precautions available to
handle wind uplift
4. FML Field Seam*
(a) Overview
(b) Extrusion Seams
(c) Fusion Seams
(d) Solvent Seams
(e) Test Strips
94
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4(a) Overview of FML Field Seams
Method
Seam Configuration Typical Rate Comments
Fillet
extrusion
Flat
extrusion
Upper and lower sheets must be ground
Upper sheet must be beveled
Height and location are hand-controlled
100 ft./hr. Can be rod or pellet fed
Extrudate must use same polymer compound
Air heater can preheat sheet
Necessary to use for difficult details
Highly automated machine
Difficult for side slopes
50 ft./hr. Cannot be used for close details
Extrudate must use same polymer compound
Air heater or hot wedge can preheat sheet
Ol
Hot wedge
Hot air
Ultrasonic
Single and double tracks available
Built in nondestructive test
300 ft./hr. Cannot be used for close details
Highly automated machine
No grinding necessary
Controlled pressure for squeeze-out
50 ft./hr. Good to tack sheets together
Hand held and automated devices
Air temperature fluctuated greatly
No grinding necessary
New technique for FML's
300 ft./hr. Sparse experience in the field
Capable of automation
No grinding necessary
Solvent
Bodied
solvent
Solvent
adhesive
Requires tack time
200 ft./hr. Requires hand rolling
Requires cure time
Requires tack time
150 ft./hr. Requires hand rolling
Requires cure time
Requites tack time
150 ft./hr. Requires hand rolling
Requires cure time
-------
4(b) Details of Extrusion Seams
Only for semi-crystalline FML's
(HOPE and VLDPE)
Extrusion fillet must be used around
details, corners, sumps, etc.
Method requires surface grinding prior
to extrudate placement
Method can be mechanized for long runs
Extrusion flat method used by one manufacturer/
installer
4(c) Details of Fusion Seams
Variations and hot wedge, hot air and ultrasonics
Regarding hot wedge method:
most widely used for PE seaming
can be used for all thermoplastics
can be single or double track
no grinding necessary
variables are tempeature, seaming rate and
pressure
very little manual labor involved
Regarding hot air method:
can be used for all thermoplastics
not widely used for primary seams
used to tack PE liners
hand held and machine types available
single or double track
no grinding necessary
variables are temperature, seaming rate and
pressure
Regarding ultrasonic method:
newly introduced for FML seaming
equipment made by only one firm
96
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4 (d) Details of Solvent Seams
Variations are solvent, bodied solvent and solvent adhesive
Regarding solvent seams:
only used on PVC
solvent squirted on lower sheet
1-3 seconds for tack time
mate surface and roll
curing time up to one month
accelerated cure procedure is available
Regarding bodied solvent seams:
used on CSPE-R, CPE, CPE-R and PVC
solvent pre-wipe may be necessary
7-15% of compound added to solvent
bodied solvent brushed on lower sheet
1-3 seconds for tack-time
mate surfaces and roll
curing time up to one month
Regarding solvent adhesive seams:
used on new-old CSPE-R (and other FML's)
5-10% compound, plus adhesive, added to solvent
solvent pre-wipe generally necessary
1-3 seconds for tack-time
mate surfaces and roll
curing time up to one month
4(e) Test Strips
narrow strips of excess FML for seam trials
extrusion and fusion seams ^.10 ft long
solvent seams ^.5 ft. long
generally made in morning and after noon break
also with change of personnel and/or equipment
shear and peel tests to be performed
note under side of seamed area for puckering
if excess deformation of sheets; faster rate, less
heat, less pressure or less solvent
97
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5. Destructive Seam Tests
shear testing
seam placed in shear
NSF #54 often used for procedure
require 70 to 90% of sheet strength for all FML's
require film tear bond (FTB)
peel testing
seam placed in tension
NSF #54 often used for procedure
requires 50 to 70% of sheet strength for PE
require various amount for others, e.g., "x" Ib/in.
require film tear bond (FTB)
SHEAF TEST
f
CV
I
t
i
PEEL TEST
6. Nondestructive Seam Tests
(a) Overview of methods
(b) Details of installers methods
(c) Details of pressure/vacuum methods
(d) Details of ultrasonic methods
(e) Newly emerging tests
98
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6(a) Overview of Nondestructive Seam Tests
Primary User
Nondestructive
test method
air lance
pick test
electric wire
Contractor
yes
yes
yes
Design engineer
inspector
yes
Third-Party
inspector*
-
Cost of
equipment
$200
nil
$500
Speed of
tests
fast
fast
fast
General comments
Cost of
tests
nil
nil
nil
Type of
result
yes-no
yes-no
yes-no
Recording
method
manual
manual
manual
Operator
dependency
very high
very high
high
dual seam yes
(positive
pressure)
vacuum chamber yes
(negative
pressure)
yes
yes
$200
$1000
fast
mod. yes-no
slow very high yes-no
manual
manual
low
high
ultrasonic pulse -
echo
ultrasonic -
impedance
ultrasonic shadow -
electric field yes
acoustic sensing yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
$5000
$7000
$5000
$20,000
$1000
moderate
moderate
moderate
slow
fast
high
high
high
high
nil
yes-no
qualitative
qualitative
yes-no
yes-no
automatic
automatic
automatic
manual and
automatic
manual
moderate
unknown
moderate
low
moderate
-------
6(b) Details of Installers Methods
Air lance test
blows air at high pressure beneath upper FML
small tunnel created if "holiday" exists
only for flexible, thin, FML's
very qualitative results
Pick test
probes beneath upper FML with a
ice pick or screwdriver
only for stiff, thick FML's
can easily damage flexible, thin FML's
very qualitative results
Electric wire method
embeds copper wire before seaming
completed circuit made after seaming
hot probe passed over seam
holiday should be indicated
mixed feedback from performance
6 (c) Details of Pressure/Vacuum Methods
Dual seam (air pressure) test
requires dual track seam
only for hot wedge, hot air or ultrasonic seams
air pressure of ± 30 Ib/in2 developed
drop in pressure signifies leak
works best on stiff FML's
long seam test runs are possible
cannot be performed around details
GRI test method GM-6 available
Vacuum box (negative pressure) test
small box over seam under vacuum
checks for bubbling soap suds
very tedious to perform continuously
somewhat subjective
difficult on side slopes
impossible around pipes, sumps, details
test needs standardization
100
-------
6(d) Details of Ultrasonic Methods
Pulse echo test
time of flight for signal to return
measures single or double thickness
actually a thickness test
only for procedures resulting in flat seams
transceiver needs water couplant
only used by one installer
Impedance test
uses calibrated dot pattern
still in research feasibility mode
Shadow test
roller transducers straddle seam
continuous signal gives quantitative assessment
rapid test for all seams and locations
test very sensitive with false negatives
needs field trials and further development
6(e) Newly Emerging Tests
electric field test
(seams and sheet)
acoustic sensing test
(only for air channel test)
others?
7. Penetrations. Appurtenances and Details
critically important issue
« difficult for rational design method
manufacturers/installers experiences are valuable
copy from successful past experience
requires best personnel, optimal time of day,
closest quality control and quality assurance
101
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EXPERT SYSTEMS
Robert E. Landreth
I. Modules for Demonstration
A. Veg Cover
B. F-Cover
C. Leachate Collection
II. Obtaining Software
103
-------
Final and Vegetative Cover
Evaluation Advisors
Computer expert systems prepared by:
U.S. Environmental Protection Agency
Center for Environmental Research Information
Risk Reduction Engineering Laboratory
Cincinnati, Ohio
&EPA/ORD
Hazardous Waste Regulations
40 CFR 264 and 265:
^ Establishes performance standards for hazardous waste landfills
^ Requires written closure plans
^ Specifies design and function of the landfill cover
dEPA/ORD
104
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Technical Guidance
EPA has developed various documents to assist preparers and
reviwevers of Resource Conservation and Recovery Act (RCRA)
permit applications.
^ Technical Documents
Final Covers on Hazardous Waste Landfills and Surface
Impoundments (EPA, 1989. Report No. EPA/530-SW-89-047)
f Expert Systems
Final Covers Evaluation Advisor (F-Cover)
Vegetative Cover Adviosr (VegCov)
«>EPA/ORD
What is an Expert System?
^ A computer program that contains knowledge unique to a
particular field
Expert systems "mimic" the knowledge and decision-making
processes of a human expert
Expert systems are valuable where expert advise is crucial, but
not easily available or economical
&EPA/ORD
105
-------
What is an Expert System?
Expert systems are gaining popularity and use in environmental
issues where scarce expertise is often required to make major
decisions on a regular basis
SEPA/ORD
Goals of the F-Cover and VegCov Expert Systems
Assist permit reviewers
Reduce time required to perform a review
Improve the quality and consistency of reviews
Improve the defensibility of a reviewer's decision
oEPA/ORD
106
-------
Final Cover Evaluation Advisor (F-Cover)
Evaluates the adequacy of final cover system design and
identifies potential design problems or oversights
Recommends a minimum multilayer final cover design
Checks for acceptability of cover design specifications by
assessing basic criteria
Writes final report
SEPA/ORD -
Final Cover
Flow Chart
Minimum Layer* Present
Subsidence Accomodaled
- Erosion Criteria Satisfied
- Leachate Movement Contained
- Mechanical Structure Sound
- Layers Structurally Sound
- Layer Infiltration Minimized,
- Layer Interaction* OK
- Drainage Adequate
- Infiltration Minimized
- Water Migration Minimized
- Acceptable Permeability
&EPA/ORD
STARTS
I
Enter Initial Data
Select Topmost Layer
Layer Selection Process
Layer 2 ^ Layer 3 > Layer N
L-^ Layer 2
ir
It Layer Configuration Correct?
1
Layer-by-Layer Data Input
Design Specification Question*
Final Report Data
\.
Coniultabon u Saved
107
-------
Vegetative Cover Advisor (VegCov)
Analyzes the properties of the topsoil and subsoil
Examines appropriateness of plant species
70 species of grasses and groundcovers
Performs "conditions of use" analysis
temperature and moisture parameters
seeding requirements
Examines general requirements
Writes conclusion report
&EPA/ORD
Vegetative Cover
Flow Chart
Tenure
Permeability
Percent of Coarse Fragment!
Ph
Conductivity
Percent of Organic*
Slope/Runoff
Planting Season
Seed Application Melhod
Mulch Type
SEPA/ORD
START
. . t
Site Identification Information
I
State
>
Soil Layers
^
Seeding Technique*
Soil Layer Characteriatia
Plant Selection
Final Report Data
t
Consultation is Saved
108
-------
Summary Reports
Upon completion of analysis, both systems compile conclusions
in a summary report that can be displayed on the screen,
sent to a system printer, or saved as a text file. Reports
present the following information:
Site identification information
r Information deficiencies
^ Site-specific design inconsistencies and shortfalls, citing
the CFR section which specifies the unmet conditions
&EPA/ORD
Hardware Requirements
^ IBM PC (AT, PS/2, 386) computer or compatible
^ 640K bytes minimum available RAM memory
f DOS version 3.0 or higher
A fixed disk configured as system device C: with a suggested
1.8 megabytes of free disk space
A 1.2 megabyte high-capacity disk drive
1.5 megabytes of extended memory (VegCov)
&EPA/ORD
109
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HYDROLOGIC EVALUATION OF LANDFILL PERFORMANCE (HELP) MODEL
FOR DESIGN AND EVALUATION OF LIQUIDS MANAGEMENT SYSTEMS
Paul R. Schroeder
I. Liquids Management Systems
A, Description
B. Definitions
C. Functions
D. Purpose
H. HELP Model
A, Introduction
1. Title
2. Description
3. Purpose
4. Status
B. Processes
1. Infiltration
a. surface water balance
b. precipitation
c. snowmelt
d. interception
e. surface evaporation
f. surface runoff
(over)
111
-------
2. Evapotranspiration
a. potential evapotranspiration
b. vegetative growth
c. solar radiation
d. temperature
e. surface evaporation
f. two-stage soil evaporation
g. plant transpiration
3. Soil water routing
a. vertical unsaturated drainage
b. saturated percolation through liners
c. leakage through flexible membrane liners
d. saturated lateral drainage to collectors
C. Input
1. Three precipitation options
2. Synthetic generation of daily temperatures and solar radiation
3. Two soil description options
4. Example
D. Output
1. Daily
2. Monthly
3. Annual
4. Average
5. Peak
6. Example
112
-------
HELP Model for Design and Evaluation
of Liquids Management Systems
by
Paul R. Schroeder
Environmental Laboratory
USAE Waterways Experiment Station
Vicksburg, MS 39180-6199
Landfills composed of two
liquids management systems-
Cover
Leachate collection/liner
system
\\// \\// \\// \\// , _
60cm
E^-E= 60 cm
filter layer
vegetation/soil
top layer
drainage layer
low-permeablllty
FML/soll layer
waste
Figure 1. EPA-recommended cover design.
*
° * "0
«
0
O
Q?
:V.'.':':V.'V.-":;".V".°
O^^^O^
V ° ^
.00
/'%
^0 o
113
-------
cobbles/soil
top layer
blotlc barrier
(cobbles)
drainage layer
low-permeabllltyj
FML/soll layer ~]_
gas vent layer
waste
60 cm
geosynthetlc filter
30 cm
geosynthetlc filter
30 cm
-* 20-mllFML
60 cm
geosynthetlc filter
30 cm
Figure 2. EPA-recommended cover design
with optional layers.
drainage layers
FML anchors
v (separate anchor trench tor each geosynthetlc)
low-permeablllty soil
waste
FML
Figure 4. Cover and liner edge configuration with example
toe drain.
Three layers for liquids
management in covers-
Top layer
Drainage layer
Hydraulic barrier layer
114
-------
Top layer designed to
Impede erosion
Promote runoff from major storms
Provide storage for evapotranspiration
Protect hydraulic barrier layer from
frost penetration and desiccation
Drainage layer designed to
Reduce infiltration into hydraulic barrier
layer by lowering hydraulic head
Limit root and animal penetration
Provide capillary break to limit
desiccation of hydraulic barrier layer
Hydraulic barrier layer designed to
Provide long-term minimization of water
infiltration into waste layer
Control gas migration
Accomodate subsidence
115
-------
Exhibit 4.1. Schematic of Single Clay Liner System for Landfill
Filter Medium
<*<*^ '*'<'''*<*'*.''*.'*;*,'*.>'*.'*.'*.'',*.<<*.'*,<'.'*.<'','*,''.<'','*,<'*<«£'*>''>
$i?i&&^;;?;^ sow was,a *$^;;#;£iiji$tf
i!jiei'!!;>:Ji::::°:^:P::'.-a'i';'i'^»i::i:i:!»?fl:i:i:»:W»i:ni:i::li
ViiiiiiiiiiniiiiiiiiiiiiiiiniiiiiiiiiiiiiihiiiiiiiiiiiiiiiiiniiiiiiimM
O Drainage Material O*^" Drain Pipes -^O
Leachate
Collection and
Removal System
Being Proposed as the
Leak Detection System
Low Permeability Soil
Native Soil Foundation
Lower Component
(compacted soil)
(Not to Scale)
Exhibit 4-2. Schematic of a Double Liner and Leak Detection System lor a Landfill
Filter Medium
Top Liner
(FML)
<«'?**'^'*'*<'*<'^«««'T'^
i^^;i?;i^^;??^;^'soiidwas,ei!io;^ii;ii!!;<>
lK-fi^PT;nq'>:i:i;i:;Oii^;i?:i:::::;:;i'*,:;:i:;:.W;:::;t':^::
Primary Leachate
Collection and
Removal System
Secondary Leachate
Collection and
Removal System
Being Proposed as the
Leak Detection System
Drainage Material
Drain Pipes -** Q
Q Drainage Material O"^~ Drain Pipes -
Low Permeability Soil
Native Soil Foundation
Bottom Composite
Liner
Upper
mponent
(FML)
Lower Component
(compacted soil)
(Not to Scale)
YDROLOGIC
VALUATION OF
LANDFILL
PERFORMANCE
116
-------
BACKGROUND
HELP was developed at the USAE
Waterways Experiment Station for the
USEPA Office of Solid Waste to provide
technical support for the RCRA and
Superfund programs.
Version 1 was released in 1984.
PC Version 1 was released in 1986.
Version 2 was released as draft in 1988.
Version 3 will be released in late 1990.
DESCRIPTION
HELP is a quasi-two-dimensional,
gradually varying, deterministic,
computer-based water budget model.
HELP performs daily sequential
analyses to generate daily, monthly
and annual estimates of runoff,
evapotranspiration, lateral drainage,
leakage through covers, leachate
collection, leakage detection, and
leakage through clay liners and FMLs.
117
-------
PURPOSE
The purpose of the HELP model is to
provide permit evaluators and landfill designers
with a tool to rapidly evaluate and compare
the performance of alternative landfill designs.
HELP aids design and permit evaluation but
requires good judgment in its use.
User must insure the integrity of the design
and data; therefore, good understanding of
the HELP model and landfill design is required.
APPROACH
Require only readily available data
Assist in data selection
Select routines that are:
1. well-accepted
2. computationally efficient
3. have minimum data needs
4. account for all major
design parameters
Make it user friendly
Package it in a form that can be
widely used (PC or mainframe)
118
-------
FILES
EXECUTABLE FILES
RUNHELPI.EXE for input/editing
RUNHELPO.EXE for running/output
PERMANENT DATA FILES
TAPE1 for synthethic rainfall coefficients
TAPE2 for other climatological coefficients
TAPE3.A for default rainfall for states A-H
TAPE3.I for default rainfall for states I-M
TAPE3.N for default rainfall for states N-O
TAPE3.P for default rainfall for states P-W
FILES
TEMPORARY DATA FILES
DATA4 for daily rainfalls at site
DATA7 for daily temperatures at site
DATA 10 for soil and design data of site
DATA 11 for other climatological data at site
DATA 13 for daily solar radiation data at site
User.Out for output of simulation
119
-------
SIMULATION PROCESSES
IM THE HELP
} \ } I { I«t*rcP4ioJ Jf
Snow
E.vapora^Dn
r i
PROCESSES MODELED
Infiltration
Evapotranspiration
Synthetic Weather Generation
Vegetative Growth
Subsurface Water Routing
INFILTRATION
Result of a surface water balance
Infiltration = Precipitation - Snowfall + Snowmelt
- Runoff - Surface Evaporation
120
-------
INFILTRATION
Precipitation from input by 1 of 3 options
Snowfall equals precipitation on days with
mean temperatures below 32 degrees F
Snowmelt computed by degree-day method
Runoff computed by SCS curve number method
Surface evaporation limited to the smaller of
the potential evapotranspiration and the sum
of interception and snow accumulation
Potential evapotranspiration computed by
Ritchie's modified Penman method
Interception computed by Morton relationship
ASSUMPTIONS AND LIMITATIONS
RUNOFF
SCS Curve Number Routine Applicable for
Landfills
Cumulative Runoff Independent of Duration
and Intensity
Runoff Nearly Independent of Surface Slope
or Curve Number Adjustable for Slope
No Surface Run-on
Infiltration Limited by Saturated Hydraulic
Conductivity of Soil Profile
121
-------
EVAPOTRANSPIRATION
Potential evapotranspiration computed by
Ritchie's modified Penman method
Two-staged soil evaporation computed by
Ritchie's square root of time method
Plant transpiration computed by CREAMS/
Agricultural Research Service method
VEGETATIVE GROWTH
Agricultural Research Sevice submodel of
Simulator for Water Resources in Rural
Basins (Arnold et al.)
Computes actively transpiring biomass
and leaf area index for computing
plant transpiration
Computes total biomass (active and
dormant) for computing interception
and total surface shading affecting
surface and soil evaporation
122
-------
ASSUMPTIONS AND LIMITATIONS
EVAPOTRANSPIRATION
Penman Method Based on Surface Energy
Ritchie Method Applicable for all Materials
Constant Evaporative Depth
Constant Albedo Typical for Grasses
Constant Vapor Pressure Gradient
Independent of Wind and Humidity
Representative Synthethic Daily Temperature and
Solar Radiation
Representative Leaf Area Indices from Vegetative
Growth Model
SUBSURFACE WATER ROUTING
Unsaturated vertical drainage computed as
Darcian flow using Brooks-Corey moisture
retention equation and Campbell equation
for unsaturated hydraulic conductivity
Saturated percolation through soil liners
computed by Darcy's law
Saturated lateral drainage computed by an
approximation to Boussinesq equation
(Darcy's law and continuity equation)
.Leakage through flexible membrane liners by
accounting for reduction in area of flow
using data of Brown et al. & Giroud et al.
123
-------
ASSUMPTIONS AND LIMITATIONS
SOIL WATER ROUTING
Darcian Flow
Spatially Homogeneous Layers of Material
Temporally Uniform Layers of Material
Brooks-Corey Relationship Applicable
No Effect of Soil Suction or Capillarity
Head Loss Gradient of Unity Vertically
Except in Soil Liner
No Subsurface Inflows (above water table)
ASSUMPTIONS AND LIMITATIONS
PERCOLATION
Darcian Flow
Spatially Homogeneous Layers of Material
Temporally Uniform Layers of Material
Percolation Only If Head Exists on Surface of Liner
Head is Distributed Across Entire Surface of Liner
Liner Underlies Entire Surface of Liner
Permanently Saturated Liner
Zero Head at Base of Liner (Above Water Table)
124
-------
FML LEAKAGE RATES ARE A
FUNCTION OF:
Number of Holes
Size and Shape of Holes
Head on Liner
Gap Width / Subsoil / Installation
ASSUMPTIONS AND LIMITATIONS
SYNTHETIC LINERS
Reduces Area of Flow
Synthetic Material is Impermeable
Flow Through Holes in Synthetic Liners
is Controlled by Material Under Liner
Leakage is Spatially Uniform
Liner Underlies Entire Surface of Landfill
Liner is Above Water Table
ASSUMPTIONS AND LIMITATIONS
LATERAL DRAINAGE
Gradually Varying Steady-State Darcian Flow
Spatially Homogeneous Layers of Material
Temporally Uniform Layers of Material
Function of Average Head or Depth of Saturation
Drain Layer Underlies Entire Surface of Landfill
Drainage Occurs from Entire Area of Liner
Average Depth of Saturation Computed from
Average Soil Moisture Content of Layers
Zero Head at Edge of Drain Layer or Collector
125
-------
APPROXIMATE ERRORS
RUNOFF
+ 25% or typically + 2% Precipitation
EVAPOTRANSPIRATION
+ 10% or typically + 6% Precipitation
PERCOLATION THROUGH LINERS
+ 10% or typically + 0.3% Precipitation
LATERAL DRAINAGE
Sum of other errors; some compensation
Typically + 7% Precipitation
CLIMATOLOGICAL INPUT
Synthetically Generates Daily Values of
Solar Radiation and Temperature
Coefficients for 183 Cities
Normal Mean Monthly Temperatures (Optional)
Latitude (Optional)
Site Specific Recommendations
Growing Season
Maximum Leaf Area Index
Evaporative Zone Depth
RAINFALL INPUT OPTIONS
1. Default data for 102 cities
(5-yr historical daily rainfall)
2. User-specified daily data
3. Synthetically generated daily
data for 139 cities (optional
user-specified normal mean
monthly rainfall)
126
-------
SYNTHETIC WEATHER GENERATOR
USDA Agricultural Research Sevice Model WGEN
by Richardson and Wrignt (1984)
Optionally computes daily precipitation
by a first-order Marchov chain
model using a two-parameter gamma
distribution function with coefficients
varying monthly
Computes daily temperature and solar
radiation values by a weakly stationary
normal distribution functions with
coefficients varying monthly
DEFAULT SOIL DATA
SOIL TYPE NUMBER
15 Soils
1 Municipal Waste with Daily Cover
2 Barrier Soils for Soil Liners
2 Manual Input of Soil Data
COMPACTION (OPTIONAL)
SOIL MOISTURE (OPTIONAL)
SOIL DATA- CORRECTIONS
VEGETATION
Increase Saturated Hydraulic Conductivity
Due to Root Channels
Multiply Unvegetated Value by 1.8, 3.0,
4.2 and 5.0, respectively, for Poor Grass,
Fair Grass, Good Grass and Excellent Grass
COMPACTION
25 Percent Reduction of Plant Available Water
Capacity and Drainable Porosity
Reduce Saturated Hydraulic Conductivity by
a Factor of 20
127
-------
SOIL WATER INITIALIZATION
USER-SPECIFIED
Program Starts Simulation with User-Specified Values
Soil Water of Barrier Soil Liners Assigned to Value
of Porosity
PROGRAM-INITIALIZED
Soil Water of Barrier Soil Liners Assigned to Value
of Porosity
Soil Water of Layers Above Top Liner Assigned to Value
of Field Capacity
Soil Water of Layers Below Top Liner Assigned to Soil
Water Yielding a Unsaturated Hydraulic Conductivity
Equal to 85% of the Lowest Saturated Hydraulic
Conductivity of a Layer Above the Layer Being Assigned
One Year of Simulation is Run Using the First Year of
Rainfall Data to Finalize Initialization
First Year is Then Repeated to Start Simulation
MANUAL SOIL DATA
Porosity
Field Capacity
Wilting Point
Saturated Hydraulic Conductivity
Initial Soil Moisture (Optional)
128
-------
DESIGN PARAMETERS
Number of Layers
Thicknesses of Layers
Types of Layers
Slopes of Lateral Drainage Systems
Lateral Drainage Path Lengths
Surface Area
Runoff Curve Number
Liner Leakage Fractions
Potential Runoff Fraction for Open Sites
LAYER TYPES
VERTICAL PERCOLATION LAYER
Nonrestrictive Vertical Water Routing
No Lateral Drainage Collection System
LATERAL DRAINAGE LAYER
High Saturated Hydraulic Conductivity
Drains to Lateral Drainage Collection System
Underlain by Soil Liner
BARRIER SOL LINER
Low Saturated Hydraulic Conductivity
Restricts Vertical Water Movement
Remains Saturation
No Evapotranspiration or Lateral Drainage
BARRIER SOL LINER WITH SYNTHETIC MEMBRANE
Same as Barrier Soil Liner But Does Not
Require Low Saturated Hydraulic Conductivity
129
-------
PRECIPITATION
EVAPOTRANSPIRATION
p- VEGETATION f » «>«
f INFILTRATION
(T) VERTICAL
^ PERCOLATION LAYER TOPSOIL
(5) LATERAL DRAINAGE LAYER SAND LATERAL DRAINAGE g
L-SLOPE
) BARRIER SOIL LINER CLAY
PERCOLATION
VERTICAL
PERCOLATION
LAYER
WASTE
SAND
LATERAL DRAINAGE LAYER
AINAGE
ILEACHATE COLLECTION)
FLEXIBLE MEMBRANE LJNER-
SAND
LATERAL DRAINAGE LAYER
LATERAL DRAINAGE
(LEAKAGE DETECTION)
BARRIER SOIL LINER
MAXIMUM DISTANCE
CLAY DRAINAGE
\
PERCOLATION (LEAKAGE)
Figure 1. Typical hazardous waste landfill profile.
CUMATOLOCICAL DATA INPUT
Default Precipitation Option
Location:
Normal Mean Monthly Temperatures in Degrees Fahrenheit (Optional)
Jan.
Feb.
Mar.
Apr.
May
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.
Dec.
Maximum Leaf Area Index:
Evaporative Zone Depth in Inches:
130
-------
DEFAULT SOIL AND DESIGN DATA INPUT
Title:
/
Do you want the program to initialize the soil water?
Number of layers: V
Layer data:
Layer 1
(a) thickness o?*/~ inches
(b) layer type ,/ (1 or 2)
(c) liner leakage fraction (only for layer type 4) ~ (0 to 1)
(d) soil texture number /£? (1 to 20)*
(e) compacted? (only for soil textures 1 to 15) /W) (Yes or No)
(f) initial soil water content (not asked if program is to initialize
the soil water or if layer type is 3 or 4) /?, &L/\r? vol/vol
(must be between wilting point and porosity)
Layer 2
(a) thickness /x7 inches
(b) layer type 2 (1 to * >
(c) liner leakage fraction (only for layer type 4) (0 to 1)
(d) soil texture number /_ (1 to 20)*
(e) compacted? (only for soil textures 1 to 15) Sj^> (Yes or No)
(f) initial soil water content (not asked if program is to initialize
the soil water or if layer type is 3 or 4) 0. 3₯ffi vol/vol
(must be between wilting point and porosity)
Layer 3
(a) thickness ipt£ inches
(b) layer type ,7
(c) liner leakage fraction (only for layer type 4) (0 to 1)
(d) soil texture number //<' (1 to 20)*
(e) compacted? (only for soil textures 1 to 15) far (Yes or No)
(f) initial soil water content (not asked if program is to initialize
the soil water or if layer type is 3 or 4) /?. 'AiY?/9 vol/vol
(must be between wilting point and porosity)
Layer 4
(a) .rrf (a)
(b) / (b)
(c) (=)
(d) /T (d)
(e) /.£> (c)
(f) ^JLP>*/7 (0
131
-------
(a) _
4
(b) ^
( c ) /?. i?
-------
OUTPUT TYPES
Daily Values (Optional)
Monthly Totals and Other Values (Optional)
Annual Totals and Other Values
Averages and Standard Deviations of
Monthly and Annual Totals
Peak Daily Values for Simulation Period
End-of-Simulation Water Storage Values
DAILY OUTPUT VARIABLES
Julian Date
Freezing Temperatures Indicator
Precipitation, Inches
Runoff, Inches
Evapotranspiration, Inches
Head on Top of Any Barrier Soil Liner, Inches
Percolation through Any Barrier Soil Liner, Inches
Lateral Drainage from Any Subprofile, Inches
Soil Water Content in Evaporative Zone, in Vol/Vol
MONTHLY OUTPUT VARIABLES
Total Precipitation, Inches
Total Runoff, Inches
Total Evapotranspiration, Inches
Total Percolation for Each Subprofile, Inches
Total Lateral Drainage for Each Subprofile,
Inches
Average Daily Head on Top of Each Liner, Inches
Standard Deviation of Daily Head on Top of
Each Liner, Inches
133
-------
ANNUAL OUTPUT VARIABLES
Total Precipitation (Inches, Cu Ft and % Prec.)
Total Runoff (Inches, Cu Ft and % Prec.)
Total Evapotranspiration (Inches, Cu Ft and % Prec.)
Total Percolation for Each Subprofile (Inches, Cu Ft and
% Prec.)
Total Lateral Drainage for Each Subprofile (Inches, Cu Ft
and % Prec.)
Soil Water in Profile at Start of Year (Inches and Cu Ft)
Soil Water in Profile at End of Year (Inches and Cu Ft)
Snow Water on Surface at Start of Year (Inches and Cu Ft)
Snow Water on Surface at End of Year (Inches and Cu Ft)
Change in Water Storage (inches, Cu Ft and % Prec.)
PEAK DAILY OUTPUT VARIABLES
Precipitation (Inches and Cu Ft)
Runoff (Inches and Cu Ft)
Evapotranspiration (Inches and Cu Ft)
Percolation for Each Subprofile (Inches and Cu Ft)
Lateral Drainage for Each Subprofile (Inches and Cu Ft)
Head on Top of Each Liner (Inches)
Maximum Soil Water in Evaporative Zone (Vol/Vol)
Minimum Soil Water in Evaporative Zone (Vol/Vol)
Snow Water on Surface (Inches and Cu Ft)
134
-------
END-OF-SIMULATION VALUES
Soil Water Content of Each Layer
in Inches and Vol/Vol
Snow Water on Surface in Inches
*************** A A* A** A A A A A ************* A*********** A *********** A A** AAAA
RCRA COVER SEMINAR
PHILADELPHIA, PENNSYLVANIA
29 MAY 90
****** AAAAAAAAAAAA**** ****THHr***VHt****iHtiHt**jHt A A A A A A A A ***
*********** ******** A*VHHHr*^***VHt*******^VHhHt****^^
FAIR GRASS
LAYER 1
VERTICAL PERCOLATION LAYER
THICKNESS - 24.00 INCHES
POROSITY - 0.3980 VOL/V°L
FIELD CAPACITY - 0.2443 VOL/VOL
WILTING POINT - 0.1361 VOL/VOL
INITIAL SOIL WATER CONTENT - 0.2739 VOL/VOL
SATURATED HYDRAULIC CONDUCTIVITY - 0.000360000005 CM/SEC
LAYER 2
LATERAL DRAINAGE LAYER
THICKNESS - 12.00 INCHES
POROSITY - 0.4170 VOL/VOL
FIELD CAPACITY - 0.0454 VOL/VOL
WILTING POINT - 0.0200 VOL/VOL
INITIAL SOIL WATER CONTENT - 0.3489 VOL/VOL
SATURATED HYDRAULIC CONDUCTIVITY - 0.009999999776 CM/SEC
SLOPE - 3.00 PERCENT
DRAINAGE LENGTH - 500.0 FEET
LAYER 3
BARRIER SOIL LINER
THICKNESS - 36.00 INCHES
POROSITY - 0.4300 VOL/VOL
FIELD CAPACITY - 0.3663 VOL/VOL
WILTING POINT - 0.2802 VOL/VOL
INITIAL SOIL WATER CONTENT - 0.4300 VOL/VOL
SATURATED HYDRAULIC CONDUCTIVITY - 0.000000100000 CM/SEC
135
-------
LAYER 4
VERTICAL PERCOLATION LAYER
THICKNESS - 588.00 INCHES
POROSITY - 0.5200 VOL/VOL
FIELD CAPACITY - 0.2942 VOL/VOL
WILTING POINT - 0.1400 VOL/VOL
INITIAL SOIL WATER CONTENT - 0.2840 VOL/VOL
SATURATED HYDRAULIC CONDUCTIVITY - 0.000199999995 CM/SEC
LAYER 5
VERTICAL PERCOLATION LAYER
THICKNESS - 12.00 INCHES
POROSITY - 0.5200 VOL/VOL
FIELD CAPACITY - 0.2942 VOL/VOL
WILTING POINT - 0.1400 VOL/VOL
INITIAL SOIL WATER CONTENT - 0.2852 VOL/VOL
SATURATED HYDRAULIC CONDUCTIVITY - 0.000199999995 CM/SEC
LAYER 6
LATERAL DRAINAGE LAYER
THICKNESS - 12.00 INCHES
POROSITY - 0.4170 VOL/VOL
FIELD CAPACITY - 0.0454 VOL/VOL
WILTING POINT - 0.0200 VOL/VOL
INITIAL SOIL WATER CONTENT - 0.0454 VOL/VOL
SATURATED HYDRAULIC CONDUCTIVITY - 0.009999999776 CM/SEC
SLOPE - 5.00 PERCENT
DRAINAGE LENGTH - 50.0 FEET
LAYER 7
BARRIER SOIL LINER WITH FLEXIBLE MEMBRANE LINER
THICKNESS - 6.00 INCHES
POROSITY - 0.4170 VOL/VOL
FIELD CAPACITY - 0.0454 VOL/VOL
WILTING POINT - 0.0200 VOL/VOL
INITIAL SOIL WATER CONTENT - 0.4170 VOL/VOL
SATURATED HYDRAULIC CONDUCTIVITY - 0.009999999776 CM/SEC
LINER LEAKAGE FRACTION - 0.00005000
136
-------
LAYER 8
LATERAL DRAINAGE LAYER
THICKNESS - 12.00 INCHES
POROSITY - 0.4170 VOL/VOL
FIELD CAPACITY - 0.0454 VOL/VOL
WILTING POINT - 0.0200 VOL/VOL
INITIAL SOIL WATER CONTENT - 0.0478 VOL/VOL
SATURATED HYDRAULIC CONDUCTIVITY - 0.009999999776 CM/SEC
SLOPE - 5.00 PERCENT
DRAINAGE LENGTH - 50.0 FEET
LAYER 9
BARRIER SOIL LINER WITH FLEXIBLE MEMBRANE LINER
THICKNESS - 36.00 INCHES
POROSITY - 0.3777 VOL/VOL
FIELD CAPACITY - 0.2960 VOL/VOL
WILTING POINT - 0.2208 VOL/VOL
INITIAL SOIL WATER CONTENT - 0.3777 VOL/VOL
SATURATED HYDRAULIC CONDUCTIVITY - 0.000001650000 CM/SEC
LINER LEAKAGE FRACTION - 0.00005000
GENERAL SIMULATION DATA
SCS RUNOFF CURVE NUMBER - 85.56
TOTAL AREA OF COVER - 1000000. SQ FT
EVAPORATIVE ZONE DEPTH - 24.00 INCHES
UPPER LIMIT VEG. STORAGE - 9.5520 INCHES
INITIAL VEG. STORAGE - 6.5736 INCHES
INITIAL SNOW WATER CONTENT - 0.0000 INCHES
INITIAL TOTAL WATER STORAGE IN
SOIL AND WASTE LAYERS - 213.8724 INCHES
SOIL WATER CONTENT INITIALIZED BY USER.
CLIMATOLOGICAL DATA
DEFAULT RAINFALL WITH SYNTHETIC DAILY TEMPERATURES AND
SOLAR RADIATION FOR PHILADELPHIA PENNSYLVANIA
MAXIMUM LEAF AREA INDEX - 2.00
START OF GROWING SEASON (JULIAN DATE) - 115
END OF GROWING SEASON (JULIAN DATE) - 296
137
-------
NORMAL MEAN MONTHLY TEMPERATURES, DEGREES FAHRENHEIT
JAN/JUL FEB/AUG MAR/SEP APR/OCT MAY/NOV JUN/DEC
31
76
*****
DAY
1
2
3
4*
5
6
7
8
9
10
11
12
13
14*
15*
16*
360
361
362
363
364
365
.20
.50
*****^
33.10 41.80 52.90 62.80 71.60
75.30 68.20 56.50 45.80 35.50
VARIABLE 1: HEAD ON TOP OF LAYER 3
VARIABLE 2: PERCOLATION THROUGH LAYER 3
VARIABLE 3: PERCOLATION THROUGH LAYER 7
VARIABLE 4: PERCOLATION THROUGH LAYER 9
VARIABLE 5: LATERAL DRAINAGE FROM LAYER 2
VARIABLE 6: LATERAL DRAINAGE FROM LAYER 8
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^StStSt^^^StSt^Ht^^StStSt^St+St'*^'
\ K rt « rt A /\ A )% /V V\ /\ rtrt f\ rt rt « rt /* ** rt iKlK JT rt « rt rt A/tAAArtAAA rt rt W « rt 7V » « W rt « rt « « W » « rt rt /\ A /\ A
DAILY OUTPUT FOR YEAR 74
RAIN RUNOFF
IN.
0.05
0.00
0.50
0.15
0.00
0.00
0.00
0.00
0.62
0.29
0.50
0.00
0.02
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.31
IN.
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.001
0.000
0.006
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
ET
IN.
0.014
0.043
0.013
0.011
0.040
0.047
0.047
0.043
0.015
0.012
0.014
0.034
0.012
0.000
0.000
0.000
0.084
0.066
0.096
0.090
0.079
0.016
VAR.
1
IN.
9.8
9.8
9.8
9.8
9.8
9.9
10.0
10.2
10.4
10.5
10.7
11.2
13.2
15.4
16.9
18.1
4.7
4.8
4.8
4.9
4.9
5.0
VAR.
2
IN.
0.0030
0.0042
0.0043
0.0043
0.0043
0.0043
0.0043
0 . 0044
0 . 0044
0 . 0044
0 . 0044
0 . 0044
0.0046
0.0047
0.0048
0.0050
0.0038
0.0038
0.0039
0.0039
0.0039
0.0039
VAR.
3
IN.
0.0037
0.0043
0.0043
0.0043
0.0043
0.0043
0.0043
0.0043
0.0043
0.0043
0.0043
0.0043
0.0042
0 . 0042
0.0042
0.0042
0 . 0041
0.0041
0 . 0041
0.0041
0 . 0041
0 . 0041
VAR.
4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
IN.
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
VAR.
5
IN.
0.012
0.017
0.017
0.017
0.017
0.017
0.017
0.018
0.018
0.018
0.018
0.019
0.020
0.020
0.020
0.020
0.010
0.010
0.010
0.010
0.010
0.010
VAR.
6
IN.
0.003
0.004
0.004
0.004
0.004
0.004
0.004
0.004
0.004
0.004
0.004
0.004
0.004
0.004
0.004
0.004
0.004
0.004
0.004
0.004
0.004
0.004
SOIL
WATER
IN/IN
0.2745
0.2727
0.2867
0.2909
0.2905
0.2894
0.2847
0.2790
0.2934
0.3059
0.3199
0.3133
0.3025
0.3016
0.3005
0.2995
0.2576
0.2530
0.2478
0.2427
0.2380
0.2452
***********************************************************************
138
-------
*******iHr**********************^
MONTHLY TOTALS FOR YEAR 74
JAN/JUL FEB/AUG MAR/SEP APR/OCT MAY/NOV JUN/DEC
PRECIPITATION (INCHES)
RUNOFF (INCHES)
EVAPOTRANSPIRATION
(INCHES)
LATERAL DRAINAGE FROM
LAYER 2 (INCHES)
PERCOLATION FROM
LAYER 3 (INCHES)
LATERAL DRAINAGE FROM
LAYER 6 (INCHES)
PERCOLATION FROM
LAYER 7 (INCHES)
LATERAL DRAINAGE FROM
LAYER 8 (INCHES)
PERCOLATION FROM
LAYER 9 (INCHES)
2.95
2.08
0.007
0.002
0.978
2.882
2.14
3.83
0.000
0.231
1.568
2.725
4.91
4.68
0.264
0.085
2.629
4.584
2.77
1.93
0.089
0.121
3.257
1.895
3.21
0.81
0.000
0.000
3.368
1.116
4.43
4.04
0.052
0.179
5.157
1.267
0.5736 0.5438 0.6033 0.5951 0.6026 0.5870
0.5887 0.5094 0.4260 0.3829 0.3204 0.2957
0.1476 0.1456 0.1605 0.1793 0.1683 0.1481
0.1387 0.1329 0.1241 0.1243 0.1169 0.1184
0.0006 0.0005 0.0006 0.0006 0.0006 0.0006
0.0006 0.0006 0.0006 0.0006 0.0006 0.0006
0.1310 0.1169 0.1283 0.1235 0.1275 0.1234
0.1276 0.1277 0.1237 0.1279 0.1237 0.1279
0.1320 0.1172 0.1284 0.1236 0.1274 0.1233
0.1275 0.1276 0.1236 0.1278 0.1237 0.1278
0.0001 0.0001 0.0001 0.0001 0.0001 0.0001
0.0001 0.0001 0.0001 0.0001 0.0001 0.0001
MONTHLY SUMMARIES FOR
AVG. DAILY HEAD ON
LAYER 3 (INCHES)
STD. DEV. OF DAILY HEAD
ON LAYER 3 (INCHES)
AVG. DAILY HEAD ON
LAYER 7 (INCHES)
STD. DEV. OF DAILY HEAD
ON LAYER 7 (INCHES)
15.12
11.24
4.19
0.74
0.00
0.00
0.00
0.00
19.00
9.33
0.20
0.51
0.00
0.00
0.00
0.00
DAILY HEADS
18.83
7.73
2.32
0.42
0.00
0.00
0.00
0.00
27.23
6.40
2.79
0.37
0.00
0.00
0.00
0.00
21.29
5.20
1.60
0.33
0.00
0.00
0.00
0.00
16.06
4.43
1.63
0.28
0.00
0.00
0.00
0.00
139
-------
0.08
0.07
0.00
0.00
0.07
0.07
0.00
0.00
0.07
0.07
0.00
0.00
0.07
0.07
0.00
0.00
0.07
0.07
0.00
0.00
0.07
0.07
0.00
0.00
AVG. DAILY HEAD ON
LAYER 9 (INCHES)
STD. DEV. OF DAILY HEAD
ON LAYER 9 (INCHES)
***********************************************************************
***********************************************************************
ANNUAL TOTALS FOR YEAR 74
PRECIPITATION
RUNOFF
EVAPOTRANSPIRATION
LATERAL DRAINAGE FROM LAYER 2
PERCOLATION FROM LAYER 3
LATERAL DRAINAGE FROM LAYER 6
PERCOLATION FROM LAYER 7
LATERAL DRAINAGE FROM LAYER 8
PERCOLATION FROM LAYER 9
CHANGE IN WATER STORAGE
SOIL WATER AT START OF YEAR
SOIL WATER AT END OF YEAR
SNOW WATER AT START OF YEAR
SNOW WATER AT END OF YEAR
ANNUAL WATER BUDGET BALANCE
(INCHES)
37.78
1.029
31.425
6.0285
1.7047
0.0070
1.5090
1.5097
0.0010
-2.221
213.87
211.65
0.00
0.00
0.00
(CU. FT.)
3148334.
85764.
2618786.
502377.
142062.
586.
125754.
125812.
85.
-185075.
17822700.
17637624.
0.
0.
-1.
PERCENT
100.00
2.72
83.18
15.96
4.51
0.02
3.99
4.00
0.00
-5.88
0.00
***********************************************************************
140
-------
KJC xx xx*x?nr ***************************]
AVERAGE MONTHLY VALUES IN INCHES
PRECIPITATION
TOTALS
STD. DEVIATIONS
RUNOFF
TOTALS
STD. DEVIATIONS
EVAPOTRANSPIRATION
TOTALS
STD. DEVIATIONS
JAN/JUL
4.59
3.67
2.53
1.95
1.478
0.414
3.008
0.556
0.973
4.199
0.246
1.766
LATERAL DRAINAGE FROM LAYER
FEB/AUG
1.88
4.46
0.66
2.49
0.053
0.212
0.066
0.195
1.485
3.565
0.220
1.593
2
V It "rt'K'ri'K ««««"« A A « A «« x A n A « A « ~j
FOR YEARS 74 THROUGH
MAR/SEP
4.09
4.17
1.00
2.07
0.290
0.302
0.181
0.596
2.701
2.998
0.089
1.536
APR/OCT
3.03
2.76
1.51
1.21
0.154
0.047
0.216
0.050
3.019
2.027
0.331
0.836
MAY/NOV
3.85
2.68
2.03
2.63
0.156
0.384
0.254
0.706
4.110
1.361
1 . 020
0.430
***********
78
JUN/DEC
4.50
3.99
2.17
1.78
0.170
0.339
0.244
0.370
4.833
1.015
1.223
0.195
TOTALS 0.4856 0.4957 0.5418 0.5476 0.5656 0.5414
0.5247 0.4530 0.3789 0.3728 0.3589 0.4268
STD. DEVIATIONS 0.1797 0.1440 0.1524 0.0954 0.0847 0.0987
0.1150 0.1025 0.0900 0.1297 0.1225 0.1686
PERCOLATION FROM LAYER 3
TOTALS 0.1548 0.1502 0.1639 0.1623 0.1567 0.1427
0.1344 0.1291 0.1209 0.1236 0.1204 0.1331
STD. DEVIATIONS 0.0391 0.0353 0.0286 0.0245 0.0182 0.0149
0.0082 0.0069 0.0060 0.0089 0.0101 0.0199
LATERAL DRAINAGE FROM LAYER 6
TOTALS 0.0006 0.0006 0.0006 0.0006 0.0006 0.0006
0.0006 0.0006 0.0006 0.0006 0.0006 0.0006
141
-------
STD. DEVIATIONS 0.0000
0.0000
PERCOLATION FROM LAYER 7
TOTALS 0.1301
0.1304
STD. DEVIATIONS 0.0015
0.0022
LATERAL DRAINAGE FROM LAYER
TOTALS
0.0000
0.0000
0.1181
0.1305
0.0023
0.0022
8
0.1302
0.1303
STD. DEVIATIONS 0.0017
0.0022
PERCOLATION FROM LAYER 9
TOTALS 0.0001
0.0001
STD. DEVIATIONS 0.0000
0.0000
0.1181
0.1304
0.0022
0.0022
0.0001
0.0001
0.0000
0.0000
0.0000 0.0000 0.0000 0.0000
0.0000 0.0000 0.0000 0.0000
0.1298 0.1257 0.1300 0.1260
0.1264 0.1306 0.1264 0.1306
0.0017 0.0018 0.0020 0.0021
0.0021 0.0022 0.0021 0.0021
0.1297 0.1256 0.1299 0.1259
0.1263 0.1305 0.1263 0.1305
0.0016 0.0018 0.0020 0.0020
0.0021 0.0022 0.0021 0.0022
0.0001 0.0001 0.0001 0.0001
0.0001 0.0001 0.0001 0.0001
0.0000 0.0000 0.0000 0.0000
0.0000 0.0000 0.0000 0.0000
***********************************************************************
AVERAGE ANNUAL TOTALS & (STD. DEVIATIONS) FOR YEARS 74 THROUGH 78
(INCHES)
PRECIPITATION
RUNOFF
EVAPOTRANSPIRATION
LATERAL DRAINAGE FROM
LAYER 2
PERCOLATION FROM LAYER 3
LATERAL DRAINAGE FROM
43.67 1
3.998 <
32.287 1
5.6928 1
1.6920 I
0.0073 1
; 7.930)
; 3.685)
; 2.428)
; 1.0786)
; 0.1508)
; 0.0002)
(CU. FT.)
3639167.
333190.
2690580.
474402 .
140998.
604.
PERCENT
100.00
9.16
73.93
13.04
3.87
0.02
LAYER 6
PERCOLATION FROM LAYER 7 1.5347 ( 0.0220)
127890.
3.51
142
-------
LATERAL DRAINAGE FROM
LAYER 8
1.5338 ( 0.0214)
127814.
3.51
PERCOLATION FROM LAYER 9 0.0010 ( 0.0000) 86. 0.00
CHANGE IN WATER STORAGE 0.150 ( 5.089) 12491. 0.34
***********************************************************************
PEAK DAILY VALUES FOR YEARS
PRECIPITATION
RUNOFF
LATERAL DRAINAGE FROM LAYER 2
PERCOLATION FROM LAYER 3
HEAD ON LAYER 3
LATERAL DRAINAGE FROM LAYER 6
PERCOLATION FROM LAYER 7
HEAD ON LAYER 7
LATERAL DRAINAGE FROM LAYER 8
PERCOLATION FROM LAYER 9
HEAD ON LAYER 9
SNOW WATER
MAXIMUM VEG. SOIL WATER (VOL/VOL)
MINIMUM VEG. SOIL WATER (VOL/VOL)
74 THROUGH
(INCHES)
3.99
2.341
0.0209
0.0068
36.1
0.0000
0.0043
0.0
0 . 0045
0.0000
0.1
4.09
0.3980
0.1359
78
(CU. FT.)
332500.0
195074.9
1744.7
567.3
2.5
359.0
371.3
0.2
340770.0
143
-------
***********************************************************************
FINAL WATER STORAGE AT END OF YEAR 78
LAYER
1
2
3
4
5
6
7
8
9
SNOW WATER
(INCHES)
6.57
4.19
15.48
167.74
3.42
0.55
2.50
0.57
13.60
0.00
(VOL/VOL)
0.2739
0.3488
0.4300
0.2853
0.2853
0.0454
0.4170
0.0478
0.3777
***********************************************************************
***********************************************************************
144
-------
SENSITIVITY OF COVER EFFECTIVENESS TO DESIGN PARAMETERS
Paul R. Schroeder
I. Comparison of Typical Cover Systems
A. Without Lateral Drainage Layer
1. Effects of climate
2. Effects of vegetation
3. Effects of topsoil thickness
B. With Lateral Drainage Layer
1. Effects of climate
2. Effects of vegetation
3. Effects of topsoil type
II. Vegetative Layer for Covers with Lateral Drainage
A. Effects of Runoff Curve Number
B. Effects of Evaporative Depth
C. Effects of Drainable Porosity
D. Effects of Plant Available Water Capacity
HI. Liner/Drain Systems
A. Clay Liner/Drain Systems
B. Composite Liner/Drain Systens
C. FML/Drain Systems
D. Effects of Drain Spacing
E. Effects of Liner Slope
F. Comparison of Liner Designs
145
-------
Sensitivity of Cover Effectiveness
to Design Parameters
by
Paul R. Schroeder
Environmental Laboratory
USAE Waterways Experiment Station
Vicksburg, MS 39180-6199
60 -
55 -
^ 50 -
CO
UJ
I 4C .
O ^°
z
** -40 -
Ul
D
3c 35 -
^ 30 -
i 25 -
<
z 20 -
UJ
2 15 -
1 O
i r» _
1 lo -
5 -
0 -
I I I
^yi A
TT-r
RUNOFF
E
VAPOTRANSPIRATION
LATERAL DRAINAGE
PERCOLATION
QQ GOOD
PQ POOR
QRA33
QRA33
SL 18- OF SANDY LOAM
SICL 18" OF 3ILTY
CLAYEY LOAM
0.0
7.6
6.2
0.8
3G
0.4
7.4
6.9
n n
PG
SL
31.1
10.4
2.6
0.3
3.1
8.8
2.2
n 3
GG PG
SICL
SANTA MARIA, CA
0.1
23.3
19.3
n
2.0
22.
9
18.0
,«
GG PG
SL
- 3.8
32.8
e.e
m
9.9
28.4
6.0
n ff
GG PG
SICL
SHREVEPORT,' LA
0.0
24.7
22.1
1,
11.1
24.
21.
,.
GG PG
SL
3
4
3.6
31.1
12.3
1.0
9.4
27.9
9.9
1.0
GG PG
SICL
SCHENECTADY, NY
Figure 4. Bar graph for hazardous waste cover design showing effect of surface
vegetation, topsoil type, and location.
146
-------
tn
LJ
x
o
z
=
UJ
j
§
60 -
45 -
40 -
35 -
30 -
25 -
20 -
15 -
10 -
5 -
0 -
'///
xxfc
GG
R
E
P
G
UNOFF
VAPOTRANSPIRATION
ERCOLAT1ON
OOD GRASS
PG POOR GRASS
18 18" OF SANDY LOAM
36 36" OF SANDY LOAM
p
1.3
8.3
4.9
GG
P
]1.6
7.5
5.3
G
18
P
>i 0.4
7.8
8.1
1
GG P
36
30.8
t
', 7.5
t
6.1
G
SANTA MARIA, CA
G
1.0
29.4
13.8
G P
3.3
25.0
'"
G
18
G
3 0.1
25.1
18.9
G P
]2.0
23.
3
18.9
G
36
SHREVEPORT, LA
G
" 4.8
29.4
14.0
G P
6.5
25.
9
15.6
G
18
G
26.3
19.9
3 P
]2.7
24.7
20.6
G
36
SCHENECTADY, NY
Figure 5. Bar graph for municipal cover design showing effect of topsoil depth,
surface vegetation, and location.
EFFECTS OF CLIMATE
AND VEGETATION
Sandy Loam Topsoil, 1 x 10~7 cm/sec Liner
0.03 cm/sec Drain, 200 ft Length, 3 % Slope
Poor Grass
Runoff
Evapotranspiration
Lateral Drainage
Percolation
Good Grass
Runoff
Evapotranspiration
Lateral Drainage
Percolation
CA
LA
NY
3.0
51.6
41.2
4.2
0.0
52.6
43.2
4.2
4.4
51.9
40.6
3.1
0.2
53.0
43.7
3.1
2.2
50.3
44.0
2.5
0.0
51.0
45.5
2.5
147
-------
EFFECTS OF CLIMATE
AND VEGETATION
Sandy Loam Topsoil, 1 x 10~7 cm/sec Liner
0.03 cm/sec Drain, 200 ft Length, 3 °/o Slope
CA LA NY
Poor Grass
Runoff 3.0 4.4 2.2
Evapotranspiration 51.6 51.9 50.3
Lateral Drainage 41.2 40.6 44.0
Percolation 4.2 3.1 2.5
Good Grass
Runoff 0.0 0.2 0.0
Evapotranspiration 52.6 53.0 51.0
Lateral Drainage 43.2 43.7 45.5
Percolation 4.2 3.1 2.5
EFFECTS OF CLIMATE
AND VEGETATION
36 Inches of Sandy Loam Topsoil
1 x 10~6 cm/sec Liner
CA LA NY
Poor Grass
Runoff 5.6 4.6 5.5
Evapotranspiration 51.8 53.0 52.1
Percolation 42.6 42.4 42.4
Good Grass
Runoff 3.1 0.2 3.5
Evapotranspiration 55.0 57.2 55.3
Percolation 42.9 42.6 41.2
EFFECTS OF VEGETATION
Vegetation
decreases runoff greatly,
increases evapotranspiration moderately,
increases lateral drainage moderately and
has little effect on percolation through
the cover
148
-------
EFFECTS OF TOPSOIL THICKNESS
AND CLIMATE
Sandy Loam Topsoil, Poor Grass
1 x 10~6 cm/sec Liner
CA LA NY
18 Inches of Topsoil
Runoff 11.2 7.5 13.4
Evapotranspiration 51.9 56.9 54.5
Percolation 36.9 35.6 32.1
36 Inches of Topsoil
Runoff 5.6 4.6 5.5
Evapotranspiration 51.8 53.0 52.1
Percolation 42.6 42.4 42.4
EFFECTS OF TOPSOIL THICKNESS
Topsoil thickness affects the storage
of water for plant use. Greater
thicknesses increase evapotranspiration.
In addition, runoff will decrease if it
reduces the duration that the cover is
saturated. Greater thicknesses allow
greater depths of saturation and
therefore greater leakage rates, but
provide better conditions for vegetation,
soil stability and less erosion.
EFFECTS OF TOPSOIL TYPE
AND CLIMATE
0.03 cm/sec Drain, 200 ft Length, 3 % Slope
1 x 10 ~7 cm/sec Liner, Poor Grass
CA LA NY
Sandy Loam
Runoff 3.0 4.4 2.2
Evapotranspiration 51.6 51.9 50.3
Lateral Drainage 41.2 40.6 44.0
Percolation 4.2 3.1 2.5
Silty Clayey Loam
Runoff 21.6 22.3 19.2
Evapotranspiration 61.2 64.4 58.6
Lateral Drainage 15.0 11.3 20.3
Percolation 22. 2.0 1.9
149
-------
EFFECTS OF TOPSOIL TYPE
Topsoil type directly affects runoff and
evapotranspiration by controlling the rate
of infiltration into and through the topsoil.
Fine-grained topsoils have lower hydraulic
conductivities; therefore, runoff is greater.
In addition, infiltrated water remains nearer
the surface for longer duration, providing
greater availibility for evapotranspiration.
Fine-grained topsoils also have greater
plant available water capacities (water
storage) and capillarity which increase
evapotranspiration.
EFFECTS OF CLIMATE
Climate affects both the magnitudes of
the water budget components in inches
and their relative magnitudes in terms
of percent of the precipitation. The
magnitudes and proportions are design
dependent.
EFFECTS OF RUNOFF CURVE NUMBER
Runoff curve number directly affects the
runoff quantity and therefore the quantity
of infiltration. An increase in curve
number for a given climate, topsoil and
design yields an increase in runoff, lateral
drainage, evapotranspiration and percolation
through the cover. Effects are small at
curve numbers below 80. Size of effects
is climate, topsoil and design dependent.
The effect on percolation through the
cover is generally very small.
150
-------
EFFECTS OF EVAPORATIVE ZONE DEPTH
Evaporative zone depth indirectly affects the
quantities of runoff, evapotranspiration. lateral
drainage and percolation through the cover. An
increase in evaporative zone depth for a given
climate, topsoil and design yields an increase in
evapotranspiration and runoff, and a decrease in
lateral drainage and percolation through the cover.
Effects are small at depths above 18 inches.
Size of effects is climate, topsoil and design
dependent. Effect on runoff from the surface
is generally very small.
EFFECTS OF DRAINABLE POROSITY
Drainable porosity is the difference between
porosity and field capacity and is a measure of
the free draining gravity water required to build
a pressure head. An increase in drainable porosity
decreases unsaturated hydraulic conductivity and
pressure head for a given climate, design and
material and, consequently, results in an increase in
evapotranspiration, and a decrease in lateral
drainage. The effects on runoff and percolation
through the cover are design dependent. Size of
effects are climate and design dependent,
EFFECTS OF PLANT AVAILABLE CAPACITY
Plant available water capacity is the difference
between field capacity and wilting point and is a
measure of the maximum capillary water storage
available for evapotranspiration. An increase in
plant available water capacity for a given material
increases available water storage and decreases
pressure head for a given climate and design.
This yields an increase in evapotranspiration and
an decrease in lateral drainage and percolation
through the cover. The effect on runoff is design
dependent. Size of effects is climate and de'sign
dependent.
151
-------
o
H-
c
UJ
CD
err
a:
o:
a
en
a:
LJLJ
i
or
cm/s
0.1 cm/s
0.01 cm/s
0.001 cm/s
o 50 in./yr Inflow
n 8 In./yr SS Inflow
KP (cm/s)
FIG. 3. Effect of Saturated Hydraulic Conductivity on lateral Drainage and
Percolation
LINER HYDRAULIC CONDUCTIVITY
Saturated hydraulic conductivity of liner is
the primary control of leakage through the
liner in the absence of a FML.
Leakage through liner is nearly proportional
to the saturated hydraulic conductivity at
values below 1 x 10~7 cm/sec.
Saturated hydraulic conductivity of drainage
layer has little impact on volume of leakage
through the liner. Impact is greater in
conjunction with poor liners in covers or
open landfills.
152
-------
LINER HYDRAULIC CONDUCTIVITY
In the absence of a FML soil liners having
saturated hydraulic conductivities of 10~6
cm/sec or greater are largely ineffective.
In the absence of a liner the net infiltration
is generally less than 10 inches/year in
most areas of this country. A liner leaking
at a constant rate of 10~6 cm/sec all
year would leak 13 inches/year.
DRAINAGE LAYER DESIGN
Saturated hydraulic conductivity of drainage
layer has little effect on leakage through
the liner in the absence of a FML. Its
primary effect is on depth of saturation in
the drain layer or pressure head on the
liner.
Similarly, drain slope and spacing also
primarily affect only the head on the liner.
153
-------
Q.
a
a
a
Q.
a
\
a
a
8 In./yr SS Inflow
f * KD - O.OO1 cm/a
O KD - 0.01 cm/a
- n KD - 0.1 cm/s
O KD = 1 cm/8 M
*
SS y < 0.1 In.
SS y - n-2 In.
SS y » 1.6 In.
SS y K 11 In.
10
10 10 10
KD/KP
10
10
FIG. 4. Effect of Ratio of Drainage Layer Saturated Hydraulic Conductivity to
Soil Liner Saturated Hydraulic Conductivity on Ratio of Lateral Drainage to
Percolation for a Steady-state (SS) Inflow of 8 in./yr
icr
I02
10'
10
,0
10
-1
10
-2
10
-3
10
-A
! 60 1 n./y r Inf 1 ow
_
*'
/ ' */'
/ ' -
/* / ''
/ / .**/
/ 4-y
/ /,/
IK' X S
7K S S
/,' /
'*'/
X
/ s <
/* /X <''' s
/ / «' /
''' /
S / 0 KD =
* O
/ n KD =
/
0 KD =
* KD =
PnnLi* 7~i **
.._..,... Pnnly T~V *-*
PnnLjf TH
,
x >^
o^
1 cm/s
O . 1 cm/s
O . O 1 cm/s
O . OO 1 cm/s
2.5 In.
91 n
i r I
24 in.
55 In.
, ,
10 10 10 10 10
KD/KP
8
10
10
8
FIG. 5. Effect of Ratio of Drainage Layer Saturated Hydraulic Conductivity to
Soil Liner Saturated Hydraulic Conductivity on Ratio of Lateral Drainage to
Percolation for an Unsteady Inflow of 50 In./yr
154
-------
n
-------
CD
0
cr
CD
Q.
CO
CD
C
c
CD
CL
a
CD
_a
E
13
10s
10"
10J
Upper bound is for 0.08-cm-dia. openings.
Lower bound is for I .27-cm-d i a. openings.
KP = 3.4 x 10
CO
en
c
c
03
a.
a
c
m
CO
CD
m
D)
c
o
D
D.
cn
CD
6
O
- 500 _
- 100
- 200
Synthetic Liner Leakage Fraction. LF
FIG. 8. Synthetic Liner Leakage Fraction as a Function of Density of Holes,
Size of Holes, Head on the Liner and Saturated Hydraulic Conductivity of the
Liner
FLEXIBLE MEMBRANE LINERS
FML Leakage Rates Are A Function of:
Number of Holes
Size and Shape of Holes
Head on Liner
Gap Width / Subsoil / Installation
156
-------
100
C- / C : \ JJ ' O :
^ / - : / T3 ' TJ /
/ ^^ / * >' V
/ r»: / -^ * / '
LF x KP (cm/s)
FIG. 9. Effect of Leakage Fraction on System Performance
o
s
C.
J^
a
CZJ
DESIGN A
DESIGN B
T^WASJE LAYER £
i DRAIN LAYER
\\ \ \ \'
. \SOIL LINER \
\ \ \ \ \
\ \ \\ \^
sNATIVESUBSOILv
\ \ \ \ \
DESIGN C
«-.'wASTE~LAYER jj,1
rDRAIN LAYER
^SYNTHETIC LINER
v::onAiN LAYER;
\ \ \ \ \
\ SOIL LINER \
\ \ \ X \
DESIGN D
..
#WASTE LAYER o.
P;;°^yp.b-h^;-^c
JDRAIN LAYER;
""- ^SYNTHETIC LINER
fDRAIN LAYER:
\ \ "V
SOILLINER
\ \ \ \ \
\\
\SOI
DESIGN E
FDRAIN LAYER:
DRAIN LAYER
SYNTHETIC LINER
SOIL LINER \
\ \ \ \
DESIGN F
°.--
?./WASTE LAYER
RDRAIN LAYER;
\
NSOIL LINER \
\ \ \ \
:-ORAIN LAYER- _
_^*~S YNTHETICL INER
\\'v
SOIL LINER \
\ \ \ \
FIG. 1. Liner Designs
157
-------
^^
"
3s
0
t._
*f
C
.
^
«
C3
100
80
60
40
20
0
, Design E
np i \
W /_ __ _^
go ii Design C
';
; /
1 /
1 1
I 1
1 l
1 i
1 l
1 l
l i
i l
l i
' l
/ 1 Design C
__^X/ ___^X
' Design E '
!0"7 10"B 10"5 10"4 10"3 ID"2 10"1 10°
Synthetic Liner Leakage Fraction. LF
FIG. 11. Percent of Inflow to Primary Leachate Collection Layer Discharging
from Leakage Detection Layer and Bottom Liner for Double Liner Systems C and E
3=
O
O
0.0! 0.10
Synthetic Liner Leakage Fraction. LF
FIG. 12. Percent of Inflow to Primary Leachate Collection Layer Discharging
from Leakage Detection Layer and Bottom Liner for Double Liner Systems D and F
158
-------
DOUBLE LINER SYSTEMS
Composite liners minimize leakage.
Bottom liner must be a composite liner
to effectively detect leakage at low
leakage rates.
FMLs without low permeability subsoils
are largely ineffective.
Double composite liners do not limit
leakage much more than a single
composite liner.
159
-------
GAS MANAGEMENT SYSTEMS
Paul R. Schroeder
I, Gas Generation
A Anaerobic Decomposition
B. Composition
C, Moisture Dependent
D. Decomposition Period
R Gas Production Rate
F. Explosive
G. Effects on Plant Life
. Gas Migration
A Convection by Pressure Head
B, Diffusion
C Paths
D. Barriers
E Seasonal
. Gas Control Strategies
A Passive
1. Gravel-filled trenches
2, Perimeter rubble vent stacks
3. Impermeable barriers
B. Active
1. Extraction well
2, Blower
C. Recovery
D. Treatment
161
-------
Gas Management Systems
by
Paul R. Schroeder
Environmental Laboratory
USAE Waterways Experiment Station
Vicksburg, MS 39180-6199
GAS GENERATION
Gas generation poses several problems:
explosion hazard
vegetation distress
odor
property-value deterioration
physical disruption of cover
toxic vapors
162
-------
GAS COMPOSITION
Product of Anaerobic Decomposition
vCH4 + wCOo + xN9 +
C_H. O N.S0 1>
a D c a e + ^ s + humus
Product is about 50% methane, 40%
carbon dioxide and 10% nitrogen after
the first year of production. Initial
composition is primarily carbon dioxide.
RATE OF DECOMPOSITION
Waste decomposition rates and hence gas
production rates are moisture dependent
Highest gas production rates occur at
moisture contents ranging from 60 to 80%.
Typical gas production rates are 20 to 50
mL/kg/day.
Gas production will continue at high rates
for decades and at lesser rates for
centuries.
GAS MIGRATION
Migration occurs by two processes:
Convection is flow induced by pressure
gradients formed by gas production in layers
surrounded by low permeability or saturated
layers. Convection is also induced by
buoyancy forces since methane is lighter
than air.
Diffusion is flow induced by concentration
gradients formed by production of methane
and carbon dioxide at concentrations
greater than in the surrounding air.
163
-------
FACTORS AFFECTING GAS MIGRATION
Refuse cell construction
Final cover design
Landfill age and gas production rate
Presence of natural and man-made conduits
and barriers
Climatic or seasonal environmental variations
GAS CORRIDORS AND BARRIERS
Corridors
Water conduits, drain culverts, buried lines
Sand and gravel lenses
Void spaces, cracks and fissures from
differential settlement and subsidence
Barriers
Clay deposits
High and perched water tables
Roads
Compacted, low permeability soils
SEASONAL VARIATIONS
Gas production is temperature and
moisture dependent.
Saturated or frozen surface layers
promote lateral migration.
Barometric pressure changes affect
outgassing.
164
-------
GAS CONTROL STRATEGIES
Passive Systems
Gravel-filled trenches, perimeter rubble vent stacks
and gas vent layers serve to direct gas migration
to the surface where it can be treated, collected
or dispersed Low permeability side walls and
liners and the water table are used in conjunction
as barriers to prevent uncontrolled lateral migration.
Active Systems
Gas extraction wells in conjunction with barriers
greater negative pressure zones to extract gas.
Air blowers have been used to create zones of
high pressure to prevent gas migration to a
particular area.
gas vent
drain layer C ;0-°
~^
- top layer
:r-^r-rr_- |_ low-permeablllty
FML/soll layer
Figure 7. Cover with gas vent outlet and vent layer.
165
-------
-~- SLOPE
FINAL COVER MATERIAL^:
'
FINAL COVER MATERIAL
'VENTED
Figure 7. Gravel vent and gravel-filled trench used to
control lateral gas movement in a sanitary
landfill. (From D. R. Brunner and D. J.
Keller, Sanitary Landfill Design and
Operation, Environmental Protection Publi-
cation SW-651S [USEPA, 1971].)
WINTER CLIMATES MAY REQUIRE
COLLECTOR WITH VERTICAL RISERS
AND SURFACE SEAL
COVER MATERIAL
REFUSE
BARRIER
MATERIAL
(IMPERVIOUS
MEMBRANE)
UNDISTURBED IMPERVIOUS MATERIAL OR WATER TABLE
Figure 10. Typical trench barrier system.
166
-------
FIGURE 4-12
GAS CONTROL BARRIERS (ROVERS, TREMBLAY, AND MOOIJ, 1977)
Permeable Trench
'ET
Impermeable Barrier
'C'
Pipe Vent
Induced Exhaust
EGENO
GAS MIGRATION
REFUSE
OH/VCU
TRENCH COVER
IMPERMEABLE BARRtR
Gas Control Barriers
167
-------
GAS FLOW
GAS FLARE
EXHAUST BLOWER
II H^-IMPERVIOUS BACKFILL
PERFORATED PIPE
GAS FLOW
-PERMEABLE MATERIAL
Figure 12. Gas extraction well for landfill gas control.
FIGURE 4-13
GAS EXTRACTION WELL DESIGN (ROVERS, TREMBLAY,
AND MOOIJ, 1977)
%;.- *
- COLLCCTION HEADER
TELESCOPIC COUPLING
-^\-PERFOHATEO PIPE
-LEQEND-
REFUSC
FINAL COVER - z'-e'
CLAT PLUG
FINE 3ANO
COARSE GRAVEL
Gas Extraction
Well Design
168
-------
FIGURE 4-14
MOISTURE CONTROL IN COLLECTION HEADER (ROVERS,
TREMBLAY AND MOOIJ, 1977)
Condensate Drain in Header 'A'
Go» Wells
Condensate Drain to Gas Wells 'B*
LEGEND
>- Gas Flow
* Cond«n«dt« In RV.C. H«ad*r
Moisture Control in
Collection Header
169
-------
CASE STUDIES
Gregory N. Richardson
I. General Closure Criteria
A. Minimum Technology Guidance
B. Erosion Control
C. Gas Control
D. Subsidence
E. Case 1: RCRA Commercial Landfill
A. Subsidence Control
B. Gas Control
m. Case 2: RCRA Industrial Landfill
A. Sliding Stability
B. Erosion Control
IV. Case 3: CERCLA Lagoon Closure
A. Sliding Stability
B. Geogrid Reinforcement
V. Case 4: CERCLA Baghouse Dust
A Landfill Closure
- Erosion Control with Hardened Cap
VL Case 5: MSW Commercial Landfill
A Sliding Stability
B. Gas Control
171
-------
CASE 1 RCRA COMMERCIAL LANDFILL
EPA REGION V
CAP SIZE = 17 acres SLOPE = 8% MIN
5% MIN
CAP PROFILE
VEGETATED TOPSOH. AND ROOT ZONE, 3 FT. MINIMUM
SYNTHETIC DRAINAGE MEDIA,GEOTEXTILE AND GEONET
f SYNTHETIC MEMBRANE (FML), 80 MIL HOPE
COMPACTED SOIL LINER, 3 FT. MINIMUM
INTERMEDIATE COVER, 6 IN. MINIMUM
WASTE
DETAIL OF COVER
SLOPE
5.8% MINIMUM
8% MAXIMUM
SECTION THROUGH LANDFILL
172
-------
Case 1 RCRA Commercial Landfill
KEY DESIGN PROBLEM - SUBSIDENCE
Large Number of Transformers
Documented Within Landfill.
22% Transformer Volume=Void
92% of Cap Subsidence Caused by
Collapse of Voids in Waste
(Murphy and Gilbert, 1985)
GEOMETRY OF SUBSIDENCE
HORIZONTAL DISPLACEMENT -
STRAIN
VERTICAL DISPLACEMENT
(SUBSIDENCE CURVE)-v.
POINT OF MAXIMUM
TENSILE STRAIN
46-
-------
Case l RCRA Commercial Landfill
SUBSIDENCE RELATED COVER PROBLEMS
CRACKS
CRACKS
^*- PONDING
LEGEND-
COVER
FILL
(AFTER MURPHY AND GILBERT, 1985)
174
-------
Case 1 RCRA Commercial Landfill
SURFACE SUBSIDENCE MODEL
Volume Void = Volume Surface Depression
Angle of Draw - 45° + 0 /2
0 = internal friction angle of waste
3-Dimensional Projection of Surface Settlement
NOTE: THE SURFACE DEFLECTIONS ARE SHOWN AS POSITIVE VALUES
FOR PRESENTATION PURPOSES ONLY. THE DEFLECTIONS WOULD
ACTUALLY BE BELOW THE PLANE OF THE CAP AS-BUILT.
175
-------
Case 1 RCRA Commercial Landfill
IMPACT OF SUBSIDENCE ON GEOMEMBRANE
20
15
|_ 10
1/1
i i
Circular Trough Model
Triangular
0 0.1 0.2 0.3
SETTLEMENT RATIO, S/2L
(Knlpichield,196S)
ALLOWABLE GEOMEMBRANE STRAIN
4000
(KEORNER,RICHARDSON-UNIAXIAL)
(STEFFEN-BIAXIAU
100
200
JOO
400
SOO
STRAIN, %
176
-------
IMPACT OF SUBSIDENCE ON CLAY LINER
1.00
0.75
O.SO
0.25
100.0
DATA FOR THIS STUDY ^ TENSILE STRAIN. %
Index of maximum settlement A/L vs tensile strain (after Gilbert and Murphy, 1987)
ALLOWABLE STRAIN IN CLAY LINER
3.5
3.0
1 2.0
1.0
I I I I I I I I I I I I I I I
LEGEND
LEONARD I BEAM n_£XUR£ TESTS )
Q TSCHE30TAHIOFF ( DIRECT TENSION TESTS )
D WES DATA ( DIRECT TENSION TESTS )
+ FOR THIS STUDY (CIU DIRECT TENSION TESTS)
I
10 100
PLASTICITY INDEX. %
Tensile strain vs plasticity index (after Gilbert and Murphy, 1987)
1000
177
-------
Case 1 RCRA Commercial Landfill
GAS COLLECTION SYSTEM
Very Low Gas Production at RCRA Facilities
Linear Collector
» /j?5:-^ ,. ""l--ll i ' \~~Y.- *z-r*c vesr &xs PIPES
-f^^^0- -4.. , "M-r- ^"
^ -Ul 1 ' \>,-
^^. «., --^ . rPrr.
'^^Jirrrr
V-*/. ^"'^
~*i3-
//
,/'/
?7'
' '
5 r~; **
^ ^- -?" /'cc GAB
§ . ^'^
ll
P
lo^
LJ
' V
rj -
A" .
-------
CASE 2 RCRA INDUSTRIAL LANDFILL
EPA Region IV
Cap size = 2.6 Acres Slope = 3H:1V max
Cap Profile
FINISHED GRADE OF CAP
4" MINIMUM THICK TOPSOIL LAYER
WITH VEGETATIVE COVER.
T-8" THICK ROOT ZONE EMBANKMENT
SYNTHETIC DRAINAGE MEDIA
-CAP GEOMEMBRAME
2'-0" MINIMUM THICK COMPACTED
SOIL CAP LINER
6" MINIMUM THICK FINAL INTERMEDIATE
COVER LAYER
LIMITS OF WASTE
TYPICAL CAP SECTION
SCALE: NONE
BOTTOM OF FINAL
INTERMEDIATE COVER
SUBGRADE OF
SOIL LINER
179
TOP OF CAP
ELEV. 1220.00
SLOPE VARIES
TYP.
TOP OF OPERATIONAL COVER
2.78%
ELEV. 1185.70
SECONDARY
-------
Case 2 RCRA Industrial Landfill
KEY DESIGN PROBLEM - SLIDING STABILITY
Incinerator Ash - Granular, 0 = 27°
Maximum Slope = 3H:1V
Minimum F.S. Slope Stability = 2.2 (Ash Only)
Cover Stability = Geomembrane to Drainage Media
Typical Friction Angle = 9-12°
Slope Stability Alternatives
Flatten Slopes
Textured Geomembrane
Reinforced Cover
Try Textured Geomembrane
180
-------
Case 2 RCRA Industrial Landfill
STABILITY ALTERNATIVE - TEXTURED GEOMEMBRANE
Option 1 - Textured HOPE
Drainage Media Alternatives
Natural Sand Layer
Geonet with bonded nonwovens
Typical Direct Shear Data
tt
Ifl
Option 2 -Bonded Flexible Membrane
Nonwoven bonded to both faces
Drainage media = natural sand
Typical Profiles
181
-------
Case 2 RCRA Industrial Landfill
SURFACE EROSION CONSIDERATIONS
MTG Criteria = Soil Loss <2 ton/acre/year
U.S.D.A. Universal Soil Loss Equation (A= RKLSCP)
Slope = 3H:1V, 50-foot long
5%, 150-foot long
LS (3:1) = 6,6, LS (5%) = ,65
Effective LS = (.71) (.65)+ (1.20) (6.6) = 4.5*
Soil Texture (k) = Silty Clay Loam
'3456 8 I0 20 30 40 60 80 IOO 200
SLOPE LENGTH , METRES
400 600
Organic matter content
Texture class
Sand
Find sand
Very fine sand
Loamy sand
Loamy fine sand
Loamy very fine sand
Sandy loam
Fine sandy loam
Very fine sandy loam
Loam
Silt loam
Silt
Sandy clay loam
Clay loam
Silty clay loam
Sandy clay
Silty clay
Clay
< 0.5 per cent
K
0.05
0.16
0.42
0.12
0.24
0.44
0.27
0.35
0.47
0.38
0.48
0.60
0.27
0.28
0.37
0.14
0.25
2 per cent
K
0.03
0.14
0.36
0.10
0.20
0.38
0.24
0.30
0.41
0.34
0.42
0.52
0.25
0.25
0.32
0.13
0.23
0.13-0.29
4 per cent
K
0.02
a 10
0.28
0.08
a 16
0.30
0.19
0.24
0.33
0.29
0.33
0.42
0.21
0.21
0.26
a 12
0.19
The values shown are estimated averages of broad ranges of specific-soil values. When a texture
is near the borderline of two texture classes, use the average of the two K. values. For specific will,
use of Figure Z6 or Soil Conservation Service K-value tables will provide much greater accuracy.
From ARS, 1975.
*Ref. EPA-600-2F-79-165, More accurate methods will yield small LS,
see Soil Erosion, M.J. Kirby, et. al.
182
-------
Case 2 RCRA industrial Landfill
Rainfall & Runoff Index, R
R = 140 - From local SCS
Cover/Management Factor, C
C = .004 to .025 for meadows
= .006 - from local SCS
Practice Factor, P
0.30
-------
Case 2 RCRA industrial Landfill
Discharge Pipe Cap Penetration
NEOPRENE GASKET
POLYURETHANE CAULKING &
STAINLESS STEEL BAND
FUTURE CAP
STAINLESS STEEL BAND
BOOT
12" WIN.
CAP GEOMEMBRANE
BOND (TYP.)
STAINLESS STEEL
BOOT FirTTED AROUND
DISCHARGE SLEEVE
80 MIL PRIMARY
GEOMEMBRANE
STAINLESS STEEL BAND
ANCHOR
TRENCH
Alternative Armoring Scheme
FILTER FA8RIC
m
184
-------
CASE 3 CERCLA LAGOON CLOSURE
EPA Region I
Cap Size = .3 Acre Slope = 3H:1V MAX
Cap Profile
, r ~"^ ' J 30 ML. -»
^e* " I -^
/-4" PERF PVC
DRANAGE PIPE
LOCATION.
-------
Case 3 CERCLA Lagoon Closure
KEY DESIGN PROBLEM - SLIDING STABILITY
c/o
co
LJ
Q/
Q/
= 17degrees
50 100 150 200 250 300 350 400 450 500 530 600
NDRMAL STRESS (PSF)
.". Sideslopes are Unstable
186
-------
Case 3 CERCLA Lagoon
SLOPE STABILITY ALTERNATIVES
Flatten Slopes
Textured Geomembrane
Reinforced Cover
REINFORCED COVER
Geotextile or Geogrid
Anchorage
Tensile Capacity
= 17.000
^= \1oto
>o
187
-------
Case 3 CERCLA Lagoon Closure
DRAINAGE LAYER CONSIDERATIONS
Filter Design
Drain Detail
12 TRAP ROCK
,PVC MEMBRANE
BENTONITE MAT
1 GEOTEXTILE CUSHION
Drain Problems
Loam Erosion Results in Sealing
Difficult Construction
188
-------
LANDFILL CLOSURE
EPA Region IV
Si2e = 4.2 acres
Cap Profile
Slope . 60/o
fi^g^^
.-.-
' CuA>C
6' FENCE
W/BARBED WIRE
UY - 0
2
20'GATE
189
/ V
Q' / DRAINAGE \
/ CULVERT ~M
-------
Case 4 CERCLA Landfill Closure
Site Characteristics
20,000 cubic yard baghouse dust
Dust contains Cadmium, Chromium, and Lead
Dust placed on-top-of MSW landfill
PLP does not own site
Adjacent to park
Advantages of Hardened Cap
Not an attractive nuisance
Low maintenance
No volunteer vegetation
No drainage layer
Maintenance of Hardened Cap
Annual inspection
Renew chip seal every 5 years
(Asphalt emulsion + gravel)
Maintain perimeter drainage
190
-------
CASE 5 MSW COMMERCIAL LANDFILL
EPA Region IV
Cap Size = 50 + Acres Max Slope = 4HL:1V
Cap Profile
- FlEliBLE UEUBRiNC LINER
-------
Case 5 MSW commercial Landfill
KEY DESIGN PROBLEM - MULTIPLE CELL COVERAGE
General MSW Cap Goals
Low Maintenance
Minimize Infiltration
Separate Stormwater From Waste
and LCR System
Integrate Gas Collection If Desired
Multiple Cells Under One Cap
MSW Cell Specifications
Contain - 2 Year Capacity
Common LCR System in Cell
Independent Sump in Each Cell
MSW SubCell Specifications
Designed to Segregate Stormwater
Subcells Do Not Interrupt LCR
Subcell Dikes Removed For Daily Cover
Typical MSW Profile
192
-------
Case 5 MSW Commercial Landfill
MULTIPLE CELL LANDFILL CAP
Operational Problems
Roadway Maintenance
Erosion of Interim Cover
Removal of Daily Cover
Maintaining Surface Water Collection
Exposure of Low Permeability Soil
Interim CAP Development
193
-------
Case 5 MSW Commercial Landfill
MSW GAS CONTROL SYSTEMS
Types of Gas Control Systems
Blanket Collector (Passive)
Linear Collectors (Passive)
- Wells (Active)
Well Collection System
PROPOSED BLOWER BUILDING
AND FLfftf -LOCATION , /
Well Construction
6 mm Sample
Topsoil 2-5 cm Concrete Pad
jlb=tt^V
10-15 cm Schedule 80 PVC Pipe
Compacted Clay
Bentomte Seal Over Geotextile Ring
20-15 cm Perforated Schedule 80 PVC Pipe
, Gravel Fill
194
-------
Case 5 MSW Commercial Landfill
Perimeter Gas Monitoring Station
One Every 1000-ft.
- 25% LEL Max.
8'DIA. STEEL PIPE
STEEL PIPE CAP W/
HINGE & LOCK
P.V.C.PIPE CAP
DO NOT CEMENT
« CONC. BENTONITE SEAL
1 DIA. SCH. 40 P.V.C. PIPE
W/ 3/I61 DIA. (MIN.) SCREEN
HOLES
PEA GRAVEL PACK
UL-p-v-c-
END CAP
4'CHA.
MIN. BORE DIA.
195
-------
Case 5 MSW Commercial Landfill
FINAL CAP CONSIDERATIONS
Drainage Layer
Not Required by Most States
Pore Water Pressure Concerns
- FLEXIBLE MEMBRANE LINER
/ 6' WIDE EDGE DRAIN, TRAPPED
W/ 4 oz. GEOTEXTILE
STRUCTURAL FILL
Sideslope Erosion
Drainage Swales @ 20-ft (V)
-OUTLET PIPE
LOCATED 200' 0/C
196
-------
EPA Seminar
Design and Construction of
RCRA/CERCLA Final Covers
REFERENCES
EPA, Technical Guidance Document: Final Covers on Hazardous Waste
Landfills and Surface Impoundments, EPA/530-SW-89-047, July, 1989.
EPA, Evaluating Cover Systems for Solid and Hazardous Waste,
SW-867, Sept, 1980.
EPA, Covers for Uncontrolled Hazardous Waste Sites,
EPA/540/2-85/002.
EPA, Closure of Hazardous Waste Surface Impoundments,
SW-873, Sept, 1980.
EPA, Geotextile for Drainage, Gas Venting, and Erosion Control at
Hazardous Waste Sites, EPA/600/2-86/085, Sept, 1986.
EPA, Seminar Publication: Reguirements for Hazardous Waste
Landfill Design, Construction, and Closure, EPA/625/4-89/022.
EPA, Geosynthetic Design Guidance for Hazardous Waste Landfill
Cells and Surface Impoundments, EPA/600/52-87/097, Feb., 1988.
197
-------
POST CLOSURE MONITORING
Gregory N. Richardson
I. Monitoring Time-Frame
A. RCRA = 30 Year Post Closure
B. Mixed Waste = 500 Year (10CFR61)
II. Key Monitoring Parameters
A. Groundwater
B. Leachate Generation
C. Gas Concentration
D. Subsidence
E. Surface Erosion
R Air Quality
III. Elements in Monitoring Program
A. Dectection
B. Allowable Level Criteria
C. Remediation Plan
199
-------
POST CLOSURE MONITORING
Gregory N. Richardson, Ph.D., P.E.
Monitoring Time-Frame
RCRA = 30 Year Post Closure
Mixed Waste = 500 Year (10CFR61)
Key Monitoring Parameters
Groundwater
Leachate Generation
Gas Concentration
Subsidence
Surface Erosion
Air Quality
Elements in Monitoring Program
Dectection
Allowable Level Criteria
Remediation Plan
200
-------
Post Closure Monitoring
GROUNDWATER MONITORING
Key Monitoring Variables
Maximum GW Elevation
Leakage Monitoring
Groundwater Monitoring Well
Well Design
PVC for inorganic contaminant
Stainless steel for organic cont.
Screen based on local geology
Well Placement
Isolation of target aquifer
Proper development of well
Sampling Frequency
Background quality = monthly
Post-operation = quarterly
Leakage Monitoring
Base Index Parameters
Temperature, Specific Conductance,
pH, Color, Odor, and Turbidity
Waste Dependent Parameters
Identify maximum mobility
201
-------
Post Closure Monitoring
Typical Well Configuration
8- 00 LOCKING PROTECTIVE
STEEL CAP
SIDE VENTED PVC WELL CASING CAP
LOCK
7'ID STEEL PROTECTIVE CASING
S'/V.LONG
4' SCH. 10 PVC RISER PIPE
ISTICK-UP)
ORAINHOLE
ORIGINAL GROUND SURFACE
REINFORCED CONCRETE CAP
MIN. 2' RADIUS W/ -4 REBAR
ON 6- CENTERS
CONCRETE PLUG EXTENDING 36'
DOWN BOREHOLE BELOW CAP
4' SCH. 40 PVC FLUSH JOINT CASING
/CONST, j
JOINT 5
-
r-2' SANDPACK
ABOVE SCREEN TOP
SCREENED INTERVAL 2
NORMALLY 5'-10'
VARIABLE CUP LENGTH,
NORMALLY S'-r
CEMENT/BENTONITE GROUT "LACED
BY SIDE DISCHARGE TREMIE PIPE;
94 LBS. PORTLAND CEMENT
5 LBS. POWDERED 9ENTONITE
6 GALS. HIATER
ILB. CALCIUM CHLORIDE
BENTONITE PELLET S£ii_-
TAMPED AND HYDRA TED
FINE SAND FILTER
SAND PACK. CONSISTING OF
WASHED S GRADED SILICA SANO.
SIZED FOR THE AQUIFER AND
PLACED BY TREMIE PIPE
FACTORY SLOTTED OR CONTINUOUS WIRE
SCREEN SIZED FOR AQUIFER GRAIN
SIZE DISTRIBUTION
TAILPIECE OR SEDIMENT CUP
CENTRALIZER (SPACED AS REQ'O.)
PVC END CAP (THREAOEDI
BOTTOM OF BOREHOLE
Monitoring Interbedded Aquifer
1 2 3
123 12
Landfill
/
Sand (K = 1 X 10~2 cm/sec)
Layer 1
Clay (K = 1 x 1CT7 cm/sec)
Layer 2
Sand (K = 1 X 10~3 cm/sec)
Layer 3
202
-------
Post Closure Monitoring
LEACHATE GENERATION
Key Monitoring Variables
Quantity vs Time
Concentration vs Time
Cell Leakage
Quantity vs Time
Volume Reduction with Time
Action Leakage Rate (ALR)
Based on 2 mm hole in PFML
5 to 20 gal/acre/day
Initials leak reporting
Rapid and Large Leakage (RLL)
Serious cell failure
2000 to 10,000 gal/acre/day
Defines failure of facility
Concentration vs Time
Increase Concentration with Time
Impact of Biological Growth?
Cell Leakage
Groundwater Monitoring
Direct Leakage Monitors
Secondary collector
External Lysimeters
203
-------
Post Closure Monitoring
Leachate Generation with Time
I
Impact of Biological Growth
BIOCISE BACXrLOSH
II
CQ
<
LU
2
cc
LU
0.
TIME
External Lysimeters
To Pump
Tube for Applying
Pressure/Vacuum
To Sample Collection
5 to 10 cm
Bentonite Seal
15 cm diameter Hole
Backtilled with Silica Sand
Porous Cup
204
-------
Post Closure Monitoring
GAS CONCENTRATION
Typical Generation Rates
RCRA = Very Low Rate
- MSW = 900+ Liters Per Dry Kg
CERCLA = Waste Specific
Underground Gas Monitoring
Simplified Well Design
Maximum 25% LEL
Sampling Frequency = Twice a Day
When Soil is Saturated or Frozen
Impact of Synthetic Liner
Gas Removal Alternatives
Passive Vents
minimum 1/acre
increased density limited by air
quantity
Active Systems
205
-------
Post Closure Monitoring
Typical Gas Well
8" DIA. STEEL PIPE
Q_
LJ
Q
UJ
1S>
=3
STEEL PIPE CAP W/
HINGE & LOCK
P.V.C. PIPE CAP
DO NOT CEMENT
CONC. BENTONITE SEAL
I1 DIA. SCH. 40 P.V.C. PIPE
W/ 3/I61 DIA. (MIN.) SCREEN
HOLES
PEA GRAVEL PACK
P.V.C. END CAP
MIN. BORE DIA.
Gas Generation vs Time
100 -\
2
ro
GC
3
T3
O
C
ca
5L Rate
5L Acids
20
206
-------
Post Closure Monitoring
SUBSIDENCE MONITORING
Measurement of Subsidence
Survey Monument Grid
Aerial Photography
Annual Subsidence Check
Allowable Subsidence
Differential Strains
(inflection points)
Clay = > 1% Maximum Strain
FML = > 10% Maximum Strain
Clay component will govern
Remediation of Local Subsidence
Repair Below Low Permeable Barrier
Potential Use of Lightweight Fills
Avoid Roof Ponding Mechanism
207
-------
Post Closure Monitoring
SURFACE EROSION
Anticipated Erosion
.5% Area Annually
Increases With Slope
Additional Problems
Biotic Intrusion
Volunteer Vegetation
Drought Endurance
Remediation Measures
Hardened Cap
Geosynthetic Matting
208
-------
Post Closure Monitoring
AIR QUALITY MONITORING
Monitoring Techniques
Passive, Using Collection Media
Grab, Evacuated Vessel
Active, Pump and Sampler
Common Air Contaminants (MSW)
Methane
Vinyl Chloride
Benzene
Threshold Limits of Air Contaminants
Threshold Limit Values of Selected Air Contaminants"
Contaminant TLV
Dust 1 mg/m3
Carbon monoxide 50 ppm
Asbestos 0.2 to 2 fibers/cm3 (depending on asbestos type)
Benzene 10 ppm
Coal dust 2 mg/m3
Cotton dust 0.2 mg/m3
Grain dust 4 mg/m3
Hydrogen sulfide 10 ppm
Nuisance particulates 10 mg/m3
Phenol 5 ppm
Vinyl chloride 5 ppm
Wood dust
Hard wood 1 mg/m3
Soft wood 5 mg/m3
J Values of TLV obtained from the American Conference of Governmental Industrial
Hvcienists (1987).
- 209 -
-------
APPENDIX A: NOTE ON THICKNESS OF COMPACTED SOIL LINERS
David E. Daniel
A-l
-------
Note on Thickness of Compacted Soil Liners
Prepared by
David E. Daniel
University of Texas
Department of Civil Engineering
Austin, TX 78712
(512) 471-4730
April 9, 1990
Introduction
This purpose of this note is to document information on the relationship between
thickness of compacted soil liners and the overall hydraulic conductivity of such liners.
Two types of information are examined: (1) data on the in situ hydraulic conductivity of
compacted soil liners, and (2) results of analyses described by Benson (1989). The
data base on hydraulic conductivity was intentionally restricted to in situ measurements
because laboratory measurements can sometimes yield unrepresentative values (Daniel,
1984; Day and Daniel, 1985; and Elsbury et al., 1990).
Data on Field-Measured Hydraulic Conductivity
I have made a careful review of the literature, my files, and information recently
compiled on test pads in Texas by one of my students (Mikus, 1989) in an attempt to
collect as much data as possible that might be used to relate in situ hydraulic
conductivity to the thickness of a soil liner. Some information has undoubtedly been
missed (particularly for test pads built outside of the state of Texas), but I am confident
that I have compiled virtually all of the data available in the open literature and in my
files.
A summary of the data is presented in Table 1. For each value of in situ
hydraulic conductivity, I have assigned a qualititave measure of the quality of
construction of the soil that was tested. Studies with undocumented construction
A-2
-------
practices are considered to have been built by poor standards. Soils compacted with
modest-sized compaction equipment, or those compacted with somewhat questionable
means (such as compacting the soil dry of optimum) are generously rated as "good"
quality construction provided full-sized equipment was used and documentation is
extensive. "Excellent" quality of construction is used to describe construction in the
field with heavy equipment and generally good construction practices; data documentation
must have been thorough for the quality of construction to have been considered
excellent. I did not include any small test cells constructed with hand-held tampers;
only soils compacted in the field with self-propelled or towed rollers were considered.
The hydraulic conductivities are plotted as a function of thickness of the liner in
Figure 1. All the data in Table 1 are included in this plot. Figure 2 presents the same
type of information, but just for soils for which the quality of construction was judged to
be "good" or "excellent." Figure 3 repeats the graphical presentation for the values
corresponding to "excellent" construction. It can be argued that for any reasonably
well-built liner, the overall quality of construction should be good to excellent.
Figures 1-3 show a tendency for in situ hydraulic conductivity to decrease with
increasing thickness of the liner. Sensitivity to the thickness of a liner is most
pronounced for thicknesses < 2 ft. For soil liners 2-ft-thick or thicker, there is only a
small decrease in hydraulic conductivity with increasing thickness. In Figure 4, I have
plotted the data for good and excellend construction and have sketched an "average" curve
(by eye -- no curve fitting technique was employed). The "average" curve In Figure 4
yields the following points:
A-3
-------
Thickness of Liner (ftt Hydraulic Conductivity (cm/s)
1.0 1 x 10'6
1.5 1 x 10-7
2.0 5 x ID'8
2.5 3 x ID'8
3.0 2 x 10'8
4.0 1 x 10'8
A large reduction (a full order of magnitude) in hydraulic conductivity occurs when the
thickness of the liner is increased from 1.0 to 1.5 ft. With each succeeding 0.5-ft
increase in the thickness of the liner, the average hydraulic conductivity is
approximately halved.
For good or excellent quality construction, the following summaries from Table 1
are presented (k denotes hydraulic conductivity):
Number of Liners Number of Liners Percent of Liners
Thickness of Liner with k > with k < with k <
(ft)
0.5 to 1.5
1 .5 to 2.5
2.5 to 3.5
3.5 to 5.0
1 x 10'7 cm/s
3
2
0
0
1 x 10'7 cm/s
1
9
8
5
1 x 10'7 cm/s
25%
82%
100%
100%
This information is presented graphically in Figure 5.
There are 23 soil liners listed in Table 1 that were built with good to excellent
construction practices and that had thicknesses of 2.0 ft or more. Of these 23 liners, 22
(or 96%) had hydraulic conductivities £ 1 x 10'7 cm/s. The one soil liner that did not
have an in situ hydraulic conductivity < 1 x 10-7 cm/s had a value of 2 x 10-7 cm/s,
A-4
-------
and this value is debatable; with longer-term testing, the in situ hydraulic conductivity
might very well have been found to be ^ 1 x 10'7 cm/s.
Benson's Analyses
Benson (1989) performed a complex analysis of water flow through multi-
layered compacted soil liners. The hydraulic conductivity was assumed to be a random
variable within each lift, and the interlift zone was modelled as a confined aquifer. The
entire system was analyzed with a Monte Carlo simulation of a random process. The idea
behind the analyses was to simulate complex flow patterns, such as shown in Figure 6,
with an analytically tractable solution. The concept behind Benson's model is shown in
Figure 7.
The main findings from Benson's work, as applied to the subject of this note, are
summarized in Figure 8. The equivalent hydraulic conductivity is plotted as a function
of number of lifts (each lift was assumed to be 6 inches, or 0.5 ft, thick). Different
graphs are presented for different values of transmissivity (T in the Figure) of the
interlift zone. The upper curve corresponds to T = 3.0 x 10'6 cm2/s, which is a high
value selected to represent poor bonding between lifts of soil. The middle curve (for T =
3 x 10'7 cm2/s) represents moderately good bonding between lifts, and the lower curve
represents excellent bonding between lifts. Benson's calculations show that: (1) the
equivalent hydraulic conductivity of a soil liner decreases with increasing number of
lifts (i.e., thickness), but little benefit is derived from increasing the number of lifts
beyond about 4; and (2) the degree of bonding between lifts is much more important than
the number of lifts. To expand on the latter finding, the results in Figure 8 suggest that
one is better off ensuring that lifts are bonded together well than in adding more lifts in
a liner with poorly bonded lifts.
A-5
-------
Conclusions
The following conclusions are offered:
1. With sound construction practices, one should be able to construct a soil liner that
has an in situ hydraulic conductivity that is less than or equal to 1 x 10'7 cm/s if
the soil liner is at least 2.0 ft thick.
2. Based on existing data, soil liners with a thickness of less than 2.0 ft have an
unacceptably high probability of having an in situ hydraulic conductivity greater
than 1 x 10'7 cm/s. For this reason, soil liners thinner than 2.0 ft are not
recommended unless data are developed for the proposed materials and construction
practices to demonstrate that the liner will have an adequately low in situ
hydraulic conductivity.
3. Increasing the thickness of a soil liner from 2.0 to 3.0 ft will likely lower the
hydraulic conductivity of the liner by a factor of about 2, increase slightly the
already high probability that the hydraulic conductivity will be less than or equal
to 1 x 10'7 cm/s, offer some buffer from possible damage of the liner due to
desiccation, frost action, or settlement, and generally add a "factor of safety" to the
design. Perhaps the answer to the question of whether a 3.0-ft-thick liner is
needed rather than a 2.0-ft-thick liner should hinge on other issues, such as
whether the soil liner will be used with a flexible-membrane liner to form a
composite (in which case the extra foot of soil liner thickness probably provides
almost no measureable improvement in performance of the composite liner).
A-6
-------
References
Albrecht, K. A., and K. Cartwright (1989), "Infiltration and Hydraulic Conductivity of a
Compacted Earthen Liner." Ground Water. Vol. 27. No. 1, pp. 14-19.
Benson, C. B. (1989), "A Stochastic Analysis of Water and Chemical Flow through
Compacted Soil Liners," PhD Dissertation, Univ. of Texas, Austin, Texas, 246 p.
Clough, Harbour & Associates (1989), "Clay Test Fill Report, Landfill No. 6, General
Electric Company, Waterford, New York," Albany, New York.
Daniel, D. E. (1984), "Predicting Hydraulic Conductivity of Clay Liners," Journal of
Geotechnical Engineering. Vol. 110, No. 4, pp. 465-478.
Daniel, D. E., and S. J. Trautwein (1986), "Field Permeability Test for Earthen
Liners," Proceedings. Use of In Situ Tests in Geotechnical Engineering, S. P.
Clemence (ed), ASCE, New York, pp. 146-160.
Daniel, D. E. (1987), "Earthen Liners for Land Disposal Facilities," Geotechnical
Practice for Waste Disposal '87. R. D. Woods (ed.), ASCE, New York, pp. 21-39.
Day, S. R., and D. E. Daniel (1985), "Hydraulic Conductivity of Two Prototype Clay
Liners," Journal of Geotechnical Engineering. Vol. 111, No. 8, pp. 957-970.
Elsbury, B. R., Sraders, G. A., Anderson, D. C., Rehage, J. A., Sai, J. 0., and D. E. Daniel
(1990), "Field and Laboratory Testing of a Compacted Soil Liner," U. S. EPA,
Cincinnati, Ohio, EPA/600/S2-88/067.
Fernuik, N., and M. Haug (1990), "Evaluation of In Situ Permeability Testing Methods,"
Journal of Geotechnical Engineering. Vol. 116, No. 2, pp. 297-309.
Goldman, L. J., Greenfield, L I., Damle, A. S., Kingsbury, G. L., Northeim, C. M., and R.
S. Truesdale (1988), "Design, Construction, and Evaluation of Clay Liners for Waste
Management Facilities," U. S. Environmental Protection Agency, Washington, D. C.,
EPA/530/SW-86/007F.
Gordon, M. E., Huebner, P. M., and T. J. Miazga (1989), "Hydraulic Conductivity of
Three Landfill Clay Liners," Journal of Geotechnical Engineering. Vol. 115, No. 8,
pp. 1148-1160.
Johnson, G. W., Crunley, W. S., and G. P. Boutwell (1990), "Field Verification of Clay
Liner Hydraulic Conductivity," paper submitted for publication in Proceedings of the
Symposium on Performance, Construction, and Operation of Waste Disposal
Facilities, ASCE, San Francisco, November, 1990.
Krapac, I. G., Panno, S. V., Rehfeldt, K. R., Herzon, B. L, Hansel, B. R., and K.
Cartwright (1989), "Hydraulic Properties of an Experimental Soil Liner:
Preliminary Results," Proceedings, Twelfth Annual Madison Waste Conference, Univ.
of Wisconsin Extension, Madison, Wisconsin, pp. 395-411.
A-7
-------
Lahti, L Ft., King, K. S., Reades, D. W., and A. Bacopoulos (1987), "Quality Assurance
Monitoring of a Large Clay Liner," Geotechnical Practice for Waste Disposal '87. R.
D. Woods (ed.), ASCE, New York, pp. 640-654.
Mikus, J. A. (1989), "Summary and Analysis of Test Fills at Hazardous Waste Land
Disposal Facilities in Texas," M. S. Special Report, University of Texas, Geotechnical
Engineering Center, Austin, Texas, 66p.
Rogowski, A. S. (1986), "Hydraulic Conductivity of Compacted Clay Soils," Proceedings
of the Twelfth Annual Research Symposium on Land Disposal. Remedial Action,
Incineration, and Treatment of Hazardous Waste, U. S. EPA, Cincinnati, Ohio,
EPA/600/9-86/022, pp. 29-39.
A-8
-------
Table 1. Data on In Situ Hydraulic Conductivity
Reference
Daniel (1984)
Day & Daniel
(1985)
Rogowski
(1986)
Description
of Liner
Central Texas
Northern Texas
Southern Texas
Mexico
Prototype 1
Prototype 2
Test Pad
Plasticity
Index
20
23-55
14-24
1 1
45
12
Quality of
Construction
Unknown
Unknown
Unknown
Good
Poor
Poor
Good
Thickness
1.0
0.7
2.0
1.6
0.5
0.5
1.0
Hydraulic
Conductivity
(k. cm/s)
4 x 10-5
3 x 10-6
2 x 10'5
1 x 10-6
9 x 10-6
4 x 10-6
5 x 10'7
Method of
Determination
ofk
Leak Rate
Infiltrometer
Leak Rate
Leak Rate
Underdrain
Underdrain
Underdrain
&
Trautwein (1986)
Cover
Excellent
3.0
8 x 10
-8
Daniel (1987)
Lahti et al.
(1987)
Goldman et
al. (1988)
Gordon et al.
Confidential
Keele Valley
Site K
Marathon Co.
Marathon Co.
Portage Co.
Sauk Co.
7-15
49-69
16-54
16-54
13-33
13-63
Excellent
Excellent
Good
Excellent
Excellent
Excellent
Excellent
1.0
3.9
1.0
4.0
4.0
5.0
5.0
2 X 10-6
9 x 10'9
1 X 10'7
2 x ID'8
5 x 10-9
5 x 10'9
2 x ID'8
Leak Rate
Lysimeters
Lysimeters
Lysimeter
Lysimeter
Lysimeter
Lysimeter
Albrecht & Test Pad
Cartwright (1989)
Excellent
3.0
4 x 10-8
SDRI
-------
Table 1. Data on In Situ Hydraulic Conductivity (continued)
Reference
Mikus (1988)
Description
of Liner
Celanese Pad
Transwestern Pad
Phillips Pad
UC-Onsite Clay
UC-Offsite Clay
Dupont - Gray Clay
Dupont - Tan Clay
Shell Pad
BPPad
GulfCoast Pad
Plasticity
Index
l%\
45-68
11-20
9-38
45-58
36-47
25-44
34-36
15-37
19-32
28-52
Quality of
Construction
Excellent
Excellent
Excellent
Excellent
Excellent
Excellent
Excellent
Excellent
Excellent
Excellent
Thickness
rm
2.0
3.0
3.0
3.0
2.0
2.0
3.5
3.5
2.5
2.0
2.0
Hydraulic
Conductivity
(k. cm/s)
4 x 10-8
1 x 10-8
2 x 10-8
1 x 10-7
5x10-8
2x10-8
3 x 10-8
3 x 10-8
3 x ID'8
1 x 10-7
1 x 10'7
Method of
Determination
of k
SDRI
SDRI
SDRI
SDRI
SDRI
SDRI
SDRI
SDRI
SDRI
SDRI
SDRI
Krapac et al.
(1989)
Elsbury et
al. (1989)
Clough-Harbour
(1989)
Fernuik &
Haug (1990)
Johnson et
al. (1990)
Test Pad
Test Pad
Test Pad
Residual Soil
Liner A
Liner B
10
41
1 1-14
35
34
Excellent
Good
Good
Excellent
Excellent
Excellent
3.0
1.0
2.0
2.0
2.0
2.0
4 x 10-8
1 x 10"*
1 x 10'7
2 x 10-7
3 x ID'8
1 x 10-8
Infiltrometers
Underdrain
SDRI
Infiltrometers
SDRI
SDRI
-------
o
>*
^-»
">
t>
13
10
10
10
-4
-5
-6
10
c
o
O
o
= 10
03
10
-7
-8
-9
0
O Poor Construction
D Good Construction
A Excellent Construction
12345
Thickness of Liner (ft)
Figure 1. In Situ Hydraulic Conductivity Vs. Thickness of Liner for All
Data.
-------
E
^
>?
">
"o
13
c
o
O
OJ
»_
"O
>
m
10
10
10
10
10
-4
-5
-6
-7
-8
10
-9
0
D Good Construction
A Excellent Construction
Thickness of Liner (ft)
Figure 2. In Situ Hydraulic Conductivity Vs. Thickness of Liner for Liners
Built with Good and Excellent Quality of Construction.
-------
U)
E
o^
>s
-t->
'>
"*
O
ZJ
c
o
O
o
"5
03
Excellent Construction
Thickness of Liner (ft)
Figure 3. In Situ Hydraulic Conductivity Vs. Thickness of Liner for Liners
Built with Excellent Quality of Construction.
-------
E
o
o
13
TD
c
o
O
05
L_
T5
10
10
10
10
10
-4
-5
-6
-7
-8
10
-9
0
D Good Construction
A Excellent Construction
Thickness of Liner (ft)
Figure 4. In Situ Hydraulic Conductivity Vs. Thickness of Liner for Liners
Built with Good and Excellent Quality of Construction. The
curve shown is an average curve drawn by eye.
-------
1 -f w
co "o £=
»- ZJ u
.E ? r^
_J O ^
M- ° °
*5 ^ ^"
^j vx
"c "5 T-
o ^ vi
CD >*
o_ n:
lilU
100
80
60
40
20
0
i i
.
-
1
-
! !! il ill
01 23456
Thickness of Liner (ft)
Figure 5. Relationship between Percentage of Liners with Hydraulic
Conductivities Less than or Equal to 1 x 10'7 cm/s and the
Thickness of the Soil Liner.
A-15
-------
(a) Poor Interlift Bonding
(b) Good Interlift Bonding
Figure 6. Pattern of Water Flow Assumed to Exist in Soil Liners. Note
the flow of water through permeable zones in each lift and
horizontally along the interface between lifts.
A-16
-------
Recharge
Interim
Zone -
(Aquifer)
Macropore (Channel )
«m W'u"
Discharge
Upper
Lift
Lower
Lift
'Soil Matrix
(Impervious)
Figure 7. Model Utilized by Benson (1989).
A-17
-------
>> 10'
_
03
_>
CT
LU
10
-9
i i i
Four Partitions
T - 3.0 E-06 cmsq/sec
T - 3.0 E-07 cmsq/sec
T - 3.0 E-08 cmsq/sec
34567
Number of Lifts
10
Figure 8. Equivalent Hydraulic Conductivity Vs. Number of Lifts (from
Benson, 1989). The lifts were assumed to be 6-inches thick,
hydraulic conductivity in each lift was assumed to be a random
variable, and T indicates the transmissivity assumed for the
interlift zone.
A-18
-------
APPENDIX B: THE OMEGA HILLS FINAL COVER TEST PLOT STUDY:
THREE-YEAR DATA SUMMARY
Robert J. Montgomery and Laurie J. Parsons
B-l
-------
THE OMEGA HILLS FINAL COVER TEST PLOT STUDY:
THREE-YEAR DATA SUMMARY
by
ROBERT J. MONTGOMERY and LAURIE J. PARSONS
ABSTRACT
Instrumented test plots have been installed at the Omega Hills
Landfill, located near Milwaukee, Wisconsin, to collect data on
the hydrologic performance of three final cover designs. Each of
the test plot designs employs natural soils installed on 3H:1V
landfill sideslopes. Two designs incorporate different
thicknesses of local silty loam topsoils over thick sections of
compacted clay soils. The third design is a multi-layered cover,
intended to take advantage of the so-called "wick effect" by
placing a sand layer between two compacted clay layers, with
topsoil above. In addition, two cover vegetation species mixes
are being evaluated in separate test areas. Data collection
began in August of 1986, and included a significant period of
drought in 1988, as well as periods of heavy precipitation.
After approximately three years of data collection, several
observations appear to be significant. The propagation of cracks
within the clay soils appears to be all-important to the
performance of the cover designs evaluated. The upper clay layer
of the multi-layered design has developed substantial cracking
which has apparently allowed transmission of large amounts of
infiltrated moisture to the intermediate sand layer. However,
percolation from the base of the multi-layered cover has remained
relatively low, apparently due to the continued moist and
homogeneous conditions in the clay layer below the intermediate
sand. The two all-clay test sections initially showed very
little percolation. However, percolation has increased
substantially through time, again apparently related to the
development and propagation of cracks through the clay soils. A
summary of the collected data is presented, as well as
observations and interpretations based on field observations and
test pits.
BACKGROUND
The Omega Hills Landfill, operated by Waste Management of
Wisconsin, Inc., 1s located approximately 20 miles northwest of
the center of Milwaukee, Wisconsin. The 83-acre site has been
active since the 1970's, and has recently completed filling of
Its approximately 14 million cu yd licensed capacity. Waste
Management of Wisconsin has conducted a very substantial program
of environmental measures to control offsite leachate migration,
provide gas control and energy conversion and to extract and
treat leachate from within the site. This program won
recognition in the American Society of Civil Engineers 1986
Outstanding Civil Engineering Achievement Awards.
B-2
-------
DESCRIPTION OF TEST PLOTS
The final cover test plot study 1s a research project being
conducted by Waste Management to evaluate the performance of
several final cover designs as part of development of a new
leachate control program for the site. The objective of the
study 1s to evaluate the hydro!ogle performance of alternative
cover designs, especially with respect to the percolation of
precipitation moisture Into the landfill.
Three cover designs and two vegetation species mixes are
arranged 1n three Instrumented test plots and 1n two vegetation
assessment areas, located on the western outboard slope of the
Omega Hills Landfill. Three main concepts are being evaluated 1n
the test plot study, 1n comparison with the approved final cover
design for the site: 1) the use of a thicker topsoil layer to
promote vegetative growth and thus enhance evapotranspiration;
2) the use of a multl-layered find/coarse/fine soil arrangement
to limit the percolation out of the upper fine-grained soil via
the so-called "wick effect"; and 3) the use of a more vigorous
and multi-specled cover vegetation to fully exploit the available
root zone to enhance evapotranspiration. A detailed description
of the design and construction of the test plots was provided by
Montgomery, et. al.* The test plot designs are as follows (see
also Figure 1):
Test Plot 1: 6 in. topsoil, primary seed mix
(Existing Cover Design) 48 in. compacted clay
Test Plot 2: 18 1n. topsoil, primary seed mix
(Thicker Topsoil Design) 48 in. compacted clay
Test Plot 3: 6 1n. topsoil, primary seed mix
(W1ck Effect Design) 24 1n. compacted clay
12 in. Intermediate sand layer
24 1n. compacted clay
Vegetation Assessment 6 in. topsoil, alternative seed mix
Area 1 48 1n. compacted clay
Vegetation Assessment 18 1n. topsoil, alternative seed mix
Area 2 48 1n. compacted clay
The cover clay soils utilized had very high silt and non-
expansive clay content (USCS CL), and were placed and compacted
1n approximately 6" lifts using conventional earth moving
equipment to 1n-place densities corresponding to lab
permeabilities of less than 1 x 10~7 cm/sec. The topsoil was an
uncompacted clay loam to sllty clay loam. The Intermediate sand
layer 1n Test Plot 3 was composed of a clean, washed medium sand.
The primary seed mix contains tall fescue (Festuca arundinacea),
creeping red fescue (Festuca rubra), annual rvegrass (Lollum
Multl-florura), perennial ryegrass (Lollurn perenne), and Kentucky
B-3
-------
bluegrass (Poa pratense). The alternate seed mix contains smooth
bromegrass (Bromus inermis), birdsfoot trefoil (Lotus corn-
iculatus), tall fescue (Lestuca arundinacea), creeping red fescue
(Festuca rubra) and perennial ryegrass (Lolium perenne).
Test Plots 1, 2 and 3 are instrumented for collection of
hydrologic data, and are also monitored for vegetation growth
parameters. Figure 2 is a schematic layout of one of the test
plots, and indicates the location of the instrumentation. Figure
3 is a schematic section through one of the test plots, showing
the runoff and percolation monitoring system, as well as the soil
moisture monitoring instrumentation. Figure 4 depicts the
overall layout of the instrumented test plots and vegetation
assessment area, all located on the western outboard slope of the
Omega Hills 1andf 111.
Construction of the basal percolation collection systems and
placement of the clay cover soils was conducted in September
through November of 1985. Topsoil placement and instrumentation
of the test plots was completed by July of 1986, and data
collection began in August.
DATA COLLECTION
Precipitation, runoff, percolation, air and soil temperature, and
soil moisture tensiometer data is collected using a data logging
system, which allowed remote access to data via telephone modem.
Precipitation data is collected using a heated tipping bucket
rain gage. Runoff and percolation data is collected for each
test plot using pressure transducers installed in collection
tanks (refer to Figure 2). The transducers indicate water level
within the tank, with the ratio of tank area to plot area used to
obtain runoff and percolation depths. Test Plot 3 utilizes a
collection tank for collecting flow from the intermediate sand
layer, as well as for percolation and surface runoff (See
Figure 4). Air temperature and relative humidity data is
collected using sensors monitored by the data logger. Cover soil
temperature is also monitored using the data logger, with sensors
buried at depths of 1, 3 and 5 ft below the surface of the 3H:1V
sideslopes of the landfill. Two nests of soil moisture
tensiometers are installed in each instrumented test plot, with
from 5 to 7 tensiometers (with tips at different levels) in each
nest. Each of the tensiometers was equipped with a pressure
transducer wired to a multiplex input to the data logger. Data
logger collection frequency was hourly from August, 1986 through
September 1989, when it was altered to four-hourly.
Soil moisture data was also collected using a neutron probe.
Seven galvanized steel access tubes were driven into each test
plot, and the probe was field-calibrated using laboratory soil
moisture data from field samples.
Vegetation density and root penetration data was collected
approximately twice-yearly, for both the alternative seed mix
B-4
-------
assessment areas, as well as for non-Instrumented sections of
Test Plots 1, 2 and 3.
Data collection has been continuous since mid-August 1986, and
the collected data is believed to present an accurate description
of overall test section performance. However, some problems have
been encountered in the data collection program, summarized
below:
The heated tipping bucket rain gage occasionally
malfunctioned, requiring the use of daily precipitation
data form the NOAA observation station at Germantown,
Wisconsin (3.2 mi NW of the landfill) to fill in the gaps.
The tensiometer pressure transducers experienced a high
rate of failure, and monitoring was discontinued in
September 1988. Soil moisture monitoring with the neutron
probe has continued.
Evaluation of vegetation density and root penetration, and
comparison of the primary and alternative seed mixes was
very difficult, due to the immaturity of the vegetation
stand (even in 1989), disturbance caused by instrumentation
maintenance and mowing, and the effects of the drought of
1988.
One of the most reliable sets of data from the test plot data are
the monthly summaries of hydrologic balance for Test Plots 1, 2
and 3. This data, for the period August 1986 through August
1989, is presented in Table I.
CLIMATE DURING DATA COLLECTION PERIOD
The data collection period includes three complete years of
September-through-August data, beginning in September 1986.
These years had widely different climactic characteristics.
The 12 month period September 1986 through August 1987 was "near-
normal", except for a period of extraordinarily high rainfall in
September 1986. This rainfall occurred with the cover vegetation
in its initial growth stages, and produced substantial runoff, as
well as surprisingly large flow of moisture from the intermediate
sand layer of Test Plot 3 (See Table I). The remainder of 1986
and the growing season of 1987 provided a near average climate,
and the vegetative cover developed substantially.
The period September 1987 through 1988 was dominated by the
severe drought of 1988. Although temperature and moisture
conditions were near-normal through April, the months of May
through August were characterized by substantially below average
rainfall, and temperatures averaging as much as 10°F above
average. These conditions quickly reduced the cover vegetation
to a dry, dormant state., and obvious cracking of the surface of
the cover soils became evident.
B-5
-------
The last year of data collection, September 1988 through August
1989 saw a return to moist conditions. Substantial rainfall in
September of 1988 restored the vegetation to an active growing
state, but also apparently allowed moisture influx to deeper
portions of the cover via cracks which had developed in the
preceding dry conditions. After a relatively mild winter, a
generally wetter-than-average growing season produced lush
vegetation growth in the summer of 1989.
TEST PIT EXCAVATIONS
The hydrologic response of the test plots observed through the
summer of 1988 indicated that moisture flow in several sections
of the cover was much more rapid than would be expected under
porous media flow conditions. These areas, especially the upper
clay of Test Plot 3, exhibited substantial flow rates which
suggested that in homogeneities had developed, possibly by
cracking due to drought conditions. In addition, the extent of
root penetration and the development of altered soil structures
within the covers was of interest. For these reasons, a series
of test pits were excavated into the cover sections in September
1988.
Five test pits were excavated in the buffer strip adjacent to
each test plot and in the vegetation assessment areas. The soil
profile in this buffer strip is representative of each adjacent
test plot. The purpose of the test pit excavations was to
characterize the final cover soil profiles and to aid in the
interpretation of the hydrologic budget data.
The 4 ft by 10 ft test pits were excavated to 6 ft deep via a
track mounted backhoe. Samples were taken at approximately one
foot increments or when material characteristics changed and soil
moisture contents (dry weight basis) were determined. Shrinkage
limits were determined on the upper and lower clay for Test Plots
1, 2 and 3 following ASTM 0427 procedures. Key results of the
test pit investigation are listed below.
The upper 8 to 10 inches of clay 1n all three test plots
appeared weathered and exhibited a medium to coarse sized
blocky structure.
Occasional larger cracks, 1/4 to 1/2 inch wide, extended 35
to 40 Inches into the clay, beyond the topsoil/clay
interface, 1n Test Plots 1 and 2 and through the entire
upper clay in Test Plot 3. A noticeable curvature of
cracks downslope was observed, particularly in Test Plots 1
and 2.
A continuous root mass penetrated 8 to 10 inches into the
clay below the topsoil/clay Interface. Further root
penetration occurred along crack planes approximately 30
Inches below the topsoil/clay interface.
B-6
-------
The clay texture at the base of each test plot exhibited
higher Moisture contents and no evidence of cracking.
- Ho distinguishable separations between lifts associated
with placenent of the clay were observed in any of the
profiles.
Shrinkage limits ranged from 10 to 1255 moisture content on
a dry weight basis (approximately 20 to 24% on a volume
basis). Tie shrinkage limit is the moisture content at
which the soil volume will not change upon further drying,
Moisture content data taken via the neutron probe during
the dry period in June-July 1988 indicated levels close to
the shrinkage limit in the upper clay of all three test
plots suggesting that acre substantial cracking than
observed (due to dessication and shrinkage) would be
unlikely.
Soil profile characteristics in the vegetation assessment
areas were similar to Test Plot 1 and 2 profiles with roots
observable at cleavage faces between cracks.
SUMMARY Of COLLECTED DATA
A. Observed Cover Percolation
Percolation rates through Test Plots 1 and 2 were low for the
first year of data collection (0.06 inches and 0.27 inches,
respectively). However, the '87 - '88 data shows an increase in
total percolation to 0.18 inches and 1.19 inches for Test Plots 1
and 2r respectively, despite the drought conditions. Review of
the data suggests that the compacted clay may have been gaining
Moisture in 1986 and early 1987 and that equilibrium conditions
were reached as percolation from all of the test plots became
sore continuous after March, 1987. The sudden production of
percolation at the base of Test Plot 2 in April 1988 could be due
to development of crack flow conditions, or could be due to
substantiated hydraulic gradients from spring noisture. The '88
- *89 data indicate a further increase in percolation rate, to
slightly above 2 inches for Test Plots 1 and 2, Percolation in
this last year of data collection has been much nore continuous
than in the past.
The timing of percolation from Test Plots 1 and 2 during 1987 was
only slightly related to the timing of precipitation events,
suggesting that moisture transmission was via porous media flow
In a low conductivity environment. Test Plot 1 percolation was
ore strongly correlated with precipitation events since April
1988 and September 1988 suggesting that some cracking through the
cover may have occurred, yet the bulk transmission rate has
remained low. Test Plot 2 percolation timing has behaved
similarly.
B-7
-------
Test Plot 3, containing the intermediate sand drain layer, has
performed much differently regarding percolation rates than was
anticipated in the conceptual design. The upper clay/topsoil
unit has allowed substantial percolation of moisture into the
intermediate sand layer, from the very beginning of data
collection (see Table I). Discharge from the intermediate sand
layer occurs within hours of the start of precipitation events
suggesting rapid transmission of water in the upper clay due to
flow through cracks. Percolation from the base of Test Plot 3
has been much more constant than for Test Plots 1 and 2, and
indicates conditions more likely to be homogeneous, as confirmed
in the test pit investigation.
B. Runoff
Runoff production during the first year of data collection was
substantial from each test plot, with Test Plot 1 producing over
7 in. of runoff. However, these runoff depths are dominated by
response to the very heavy rains of September, 1987, and are also
probably due to the immature growth of the cover vegetation. It
is interesting to note that runoff from Test Plot 3 was even
higher than that for Test Plot 1, if the moisture flow from the
intermediate sand layer is included.
Runoff production declines substantially in the second and third
years of data collection. The obvious reason for low runoff in
1987-1988 is the drought. However, the intermediate sand layer
continued to produce moisture in response to the small rainfall
events which occurred in the summer of 1988, indicating very
rapid percolation through the cracked soils of the upper clay
layer. During the 1988-1989 period, runoff from Test Plots 1 and
2 was similar, while runoff from Test Plot 3 was the largest.
This surprising result may be due to the continued poorer
condition of the vegetation on Test Plot 3. The collected data
does not indicate that the greater topsoil thickness (and hence
possibly larger rapid infiltration capacity) of Test Plot 3
serves to reduce runoff.
C. Evapotranspiration
The calculated evapotranspiration (ET) term of the water budget
accounts for a significant fraction of total precipitation for
each of the test plots. Approximately 90% of the total two year
precipitation was calculated as lost to ET in Test Plot 1 and 94%
in the thicker topsoil, Test Plot 2. Lower ET rates were
calculated for Test Plot 3 (approximately 57% of the total
two-year precipitation in 1987 and 1988). This was attributed to
the substantial moisture flow through cracks in the upper clay
layer and interception by the intermediate sand layer, thus
reducing moisture availability for evaporation or transpiration.
Evapotranspiration percentages are higher for later periods of
the study, when vegetation was better established and without the
influence of the record rainfall rates occurring in September
B-8
-------
1986. Thus, the 18 Inch topsoll 1s apparently providing some
Increase 1n evapotransplration, but the anticipated Increase 1n
ET moisture retention capacity (and hence ET) of the upper clay
1n Test Plot 3 has not occurred. Calculation of ET values for
the third year of data collection awaits reduction of neutron
probe soil moisture data.
D. Soil Moisture Content Variations
Monthly soil moisture storage changes were Interpreted from CRN
neutron probe data collected at 6 Inch to 12 Inch Intervals at
seven locations 1n each test plot. Little horizontal variation
of soil moisture content within each test plot was noted.
However significant variations in moisture content occurred with
depth. In general, drying influences were seen through the upper
three feet of each cover during summer months, particularly
during the drought period in 1988. Below depths of 3 feet 1n
Test Plots 1 and 2 moisture contents remained fairly static.
The observed hydrologic responses of Test Plot 3, where
substantial moisture was transmitted through the upper clay
layer, correlated with moisture content data 1n that lower clay
moisture contents have remained very stable. This suggests that
the Intermediate sand layer 1s providing an effective barrier to
upward migration of moisture in drying periods.
In general, the tenslometer data correlated with the neutron
probe data regarding long-term moisture content fluctuations.
The value of the tenslometers in monitoring short-term
Infiltration response was limited, due to the substantial failure
rate. The limited data suggest that soil moisture contents below
several feet 1n depth did not show rapid response to rainfall.
The tenslometers did however indicate a deep and long lasting
drying during the drought of 1988.
The maximum depth of soil moisture which could be absorbed by the
cover sections 1s 1n the range of 18 to 24 Inches. Even
considering the fact that more than half of this amount will be
very tightly held by the clay-rich soils, soil moisture storage
represents a relatively large reservoir through which the much
smaller monthly and yearly percolation depths pass. Therefore,
1t 1s Important to review the soil moisture storage changes
(Table I) when Interpreting the water balance results, especially
with respect to calculated evapotransplration.
E. Soil Temperature
Data from the nest of soil temperature probes Indicates
substantial moderation of temperature fluctuations in the soil
.cover, as compared to air temperature. At a depth of 5 feet
below the cover surface, soil temperatures ranged from
approximately 80°F during the high temperatures experienced 1n
August 1988, to no colder than 45°F during the winter months.
B-9
-------
Soil temperatures fluctuated over a greater range at a depth of 1
foot, but dropped below freezing only several times throughout
the three-year period. The longest period of freezing at 1 foot
depth was approximately 8 weeks, 1n early 1989. However, the
soil at 3 feet in depth was well above freezing during this
period. Apparently, heat being generated within the landfill is
keeping the cover soils substantially warmer in the winter months
than would be expected in Wisconsin, and therefore probably
limiting the effects of freeze-thaw action on the cover soils.
F. Vegetation Growth Summary
Cover vegetation growth characteristics were assessed annually in
1986 and 1987, twice 1n 1988 and once 1n 1989, by evaluating
percent cover, above ground biomass productivity (except 1989)
and root growth development on each test plot and in the
vegetation assessment areas. In general, vegetation suffered
during the drought 1n 1988, with productivities lower than
observed 1n the first year of growth. Vegetation growth in 1989
was much more vigorous than preceding years.
Percent cover analyses typically indicated slightly better growth
on the vegetation assessment areas (alternative mix) than in the
test plot area (primary mix). Biomass productivity comparisons
between the primary mix and alternative mix areas have been
difficult due to mowing which occurred at different times in 1986
and 1987. However, productivities were generally higher for the
alternative species mix, and were also higher on the 18 inch
topsoil plots. Biomass productivity on Test Plot 3 tended to
decline through the growing season, suggesting that moisture
transmission through the upper clay unit was producing droughty
conditions which hampered plant growth. This observation is also
consistent with the much lower calculated evapotranspiration
rates for Test Plot 3. Root densities have been consistently
higher in the 18 inch topsoil (Test Plot 2) and have
progressively become more dense and more deeply penetrating into
the clay soils. The density data was not noticeably different
for primary vs. alternative vegetation mixes.
CONCLUSIONS
A great deal of data on final cover performance has been obtained
from the Omega Hills Test Plot Study, of a type which is not
generally available. The principal long-term value of the
project may be the development of this large body of record
information, which could be utilized for development of improved
analysis techniques or alternative cover design development.
Regarding the specific objectives of this project, the following
conclusions can be drawn at this time:
1. The timing and response of percolation data suggests, and
the test pit investigations have tended to confirm, that
the development and propagation of cracks in the cover
B-10
-------
soils dominates the factors controlling percolation
performance. The apparent Impact of desslcatlon cracks
1n the cover soils indicates that drought conditions may
be much more damaging to cover performance than a
continuous supply of moisture.
2. Analysis procedures which are based on assumptions of
either saturated or unsaturated porous media flow may not
be applicable to many practical landfill cover situations
without careful evaluation.
3. The multi-layered cover design did not result in lower
percolation rates due to retention of soil moisture 1n
the upper clay layer. To the contrary, the upper clay
became thoroughly cracked, allowing rapid infiltration of
moisture to the intermediate sand layer.
4. The thicker topsoil utilized in Test Plot 2 has not
noticeably reduced cover percolation. The effects of
increased moisture retention 1n the thicker topsoil
during the dormant season may outweigh the possible
effect of increased evapotranspiration.
5. Although the alternative vegetation species mix appears
to produce a more vigorous vegetation cover, comparison
of the two sets of vegetation regarding cover percolation
performance 1s not possible.
The above conclusions are based on data drawn from a particular
set of soils, construction and climatic conditions, over a
specific observation period. Extreme caution should be taken 1n
attempting to generalize these conclusions to other sites or
conditions.
PROJECT STATUS
Data collection for the Instrumented test plots and the
alternative vegetation areas 1s continuing, and Is expected to be
conducted for the next several years. Additional test pit
Investigation of representative areas across the landfill 1s
planned, with possible additional data analysis and/or modeling
at some time 1n the future.
ACKNOWLEDGEMENTS
Preparation and presentation of this paper was encouraged and
supported by Waste Management of Wisconsin, Inc. and by Warzyn
Engineering Inc.
THE AUTHORS
Robert Montgomery 1s an environmental engineering section leader
1n Warzyn Engineering's Madison, Wisconsin office, and Laurie
B-ll
-------
TABLE I - PAGE 1 OF 3
SEPTEMBER 1986 THROUGH AUGUST 1987
RECORDED MONTHLY PRECIPITATION, RUNOFF, PERCOLATION AND
COMPUTED MONTHLY WATER BALANCE
PRECIPITATION
TEST PLOT 1
TEST PLOT 2
TEST PLOT 3
f
I-J
ro
MONTH
SEP
OCT
NOV
DEC
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
LONG.
TERM1
2.88
2.25
1.98
2.03
1.64
1.33
2.58
3.37
2.66
3.59
3.54
3.09
ACTUAL2
9.78
1.63
0.86
0.86
0.65
0.89
1.81
4.31
1.32
1.48
7.28
4.41**
RUNOFF
4.40*
0.40*
0.00
0.00
0.00
0.31
0.00
1.60
0.00
0.10
0.19
0.11
PERC
0.00
0.00
0.00
0.00
0.00
0.02
0.00
0.0
0.00
0.00
0.01
0.03
STORAGE
1.30
0.00
0.00
-0.59
0.16
0.27
-0.16
-0.70
-0.43
-1.51
0.70
0.97
CALC ET
4.08
1.23
0.86
1.45
0.49
0.29
1.97
3.37
1.75
2.89
6.38
3.30
RUNOFF
2.80*
0.18
0.00
0.00
0.00
0.08
0.00
0.82
0.00
0.10
0.20
0.13
PERC
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.06
0.05
0.03
0.05
0.08
STORAGE
1.72
0.13
0.00
-0.13
-0.20
0.20
0.00
-0.99
-0.59
-2.11
0.66
1.32
CALC ET
5.26
1.32
0.86
0.99
0.85
0.61
1.81
4.42
1.86
3.46
6.37
2.88
RUNOFF
2.80*
0.32
0.00
0.00
0.00
0.26
0.08
0.06
0.00
0.07
0.09
0.12
PERC
0.20
0.18
0.00
0.00
0.00
0.01
0.06
0.34
0.19
0.13
0.27
0.21
SAND
4.90*
0.80*
0.04*
0.40*
0.50*
0.04*
2.15*
1.39
0.53*
0.14
2.34
0.16
STORAGE
2.18
-0.07
-0.20
-0.53
0.53
0.26
-0.20
-1.12
-0.66
-1.45
0.92
0.99
CALC ET
-0.30
0.40
1.02
0.99
-0.38
0.32
-0.28
3.64
1.26
2.59
3.66
2.93
TOTAL 30.94 35.28
7.11 0.06
0.01
28.06
4.31
0.27 0.01 30.69 3.80 1.59 13.39 0.65
15.85
Notes: All units in dimension of inches of water depth.
Precipitation Data: (1) Long Term Normal Recorded at Milwaukee Mitchell field NOAA Station based on the
1951-1980 record period.
(2) Measured On-Site at Omega Hills Test Plots
CALC ET Calculated Evapotranspiration
STORAGE » Change in moisture content from Neutron Probe data, expressed in inches.
* Estimated for period Sep 4-24, 1986 and for later periods of tank overflow.
** On-site record augmented using Germantown NOAA Station Data for periods of site raingaqe failure.
-- Soil moisture storage data for period Oct. 1988-Aug. 1989 to be compiled in October 1989.
-------
TABLE I - PAGE 2 OF 3
SEPTEMBER 1987 THROUGH AUGUST 1988
RECORDED MONTHLY PRECIPITATION, RUNOFF, PERCOLATION AND
COMPUTED MONTHLY WATER BALANCE
PRECIPITATION
TEST PLOT 1
TEST PLOT 2
TEST PLOT 3
MONTH
SEP
OCT
NOV
DEC
JAN
FEB
MAR
APR
MAY
JUH
JUL
AUG
LONG,
TERM1
2.88
2.25
1.98
2.03
1.64
1.33
2.58
3.37
2.6
3.5
3.54
3.09
ACTUAL2
3.28
1.11
2.49
3.61**
2.52**
0.43**
1.08**
3.54**
0.37
0.97**
1.21**
2.16**
RUNOFF
0.05
0.00
0.15
0.11
0.32
0.13
0.00
0.52
0.02
0.05
0.07
0.03
PERC
0.02
0.00
0.00
0.01
0.02
0.05
0.03
0.03
0.0
0.01
0.00
0.01
STORAGE
0.00
-0.76
1.08
-0.27
0.49
0.00
0.27
-0.43
-1.57
-1.67
-0.38
0.27
CALC ET
3.21
1.87
1.26
3.76
1.69
0.25
0.78
3.42
1.92
2.58
1.52
1.85
RUNOFF
0.18
0.14
0.00
0.14
0.47
0.05
0.13
0.20
0.03
0.07
0.03
0.10
PERC
0.09
0.02
0.03
0.23
0.03
0.05
0.06
0.52
0.14
0.02
0.00
0.00
STORAGE
0.26
-1.25
1.32
0.00
0.66
0.07
0.26
-0.46
-1.85
-2.51
-0.73
0.33
CALC ET
2.75
2.20
1.14
3.24
1.36
0.26
0.63
3.28
2.05
3.38
1.91
1.73
RUNOFF
0.02
0.03
0.00
0.27
0.76
0.04
0.04
0.18
0.02
0.02
0.0
0.02
PERC
0.14
0.08
0.01
0.12
0.05
0.01
0.05
0.18
0.12
0.06
0.03
0.02
SAND
0.46
0.03
0.32
0.71
0.28
0.49
0.21
1.45
0.35
0.04
0.01
0.21
STORAGE
0.13
-0.92
1.25
-0.13
0.33
0.13
0.59
-0.79
-1.52
-1.85
-0.59
0.26
CALC ET
2.53
1.89
0.91
2.64
1.10
-0.23
0.19
2.53
1.40
2.70
1.71
1.64
TOTAL 30.94 22.77
1.45 0.18 -2.97
24.11
1.54
1.19 -3.90 23.93 1.45 0.87 4.56 -3.11
19.01
Notes: All units in dimension of inches of water depth.
Precipitation Data: (1) Long Terra Normal Recorded at Milwaukee Mitchell field NOAA Station based on the
1951-1980 record period.
(2) Measured On-Site at Omega Hills Test Plots
CALC ET Calculated Evapotranspiration
STORAGE Change in moisture content from Neutron Probe data, expressed in inches.
* Estimated for period Sep 4-24, 1986 and for later periods of tank overflow.
** On-site record augmented using Germantown NOAA Station Data for periods of site raingage failure.
-- Soil moisture storage data for period Oct. 1988-Aug. 1989 to be compiled in October 1989.
-------
TABLE I - PAGE 3 OF 3
7
SEPTEMBER 1988 THROUGH AUGUST 1989
RECORDED MONTHLY PRECIPITATION, RUNOFF, PERCOLATION AND
COMPUTED MONTHLY WATER BALANCE
PRECIPITATION
TEST PLOT 1
TEST PLOT 2
TEST PLOT 3
MONTH
SEP
OCT
NOV
DEC
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
LONG
TERM1
2.88
2.25
1.98
2.03
1.64
1.33
2.58
3.37
2.66
3.59
3.54
3.09
ACTUAL2
4.81**
1.95
3.70
1.22
0.57
0.30
1.22
0.89
3.41
3.05**
5.08**
6.17**
RUNOFF
0.13
0.05
0.18
0.13
0.00
0.00
0.25
0.08
0.14
0.23
0.26
0.23
PERC
0.79
0.03
0.50
0.16
0.08
0.04
0.19
0.05
0.07
0.13
0.08
0.07
STORAGE
2.54
-0.22
0.70
0.11
0.05
0.11
0.05
-0.38
-0.27
-0.05
-0.27
0.49
CALC ET
1.35
2.09
2.30
0.82
0.44
0.15
0.73
1.14
3.47
2.74
5.01
5.38
RUNOFF
0.26
0.03
0.15
0.03
0.00
0.00
0.70
0.07
0.14
0.18
0.20
0.20
PERC
0.02
0.02
0.59
0.24
0.26
0.25
0.27
0.09
0.10
0.31
0.08
0.12
STORAGE
2.24
-0.33
2.19
0.20
0.07.
0.13
0.13
-0.59
-0.66
-0.59
-0.33
1.39
CALC ET
2.28
2.23
1.51
0.75
0.24
-0.08
0.12
1.32
3.83
3.15
5.13
4.46
RUNOFF
0.11
0.00
0.00
0.06
0.09
0.01
2.03
0.01
0.08
0.07
0.06
0.08
PERC
0.06
0.04
0.23
0.14
0.08
0.03
0.10
0.11
0.12
0.23
0.22
0.24
SAND STORAGE CALC ET
0.71 2.706 1.23
0.01 -0.53 2.43
0.96
0.70
0.52
0.25
0.90
0.17
0.32
0.30
0.15
0.22
TOTAL 30.94 32.40
1.68 2.19 2.86
25.62
1.96
2.35 3.85 24.94 2.60 1.60 5.21
Notes: All units in dimension of inches of water depth.
Precipitation Data: (1) Long Terra Normal Recorded at Milwaukee Mitchell field NOAA Station based on the
1951-1980 record period.
(2) Measured On-Site at Omega Hills Test Plots
CALC ET Calculated Eyapotranspiration
STORAGE Change in moisture content from Neutron Probe data, expressed in inches.
* Estimated for period Sep 4-24, 1986 and for later periods of tank overflow.
** On-site record augmented using Germantown NOAA Station Data for periods of site raingaqe failure.
-- Soil moisture storage data for period Oct. 1988-Aug. 1989 to be compiled in October 1989.
-------
Test Plot 1
(CURRENTLY APPROVED COVER)
Test Plot 2
Test Plot 3
6" TOPSOIL
40" CLAY
©
18" TOPSOIL
48" CLAY
© 6"
TOPSOIL
24" CLAY
12" SAND
© 24" CLAY
FIGURE 1; COVER DESIGNS INSTALLED AT OMEGA HILLS TEST PLOT SITE
-------
50'
s
L
SURFACE RUNOFF
ISOLATION BARRIER
OF
PERCOLATION
COLLECTION LYSIMETERj
(BELOW COVER)
INSTRUMENTATION
CABLING
^
VEGETATION
ASSESSMENT
AREA
-v
COLLECTION PIPE FOR PERCOLATION
COLLECTION LYSIMETER (BELOW
COVER)
RUNOFF COLLECTION
TANKS
LEGEND
NEUTRON PROBE ACCESS TUBE
TRANSDUCER-EQUIPPED TENSIOHETER
TANK LEVEL TRANSDUCER
PERCOLATION
COLLECTION TANK
FIGURE 2: PLAN VIEW OF TYPICAL TEST PLOT
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RUNOFF ISOLATION
BARRIER
RUNOFF COLLECTION
PIPE AND TANK
SAND FILLED SUMP WITH
OUTLET PIPE TO PERCOLATION
COLLECTION TANK
- s-NEUTRON ACCESS
/ i
DRAINAGE GRID
HYPALON MEMBRANE-
EXISTING INTERMEDIATE
COVER
FILTER FABRIC
SAND BEDDING
FIGURE 3; SCHEMATIC SECTION OF TYPICAL TEST PLOT
-------
00
3
3
INSTRUMENTATION
CABLING (TYP.
RUNOFF COLLECTION
TANKS (TYP.)
PERCOLATION COLLECTION
TANK (TYP.)
Test Plot 1 Test Plot 2 Test Plot 3
N
rnu
_!--
I
r
~L
SHED'
ACCESS
AIR TEMPERATURE/
HUMIDITY GAGE
TIPPING BUCKET
RAIN GAGE
SOIL TEMPERATURE
p_ PROBES
T-
SURFACE RUNOFF '
ISOLATION BARRIER
(TYP.) | i
VEGETATION
ASSESSMENT AREA
ROAD
LIMITS OF FILL'
FIGURE 4: SCHEMATIC SITE PLAN
-------
Parsons 1s an environmental engineer 1n Warzyn's Milwaukee,
Wisconsin office. They have both been Involved with the test
plot project since Its beginning.
REFERENCES
1 Montgomery, R.J., PhllUppI, T.C., and Vrabec, S.H., "Field
Evaluation of Natural Soil Landfill Cover Designs at Omega
Hills Landfill, Wisconsin", 1n Proceedings of the Ninth
Annual Madison Waste Conference, University of Wisconsin-
Madison, 1986.
[dlk-600-09]
This article was presented at the 1989 Annual Meeting of
the National Solid Waste Management Association,
Washington, D.C. For more information about the study,
contact Robert J. Montgomery, Project Manager, Warzyn
Engineering, P.O. Box 5385, Madison, Wl, Phone: 608-273-
0440.
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APPENDIX C: WATER CONTENT-DENSITY CRITERIA FOR COMPACTED SOIL LINERS
David E. Daniel and Craig H. Benson
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- DRAFT -
Water Content-Density Criteria for Compacted Soil Liners1
by
David E. Daniel2 M. ASCE, and Craig H. Benson3 A.M. ASCE
ABSTRACT
Soil liners have traditionally been compacted in the field to a minimum dry unit
weight over a specified range in water content. This approach evolved from practice for
structural fills for which strength and compressibility are of primary concern. With
soil liners, hydraulic conductivity is usually of paramount importance. Data are
presented to show that the water content-density criteria for compacted soil liners can
be formulated differently from the procedure currently utilized by many engineers. The
recommended approach is based on defining water content-density requirements for a
broad, but representative, range of compactive energy, and relating those requirements
to hydraulic conductivity and other relevant factors. A case history illustrates the
recommended procedure and its implementation.
INTRODUCTION
Compacted soil is widely used to line landfills and waste impoundments, to cap
new waste disposal units, and to close old waste disposal sites. In the U.S., nearly all
regulatory agencies require that compacted soil liners and covers be designed to have a
hydraulic conductivity less than or equal to a specified maximum value. Typically, the
hydraulic conductivity must be less than or equal to 1 x 10'7 cm/s for soil liners and
covers used to contain hazardous waste, industrial waste, and municipal solid waste.
Successful design and construction of soil liners and covers involves many facets,
e.g., selection of materials, assessment of chemical compatibility, determination of
construction methodology, analysis of slope stability and bearing capacity, evaluation of
subsidence, consideration of environmental factors such as desiccation, and development
and execution of a construction quality assurance plan (Daniel, 1987; Oakley, 1987;
1 Work performed by the Y-12 Oak Ridge Plant operation by Martin Marietta Energy Systems,
Inc., for the U. S. Department of Energy under contract DE-ACO5-84OR21400.
2 Assoc. Prof, of Civil Engineering, Univ. of Texas, Austin, TX 78712
3 Asst. Prof, of Civil and Environmental Engineering, Univ. of Wisconsin, Madison, Wl 53706
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U.S. EPA, 1988; and Elsbury et al., 1989). Most engineers rely primarily on field-
measured water contents and dry unit weights to verify proper compaction of the soil.
The focus of this paper is hydraulic-conductivity-based, water content-density criteria
used for construction quality assurance (QA) of soil liners.
Over the past three years, the authors have reviewed the results of hundreds of
hydraulic conductivity tests on compacted soil and have found that the water content-
density criteria in common use today often do not correlate well with hydraulic
conductivity test results. From this work, a method for establishing criteria for water
contents and dry unit weights evolved. The recommended procedure has some common
elements with the methodology described by Mundell and Bailey (1985) and Boutwell
and Hedges (1989). The recommended procedures are described, beginning with a
review of criteria that are currently in use and ending with a case history illustrating
the suggested procedure.
TRADITIONAL APPROACH
Methodology
Currently, design engineers usually require that soil liners be compacted within
a specified range of water content and to a minimum dry unit weight. The "Acceptable
Zone" shown in Fig. 1 represents the zone of acceptable water content/dry unit weight
combinations based on typical current practice. The designer will usually require that
the dry unit weight (yd) of tne compacted soil be greater than or equal to a percentage
(P) of the maximum dry unit weight (yd,max) fr°m a laboratory compaction test:
p
Yd ^ 75~Q Td.max (1 )
Herrmann and Elsbury (1987) reported that P is usually 95% of Yd,max from standard
Proctor compaction (ASTM D-698) or 90% of Yd,max from modified Proctor
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compaction (ASTM D-1557). The range of acceptable water content varies with the
characteristics of the soil, but, for soil liners and covers, might typically be about 0 to
4 percentage points wet of standard or modified Proctor optimum.
The shape of the Acceptable Zone in Fig. 1 evolved empirically from construction
practices applied to roadway bases, structural fills, embankments, and earthen dams.
The specification is based primarily upon the need to achieve a minimum yd for adequate
strength and limited compressibility. Soil liners are compacted wet of optimum because
wet-side compaction minimizes hydraulic conductivity (Bjerrum and Huder, 1957;
Lambe, 1958; Mitchel et al., 1965; Boynton and Daniel, 1985; and others). In the next
subsection, published results of hydraulic conductivity tests are reviewed and compared
with the Acceptable Zone sketched in Fig. 1.
Analysis
The most extensive study illustrating how molding water content and dry unit
weight influence the hydraulic conductivity of compacted clay was published by Mitchell
et al. (1965), who demonstrated that the energy and method of compaction significantly
influence the hydraulic conductivity of compacted clay. For a given method of
compaction, increasing the compactive energy decreases the hydraulic conductivity of
the soil (Fig. 2).
The compaction data from Fig. 2 are replotted in Fig. 3 with open symbols used to
denote compacted specimens that had a hydraulic conductivity (k) > 1 x 10'7 cm/s and
solid symbols used for compacted specimens with k <, 1 x 10'7 cm/s. The "Acceptable
Zone" in Fig. 3 encompasses the solid symbols (specimens with k <, 1 x 10'7 cm/s) and
rejects the others. The shape of the Acceptable Zone in Fig. 3 bears no resemblance to
the one shown in Fig. 1.
Another group of data published by Mitchell et al. are summarized in Fig. 4. Four
contour curves in this figure represent w-yd combinations that yielded k's of 10~8,
10'7, 10'6, and 10'5 cm/s. The curves of equal k values were drawn using results of
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tests on soils compacted at different compactive efforts. Neither the shapes of the
contour curves shown in Fig. 4 nor the zone of w-yd combinations that yielded k <, 10'7
cm/s have the shape of the Acceptable Zone shown in Fig. 1. An Acceptable Zone of the
type presented in Fig. 1, with P (Eq. 1) equal to 90% of Yd.max from modified Proctor
and w's between 0 and 4% wet of optimum, is superimposed on the data in Fig. 4. Note
that a significant portion of the Acceptable Zone based on typical current practice
contains w-yd combinations that yielded k's > 1 x 10'7 cm/s.
Two extensive data sets were documented by Benson and Daniel (1989) and by
Boutwell and Hedges (1989). Benson and Daniel's data are shown in Fig. 5 in a format
similar to that of Fig. 3, except that the typical Acceptable Zones based on current design
methodology are superimposed. The Acceptable Zones in Fig. 5 were drawn with P (Eq.
1) equal to 90 and 95% for modified and standard Proctor, respectively, and a range in
water content of 0 to 4% wet of optimum (a different range in water content could have
been selected; 0-4% wet of optimum was chosen in this case as typical of current
practice). For the data set in Fig. 5, all w-yd points within the Acceptable Zones
correspond to compacted soils with k < 1 x 10'7 cm/s; some w-yd points outside the
Acceptable Zone also represent compacted soils with k £ 1 x 10'7 cm/s. It is not evident
from the data in Fig. 5 why the Acceptable Zones should be shaped as they are or limited
in extent as they are.
Boutwell and Hedges (1989) plotted contours of hydraulic conductivity and shear
strength as shown in Fig. 6. The Acceptable Zone in Fig. 6 applies to P=95% and an
acceptable water content 0 to 4% wet of optimum. All w-yd points contained within the
Acceptable Zone correspond to test specimens with k <; 1 x 10^7 cm/s, but the shape and
boundaries of the Acceptable Zone in Fig. 6 correlate with neither hydraulic conductivity
nor shear strength.
Shear strength and hydraulic conductivity are not the only parameters that
concern the engineer who designs soil liners and covers; potential for desiccation,
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resistance to chemical attack, interfacial frictional with overlying geomembranes, and
ability to deform without cracking when settlement occurs are but a few of the additional
parameters that often require consideration. Clearly, the best way to establish an
appropriate Acceptable Zone is to measure the parameters of interest and then to relate
those parameters to water content and dry unit weight. Because hydraulic conductivity
is the key parameter for most soil liners and covers, great attention is generally focused
on ensuring that low hydraulic conductivity is achieved. Indeed, the procedure outlined
in the rest of this paper deals mainly with hydraulic conductivity. However, after the
acceptable range of water content/dry unit weight is established based on hydraulic
conductivity, one must carefully consider all other factors and adjust the acceptable
range of water content/dry unit weight to account for those factors.
THE RECOMMENDED PROCEDURE
Basis
Rational design of compacted soil liners should be based upon test data developed
for each particular soil. Field test data would be better than laboratory data, but the cost
of determining compaction criteria in the field through a series of test sections would
almost always be prohibitive. For the design engineer, laboratory tests utilizing the
most appropriate method of compaction (to match field compaction as closely as
possible) are recommended. However, laboratory-scale compaction can never perfectly
duplicate the repeated passage of heavy compaction equipment over a lift of soil in the
field. Even if the method of laboratory compaction could be made to match field
compaction, the compactive effort in the field is impossible to determine in advance and
will undoubtedly vary from point to point. Given these facts, one is hard pressed to
justify a single, arbitrary compactive effort for use in laboratory testing.
A logical approach is to select several compactive efforts in the laboratory that
span the range of compactive effort anticipated in the field so that the water content/dry
c-6
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unit weight criterion applies to any reasonable compactive effort. This approach is
similar to the onedescribed by Mundell and Bailey (1985).
For most earthwork projects, modified Proctor (ASTM D1557) effort
represents a reasonable upper limit on the compactive effort likely to be delivered to the
soil in the field. Standard-Proctor effort (ASTM D698) likely represents a medium
compactive effort. It is conceivable that on many projects, soil in at least a few locations
will be compacted with an effort less than that of standard Proctor. The authors have
recently worked with an altered standard Proctor procedure, called "reduced Proctor,"
in which the standard Proctor procedures are followed except that only^lS drops of the
hammer per lift are used instead of the usual 25 drops. The "reduced Proctor"
procedure is the same as the "15-b!ow compaction test" described by the U. S. Army
Corps of Engineers (1970, p. VI-13). The reduced Proctor effort is expected to
correspond to a reasonable minimum level of compactive energy for a typical soil liner
or cover. Other compaction methods, e.g., kneading compaction, could be used. The key
is to span the range of compactive effort expected in the field with the laboratory
compaction procedures.
Methodology
The recommended procedure involves establishing w-yd ranges needed to achieve
the required hydraulic conductivity and then modifying these ranges to account for other
factors besides k. The approach that is recommended is as follows:
1. Compact soil in the laboratory with modified, standard, and reduced Proctor
compaction procedures to develop compaction curves as shown in Fig. 7a.
Approximately 5 to 6 different specimens should be compacted with each effort.
Other compaction procedures can be used if they better simulate field
compaction and span the range of compactive effort expected in the field.
2. The compacted soils should be permeated to determine the hydraulic conductivity
of each compacted specimen. Care should be taken to make sure that permeation
C-7
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procedures are correct, with important details such as degree of saturation and
effective confining stress carefully selected. Guidance on these details may be
found in Daniel et al. (1984, 1985) and Carpenter and Stephenson (1986).
The measured hydraulic conductivities should be plotted as a function of
molding water content as shown in Fig. 7b.
3. As shown in Fig. 7c, the dry unit weight-water content points should be replotted
with different symbols used to represent compacted specimens that had
hydraulic conductivities greater than the maximum acceptable value and
specimens with hydraulic conductivities less than or equal to the maximum
acceptable value. The "Acceptable Zone" should be drawn to encompass the data
points representing test results meeting or exceeding the design criteria. Some
judgment may be necessary in constructing the Acceptable Zone.
4. The "Acceptable Zone" should be modified (Fig. 7d) based on other considerations,
e.g. shear strength, interfacial friction with an overlying geomembrane,
shrink/swell considerations, concern over cracking when settlement occurs,
concern for constructability, or local practices. For example, if shear
strength is of concern, a limit on the water content and/or dry unit weight
should be specified to ensure that excessively weak soils are not produced.
Figure 8 shows how one might overlap acceptable zones defined from hydraulic
conductivity and shear strength considerations to define a single Acceptable
Zone. The same procedure can be applied to other factors, e.g., shrink/swell
potential, that are relevant for any particular project.
08
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CASE HISTORY
In 1988-89, a large construction project was initiated near the Oak Ridge Y-12
Plant at the U.S. Department of Energy's Oak Ridge Operations near Oak Ridge, Tennessee,
to close and cap old disposal grounds. The engineered cap consisted of 2 ft (600 mm) of
compacted soil designed for a hydraulic conductivity measured in the laboratory < 1 x
10'7 cm/s, overlain by a geomembrane, surface water collection and removal system,
geotextile filter, and topsoil. Requirements for the soil barrier focused almost
exclusively on hydraulic conductivity. Shear strength was of little concern because the
ground surface was essentially flat. Desiccation was not thought to be a problem given
the high rainfall in the area, high moisture content of subsoils, and the fact that the soil
barrier was overlain by a geomembrane liner. Underlying contaminated soils had little
potential for settlement.
Soils used for the construction were termed Type A, B, and C materials. Index
properties of the soils are given in Table 1. The soils were excavated from east and west
borrow areas, which were located about 5 mi (8 km) apart but which were geologically
identical.
Type A soil was the best material; it contained a mixture of sand, silt, and clay,
and could be compacted to yield hydraulic conductivities as low as 1 x 10-8 cm/s. Type
B soil was much sandier and could only be compacted to yield a hydraulic conductivity <
1 x 10'7 cm/s with difficulty. Type C soils were silty soils that could not be compacted
to produce the desired low hydraulic conductivity.
The methodology described previously was applied to the Oak Ridge soils.
Compacted specimens were prepared utilizing modified, standard, and reduced Proctor
procedures. Test specimens were permeated in rigid-wall permeameters without
backpressure. Tests were performed without backpressure because the soil is being
used in a cap near the ground surface and will never become fully saturated. However,
some comparative tests with flexible-wall permeameters were performed with
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backpressure saturation. The results of the flexible-wall tests showed that the same k
was measured; hence, the method of permeation turned out to have no significant
influence on the test results. Permeation continued until rates of inflow and outflow
were equal and k was steady.
Results for Type A Soil
The compaction curves for Type A soil from the east borrow area are shown in
Fig. 9. The corresponding hydraulic conductivities are shown in Fig. 10. Type A soil
could be compacted to a hydraulic conductivity <, 1 x 10'7 cm/s, but over different
ranges of molding water content for different compactive energies. The compaction data
are replotted in Fig. 11; the Acceptable Zone includes data points for specimens with k <,
1 x 10'7 cm/s and excludes the others.
Similar data were developed for Type A soil from the west borrow area.
Compaction data for Type A soil from both borrow areas are combined in Fig. 12; a single
Acceptable Zone was defined for soils from the different borrow sites.
Results for Type B Soil
Type B soils were much sandier than Type A soils. Compaction curves for Type B
soil from the west borrow area are shown in Fig. 13 and k is plotted as a function of
molding water content in Fig. 14. As seen in Fig. 14, k £ 1 x 10~7 cm/s could be
achieved with modified Proctor compaction but not with reduced Proctor compaction.
With standard Proctor compaction, k < 1 x 10'7 cm/s could be achieved only for an
extremely narrow range of molding water content. For this sandy material, it was
essential that the soil be compacted with a large compactive effort to a high dry unit
weight.
The data for Type B soils from both borrow areas are combined in Fig. 15. A
single Acceptable Zone was defined. The lower bound of the Acceptable Zone for Type B
soil lies above the lower bound of the Acceptable Zone for Type A soils and does not extend
to as large a water content, as shown in Fig. 16.
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Results for Type C Soils
Type C soils had very low yd's (< 80 pcf or 12.6 kN/m3) and high k's (1 x 10'6
to 1 x 10'5 cm/s) when compacted with standard Proctor effort. It was obvious that
Type C materials were unsuitable. The w-yd points for Type C soil were all outside the
Acceptable Zones for Type A and B soils. Thus, if Type C soil were inadvertantly
introduced into the cover, the w-yd points would not fall within the Acceptable Zone of
either Type A or B soil and the material would automatically be rejected.
Implementation
The test results just described were implemented as follows. In the field, the
technicians first classified the soil as Type A, B, or C (this was relatively easy because
of differences in color and sand content between the soils)/ One-point standard Proctor
compaction tests were occasionally used in the borrow pits to help classify questionable
materials. After the materials had been placed and compacted in a lift, technicians
measured w and yd in the field. The field-measured yd was then compared with the
minimum value required using the appropriate graph, e.g., Fig. 12 or 15. If the field-
measured yd exceeded the minimum required yd, no further action was needed. If the
field-measured yd was less than the minimum required yd, then additional compaction
was provided until yd exceeded the minimum required value.
The approach taken on this project had three practical advantages for QA
personnel in the field: (1) compliance with the specifications was easy to check (a w-yd
point was plotted on a graph and a pass/fail decision was made immediately); (2)
because P from Eq. 1 was not a part of the acceptance criteria, there was no need to
assume a value for yd, max for each field test, which simplified the qualification process
in the field; and (3) the method provided a second check that ensured that Type C soils
were not used (w-yd points for Type C soil did not fall within either Acceptable Zone and
thus could never be accepted under these criteria).
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Earlier on this project, the construction specifications had required that the soil
be compacted to yd ^ 95% of Yd,max from standard Proctor at a water content between
3% and 6% wet of standard Proctor optimum. With the approach described herein, the
allowable water content was not constrained to such a narrow range. Rather, for a given
water content, the recommended approach required that adequate compactive effort (as
reflected by yd) be delivered to the soil. Construction operations were significantly
accelerated when the contractor was not constrained to an extremely narrow range of
water content. Also, for wet soils, it is difficult to compact soils to yd > 95% of yd,max
from standard Proctor; the approach described herein made it much easier to compact
wet soils and still pass the water content-density requirements.
ADDITIONAL ANALYSIS AND COMMENTS
The lower limit of the Acceptable Zone is typically parallel to the zero air voids
curve. For some soils, it may be possible to utilize a specified degree of saturation (Fig.
17a), such as used by Lahti et al. (1987), or line of optimums (Fig. 17b), such as
recommended by Mundell and Bailey (1985), as the lower bound of the Acceptable Zone.
In some cases, a line parallel to the line of optimums, perhaps offset slightly by a
certain water content, may prove to be a good way of defining the lower bound of the
acceptable zone (see Mundell and Bailey, 1985, for further detail).
Calculated degrees of saturation are sometimes greater than 100%
(Schmertmann, 1989), which causes a w-yd point to lie above the zero air voids curve.
All that is important is that the field w-yd point lie above the lower bound of the
Acceptable Zone.
The procedure recommended herein involves compaction and permeation of
approximately 5 to 6 soil samples at each of 3 different compactive efforts, or a total of
15 to 18 compaction/permeability tests for each soil to be investigated. A typical
geotechnical engineering laboratory should be able to complete such a scope of testing in
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a few weeks. The number of tests required, the time required to develop the data, and the
cost of developing the data are not expected to be prohibitive for an important soil liner
or cover project.
Tests to determine compatibility with chemical wastes are occasionally
performed on laboratory-compacted soils. The testing program recommended in this
paper is intended to establish w-yd requirements for soil permeated with water. To test
for chemical compatibility, the authors recommend that one or two test specimens near
the lower bound of the Acceptable Zone be selected for compatibility testing.
Finally, there is more to good construction than control of water content and dry
unit weight. Good mixing of the soil, effective bonding of lifts, proper protection of
completed lifts from desiccation and freezing, and careful inspection by qualified
personnel are essential ingredients to good QA of soil liners and covers.
CONCLUSIONS
At the present time, engineers are commonly using water content-density
criteria originally developed for structural fills in their specifications for compacted
soil liners and covers. These criteria typically require the soil to be compacted to a
minimum dry unit weight (yd) over a specified range in molding water content (w), as
shown in Fig. 1. The approach is based on historical practice for structural fills, where
strength and compressibility are the main concerns, and not upon a careful consideration
of requirements for achieving low hydraulic conductivity. An examination of available
data shows that the commonly-used approach does not succeed very well in
discriminating between w-yd points that correspond to soils with hydraulic conductivity
(k) < 1 x 10'7 cm/s, which is a common regulatory maximum, and w-yd points
corresponding to k > 1 x 10'7 cm/s.
A procedure that is based primarily upon hydraulic conductivity considerations
is proposed. The procedure, illustrated in Fig. 7, is as follows: (1) soils are compacted
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over a range in water content using three compactive efforts that represent the
maximum, typical, and minimum compactive effort expected in the field; (2) the
compacted specimens are permeated to determine k; (3) the compaction data (w-yd) are
plotted on one figure with different symbols used for specimens with k < 1 x 1fr7 cm/s
(or some other maximum, if the design criterion is not 1 x 10'7 cm/s) and specimens
with k > 1 x 10'7 cm/s; (4) an Acceptable Zone is drawn (typically with some
engineering judgment applied) that encompasses the test results meeting or exceeding
the design criteria; and (5) the Acceptable Zone is modified to account for other factors,
such as shear strength considerations, shrink/swell criteria, and local construction
practices, that may be relevant on any given project. Tests to develop the data needed to
account for these "other factors" should be performed on test specimens prepared as
outlined in Step 1 above; the tests might involve measurement of many parameters,
depending on the specific job requirements, but could include strength tests, swelling
tests, shrinkage tests, tests of interfacial shear with geomembrane materials, or
"custom-designed" tests aimed at evaluating a particular concern such as the effect of
settlement on the hydraulic integrity of a cover material.
The recommended procedure was applied to site remediation work at the Oak
Ridge Y-12 Plant Operations, where hydraulic conductivity was the parameter of main
concern, and was found to work very well in discriminating between w-y
-------
basis for design than the existing empirical approach, is convenient to apply in the field,
and warrants consideration by the engineer.
DISCLAIMER AND ACKNOWLEDGMENTS
This work was sponsored by the Oak Ridge Y-12 Plant Operations by Martin
Marietta Energy Systems, Inc. (MMES), for the U.S. Dept. of Energy under contract DE-
AC05-840R21400. This paper was prepared partly utilizing results of work
sponsored by an agency ot the U.S. Government. Neither the U.S. Government nor any
agency thereof, nor any of their employees, makes any warranty, express or implied, or
assume any legal liability or responsibility for the accuracy, completeness, or
usefulness of any information, apparatus, product, or process disclosed, or represents
that its use would not infringe privately owned rights. Reference herein to any specific
commercial product, process, or service by trade name, trademark, manufacturer, or
otherwise, does not necessarily constitute or imply its endorsement, recommendation,
or favoring by the U.S. Government or any agency thereof. The views and opinions of
authors expressed herein do not necessarily state or reflect those of the U.S. Government
or any agency thereof.
Many individuals at MMES were closely involved in this work; the authors are
grateful for their support and input. Particular gratitude is expressed to Ken Brady,
Jim Stone, Bill Manrod, Bob Barnett, Harry Harper, and Bill Barton. David Lutz helped
to perform the laboratory hydraulic conductivity tests.
The QA on this project was performed by S&ME (now Westinghouse
Environmental and Geotechnical Services, Inc.), Blountville, Tenn. The cooperation and
assistance of James Belgeri and Terrell Reece are sincerely appreciated. The author is
also grateful to Greg Richardson for his support and constructive critique of an earlier
version of this manuscript. Thanks are also extended to Linda Locke, Gary Johnson,
Denys Reades, and Charles Williams for reviewing an earlier draft of the paper.
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REFERENCES
Benson, C.H., and Daniel, D.E. (1989), "The Influence of Clods on the Hydraulic
Conductivity of a Compacted Clay," Journal of Geotechnical Engineering (in press).
Bjerrum, L, and Huder, J. (1957), "Measurement of the Permeability of Compacted
Clays," Proceedings, Fourth International Conference on Soil Mechanics and
Foundation Engineering, London, 1, 6-10.
Boynton, S.S., and Daniel, D.E. (1985), "Hydraulic Conductivity Tests on Compacted
Clay," Journal of Geotechnical Engineering, 111(4), 465-478.
Boutwell, G.P., and Hedges, C. (1989), "Evaluation of Waste-Retention Liners by
Multivariate Statistics," Proceedings, Twelfth International Conference on Soil
Mechanics and Foundation Engineering, Rio De Janeiro, Vol. 2, pp. 815-818.
Carpenter, G.W., and Stephenson, R.J. (1986), "Permeability Testing in the Triaxial
Cell," Geotechnical Testing Journal, 9(1), 3-9.
Daniel, D.E. (1987), "Earthen Liners for Land Disposal Facilities," in Geotechnical
Practice for Waste Disposal '87, R.D. Woods (ed.), American Society of Civil
Engineers, New York, 21-39.
Daniel, D.E., Trautwein, S.J., Boynton, S.S., and D.E. Foreman (1984), "Permeability
Testing with Flexible-Wall Permeameters," Geotechnical Testing Journal, 7(3),
113-122.
Daniel, D.E., Anderson, D.C., and Boynton, S.S. (1985), "Fixed-Wall Vs. Flexible-Wall
Permeameters," in Hydraulic Barriers in Soil and Rock. Johnson et al. (eds),
Special Technical Publication 874, Americal Society for Testing and Materials,
Philadelphia, 107-126.
Elsbury, B.R., et al. (1989), "Field and Laboratory Testing of a Compacted Soil Liner,"
U.S. EPA, Cincinnati, Ohio (in press).
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Herrmann, J.G. and Elsbury, B.R. (1987), "Influential Factors in Soil Liner
Construction for Waste Disposal Facilities, in Geotechnical Practice for Waste
Disposal '87, R.D. Woods (ed.), American Society of Civil Engineers, New York,
522-536.
Lahti, L R., King, K. S., Reades, 0. W., and Bacopoulos, A. (1987), "Quality Assurance
Monitoring of a Large Clay Liner," in Geotechnical Practice for Waste Disposal '87,
R.D. Woods (ed.), American Society of Civil Engineers, New York, 641-654.
Lambe, T.W. (1958), "The Permeability of Fine-Grained Soils," American Society for
Testing and Materials, Special Technical Pub. 163, Philadelphia, 55-67.
Mitchell, J.K., Hooper, D.R., and Campanella, R.G. (1965), "Permeability of Compacted
Clay," Journal of the Soil Mechanics and Foundations Division, ASCE, 91(SM4),
41-65.
Mundell, J. A., and B. Bailey (1985), "The Design and Testing of a Compacted Clay
Barrier Layer to Limit Percolation through Landfill Covers," in Hydraulic
Barriers in Soil and Rock. Johnson et al. (eds), American Society for Testing and
Materials, Special Technical Publication 874, Philadelphia, pp. 246-262.
Oakley, R.E. (1987), "Design and Performance of Earth-Lined Containment Systems,"
in Geotechnical Practice for Waste Disposal '87, R.D. Woods (ed.), American
Society of Civil Engineers, New York, 117-136.
Schmertmann, J.H. (1989), "Density Tests above Zero Air Voids Line," Journal of
Geotechnical Engineering, 115(7), 1003-1020.
U. S. Army Corps of Engineers (1970), "Laboratory Soils Testing," Engineer Manual
EM-1110-2-1906, Dept. of the Army, Washington, DC.
U.S. Environmental Protection Agency (1988), "Design, Construction, and Evaluation of
Clay Liners for Waste Management Facilities," EPA/530/SW-86/007F,
Washingtin, DC.
C-17
-------
Table 1. Properties of Soils
Std. Proctor Compaction
Borrow
Area
West
East
West
East
East
Soil
Typ9
A
A
B
B
C
Group
1
2
1
1
2
1
Liquid
Limit (%}
55
53
55
34
34
46
"
Plasticity
Index (%)
24
19
27
18
20
16
~
Optimum
w (%}
23
28
29
17
15
23
35
Maximum
YH (pcft
98
92
92
109
111
101
81
Note: 1 pcf = 0.157kN/m3
C-18
-------
-------
C/D
£
o
o
c
o
O
Molding Water Content (%)
o
Q.
0)
120
110
5 100
90
15
(B)
20
25
Molding Water Content (%)
Figure 2 Data from Mitchell et al. (1965) for a Silty Clay
Compacted with Impact Compaction. (A) Hydraulic
Conductivity vs. Molding Water Content, and (B)
Compaction Curve. Note: 1 pcf » 0.157 kN/m3.
C-20
-------
o
Q.
D)
120
110
100
90
Acceptable Zone J
10
15
20
25
Molding Water Content (%)
Figure 3 Compaction Data for a Silty Clay (from Mitchell et al.,
1965). Solid symbols represent specimens with a
hydraulic conductivity £ 1 x 1Q/7 cm/s and open symbols
represent specimens with a hydraulic conductivity > 1 x
10'7 cm/s.
C-21
-------
o
D)
'CD
Q
120
110
100
90
10
10-5
Mod.
Proctor
Curve
Acceptable Zone Based on
Typical Current Practice:
yd > 0.9 Tti.max and
w = 0 - 4% Wet of w0pt
15
20
25
Molding Water Content (%)
Figure 4 Contours of Constant Hydraulic Conductivity for a Silty Clay Compacted with Kneading
Compaction (Mitchell et al., 1965). Also shown is the modified Proctor compaction
curve and the Acceptable Zone as typically defined in current practice.
-------
o
Q.
CD
'0
130
120
110
100
90
80
Acceptable Zones
from Tradational
Design Approach
15
25
35
Molding Water Content (%)
Figure 5 Standard and Modified Proctor Compaction Curves for a
Highly Plastic Clay (Benson and Daniel, 1989). Solid
symbols represent compacted specimens with a hydraulic
conductivity <, 1 x 10'7 cm/s and open symbols represent
specimens with a hydraulic conductivity > 1 x 10'7 cm/s.
023
-------
>£>
CO
E
g>
'CD
Q
18
17
16
15
14
1 x 10-8 cm/s
Acceptable
Zone
Standard
Proctor
- 1 x 10-7 cm/s
i- 5x10-7 cm/s
200
0
10
20
30
Molding Water Content (%)
Figure 6 Contours of Constant Hydraulic Conductivity (cm/s) and Shear Strength (kPa) from
Boutwell and Hedges (1989). A standard Proctor compaction curve and the typical
Acceptable Zone based on current practice are also shown.
-------
r« *>* C^o n £±ti£» n*
»H £*.«"*«= l-l^<=ft<=ie.^
O)
"%
[>
'»-
O
5 '' (B)
C
o
O
o
"B
(0
Z± Modified Proctor
O Standard Proctor
Q Reduced Proctor
Maximum Allowed k
D)
'CD
c
Z)
Molding Water Content
(D)
D
Acceptable Zone
Modified to Account
for Other Factors
Molding Water Content
Figure 7 Recommended Design Procedure. (A) Determine Compaction Curves with Modified,
Standard, and Reduced Proctor Compactive Effort; (B) Determine Hydraulic Conductivity
of Compacted Specimens; (C) Replot Compaction Curves Using Solid Symbols for
Compacted Specimens with Hydraulic Conductivities < Maximum Allowable Value; and
(D) Modify Acceptable Zone Based on Other Considerations Such as Shear Strength or
-------
>
Overall Acceptable
Zone
Acceptable Zone
Based on Shear
Strength
Acceptable Zone
Based on Hydraulic
Conductivity
Molding Water Content
Figure 8 Use of Hydraulic Conductivity and Shear Strength Data to
Define a Single Acceptable Zone
C-26
-------
0
105
20
Molding Water Content (%)
East Borrow Area
Type A Soil
D Red. Proctor
O Std. Proctor
A Mod. Proctor
Figure 9 Compaction Curves for Type A Soil from the East Borrow
Area
C-27
-------
25 30 35
Molding Water Content (%
East Borrow Area
Type A Soil
D Red. Proctor
O Std. Proctor
A Mod. Proctor
40
Figure 10 Hydraulic Conductivity vs. Molding Water Content for Type
A Soil from the East Borrow Area
C-28
-------
.c
D)
1
Acceptable Zone
East Borrow Area
Type A Soil
D Red. Proctor
O Std. Proctor
A Mod. Proctor
Molding Water Content (%)
Figure 11 Compaction Data for Type A Soil from the East Borrow
Area. Solid symbols represent compacted specimens
with a hydraulic conductivity £ 1 x 10"7 cm/s and open
symbols represent specimens with a hydraulic
conductivity > 1 x 10'7 cm/s.
C-29
-------
110
o
CL
D)
100
90
80
Acceptable Zone
15
20
25
30
35
40
Molding Water Content (%)
Figure 12 Compaction Data for Type A Soil from Both Borrow Areas.
Solid symbols represent compacted specimens with a
hydraulic conductivity < 1 x 10'7 crn/s and open symbols
represent specimens with a hydraulic conductivity > 1 x
10'7 cm/s. Squares are for the west borrow area and
circles for the east borrow area.
C-30
-------
1 JU
& 120
*->
O)
| 110
c
>, 100
Q
nn
/
<
r
\
Y
/
-V
\
\
A
\
/
tf
^
i
N
\
s»
T3
^
^
7f
^*Ci
^/\,
^
>ro Air
jrve
\
^
Voids _
s.
X
0^
West Borrow Area
Type B Soil
D Red. Proctor
O Std. Proctor
A Mod. Proctor
10 15 20 25 30
Molding Water Content (%)
Figure 13 Compaction Curves for Type B Soil from the West Borrow
Area
C-31
-------
-3
10 15 20 25
Molding Water Content (%)
West Borrow Area
Type B Soil
D Red. Proctor
O Std. Proctor
A Mod. Proctor
Figure 14 Hydraulic Conductivity vs. Molding Water Content for Type
B Soil from the West Borrow Area
C-32
-------
O
CL
>
Acceptable Zone
10 15 20 25 30
Molding Water Content (%)
Figure 15 Compaction Data for Type B Soil from Both Borrow Areas.
Solid symbols represent compacted specimens with a
hydraulic conductivity £ 1 x 10'7 cm/s and open symbols
represent specimens with a hydraulic conductivity > 1 x
10-7 cm/s. Squares are for the west borrow area and
circles are for the east borrow area.
C-33
-------
o
Q.
CD
120
110
100
90
80
Type A Soil
10 15 20 25 30 35 40
Molding Water Content (%)
Figure 16 Acceptable Zones for Type A and Type B Soils
C-34
-------
o
Q.
140
~ 120
100
80
60
(A)
Voids
80%
S=40%
60%
10
20
30
40
Molding Water Content (%)
o
Q.
CD
140
~ 120
100
80
60
(B)
Line of Optimums
0 10 20 30 40
Molding Water Content (%).
Figure 17 Possibfe Approaches for Specifying Lower Limit of
Acceptable Zone: (A) Minimum Degree of Saturation (S), or
(B) Line of Optimums
C-35
-------
APPENDIX D
Information Pertaining to the Hydrologic Evaluation of
Landfill Performance (HELP) Model
1. Volume III - User's Guide for Version 2
2. Volume IV - Documentation for Version 2
3. Volume V - Verification of Version 2 Using Field Data
HELP Model User Letter
Evaluation of Landfill Liner Designs
R. Lee Peyton and Paul R. Schroeder
D-l
-------
Author's Draft 10/26/88
Do Not Cite Without Permission
THE HYDROLOGIC EVALUATION OF LANDFILL
PERFORMANCE (HELP) MODEL
Volume III. User's Guide for Version 2
by
P. R. Schroeder, R. L. Peyton, B. M. McEnroe, and J. W. Sjostrom
US Army Engineer Waterways Experiment Station
Vicksburg, MS 39181-0631
Interagency Agreement Number DW21931425-01-3
Project Officer
R. Landreth
Landfill Pollution Control Division
Hazardous Waste Engineering Research Laboratory
Cincinnati, OH 45268
HAZARDOUS WASTE ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
US ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OH 45268
OFFICE OF SOLID WASTE AND EMERGENCY RESPONSE
US ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, DC 20460
D-2
-------
Author's First Draft 10/21/33
Do Not Cite Without Permission
THE HYDROLOGIC EVALUATION OF LANDFILL
PERFORMANCE (HELP) MODEL
Volume IV. Documentation for Version 2
by
P. R. SchrOeder, B. M. McEnroe, R. L. Peyton, and J. W. Sjostrom
US Army Engineer Waterways Experiment Station
Vicksburg, MS 39181-0631
Interagency Agreement Number DW21931425-01-3
Project Officer
R. Landreth
Landfill Pollution Control Division
Hazardous Waste Engineering Research Laboratory
Cincinnati, OH 45268
HAZARDOUS WASTE ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
US ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OH 45268
OFFICE OF SOLID WASTE AND EMERGENCY RESPONSE
US ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, DC 20460
D-3
-------
Author's Draft 2/1/89
Do Not Cite Without Permission
THE HYDROLOGIC EVALUATION OF LANDFILL
PERFORMANCE (HELP) MODEL
Volume V. Verification of Version 2 Using Field Data
by
R. L. Peyton, and P. R. Schroeder
US Army Engineer Waterways Experiment Station
Vicksburg, MS 39181-0631
Interagency Agreement Number DW21931425-01-3
Project Officer
R. Landreth
Landfill Pollution Control Division
Hazardous Waste Engineering Research Laboratory
Cincinnati, OH 45268
HAZARDOUS WASTE ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
US ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OH 45268
OFFICE OF SOLID WASTE AND EMERGENCY RESPONSE
US ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, DC 20460
D-4
-------
Evaluation of Landfill Liner Designs
by R. Lee Peyton and Paul R. Schroeder, Members, ASCE
Abstract
The effectiveness of landfill liner designs are evaluated in terms of the
slope, drainage length, and saturated hydraulic conductivity of the lateral
drainage layer, the saturated hydraulic conductivity of the soil liner and the
fraction of the area under a synthetic liner where leakage is occurring. The
evaluation i& performed using Version 1 of the Hydrologic Evaluation of
Landfill Performance (HELP) model. The effectiveness is quantified by
comparing the lateral drainage rate to the vertical percolation rate expressed
as percentages of the total inflow. The two multiple liner systems specified
in the Hazardous and Solid Waste Amendments (HSWA) minimum technology guidance
are shown to have different leakage detection characteristics. One system
will detect significant leakage before leakage percolates out of the landfill,
whereas the other system will detect leakage only after significant leakage
percolates out of the landfill. Four other designs were also examinedtwo
with single liners and two with double liners. The two HSWA designs detected
leakage at lower synthetic liner leakage fractions, but all designs with
composite liners were nearly equally effective in reducing leakage from
landfills.
D-5
-------
DEPARTMENT OF THE ARMY
WATERWAYS EXPERIMENT STATION. CORPS OF ENGINEERS
3909 HALLS FERRY ROAD
VICKSBURG, MISSISSIPPI 39180-6199
REPLY TO
ATTENTION OF
Environmental Laboratory
Dear HELP Model User:
Version 2 of the Hydrologic Evaluation of Landfill Performance (HELP)
model is now being released in draft form to interested HELP model users.
The purpose of this release is to provide a thorough testing and review of
this new version before widespread release and final publication of its
documentation. This version has been undergoing testing, calibration and
verification since July, 1987 and has been thoroughly reviewed in-house.
However, it is impossible to examine the model throughout the range of
conditions that users may specify; therefore, any review comments that you
care to provide me would be appreciated as I prepare the final
documentation. The program has been used by a test group since February
1988, was revised in August 1988 based on the test group's findings and
comments and revised again in October 1988 based on results of comparisons
of model predictions with field results. I am presently conducting a
sensitivity analysis and revising the input to permit greater flexibility in
running the model on computers with multiple drives and to allow more input
of climatological data. I am also revising the set of default soil data and
the routines for computing leakage through flexible membrane liners, and
runoff from steeply sloped surfaces. If you encounter any problems or have
any suggestions for improving this version, please contact me at your
earliest convenience. Due to the additional work and revisions the final
documentation will not be available for release through NTIS until Fall, 1990.
The final documentation will be for Version 3.0 of the model which will be
released simultaneously. It will be necessary to update your version at that
time. Final documentation will contain a user's guide, engineering and
program documentation, verification with field data, and a sensitivity
analysis.
I am enclosing a copy of Version 2.05 of the Hydrologic Evaluation of
Landfill Performance (HELP) model and instructions describing how to run the
model on an IBM compatible personal computer. I have also included a brief
guide for users who are familiar with running HELP Version 1. The guide
highlights the major changes to Version 1 which have been incorporated into
Version 2. As mentioned above, a complete user's guide, documentation and
verification report is currently being finalized and work on the sensitivity
analysis is presently in progress.
For users inexperienced in running HELP Version 1, a user's guide and
a documentation report that support both the mainframe and PC versions of
Version 1 have been published by the USEPA; their respective numbers are
EPA/530-SW-84-009 and EPA/530-SW-84-010. These reports are available from
the National Technical Information Service (NTIS) and their NTIS accession
numbers are respectively PB85-100-840 and PB85-100-832. Orders from NTIS
may be placed by calling (703) 487-4650.
HYDRAULICS GEOTECHNICAL STRUCTURES ENVIRONMENTAL COASTAL ENGINEERING INFORMATION
LABORATORY LABORATORY LABORATORY LABORATORY RESEARCH CENTER TECHNOLOGY LABORATORY
D-6
-------
Two verification studies of the HELP model Version 1 have been
completed and published by the USEPA. The first is entitled "Verification
of the Lateral Drainage Component of the HELP Model Using Physical Models"
and has a document number of EPA 600/2-87-049. The second is entitled
"Verification of the HELP Model Using Field Data" and has a document number
of EPA 600/2-87-050. Their NTIS accession numbers are PB87-227104 and PB87-
227518, respectively.
If you have any problems running HELP Version 2 or have constructive
criticism and suggestions for consideration in Version 3, please contact me at
(601) 634-3709. Written comments on the model will be appreciated.
Sincerely,
Paul R. Schroeder, PhD, PE
Research Civil Engineer
Water Resources Engineering Group
Encl as
D-7
-------
Evaluation of Landfill Liner Designs
by R. Lee Peyton1 and Paul R. Schroeder2, Members, ASCE
INTRODUCTION
This paper examines the effectiveness of landfill liner desjlgns as
affected by the slope, drainage length, and saturated hydraulic conductivity
of the lateral drainage layer, by the saturated hydraulic conductivity of the
soil liner and by the fraction of the area of the synthetic liner (flexible
membrane liner or geomembrane) that leaks. Understanding the influence of
these variables on landfill performance is necessary to meet the Subtitle C
landfill design regulations of the Resource Conservation and Recovery Act
(RCRA) as amended by the Hazardous and Solid Waste Amendments (HSWA) of 1984
and the minimum technology guidance on double liner systems (Federal Register
1987; U.S. Environmental Protection Agency 1987; 1988).
These regulations require that RCRA landfills have double liners with a
leak detection system in between. The guidance indicates that double liner
systems should consist of (from top to bottom) a primary leachate collection
and removal system, a synthetic liner, a secondary leachate collection and
removal system, and a composite liner (synthetic liner plus low permeability
soil) or a thick, low permeability soil liner. The low permeability soil
liner should have an in-place saturated hydraulic conductivity not more than 1
x 10 cm/sec and a thickness of not less than 3 feet. The primary and
secondary leachate collection and removal systems should have at least a one-
1. Asst. Prof., Dept. of Civil Engr., Univ. of Missouri-Columbia, Columbia
MO 65211.
2. Research Civil Engr., Water Resources Engr. Group, U.S. Army Engineer
Waterways Experiment Station, Vicksburg, MS 39180.
D-8
-------
foot-thick, chemically-resistant drainage layer with a saturated hydraulic
conductivity not less than 1 x 10"2 cm/sec and a minimum bottom slope of 2
percent. The leachate collection and removal system must ensure that the
leachate depth does not exceed one foot.
This paper presents a quantitative analysis of these RCRA regulations and
compares these designs with possible alternatives shown in Fig. 1. In
evaluating the liner systems, two types of vertical inflows were considered.
First, an inflow rate of 50 in./yr (127 cm/yr) was used to represent unsteady
infiltration at an open landfill. This inflow was distributed in time
according to actual rainfall patterns at Shreveport, LA. Second, an inflow
rate of 8 in./yr (20 cm/yr) uniformly distributed in time was used to
represent steady-state infiltration at a covered landfill.
MATHEMATICAL DESCRIPTION
The numerical model used to evaluate the landfill design variables was
Version 1 of the Hydrologic Evaluation of Landfill Performance (HELP) model
(Schroeder et al. 1984a; 1984b). This model performs a sequential daily
analysis to determine runoff, evapotranspiration, percolation and lateral
drainage from the landfill and obtain daily, monthly, and annual water
balances. It is currently used by landfill designers and regulatory agencies
to document and evaluate design decisions. This model was recently tested
using available field data and found to reproduce measured results with
average percent errors that were considerably less than the variance in the
measured data for identical landfill cells (Peyton and Schroeder 1988).
The equation used to compute lateral drainage was derived by Skaggs
(1983) and modified by Schroeder et al. (1984b). As summarized here, the
equation is a steady-state linearized, approximation to the Boussinesq free-
surface drainage equation. The steady-state assumption is justified by
D-9
-------
selecting a sufficiently short time step so that there is little change in
head. The equation is
QD _ ic1i,1*. a)
where QD = lateral drainage rate per unit area of liner; C^ = correction
factor for linearized Boussinesq equation; KD = saturated hydraulic
conductivity of lateral drainage layer; y = average saturated depth above soil
liner (in.); hQ = head above drain at crest of drainage layer (in.); and L =
horizontal projection of the drainage length (in.). The correction factor,
Ci, is computed as follows:
Cl = 0.510 + 0.00205 ctL (2)
where a = slope of lateral drainage layer (ft/ft) and aL = product of slope
and drainage length (in.) and represents the height of the crest of the soil
liner above the drain. The head above the drain at the crest of the drainage
layer is computed as follows:
h = y + ccL (3)
where yQ = saturated depth above the liner at x = L (in.) and x = lateral
distance measured from drain (in.). The saturated depth above the soil liner
at x = L is approximated as,follows:
y0 =
This saturated depth becomes very small for steep slopes, small infiltration
rates, long drainage lengths and large KD. Fig. 2 depicts the lateral
drainage configuration.
D-10
-------
The equation used to compute the vertical percolation rate through the
soil liner is based on Darcy's law where flow through the soil liner is
assumed to be saturated and unrestricted by conditions below the liner. The
vertical percolation rate is computed as follows:
QP - (LF)(KP) y + T (5)
T
where QP = vertical percolation rate per unit area of liner; LF = leakage
fraction; KP = saturated hydraulic conductivity of soil liner; and T =
thickness of soil liner (in.). Eqs. 1 and 5 along with the continuity
equation are solved simultaneously to compute QD, QP and y.
Leakage fraction is defined as the fraction of the horizontal area of
soil through which percolation is occurring under the leaking synthetic liner.
The use of the leakage fraction in Eq. 5 has the same effect as adjusting the
hydraulic conductivity in Darcy's law to equal the product of the leakage
fraction and the saturated hydraulic conductivity of the soil (liner soil,
drainage media or native subsoil) underlying the synthetic liner. When no
synthetic liner is present, LF = 1.0.
SOIL LINERS
A single soil liner underlying a leachate collection system will first be
examined to demonstrate the influence of saturated hydraulic conductivity,
slope and drainage length on leachate collection efficiency. This design is
identical to Design A in Fig. 1.
Hydraulic Conductivities
The combinations of KD and KP values used in this analysis are listed in
Table 1 along with average annual volumes of lateral drainage and vertical
percolation expressed as a percentage of annual inflow. Values of KD ranged
D-ll
-------
from 10~3 to 1 cm/s while those of KP ranged from 10"8 to 10"5 cm/s. The
slope was 3 percent, and the drainage length was 75 ft"(23 m).
For the larger inflow of 50 in./yr (127 cm/yr), only eight out of sixteen
cases produced percolation volumes less than 5 percent of the inflow, all with
soil liner hydraulic conductivities of 10"' cm/s or less. Only the cases with
KP equal to 10 cm/s restricted percolation to less than 1 in./yr (2.5
cm/yr). For the smaller inflow of 8 in./yr (20 cm/yr), only the cases with KP
Q
equal to 10 cm/s produced a percolation volume less than 5 percent of the
inflow. These were the only cases which restricted percolation to less than 1
r\
in./yr (2.5 cm/yr). Using the RCRA minimum technology requirements (KD = 10
cm/s and KP = 10 cm/s) a percolation of 1.7 in./yr (4.3 cm/yr) resulted
for the larger inflow and 1.3 in./yr (3.3 cm/yr) for the smaller inflow.
Fig. 3 shows graphically how the hydraulic conductivities affected
lateral drainage and percolation. In particular, the curves for the smaller
inflow show that almost all inflow leaves as percolation at KP values of 10
cm/s and greater. The importance of achieving a KP value in the field equal
to or less than 10 cm/s is clearly shown in Fig. 3.
Similar effects are also seen in Figs. 4 and 5 which relate the KD/KP
ratio to the ratio of lateral drainage to percolation. The curves in Fig. 4
are log least squares regressions for several ranges of steady-state heads
resulting from a steady-state inflow of 8 in./yr (20 cm/yr), while the curves
in Fig. 5 are log least squares regressions for several ranges of peak y
resulting from a unsteady inflow of 50 in./yr (127 cm/yr). The plotted points
are QD/QP ratios for the given KD/KP ratio; their symbols indicate the value
of KD used in obtaining the result. The actual steady-state y and peak y
values, listed in Table 1, were both grouped into four ranges of heads. In
Fig. 4 steady-state heads ranging from 10.2 to 12.1 in. (26 to 31 cm) were
D-12
-------
grouped together as were heads ranging from 1.4 to 1.6 in. (3.6 to 4.1 cm),
equalling 0.2 in. (0.5 cm), and less than 0.05 in. (0.1 cm). In Fig. 5 peak
heads ranging from 2.4 to 2.5 in. (6.1 to 6.4 cm) were grouped together as
were heads ranging from 7.6 to 9.3 in. (19 to 24 cm), from 16.2 to 27.4 in.
(41 to 70 cm), and from 45.7 to 60.3 in. (116 to 153 cm). The figures show
that at ratios of KD/KP below 107, percolation tends to dominate as heads
decrease. When heads remain constant, the ratio of lateral drainage to
percolation is a linear function of KD/KP as can be seen by dividing Eq. 1 by
Eq. 6. When plotted on a log-log plot, the slope would equal 1.0 and the
intercept would be a function of the steady-state y. Using the maximum head
allowed by RCRA of 12 in. (30 cm) and the current minimum KD/KP ratio implied
by RCRA of 10 , a percolation of 2.37. of inflow results; the steady-state
inflow required to achieve this condition is 80 in./yr (200 cm/yr) or 0.22
in./day (0.56 cm/day).
Slope and Drainage Length
The combinations of slope and drainage length used in this analysis are
listed in Table 2 along with average annual volumes of lateral drainage and
percolation expressed as a percentage of annual inflow. The table also
contains the resulting maximum heads above the soil liner. The slope ranged
from 0.01 to 0.09 ft/ft (1 to 9 percent), while the drainage length ranged
from 25 to 225 ft (8 to 69 m). The hydraulic conductivities of the lateral
drainage layer and soil liner were 10"2 and 10"' cm/sec, respectively,
corresponding to the current RCRA minimum technology requirements for liner
systems. The product aL and the ratio L/a ranged from 0.25 to 6.25 ft. (0.1
to 1.9 m) and 280 to 22.500 ft (85 to 6858 m), respectively.
For a small infiltration rate, y is small. Therefore, h is approxi-
ma
tely equal to aL from Eq. 3. Using this approximation in Eq. 1,
-------
(QD/KD) (L/a)
where QD and KD have the same units and y and L are in inches. For the range
of a and L values examined in this study, variations in C^ and QD were small.
Therefore, y could be considered an approximately linear function of L/a as
well as (1/KD) for steady-state drainage. This linearity is shown in Fig. 6
using the simulation results in Table 2 for the 8-in./yr (20-cm/yr) steady-
state infiltration rate. A best-fit straight line is drawn through the
points. For the 50-in./yr (127-cm/yr) unsteady infiltration rate, the maximum
average head was also a function of L/a but the relationship was no longer
linear due to storage effects in the lateral drainage layer.
As the drainage length increases and the slope decreases, the lateral
drainage rate decreases. As a result, the head increases and is maintained at
greater depths for longer periods of time. Consequently, the percolation
increases as predicted by Eq. 5. Since percolation is a linear function of y
and y is a linear function of L/a (according to Eq. 6 when y is small),
percolation increases linearly with increases in L/a. This relationship is
plotted in Fig. 7 using the data in Table 2. Best-fit straight lines are
drawn through the points.
The term aL is a measure of head above the drain resulting from the
sloped soil liner. While an increase in head generally increases the lateral
drainage, an increase in aL resulting from an increase in drainage length does
not increase lateral drainage because lateral drainage is also a function of
ry
III. , as seen in Eq. 1. An increase in aL resulting from an increase in slope
does increase the lateral drainage. At constant values of aL, lateral
drainage decreases as the drainage length increases.
D-14
-------
SYNTHETIC LINERS
A single synthetic liner under a leachate collection system as shown in
Design B in Fig. 1 will next be examined. It is assumed that the synthetic
liner was laid directly on a 10-ft (3-m)-thick layer of native subsoil. This
case will be used to demonstrate the influence of the synthetic liner leakage
fraction and the saturated hydraulic conductivity of the native subsoil on the
liner system performance.
Relationship Between Holes and Leakage Fraction
Brown et al. (1987) conducted laboratory experiments and developed
predictive equations to quantify leakage rates through various size, holes in
synthetic liners over soil. They assumed a uniform vertical percolation rate
equal to the saturated hydraulic conductivity through a circular cross-
sectional area of the soil liner directly beneath the hole. They developed
predictive equations for the radius of this flow cross section as a function
of hole size, depth of leachate ponding, and saturated hydraulic conductivity
of the soil. They found that this radius of saturated flow was significantly
greater than the radius of the hole in the synthetic liner. In this paper,
the cross-sectional area of saturated flow was multiplied by the number of
holes per unit area of synthetic liner to compute the synthetic liner leak-
age fraction. Fig. 8 presents these results. This figure provides guidance
in choosing synthetic liner leakage fractions for landfill modeling given a
specific level of synthetic liner degradation such as number of openings per
unit area or average spacing between openings.
Effect of Leakage Fraction on System Performance
The percolation rate through a leaking synthetic liner is a linear func-
tion of the leakage fraction for a given subsoil when y is constant as shown
in Eq. 5. The percolation rate expressed as a percentage of inflow rate is
D-15
-------
shown graphically in Fig. 9 as a function of the leakage fraction. This
relationship is shown for a range of constant values of y and for a constant
inflow rate of 8 in./yr (20 cm/yr). Fig. 9 emphasizes the significant
influence of y on controlling the distribution of the inflow between vertical
percolation and lateral drainage. This figure shows that to maintain the
vertical percolation rate at less than 1 percent of the inflow rate for heads
greater than 0.1 in., the leakage fraction for a clay subsoil (KP = 10 cm/s)
must be less than 5 x 10 and for a sandy subsoil (KP = 10 cm/s) must be
less than 5 x 10" .
Eq. 5 can also be used to determine the effectiveness of a leaking
synthetic liner placed over a native subsoil in terms of the equivalent
saturated hydraulic conductivity (KPE) of a constructed soil liner. Equating
the vertical percolation rate in each case using Eq. 5 and solving for KPE
results in
TE T + y
KPE = (LF)(KP) ^T (7)
T TE + y
where T = thickness of the native subsoil and TE = thickness of the con-
structed soil liner. For instance, using Eq. 7 and Fig. 8, one would deter-
mine that a synthetic liner with eighteen 0.08-cm-diameter holes per acre over
a 10-ft (3-m)-thick native subsoil with KP = 3.4 x 10"^ cm/s and y = 0.33 ft
(10 cm) would achieve the effectiveness of a 3-ft (0.9-m)-thick soil liner
with a saturated hydraulic conductivity of about 1.1 x 10"7 cm/s. For very
small y, KPE is approximately equal to LF x KP and soil thickness is not a
significant factor in controlling vertical percolation.
Current regulations indicate that a soil liner should have a saturated
hydraulic conductivity not more than 1 x 10"7 cm/s, have a thickness of not
less than 3 feet, and maintain heads at depths less than 1 ft. However, soil
D-16
-------
liners that do not comply with these specifications, but are overlain by syn-
thetic liners, can limit vertical percolation to levels equivalent to the soil
liner specified in the minimum technology requirements. Fig. 10 shows maximum
allowable synthetic liner leakage fractions for a range of soil liners that
would make them equivalent in effectiveness to the soil liner specified in the
regulations, assuming a head of 1 foot.
MULTIPLE-LINER SYSTEMS
Four multiple-liner systems shown as Designs C through F in Fig. 1 are
examined in this section. These designs are presented here to illustrate the
strengths and weaknesses of various multiple-liner configurations and to show
why certain designs presented here should not be permitted. The designs are
evaluated for effectiveness in early leak detection and for minimization of
vertical percolation out of the landfill.
For this discussion it is assumed that the slope of the drainage layer is
3%, the drainage length is 75 ft (23 m), the saturated hydraulic conductivity
_ *y
of the drainage layer is 10 cm/s, and the saturated hydraulic conductivity
of the soil liner is 10 cm/s. In evaluating designs with double synthetic
liners, it was assumed that the degree of degradation of each synthetic liner
was identical. However, identical degradation would not yield identical
leakage fractions for both liners since they have different heads on the
liners and different subsoils. For Design E the leakage fraction of the lower
liner was increased by a factor of 8 to account for different subsoils, but
this corrected leakage fraction was then reduced by a factor ranging from 1 to
24 to account for different heads. For Design F the leakage fraction of the
lower liner was reduced by a factor between 8 and 24, varying as a function of
the differences between the heads on the two liners. Larger reduction factors
D-17
-------
were used for smaller leakage fractions in both designs. The leakage fraction
used for the top synthetic liner is used for reporting'the results.
Designs C through F were evaluated using the HELP model which predicted
lateral drainage in each drainage layer and vertical percolation through each
synthetic liner and each soil liner. These predictions were based on 8 in./yr
(20 cm/yr) of infiltration passing through the waste layer and reaching the
primary leachate collection system. This inflow was distributed uniformly in
time. Figs. 11 and 12 show the results in terms of lateral drainage from the
secondary drainage layer and vertical percolation through the bottom soil
liner as functions of synthetic liner leakage fraction of the top membrane.
Design C consists of a primary leachate drainage layer underlain by a
synthetic liner, a secondary drainage layer and a soil liner. As shown in
Fig. 11, this design is not very effective. Large quantities of leakage
occurred at fairly low leakage fractions and no leakage (lateral drainage) was
detected from the secondary drainage layer until the synthetic liner leakage
fraction exceeded about 10" . At smaller synthetic liner leakage fractions,
the leachate percolated vertically through the soil liner as fast as the
leakage through the synthetic liner occurred. The product of the saturated
hydraulic conductivity of the secondary drainage layer times the synthetic
liner leakage fraction must be greater than or approximately equal to the
saturated hydraulic conductivity of the soil liner before leakage will be
detected using this design. At the time leakage is detected, the vertical
percolation rate through the soil liner could be about 16% of total inflow.
Design D consists of a primary drainage layer underlain by a synthetic
liner, a soil liner, a secondary drainage layer and a second soil liner. The
soil liner immediately below the synthetic liner is very effective in
minimizing vertical percolation (leakage through the primary liner); however,
D-18
-------
a synthetic liner leakage fraction greater than 10 to 10 would be required
before leachate would be collected from the secondary drainage layer. Because
the vertical percolation through the first liner is so small, practically all
of the leakage is removed by vertical percolation through the bottom soil
liner as shown in Fig. 12. This design is ineffective since the~leakage
detection system would not function.
Design E consists of a primary drainage layer underlain by a synthetic
liner, a secondary drainage layer, a second synthetic liner and a soil liner.
In this case, any leakage through the upper synthetic liner will readily pass
through the underlying drainage medium to the lower synthetic liner. Since
the lower synthetic liner is underlain by a soil liner, most leakage will be
collected by lateral drainage. Fig. 11 shows that leakage will be detected
far in advance of significant vertical percolation from the landfill. That
is, the leakage fraction of the synthetic liners at which leakage detection
will occur is several orders of magnitude smaller than the leakage fraction at
which significant vertical percolation from the landfill will occur. The
leakage lost by percolation is virtually the same as for Design D but detec-
tion is much better. This design is effective at minimizing leakage from the
landfill and at detecting leakage through the primary liner but significant
leakage through the primary liner may occur at fairly low liner leakage
fractions.
Design F consists of a primary drainage layer underlain by a synthetic
liner, a soil liner, a secondary drainage layer, a second synthetic liner and
a second soil liner. Fig. 12 shows that the addition of the lower synthetic
liner improves the system performance in comparison to the performance of
Design D. Leakage is detected whenever leakage occurs. Even at leakage frac-
tions of 10"3 when only 0.027. of the inflow leaks through the primary liner,
D-19
-------
half of the leakage is collected in the secondary drainage layer. The depth
of saturation in the secondary drainage layer is lower "than in the primary
layer. This sufficiently reduces the leakage through the second synthetic
liner to permit detection whenever the primary liner leaks. Design F is a
very effective double liner design because it minimizes the leakage through
the primary liner and from the landfill and collects leakage at all leakage
fractions.
A comparison of the four designs shows that Design F is the most effec-
tive in detecting the earliest leaks with the least amount of vertical leakage
through the primary liner and also through the bottom soil liner. Design D
yields the same quantity of leakage through the primary liner; however,
leakage in Design D would probably never be detected or collected. Therefore,
the bottom liner in Design D is not functional. Designs D and E yield the
same leakage through the bottom liner but Design E detects leakage through the
primary liner at the lowest leakage fraction. Design C also detects leaks at
very small leakage fractions but allows significant vertical percolation
through the bottom soil liner before detection. The leakage through the
primary liner in Designs C and E is large even at low leakage fractions.
Therefore, synthetic membranes placed on highly permeable subsoils are
ineffective except for very low inflows and for very low leakage fractions.
Synthetic membranes are best used in conjunction with a low-permeability
soil as a composite liner. Comparison of the results for Designs B and C
demonstrates this point. Both designs are composed of one synthetic membrane
and one soil liner, but the leakage from the composite liner (Design B) shown
in Fig. 9 as the curve for 8 in./yr steady inflow is much lower than the
leakage from the double liner system (Design C) as shown in Fig. 11.
It is interesting to compare the single-liner performance of Design B to
D-20
-------
the double liner performance of Design D, assuming the soil liner saturated
hydraulic conductivity in Design B is the same as Design D. The vertical
percolation leaving the system in Design B is essentially the same as that
leaving the secondary liner in Design D as seen by comparing Fig. 12 to the
curve in Fig. 9 for 8 in./yr steady inflow. The secondary liner in design D
is nonfunctional since the percolation rate of the second soil liner is
generally equal to or greater than the leakage rate.
CONCLUSIONS
The objective in soil liner design is to maximize the ratio of lateral
drainage to vertical percolation, QD/QP, to reduce vertical percolation to
acceptable levels. The ratio QD/QP is a linear function of KD/KP when y, a, L
and T are constant. The ratio QD/QP is an inverse linear function of L/ot when
y is small and y, T, KD and KP are constant. Therefore, the design objectives
can be met by maximizing KD/KP and minimizing L/a. The minimum KD and maximum
KP allowed by RCRA can result in a significant percentage of total inflow
percolating through the soil liner when y is small (that is, when inflow rates
are small). This will occur since QD/QP decreases with decreasing y (or
inflow rates) when other design variables remain constant.
The synthetic liner leakage fraction is a function of hole size, depth of
leachate ponding and saturated hydraulic conductivity of the underlying soil.
The leakage fraction can be up to six orders of magnitude greater than the
fraction of the synthetic liner which is occupied by holes. A leaking synthe-
tic liner over native subsoil could provide protection against vertical perco-
lation equivalent to a soil liner several feet thick with a saturated hydrau-
lic conductivity of 10"' cm/s. For very low heads, the vertical percolation
rate through soil liners or composite liners (soil liner plus leaking synthe-
tic liner) is not sensitive to the soil liner thickness.
D-21
-------
The two multiple-liner systems specified in RCRA guidelines (Designs C
and E in Fig. 1) have different leakage detection characteristics. Design E
is preferable of the two but Design F, composed of two composite liners, is
the most effective system. For this design, leakage detection and collection
occurs whenever the primary liner leaks. This is not the case for Designs C
and D where vertical percolation will occur at synthetic liner leakage
fractions smaller than the leakage fraction at which leakage detection will
occur. These two designs are ineffective. Systems with composite liners
allowed less leakage to escape from the landfill than systems composed of just
synthetic liners or soil liners. Design F with two composite liners yielded
the lowest leakage from the landfill.
ACKNOWLEDGMENTS
The evaluations described and the results presented herein, unless other-
wise noted, were obtained from research conducted under sponsorship of the
Risk Reduction Engineering Laboratory of the U.S. Environmental Protection
Agency by the Environmental Laboratory of the U.S. Army Engineer Waterways
Experiment Station. Permission was granted by the Chief of Engineers to
publish this information.
APPENDIX. REFERENCES
Brown, K.W., Thomas, J.C., Lytton, R.L., Jayawickrama, P., and Bahrt, S.C.
(1987). "Quantification of leak rates through holes in landfill liners."
EPA/600/S2-87-062, U.S. EPA, Ofc. of Research and Development, Cincinnati,
OH.
Federal Register. (1987). "Draft minimum technology guidance documents for
single and double liner systems." Vol. 52, No. 74, April 17, 1987.
D-22
-------
Peyton, R.L. and Schroeder, P.R. (1988). "Field verification of HELP model
for landfills." J. Envir. Engrg., ASCE, 114 (2), 247-269.
Schroeder, P.R., Morgan, J.M., Walski, T.M., and Gibson, A.C. (1984a). "The
hydrologic evaluation of landfill performance (HELP) model." Vol. I.
User's Guide for Version 1. EPA/530-SW-84-009, U.S. EPA, Ofc. of Solid
Waste and Emergency Response, Washington, D.C.
Schroeder; P.R., Gibson, A.C., and Smolen, M.D. (1984b). "The hydrologic
evaluation of landfill performance (HELP) model." Vol. II. Documentation
for Version I. EPA/530-SW-84-010, U.S. EPA, Ofc. of Solid Waste and
Emergency Response, Washington, D.C.
Skaggs, R.W. 1983. "Modification to DRAINMOD to consider drainage from and
seepage through a landfill." Draft Report, U.S. EPA, Municipal Environ-
mental Research Laboratory, Ofc. of Research and Development, Cincinnati, OH.
U.S. Environmental Protection Agency. 1987. "Draft minimum technology
guidance on double liner systems for landfills and surface impoundments
design, construction, and operation." EPA/530-SW-87-014, May 24, 1985, U.S.
EPA, Ofc. of Solid Waste, Washington, D.C.
U.S. Environmental Protection Agency. 1988. "Guide to technical resources
for the design of land disposal facilities." EPA/625/6-88/018, December
1988, U.S. EPA, Risk Reduction Engineering Laboratory and Center for
Environmental Research Information, Cincinnati, OH.
APPENDIX II. NOTATION
The following symbols are used in this paper:
QD = lateral drainage rate per unit area of liner
C-i = correction factor for lateral drainage rate
KD = saturated hydraulic conductivity of lateral drainage layer
D-23
-------
y average saturated depth above liner (in.)
hQ » head above drain at crest of drainage layer (in.)
L « drainage length (in.)
a » dimensionless slope of lateral drainage layer
y0 ** saturated depth at crest of drainage layer (in.)
QP = vertical percolation rate per unit area of liner
LF «= synthetic liner leakage fraction
KP = saturated hydraulic conductivity of soil liner
T - thickness of soil liner (in.)
KPE = equivalent saturated hydraulic conductivity for leaking synthetic liner
TE ** soil liner thickness of comparisons with synthetic liners
D-24
-------
TABLE 1. Sensitivity of Lateral Drainage and Liner Percolation
to Hydraulic Conductivity
n ^
Avg. Annual Volume
(7. Inflow)
Annual^"'
Infilt. KD(2) KP(3)
(in.
50
50
50
50
50
50
50
50
50
50
50
50
50
50
50
50
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
(1)
) (cm/sec)
10"°
10-0
io-°
10"°
10'1
ID'1
lO'1
lO'1
ID'2
10"2
10"2
ID'2
io-3
io-3
_ "5
10 I
io-3
io-°
10"0
io"0
10"0
io-1
io-1
io-1
io-1
ID'2
1C'2
IO-2
lO-2
1C'3
ID'3
io-3
ID'3
Value of 50 in.
(cm/sec)
ID'5
10"6
io-7
ID'8
ID'5
10"6
ID'7
io-8
io-5
10"6
ID'7
10"8
10"5
10"6
_ 7
10 I
10"8
1C'5
10"6
io-7
10"8
ID'5
io-6
io-7
10"8
ID'5
io-6
ID'7
10"8
ID"5
1C"6
1C'7
10"8
KD
KP
IO5
IO6
IO7
IO8
IO4
IO5
IO6
IO7
IO3
IO4
IO5
IO6
IO2
IO3
/,
IO4
IO5
IO5
IO6
IO7
IO8
IO4
IO5
IO6
IO7
IO3
IO4
IO5
IO6
IO2
IO3
IO4
IO5
Lat.<4>
Drng.
60.13
92.22
99.03
99.89
31.32
82.92
97.72
99.75
7.59
68.31
96.62
99.66
0.89
47.45
93.33
99.32
5.63
37.17
85.47
98.46
0.59
5.65
84.41
98.44
0.06
0.59
83.63
98.35
0.01
0.06
78.01
97.68
/yr represents inflow through an
temporal distribution is
LA. Value of 8
based on
in./yr represents
temporal distribution is
(2)
(3)
(4)
(5)
KD - hydraulic
KP - hydraulic
uniform
Liner<5)
Perc.
39.87
7.78
0.97
0.11
68.68
17.08
2.28
0.25
92.41
31.69
3.38
0.34
99.11
52.55
6.67
0.68
94.37
62.83
14.53
1.54
99.41
94.35
15.59
1.56
99.94
99.41
16.37
1.65
99.99
99.94
21.99
2.32
Max.
Head
in L"f -
Drng.
(in
2.
2.
2.
2.
7.
9.
9.
9.
16.
25.
27.
27.
20.
45.
58.
60.
-------
TABLE 2. Sensitivity of Lateral Drainage and Liner Percolation to
Lateral Drainage Slope and Length
Avg. Annual Vol.
t 1 \
Annual u'
Infilt.
(in.)
50
50
50
50
50
50
50
50
8
8
8
8
8
8
8
8
(7. Inflow)
Slope
a
(ft/ft)
0.01
0.01
0.01
0.03
0.03
0.03
0.09
0.09
0.01
0.01
0.01
0.03
0.03
0.03
0.09
0.09
Length
L
(ft)
25
75
225
25
75
225
25
75
25
75
225
25
75
225
25
75
aL
(ft)
.25
.75
2.25
.75
2.25
6.75
2.25
6.75
.25
.75
2.25
.75
2.25
6.75
2.25
6.75
L/a
(ft)
2500
7500
22500
830
2500
7500
280
830
2500
7500
22500
830
2500
7500
280
830
Lat.<2>
Drng.
96.71
95.89
93.43
96.85
96.36
95.10
97.37
96.87
83.73
82.29
78.51
84.16
83.59
82.28
84.35
84.23
Liner'3'-
Perc.
3.29
4.11
6.57
3.15
3.64
4.90
2.63
3.13
16.27
17.71
21.49
15.84
16.41
17.72
15.65
15.77
Max. Head
in Lat.
Drng. Layer
(in.)
13.8
29.7
58.2
12.3
24.8
42.3
8.5
16.2
1.2
3.4
9.4
0.5
1.1
3.5
0.2
0.4
(1) Value of 50 in./yr represents inflow through an open landfill; the
temporal distribution is based on rainfall records for Shreveport, LA.
Value of 8 in./yr represents inflow through landfill cover; the
temporal distribution is uniform throughout the year.
(2) Lateral drainage from a layer having a slope of 37,, drainage length of
75 ft, porosity of 0.351 vol/vol, field capacity of 0.174 vol/vol, and
a saturated hydraulic conductivity of 10 cm/sec.
(3) Percolation through a 24-in.-thick soil liner having a saturated
hydraulic conductivity of 10 cm/sec.
D-26
-------
FIGURE CAPTIONS
FIG. 1. Liner Designs
FIG. 2. Lateral Drainage Definition Sketch
FIG. 3. Effect of Saturated Hydraulic Conductivity on Lateral Drainage and
Percolation
FIG. 4. Effect of Ratio of Drainage Layer Saturated Hydraulic Conductivity to
Soil Liner Saturated Hydraulic Conductivity on Ratio of Lateral Drainage to
Percolation for a Steady-state (SS) Inflow of 8 in./yr
FIG. 5. Effect of Ratio of Drainage Layer Saturated Hydraulic Conductivity to
Soil Liner Saturated Hydraulic Conductivity on Ratio of Lateral Drainage to
Percolation for an Unsteady Inflow of 50 in./yr
FIG. 6. Effect of Ratio of Drainage Length to Drainage Layer Slope on the
Average Saturated Depth in Drainage Layer (KD = 10 cm/s) Above a Soil Lit
(KP = 10 cm/s) Under a Steady-state Inflow Rate of 8 in./yr
FIG. 7. Effect of Ratio of Drainage Length^to Drainage Layer Slope on
Percolation Tl
(KD = 10 cm/s)
Percolation Through a Soil Liner (KP = 10 cm/s) Beneath a Drainage Layer
FIG. 8. Synthetic Liner Leakage Fraction as a Function of Density of Holes,
Size of Holes, Head on the Liner and Saturated Hydraulic Conductivity of the
Liner
FIG. 9. Effect of Leakage Fraction on System Performance
FIG. 10. Composite Liner Design Equivalent to Minimum Design Guidance for a
RCRA Soil Liner
FIG. 11. Percent of Inflow to Primary Leachate Collection Layer Discharging
from Leakage Detection Layer and Bottom Liner for Double Liner Systems C and E
FIG. 12. Percent of Inflow to Primary Leachate Collection Layer Discharging
from Leakage Detection Layer and Bottom Liner for Double Liner Systems D and F
INFORMATION RETRIEVAL ABSTRACT
The effectiveness of landfill liner designs are evaluated in terms of the
slope, drainage length, and saturated hydraulic conductivity of the lateral
drainage layer, the saturated hydraulic conductivity of the soil liner and the
fraction of the area under a synthetic liner where leakage is occurring. The
evaluation is performed using the Hydrologic Evaluation of Landfill
D-27
-------
Performance (HELP) model. The effectiveness is quantified by comparing the
lateral drainage rate to the vertical percolation rate expressed as
percentages of the total inflow. The two multiple-liner systems specified in
RCRA guidelines are shown to have different leakage detection characteristics.
One system will detect significant leakage before leakage percolates out of
the landfill, whereas the other system will detect leakage only after
significant leakage percolates out of the landfill. Four other designs were
also examined--two with single liners and two with double liners. A system
with two composite liners was the most effective for reducing leakage,
detecting leakage and minimizing migration of leachate from the landfill.
All designs with composite liners were nearly equally effective in reducing
leakage from landfills.
KEYWORDS
Landfills, liners, liner leakage, leachate collection
REPRINT SALES SUMMARY
Landfill liner designs are examined to determine the effects of slope,
drainage length, saturated hydraulic conductivity of the lateral drainage
layer, saturated hydraulic conductivity of the liner and leakage fraction of
the synthetic liner.
D-28
-------
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DESIGN B
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D-29
-------
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r * KD - 0.001 cm/s
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O.OOI cm/s
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9 In.
24 in.
55 In.
102 103 104 10E
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6
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10
8
KD/KP
-------
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(3
10
10'
10
,0
10
-1
10
-2
5O In./yr Inflow
' t
-------
7
w
U1
Q.
a
\
a
a
8 ln./yr SS Inflow
KD - 0.001 cm/s
O KD - 0.01 cm/s
fe- n KD - 0.1 cm/s
O KD = 1 cm/s
SS y < O.1 in
SS y - O.2 In
~ 1.5 In
SS y s 11 In.
X x-
1O
1O
1O
-4
10
KD/KP
-------
o
en
LU
to
a:
ac
LLI
>
a:
10 15
L/a (1000 ft)
25
-------
w
-J
O 8 In./yr RLL SLOPES
o 50 In./yr SLOPE - 0.0!
O 50 In./yr SLOPE - 0.03
*
o
OL
C9
0
o:
LU
a.
L/a (1000 ft)
-------
7
u>
CO
CD
i_
O
cr
CD
CL
CO
CD
c
c
CD
CL
a
CD
105
104
f Upper bound is for 0.08-cm-dia,
Lower bound is for 1.27-cm-dia
101
10°
10
,-1
open ings.
openings.
KP = 3.4 x 10
KP = 3.4 x 10
10
20
50
100
CO
CD
C
c
CD
CL
a
c
CO
CD
CD
m
CD
c
u
a
a.
en
200 CD
E
1_
o
500 ^1
10-
10'5
10'
,-4
10"'
10
,-2
10-1
10°
Synthetic Liner Leakage Fraction. LF
-------
100
i /c: N°/
-------
7
o
C
O
o
a
CD
CD
a
_^
a
CD
CO
c
O
+j
CD
JI
-*-»
C
CD
Soil Liner Thickness
1 ft
2 ft
10 ft
10-7
10
r6
10
KP Ccm/s)
-------
100
80
- 60
40
eo
0
o
H-
c
o
QP
GD
;/
,
I
^ Design E
Design C
Design C
Design E
10
-7
10
-6
10
-5
10
"4
10
~3
10
"2
10
"1
10
°
Synthetic Liner Leakage Fraction. LF
-------
o
o
V
*-
NJ
O
**-
c
CD
16
14
12
10
8
6
4
2
0
QP
QD
Design D/,
xx^ Design F
Design D
0.01
0.10
1.00
Synthetic Liner Leakage Fraction. LF
------- |