PB86-208733
Avoiding Failure of Leachste
Collection and Cap Drainage Systems
Little (Arthur D.)r Inc., Cambridge, K
Prepared for
Environmental Protection Agency. Cincinnati, OH
Jun 86
I II
; . a
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EPA/600/2-86/058
June 1986
AVOIDING FAILURE OF LEACHATE COLLECTION AND CAP DRAINAGE SYSTEMS
by
Jeffrey Bass
Arthur D. Little, Inc.
Cambridge, MA 02140
Contract No. 68-03-1822
Project Officer
Jonathan Herrmann
Land Pollution Control Division
Hazardous Waste Enginee- ing Research Laboratory
Cincinnati, OH 45268
HAZARDOUS WASTE ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI. OH 45268
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TECHNICAL REPORT DATA
fflease reed Instructions on the reverse before completing}
1. REPORT NO.
EPA/600/2-86/058
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Avoiding Failure of Leachate Collection and
Cap Drainage Systems
5. REPORT DATE
June 1986
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Jeffrey M. Bass
8. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Arthur D. Little, Inc. '"'
Cambridge, MA 02140
10. PROGRAM ELEMENT NO.
BRD1A
1 1. CONTBACT/GflANT NO.
68-03-1822
12. SPONSORING AGENCY NAME AND ADDRESS
Hazardous Waste Engineering Research Laboratory
u. S. Environmental Protection Agency
Cincinnati, OH 45268'
13. TYPE OF REPORT AND PEF.IOO COVERED
September
14. SPONSORING AGENCY CODE
EPA/600/14
IS. SUPPLEMENTARY NOTES
Project Officer: Jonathan G. Herrmann (513)569-7.839
16. ABSTRACT
aUSe Van'^ty °f mechanisms> Is com, to drainage systems of all
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lOENTIFIEflS/OPEN ENDED TERMS C. COSATI Field/Croup
8. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS fThis Rtporll
21. NO. OF PACES
142
20. SECURITY
Unclassified
22. PRICE
EPA Form 2230-1 (Rov. 4-77) . PKKvioui BDITION i* OMOIETE
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DISCLAIMER
The information in this document has been funded wholly or in
part by the United States Environmental Protection Agency under
Contract 68-03-1822 to Arthur D. Little, Inc. It has been subject to
the Agency's peer and administrative review and it has been approved
for publication as an EPA document. Mention of trade names or
commercial products does not constitute endorsement or recommendation
for use.
ii
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FOREWORD
Today's rapidly developing and changing technologies and
industrial products and practices frequently .carry with them the
increased generation of solid and hazardous wastes. These materials,
if improperly dealt with, can threaten both public health and the
environment. Abandoned waste sites and accident?! rp.Vases of toxic
and hazardous substances to che environment also have important
environmental and public health implications. The Hazardous Waste
Engineering Research Laboratory assists in providing an authoritative
and defensible engineering basis for assessing and solving these
problems. Its products support the policies, programs and regulations
of the Environmental Protection Agency, the permitting and other
responsibilities of state and loc,-il governments and the needs of both
large and small businesses in handling their wastes reponsibly and
economically.
This doument provides information on the design, construction,
inspection, maintenance and repair of leachate collection and cap
drainage systems to avoid systems failure. The intended audience for
this document includes those involved in the review of new and
existing hazardous waste facilities. For further information, please.
contact the Land Pollution Control Division of the Hazardous Waste
Engineering Research Laboratory.
Thomas R. Hauser, Director
Hazardous Waste Engineering Research Laboratory
ill
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ABSTRACT
Failure, caused by a variety of mechanisms, is common to drainage
systems of all kinds. Leachate collection and cap damage systems,
which remove excess liquid from hazardous waste land disposal
facilities, are no exception. Failure of these systems, however, may
be a greater cause for concern than failure, for example, of
agricultural drainage systems. This is especially true for leachate
collection systems at hazardous waste disposal facilities. Undetected
failures may cause leachate to build up on top of the liner. This can
lead to failure of the 15.ner system and contamination of groundwater.
Furthermore, failures which are detected may be difficult to repair,
and replacement is no longer a simple last' resort since excavation of
hazardous wastes would be required. Information is prf.'erted in this
document on those mechanisims which may cause leachate collection and
cap drainage system failure. Furthermore, information o:» design,
construction, inspection, and maintenance for these systems is
presented in order to minimize the potential of failure. Techniques
to repair a failed system are also described.
This report was submitted in fulfillment of Contract Number
68-03-1822 under the sponsorship of the U.S. Environmental Proteccion
Agency. This report covers the period from September, 1983 to
November, 1985, and work was completed as of January, 1986.
iv
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CONTENTS
Foreword iii
Abstract iv
Figures vii
Tables ix
Acknowledgements xi
1.0 Introduct i.on 1
1.1 Leachate Generation and Control 1
1.2 Applicable Federal Regulations 3
1.3 Minimum Technology Guidance . . . .' 7
2.0 Failure Mechanisms 10
2.1 Discussion Of Potential Mechanisms 10
2.1.1 Clogging Mechanisms .10
2.1.2 Non-Clogging Mechanisms 12
2.2 Confirmation Of Mechanisms 12
2.2.1 Confirmation by Experience .13
2.2.2 Confirmation by First Principles 17
3.0 Design 21
3.1 Introduction .21
3.2 System Layout 21
3.2.1 Leachate Collection System 21
3.2.2 Cap Drainage System 26
3.3 General Design Considerations 28
3.3.1 Material Selection 28
3.3.2 Control of Leachate Characteristics 34
3.4 Drainage Layer 36
3.4.1 Material Selection 36
3.4.2 Design Considerations 36
3.5 Collection Pipe Network 39
3.5.1 Capacity 39
3.5.2 Structural Stability 41
3.5.3 Perforations 46
3.6 Filter Layer 47
3.6.1 Granular Filters 49
3.6.2 Geotextile Filters , 53
3.7 Other Components 54 .
3.7.1 Sumps 54
3.7.2 Pumps 56
3.7.3 Discharge Lines 56
3.7.4 Manholes 57
3.7.5 Liquid-Level Monitors 57
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CONTENTS (continued)
4.0 Construction 58
4.1 Introduction 56
4.2 Plans and Specifications 58
4.2.1 Detail .- 58
4.2.2 Specific Plans : 59
4.2.3 Phased Development 60
4.2.4 Material 60
4.2.5 Installation Procedures 61
4. 3 Construction Quality Assurance Plan 63
4.3.1 Elements of a CQA Plan 63
4.3.2 Inspection Activities 64
5.0 Inspection 69
5 .1 Introduction. . 69
5. 2 Regular or Periodic Inspections. 70
5.2.1 Visual Inspection 72
5.2.2 Loachate Level Over Liner 75
5.2.3 Leachate Quantity 79
5.2.4 Leachate Quality 83
5.2.5 Tslevision and Photographic Inspection 87
5.2.6 Inspection During Pipe Maintenance 89
5 . 3 Special Inspections 89
5.3.1 After Construction; 92
5.3.2 After First Lift Has Been Placed 92
5.3.3 When Problems Are Identified With
System Performance . 92
6.0 Maintenance 96
6.1 Introduction 96
6.2 Mechanical Methods 97
6.2.1 Rodding/Cable Machines 97
6.2.2 Buckets 101
6.3 Hydraulic Methods 103
6.3.1 Jetting 103
6.3.2 Flushing 105
7.0 Repair 109
7.1 Introduction. 109
7.2 Maintenance Techniques 110
7.3 Chemical Techniques Ill
. 7.4 Replacement Techniques 114
7.4.1 Conventional Systems 116
7.4.2 Alternative Systems.. 118
References . 123
Copyright Notice 129
vi
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FIGURES
dumber Page
1 Schematic of a closed landfill cell. . . . .' 2
2 Leachate collection system layout providing alternative
paths of leachate flow 23
3 Leachate collection system layouts providing access
to collection pipes 25
4 Schematic of a landfill cap 27
5 Landfill geometry assumed for calculating maximum
height of leachate over the liner 40
. 6 Collection pipe installation in a trench 42
7 Collection pipe installation above liner 43
8 Schematic of granular and geotextile filters 48
9 Potential design options for collection or transport
of fines 50
10 Particle-size distribution curve. 51
11 Typical sump designs 55
12 Checklist for visual and leachate level inspections 74
13 Probable leachate levels before and after clogging
at observation points under varying flow conditions 76
14 Analysis of leachate prediction models 82
15 Checklist for television or photographic inspjction 90
16 Checklist for maintenance-related inspection 91
vii
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FIGURES (continued)
lumber Page
17 Checklist for collection pipe maintenance 98
18 Power redding machine 99
19 Typical attachments for rodding and cable machines 100
20 Schematic of bucket machine cleaning 102
21 Nozzle designs for high-pressure cleaning 104
22 Sewer ball 106
23 The hinged-disc cleaner (or "scooter") 107
24 Toe drain design 120
viii
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TttBLES
Number
1 Summary of Westat Data, for Leachate Collection Systems . ft
2 Failurf Mechanisms 11
3 Confirmation 'of Failure Mechanisms 1ft
ft Experience with Leachate Collection Systems 15
5 Summary by Facility Type 16
6 Summary by Cause 16
7 Potential for Clogging of Leachate Collection Systems
Relative to Agricultural Drains 18
8 Maximum Leachate Levels Given Various Design Assumptions 24
9 Organic and Inorganics Which May Be Present in Waste
Leachates 29
10 Chemical Resistance of Polypropylene Versus Polyester 32
11 Chemical Resistance of Cast Iron, Stainless Steel,
Bronze, and Monel 33
12 Properties of Typical Geotextile Drainage Materials 37
13 Design Equations for Calculating Vertical Loading
Stresses on Flexible Pipe Used in Landfill Drainage
Systems ;.-..- ftft
I/! Particle-Size Requirements for Filters 52
10 CQA Test Procedures 66
16 Summary of Inspection Methods.. . 71
17 Annual Leachate Predictions and Monthly Mean Error
Compared to Actual Leachate Production 81
ix
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TABLES (continued)
Number
18 Jiagnosing Problems ' 9'*
19 Quantities of S0_ and Water for Treatment of Various
Sizes of Tile Drains '. 113
20 The Solubility of Iron and Manganese Tile Deposits
in Various Chemiccl Reagents 115
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ACKNOWLEDGEMENTS '
Arthur D. Little, Inc. (ADL) prepared this document for EPA's
Hazardous Waste Engineering Research Laboratory under Contract No.
68-03-1822. Jonathan Herramann was the EPA Project Officer. Input to
Sections 3 and 4 of the document was provided by the E. C. Jordan
Company of Portland, Maine, under subcontract to ADL. Principal
.technical contributors to the report were Jeffrey Bass (Project
Manager), Patricia Deese, John Ehrenfeld, Mildred Broome and Kate
Findland for ADL, and Douglas Allen, Dirk Brunner, Guy Cote, Mark
Larochelle, Matthew Muzzy and Kenneth Whittaker for E. C. Jordan.
Peer review comments on'the draft report were provided by Peter
Kraet of the Washington Department of Ecology, Jean-Pierre Giroud of
Geoservices, Inc., and Fred Erdmann of Soil & Material Engineers, Inc.
Their comments, along with those of the' Project Officer, were
extremely useful in preparing the final report.
xi
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1.0 INTRODUCTION
This document summarizes current knowledge and experience regarding
potential failure mechanisms and presents information on factors to consider
in design, construction, inspection, maintenance and repair o£ leachate
collection and cap drainage systems. It was written to provide general
guidance to design engineers, facility operators, and state and Federal
regulatory officials. It should not be considered as a comprehensive design
and operation manual for leachate collection' and cap drainage systems.
Detailed design and operation plans for leachate collection and cap drainage
systems at a specific facility should be prepared by a qualified design
engineer based on site-specific conditions.
Emphasis is placed throughout the document on avoiding failure of
leachate collection systems at .hazardous 'waste facilities. Most of the
information presented for leachate collection systems can also be applied to
cap drainage systems, since the basic components of the two systems are
similar. Failure of cap drainage systems, however, is less critical than
failure of leachate collection systems since the cap drainage system is
accessible and therefore can be more readily maintained or repaired. Cap
drainage systems are discussed separately in this document only when the
information presented is significantly different from the discussion of
leachate collection systems. The mechanisms by which drainage systems can
fail and experience with these mechanisms in leachate collection systems are
discussed in Section 2. Sections 3 through 6 describes the design,
construction, inspection and maintenance of these systems to avoid failure.
Repair of failed systems is discussed in Section 7.
A schematic of a closed- landfill cell, showing the leachate collection
system and the cap drainage system, is presented in Figure 1. The basic
components of the leachate collection system shown are the drainage layer, the
collection pipe and the filter layer. Other important components include
manholes, cleanout risers, sumps, monitoring equipment and pumps. The
function of these components is described in Section 3. The basic components
of a cap drainage system are the drainage layer, filter layer and perimeter
collection pipes. The cap drainage system collects liquid from over the cap
liner which is designed to prevent liquid from infiltrating the waste.
1.1 LEACHATE GENERATION AND CONTROL
Leachate is defined as "any liquid, including any suspended components in
the liquid, that has percolated through or drained from hazardous waste" (40
CFR 260.10). Leachate results from the seepage of liquid wastes (or liquids
contained in primarily solid wastes) placed in the facility. Leachate is also
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Gas Vent
(if needed) Vegetation
Filter Layer
Cap Drainage
System
Barrier Layer
(FMU
Protective Soil or Covei
(Optional)
S^^S^i^liSS:
" .* ^* &.*"''*> " ' o, o '*"* "* */*\'«' . ' !» '"OJf
-^VfT'" .' _ ' ^> . a 1 . " ^-*» r i ..''. ti*. X
I I KUIUIIlTTIi I Illll lil I I III I
System
Leak Detection
System
Lower Component
(compacted soil)
Bottom
Composite
Ltner
Figure 1. Schematic of a closed landfill cell.
(Source: after EPA, 1985 a )
(Not to Scale)
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generated when water contacts the waste mass and becomes contaminated with
waste constituents.
Leachate quality depends on the amount of precipitation, type of leachate
collection system, types of wastes, time and location of waste placement, and
site operating methods. In general, leachate qua1ity is difficult to predict,
and may vary considerably from site to site and among different locations in
the same facility. Factors affecting leachate quality are discussed in
Shuckrow et al. (1982), and information on leachate quality from a number of
facilities is presented in Ghassemi et al.(1983).
The quantity of leachate generated at a .facility is determined by the
water (or liquid) balance at the site. Liquid inputs include liquids in the
deposited waste and precipitation. Groundwater flow may also contribute to
leachate quantity in facilities constructed in the saturated zone (depending
on liner design). Liquid outputs include evaporation, transpiration, and
seepage out of the facility. Water storage in the. waste mass is also
important; the leachate quantity increases as the waste mass reaches
saturation. Leachate generation can be minimized by controlling the various
parameters in the water balance. The water balance for a facility is
discussed in detail in Lutton et al. (1979), and techniques for estimating
leachate volume are discussed in Perrier and Gibson (1982).
Low permeability soil and flexible membrane liners are installed to
contain waste and leachate and to prevent the contamination of groundwater and
surface water near the disposal facility. High leachate levels increase the
potential for seepage through a liner system. Leachate collection systems are
used to control leachate levels over the liner and thereby reduce the
potential for leachate migration. Leachate collection systems that meet
current regulatory requirements are designed to maintain liquid levels over
the liner at less than 30 cm (1 ft). The system is intended to function
effectively through the facility's active life and closure period and until
leachate generation has ceased.
Experience with leachate collection systems is limited. The first
leachate collection systems were installed in landfills in the early 1970s.
Since then, design and operating practices have changed significantly. As a
result, experience with "modern" leachate collection system design performance
is even more limited. According to the WESTAT data base (EPA, 1983a),
approximately 40 percent of the 200 landfills which accept hazardous waste
have leachate collection systems. A summary of the WESTAT data pertaining to
leachate collection systems is given in Table 1.
1.2 APPLICABLE FEDERAL REGULATIONS
Regulations promulgated under the Resource Conservation and Recovery Act
(RCRA) require the use of leachate collection systems for new landfills and
waste piles which dispose of hazardous wastes. Regulations which apply to
leachate collection and cap drainage systems, or directly apply to the water
balance at the site, include (40 CFR 264.301-.310):
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TABLE 1
SUMMARY OF WESTAT DATA FOR LEACHATE COLLECTION SYSTEMS
Question
Active Landfill
Leachate Collection System (LCS)
-yes
-no
LCS has gravel
LCS has sand
LCS has geotextile
LCS has pipe
LCS has sumps
one
two
three
four
six
seven
LCS has sump pumps
LCS has intermediate storage
in tanks
in surface impoundments
in containers
other method
Ons ite leachate treatment
Surveyed
Number
79
31
48
23
12
5
27
25
14
4
1
2
2
1
20
21
8
10
1
3
20
Landfills
Percent
100
39.2
60.8
74.2
38.7
16.1
87 , 1
80.6
58.3
16.7
4.2
8.3
8.3
4.2
64.5
67.7
38.1
47.6
4.8
14.3
66.7
Estimate of
all Landfills
Number
199
78
121
58
30
12
67
62
36
10
3
5
5
3
50
54
20
25
2
8
48
(continued)
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TABLE 1 (continued)
Question
Surveyed Landfills
Number Percent
Estimate of
all Landfills
Number
Year LCS Installed
1973
1975
1976
1977
1978
1979
1980
1981
1982
1
2
3
2
3
3
6
5
5
3.3
6.7
10.0
6.7
10.0
10.0
20.0
16.7
16.7
2
5
7
5
7
7
15
12
12
Total Cost of Materials per LCS
maximum $1,470,000
median $ 200,000
minimum $ 15,000
Quantity Leachate Collection in 1981
maximum
median
minimum
5,550,000 gal.
22,500 gal
0 gal
Source: EPA, 1983a
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264.301 Design and operating requirements.
(a) A landfill (except for an existing portion of a landfill) must have:
(1) A liner that is designed, constructed, and installed to prevent
any migration of wastes out of the landfill to the adjacent
subsurface soil or groundwater or surface water at any time
during the active life (including the closure period) of the
landfill. The liner must be constructed of materials that
prevent wastes from passing into the liner during the active
life of the facility.
(2) A leachate collection and removal systum immediately above the
liner that is designed, constructed, naintained, and operated
to collect and remove leachate from the landfill. The Regional
Administrator will specify design and operating conditions in
the permit to ensure that the leachate depth over the liner
does not exceed 30 cm (one foot). The leachate collection and
removal system must be:
(i) Constructed of materials that are:
(A) Chemically resistant to the waste managed in the
landfill and the leachate expected to be generated;
and
(B) Of sufficient strength and th.ickness to prevent
collapse under the pressures exerted by overlying
wastes, waste cover materials, and by any equipment
used at the landfill; and
(ii) Designed and operated to function without clogging through
the scheduled closure of the landfill.
(c) The owner or operator must design, construct, operate, and maintain
a runon control system capable of preventing flow onto the active
portion of the landfill during peak discharge from at least a
25-year storm.
(e) Collection and holding facilities (e.g., tanks or basins) associated
with runon and runoff control systems must be emptied or otherwise
managed expeditiously after storms to maintain design capacity of
the system.
264.302 Double-lined landfills.
(3) A leak detection system must be designed, constructed,
maintained, and operated between the liners to detect any
migration of liquid into the space between the liners.
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264.303 Monitoring and inspection.
(b) While a landfill is in operation, it must be inspected weekly and
after storms to detect evidence of any of the following:
(1) Deterioration, malfunctions, or improper operation of runon and
runoff control systems;
(2) The presence of liquids in leak cei.ection systems, where
installed to comply with 264.302;
(4) The presence of leachate in and proper, functioning of leachate
collection and removal systems, where present.
264.310 Closure and post-closure care.
(a) At final closure of the landfill or upon closure of any cell, the
owner or operator must cover the landfill or cell with a final cover
designed and constructed to:
(1) Provide long-term minimization of migration of liquids through
the closed landfill;
(3) Promote drainage and minimize erosion or abrasion of the cover;
(b) After final closure, the owner must:
(1) Maintain the integrity and effectiveness of the final cover,
including making repairs to the cap as necessary to correct the
effects of settling, subsidence, erosion, or other events.;
(2) Maintain and monitor the leak detection system in accordance
wi ;h 264.302, where such a system is present between double
liner sys tarns;
(3) Continue to operate the leachate collection and removal system
until leachate is no longer detected;
(4) Maintain and monitor the groundwater monitoring system.
1.3 MINIMUM TECHNOLOGY GUIDANCE
EPA (1985a) provides technical guidance on how to meet the double liner
standards set forth in the Hazardous and Solid Waste Amendments of 1984.
Specific guidance on leachate collection system design includes:
A granular drainage layer should be at least 3p cm (12 in.) thick
with a minimum hydraulic conductivity of 1x10 cm/s and a minimum
bottom slope of 2 percent.
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Synthetic drainage layers may be used if they are equivalent to the
granular design, including chemical compatibility, flow under load,
and protection of the FML.
The drainage layer should include a pipe network which is designed
to efficiently collect leachate. The pipe and drainage layer
materials should be chemJoally resistant to the waste and leachate.
The pipe should also be strong enough to withstand expected loading.
A filter layer (granular or synthetic) should be used above the
drainage layer to prevent clogging.
The leachate collection system should cover the bottom and sidewalls
of the unit.
Specific guidance on leachate collection system construction includes:
Granular drainage and filter material should be washed prior to
installation to remove fines.
A written construction quality assurance plan should be followed
during construction of the leachate collection system.
Construction documentation should be kent onsite.
Specific guidance on leachate collection system operation includes:
Tho leachate cemoval system should be capable of continuous and
automatic functioning, and should operate automatically whenever
leachate is present in the sump. The sump should remove accumulated
leachats at the earliest practicable time to minimize leachate head
on the liner.
Tne system should be inspected weekly and after major storms, and
records should be kept to provide sufficient information that the
system is functional and operated properly. Weekly recording of the
quantity of leachate collected is recommended.
Collection pipes in the drainage layer should be cleaned out
periodically.
In addition, the guidance for flexible membrane liners (FMLs) states:
FMLs in landfill units, and in units with the minimum recommended
thickness, should be protected from damage from above and below the
membrane by at least 30 centimeters (12 inches) nominal, 25 centimeters
(10 inches) minimum, bedding material (no coarser than Unified Soil
Classification System (SCS) sand (SP) with 100 percent of the washed,
rounded sand passing the 1/4-inch sieve) that is free of rock, fractured
stone, debris, cobbles, rubbish, and roots, unless it is known that the
FML material is not physically impaired by the material under load (EPA,
1985a).
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This guidance may affect leachate collection system design since a
maximum particle size over a liner is specified. A geotextile between the
liner and drainage layer which is demonstinted to provide adequate protection
to the liner would be needed if larger particle sizes are used for the
drainage layer.
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2.0 FAILURE MECHANISMS
Leachate collection and cap drainage systems can fail or clog due to a
variety of physical, chemical, biological, and biochemical mechanisms (Table
2). These mechanisms are discussed in detail in Young, et a_l. (1982) and Bass
et al. (1984). Some of the most common failure mechanisms are those which
lead to system clogging. Clogging is defined as the physical buildup of
material in the collection pipe, drainage layer, or filter layer to the extent
that leachate flow is significantly restricted. Other failure mechanisms
which do not involve clogging include differential settling and deterioration
of the collection pipe because of chemical attack or corrosion. Failure may
also occur because the design capacity is exceeded. . In this case liquid is
not adequately removed from the system, even though system components may not
be physically blocked.
2.1 DISCUSSION OF POTENTIAL MECHANISMS
2.1.1 Clogging Mechanisms
Clogging can be caused by the buildup of soil, biological organisms,
chemical (and biochemical) precipitates, or combinations of the three. This
buildup can occur either in the collection pipe or in the surrounding drainage
or filter layers. Soil clogging (sedimentation or siltation) requires both a
source of soil? and a mechanism by which they can settle out. Surrounding
soils can enter the drainage or filter layers if the particle size in these
layers is too large. Alternatively, soil from the drainage and filter layers
will enter the collection pipe if the particle-size distribution is too small,
or the pipe slot-size is too large. After soils have entered the pipe they
can settle out if the flow is insufficient to keep them suspended. Low flow
rates can occur throughout the pipe if the slope is too small, or locally in
areas of hydraulic perturbations such as poorly designed or installed pipe
joints, turns, or intersections. Sedimentation of soils in the collection
pipe is one of the most widely recognized clogging mechanisms.
Biological clogging occurs when organism growth fills the collection pipe
or interstices of the drainage or filter layers and interferes with normal
system flow. Biological growth is dependent on the presence of
micro-organisms together with the appropriate nutrients, growth conditions and
energy sources. In particular, Vitreoscilla. a filamentous slime-forming
organism, and Pseudomonas. a common soil bacteria, are known clogging agents
when iron is not pres.».it. Enterobacter is also known to contribute to
clogging of the area abutting the drain in agricultural systems (Young et al.,
1982). Factors thought to influence biological clogging include carbon-
to-nitrogen ratio in the leachate, rate of nutrient supply, the concentration
10
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TABLE 2
FAILURE MECHANISMS
Mechanism
Description
Sedimentation
Biological growth
Chemical Precipitation
BiocViemtcal Precipitation
Pipe Breakage
Pipe Separation
Pipe Deterioration
Other non-clogging problems
build-up of solid materials in pipe,
drain layer or filter layer. Also,
siltation or soil clogging.
build-up of biological materials in
the pipe, drain layer or filter layer.
build-up'of chemical materials in the
pipe, drain layer or filter layer due
to chemical reactions.
build-up of chemical or chemical and
biological material in the pipe,
drain layer or filter layer due to
biological activity.
collapse of pipe due to overburden or
equipment loading which allows
entrance of surrounding materials.
two adjacent sections of pipe are
pulled apart because of overburden or
equipment loading or problems with
the joint.
pipe material is weakened or
destroyed by chemical attack,
oxidation or corrosion, causing
failure as with pipe breakage, above.
includes failure of system
components, such as pumps or tanks,
and exceeding system or component
design capacity.
11
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of polyuronides, teiaperature, and soil moisture (Avnimelech and Nevo, 1964;
Kristiar.sen, J.981).
Chemical precipitation can occur as the result of siaple chemical
processes or more complex biochemical processes. Chemical processes include
the precij 'tation of calcium carbonate, manganese carbonate (rlmdochrosite)
and other insoluble forms (such as, sulfides and silicates). Chemical
precipitates can form when the pH exceeds 5, and are also dependent on the
hardness and total alkalinity of the leac.hate. Precipitation can be caused by
the presence of oxygen, changes in pH, changes in pressure or partial pressure
of CO-, or evaporation of res.'dual liquid.
The principal biochemical precipitates are Fe(OH), and FeS, although
manganese compounds may also be involved. The biochemical process for iron
depends primarily on the availability of dissolved (free) ions (influenced by
recox potential, pH, and cornelexing agents) and on the presence of
iron-reducing bacteria. The precipx-ate is generally mixed with a biological
slime, creating a product which is quite adherent and vhlch can very rapidly
block flow through a drainage system. The precipitates produced as a result
of biochemical activity are gewrally quite different in form or structure
from those resulting from chemical processes alone, and may be more effective
in leading to clogging. Chemically precipitated iron, for example, does not
adhere to plastic pipe as readily and is more porous than biochemically
precipitated iron (Ford, 1980).
2.1.2 Non-Clogging Mechanisms
Design capacity can be exceeded if 'the system or a component of Uhe
system is so undersized that the amount of liquid to be removed is greater
than the amount which can be handled by the system. Underestimation of
maximum design flow can be the result of j design error, an unanticipated
event which causes flows in excess of design limits (such as failure of run-on
diversion structures), or a condition which was inadequately accounted for in
the original design (such as groundwater inflow). Differential settling can
cause insufficient or inconsistent slope and displacerent or crushing of
collection pipes and can result in the buildup of leachate in localized areas.
Problems with slope or pipe displacement and crushing can also be a result of
errors in design or construction. Finally, deterioration of construction
materials can be caused by chemical attack (acids, solvents, oxidizing agents)
or corrosion.
2.2 CONFIRMATION OF MECHANISMS
Much of the above discussion is based on experiences with agricultural
drainage systems which do not handle hazardous leachates. Confirmation
testing was therefore conducted to verify that the failure mechanisms
described above are indeed possible for hazardous waste leachate collection
systems. Cap drainage systems are not addressed because they do not handle
hazardous leachate.
A three-step approach was utilized to confirm the failure mechanisms:
12
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Step 1: Crnfirmation by experience;
Step 2: v .ifirmation by first principles;
Step 3: Jonfirmation by laboratory investigation.
The first step, confirmation by experience, is the oroferred method since
it gives positive proof that the mechanism can occur. For example, disposal
of waste in the wrong cell caused collection pipe deterioration in a leachate
collection system at a hazardous waste landfill. The mechanism, collection
pipe deterioration, is confirmed by the fact that it has already happened.
The second step, confirmation by first principles, confirms by
mathematical and scientific principles, and by common sense rationale, those
failure mechanisms which have not yet been experienced. For example, a
bulldozer driving over a weak collection pipe, is likely to crush the pipe,
whether experience with pipe crushing can be found at a land disposal facility
or not. Design, construction, and operation of leachate collection systems
must address the possibility of pipe crushing based on an understanding of
mechanical principles. In addition, first principles are used to determine
whether experience with leachate collection systems at facilities which 4o not
dispose of hazardous wastes i.: applicable to hazardous waste facilities.
Mechanisms vhich can be demonstrated to be obviously possible independent of
actual experience at a hazardous waste facility are considered to be confirmed
by first principles.
Finally, mechanisms which were not adequately confirmed by experience or
first principles were considered candidates for laboratory investigation.
Conclusions from laboratory testing of biochemical precipitation, however,
were inconclusive and iiid noi. affect the confirmation testing resulLs.
The conclusions made from the three-step confirmation testing process
conducted as part of this study are summarized in Table 3. These results
indicate that all the failure mechanisms must be considered in the design,
construction and operation of leachate collection systems. Special attention
should be given to the seven mechanisms which are confirmed or strongly
suspected. Consideration must also be given to the prevention of biochemical
precipitation since the mechanism is still considered a possibility. The
confirmation testing process is described in more detail below.
2.2.1 Confirmation bv Experience
Experience with leachate collection system failure mechanisms is
summarized in Tables U, 5 and 6. These tables are based on interviews
conducted by Arthur D. Little in late 1983 and on a review of the literature.
The interviews included 16 individuals from companies or agencies which
design, construct, operate, and/or regulate landfills which have leachate
collection systems.
The purpose of the interviews was to determine whether the failure
mechanisms discussed above have indeed occurred in the field, not to provide a
statistical basis for determining service life or quantifying the potential
for failure of leachate collection systems. Information was based on the
13
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TABLE 3
CONFIRMATION OF FAILURE MECHANISMS
Mecha;.ism
Sedimentation
Biological
precipitation
Chemical
precipitation
Biochemical
precipitation
Pipe breakage
Pipe separation
Pipe deterioration
Other non- clogging
problems
Experience
strong
moderate
weak-moderate
weak
moderate
moderate
confirmed
confirmed
First
Principles
strong
moderate
moderate -
strong
moderate
strong
strong
-
Laboratory Conclusion*
Confirmed
Strongly
suspected
Strongly
suspected
weak Suspected
Confirmed
Confirmed
Confirmed
Confirmed
*A mechanism is
confirmed if it has occurred at a hazardous waste facility, or if
experience at other facilities is considered to be directly applicable,
based on first principles.
strongly suspected if experience at other facilities is not directly
applicable, but first principles indicate the mechanism can occur in
hazardous waste facilities.
suspected if experience and first principles are inconclusive, but the
mechanism cannot be ruled out at hazardous waste facilities.
14
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TABLE 4 '
EXPERIENCE WITH LEACHATE COLLECTION SYSTEM
Failure Mechanism
Sedimentation
Sedimentation
Sedimentation
Sedimentation
Sedimentation
Sedimentation
Biological growth
Biological growth
Biological growth
Biological growth
Chemical
precipitation
Chemical
precipitation
Chemical
precipitation
Biochemical
precipitiitiou
Pipe breakage
Pipe breakage
Pipe separation
Pipe deterioration
Pipe deterioration
Tank failure
Capacity exceeded
Capacity exceeded
Outlet inadequate
Facility
Type
NS
NS
co-disposal
co-disposal
municipal
NS
industrial
municipal
municipal
co-disposal
municipal
co-disposal
co-disposal
co-disposal
NS
municipal
municipal
NS
hazardous
co-disposal
co-disposal
hazardous
co-disposal
Cause
C
U
U
U
ij
r.
D
I)
U
U
0
U
0
U
0
D
C
D
0
D
D
0
D
Comments
no filter installed
general experience
in 1 .year old system
of gravel layer and pipe
general, experience
general experience
100 ft. long biological growth
flushed out under high pressure
reduction in flow every 2 years;
flushed out
of filter fabric
on 3/4 inch stone, not clogged
EPA test cell, not clogged
iron oxide, not clogged
attributed to waste
characteristics
in leachate collection wells
by clean-out equipment if
bends greater than 22°,
general experience
differential settling,
improper bedding
joints not glued
problems with ABS pipe,
general experience
from acid or solvent
disposed of in wrong cell
leachate holding tank
under-design, other problems
noted
periodic rather than
automatic pumping of sump
caused leachate buildup
NS = not specified; 0 = operation related; D -- design related;
C * construction related; U = undetermined.
15
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TABLE 5
SUMMARY BY FACILITY TYPE
Facility Type
Mechanism Municipal
Sedimentation 1
Biological growth 2
Chemical precipitation 1
Biochemical precipitation
Pipe breakage 1
Pipe separation 1
Pipe deterioration
Other non-clogging
problems
TOTAL 6
Co-disposal/
Industrial Hazardous
>.
2
2
1
-
-
1
3 1
10 . 2
Not
Specified Total
3 6
4
3
1
1 2
1
1 2
4
5 23
TABLE 6
SUMMARY BY CAUSE
Design related
Construction related
Operation related
Unknown
6
3
5
9
16
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experience of the individuals interviewed. Information which is based on
general experience is noted in the comments oJ: Table 4.
Based on an analysis of Tables 4, 5, and 6 the following preliminary
conclusions and observations can be made regarding the failure mechanisms:
Exceeding design capacity was confirmed by experience at a hazardous
waste landfill. Failure occurred when an operator failed to activate the
sump pump, allowing leachate to back up in the facility. This uype of
failure would not occur if an automatic sump pump were used, provided the
pump was turned on and properly maintained.
« Collection-pipe deterioration was confirmed by experience at a hazardous
waste landfill. Failure occurred when an operator disposed of a waste
which was incompatible with the materials of construction of the leachate
collection system. This type of failure could occur with any type of
leachate collection system, regardless of design.
There is strong evidence that sedimentation is a problem at all types of
leachate collection systems. Two of the six sedimentation mechanisms
noted in Table 4 were based on general experience where the facility type
was not specified. This experience may include hazardous waste leachate
collection systems.
In addition to the problem of exceeding design capacity, other
non-clogging problems noted include tank failure and inadequate outlet
design capacity. These problems are independent of the type of waste
handled by the facility and independent of operational practices.
» Biological growth was a problem at four sites which did not exclusively
dispose of hazardous waste. Three of the four sites handled municipal
waste (one as co-disposal). Confirmation by first principles is needed
to demonstrate that biological growth may be a problem in sites which
exclusively dispose of hazardous wastes.
While chemical precipitation was noted at three sites, two of these did
not involve system clogging. As with biological growth, the potential
for chemical precipitation in a hazardous waste environment should be
demonstrated.
Biochemical precipitation was noted in only one site where leachate
collection wells rather than a more conventional leachate collection
system were utilized.
2.2.2 Confirmation by First Principles
Confirmation by first principles is based on the analysis conducted by
Bass et al. (1984). The conclusions of this analysis are summarized in Table
7. Bass et al. (1984) utilized failure mode analysis to examine drainage-
system failure mechanisms and to determine the conditions needed for the
mechanisms to occur. The conditions expected to be present at agricultural
drainage systems, sanitary landfill leachate collection systems, and hazardous
17
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TABLE 7
POTENTIAL FOR CLOGGING OF LEACHATE COLLECTION SYSTEMS
RELATIVE TO AGRICULTURAL DRAINS
Mechanism
Hazardous
Agricultural Sanitary Waste Significant
Drains Landfills Landfills Differences
Sedimentation
Chemical (CaCO.)
Biochemical
(Ochre, Fe)
Biological
Differential
Settling.
Crushing
Deterioration
Exceed Design
Capacity
*
*
*
*
More careful design
and construction
expected
Lower pH expected
Toxicity to indige-
nous bacteria,
lower pH
Toxicity to indige-
nous bacteria,
lower pH
Compaction, greater
equipment loading
Chemicals, solvents,
lower pH
Daily cover
restricts leachate
flow to system
- - less likely
+ - more likely
* - same likelihood as agricultural drains
Source: Bass e_t al.. 1984.
18
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waste landfill leachate collection systems were then compared to estimate the
relative potential for system failure.
A similar approach is used in the present study to relate experience at
municipal, co-disposal and industrial facilities, as well as experience which
is not facility specific, to expected conditions at hazardous waste
facilities. Mechanisms which were found to be active in other facilities, due
to design, construction or operational conditions that may also be found at
hazardous waste facilities, are considered to-be possible at hazardous waste
facilities.
Table 4 gives six examples of sedimentation problems at leachate
collection systems, two of which are based on general experience. The cause
.of sedimentation is generally difficult to determine, although in two cases
construction problems were cited. The construction problems were of the type
that could occur at any facility; sedimentation in one case was due to a
construction error and in the other case related to construction techniques
which allow surface sediments to wash into open excavations. Any leachate
collection system will need to be designed, constructed and operated to avoid
clogging with sediments.
Biological growth was noted at four sites--two municipal, one co-disposal
and one industrial facility. The industrial site was a paper mill sludge
disposal facility with a leachate collection system designed with a- 0% slope.
The lack of flushing action in the pipe may have been a factor in the
formation of the 30 m (100 ft) long biological mass which packed the leachate
collection pipe. This case is particularly interesting because of the degree
of clogging experienced, and because it is the only one of the four cases of
biological clogging noted where municipal refuse was not present. Research
conducted by Kobayashi and Rittmann (1982) indicates that micro-organisms can
be used to biodegrade a wide variety of hazardous organic compounds.
Furthermore, Ghassemi et al. (1983) found that organic and inorganic
constituents identified in 30 different leachates from eleven hazardous waste
landfills fall within the reported ranges for municipal landfill leachates.
While data on microbiological populations in actual hazardous waste leachates
are limited, the above observations indicate that micro-organisms are expected
to be active in hazardous waste leachate collection systems. Given the range
of micro-organisms found in the environment'and in waste materials, and given
the range of conditions which can be expected in various leachate collection
systems, it would be difficult to rule out biological clogging as a failure
mechanism based on first principles.
Chemical precipitation was found at one municipal and two co-disposal
sites. In two of these cases, the chemical precipitate coated only portions
of the drainage layer, causing the gravel to be cemented together in one case,
but in neither case was leachate flow significantly restricted. Chemical
precipitation involves relatively simple chemical reactions. Since chemicals
which can form precipitates, including Ca, Fe, Mn and Mg, are relatively
common leachate constituents (Ghassemi et al., 1983), chemical precipitation
would be expected to occur in some hazardous waste leachate collection systems
just as it has occurred at municipal and co-disposal facilities. However, the
19
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ability of the precipitates to actually clog a leachate collection pipe,
drainage layer or filter layer has not been demonstrated.
Experience with biochemical precipitation in leachate collection systems
is extremely limited. In addition, the conditions needed for biochemical
precipitation to occur are more complex than those needed for chemical
precipitation or biological growth alone. Biochemical precipitation of iron,
however, is a common and serious problem in certain agricultural drainage
systems (Ford, 1980), and the range of conditions expected in hazardous waste
leachate collection systems does not rule out this mechanism in every case.
Breakage of collection pipe (due to operational problems (improper use of
clean-out equipment) and design problems (differential settling, improper
bedding, pipe bends)), was noted in two cases in Table 4. Collection pipes
can also be damaged by equipment loading during construction and during
placement of the first lift of waste. To avoid damaging collection pipes,
leachate collection system design and operation may include:
placement of collection pipes in trenches;
careful attention to pipe bedding and material
selection; and
establishment of specific traffic patterns to keep heavy
equipment off all collection pipes.
In addition, collection pipes may be physically inspected after construction
and after the first lift of waste is placed to make sure that the pipe has not
been damaged or broken.
Experience found with separation of collection pipe is limited to a
single instance at a municipal landfill. In this case, a contractor neglected
to glue the pipe joints as specified in the design. The problem was
discovered during a preliminary inspection and was corrected prior to
placement of the first lift of waste. Construction errors are independent of
facility type, and are a function of the level of construction quality
assurance used.
Deterioration of collection pipe and exceeding of design capacity were
confirmed by experience at hazardous waste landfills. Experience with other
non-clogging mechanisms includes failure of a leachate holding tank because of
inadequate design, and high leachate levels due to insufficient outlet
capacity. Both of these mechanisms, as well as a second case of exceeded
capacity, occurred at co-disposal facilities which accept municipal,
industrial and/or hazardous wastes. The failure mechanism in each case,
however, is independent of waste type, and could have occurred at a hazardous
waste facility.
20
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.3.0 DESIGN
3.1 INTRODUCTION
Beginning July 26, 1982, RCRA regulations for hazardous waste treatment,
storage, and disposal facilities (40 CFR Part 264) required the use of leachate
collection systems in new, or new portions of, waste piles and landfills. The
leachate collection system is designed to collect and remove leachate above the
primary liner throughout the lifetime of the facility. in addition, Lutton
(1979) recommends the use of drainage layers in cap or final cover systems for
disposal units to collect and remove infiltrating precipitation. This
eliminates additional liquid inputs to the waste mass during the facility's
closure and post-closure care period.
Regulatory requirements for leachate collection and cap drainage systems
in hazardous waste disposal facilities are presented in Section 1.2. Design
guidance for leachate collection systems based on the Hazardous and Solid Waste
Amendments of 1984 is summarized in Section 1.3.
The basic cc-iiponent of a leachate collection or cap drainage system is the
drainage layer. The drainage layer generally consists of 30 cm (1 ft) or more
of granular soil containing a network of perforated pipe, but may also be made
of synthetic materials (i.e., geotextila). The Minimum Technology Guidance
(EPA, 1985a) recommends that the drainage layer cover the entire liner, have a
hydraulic conductivity of 10 cm/s or more, and have a minimum slope of 2
percent. A granular or synthetic (geotextile) filter layer is generally placed
between the drainage layer and the waste (or topsoil for a cap) to keep small
particle-size soils and other materials from clogging the drainage layer.
Other components of these systems include sumps, punips, access structures, and
monitoring and control devices.
This Section addresses the design considerations important in preventing
failure of leachate collection and cap drainage systems. General guidance on
leachate collection system design can be found in EPA (1983b).
3.2 SYSTEM LAYOUT
Layout or configuration of leachate collection and cap drainage systems
varies from site to site depending on factors such as the type of waste
material being deposited, site topography, facility size, climatic conditions,
design preference and regulatory requirements.
3.2.1 Leachate Collection System
The leachate collection system is designed to facilitate leachate flow
over the liner and out of the system. Leachate flows out of the waste and
through the drainage layer to a collection point (sump) where it is pumped out
21
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of the containment area for treatment. Layout of the system should provide
alternative paths for leachate to flow to the collection point, should allow
for access to the drainage layer and collection sump for inspection and
maintenance, and should allow for minor subsidence of the drainage layer.
3.2.1.1 Alternative Paths of Leachate Flow
Figure 2 is an example of a leachate collection system which provides
alternative paths of leachate flow. The system is designed to maintain
leachate levels at less than 30 cm (1 ft) even if clogging decreases the
hydraulic conductivity of the drainage layer or one or more of the collection
pipes clogs. Table 8 gives the estimated maximum leachate level over the liner
at different drainage-layer permeabilities and collection-pipe spacings. A 6 m
(20 ft) pipe spacing is effective in maintaining leachate levels at less than
30 cm even if the hydraulic conductivity of the drainage layer decreases nearly
two orders of magnitude (Cases 1, 2 and 3), or if a pipe clogs (effectively
increasing the spacing between pipes, as in Cases 4 and 5). However, if Case 5
were the initial design (collection pipes at a 24 m (79 ft) spacing), an order
of magnitude decrease in hydraulic conductivity would result in leachate levels
in excess of the 30 cm standard (Case 6).
3.2.1.2 Access
. Layout of the leachate collection system should also allow for access to
the entire collection pipe network, including the sump, for inspection and
cleaning. This is important for two reasons. First, since access to the
granular or synthetic drainage material is not possible, access to the pipe
network is needed in case the capacity of both components is reduced by
clogging (as in Case 6 in Table 8) . The pipe network can be unclogged and
maintained to maximize system capacity if access is provided. Second, the
collection pipe network is sensitive to damage, especially during construction
and during placement of the first lift of waste. Access is needed to allow for
inspection of the pipe network to ensure that the network was constructed as
designed, and was riot damaged in the initial placement of waste. If problems
are found, the pipe network can be repaired before leachate collection problems
occur, and before the damaged area is buried in several layers of hazardous
waste.
Access to the collection pipe network is provided by installing a manhole
or a riser pipe at each end of every pipe. Two possible designs are shown in
Figure 3. Access at both ends of the collection pipe is needed for most
inspection and maintenance procedures (Sections 5 and 6). In addition, bends
or branches in collection pipes at angles greater than 45 degrees and pipe
lengths greater than 300 m (1000 ft) between access points should be avoided.
The designs in Figure 3 are intended to minimize the number of manholes
required in order to minimize stress on the liner, reduce construction costs
and simplify waste placement.
Optimum spacitig of the collection pipe, manholes and riser pipes to
maintain leachate levels less than 30 cm (1 ft)and allow for access to the
system may be determined using site-specific information such as topography,
climate, waste characteristics (e.g., expected leachate generation, propensity
22
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3:1
Collection Pipe- ~
Manhole.: U
9 ,'Riser.-,-
Synthetic
Drain Net
on Side Slopes
2%
2% Slope
-30m-
Collection
Pipes
46mJ.
\
Plan View
Synthetic Filter Layer
@ 10'2 cm/s
30 cm Drain Layer
@ 10'* cm/s
Section A-A'
Figure 2. Laachais collection system t&yout providing alternative
paths of leachata flow.
23
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TABLE 8
MAXIMUM LEACHATE LEVELS GIVEN VARIOUS DESIGN ASSUMPTIONS
Parameter Unit Case 1 Case 2 Case 3 Case 4 Case 5 Case 6
Maximum Leachate
Level* cm 5 17 29 11 21 67
Permeability cm/s 10"2 10"3 3.5xlO~4 10"2 10"2 10"3
Pipe Spacing m 66 6 12 24 24
Leachate
Production
Rate cm/year 100 100 100 100 100 100
Slope -- .02 .02 .02 .02 .02 .02
^'Approximate level based on Figure 2; calculated using the equation in Koore
(1980) (see Section 3.4).
24
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3:1
Manhole
2%
\ A'
Riser
Crott-Swtion A-A' Through Colbction Pips
Collection Pipe
Manhols
Riser
2%
Figure 3. Leachate collection system layouts providing access to collection pipes.
25
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for clogging), and facility size including future expansion needs. (See
Sections 3.4 and 3.5.)
3.2.1.3 Minor Subsidence
Subsidence of the waste or sublayers may result in a final grade which
does not allow flow of leachate through the .drainage layer to the sump. Uneven
settling in localized areas of the disposal cell may result in low spots in the
drainage layer and lead to pooling of the leachace and eventual clogging.
Settleraen^ may also result in the buckling of collection pipes, the breaking of
joints, and eventual failure of the drainage system. Subsidence may be
controlled by prej^sding...tisa.sU'aste di&p-osal area during construction to allow
the sublayers to come .to. £iiJ»l nj-grade -before the drainage system is installed
and the wastes are placed. A more commonly used approach in controlling
subsidence is to factor in the effects of subsidence on final grade slopes in
the design calculations. The expected consolidation of the wastes and
sublayers can be calculated based on knowledge of the sublayer material
properties (e.g., density, composition, compatibility) and waste
characteristics (e.g., void fraction, density). An allowance or safety factor
may then be incorporated into the design to ensure that the final slope after
settlement will be as specified in the design. In addition, flexible joints
should be used between collection pipes which may be subjected to stresses
created by uneven waste subsidence.
3.2.2 Cap Drainage System
The primary purpose of the cap is to minimize infiltration of
precipitation into the waste mass after closure by increasing runoff and
evapotranspiration. The oap is generally constructed in several layers,
including a low permeability barrier layer, a drainage layer, a filter layer,
and a vegetated topsoil layer which is graded to increase runoff and reduce
erosion (Figure 4). The drainage layer removes precipitation which infiltrates
through the upper layers of the cap and prevents liquid from accumulating over
the barrier layer. Cap design is discussed in Lutton et al. (1979).
The drainage., lay§jc.-«,is ...typlcal-lyiva granular soil, although geotextile
materials may also be used. The U.S. Environmental Protection Agency (EPA,
1982) recommends, that a drainage layer be at least 30 cm (1 ft) thick (if soil
is used) and have a permeability of at least 10 cm/s.
The layout of a cap drainage system is less compile ited than a leachate
collection system since a collection pipe network is generally not incorporated
in the drainage layer (although perforated or slotted pipe located at the
perimeter of the cap is used to convey water from the drainage layer to surface
drainage facilities). A major concern is that the cap drainage system be able
to function with minimum maintenance (pursuant to 40 CFR 264.310), even with
minor subsidence of the cap. As a result, steeper slopes than would be
necessary for drainage alone are used so that flow through the drainage system
is maintained. The optimal slope will be shallow enough to minimize erosion of
the topsoil layer from surface runoff, and steep enough to avoid ponding of
water over the barrier layer if minor subsidence occurs.
26
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Figure 4. Schematic of a landfill cap.
-------
3.3 GENERAL DESIGN CONSIDERATIONS
Leachate collection system design is affected by the characteristics of
both the expected waste to be disposed of and the expected leachate to be
generated from that waste. The liquid content of the waste contributes to the
volume of leachate expected, and the particle size of the waste influences
design of the filter layer. Hydraulic conductivity of the waste also affects
the ability of the leachate to reach the collection system.
Leachfcte characteristics which influence design include the volume
expected, suspended solids, pH, redox potential, and chemical constituents such
as organics, calcium, iron, manganese and nutrients. These characteristics are
considered in sizing system components, selecting construction materials, and
designing individual components to avoid failure by the mechanisms discussed in
Section 2.
This section discusses material selection for chemical compatibility and
the ability to influence leachate characteristics once the facility is in
operation. The application of this information is limited to leachate
collection systems since cap drainage systems are not exposed to waste.
Specific design considerations for. each component are discussed in subsequent
sections.
3.3.1 Material Selection
Each component of a leachate collection system must be constructed of
materials which are chemically resistant to the waste managed and leachate
expected at the facility (40 CFR 264.301a). In assessing chemical/material
compatibility, the designer should recognize that the resistance of any given
material to chemical attack is a function of several, elements includivig the
specific chemical, the concentration of the chemical, temperature, and duration
of contact. Examples of organic and inorganic constituents that may be present
in leachate are given in Table 9.
In general, data regarding the resistance of various construction
materials to specific chemicals are limited. The data that are available
originate from sources such as manufacturers' product testing information,
reference texts and engineering handbooks, reports from private or academic
research and testing institutions and government-sponsored studies. These data
are typically reported for pure compounds, with limited information on dilute
solutions.
Little information is available on the chemical resistance of granular
materials that would be used in filter or drainage layers. A number of studies
have shown that strong bases will partially solubilize silica - containing soil
constituents (Nutting, 1984; Grim, 1953). Since sand is predominantly silica
in composition, drainage or filter layers constructed of sand which come in
contact with alkaline wastes may be susceptible to structural damage. Silica
dissolution may cause the formation of large voids and channels and may
ultimately lead to collapse of the filter or drainage layers.
Geotextiles are made from various single or multi-component petroleum-
based polymers such as polypropylene, polyester, and polyethylene. The
28
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TABLE 9
ORGANICS AND INORGANICS WHICH MAY BE PRESENT IN WASTE LEACHATES
Type
Group
Class
Examples
Organic
Acids
Bases
Neutral Polar
acetic, propionic, butyric,
lactic
aniline
Alcohols & methanol, isobutanol, phenol,
Phenols pentachlorophenol
Acid aceticanhydride
Anhydrides benzoic anhydride
Glycols ethylene glycol
Aldehydes formaldehyde
butyraldehyde
Esters bis(2-ethyl hexyl) phthalate
di-n-butylphthalate .
Ethers methyl ethyl ether
diethylether
Ketones acetone, methylethyIketone
2-hexanone
Haloganated vinyl chloride, chlorinated
ethanes, ethylenes,
methylene chloride,
chloroform
Neutral
Non-Polar
Aliphatic propane, butane, methane
Hydrocarbons
Aromatic benzene, toluene, xylene
Hydrocarbons naphthalene
Inorganic
Acids
hydrochloric, hydrofluoric,
nitric, sulfuric
(continued)
29
\
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TABLE 9 (continued)
Type
Group
Class
Examples
Bases
(Alkalies)
soda ash (NaOH)
potash (KOH)
mag.v.sium hydroxide
Salt
Metals
Acid ammonium chloride
Base sodium acetate
sodium carbonate
Neutral sodium chloride
potassium sulfate
lead, chromium, mercury
Source: From Haxo, 1983
30
%
-------
majority of all geotextile fabrics are composed of either polyester or
polypropylene. As shown in Table 10, geotextiles made from polypropylene are,
in general, more resistant to chemicals than are »eotextiles made from
polyester.
The most commonly used materials for leachate collection pipe are
thermoplastics, although vitrified clay, asbestos cenent and concrete, ductile
iron and fiberglass may also be used. With the exceptions of fiberglass and
thermoplastics, data regarding resistance of these materials to specific
chemicals are limited. Data regarding the resistance of fiberglass and
thermoplastic materials to specific chemicals are often supplied in
manufacturers' product literature. Since there are many formulations for
thermoplastics (e.g., polyvinyl chloride (PVC), chlorinated polyethylene (CPE))
and fiberglass (using various polyethylene and polyester resins) care must be
taken to select the proper formulation of piping material for a specific waste
application.
Sump materials must be compatible with the physical and chemical
properties of the leachate. Materials which may be used include:
concrete;
e concrete with fiberglass, plastic, or brushed-on epoxy liner
material; and
PVC, ABS or fiberglass reinforced vessels.
Pump materials should be resistant to the corrosive or chemically-active
environment. Normally pumps are constructed of cast iron with stainless steel
or bronze shafts, gates and seals. Table 11 presents general information on
the chemical resistance of these materials. Pumps may also be constructed of
stainless steel and PVC, and may be coated with Teflon liners, aliphatic
urethane coatings, or epoxy coatings. Valves are available in fiberglass, PVC,
CPE, polyethylene, stainless steel, and metal fabricated with a variety of
chemically resistant coatings.
Chemical resistance data for many chemical/material combinations either
are not available or are limited in scope. Empirical methods or laboratory
testing may be necessary to estimate the chemical resistance of certain
materials to chemicals.
In general, two types of testing can be performed: exposure testing, and
material property testing. Exposure testing attempts to simulate expected
in-service conditions to which a material in direct contact with chemicals will
be subjected. Testing conditions such as temperature, duration of exposure and
chemical concentration may be varied to provide information on the short- and
long-term resistance of the material. The most widely used exposure test
method is the immersion test. Procedures for conducting immersion tests can be
found in ASTM D471-79 (Rubber Property - Effect of Liquids) or ASTM D543
(Resistance of Plastics to Chemical Reagents). Similar procedures could be
adopted for immersion testing of other construction materials. For example,
EPA requires waste-liner compatibility testing for flexible membrane liners.
Two methods, EPA 9090 and NSF Standard No. 54, are generally recommended.
These and other test method are evaluated in Tratnyek et al. (1984).
31
-------
TABLE 10
CHEMICAL RESISTANCE1 OF POLYPROPYLENE VERSUS POLYESTER
Mineral Acids, weak
Mineral Acids , strong
Oxidizing Acids, cone.
Alkalies, weak
Alkalies, strong
Alcohols
Ke tones
Esters
Hydrocarbons, aliphatic
Hydrocarbons , aromatic
Oils, vegetable, animal, mineral
Polypropylene
Excellent
Excellent
Good to Poor
Excellent to Good
Excellent to Good
Excellent to Good
Excellent to Good
Excellent to Good
Good to Fair
Good to Fair
Good
Polyester
Good
Poor
Poor
Good
Poor
Good
Pool-
Good
Good
Poor to Fair
Good
Source: Bolz and Tuve, 1976.
32
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TABLE 11
CHEMICAL RESISTANCE OF CAST IRON
STAINLESS STEEL, BRONZE AND MONEL
Metal
Subject to Corrosion by
Cast Iron
Stainless Steel
Bronze
Monel
all water solutions;
moist gases, dilute acids,
acid-salt solutions
inorganic acids,
ammonia, mercury, oxidizing
salts (Fe, Cu, Hg)
mercury and its salts,
aqueous ammonia, saturated
halogen vapors, sulfur and
sulfides, oxidizing acids
(nitric, concentrated sul-
furic), oxidizing salts (Hg
Ag, Cr, Fe, Cu), cyanides
inorganic acids, sulfur,
chlorine, acid solutions
of ferric, stannic or
mecuric salts
Resistant to
concentrated acids (nitric,
sulfuric, phosphoric),
weak or strong alkalies,
organic acids
water, caustic and mild
alkalies, organic acids,
neutral and alkaline or-
ganic compounds, dry gases
water, sulfate and carbon-
ate solutions, dry halo-
gens alkaline solutions,
petrochemicals, non-
oxidizing acids (acetic,
hydrochloric, sulfuric)
food acids, neutral and
alkaline salt solutions,
dry gases, most alkalies,
ammonia
Source: Bolz and Tuve, 1976.
,\
-------
Material property testing is usually performed before and after exposure
tests to provide a comparative basis for establishing changes in properties
after the material has been exposed to a chemical or leachate. Commonly
measured properties include:
weight change;
e swelling or shrinking;
tensile strength; and
e hardness.
Visual inspections, optically aided or unaided, may also be useful for
assessing changes not necessarily detectable in any of the above property
tests. Surface cracks, inclusions and other material defects may be uncovered
in materials such as vitrified clay, ductile iron, and concrete or cement.
Visual inspection may uncover reactivity of leach.ite with a plastic material as
manifested by discoloration, delamination or bubbling of the material.
Numerous methods are available for conducting exposure and material
properties tests. The selection of the most appropriate technique depends on
the particular material and property to be tested.
3.3.2 Control of Leachate Characteristics
Controlling the wastes placed in a landfill'may provide a means to prevent
or mitigate the potential for failure of leachate collection systems. In many
cases, the failure of a leachate collection system is attributed at least in
part to the wastes disposed of at the facility. For example, at a site in
California which experienced chemical deposition and solidification, clogging
was attributed to "the variations in the type of waste handled and hence ....
the leachate characteristics" (MEESA, 1984). Attention must be given both to
the chemical and physical characteristics of the waste, as well as the manner
in which the waste is placed.
The first step in controlling leachate characteristics to minimize failure
of a leachate collection system is to not dispose of wastes which may adversely
affect the functioning of the system. This would include not accepting any
liquid wastes or any wastes which are incompatible with system components. Not
accepting bulk liquid wastes, which is required under the Hazardous and Solid
Waste Amendments of 1984, significantly reduces leachate generation. In the
California facility mentioned above, about 30% of the wastes were liquid
industrial wastes. Not accepting incompatible wastes is necessary since the
system is constructed of materials which are resistant only to certain types of
waste. Disposal of incompatible wastes can result in failure of a component
due to material degradation. In one case discussed in Section 2, for example,
failure of a hazardous waste leachate collection system was attributed to
disposal of a solvent or acid in a cell which was not designed for such wastes.
Segregating wastes with different chemical characteristics into different cells
may also be useful in avoiding leachate collection system failure, since
construction materials can be selected for a narrower range of waste
characteristics.
The second step for controlling leachate characteristics to avoid failure
involves careful selection of wastes placed in the first lift. These wastes
34
-------
should be high-permeability wastes and may have special chemical
characteristics. High-permeability wastes are placed in the first lift to
facilitate the flow of leachate to the collection system. Special waste
characteristics may include wastes of relatively low pH, wastes which inhibit
biological activity, and wastes which do not contain high iron, calcium,
magnesium, nutrient, or sediment content. The chemical characteristics
desirable in the first lift of waste vary with the leachate characteristics
expected at the facility, and the failure mechanisms which are expected to be
active.
Proper placement of the first lift of waste is also critical in
maintaining leachate collection system performance since wastes are deposited
directly on Cop of the exposed leachate collection system. The movement of
equipment and careless dumping of t'r.a waste on top of a granular filter layer
may result in ruts and/or compaction of a granular filter layer beyond design
specifications for proper filtration. Filter layers of geotextiles may be
ripped or punctured during careless waste placement activity. The underlying
leachate collection piping may also be damaged (e.g., pipe buckling, breaking
of joints) during waste placement. Initial placement of wastes should be
performed using equipment properly sized for the job. Sizing of equipment
should consider the ability of the underlying drainage and filter layers to
withstand vertical loading, which is a function of the characteristics of the
drainage or filter materials and the maximum allowable loading stresses for the
collection pipes. Waste placement should proceed ahead of the placement
equipment, and wastes should be dumped as close to ground level as possible.
Equipment movement on the waste placement area should be limited to the portion
covered with the initial or subsequent layers of wastes.
Controlling waste characteristics in later lifts may oe difficult because
of restrictions on storing wastes onsite and the difficulty in controlling the
wastes which come through the gate. This may also be a problem during the
first lift of waste. Where possible, however, waste should be placed to reduce
the possibility of clogging. For example, placing iron-containing waste in
portions of the landfill where the leachate pH is low and/or the redox
potential is low (i.e., oxidizing) should maintain any iron leached out at the
higher ferric oxidization state and reduce the possibility of iron deposition
since ferrous ions are oxidized rapidly in acidic conditions. This approach,
however, will have limited applicability in large landfills which accept a
variety of wastes, and where leachate from several parts of the cell drains
into a common leachate collection system. In this case leachate
characteristics in the collection system itself would be very difficult to
control.
In general, the effects of waste characteristics on the leachate
collection system should be considered in the placement of wastes in the
landfill. This is especially important during placement of the first lift of
waste. While waste placement may be difficult to control at some facilities,
waste characteristics do influence the function of the leachate collection
system. This correlation should be understood by the facility operator and
waste placement should be controlled where possible to avoid potential problems
with the leachate collection system.
35
-------
3.4 DRAINAGE LAYER
3.4.1 Material Selection
Drainage layers generally consist of granular soils such as coarse sands
which provide the required hydraulic conductivity (10 cm/s) and protect the
underlying flexible membrane liner. The particle-size distribution of the
drainage layer must be selected to allow liquid transport, prevent puncture of
the underlying synthetic liner, and minimise migration of filter-layer
materials into the drainage layer.
Geotextiles may be used as a substitute for granular material in portions
or all of the drainage layer. Geotextile materials include needlepunched,
non-woven . polypropylene or polyester fabric and polyethylene grids.
Combinations of the two may also be used; for example, placing a grid between
two layers of geotextile fabric. Properties of typical geotextile drainage
materials are given in Table 12.
The primary advantages of using a geotextile drainage layer are:
geotextiles may be more accessible or less expensive than granular
material in a given location;
geotextiles are thin compared with . granular drainage layers and
therefore allow for larger disposal capacity; and
geotextiles can be placed on steeper side slopes than granular
materials, again allowing for larger disposal capacity.
The primary disadvantages of using a geotextile drainage layer are:
geotextiles are thin and may be more susceptible to clogging than
granular materials;
the hydraulic conductivity of some geotextiles may decrease up to two
orders of magnitude under loading conditions (Giroud, 1981); and
experience with geotextiles in land-disposal applications is limited
and their ability to perform on a long-term basis is unproven.
3.4.2 Design Considerations
The design of the drainage layer will be based primarily upon the system
hydraulics necessary to maintain a leachate level over the liner of less than
30 cm (1 ft). Protection requirements for the synthetic liner should also be
addressed as well as the physical properties of the materials (e.g., ability to
place granular materials on side slopes, physical strength of geotextiles).
The design for the filter layer (Section 3.6) will usually follow drainage
layer design. Design of the collection pipe network (Section 3.5) will occur
concurrently.
36
-------
TABLE 12
PROPERTIES OF TYPICAL GEOTEXTILE DRAIHAGE MATERIALS*
Product Name I3anufactur<5r
Typar Spjnbonded, 3601 . DuPont £
:.
GTr-1250 Exxon i"
:
Fibretex, AOO Crown ZellerlJach
-, ''' '
Bidiro, U34 Ouline Corp;..
" .
u> "
-4 Trevira Type 1120 American
Hoest Corp.
Tensar DH-3 Tensar Corp.
!f
Conued Geo-Het XB8200 Conued
Weight,
Material oz/yd
Type (ASTM D19'0)
non- woven, 6
polypropylene
non- woven, 4
polypropylene
non- woven, no data
polypropylene
non- woven, 8
polyester
non- woven, 6
polyester
polyethylene 20.6
grid
polyethylene 20.2
grid
Thickness, Equivalent Opening Size,
mils Permeability, U.S. Std. Seive Size
(ASTHD1777) . cm/S ', (COE CU-02215)
18 1.4 .»;:|0"2 140 170
* fV:
45 1 x. JO"1 50 - 100
** (ASTM .03.81.08)
It
110 ) 3 x" id)!,,1 80 - 100
'$ !:
; 100 , 3;x ^10" 1 70 - 100 :|
100 ho data 50 - 70
160 5 x 10"* m2/s** ' 7mm x 7mm
' ;
160 5 x 10"* m2/s*« no data
1 oz/yd2 = 33.9 gro/ro2
1 mil » 1.0254mm
1 Ib a .45 kg
Transmissivity under pressure. For comparison, a 30 cm ( 1 ft) thick granular
layer with a permeability of 1 x 10"1 cm/s has a transmissivity of 3 x 10~* m2/s
Source: Vendor product information.
-------
The movement of leachate through the drainage layer is primarily a
function of the liner slope, collection-pipe size and spacing, the number and
size of perforations in the collection pipe, hydraulic conductivity of the
drainage material, and rate of leachate generation. A variation in any one of
these parameters may affect the requirements of the other parameters if a
maximum head of 30 cm (1 ft) is ,to be maintained.
The anticipated volume of leachate within the drainage system must be
determined so that the components of the drainage layer can be sized
appropriately. Leachate within the landfill can.come from the liquid in the
waste, precipitation and, in some cases, groundwater flow. The amount of
liquid generated from the waste may be determined if the moisture content of
the waste is known. As a conservative estimate, it can be assumed that the
quantity of leachate generated from a waste is equal to the moisture content of
the waste times the volume of waste deposited. In.reality, however, the amount
of leachate generated from the waste will be less than this value since the
waste will retain and store a certain volume of liquid (called the "field
capacity"). In some cases, liquid in the waste may not make any contribution
to leachate quantity, but may reduce the time required for leachate to appear
in the leachate collection system (i.e., the field capacity of the waste will
be reached more quickly).
Leachate produced from infiltrating precipitation may be estimated using a
computer ^cdel. Two examples of computer models are:
1. HELP (Schroeder et al., 1984); and
2. HSSWDS (Perrier and Gibson, 1982).
HELP and HSSWDS are very similar, and both give output on water movement
through the system including percolation, drainage, evapotranspiration, runoff
and soil water storage. These results are based on a variety of climatologic
and soil data for each layer of soil or waste. The function of each layer is
considered, as is the distance between collection piping, the slope of the
drainage layer, and an anticipated percentage of leachate that leaks through
the liner. Other equations that model water movement through soil and waste
are available, and many can be easily adapted to a computer program.
An important consideration in drainage-layer design is the maximum height
to which leachate rises in the drainage layer. Leachate tends to mound up in
granular drainage layers due to viscous resistance to horizontal flow. The
maximum height of this mounding must not exceed 30 cm (1 ft), as stipulated by
RCRA regulations. For a particular drainage-layer configuration, drainage-
layer permeability, and liquid infiltration rate, the maximum height of
leachate mounding in the drainage layer can be calculated by the following
formula (Moore, 1980):
h
max
38
-------
where: h - maximum height of leachate over the liner (cm)
ma£ - length of spacing between drainage pipes (cm)
e - quantity of leachate seeping into drainage layer
(cm/sec)
k - permeability of drainage layer (cm/sec)
s - slope of liner
Figure 5 illustrates a drainage layer geometry for this formula and
identifies formula variables. Given a value for e (representing infiltrating
precipitation and liquid generated by the waste itself) , this equation may be
used to select combinations of values for L, s, and k which will maintain an
h of 30 cm (1 ft) or less.
max
It should be noted that the above equation for h gives only an
approximate value. A more rigorous, non-linear equation can Be found in HcBean
££ al. (1982). It should also be noted that the second term of the equation
goes to one if the slope equals zero. This gives a simplified equation which
slightly overestimates h , but which can be more easily solved.
The designer should consult additional references for a more detailed
explanation of this design calculation using other drainage -layer geometries
and associated design equations (EPA, 1983b; Harr, 1962; Bear, 1972).
Although EPA (1982) recommends a drainage -layer thickness of 30 cm (1 ft),
thicker layers should be considered to increase drainage efficiency (EPA,
1985a) . The drainage -layer design should include a safety factor to account for
possible clogging because of solids infiltration or other clogging mechanisms.
A safety factor can be achieved by increasing liner slope, decreasing pipe
spacing, or increasing drainage -layer permeability or thickness.
3.5 COLLECTION PIPE NETWORK
The collection pipe network of a leachate collection system drains,.
collects and transports leachate through the drainage layer to a collection
sump where it is removed for treatment or disposal. The pipes also serve as
drains within the drainage layer to minimize mounding of learhate in the layer.
In a cap drainage system, pipes are used to collect and transport water from
the drainage layer to surface drainage facilities. Specific information on
design of drainage pipes which may also be applicable to collection pipe design
is given in USBR (1978).
3.5.1 Capacity
Pipes must be sized and spaced to remove liquid from the drainage layer
without causing any significant back-up. In a leachate collection system, the
collection pipes must be designed to carry the leachate without allowing more
than 30 cm (1 ft) of leachate buildup within the drainage layer.
Many factors must be considered in designing the collection pipe network.
The slope of the cell bottom and the distance between collection pipes are
parameters used in the HELP Computer Model. Other factors include the flow
through the pipe perforations, the slope of the pipe, the layout of the pipe
network, and the maximum amount of liquid expected to be carried by the pipe.
39
-------
i I
Figure S. Landfill geomstry assumed for Retaliating maximum haight of leachato over liner.
\
-------
Darcy's Formula or flow net calculations can be used to determine the
design capacity of collection'pipe. These techniques are discussed in detail
in Cedergren (1977). Typically, based on flow considerations, 10 era (A in.)
diameter pipe is considered adequate for drainage system laterals while 15 cm
(6 in.) diameter pipe ic used for collection headers in nost landfill
applications. Increasing the lateral pipe diameter to 15 cm (6 .In.) and the
collection header diameter to 20 cm (8 in.) would allow easier access for
inspection and maintenance equipment, provide a greater cross-sectional area
for lea^hate flow, and reduce blockage of leachate flow from partial clogging
within tha pipe.
3.5.2 Structural Stability
Piper, useu t^ collect and convey leachate from leachate collection systems
must be structurally stable to.withstand the loading of the overlying filter
and drainage layers, waste?, cap materials, and vehicular traffic that may move
over the disposal cell. Collection pipes in landfill draimge systems may bo.
rigid (e.g., concrete and cast iron) or flexible (e.g., plastic anc
fiberglass), and may be placed ii: trenches (Figure 6) or above-grade (i.e.,
positive projection, Figure 7). Since many landfills, experience some uneven
settling, flexible pipe with fittings designed to withstand this settlement is
recommended, especially for the cap drainage system.
Factors which must be considered in determining the required structural
stability of the collection pipe include, but are not limited <:o:
vertical loading;
perforations;
. deflection;
buckling;
compressive strength;
backfill compaction; and
loadings during construction.
Design equations for calculating the vertical loads acting on flexible
pipe because of overlying materials are summarized in Table 13. The equations
can be used to calculate the vertical loading stress acting on perforated
collection pipe installed in trenches or above grade, and to calculate flexible
pipe deflection. A complete explanation on the use of these equations may be
found in Haxo (1983). A problem in using these equations with respect to
landfill sites is that it may be difficult to determine the average unit weight
of fill since dense waste (high unit weight) may be placed in a single area,
rather Chan spread evenly over the site. The designer should include a safety
factor to account for thrse uncertainties. The selection, for example, of the
next greater standard wall thickness would provide an extra measure of
protection against excessive loading on the pipe.
Most pipe standards assume flexible pipe failure at a deflection of 5 to
7.5 percent, although pipe deflected beyond this point may still conduct fluid
(Personal Interview, P. Kmet). A severely deflected collection pipe may
develop bottlenecks that could restrict flow. Pipe deflection depends greatly
on the bedding compaction. Compaction is often difficult to achieve at a site
with soft clays. Although sand and gravel are acceptable bedding materials,
41
-------
Filter Layer (Geotextile
or Granular Material)
Drainage Layer (Granular
Material or Drainage Net)
Geotextile
Geomembrane
Perforated/Slotted Pipe
Figure 6. Collection pipe installation ir trench.
-------
Filter Layer (Geotextile or
Granular Material)
Drainage Layer (Granular or
Drainage Net)
Geomembrane
Perforated/slotted Pipe
Figure 7. Collection pirie installation above liner.
-------
TABLE 13
DESIGN EQUATIONS FOR CALCULATING
VERTICLE LOADING STRESSES
ON FLEXIBLE PIPE USED IN
LANDFILL DRAINAGE SYSTEMS
Description
Equations
Vertical loading stress acting on
pipe installed in:
- Trench
Where:
-2KM(Z/Bd)
^2KjJ
-2Ku(Z/Bd)
- Above Grade
= (wf)(Hf)
Increased vertical stress for
perforated pipe:
Flexible pipe deflections under
vertical loading:
12
design TPTp actual
kWrJ
El
(continued)
44
-------
TABLE 13 (continued)
Definitions:
o = vertical pressure at the top of the pipe (psi)
Bd = width of trench (ft)
u) = unit weight of backfill (lb)
K = lateral pressure coefficient of backfill (psi)
p = coefficient of friction between backfill and the walls
Z = height of backfill above pipe (ft)
qr = vertical pressure at the bottom of the waste fill (psi)
Hf = height of waste fill (ft)
Ip = cumulative length (ia iaches) of perforations per foot of pipe
Ay = horizontal and vertical deflection of the pipe (inches)
D = a factor, generally taken at a conservative value of 1.5, compensating for
the lag or time dependent behavior of the soil pipe system
W = vertical load action on the pipe per unit of pipe length (Ib/in)
r = mean radius of the pipe (inches)
E = modulus of elasticity of the pipe materials (psi)
E = modulus of passive soil resistance (psi), (normally estimated to be 300
psi for soils of proper density of 65% and 700 psi for soils of proper
density of at least 90%)
k = bedding constant, reflecting the support of the pipe receives from the
bottom of the trench (diinensionless) (a conservative value generally
taken 0.107)
I = moment of inertia of pipe wall per unit of length (in7/in); for any round
o
pipe, J = t /r,where t is the average thickness (inches)
Source: Haxo, 1983-
-------
crushed scone is easier to compact end offers greater strength to the pipe.
Crxished stone, however, should not be placed directly over the liner. The
Krsiraua Technology Guidance (EPA, 1985a) states that granular materials coarser
-h.au fine sand should not be in contact with the liner.
The pipe manufacturer should be consulted for information on buckling and
coonpressive strength which are specific to each kind of pipe. The strength of
plastic pipe may be reduced with age and warmer temperatures (greater than
21 C). Plasticizers may be broken down with time, reducing pipe strength.
Some compounds in pipes are broken down by ultraviolet rays. . This can be
Btlnieized by covering pipes during storage prior to use, covering installed
pipe with a layer of soil, and protecting risers from exposure with a steel
outer casing or similar device. As with all components in a leachate
collection system, the collection pipe should be compatible with the leachate.
3.5.3 Perforations
Design of collection pipe must consider the size, spacing and orientation
of holes or slots used to perforate the pipe.- Perforations must allow free
passage of leachate but prevent the migration of drainage media into the
collection pipe. The size or diameter of these perforations therefore depends
on media particle size and the volume of leachate that must be removed from the
drainage system. For slotted pipe. Cedergen (1977) suggests:
Dg5 of the filter
Slot Width
and for pipes with circular holes:
Di. of the filter
_
Hole diameter
> 1.0
vfcere D., is the particle size which 85 percent of the soil particles are
smaller Chan (on a. dry-weight basis, as determined by ASTM D421 and D422).
Alternately, USER (1977) recommends:
D0, of the filter
Maximum pipe opening
L 2
Cedergren (1977) concludes that all three equations represent a reasonable
range over which satisfactory performance can be expected.
Spacing of perforations depends on flow as well as pipe strength
considerations. The U.S. Soil Conservation Service and the U.S. Bureau of
Reclamation require a minimum open area of 21 cm /m (1 in. /ft) for drainage
pipe (Mohammad and Skaggs, 1983). The number of perforations per length of
pipe affects the effective radius of the pipe used in design calculations. Use
of effective radius in pipe design is discussed in Mohammad and Skaggs (1983)
46
-------
and in Skaggs (1978). The number of perforations per length of pipe also
affects pipe strength, as shown in Table 13. Both factors should be taken into
account in the design of perforated collection pipe.
Orientation of perforations on the pipe depends on flow and clogging
considerations. Mohammad and Skaggs (1983) found that orientation of the
perforations did not affect the rate of flow when the pipe was full of water.
However, Luthin and Haig (1972) found that the rate of flow in a pipe which was
not full was greater when perforations were at. the bottom of the pipe due to
the increased head difference between the water level and the entry points.
Since collection pipes will not always be full of liquid, these studies suggest
that placing perforations near the bottom of the pipe will increase collecti'-n
efficiency. This also minimizes the depth over the. liner required for leachace
to enter the pipe. However, placing additional perforations in the upper
portion of the pipe will increase the ability of the pipe to collect leachcite
and rfill be just as effective as other perforations when the pipe is running
full.
To prevent the perforations from plugging with sediment, the perforations
should not be placed straight down but should be offset at an angle (eg. 30
degrees) from the straightdown position. In addition, holes should not be
drilled along the pipe seam as this weakens the pipe.
3.6. FILTER LAYER "
Two types of filters are typically used in engineering practice: granular
filters and geotextile filters (Figure 8). Granular filters were first
introduced in the 1920's (Terzaghi and Peck, 1967) and consist of a soil layer
or combination of soil layers having a coarser gradation in the direction of.
seepage than the soil to be protected (i.e., the material above the filter
layer). Geotextiles, first introduced in the 1970's (Hoare, 1982), are
cloth-like sheets made of synthetic fibers and are sometimes referred to as
filter fabrics or geofabrics. Geotextilet; are manufactured in two varieties --
woven and non-\»oven. Woven geotextiles are similar to screens which have
uniform sized openings whereas the non-woven variety consists of fibers placed
in a random orientation. Both types can be made with high permeability
relative to most soils while having an opening or mesh size sufficiently small
to prevent soil particle movement.
The filter layer is used above the drainage layer in both leachate
collection and cap drainage systems to trap fines and prevent waste and other
solid materials from entering the drainage layer while allowing the passage of
liquid. Information regarding physical characteristics of the fines and the
anticipated loading rates is needed to formulate design criteria for
constructing a filter that will continue to function through the design life of
the drainage system. Information on the selection and sizing of the filter
medium is presented in this section.
Some designers argue that a filter layer is not necessary when the
quantity and loading rate of fines introduced to a drainage layer are small
enough to allow infiltration into or transport through the drainage layer
without adversely affecting the performance of the drainage layer. Physical
characteristics of fines such as the particle size and shape may dictate
47
-------
Protected Soil/
Waste Layer
Nominal Boundary
Before Stabilization
Under Seepage
Filter Medium
Drainage Medium
Granular Filter
Protected Soil/
Waste Layer
Geotextile
> Drainage Medium
Geotextila Filter
^.{--Ti-^v.. :-*- >,t;.!..', i.v- rtj-ol _<|tj?4o.v<.')v
Figure 8. Schematic of granular and (jaotoxtiia filters. .
48
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whether It is practical to design a filter layer to trap fines or a drainage
layer to allow transport of fines. Information on physical characteristics of
the fines, such as the particle mass and density, coupled wi'ch anticipated flow
velocity of liquid through the drainage system, will aid in determining whether
transport of fines will be possible.
The factors that .nfluence ' the decision to include a filter layer in a
drainage system will also influence the decision whether or not to wrap
collection piping or the pipe trench with geotextile. It is generally
considered unwise to wrap a pipe since the geotextile may clog with fines.
However, where it can be conclusively demonstrated that fines will not he a
problem, wrapping -the pipe with a compatible geotextile would be effective in
preventing raigratsejsj of drainage.'media into the pipe and may allow for larger
perforations in the pipe.
The designer .of a leachate collection system will need to balance the
presence of fines in-.the deposited waste against the advantages (i.e., meeting
the design goals) and the disadvantages (i.e., potential causes of
sedimentation) of using a filter layer and/or wrapping collection piping or the
trench the pipe is in with geotextile. Figure 9 presents design goals which
need to be addressed...in considering the use of a filter layer or geotextile-
wrapped pipe. In most cases, a filter layer will be needed to prevent
migration of overlying materials into the drainage layer. EPA (1985) recommends
the use of a granular or synthetic filter layer above the drainage layer to
prevent clogging.
3.6.1 Granular Filters
Various design criteria are available for granular filters (Peck et al..
1974; Cedergren, 1977; U.'S. Bureau of Reclamation, 1977; U.S. Army Corp of
Engineers, 1955; Canada Centre for Mineral and Energy Technology, 1977; and
Sherard et al. , 1984a and b). Review of these publications shows that the
variations among design criteria are minimal.
Generally, filter design is based on the particle-size distribution of the
overlying soils. -For a leachate collection system the overlying soil would
most likely i>e~ thes"waste, and for a cap drainage system the overlying soil
would most likely be the topsoil. Particle-size distribution or gradation of
soil is the relative proportion of each particle size on a dry-weight basis.
Determination of a soil's gradation is defined in ASTM Specifications D421 and
D422 (1982). A soil's gradation is commonly shown graphically in the form of a
particle-size (or grain-size) distribution curve (Figure 10).
Peck g£ al. (1974) present design criteria for granular filters based on
the concept of filter ratios '(Table 14). Peck et al. (1974) also recommend
that the particle-size curve representing the filter material should have a
smooth shape without pronounced breaks and should be roughly parallel to that
of the soil being protected.
Cedergren (1977) suggests the following two criteria for granular filters:
49
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in
O
1
1
1
Filter
QMb^n PMfiiM* 1
Pipa P:pe&
Dsd^n Fines removed
Costs '" at filter
Drainage media
migration con-
trolled by
perforation
sizing and
orientation
Potential Drainage media
Fxllurc
_ __ * m 13^3^1 on Into
, f₯!O9tcn ism
i P'pe
Filter plugs
Fines deposition
and pipe plugging
if filter fails
r - -
Fines
|
_,
Geofabric Wrap
Finos removed
at filter
Drainage media
migration con-
trolled by geofabric -
,
Filter plugs
Geofabric plugs
WASTE
1 ' ' 'i
r
Nc Fines
ll
1 1
No Filter
No Filter ,
1 1!
1 ; i| ' | |
Pipe ' Pipe * Geofabric Wrap Pipe Pipe & Geofabric Wrap
Fines transported Fines removed Drainage media migration Drainage media
through drainage at geofabric controlled by perforation migration controlled
system sizing end orientation by geofabric
Drainage media Drainage media '
migration con- migration
trolled by controlled by
perforation sizing geofabric
and orientation
Drainage media » Gcofebric plugs Drainage media migration « Geofabric plugs
migration into Into pipe with drainage
pipe media, unexpected
fines
Fines deposition
and pipe plugging
If transport 1
velocity is inadequate
Figure 9. Potential design options for collection or transport of fines.
-------
Ol
h>
too
Ol
300
US.STANDAHO 5.EVE OPENING IN INCHES U.S. STANDARD SIEVE NUMb*RS
* ' * '° I4'a »° S0 ro "0140 200
IOO 3O
10
' 0-» O.I 0.05
PARTICLE SIZE (MILLIMETERS)
HYDROMETER
O.OI O.OO5
1 O
t-
z
z
UJ
Fi(jure 10. Particle-»ize (or grain-iize) dittribution curve.
-------
TABLE 14
PARTICLE-SIZE REQUIREMENTS FOR FILTERS
Grading of Filter Material
Uniform
**
Nonunlform , subrcunded
particles
"JfJc
Nonuniform , angular particles
50
5 to 10 .
12 to 58
9 to 30
No requirements
12 to 40
6 to 18
R - the filter ratio for the n percent size =
D of Filter
n
D of overlying soil
D - particle size which n percent of the soil particles are smaller than
(on a dry-weighr basis, as determined by ASTM D421 and D422).
The filter material is considered nonuniform if D,0/D-0 (coefficient of
uniformity) is greater than 4.
Source: Peck e£ al.. 1974
52
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Criterion 1:
D,, of the filter
< A to 5
> 4 to 5
Doe of the overlying soil
OJ
Criterion 2:
D. e of the filter
-J2 -- : -
D._ of the overlying soil
. f . -
where D is defined in Table 14.
n
The first criterion is intended to prevent migration of overlying soils into
the filter layer, and .the second to allow sufficient hydraulic conductivity to
prevent buildup of liquid above the filter.
Where the particle-size difference between the overlying soil and the
underlying soil is great, a single filter layer which meets the design criteria
may not be possible. In this case, several filter layers may be necessary
(e.g., the "overlying soil" for one filter layer may be a second filter layer).
In addition, the above criteria m'"3t be satisfied between the drainage layer
and the filter layer to prevent migration of filter soils into the drainage
layer and to ensure sufficient hydraulic conductivity between the two layers.
3.6.2 Geotextile Filters
Filter design criteria are not as well established for geocextiles as they
are for granular materials. This is mainly due to the short time geotextiles
have been available for engineering use. Discussions of design criteria for
geotextiles are presented in publications by Cedergren (1977), Koerner and
Welsh (1980), Chen et a],. (1981), Giroud (1982), Lawson (1982), Carrol (1983)
and Horz (1984) .
Chen ej; si. (1981) suggest the following criteria:
Criterion 1:
< 2
P_5 of the geotextile
D-c of the overlying soil
Criterion 2:
P _ of the geotextile
9-> >
D-5 of the overlying soil "~
53
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where: ?,. - pore diameter of the geotextile which 95% of the pores are
smaller than (also called the equivalent opening size or
EOS)
D is defined in Table 14.
n
The first criterion is intended to prevent overlying soils from passing through
the filter, and the second to prevent clogging of the geotextile with fines.
Procadures for determining ? are found in Carrol (1983..
In addition, Carrol (1983) recommends that the hydraulic conductivity of
the geotextile be greater than ten tines the hydraulic conductivity of the
overlying soil, and that the gradient ratio be less than or equal to 3. The
gradient ratio is a laboratory parameter determined by comparing head losses
across the geotextile and the immediately adjacent protected soil to head
losses across the undisturbed protected soil. Procedure? for determining the
hydraulic conductivity of a geotextile can be found in Celanese Fibers
Marketing Company (1981). Procedures for determining the gradient ratio for a
geotextile are presented by Haliburton and Wood (1982).
Giroud (1982) provides a critique of conventional geotextile filter
criteria, claiming they are overly restrictive. He suggests alternative
criteria based on a theoretical analysis of the governing equations.
3.7 OTHER COMPONENTS
3.7.1 Sumps
Collection pipes typically convey the leachate by gravity to one or more
sumps depending upon the size of the area drained. Leachate collected tn the
sump is removed by pumping directly to a vehicle, to a holding facility for
subsequent vehicle pickup, or to an on-site treatment facility.
Sump dimensions are governed by the amount of leachate to be stored, pump
capacity and minimum pump drawdown. Two possible sump designs are given in
Figure 11. Manholes may also be used as sumps (see Section 3.7.4).
The volume of the sump must be sufficient to hold the maximum amount of
leachate anticipated between pump cycles, plus an additional volume equal to
the minimum pump drawdown volume (i.e., liquid reservoir to keep pump from
running dry). Sump size should also consider dimensional requirements for
conducting maintenance and inspection activities, including equipment and
personnel access. Sump pumps may operate with preset cycling times (e.g., 15
minutes) or, if leachate flow is less predictable, the pumps may be
automatically switched on when leachate reaches a certain level. The Minimum
Technology Guidance (EPA, 1985a) states that sumps should have the capability
of continuous and automatic operation. This avoids the problem of leachate
buildup when an operator fails to activate the pump when the sump is full.
This problem was noted in the interview results in Section 2.
54
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Top Liner
(FMU
Bottom Liner,
Standpipe
Leak Detection System
Geotextile
Over FML
- Filfr Layer
Drainage Layer
Chemically Resistant
Concrete Manhole
Drain Envelope
Bottom Liner,
-Filter Layer
| Drainage Layer
Figur* 11. Typical tump detigns.
55
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3.7.2 Pumps
Smnp pumps should be designed to provide adequate head and volume to
discharge leachate from the collection sum? zo either a collection vehicle or
holding facility. Sizing pumps for pinning ca.pacity greater than the
anticipated design capacity will ensure that unpredicted surges in leachate
flow may be accommodated without causing a build'-up in leachate within the
facility. Where multiple pucps are used, it say be advantageous to size pumps
for a capacity equal to the total flov? rate of the Leachate collection. In the
event that one or more pumps fail to operate, cbe remaining pump(s) could
accommodate the increased load.
When the pump is discharging directlj to a collection vehicle, the pump
capacity should be large enough to empty the sunnp contents in an efficient
manner. An alternative to pumping directly from the suap is to use a diaphragm
pump or vacuum pump system mounted directly on tbe collection vehicle, much
like septic tank scavenger vehicles. These vehicles typically hold several
thousand gallons.
Pump types which may be used to pcmp leschate include submersible,
centrifugal-type pumps, which offer economical capital and operating costs.
Shaft-driven centrifugal pumps are also applicable' in leachate pumping because
the motors are mounted above the susip sod out of the liquid. End suction
centrifugal pumps may be used if suction lifts are liaited to 4.5 m (15 ft).
Diaphragm pumps are not rtoonmended because o£ .high maintenance and low
reliability resulting frcji loss of prime.
In cold weather climates, provisions nay be raeeded to heat enclosures fcr
exposed pumps and motors. Pump controls for pumps, that discharge to collection
vehicles should be equipped with a lockable on-off svitch. A low-level float
may be used to turn off the pump to prevere motor overheating or loss of prime.
Pumps discharging to holding tanks or surface impoundments should include
float or liquid-level control devices to perform toe following functions.
low-level cutoff;
pump start;
high-water alarm in storage tank and sump; and
second pump start if two pumps are used.
3.7.3 Discharge Lines
The discharge lines should feed through a valve pit that contains a
suitable valve (gate, butterfly or ball type). A check valve should also be
installed after the main control valve to prevent back-siphonage. The volume
of leachate should be monitored by inserting a flow meter into the discharge
line and recording the amount pumped and -risually indicating the rate of flow.
The flow meter and recorder can also be placed irt the valve pit. The meter may
be a differential head type consisting of a ventuori tube, a magnetic meter, or
a Doppler meter. A flow totalizer may also be installed to document system
operation.
56
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i. / .t rcannoies
Manholes may be placed at the junction of leachate collection pipes to
allow access to the collection system for inspection and maintenance. They
should be placed within the containment area so the leachate collection pipe
does not penetrate the liner. Manholes should be designed to minimize stresses
on the liner and to maintain structural integrity over the lifetime of the
facility.
Manholes normally are fabricated concrete structures. The normal entrance
should be at least 60 cm (24 in.) in diameter to allow for personnel and
equipment entry. Larger diameter openings may be. necessary to accommodate
bulky inspection equipment, or workers using self-contained air supplies. The
manhole should be 1.2 m (4 ft) in diameter with an eccentric conical section to
make the transition to the diameter of the entrance section. The channel of
the manhole should be shaped . with a channel of the same diameter as the
entering pipe with the channel depth equal to the pipe radius. This channel
should be lined with appropriate material to prevent deterioration. A wide
base should be used to increase stability and minimize stresses on the liner.
In addition, pipe couplings to manholes should be made with flexible,
chemically-resistant boots.
3.7.5 Liquid-Level Monitors
Liquid-level monitoring provides information on the level of the leachate
at selected points within the site. Level monitoring coupled with high level
alarms will ensure that leachate levels above the liner will not exceed 30 cm
(1 ft) or that leachate in storage tanks will not overflow before being
transported to a treatment facility. Liquid-level monitoring devices are
discussed in Section 5.2.2.
57
\
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4.0 CONSTRUCTION
4.1 INTRODUCTION
Following the design of a leachate collection or cap drainage system,
construction documents are prepared. These document? provide the necessary
information in the form of graphical plans, specifications and a construction
quality assurance plan to describe and control construction of the system.
The construction documents also include estimated costs to construct the
system and provide quality assurance. These documents may also address the
prevention of drainage system failure during and after the construction phase.
The terir. "drainage system" is used to refer to both leachate collection and
cap drainage systems.
4.2 PLANS AND SPECIFICATIONS
x
" Tlans are working drawings which describe in graphic form the dimensions,
location, size, arrangement, layout, and spatial relationships of the drainage
system to be installed. Specifications are written documents that specify the
amount, type and quality of materials required, details of work to be
performed, quality control requirements, and construction schedules.
4.2.1 Petnll
The detail, contained in the pians and specifications should be complete
enough to provide a high degree of confidence that the constructed drainage
system will perform as designed. Recommended methods of component
installation* aimed at preventing failure of the drainage system, should be
clearly presented in graphic and written form. Particular attention should be
given to ensure that dimensions are correct and consistent, and that
step-by-step written procedures for .installation of components are concise,
accurate, ar.d follow a logical sequence. For example, plans and
specifications for collection, pipes should contain 'detailed drawings and
written descriptions of: '
placement of "bedding material around pipes; ,
spacing, size, and circumferential location of holes or slots in
collection laterals;
orientation of collection laterals with respect to grade, and
orientation of holes or slots; and
Joining of pipe sections and alignment of pipe to manholes.
'' 58 \
-------
Strict adherence to detail contained in tne plans and speciricacions win neip
ensure that the installed drainage system will function as designed according
to the criteria established to prevent failure.
The contract drawings should contain details of all components of the
project such as:
typical sections of the liner, filter layer, and ". linage layer;
collection pipe trenches;
manholes and sumps; and
specific details for variances from these-'typieai^ections-.
4.2.2 Specific Plans
Plans and specifications should include a layout of the existing facility
or site, a geometric plan of drainage system components, and a grading plan.
A layout of the site should be prepared showing, at a minimum, the
following details:
location of all physical features within the proposed limit of work;
« survey baseline;
all utility locations and elevations;
north arrow;
c graphic scale;
contours of rfi-°i;idge system layers; and
horizontal and vertical orientation and type and quantity of all
drainage system components.
A geometric plan should show elevation and location of all major
components of the project such as excavation limit, the horizontal and
vertical limits of the filter and drainage layers, liner, utilities, and
leachate removal structures. The plan should also show orientation of the
collection pipe network including spacing between laterals, and vertical and
horizontal positioning of the pipe within the drainage layer and with respect
to established baselines and benchmarks. Before construction starts,
installation location data given on the plans should be verified to determine
whether the control points are as stated and undisturbed. This verification
will determine whether these points can be maintained during construction. If
not, the plans and specifications should provide for alternative working
baselines and benchmarks. The essential element is to establish points that
are sure to remain undisturbed or that can be replaced from secure reference
points.
59
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me grading pian is a grapnic representation 01 cne Linisnea eievauion OL
the various components of the work relative to the existing conditions. The
grading plan should contain enough data to allow the contractor to compute the
cut-and-fill requirements of the project, and establish heights of
surface-water-control structures needed. Of primary importance is the
illustration of run-on and runoff control structures and conformance with
locations for surface-water interception or control facilities.
4.2.3 Phased Development
For landfills, common practice is to deposit wastes in functional units
called cells. Each cell is sized to handle an estimated volume of waste
within a specified time frame. Typically, cells are constructed to final
-dimensions even..though* the ..vcell may be filled with .waste over a period of
time. During the active life of" Che -cell, the filter and drainage layers
(including the col-lection pipe) -not covered by wastes will be exposed and
subject to potential damage. Climatic events such as rain storms iiay cause
serious erosion of the filter and drainage layers and result in loss of
structural integrity. High ambient air temperatures may cause thermal
expansion of plastic collection-pipe within the drainage layer that
permanently displaces the pipe and breaks pipe joints. Photo-oxidation of
plastic materials may cause embrittlement or failure of components such as
geotextiles arid pipes.
Phased development of individual disposal cells is an alternative
construction technique to alleviate the problems mentioned above. Using this
approach, only that area of the cell which would soon be covered with wastes
is constructed. This minimizes the time these components are subject to
potential damage from exposure. However, wastes should not be placed in the
cell until all components are installed and certified as functional.
Another alternative would be to construct the entire cell but cover
unutilized portions with a temporary synthetic or natural (i.e., soil)
protective cover. A disadvantage of this alternative is the potential
difficulties in applying and removing the temporary cover without damaging the
underlying drainage-system components.
The plans-anid specifications should" consider operational procedures and
schedules to reduce the potential for these factors to clog and affect
drainage-system performance.
4.2.4 Material
The quantity, size, type and quality of all construction materials must
be identified in the plans and specifications. Reference to established
material specifications such as state highway specifications for soils, the
National Sanitation Foundation or American Water Works Association for pipe
and fittings and the Underwriters Laboratory for electrical equipment are
appropriate. Additional specification of the quality of material may be
required, particularly for drainage-system components that require special
materials or where chemical resistance of construction materials is important
in preventing failure.
60
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Material specifications should also identify how drainage-system
components will be placed or joined together. For example, the method for
connecting multiple lengths of perforated pipe should be specified, as should
the connection of collection pipe to manholes. Compaction requirements of
soil or granular components should also be specified.
Material specifications should include all installed pumping, monitoring,
inspection and maintenance equipment. Sizes of materials and equipment should
be checked to verify that specifications for different materials are
compatible with each other. Specifications of materials should also include
climatic conditions that will influence proper placement. For example, the
placement of plastic materials in extremely cold temperatures may cause
cracking or other thermal defects. Curing of concrete or special coatings may
require a minimum temperature to assure proper performance.
All materials used in the construction of the drainage system should be
verified for conforiaance to design criteria as specified in the plans and
specifications. This verification should be performed in accordance with the
Construction Quality Assurance (CQA) plan discussed in detail in Section 4.3.
4.2.5 Installation Procedures
4.2.5.1 Drainage Layer and 'jollection Pipe
Plans and specifications for the installation of the drainage layer
(including collection pipe) should provide detailed information concerning
material placement, construction sequence, phased or staged construction, and
testing and inspection.
The drainage-layer material should be placed using equipment and
techniques that accomplish the task without dar.aging the materials or the
structural integrity of the finished drainage layer or the underlying liner.
Materials used in the construction of the drainage layer include the drainage
medium, collection pipe, bedding material for the pipe, and geotextile for
wrapping the bedding material (when used). Granular material should be washed
prior to placement to eliminate fines and should be placed directly on top of
the liner system in a manner that avoids dumping of materials or operation of
equipment directly on the liner. Equipment used to place aggregate material
should operate only on the placed granular material and should be compatible
with the selected allowable design loads on the liner system. A small
front-end loader generically referred to as a "Bobcat" may be a suitable piece
of equipment to place granular material even though its daily output might be
substantially lower than that of a heavy-duty front-end loader. All
construction equipment, including Bobcats, should avoid sharp turns that nay
create tearing or shearing stresses in the liner.
Procedures for testing and inspection of the drainage layer should be
detailed in the plans and specifications and performed in accordance with the
construction quality assurance (CQA) plan discussed in Section 4.3. Specific
items which should be addressed include:
61
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. grade (slopes) of finished drainage layer;
drainage-layer thickness;
correct horizontal and vertical alignment of collection pipe;
correct orientation, size and spacing of slots or holes in
collection pipe;
proper construction of pipe section joints;
construction sequence; and
control of fines during construction.
4.2.5.2 Filter Layer
Plans and specifications for the installation of the filter layer should
provide detailed information on material placement, and on testing and
inspection procedures.
The filter-layer will consist of either a specified granular or
geotextile material. Granular filter-layer material should be placed with
care to minimize potential damage to the underlying drainage layer. Equipment
should be selected to minimize vertical loadings and care should be taken
during equipment operation to avoid quick turns (causing ruts which could
damage the underlying drainage layer). The granular material should be spread
uniformly to grade and depth in accordance with the plans and specifications.
A geotextile filter fabric should be placed with care to avoid ripping or
puncturing the fabric. Adjacent runs of fabric should overlap as specified in
manufacturer's recommendations to prevent short-circuiting of leachate.
The installed filter layer should be tested and inspected in accordance
with the CQA plan discussed in Section 4.3. Specific items which should be
addressed include:
final grade slope;
thickness;
particle-size analysis (or geotextile properties); and
hydraulic conductivity.
4.2.5.3 Other Components
Installation procedures for manholes and sumps detailed in the plans and
specifications should address procedures for verification of vertical and
horizontal positioning of manholes and their foundations. Proper orientation
of the manholes is important with respect to collection-pipe connections.
Flexible Joints should be used to connect manholes and collection pipes.
62
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Manhole Installation procedures should also Include details on access
doors, interior steps or ladders, ventilation ports and locking devices to
limit access to the manhole. Installation of monitoring equipment installed
in the manholes, such as flow meters or level alarms, should also be detailed
in the plans and specifications.
In some instances, it may 'be necessary to apply chemically-resistant and
leak-proofing coatings to manholes or sumps in the field. Details of
application procedures and coating thicknesses should be provided in the plans
and specifications.
The installation details of pumps and discharge piping should address
locations and should reference appropriate benchmarks for the piping and, in
the case of pumps, any special installation and testing cited by the
manufacturer.
The removal system should be tested and inspected in accordance with the
CQA plan and should focus on the following items:
testing for alignment of manholes and collection headers;
inspecting integrity and thickness of any coatings; and .
inspecting and circuit testing all electrical connections, control
devices, and monitoring and pumping equipment.
4.3 CONSTRUCTION QUALITY ASSURANCE PLAN
Construction quality assurance (CQA) for a leachate collection and cap
drainage system is needed to assure, with a reasonable degree of certainty,
that the completed system meets or exceeds the specified design. This
Involves monitoring and documenting the quality of materials used and the
conditions and manner of their placement. CQA serves to detect variations
from design, whether as a result of error or negligence on the part of the
construction contractor, and to provide for suitable corrective measure before
wastes are accepted at the facility. Without proper CQA, problems with the
leachate collection or cap drainage system that are due to construction may
not be discovered until the system fails during operation.
4.3.1 Elements of a COA Plan
The Construction Quality Assurance Plan is the written document
describing the specific approach to be followed in attaining and maintaining
consistently high quality in the construction of a hazardous waste disposal
facility so that the completed facility meets or exceeds the specified design.
While the overall content of the CQA plan will depend on the site-specific
nature of the proposed facility, specific elements that should be included in
the plan are (EPA, 1985b):
» Responsibility and Authority--The responsibility and authority of
all organizations and key personnel involved in permitting,
63
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designing, and constructing the hazardous waste land disposal
facility should be described fully in the CQA plan.
CQA Personnel Qualifications--The qualifications of the CQA officer
and supporting inspection personnel should be presented in the. CQA
plan to demonstrate that they possess the training and experience
necessary to fulfill their identified responsibilities.
Inspection Activities--The observations and tests that will be used
to monitor the installation of the leachate collection system should
be summarized in the CQA plan.
Sampling Requirements--The sampling activities, sample size, sample
locations, frequency of testing, acceptance and rejection criteria,
. and plans for implementing corrective measures as addressed in the
project specifications should be presented In the CQA plan.
Documentation--Reporting requirements for CQA activities should be
described in detail in the CQA plan. Tills should Include such items
as daily summary repots, inspection data sheets, problem
identification and corrective measures reports, block evaluation
reports, design acceptance reports, and final documentation.
Provisions for the final storage of all records also -nould be
presented in the CQA plan.
Each of these elements is described in detail In EPA (1985b). In addition,
inspection activities for leachate collection systems are discussed below.
4.3.2 Inspection Activities
Observations and tests are performed by CQA inspectors to verify that the
materials and procedures used during construction are in conformance with the
plans and specifications. Observation and testing is conducted throughout the
construction process, beginning with the materials selected for use and
continuing through verification that the entire s'ystem has been constructed as
designed.
4.3.2.1 Types of Testing
The three types of testing generally used by CQA inspectors are:
visual inspection (observation);
non-destructive testing; and
destructive testing.
Visual inspection is used to evaluate and document the overall quality of
materials and procedures used during construction, including:
construction materials (storage conditions, conformance with
specifications, material quality, defects);
64
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Installation procedures (overall quality, methods used);
work conditions (temperature, precipitation, wind);
personnel and equipment utilization (vehicle routing, crew
assignments); and
o construction sequence.
Experience and training of the inspector are particularly important in
controlling quality by visual inspection.
Non-destructive testing is used to evaluate installed components of the
drainage system. It has the advantage that the component being tested is not
damaged by the test. Non-destructive testing is used to verify dimensional,
physical or mechanical characteristics to locate defects. Tests to determine
dimensional, physical and mechanical characteristics may. include permeability
analysis of soil layers, or physical measurement of elevation, grade or
location of placement of system components. Defects may be located by methods
such as cleaning out lengths of collection pipe to verify continuity of the
pipe network (see Section 5) .
Destructive testing often involves preparation of specimens taken from
the installed component which are tested to either partial or complete
destruction. Destructive testing is often performed to determine the tensile,
compressive or ultimate strength of installed materials, and usually requires
repair or replacement of a portion of the component from which the specimen
was taken.
4.3.2.2 Test Methods
Testing performed as part of a CQA program should be conducted in
accordance with standard procedures. Applicable procedures that are
well-established and generally accepted by professional consensus should be
selected. Typical sources of consensus standards include the American Society
of Testing and Materials (ASTM), the American Association for State Highway
and Transportation Officials (AASHTO), and the American Water Works
Association (AWWA). Non-standard test procedures should be avoided. When
non-standard procedures are used, they should be. described in detail to assure
consistent application of measurement throughout the CQA program. Commonly
used testing procedures that are applicable for drainage system quality
assurance are listed in Table 15.
65
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TABLE 15
CQA TEST PROCEDURES
Component
Factors to be
Inspected
Inspection Methods
Test Method Reference
Granular drainage and
filter layers
Synthetic drainage and
filter layers
Thickness
Coverage
Soil type
Density
Permeability (laboratory)
Material type*
Handling and storage
Coverage
Overlap
Temporary anchoring
Folds and wrinkles
Geotextile properties
Surveying; measurement
Observation
Visual-manual procedure
Particle-size analysis
Soil classification
Nuclear methods
Sand cone
Rubber balloon
Constant head
Manufacturer's certification
Observation
Observation
Observation
Observo' Ion
Observation
Tensile strength
Puncture or burst resistance
Tear resistance
Flexibility
Outdoor weatherability
NA
NA
ASTH 02438-84
ASTK D422-63
ASTM 02487-85
ASTM D2922-81
ASTM D1556-82
ASTM D2167-84
ASTM 02434-38
NA
NA
NA
NA
NA
HA
Horz (198
Horz (1984)
Horz (1984)
Horz (1984)
Horz (1984)
(cont inued)
-------
TABLE 15 (continued)
Component
Factors to be
Inspected
Inspection Methods
Test Method Reference
Pipes
Material type
Handling and storage
Location
Layout
Orientation of perforations
Jointing
'Solid pressure pipe
Perforated r-'pe
Short-term chemical resistance
Fabric permeability
Percent open area
Manufacturer's certification
Observation
Surveying
Surveying
Observation
Hydrostatic pressure test
' Observation
Horz (1984)
Horz (1984)
Horz (1984)
NA
. NA
NA
NA
NA
Section 4, AVWA C600-82
NA
Cast-in-place concrete Sampling
structures
Consistency
Compress ive strength
Air content
Unit weight, yield, end air
content
Sampling fresh concrete
Slump of portland cement concrete
Making, curing, and testing
concrete specimens
Pressure method
Gravimetric method
ASTM C172
ASTM C143
ASTM C31
ASTM C231
ASTM C138
(continued)
-------
TABLE 15 (continued)
00
Component
Electrical end mechanical
equipment
Factors to be
Inspected
Fora work inspection
Equipment type
Material type
Operation
Electrical connections
Insulation
Grounding
Inspection Methods
Observation
Manufacturer's certification
Manufacturer's certif ice'cion
As per manufacturer's instruction
As per manufacturer's instruction
As per manufacturer's instruction
As per manufacturer's certification
Test Method Reference
NA
NA
NA
NA
NA
NA
NA
Source: EPA, 1985b.
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5.0 INSPECTION
5.1 INTRODUCTION
Leachate collection and cap drainage systems must be inspected to ensure
that the constructed system continues to operate according to design
specifications. Undetected failure of drainage-system components can lead to
buildup of excess liquid over the liner, liner failure, and/or contamination
of groundvater. Inspections serve to discover failed components of the system
as well as to determine where failure mechanisms are active. In addition,
inspection of the drainage system can be useful in discovering problems with
other components of the disposal facility, especially the liner. Reduced
outflow from the drainage system, for example, may indicate a variety of
problems vith the drainage system or a leaky liner.
Federal regulations under the Resource Conservation and Recovery Act
require the leachate collection systems to be inspected. While in operation,
a landfill, for example, "must be inspected weekly and after storms to detect
evidence of the presence of leachate in and proper functioning of leachate
collection and removal systems, where present" (40 CFR 264.303(b)). The
Minimuu Technology Guidance (EPA, 1985a) also recommends that records be kept
"to provide sufficient information that the primary leachate collection system
is functional and operated properly" and that "the amount of le&chate
collected be recorded in the facility operating record for each unit on a
weekly basis." A plan for inspecting the leachate collection system should be
included in a Part B permit application as part of the overall Facility
Inspection Plan under 40 CFR 270.14(b)(5).
There are no similar Federal requirements for inspection of cap drainage
systems at closed facilities, although the "integrity and effectiveness of the
final cover" must be maintained (40 CFR 264.117). This implies the need for
inspection to make sura that the cap drainage system is functioning as
Intended.
State regulatory agencies may make requirements for inspecting leschate
collection or cap drainage systems in addition to the Federal requirements.
Requirements vary from state to state, and often from facility to facility
within a state. The Wisconsin Departru.nt of Natural Resources (WIDNR), for
example, does not have a standard set of requirements for the inspection of
leachate collection systems. Typical requirements, based on VIDNR permi:
approvals and conversations with WIDNR staff (Personal Interview, P. Kmet),
include:
cleaning the collection pipe after construction and after the first
lift of waste is placed to verify continuity of the lines (cciducted
with Department representative present);
field-checking collection pipe for clogging at least annually;
69
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daily recording of leachate levels in leachate collection tanks;
quarterly recording of levels in leachate-level wells installed au
site closure.
Inspections required at the Federal and state levels are intended to
provide enough information to the regulatory agencies to ensure that the
leachate collection or cap drainage system is performing adequately. They
also provide the owner/operator with performance data. Guidance on how to
conduct the required inspections, however, is generally not given; it is left
up to the facility owner to specify in the permit application how the
requirements will be met. This section presents information on inspection
procedures which can be used to meet state or Federal regulations or the
requirements of the facility owner.
Two cypes of inspection procedures may be used. The first, Regular or
Periodic Inspections, includes visual inspection, monitoring leachate level
over the liner, indicators of system failure or clogging, and direct
inspection methods. The second section, Special Inspections, includes
cleaning to verify the continuity of system after construction and after the
first lift of waste is placed, and methods to locate and diagnose leachate
collection system problems. A summary of the inspection methods addressed is
given in Table 16.
Inspection can most easily be accomplished by using a checklist which
summarizes the inspection protocol and provides an example record. Example
checklists provided herein can be used as a reference vhile the procedure is
conducted or as a guide in making data sheets to record test results for a
specific facility.
5.2 REGULAR OR PERIODIC INSPECTIONS
Regular (weekly and after storm) inspections may include visual
inspection, monitoring the leachate level over the liner, correlating amount
of precipitation and site parameters with leachate quantity and correlating
leachate quality with clogging indicators. The regulations do not specify the
type of inspection which must be performed weekly and after storms, so
selection of the appropriate methods is left up to the owner/operator (with
the approval of the permitting agency).
Periodic inspections may include procedures which are conducted on a
monthly, quarterly or yearly basis. These longer frequency inspections may be
required by the state or performed as part of the facility owner or operator's
own inspection and maintenance plan. These inspections are more involved and
more costly uhan the methods used on a weekly basis, but provide a direct
evaluation of the condition of the drainage system. Methods include
television and photographic inspection and maintenance related techniques such
as checking system continuity by passing sewer-cleaning equipment through the
collection lines.
The first four inspection procedures discussed below (visual, leachate
level, leachate quantity, leachate quality) provide primarily indirect
70
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TABLE 16
SUKMARr OF INSPECTION METHODS
Method
Visual
Recommended
Frequency
weekly and
after storms
Purpose
verify presence of leachate
in and proper functioning
of leachote collection
system
Comments
required by RCRA; does not
determir.e cause of problem;
not useful for prevention
Leachate Level
Neasurenent
Leachete Quantity
Analysis
Leachate Quality
Analysis
quarterly or
when problems
suspected
quarterly
as needed
locate areas where leachate
level over liner is greater
than one foot
evaluate overall performance
of system in removing
leachete from over liner
evaluate potential for
failure mechanisms to occur
can locate general area of
problem but does not determine
cause
does not determine cause of
problem; should be verified
by other techniques
additional research needed
to determine usefulness of
this method
Television and
Photographic
Maintenance Related
Excavation
annually
annually, after
construction,
after placement
of first lift
of waste
as needed
observe condition of pipe
network, determine cause .
ond location of problem
verify continuity of pipe
network, determine cause
and location of problem
determine cause of problem
requires adequate access
to pipe network
requires adequate access
to pipe network
used when problem is already
located; used in conjunction
with repair See Section 7
-------
WA.WXV££ji£V*. Jf O \f A. C&-A, WJ. 4J A. 4. 4. Jf J ^
leachate characteristics and flow through the system. Direct inspection
methods (television and photographic, inspection during pipe maintenance) find
the problem itself (e.g., a clogged pipe) and do not depend on the effects of
the problem (e.g., restricted flow). The direct methods discussed below are
applicable only to collection pipe which is accessible to the equipment used.
No direct methods exist for the periodic inspection of buried granular
drainage and filter layers, or, of- course, for collection pipe without
adequate access.
5.2.1 . Visual Inspection
Discussion
Visual inspection is the simplest inspection procedure. It requires the
inspector to use no more than his or her senses and perhaps some basic
equipment such as a flashlight or liquid level measuring device. Visual
inspection is limited because most of the system is buried and not accessible
to the inspector. Access is provided primarily by manholes and riser pipes;
visual inspection therefore focuses on the information obtained via these two
features. Components of the system which are not buried can also be
inspected.
The purpose of visual inspection is to verify qualitatively that the
leachate collection system is functioning as intended. Thfc inspection
required by RCRA, referred to in Section 5.1 above, would likely be a visual
inspection. The purpose of that inspection is -to detect whether leachate is
in the system and determine whether any problems are apparent.
Visual inspection is relatively inexpensive and can be performed as part
of the regular routine of facility operation. It also can provide the first
evidence that problems exist in the drainage system. An example of this would
be finding no flow in a manhole where flow is expected. Visual inspection,
however, is qualitative and does not reflect failure mechanisms which are in
progress but are not readily evident. There may be flow in a manhole, for
example, even when the drainage layer is partially clogged. More quantitative
techniques are needed to discover a reduction rather than a stoppage of flow.
Visual inspection Is therefore less useful in preventing problems since it
primarily indicates when maintenance or repair is required.
Protocol
The protocol for visual inspection at a given facility will depend on the
site-specific layout of the leachate collection or cap drainage system. In
particular, it will depend on the number, type and location of access points
to the buried system, and on the parts of the system which are not buried.
Access points to the system may include:
manholes;
riser or clean-out pipes;
risers for collection sumps or tanks;
system outflows; and
72
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leachate level wells.
Each of these access points should be checked for the presence of
leachate and the ovsrall condition of the access structure. Leachate flow
rate and level of standing leachate should be measured, where possible.
Methods for measuring leachate level are discussed in Section 5.2.2.
Components which may be accessible above ground include:'
mechanical equipment and controls;
system outflows; and
leachate storage tanks or surface impoundments.
The inspector should make sure that all mechanical equipment (monitors,
meters, pumps) is functioning properly, and should check leachate flow
(presence and rate) at system outflows and leachate level in tanks or surface
impoundments. The overall condition of each component should also be
evaluated.
All observations made during a visual inspection should be recorded. A
generic checklist for visual inspections is provided in Figure 12. The
checklist provides an example of the type of information to be recorded for
each component mentioned above. The facility operator should design a
checklist for a specific facility based on the layout of the leachate
collection or cap drainage system at that facility.
Inspection results which indicate potential problems with the leachate
collection or cap drainage system include:
ff irregular flow patterns;
no flow when expected;
significantly higher or lower flow than expected;
high leachate levels over the liner;
full collection tank or sump;
declining level in tank or sump which has not been pumptd;
inoperable equipment; and
mechanical or structural problems, including seepage, cracks, and
broken parts.
Leachate levels, flow rates, ar.d location where leachate was noted. or
measured can be plotted on a diagram of the leachate collection system.
Preparing such a diagram weekly facilitates the analysis of visual inspection
data in assessing the performance of a leachate collection system over time.
The status of facility operations (e.g., operating areas, number of lift(s) in
place, waste types disposed of) on the day of inspection should also be
recorded on the diagram.
73
i N.
-------
Basic Dan
Name:
Time: a.m. /p.m.
Date- / /
Weather Conditions:
Precipitation since previous inspection:
Depth of snow pack :
Type of Inspection
n-i'iy ,
V/ookly . _.
After
Storm
Other:
Storm Data
Date(s) of storm
Qiiratinn
Amount Rain .
Comments:
hrs.
in.
Manhole'
1. Location or ID:
2. Flo« observed? yes/no
a If yes. rate cfm
b Meas. techn:
3. Pump on or off
4. Standing leachate? ves'no
a If yes. level: ft
b Meas. techn: _____
5. Problems noted:
6. Comments
1. Locationc* ID: _
2. Leachate present yes/no
a If yes. level: _ ft
b Meas. techo: _
3. Problems noted:
4. Comments:
'Attach diagram of entire leachate collection
system with results recorded.
Sump/Tank*
1. Location or ID:
2. a Leachate level ft
b Meas. techn:
3. Flow observed? yes/no
a If yes. rate _j
b Meas. techn:
cfm
4. Pump on or off
5. Problems noted:
6. Comments:
Outflow*
1. Location or ID:
2. a Flow fate ___
b Meas. Techn.
3. Problems/Comments:
_cfm
Mochenical Equipment*
1. Location or ID: _
2. a Operating:
3. Problems:
4. Comments:
yes/no b operable: yes/no
Inspector:
Signature: Date:
Approved by:
Signed:
(print)
Date:
Figure 12. Checklist for visual end teechate level inspection*.
""" ' 74 . '
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b.2.2 Leachate Level Over Liner
Discussion
While visual inspection of leachate collection, systems will indicate
whether leachate is being generated, it will not address the basic questions
of whether all the leachate generated is being collected. Observing the
leachate level above the liner provides a direct measurement of leachate
collection system performance. Since the leachate collection system is
designed to maintain leachate levels over the liner at less than 30 cm (1 ft),
higher levels may indicate problems with the leachate collection system. This
is especially true if levels are significantly higher or occur over prolonged
periods. Therefore, observation of the leachate level above the liner should
be an integral part of an inspection program.
The preferred method for observing and measuring leachate level above the
liner is through the use of observation wells installed specifically for this
purpose. Design of observation wells is similar to that of groundwater
monitoring wells, which are discussed in detail in Fenn et al. (1977). The
observation-well casing pipe is extended down to a point in the drainage layer
below the desired maximum liquid level. The bottom meter (or more) of the
pipe is packed in gravel and the- pipe screened to allow free movement of the
liquid through the pipe.
When observation wells are not available, some insights into the probable
leachate level above the liner can be derived by analyzing measurements of the
leachate level at key points in the leachate collection system. This analysis
is recommended even in cases where observation wells are available in order to
give a more complete picture of leachate conditions.
Figure 13 summarizes the probable leachate levels in observation wells
and leachate collection system measurement points under different leachate and
system performance conditions. This figure demonstrates that leachate levels
in a sump or riser pipe may not give an accurate indication of leachate levels
over the liner. This is due to drawdown of leachate levels in the vicinity of
leachate collection pipe, and abrupt changes In leachate level which may be
caused by clogged pipe or drainage material. Only a properly installed
observation well gives a reliable measurement of leachate level over the liner
at a given point. While measurement points in the collection system will
provide some information on leachate level above the liner in landfills with
no observation wells, these results must be used cautiously and in conjunction
with other data. Ideally it will be possible to measure leachate levels in
observation wells and the collection system. In such cases, the data can be
used not only to identify situations of high leachate level but also as a
diagnostic tool to determine the type and location of the collection system
failure.
Protocol
During the design and initial start-up phase of a facility, the operator
should work closely with the design engineer to establish a site-specific
75
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Clogged Area
fa *
1 &L
C\ ' M*fa\ f
-"W*
Oft
. i
Or
x^
R2\
:>
n
i
-------
protocol for collecting, recording, and analyzing leachate level data. At an
existing facility, ths operator should complete the following preparation
steps prior to initiating a comprehensive leachate level measurement program:
Step 1 - Identify Measurement Points: All points where leachate level
can be measured should be identified and labeled. In addition to
observation wells, points in the leachate collection system such as
manholes, risers, and suinps should be included. Factors should be
developed for converting the anticipated 'field measurement (e.g.,
distance from top of observation well to leachate level) to the leachate
level above the liner for analysis.
Step 2 - Map Measurement Points: All identified measurement points
should be plotted on a- site map.
Step 3 - Develop Conceptual Leachate Flow Model: An expected leachate
flow pattern, expressed in terms of the likely relationships between
measurement points, should be developed. These relationships depend on
the specific leachate collection system design.
Step 4 - Record and Store .Data: A system should be developed for
plotting or recording data so that it is easy to observe trends at
related measurement points. A leachate level recording sheet should be
developed in conjunction with the visual inspection recording sheet
(Figure 12). In addition to providing space for recording leachate level
at Inspection points and observation wells, this sheet should include a
record of weather conditions on the day of the inspection, accumulated
precipitation since the previous inspection, and depth of sncw pack.
In most casaa a single absolute measurement of leachate level may not
provide significant information when taken out. of context, since leachate
levels will vary across the facility arid with timel As a result, it will
be important to develop a recording procedure which will allow the
facility operator to readily identify situations where area! and temporal
trends are not consistent. The data are multidimensional and therefore
require careful presentation to ensure trends can be readily identified.
The recording of leachate level data is an ideal application for a
personal computer. Using commercially available spread sheet programs a
facility owner/operator can develop a site-specific data management
procedure. A carefully designed system would allow direct entry of field
data in the order in which the measurement points have been inspected.
The data could then be automatically converted to depth above liner and
plotted against historical data in order to provide an easy means for
evaluating changes with time. Similarly, the data could be automatically
plotted on a grid with contour lines to allow for evaluation of areal
trends. Incorporating data in a computer data base would permit
manipulations such as three point running averages to identify trends
more clearly. Further, a program could be developed which would
automatically compare the leachate level trends in measurement points
which are expected to have .similar leachate levels. This automatic
77
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comparison could provide a readout of situations in which the temporal
trends observed at adjacent measuring points are inconsistent.
In situations where a personal computer is not available for data
management, or where the number of measuring points is very small, the
operator may wish to plot the liquid-level 'data for each point against
time in order to observe changes with time. In any case, the operator
should plot the data for a given inspection on a site map to allow quick
evaluation of areal inconsistencies, and to provide a consistent format
for data presentation.
Leachate Level Measuring Devices
A number of methods can be used to measure the level of leachate at
measurement points throughout a facility. Some methods measure the distance
from the surface and others measure the depth of leachate above a fixed point
(e.g., bottom of the-manhole). In either case the raw field data will have to
be calibrated to a level above the liner for analysis.
Methods which measure distance from surface to leachate level include:
Conventional Tape Method
A weight is placed on the end of a measuring tape. The last several
centimeters of the tape are marked with -chalk before it is loweied into
the measuring point. When a splash sound indicates that the weight has
reached the leachate, the tape is lowered an additional few centimeters
into the measuring point and a reading is taken against a reference point
on the surface. The tape is then brought to the surface. The distance
the tape extended into the leachate (as noted by the chalk becoming wet
or washing away) is subtracted from the first reading to give the
distance from the reference point to the leachate level. An alternative
conventional tape method is to use a cylindrical weight, or "popper",
which makes a distinct "pop" noise when the. weight reaches the leachate.
Depth to that level can then be measured from the tape. Both methods are
fairly inaccurate compared to other methods, described below. If used,
the procedure should be repeated several times and the results averaged
for a more precise measurement.
Electronic Gauge
An electronic gauge can be used in combination with a measuring tape to
more accurately identify the liquid level. The device, which may have
both float and conductivity level detection systems, Is attached on a
measuring tape and lowered into the well or manhole. When any liquid is
encountered the float light is activated. When a conductive liquid is
encountered the conductivity light is also activated. Using this device
it is possible to determine whether an oily, nonconductive layer is on
top of the leachate and to estimate its thickness. The lights are
located directly, on the gauge and are viewed by looking down the well.
When the lights are activated the operator takes a reading of the tape
against the fixed reference point on the surface.
: 78
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Automatic Level Measurement
An automatic mechanical float or conductivity gauge can be used to
provide continuous leachate-level measurements. As the liquid level
rises the float or gauge also rises and the slack in the wire is taken up
by a spring mechanism on the surface. The spring mechanism is calibrated
to indicate the depth to liquid level. The depth can be read as needed
by an operator or continuously recorded on a graph.
Methods which measure depth of leachate above a fixed point include:
. Electronic Float Level Detector
This type of device has a float which activates a series of magnetic
switches when lowered to the bottom of the observation point. A similar
design can be permanently installed in a measuring point and provide an
electronic readout of leachate depth. The switches are typically spaced
at 2.5 cm (1 in.) intervals.
Conductivity Float T«.vel Detector
Conductivity switches can be placed at 0.6 cm (.25 in.) intervals rather
than the 2.5 cm (1 in.) intervals described for float-activated magnetic
switches. While it is possible to get significantly greater precision
using conductivity switches, several disadvantages are associated with
tha technology. The switches can be fouled easily, it is possible to get
a creeping of liquid up the sides of the gauge causing incorrect
measurenents, and contamination may result in incorrect measurements.
Therefore, conductivity gauges are not recommended.
Pressure Transducers
A pressure transducer can be installed in the bottom of each measuring
point. The transducers are sensitive to an increase in the pressure
caused by increased liquid levels. Unlike the conductivity gauge and the
float gauge, the pressure transducer provides a continuous measurement
rather than an incremental measurement of liquid level. Pressure
transducers tend to be fairly sensitive and are therefore not recommended
for portable gauges but only for permanent installations. Readouts from
pressure transducers can be transmitted electronically and recorded
automatically.
5.2.3 Leachate Quantity
As noted above, the Minimum Technology Guidance (EPA, 1985a) recommends
that records be kept of the quantity of leachate collected. Comparing these
data with the quantity of leachate expected over the same period can provide
useful information on leachate collection system performance. Empirical
methods can be used to analyze trends in leachate quantity data. Predictive
models, such as those used in leachate collection system design, provide a
more quantitative approach to the evaluation. These two techniques are
discussed below.
79
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5.2.3.1 Empirical Method
The quantity of leachate collected at a facility can be expected to
follow some basic trends over the lifetime of the facility:
Prior to and during placement cf the first lift of waste, leachate
generation may closely correspond to precipitation, since the
precipitation falls directly on the li-.achate collection system.
As the collection system is covered with waste, leachate generation
should decrease or go to zero since the waste will absorb much of
the precipitation.
As the wastes become saturated with liquid (i.e., reach field
capacity) leachate generation should increase, although each new
lift of waste increases the capacity of the landfill to store
liquid.
At some point, a steady-state condition may be reached where a
correlation can be found between precipitation and leachate
generation. For example, leachate generation may be 80 percent of
precipitation with a lag time of 1 week, with the other 20 percent
being absorbed in the uppermost lift of waste.
« This steady-state condition may continue until the landfill is
closed with a final cover. Leachate generation would then be
expected to decrease since precipitation inputs to the waste mass
are eliminated or greatly reduced.
c Laachate generation should eventually drop to zero, or to .scnia crsall
amount If the cover is not completely effective in eliminating
liquid inputs.
These trends will vary depending on site-specific conditions such as the
absorptive capacity of the waste, waste placement procedures, climate,
precipitation patterns in a given year, and surface araa of the open portion
of the cell. Leachate generation records can be compared with expected
patterns for a given collection point, with generation records at other
collection points in the same cell, or with generation records from other
cells at the sane facility. Any major deviations from leachate generation
trends expected at a given site may indicate problems with the leachate
collection system.
5.2.3.2 Leachate Prediction Models
A number of analytical tools are now available which are used to predict
leachate generation, primarily for design purposes. Gee (1983) compared
leachate predictions from three water budget models and one empirical model
with actual leachate generation in a field soli4, waste lysimeter. The
results, shown In Table 17, indicate considerable variance between predictions
and actual leachate generation even when aggregated to a yearly base. Figure
14 presents the same data expressed as percentages of actual leachate
production. The figure illustrates that the state of the art for predicting
80
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TABLE 17
ANNUAL LEACHATE PREDICTIONS AND MONTHLY MEAN ERROR COMPARED
TO ACTUAL LEACHATE PRODUCTION*
Prediction Method 1972 ]J?74 1975 Overall
Rainfall Simulator Model:
Mean Monthly Abs. Error (in.) .40 .38 .34 .37
Total Leachate (gal.) 9,434 8,955 7,108 25,497
HELP Model:
Mean Monthly Abs. Error- (in.) .29 .67 .38 .45
Total Leachate (gal.) 6,809 10,277 8,477 25.563
HSSWDS Model:
Mean Monthly Abs. Error (in.) .75 .81 .78 .78
Total Leachate (gal.) 12,212 15,123 12,603 40,138
Thornthwaite Water Balance:
Mean Monthly Abs. Error (in.) .44 .69 .61 .5«
Total Leachate (gal.) 10,423 15,130 10.654 36,117
Actual Average Monthly
Leachate Production Cell 1 (in.) .69 .71 .36 .59
Total Actual Leachate (gal.) 8,998 9,184 4.740 22,922
*1 inch - 2.54 cm
1 gallon - 3.785 liters
..Source: Gae, 1983.
81
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UJ
100%
L
i
RAINFALL
SIMULATOR
HELP
HSSWDS THORNTHWAITE
Total Annual Leachate Prediction
I I
H
100%
THORNTHWAITE
M*an Monthly AbwIuM fcrror
Figure 14. Anilytis of Icachate prediction moditt.
-------
leachate generation for short time intervals, .evp.n using an empirical model
developed for the specific, site conditions, is very rudimentary. Mean
absolute errors in Figure 14 range from 40 to 200 percent of flow for the
short-time period predictions which would be es'sential lor monitoring leachate
collection system performance.
Since leachate prediction techniques have been used to estimate the
maximum anticipated leachate flow for sizing collection and treatment systems,
these inaccuracies can be accounted for in traditional factors of safety and
over-design. Except for precipitation, users of these techniques must
estimate values for a number of site-specific variables.' The outcome of the
calculation is very sensitive to the levels assigned to each of these
estimated variables. Based on the results of a sensitivity analysis of the
EPA Water Balance Method to variations in the coefficient of runoff and
available soil moisture, Kmet (1982) concludes "it is apparent that given the
right set of assumptions practically any percolation rate (leachate generation
rate) c«\ be justified." Further, there has been limited verification of
leachate prediction methods with actv.al leachate production records at
full-scale facilities.
Because of the high degree of sensitivity of the various leachate
prediction models, it would bo impossible to determine whether production of
leachate at lower-than-predicted levels is the result of a system failure or
poor modeling. Therefore, caution should be exercised when using Isachate
prediction methods for ongoing monitoring of leachate collection system?.
Protocol
Precipitation data either can be collected onsite in a small
meteorological station or can he obtained from the nearest U\S. Weather
Service Station. Leachate generation data should be gathered from as many
discrete -oints as the facility design permits. In most cases, leachate
quantity data will be obtained from leachate pumping records. If there arw a
number of pumping stations throughout the facility, records should be
maintained for each station separately, so that the leachate generation
patterns in adjacent sections of the same facility can be compared.
To facilitate recordkeeping the site operator should develop a chart to
convert leachate quantities from liters (or gallons) to centimeters (or
inches) for the drainage area. Leachate generation in centimeters (inches)
can then bo plotted on the sams graph with precipitation in centimaters
(inches). Weekly records are recommended.
5.2.4 Leochate Quality
Analysis cf leachate quality may provide information indicative of the
potential for failure of a leachate collection system by the various failure
aechanismo. The appropriate indicator parameters depend on which of the
failure modes is involved. Analysis of leachate quality may be useful in
determining the susceptibility of the system to pipe deterioration,
sedimentation, biological growth, chemical precipitation, or biochemical
precipitation.
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Analysis of leachate quality may indicate whether conditions conducive to
failure are present. None of the techniques discussed below, however,
provides absolute confirmation of a problem; they are indications of the
possibility that a problem may exist. On the other hand, the absence of a
positive indication may suggest a small likelihood of failure by the mechanism
being examined.
Analysis of leachate quality is primarily a conceptual technique for
analyzing leachate collection system 'performance. Therefore, specific
protocols are not provided. The technique is discussed since it may provide
useful information about the failure mechanisms discussed in Section 2. It
also may provide useful information about the potential for clogging of the
drainage and filter layers, for which no direct inspection methods are
available.
5.2.4.1 Pipe Deterioration
Pipe deterioration can be caused by a variety of mechanisms, including
corrosion, oxidation, chemical attack, or other chemical reactions. The
susceptibility of collection pipe to chemical attack will depend on the pipe
material used. Generally, waste constituents which can damage a pipe are
considered to be incompatible wastes and are excluded from disposal in the
cell. Periodic monitoring of leachate pH and analysis for chemicals of
concern (e.g., organic solvents) provide a -check that incompatible wastes have
not been disposed of in the cell. If this analysis indicates potential
problems, corrective measures may be possible to prevent pipe failure.
5.2.4.2 Sedimentation
Analysis of a single leachate sample for sediment loading does not
provide an indication of the potential for sedimentation clogging of the
system. A low sediment-load may indicate that no sediments are entering the
system, or that all the sediments are settling out somewhere in the collection
pipe. Similarly, a high sediment-load may indicate a problem with the filter
or drainage layer, or may show that flow is sufficient to remove sediments
which would otherwise accumulate in the collection pipe over time.
A better approach would be to consider sediment loading over time and
over different sampling points in the same cell. A gradual decrease in
sediment load to a steady-state level indicates that the filter is working as
expected. A sharp change in the sediment content of samples from a particular
location, however, may indicate a change in the status of the system (e.g.,
sedimentation is now occurring in the pipe; the filter layer has failed at
some point upgradient of the sampling location). Historical data can be used
in a manner similar to leachate quantity data described in Section 5.2.3,
above. For example, large differences in sediment loading at two adjacent
sampling points may indicate sedimentation problems between those two points.
5.2.4.3 Biological Growth
Clogging because of biological growth occurs when naturally-occurring
micro-organisms metabolize organic constituents of the waste. Slime-forming
organisms can clog collection pipes and the drainage and filter layers.
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Detection in the leachate of organisms known to form slimes, and nutrients,
contaminant levels, and oxygen conditions within an appropriate range to
support growth would indicate potential problems.
Ford (1979 and 1980) has identified three organisms associated with
clogging in drain systems: Vltreoscilla. Enterobacter . and Pseudomonas . The
last is a common soil bacteria. Conservatively, if any of these species is
detected, it may be presumed that biological clogging is possible. Samples of
the leachate can be cultured to determine whether growth would occur under the
conditions existing in the system. The sample should be taken and cultured
under the conditions existing in the system, and the culture tests should be
performed with a range of conditions reflecting variations in nutrient and
organic composition observed over a year. This type of laboratory work,
however, can be very expensive.
5.2.4.4 Chemical Precipitation
The principal mechanism for chemical deposition is the precipitation of
calcium carbonate (CaCO.) or, to a lesser extent, manganese carbonate.
Precipitates may form whenever the concentrations of free calcium ion (Ca )
and bicarbonate ion (HCO, ) exceed the equilibrium concentrations at a
particular pH. The equilibrium relation can be expressed in terms of the
Incrustation Potential Ratio (l.P.R.) as follows (Baron, 1982):
I.P.R. - t'Total alkalinity) (Hardness)
10.3 x 10
where total alkalinity and hardness are both expressed in py.m CaCO,.
If the I.P.R. is less than 1, no carbonate deposition should occur. If,
on the other hand, the I.P.R. is greater than 1, deposition is possible, but
will not necessarily occur.
Further, other researchers have suggested ranges of these parameters for
which deposition potential is positive. Shuckrow et al. (1981) developed the
following ranges for the parameters appearing in the I.P.R. expression:
Alkalinity (as ppm CaCO,): 20.6 to 5400
Hardness (as ppm CaCO ): 700 to 4650
pH: 3 to 7.9 J
All the parameters involved can be measured with conventional instruments and
methods .
In addition to determining the I.P.R. for the current sample, the I.P.R.
for a leachate based on a saries of samples over the past year would indicate
the possibility of clogging under the highly variable conditions at a site.
For a conservative indif.r.tion of clogging potential, the I.P.R. would be
calculated using values of alkalinity, hardness, and pH corresponding to the
mean plus one standard deviation. The probability that any combination of
conditions will produce & larger value of I.P.R. is about 10%. Samples taken
85
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over a period of several months should be included for an accurate indication
of leachate variability. Shorter averaging times may be appropriate if
overall conditions within the system are1 known to be changing. Seasonal
averages may be more appropriate in some locations.
5.2.4.5 Biochemical Precipitation
The principal biochemical process leading to potential clogging is the
precipitation of fr.rric oxide (hydroxide) complexes from soluble ferrous mixes
by biological oxidation. Manganese can be deposited in a similar manner.
Iron precipitation is a complex process which can occur with various
bacteria under a variety-of conditions. Kuntze (1978) suggests that pipes are
likely to clog when iron concentrations' are greater than 1 ppm and pK is less
than 7, if the iron is from a source other than the surrounding soils
1. drainage layer). Iron clogging has been observed in the field at iron
concentrations as low as 0.2 ppm and at pH ranging from 2.5 to 8.5 (Lidster
and Ford, undated). Concentration of dissolved oxygen and redox potential
also influence biochemical iron precipitation.
Leachate samples to be used in developing data to compare with these
conditions should be taken, if possible just outside of the drainage layer.
If iron precipitation is occurring, the resulting iron levels in the leachate
exiting the system may be so low that the test results would indicate no
potential problem.
In many systems, it may be possible to obtain leachate samples only at
the exit. In this case, if the presence of iron or manganese-reducing
bacteria along with iron or manganese is detected in the leachate, biochemical
precipitation should be considered as a possibility.
If the leachate analysis indicates the possibility, a more definitive
indication can be obtained by culturing samples of the leachate, augmented by
ferrous ions at the raaximurc concentration previously observed in the leachate.
Experimental conditions should include a range of redox potential (oxygen
level) and pH derived from historical leachate monitoring at the site. Iron
precipitation can be quite rapid, resulting from sudden changes in pH or, mere
dramatically, from changes in oxygen conditions due to the introduction of air
into a normally anaerobic system.
Iron deposici." can also form by the precipitation of ferrous sulfide
through the reaction of soluble ferrous ions in the leachate with hydrogen
sulfide (H?S) produced from anaerobic sulfate-reducing bacteria (Young et al.,
1982). Anaerobic conditions can arise in the drainage and filter layers in
all systems, and in the collection pipes if che exit sumps are sealed from the
atmosphere. If it is possible to draw a sample from the anaerobic portions of
a collection system, indications o* potential clogging can be determined by
culturing the leachate to determine whether the necessary bacteria are
present. If sulfate is also p-.esent at levels greater than a few parts per
million, and iron has been '/oserved ir. that sample or in previous samples
clogging should be considered a possibility.
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5.2.4.6 General Considerations
The above criteria can be used to indicate whether the mechanism
described is likely to occur in the facility. A negative result, however,
does not indicate that the mechanism will not occur. The criteria are based
on experience found in the literature and do not account for the presence OL
particular waste constituents, or unique, site-specific conditions which may
hinder or enhance the failure mechanism.
Establishing the particular range of considerations under which failure
mechanisms can occur at the site would help address this problem. The
validity of the I.P.R. expression, for example, depends on the absence of
species that would interfere with the equilibrium processes that throw calcium
out of solution. Deviations from the theoretical bounding value of unity
could be determined by carrying out a set of laboratory experiments using
actual leachate samples at the site. Samples of leachate with the principal
parameters (alkalinity, hardness, and pH) adjusted to reflect the variations
observed over a period of time would be used as a basis for determining the
critical I.P.R. valid at the site. Future leachate analysis would be
evaluated with respect to the site-specific criteria. This procedure would
reveal, to the extent that the samples used in the experiment are
representative of the full range of leachate composition, the effects of
interferences and deviations from the conditions for which the criteria were
derived.
Similarly, it would be possible to determine a range of conditions for
the biochemical oxidation of iron, parallel to the general conditions reported
above, applicable to the particular site. Experiments involving biochemistry
are more difficult to systematize because the microbiological flora present
are hard to characterize fully and to control. Nevertheless, it should be
possible to obtain values that more closely, reflect specific conditions at the
site than do the general indices noted in the literature.
5.2.5 Television and Photographic Inspection
Discussion
Television and photographic inspection of sewer lines is a well developed
technology for locating groundwater infiltration, root penetration, and other
problems with sewer lines. The same technology is applicable to leachate
collection .-md cap drainage systems to find clogging and inspect the condition
of collection lines, provided adequate access is available.
The primary advantage of television inspection is that it allows the
operator to directly observe the condition of the collection pipe and
precisely locate problems. Problems in their early stages (e.g., cracked
pipe, biological buildup) which do not yet affect flow or the passage of
maintenance equipment can be detected. In addition, a videorecorder can be
used to record inspection results. The disadvantages of television inspection
are that the procedure is somewhat involved and that it can be conducted only
in lines with adequate access (e.g., 15 cm (6 in.) minimum diameter, access to
both ends of the pipe).
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Photographic inspection is ^.ess expensive than television inspection
while providing most of the same benefits. Additional drawbacks of
photographic inspection, however, include decreased reliability since it is
not known whether the lens is blocked until after the film is developed,.and
it is necessary to wait for film to be developed.
Protocol
Equipment used in television and photographic inspection of collection
pipe includes (Foster and Sullivan, 1977):
1. A skid mounted camera. Types of cameras include various types of
color, black and white video units-and 35-mm photographic equipment.
2. A light source for the camera.
3. Television cable and steel cable (on reels) with measuring equipment
to determine the location of the camera in the collection pipe.
4. Sheaves or pulleys for the cables and a winch at one end to pull the
camera through the pipe.
5. A control unit with a television monitor (for television
inspection), communication equipment, and a camera and/or video
recorder to photograph and record key locations in the pipe.
6. An electric generator if no power supply is available onsite.
Prior to ^elevision or photographic inspection, the collection pipe
should be thoroughly cleaned (see Section 6), unless the purpose of the
inspection is to determine the condition of the line prior to any cleaning.
Then, the camera is rigged between two access points (e.g. using a rodding
machine), with the camera at one end of the line connected by cable to a winch
at the opposite end, which pulls the camera slowly through the line. Televi-
sion cameras monitor the line continuously and photograhic equipment can be
set to take a picture at regular intervals (e.g., every meter). A meter on
the winch or cable reel records the distance of movement of the cable and
therefore measures the location of the camera in the line. Some units display
this distance on the television monitor. Cameras are available to inspect
lines from 8 cm (3 in.) to 150 cm (60 in.) in diameter (although many systems
only go down to 15 cm (6 in.)), and are on the order of 300 m (1000 ft) in
length.
Television or photographic inspection can be conducted annually as part
of regular system inspection and maintenance. This would help identify
problems which may go unnoticed by other inspection and maintenance
procedures. The technique can also be used to locate or identify problems
which are discovered or suspected by other methods. Television inspection,
for example, can be used instead of excavation to identify the cause of pipe
blockage discovered during routine flushing (assuming the pipe is not totally
blocked and the camera can be rigged between two access points).
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A checklist for television or photographic inspection is given in Figure
15. It is important to record the type of inspection-being conducted and the
precise location of collection lines being inspected. A description of all
problems noted, including location, should be given. Problems which can be
identified by television or photographic inspection include:
0 partial clogging of the pipe;
total or partial clogging of the pipe openings;
deviations in the line (straightness) and grade (slope) of
the pipe;
broken or cracked pipe;
separated or uneven pipe joints;
foreign objects in the pipe; and
areas of leachate accumulation. .
5.2.6 Inspection During Pipe Maintenance
Discussion
Pipe maintenance techniques, discussed in Section 6, can also be used
(simultaneously) to inspect collection lines. The fact that maintenance
equipment can pass through the collection lines indicates that there are no
major clogs or broken pipes, and that the system is continuous. The only
major difference between running a low-pressure jet, for example, through a
collection lir.e for inspection as well as maintenance rather than maintenance
alone is that the former utilizes a meter to measure the location of the jet
in the pipe. When the progress of the jet is hindered, therefore, the
location of the problem can be discerned.
Protocol
Inspection via maintenance related techniques occurs whenever maintenance
equipment is run through the collection line. Regular inspection can occur
quarterly, semi-annually or annually. Special inspections using this
technique are discussed in Section 5.3.
A checklist for inspection using maintenance techniques is given in
Figure 16. This checklist can be used for both regular and special
maintenance-related inspection. The primary data inputs are the status of
each section of line (defined by adjacent access points or one access point
and a label) and the location of the blockage in unpassable sections. A
diagram of the leachate collection system should also be provided with access
points, and labels, and the status of each line should be clearly marked.
Protocols for maintenance techniques are given in Section 6.
5.3 SPECIAL INSPECTIONS
Special inspections are required at specific times in the life of a
leachate collection system. The most significant times for special
inspections are:
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Basic Diita
Name:
Time: a.m. /p.m.
Date: / /
Type Record Kept
Photo . ,..,
Video __
Notes
Type of Inspection
TV
Photo ....
Pipe Pre-cleaned
Date: / /
Technique:.
Bv:
None
Reason:
Inspection fay:
Company Name:
Address:
Reason for Inspection
Annual
Problem Noted
describe:
Other _ L
describe:
Location of Inspection*
Cell or area
1st access
last access
distance between
access points f
'Attach diagram of inspected
area with access points labelled,
problems and locations noted.
Comments:
Results
No problems
Type
Clogged pipe
Clogged Slots
Pipe line/grade
Pipe cracked
Pip't broken
Pipe joints
Ponded teachate
Other:
Description
Location
Inipector:
Signature: Date:
Approved by:
Si.jned:
(print)
Date:
. Figure 15. Checklist for television or photographic inspection.
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Basic Data
Name
Time
Date / /
a.m./p.m.
Maintenance by:
Company Name:
Address:
Technique:
Firrt
Access Point
Second Access
Point or
Line Label
^Results*
Clear
Blocked
Location of
Blockage
Comments
'Attach diagram of inspected area with
access points, line labels, clear lines.
blocked lines, un-inspected lines, and
location of problems noted.
Inspector:
Signature:
Date:
Approved by:
Signed:
(print)
Date:
16., Checklist for maintenanoa-relstcd inspection.
-------
after construction is completed;
» after the first lift of waste has been placed; and
when problems are identified with system performance.
5.3.1 After Construction
After construction, inspection is needed to verify that the leachate
collection system was constructed as described in as-built documentation.
This inspection, called an as-built inspection, can be carried out as part of
the Construction Quality' Assurance Plan. The inspection can be either a
maintenance-related inspection or a television or photographic inspection.
Inspection protocols for these techniques are discussed above.
The main purpose of an as-built inspection is to verify that the
collection line is continuous and not blocked. Television or photographic
inspection can also verify that the alignment and overall condition of the
line is satisfactory. Problems noted during an as-built inspection can be
easily corrected since waste has not yet been placed at the facility.
5.3.2 After First Lift Has 3aen Placed
Inspection of the collection pipe after the first lift of waste is placed
is important to ensure that the pipes were not damaged during placement and
compaction of the waste. Pipes are moat susceptible to crushing or
displacement during placement of the first lift of waste since there is not
yet a sufficient depth of waste to help diffuse equipment loading. Inspection
after the first lift would be a maintenance-related or a television or
photographic inspection. Inspection protocols for these techniques are
discussed above. If the pipes have been inspected after construction, this
inspection need only determine whether damage has occurred during placement of
the first lift of waste. Problems noted can still be corrected with relative
ease since only one layer of waste above the damaged section would have to be
excavated.
5.3.3 When Problems Are Identified with System Performance
In order to address problems noted during inspections, it is necessary to
locate and diagnose the extent and nature of the problem. Often, the location
and nature of a problem will be discovered during the inspection procedure. A
direct inspection technique, for example, discovers the exact location in a
collection pipe where the clog begins and may be able to determine the
mechanism of failure. Alternatively, high leachate-levels in observation
wells do not reveal the cause of the problem, only the location of the effect.
When a problem is suspected as a result of one type of inspection, other
inspection techniques described above can be used to locate the problem.
Clogged collection pipe can be accurately located using direct inspection
methods, provided there is adequate access to the pipe network. Problems in
the drainage or filter layers «~.an be located by examining data from various
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access points ana leachate-level indicators. Additional observation wells can
be -installed in the area of concern to provide further information and
document the problem. Once the cause of the problem has been located,
excavation can be used, if necessary, for further diagnosis.
Table 18 provides general information on diagnosing problems in leachate
collection systems.
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TABLE 18
DIAGNOSING PROBLEMS
Symptom
Possible Causes
High leachate levels above liner,
constant over time
High leachate levels after rain-
fall only, leachate drains
slowly during dry weather
High leachate levels, condition
improves after cleaning
High leachate levels, condition
does not improve after cleaning
Historical records indicate
lower leachate flow than
expected
Historical records indicate
higher leachate flow than
expected
e Leachate levels in sump remain
high even during pump cycles
Cleaning difficult or cannot be
accomplished using conventional
equipment
clogged collection lines
clogged drainage layer
clogged filter layer
full sump
local ponding due to differential
settling
partially clogged collection lines,
drainage layer or filter layer
undersized system
clogged collection lines
clogged drainage layer or filter layer
local ponding due to differential
settling
» clogged collection pipe openings
clogged collection lines, drainage
layer or filter layer
ponding in waste layers
no system problems, errors in tfater
balance modeling
* no system problems, errors in water
balance modeling
undersized pump, pump cycles too
short
e crushed, separated or clogged
(mature deposit) collection lines
e bend in collection line or access
point too sharp
spacing between access points too
great
a foreign object in collection line
(contir.ued)
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TABLE 18 (continued)
Symptom
' Possible Causes
material from drainage or filter
layer in sump
No flow at inspection point when
expected
"Clog" material in outflow
Leachate ponding or seepage out
of waste
9 broken or separated collection pipe
collection pipe opening too large
improper particle pize distribution
upgradient clog of collection line,
drainage layer or filter layer
partially clogged collection pipe, pip
openings or drainage layer
high leachate levels, see above
local leachate ponding due to
impermeable waste or intermediate
ccv^r l&yers
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6.0 MAINTENANCE
6.1 INTRODUCTION
Maintenance of a leachate collection and cap drainage systems is needed to
ensure that liquid will be effectively removed from over the liner throughout
the lifetime (and post-closure care period) of the facility. There has been
little experience, however, with maintenance of these systems. Typically,
collection pipes are maintained only when, problems are noted; that is,
maintenance techniques are used as repair measures rather than for system
maint3nance.
The notion that the need for preventive maintenance is obviated by the
ability to repair these systems seems shortsighted for at least two reasons.
First, historical evidence indicates that drainage systems of all types require
preventive maintenance to operate at maximum efficiency and to prolong service
life (Smith, 1976). Second, some failure mechanisms may be extremely difficult
to stop once the pipe is clogged. Young iron deposits, for example, may be
easily removed by preventive maintenance techniques even though the effect of
the deposit may not yet be noticeable. However, mature deposits which do
affect leachate flow may be extremely difficult, if not impossible, to remove
by standard maintenance or repair methods (Ford, 1979).
The basic objectives of a maintenance program are (Smith, 1976):
1. To keep the system operating near maximum efficiency;
2. To obtain the longest operating life of the system; and
3. To accomplish the above two objectives at minimum cost.
Underground drainage systems, in general, require minimal maintenance
(Smith, 1976). The amount of maintenance required for a leachate collection or
cap drainage system will vary depending on design, construction quality,
operating procedures, and leachate characteristics (quantity and quality).
Collection pipes, for example, may need to be cleaned several times a year if
the leachate has a high sediment load or if the system is highly susceptible to
other forms of clogging. Alternatively, annual cleaning may only be a safety
measuro at facilities where clogging mechanisms are not active. At all
facilities, regular maintenance of mechanical equipment (e.g., pumps) is
required. Further research is needed to determine the cost-effectiveness of
preventive maintenance in meeting the above objectives.
Mechanical and hydraulic methods for cleaning collection pipes are
discussed below. These techniques were developed for maintenance of sewer
pipes. Experience with these techniques for leachate collection system
96
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maintenance is limited. Two major constraints on using these techniques for
leachate collection systems are more limited access (e.g., risers used instead
of manholes, manholes surrounded by waste) and the use of plastic pipe.
Operator safety is also of greater concern for leachate collection system
maintenance because of the potentially hazardous nature of the leachate.
Safety considerations are discussed in Water Pollution Control Federation
(1980).
Procedures are not given for maintenance of drainage layers and filter
layers since no methods are currently available to mitigate failure mechanisms
which may be active in these layers. Potential failure of drainage and filter
layers is addressed through design, construction and system operation,
including control of waste characteristics, discussed in Sect5.cn 3. In
addition, maintenance of mechanical equipment is not discussed. It is
recommended, however, that manufacturers' recommendations for equipment
maintenance be carefully followed. Information on equipment maintenance and on
maintenance of drainage systems,, in general, can be found in Smith (1976).
Figure 17 gives an example of a collection pipe maintenance checklist for
use with the methods described in Sections 6.2 and 6.3. The checklist can be
used to record the reason for the maintenance, the maintenance method used, and
maintenance results. Actual checklists used should be tailored to- meet the
needs of a specific facility, and may include a schematic of the drainage
system.
6.2 MECHANICAL METHODS
6.2.1 Rodding/Cable Machines
Discussion
Rodding machines and cable machines are both designed to power the
rotation of various attachments used to clean sewer lines. Rodding machines
use a series of rigid rods, joined to make a flexible line, and cable machines
use a continuous cable to both spin the attachment and push and/or pull it
through the collection line or sewer. A typical rodding machine is shown in
Figure 18, and typical attachments for both types of machines are shown in
Figure 19. Special attachments are available for use in plastic pipe.
Both roddir.g and cable machines can be used to clean collection lines and
remove cl^0. Cables are applicable to smaller lines (5 to 30 cm; 2 to 12 in.)
and rods to larger lines (15 to 122 cm; 6 tc 48 in.). The efficiency of
rodding in lines greater than about 38 cm (lv in.) may be limited by the
tendency of the rods to bend at the joints, thereby reducing their power
(Foster and Sullivan, 1977). Both types of machines can be used in rur.f. up to
300 m (1000 ft), and both have the advantage that "threading" is not required.
Since the apparatus does not need to be pulled through the line, only one
access point is required. Rodding and cable equipment can be used to thread
the line for other equipment which does need to be pulled, such as a television
inspection camera or cleaning bucket.
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Basic Data
Name:
Time: a. in. /p.m.
Date: _/ /
Reason
^VM^-A^^V
Scheduled.
- Period:
Special
-Specify:.
.MX
Company: ,
Address:
Contact:
Methods Used:
1. Cable machine
2. Rodding machine .
3. Jetting
4. Propelled dev
5. Other
Attachments: a.
Specify:
Specify:
a..
a..
c..
c..
c..
c..
H.
d..
d..
Results
Section Cleaned*
Method No.
Meterial Removed
'Schematic attached: Yes No
Problems/Comments
Comments:
Inspector:
Signed:
Date:
Approved by:_
Signed:
Date:
\ Figure 17. Checklist for colbction pipe maintenance.
98 -
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HOSE GUIDE
ROD REEL
INSIDE HOUSING
GUIDE BRACE ,
SEWER '
~~'*
CLEANING TOOL
I Figure 18. Power redding machine.
(Source: Hammer, 1975.)
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DOUBLE EDGE CUTTER
FOR CABLE MACHINES
CUTTER BLADES
FOR CABLE MACHINES
AUGERS
FOR CABLE MACHINES
HEAVY DUTY ROOT SAWS
FOR CABLE MACHINES
ROUND STOCK CORKSCREW
SQUARE BAR CORKSCREW
PICK-UP TOOL
SPEAR HEAD
v*"Tfr^'^yiaS5Ei3S5r;V y~r .<- v
«£*4»-1^'"^ ~" "* "" T-ifa
AUGER FOR STEEL RODS ^X
'lEsr -»
Figure 19. Typical attachment! for rodding and cabin machines.
. . (Source: W.S. Darley& Co., Maltose Park, IL.)
100
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The primary disadvantage of rodding/cable cleaning is that the dislodged
materials may not be removed from the line. Large quantities of water may be
required to flush the lines subsequent to redding or cable cleaning.
Rodding/cable cleaning will be most applicable to leachate collection or
cap drainage systems in situations when flushing or jet cleaning alone is not
effective or is not applicable. An example would be a line where flushing does
not remove biological buildup and jetting is either not available or has been
shown to damage the drainage layer because of the configuration of pipe
perforations. In addition, rodding or cable cleaning may be less expensive
than jetting in certain a~eas.
Protocol.
The same protocol is used for rodding and cable cleaning. The power
supply for the equipment is placed at the downstream manhole which provides
access to the line to be cleaned. An appropriate attachment is selected and
installed at the end of the rod or cable. The cable or rod is then placed in
the line, and the machines turned on. Controls include various lateral speeds
to move the equipment forward or backward through the line, and rotational
speeds to regulate the spin of the attachment. Maximum rotating speed should
be used when the equipment is moving forward in the line (Foster and Sullivan,
1977). Specific procedures for operating rodding or cable machines can be
obtained from the equipment manufacturer. It is anticipated that operators of
land disposal facilities will hire an outside firm to clean collection lines by
this method, although purchase or rental of appropriate equipment is possible.
Problems encountered during cleaning should be described in the
maintenance record. (For example, see Figure 19.) Potential problems include
sections which are difficult or impossible to clean. The location of these
sections and the attachments used should be noted. Most cable and rodding
machines have a meter which measures the distance of the equipment in the line.
The meter should be zeroed as the equipment is placed in the line. In
addition, dislodged material should be inspected before (or after) it is
removed from the manhole. Pieces of pipe, drainage-layer material, or was*:e in
the debris indicate a broken or deteriorated section of collection pipe.
Chunks of biological material and chemical precipitation, or excessive
sediments in the outflow indicate clogging mechanisms at work and may require
further investigation.
6.2.2 Buckets
Discussion
Buckets may be used to remove large quantities of sand, gravel, and other
materials i:rom collection lines. The bucket is pulled through the line by a
steel cable connected to a powered winch at the upstream manhole. When the
bucket is full, it is pulled by a winch at the downstream manhole and emptied.
Buckets are designed to open when pulled in one direction and to close when
pulled in the other. The apparatus used for bucket cleaning is shown in
Figure 20.
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POWER WINCH WITH
LOADING CHUTE
ROLLER BRACED
IN MANHOLE
"ROLLER / ^»-BUCKET
^Figure 20. Schematic of bucket machine cleaning.
(Source: Hammer, 1975.)
102
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The primary advantage of bucket cleaning is that large quantities of
material can be dislodged and removed. Various accessory tools are also
available, once the equipment is set up, to remove materials not dislodged by
the bucket. These tools include a "porcupine," which is similar to a stiff
wire brush, and a "squeegee," made of strips of rubber (Foster and Sullivan,
1977).
The primary limitation of bucket cleaning is that access to a manhole at
each end of the pipe is required, and the line must be threaded. A rodding
machine, for example, can be used to push a cable through the line to be
attached to the bucket, which needs to be pulled in both directions.
Buckets are available' for use in lines as small as 15 cm (6 in.) and are
applicable in lines up to 230 re (750 ft) long (B'oster and Sullivan, 1977). It
is important that the type of bucket selected be based on the construction
material of the pipe to be cleaned. A bucket designed for concrete sewer pipe,
for example, may damage a plastic collection pipe.
Protocol
The power winches are set up at adjacent manholes, the pipe is threaded,
and the bucket is pulled through the collection pipe to dislodge and collect
materials. As with other maintenance procedures, the collected materi?;l should
be inspected for evidence of failure or clogging mechanisms. If materials do
indicate a problem, further investigation is warranted.
6.3 HYDRAULIC METHODS
6.3.1 Jetting
Discussion
High-pressure water cleaning is one of the most effective sewer-cleaning
techniques. Water is pumped through a hose connected to a special nozzle which
directs the higV.-pressure stream of water in several directions. Various
nozzle designs ar- available, as shown in Figure 21. The force of the water is
used both to propel the nozzle through the line and to dislodge materials which
may have built uj.on the pipe. High-pressure jets can operate at pressures of
0 to 140,000 g/c:a (0 to 2000 psi).
Ford (1974) experimented with jet cleaning of plastic drains clogged with
ochre in Florida. He found that high-pressure jets (84,000 g/cm (1200 psi) at
the pump) damaged the drainage layer by displacing drainage-layer material, and
recommends low-pressure (e.g., 4900 g/cm ; 70 psi) jetting. The drainage
layers tested, however, were only abour 5 cm (2 in.) thick. In addition, it
was found that low-pressure jets were less effective than high-pressure systems
for "more seriously clogged drains," and that low-pressure systems were
somewhat more difficult to use (the nozzle is no longer self-propelled).
Experience with jet cleaning of leachate collection systems is limited.
Jetting has been shown to be effective in removing clogs from collection pipes,
but the effect of high-pressure jets on the drainage layer should be considered
in selecting the optimal cleaning pressure.
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Standard Nozzto
15° and 30° Combination Nozzle
(Dual Degree)
Bullet Nozzle with Forward Jet
'f^ '"; '"-?/:' ""1
ggfet Ml )
. .**:-..f r~. . . : i li _ ' -*i
Penetrating Nozzle
Nozzle
Sand and Sludge Nozzle
Standard Mozzt* with Forward Jet
Lance Nozzle
Figure 21. Nozzle designs for high-pressure cleaning.
'-: (Source: W.S. Parley & Co., Melrose Park, IL.)
-------
The main advantage of jet cleaning is that it is expected to be effective
in removing most types of clogs and accumulated materials from the collection
pipe. In addition, it is relatively easy to use, requiring minimal setup and
access only at the downstream end of the pipe.
Limitations include the need for an accessible water supply and the
potential of damaging the drainage layer. Jetting may also not be effective
for large or heavy debris, or for mature iron deposits. A method to remove Che
debris flushed out by the jet is also needed. A vacuum truck, for example, is
often used to remove debris accumulated in the downstream manhole.
Protocol
Jetting equipment is set up at the downstream access point of the
collection pipe to be cleaned. Nozzle type and size, pump pressure, and rate
of entry and withdrawal should be based on pipe size, length, and conditions
expected. More thorough cleaning is accomplished at higher pressures and
slower rate of entry and withdrawal. Thorough cleaning, however, is also more
expensive since more time and more water are required.
The specific protocol used for jet cleaning will depend on the design of
the system and on the capabilities of the cleaning equipment available.
Typical maximum lengths of pipe which can be jet cleaned range from 90 to 300 m
(300 to 1000 ft) at depths of about 15 m (50 ft). Jet cleaning service should
}>e available from local sewer cleaning firms, and the equipment is available
for purchase from a variety of manufacturers. (See Foster and Sullivan, 1977.)
6.3.2 Flushing
Discussion
Collection lines can be flushed using a hose connected to a fire hydrant
or other water supply. Leachate can also be used if it does not contain a high
sediment load. The action of a large quantity of liquid blowing through the
pipe serves to remove loosely attached debris or sediments from the pipe.
Various hydraulically propelled devices are also available to increase the
effectiveness of this technique. These devices include sewer balls and
hinged-disc cleaners (sewer scooters).
A sewer ball (Figure 22) is an inflatable rubberized ball attached to a
cable which limits the cross-sectional area available for flow at a specific
point in the pipe so that water flows around the ball at higher, more turbulent
velocities. Use of the sewer ball increases the ability of the water to
dislodge and flush away debris which has accumulated in the pipe. Sewer balls
require a certain amount of operator skill for effective use and are available
in sizes as small as 15 cm (6 in.).
A hinged-disc cleaner (Figure 23) provides the same function as a sewer
ball, increasing the effectiveness of flushing. The machine is pushed through
the pipe by the flushing water. When debris is encountered, the machine stops,
causing water to accumulate in the pipe. The operator then pulls the cable to
release the top half of the disc, allowing the accumulated water to flush away
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Figure 22. Sewer bell.
(Source: Water Pollution Control Federation: 1980)
106
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Figure 23. The hinged disc cleaner (or "teooter").
(Source: Water Pollution Control Federation: 1980)
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the debris. The velocity of th.? water is generally three to four times the
normal flow velocity, depending on the size of the pipe. The debris is washed
downstream and can be removed through a manhole or clean-out.
Simple flushing requires access to at least the downgradient portion of
the pipe to be maintained, and preferably access to both ends of the pipe.
Access to both ends of the pipe is required when the sewer ball or hlnged-disc
cleaner is used. Flushing is simpler and less expensive than other maintenance
measures, but may be less effective in removing debris attached to the pipe.
Protocol
Generally, flushing is accomplished by directing the source of water into
the upgradient access point. Propelled devices are designed for use from a
manhole, but flushing water may be added through a clean-out or riser pipe.
Debris flushed out of the pipe is removed from the downgradient access point
which has been plugged to capture debris but allow the water to pass through.
(See Figure 23.)
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7.0 REPAIR
7.1 INTRODUCTION
Leachate collection and cap drainage systems must be repaired vmen the
mechanisms discussed in Section 2 cause the systems to fail. Failure occurs
when the system becomes unable to remove leachate (or precipitation) and
allows liquid to accumulate over the liner. Maintenance procedures are used
to address failure mechanisms before actual failure of the system occurs.
Repair procedures are used to correct the problem after it occurs, thus
allowing liquid to be removed from over the liner.
Leachate collection and cap drainage systems can fail as a result of
problems in the collection pipe, filter layer, drainage layer and othsr system
components, including sumps and pumps. Problems with components of the system
that are buried under the wa?te are of particular concern since access to
these components is difficult. Evidence of system failure includes:
no flow out of the system when flow is expected;
high leachate levels in portions of the facility; and
leachate ponding or seepage at the surface of the waste mass (or
cap).
An investigation may be needed to gain an understanding of the cause of
the problem before selecting the appropriate repair option. Locating and
diagnosing problems are discussed in Section 5.3.3.
A variety of repair options are available to correct problems with failed
leachate collection or cap drainage systems. The maintenance techniques
described in Section 6 can be used as repair methods primarily for clogged
collection pipe. Chemical methods may also be useful to remove (dissolve)
material clogging a collection pipe and may be applicable to address clogging
of the drainage or filter layer. Finally, the failed portion of the system
can be replaced with a new system.
Selection of the appropriate repair option depends on a number of
factors. Location of the problem influences the choice considerably. Some
repair options, for example, are applicable only to the collection pipe and
would not be of use for a clogged drainage layer. The type and extent of the
problem are also important. Clogging of the drainage layer around the
collection pipe, for example, might be addressed by chemical methods while
chemical methods would not be applicable to extensive clogging of the drainage
or filter layer away from the pipe. Also, the physical and chemical
characteristics of the clogging material are important in determining the
effectiveness of a repair option. In general, maintenance techniques and
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chemical methods are applicable to problems in and around the immediate area
of the collection pipe, and replacement techniques are required for problems
away from the pipe area.
Landfill design and waste characteristics must also be considered in
selecting the appropriate repair option. Maintenance techniques, for example,
may not be the best option for a clogged collection pipe if access to the pipe
was not provided in the landfill design. Similarly, excavation and
replacement may depend on the number of lifts of waste which have been placed
and how "dangerous" those wastes are (e.g., explosive, reactive, volatile,
unknown composition).
This section addresses the three major categories of repair methods:
maintenance techniques, chemical techniques and replacement techniques. This
section does not address repair of components such as pumps and sumps which
are not buried by the wastes. Standard construction and system maintenance
techniques can be used for repair of these components.
In some cases, the effect of leachate collection system failure can be
eliminated by significantly reducing leachate generation. This would be
accomplished, for example, by closing the site with a final cover to control
the water balance at the site. Decreasing the quantity of precipitation and
groundwater flow, and increasing runoff, surface storage and
evapotranspiration can also be used to reduce the quantity of water available
for leachate generation at the site (Pacey and Karbinski, 1979). The
discussion below assumes that leachate generation has been minimized and
repair of the leachate collection system is required.
7.2 MAINTENANCE TECHNIQUES
Maintenance techniques which can be used for leachate collection system
repair include:
redding;
cable tool;
buckets;
jetting;
flushing alone; and
flushing with hydraulically propelled devices.
These techniques, described in Section 6, are Applicable to collection pipes
clogged with sediments, biological growth, chemical precipitates and
biochemical precipitates. It is also necessary that sufficient access to the
pipe be available through manholes or risers. Buckets additionally require
that the pipe be able to be threaded, and is therefore not applicable to
totally blocked pipes.
The information provided on these techniques in Section 6 is generally
applicable for their use in system repair. One major difference is that more
effort may be required to remove the material which has blocked the flow in
the collection pipe than to remove material that has not yet accumulated
significantly. This additional effort would increase the cost of the
operation since it would take longer to clean a section of pipe. Several
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techniques may also need to be tried before the clog is successfully removed.
Care should be taken to ensure that the techniques tried do not damage tho
collection pipe. It is likely that the equipment operator will be most
experienced with sewer cleaning and may not fully appreciate the differences
between plastic and concrete pipe. It is up to the facility operator to make*
sure that a difficult clog is not attacked so aggressively that the collection
pipe is damaged. This may require the use of tools specially designed for
plastic pipe, or lower water pressures for jetting even though different tools
or highsr pressures may be more effective in removing the clog.
The expected success of maintenance techniques as repair methods will
vary with the nature of the clog. Some clogs may be quite difficult if nor.
impossible to remove, while others may be removed quite easily. The expected
success of the technique will depend not only on the type of clog but also on
its location and extent. Clogs which extend only a few centimeters are likely
to be easier to remove than a similar clog which extends several meters. In
one example from Section 2, biological material filled a 30 m (100 ft) section
of pipe. The clog was removed by flushing with water under high pressure.
Although the facility owner was concerned that the pressure might damage the
pipe, the clog was successfully removed. In addition, clogs which are near an
access point would be easier to remove than clogs which are midway between two
access points, since the effectiveness of most techniques diminishes with
distance from the access point.
7.3 CHEMICAL TECHNIQUES
Various chemicals have been used or tested for the cleaning of sewers,
agricultural drainage systems, and septic drain fields. Commercially
available biocides, enzymes, bacteria?, cultures, caustics, hydroxides and
neutralisers can be used to remove grease deposits from sewer lines. Sulfur
dioxide gas, dry pelletized sulfaroic acid and liquid acids have been shown to
be effective in removing mineral deposits and organic material from
agricultural drain lines. Also, a method using hydrogen peroxide has been
developed to clean septic drain fields which have been clogged with organic
material. Chemical treatment is particularly important since it is applicable
to mineral deposits, such as iron precipitates, which may be difficult to
remove by other methods.
Discussion
Chemicals which have been used to dissolve clogs in drain lines and woll
points include hydrochloric acid, sulfamic acid, hydroxyacetic acid,
hydrochloric acid with ammonium chloride, and sulfur dioxide gas (Grass and
McKenzie, 1970). Sulfur dioxide gas and dry pelletized sulfamic acid are
considered the most promising chemicals for acid treatment since they can bo
handlsd more easily and safely and have provided excellent results.
Acid treatment is applicable to iron deposits, manganese deposits,
calcium carbonate incrustation, organic deposits and other materials which
dissolve readily in acid. It is useful primarily for clogs in the pipe or
pipe slots. Treatment, however, may also extend into the drainage layer
immediately around the pipe.
Ill
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The acid treatment techniques presented below were developed for use with
agricultural drainage systems. Special care should be taken in applying these
techniques to hazardous waste leachate collection systems. Compatibility of
the acid with the pipe material, liner material and waste materials present
should be carefully evaluated. Acid treatment should be used only in cells
which are designed to handle low pH waste.
Protocol
The protocol for acid treatment has been derived from the protocol used
for agricultural drainage systems as discussed in Grass and McKenzie (1970)
and Lidster and Ford (undated) .
The -fi-rsv-j^t-ep- in -:ae'id ^treating a collection line is to clean the line by
flushing or with a" high-pressure" jet. This selves to remove any silt or
deposits which are not strongly adhered to the pipe and allows the acid to
work only on the materials which are most difficult to remove. Once the pipe
is cleaned, acid is introduced into the upgradient end of the pipe. When the
acid reaches the downgradient end of the pipe, the downgradient end is plugged
so that acid will accumulate in the pipe. For sulfur dioxide treatment, SO-
gas and water are injected together into the pipe. The amount of water and
gas used depends on the pipe size and the length of the lines . Table 19 shows
the quantities of SO. and water for treatment of various diameter drain lines
per 30 m (100 ft) length. SO- gas is injected from a tank through a hose
extending to the bottom of the riser or manhole. Water is pumped into the
drain through a hose which terminates just below the top of the riser or
manhole. The tank weight is measured to determine the rate of gas flow, which
is adjusted to the amount of water being pumped into the pipe to maintain a 2%
solution by weight of S0?. Water pumping rates vary between 150 and 280
liters per minute (40 and" 75 gallons per minute) using 2-5 kg (5-10 Ibs) of
S0_ gas per minute. Flow rates from the tank vary with temperature and with
the volume of gas remaining in the tank. Nitrogen can be injected into the
tank to maintain pressure at a constant flow rate of gas.
The acid solution is held in the line for up to several days if possible.
Depending on the amount of ...clogging. .in the drainage layer it may be difficult
to hold *bs.;=sc.id;-:in..a: 'leacii&e collection pipe since the pipe is slotted.
Best iresults would likely be obtained when the liquid level in the leachate
collection system is at the bottom of the pipe. Leachate in the area above
the clog may need to be dewatered for acid treatment to be effective.
Alternatively, ---addition of water or waiting until the collection system is
saturated may be necessary if the leachate collection system is dry. The pH
of the liquid in the pipe can be measured to determine the progress of the
treatment. Treatment is finished when the pH in. the pipe approaches that of
the leachate prior to treatment. When the treatment is finished, the plug at
the downgradient end of the pipe is removed to allow the leachate to drain
from the pipe. The pipe is then flushed or jetred to remove deposits which
are only partially dissolved or loosened as a result of the acid treatment.
Safety in handling the chemicals is a major concern in acid treatment.
The primary health hazards are from inhalation of SO. vapors and direct
contact with liquid acid. Pumping rates should be adjusted so that the acid
does not overflow from the riser pipe during injection, and all contact with
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TABLE 19
QUANTITIES OF SO. AND WATER FOR TREATMENT
OF VARIOUS SIZES OF TILE DRAINS
Tile. Diameter (in.)
Pounds of S0» per
100 ft i
Gallons of Water
per 100 ft
345 6 8 10 12
6 11 17 24 44 68 98
37 65 102 147 261 408 588
* 2% SO- solution: 1 Ib SO. per 6 gal water.
1 inch - 2.54 cm
1 gallon - 3.785 liters
Source: Grass and McKehzie, 1972.
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acid should be avoided. Personnel should be aware of proper handling
procedures for the SO- gas and of safety precautions in conducting the acid
treatment.
Acid treatment has been successful ir. removing iron and manganese
deposits from tile drains in agricultural systems. Results of testing by
Grass and McKenzie (1970) are given in Table 20. Experience with S0?
treatment in Imperial Valley, California, conducted by Grass and McKenzie,
indicate a 2- to 250-fold increase in flow rate depending on the severity of
the clog in the system. Dennis (1978) reports an example of an iron clog
which was not corrected either by conventional cleaning techniques, such as
drain rodding or water jetting, or Ly sulfur dioxide treatment. The expected
success of acid treatment for leachate collection systems will depend
primarily on the. type and extent of the clog and the ability of the acid to
maintain contact with the clogged portion for an extended time. Acid
treatment, therefore, may be most effective when the drainage area beneath the
pipe Is also clogged and may be less effective when only the pipe itself is
clogged.
Additional research is reeded to adapt the procedures developed for
agricultural drainage systems to leachate collection systems.
7.4 REPLACEMENT TECHNIQUES
Two categories of replacement techniques are discussed in this section.
The first category includes those techniques which repair, modify, or replace
components of an existing leachate collectior. system, or retrofit a new
conventional leachate collection system at a facility which previously had
none. A conventional leachate collection system includes any 'drainage system
which would be pieced beneath or within the waste mass at a new facility to
collect leachate. Typical leachate collection system designs are discussed in
Section 3. The second category of replacement techniques involves using
alternative i-ystems to remove leachate from a facility where a conventional
leachate collection system has failed or was never installed. Alternative
systems include peripheral toe drains and caissons or wells installed through
the waste.
Replacement techniques may be required to control leachate in a facility
under a variety of circumstances including:
a severely clogged section of collection pipe which ( nnot be
cleaned by conventional sewer-cleaning techniques;
extensive clogging in the drainage layer;
extensive clogging in the filter layer;
a poorly designed leaehate collection system including inadequate
access to pipes and insufficient system capacity;
operational errors including impermeable waste material which causes
ponding of leachate within the waste mass;
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TABLE 20
THE SOLUBILITY OF IRON AND MANGANESE TILE
DEPOSITS IN VARICUS CHFJUCAL REAGENTS*
Amount Dissolved (%)
3.7%
4.9%
4.9%
4.9%
2.5%
1.8%
4.9%
10%
2.5%
2.5%
10%
2.5%
Solvent
HC1 + 2% Na2S205
**
H2S04 + 1% Na2S205
H2S04 + 1% Oxalic Acid
**
HC1 + 1% Na2S205
H2S04 +0.5% Oxalic Acid
Hydroxyacetic Acid
H2S04 + 1% Oxalic Acid
H2S04 + 1% Na2S205
Sulfamic Acid
H2S04 +0.5% Oxalic Acid
^U^U^U
4% Sulfamic Acid
Manganese
Deposit
100
83
57
56 '
81
63
38
66 .
51
56
-
29
20
Iron
Deposit
100
98
96
94
52
66
89
61
56
51
53
43
Average
100.0
90.5
76.5
75.0
66.5
64.5
63.5
63.5
53.5
53.0
53.0
36.0
20.0
*lgm of deposit in 20 ml of solution.
**Equivalent to SO- g&s.
***Above 4% concentration amount dissolved remained unchanged.
Source: Grass and McKenzie, 1970.
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construction errors including crushed collection pipe or failing Co
install an important system component such as a filter layer;
differential settling that causes ponding of leachate over the
liner.
Any of these problems can lead to high leachate levels or leachate seepage out
of the waste mass.
Experience with replacement techniques for leachate collection systems is
limited to older facilities which either did not initially have leachate
collection systems or used state-of-the-art designs which have since been
superceded. Replacement techniques were used at these facilities to control
leachate problems which developed and/or to meet RCRA standards for landfill
design. Experience with these older facilities is applicable to RCRA-designed
facilities as well since the same techniques would be used when repair is
required. The primary difference is that excavating through hazardous waste,
especially where drummed wastes are present, is more complicated and more
hazardous than drilling or excavating through refuse or homogeneous wastes.
The need for replacement techniques at RCRA facilities will likely be
less than at older facilities because of the more sophisticated practices used
and the measures to reduce leachate production (e.g., not accepting liquid
wastes). However, replacement techniques may be required at RCPA facilities
for the reasons described above. Construction orrors, for example, can occur
at any type of facility no matter what the design is. In addition, RCRA
facilities as yet employ no standardized leachate collection system design so
design features will vary. Providing access to the collection pipes, for
example, is not required by RCRA and is not a feature in several recently
designed facilities. Furthermore, unforeseen problems could develop with
certain unproven technologies currently used in leachate collection systems.
An example of thi^; is the use of geotextile drainage or filter layers since
the potential for clogging of these layers is unknown. Some design firms use
geotextile materials as common practice. Others deem it wise to avoid them at
this time. The potential for clogging of geotextile, however, does exist and
would require replacement as a corrective measure.
The following sections discuss replacement techniques for leachate
collection systems. Examples are given of six facilities which have used
these techniques to correct problems with their leachate collection systems.
7.4.1 Conventional Systems
Replacement techniques which are based on conventional leachate
collection system design include repairing failed portions in-place, modifying
the existing leachate collection system with features not included in the
original design, replacing failed portions' of the leachate collection system
with new components, and installing a new leachate collection system where
there was none before. All these methods involve excavating through the waste
to gain access to the leachate collection system or the bottom of the waste.
The usefulness of these methods therefore will depend to a large extent on the
thickness of the in-place waste, the availability of information about the
in-place waste, and the characteristics of the in-place waste. Excavating
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through one lift of hazardous material is less complicated than excavating
through several lifts, and excavating through a monofil of bulk material is
less complicated than excavating through a mix of bulk wastes and drummed
material. These factors affect the hazard Involved in excavation and
significantly affect the cost of the operation.
Repair or replacement of the existing leachate collection systems may be
required when the problem cannot be corrected by other . means. This may
include fixing or replacing broken or badly clogged leachace collection pipes
or portions of the drainage layer or filter layer. It also might include
correcting construction errors such as placing a collection pipe, drainage or
filter layer where one should have been installed.
Excavation can also be used in modifying the existing system. For
example, manholes or risers can be added at collection pipe intersections or
at the end of collection pipes where access is not provided. This would
allow cleanout, inspection or repair of the pipe by more conventional means.
It would also be possible to add new lines or connections to augment
functioning of the existing leachate collection system. Alternatively,
excavation can be used to install a new leachate collection system where there
was none before.
The use of replacement techniques based on conventional leachate
collection systems is illustrated by the following examples.
Seven Mile Creek Landfill
Ttie Seven Hile Creek Landfill is a sanitary landfill in Eau Claire,
Wisconsin. According to a letter sent to the City of Eau Claire from the
Department of Natural Resources (Murray, 1980), the City had agreed to check
the collection lines at the Seven Mile Creek Landfill to determine whether any
sections of pipe were damaged. The City sewer crew therefore rodded a section
of pipe to 35 m (116 ft) from the collection tank and hit an obstruction.
This obstruction was thought to be a 45 degree elbow which the rod could not
pass through. A month later the area where the elbow was located was
excavated and a manhole installed to facilitate cleaning the 244 m (800 ft)
run out into the fill area. The sewer crew then jetted the line to an
obstruction approximately 15 m (50 ft) west of the elbow where the manhole was
installed. A piece of ABS pipe was found which indicated a possible break in
the line.
The garbage was then excavated in this area and a break was found between
the east sidewall slope and the collection tee. A 3 m (10 ft) section of 15
cm (6 In.) ABS pipe was replaced. The area around the pipe was backfilled
with gravel using No. 60 rolled roofing between the gravel and clay and
mounded approximately 0.6 m (2 ft) of gravel over the pipe. Garbage was then
pushed back into the hole. The cause of the break could not be determined at
the time of excavation.
Maryland Chrome Ore Tailings /.andfill (excerpted from MEE3A, 1984)
Old chrome ore tailing cells were retrofitted with leachate collection
systems at a site in Maryland for leachate removal and reuse by the generator.
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Initially, the owner attempted horizontal drilling into the cells. This
method proved unsuccessful because of difficulties and delays in drilling
through the sandy tailings which tend to cement together over time. Leachate
collection systems were finally installed by open cut trenching and laying a
PVC pipe. Prior to the installation of the leachate collection system,
borings indicated a '-:-3 m (5-10 ft) leachate head in the old tailing cells.
Each leachate collection system consisted of a single PVC pipe header and
lateral collection pipes. The laterals are 15 cm (6 in.) diameter perforated
PVC pipe placed at the bottom of 1 m (3 ft) wide trenches which are excavated
to the bottom of the cell. The bottom meter (3 ft) of each trench was then
filled with crushed stone which was encased with a Mirafi 140 geotextile.
Chrome tailings waste was then placed on top of the geotextile to fill up the
trench. There are three trenches containing laterals in Area 5 and 14
trenches in Area 3. The trenches in Area 3 vary in length from 32 m (106 ft)
to 79 m (260 ft). The three trenches in Area 5 are approximately 24 m (80
ft), 47 m (155 ft) and 61 m (200 ft) in length. The collected leachates flow
by gravity to a sump. The sump pumps transfer the leachate to storage tanks.
Problems during construction of these systems included (1) trenching
through cemented tailings in several areas; and (2) exposure of excavated
tailings to rain.
Manholes were provided outside the cells on the main collection header at
all bends and junctions and at spacing not greater than 122 m (400 ft). This
allows closed-circuit television monitoring of the condition of the pipe,
cleaning and to a limited extent physical repairs to be made to the pipe
without excavation.
7.4.2 Alternative Systems
Alternative methods of leachate control are needed when it is impractical
or impossible to excavate through the waste mass to replace or repair the
leachate collection system or install a new system. Alternative methods
include installing toe drains at the periphery of the cell and drilling
caissons or wells through the waste to pump out leachate.
Toe drains are french drains typically installed at the base of the
landfill. Toe drains are used to control problems with leachate seepage, and
they also provide a means to retrofit a leachate collection system at a
facility without excavating through the waste.
Caissons or wells can be installed through the waste at a facility to
allow removal of leachate. Caissons are simply large diameter wells. They
can be installed at low spots in the *aste cell to collect leachate which can
flow, or in areas of ponded leachate. The effectiveness of the caisson or
well is limited by the ability of the leachate to flow to the well. Special
care must be taken in installing a caisson or well through hazardous waste,
especially if drummed materials are present. In addition, care must be taken
to avoid drilling the caisson or well through the liner.
The following examples illustrate the use of toe drains, caissons and
wells as repair methods for leachate collection systems.
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Western Lake Superior Sanitary District Landfill (Knight et al.. 1983)
The Western Lake Superior Sanitary District purchased a co-disposal
landfill in 1979 which was having significant environmental problems because
of leachate generation. Leachate was migrating to a nearby creek through
seepage at the toe of the fill area and to groundwater contamination beneath
the fill area. A toe drain was therefore designed to capture both the toe
seeps and the contaminated groundwater.
The toe drain design is shown in Figure 24. The drain was designed to
prevent surface water from infiltrating into the drain and causing increased
treatment costs. Care was taken during construction to provide a 1 m (3 ft)
interface of the sand filter with the refuse to control seepage at the toe of
the fill. In addition, the drain was placed at the depth required to control
the contaminated groundwater and collect th«. flow of groundwater from both
sides.
Since no records were available about the type of waste disposed of at
the facility over the years, special consideration was given to safety during
construction of the toe drain.
Surface-water monitoring data for the creek, data for groundwater along
the line of the drain, and leachate sampling data indicate that the collection
system is performing as designed. Flow rates vary seasonally from 76 to 265
liters per minute (20 to 70 gallons per ninute). The system had been in
operation for 2 years in 1983.
Omega Hills Landfill (Personal Interview, Mark Gordon, 1984)
The Omega Hills landfill was the largest hazardous waste disposal site in
Wisconsin. It was originally designed as a co-disposal site, accepting
municipal, liquid and hazardous wastes. The facility was designed as a zone
of saturation landfill, which depended on the pumping of leachate to maintain
groundwater gradients toward the landfill.
The State regulators became concerned when they began to balance the
quantity of liquids being delivered to the landfill against the leachate being
pumped out. This concern, combined with general uneasiness about the extent
and quality of groundwater monitoring, was sufficient to initiate an
investigation at the site. A number of leachate head wells were drilled into
the waste, and it was discovered that there was considerable leachate at the
site, in some areas 9-12 m (30-40 ft) above the bottom of the waste. Further
investigations indicated that the clay was not homogeneous. Around the site
were sand seams that allowed leachate to migrate beyond the landfill border.
It was also found that the stone-filled sump was clogged with silt, making it
difficult to pump leachate out of the sump.
At this point, the State terminated all hazardous and liquid waste
disposal at the facility. Approximately three years of municipal solid waste
capacity remains at the site. The disposal of municipal waste has continued
in an effort to help achieve a final grade which will reduce infiltration and
leachate generation at the site.
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<
a:
Q
12" MIN. COMPACTED-
CLAY TILL COVER
12" MIN. OF ROCK
FILTER (TYPE II)
AROUND <0"£
SLOTTED PVC PIPE
v*"Pr"niW.lW.IW/WV.^
MINERAL SOIL (TILL)
SAND FILTER
(TYPED
(Vflf. V.MW-"' VMS. SW VMl m1!
12'
^ MINERAL SOIL (TILL)
- >-
Figure 24. Toe drain deiign.
'-.] (Source: Knight et al, 1983.)
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The owner has been involved in a $10-14 million cleanup, consisting of
the following elements:
Construction of a leachate pretreatment facility to reduce the BOD
of the leachate by 70-80%. Prior to pretreatment the average
leachate BOD is approximately 30,000 ppm. Prior to construction of
the pretreatment facility, leachate was trucked directly to the
Milwaukee Metropolitan Sanitary District for treatment. However,
because of limited capacity at the POTW, only about 45,000 liters
(12,000 gallons) of the high-HOD leachate could be trucked from the
landfill per day. This restriction en leachate disposal adversely
affected the operation of the facility.
Removal of waste around the perimeter and construction of new side
walls as a barrier for leachate migration beyond the site. The side
walls are 30 cm (12 in.) clay cutoff walls with a 2 ra (5 ft) toe.
a A perimeter leachate collection system was installed in conjunction
with the clay cutoff wall. This installation is at approximately
the same elevation as the bottom limits of waste, and at an
elevation similar to that of the existing leachate collection
system. Wherever possible, piping from the old leachate collection
system was interconnected with the new system.
PVC risers have been replaced with 2 ra (6 ft) diameter steel
manholes. In the initial design, PVC slanted risers were to provide
access to the leachate collection system. This design proved
inadequate because the PVC could be crushed or distorted during the
settling of the wasce, and there was inadequate sump at the terminus
of the risers to permit adequate pumping at these points in the
collection system.
Cleaning of leachate collection lines using a water jet.
California Co-Disposal Facility (MEESA, 1984)
Clogging, apparently the result of chemical deposition and
solidification, was a recurring problem at a co-disposal landfill in
California. About one-third of the waste disposed of at the facility was
hazardous and about one-third was liquid waste. The clogging was very
non-systematic and occurred only in certain locations while other areas within
the same cell performed satisfactorily. Corrective measures included total
replacement of sections of the leachate collection system. The collection
system consisted of a series of well points and headers which had been
installed after waste placement to control leachate. When the well points
clogged they were removed from the waste, and new well points were installed
(Personal Interview, J. Johnson, 1984).
Maryland Landfill (MEESA, 1984)
This landfill initially was constructed without a leachate collection
system. Completed cells at the landfill, however, were retrofitted with a
leachate collection system in order to facilitate leachate collection and
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removal. Standpipe wells were drilled at the low points in the cells and
subsequently backfilled with drain rock. Leachate flows through the waste to
the wells and is pumped out. The standpipe depths range from 12-24 m (40-80
ft). Because of the large size of the cells, the effectiveness of the
leachate collection system is low. It was also considered prohibitively
costly to excavate trenches through the waste to place leachate collection
lines and to install additional leachate standpipes to enhance removal.
Further, the drainage material surrounding the standpipes that were installed
is filling with sediment and is expected to .eventually clog the system.
122
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COPYRIGHT NOTICE
Figure 20 From Water and Waste-water Technology. John Wiley and Sons,
Inc., New York, 1975. Used by permission of the publisher.
Figure 22 From Uater and Waste-water Technology. John Wiley and Sons,
Inc., New York, 1975. Used by permission of the publisher.
V'igure 24 From "Operation and Maintenance of Wastewater Collection
Systems" by ' the Water Pollution Control Federation.
Washington, D.C., 1980. Used by permission of the Water
Pollution Control Federation.
Figure 25 From "Operation and Maintenance of Wastewater Collection
Systems" by the Water Pollution Control Federation.
"Washington, D.C., 1980. Used by permission of the Water
Pollution Control Federation.
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