Multidisciplinary Energy and Environmental Systems
and Applications, San Pedro, CA.
EPA/600/2-36/017
January 1906
LEACHATE COLLECTION AND GAS MIGRATION AND EMISSION PROBLEMS
AT
LANDFILLS AND SURFACE IMPOUNDMENTS
by
Masood Ghassenu, Kimm Crawford and Michael Haro
MEESA
San Pedro, California 90732
EPA Contract No. 68-03-1828
Project Officers:
Norrna Lewis and Vincent Salotto
Land Pollution Control Division
HAZARDOUS WASTE ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI. OHIO 45268
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TECHNICAL REPORT DATA
fftetir rrej /ntlrueiioni on iht rrvtni btfort complaint)
REPORT NO
EPA/600/2-86/017
3 RECIPIENT S ACCESSION NO
b"
S
I TITLE ANDSUBTITLE
LEACHATE COLLECTION AND GAS MIGRATION AND EMISSION
PROBLEMS AT LANDFILLS AND SURFACE IMPOUNDMENTS
6 REPORT DATE
January 1936
6 PERFORMING ORGANIZATION CODE
AUTHORIS)
Masood Ghassemi, Kimm Crawford, and Michael Haro
B PERFORMING ORGANIZATION REPORT NO
1 PERFORMING ORGANIZATION NAME AND ADDRESS
*1EESA Corporation
San Pedro, CA 90732
to PROGRAM ELEMENT NO
BRD1A
11 CONTRACT/GRANT NO
68-03-1828
12 SPONSORING AGENCY NAME AND ADDRESS
tezardous Was:e Engineering Research Laboratory--Cin.,OH
Dffice of Research and Development
J.S. Environmental Protection Agency
Cincinnati, OH 45268
13 TYPE OF REPORT AND PERIOD COVERED
Final Report 9/83-3/85
14 SPONSORING AGENCY CODE
EPA/600/ 12
15 SUPPLEMENTARY NOTES
Project Officers: Robert E. Landreth FTS: 569-7836
16 ABSTRACT
Clogging of leachate systems and gas migration and emission problems were
evaluated at hazardous waste landfills and surface impoundments. Collective
and preventive measures were identified along with research and development
needs. The analysis used literature and information obtained by interviews
with experts at 16 design firms, state regulatory agencies, and public
organizations.
Problems related to leachate collection systems and gas emissions can best
be addressed through preventive measures involving design, construction, and
operation practices. These measures are aimed at reducing leachate and gas
generation by improving leachate management, cell-by-cell design, waste
segregation and disposal, design redundancies, and using flexible membrane
liners.
17
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b IDENTIFIERS/OPEN ENDED TERMS
c COSATI Field/Croup
18 DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19 SECURITY CLASS (Thil Report}
UNCLASSIFIED
206
20 SECURITY CLASS fTlutpage/
UNCLASSIFIED
22 PRICE
EPA Form 2220-1 (Re*. 4-77) PMIVIOU* COITION 11 OBSOLETE .
1
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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 68-03-1828 to MEESA of San Pedro, California. It
has been subjected to the Agency's peer and administrative
review, and it has been approved for publication as an EPA
document. Mention of trade or commercial products does not
constitute endorsement or recommendation for use.
11
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Regional Center for Environmental Information
US EPA Region ID
1650 Arch St.
Philadelphia. PA 19103
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 accidental
releases of toxic and hazardous substances to the environment
also have important environmental and public health implications.
The Hazardous Waste Research Engineering 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 local governments and the needs of both large and small
businesses in handling their wastes responsibly and economically.
This document presents an analysis of problems and applica-
ble preventive and corrective measures for hazardous waste land-
fills and surface impoundments. The areas addressed include land-
fill leachate collection systems and. atmospheric emissions and
controls for landfills and surface impoundments. The analysis
draws upon the published literature which was supplemented by
data and information obtained through discussions with some six-
teen design engineering firms, owners and operators of hazardous
waste management facilities, and cognizant state regulatory agen-
cies. The findings will be useful to operators and owners of
hazardous waste sites as well as design engineers who need to
initiate corrective measures. For further information, please
contact the Land Pollution Control Division of the Hazardous
Waste Engineering Research Laboratory.
David G. Stephan
Director
Hazardous Waste Engineering
Research Laboratory
111
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ABSTRACT
Potential problems with leachate collection systems (LCS) in
hazardous waste landfills (HWLF), gas migration and emissions
problems at HWLF, and gas emission problems at surface impound-
ments (SI) were evaluated; applicable corrective and preventive
measures together with research and development (R&D) needs were
identified. Published literature and information obtained through
discussions with experts at sixteen engineering firms, state
regulatory agencies and public and commercial waste management
companies or organizations were used in the analysis.
There has been limited operating experience with properly
designed LCS and hence very little opportunity for corrective
action at such sites. Most clogging problems are expected to be
localized and of minimum consequence due to many excess design
features which are incorporated. Gas generation and migration
problems are largely associated with municipal and co-disposal
landfills and are not generally applicable to HWLFs where there
would be little biological activity. Very limited gas emission
data have been developed for HWLFs; and ambient concentrations of
most gaseous pollutants at Sis are near the detection limits of
the sampling and analytical procedures used.
Leachate -collection systems problems and gas-/emission-
related problems at HWLFs and Sis can best be addressed through
preventive measures such as incorporating design redundancies or
waste pretreatment.
Areas for R&D include development of improved basis for LCS
design, evaluation of innovative approaches to LCS design, eval-
uation of cost-effective methods for retrofitting older sites
with LCS, parametric evaluation of various cover systems for
landfills from the standpoint of emissions control, and evalua-
tion and expansion of the current data base on emissions.
This report was submitted in fulfillment of Contract No. 68-
03-1828 by MEESA under the sponsorship of the U.S. Environmental
Protection Agency. This report covers the period of September
1983 to February 1985 and work was completed as of February 1985.
IV
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CONTENTS
Disclaimer 11
Foreword 111
Abstract iv
Figures vn
Tables ix
Abbreviations xi
Acknowledgments xni
1. Introduction 1
2. Conclusions and R & D Recommendations 3
2.1 Leachate Collection System (LCS) 3
2.2 Gas Generation, Migration and Emissions at HWLFs 4
2.3 Gas Migration and Emissions Control at
Municipal and Co-Disposal Sites 5
2.4 Emissions Control for Hazardous Waste
Surface Impoundments 6
2.5 R&D Recommendations ? 6
3. Data Base Development Methodology 7
4. Leachate Collection Systems 13
4.1 Regulatory Background and Some
General Considerations 13
4.2 Previous Studies 13
4.3 Problem Overview 17
4.4 Operating Factors Affecting and the
Experience with the Performance of
Leachate Collection Systems 21
4.5 Preventive and Corrective Measures 22
4.5.1 Design Considerations 23
4.5.2 Construction and QA/QC Considerations 26
4.5.3 Operating Considerations 30
4.6 Research and Development Needs 35
4.6.1 Developing Improved Basis for Design . 37
4.6.2 Investigation of Novel De-
sign Concepts and Approaches .... 38
4.6.3 Miscellaneous Studies 38
5. Emissions and Gas Control Problems at Land-
fills and Surface Impoundments 40
5.1 Problem Overview 40
5.2 Regulatory Background 41
5.2.1 U.S. EPA Regulations 41
5.2.2 State Regulations and Concerns .... 42
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5.3 The Available Data Base on Landfill
Emissions 47
5.3.1 Gas Generation and Migration
at Municipal Landfills 48
5.3.2 Gas Production and Migration
at Hazardous Waste Landfills 49
5.3.3 Results from Actual Field
Monitoring Programs 50
5.3.4 Results from Discussions with Experts 56
5.4 The Available Data Base on Surface
Impoundment Emissions 62
5.4.1 Some Fundamental Considerations ... 62
5.4.2 Results from Previous Studies ... 64
5.4.3 Results from Discussions with Experts 68
5.5 Corrective and Preventive Measures 68
5.5.1 Landfills 68
5.5.2 Surface Impoundments 83
5.6 Research and Development Needs 89
References 91
Appendices 98
A. Technical Discussion (T.D.) Reports 98
A.I T.D. No. 1, Sanitation Districts of
Los Angeles County 98
A.2 T.D. No. 2, CH2M-Hill 103
A.3 T.D. No. 3, CH2M-Hill 107
A. 4 T.D. No. 4, Lockman and Associates 109
A. 5 T.D. No. 5, Maryland Department of
Health and Mental Hygiene 112
A.6 T.D. No. 6, Maryland Environmental
Service 113
A.7 T.D. No. 7, Duffield Associates 118
A. 8 T.'D. No. 8, Residuals Management
Technology 122
A.9 T.D. No. 9, Wisconsin Department of
Natural Resources ' 125
A. 10 T.D. No. 10, Warzyn Engineering 132
A.11 T.D. No. 11, Black and Veatch 136
A.12 T.D. No. 12, New York Department of
Environmental Conservation 139
A.13 T.D. No. 13, Facility A 147
A. 14 T.D. No. 14, Wehran Engineering 149
A.15 T.D. No. 15, Emcon Associates 152
A.16 T.D. No. 16, Getty Synthetic Fuels 157
B. Corrective and Preventive Measures for Cover
and Bottom Liner Systems 160
B.I Background and Objectives 160
B.2 Liner and Cover Systems Problems
and Applicable Measures 160
B.3 Conclusions and R&D Recommendations
of the "Surface Impoundment" Study 175
B.4 Summary and Conclusions of the "Liner" Study . 180
VI
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FIGURES
Number Page
1 Schematic of a Typical Leachate Collection
System 14
2 Typical Pipe Configuration for LCS in a Cell
at a Hazardous Waste Landfill 15
3 A Cross Section of Leachate Collection Sump
for LCS at a Hazardous Waste Landfill 16
4 Typical Cross Section of a Pre-Engineered
Aluminum Framed Cover Structure for Sis 32
5 Sketch of an Air Supported Structure 33
6 Gas Venting Detail for a Closed Cell at a
Hazardous Waste Landfill 70
7 Trench Barrier System for Gas Migration
Control 76
8 Schematic Drawing of Vertical Gas Extraction
Well 78
9 Landfill Gas Recovery in Horizontal Tren-
ches: Trench Construction Methods 79
10 Schematic of a UCFPSR Cover 86
11 Schematic Overview and Cross Section of a
Patented Floating Cover with Gas Collection
System 87
12 Sketch Showing the Use of a Double-Drainage
System for Leachate Collection and Intercep-
tion of Perched or Spring Water 100
VII
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Number Page
13 Area Location Map for Hawkins Point Landfill 115
14 Leachate Collection Trench 120
15 Sewer Cleanout 121
16 Examples of Progressively Increasing Redun-
dancies for LCS 123
17 Positive and Negative Projection Drain
Designs 127
18 Cross Section of LCS for the Proposed Expan-
sion to Hawkins Point Landfill 137
19 Effect of Installing Level-Activated Automa-
tic Leachate Removal System on the Volumet-
ric Rate of Leachate Collected 141
20 French Drain Leachate Collection Lateral at
SCA SLF No. 10 143
21 Schematics of a Double-lined Landfill Incor-
porating Leak Detection System 171
22 Leak Detection System at a Surface Impound-
ment Facility in the Southwest 172
Vlll
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TABLES
Number Page
1 Companies and Organizations with Whom Tech-
nical Discussions Were Held 8
2 EPA Minimum Guidelines for the Design of LCS .... 12
3 Summary of Clogging Mechanisms 18
4 Sewer Inspection and Cleaning Methods 24
5 Design Considerations for Improving Site
Performance from the Standpoint of Leachate
Management 27
6 Summary of Operation-Related Leachate Mana-
gement Problems and Applicable "Non-Design"
Preventive/Corrective Measures 36
7 State of New Jersey Contaminant Listing
Requirements for Direct Atmospheric Venting
and Combustion of Landfill Gas 46
8 Key Survey Programs Relating to Toxic Emis-
sions From Landfills 51
9 Independent Monitoring Programs at LFs Rela-
ting to Toxic Emissions 53
10 Organic Compounds Identified in Landfill Gas 57
11 Levels of Organic Compounds Reported in
Samples of LF Gases from Interior Extraction
Wells 58
12 Key Programs Relating to Toxic Emissions
from Surface Impoundments 65
IX
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Number Pag
13 Preventive/Corrective Design-Related Meas-
ures for Gas Generation and Migration/Emis-
sion Control at Hazardous Waste Landfills 71
14 Preventive/Corrective Operation-Related
Measures for Gas Generation and Migration
Control at Hazardous Waste Landfills 72
15 Key Laboratory/Support Studies Related to
Volatilization of Toxic Organics from Wastes
and Sorption/Biodegradation in Soils 73
16 Passive Systems for Landfill Gas Emission
Control 75
17 Key Features of Active LF Gas Extraction
Systems for Gas Recovery and/or Migration
Control 77
18 Permeability of Polymeric Membrane Liners to
Gases at 23 C 81
19 Preventive/Corrective Measures for Volatile
Emissions from Surface Impoundments 84
20 Examples of Liner and Cover Systems Problems
and Applicable Preventive and Corrective
Measures 161
21 Testing and Inspection for Subgrade Prepara-
tion and Materials and Equipment 165
22 Testing and Inspection for Liner Placement,
Connecting to Appurtenances, Anchoring and
Backfill Placement 166
23 Methods for Detecting Liner Leaks 169
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ABBREVIATIONS
AQMD
ASTM
GARB
cm
C-P
CPE
CSI
cu ft
cu yd
Eq.
FML
gal
GC
GC-MS
Ha
HW
HOPE
HWLF
lERL-Ci
IFC
in.
kg
LCS
LDS
LF
MERL
MMCF
MWLF
OSHA
PE
ppbv
ppm
PVC
QA/QC
Ref.
RCRA
R&D
Air Quality Management District
American Society of Testing and Materials
California Air Resources Board
Centimeter, centimeters
Concentration profile
Chlorinated polyethylene
Confined space indicators
Cubic foot, cubic feet
Cubic yard, cubic yards
Equation
Flexible membrane liner
Gallon, gallons
Gas chromatography
Gas chromatography-mass spectrornetry
Hectare, hectares
Hazardous waste
High density polyethylene
Hazardous waste landfill
Industrial Environmental Research Laboratory in
Cincinnati (EPA)
Isolation flux chamber
inch, inches
Kilogram, kilograms
Leachate collection system
Leak detection system
Landfill
Municipal Environmental Research Laboratory (EPA)
Million cubic feet
Municipal waste landfill
Occupational Safety and Health Administration
Polyethylene
Parts per billion concentration by volume
Parts per million
Polyvinyl chloride
Quality assurance/quality control
Reference
Resource Conservation and Recovery Act
Research and development
XI
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SCAQMD -- South Coast Air Quality Management District
(Southern California)
sec Second, seconds
SHWRD -- Solid and Hazardous Waste Research Division (of
EPA's MERL)
SI -- Surface impoundment
SLF Secure landfill
sq ft Square foot, square feet
T.D. No. -- Technical discussion summary reports presented in
Section 7
TLV -- Threshold limit value
TSDF -- Treatment, storage and disposal facilities
uv -- Ultraviolet
VOC -- Volatile organic compounds
yr -- Year, years
XII
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ACKNOWLEDGMENTS
This work has been carried out by MEESA for the -Land
Pollution Control Division of EPA's Hazardous Waste Engineering
Research Laboratory (Cincinnati. Ohio) through Contract No. 68-
03-1828. MEESA wishes to express its gratitude to the EPA
Project Officers, Ms. Norma Lewis and Mr. Vincent Salotto, for
their advice and guidance during the course of the project, and
to other technical staff of the Land Pollution Control Division,
in particular to Messrs. Robert Landreth, . Paul de Percin,
Benjamin Blaney, Jonathan Herrmann and Steven James, for
providing reference materials and suggesting contacts for data
acauisition.
Xlll
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SECTION 1
INTRODUCTION
EPA's Hazardous Waste Engineering Research Laboratory
(HWERL) is investigating the use of landfills (LFs) and surface
impoundments (Sis) in hazardous waste management. The primary
aims of this research are to develop criteria for improved dis-
posal site design and operation and to identify potential problem
areas and applicable corrective measures. The research results
are made available to the user community (i.e., site designers
and construction engineers, owners and operators of hazardous
waste management facilities, regulatory/permitting agencies and
researchers) through the publication of technology transfer type
documents such as this report.
Potential problem areas identified as requiring studies to
better define the nature and extent of each problem area and
applicable corrective measures include (a) leachate collection
systems in hazardous waste landfills (HWLF), (b) gas migration
and emission problems at HWLF, and (c) gas emission problems at
surface impoundments (SI).
A literature review indicated very little information avail-
able in the areas of interest. Accordingly, the data base devel-
opment effort for this study has relied heavily on acquisition of
information from design engineers, owners and operators of land
disposal facilities and cognizant state regulatory agencies.
This document is organized into 5 sections and two appen-
dices. This first section reviews the background and the intend-
ed uses of this document. Section 2 presents the conclusions of
the study, including R & D recommendations. Section 3 describes
the methodology for data acquisition and identifies individuals
and organizations providing input to the study in connection with
the technical discussions-with-experts element of the program.
Sections 4 presents a review of the previous studies and the
results of the present study regarding LCS problems and applica-
ble corrective and preventive measures. Similar discussion for
gas migration and emissions control is presented in Section 5.
The discussions in Sections 4 and 5 draw heavily on the informa-
tion collected in technical discussions with various individuals
and organizations with expertise in the subject areas; summary
reports on individual discussions are presented in Appendix A.
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Tabular summaries of corrective and preventive measures for liner
and cover systems are presented in Appendix B, based largely on
the information in previous studies.
The individuals and organizations whose perspectives are
included in Appendix A represent some of this country's leading
design engineering firms, process developers (for landfill gas
recovery) and regulatory agencies of states which have been in
the forefront of regulatory development and enforcement
activities. To this end, and insofar as that not all the
materials contained in Appendix A have been covered or discussed
in detail in the remaining sections of the report, Appendix A has
been organized as an independent section and is recommended for
review as an independent output of the present effort. Based on
the feedback received on the reports for two predecessor studies
(1,2), which included similar compendiums of professional
perspectives, regulatory agencies, owners and operators of waste
disposal sites, researchers and design engineers should find
Appendix A very informative and of value to them in broadening
their own perspectives. Some differences of opinions which are
expressed are generally more reflective of the .differences in the
nature of problems encountered in different regions of the
country than the differences in the approach to solving the same
problem.
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SECTION 2
CONCLUSIONS AND R&D RECOMMENDATIONS
2.1 LEACHATE COLLECTION SYSTEM (LCS)
There is very limited experience with properly designed LCS
at hazardous waste landfills (HVJLFs). Much of the documented
problems with the existing LCS relate to older municipal or
co-disposal sites which lacked sophisticated designs, did
not incorporate design redundancies and in many cases
consisted merely of simple toe drains, interceptor pipes or
gravel drains. These systems were also poorly constructed
and received little or no QA/QC attention. Some designers
believe that even if some clogging occurs, the problem
should not be of any major consequence due to the extreme
redundancies (excesses) which would be incorporated in the
state-of-the-art designs.
The actual or potential problems with LCS (and with gas
generation, migration and emissions) at HWLFs can best be
addressed through preventive measures incorporated in
design and operating practices.
Design efforts for improving site performance from the
standpoint of leachate management and LCS functioning are
aimed at minimizing potential for leachate generation,
improving -leachate control capability and reducing impact on
LCS and the consequence of any localized malfunction. These
preventive design-related measures include: (a) use of
progressive designs which allow for some experimentation and
incorporation of experience from previous cells and which
limits the active life of a cell to only 2 to 3 years, (b)
employing the state-of-the-art liner and cover designs
including interception of subsurface water, (c) use of
multiple cells for segregated waste disposal, (d)
incorporation of much redundancies (excesses) in design, (e)
traffic routing to avoid excessive stress on collection
pipes, (f) automatic leachate pumping, (g) use of specially
fabricated pipe connectors and sweep bends, (h) freeze
protection of pipes, and (i) use of suitable slopes and
protective cover for landfill side slopes and geotextile
liners for LCS trenches.
Operating controls for preventing LCS failure and for
mitigating other leachate management problems include:
source control (i.e., placing restrictions on type of
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wastes, such as liquids, which can be accepted in a land-
fill), waste neutralization/inactivation prior to disposal,
surrounding specific waste loads with absorbents or neu-
tralizers, placing the potentially troublesome wastes near
top and definitely not in the first lift, use of permeable
material as intermediate cover, use of temporary domes or
roofs during operation, and rigorous implementation of in-
spection and maintenance programs, including demonstration
of the functioning of the LCS after the first or second lift
of waste is in place.
Although there has been little opportunity for corrective
actions at RCRA-designed hazardous waste sites and
situations requiring drastic reparative measures are not
anticipated at such sites, some such measures which have
been used at older municipal and co-disposal sites may be
applicable to and constitute contingency measures for RCRA
sites. These reparative measures, some of which have proved
too costly and expensive substitutes for preventive design
and operating measures, include use of barriers such as
slurry trench to contain leachate, use of gravel trenches
and pipes to intercept seepage, installing caissons in
landfills and pumping out the perched leachate, and
replacing sections of the collection system.
2.2 GAS GENERATION. MIGRATION AND EMISSIONS AT HWLFs
Gas generation and migration problems which are encountered
at municipal and co-disposal landfills would not be a
concern at strictly hazardous waste sites. Because of the
extreme toxicity of waste and the operating practice of not
accepting putrescible wastes, little, if any, biological
activity resulting in production of decomposition gases is
expected at these sites. Pressure monitoring inside the
capped gas vents at some closed hazardous waste sites has
not indicated a buildup of gas pressure.
Much of the recent emissions monitoring and source testing
efforts at hazardous waste landfills have been concerned
with development and field evaluation of sampling and
analysis protocols and with verification of predictive
models.
The current emissions data base indicates that even though
closed hazardous landfills may emit some VOCs, the
measured/calculated ambient concentration levels of specific
compounds are very low (usually near or below the detection
limits of the methods employed) and nearly always less than
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the permissible OSHA exposure levels. These results.
however, may not be valid or representative because of (a)
the limited number of sites tested, (b) the existence of
multiple sources of emissions at or in the vicinity of
facilities tested, and (c) the wide variations in the
results obtained using different protocols.
Preventive/corrective design-related measures for gas
generation, migration and emissions control at hazardous
waste landfills include use of multiple cells for segregated
v:aste disposal, state-of-the-art liner and cover designs,
and capping of vents, sumps and cleanouts. Operation-
related measures for reducing landfill emissions include
source control (i.e., not accepting, or restricting disposal
of, solvents, putrescible wastes or liquids), use of
permeable material as intermediate cover (to avoid barriers
to gas flow) and control of runoff and infiltration thereby
suppressing potential for leachate generation and biological
activity. Fugitive emissions due to waste handling and
placement activities can be reduced by limiting the exposed
working face of landfill, operating under low temperature
and low wind speed (when possible), covering waste with
suitable material immediately after disposal, and processing
waste in enclosed areas equipped with emissions control.
2.3 GAS MIGRATION AND EMISSIONS CONTROL AT MUNICIPAL AND
CO-DISPOSAL SITES
Gas generation and migration are problems primarily
associated with co-disposal and municipal landfills where
the waste undergoes decomposition. Landfill gas contains
primarily methane (which presents explosion hazards) and
carbon dioxide, but also traces of hydrogen sulfide,
hydrogen, ammonia and aliphatic, aromatic and chlorinated
organics (e.g., vinyl chloride). In general, the quantity
and characteristics of landfill gas are highly variable and
extremely site-specific and these variations are not
necessarily related to any regulatory or conventional
classification of sites as co-disposal, sanitary, etc.
Unless it is recovered, in addition to safety hazards
associated with its offsite migration, landfill gas can
constitute a major source of air pollution, emitting large
quantities of reactive organics and substantial amounts of
potentially hazardous substances which are present in the
gas as trace constituents. Landfill covers will not
prevent, but merely postpone, gas emissions. Passive
controls involving interception and direct atmospheric
venting of gas can eliminate the gas migration problem but
would not constitute an emissions control measure.
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Properly designed and operated active gas control systems
can provide for both emissions and gas migration control.
These systems use blowers to collect gas through a network
of extraction wells and/or trenches. The collected gas is
either disposed of by flaring or combusted for energy
recovery. In either case, a high degree of destruction of
toxic organics can be achieved when combustion temperatures
are kept at about 800°C or greater.
2.4 EMISSIONS CONTROLS FOR HAZARDOUS WASTE SURFACE-, IMPOUNDMENTS
As with HWLFS, much of the emissions monitoring and source
testing efforts at hazardous waste surface impoundments have
been concerned with methods development and verification of
predictive models. Results also indicate ambient
concentration levels close to detection limits of the
analytical procedures used, large variations between results
using different methods, and large discrepancies between
measured values and estimated levels using models.
Preventive and corrective measures for reducing VOC
emissions from surface impoundments include source control,
proper siting, site enclosure and use of floating cover,
surface films, competitive solvent phase and wind fences.
Source control (which may include waste pretreatment for VOC
removal) is considered by many to be the most viable
approach to emissions control.
2.5 R&D RECOMMENDATIONS
Development of improved basis for LCS design through case
studies of LCS performance in full-scale facilities and
long-term parametric studies at full-scale sites reflecting
actual field operating conditions and practices.
Evaluation of cost-effective approaches to retrofitting
older sites with LCS.
Development of reliable systems for monitoring the
functioning of LCS.
Evaluation of innovative design concepts to leachate collec-
tion such as the draining of the entire LCS trench or
blanket and not merely the embedded pipe or the possible use
of a single system to simultaneously collect leachate and
the gas.
Parametric evaluation, in "real world" facilities, of
various cover systems for landfills from the standpoint of
emissions control.
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SECTION 3
DATA BASE DEVELOPMENT METHODOLOGY
As noted in Section 1, only limited information could be
found in the literature regarding the potential operating prob-
lems associated with leachate collection and gaseous emissions at
hazardous waste disposal sites. To expand the data base for the
study, results from recent and on-going EPA-sponsored studies
were included. Also information was obtained from owners and
operators of certain was'te disposal sites, personnel of cognizant
regulatory permitting agencies and several leading consulting
engineering firms engaged in design and construction of LFs and
Sis. Table 1 lists the 16 organizations that contributed to the
study.
Information was obtained on the following topics:
Leachate Collection System
-Actual experience with, or potential for
inadequate performance (e.g., clogging)
-Factors (design, construction and operation) of
contributing to satisfactory or unsatisfactory
performance
-Applicable corrective measures
Gas and Emissions Control
-Factors affecting gas generation, gas composition
and emissions at strictly hazardous waste sites
-Applicability of data and controls from co-
disposal and municipal sites to strictly
hazardous waste sites
Research and Development Needs
Miscellaneous
-Regulatory considerations
-Other data sources and contacts
-Etc.
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TABLE 1.
COMPANIES AND ORGANIZATIONS WITH WHOM TECHNICAL
DISCUSSIONS WERE HELD
Technical
Discussion
No.
Date
Individual(s), Company/Organization
and Address
4/13/84
4/16/84
4/17/84
4/23/84
4/24/84
4/25/84
R. Huitric, J. Lu
San. Districts of Los Angeles Co.
1955 Workman Mill Rd.
Whittier, CA 90607
(213) 699-7411
Larry Well
CH2M-Ha.ll
2300 N.W. Walnut Blvd.
Corvallis. OR 97339
(503) 752-4271
Mike Kennedy
CH2M-Hill
2020 S.W. 4th Avenue
Portland, OR 97201
(503) 224-9190
J. Johnson, W. Lockman, R.Lofy
Lockman and Associates
249 E. Pomona Blvd.
Monterey Park, CA 91754
(213) 724-0250
R. Beyer, W. Bonta, L. Martino,
R. Rosnick
Hazardous Waste Management Div.
Waste Management Administration
201 West Preston Street
Baltimore, MD 21201
(301) 383-5736
D.R. Foster
Maryland Environmental Service
60 West Street
Annapolis, MD 21401
(301) 269-3666
(Continued)
8
-------
TABLE 1. (Continued)
Technical
Discussion
No.
Date
Individuals(s ) , Company/Organization
and Address
10
11
12
4/26/84
4/30/84
5/01/84
5/02/84
5/22/84
5/23/84
13
5/24/84
J. Bross, G. Elliot
Duffield Associates, Inc.
5350 Limestone Road
Wilmington, DE 19808
(302) 239-6634
John Reinhardt
Residuals Management Technology
1406 East Washington Ave., #124
Madison, WI 53701
(608) 255-2134
M. Gordon, P. Kmet, G. Mitchell
Department of Natural Resources
101 S. Webster St.
Madison, WI 53707
(608) 266-8804
R. Cooley, D. Kolberg, D. Viste
Warzyn' Engineering, Inc.
1409 Emil Street
Madison, WI 53715
(608) 257-4848
Joe David, R. Koltuniak
Black & Veatch
Engineers-Architects
7315 Wisconsin Avenue, Suite 850N
Bethesda, MD 20814
(301) 986-8980
E. Belmore, J.Coyle, M. Hans,
F. Grabar
NY Dept. of Environ. Conservation
600 Delaware Street
Buffalo, NY 14202
(716) 847-4585
Site A
(Continued)
-------
TABLE 1. (Continued)
Technical
Discussion
No.
Date
Individual(s), Company/Organization
and Address
14
15
5/25/84
6/29/84
16
7/10/84
S. Arlotta
Wehran Engineering
666 East Main Street
Middletown, NY 10940
(914) 343-0660
F. Cope, J. Pacey, R. Van Heuit
Emcon Associates
90 Archer Street
San Jose, CA 95112
(408) 275-1444
L. Ceilings, J. Pena, W. Taylor
Getty Synthetic Fuels, Inc.
2750 Signal Parkway
Signal Hill Parkway
Signal Hill, CA 90806
(213) 595-4964
10
-------
SECTION 4
LEACHATE COLLECTION SYSTEMS
4.1 REGULATORY BACKGROUND AND SOME GENERAL CONSIDERATIONS
The land disposal regulations promulgated by the U.S.
Environmental Protection Agency (EPA) in July 1982 as Interim
Final regulations (40CFR 264.301) require the installation of
leachate collection systems (LCS) for all newly constructed
hazardous waste landfills. The purpose of the LCS is to
intercept and remove the leachate from the landfill thereby
preventing the build-up of leachate in the landfill and hence the
stress on the liner. Leachate removal should thus prolong the
liner life, reduce the potential for leachate migration and allow
for treatment and disposal of the leachate under controlled
conditions.
The interim regulations specify a maximum leachate head of
30 cm (1 ft) above the liner and direct the EPA Regional
Administrators to specify, as part of the permitting process,
design and operating conditions which would ensure that this
maximum leachate head specification is not exceeded. The
regulations also state that the LCS construction material (pipes)
should be (a) of sufficient strength and thickness to prevent
collapse under the pressures exerted by the overlying wastes,
waste cover materials, and by any heavy equipment; and (b)
chemically resistant to the wastes managed and expected leachate.
Finally, the regulations state that the LCS must be designed and
operated to function without clogging through the scheduled
closure of the landfill.
Although EPA (3) and others (4-7) have provided some
guidelines on design and construction of LCS (see Table 2 for EPA
guidelines), very little information is available on the
effectiveness of the suggested design and construction practices
in preventing LCS clogging. These guidelines (e.g., the
specifications for graded granular material or fabric filters)
are largely based on experience from other fields (e.g., the
general construction, agricultural drainage, and water well
industries) and have not been verified in waste disposal
applications. Indeed, there is very little feedback on the
performance of LCS in few facilities which have utilized the
state-of-the-art design. Accordingly, the actual or potential
clogging of LCS and the extent of the problem appear at this time
to be matters of conjecture rather than documented observations.
11
-------
TABLE 2. EPA MINIMUM GUIDELINES FOR THE DESIGN OF LCS (3)
At least a 30 cm (12-inch) drainage layer with a
hydraulic conductivity 1 x 10 cm/sec and a minimum
slope of 2 percent
A graded granular or synthetic fabric filter above the
drainage layer to prevent clogging, except in the case
of secondary leachate detection, collection and removal
systems that are in direct contact with the primary
synthetic liner. If a granular filter is used , the
grain size should meet the following criteria:
D15 (Filter soil)
< 5
D85 (Drainage layer)
D50 (filter soil)
D50 (drainage layer)
< 25
D15 (filter soil)
and =5-20
D15 (drainage layer)
where:
D15 = grain size in millimeters, at
which 15% of the filter soil
used, by weight, is finer
D85 = grain size, in millimeters, at
which 85% of the filter soil
(or layer media) used, by
weight, is finer
D50 = grain size, in millimeters, at
which 15% of the filter soil
used, by weight, is finer
A drainage tile system of appropriate size and spacing
and a sump pump or other means to efficiently remove
leachate
12
-------
They are, nevertheless, of some concern to design engineers,
ov:ners and operators of landfills and regulatory agencies, as it
is often difficult to readily ascertain the functioning of the
LCS and remedial actions can be very expensive after a
significant volume of waste has been deposited at a site. The
concern over the performance of LCS has promoted certain state
regulatory agencies (e.g^, Wisconsin Department of Natural
Resourcessee T.D. No. 9 ) to establish stringent requirements
for LCS design and to require a demonstration of the workability
of the cleanout feature of the system.
The objective of the LCS segment of the present study has
been to provide a better definition of and the experience with
clogging and to identify corrective measures applicable to the
identified problems and areas requiring R & D. Since the
discussion in this and subsequent sections refer to various
components of LCS, a schematic of a typical LCS is shown in
Figure 1. Figures 2 and 3 show, respectively, pipe configuration
and sump cross section for LCS in a cell at a hazardous waste
disposal landfill site. It should be noted that the design and
the waste placement practice depicted in Figures 2 and 3 are for
a particular site and are not typical of operating hazardous
waste landfills.
4.2 PREVIOUS STUDIES
Under the sponsorship of the U.S. EPA, two studies were
recently conducted by GCA Corporation (9) and by Arthur D. Little
(ADL), Inc. to compile the relevant available information and to
provide a better definition of the LCS clogging problems.
The GCA study resulted in a "white paper" for use by EPA in
addressing the subject of LCS design in its Interim Final land
disposal regulations. The paper drew together documented
information on the clogging of agricultural drainage systems and
water supply wells and assessed the potential for LCS clogging
based on some theoretical considerations and inference from the
experience with these other systems. Assuming that LCS failure
due to clogging was a real possibility, the paper presented a
theoretical discussion of the physical, chemical and biological
factors which can contribute to such failure and of applicable
preventive and corrective measures.
The ADL study extended the GCA study to include additional
telephone interviews with landfill operators and an investigation
of some cemented materials found in gravel around a drain at an
EPA demonstration landfill in Boone County, KY, to determine
"T.D. No." references refer to the technical discussion summary
reports presented in Appendix A.
13
-------
Figure 1. Schematic of a typical leachate collection system (8)
-------
/I .} I ' , i«|.>--«.
1 ' '' ,i ". V ',!. "' .,' '
..' ' , ' < "V",, I ' ,, i,
-8 0 SOLID HOPE GRAVITY LINE
MAX. SDR = 11 O
BO MIL HOPE MCMQRANC
Figure 2. Typical pipe configuration for LCS in a cell
at a hazardous waste landfill (T.D. No. 13)
-------
48" NOMINAL WA. PRESTRESSTO
CONCRETE CYLINDER PHt (LOCK
JOINT SP-12 OR CQUIVI WITH
BELL BOLT JOINTS LAID LENGTH»
V* STONE PLACED AROUND
Bistfl AS CANDFILLINO
PflOOHESSES
I'-O" COMPACTED CLA» MAX
KHMEAMLITV IOHO-7 CM/SEC
OPENING FOR
LEACHATE
COLLECTION
PIPE
48 PRECAST CONCRETE
END CAP
GRAVEL M.fcCFD
f DETWEF.N LANDril.l.m
I DABREL3 (PIRST I.I IT
L ONLY)
^"|
f'
C-0" GRAVEL
I'-O"
MIRAF) 700X
CEOTEXTI.E FAORIC
OR EOUIV
60 MIL HOPE
MEMBRANE
Figure 3. A cross section of leachate collection sump for LCS
at a hazardous waste landfill (T.D. No. 13)
-------
causual mechanisms. The ADL study also reviewed the possible
mechanisms of clogging and discussed potentially applicable
preventive and remedial measures, A summary of the clogging
mechanisms identified is presented in Table 3.
4.3 PROBLEM OVERVIEW
There is currently limited information on the extent of LCS
clogging experience in full-scale facilities. This lack of
information stems from (a) the relatively young age of LCS in
current service, (b) progression and continuous advancements in
LCS design and operating practices, (c) lack of a standard
definition of what constitutes clogging and of monitoring systems
to detect problem, (d) a lack of concern on the part of many
operators who have traditionally viewed the clogging not as a
major problem but as a minor and manageable nuisance and their
general reluctance to openly discuss their experience (if any)
with LCS clogging, and (e) the general perception by design
engineers that the extensive redundancies which are incorporated
in the latest designs render any potential clogging a localized
problem and inconsequential to the overall performance of LCS.
The actual experience with engineered sites featuring LCS is
very limited (T.D. Nos. 3, 8 and 15). For example, in Wisconsin,
which has been a leader in incorporating the state-of-the-art in
design and regulations, the first generation engineered sites
went into service only in about mid-1970s and. it was not till
about 1980 when some operating data became available for some of
these sites (T.D. No.8) . Even during such a short time span,
there have been considerable and continuous advances in LCS
system design and operating practices (T.D. No. 14) that
collection of extensive performance data for older systems have
not been apparently justified. (This progression of design and
changes in operating practice which incorporate lessons learned
from previous experiences, is best illustrated by the cell-by-
cell operation at certain hazardous waste management facilities--
see T.D. Nos. 12, 13 and 14.)
There is currently no firm basis/criteria for determining
whether a leachate collection system is experiencing clogging
(T.D. Nos. 3 and 8). The water budget method of determining
leachate flow for design purposes may be inaccurate as a basis
for determining the extent of clogging. Use of head wells for
direct observation of leachate levels is a preferred method and
the one which is now required in Wisconsin (T.D. Nos. 8 and 9).
The design requirements for a head well leachate level monitoring
system from the standpoint of number and locations of wells
needed to produce reliable data, however, have not been
established. Traditionally, a very significant reduction in the
normal leachate flow or the absence of a noticeable increase in
flow following a major storm has generally been assumed to
17
-------
TABLE 3. SUMMARY OF CLOGGING MECHANISMS (8,9)
PHYSICAL MECHANISMS
1) Inadequate carrying capacity related to inadequate
design:
-Inadequate pipe spacing, slope, or diameter
-Insufficient slot area
-Undersized pump or sump outlet diameter
-Improper or insufficient drainage media
2) Structural failure or collapse caused by mechanical
crushing or displacement, and possibly aggravated
by physical deterioration of drainage materials:
-Compaction and trafficking over drainage
materials during installation
-Compaction of waste (loading) during normal
operation
-Consolidation settlement of waste and underlying
soil
-Physical deterioration caused by pH extremes,
oxidizing (metal pipes) or organic solvents
(plastic pipes)
-Penetration of drains by refuse
3) Sedimentation or trapping of solids (arising from
the waste, daily cover cap, envelope, or filter
materials) in pipe or sump due to:
-Incorrectly selected grain size distribution
-Improper pipe slot size
-Piping of the envelope due to hydraulic failure
or scouring
-Low flow due to shallow pipe slope, installation
of impermeable cover, source control
CHEMICAL MECHANISMS
1) Formation of insoluble precipitates (calcium
carbonate, manganese carbonates, sulfides, and
silicates) under basic, neutral, or slightly
acidic conditions which deposit on drainage
materials by trapping or evaporation during dry
periods.
(Continued)
18
-------
TABLE 3. (Continued)
BIOCHEMICAL AND BIOLOGICAL MECHANISMS
1) Ferric hydroxide or ferric sulfide precipitate
formation as a result of anaerobic and then
aerobic bacterial action leading to a mix of
biological slime and precipitates called ochre.
Blocked drainage systems can result depending on:
-presence of iron and/or sulfate reducing
bacteria, ferric ions (from soils or waste) and
sulfates
-pH conditions and redox potential
indicate LCS malfunctioning. The former criterion requires
historical flow data (T.D. No 3), which is not generally
available for most sites, and the latter criterion is qualitative
and will not detect clogging unless it is very drastic and
advanced. Accordingly, the landfill operators generally do not
have a solid basis to determine how well or poorly an LCS is
actually performing.
Nearly all design engineers with whom technical discussions
were held in the present study (see, for example, T.D. Nos. 4, 8,
10, 14 and 15) saw little potential for any clogging of
consequence with the new LCS designs, because of the considerable
built-in redundancies. These redundancies relate to (a) the
oversizing of the pipes, (b) availability of alternate flow
routes (i.e.,other laterals and the drainage trench/blanket) in
the event that one or more laterals become plugged, and (c)
provisions for cleaning access to pipes. Much of the documented
problems with the existing LCS relate to older systems (primarily
municipal or co-disposal sites), which lacked sophisticated
designs, did not incorporate design redundancies, and in many
cases consisted merely of simple toe drains (T.D. No. 15). With
the reference and guidance documents which have been made
available to the designers in recent years (e.g., the EPA
Technical Resource Documents), the opportunities for making
mistakes are far less today than they were previously when the
older systems were being designed (T.D. No. 15). Some designers
feel that with the state-of-the-art design and operating
practice, a dry landfill is an achievable goal (T.D. No. 14), and
LCS in some landfills in a dry climate have been installed
primarily as a precautionary measure rather than to actually
remove any leachate (T.D. No. 1).
Some designers (T.D. No. 10) pointed out that getting the
leachate to drain through the refuse mass and reach the LCS
represents a much greater design and operation challenge than
getting the ' leachate to exit through the underdrain once it
19
-------
reaches it (see also T.D. No. 9 for actual experience with
leachate perching in landfills). The differences between the
permeabilities of the waste and the LCS drainage material has
been taken advantage of in a new "air gap" design concept where
the leachate head on the liner is limited to that in the drainage
layer which is made independent of the actual head in the fill
which can be possibly much higher than that in the drainage layer
(T.D. No. 14).
Design engineers who were familiar with the agricultural
drainage systems thought that it would be inappropriate to draw
conclusions as to the expected performance and service life of
the LCS based on experience with the agricultural drainage
systems {T.D. Nos. 8, 10 and 15), because of the differences in
design, construction and maintenance practices for the two
systems. For example, tile pipes used in agricultural drainage
systems are constructed with open points, the construction
receives little or no QA/QC, and there is no subsequent
maintenance (cleaning) and repair program for these systems.
Given the above considerations, it is not surprising that
the present study did not identify LCS clogging as a problem of
major concern. For the sample of sites represented by the
owners, designers, state regulatory agencies and a commercial
sewer inspection and cleaning company with whom technical
discussions were held, LCS clogging was a problem of major
concern at only one site (a unique co-disposal facility handling
a significant volume of liquid industrial wastes) (T.D. No. 4),
with two hazardous waste facilities reporting some previous
experience with minor siltation in the LCS standpipes (T.D. No.
12). The inspection of a section of LCS at two municipal
landfills in Wisconsin indicated no evidence of clogging or
deterioration after some 10 years of actual service; except for
some discoloration, the gravel in the trench was very clean and
appeared intact (T.D. No. 10). Biological growth has been noted
in and around the LCS pipes at some sites in Wisconsin (10). The
annual jet cleaning of the lines, however, has been effective in
dislodging the biological growth as well as silt accumulation
which has been noted at certain sites (10). At some older
municipal sites where crushed limestone has been used as the
bedding material in the LCS trenches, reaction with the acidic
leachate has resulted in the cementation of the drainage material
into solid blocks (10). In newer designs, the limestone has been
replaced with inert "washed stone" (10).
The reported experiences with LCS are discussed in the
following section.
20
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4.4 OPERATING FACTORS AFFECTING AND THE EXPERIENCE WITH THE
PERFORMANCE OF LEACHATE COLLECTION SYSTEMS
With the latest design practices, the proper functioning of
LCS appears to be a case-specific problem depending to a large
extent on the type of waste handled, waste placement method, the
kind of material used for cover and cover placement method.
Accepting a significant volume of liquid wastes, sludges
with considerable amounts of fines and wastes with low
permeabilities have . been identified as causes of poor LCS
functioning at a number of sites. At one hazardous-municipal co-
disposal site (T.D. No. 4) where about 30% of the waste handled
is comprised of liquid industrial wastes, the clogging of the LCS
(including the sand and gravel) has been a recurring problem. At
this site the clogging, which is due to chemical deposition and
solidification, is very nonsystematic and appears to be related
to the variations in the type of waste handled and hence in the
leachate characteristics.
Some siltation has been noted at the bottom of the leachate
collection standpipes (sumps) in older cell designs employed at
two hazardous waste facilities in New York (T.D. No. 12). The
problem has been mostly in the cells dedicated to heavy metal
sludges and has been attributed to the passage of fines through
the gravel drainage into the LCS collection pipes as well as
possibly through the joints of the standpipes. At a facility in
Wisconsin, where the drainage envelope also consisted of gravel
only with no sand layer filter media on top of gravel and where
paper mill sludges were included in the first few lifts, leachate
perching and mounding were observed and were attributed in part
to a blinding of the gravel envelope by the fine particles in the
paper mill sludge which penetrated it (T.D. No. 9).
Inadequate drainage through the waste and/or materials used
as intermediate cover has resulted in leachate perching and
excessive mounding at some sites. At a hazardous waste site in
New York (T.D. No. 12), some leachate perching which was observed
was attributed to the use of water treatment sludges as
intermediate cover. Similar perching phenomena have been
observed at other sites where shredded refuse and/or paper mill
sludges were accepted and where low permeability materials (such
as shredded refuse or clayey soils) were used as intermediate
cover (T.D. Nos. 9, 10, 12). Because of their relatively low
permeability, these wastes and intermediate covers can act as
barriers to leachate (and gas) movement. The buildup of leachate
and of high gas pressures (T.D. No. 9) have led to some
documented cases of "leachate geysers" in landfills.
At many sites the pumping of leachate from sumps is on an
infrequent basis. This at times can result in excessive leachate
21
-------
acca.T'Ulation (long residence time) in the sumps and very high
(perhaps as much as 10 to 20 ft) heads in the landfill. A very
long residence time in the sumps can result in particle settling
and silt accumulation (T.D. Nos. 12 and 13). Automatic leachate
punping whereby the leachate level in the sumps will always be
maintained lower than a certain level has been successfully used
in Eoiie hazardous waste sites (T.D. Nos. 12, 13, 14) to increase
drainage and to reduce potential for long residence time in the
sump.
4.5 PREVENTIVE AND CORRECTIVE MEASURES
As noted previously, there has been little opportunity for
LCS-related corrective action at RCRA-designed hazardous waste
landfills. Some corrective actions which have been used in some
older co-disposal sites, and which may be applicable to hazardous
waste sites, include the following:
-Use of gravel trenches or pipes to intercept leachate (T.D.
Nos. 6, 10 and 15).
-Drilling caissons in landfills and pumping out the perched
leachate (T.D. Nos 5. 10 and 15).
-Replacing sections of the collection system (where the depth
of the overlying waste is not significant) (T.D. Nos. 4 and
15).
Indeed, at one site where LCS clogging has been a recurring
problem (T.D. No. 4), the corrective measure used has been that
of replacing various affected sections of LCS. The reparative
measures which have been considered and/or are being undertaken
at one site experiencing leachate perching and poor drainage
include drilling caissons to various depths within the fill and
constructing a gravel "trench" all the way to the bottom of the
fill along the inside periphery of the site (T.D. No.10).
The corrective actions, or in general the retrofitting of
older sites with leachate collection systems can be very costly,
especially for large landfills and, in the case of hazardous
waste sites, can present considerable risk and safety hazards.
Based on the information collected in the present study, the
problems associated with the functioning of LCS in hazardous
waste (or other types of) landfills can best be addressed through
preventive means involving a combination of good design and
appropriate operating practices. Failure to implement suitable
preventive measures can lead to major problems for which
practical corrective measures may be prohibitively expensive.
For example, at the present time there is no practical corrective
measure (short of total system replacement) for restoring the
hydraulic capacity of the LCS drainage blanket if it becomes
totally ineffective due to sedimentation and chemical deposition
(T.D. Nos. 3, 5 and 7). Excavation in hazardous waste landfills
22
-------
can be very dangerous and sometimes exceedingly difficult (T.D.
Nos. 3, 5 and 6).
As long as the leachate collection and conveyance pipes are
provided with adequate cleanout accesses, restriction of flow due
to simple siltation and accumulation of chemical/biological
deposits should be correctable (and have been corrected) by use
of conventional sewer cleaning techniques. On a number of
occasions, the expertise and services of the sewer cleaners have
indeed been called upon to restore the capacity of clogged
leachate lines or to provide preventive maintenance services (see
Section 4.5.3). The Water Pollution Control Federation has
published a manual of practice on operation and maintenance of
wastewater control systems (11) which provides detailed
discussions of the state-of-the-art sewer inspection and cleaning
techniques and equipment, including safety hazards and measures
for preventing explosions and injuries from oxygen deficiency and
obnoxious gases. There are many devices which can be used to
detect the presence of flammable vapors and toxic gases. Ref. 11
lists some 55 flammable and toxic gases which' can be tested for
by portable testing equipment.
A summary of sewer inspection and cleaning methods is
presented in Table 4. Based on the reported experience (10, 12
and T.D. No. 7), jetting appears to be very effective and most
appropriate for cleaning LCS lines. Although there is no reported
experience with the use of television inspection for LCS lines,
the technique was successfully employed recently to obtain the
profile of in-place waste at a co-disposal site in Wisconsin
where caissons were being drilled for the removal of perched
leachate (10). According to a commercial sewer cleaning company
which has provided LCS cleaning service in Wisconsin and several
other states in the region (12), as long as LCS lines are
properly designed (i.e., lines are 6-in. or greater in diameter
and cleanout accesses are provided at strategic locations
including at places where there is a change in the direction of
flow), the cleaning of the LCS lines does not present any
technical problem which can not be handled with the available
equipment and procedures. Due to the nature of waste and often
the unknown environment, however, the personnel may have to
exercise more caution when servicing LCS lines.
Use of some of the methods listed in Table 4 for cleaning
and restoring the hydraulic capacity of contaminated sewer lines
located downgradient of hazardous waste disposal sites are
discussed in the Handbook for Remedial Action at Waste Disposal
Sites (6).
4.5.1 Design Considerations
Design considerations for improving the functioning of a
23
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TABLE 4. SP:WER INSPECTION AND CLEANING METHODS (11)
Description
Reiiuika
Closed Circuit
Television Inspection
Cower Podding
Dal ling
Flushing
Jetting
WMllc tho camera skid Is pulled between
two manholes, tho TV camera scans tho
area in front of the skid and transmits
It to monitor screen. A tag lino la
tilso attached to tho rear of the camera
assembly making It possible to back up
for viewing a problem or to retrieve
the camera if it is impossible to pull
it completely through the line.
The power equipment applies torque to
the rod as it is pushed through tho
line, rotating tho cleaning device.
Hydraulic cleaning a pipe by using tho
oressure of a water head to create
high velocity water flow around the
ball. The ball is restrained by a
rope or cable while the water washes
past it at high velocity.
Hydraulic cleaning involving introduc-
tion of a heavy flow of water into the
line at a manhole.
Hydraulic cleaning method whereby high
velocity streams of water arc directed
against the pipe walls at various
angles. Jetting equipment consists of
a water supply tank that holds usually
1000 gal. or more, a high-pressure
water pump, an auxiliary engine, a
powered drum reel holding at least
1500 ft of 1-in. inside diameter hose
on a reel having speed and direction
controls, a variety of interchangeable
nozzles, and necessary tools such as
hose rollers and guides.
Most offoctlvo method of determining
nature of internal problem. Can bo
iiaod on all pipes down to 4 in. diam-
eter. Most municipal it lea own and
operate theao equipment. Somo contract
out for florvlco.
Folrly efficient in linos up to 12 in.
Used for routine preventive maintenance
breaking up grease deposits, cutting
roots, threading cables for bucket
machine or TV inspection equipment.
Very effective for removing deposits of
settled Inorganic material (grit) and
grease buildup insldo tho lino. The
material removed by balling should
bo caught and removed at tho downstream
manhole.
Effective for removal of flootablos and
some sand and grit but is not very
effective for removal of heavy solids.
Less frequently used slnco introduction'
of the high-pressure water jot cleaners
(see below).
Very effective In cleaning small
diameter, low-flow pipes and to clean
stoppage caused by debris. Desirable
to remove loosened material with vacuum.
(Continued)
-------
TABLE 4. (Continued)
Method
Description
Remarks
Scooter
Kites, Dags, Tires and
Poly Pigs
Ducket Machine
NJ
en
Hydraulic cleaning method whereby the
pressure of water behind the shield of
a ocooter moves tho scooter downstream
and tho water forces past tho shield
rim and scours tho pipe walls as with
the balling method.
Devices used to hydraulically clean
large pipes in a manner similar to
hailing. Water pressure moves the.ao
devices against the tension of their
restraining lines.
A mechanical cleaning device effective
in partially removing large deposits
of silts, sand, gravel, and somo types
of solid waste. When tho bucket la
pulled in the opposite direction by
the working machine, the jaws are
forced closed, and any material re-
tained in the bucket is pulled out
through the manhole.
Requires tank truck of 1000 to 2000 gal.
capacity, efficient cleaning tool and
effective in removing blockage.
Effective in linos up to 95 in.i good
preventive maintenance.
Same as for scooter.
Used to remove dobria from a break or
accumulation that cannot bo cleared by
hydraulic cleaning. Slow and very
costlyi recommended for special condi-
tions only.
-------
facility from the standpoint of leachate management can be
broadly grouped xnto three somewhat overlapping categories:
Those aimed at reducing the potential for leachate generation;
those aimed at providing better leachate control; and those aimed
at reducing impacts on LCS and the consequences of malfunctions
and failures. Examples of design considerations in the first
category are (a) use of "progressive design" (T.D. No. 14) where
a cell-by-cell design approach would limit the size of an active
cell/area and hence the amount of leachate due to water inflow
prior to closure; and (b) proper design and maintenance of cover
to minimize infiltration. Progressive design also enables some
experimentation to incorporate design modifications based on
experience from preceeding fill operations or general
technological advances. Improved leachate management
capabilities can be achieved through designs which allow for
waste segregation and sreparate disposal by waste type category.
Incorporating redundancies in design (e.g., oversizing of
laterals), use of automatic level-controlled leachate pumping
systems and use of geotextiles as separators to prevent or
reduce penetration of drainage blanket by soil or waste particles
are two examples of design considerations for reducing the
potential adverse impact on LCS functioning and the consequences
of partial LCS clogging.
The above-mentioned and other related design considerations
which reflect the experience and perspectives of those with whom
discussions were held in the present study are summarized in
Table 5. Guides and recommendations on detailed design of
landfills and its components are discussed elsewhere and will not
be addressed here. It should, however, be pointed out that the
detailed design (and also often the general design approachsee
T.D. Nos. 1, 4, and 8) have to take into account site- and
situation-specific conditions and must be tailored to the
specific job requirements.
4.5.2 Construction and QA/QC Considerations
Use of proper construction techniques and QA/QC procedures
are very important in avoiding subsequent LCS malfunction due to
poor construction methods and deviations from specifications
which were not caught because of inadequate inspection.
Construction- and QA/QC-related considerations have been
discussed in several recent publications (1, 2, 4, 13). Some
relevant experiences which were conveyed to this study by the
individuals with whom technical discussions were held follow.
A well-designed chemical landfill in Michigan is an example
of how poor construction technique and QA/QC oversight can result
in system clogging and subsequent leakage from connections (14).
While excavating to install leachate sumps for new cells, liquid
began to flow out in an excavated gravel area where leachate and
26
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TABLE 5.
Conaiderat ions
and References
DESIGN CONSIDERATIONS FOR IMPROVING STTC PERFORMANCE
FROM THE STANDPOINT OF LEACIIATE MANAGEMENT
Objectivc
Doacr Jpt1 on/Commont
Progreaaivu
deaign
(T.D. No. 14)
State-of-the-art
cover design and
subsurface water
Intercept ion
(T.D. Nos. I. 2.
13. 14)
Multiple cell
design for
segregated waste
disposal
(T.D. Nos. 1. 2,
13. 14)
Incorporation of
design redundan-
cies (T.D. Nos.
7. 8. 10. 14.
15)
-Moie rapid achievement of a
"dry" landfill operation
-Incorporation of experience
from preceding designs and
the technological advances
-Limiting risk to small areas/
units and implementation of
corrective actions leas costly
-Minimize infiltration
-Provide for better operating
control
Provide for adequate safety
factor and contingencies
-Cell-by-coll design thereby limiting tho slzo of tho
active coll/area to that which can t>u filled and
closed within 1-2 yrs. The luachato to bo pumped tint
thus restricted to water entering site during ohort
active life
-Cover design to allow little or no water infiltration
to a closed coll, thereby limiting tho loachato to bo
pumped out to water entering alto during waoto
placement
-Use of subsurface drains to intercept perched or
spring water and proper surface drainage to divert/
intercept surface runoff
-Dedicating specific landfill calls/area^ to specific
wastes or waste categories (e.g.. heavy metal sludges)
and tailoring coll design and operation to waste-
specific properties requirements
-Ovcrsizlng and closer spacing of LCS pipes
-Use of drainage media (e.g.. appropriate gradation of
conventional sand and gravel filter which would allow
rapid drainage and prevent head build-up and yet
effectively retain waste particles without plugging
-Use of drainage blanket (in preference to drainage
trench) to provide positive connection across tho
entire base of the landfill
-Providing adequate number of clcanout accesses (i.e.,
one for every 1000 ft of pipe) and avoiding sharp
bends at pipe connections
-Placing Icachate riser pipes in the landfill wall
rather than in the fill or on the surface of tho side
wall, to avoid potential damage due to waste load and
movement
-Placing gravel or similar material around standpipos
in a vertical column extending to the top, to promote
leachate drainage
(Continuud)
-------
TABLE 5. (Continued)
Considcrat Ions
and References
Objective
Rescript ion/Comment
NJ
00
-Prevent reaction with tha
Icachate
-To enable bettor access to
pipes for maintenance purposes
including use of TV camera for
inspection
Use of inert
materials as
drainage bed
for LCS (10)
Use of specially
fabricated pipe
connectors, sweep
bends, and 6-ln.
or larger pipes
and providing
clcanout accesses
at strategic
locations (10. 12.
T.D. Nos. 9. 15)
Equipping manholes -To prevent debris from entering
and clcanouta with lines
covers
Traffic load on
collection pipes
(T.D. No. 9)
Automat ic
Icachate pumping
(T.D. Noa. 9. 12.
U, H)
-To minimize potential for pipe
collapse due to traffic load
Prevent leachate head buildup
in collection sump and in the
landfill
-Use of crushed Hernia Lone as hodding materials at some
older situs had resulted in cementation and formation
of solid blocks duo to reaction with acidic loachato
-Depending on specific Job conditions, specially
fabricated pipe connectors, use of slotted pipes (in
preference to perforated pipes) and use of swoop bonds
instead of sharp bonds at connections may promote
bettor access to pipes or easier pipe maintenance
-Unless thcso openings are kept covered, debris and
other wind-blown materials can enter linos and result
in flow obstruction. This has boon identified as a
source of problem at several sites requiring lino
cleaning to restore hydraulic capacity
-Site design (and operation) to eliminate traffic over
collection pipes
-Use of half or whole corrogated pipes whore there is
trafficking
-Use of level-activated leachato pumping system to
maintain leachate level in collection sump at or below
the Invert of incoming collection pipe, thereby
promoting drainage and minimizing opportunity for
clogging
-Providing high sump level alarms to signal system
malfunction
-Providing leachate head wells in the fill for direct
observation of Icachate head
(Continued)
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TABLE 5. (Continued)
Considerations
and References
Objective
DcscrIptIon/Comment
vo
Combining
Icachatoo from
various cells vs.
separate pumping
Use of
gcotcxtlies
(T.D. Noa. 9. 11.
12. 14, IS)
Freeze protection
of pipes
(T.D. No. 12)
Suitable slope
and protective
cover
(T.D. No. 9)
-Reduce coat and pump
maintenance (combined pumping)
-provides better controls
(separate pumping)
-As a separator or filter to
prevent LCS siltation
-To prevent flow disruption due
to winter freezing in cold
climates
-To prevent erosion washing of
clay from side slopes
-Assuming compatabillty, lunchato from various colls
can be directed to a common sump prior to pumping
-Design for combined pumping con incorporate
contingency provisions for Icachato segregation and
separate pumping If necessary
-Using gcotextllcs to envelope the granular material
in the drainage trench or as a separator between tho
clay liner (or clay protective liner for FML) and
gravel drainage blanket to prevent siltation by
waste particle or soil from trench walla or liner
-Some designers and regulatory agencies do not recom-
mend use of gcotcxtilc as a filter medium in hazardous
waste sites due to lack of previous experience
-Use of underground pumps for Icachate removal from
sumps and conveyance to treatment/disposal centers
-Locating conveyance pipes in sufficient depth and
designing them for gravity flow
-Use of suitable side slopes (at least 3ltilV) and
placement of protective cover (e.g.. sand layer) on
landfill aide slopes to prevent erosion washing of
of clay, aome of which might find its way into and
clog LCS
-------
underliner collection sewer lines from the existing cells had
been terminated and capped during the original installation. A
13-ft head build-up was noted in one of the manholes along the
collection line whereas a second manhole immediately downstream
had only about one inch of water. This indicated a possible
blockage in the the connecting line between the two manholes.
While preparing to enter the downstream manhole with a TV camera
to determine the nature and location of the obstruction, workers
pulled a 6-ft section of an 8-in. polyethylene pipe from this
manhole and water began to flow at a substantial rate. Apparently
this pipe had wedged into the leachate collection line at an
angle just right to cut off almost all flow through this manhole.
To avoid damage to the LCS pipes during construction and
initial waste placement, the state of Wisconsin has required use
of half or whole corrugated pipes to cover trenches where there
is trafficking (T.D. No. 9). This requirement, however, has only
been partially effective as the traffic path constantly changes
as the operation proceeds. Site design to eliminate traffic over
the collection pipes is believed to be a more effective approach.
To provide for early detection of construction-related
damages and timely implementation of corrective measures, the
state of Wisconsin requires that, as a condition for obtaining an
operating permit, the site owner/operator demonstrates ability to
clean all leachate collection lines (T.D. No. 9). The test
demonstration of a water jet cleanout system at one site resulted
in the discovery of a broken pipe which was then replaced (9).
The state also recommends that the lines be flushed after the
first lift (T.D. No. 9).
4.5.3 OPERATING CONSIDERATIONS
Operating practices which improve the functioning of a
facility from the standpoint of leachate management and impact on
LCS primarily relate to source control (i.e. type of waste
allowed in a landfill), waste placement method, type of material
used as intermediate cover and cover placement.
Not accepting liquid wastes in landfills (or solidifying
such wastes or mixing them with absorbents prior to placement)
will eliminate waste as a leachate source. Containment and
subsequent removal of rainwater which enters the site during
operation also reduces the liquid volume which would have to be
subsequently pumped out as leachate. Any ponded rainwater is
considered contaminated and, at one facility (T.D. No. 13) it is
removed and sewered. Use of temporary domes and roofs to keep
the rainwater out when the site is open has also been considered
and experimented with. After site closure, cover maintenance is
essential to minimizing infiltration through the cover.
30
-------
It is generally believed that it would be more cost
effective to prevent the rainwater from entering the site during
operation than to provide for any subsequent leachate collection
and treatment. One commercial site reportedly employed a mobile
inflatable dome covering a cell area of approximately 300 ft by
600 ft for this purpose (15). Due to events not related to the
disposal operation (apparently a power failure), this inflatable
dome was seriously damaged by a storm during a time when it was
not in operation and is apparently no longer functional. A
similar cover dome concept has reportedly been used at another
commercial hazardous waste LF (15).
The use of structural cover systems to prevent overflowing
of Sis due to rain and snow has been evaluated for application to
clean-up of uncontrolled hazardous waste sites (16). As long as
the active LF cell/area is kept relatively small, some such
structures may conceivably also be applicable to LFs. Three
promising structural systems on the market today which could be
used for this purpose, and which have been analyzed in Ref. 14
for applicability to Sis are the following:
Pre-engineered steel framed building with roof cover made of
metal skin over longitudinal purlins and the walls made of
metal skin over girts.
Pre-engineered aluminum framed structures which would use
aluminum frame and a flame retarded fabric (see Figure 4).
Air supported structures consisting of tension cables
covered with a fabric liner which is held up by application
r\f an T irt-o T-n a 1 -m-oc cm-o I croo f-\ mir-a ^ ^
covered witn a raoric .Liner wnicn is
of an internal pressure (see Figure 5)
The costs for SI application of pre-engineered steel framed
buildings and air supported structures (including site
preparation and erection) have been estimated at $10.25/sq ft and
$5.47/sq ft, respectively (16). The cost of pre-engineered
aluminum framed structures is a function of the span. "Budget"
costs for this type of structure F.O.B. at the site have been
reported as follows (16):
-spans 30 to 60 ft: $ 9.90/sq ft
-spans 88.6 ft: $10.90/sq ft
-spans 120 ft: $16.90/sq ft
Since LCS clogging has been related to the characteristics
of the wastes and of the resulting leachate (T.D. Nos. 4 and 9),
source control can reduce potential for LCS clogging ( as well as
adverse impacts on the liner). Heavy metals, paper mill sludges
and other wastes containing fine particles should thus be placed
near top and definitely not in the first lift (T.D. No. 9). At
hazardous waste management facilities handling largely drummed
31
-------
U)
SPAN STANDARD 30' to 140'
VARIES
Figure 4. Typical cross section of a pre-engineered aluminum framed
cover structure for Sis (16)
-------
Ul
u>
5. Sketch of an air
an air supported structure (16)
-------
wastes, placing drums containing wastes which would not readily
mobilize (even if the drums fail) at the very bottom lift is an
excellent approach to minimizing some of the leachate and LCS
problems (T.D. No. 14). One facility uses lime waste and ferrous
sulfate in the intermediate cover, and surrounds specific waste
loads with such chemicals to effect immobilization and
neutralization in the event of leakage from drums and the
eventual corrosion of drums (T.D. No. 13).
The placement of low permeability wastes (e.g., shredded
refuse and paper mill and water treatment sludges) over large
contiguous areas or use of such wastes as well as clayey soil as
intermediate cover can interfere with the downward movement of
leachate and result in leachate perching and excessive mounding
(T.D. Nos. 9, 10, 12). Low permeability waste should be blended
with more permeable wastes as much as possible or placed in
smaller isolated areas which are not connected (T.D. No. 9).
Landfill operators have generally used as daily cover
whatever material is available to them at the site or nearby.
This practice has resulted in leachate perching at a number of
sites where clayey soils have been used as intermediate cover
(T.D. Nos. 9, 10, 12). Since berms are usually wider than
designed, the excess clay is removed before waste placement and
often used as cover material. Because of these practices,
operating permits for certain sites now specify the permeability
of the cover material. For example, the permit for one site in
New York stipulates the use of cover material with a permeability
greater than 10~ cm/sec in at least every fourth lift and
greater than 10~ cm/sec for all other lifts"(T.D. No. 12). The
state of Wisconsin Department of Natural Resources (T.D. No. 9)
now advises against the use of clay or other low permeability
materials as daily cover and recommends the use of sand as cover
material at least for the first lift.
Stripping the previous day's cover is used at one co-
disposal site to prevent leachate perching (T.D. No. 10). This
practice, however, was considered inapplicable to hazardous waste
sites handling drummed wastes given the likelihood for disturbing
the carefully placed drums (T.D. No. 12).
As discussed previously, clogging of leachate collection
pipes does not appear to be a problem of major concern to site
owner/operators. Even though some sediments may deposit in LCS
laterals and mains, the lines can be cleaned using the well-
established sewer system cleaning technology. Periodic (e.g.,
once-a-year TV inspection of at least selected lines for clogging
is considered by some designers (T.D. No. 8) as an element of a
good maintenance program. Some designers have recommended
cleaning of laterals and mains after the first six months of
operation and inspection and cleaning of these lines every 2 to 3
34
-------
years thereafter (T.D. No. 7). Video monitoring of pipes is a
recommended inspection procedure for 6-in. diameter 05 larger
pipes (the required equipment will not fit smaller pipes ) (T.D.
No. 7). The pipes can be cleaned with rotorooters or
hydroblasting (also referred to as jetting or jet rodding).
Hydroblasting with jets is very effective and also cleans pipe
perforations" (10, 12 and T.D. No. 7). (See Table 4 for
description of sewer cleaning methods.)
In Wisconsin, the requirement for inspection and cleaning of
LCS laterals and mains is in addition to the requirement for
monitoring leachate head levels in the landfill to detect
clogging problems. Annual cleaning is believed to result in
flushing of any accumulations before they become too difficult to
dislodge and hence a good preventive measure. Since there is no
substantial difference between cleaning techniques for sewer
lines and for leachate conveyance pipes, commercial sewer
cleaning companies are generally called upon for service (10, 12
and T.D. No. 9). The cleaning cost is considered to be
relatively small and, depending on the lines involved, the
cleaning would require no more than two days' effort (T.D. No.
9). Sewer maintenance contractors are located in all major
cities and typically charge $1000/day for video inspection and
cleaning (which is equivalent to approximately 900 ft of pipe)
(T.D. No. 7).
According to a commercial sewer cleaning company which has
carried out LCS cleaning in Wisconsin and several other states in
the region (12), many of the LCS flow obstruction problems can be
avoided if the cleanouts, manholes and other opennings are kept
capped to prevent wind blown debris from entering the system.
A summary of the operation-related leachate management
problems and of applicable "non-design" preventive and
corrective measures is presented in Table 6.
4.6 RESEARCH AND DEVELOPMENT NEEDS
For discussion purposes, the R & D needs identified by site
owners and operators, designers and regulatory agencies are
organized here under the categories of (a) developing improved
basis for LCS design through studies reflective of actual
conditions and/or through case studies of actual facilities, (b)
investigation of novel design concepts and approaches, and (c)
*
Recent developments in closed circuit TV inspection includes
one unit that can be used in 4-in. pipes (11). However, the
cables for the smaller cameras are usually shorter (e.g., 150-ft
for the camera for a 4-in. line compared to 1,000-ft for the
camera for a 6-in. line (12).
35
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TABLE 6.
I'roblcmu
tXCO381VC
ludchalc
l.cachdtc
perching
OJ
LCS clogging
Collapse of
drainage pipe
SUMMARY OF OPERATION-RELATED LEACIIATE MANAGEMENT PROBLEMS
APPLICABLE NON-DESIGN PREVENTIVE/CORRECTIVE MEASUR ES
Causes Applicable Pravont1vo/Coirentivn Muaauraa
-Accepting liquid wastes
- Inf i Ural ion
-Improper handling of low
permeability wastes
-Use of low permeability
material as intermediate
cover
-Clogging of drainage
material by Cine particles
and precipitates
-Clogging of pipes due to
siltation. chemical and
biological deposition and
wind-blown debris entering
lines when the openings
are not kept capped
-Excessive traffic load
-Not allowing liquidu in landfill
-Placing sludyna near top and definitely not in tho
first lift
-solidifying liquid wauti-a or mining them with
absorbents prior to p liicumoiil
-surrounding specific load with absorbents
-Runoff diversion and containment and removal of
rainwater entering active olio
-Use of temporary domos and roofs during operation
-Use as temporary covoi in lieu of soil for daily
cover
-Proper cover maintenance after closure
-Removal of ponded rainwater during active life
-Source control (protrcating or not accepting
troublesome wastes)
-Placing troublesome waste (shredded refuse, paper
mill sludges, etc.) near top and not in tho first
lift and in isolated areas rather than in continuous
sections
-Not using clayey soils or low permeability wastes as
intermediate cover
-Using sand or other permeable material as Inter-
mediate cover (at least in the first lift)
-Breaking the previous day's cover in tho active
filling area
-Source control (pretreating or not accepting
troublesome waste or placing wastes such as motal
sludge) near top and not in first lift
-Replacement of drainage material
-Preventive maintenance (e.g., annual cleaning) using
conventional sewer cleaning techniques
-Replacement of pipes
-Use of gravel trenches to intercept leachato
-Drilling caissons in landfills and pumping out the
perched Icachate
-Keeping cJeanouts and manholes capped at all times
-Use of half or whole corrogoted pipes to cover
trenches where there is trafficking
-Reroute traffic (or design site) so as to avoid
traffic over collection pipes
-Replacement of broken pipes (when discovered early)
-------
miscellaneous studies. The technical discussions presented in
Appendix A and referenced in the following discussion should be
consulted for elaboration.
4.6.1 Developing Improved Basis for Design
As noted previously. at the present time there is little
hard data on the long-term performance of LCS in full-scale
facilities. Because some systems have now been in service for a
number of years, it should be possible to obtain somewhat longer-
term performance data for these systems so that the performance
can be correlated with the designs actually employed. Case
studies of LCS performance in full-scale facilities and long-term
parametric studies at full-scale sites reflecting the actual
operating practices and conditions were thus recommended by a
number of designers (T.D. Nos. 4, 8, 10, 11, 14). In some
instances, the evaluation of LCS performance may necessitate
actually digging out sections of the system for direct
observation. Pilot scale studies using real wastes can provide
some performance data, although the results would not be as
reliable. Case studies and full-scale or pilot-scale long-term
parametric studies can provide information on or evaluate the
following:
Site/system performance versus design, construction and
operating factors (T.D. No. 10).-
Permeability of various wastes relative to that of the
drainage envelope/blanket (T.D. Nos. 10, 12, 13 and 14);
considerable cost savings and improvements in design can
result if LCS can be tailor-designed to handle specific
waste type/placement practices (T.D. No. 14).
Number and location of leachate monitoring head wells neces-
sary to provide reliable information on LCS performance.
Longevity of plastic pipes (T.D. No. 8) and geotextiles
(T.D. Nos. 2, 9) in the harsh landfill/leachate environment
and effectiveness/suitability of geotextiles as filter media
in LCS applications (T.D. Nos. 12, 14 and 15).
Applicability of standard civil engineering design curves
and equations for pipe sizing to the unique conditions of
LCS (i.e., small pipes in relatively narrow trenches and
often subjected to high waste loads) (T.D. No. 10).
Applicability of sewer design, construction and maintenance
methods to LCS for hazardous landfills (T.D. No. 3).
Geographic and local conditions which necessitate (a)
differences in site design and flexibility in regulatory
37
-------
requirements (T.D. No. 4), and (b) greater uniformity among
regulatory requirements and enforcement policies of states
with similar environmental setting (T.D. No. 10).
' . o, 2 Investigation of_ Novel Design Concepts and Approaches
Evaluation of design innovations is considered by many
designers as a very important area of R & D with potential for
i-iouificant economic and environmental benefits. Some designers
IT.P. No. 10) even suggest promotion and demonstration of new
vVsign approaches through government financial support for
projects featuring design innovations.
Three cited examples of possible design innovations
specifically relating to LCS are (a) provisions which would
enable draining of the entire LCS trench/blanket and not merely
the embedded pipe, (b) improving leachate drainage by extending
the drainage blanket to also cover the side slopes (T.D. No. 12),
v'uul (c) use of a single system to simultaneously collect both
-leachate and the gas from landfills (T.D. No. 4-).
One general design innovation which can perhaps
rc\olutionize the entire approach to the disposal of municipal
imd/or industrial waste would view landfills not as waste
containment cells and repositories of indefinite and uncertain
Life requiring long-term care, but as reaction vessels and energy
recovery centers with a definite service life (T.D. No. 10).
Act.i\e degradation of waste and gas generation would be
»ntentlonally promoted and the operation would be aimed at
achieving these objectives. The ability to predict service life
wou.Ul enable design for an estimated life and this would
eliminate current uncertainties as to the long-term performance
of the system components (e.g., LCS and liner) and the transfer
of potential problems to future generations.
1 *>. ? Miscellaneous Studies
Included in the category presented below are not only some
mii-cel laneous LCS-related R 6. D needs but also some R & D areas
\\hioh relate to the general topics of leachate management and
characteristics and landfill design, including its components.
I'valuation of various approaches to retrofitting older sites
\>\th LCS (T.D. No. 11) .
IVtter characterization of the type of wastes which are now
s-cnt to disposal sites and the expected future trends and
their impacts on leachate characteristics (T.D. No. 15).
development of detailed specifications and guidelines on
\\nste disposal site design and operation (T.D. No. 13); such
38
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specifications should not provide strict standards, but
rather guidelines for engineers to follow in examining
options for developing solutions to site- and situation-
specific conditions.
Dissemination of the experience from full-scale facilities
(T.D. No. 11).
Development of background information and assessment of
leachate problems associated with existing municipal land-
fills (T.D. Nos. 10 and 11). In general the environmental
problems for these sites (many of which have little or no
engineering design and have received large amounts of
hazardous wastes presumably from numerous small generators)
may be far greater than those from properly designed,
dedicated hazardous waste sites.
Developing means for predicting leachate characteristics at
the time of design (T.D. No. 11).
Development of cost-effective methods for leachate disposal
(T.D. No. 11).
Evaluation of the attenuation capacity of clay liners for
leachates generated in municipal landfills (T.D. No. 9).
-------
SECTION 5
EMISSIONS AND GAS CONTROL PROBLEMS-AT LANDFILLS
AND SURFACE IMPOUNDMENTS
5.1 PROBLEM OVERVIEW
Based on the limited emissions monitoring data which are
currently available and the consideration of the fundamental
nature and mechanism of gas production in landfills, little or no
gaseous emissions would be expected from a properly operated
strictly HWLF after its closure. Emissions from such landfills
should be primarily related to the operating activities during
waste placement and/or to the loss of volatile constituents from
the leachate when and if the leachate comes in contact with open
air (e.g., in the leachate collection sumps, standpipes and
cleanouts when such appurtenances are left uncapped). As long as
readily biodegradable wastes are not admitted, decomposition
gases such as methane, which are produced in municipal and co-
disposal sites and which require migration and emission control,
should not- be encountered in strictly HWLFs. Even if some
biodegradable wastes are accepted, the toxicity of some hazardous
wastes and the harsh disposal environment of certain sites can
prohibit substantial biological activity in 'the mixed waste.
Strictly hazardous waste sites represent premium disposal space
and it would be essentially a mistake to send degradable wastes
to or to accept such wastes in strictly HWLFs.
Gas can be produced in a HWLF as a result of chemical
reactions and volatilization. This mechanism, however, would not
be an important one in a properly operated site where strict
controls are exercised so that solvents and bulk volatile wastes
are not admitted and reactive wastes are passified before
disposal or isolated in the disposal environment.
At co-disposal sites where hazardous wastes are admitted
along with municipal refuse and/or degradable industrial wastes,
the decomposition gases can pick up volatile toxic constituents
from the hazardous waste. Since there are perhaps no municipal
landfills in the country which have not received volatile toxic
wastes (at least from the many small volume hazardous waste
generators) or wastes which yield volatile toxic substances upon
decomposition, all municipal landfills may be considered co-
disposal sites presenting a potential for the emission of
hazardous constituents to the atmosphere. This assertion is
40
-------
consistent with the results of surveys of the incoming wastes at
municipal landfills and by the limited landfill gas data which
indicate the presence of a variety of chlorinated and/or aromatic
hydrocarbons in the municipal landfill decomposition gas.
The above concept of landfill emissions (i.e., considering
municipal and co-disposal sites capable of emitting hazardous
substances) is the basis for the discussion in this report.
The recently published Surface Impoundment Assessment
National Report (17) indicated more than 180,000 active Sis in
the U.S. These Sis are used for storage, treatment and disposal
of a range of industrial, municipal and agricultural wastes.
Although the potential threat of the Sis containing hazardous
wastes to ground waters and surface waters has been recognized
and received increasing attention in recent years, up to now
little effort has been directed toward developing quantitative
assessment of volatile toxic emissions from Sis and defining
control technology requirements. Much of the concern over SI
emissions has involved odor complaints in connection with
specific Sis and source control and proper siting (in case of new
Sis) have been the common mitigation measures used. As will be
discussed in Section 5.4.2, much of the current and recent effort
related to SI emissions involve development of sampling and
analytical protocols and verification of emissions models.
5.2 REGULATORY BACKGROUND
5.2.1 U.S. EPA Regulations
Except for a general requirement in Part 264.301(f) of RCRA
that the owners and operators cover or otherwise manage landfills
to control wind dispersal of particulate matter, air emissions
from hazardous waste landfills and surface impoundments are not
specifically addressed by RCRA. The proposed RCRA
reauthorization bills currently under consideration in Congress,
however, will require EPA to promulgate regulations for
monitoring and control of air emissions from hazardous waste
treatment, storage and disposal facilities (TSDFs) as needed.
In preparing for its anticipated regulatory mandate, EPA has
taken steps to consolidate its various relevant programs and as
of February, 1984, the Office of Air Quality Planning and
Standards (OAQPS) has been given the responsibility to develop
appropriate programs for monitoring and controlling air emissions
from TSDFs. Based on past experience it may take approximately
24 to 30 months, from the time that RCRA is reauthorized, to
promulgate appropriate regulations (18). Because of the
heretofore lack of hard data on TSDF emissions and control
technology requirements, the focus of the current OAQPS programs
is to determine the types and quantities of compounds being
4 1
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emitted. Considerable emphasis is being placed on developing
sampling protocols, sampling and emissions measurements at
selective sites, and verifying predictive models (18).
5.2.2 State Regulations and Concerns
Regulatory agencies of several states were contacted in the
present program to develop an assessment of the state concerns
and regulatory programs relating to emissions from LFs and Sis.
In general, a certain degree of uncertainty was expressed as to
the extent of emissions problems associated with LFs and Sis and
of the control technology requirements. Because of these
uncertainties, some states have implemented or plan to implement
certain monitoring programs to better define the problem.
Emissions control programs and requirements for LFs are generally
specified on a case-by-case basis through the permit process. In
general, gas migration and emissions controls is not considered
to be a problem at strictly hazardous waste sites (except for the
emissions associated with the open disposal activities),
primarily because of expected absence of biological activity at
these sites. Contingency provisions for gas collection and
treatment, however, have been required at certain sites in the
event that gas monitoring indicates the presence of high levels
of toxic emissions associated with the vent gas.
Because of the heretofore absence of regulatory mandate from
RCRA, some states have relied on the provisions of the Clean Air
Act to regulate emissions from landfills through the permitting
process and to evaluate air emissions from uncontrolled hazardous
waste sites for cleanup under the Superfund Program.
A brief review of state programs and concerns is presented
below. based on discussions with the representatives of the
states of California, Michigan, Wisconsin, New Jersey and New
York.
State of California (19)
Since the discovery that vinyl chloride concentration levels
in residential areas surrounding two LFs in Southern California
exceeded air quality standards, the state has been very concerned
with potential emission of toxic substances from LFs and Sis.
The state Air Resources Board (ARE) is currently working with the
State Department of Health Services (DHS) to develop air
monitoring programs that will be incorporated into RCRA permits
for HWLFs and Sis. Some form of periodic sampling around sites
would most likely be required to determine impact of emissions on
local air quality. Because air monitoring is very expensive, the
state is currently seeking lower cost, less labor-intensive
methods for measuring site emissions. Currently, gas migration
control systems are specified on a case-by-case basis; individual
42
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Air Quality Management Districts (AQMDs) are proposing their own
requirements for methane, odor, and toxics control at landfills.
State of Michigan (14)
Because the current RCRA regulations largely ignore air
emissions from LFs and Sis, the state has relied on the Clean Air
Act for authority in regulating these facilities. Under
Michigan's Hazardous Waste Management Act, new and existing
facilities must perform an environmental assessment before a
permit can be issued. The assessment should include an estimate
of the potential air emissions for the site. In the review
process, the estimates of criteria pollutant emissions are
compared with the National Ambient Air Quality Standards and
noncriteria pollutant emissions (e.g., metals) are compared with
standards developed by state.
Air monitoring requirements (e.g., sampling for acid fumes,
metals, VOCs etc.) are set on a case-by case basis. However,
all landfill owners must provide upwind and downwind sampling of
total suspended particulates. No liquids of any kind are allowed
to be disposed of in LFs as bulk liquids are considered to be a
major source of VOC emissions and a potential for ground water
contamination. The state also does not allow the impoundment of
any volatile wastes in ponds and this is considered the best
method of air emissions control for Sis.
State of Wisconsin (T.D. No. 9)
Emissions from LFs and Sis have not been an issue in
Wisconsin, as most sites are located in isolated areas. At one
or two bigger sites, the state has required emissions monitoring,
mainly for particulates. Passive gas management (venting) is
required at all LFs, with the additional requirement that the
system can be readily converted to active system, if necessary.
State of New Jersey *
The potential emissions from LFs and Sis are of recent
concern in New Jersey, and the state is now in a learning process
as far as regulatory requirements are concerned. The current
state implementation plan calls for an emission rate of less than
7 Ib/hr volatile organic substances for both active and closed
LFs (this will soon be reduced to 3.5 Ib/hr). Eleven organics,
eight of which are chlorinated compounds, have been designated as
* This section concerning the State of New Jersey has been re-
viewed by and incorporates comments received from Mr. William
O'Sullivan, Chief, Engineering & Technology, Div. of Environmen-
tal Quality, New Jersey Department of Environmental Protection.
43
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toxic and their emissions cannot exceed 0.1 Ib/hr unless state-
of-the-art air pollution controls are used. (The list of these
toxic compounds, known as "Subchapter 17" compounds, will also be
expanded to include non-chlorinated organic substances such as
arsenic as well as other chlorinated compounds.)
There are also few (if any) municipal landfills in New
Jersey (or perhaps anywhere else) which have not received
hazardous wastes in the past. For the purpose of developing
emissions monitoring programs, at the present time the state
plans to rely on emissions monitoring results to establish
control requirements on a case-by-case basis. (Based on landfill
gas composition data which have been reported in the literature,
toxic volatile organic substances can account for up to 1% of the
raw gas collected from certain municipal sites).
The gas/emissions control activities in New Jersey are
closely tied into and coordinated with the water pollution
control and Superfund programs. It is believed that the removal
of volatiles from a landfill through the use of gas
collect ion/vent ing/control system should also reduce the level of
such chemicals in the leachate, in addition to the prime benefit
of providing for odor control by reducing air emissions.
About one year ago the state required vent systems for
landfills (or landfill cells) which are closed. If the emissions
monitoring indicates release of significant quantities of
volatile organics, control of vents is required. It is estimated
that about two years of emissions sampling may be required to
develop the data base needed for problem definition. Landfill
vent gases have been successfully burned in industrial process
equipment and diesel engines. Two landfills are now installing
gas collection and venting/flare systems.
The following is a preliminary draft of criteria which may
be used by the state to judge the acceptability of an air
pollution control permit application for venting landfills. The
criteria apply to both hazardous waste and sanitary LFs, with the
exception that the cost-benefit criteria will be $10 (1982
dollars) per pound of air contaminant prevented from being
emitted into the atmosphere from a hazardous waste landfill
emitting suspect volatile organic carcinogens:
-No odors off property line; and
-Less than 3.5 Ib/hr volatile organic substance emissions or
air pollution control at least 85% efficient; and
-Less than 0.1 Ib/hr of each toxic volatile organic
substance (TVOS) emitted or air pollution control designed
for 99% efficiency with no less than 95% actual efficiency.;
and
-Cancer risk less than 1 in a million, calculated with the
44
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EPA Cancer Assessment Group risk factors and maximum annual
ground level concentration off the property line, for a 70-
year period; and
-Any additional reductions in air contaminant emission which
would be cost effective, generally ranging from $1 to $10
(1982 dollars) per pound of air contaminant prevented from
being emitted, depending on the substance.
The proposed New Jersey hazardous waste land disposal reg-
ulations will require a gas monitoring system, a gas monitoring
program and gas venting if gas is detected outside the LF
boundary, the state must be immediately notified and an abatement
program must be submitted within 30 days of detection
detected outside by sense of smell in any area of human use or
occupancy.
Based on the state's experience with sanitary landfills, and
depending on gas characteristics, the state may approve one of
the following combustion technologies (all of which are proven
control methods) for eliminating emissions of toxic vapors from
landfills:
-"Enclosed" flare system such as that developed by Surlight
Co.
-Venting to an industrial process furnace
-Venting to a diesel engine (catalytic converter requirement
is being considered)
-Gas cleaning (upgrading) to pipeline quality (This
technology may not be applicable to strictly HWLFs)
The state experience with carbon adsorption system for gas
control has been very poor due to maintenance problems and the
difficulty in estimating when the carbon bed needs changing or
reactivation. Accordingly, this particular control is not
recommended by the state. Table 7 presents the proposed New
Jersey contaminant listing requirements for direct atmospheric
venting or combustion control of LF emissions. These
requirements are tentative and will change per results from
ongoing and planned landfill monitoring programs.
At the present time, the state does not require any types of
controls for HW Sis.
State of New York (20, T.D. No. 12)
Based on the limited avaialbale data, the state feels that
it is very difficult to ascertain whether toxic vapor emissions
from RCRA-designed LFs and Sis are indeed a real problem (or
merely a public concern). The state plans to conduct emissions
source testing at HW LFs and Sis to develop quantitative
estimates of emission rates. State personnel have monitored for
45
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TABLE 7. STATE OF NEW JERSEY CONTAMINANT LISTING
REQUIREMENTS FOR DIRECT ATMOSPHERIC
VENTING AND COMBUSTION OF LANDFILL GAS
A. Direct Venting to Atmosphere (no pollution control
device)
-Total organics as equivalent methane
-Methane
-Any non-methane organics of a concentration of 1
ppmv or greater
-All Subchapter 17 compounds and vinyl chloride
monomer
-Hydrogen sulfide and any other odorous compounds
-Carbon monoxide
-Carbon dioxide
-Moisture
-Heat value in Btu/standard cubic foot
-Total volume flow rate of gases
-Temperature of gases
B. In-situ or Off-site Combustion Control
Prior to Combustion:
-Total organics as equivalent methane
-All Subchapter 17 compounds and vinyl chloride
monomer
-Total chlorine
-Total sulfur
-Carbon monoxide
-Carbon dioxide
-Oxygen
-Moisture
-Heat value in Btu/standard cubic foot
-Total volume flow rate of gases
-Temperature of gases
-Any non-methane organic with a concentration of
100 ppm or greater.
After Combustion:
-Particulates
-Sulfur Oxides
-Hydrochloric Acid
-Carbon monoxide
-Nitrogen oxides
-Total organics as equivalent methane
-Any non-methane organics that are greater than
100 ppmv in the inlet gas
46
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two years (through ambient air sampling) emissions from the two
large commercial HW disposal sites in the state (i.e., the CECOS
and the SCA facilities). One 24-hour sample is taken per month
and analyzed using GC-MS techniques. During this period, only
once have volatile organics been detected; concentrations of
methyl ethyl ketone and carbon tetrachloride were in the low ppm
to ppb range. However, particulates have been measured in much
larger concentrations. Because of the multiplicity of emission
sources at or in the vicinity of a complex facility such as SCA,
it would oe very difficult to assess the contribution from a
specific source category (e.g., a specific LF or SI).
The LFs at CECOS and SCA facilities have gas vents which are
capped and no pressure build-up has been noted. Since the
leachate collection sumps are open to the atmosphere, there is a
potential for emission of some volatile organic constituents
present in the leachate, which may pass into the air space above
the leachate surface. Measurement of the actual emissions from
these sources has been heretofore hampered by a lack of reliable
sampling protocols.
The state monitors the emissions from disposal operations at
the two commercial hazardous waste sites using state-employed
"on-site monitors". These monitors are graduate chemists that
observe and approve of all disposal operations at the sites and
report weekly to the state Air and Hazardous Waste Departments.
The Air Programs Department relies heavily on these monitors in
regulating these facilities. The state has requested that the
monitors be given access to the operators' "selective adsorption
tubes" (used per OSHA requirements in the work place) to assure
that TLVs are not violated during disposal activities.
5.3 THE AVAILABLE DATA BASE ON LANDFILL EMISSIONS
Gases are generated by the decomposition or volatilization
of many types of wastes disposed in landfills. When the gas
generation rate is sufficiently high to produce an internal
pressure within a landfill, convective gas transport can occur.
When only small amounts of gases are internally generated, migra-
tion occurs primarily by diffusion. In either case gas movement
is primarily in the direction of least resistance to flow, which
can be laterally into surrounding strata or vertically into and
through the cover material. While it is common to draw a
distinction between municipal and hazardous waste landfills based
on the types of wastes disposed, it should be remembered that
some amounts of potentially volatile hazardous wastes are sent to
municipal sites. Thus there is always a potential for a toxic
emissions at any landfill. The difference between municipal and
hazardous landfills is the potential quantity of gas generated
rather than and the presence or absence of toxic substances in
the gas. Considerable experience has accumulated in dealing with
47
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gases from municipal and co-disposal landfills and the discussion
which follows focuses first on decomposition gas generation and
its control at municipal sites.
5.3.1 GAS GENERATION AND MIGRATION AT MUNICIPAL LANDFILLS
Gas evolution within a landfill is a process of gradual
volatilization and degradation of waste components via chemical
reactions or microbiological processes. Landfill gases are
produced slowly for months or years until waste constituents
approach physical and chemical equilibrium and/or biodegradable
materials have been exhausted (21-23). Municipal landfill gases
are composed primarily of methane and carbon dioxide generated by
biodegradation of carbonaceous wastes, but also contain hydrogen,
ammonia, hydrogen sulfide, and aliphatic, aromatic and
chlorinated organics. Landfill gas is usually odorous and can
present explosion hazards if it concentrates in confined spaces.
The rate and quantity of gases generated are site-specific
and depend on the moisture content of the waste medium, the
amount and type of organics present, depth of the landfill, local
climate, and acidity or alkalinity of the waste media (21). The
pressure from internal gas generation is exerted in all
directions and the gas will migrate through the most porous or
fractured medium around the confined waste. Ultimately, most of
the gas will diffuse to the atmosphere through the cover (or
engineered vent systems) since lateral movement of landfill gas
is restricted by static pressure within the fill and by the
permeability of the surrounding liner or strata. Covers on
landfills are perhaps the most difficult to seal, due to the
effects of settling, freezing and thawing and burrowing animals
(5). However , lateral migration can occur when very tight
covers are established and/or the surrounding formation is highly
porous and confining liners have not been properly engineered.
Emissions at the surface of or around a LF has historically
been perceived primarily as a nuisance odor problem or as an
explosion hazard (21, 23). In recent years it has also been
recognized that LF gases contain reactive organics which can
contribute to photochemical oxidant levels in ambient air (21,
23, 24). The presence of chlorinated and aromatic hydrocarbons
in LF gases has been confirmed at a number of sites (25, 26).
In response to methane hazards and odor complaints, a number
of operating or closed municipal landfills have been retrofitted
with gas migration control systems, and most new sites have been
required to provide such systems (e.g., see T.D. No. 9). Control
systems may be either passive or active, but in either case they
provide a porous conduit for gases to migrate to the surface for
venting, incineration or energy recovery. It is now widely
recognized that gas will form to some extent at landfills which
48
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have received carbonaceous wastes and that such gas will eventu-
ally migrate to the atmosphere. Designs and operating practices
have evolved to provide for migration and disposal of gas.
Fugitive gaseous and particulate emissions also occur at
all municipal landfills as a result of daily operations. Exposure
of minimum waste area and application of daily cover serve to
minimize emissions of odorous substances. Fugitive particulate
emissions resulting from equipment use at the site. are perhaps
more difficult to control, although often the particulate is
primarily soil dust rather than waste components (23).
5.3.2 GAS PRODUCTION AND MIGRATION AT HAZARDOUS WASTE LANDFILLS
The nature of gas'generation and movement at landfills which
receive primarily or exclusively industrial hazardous wastes is
different from that associated with municipal landfills.
Although the types and characteristics of hazardous wastes can
vary enormously, in most cases the wastes are not readily
biodegradable and generation of methane and carbon dioxide is
minimal. Although the trend is toward not accepting wastes which
contain large amounts of potentially volatile substances, some
wastes will contain small amounts of substances which can
volatilize within the void space of the landfill medium.
The rate of waste volatilization in a landfill is highly
dependent upon the physical and chemical properties of the waste
and of the surrounding environment. Three related processes are
involved in the volatilization of organic wastes: 1)
volatilization of organic chemicals or mixtures of chemicals in
liquid form, 2) volatilization of organics from water, and 3)
volatilization of organic liquids absorbed by or adsorbed on
waste solids or soils (27). Volatilization is driven by the
equilibrium vapor pressure of individual substances in contact
with the liquid or solid media and by the diffusion rate away
from the waste source, which is in turn largely determined by the
permeability of the waste medium and surrounding barriers.
Escape of volatile substances from the HWLF environment can
be vertically through the cover material, laterally through
porous formations or breaks in engineered barriers, and through
engineered gas vent systems and leachate control plumbing. In
the latter case, offgassing of collected leachate itself may be
an important concern (28, T.D. No. 12). Unlike the situation
with municipal landfills, however, it is in principle possible to
engineer a nearly gas-tight hazardous fill since there is little
internally generated gas pressure to promote migration.
Most natural soil and organic materials have the capacity
for sorption of volatile organic substances (27, 29, 30). Thus
the1 intermediate and final cover used at a HWLF can serve as a
-------
buffer to reduce volatilization of waste components. There is
also evidence that many organics which are otherwise not readily
biodegradable in concentrated form can, under proper conditions,
be degraded by microorganisms when absorbed/adsorbed on sur-
faces of soil and/or organic particles. Of course such materials
have a finite capacity and can be overloaded if large amounts of
volatiles are generated within the fill.
5.3.3 Results from Actual Field Monitoring Programs
A nimber of landfill source testing and ambient monitoring
programs have been carried out in, recent years. For discussion
purposes, these programs can be grouped into two categories 1 The
first category of studies, which is reviewed in Table 8, has been
of the general survey nature and has involved multiple site
testing. The second category of studies, described in Table 9,
has involved testing at specific sites and is largely in response
to local complaints about odors and public health concerns.
As noted in Tables 8 and 9, the very - limited number of
recent attempts at systematic evaluation of emissions from HWLFs
have been largely of a problem definition nature with a major
objective of developing suitable sampling and analytical proto-
cols. These preliminary and exploratory studies have yielded
variable results (e.g., large data scatter) which have been
attributed to emissions contributions from other sources and
activities at the disposal sites tested and the yet unproven
reliability and accuracy of the sampling and analysis protocols
used (e.g., as indicated by the disagreements between results
using different measurement techniques). Moreover, the repre-
sentativeness of the sites has not been established. Given these
limitations, the data from the limited source testing and ambient
monitoring efforts indicate that even though closed hazardous
waste landfills may emit some volatile organics, the measured or
calculated ambient concentration levels of specific compounds
(which can well include contributions from other activities at or
outside the facility) are very low (usually near or below the
detection limits of the methods employed) and nearly always less
than the permissible OSHA exposure levels.
Considerable monitoring efforts have been conducted at and
near the BKK Landfill in West Covina, California (see Table 9).
The landfill is a co-disposal site and accepts a significant
volume of hazardous wastes. Although over 40 organic compounds
have been identified, including benzene, chloroform and vinyl
chloride, the measured ambient concentration of these compounds
has not exceeded the OSHA TLVs by more than a few percent.
Hydrogen sulfide was identified as the primary source of odor.
The working face of the landfill and the landfill gas flare
system were identified as major emission sources.
50
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TABLE 8. KEY SURVEY PROGRAMS RELATING TO TOXIC EMISSIONS FROM LANDFILLS
Program
Sponsor
Objectives
Description, findings, and Significance
Air Pollution Sampling
and Monitoring At Hazar-
dous Waste Facilities.
OD
CPA/KCRL-
Cl
Collect data on ambient
air quality near hazar-
dous waste treatment
and disposal facilities
and conduct preliminary
health risk assessment
Evaluation of Air Emis-
sions from HW treatment
storage I disposal
facilities in support
of JtCRA air emission
regulatory Impact anal-
ysisSite* 2 and S (28)
EPA/IERL-
Cl
Develop and verify
techniques for deter-
mining air emissions
from HW facilities.
IS liw sltoa. 8 of which involved landfill operations,
were monitored for selected aliphatic and aromatic
hydrocarbons In
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TABLE 0. (Continued)
Program
Sponsor
Objectives
Description, Findings, and Significance
Landfill methane Gas
recovery Part IIi Research
Gas characterization Institute
(25)
Develop standardized LF
gas sampling/analytical
procedures and a data
base for volatile or-
ganic compounds (VOCo)
In raw and processed
LF gases.
NJ
Tho otudy results are inconclusive. Apparently.
emissions of toxic organlcs wore measurable from active
IIWLFs but the best monitoring approach for quantifying
emissions was not established. Also, the basis for
selection of the monitored IIWLFs is not knowni conse-
quently the representativeness of the study results
cannot bo assessed.
9 MLFs in different parts of tho U.S. were monitored
for VOCs In well gases and surface gos samples (from
confined apace Indicators. CSIa). Tho altos wore chosen
to cover tho range of LF gas processing which currently
exists In tho U.S.
VOCs wore found In raw and processed gas froit all
9 LFs. although total VOC levels and especially chlor-
inated organics. decreased with increasing levels of
gas upgrading.
Samples from CSIs showed large VOC variability both
within a LF and among LFa. No correlation was found
between C5I VOC levels and LF location or design fea-
tures. It is not known whether any of tho 9 MLFs was
indeed a codlsposal facility. Tho results do indicate
that chlorinated and aromatic hydrocarbons are likely
to be present In decomposition gases from most LFs.
regardless of type of wastes received.
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TABLE 9. INDEPENDENT MONITORING PROGRAMS AT LFS RELATING TO TOXIC EMISSIONS
Site Name/Location
Sponsor
ObjectivoB
Description, Findings, and Significance
DKK IIWLF.
West Covlna. CA
(26)
BKK
(32. 33)
u>
Palos Verdas IIWLr.
Rolling Hills Estate*.
CA
So. Coast
Air
Quality
Management
District
(SCAOMD).
California
Air
Resources
Board
(CARD)
CARB
Identify sources and
nature ot odorous sub-
stances which havo led
to local complaints and
(command appropriate
corrective measure*.
Determine effectivenesa
of corrective actions
taken by BKK, identify
ambient levels of toxic
organic*, provide data
base for public health
risk.
Survey of ambient air
quality at LFa in CA.
Field test recently
adopted monitoring
procedures.
In 1900. the IIWl.F owner contracted with tho Univ. of
So. Callfornln to conduct a monitoring program and a
ravjew of manifest data for completeness and accuracy.
Ambient air and surface gas aam|ilos (confined space
lndicators--CSIs) wore taken on and around tho LF site.
Over 40 organic compounds were quantified including
benzene, chloroform, and vinyl chloride. No compounds
were found at levels of more than a few percent of tlia
OSIIA TLVs, although vinyl chloride often exceeded the
California ambient standard of 10 ppbv. Hydrogen sul-
fldo was the primary odor-causing aubstnncoi benzene
was tho most commonly found organic in tho samples.
Tho working face and tho LF gas flare (which wore sub-
sequently modified) were implicated as tho major
emission sources. Additional gas extraction wells.
Improved operating practices and stricter enforcement
of manifest requirements woro recommended for reducing
odor problems.
During the summer of 1902, ambient monitoring indicated
that levels of halogcnatod and aromatic hydrocarbons
downwind of DKK wero well below OSIIA TLVs but periodic
exccedoncoa of tho California ambient vinyl chloride
standard woro still occurring. A nource test of the LF
gas incinerator found that halogcnated organics and
benzene were destroyed with greater than 99.71 effi-
ciency. No additional health risk was estimated for
persons living within ono mile of tho site.
The PV LF is a co-disposal facility which was closed in
1981. Onslto monitoring in 1983 Indicated emissions
of toxic organic* due to cracks in the LF surface,
vaults associated with collection wells, leaks at flare
stations, and tho vacuum dosorptlon exhaust of tho LF
gas recovery system. Although a nu-nbor of halogcnated
and aromatic hydrocarbons woro detected, the onsito
benzene level of 100 ppbv was estimated to pose the
greatest health risk (approximately I excess cancer in
200 persons exposed).
(Continued)
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TADLE 9. (Continued)
Site Namo/Location
Sponsor
Objective*
Description, findlrnju. and Significance
Puente Illlll HLP,
Loi Angeles County
(34, 35)
CARB
Same a* above.
cn
Operating Industrial (01) SCAOMD
HLF, Monterey Park,
CX (36. 11)
Enforcement monitoring
of ambient air quality
regulation*.
Mountain View MLF,
Mountain View, CA
(38.39)
Pacific
Gas 4
Electric
U.S. Oept.
Comprehensive 945
characterisation as part
of an experimental LP
gas recovery project.
Pucntc Hills is a largo, active MI.F which accepts
limited amounts of liquid nonhazardous waste. Although
hazardous waatos wore not knowingly accepted at tho
site, ambient air monltprlng in 190) Indicated tho
presence of halogonatcd and aromatic hydrocarbons. A
preliminary risk assessment Indicated approximately
1 excess cancer In SO persona exposed to tho 400 ppbv
of benzene which was meagtirod. Waste sampling pro-
grams, conducted In 1982 and 1983 to identify any
hazardous waste In tho Incoming waste, found only a
few tenths of a percent unacceptable matorial In
household/commercial wastes. from thoso programs. It
Is not clear whether tho small routine amount* of
hazardous waste are tho source of toxic emissions or
whether these emission* originate from previously dis-
posed wastes (before stringent enforcement) or
result from degradation of plastic* and other nonhaz-
ardous wastoa.
There ha* been a long-term odor problem at the OI MLP
site and several enforcement action* have been taken
to mitigate omission* of odorous/toxic substances.
Vinyl chloride has periodically exceeded tho California
ambient 10 ppbv standard and the source of this
compound Is not known since the LP does not accept
industrial hazardous wastoa. An impermeable plastic
cover was installed over a portion of the LF in 19B2
to enhance gas recovery. Soon thereafter, lateral gas
migration problems led to increased Incidence of odor
complaints which prompted a now round of monitoring
activities and court actions.
Tha Mountain View LF was ono of the first In tho U.S.
to havo a LF gas recovery system. The raw LF gas had
relatively high levels of aromatlcs (140 ppmv) and
halogcnatcd hydrocarbons (100 ppmv) despite tho fact
that the hazardous waste had not been knowingly accepted
at tho site. Ambient gas samples at tho site also
showed higher levels of chlorinated organlcs than did
offslto samples. Gas upgraded to pipeline standard had
much lower levels than raw gases, but offgasea fro-n tha
upgrading process contained some of tho toxic organlcs
In the raw gas.
(Continued)
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TABLE 9. (Continued)
Site Name/Location
Sponsor
Objectives
Description, Findings, and Significance
Misc. IIWLFsi
Stockton, CA (40)
New Vork
(20, T.D. No. 12)
Model City, N»
(41, T.D. No. 12)
CARD Monitoring for toxic
emissions as part of
NV DEC permit requirements of
survey programs.
SCA Estimate potential
Chemical emissions from leachate
Waste collection system (LCS)
Services at a HWLF in support of
operating permit.
Ambient and/or gas vent monitoring at several alto* has
indicated that llttla or no emissions are occurring at
closed IIWLFs. Host measurements for toxic organic* arc
at or noar analytical detection limits.
Tho subject I.F was required to demonstrate that toxic
emissions fro-n the LCS wore below 'do minimus" levels
in order to avoid installation of controls. Emissions
wore estimated using actual loachato composition data
and a vaporization model based on Henry's Law constants
for the identified organlcs. (See T.D. No. 12 for
estimated emission values.
tn
-------
The characteristics of the landfill gas have been of consi-
derable interest to companies/organizations which actively pursue
energy recovery from landfills (see, for example, Refs. 25 and 42
and T.D. No. 16). Much of this interest has been in connection
with development of suitable gas cleaning and upgrading proces-
ses, including mitigation of the corrosion problem in such sys-
tems. To date, the most extensive study of landfill gas charac-
teristics, the results of which have been made public, is that
carried out by ESCOR, Inc. Under the sponsorship of the Gas
Research Institute, GRI (see Table 8). This effort involved a
survey of the characteristics of gases extracted from nine LFs
which apparently were primarily municipal sites with perhaps one
or two co-disposal sites. Table 10 presents a list of the repre-
sentative organic compounds identified in landfill gas. Since,
unless a landfill is equipped with an effective gas extraction
system, the gas would be gradually and eventually emitted to the
atmosphere, compounds such as those shown in Table 10 should be
considered as components of the atmospheric VOC emissions from
LFs. The study indicated large variations in the VOC content of
the gas, both among landfills and within a landfill (see also
T.D. No. 16).
Table 11 presents the reported data on the concentrations of
several specific' chlorinated organics and aromatics and levels of
total oxygenated organics and alkanes in the gas samples taken
from interior gas extraction wells at several so-called municipal
landfills, two known co-disposal sites, and one site which
reportedly handled primarily nonhazardous industrial/commercial
wastes. The data in this table indicate that (a) chlorinated
and/or aromatic hydrocarbons are present in all landfills,
regardless of the conventional/regulatory classification of a
landfill as co-disposal, municipal, sanitary, nonhazardous, etc.
site; and (b) the levels of these substances, which include some
very hazardous compounds such as benzene, are not necessarily
higher in the co-disposal sites which have knowingly accepted
hazardous wastes. These conclusions are consistent with the
information in Table 8 which indicates no correlations between
odor problem (or vinyl chloride emissions) and the classification
of the landfill. The variations in the level of individual
substances or classes of substances among landfills shown in
Table 11 indicate that gas composition is very site-specific (See
also T.D. No. 16 and the discussion in Section 5.3.4).
5.3.4 Results From Discussions with Experts
The professional perspectives of those with whom technical
discussions were held on the subject of emissions and gas
migration problems at landfills are contained in the technical
discussion summary reports presented in Appendix A. These
perspectives, which generally reflect first hand experience with
landfill design and operation, are consistent with the analysis
56
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TABLE 10. ORGANIC COMPOUNDS IDENTIFIED IN LANDFILL GAS (25)
Benzene Isopropylbenzene
Butylcyclohexane Iso-octane
Chlorobenzene Iso-octanol
Cycloheptane Methylbenzene
Cyclohexyl-eicosane Methylcyclopentane
Decahydroaphthalene Methylene-butanediol
Decane Methylneptane
Dichloroethane Methylhexane
Dichloroethene Methyl(methylethenyl)-cyclohexene
Dichloromethane Methylpentane
Dichlorofluoromethane Methylpentylhydroperoxide
Diethylocyclohexane Methylpropylpentanol
Dimethylbenzene ' Methylnonene
Dimethylcyclohexane Octahydromethylpentalene
Dimethylcyclopentane Octane
Dimethylheptane Naphthalene
Dimethylhexane Pentane
Dimethylhexene Propylbenzene
Dimethyl(methylpropyl)cyclohexane
Dimethylpentane Nonane
Ethylbenzene Nonyne
Ethylbutanol Tetrachloroethene
Ethylcyclohexane Tetrahydrodimethylfuran
Ethylmethylbutene Tetramethylbutane
Ethylmethylcyclohexane Tetramethylcyclopentane
Ethylmethylcyclopentane Tetramethylhexane
Ethylmethylheptane Tetramethylhexenen
Ethylpentene Tetramethylpene
Heptane Tnchloroethane
Heptanol Trichloroethene
Hexadiene Trimethylcyclohexane
Hexane Tnmethylcyclopentane
Hexene
presented above in Sections 5.3.1, 5.3.2 and 5.3.3. There is a
substantial agreement among experts on some very key issues
(e.g., the nature and extent of problem at strictly hazardous
waste sites versus municipal or co-disposal sites). Some of the
key points of the technical discussions with experts are
presented below, along with reference to specific discussion
(T.D. No.), which should be consulted for detail.
RCRA-Designed Hazardous Waste Landfills--
Gas generation and migration/emissions control should not be
of much concern at strictly hazardous waste sites after
closure (T.D. Nos. 11 through 15), provided that such sites
57
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TABLC 11. LEVELS OF ORGANIC COMPOUNDS REPORTED IN SAMPLES OF LF GASES
FROM INTERIOR EXTRACTION WELLS (ppmv)
CD
Landfill
Compound
CHLORINATED OHGANICS
1 , 2-Dichlorocthylene
1, 1-Dichloroothylone
Trichlorocthofic
Dichloromcthano
Tctrachloroothcnc
Chlorocthcnc**
1 , 1-Dlchloroethane
Chlorobenzcnes
Total Chlorinated
AROMATICS
Benzene
Toluene
Xylene
Naphthalene
Total Aromatics
TOTAL OXYGENATED
ORCANICS
TOTAL ALKANES
Mt . View 9 MLPs Asron, Pucnte
CA*(3fl) (25)t CAJ(38) Hills.
Mtix Mean CA* ( 34 )
1.3
. -
1.9
_
0.6
-
-
0.9
11011
__
1.1
0.5
-
140tt
175tt
3400
3.6
1.1
7.6
5.6
8.3
.
5.2
11
396
23
100
115
0.1
311
-
94
0.7 - 0.1
0.1 - 2.4
0.7 - 60
0.7
o.a - 70
24
0.32
0.41 4.1
12.7
1.6 5.5 50
7 20.4 350
4.6 14.9 350
0.01
30 80
60
7 114
Paloa OKK, Misc. LFa,
Vordos, CAD CAH(42)
CA§(34) (33) Max Min Moan
0.1 190 -
6.2 70
6 265
-
7 430 -
7 600 -
-
_____
1500 10 20
200 200 112 2.7 32
400 - 533 32 221
600 - 765 24 220
_
1500 60 500
_
_
Municipal landfills
tAlthough not identified, there are indications that one or two
co-disposal sites may have been included in the sites surveyed
JSite handled primarily nonhazardous industrial wastes
UNumber, location or classification of sites not identified
§To-disposal site
**Vinyl chloride
ttCompound class data (i.e., 'totals') are for a sample other than
that u»ed for individual compound analysis
-------
were designed, operated and closed per RCRA requirements.
Source control. which disallows accepting bulk wastes which
are readily decomposable or reactive or contain volatile
substances, and the toxicity of the waste environment should
suppress biological activity (which results in the formation
of decomposition gases) and waste volatilization. Even if
some waste volatilization and degradation occurs, the
internal gas pressure would not be very high to effect gas
migration via convective mechanism; a properly designed and
maintained soil cover will have sufficient adsorptive
capacity to prevent significant emissions (T.D. Nos. 1, 4
and 15). Gas venting systems which have been provided at
some closed hazardous waste landfill cells have been
primarily as a precautionary measure (T.D. Nos. 12, 13-, 14)
and no pressure buildup has been noted based on monitoring
of gas pressure in the capped vents (T.D. No. 13).
Little actual emissions and ambient monitoring data are
available to quantify the extent of emissions (if any) from
HWLFs. Some state requirements for monitoring at certain
sites and for provisions for gas contro.l should a problem
develop (T.D. Nos. 12 and 14) primarily reflect the
uncertainty as to the nature and extent of emissions and
stem from public concern rather than hard data indicating
emissions of hazardous constituents (T.D. No. 14).
Ambient and source testing . for landfill emissions is
currently in an evolutionary stage and no reliable protocols
have yet been developed (T.D. Nos. 10 and 12). The problem
is complicated due to multiplicity of emissions sources at
or around ma^or sites which makes it very difficult to
interpret ambient air monitoring results (T.D. No. 12).
At a properly operated landfill site, emissions from pre-
treatment and waste processing activities, which preceed the
actual disposal, would be of greater significance than emis-
sions from waste placement and/or landfill after it is
closed (T.D. Nos. 4 and 15). In this regard, hazards to
landfill personnel and maintenance crews are of greater
concern than emissions from closed LFs (T.D. No. 15).
Leachate collection sumps, standpipes and accesses can
conceivably be a source of atmospheric emissions at closed
hazardous waste landfills. Very limited testing data which
have been developed have been inconclusive due to lack of
appropriate testing protocols (T.D. No. 12) or have
indicated no emissions of consequence (T.D. No. 14).
Leachate collection sumps and cleanout accesses are
generally kept closed; they can, at most, represent only a
potential source of intermittent emissions when they are
opened for maintenance purposes (T.D. No. 15).
59
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The potential for emissions from closed hazardous waste
landfills would even be less in the future due to increasing
emphasis on source control and waste treatment and
passification prior to disposal (T.D. No. 15).
Municipal and Co-disposal Sites--
Gas generation and migration are problems which are
primarily associated with co-disposal and municipal
landfills where the waste undergoes decomposition (T.D. Nos.
9, 14, 15 and 16). The migrating gas can contain traces of
toxic substances and hence present emission problems. These
toxic substances can originate from wastes containing toxic
volatiles and/or result from degradation of otherwise inert
wastes (e.g., vinyl chloride produced from the degradation
of plastics) (T.D; No. 15).
The quantity (e.g., yield) and characteristics of landfill
gas are highly variable and extremely site-specific and
these variations are not necessarily related to any
regulatory or conventional classification of sites as co-
disposal, municipal, sanitary, etc. (T.D. No. 16).
Gas monitoring data have indicated no substantial
differences in the gross composition of the gas from the co-
disposal and the so-called municipal landfills (T.D. Nos. 4
and 15)-. Thus compounds such as xylene, toluene and benzene
which have been identified as trace hazardous constituents
in the gas from co-disposal sites, have also been identified
in the gas from municipal landfills (T.D. No. 15). This
compositional similarity is not surprising since all
municipal landfills receive various quantities of hazardous
wastes (e.g., from small volume hazardous waste generators).
Thus the differences in the composition of gas from
municipal and co-disposal sites and hence the emission
problems appear to be a matter of degree rather than kind
(T.D. No. 15). Gas and emission control systems for the two
landfill types would also be the same in fundamentals but
vary in complexity and details (T.D. No. 15).
Unless the gas from municipal and co-disposal landfills is
recovered, in addition to safety hazards associated with
off-site gas migration, landfill gas can constitute a major
source of air pollution (T.D. No. 16). Since landfill
covers only postpone gas emission (i.e., after steady-state
conditions are reached, soil covers are ineffective in
preventing gas escape), landfills can emit very large
quantities of reactive organics and substantial amounts of
potentially hazardous substances which are present in
landfill gas as trace constituents.
60
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The nature and extent of emissions at municipal and co-
disposal sites are largely a function of the extent of waste
screening and processing to eliminate or passify problem
wastes, waste placement practices and the control systems
employed (T.D. Nos. 1 through 4, 9, 10 and 12 through 16).
No significant emissions would be expected from landfills
which employ an active gas control systems which is very
large in extent and which maintains a vacuum in the
collection system (T.D. No. 1). Actual .ambient monitoring
data around some such landfills have indicated no
substantial differences between upwind and downwind
conditions (T.D. Nos. 1 and 15). Passive control systems
employing direct atmospheric venting do not eliminate the
emissions problem since any toxic substances in the gas
would still be released to the atmosphere (T.D. No. 15).
The state of Wisconsin requires passive gas management at
all sites, with the additional requirement that the system
can be readily converted to active system if necessary (T.D.
No. 9). When the vent gases are flared, little or no
emissions of reactive organics are expected due to high
temperature of the flare (1400-1500°F) (T.D. Nos. 1 and 4).
At sites in California where flaring has been employed, the
flare emissions have met the very restrictive local air
quality standards (T.D. Nosi 1 and 4).
At least in the dry climates such as in Southern California,
underground fires in the landfills are a rule rather than an
exception (T.D. No. 4). The heat from such fires can
increase volatilization and hence the potential for
emissions of hazardous air pollutants (T.D. No. 4).
Underground fires have not been a problem in Wisconsin due
to the wet climate and strict regulation and inspection
which would prevent disposal of hot ashes and flammable
wastes in landfills (T.D. No. 9).
Installation of covers for landfills to minimize infiltra-
tion, increases the potential for gas migration and hence
necessitates gas venting (T.D. No. 11). Properly designed
soil covers can reduce emissions of some hazardous
substances through adsorption and/or biological degradation
(T.D. No. 4). Odor measurements have indicated several
orders of magnitude reductions in the odor as the gas passes
through the cover (T.D. No. 1). The odor reduction is
believed to be due to aerobic biological activity within the
cover (T.D. No. 1) which has been shown to occur in the
bottom layer of the soil cover (T.D. Nos. 1 and 4).
Few odor and gas complaints are received on many landfills,
since they are located in remote areas (T.D. Nos. 5 and 9).
Gas generation in landfills should not be viewed as a
61
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problem area to be contended with, but as an opportunity to
recover a valuable resource (T.D. No. 10). Thus, landfill
design and operation should be geared toward the goal of
recovering maximum amount of gas requiring minimal
pretreatment prior to use. In addition to source control,
whereby wastes are screened and troublesome wastes are
identified for proper handling (i.e., sent to strictly
hazardous waste disposal sites, treated, or disposed of in
segregated areas), operating procedures should promote
active waste degradation (e.g., through leachate recyling
and biological seeding) and eliminate internal barriers to
gas movement (e.g., using permeable materials as
intermediate cover). Use of horizontal trench gas recovery
systems, which are constructed in the fill as the waste is
placed, or shortly thereafter, enables recovery of a greater
amount of energy (and better odor control) than the
conventional vertical well gas extraction systems placed in
a completed landfill (T.D. No. 1).
To promote energy recovery from landfills and in line with
the consideration that landfills can" emit significant
quantities of reactive and hazardous substances to
atmosphere, from a regulatory standpoint landfills should be
considered as point sources of emissions and gas recovery as
the "Pollution control device" for landfills (T.D. No. 16).
5.4 THE AVAILABLE DATA BASE ON SURFACE IMPOUNDMENT EMISSIONS
5.4.1 Some Fundamental Considerations
Volatile chemicals in the wastewaters discharged to Sis can
escape into the air and result in an area-source of emissions.
The rate of escape of a volatile substance from a liquid surface
may be expressed by the following equation (43):
(ERP)i=(KOA)A(xi-x.L*)M.L (a)
where (ERP) =emission rate potential of a compound, g/sec;
K_=overall mass transfer coefficient, g-mol/cm2-sec;
H=SI surface area, cm2
x =concentration of the compound in the
I1c wastewater, mole fraction;
x =equilibrium concentration of the compound
in liquid corresponding to its partial
pressure in the gas phase, mole
fraction; and
M =molecular weight of the compound, g/g mol.
Expressing the solute concentration as Ci in mg/1, the
emission rate potential equation becomes:
62
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(ERP)i={18 x 10 )(K)A C (b)
The critical variable of the estimation depends upon the
overall mass transfer coefficient K^A . K can be calculated
from K , KG, and K, using the well established "two resistance"
theory as follows:
1/KOA=1/KL+1/KKG (c)
wnere K=liquid phase mass transfer coefficient, g-mol/
cm2-sec ;
K =gas phase mass transfer coefficient, g-mol/
cm2-sec; and
K=equilibrium constant of liquid and gas phases,
dimensionless '.
The K value can be determined by the following equation:
K=(H /PM) x 10 (d)
Where H =Henry's law constant of the compound, atm/(g-mol/m );
P=total pressure, atm; and
M=average molecular weight of the liquid, g/g-mol
(the factor of 10 is derived from
conversion of liquid weight into volume.)
Eq. (c) represents the addition of two phase resistances in
series to yield an overall resistance. The relative contribution
of each resistance can be calculated. Most of the resistance to
volatilization lies in the few millimeters above or below the
gas-liquid interface. In many situations either liquid phase
resistance or gas phase resistance controls; but in some cases,
both resistances control. If "KT " is very small compared to
"KK ", the liquid phase resistance controls and "K " may be
ignored, and vice versa. The distribution of resistance depends
on K- , K_ , and K which must be quantified. For H. values above
10-3, the transfer is liquid phase controlled and the gas phase
may be ignored for practical purposes, i.e., K = K.. .
Based on the above theoretical considerations, the loss of
volatiles from Sis would be highly variable and site- and
situation-specific. The volatilization rate would depend on the
degree of turbulence at the gas-liquid interface and would be
greatly influenced by the presence of surface materials such as
floating solids and/or liquid films. Because of the complicated
effects of surface materials, turbulence and the meteorological
conditions, which may vary appreciably with time, it is very
difficult to quantify various film resistance coefficients (K_,
K_ and K) and develop reasonably accurate estimation of
volatilization losses based on theoretical considerations. As
will be discussed in Section 5.4.2, some of the mathematical
models which have been developed for predicting emissions, based
on theoretical considerations such as those presented above, have
63
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yielded emissions estimates which have differed from the results
obtained via direct measurement. Since a predictive capability
would be helpful to permit writers while the proposed impoundment
is in planning and design stages, considerable emphasis is being
placed on model verification and improvement.
5.4.2 Results from Previous Studies
Table 12 describes and presents the results from three
recent SI emissions monitoring programs and one general study of
atmospheric release of chlorinated organic compounds from the
activated sludge process. This latter study, which is an example
of a number of studies (e.g., Refs. 47 and 48) addressing the
loss of volatile organic substances from wastewater during
various treatment processes, has been included to illustrate the
impact of wastewater characteristics (e.g., molecular weight of
organics, presence of biological floes, etc.) and the treatment
processes themselves on the volatilization of organic substances.
These studies have indicated that low molecular weight
halogenated and aromatic hydrocarbons can be readily volatilized
from Sis. In one study of an aerated lagoon (48), half lives
calculated from emissions data were only a few hours. Data from
open primary and secondary wastewater treatment systems also
indicate very short half lives for the low molecular weight
organics (45). Even less volatile organo-chlorine pesticides and
pesticide metabolites are reportedly lost to a large extent to
the atmosphere in highly aerated treatment systems.
As noted in Table 12, the SI monitoring studies have been
mostly concerned with comparative testing of various sampling
protocols and equipments and with verification of various models
for predicting emissions. Since only a very limited number of
Sis have been included in these studies, the results, which
generally indicate very low VOC emissions (often near the detec-
tion limit for the sampling and analytical methods used), may or
may not be representative of the emissions from Sis. Moreover,
there have been some significant disagreements between the
results using different sampling protocols such as emission iso-
lation flux chamber (ICF) vs. concentration profile method (C-P)
and between the measured values and those predicted using models.
These discrepancies thus cast some serious doubt as to the
validity of the current data base on SI emissions and underline
the need for additional R & D to develop improved sampling
methods and equipment and for field measurements at additional
sites. The following excerpt from the Conclusions Section in the
final report for the second study in Table 12 (Ref. 44)
illustrates the discrepancies and variability in the data:
VOC emissions were measured using a modification
of the C-P technique at two chemical waste treatment
1 facilities, one using an aerobic bio-oxidation pond
64
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TABLE 12. KEY PROGRAMS RELATING TO TOXIC EMISSIONS FROM SURPACE IMPOUNDMENTS
Program
Sponsor
Object Ivos
Description, findings, and SlgnlfIcanco
U!
Evaluation of air emis-
sions fro.ti hazardous
fcaste treatment,
storage and disposal
facilities In support
of RCRA air emission
regulation Impact
analysisSites J and
6 128)
EPA/IERL-
Cl
Evaluation of VOC emis-
sions from wastevater
systems (secondary
emissions) (44)
EPA/IEBL-
Cl
Develop and verify tech-
niques for determining
air emissions from SI*
and to validate avail-
able emltslons models.
Obtain data for evalua-
ting carbon (VOC)
emissions from waste-
water treatment
facilities for the
synthetic organic
chemicals manufacturing
industry.
Ai part of a larger, multi-alto monitoring program at IIW
facilities, emissions wore measured from a reducing
lagoon, an oxidizing lagoon, a wastowater holding pond,
and a spray evaporation pond. The first three typos of
Sis woro monitored using tha emission isolation flux
chamber (IFC) and concentration profile (C-P) techniques.
For most compounds, the IFC yloldod higher rates than
the C-P technique. Measurements by either technique
wcro generally much lower for the two lagoons than that
predicted by the models employed (which used liquid -
phase concentration data). For the holding pond, pre-
dicted rates woro greater than C-P values but less than
IFC values for the spray evaporation pond. Emissions
were measured by the transect technique, and the
results were much lower than those projected by tha
model calculations. Considerable variability was found
in both tha gas and aqueous sample data which contrib-
uted to wide confidence intervals for both predicted
and measured emissions rates. The lack of agreement
between model and measured rates was attributed in part
to effects of oils and solids in the Sis and. in the
case of the spray pond, to atomliation and evaporative
cooling effects duo to spray nozzles.
VOC emissions wore measured using tha C-P technique at
oxidation pond and a non-aerated pond. Emissions at
both ponds were near the detection limits for monitor-
Ing techniques employed (] ppbv. Model predictions
tended to overestimate measured emissions for most or-
ganic* by factors of 3 or more for the aerated systems
and 6 or more for the non-aorated systems. For at
least two polar organics, measured emissions rates were
less than those predicted by model calculations, which
may bo a consequence of low analytical data for the
'purge and trap* sample collection technique for pond
water organics.
(Continued)
-------
TABLE 12. (Continued)
Program
Sponsor
Objectives
Description, findings, and Significance
Air emission* monitoring
of hazardous waste cites
MS)
Atmospheric rolcaso of
chlorinated organic
compounds from the
activated sludge
procesa (46)
EPA/MERL
Solid «
Hazardous
Waste
Research
Division
EPA/U.S.
Air Force
Identify volatile
organlcs from Sis and
compare results with
modal predictions.
Identify locations in
wastowatcr treatment
process whore emissions
of chorinated ofganica
occur.
Fmissions of chlorinated nnd nromatlc hydrocarbons wore
measured using tho C-P technique at an oxidation pond
which handled Industrial wactowatcr. C-P emission*
jates agreed with modal calculations within a factor of
2. Half lives for volatilization of benzene and
1,1-dlchloroothano from the Sis wore around 3 hours for
aerated SI and 7 hours for tho holding pond. The
transport process for volatilization of chemicals from
the Sis was found to bo liquid phaso controlled.
Aqueous and gaseous samples worn taken at various loca-
tions within an activated aludga plant to estimate
stripping of low-and-high molecular weight chlorinated
hydrocarbons at various stages of processing. Tho low
molecular weight compounds were largely lost at early
processing stages (o g , at tho grit chamber wior)
while higher molecular weight organlcs were lost mostly
at tho contact aeration basins. Relatively nonvolatile
compounds such as hexachlorocyclohcptcno appeared to bo
adsorbed onto tho blomass which were recycled to
aeration basins from clarifiors, prolonging their
atmospheric release. Tho low molecular weight organlcs
were 80-991 volatilized during the process, while high
molecular weight organics wore about SOI volatilized.
-------
(site FB), and the second using a nonaerated pond
(site TB). Emissions from both sites were very low,
near the detection limits for the sampling and
analytical methods which were used (3 ppbv-C). VOC
flux rates were calculated for benzene, diethyl ether,
indene, and styrene at site FB. Also, a flux rate was
determined for the total aromatic content in the air
above the pond surface. Measured flux rates at this
site ranged from 430 kg/Ha-yr for styrene to 3660
kg/Ha-yr for diethyl ether. The average flux rate for
total aromatics at this site was 20,400 kg/Ha-yr. VOC
flux rates at site TB were determined for benzene,
cyclohexane and acetone. Measured flux rates at this
site ranged from 130 kg/Ha-yr for benzene to 1550
kg/Ha-yr for acetone. Standard errors and confidence
limits were calculated for all analytical and
meteorological measurements. Because of the low levels
of VOC species which were present above the ponds and
sampling and analytical variabilities, a zero flux rate
was within the 95% confidence level for all flux
measurements.
Flux rates determined using the modified C-P
technique were compared to flux rates predicted by the
models of Thibodeaux and Hwang. Results of the
comparison were variable, and seemed to be related to
the type of compound and whether or not aerators were
used. For the site containing aerators (FB),
predictive flux rates for the three aromatic compounds
were approximately 3.5 times higher than measured flux
rates. However, for diethyl ether, the predicted flux
rate was only 35% of the measured flux rate. Predicted
flux rates for diethyl ether and styrene were within
the 95% confidence limits for the measured rates, while
benzene and styrene were outside the 951 confidence
limits. The predictive model indicated that 85-95% of
the overall emissions resulted from aeration (turbulent
phase).
For the site not containing aerators (TB),
predictive flux rates for benzene and cyclohexane were
greater than measured rates by factors of 10.0 and 5.9,
respectively. The predicted flux rate for acetone at
this site was 15% of the measured rate. The predicted
flux rate for acetone was within the 95% confidence
limits for the measured value, while predicted flux
rates for benzene and cyclohexane were not.
As with LFs, a major problem with quantifying emissions from
Sis has been that the Sis tested are often located at sites where
there are other sources of emissions. At these sites it is very
67
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difficult to separate SI emissions from the background levels or
from emissions caused by other on-site or nearby off-site
activities (see also T.D. No. 12). The following conclusions
from the third study listed in Table 12 illustrates the point:
Levels of chlorinated hydrocarbons, including 1,1-
dichlorethane, and total hydrocarbons, including
benzene, were observed in both the water and air
boundary layers of two Sis of a hazardous waste
facility. Concentration gradients in the air boundary
layer above the SI indicate that the ponds are a source
of VOCs; however, periodic wind shifts move air with
high concentration of VOC from other areas of the
facility over the impoundments so that chemical
absorption onto the water is indicated.
5.4.3 Results from Discussions with Experts
Perhaps because of their temporary nature and the greater
flexibility in controlling their emissions, the problem of
emissions from Sis have not been of major concern. The problem
with potential odor has generally been addressed through siting
and source control (i.e., not accepting odorous wastes or wastes
which would react to produce malodorous compounds) (49) For
example, in Maryland, the volatile wastes are shipped out of
state for treatment and disposal (T.D. No. 5) and in Wisconsin
and Maryland odor and emissions have not been a problem because
TSDFs are located away from residential areas (T.D. Nos. 5 and
9). The state of New York has developed rules on the type of
waste which can be admitted to a hazardous waste disposal site.
At. major commercial hazardous waste sites, the rules are strictly
enforced by on-site state inspectors (T.D. No. 12). As with the
hazardous waste landfills, because of the multiplicity of
emissions sources at and the locations of some commercial sites
it has been and would be difficult at these sites to separately
measure the emissions contributions from individual Sis (T.D. No.
12). Chemical Securities System, which operates a major
hazardous waste in Arlington, Oregon, has recently initiated a
monitoring program to determine the nature and characteristics of
emissions from some 18 Sis which are present at the site (50).
5.5 CORRECTIVE AND PREVENTIVE MEASURES
5.5.1 Landfills
RCRA-Designed Hazardous Waste Landfills
As noted in Section 5.3, the very limited actual emissions
and ambient monitoring data which are currently available for
hazardous waste landfills and the consideration of the
fundamental nature of gas generation and migration in landfills
68
-------
would, suggest that gas migration and emission should not be of
major concern at strictly hazardous waste sites which meet or
exceed RCRA design, operation and closure standards. Since
biological activity at these landfills is minimal, emission at a
closed landfill primarily relates to waste volatilization and
this can be addressed through source control and site design.
Because of the uncertainty regarding the nature of emissions
problems at strictly hazardous waste sites and a possible need
for add-on controls, some such sites feature gas venting systems
for the closed cells (T.D. Nos. 12, 13 and 14); the vent pipes
are capped, but can be converted/connected to gas collection and
treating system, if gas monitoring data point to such a need.
Figure 6 presents detail of a gas venting system for a closed
cell at a hazardous waste landfill.
Many of the measures for controlling gas emissions in hazar-
dous waste landfills are preventive rather than corrective in
nature. These measures, along with those for controlling
fugitive emissions from waste handling and placement, have been
grouped into design- and operation-related categories and are
briefly described in Tables 13 and 14, respectively.
In reviewing control measures, it should be noted that, such
measures should be integrated with and are affected by leachate
control methods (see Section 4.5). Thus a tight cover design
which reduces infiltration and hence leachate generation can
necessitate incorporation of vents in the cover design as a gas
pressure release contingency measure. Similarly, source control
measures for control of leachate volume and characteristics
(e.g., not accepting bulk liquids and degradable wastes) also
reduce the potential for generation of decomposition gases.
A number of studies have been conducted in recent years
aimed at determining the factors which affect the rate of volati-
lization of toxic organics in a landfill environment so that
better controls can be developed. These studies which have been
largely laboratory-type and research-oriented are listed in Table
15. Three of the studies listed in the table measured volatili-
zation rates for specific organics from real or synthetic wastes
when the waste was covered by materials having different porosi-
ties and water contents. Compacted clays, soils, and organic
materials were found not only to reduce the rate of volatiliza-
tion, but also provide adsorption capacity for many organics.
Higher water contents in clays serve to decrease porosity which
in turn decreases volatilization rate from underlying waste.
There is some evidence that organic matter in the final
cover of a landfill can, in addition to providing physical
sorptive capacity for toxic substances, contribute to the
eventual biodegradation of some of these substances. Organic
matter added to cover soil can provide seed organisms which may
69
-------
-j
o
'o
O
"to
2H0Htlj
"COMPACTED CLAY
''7 C(W
-SCREW CAPS WITH INSTRUMENT VALVE CONNECTOR CAPABLE
OF SHUT OFF (DWYER INSTRUMENT A3ia OR EQUIVALENT)
GAS VENT PIPE
6" UNCOMPACTED CLAY
I'-O" COMPACTED CLAY
SYNTHETIC LINER
NOTE«
SOLID 6" 0 PVC SCH 40
GRAVEL TRENCH 2
:l-o"x2'-o"-J
LINER TO BE FASTENED TO PIPE PER
LINER MANUFACTURER'S SPECIFCATIONS
GRAVEL BACKFILL
PERFORATED PV.C. SCH 40
Figure 6. Gas venting detail for a closed cell at a hazardous waste
landfill (T.D. No. 13)
-------
TABLE 13.
PREVENTIVE/CORRECTIVE DESIGN-RELATED MEASURES FOR
GAS GENERATION AND MIGRATION/EMISSION CONTROL AT
HAZARDOUS WASTE LANDFILLS
Measure
Description and Comment
Multiple cell
design for
segregated
waste disposal
State-of-the-
art liner and
cover design
Use of capped
vents, sumps,
cleanouts,
etc.
-Dedicating specific landfill cells/areas to specific waste
categories would allow for tailoring design and operation
Lo waste-specific properties thereby providing for more
cost-effective gas migration and emissions control.
-Prevent lateral gas migration and allow for engineered gas
venting through cover and possible collection and treat-
ment of gas before release.
-Reduce infiltration into the landfill thus reducing leach-
ing and potential for biological activity.
-Prevent potential uncontrolled release of volatile toxic
substances to atmosphere.
-Allow for monitoring of pressure and composition of land-
fill gas or leadhate off-gas.
-------
TABLE 14. PREVENTIVE/CORRECTIVE OPERATION-RELATED MEASURES FOR GAS GENERATION
AND MIGRATION CONTROL AT HAZARDOUS WASTE LANDFILLS
Measure
Description and Comment
Source control
Prevent formation of Internal
barriers to gas flow.
Control of runoff and
and infiltration (to suppress
Icachate formation and
biological activity).
Control of fugitive omissions
due to waste handling and
placement activities.
-Not accepting solvents.
-Not accepting or passlfying (e.g. through solidification) liquid wastes,
reactive wastes, wastes high in volatllos, readily biodegradable matters.
-Surrounding specific waste loads with absorbents as a contingency measure.
-Use of sand or other permeable material as intermediate cover.
-Providing discontinuities in the intermediate cover or breaking previous
day's cover in the active filling area.
-Runoff diversion and containment and removal of rainwater entering active
site.
-Use of temporary domes and roofs during operation.
-Proper cover maintenance after closure.
-Removal of ponded water during active life.
-Limiting the exposed working face of landfill.
-Source control (see above).
-Conducting waste processing in enclosed areas equipped with emission
control.
-Operating under low temperature and low wind speed (when possible)
-Covering the waste immediately after disposal with suitable cover
-------
TADI.C 15. KEY LABORATORY/SUPPORT STUDIES RELATED TO VOLATILIZATION OF TOXIC
ORGANICS FROM WASTES AND SORPTION/DIODEGRADATION IN SOILS
Study Title
Objectives
Description, Findings And Significance
to
Studies of Emissions
and Control of Vola-
tile Organics in IIWLFs
(51)
Problems Associated
with Land Disposal
of Hazardous Waste
Containing llexochloro-
benzcne (MCD) (29)
Can Chromatographic
Studies of Sorptive
Intersections of
Normal & Halogcnated
Hydrocarbons with
Water-Modified Soil.
Silica, and Chromosorb
W (52)
Investigations of the
cover of a closed
HWLF as an odor sup-
pressant (T.D. No. 1)
Determine factors con-
trolling movement of
volatile organlcs away
from wastes in a simu-
lated LF environment.
Determine effects of
various cover materials
on IICB volatilization
rate in simulated
waste environment.
Quantify sorption
properties of various
materials for hydrocar-
bons under GC condi-
tions.
Determine the effec-
tiveness of final
cover in reducing
odor emissions
Using benzene as a model toxic waste component, tho study
investigated volatilization rates from simulated wastes
covered with clay, soil, and organic matter. Cover material
had varying capacities to aorb benzene. At steady otato
(cover saturation) the volatilization rate was directly re-
lated to cover porosity and inversely to cover moisture con-
tent .
IICB containing waste was covered with soil, polyethylene
film, water and tho volatilization flux measured. Soil and
water were both very effective in reducing steady state
flux. The soil adsorption capacity retards the time
required to reach steady state. Thin polyethylene film did
not greatly affect volatilization.
Using soil, silica and Chromosorb W as GC column materials,
the sorption of halogcnated and normal hydrocarbons was
investigated. Wet soil is highly effective in sorbing
organics, with greater sorption constants exhibited for
higher than for lower molecular weight organica.
L.A. County Sanitations Districts has mode numerous odor
measurements at its Palos Verdcs Landfill and has deter-
mined several orders of magnitude reduction in odor as
the gas passes through the cover. The reduction in odor
has been attributed to biological activity within the
the cover.
-------
develop the ability to degrade toxic organics. Organic matter
also provides a large surface area and nutrients for
microbiological growth, and porosity for diffusion and movement
of organic vapors, water vapor and metabolic wastes in the soil.
In this regard sewage sludge, wood chips, mulch or compost,
shredded newspaper, and similar materials may be beneficial as
part of the final cover for landfills.
Municipal and Co-disposal Landfills--
Fugitive emissions of toxic substances at municipal and co-
disposal sites can result from operating activities and from
migration of decomposition gases containing toxic substances as
trace contaminants. Source and operating controls, venting,
interception and/or collection of gas for incineration with or
without energy recovery constitute controls for gas migration and
emissions problems at municipal and co-disposal sites. As with
the controls for hazardous waste sites, some of these measures
are primarily preventive rather than corrective.
Source controls at municipal and co-disposal sites are
primarily aimed at (a) excluding disposal of bulk solvents and
waste containing a high concentration of volatiles and/or (b)
passification of certain troublesome wastes (e.g., via
solidification) prior to disposal. To prevent lateral migration
of gas to nearby structures, and to facilitate gas collection for
energy recovery, operating controls, are aimed at eliminating
internal barriers to gas movement (e.g., through use of sand or
other permeable materials as intermediate cover).
Various systems have been employed at a number of municipal
and some co-disposal sites for interception and venting and for
collection and disposal or use of landfill gas. These systems
fall into two categories: passive and active systems. Key
features of these systems are listed in Tables 16 and 17,
respectively. The passive systems are aimed at releasing the
internal gas pressure by providing wells and trenches in or
around landfills for venting of the gas to the atmosphere. Pas-
sive systems would not be considered acceptable emissions control
since any toxic substances in the gas would still be released to
the atmosphere (T.D. Nos. 10 and 15). Passive systems can also
constitute safety hazards, especially in areas where there is a
likelihood for trespassing and there has been some consideration
for posting warning signs near these potential emissions sources
and/or constructing taller vents to promote gas dispersion (T.D.
No. 10). From a public relations point of view, the active
systems have an advantage over the passive systems since the
public "feels" more comfortable ("safer") as it sees or hears the
blowers in operation (T.D. No. 10). As noted previously, the
state of Wisconsin now requires passive gas systems at all LFs
with the additional requirement that such systems can be
74
-------
TABLE 16. PASSIVE SYSTEMS FOR LANDFILL GAS MIGRATION CONTROL (21. 23)
Control Systeit
Description
Advantages
Disadvantage*!
Trench with granular
backfill
Trench with
synthetic roombrana
liner (See Figure
7)
Natural Induction
wells
Natural Induction
wells with subsur-
face collector pipes.
Along all boundaries to com-
pletely enclose each site.
Gravel backfill greater than
6.4 m. Oapthi 6.1 m
or to groundwater table or
bedrock, whichever is less.
Along all boundaries to com-
pletely enclose each site.
Synthetic liner, 30-mil
thickness. Depthi to ground-
water or unflssured bedrock.
Perimeter and Interior
spaced same as forced
Induction wells. Depthi
same aa above.
Perimeter and Interior
same as forced induction wells.
Depthi sama as above.
Low cost at depths up to
J.7 m. Llttlo maintenance
la required. The granular
backfill provides a highly
permeable region venting
to the air to allow low-
resistance passage of gas.
Low costs at depths between '
3.7 and 9.1 m. The mcm-
brano can provide a positive
seal and be a barrier against
gas end leachate. Little
maintenance is required.
Granular backfill on tha
landfill side of tha membrane
allows methane gas to vent
to the air.
Can install at depths greater
than 30.5 m. Can cover a
large area. Negligible main-
tenance and comparatively
low operating costs.
Can Install wells to depths
greater than 3D.5 m. Can
install collector pipes at
varying depths. Can cover
a largo area of landfill
surface using Interconnecting
collectors between walls.
Negligible maintenance and
operating coats.
Costs escalate rapidly at depths
groator than 6.1 m. The barrier
may not bo effective if
pervious natural soil layers
exist on tho outside of the
trench. Cns could migrate
and/or dlffuao across tho
barrier. Difficult to construct
at depths groator than 9.1 m
and Impractical to construct
at depths groator than 14 m.
Not controllable.
Costs become exceptionally
high below a 9.1-m depth. The
barrlor may not be effective
unless it extends into tho
groundwater table to eliminate
gas migration beneath tho
membrane. Difficult to
construct at depths greater
than 9.1 m and impractical at
depths greater than 14 m. Not
controllable.
Localized venting of methane.
Largo number required to
achieve control of migration.
la uneconomical. Reliability
and effectiveness have been
inadequate. Not controllable.
Extcnslvo piping end well
ayatcm la needed at high coat.
Reliability and effectiveness
may be unsatisfactory, since
this system basically combines
tho trench and well systems.
Not controllable.
-------
^Winter Climates may require
collector w/vertical risers 8k
surface seal
0>
Barrier material
(synthetic liner
Undisturbed material or water table
Figure 7. Trench barrier system for gas migration control (21)
-------
TABLE 17. KEY FEATURES OF ACTIVE LF GAS EXTRACTION SYSTEMS FOR GAS RECOVERY AND/OR
MIGRATION CONTROL (23, 55. T.D. No.l)*
Control
Descrlpt ion
Advantages
Disadvantages
Vertical gas
extraction wolla-
intorior
Horizontal gas
extraction walls-
finished lifts
Vertical gas
migration preven-
tion wells-
pcr iphcry
Horizontal gas
migration preven-
tion wells-
periphery
Designed to create
a zone of negative
prcuaiirc within
the I.F to collect
dccomposIt ion
gases. Usually
spaced about 60
meters on center.
Short sections of
pipe connected
with loose fitting
sleeves arc placed
within horizontal
gravel trenches on
finished lifts of
an jctivo LF.
Designed to create
a zone of negative
pressure between
I.F and neighboring
propertics.
Spacing usually
about 30 meters
on center.
Consists of hori-
zontal pipe buried
in coarse gravel
along the corner of
a LF formed by the
bottom and
excavated side of
the fill.
Gas from Interior wells has a high
methane content and can be used in
a number of onsito or offulto
energy recovery operations. This
typo of well has al^o been usod
for odor control on slope faces of
LFs. lias bucn demonstrated at
over two dozen LFs in the U.S.
A grid work of ouch trenches can
cover the entire surface of a lift
and capture significant quantities
of gas migrating toward the f.F sur-
face. Additional lifts of waste
can bo placed over these trenches
without impeding collection effi-
ciency. The major advantage to
this type of well Is that gas can
be recovered prior to completion
of the LF and a greater portion of
the gas can be captured than with
vertical wells installed after
complct ipn.
Periphery wells arc effective In
dry porous soils surrounding a LF
Drilling in undisturbed soil Is
safer and less expensive than
drilling into waste. Periphery
wells can bo established prior to
closure of the LF. lias been demon-
strated at a large number of LFs
in the U.S.
Permits gas removal from the bulk
of the refuse as soon as it begins
Gas flow can be regulated to cap-
ture reasonably air-free gas.
Drilling into the refuse is not
necessary.
Kclativoly costly and requires
periodic maintenance. Wells
cannot bo established before
I.F is closed. Special pre-
cautions are necessary for
drilling into wnsto. Wells
can be damaged by local
nettling of waato.
Potentially subject to com-
pression damage from equipment
operating on lift and from
settling of refuse. Cannot bo
readily repaired once damaged.
Limited experience to data
'with the system.
When soils are wot or rela-
tively nonporous, the radius
of influence IB small.
Collected gas has consider-
able air content which limits
energy recovery options.
Requires integration with
Icachato collection system.
care must bo exorcized during
emplacement of the first lift
to avoid damage. Difficult to
repair if clogged or damaged.
Limited experience to date.
Figures 8 and 9 for schematic representation of these measures,
-------
CONCRETE
VALVE BOX
30 COVER
VALVE
UBBER COUPLING
PVC HEADER PIPE
6 DIA PERFORATED
PVC PIPE
4" DIA PVC PIPE
SLIP-JOINT
COUPLING DETAIL
4 DIA. PERFORATED
PVC PIPE
6 DIA. PERFORATED
PVC PIPE
PVC RING
CEMENTED TO
4" PIPE
6" DIA PVC PIPE
GRAVEL BACKFILL
DIA.
NOT TO SCALE
Figure 8 . Schematic drawing of vertical
gas extraction well (56)
78
-------
SOIL COVER
TRENCH
o
o
T- 20*. REFUSE'. UFT (TYP) ' .'
SOIL COVER
A. Place at side toe of lift
TRENCH
o
T
T 26* REfUSf LIFT IjVP)
B. Trench into deck
Figure g .
Landfill gas recovery in horizontal trenches
trench construction methods (57)
-------
converted to active systems if necessary (T.D. No. 9).
As noted in Table 16, passive systems can incorporate use of
synthetic liners (or other types of liners such as admixes and
clay soils) for containing gas flow. Polyvinyl chloride (PVC)
liners are frequently used because they are more impermeable to
methane in comparision to materials such as polyethylene and are
relatively inexpensive (21). As with uses in connection with
landfill lining and closure, the integrity of the installed liner
is critical and the liner must be put down to avoid puncture, and
usually layers of sand or soil must be placed on both sides.
While effective in controlling convective gas flow, even the
best passive systems which employ synthetic liners would not be
totally effective in controlling diffusive gas flow. Even though
synthetic liners have often been referred to as "impermeable"
liners, and depending on the type and characteristics of the
liner, some amount of gas would be expected to diffuse through
the synthetic liner and into the surrounding soil. Haxo et al
(53) have reported on laboratory measurements of the permeabili-
ty of polymeric membrane lining materials. Permeabilities to
three gases of interest (carbon dioxide, methane and nitrogen),
water vapor and five solvents (methanol, acetone, cyclohexane,
xylene and chloroform) were measured for a broad range of commer-
cial polymeric membranes, primarily those used in waste manage-
ment applications. Data for permeability at 23 C of a series of
liners to the three tested gases are. presented in Table 18 on
both the basis of the gas transmission rates which are indicative
of liner performance and on the basis of permeability coeffi-
cients which are material properties and reflect the permeabili-
ties of the liner compounds. Haxo et al (53) concluded that:
There are major differences in permeability among the
membranes reflecting variation in polymer type, compound
composition, and thickness.
Permeability of polymeric liner materials can differ for a
given generic polymer type due to compound variation (e.g.,
filler and plasticizer contents).
Permeability of a membrane can differ greatly with the gas.
Gas transmission of a membrane decreases with increased
thickness.
Higher polymer crystallinity yields lower permeability, as
shown when comparing LDPE, LLDPE (linear low-density
polyethylene), and HOPE.
Permeability of polymeric membranes to gases increases with
temperature in accordance with Arhenius equation.
80
-------
TABLE 18. PERMEABILITY OF POLYMERIC MEMBRANE LINERS TO GASES AT 23°C
DETERMINED IN ACCORDANCE WITH ASTM D1434, PROCEDURE V (53)
CO
Li nor Detcrlptlon
Polymer
Butyl
CPE
CSPE
CSPE
ELPO
EPOM
EPOM
EPDM
'Icoprcno
PO
HOPE
HOPE
LDPE
LLDPE
PVC
pvc
PVC
Linor
Serial No
44
77
6R
55
36
83R
91
8
90
221
265
269
2)
261
93
aa
59
Thickneaa
.| nun
1.60
0.72
0.62
0.86
0.56
O.B9
0.90
l.SO
0.90
0.71
0.61
0.66
0.25
0.46
0 25
0.49
0.81
Compound
type!
XL
TP
TP
TP
CX
TP
XL
XL
XL
CX
CX
CX
CX
CX
TP
TP
TP
Caa Transmission Rato
mL(STP*)/sq m.d
C02
512
1061
122
418
1450
2720**
5260
-
716
818
729
467
6180**
1370
7730»»
3010
2840»»
CII4
120
6.3lf
21.6
124
280
_
1400
470tt
BO. 9
248
130
104
1340»»
322
1I50»»
446
285».
-------
It should be noted that the gas permeability data such as
those presented above as well as similar laboratory-generated
perreability data for landfill leachate constituents (e.g.,
reported in Ref. 54) may be substantially different than the
actual leakage rates experienced in the field. This would be due
to the differences between the field conditions and the
laboratory conditions under which the permeability is measured
(e.g., steady state conditions and use of clean, unsupported
liner specimens). As pointed out by Haxo et al (53), in actual
service a membrane liner is placed on a porous layer (e.g., soil
or ceotextile), the permeability of which can range greatly.
Also, a liner is often covered or becomes covered with soil, sand
or sludge. These materials will tend to retard the transmission
of waste constituents. Thus, the transmission rates indicated in
Table 18, even though very low, may be viewed as representing the
upper limit (worst-case) conditions.
Active gas systems use blowers to collect gas through a
network of extraction wells and/or trenches. The collected gas
is either disposed of by flaring (which may often require the use
of supplementary fuel) or combusted (e.g., in turbines) for
energy recovery. In either case, a high degree of destruction of
toxic organics can be achieved when combustion temperatures are
kept at about 800 C or greater. Carbon adsorption units can in
principle be used in conjunction with both passive and active
systems to remove toxic organics from the landfill gas. However,
as noted in Section 5.2, the reported experience with the use of
carbon adsorption for gas control has been very poor due to
maintenance problems and the difficulty in estimating when the
carbon needs changing or reactivation. When control of the
landfill odor is of primary concern (e.g., in Southern
California), excess air is sucked in through the landfill cover
and this can reduce the heating value of the gas and hence affect
the choice of the energy recovery method (e.g., power generation
in turbines vs. upgrading of gas to pipeline quality).
The technology for gas collection and flaring (and to a
lesser extent, for recovery of energy from landfill gas) are well
established, and a number of manuals and guideline documents are
available covering the design and operation of such systems
(e.g., Refs. 21-23). The detailed application of these techniques
and their economics tend to be highly site-specific, since envi-
ronmental conditions and gas yield vary greatly among landfills
(T.D. No. 16). Gas recovery from landfills, including potential
problems and opportunities, has been the subject of several
recent workshops and symposia (e.g., Refs. 58-60). Much of the
current research and development and full scale testing activi-
ties are aimed at improving energy recovery systems and equipment
designs and identifying potential long-term operating problems
(e.g., equipment corrosion). For example, at Puente Hills LF in
Southern California, where gas is collected and used to generate
82
-------
power serving the electrical needs of approximately 5,600 homes,
two dissimilar turbine designs are under evaluation to determine
comparative performance and reliability in the landfill gas ap-
plication (61). Substantial combustor and fuel systems modifica-
tions were required to allow operation on landfill gas, given
that industrial gas turbines are normally designed to operate on
natural gas, which has three times the heating value of the
landfill gas at Puente Hills.
5.5.2 Surface Impoundments
Although actual data on their extent of use and
effectiveness are not available, there are a number of measures
for reducing SI emissions. These measures, which are described
briefly in Table 19, may be classified as preventive or
corrective depending on whether they are incorporated features of
the original design or are implemented after the problem has
surfaced. Proper siting and source control are considered by
some (see Section 5.4.3) to be the most viable approach for
reducing emissions. Source control involves reducing the
concentration of volatiles in the raw wastewater: or the potential
for their emissions through in-plant controls (e.g.,
process/equipment selection or modification, waste segregation,
material recovery, operating considerations and good
housekeeping) and/or wastewater pretreatment (e.g., via solvent
extraction or distillation to remove VOCs).
Floating covers have been successfully used for water supply
reservoirs (e.g., to reduce high levels of coliform bacteria and
maintain chlorine residuals in the water systems (62). These
covers have recently been considered for use to prevent
overtopping of Sis by rain and snow (16, 63). A range of patented
reservoir cover designs are available (64). Most designs feature
sump systems for collection and removal of precipitation. Figure
10 shows schematics of a simple design, referred to as
"untensioned, centrally floated, peripheral sump reservoir cover"
(or UCFPSR), for a sloped-sided rectangular reservoir. the plan
view shows the network of floats beneath and attached to the
cover (bold line in the center). Usually the central float is
placed down the longest axis of the reservoir, with the parallel
floats running perpendicular from the central float, spaced 20 to
30 ft apart. It is intended that this central portion will form
a series of parallel paths which direct rainwater to the
peripheral space outside of the centrally-floated area and inside
the perimeter of the reservoir. This is intended to form a
peripheral sump between the central float portion and the anchor
means at the perimeter of the reservoir. The cross-sectional
view of this reservoir in Figure 10 shows the UCFPSR Cover as the
reservoir goes from the empty state to the full state, with both
the peripheral sump substantially full (rainwater not removed
from the sump area) and substantially empty. Figure ]_j_ is a
83
-------
TABLE 19.
PREVENTIVE/CORRECTIVE MEASURES FOR VOLATILE EMISSIONS
FROM SURFACE IMPOUNDMENTS
Control Measure
bcscription
Advantages
Disadvantage*
Source Control
Site Location
00
Side
Enclosure (with
or without
add-on vent con-
trols)
Floating Cover
Pretroatmont of waste
segregation to
minimize volatile*
content of Incoming
waste to SI.
Temperature reduction
may also be applicable
for warm Influent.
Locating Sis away from
and/or downwind of
areas with a high
potential for human
exposure (e.g., resi-
dential or light
commercial zones).
Consideration of natu-
ral winds and wind
barriers In selection
of a site.
Rigid or Inflatable
cover over SIi use of
covered tank system.
Blanket of plastic or
other flexible material
suspended on surface of
SI.
Minimizes or eliminates
tho need for add-on
controls. Can be the
most cost-effective
approach In some cases.
Can minimize levels of
toxic substances In
ambient air where per-
sons are exposed. Can
minimile odor complaints.
Emissions aro confined
to air space above liquid
surface and within the
enclosure. .Equilibrium
vapor pressure will bo
approached for volatile
waste compounds, with
little additional vola-
tilization. Source
enclosure of aerated
systems, with control of
overhead gases via
activated carbon or
Incineration offers tho
greatest potential for
volatile emissions re-
duction.
Reduces wind-Induced tur-
bulanco of the SI surface
and decreases area ex-
posed to atmosphere.
Less expensive than
enclosure.
Hot feasible for somo waste streams
and/or somo volatile constituents.
Commonly, easier to Implement at newar
facilities than at older ones.
Hay not necessarily reduce absolute
emissions level*.
Impractical for large Sis. Without
further controls, breathing losses may
occur. Not applicable to evaporation
ponds.
Impractical for large Sis. Covers are
subject to damage by winds. Unless
selected of suitable materials, covers
may also bo subject to degradation by
waste and UV light. Not applicable to
evaporation ponds.
(Continued)
-------
TABLE 19. (Continued)
Control Measure
Description
Advantages
Disadvantages
Surface PI 1ml
Competitive
Solvent Phase
Wind Fences
00
in
Thin floating layer of
Immiscible liquid
(e.g., mineral oil)
placed on SI surface.
Serves as a physical
barrier to volatiliza-
tion.
Mixing an Immiscible
solvent with wasto-
wator.
Wood, plastic, metal,
or vegetative fences
to deflect and/oc dis-
perse winds around an
SI.
Can reduce emissions of
compounds which aro tnoro
soluble In water than in
the film liquid. Not
subject to physical dam-
age as Is a plastic
floating cover.
Can reduce emissions of
compounds which are more
soluble in solvent than
In water. Not subject
to physical damage as la
a plastic floating cover.
Can rcduco wind-induced
turbulanco of the SI
surface. Relatively In-
expensive and maintenance
free. Hay also improve
visual appearance.
Hay not bo offeciva for organic* which
aro more soluble In the organic liquid
than in water. May require separation
of organic liquid from water prior to
discharge. Not suitable for aerated
systems, in heavy winds, or for evap-
oration ponds.
Recovery, treatment and disposal of
solvent which contains volatile com-
pounds may bo required. Forced mixing
may bo necessary to effect extraction
of target organlcs from tha aqueous
phase. Not applicable to evaporation
ponds.
Effectiveness highly site-specific.
-------
ocm v totneii
or tiva
a
uo uit or utncn
fitrr nf
uu IOL *a» a«rvo. natr
A. Plan-view
-(incut, umurti iu* (FM.I or ui
>-3>iiu aur
III* 1L1CI (JI KUI[KO)
j<. nur
B. Cross-sectional view
Figure 10. Schematic of a UCFPSR cover (64)
86
-------
Cu
fa
i'
Air Cumev
Flexible Gu
Figure n. Schematic overview and cross section of a patented
floating cover with gas collection system (63)
87
-------
schematic of a floating cover with provisions for removal of gas
accumulating underneath the cover.
The study referenced above on the applicability of floating
covers to Sis for the purpose of preventing overtopping by rain
and snow included a state-of-the-art review of the floating
covers. The review, which was based on the very limited data
available in the literature, patent descriptions, and information
obtained from several manufacturers and installers of floating
covers, indicated the following (63):
At the present time, Globe Linings has installed
approximately 200 covers while Burke and five other
companies have installed about 100 more. These covers
usually range in size from about 15,000 sq ft to about
700,000 sq ft. Larger covers have been made. One
cover, now under construction in the Los Angeles,
California area, spans 2,000,000 sq ft.
According to industry officials, approximately 80
to 85 percent of all floating covers have been
constructed over potable water reservoirs. The
remaining 15 to 20 percent have been used on
biodegradation facilities, at slaughtering houses, on
chemical treatment ponds, on toxic waste lagoons and on
fish hatchery ponds. The covers for biodegradation
facilities were developed to collect methane gas for
use in boilers or electric generators. Odor control is
the main purpose cited for covering pits at
slaughtering houses. Fish hatchery ponds are covered
to prevent algal blooms which can kill fish. Covers on
chemical treatment ponds and toxic waste lagoons were
used to prevent overtopping due to precipitation. Very
little data were available on the types of chemicals or
facilities involved in covering waste lagoons due to
the proprietary nature of these activities.
The applicability and effectiveness of floating covers and
other controls shown in Table 19 are very waste- and site-
specific. Some measures (e.g., source enclosure or use of
floating covers) would most likely be inapplicable to (or not
economical for) very large impoundments or where Sis are to serve
as evaporation disposal ponds. Also, at the present time there
is very little experience with the use of these systems in full
scale facilities. Moreover, unless the volatile constituents in
the wastewaters are biodegraded or modified, or collected and
destroyed (e.g., via incineration of overhead vapors), the
emissions control for Sis may only serve a temporary purpose and
the problem is accumulated or transferred to some downstream
treatment systems. When the discharge to an SI is on an
intermittent basis (e.g., from batch operation), and depending on
88
-------
the system design, some degree of control may be exercised
through scheduling to avoid discharge or operation under
unfavorable weather conditions. Maintaining aerobic conditions
in some ponds (through supplemental aeration and/or chemical
addition) may also be applicable for odor control at some Sis.
A number of EPA studies are currently in progress to
evaluate emissions control technology needs and effectiveness for
Sis. One study, which involves engineering and economic
analysis of alternative add-on controls, is being carried out by
Arthur D. Little (ADL) Corporation for EPA's Office of Air
Quality Planning and Standards (OAQPS). In another study,
Research Triangle Institute (RTI) is evaluating effectiveness
of wastewater pretreatment as a control method for Sis.
5.6 RESEARCH AND DEVELOPMENT NEEDS
As noted previously, the "very limited actual emissions
monitoring which has been carried out at a number of closed
hazardous waste landfills indicates insignificant emissions from
such sites (certainly in comparison with emissions from waste
treatment and open disposal activities which are part of the
operation at such sites). Similarly, surface impoundment
emissions, which have been measured at only a very few sites,
have been very low, generally near the detection limits of the
sampling and analytical methods used. The representativeness of
the facilities included in these limited surveys is not known.
Thus, establishment of the representativeness of the available
data, which may necessitate emissions measurements at additional
sites, appears to be an area for further R & D.
The need for '-- additional field data was especially empha-
sized by some state agencies with whom technical discussions were
held (see Section 5.2.2). While recognizing the desirability of
developing predictive emissions models for regulatory purposes,
so-ne researchers (e.g., Ref. 65) point out that the models which
have been developed require too many inputs which are difficult
to accurately define and that models (the simple ones) can best
be only used to obtain rough, order of magnitude ideas and hence
R & D effort should place a greater emphasis on collection of
field data than on development of new models or refinement of
models which have been shown to yield estimates differing from
actual measurements by several orders of magnitude. R & D ef-
forts to develop emissions controls for Sis should also emphasize
realistic conditions and testing in large-scale or actual facili-
ties. Source testing to determine emissions and evaluate effec-
tiveness of controls may require further development and refine-
ment of specialized techniques and protocols (e.g., for sampling
emissions from leachate standpipes --see T.D. No. 12).
89
-------
From the standpoint of emitting toxic and reactive sub-
stances to the atmosphere, municipal and co-disposal sites can
conceivably have a. greater total impact on the environment than
'HWLFs. Accordingly, the nature of emissions from the municipal
and co-disposal sites and their air quality significance need to
be assessed (T.D. No. 16). Although some assessments have been
made by the private sector, much of the data base for the asses-
sment is not publicly available. If municipal and co-disposal
landfills are determined to be major emission sources, active gas
extraction may prove the most cost-effective control method. To
promote gas recovery from landfills, it may be necessary to
introduce some flexibility in the existing regulations (see T.D.
No. 16). The kind and extent of necessary regulatory changes
need to be studied.
From a design optimization viewpoint, and in the light of
the data presented in Table 15, parametric evaluation, in full-
scale "real world" facilities, of various cover systems for
landfills from the standpoint of emissions control effectiveness
has been suggested (T.D. No. 4). Parameters to be evaluated in
such studies should include soil type, density, organic content,
moisture level, etc. Such studies can provide the basis for
tailoring cover design and maintenance procedures to specific
locational/geographic requirements (T.D. Nos. 1 and 4). In
connection with cover system design, investigation of the effect
of landfill gas and volatile substances on FML covers has been
suggested as an item for R & D (T.D. No. 2).
Some of the R & D needs discussed in Section 4 in connection
with the leachate management system (e.g., investigation of novel
design concepts, documentation and dissemination of experience
from full scale facilities, better characterization of the type
of wastes which are now sent to disposal facilities and the
expected future trends) would also be applicable to landfill gas
management and are not repeated here. A number of other gas- and
emissions-specific R & D recommendations provided by various
individuals with whom discussions were held in the present study
are as follows:
Investigation of how the refuse mass behaves in the landfill
environment from the standpoint of permeability to gas (T.D.
No. 10).
Evaluation of impact of impurities in landfill gas streams
(e.g., heavy metals and halogenated compounds) on its
potential uses (T.D. No. 3).
Assemblance of information on models that predict gas
generation rates and verification of models using results
from actual field monitoring (T.D. No. 3).
90
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REFERENCES
1. Ghassemi, M., et al. Assessment of Technology for Construc-
ting and Installing Cover and Bottom Liner Systems for
Hazardous Waste Facilities; Volume I--Data Base Development:
Perspectives of Industry Experts, State Regulators, and
Owners and Operators, and Volume II--Technical Analysis.
Final report prepared by TRW, Inc. for EPA under Contract
No. 68-02-3174, Work Assignment No. 109, 1983, 424 pp.
2. Ghassemi, M., M. Haro and L. Fargo. Assessment of Hazardous
Waste Surface Impoundment Technology: Case Studies and
Perspectives of Experts. Final report prepared by MEESA for
the Solid and Hazardous Waste Research Division of EPA's
Municipal Environmental Research Laboratory, Cincinnati,
Ohio, under Contract No. 68-02-3174, 1984, 300 pp.
3. U.S. Environmental Protection Agency. Draft RCRA Guidance
Document: Landfill Design, Liner Systems and Final Cover
[To Be Used with RCRA Regulations Sections 264.301(a) and
264.310(a)], 1982, pp. 12-15.
4. U.S. Environmental Protection Agency. Lining of Waste
Impoundment and Disposal Facilities. SW-870, 1983. 448 pp.
5. McAneny, C.C., et al. Technical Handbook on Design and
Construction of Covers for Uncontrolled Hazardous Waste
Sites. Draft report prepared by U.S. Army Waterways Experi-
ment Station for EPA's Municipal Environmental Research
Laboratory, Cincinnati, Ohio, under EPA Interagency Agree-
ment No. AD-96-F-2-A144, 1984, 706 pp.
6. U.S. Environmental Protection Agency. Handbook: Remedial
Action at Waste Disposal Sites. EPA-625/6-82-006, 1982.
497 pp.
7. Emcon Associates. Technical Manual: Hazardous Waste Land
Disposal/Land Treatment Facilities. Report prepared for the
Department of Army, Huntsville Div. Corps of Engineers,
Project 589-3,1, TM5-814-7, 1983.
8. Arthur D. Little, Inc. Potential Clogging of Landfill
Drainage Systems. Draft report prepared for EPA's Municipal
Environmental Research Laboratory under Contract No. 68-01-
5949, 1983. pp.44.
91
-------
9. Young, C.W., et al. Clogging of Leachate Collection Systems
Used in Hazardous Waste Land Disposal Facilities. Draft
White Paper prepared by GCA Corp. for EPA's Office of Solid
Waste, under Contract No. 68-02-3168, Technical Directive
No. 60-(3), 1982, pp. 68
10. Koch, H.A. Waste Management of Wisconsin, Inc. Personal
communication to Masood Ghassemi of MEESA, October 26, 1984.
11. Water Pollution Control Federation. Operation and
Maintenance of Wastewater Collection Systems, Manual of
Practice No. 7, 1980. 88 pp.
12. Cleary, J. Visu-Sewer, Clean and Seal, Inc. Personal
communication to Masood Ghassemi of MEESA, October 28, 1984.
13. Spigolon, S.J., and M.F. Kelley. Evaluation of Geotechnical
Data used in Construction of Disposal Facilities. Draft
report prepared by the U.S. Army Engineer Waterways
Experiment Station (WES) for EPA's Municipal Environmental
Research Laboratory under Interagency Agreement No. AD-96-F-
2-A077. 1982, 210 pp.
14. Roycraft, P. and J. Sygo. Hazardous Waste Div., Michigan
Department of Natural Resources. Personal communication to
Michael Haro of MEESA, Feb. 1, 1984 and May 1, 1984, and to
Masood Ghassemi of MEESA , October 29, 1984.
15. Menoff, S. Waste Management, Inc. Personal communication
to Masood Ghassemi of MEESA, July 23, 1984.
16. Mason & HangerSilas Mason Co., Inc. Waste Lagoon Spillage
Control System, Phase 1. Lexington, Kentucky, 1983. 34 pp.
17. Surface Impoundment National Report. EPA 570/9-83-002, U.S.
Environmental Protection Agency, Office of Drinking Water,
Washington, D.C., 1983. 84 pp.
18. Durham, J., EPA Office of Air Quality Planning and Standards
(OAQPS). Personal communication with Michael Haro of MEESA,
April 5, 1984.
19. Saito, D. California Air Resources Board, Toxic Pollution
Branch, Source Evaluation Section. Personal communication
with Michael Haro of MEESA, April 20, 1984.
20. Fossa, A. State of New York Department of Environmental
Conservation, Region 9, (Buffalo). Personal communication
with Michael Haro of MEESA, February 2, 1984.
21. Shafer, R.A. et al. Landfill Gas Control at Military
92
-------
Installations. Technical Report N-173. U.S. Corps of
Engineers Construction Engineering Research
Laboratory, Champaign, Illinois, 1984, 42 pp.
22. Ham, R.K., et al. Recovery, Processing, and Utilization of
Gas from Sanitary Landfills. EPA-600/2-79-001, U.S. Envi-
ronmental Protection Agency, Cincinnati, Ohio, 1979, 146 pp.
23. EPA Region VIII. Methane on the Move--Your Landfill Silent
Partner. An Administrative Guide Developed by the
Intergovernmental Methane Task Force.
24. Landfill Gas Emissions Task Force, South Coast Air Quality
Management District. Landfill Gas Emissions. El Monte,
California, 1982. 77 pp.
25. Lytwynshyn, G.R., et al. Landfill Methane Recovery Part II:
Gas Characterization. GRI-81/0105, Gas Research Institute,
Chicago, Illinois, 1982, 144 pp.
26. University of Southern California, Environmental Engineering
Program. Investigation of Odorous and Volatile Compounds
for BKK Class I Landfill Site in the City of West Covina.
Los Angeles, California, 1981, 63 pp.
27. Shen, T. and J. Tofflemire. Air Pollution Aspects of Land
Disposal of Toxic Wastes. ASCE Environ. Engr. Div.,
106(EE1):211-226, 1980.
28. Radian Corp. Evaluation of Air Emissions from Hazardous
Waste Treatment, Storage, and Disposal Facilities in Support
of the RCRA Air Emission Regulatory Impact Analysis (RIA),
Data Volumes for Sites 2, 4, 5 and 6. Draft reports pre-
pared under EPA Contract 68-02-3174. Austin, Texas, 1984.
29. Farmer, W.J., et al. Problems Associated with the Land
Disposal of an Organic Hazardous Waste Containing HCB, Paper
from Dept. of Soil Sci., University of California,
Riverside, CA, July, 1976. In: T. Shen and J. Tofflemire,
Air Pollution Aspects of Land Disposal of Hazardous Waste,
ASCE Environ. Engr. Div., 106(EE1):211-226, 1980.
30. Chou, S.F.J., and R.A. Griffin. Adsorption of PCBs by
Cellulose Fiber Filter Aids and Carbonaceous Adsorbents Used
for Water Treatment. In: Proceedings of the Fourth Annual
Madison Conference of Applied Research and Practice on
Municipal and Industrial Waste, Department of Engineering &
Applied Science, University of Wisconsin Extension,
Madison, Wisconsin, 1981, pp. 238-249.
31. Ase, P.K. Air Pollution Sampling and Monitoring at Hazard-
93
-------
ous Waste Facilities. Draft report Prepared by IIT Research
Institute for EPA Contract No. 68-03-2654, 1981, 295 pp.
32. California Department of Health Services, et al. Ambient
Air Monitoring and Health Risk Assessment for Suspect Human
Carcinogens Around the BKK Landfill in West Covina.
Sacramento, California, 1983, 29 pp.
33. California Air Resources Board. Air Sampling Program, BKK
Landfill. Memo from J. Morgester, Chief of Enforcement
Division to R. Stephens, Deputy Director of Toxic Substances
Control, California Department of Health Services, October
27, 1982. Sacramento, California.
34. California Department of Health Services. Air Monitoring at
Palos Verdes and Puente Hills Landfills. Memo from R.D.
Stephens, Chief of Hazardous Materials Laboratory Section to
J.J. Morgester, Chief of Enforcement Division, Air Resources
Board. May 13, 1983. Sacramento, California.
35. County Sanitation Districts of Los Angeles County. Control
of Infectious, Hazardous and Radioactive Waste Disposal at
Puente Hills Landfill. Whittier, California, 1983, 18 pp.
36. South Coast Air Quality Management District. Public
Hearings on Operating Industries, Inc., Case No. 2121-2.
June 16. 21, 22, 23, 29 and 30, 1983 and July 1, 18, 19, 20,
22, 27, 28, 1983.
37. South Coast Air Quality Management District. Public
Hearings on Operating Industries, Inc., Case No. 2121-1.
March 3, 17, 28, 29 and 31. 1983 and April 5, 1983.
38. Zimmerman, R.E. and M.E. Goodkind. Landfill Methane
Recovery Part I: Environmental Impacts. GRI-80/0084. Gas
Research Institute, Chicago, Illinois, 1981, 91 pp.
39. Treatment and Utilization of Landfill Gas, Mountain View
Feasibility Study. SW-583, U.S. Environmental Protection
Agency, Washington, D.C., 1977, 113 pp.
40. California Air Resources Board. Sampling at Forword, Inc.
Class II-l Landfill in Stockton. Memo from Jannet Munson
and Rich Vincent to Roy Menebroker, January 11, 1984.
Sacramento, California.
41. Emission Calculations, Secure Landfill No. 11, Initial
Active Section, SCA Chemical Waste Services, Inc., Model
City, NY. Material provided by Mr. James Coyle of New York
Department of Environmental Conservation to Masood Ghassemi
of MEESA, May 24, 1984.
94
-------
42. Pena. J.R. Landfill Gas Processing Techniques. Paper
presented at the Eighth Annual Meeting on Energy from
Biomass and Wastes, Institute of Gas Technology, Lake Buena
Vista, Florida. January, 1984.
43. Shen, T. Estimation of Organic Compound Emissions from
Waste Lagoons. J. of the Air Pollution Contl. Assoc.,
32(l):80-82. 1982.
44. Cox, R.D., et al. Evaluation of VOC Emissions from Wastewa-
ter Systems (Secondary Emissions). Draft report prepared by
Radian Corporation under Contract No. 68-03-3-38 for EPA's
Industrial Environmental Research Laboratory, Cincinnati,
Ohio, 1983, 152 pp.
45. Thibodeau, L.J., et al. Air Emission Monitoring of
Hazardous Waste Sites. In: Proceedings of National
Conference on Management of Uncontrolled Hazardous Waste
Sites, Washington, D.C., 1982. pp.70-75.
46. Lurker, P.A., C.S. Clark, and V.J. Elia. Atmospheric Re-
lease of Chlorinated Organic Compounds from the Activated
Sludge Process. J. Water Poll. Contl. Fed., 54(12):1566-
1573, 1982.
47. Petrasek, A.C., et al. Fate of Toxic Organic Compounds in
Wastewater Treatment Plants. J. Water Poll. Contl. Fed.,
55(10)-.1286-1295, 1983.
48. Roberts, P.V. and P.G. Dandliker. Mass Transfer of Volatile
Organic Contaminants from Aqueous Solution to the Atmosphere
During Surface Aeration. Environ. Sci. and Technol.,
17(8):484-489, 1983.
49. Bauer, F. IT Corp. In: Ghassemi, M., M. Haro and L. Fargo,
Assessment of Surface Impoundment Technology, Case Studies
and Perspectives of Experts; (Cited as Ref. 2 above).
50. Lepic, K. Chem. Securities System. Personal communication
with Masood Ghassemi of MEESA, June 15, 1984.
51. Karimi, A.A. Studies of the Emission and Control of Vola-
tile Organics in Hazardous Waste Landfills. Dissertation,
University of Southern California, 1983. 151 pp.
52. Okamura, J.P. and D.T. Sawyer. Gas Chromatographic Studies
of Sorptive Interactions of Normal and Halogenated Hydrocar-
bons with Water-Modified Soil, Silica, and Chromosorb W.
Cited in: Duncan, M., H.L. Bohn and M. Burr, Pollutant
Removal from Wood and Coal Flue Gases by Soil Treatment, J.
Air Poll. Contl. Assoc.. :1175-1179, Nov. 1982.
95
-------
53. Haxo, H.E. et al. Permeability of Polymeric Membrane Lining
Materials for Waste Management Facilities. Paper presented
at the 126th Meeting, Rubber Division, American Chemical
Society, Denver, CO. October 23-26, 1984.
54. August, H. et al. Study of the Permeation Behavior of
Commercial Plastic Sealing Sheets as a Bottom Liner for
Dumps Against Leachate, Organic Solvents, and their Aqueous
Solutions. Report prepared by Bundesanstalt fur
Materialprufung (BMA), Labor 3.12 "Physik und Technologie
der Kunststoffe", Unter den Eichen 87, D-1000 Berlin 45,
Report No. 103 02 208, March 1984, 108 pp.
55. Van Huit, R.E. Recovery of Decomposition Gas from
Landfills, paper presented at the 1980 ASCE Annual
Convention, Hollywood-by-the-Sea, Florida, Oct. 30, 1980.
56. Los Angeles County Sanitation Districts. . Draft Environmen-
tal Impact Report, Puente Hills Landfill, 1982, 317 pp.
57. Lu, J. (Los Angeles County Sanitation Districts). Landfill
Gas Recovery in Horizontal Trenches. Personal Communication
with Masood Ghassemi of MEESA, May 9, 1984.
58. GRCDA 7th International Landfill Gas Symposium, Piscataway,
New Jersey, April 11-13, 1984.
59. GRCDA 6th International Landfill Gas Symposium, Industry
Hills, California, March 14-18, 1983.
60. Methane from Landfills: Hazards and Opportunities, EPA
Symposium, Denver, Colorado, March 21-23, 1979.
61. Carry, C.W., et al. Turbines Produce Energy from L.A.
Landfill. World Wastes, 27(6):12-13, 1984.
62. Kittredge, D. Performance of Flexible Membrane Floating
Covers. In: Proceedings of the International Conference on
Geomembranes, Industrial Fabric Association International,
Denver, Colorado, June 20-24, 1984. pp. 85-88.
63. Evans, M.L. and J.P. Meade. Floating Cover Systems for
Waste Lagoons: Potential Application at the Old Linger
Site. Draft report by JRB Associates under Contract No. 68-
03-3113 for EPA's Oil and Hazardous Materials Branch,
Edison, New Jersey, 1984, 75 pp.
64. Gerber, D.H. Floating Cover Reservoir Designs. In:
Proceedings of the International Conference on Geomembranes,
Industrial Fabric Association International, Denver,
Colorado, June 20-24, 1984. pp. 79-84.
96
-------
65. Shen. T. (Div. of Air Resources. New York Dept. of
Environmental Conservation, Albany, New York). Personal
communication with Masood Ghassemi of MEESA, April 20, 1984.
66. Shultz, D.W., Duff, B.M. and Peters, W. Performance of an
Electrical Resistivity Technique for Detecting and Locating
Geomembrane Failures. In: Proceedings of the International
Conference on Geomembranes, Industrial Fabric Association
International, Denver, Colorado, 1984. pp. 445-449.
67. System Detects Leak in Liquid Impoundments. Chem. & Eng.
News, July 16, 1984, p. 30.
68. New Way to Find Leaks in Landfills. Chem. Eng., August 6,
1984, p. 29.
69. Waller, M.J., and R. Singh. Leak Detection Techniques and
Repairability Options for Lined Waste Impoundment Sites.
In: Proceedings of the National Conference on Management of
Uncontrolled Hazardous Waste Sites, Hazardous Materials
Control Research Institute, Washington, D.C., 1983, pp.
147-153.
70. Davis, J.L., et al. Innovative Concepts for Detecting and
Locating Leaks in Landfill Liner Systems: Part I--Acoustic
Emission Monitoring, and Part II--Time-Domain
Reflectometry. Final reports prepared by EarthTech
Research Corporation (Baltimore, MD) for EPA under Contract
No. 68-03-3030, Sept. 1981.
71. Cooper, J-.W., and D.W. Shultz. Development and Demonstra-
tion of Systems to Retrofit Existing Surface Impoundment
Facilities with Synthetic Membrane. In: Proceedings of the
National Conference on Management of Uncontrolled Hazardous
Waste Sites, Hazardous Materials Control Research Institute,
Washington, D.C., 1982. pp. 244-248.
72. Larson, R.J., and J.H. May. Geotechnical Aspects of Bottom
Sealing Existing Hazardous Waste Landfills by Injection
Grouting. In: Proceedings of the First Annual Hazardous
Materials Management Conference, Tower Conference Management
Company, Philadelphia, Pennsylvania, 1983. pp. 513-529.
73. Technologies and Management Strategies for Hazardous Waste
Control. OTA-M-196, Congress of the United States, Office
of Technology Assessment, VJashington, D.C., 1983, 407 pp.
74. Lutton, R.G., G.L. Regan, and L.W. Jones. Design and Con-
struction of Covers for Solid Waste Landfills. U.S.
Environmental Protection Agency, Cincinnati, Ohio, 1979.
249 pp.
97
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APPENDIX A
TECHNICAL DISCUSSION (T.D.) REPORTS
A.I TECHNICAL DISCUSSION NO. 1
Sanitation Districts of Los Angeles County: Raymond Huitric
James Lu
MEESA: Masood Ghassemi, Michael Haro
April 13, 1984
Leachate Collection
Because of the unique features of the six landfills under
the jurisdiction of the County Sanitation Districts of Los
Angeles County * (hereafter referred to as the Districts),
and the special strategy which the Districts uses to
minimize leachate generation (see below), no leachate has
been observed in any of the leachate collection systems for
these landfills. Some liquids which have been noted are
believed to be perched or spring water which has been
intercepted. Because leachate collection systems do not
carry leachates and are employed primarily as a
precautionary measure. no problems have been noted or are
anticipated with the leachate collection systems at the
Districts' facilities. Such problems are more
characteristics of the sites in the East and ^hose not
governed by strict regulations on waste handling and
placement practices. There have been some occasional
problems with the accumulation of silt/sand in the
collection wells. But the problem has been easily corrected
through simple cleanout of wells.
The landfills under the Districts' jurisdiction are very
unique from the standpoint of location, topography and
climate (i.e., the low precipitation and high evaporation
* The six~Districts' landfills are Calabasas, Mission Canyon,
Palos Verdes, Puente Hills, Scholl Canyon and Spadra. Of
these, only Palos Verdes (now closed) and Calabasas sites
have received hazardous wastes and are co-disposal sites.
Calabasas site no longer accepts hazardous waste and is now
a strictly municipal waste disposal site. The other four
are considered municipal refuse sites.
98
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rates, the significant distance to ground water and disposal
in canyons/ravines as opposed to in excavated land or on
flat ground). Because of these features, it is possible to
prevent leachate formation at these sites. To achieve this,
the Districts rely on the following strategy:
-Use of french drains to intercept subsurface drainage
(i.e., perch water or spring water). In newer designs, a
double drainage system (see Figure 12 ) has been employed to
intercept the spring water or perch water (which, inciden-
tally, can exert a significant pressure on the liner) and to
remove any leachate. Both drain systems are connected to a
single collection pipe which discharges into public sewers.
-Use of leachate barriers and extraction systems in conjunc-
tion with french drains to intercept any leachate formed.
-Limiting liquids and dewatered sludge disposal in land-
fills. In the past, liquids were accepted at some
landfills (e.g., Palos Verdes) to the extent that the amount
admitted would remain far below the absorptive capacity of
the refuse. (This previous approach can still be utilized
when a liquid waste is solidified or mixed with absorbents).
-Designing, constructing and maintaining covers which mini-
mize infiltration.- Although a material with a permeability
of 10 to 10 cm/sec is considered suitable as cover
material, the permeability is viewed as only one of the
several factors which determine the effectiveness of a cover
design. Other factors include thickness of the cover and
climatic conditions, which should be considered in a water
balance analysis to determine optimum design. TheRcover at
the Palos Verdes landfill consists of 5-ft. of 10 to 10
cm/sec permeability clay. There is a temporary irrigation
system which can be removed when appropriate vegetation
cover has been established.
-Because California conditions and vegetations are different
than those elsewhere, specific cover maintenance procedures
developed elsewhere would not be applicable here. Accord-
ingly, the Districts has a plan to undertake a 1 to 2 year
field study to determine the type of vegetation and irriga-
tion system which can maintain a cover, but yet prevent
water percolation into the waste fill.
There is little guidance on leachate drainage system design
in the open literature.
Gas Control
The Districts has been the pioneer in extracting gas from
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o
o
Figure 12. Sketch showing the use of a double-drainage system for leachate
collection and interception of perched or spring water
-------
landfills and all six Districts' landfills have or soon will
have (by year end) gas collection systems.* By maintaining
a vacuum in the collection system and designing a collection
system of sufficient extent, an active gas control system
would minimize atmospheric emissions. This was verified in
a recent study for EPA by the Illinois Institute of Techno-
logy Research Institute (IITRI). The study involved air
pollution sampling and analysis at hazardous waste facili-
ties which included some of the Districts' sites. The
collected data could not distinguish between upwind and
downwind conditions.
The gases recovered from Districts' sites are either flared
or used as energy source. When the gas is flared, any
volatile organics in the gas are destroyed. Current flare
systems at the Districts' sites operate at a temperature of
close to 1300 F; planned design modifications will increase
the flare temperature to 1400 to 1500°F. At these
temperatures, there should be little or no emissions of
reactive organics. Emissions of halogenated organics is
also not expected to be a problem and the emissions meet
applicable Air Quality Management District emissions
regulations. When the gas is used in turbines, corrosion
can be a problem of concern which has to be mitigated
through proper design (e.g., use of appropriate alloys or
coatings) or via gas pretreatment. At the Palos Verdes
landfill, the recovered gas is used in turbine for power
generations. In a separate operation at this site, Getty
Synthetic Fuels, Inc. uses activated carbon and molecular
seive adsorption systems as part of a gas treatment system
to produce substitute natural gas (SNG).
Typical gas collection systems designed by the Districts in
the past consisted of vertical wells and collection pipe-
lines located in completed sections of the landfills. This
approach avoids operational conflicts at the active landfill
site. However, collection systems installed after comple-
tion of landfilling cannot prevent escape of odor during the
operating life of the landfill. In addition, energy that may
be recovered from landfill gas generated prior to completion
of the landfill is lost. These two concerns are eliminated
by use of a horizontal trench gas recovery system which has
been developed and tested by the Districts. The new system
consists of a network of pipelines laid horizontally in
trenches within the buried solid waste and backfilled with
one to two-inch size gravel. These trenches are constructed
in the fill as the waste is placed, or shortly thereafter.
Gas collection systems for Calabasas and Spadra sites are
under construction.
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thereby providing odor control (and energy recovery) prior
to completion of the fill.
A vertical trench interval such as 80 ft and a horizontal
trench interval such as 300 ft are being considered for
installation at the Puente Hills landfill. The pipelines
will be installed with frequent slip points to allow for
settlement. Gas will be withdrawn from surrounding waste
after a lift (18- to 25-ft layer) of waste is placed over
the trench system. The pipes within the gravel trenches
will be connected to header collection pipelines located
along the outside slopes of the landfill. These pipelines
will deliver gas from the trenches to the energy generation
facilities and/or flaring stations. The construction of the
trench system is coordinated with and part of the daily
landfill operation..
Properly designed and constructed soil covers can be effec-
tive in preventing landfill emissions. The available infor-
mation indicates that both adsorption and biological activi-
ty in the soil are responsible for emission control. At its
Palos Verdes landfill, the District has made numerous odor
measurements and has determined several orders of magnitude
reduction in the odor as the gas passes through the cover.
The reduction in odor is believed to be due to aerobic
biological activity within the cover.
Waste Handling
Suitable waste handling and placement procedures (e.g.,
waste segregation, removal of incompatible wastes, etc.) and
appropriate methods for ensuring compliance with these pro-
cedures (e.g., use of on-site inspectors and radiation moni-
tors, manifest system, laboratory testing of randomly selec-
ted samples, etc.) have been well developed and extensively
discussed in the literature.* Waste placement practices,
however, can impact air emissions control and leachate man-
* For example, the following documents include discussions of
waste handling and inspection procedures and the results
from such effort:
-"Control of Infectious, Hazardous and Radioactive Waste
Disposal at Puente Hills Landfill", a report summarizing the
Districts 'effort at the subject site, dated Dec. 2, 1983.
-Van Heuit, R. E., "Disposal of Hazardous Waste and Indus-
trial Residues in Sanitary Landfills", paper presented at
the California Water Pollution Control Association, Southern
Reg. Ind. Waste Conf., Airport Marina Hotel, Dec. 9, 1976.
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agement effort and for the purpose of our study should
receive attention in that context.
In the past, waste solvents were segregated and separately
disposed of in the Palos Verdes landfill using injection
wells. This approach, however, is no longer considered
suitable and is not practical at any of the Districts'
sites, as it is felt that solvents will gradually volatilize
from the landfill and it is better to dispose of them by
other means (e.g., incineration or reclamation). Emissions
resulting from past solvent injection practices are mini-
mized by use of gas extraction systems.
Miscellaneous
The issue of liner-waste incompatibility has been somewhat
blown out of proportion by results from studies which have
used test solutions (e.g., pure organic solvents) having
little resemblance to wastes and leachates which actually
come in contact with the liner in a "real world" facility.
At the Districts' sites, there is very little chance for a
waste solvent" to come in contact with the liner, since there
is a 25-ft. depth of fill (refuse) before any hazardous
waste is placed in a landfill; any hazardous waste released
will be absorbed by the 25-ft. depth of fill. The leachate
(if any) which may reach the liner is also a very dilute
aqueous solution containing organics in the ppm levels.
A.2 TECHNICAL DISCUSSION NO. 2
CH2M-Hill Larry W. Well
MEESA: Masood Ghassemi, Michael Haro
16 April 1984
(Note: Mr. Well is a recognized expert on liner
design. At CH2M-Hill he functions as a "consultant",
providing advice on matters relating to liner design
and placement. Accordingly, much of the discussion
with Mr. Well centered on various aspects of liner
design, installation and performance.)
Leachate Collection
Mr. Well personally is not aware of any leachate collection
system that has been clogged.
The best way to manage leachate is to prevent its formation
through proper site design and operating procedures.
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Most solvents are lighter than water and would not enter the
leachate collection system as distinct phases. However, at
the present time little is known about emulsion formation in
the leachate and what levels of emulsions can be tolerated
by the system.
PVC pipes have been widely used in leachate collection
systems because they are easier to work with and cost less
compared to materials such as polyethylene which may have
the advantage of being somewhat more resistant to chemical
attack.
Gas Control
When gas is to be contained (for recovery or odor control)
through installation of an FML cover, PVC may not be the
ideal cover material because of its potential susceptibility
to chemical attack. In this respect, HOPE may be a pre-
ferred material due to its greater inertness. HOPE, how-
ever, is more difficult to work with and throughout the
country there are perhaps only a handful of installers who
can be trusted to do a good job of installing HOPE. CH2M-
Hill has successfully used HOPE in a ]ob in Idaho involving
recovery of methane (and control of odor) in anaerobic
digestion of potato processing waste.
Waste Handling and Placement
Segregation of waste in subcells is very important from the
standpoint of developing the best design and for operation
control.
There is no practical way to exert complete control over the
actual disposal operation to ensure that restricted wastes
are not accepted and that appropriate waste segregation and
placement practices are followed. Use of manifests, inspec-
tion, and random sampling, although very effective, are not
100% fool-proof. Accordingly, it is best "to plan for the
worst and hope for the best".
Leak Detection and Liner Repair
Compartmentalization of operation and designs which provide
for separate leak detection systems for individual compart-
ments or subcells, can conceivably allow for the identifica-
tion of a leaking subcell so that corrective measures can be
limited to a smaller area rather than a very large cell or
entire landfill. This, however, is not very practical for
large landfills where cells and subcells would also be very
large. Even if a leak is detected in a large facility, it
would be prohibitively expensive to remove the waste in
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order to mend or replace the leaking liner. The design
approach, however, is practical on a small scale and has
been used by CH2M-H111 at a unique facility in Times Beach,
MO for containment of PCB-contanimated soil. (The Times
Beach facility has a 240 ft by 400 ft concrete floor, 14-ft
concrete walls, spray-on membrane on top of concrete and
polyurethane spray/foam on top of the membrane; the storage
site has been subdivided into several cells, with each cell
provided with its own leak detection system.
Assuming that the leaks can be located, leak repair success
depends on a number of factors such as type and age of liner
and environment to which the liner has been exposed. For
example, because Hypalon cures as it ages, it is not possi-
ble to properly patch a very old Hypalon liner; for a system
which is only about one or two years old, it is possible to
scrub the liner to get to the uncured material and thus
obtain a good seal. HOPE, on the other hand, does not
suffer from this aging problem.
In inspecting and accepting a completed liner, it is virtu-
ally impossible to detect all leaks (unless they are major
ones) through standard tests such as measurement of evapora-
tion rates for use in water balance calculations. Inspec-
tion of the entire subsoil for "soft spots" is also imprac-
tical. Thus leak detection is very difficult even in clean
systems, let alone for liners used in waste management
applications. The best approach would thus be to strive for
developing a leak-proof system in the first place. A rigo-
rous QA/QC program, which includes use of reputable instal-
lers and third party inspection employing thorough and con-
scientious inspectors, is very essential in achieving an
adequate installation. There are a large number of docu-
mented cases of liner leakage due to the owner "overtrust-
ing" the installers and not carrying out an independent
inspection.
There has been some R&D work in Europe on potential animal
damage to liners. Results indicate that PVC is possibly
more susceptible to damage by rodents than an 80- to 100-
mil HDPE. Apparently the odor of the new PVC liner is
attractive to rodents. Burrowing animals are known to dig
through concrete, and hence potential for similar damage to
FML remains.
Miscellaneous Cover/Liner Considerations
Use of FML instead of clay in some locations is dictated by
economics. In certain geographic areas and at specific
sites it may be too expensive to bring in clay or other
specialty products such as bentonite. Sites with adequate
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in-situ clay are not very plentiful in the Northwest or in
many western states (e.g., CA, OR, WA, UT, and AZ.). Also,
clay may often be more difficult to work with; after a rain,
clay may not be workable for sometime, whereas FML can be
reworked as soon as the weather improves.
For certain liners clean water can present a harsher envi-
ronment -than waste or leachate. For example, loss of plas-
ticizer from PVC (due to leaching) is believed to be more
pronounced in a clean water environment. Data from sewage
ponds lined with bentonite clay appear to indicate an in-
crease in liner permeability over time, probably due to the
ion exchange effect whereby the sodium ions in the bentonite
are replaced with the calcium and magnesium ions from the
waste.
Potential failure of the cover due to differential settle-
ment is of greater concern than failure due to broad, uni-
form settling, as the latter can be adequately addressed in
the design. Even if the liner can elongate 500% to 800%
without failing, this extent of elongation may not be suffi-
cient to absorb impact due to a major localized subsidence.
Recent studies have shown the coefficient of friction of
some FML materials like HOPE is low. This limits the place-
ment of protective soil cover, as in landfill, to shallow
slopes.
One possible solution to the problem of keeping FMLs on
slopes in high-wind areas is to put air vents on slopes.
When the wind blows across vents, it creates a negative
pressure under the liner and theoretically should hold the
liner on the slope.
Puncturing holes in liner "bubbles" which may appear in
certain poorly-designed impoundments is not a corrective
measure; such an action will not cause the raised liner to
settle to its original position and will only further damage
the liner. The volume under the bubble is largely liquid
and may contain only a few percent gas.
The experience with the use of FML in waste disposal appli-
cations is not very extensive. There have been major design
errors in the past (e.g., not providing a protective cover
for PVC liners), but the designers have learned from past
mistakes and errors occur less frequently now than in the
past. The pouring of concrete is a practice which is sev-
eral centuries old, but still mistakes are made once in a
while, producing a bad batch of concrete.
CH2M-Hill has made a large number of liner installations for
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"clean" systems. Many of these installations have been in
service for more than several years and the experience with
them has been very good.
R&D Needs
Evaluation of the use of geotextiles as a component of the
leachate collection system and development of design
criteria for such an application.
Studies of the effect of landfill gas and volatile waste
components on FML covers.
Evaluation of the effectiveness of various methods (e.g.,
inducing ground vibration) for control of burrowing animals
in the vicinity of lined facilities.
Better method to measure leakage or leak test a completed
facility.
A.3 TECHNICAL DISCUSSION NO. 3
CH2M-Hill M. Kennedy
MEESA: M. Ghassemi, M. Haro
17 April 1984
Leachate Collection
Because there is no long-term experience with leachate col-
lection systems for hazardous waste management applications,
there are little data available to evaluate the performance
of these systems. There is no clear definition of what
constitutes clogging or a standard method for measuring
leachate head, which has been used as an indicator of
leachate collection systems' performance. Accumulation of
leachate in the collection sump is not conclusive evidence
that the system is functioning properly, since it provides
no information on the rate of leachate flow. When the
pattern of leachate flow has been well established over a
long period of time, a substantial reduction in flow can be
interpreted to indicate system clogging. The most direct
method for assessing the system performance is perhaps
through excavation and direct observation of the conditions
of the lines and sand and gravel envelopes; this, however,
is not a practical approach and could be very costly.
Although we know, based on experience with sewer lines and
agricultural drainage systems, how to clean up leachate
collection pipes when there is major clogging, and the
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designs provide for such cleanup contingencies, there is
currently no practical way to clean up drainage envelopes
consisting of sand, gravel, and/or stone if and when they
become clogged. It would be very costly to replace the
drainage media in a hazardous waste site. Excavation in a
hazardous waste can also be very dangerous. There is no
practical and economical method to replace even the piping
system in a landfill which contains a substantial amount of
waste. Thus, the only workable approach is thorough preven-
tive measures such as incorporation of redundancies in de-
sign and execution of rigorous QA/QC during all steps lead-
ing to the development of a completed system (e.g., during
construction, thorough inspection to ensure use of specified
drainage aggregates, pipe slope, field tests, etc.).
The conservative design philosophy and incorporation of
redundancies in the leachate collection system is best
illustrated in the following system designed for a commer-
cial hazardous waste disposal firm by CH2M-Hill. This
secure landfill, located in the Northwest, is situated 200
to 300 feet above the uppermost aquifer in low permeability
soil; the average annual rainfall is 7 inches. Although
design calculations indicated little leachate production
could be expected, it was nevertheless designed for a worst-
case scenario of 7 inches of rain occurring in a one-month
period. The leachate collection system is designed to allow
up to a maximum of 0.8 feet of head on the liner. The
system consists of a 12-inch sand layer, a geotextile for
separation, a 12-inch drain rock layer, 4-inch diameter
perforated HDPE collector pipe, 6-inch diameter perforated
HOPE header pipe, and leachate collection sumps, all over an
HDPE and clay liner system. The header and collection pipe
have a minimum slope of 2%; cleanouts are provided at the
ends of each pipe and in the sumps.
Gas Management
The most relevant CH2M-Hill experience with gas management
problems is with a municipal landfill site in Oregon City,
Oregon, where there were considerable odor complaints.
Based on experience at other problem sites, collection and
combustion of the gases was considered the most effective
way of controlling the odors. The cause of the odor problem
was determined to be due to: 1) the disposal of sulfur-
laden sludge; and 2) the saturated condition of the landfill
cells (i.e., situated in the water table) leading to rapid
biodegradation of the wastes.
R&D NEEDS
Evaluation of the relationship between leachate collection
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system design and operation in the context of overall site
management.
Evaluations of the impacts of impurities in landfill gas
streams (e.g., heavy metals and halogenated compounds) on
its potential uses.
Assemblance of information on models that predict gas
generation rates and evaluation of models using results from
actual field monitoring.
Assessment of the applicability of sewer pipeline design,
construction and maintenance methods to the leachate
collection systems in hazardous waste landfills.
A.4 TECHNICAL DISCUSSION NO. 4
Lockman and Associates: J.Johnson, W. Lockman, R. Lofy
MEESA : M. Ghassemi, K. Crawford
April 23, 1984
Leachate Collection
The clogging of the leachate collection system (including
the sand and gravel filter media) has been a recurring
problem at one landfill which Lockman and Associates is very
familiar with. This, however, is a very unique site from
the standpoint of the type and variety of the wastes han-
dled. The split between "hazardous" and "non-hazardous"
wastes at this site is about 33% hazardous to 67% non-
hazardous. About 50% by weight of the waste is inorganics
and water (the other 50% of the waste is oily organics).
The wastes include about 30% liquid wastes and cover a
spectrum of industrial wastes. The clogging appears to be
due to chemical deposition and solidification. It is very
non-systematic in that it occurs only at certain locations
while other locations within the same cell perform satisfac-
torily. The problem thus appears to be related to the
variations in the type of waste handled and hence in the
leachate characteristics. At this particular site, the
corrective measures have included total replacement of sec-
tions of the leachate collection system. In general the
clogging potential can be minimized or mitigated through
proper design to include redundancies in piping, use of
suitable sand/gravel gradation for the filter medium, and
allowing provision for easy access to the piping system for
cleaning.
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Gas Mitigation Control
Considerable gas composition data which have been reported
in the literature indicate no substantial differences in the
composition of gas from conventional municipal refuse sites
and the gas from co-disposal sites which also accept hazar-
dous wastes. In general, the amount of hazardous wastes
accepted at co-disposal sites is very small relative to the
total waste volume.
The limited number of landfill emissions studies which have
been conducted in recent years indicate that such emissions
are primarily related to open disposal activities and impro-
per waste handling.
Emissions from landfills can be effectively controlled via
appropriate waste segregation/handling and through proper
design including adequate cover, venting/flare systems, and
active gas controls. Banning highly volatile wastes from
landfills can reduce potential for emission of volatiles.
Some industrial wastes contain significant amounts of vola-
tiles which can even be reclaimed for reuse.
Although a soil cover of three feet, which is required per
regulations, may not be adequate to control emissions, in-
creasing the depth of the soil cover would increase the gas
pressure and hence the potential for lateral migration and
venting through cracks and discontinuities. Depending on
the availability of cover soil, the cost of placing a very
thick soil cover (e.g. up to 6 feet) may be less than that
of using flexible membrane liners (at least in the Southern
California area). Soil cover generally acts as an adsorption
system, and unless there is active biological activity in
soil, its adsorption capacity will be eventually exhausted.
Presence of organics and biological seeds in the soil can
promote establishment of a biological "filter" which will
effect actual removal of the gas constituents. The Los
Angeles County Sanitation Districts have reportedly
experimented with the use of sewage sludge in the soil cover
or as a refuse cover underneath the soil cover to promote
biological activity for emission control.
Where landfill gases are flared, effective destruction of
organics are achieved due to the high temperature and the
modern flare designs. The concentration of troublesome
combustion products (e.g., HC1) is very small and of no
significance to the flare system or the environment. Actual
measurements of emissions from these flares in the Los
Angeles area has indicated compliance with the very strict
requirements of the Air Quality Management District (AQMD).
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Considerable material compatibility problems have be^ expe-
rienced at a number of sites with active control systr-w* for
gas recovery. Extensive corrosion of the equipment n< one
site resulted in the use of a glycol gas pre-cleaninc; nygte;?
to remove condensate (and C02). In one application the
problem was mitigated by keeping the gas hot to jn ovent
condensate formation.
At least in the dry climates such as in the Southern Cali-
fornia area, underground fires in the landfills arc a rule
rather -than an exception. The heat from such fires can
increase volatilization and hence the potential for emission
of hazardous air pollutants. The fire and heat have been
shown to cause collapse of the gas collection pipes and
perhaps can also be detrimental to the leachate collection
system pipes and plastic material used as cover or bottom
liners. The gas and leachate collection systems, which can
act as conduits to provide air, can actually promote under-
ground fires.
Although there has been some consideration to using hori-
zontal trenches for gas recovery (instead of vertical
wells), such systems would be subject to damage due to
subsidence and waste/equipment load. The advantage claimed
for the horizontal gas collection trench system, which would
be installed at various layers as the filling proceeds, is
that the gas recovery operation does not have to await
completion of the filling operation. Los Angeles County
Sanitation Districts reportedly have experimented with the
horizontal gas collection system.
R&D Needs
Parametric evaluation, in full scale "real world" facili-
ties, of various cover systems from the standpoint of
emissions control effectiveness. Parameters to be evaluated
can include soil type, density, organic content, moisture
level, etc.
Assessment of various configurations for gas/leachate
collection systems including some novel designs which would
facilitate system maintenance. It is very conceivable that
a single system can be provided for simultaneous collection
of both gas and the leachate. Design engineers should be
more willing to investigate new design approaches and
environmental/regulatory agencies should actively promote
investigation of novel designs.
Investigation of differences in geographic and local
conditions which necessitate differences in site design and
flexibility in regulatory requirements. For example, the
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landfills in Southern California are largely canyons that
have been or are being filled and the very steep canyon
walls defy any regulatory requirement for
placing/maintaining cover on the liners.
A.5 TECHNICAL DISCUSSION NO. 5
Maryland Dept. of Health and Mental Hygiene: R. Beyer, W. Bonta
L. Martino, R. Rosnick
MEESA: M. Haro
24 April 1984
Leachate Collection
The state has no direct experience with the leachate
collection systems which have been engineered in the
original design of hazardous waste landfills. Some
experience, however, is available on retrofitting older
sites with leachate collection systems, somewhat as a
reparative and remedial action measure.
At two older hazardous waste landfills in Maryland, the
completed cells have been retrofitted with leachate collec-
tion systems, in order to facilitate leachate collection and
removal. At one site, a number of deep (40 to 80 ft) stand-
pipe wells were drilled at the low points in the large cells
and were subsequently backfilled with drain rock. Leachate
drainage is by gravity flow through the waste to the sumps.
The drain rock in the standpipes is slowly filling with
fines and will eventually clog the system. Due to the large
size of these particular cells, trench excavation for place-
ment of leachate drainage lines was not considered feasible
and construction of addtional standpipes was considered cost
prohibitive. Thus, this case shows from a corrective meas-
ures standpoint that retrofitting a collection system, once
the original system fails, is not practical especially for
landfills with large cells. At the other site, old chrome
ore tailings cells were retrofitted with leachate collection
systems for leachate removal and reuse by the generator.
Initially, the owner attempted horizontal drilling into the
cells. This method proved unsuccessful because of difficul-
ties and delays in drilling through the sandy tailings which
tend to cement together over time. Leachate collection
lines were finally installed by open cut trenching and
laying of PVC pipe every 100 feet and backfilling with drain
rock. As far as can be determined, this collection system
has performed adequately for a number of years.
Not all hazardous landfills can be safely retrofitted with
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leachate removal systems, due to the potential risks and
safety problems associated with drilling and excavation in
such landfills. At the particular facility cited above, the
owner was able to install retrofits because of the certainty
regarding the nature and the inertness of the waste.
V>'aste Handling
In general, the potential for problems stemming from waste
incompatibilty is greater at commercial sites than at on-
site facilities, because of the greater variety of wastes
received at commercial sites and the lack of detail
familiarity of the site operator with the characteristics of
the various wastes received.
In reviewing TSDF permit applications, the permit review
team relies on the waste compatibility guide in 40 CFR 264
to identify possible waste incompatibility problems. At the
recently closed commercial disposal site, waste incompatibi-
lity problems usually occurred during placement of the waste
if the generator failed to properly identify the nature of
his waste before shipping it to the site.
To reduce the possiblity of transporting waste off-site, the
state requires a truck wash facility at all commercial
TSDFs.
Gas Management
Gaseous emissions from TSDFs are not a significant problem
in Maryland primarily because most of the volatile organic
wastes generated in the state are shipped out of state for
disposal or are recyled. The Air Programs Branch depends on
inspectors from other departments (e.g., RCRA inspectors)
and the public to notify them of any odor or toxic vapor
problems at a particular site. Few odor/gas complaints are
received primarily because most TSDFs are located away from
residential areas.
A.6 TECHNICAL DISCUSSION NO. 6
Maryland Environmental Service: David R. Foster
MEESA: Michael Haro
25 April 1984
Background
Maryland Environmental Service (MES) is a nonprofit public
corporation .that operates a number of state and public waste
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treatment facilities in Maryland. One such facility is the
Hawkins Point Hazardous Waste Landfill in Baltimore. The site
was originally started under Maryland Port Authority (MPA). In
1975, MPA put chrome tailings in a section of the site. (Pre-
viously the chrome tailings were used as a fill material in the
Baltimore area.) MES has developed plans and detail designs for
expanding the operation at the site and has applied for a permit
to carry out the proposed expansion. This technical discussion
reviews the background and the design philosophy for site expan-
sion with special emphasis on areas of interest to this project.
Figure 13 is the map of the Hawkins Point Landfill, showing
six areas which the site would be divided into under the ultimate
site development plan. Under this plan, "Area 3" will provide
for containment of general hazardous waste whereas "Area 5" will
be used for disposal of chrome tailings waste. Chrome tailings
wastes have been previously disposed of in both of these areas.
In Area 5, three below grade cells were also filled with chrome
tailings. These cells and the disposal site in Area 3 repre-
sented the existing landfill under RCRA Part A Interim Status.
Because of limited availability of land, the proposed expansion
plans call for expanding Areas 3 and 5 in the vertical direction
by building up vertical lifts/cells above grade.
The first above ground cell ("Cell 40") is already in place
in Area 3. It has an HDPE-clay composite liner and a leachate
collection system. Additional cells to be constructed on top of
Cell 40 will be lined on the interior side slopes with HDPE-clay
composite liner. These cells will not have individual leachate
collection systems and their leachates will be removed via the
collection system for the bottom cell (i.e., Cell 40). Three
above ground cells have already been constructed in Area 5.
These bottom cells do not have a composite liner or a leachate
collection system similar to those for Area 3 and are only lined
on the sides with HOPE. The older (bottom/below ground) cells in
both Areas 3 and 5 have been retrofitted with leachate collection
systems which discharge to separate collection header pipes.
Basis for Liner Selection
Cells of the Part A landfill expansion were originally
designed with a clay liner only; however, after RCRA land
disposal regulations were published in July, 1982, the
design was changed to include an FML as a part of the liner
system (this was not an immediate technical requirement
but it provided an example for private industry to follow).
A clay-FML liner system was considered superior to either
clay or FML alone, as such a composite system would
compensate for the shortcomings of the individual liner type
and would take advantage of the desireable characteristics
of both systems. Of particular concern here was the
114
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\ AREA « /
V\ J'WEDGE"! ./
Figure 13. Area location map for Hawkins Point Landfill
-------
reported literature data which indicated adverse impact of
certain chemicals on clay permeability and the difficulties
in installing a leak-proof FML.
The selection of an 80-mil high density polyethylene (HOPE)
liner for the expansion cells was based upon the following:
1) the reported satisfactory operational experience with
this material at other hazardous waste landfills in the
Northeast; 2) the versatile, inert, puncture resistant and
elongation properties of this particular FML; and 3) the
state's role in setting high standards for industry in
Maryland.
Having the best possible containment system, and not neces-
sarily the cost, was the primary criterion for liner selec-
tion. Thus, an 80-mil thick HOPE was selected over a less
costly 40-mil version due to its superior puncture and tear
resistance.
Waste-Liner Compatibility
Because of schedule constraints (and the cost factor), no
independent studies were conducted to select the liner most
compatible with the expected waste streams at Hawkins Point.
The liner-waste compatibility evaluations were based on
actual reported operational experience (both good and bad)
with various liner types.
For the Area 3 expansion cell (the general hazardous waste
cell 40), a major problem in evaluating compatibility was
not knowing the types of wastes that might be disposed of
there. Thus, the use of a synthetic leachate (as requested
by EPA) for testing with the HOPE was not possible.
Problems During Construction
The greatest problem during construction was the weather.
The installation was scheduled for winter because of time
constraints. Earth-work was completely halted during and
after rain and snow and liner seaming was not done during
high wind conditions.
Retrofitting A Leachate Collection System
Disposal of chrome wastes in Area 3 began in 1975; it had
been then assumed that Area 3 had a continuous clay lining
and would provide for adequate containment. However, it is
now known that the clay under this site is discontinuous.
Because borings indicated a 5 to 10 ft leachate head in the
old tailings cells (Area 3), the state ordered MPA to dewa-
116
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ter ' the cells; thus, retrofitting a leachate collection
system into these cells became necessary. The construction
cost for retrofitting the approximately 16-acre area was
$500,000.
Each leachate collection system consists of a single PVC
pipe header and lateral collection pipes. The laterals are
6-inch diameter perforated PVC pipe placed at the bottom of
3 ft wide trenches which were excavated to the bottom of the
cell. The bottom 3 ft of each trench was then filled with
crushed stone which was encased with Mirafi 140 geotextile.
Chrome tailings waste was then placed on top of the geotex-
tile to fill up the trench. There are 3 trenches containing
laterals in Area 5 and 14 trenches in Area 3. The trenches
in Area 3 vary in length from 160 to 260 ft; the three
trenches in Area 5-are approximately 80, 155, and 200 ft in
length. The collected leachate flows by gravity to a sump;
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 of the cells on the main*
collection header at all bends and junctions, and at spacing
not greater than 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 collector without excavation.
Headers and sumps were located outside the containment areas
because of the proposed vertical expansions. Although
leachate collection systems located totally within the cell
may provide better containment (i.e., no appurtenances
crossing the liners), stacking 2 or 3 cells vertically would
require very tall manhole towers which might cause greater
potential damage to an FML.
Miscellaneous
Provided that the bottom cells are provided with a reliable
liner system, vertical expansion of a landfill (i.e., new
cells placed on top of starter cells) would perhaps be more
cost-effective than expanding the landfill outward. In
general, however, above ground landfilling is much more
expensive than excavation landfilling.
At least a one-ft layer of soil should be placed over FML
sections during installation at the end of each work day ;
otherwise, the liner will billow and tear during windy
periods. Seaming should begin on the uphill end of the cell
117
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to avoid collection of rainwater under the liner.
A concrete unloading ramp (for bulk wastes) located in the
cell can save valuable disposal space and affords protection
for the bottom liner. A front end loader operating on a
concrete pad can pick up bulk wastes without fear of excava-
ting too deeply into the cell bottom. The pad also elimi-
nates the need for replenishing soil in the pickup area.
EPA's one-ft leachate head requirement may not be a practi-
cally achievable standard; it would require crushed stone or
gravel to. provide adequate permeability which might threaten
the integrity of the liner. Furthermore, there would be a
substantial additional cost for placing laterals very close
together if the drainage layer was composed of sand.
In areas where differential settlement may be expected, the
use of a flexible plastic collection pipe (lateral) may have
an advantage over rigid pipe. Even if the pipe partially
closes due to overhead stresses, leachate will still be
collected, whereas a broken rigid pipe may stop the flow.
A.7 TECHNICAL DISCUSSION NO. 7
«
Duffield Associates, Inc.: Jeffery M. Bross, Glenn K. Elliot
MEESA: Michael Haro
April 26, 1984
Leachate Collection
All landfills will generate leachate at some point even in
the arid Southwest; hence, prudent attention to leachate
collection system design for hazardous waste landfills is a
necessity. In general, the experience of the design
engineer with actual landfill operation and his familiarity
with the complexities involved is prerequisite for
developing a good leachate collection system design. Such a
design would feature the following:
-use of very resistant pipe material based on the
anticipated leachate characteristics;
-use of copious quantities of large diameter drain rock
(preferably quartz- or silica- based stone);
-use of large diameter perforated pipe;
-spacing of drainage laterals 200 to 300 ft apart;
-responsiveness to site-specific factors such as waste
properties, hydrology, etc.
Based on actual experience with engineered landfill sites
118
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featuring leachate collection systems, it is imperative that
large diameter rock, preferably crushed stone,(minimum size
of 1-1/2 in.) be used in drainage collectors to provide a
hydraulic backup layer in case leachate collection pipes
should clog. Based on experience with leachate collection
pipes that have filled with migrating fines and anaerobic
scum, the larger the drainage aggregate, the longer and more
effectively the drainage system will perform. The aggregate
should be placed against the waste so that even when fines
from the waste enter the system, the large rock provides
adequate porosity to maintain leachate flow. A filter fab-
ric should never be placed between the waste layer and the
leachate drainage system as these materials are likely to
clog. A geotextile is not a substitute for an aggregate in
this situation.
An example of - a leachate collection system designed to
prevent lateral migration away from the landfill .is provided
in Figure 14 . This system incorporates the large drain
rock, washed gravel, perforated PVC pipe, and an FML. After
eight years of service in a landfill in the Northwest, parts
of a leachate collection system, similar in design to that
shown in Figure 14, were excavated in order to determine the
integrity of the drains. The pipes and drain rock were
still very porous and in excellent working order.
Those landfills which feature, sand drainage layers for
leachate collection are likely to have problems. Sand is
simply too fine a material to be used as a drainage medium
for leachate collection applications and certainly would not
meet EPA's one foot leachate head requirement.
(Realistically, most of even the best designed systems would
fail to meet this head requirement. Conceivably, and
depending on "sand" gradation, it would require spacing
leachate collection laterals no more than 20 feet apart to
satisfy the one foot leachate head requirement.)
The major problem with leachate collection systems is that
once the drainage medium becomes clogged, it cannot be
cleaned out; therefore, the design must incorporate
considerable redundancies (e.g., use of as large an
aggregate material for drainage as is feasible).
Landfill operators should draw upon sewer system technology
in developing leachate collection system inspection and
maintenance programs. A significant amount of sediments
will deposit in leachate collection laterals and mains to
require cleaning after the first six months of operation.
Thereafter, laterals and mains should be inspected and
cleaned every 2 to 3 years. Video monitoring of pipes is a
recommended inspection procedure for 6-inch diameter or
119
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6* Topdresii se«d
and Bulch all
disturbed areas
Mound top of
trench 6*
Existing grade
varies
Mln. cover
depth to be 12*
This line indicates
Unit of payment
only. Actual trench
side to be sloped as
required to provide
adequate stability.
Landfill side of trench
Slope shown is
nay be adjusted (flatter) 1
in field depending on
thickness of refuse layer
encountered
Min. 12" lap of
impermeable liner
and filter fabric
6" Pert PVC CPPVC) pipe
Impermeable liner to
top of 6" PPVC
Liner height for
installation convenience
(to minimize
liner
damage)
Figure 14. Leachate collection trench
(not to scale)
120
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greater pipe (the required equipment will not fit in smaller
sized pipe). The pipes can be cleaned with rotorooters or
hydroblasting. Rotorooting is not recommended for perforated
PVC because of potential damage; sewer jet is recommended
for this type of pipe. Hydroblasting with sewer jets is very
effective and also cleans out pipe perforations but is only
effective for a certain length of pipe. Depending on equip-
ment capability, the maximum length of pipe that can be
cleaned is 500 to .700 feet for both methods. Therefore,
manholes and cleanouts should be sited based on these limi-
tations. An examples of a cleanout station is shown in
Figure 15. Sewer maintenance contractors are located in
most large cities and typically charge about $1000 per day
for video inspection and cleaning (which is equivalent to
approximately 900 feet of pipe).
Scrtv --on Cap
E SPVC pipe
Figure i?. Sewer Cleanout
121
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A.8 TECHNICAL DISCUSSION NO. 8
Residuals Management Technology,Inc. (RMT): John J. Reinhardt
MEESA: K. Ghassemi, K. Crawford
April 30, 1984
Leachate Collection
Actual experience with engineered sites featuring leachate
collection systems is very limited. In Wisconsin, for exam-
ple, first generation engineered sites went into service
about mid 1970's and it was not until about 1980 when some
operating data became available for these sites. As with all
engineered systems, and despite the use of best engineering
judgment in design, there will undoubtably be some failures
of the leachate collection systems. Information on what
designs will or will not work over a very long design life
is not currently available and the engineers have to contin-
ue to rely on their best engineering ^judgment in designing
such systems. Even though the systems which have been
designed by RMT do not have a very long operating record, to
date there has been no problem with any of their designs.
The oldest operating site with a leachate collection system
in Wisconsin is the "Olin Avenue" site which was placed in
service in 1970; the leachate collection system at this site
is still functioning adequately. Other sites in the state
for which about 3-4 years of experience is available are
Brown County, Madison, Winnebago County, Outagamie County,
and Marathon County sites. A similar length of experience
also exists for the Kent County Site in Michigan.
The current approach to minimizing potential future problems
with the leachate collection systems is to incorporate much
redundancies in the design. The sketches in Figure 16
illustrate examples of progressively increasing redundancies
involving extending the collection laterals and header pipe
to outside the fill area (Sketch B) to make them more acces-
sible for maintenance , use of manholes at the connection
points (Sketch C), and use of an auxiliary gravel trench to
intercept any leachate not drained through the piping system
(Sketch D).
There is currently no uniform approach to leachate collec-
tion system design. Although RMT has a generic design
approach (philosophy), the design is tailored to a specific
case and takes into account the often changing requirements
of the permitting agencies. Wisconsin Department of Natural
Resources, for example, now requires the use of geotextile
to line the interior side walls and the bottom of the gravel
122
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\
(A)
(B)
(C)
Leachato
collection
Laterals
(D)
Access Manhole
u>
Gravel trench
leachate interceptor
Figure 16. Examples of progressively increasing redundancies for LCS
-------
trench. There are also some differences between "hazardous "
and conventional "non-hazardous" waste sites which have to
be taken into account in the design; these differences
relate to differences in leachate characteristics (e.g.. use
of limestone-based drainage gravel may not be advisable when
the leachate has low pH), waste densities and water content
and drainage characteristics of the wastes.
There is no firm basis/criteria for determining whether a
leachate collection system is experiencing clogging. The
water budget method of determining leachate flow for design
purposes may not be accurate as a basis for determining the
extent of clogging. Use of head wells for direct observa-
tion of leachate levels is a preferred method and the one
which is now required by Wisconsin Department of Natural.
Resources.
Periodic (e.g., once-a-year TV) inspection of at least
selected lines for clogging is an element- of a good
maintenance program, although the exact maintenance
requirements are dictated by the regulatory agencies. There
is no substantial difference between cleaning techniques for
sewer lines and for leachate drainage pipes.
The clogging and service life experience with the
agricultural drainage systems would not be applicable to the
leachate collection systems because of the differences in
design and construction practices and the lack of rigorous
QA/QC in the construction of tile drain systems for agricul-
tural drainage.
R&D Needs
Case studies must be carried out to assess the performance
of full-scale leachate collection systems which have been in
service for a number of years. In the coming years, it
should be possible to obtain somewhat longer-term operating
data for a number of sites. In certain instances the eval-
uation of the performance may necessitate actually digging
out part of the collection system for direct observation.
Pilot scale lysimeter-type studies using real wastes can
also provide some performance data, although the results
would not be as reliable. Some sort of plastic is now used
as the piping material for the leachate collection systems.
Only through long-term field studies can information be
obtained on the longevity of these pipes in the harsh (e.g.,
potentially high temperature) landfill/leachate environment.
]24
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A.9 TECHNICAL DISCUSSION NO. 9
Department of Natural Resources
State of Wisconsin: M. Gordon, P. Kmet, G. Mitchell
MEESA: M. Ghassemi, K. Crawford
May 1, 1984
General
The State of Wisconsin does not have specific regulations
for design of clay liners and caps, leachate collection
systems and gas venting and recovery devices. The
Administrative codes (written in 1971 and revised in 1980)
are sufficiently general to allow varying interpretations in
connection with the site approval process. This regulatory
flexibility is necessary as the technology advances and
operating data from previously approved sites/designs become
available. The issue of waste handling and placement is
also handled primarily as part of the site approval process.
Currently there are no active hazardous waste disposal
sites in the state. At one time there were three co-
disposal sites in the state (two operated by Waste
Management, Inc.), which mixed hazardous waste with typical
municipal and commercial waste. These sites stopped
accepting hazardous waste in January 1983 when the new RCRA
land disposal regulations came out. These sites are also
"grandfathered" sites which have been continuously expanded
and to which various features and subsystems have been added
over the years. One facility is currently undergoing
remedial action to cut off permeable seams with bentonite
slurry, clay cut-off walls and leachate collection systems.
There are about 1200 "licensed" disposal sites in the state,
of which about 900 are small ( 50,000 cu yd) modified dump
sites which also fall in the "natural attenuation" site
category. A limited number of these small sites have some
sort of leachate collection back-up system (e.g., "toe"
leachate collection systems). The remaining 300 sites fall
into the following categories:
-Clay-lined landfills (lined typically with four to five
feet of clay) with leachate collection systems. These
sites are typically larger ( 200,000 cu yd) and newer
sites (or expansions of the older, existing sites).
-"Zone-of-Saturation" landfills, which are constructed
in low permeability clay soils below the water table
125
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and required to have leachate collection systems and to
maintain a low leachate head ( 1 ft).
-Remedial action sites ( where, for example, cut-off
walls and trenches with leachate collection systems
have been installed).
In 1976-77 Wisconsin began to require installation of
leachate collection systems and there are n.ow about 50 sites
with leachate collection systems.
There are about 20 landfills handling mostly paper mill
wastes.
- There are not very many surface impoundments in Wisconsin;
the surface impoundments handle mostly metal plating wastes.
Although Wisconsin has considerable experience with leachate
collection systems, its experience with gas management
systems is limited. There are currently less than 10
"active" gas venting systems in use. All new and expanded
landfills since 1980 are required to include a passive
venting system at a minimum.
Leachate Collection
Typical Designs and Related DNR Requirements--
Typical leachate collection designs use 6-inch PVC pipes 14-
inch pipes were used in the mid to late 70s but due to ease
of cleanout, all new systems require 6-inch pipe), although
ABS pipes have also been used in some installations. As a
general guideline, "Schedule 40" pipes are required where
the waste fill is not expected to be greater than 50 ft;
"Schedule 80" pipes are required when the fill depths would
exceed 50 feet. Schedule 40 pipes have predrilled perfora-
tions whereas the Schedule 80 pipes require drilling at the
site. Because of the field drilling requirement, there has
been some reluctance to the use of the Schedule 80 pipes
when not structurally required.
In the earlier designs, the leachate collection laterals
were typically not buried in trenches (in the form of a
"negative" projection) but placed on the landfill bottom and
covered with the drainage medium (as "positive" projections)
(see Figure 17 ). Because of some problems due to waste
movement, damage of the lines by equipment movement and the
potential for washout of the drainage material with the
positive projection type design, the negative projection
design (A in Figure 17 ) is now required. The use of a sand
layer on the liner and mounding of the gravel over the
126
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Refuse
Sand % .
drain'ace
blanket-.'
Geotextile
^-(optional)
Liner
(clay, geomembrane)
*£* j,V?^-Drainage
granular fill
Perforated
pipe
A. Negative projection mode
Geotextile
'(optional)
Refuse
Drainage
granular fill
Liner
(Clay, geomembrane)
Perforated pipe
B. Positive projection mode
Figure 17. Positive and negative projection drain designs
121
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trench (see sketch) is necessary to promote drainage.
Lining the interior of the drainage trench with geotextiles
has been required for most new designs. Geotextiles have
been used in this mode of application in about 25 installa-
tions in Wisconsin. The lining of the trench is intended to
prevent soil particles from the liner to enter the drainage
envelope and cause siltation. Some sites have experimented
with extending the geotextile to cover the top of, and hence
envelope, the gravel trench. This design, however, is some-
what controversial and the long-term effectiveness of geo-
textiles in providing adequate drainage remains to be seen.
At some natural clay sites where the side walls have been
very steep (nearly vertical at some areas) there have been
problems with- eros'ion of the clay material, some of which
subsequently found its way into the leachate drainage sys-
tem. To avoid the potential clogging problem, the state now
requires that even the natural clay sites be provided with a
side slope of at least 3:1 (H:V) and that a sand layer be
placed on the side slope to prevent erosion washing of clay.
The leachate collection pipes are required to have 500-ft
cleanout access (i.e., 1000 ft. maximum pipe length between
two cleanouts) and that leachate head wells are to be
installed in each major phase of the landfill (at least one
at the low end and one halfway up the slope).
Use of "sweep" bends instead of sharp bends (90 turns) at
pipe connections (to provide better access for cleaning) and
construction of the leachate riser pipe in the wall of the
landfill (instead of placing it in the fill or on the sur-
face of the sidewall where there may be a potential for
damage due to waste load and movement) constitute good
design practices.
Operating Practices and Related DNR Requirements
As part of the requirements for obtaining an operating
permit, site owners/operators must demonstrate ability to
clean all leachate collection lines. The state also
recommends that the lines be flushed after the first lift of
waste has been placed. During the site operation, the
leachate level in the head wells must be monitored and the
leachate flow (i.e., the volume of leachate pumped out) must
be recorded and the records (along with the ground water
monitoring data and leachate composition analysis) must be
submitted to DNR on a quarterly basis.
DNR currently requires annual cleaning of all leachate col-
lection lines. A report documenting each cleaning effort
128
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including identification of the lines cleaned and success or
failure of the cleanout is to be submitted to DNR. The
report should include photo documentation and should present
proposals for reparative measures in the event that a
cleaning effort has not been successful. DNR is also to be
notified at least two weeks in advance of cleaning date so
that a representative can observe the effort.
The DNR's requirement for annual cleaning of the leachate
collection lines has been formally challenged by at least
one site owner/operator who feels that monitoring of
leachate flow by itself is sufficient to detect problems,
and that only after a problem has been detected should
cleaning effort be undertaken. The DNR rebuttal to this
assertion, however, is that (a) in general, industry has not
demonstrated a good record for self-policing, (b) the annual
cleaning would be a good preventive measure as it would
flush out any accumulation before it becomes too difficult
to dislodge, and (c) the cleaning cost is relatively small
(depending on the number of lines involved, the line
cleaning would require a maximum of only two days' effort).
Cleaning of leachate collection pipes is carried out by
commercial sewer cleaning companies and there are no
specific companies specializing in leachate collection pipe
cleaning service.
Use of half or whole corrugated pipes to cover trenches
where there is trafficking has been required by DNR. This
requirement, however, has only been partially effective as
traffic path constantly changes as the operation proceeds.
Therefore, sites are designed to eliminate traffic on the
liner and over the collection pipes.
Leachate perching and seepage due to inadequate drainage
through the waste has been a problem at one Wisconsin land-
fill which has received significant percentages of shredded
refuse and paper mill sludge and which has used on-site clay
soil for daily, intermediate and final cover. The low
permeability of clay soil and shredded refuse acted as
barriers to leachate (and gas) movement. It is also be-
lieved that since the leachate collection system drainage
envelope consisted only of gravel with no sand layer filter
media on top of gravel, the fine particles in the paper mill
sludge penetrated and clogged the gravel layer. (Based on
the information provided in the reference cited below, over
half of the refuse received by Phase I was shredded and more
than 200,000 tons of the in-place waste is paper mill sludge
Reference: Stecker, P.P. and Garvin, J.W., "Control and
Prevention of Landfill Leachate Seeps", Proc. 6th Annual
Madison Conference of Applied Research and Practice on Muni-
129
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cipal and Industrial Waste, Sept. 14-15. 1983, Dept. of
Engineering and Applied Science, Univ. of Wisconsin.)
To avoid drainage problems similar to that experienced at
this site, DNR now advises against the use of clay or other
low permeability material as daily cover and recommends the
use of sand as cover material at least for the first lift
and scarification of clay cover in the upper lift prior to
placing new refuse. (In the past, landfill operators have
generally used as daily cover whatever material was
available onsite or nearby):
The placement of low permeability wastes (e.g., shredded
refuse) over large continuous areas is considered a poor
practice and should be avoided. Low permeability wastes
should be blended with refuse as much as possible or placed
in smaller isolated areas which are not interconnected.
Wastes containing fine particles and leachable materials
(paper mill sludge, ash and foundry waste) should be placed
near the top and definitely not in the first lift.
Leachate entrapment due to poor drainage has also been a
major problem at another site. Based on leachate levels
measured in the various head wells, perched leachate levels
exist at this site. The mounding of the leachate has been
attributed to the clayey nature of the cover material used.
As each daily refuse cell was encapsulated with cover, it
was effectively sealed and downward leachate migration was
restricted. The operating practice has since been modified
at the site and the operator now strips the previous day's
cover in the active filling areas to promote downward
migration of leachate.
Gas Control
DNR requires passive gas management (venting) at all post-
1980 sites, with the additional requirement that the system
can be readily converted to active system if necessary.
Only at one site in Wisconsin is gas recovered as an energy
source ( at this site, the recovered gas is used to heat on-
site buildings).
Underground fires have not been a problem at Wisconsin
landfills due to the wet climate and the strict regulations
and inspection which would prevent disposal of hot ashes and
flammable wastes.
Type of waste handled and waste placement practices can have
a significant impact on gas migration potential. At the
landfill reviewed above, exceptionally high gas pressures
130
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have been documented.* The presence of high proportion of
pulp mill sludge and shredded refuse in the fill and the us°
^f clayey soil as daily and intermediate cover are believed
to be responsible for the gas pressure buildup. At another
site, where only shredded refuse was-handled without any
daily cover, pressure buildup resulted in lateral gas migra-
tion and an explosion at a nearby structure. An active gas
control system was in place along one edge of the landfill,
but because of the compact nature of the waste the system
was apparently ineffective in collecting the gas from the
entire site. Corrective measures, which were subsequently
implemented, involved extension of the gas suction system
around the entire perimeter. The collected gas is flared at
this site.
Emissions from landfills and surface impoundments have not
been an issue in Wisconsin, as most sites are located in
isolated areas. At one or two bigger sites, DNR has
required emission monitoring, mainly for particulates. Odor
problems have been dealt with by venting and flaring
landfill gas or placement of bark waste" over paper mill
sludge waste.
R&D Needs
Assessment of the use and the long-term performance of
geotextiles in tHe landfill environment, including criteria
for selection of suitable geotextiles and potential for
formation of and growth of biological floes on the matrix.
Evaluation of the attenuation capacity of clay liners for
leachates generated in municipal landfills. The leachate
from some of these sites can be significantly more
troublesome due to variability than those from the so-called
hazardous waste sites. Use of lysimeters (small collection
basins directly beneath the clay liner) such as those now
required by DNR for new sites can provide the answer to the
question of how much of what leachate components does
actually go through the liner. (DNR now requires the use of
Typical landfill gas pressure ranges from tenths of an inch
up to two inches of water column. However, gas pressure
measurements at this site indicated pressures of several
inches of water column or more at most locations, 20 inches
or more at many locations, and greater than 150 inches at
some locations (Stecker, P.P. and Garvin, J.W., "Control and
Prevention of Landfill Leachate Seeps", Proc. 6th Annual
Conference of Applied Research and Practice on Municipal and
Industrial Waste, Sept 14-15, 1983, Dept. of Engineering and
Applied Science, University of Wisconsin, Madison, WI.)
131
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lysimeters under most clay-lined sites to check the permea-
bility of the liner and to evaluate its attenuation capacity
for the portion of leachate not collected in the leachate
system. This requirement, however, has been challenged on
the ground that it constitutes an R & D effort and should
not be a design requirement for operating sites.)
A.10 TECHNICAL DISCUSSION NO. 10
Warzyn Engineering, Inc.: R. Cooley, D. Kolberg, D. Viste
MEESA: M. Ghassemi, K. Crawford
May 2, 1984
Leachate Collection
Even though extensive operating experience is not yet avai-
lable, clogging of leachate collection systems is not expec-
ted to be a potential problem because of the considerable
redundancies which are incorporated in the design of such
systems. These redundancies include (a) use of collection
pipes which are significantly oversized for the flows which
they are to carry, (b) relatively close spacing of the
collection trenches (i.e., a large number of laterals) which
would allow for the leachate to flow through alternate paths
in the event that specific line(s) fail and (c) the signifi-
cant hydraulic capacity of the gravel trench itself to
convey fluid. In addition, providing cleanouts and follow-
ing an inspection program affords an opportunity to remove
debris that does accumulate. This assessment is supported
by the experiences from at least two major sites in Wiscon-
sin where inspection of a section of the leachate collec-
tion system indicated no evidence of clogging or deteriora-
tion after some 10 years of actual service. Except for some
discoloration, the gravel in the trench was very clean and
appeared intact.
It is inappropriate to draw conclusions as to the expected
performance and service life of the leachate collection
systems based on experience with the agricultural drainage
systems, because of the differences in design, construction
and maintenance practices for the two systems. For example,
tile pipes used in agricultural drainage systems are con-
structed with open joints, the construction effort receives
little or no QA/QC and there is no subsequent maintenance
(cleaning) and repair program for these systems.
Getting the leachate to drain through the refuse and reach
the leachate collection underdrain presents a much greater
design and operation challenge than getting the leachate to
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exit through the underdrain once it reaches the underdrain.
Use of appropriate material for the daily cover and imple-
mentation of proper waste handling and emplacement practices
are critical in promoting leachate flow through the waste.
At one major Wisconsin site, the mounding of leachate and
the existence of perched leachate levels have been
attributed to the clayey nature of the soil used for daily
cover. As each daily refuse cell was encapsulated with
cover, it effectively sealed the waste and downward leachate
migration was restricted. Reparative measures which have
been considered and/or are being undertaken at this site to
promote leachate flow and removal include drilling caissons
to various depths within the fill and constructing a gravel
"trench" all the way to the bottom of the fill along the
inside periphery of the site. These reparative measures are
very costly (considering a fill depth of up to 200 ft) and
may not have been needed if a more permeable material had
been used for the daily cover. At the present time the
operation at this site has been modified so that a previous
day's cover in the active filling areas is stripped to
promote downward leachate migration. Experience at other
sites has indicated that shredding of the refuse prior to
placement in the fill (to conserve space and eliminate need
a for daily cover) can also result in a decrease in waste
permeability, and hence leachate perching.
Gas Migration Control
Warzyn considers "active" systems for gas migration control
more effective, environmentally safer, and publicly more
acceptable than the "passive" systems. They have used
active systems in some designs. Gas control systems may
emit potentially hazardous materials to air and constitute a
safety hazard, especially in areas where there is a
likelihood for trespassing. There has been some
consideration for constructing taller vents to promote
dispersion and/or posting warning signs near these potential
emission sources. The public also generally "feels" more
comfortable ("safer") with the active systems as it sees or
hears the blowers in operation.
As with the leachate management system, the effectiveness
and cost of active gas control systems are impacted by the
type of waste handled and the operating practices.
Shredding of refuse can result in a dense waste which can
impede gas movement. Leachate recirculation, seeding of the
daily cover and use of permeable material for daily cover
can enhance gas production and recovery. Provided that the
landfills are specifically designed and operated for gas
recovery, they can perhaps prove to be desirable and cost
133
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effective resource recovery systems, if these considerations
are targeted early as major objectives.
Air quality monitoring around landfills is perhaps in an
evolutionary stage now and there are currently no protocols
nor guidelines for such monitoring. In the past emission of
particulates (dust) has been the primary concern. A limited
ambient air monitoring effort is currently underway at sev-
eral Wisconsin sites. Perhaps a matter of greater concern
at operating sites is workers' safety in connection with
waste placement and reparative measures projects.
R&D N'eeds
Parametric studies should be conducted at full scale sites
to relate design,. construction and operating factors to
performance. Factors that could be studied include waste
stabilization, resource recovery, environmental safety and
long-term cost impacts. Many of the parametric studies in
the past have utilized small scale units which do not ade-
quately represent operating practices and conditions in full
scale landfills (e.g. use of daily covers). Large scale
studies can best be carried out at these facilities for
which substantial background data (e.g., runoff, precipita-
tion, leachate volume, etc.) already exist. The background
data should be used to first "calibrate" the models which
have been proposed to estimate leachate quantities and per-
colation rates. Evaluation of factors affecting leachate
and gas generation, quality and flow should then follow.
Factors to be varied in such an evaluation can include
leachate recycling rates, the extent of seeding of cover
layers, and waste properties.
Investigation of how the refuse mass behaves in the landfill
environment from the standpoint of permeability to gas and
leachate. For example, it is not currently known what size
particles result from waste degradation and their potential
for deposition in the leachate collection system.
Evaluation of various approaches to retrofitting older sites
with leachate collection systems (i.e., what are the cost-
effective methods for extracting/intercepting the leachate
from these older sites), when such systems were not
originally incorporated into the design, or when original
systems are shown to be ineffective.
Verification of the applicability of the standard civil
engineering design curves and equations for pipe sizing to
the unique conditions of the leachate collection systems.
For example, estimation of pipe deflection as a basis for
sizing currently uses equations which have not been specifi-
134
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cally developed for small pipes in relatively narrow
trenches and subjected to often high waste loads. Some
extrapolation from standard curves/equations is often made
and the accuracy of the standard curves and equations at
these very "low ends of the scale" remains to be verified.
Evaluation/promotion of design innovations (perhaps through
government financial support for such projects). One innova-
tion in design which can perhaps revolutionize the entire
approach to waste disposal would be to view landfills not as
waste containment cells and repositories of indefinite and
uncertain life requiring long-term care, but as reaction
vessels and resource recovery centers with a finite service
life. Active degradation of waste and gas generation would
be intentionally promoted and the design and operation would
be aimed at achieving these objectives. The ability to
predict service life would enable engineers to design their
systems for an estimated life. This would eliminate the
current uncertainties as to the long-term performance of the
system components (e.g., liner, leachate collection system,
etc.) and the transfer of potential problems to future
generations.
One design innovation which specifically relates to the
leachate collection system, and one which has been given
some serious consideration at Warzyn, involves provisions to
allow draining of the entire leachate collection trench, and
not merely the embedded pipe. The gravel trench is capable
of carrying a significant volume of flow, especially in
deeper landfills for which the gravel trench would be deep
and the pipe cross section would only be a small fraction of
the total drainage cross section.
Development of background information and assessment of
pollution problems associated with existing municipal solid
waste disposal sites. Considering the large amounts of
hazardous wastes which have been previously deposited at
these sites, and the wastes from numerous small volume
hazardous waste generators which continue to be deposited at
these sites, the environmental impacts for these sites (many
of which have little or no engineering design) can be far
greater than those from properly designed dedicated
hazardous waste sites.
Development of approaches for achieving greater uniformity
among regulatory requirements of states with similar envi-
ronmental settings. One approach worthy of consideration is
Federal review of state regulations and enforcement poli-
cies. Promotion of exchange of information and experience
among states located in regions with similar conditions and
characteristics would also be helpful in promoting more
135
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uniform regulatory interpretation and enforcement policies.
A.11 TECHNICAL DISCUSSION NO. 11
Black & Veatch : - J. David, Jr.; R. Koltuniak
MEESA: M. Ghassemi
May 22, 1984
Leachate Collection
Conventional filter design techniques commonly used in con-
struction and agricultural applications were utilized in the
design of leachate collection systems for the Virginia
Beach, Virginia, Sanitary Landfill No. 2 and the Maryland
Environmental Service, Hawkins Point Landfill.
The drainage layer, as designed, consists of 12 inches of
select drainage materials, similar to American Association
of State Highway and Transportation Officials (AASHTO) M43,
size no. 8, with an average hydraulic conductivity of 1.0 x
10 cm/sec. To prevent clogging of the drainage layer, a
non-woven filter fabric similar to Mirafi 140N is installed
above the drainage layer. This fabric will prevent fine
particles from clogging the drainage media. To protect the
filter fabric from possible equipment traffic and deteriora-
tion, a 12-inch layer of coarse aggregate, similar to AASHTO
M43, size no. 57, is placed over the filter fabric. To
prevent clogging of the leachate collecting piping, a coarse
aggregate bedding material will envelope the pipe. The
bedding material is entirely surrounded by a non-woven fil-
ter fabric (see Figure ig) This should effectively elimi-
nate fine particles from entering the coarse aggregate and
clogging the perforated pipe. The coarse aggregate sur-
rounding the pipe should meet the requirements of AASHTO
M43, size no. 57. The minimum particle size will be 4.75
millimeters (mm), and limited to 5 percent by weight of the
material. Perforations of standard 6-inch diameter poly-
ethylene piping are approximately 2.0 mm; therefore none of
the coarse bedding should enter the pipe, and clogging
should not occur.
In the unlikely event clogging does occur, and in order to
allow for periodic inspection, the system has been designed
to be accessible from a series of manholes. Manholes are
provided outside of the cells in the main collection header
at all bends and junctions, and at a spacing not greater
than 400 feet. This will allow closed-circuit television
monitoring of the condition of the pipe, cleaning, and, to a
limited extent, physical repairs to be made to the collector
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Select drainage
material (clean
aggregate, permeability
greater or equal to
12 in. min
overlap
Mirafi 140N
geotextile
OJ
2% slope
typical
12 in. of coarse
aggregate to protect
geotextile
3 in
6 ft
'Coarse
aggregate
80-mil HOPE polymeric
membrane over 2 ft of
recopacted clay _7
(permeability< 10 cm/sec)
6-in. flexible
heavy-duty polyethylene
corrogated pipe
Figure 18.
Cross section of LCS for the proposed expansion
to Hawkins Point landfill
-------
without excavating. It wall also enable leachate samples to
be obtained at various locations in the collection system.
In general, there is limited experience with the performance
of leachate collection systems used in full-scale facilities
(about 2 years for systems designed by Black & Veatch.)
The potential for clogging of the leachate drainage systems
would be expected to be partially dependent on the type of
the leachate to be handled, and extensive information gen-
erally does not exist on the characteristics of the
leachate. This problem is especially difficult to address
when the facility is to receive a wide range of wastes
containing numerous individual compounds (or classes of
compounds), thereby yielding a leachate which would be very
complex and variable in characteristics. The problem of
predicting leachate characteristics is perhaps more managea-
ble when the facility is compartmentalized and operated as
separate cells (approaching a monofill-type operation).
When leachate of varying characteristics are to be handled
at a site (e.g., leachate from separate cells handling
different waste types or from old and new cells), the design
of any combined leachate conveyance system should take into
account the possibility of precipitate formation and
deposition due to mixing of possibly incompatible leachates.
A cross sectional sketch of the leachate drainage system for
the proposed expansion to the Hawkins Point hazardous waste
site is shown in Figure 18. Except for the elimination of
the coarse aggregate layer on top of the select drainage
material (sand), this same design has been used for the
expansion ' of the Virginia Beach landfill. Recognizing the
lack of experience with the use of filter fabrics in
leachate collection system, the selection of the particular
geotextile to promote drainage was based on reported
experience with the non-woven fabric filter in drainage
systems. The preference for heavy duty polyethylene (HOPE)
pipe for leachate collection over PVC resulted from cost,
chemical compatibility and engineering considerations (e.g.,
ease of installation, crushing strength and"wall buckling)
and some cracking of rigid PVC pipes reportedly experienced
with the use of such pipes in gas collection systems
(attributed to the subsidence problems).
Gas Collection
Because of the nature of the waste handled at the Hawkins
Point Landfill, gas generation due to microbial activity is
not a concern at this site.
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At the Virginia Beach Sanitary Landfill No. 1 (which has
been closed for some 15 years), the proposed construction of
remedial closure system incorporating a clay cap to minimize
infiltration will necessitate the installation of a passive
gas venting system. Because the site has been converted to
a park, aesthetic considerations were a factor in vent
design. Gas from this landfill will be vented through 25-
foot tall stacks which serve the dual purpose of flag-
standards for the park. (Engineering analysis indicated that
because of the landfill age and size, the gas from this site
was not sufficient in quantity or suitable in quality to
allow economic recovery of energy; the gas for Landfill No.
2, however, will be collected and used as an energy source).
RSD Needs
The issue of how to design an FML system or a leachate
collection system to be compatible with a leachate whose
characteristics are not known at the time of design.
Because of the complex nature of leachate, manufacturers'
charts of product compatibility with specific individual
chemicals are of little help to design engineers in
selecting suitable liners.
Collection and dissemination of the experience from full-
scale facilities (e.g., experience, if any, with the
clogging of leachate collection systems).
Evaluation of the most appropriate means for handling
leachates from municipal landfills (i.e.. what to do with
the leachate once it is collected?). The evaluation should
particularly address merits and demerits of the leachate
recycling approach.
A.12 TECHNICAL DISCUSSION NO. 12
New York State Dept. of Environmental Conservation (DEC) :
E. Belmore , J. Coyle, M. J. Hans, F. Grabar
MEESA: M. Ghassemi
May 24. 1984
Leachate Collection
Some siltation has been noted at the bottom of leachate
collection standpipes (sumps) in the older designs employed
previously at both the CECOS and the SCA facilities (in
Niagara Falls and Model City, NY, respectively). The
problem has been mostly in the cells dedicated to heavy
metal sludge disposal. It has been attributed to the
139
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passage of fine particles through the gravel drainage into
the collection pipe as well as possibly through the 3Oints
of the standpipe. In the newer units (SLF No. 5 at CECOS
and SLF No. 11 at SCA, currently under construction), a
graded filter media drainage blanket, which will cover the
entire liner on the bottom, will replace the gravel-only
drainage envelope and this should minimize the escape of
waste particles to the collection pipe. The use of
automatic level control, which has now been instituted (see
below), should also eliminate the very long leachate
residence times in the sumps, thus preventing substantial
particle settling in the sumps.
The depth of the sediment buildup in the sumps at both CECOS
and SCA facilities seldom exceeded 2 ft. At both sides the
problem was mitigated by use of a high pressure water hose
which enabled pumping out of the deposit as a slurry. (At
the SCA site, the use of a scooper to bucket out the deposit
was also considered but rejected in favor of the slurry
pumping, method). As far as DEC can determine, sediment
accumulation in the sumps was never a major problem at
either sites, and cleaning was only required 2 or 3 times
over a 3-4 year period.
In the past the pumping of the leachate from the sumps has
been on an infrequent basis and this at times has resulted
in excessive leachate accumulation in the sumps and very
high (perhaps as much as 10 to 20 feet) heads in the land-
fill. Automatic leachate pumping whereby the leachate level
in the sumps will always be maintained lower than a certain
level, would thus (a) eliminate excessive head buildup in
the sump and the landfill, (b) reduce the potential for long
leachate residence time in the sump and (c) increase
leachate flow to the sump by decreasing the back pressure
due to high leachate levels in the sump. This last asser-
tion is supported by the leachate monitoring data (see
Figure 19 ) which indicates an increase in the observed
leachate volume upon installation of an automatic leachate
pumping system.
At the SCA's SLF No. 11, the automatic leachate withdrawal
system will be electrically controlled and will consist of a
pump in each sump, high and low automatic controls, and a
high level alarm. The system is thus designed to drain
leachate from facility without building up a storage head
above the lining system. Each pump will turn on when
leachate levels in the sump have accumulated to the invert
of the incoming collection pipes. The high level alarm will
be installed at a level of one foot above the drainage
blanket to alert plant personnel of possible malfunctioning
equipment.
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0)
4->
S3
K
C
o
H
4J
O
0)
O
CJ
0)
*J
<0
£
o
(0
0)
Figure 12.
Years After Closure
Effect of installing level-activated automatic
leachate removal system on the volumetric rate
of leachate collected
At some older landfill units at SCA where water treatment
sludges had been used as intermediate covers, there was some
evidence of leachate perching in the landfill. To eliminate
the problem at the currently active and future units, DEC
now requires SCA,to use cover materials with a permeability
greater than 107 cm/sec in at least every fourth lift and
greater than 10 cm/sec for all other lifts. The breaking
of the previous cover was considered as a means for elimina-
ting the potential for leachate perching but was rejected as
impractical given the likelihood for disturbing the careful-
ly placed drums. To prevent hydraulic continuity of the
intermediate cover, one consultant had suggested the use of
a grid system whereby cover materials having a range of
permeabilities would be used on different sections of the
same lift.
Since berms are usually wider than designed, the excess clay
is removed prior to waste placement. If this clay is used
as cover material, it can interfere with effective leachate
-------
drainage within the fill.
Other means for. facilitating downward movement of leachate
include placing gravel or similar material around the
standpipes in a vertical column which will be extended
upward as more lifts are placed and the landfill surface is
raised. This design is featured in CECOS1 SLF No. 5,
currently under construction. The extent of difficulty in
erecting and maintaining the gravel column around the
standpipe remains to be determined. It is possible that any
construction difficulty could be eliminated via use of wire
mesh to retain the integrity of the gravel column.
French drains (see Figure 20) have been used as the leachate
collection laterals at the SCA's SLF No. 10. To improve the
leachate collection effectiveness, in SLF No. 11 these
french drains will be replaced with 4 in. diameter slotted
HDPE pipes embedded in 1-ft. deep layer of gravel conforming
to NYSDOT specifications for Class 1A (90 to 100% by weight
passing a 1/4-in. screen and 0 to 15% by weight passing a
1/8-in. screen). The gravel layer, which will cover the
entire landfill floor, will be placed on top of 1-ft. of
clay compacted on top of a geomembrane. The slotted HDPE
pipes will have a minimum grade of 0.5 percent and will be
spaced approximately 73 ft. apart to divide each subcell
into four approximately equal areas.
There has been no reported incidence of damage to standpipes
caused by the operation of landfill equipment at either SCA
or CECOS site. The 48-in. standpipe is constructed of
sections which are added as required during the operation,
with the top of the pipe always maintained above the working
grade and visible to the equipment operators. The pipe
sections are bolted together and provide a very sturdy
structure capable of sustaining any accidental bumping by
equipment, which are generally small drum pickers (and not
very large equipment).
New designs at both CECOS and SCA facilities (SLF No. 5 and
SLF No. 11) include collecting the leachate from various
cells into a single main sump from which the combined flow
will be pumped out. Each cell, however, has its own
standpipe and sump system, if leachate segregation and
separate removal become necessary. Based on past
experience, the leachates from individual cells are very
diluted and mixing them together should not present any
incompatibility problem. A single pump in a main sump would
be much easier to maintain than several pumps in individual
cell sumps.
142
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Lap fabric over
Waste
Drum
9-ft wide filter
fabric
Waste
Drum
-
1 ft*1
2-f
lir
Hypalon
liner
Figure 20.
French drain leachate collection lateral
at SCA SLF No. 10
A geotextile filter fabric (Murafi 140N) had been considered
for use in the SFL No. 5 at CECOS. The fabric would have
been placed over the top of the gravel blanket to minimize
penetration of the blanket with waste particles. This use
of geotextile, however, has not been approved because of
lack of experience and hence reliable standards for design.
The SLF No. 5 design, however, incorporates use of a filter
fabric (Murafi 700X) as a separator between the liner
protective clay layer and the gravel drainage layer.
At both CECOS and SCA facilities, there have been some
occasional problems with the freezing of the leachate
collection lines located near the surface during winter
conditions. The problem has now been corrected by locating
the pipes in sufficient depths and designing lines for
gravity flow.
Waste handling and placement practices would have signifi-
cant impacts on the amount of leachate produced and its
characteristics and hence on the design and performance of
the leachate collection (and the liner) system. The state
is very strict on this point and has inspectors at the site
to ensure compliance with waste handling requirements, which
143
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are written into a facility's operating permit. In addition
to the requirements for disposal of wastes into different
cells (or in different areas within a cell) according to
waste class (or subclass), there are restrictions on what
wastes can or cannot be accepted at a site. For example,
wastes containing more than 1% free cyanides, or having a
reactivity ranking of greater than "3" (under the NFPA
definition) are rejected. Wastes containing high levels of
sulfide and cyanide are diverted to certain treatment faci-
lities in the state which can handle such wastes.
To protect the liner, attention is now being directed toward
placing restrictions on organic wastes allowed in landfills,
especially wastes which would separate into a two-phase
system upon storage and/or reaction with other wastes, with
the organic phase being the heavier (bottom) layer. Two-
phase system wastes "are produced by some of the local
industries. As a result of the recent public hearings on
proposed expansion of the SCA operation (i.e., construction
of SLF No. 11), SCA has been required to conduct some
waste/leachate-liner compatibility studies including
evaluation , in a test cell, of the impact of waste/leachate
on clay liner permeability.
Gas Control
Although actual verification hot available, it is very
difficult to imagine any significant biological activity at
a strictly hazardous waste disposal site such as the SCA or
the CECOS facility, primarily due to waste toxicity and the
harsh disposal environment. Accordingly, biological
decomposition gases, which would require control at
municipal or co-disposal sites, are not expected in a
strictly hazardous waste site.
Both SCA and CECOS sites have gas venting systems installed
at their closed landfills. Currently the vent pipes are
capped, but can be connected to a gas collection and
treating system, if such a need ever arises. The vent pipes
are fitted with manual gas sampling valves. The primary
purpose of the gas venting system is to provide safety
pressure relief during emergencies.
Since the leachate collection sumps/standpipes are open to
the atmosphere, there is a potential for emission of some
volatile organic constituents present in the leachate, which
may pass into the air space above the leachate surface. At
the present time, there are no accurate and reliable
protocols for sampling emissions from standpipes. Using data
on the concentrations of ten volatile organics in an actual
leachate sample, and a number of assumptions including the
144
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applicability of certain gas transfer equations, an ambient
air temperature of 70 F, an ambient pressure of 1 atmosphere
and a wind velocity of 4 m/sec, the total probable emissions
from the five leachate standpipes at SCA's SLF 11 have been
estimated to be as follows:
Compound Ib/yr
Acetone 499.3
Benzene 4.835
Carbon tetrachloride 11.76
Chloroform 10.03
Ethyl acetate 9.723
Ethyl amine 1997
Methanol . 1159
Phenol 0.959
PCB 0.001
Toluene 13.00
At the public hearings for the proposed expansion at the SCA
Site, there was considerable public concern on air emissions
from the facility. However, because of multiplicity of the
sources of air emission at a complex facility such as SCA,
it would be very difficult to assess the significance of air
emissions (if any) from a particular landfill cell.
R&D Needs
Evaluation of the performance of the graded filter in a
leachate collection system as a function of the type of
waste handled.
Evaluation of the effect on leachate collection system
performance when clay or sludges are used as intermediate
cover (is it a problem and to what degree?).
Evaluation of means for improving leachate drainage such as
extending the drainage blanket to also cover the side
slopes.
Development of reliable protocols for sampling air emissions
from leachate standpipes.
Development of practical means for detecting leaking
landfills.
Miscellaneous
DEC does not have strict criteria on design and operation of
145
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hazardous waste facilities, and the requirements are estab-
lished on a case-by-case basis. At CECOS and SCA there have
been considerable changes in design and operation over the
years as the result of the experience gained from operating
various units and from the general advances in waste manage-
ment technology. The following changes in the design for
the various landfill units at CECOS illustrate this point:
-SLF No. 1, built in 1976, had no leachate collection
pipes at the bottom; the landfill bottom was sloped to
allow leachate flow to standpipes. There was no cell
subdivision within the landfill to allow segregated
disposal of waste by class.
-SLF No. 2 was divided into three cells. Vitrified clay
pipes were used at the bottom to direct flow to
standpipes.
-SLF No. 3 has a design similar to that for No. 2,
except that (a) the unit was subdivided into five
cells, (b) an HOPE liner was used in the PCB cell, and
(c) the leachate collection pipe was surrounded with
gravel. A flexible hose which would be inserted into
the standpipe from the top was used to pump out the
leachate from the standpipe.
-SLF No. 4, built in 1981-1982, had a drainage blanket
extending over the entire bottom. The empty spaces
between the waste drums placed on the bottom were
filled with gravel up to a depth of 2/3 of the drum
height. SLF No. 4 was also the first landfill to have
side riser as well as automatic leachate removal system
based on the leachate level in the standpipe.
-SLF No. 5, currently under construction, will have
one foot of gravel over the entire bottom, below the
"drum-gravel layer". No bulk loads will be allowed in
the first lift.
The leachate from some municipal landfills can potentially
present equal if not greater hazard to environment. DEC now
requires that all new municipal landfills be lined.
Leachate monitoring requirements are also being extended to
municipal landfills.
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A.13 TECHNICAL DISCUSSION NO. 13 (SITE A)
MEESA: M. Ghassemi
May 23, 1984
Leachate Collection
The clogging of the leachate collection system has not been
a major problem nor expected to be a significant problem at
SITE A because of the special design and operating
procedures employed (see below). The only problem which has
occurred in previously active landfills is some silt
accumulation in the leachate collection sumps/standpipes
which resulted in burning up of electrical pumps. The
problem has been resolved by use of better pumps. The
siltation has been attributed to lack of suitable gradation
in the drainage envelope to retain fine particles
(originating from some inorganic sludges). Siltation,
however, was never more than a periodic nuisance which could
be effectively dealt with by stirring using a water jet from
a fire truck available on-site. The rapid increase in the
leachate level in the sumps and the absence of ponding on
the surface of operating landfills after major storms have
been assumed to indicate that the drainage layers had not
been blinded by silt accumulation.
Based on monitoring of the leachate flow from closed units,
and considering the improvements which are now incorporated
in the design of the new units (e.g., at SCMF currently
under construction), SITE A estimates that the leachate flow
from new units should essentially cease within 5 years of
site closure. (Flow from a SCMF closed in 1978 now averages
about 75 to 100 gallons per day).
In general, the best approach to the management of leachate
and elimination of any potential for leachate collection
system failure is to operate the landfills in as dry a
condition as possible. This can be done through a
combination of good design and operating procedures,
including proper waste handling and placement practices.
The following, which are featured at the SITE A facility,
would reduce leachate volume and potential problems with the
leachate collection system:
Design Considerations--
-Use of effective covers and surface drainage features
to reduce water entering landfill.
-Multiple cell designs to allow for separate disposal of
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wastes according to some general waste categories
(e.g., metal sludges, pseudometals, flammables,
pesticides, etc.).
-proper design of the leachate collection and conveyance
systems to facilitate flow of the leachate to the
collection sumps. (key design features of a new SITE A
SCMF are -depicted in Figures 2 and 3; in this design,
leachates from various cells are directed to a common
SUTID for removal. Even though compatibility studies
have indicated no problems with combining leachates,
leachate from each cell can be pumped out separately,
as a contingency measure).
Operation Considerations--
-Not accepting liquid wastes in landfills. (At the SITE
A facility, liquid wastes are solidified before
placement in the fill).
-Use of permeable material (sand, foundry ash, slag,
etc.) as the intermediate cover material to prevent
leachate perching within landfill.
-Use of materials such as lime and ferrous sulfate in
the intermediate cover or to surround specific waste
loads to effect immobilization.
-Removal of rainwater entering the active cells. (At
the SITE A facility, this water is considered
contaminated and is processed as leachate in the on-
site wastewater treatment plant.)
Consistently maintaining the leachate head over the liner to
less than one foot, as required per RCRA interim
regulations, has been a problem at SITE A. There is also a
question as to where the one-foot head should be measured
considering the fact that there is a slope to the liner.
Where to put the leachate has been a problem at some sites.
SITE A has on-site facilities for treatment of leachate and
has a permit from the state for temporary on-site lagooning
of the leachate in the case of an emergency during periods
of heavy precipitation.
Gas Control
Biological activity is suppressed (and perhaps nonexistent)
at strictly hazardous waste landfills and hence no
significant amounts of deocmposition gases would be
expected. Gases may evolve, however, as a result of
volatilization or chemical interaction if the wastes are not
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properly pretreated or emplaced.
The landfill units which are closed at SITE A are provided
with gas venting pipes (See Figure 6). Periodic monitoring
of the gas pressure at these vents (which are capped) has
indicated no gas pressure buildup. This is understandable
due to the toxic nature of the wastes handled and the
practices of waste pretreatment, in-place
neutralization/immobilization and segregated disposal of
different waste categories. SITE A does not accept any
putrescible wastes in its hazardous waste landfills.
SITE A has a source emission permit from State covering all
leachate standpipes as well as the gas vents.
R&D Needs
Establishment of basis for design of drainage filter
gradation system taking into account specific waste
properties such as particle size distribution and mobility.
(As noted above, SITE A experience indicates that heavy
metal sludges exhibit a greater potential to penetrate and
move through the leachate collection drainage envelope than
other wastes handled at the site.
Development of detailed specifications and guidelines on
waste disposal site design and operation. Such
specifications should not provide arbitrary standards (as is
commonly done in regulations) but rather provide basis for
engineers to develop solutions to site- and situation-
specific conditions.
A.14 TECHNICAL DISCUSSION NO. 14
Wehran Engineering : Salvatori Arlotta
MEESA: M. Ghassemi
May 25, 1984
Leachate Collection
There have been considerable changes and improvements in the
leachate collection system design over the years. The
progression of technology spans the use of toe drains only
in the older systems, the use of gravel drains and fabric
filters in later designs and the use of conventional sand
and gravel filters in the latest designs.
Wehran has used geotextiles as filter media in some munici-
pal landfill leachate collection systems. Even though the
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length of experience is not significant, so far there are no
indications of a clogging problem at these installations.
Wehran's philosophy is now not to use fabric filters for
hazardous waste sites at all, but instead rely on tradition-
al graded filters for which the technology is better known.
With the older systems, leachate heads of 10 to 15 ft. or
higher within the landfill were not uncommon. In the latest
designs, however, even though there may be some buildup of
leachate head within the waste mass, the actual head on the
liner itself may be very small or negligible. In these
designs, the permeability of the drainage blanket far ex-
ceeds that of the waste and the leachate level in the col-
lection sump is maintained at or below the invert of incom-
ing collection pipes (via automatic level-activated
pumping), thus preventing a build-up of leachate storage
head above the liner. Under these conditions, an air gap
layer (an "unsaturated zone") will always exist within the
drainage blanket, limiting the head on the liner to that due
to the fluid level within the blanket. This air gap design
has been used by Wehran in two installations which are now
in operation, and one installation which is under design.
The potential for clogging of the leachate collection system
is very low or essentially non-existent with the new
designs, because of the considerable built-in redundancies.
These redundancies relate to (a) the oversizing of the
pipes, thus providing for a much greater carrying capacity
than the actual or anticipated flows, (b) availability of
alternate flow routes (e.g., other laterals, in the event
that one or more laterals become clogged, (c) provisions for
cleaning access to pipes, and (d) the flow carrying capacity
of the drainage blanket itself which makes a positive
connection across the entire base of the landfill.
With the present day cover design and construction technolo-
gies, little rainwater is expected to enter a landfill after
it is closed. The leachate which is pumped out after clo-
sure is essentially the water which entered the site during
waste placement. The goal of having a dry landfill can thus
be achieved more quickly, if the size of an active landfill
cell (area) is limited to that which can be filled and
closed within one to two years. This cell-by-cell "progres-
sive" design and operation approach also provides for some
experimentation and enables design modifications to incorpo-
rate the experience from preceeding fill operations (or
other advancements in the general landfill technology).
In addition to improvements in the operation, progressive
design can result in significant cost savings. For example,
the experience from the CECOS SLF No. 4 indicated that
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leachates from individual cells are compatible and can be
combined prior to pumping. Thus, in SLF No. 5, currently
under construction, the leachates from various cells will be
directed to a common sump from which the mixed flow will be
pumped out. This will eliminate the need for multiple pumps
to separately remove leachates from individual cells, thus
reducing both the pumping cost and the maintenance required.
(At SLF No. 5. each cell would have its own standpipe and
side riser which can be used for leachate segregation and
separate removal, in the event that such action become
necessary in the future. The option of initial design for
pumping of the combined leachate via single pumping system
has been offered by Wehran to some of its clients at other
sites; in some -instances, the clients have preferred
separate pumping for individual cells, presumably due to
improved leachate management control.)
To promote the concept of progressive design, some changes
to permitting procedures may be necessary. Under the pres-
ent permitting system, a new permit would be required for
design changes which would be considered as "significant"
modifications. To avoid obtaining a new permit (which in-
volves very complex procedures and requires public hearings
as part of the approval process), the designs which are
actually constructed are often several years old and do not
necessarily incorporate the state-of-the-art. An ideal
permitting approach is one which would issue only one um-
brella permit for the entire site, with modifications to
designs requiring only state review and approval (and not a
new permit and attendant public hearings).
Placing drums containing wastes which would not readily
mobilize (even if the drum fail) at the very bottom lift is
an excellent approach to minimizing some of the leachate and
leachate collection system problems. However, adequate
number of suitable drums are not always available at the
time that the first lift is placed and the operators use
whatever drums (or bulk wastes) which are available to them
at the time. The situation can be improved if the
regulatory agencies allow the operators to keep on hand
(i.e., to temporarily store on site) an adequate number of
drums containing suitable wastes.
Gas Control
At strictly hazardous waste disposal sites such as the SCA
or the CECOS site in New York, there would be essentially
little or no potential for biological activity due to the
toxicity of the waste and the operating practice of not
accepting putrescible material. Thus biodegradation gases.
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such as methane, which are produced at municipal and co-
disposal sites, and which require migration control, are not
encountered at strictly hazardous waste sites. At co-
disposal sites there is also a potential for the emitted gas
to pick up and carry some hazardous constituents.
The potential for emissions from landfills was a greater
concern some years back when there were inadequate
restrictions on the type of wastes accepted.
The cover systems designed for hazardous waste facilities
are generally provided with gas-venting pipes which can be
hooked up to a gas cleaning system in the event that
emissions control becomes necessary.
The state requirements for emissions and ambient air
monitoring at certain sites have primarily stemmed from
public concern rather than actual data indicating emissions
of hazardous constituents. (Some cursory, "one shot"
analysis of the emissions from standpipes at a hazardous
waste landfill unit at a client site has indicated no
emissions of any consequence from this source).
R&D Needs
Case studies of design versus performance for the leachate
collection systems in actual full-scale use. Such studies
can provide information on permeability of various wastes
relative to that of the drainage envelope and thus correlate
the leachate head in the waste with that in the drainage
layer. Significant cost savings and improvements in design
can result if the leachate collection systems can be tailor
designed to handle specific waste types/placement practices.
Demonstration of liner-waste compatibility using actual
waste or leachate.
A.15 TECHNICAL DISCUSSION NO. 15
Emcon Associates: Fred Cope, John Pacey, Robert Van Heuit
MEESA: Masood Ghassemi, Kimm Crawford
29 June 1984
Leachate Collection
With the reference and guidance documents which have been
made available to the designers in recent years (e.g., the
EPA Technical Resource Documents), engineers now feel more
comfortable with the design of leachate collection systems.
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Extensive experience with and feedbacks from systems which
have been placed in service in recent years are not yet
available; little problems, however, would be expected with
these new systems which have followed the recommended guide-
lines. Although there still remains certain uncertainty and
gray areas (e.g., as to the needed adjustments to the pipe
design equations, which have been developed for clay tiles
in construction drainage applications but are used to design
plastic pipes for leachate collection), the opportunities
for avoiding mistakes are far greater today than they were
previously when the older systems were being designed.
Much of the documented problems with the existing leachate
collection systems relate to older systems (primarily muni-
cipal or co-disposal sites), which lacked sophisticated
designs, did not incorporate design redundancies, and in
many cases consisted merely of simple toe drains, intercep-
tor pipes or gravel drains, with no consideration for mini-
mizing potential for siltation (e.g., through the use of
fabric filters). These systems were also poorly constructed
and received little or no QA/QC, with some lines already
damaged or partially clogged before they went into service.
Minimizing potential for leachate generation, removing the
leachate from the landfill once it is produced, and provid-
ing easy access to lines for cleanout and preventive mainte-
nance were not generally key design and operating objec-
tives. The current practices, which limit or ban the dispo-
sal of bulk sludges and liquid wastes and set requirements
on the type of material used for intermediate cover (to
ensure low permeability and hence avoid potential for
leachate perching) were not also observed in the previous
practices at many older sites. Because of these considera-
tions, the existing clogging or other experience with the
leachate collection systems in the older systems would not
necessarily be applicable to RCRA-designed sites.
^
There has been little opportunity for corrective action at
RCRA-designed hazardous waste landfills. Use of barriers
such as a slurry trench to contain leachate, use of gravel
trenches or pipes to intercept seepage, drilling caissons in
landfills and pumping out the perched leachate, and replac-
ing sections of the collection system (where the depth of
the overlying waste is not significant) are among the cor-
rective measures which have been used in older co-disposal
sites.
It is not appropriate to make comparisons between the per-
formance of the agricultural drainage systems and the
leachate collection systems because of the differences in
design and construction of the two systems. Agricultural
drainage tiles are designed for a much greater hydraulic
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loading and are wrapped in filter fabrics to minimize
clogging. PVC or polyethylene pipe used for leachate
collection should not normally be wrapped in such filters.
Because of the establishment of certain regulatory operating
and performance standards (e.g., the RCRA requirement for
maintaining a leachate head of less than 1 ft above the
liner), there will be a greater uniformity in future de-
signs. Engineering judgement and use of special features,
however, will continue to govern the detailed design which
must take into account job-specific considerations and the
preference and experience of individual designers. On many
jobs, for example, Emcon has specified specially-fabricated
pipe connectors for the leachate collection system to pro-
mote better access for maintenance purposes. Based on its
experience, Emcon prefers the use of slotted pipes over
perforated pipes as leachate collection laterals. Emcon
uses geotextile as a separator to line the interior of
gravel trenches, thus allowing the use of coarser gravel in
the trench. Any proposed overlapping arrangement of geotex-
tile to cover the gravel mound on top of the trench is
evaluated for potential clogging of the geotextile, which
can lead to poor drainage.
Controlling the amount of rainwater which would enter a
landfill during active life would reduce the volume of the
leachate which would be generated. Some sanitary landfills
have successfully used tarps as a temporary cover (e.g., in
lieu of the daily cover) to divert rainfall from the active
surface. Storage of the processed (e.g., solidified) waste
in a roofed storage area during rain for transfer to
landfill when the weather improves would reduce quantity of
water contacting waste and hence the leachate production.
From the standpoint of an overall site performance, the
potential for liner system failure is of much greater con-
cern than the possibility of a leachate collection system
failure.
Gas Control
With the present practices and the trend toward stricter
source control, gas generation and migration/emissions
control are not of much concern at strictly hazardous waste
facilities which are designed per RCRA requirements. At
such facilities, emissions from pretreatment and waste proc-
essing activities, which preceed the actual waste disposal,
would perhaps be of greater concern than emissions from
waste placement and/or the landfill after it is closed.
Even if some waste volatilization and degradation occur in a
RCRA-designed site, the internal gas pressures at these
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sites are not very high to effect gas migration by a convec-
tion mechanism and the cover system will have sufficient
adsorptive capacity to prevent significant emissions of
volatile toxic substances to the atmosphere.
Because of the very high cost of disposal in hazardous waste
sites, there is a conscious attempt on the part of the
industry to reduce volume of waste destined for land dispos-
al. Thus the trend is toward greater material recovery and
equipment/process modification to affect waste quantities
and characteristics. To avoid operating problems, the site
operators also exercise considerable control over the type
of waste which they place in a landfill. Thus to avoid gas
generation, which can be damaging to the integrity of the
cover after the site is closed, decomposable wastes and bulk
liquids are not admitted to a hazardous waste site. Vola-
tile substances are removed or passified through proper
pretreatment. In California, the disposal space in Class I
and Class II sites, which can accept hazardous wastes, is a
premium space and it would be foolish to use these sites for
the disposal of wastes which can be handled more economical-
ly by other means.
Because of the above considerations, source control appears
to be the most effective and the future trend for the con-
trol of emissions from hazardous waste sites. Based on
information from industry and the thinking in the state
regulatory agencies, it appears almost definite that, at
least in California, waste solidification prior to disposal
will become a prevalent practice. Solidification may not
totally prevent loss of volatiles from a waste, but would
certainly reduce it significantly. There will also be more
restrictive requirements for source control, including more
detailed waste documentation and the use of a three dimen-
sional grid system to identify the exact location of a waste
load within the landfill.
Again, because of the above considerations, Emcon has not
incorporated gas collection and treatment in the closure
plans for any hazardous waste sites which it has designed.
Up to now, Emcon has also not done any emissions monitoring
at these sites. Leachate off-gases can only be a potential
source of intermittent emissions since in all Emcon designs
sumps and cleanout accesses are capped and may present a
potential for emissions only when they are opened for
inspection and maintenance. In this regard, the safety of
the maintenance personnel rather than the potential for
atmospheric emissions has been the primary concern.
Gas generation and migration control problems are primarily
associated with co-disposal and municipal sites where the
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waste undergoes degradation and the high pressure of the
decomposition gases can cause gas migration and atmospheric
emissions. Although all possible mechanisms are not known,
the hazardous constituents present in the gas from these
landfills can originate from waste volatilization and/or
degradation (e.g., vinyl chloride from degradation of
plastics or toxic vapors from volatilization of solvents
contained in plastic manufacturing wastes.). Since
municipal landfills receive various quantities of hazardous
wastes (e.g., from small volume hazardous waste generators),
it is not surprising that compounds such as benzene,
toluene, xylene, which have been identified as trace
constituents in the gas from co-disposal sites, have also
been found in the decomposition gas from the so-called
municipal landfills. It thus appears that the differences
in the composition of gas from municipal and co-disposal
sites are a matter of degree rather than kind. Gas and
emissions control systems and procedures for the two
landfill types would also be the same in fundamentals but
vary in complexity and details. In general, passive control
systems would not be an acceptable emissions control (at
least at co-disposal sites) since any toxic substances in
the gas would still be released to the atmosphere.
R&D Needs
Use of geotextile in waste disposal application is of
considerable interest and hence worthy of more detailed
investigation. Provided that it meets the compatability and
longevity requirements, and can provide in-plane
permeability, geotextile may be potentially a far more
suitable media than the conventional sand and gravel
filters.
There is a need for additional leachate-liner compatability
data. At the present time designers have to rely primarily
on liner manufacturers' data and claims, much of which will
need to be independently verified.
The regulatory, economic and legal considerations have
brought about significant changes in the nature and make-up
of the wastes now destined for land disposal. A study which
would better characterize the type of wastes which are now
sent to disposal facilities and the expected future trends
can be very helpful in improving site design and operating
practices to reflect these changes and trends.
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A.16 TECHNICAL DISCUSSION NO. 16
Getty Synthetic Fuels. Inc.: L. Ceilings, J. Pena, W. Taylor
KEESA: Masood Ghassemi, Kimm Crawford
10 July 1984
Gas Control
Getty Synthetic Fuels, Inc. (GSF) bases its decision to
develop a landfill gas recovery project primarily on data
obtained during testing and on technical ability to prof-
itably produce acceptable product gas. In general, however,
because of the need for additional gas processing to meet
product specifications (e.g., for pipeline gas), GSF has
intentionally stayed away from landfills which have received
significant quantities of hazardous wastes, unless the haz-
ardous waste disposal has been in a confined section of the
landfill which can be excluded from contributing to the
collected gas. Only two sites which have accepted large
volumes of hazardous wastes have been included in GSF's
landfill gas recovery projects. These are the Palos Verdes
Landfill in Rolling Hills Estates, California, which was the
first site for a GSF project, and CID Landfill in Calumet
City, Illinois, where the hazardous waste disposal has been
confined to isolated sections of the landfill. With the
availability of a large number of municipal landfills from
which substantial quantities of relatively clean gas can be
extracted, GSF has not seen a justification to even consider
extracting gas from sites which have received substantial
volumes of hazardous (especially liquid) wastes.
As part of its market assessment program and in connection
with its various gas recovery projects, which now span some
ten years, GSF has conducted extensive field surveys of
landfills to determine their suitability for gas extraction
and/or develop a basis for gas recovery and processing
system design. These efforts have involved drilling in the
landfills to determine the profiles of in-place wastes,
detailed chemical analysis to determine gas composition,
sampling and characterization of the incoming waste, and
examination of the historical record on the quantity and
types of various wastes admitted. The extensive data base
which has thus been developed indicates that the quantita-
tive yield and the quality of gas (e.g., the gas composition
with respect to trace constituents) are highly variable and
extremely site-specific and that these variations are not
necessarily related to the regulatory or conventional clas-
sification of sites as municipal,, municipal/industrial,
sanitary co-disposal, etc. It is because of this extreme
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site-specificity that the final selection of a site for gas
recovery is preceeded by extensive site evaluation. This
evaluation and the development of the basis for gas recovery
and processing are very expensive and time consuming. The
on-site testing and sample collection alone take 3 to 4
months at more than $250,000 per site. An additional 4 to 5
months of laboratory analysis of the refuse and the gas
samples, and computer modeling of results may increase the
actual total cost to $500,000 per site. Failure to recog-
nize the need for detailed site evaluation and the require-
ment for tailoring of the design to the specific gas charac-
teristics has resulted in a number of costly failures (e.g.,
involving lack of gas for processing, unanticipated gas
declines and extensive corrosion of equipment).
Although significant problems with equipment corrosion were
encountered in the early gas processing projects (e.g.,
initially at the Palos Verdes site), GSF now has developed
the know-how for addressing the problem and no longer consi-
ders corrosion a major design problem for new plants. The
gas treating systems which have been developed are capable
of removing chlorinated organics and sulfur-containing com-
pounds to levels which would meet product specifications and
would not present corrosion problems. These systems are
equipped with pollution control devices and provide for safe
disposal of pollutants removed from the new gas.
Based on analysis which it has conducted, GSF projects only
a slight change (10 to 15% increase in organic content) in
the composition of wastes entering municipal landfills
between now and the year 2000. As long as landfills which
are candidates for gas recovery have to be evaluated on a
case-by-case basis, small changes in the overall composition
of wastes entering landfills would be of little significance
from the standpoint of project planning and design.
In connection with and in support of its gas recovery
projects, GSF has developed extensive computer models of gas
generation and migration in landfills. These models are
considered valuable tools and are used by GSF for first
order approximation in connection with assessing project
feasibility, plant sizing, screening design options and
preliminary cost analysis.
Unless the gas from municipal landfills is recovered, in
addition to the safety hazards associated with off-site gas
migration, landfill gas can constitute a major source of air
pollution. Since landfill covers can only postpone gas
emissions (i.e., after steady-state conditions are reached,
soil covers are ineffective in preventing gas escape),
landfills can emit large amounts of reactive organics and
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substantial amounts of potentially hazardous substances
which are present in the landfill gas as trace constituents.
For example, before installation of gas collection for ener-
gy recovery/disposal at the Puente Hills landfill near Los
Angeles, this landfill was the single largest stationary
point source of hydrocarbon emissions in the Los Angeles
basin. Because of these considerations, gas recovery, which
significantly reduces uncontrolled emissions, appears the
most logical pollution control approach which at the same
time enables recovery of energy. Although the hydrocarbon
content of landfill gas is very site specific and is found
in a wide range of concentrations, a very rough estimate
would indicate that for every 4 MMCF of landfill gas re-
covered for processing, about 1 ton per day of reactive
hydrocarbon emissions may be eliminated.
R L D Needs
Source testing and monitoring at municipal landfills to
expand the current data base on emissions from landfills and
their air quality significance.
Evaluation of means for promoting the concept that landfills
are point sources of emissions and that the gas recovery is
the "pollution control device" for landfills. Such studies
should include identification of regulatory approaches (or
changes to existing regulations) which would promote gas
recovery and enhance cost-effectiveness of gas recovery
projects. Some regulatory considerations which can
encourage gas recovery projects are (a) consideration of gas
recovery system not as a new source for regulatory purposes
but as a control device for an existing source (i.e., the
landfill), thereby allowing the use of "bubble concept" to
give a "credit" to gas recovery facilities for the emissions
reductions they create at landfills; (b) allowing return to
the landfill of condensate moisture which results from
landfill gas processing; (c) use of "performance" (as
opposed to "equipment" or "process") standards to allow and
encourage private sector innovation in landfill methane
recovery; (d) simplifying the permitting process so that
project development can proceed expeditiously; and (e)
separating the permit for the gas recovery and treating
operation from the permit from the landfill operation so
that regulatory actions against landfills will not
necessarily shut down the gas recovery operation and hence
aggravate the problem. These regulatory considerations have
been discussed in detail in the following paper by Mr.
William R. Taylor of GSF: "Regulatory Barriers to Landfill
Gas Recovery Projects"; paper presented to Distribution and
Transmission Conference, American Gas Association, San
Francisco, CA, May. 1984.
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APPENDIX B
CORRECTIVE AND PREVENTIVE MEASURES FOR COVER
AND BOTTOM LINER SYSTEMS
B.I BACKGROUND AND OBJECTIVES
As noted in Section 1, the technology for constructing and
installing cover and bottom liner systems for LFs and Sis was
recently evaluated in two studies for EPA (1, 2). These studies,
which identified a number of problem areas and analyzed applica-
ble preventive and corrective measures, used as data bases the
published literature and information collected through some 50
face-to-face interviews with liner manufacturers, fabricators and
installers, design engineering firms, active researchers, hazard-
ous waste management facility owners and operators, and state
regulatory agencies. One of the studies (2) also included nine
SI case studies whereby the actual site performance was compared
with that projected based on design and reasons for any devia-
tions (or lack of deviations) were identified.
Although liner and cover systems were not the focus of the
present study, the data acquisition effort generated some addi-
tional information on actual or potential problem areas and
approaches for preventing or correcting them. For the purpose of
completeness, the results from the previous studies as well as
the information collected in the present study relating to liner
and cover systems problems and applicable corrective and preven-
tive measures are presented here in this Appendix. (The summary
and conclusions and recommendations sections of the two predeces-
sor studies are reproduced as Sections B.3 and B.4).
B.2 LINER AND COVER SYSTEMS PROBLEMS AND APPLICABLE MEASURES
Table 20 presents a summary of liner and cover systems
problems and applicable preventive and corrective measures. Two
problem areas which have been of considerable concern and which
were suggested by a number of individuals with whom technical
discussions and interviews were held in the present and the
predecessor studies as requiring additional R&D relate to (a)
liner leak detection and repair, and (b) cover settlement. These
two areas are briefly reviewed below.
B.2.1 Liner Leak Prevention vs. Detection, Location and Repair
of Leaks and Restoration of Groundwater
At the present time there is no reliable, practical and
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TABLE 20. EXAMPLES OF LINER AND COVER SYSTEMS PROBLEMS AND APPLICABLE
PREVENTIVE AND CORRECTIVE MEASURES
Problem
Prevent we/Corrective Measure
CTi
General problem areas (both clay and FH.)
Poorly written and dlfflcult-to-follow specifications
and guidelines
Inadequate QA/QC
Liner-wastfi/leachate Incompatibility
locating leaks
Facility foundation (both clay and FM.1
Compaction to less than the required density (resulting
possibly In later differential settlement which can
Induce stresses In the overlying liner)
Permitting the foundation to develop a moisture con-
dition that Is Incompatible with subsequent Uner
placement steps
Inadequate surface finishing to reduce the potential
for liner puncture (this Is generally a concern for
FHL only)
Inadequate sterilization of foundation soils to suppress
the growth of vegetation which can potentially penetrate
the liner
Clay liners and caps
Where In-sltu clays are Involved - fatting to detect
and remove discontinuities from the clay such as sand
or silt lenses, roots, rocks, etc
Where recompacted emplaced soil liners are used -
inadequate protection of stockpiles from contamination
Failing to attain the desired permeability which gen-
erally results from the difficulty of ensuring that
conditions In the field closely meet those specified
In the design specifications
Prevention of cracking, particularly by dedication.
between the time that the liner is completed and when
It Is backfilled or put directly into service
Flexura) cracking of the cap during installation due to
the operation of heavy equipment on spongy waste
Requiring (educating) designers and suppliers to write lucid and
easy-to-follow specifications
Developing and Implementing adequate QA/QC at all steps of design.
construction. Installation, and operation of facility
Selection of suitable liner based on literature data, Manufacturer's
Information, actual or es Una ted waste characteristics, liner-waste
compatibility testing
Use of methods (some still in the developmental stage) for leak de-
tection, examples water balance for surface Impoundments, elec-
trical conductivity method, use of observation wells, groundwater
monitoring, visual inspection of caps
Use of the state-of-the-art earthwork techniques and practices, and
an adequate QA program to ensure that such practices are actually
utilized
Detailed soils Investigation to determine the applicability of
over-excavation and recompactlon of the clay
Covering stockpiles (or seeding for lenghty storage). Inspection to
detect and remove contaminants, and adjustment of moisture content
Use of laboratory oermeabillty tests for general guidance during
final design In conjunction with field permeability tests on Indivi-
dual lifts and on the completed liner for construction verification
Inspection of moisture content, destruction of large clay clods
during construction, immediately after Installation, placement of
backfill, synthetic material, or fluid over the liner
Placement of additional lifts on an as-needed basis, reduce spongl-
ness of waste fill by mixing soil or granular waste Into soft wastes
or reducing thickness of cells containing soft wastes
(Continued)
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TABLE 20. (Continued)
Problem
Preventive/Corrective Measure
FML liners and caps
Damage to liner material due to exposure to adverse
weather, vandalism, and repeated folding and unfolding
Placement of panels in a wrong configuration (e g . seams
on side slopes oriented parallel rather than correctly
perpendicular to the side)
Placements that bridge a gap between two surfaces (e g .
at penetrations)
Improper anchoring (e g , backfilling anchor trenches
before seaming Is completed)
Improper timing (for example, placement during inclement
weather, including windy conditions)
Placement of the liner with little clearance between it
and the leachate collection pipes This Is often un-
avoidable per the requirements of the leachate collection
system, but any ruptured pipe could potentially puncture
the liner
Inadequate seams resulting from use of Inadequate seaming
techniques, seaming during adverse weather conditions.
seaming with Inadequate materials, seaming new material
to old liner material, and not paying special attention
to seaming around penetrations
Mechanical damage to liner during placement of backfill
Storing liner material In a secured area, reducing time between
delivery and placement of liner, avoiding unnecessary folding/un-
folding, and Inspecting materials
Identification of panels by number at manufacture and fabrication
and strict adherence to design specifications
Ensuring complete liner contact with supporting soil and proper sub-
grade compaction around appurtenances
Anchoring panel edges with sandbags before seaming; careful opera-
tion of equipment during anchor trench backfilling
Avoiding Installation during inclement weather and effective QA to
ensure this, seaming and patching U> correct BIOSt wind-related
damage
Careful placement and compaction of drainage beds
Strict adherence to the seaming procedures (e g . type and amount
of solvents, pressure applied to seams, etc ) recommended for the
specific liner material at hand, use of experienced Installers (at
least at the foreman level). Installation during suitable weather
conditions
Removal of slack and wrinkles, except those Included Intentionally
to allow for thermal expansion/contraction
Allowing enough time for the completed seam to develop strength
before loading
Giving special attention to making connections between the liner
and structures
Taking special precautions when new cap material is seamed to old
liner material (e g . ensuring that the bottom liner and cap are
compatible when seamed, removing of the surface cure from the
bottom liner using solvents and scrubbers, and repairing damage
that the bottom liner suffers when It is uncovered)
Use of a minimum soil lift of 12 to IB inches, careful operation
of equipment on backfill, specify maximum weight to be driven on
liner, use of temporary ramps for equipment to drive on and off the
disposal unit
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foolproof testing and inspection procedure for determining all
leaks (unless they are ma^or ones) in a completed liner before it
is placed in service or while in service. Although some R&D
effort has been devoted in recent years to the investigation of
innovative concepts for leak detection, such concepts have not
yet been adequately developed for full scale application (see
Section B.2.2). Leak detection is very difficult even in clean
systems (e.g., lined water reservoirs) let alone liners used in
vraste management applications. Thus in acceptance inspection of
co-r.pleted liners, it is virtually impossible to detect all leaks
(unless they are ma^or ones) through standard tests such as
evaporation rates for use in water balance calculations (T.D. No.
12). Inspection of entire subsoil for "soft spots" is also
i-ipractical. Thus the need persists for capabilities to develop
installed liners which will not leak and for reliable techniques
to detect, locate and repair leaks in operating facilities before
the escaping leachate or waste can seriously damage the ground
water. Although methods for control of ground water contamination
are available*, these methods can be very expensive and may not
be completely effective under all circumstances. Thus, prevention
of ground water contamination is preferred over taking corrective
action after the ground water has been contaminated.
Even if leaks can be detected in time in an operating
facility, it may not always be practical or economical to repair
the liner (e.g., when a significant volume of waste is already in
place in a landfill or when a liner material such as Hypalon has
undergone considerable curing due to aging).
Tnus the best approach to eliminate leaks would be to
strive for developing and maintaining leak-free systems in the
first place. As noted in Sections B.3 and B.4 and in T.D. No. 2,
the attainment of this goal requires execution of an effective
QA/QC program which covers all aspects of liner design,
*C-round water that has been contaminated can be dealt with in a
nuTiber of ways. Impermeable barriers constructed of bentonite
slurry, cement or chemical grouts, or sheet piling can be in-
stalled vertically to (a) prevent ground water from migrating
away from the site; or (b) divert ground water so that contact
with waste materials is prevented. Another potential method of
dealing with contaminated ground water is to allow it to flow
through permeable treatment beds (limestone and/or activated
caroon) in which the contaminants would be removed as the ground
v;ater flows through the bed. The above two treatment methods
can be considered passive ground water controls. The pumping of
ground water with subsequent surface treatment is considered an
active remedial measure. Pumping can be specifically designed to
lower the water table in the area of a disposal site or it can
be designed to contain a contaminated water plume.
153
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manufacturing, fabrication and installation and includes use of
reputable installers.
B.2.2 Testing and Inspection to Prevent FML Failure
features of FML installation which require testing and in-
spection to prevent liner failure include: subgrade preparation,
-la^enal handling and storage on site before placement,
placement, seaming, anchoring, connecting to appurtenances and
oackfill placement. Some examples of the inspection and testing
procedures applicable to these features (except for the seaming
vhich is reviewed below) are presented in Tables 21 and 22.
Seaming, especially the field seaming, is one of the most
critical steps in FML installation and the seam integrity gener-
ally determines the integrity of the entire ;job. A brief discus-
sion of the factors involved and the current experience and
philosophy in testing field seams is presented below to illus-
trate the type of information which is available. Some of the
tests and inspection procedures (e.g., visual inspection, vacuum
testing, shear strength and peel adhesion) are equally applicable
to factory seams which are done under more controlled conditions
and hence are generally viewed as less subject to defects.
Different types of tests are available to measure various
seam properties and for various seaming systems. These tests
fall into two general categories, non-destructive (qualitative)
and destructive (quantitative). A good quality control program
will include tests of both types, since no one test is foolproof
The recommended procedure requires that all field seams be non-
destructively tested over their full length. This non-destruc-
tive testing should include ooth visual inspection and at least
one other applicable method: air lance, vacuum, or ultrasonic
testing. It should be done as the seaming work progresses, not
at the completion of all field seaming. Visual seam inspection
includes the following steps: checking the width of the seam
overlap, inspecting for any defects such as blisters, tears,
etc.; and checking for exposed scrim at the edge of each panel.
HDPE seams are usually tested with a vacuum or ultrasonic
test unit; butyl, PVC, CPE and related material seams are usually
tested with an air lance or vacuum test unit. Vacuum testing is
not considered to be as reliable for thin, flexible materials as
it is for thick, stiff materials. Some liner installers feel that
because HDPE welds are designed to be homogeneous, inhomogenei-
ties such as gaps, bubbles, and holes in the welds are easily
detected by ultrasonic testing. It has been reported that on one
300, one mile of seaming was checked and the ultrasonic test was
in error on only four inches. However, ultrasonic methods are
generally not capable of detecting a seam holiday less than one
millimeter in size and the reliability of ultrasonic test methods
164
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TABI.C 21 TESTING AND INSPECTION FOR SUBGRADE PREPARATION AND MATERIALS AND EQUIPMENT
Criteria/
R lenient
Problem/
Cancern
Testing and Inspection
I'jrlicle
MI ze
l.incr puncture
Compact ion
U!
S 1 ope
Herbicide
l.incr
dandling
and
storage
Materials
and
equipment
l.incr failure duo
to difforntial
a iibs id°ncc
Liner sliding from
side s lope;Inadcqute
gas venting
Growth of vegetation
through liner
Damage due to wind,
sunlight, hail and
vandalism; crimps
and weak spots in
liner
Use of defective or
wrong material
-Visual inspection to verify removal of na many rocka,
sticks from the suhgrado an possible before placement of
additional materials
-Checking of the ooil to be plnccd 03 oiibgrado to onnuro
it Is free of any objects that might damage liner
-Grain-size distribution (e.g.. via ASTM O122)
-Verification of the thickness of the m.itorial placed
under the llncrje.g.. sand layer)
-Measurement of the thickness of the uncompacLcd or
loose lift at several locations in a layer of fill,
using marked staff or shovel blade, with survey lovols
made every few lifts for verification
-Continuous field testing of compaction moisture content
and density, using nuclear guagc. thin-walled tube or
driven cylinder to obtain undisturbed samples of cohe-
sive soilsi sand cone or rubber baloon method (ASTM
D1556 and 02167. respectively) to obtalnag samples of
gravelly soils
-Use of standard surveying techniques to verify side
slopes and the amount and direction of bottom slope
-Inspection of the sterilization procedures to ensure
conformity to the procedures recommended by tho herbi-
cide manufacturer
-Sampling and chemical analysis to verify uso of correct
herbicide and application rate
-Visual inspection of the storage facility and condi-
tions and of handling practices, defects in manufactur-
ing/fabrication, damage during transportation, etc.
-Inspection and/or verification of the receipt of correct
material (e.g..by comparing the suppliers material iden-
tification marks with the purchase order or catalog de-
scription), good working conditions of equipment, and
correct number of pannols
-Test seams to verify above
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can be affected, by temperature and humidity variations.
The air lance method of testing field seams is considered by
some to have fewer disadvantages than the other two tests. The
U.S. Bureau of Reclamation considers it an invaluable method that
should be specified for all jobs involving FMLs similar to the
CPE installed at the Bureau's Mt. Elbert project. However, this
method only determines whether or not there is
interface and does not indicate seam strength.
a leak across the
The U.S. Bureau of Reclamation studied a thermal infrared
scanning method of non-destructive field seam testing during the
lit. Elbert project. The theory of the test was that the IR
scanner vould detect air voids caused by imperfect seam bonding
TABLE 22. TESTING'AND INSPECTION FOR LINER PLACEMENT,
CONNECTING TO APPURTENANCES, ANCHORING AND
BACKFILL PLACEMENT
Element
Testing and Inspection
Liner
Placement
Anchoring
Connecting
to appurte-
nances
Protective
cover
-Laboratory chemical fingerprinting and
compatibility tests to verify liner being
used is the same as selected in chemical
compatibility tests
-Inspection to verify correct placement
of panels and patching and for blisters,
scrim defects, delamination, tears, etc.
-Inspection for evidence of wind damage
during installation due to inadequate
anchoring
-Inspection of anchor trench construction
to verify conformance to design
-Inspection to verify use of compatible
materials (e.g., for pipes) and proper
liner thickness (e.g., doubling) or use
of geotextile cushions per specifications
-Inspection to verify thickness of cover
material (including rip-rap for surface
impoundments) and for evidence of poor
equipment operation during soil placement
-Tests for grain-size requirements and
inspection for freedom from fractured
stones, debris, cobbles, roots, etc.
166
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by sensing and displaying temperature differences; the air pock-
ets are cooler than the surrounding surface and should show up
darker on the display screen. However, it was difficult to
distinguish oetween air pockets in the seams and those caused by
the uneven subsurface. In addition, the small size of the target
air pockets tended to approach the resolution capability of the
instrument. Thus, the test method was considered to be incapable
of identifying imperfections in the field seams.
Destructive seam testing involves cutting out a sample of an
existing seam for the purpose of verifying seam conditions
through laboratory testing. Conmonly performed lab tests for
seams include those for peel adhesion (ASTM D413, Method Type 1,
and D1876) and shear strength (ASTM D816, Method B, modified, and
D882, Method A, modified). Test samples may be cut either from
the liner itself or from specially-prepared sample seams
constructed under the same conditions as the actual liner seams.
These samples are usually prepared several times per day.
Peel strength tests measure the relative bonding strength
oetween the two FML sheets in a peel mode of failure. Although
this failure mode may not occur in practice, the test can be used
to indicate the strength of the bond. Shear strength tests
measure the strength of the bond between the FML sheets at the
seam under a rapid shear loading situation such as would occur
when the FML is stressed in tension during installation.
Some contend that seams are stronger in shear than in peel
and that as a result the peel test is the only one of the two
that is relevant. The U. S. Bureau of Reclamation prefers the
peel test over the shear test because it shows how homogeneous
the material is an where and when interface failure occurs. It
provided them with much important information during the Mt.
Elbert project. The peel test of seam strength is also more
sensitive to the effects of aging and exposure than is the shear
test. The results of the shear test can be improved simply by
increasing the width of the seam.
When test samples are cut out of the FML, the hole should be
repaired immediately with a round or oval patch made of the same
type of FML material. New seams in the repaired area should be
tested with the same non-destructive test methods that were used
previously. Some inspectors believe that where cut-out samples
are tested, the benefits gained from testing outweigh the draw-
backs of having to patch an equal number of cuts in the liner.
The U.S. Bureau of Reclamation used both cut-out samples and
prepared samples for destructive testing at Mt. Elbert. They
found that the peel failure rate was significantly higher in the
field cut-out samples than in the field fabricated samples and
attributed this to the better workmanship exercised in preparing
167
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samples that were known to the workers to be intended for test
purposes. On the other hand, some contractors contend that cut-
ting out samples for destructive testing should be minimized
because the integrity of the patched seams is uncertain. Some
also recognize, however, that when the seaming crew knows where
sa-nples are to be taken they are likely to do an especially
careful job in that location, and that such samples are not
representative of overall field seam quality.
Although contractors report no difficulty with patching
holes from cut-out samples, some do suggest an alternative. This
is to surprise the seaming crew by periodically requiring them to
construct a seam on scrap material using the exact technique that
vas just being used on the liner. For example, if the weather is
cool and the crew was not using a heat gun, no heat gun is
permitted on the test 'strip. This method is said to give a
fairly representative indication of how well the seams are being
constructed.
i
Seams in special locations (e.g., around pipes and appurte-
nances) should be nondestructively tested if the seam is acces-
sible to testing equipment. If the seam cannot be tested in-
place, but is accessible to testing equipment prior to final
installation, the seam should be nondestructively tested at that
time. If the seam cannot be tested either in-place or prior to
final installation, it should be inspected for uniformity and
completeness.
If seams not meeting specifications are detected during
inspection and testing, further testing should be done in both
directions to the point where the seam again meets specification
requirements. Then a cap strip should be placed over the suspect
seam between the points where the seam meets the specification
requirements. The cap strip should then be seamed using standard
seaming methods (applied with extra care). Upon completion of all
repair work, the full length of all seams should be reinspected
to ensure that all defective areas were repaired or completed.
B.2.3 Leak Detection and Repair for In-Service Liner Systems
Leaks in the liner can be detected through the use of
subdrain leak detection systems, ground water monitoring or
methods such as acoustic emission monitoring, time-domain
reflectrometry and electrical-resistivity measurement, which are
currently under development. Pertinent features of these leak
detection systems (LDS), including their advantages and
limitations, are listed in Table 23. Provided that the
effectiveness of a subdrain LDS can be demonstrated before the
system is placed in service, at this time the subdrain system
appears to be the preferred method over ground water monitoring
or the survey methods which use the developmental technologies.
168
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TABLE 23. METHODS FOR DETECTING LINER LEAKS
Method
D'.'scr 1 pi Jon
Advantages
1)1'
Stihdrain Leak Octcction
System
Ground water Monitoring
A Jyajmctcr typo sy^t Irui r<-1 I rtbi I I ty.
-Might bo difficult to n-movo
rainwater which mny Meep
between tho liners dining con-
struct ionj cluMoicnl minly: lu
may be ro a single- linod fac.lHty, I.DK
may not dolcct Icnk unloss I ho
f.OS covora n a Ign 1 f ic/int nren
under tho liner.
-May foil to detect minor lenks.
-Design of iiiitahlo monitoring
system requires good knowledge
of groundwatcr conditions and
flow regime.
-Monitoring systems and programs
should be designed on a cnso-
by-case baa Is.
-Unless suitable target species
species can be monitored, it
mny be difficult to detect
minor changes In water quality
due to leakage
-Installation of observation
wclli. and subsequent water
quality monitoring can be very
cxpcns ive
(Continucd)
-------
TABI.C 23. (ConUnuod)
I>o3cr ipl JOM
Dl '
i ,ig<>«
I'lt.cti Jtdl Demistivity
Mf.i jurcnu'Mt (66-00)
Accoustic Emission
Monitoring (69, 70)
Time-Domain
Reflectomctry (69. 70)
geomcinhranc liners
exhibit high electrical
rei ist cincc , conductive
fluid Clow through the
leak establishes an
electrical shunt
through the linor.
This low resistance shunt
forms an electrically
detectable region which
permits detecting and
locating leaks when a
current source is used
lo inject current across
the boundary of the
liner. Tests at 1.5
million gal. impoundment
have shown that the
system can detect a
1-in. hole in the liner
and can pinpoint its
location within 1 ft.
(67)
Accoustic sounds are
emitted when water flows
in a turbulent regime
through soils. Good
accoustic coupling of the
sensor near the liner
material may permit leak
detection and location
A high frequency electro-
magnetic technique which
can measure the electri-
cal properties of materials
in and around conductors of
a transmission line. The
electrical properties of
a icachate-saturated soil
will usually be different
from those of the host
soil and thus the tech-
nique will be able to
detect the Icachatc.
-Nondestructive method
of leak detection.
-As few as two workers
arc needed to perform
a tost, record
measurements and
analyze results on a
computer (67).
-Method still experimental and
iindur flow lopmont .
-Applicability to landfill)) and
and full scalo waoto
impoundment!) remains lo bo
demonstrated.
-Nondestructive method
of leak detection.
-Method still experimental and
requires further development.
-Nondestructive method
of leak detection.
-Method still experimental and
requires further development.
-------
Liners
Leak detection system between liners
Leachate
\collectiop
system
Unsaturated
zone
Ground water
Figure 21
Schematics of a double-lined landfill
incorporating leak detection system (73)
The liner repair techniques can be broadly grouped into
three categories: Patching, mechanical plugging and sealing with
soil grouts. A state-of-the-art review of liner repair tech-
niques which are being utilized in all types of emplaced liner
systems has been carried out recently as part of a broader EPA-
sponsored liner repairability program (69). According to this
review, some repair techniques are currently being applied in the
field to effect localized repairs to liner systems. These vary
widely, depending upon the type of liner being repaired, the
extent of problem and the expertise involved in design and imple-
mentation of the repairs. The success of these repairs is also
widely variable. However, in all cases the repair of in-service
liner systems is highly complex, and dependent upon a number of
factors which are very site- and situation-specific. These fac-
tors include swelling of membranes due to exposure to waste or
leachate, the use of dissimilar liner materials, accessibility of
liner and the cost for waste removal to gain access to liner.
CoT.partmentalization of operation and designs which provide for
separate leak detection systems for individual compartments or
subcells, can conceivably allow for the identification of a
leaking subcell so that the repair can be limited to a smaller
area rather than a very large cell or entire landfill (T.D. No.
2). This, however, would not be very practical for large land-
fills where cells and subcells would also be very large. Thus.
171
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10'
0.25J Slopo
Lid
22'
L
12-
ro
Catch Das In
12 mil PVC Pond Oottom Llnor.
4 mil PE Cover Over Gravel
Gravel
3" PVC Plpo
30 mil PVC
Figure 22. Subdrain leak detection system at a surface impoundment facility
in the Southwest (2)
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giver the complexity of the problem, each repair solution would
probably be a problem unto itself, requiring site-specific analy-
, sis and design .
Although in-service liner repair efforts have been underta-
ken at full-scale facilities, there has been little feedback on
the success (or failure) of these attempts and there has not been
any systematic analysis of the circumstances involved, repair
procedures used, costs incurred and results obtained. Under EPA
sponsorship, a laboratory study is currently underway (69) to
evaluate the promising liner repair techniques and to develop the
data base for (a) technical and economic assessment of existing
repair technology, (b) identification of gaps in existing tech-
niques, and (c) definition of future research direction. Broad
goals of the laboratory evaluation are as follows (69):
An assessment of field seaming procedures for in-place
repairs, including those recommended by manufacturers, as
veil as " tricks-of -the-trade" applied by practitioners in
the field
The feasibility of drying out and repairing a dried out
piece of previously exposed liner
The reliability of a variety of adhesive bonds after
exposure to several leachates under both shear - and peel
testing
Preliminary injection parameters for various repair
compounds: epoxy resins, silicones, chemical and
particulate grouts
Durability over time of the same compounds (by destruction
testing)
The feasibility of conducting repairs under several
different conditions, as in leachate impregnated soils or in
the 'presence of running or stagnant water
Although the above laboratory program is seen as exploratory
in nature, the importance of conducting the first stages of
laboratory evaluations of liner repair systems under controlled
conditions with the total procedure exposed to view cannot be
overestimated. Once these issues are well understood, work will
be extended to include attempts at field repairs in dif f icult-to-
access environments, underneath or at the bottom of in-service
impoundments .
In another ongoing EPA-sponsored study (71), several
concepts for retrofitting liquid surface impoundment facilities
with synthetic membrane are being evaluated. Retrofitting of
173
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membrane liner systems offers a potential for reducing or
stopping seepage at a leaking site. The procedure may be used as
a permanent step to upgrade a leaking or untrustworthy facility,
cr as a temporary measure while a new replacement facility is
being constructed. Also under investigation under EPA
sponsorship is the determination of the geotechnical feasibility
of utilizing selected grouts and state-of-the-art techniques in
solving the problems associated with the in-situ bottom sealing
of existing hazardous waste sites (72).
B.2.4 Cover Settlement; Causes, Prevention and Repair
The function of the cover or cap is to prevent infiltration
of precipitation into landfill cells. The cover is usually
constructed with low permeability synthetic and/or clay material
and with graded slopes to enhance the diversion of water. Cover
subsidence or settlement has been identified as one of the most
critical factors resulting in poor landfill performance (73, 74).
Subsidences can bring about cracking or collapse of cap and
localized depressions, allowing ponding and increased
infiltration. Causes of subsidence are primarily shifting,
settling or release of landfill content over time. Although a
certain degree of uniform subsidence can be handled through
proper cover design, differential settlement is more difficult to
predict and mitigate through design. The following excerpt from
Ref. 73 illustrates the problem:
Comparatively uniform subsidence might be expected to
occur for landfills containing one form of waste (i.e.,
a monofill). Many landfills, however, contain a variety
of wastes, both containerized and in bulk. Bulk liquids
and sludges provide little internal structural support.
Vaporization may also be a problem. Containers do
provide short-term support, but they deteriorate, often
within a few years. The rate of container deterioration
is difficult to predict; it depends on site- and waste-
specific factors. It may not be possible to compact a
mixed waste landfill sufficiently, e.g., compaction
comparable to preparation of a building foundation.
Further, the internal structure of the landfill cells is
constructed of compacted support walls, which retain
their original height while the wastes within settle.
Cracking around the perimeter of the cover has resulted.
Finally, the extraction of collected leachate produces
void spaces and exacerbates settling.
Some of the design and operating procedures which are aimed
at management of leachate and gas migration/emissions can reduce
or enhance the potential for cover failure due to subsidence.
Thus, leachate and gas extraction, which promotes waste
consolidation, would also enhance potential for waste settlement.
174
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On the other hand, leachate and gas control, through source
cor.trol measures such as limiting disposal of bulk liquids,
solvents or solidifying waste prior to placement, which would
enhance the structural stability of the landfill, would also
reduce settlement potential. Because of these conflicting
effects and objectives, the subsidence problem and its mitigation
should be addressed in the context of an overall waste management
plan and objective and on a site-by-site basis. In general, the
applicable preventive and corrective measures for cover
subsidence problems include the following:
Proper cover design (see Refs. 1, 5 and 7 for analysis and
procedures)
Source control
Progressive design and multiple cell design for segregated
waste disposal (see Table 5 for description)
Placing drummed waste on its side, a position providing less
structural support, in order to hasten the collapse and
settling of the buried drums (73)
Adequate waste compaction during placement and prior to
installing the final cover to enhance structural stability
Surveillance and maintenance of the cover
The ease (or difficulty) and the cost of repairing a failed
cover depends on the nature and extent of the cover failure and
the degree of complexity and sophistication of the cover design.
The repair may require carefully peeling back each protective
layer until each is found to be sound, partial reconstruction of
gas venting and cover drainage system, recompaction of soil
layers and revegetation of the top soil (73).
B.3 CONCLUSIONS AND R&D RECOMMENDATIONS OF THE "SURFACE
IMPOUNDMENT" STUDY (2)
B.3.1 Lessons from the Case Studies
Adequate site investigation, good project planning during
the design and construction phase, and rigorous execution of
a comprehensive QA/QC are essential to developing successful
facilities. Problems resulting from inadequate site
investigation and poor design and construction practices
cannot be fully and permanently corrected through piecemeal
remedies applied as the problems surface.
Construction supervision and inspection by competent and
conscientious inspectors to ensure adherence to recommended
175
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specifications, and rigorous documentation and recordkeeping
are cornerstones of an effective QA/QC program. The program
snould cover all steps (i.e., planning, design, construc-
tion, etc.) leading to the development of a completed faci-
lity ard should encompass all system elements, support faci-
lities, operations and corrective measures (i.e., monitoring
veils, leak detection subdrains, dredging, repairs, etc.)
QA/AC programs for facilities lined with FML should
emphasize liner-waste compatibility as a criterion for liner
selection, proper installation procedures (particularly in
tne seatiing step), and the use of protective cover
(especially when the liner would be exposed to severe
stresses of the elements).
Unless properly designed, ground water monitoring programs
would not be reliable substitutes for subdrain leak detec-
tion systems. These systems would be more reliable in
providing advance warning of a site failure, thus allowing
appropriate measures to be implemented in a timely fashion.
The successful performance of surface impoundments at two of
the facilities studied is attributable to: (a) use of a very
impermeable clay as liner material; (b) extensive waste-
liner permeability studies; (c) use of competent design,
construction, and inspection contractors; (d) close scrutiny
of all phases of design, construction, and QA inspection by
the owner/operator; (e) excellent QA/QC and record-keeping
during all phases of the project; and (f) good communication
between all parties involved in establishing the sites.
Case studies documenting the performance of hazardous waste
facilities (successes and failures) can provide the feedback
needed for evaluating the performance of various designs and
construction techniques and can yield valuable lessons for
improving design, construction, monitoring and operating
procedures.
The nine case study facilities reviewed here were selected
from a much larger number of sites that were screened for
suitability to the study objective. Many facilities were
rejected because of one or more of the following reasons:
(a) not representing an engineered site, (b) presence of
other actual or potential sources of pollution at the site,
(c) little or no data available on the hydrogeological
settings and site construction, and (d) no or insufficient
monitoring data to enable performance evaluation. Based on
the sample of Sis examined, these rejected facilities more
accurately represent the existing SI practices than the nine
case studies that were selected for design versus
performance evaluation.
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5.3.2 Professional Opinions and Experience of Experts
Siting in suitable geological formations is the best
protection and the first line of defense against ground
water contamination, regardless of whether the facility will
be lined with FML, clay, or other liner types.
In the "intragradient" design, in which the facility is
intentionally located in the saturated zone, the nigh ground
water table provides a positive pressure that can prevent
release and outward migration of leachate or waste in the
event of failure.
Geotechnical support should be a continuous effort covering
rot only site investigation and facility design but also the
construction activities. The support is especially impor-
tant in preparing construction specifications and during
pond and borrow pit excavation, when major changes in soil
pr oerties must be detected and appropriate modifications
nade to the original design and construction specifications.
Even with the soundest design and support studies, the
adequacy of a completed facility cannot be guaranteed
without assurance that the construction has.been carried out
according to specifications. This underlines the importance
of an effective QA/QC program, the key elements of which
should include thorough construction inspection, use of
competent and conscientious inspectors, and detailed
documentation and record-keeping.
The most critical factor in clay liner construction is
compaction under proper moisture conditions. Compaction
should be aimed at eliminating all air spaces and not
necessarily at achieving certain arbitrary Proctor density
levels. Compaction wet of optimum is generally sufficient
to ensure elimination of air spaces and development of a
very impermeable liner.
Desiccation cracking of clay is a highly site- and
situation-specific problem that depends not only on the type
of clay and its silt content but also on the moisture level
and construction technique. Since liners are constructed in
lifts and there is little chance for alignment of cracks in
adjacent lifts, a limited number of shallow cracks that may
go unnoticed during lift inspection should not present a
major leakage problem.
Selection of suitable liner material, use of proper
installation procedures, rigorous QVQC, and providing and
maintaining protective cover for the liner are critical
factors in ensuring a successful FML installation.
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Even though waste-liner compatibility tests provide valuable
data for selecting a suitable FML, a problem often encoun-
tered is that the characteristics of the waste that will
cone in contact with the liner are not known at the time of
design and that the characteristics may change during site
operation. Thus, the compatibility issue should be re-exa-
mined any time the character of the waste changes.
Practical measures for mitigating the liner-waste
incompatibility problems relate to good site design and
operating practices and include waste segregation,
pretreatment and banning disposal of certain wastes.
FML field installation problems can be minimized by the use
of experienced workers who will carry out the actual instal-
lation. Providing good field supervision and technical
assistance to the installer, and minimizing field seaming by
use of larger liner sections (whereby much of the seaming
has been done in the plant) will also minimize problems.
Providing and maintaining protective cover for a liner is
extremely important in preventing damage as a result of the
elements and minimizing problems because of vandalism,
pinholes, animals, and chemical incompatibility.
Use of FML in conjunction with clay in a double liner system
would take advantage of the desirable properties of both
liner types and compensate for the possible shortcomings of
the individual systems. Where such combination systems have
been used, the design calculations, however, rely solely on
clay as the protector, assuming that FML would not be
available as a backup system.
Despite considerable improvements that have occurred in the
recent past in leachate collection systems design and
construction, the apparent sporadic plugging of the
underdrain systems remains a problem area. At the present
time, there is no practical corrective measure for restoring
the hydraulic capacity when a sand and gravel drainage
system is plugged.
Subdrain leak detectors, which permit direct observation,
have merits over monitoring wells (or other indirect
methods) by allowing more rapid detection of failure,
permitting monitoring over a relatively large area under the
liner and yielding more reliable results. Unless ground
water monitoring is tailored to the specific hydrogeological
and other features of a site, it may prove inadequate in
providing a true picture of the background conditions and
changes in water quality.
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The proposed. California regulations, which require double
lining vith clay and FML in addition to siting in Class I
areas is considered by some to be unnecessarily
overstringent. This apparently excessive stringency is
based on the state's experience that (a) even some well
designed facilities that have used the state-of-the-art
technologies have failed. (b) geological deposits are often
discontinuous and the potential for lateral or vertical
migration of waste, cannot be fully eliminated, and (c) when
damage occurs, the cost of cleanup can be very high.
The requirement for the use of FML in state regulations is
primarily in response to the requirement in the current
interim final RCRA regulations.
A considerable amount of accumulated experience in the waste
disposal field needs to be collected, analyzed and dissemi-
nated as a technical manual that discusses in some detail
how all of the elements of facility site selection, design,
construction, operation, monitoring, maintenance and repair
fit together.
B.3.3 R&D Recommendations
Extension of the present study to include additional case
studies and experiences of technical experts, with
dissemination of the extended study results to practicing
engineers, owners/operators of hazardous waste management
facilities, regulatory agencies and active researchers.
Evaluation and documentation of the effectiveness of various
FMLs, seaming methods, QA/QC procedures for installation,
and FML compatibility with various wastes/leachates under
field conditions.
Development and standardization of practical and economic
waste-liner compatibility tests for use in liner selection
and as a means for accepting or rejecting waste loads by
facility operators. The effort should include development
of practical tools for predicting the characteristics of
leachates from landfilling of various waste types.
Investigation and documentation of the "intragradient" and
the "hydraulic barrier" design concepts for landfills and
surface impoundments.
Identification of proper design, construction and operating
practices that would minimize the potential for clogging of
the leachate collection systems and development of
corrective measures for clogged systems.
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Development of laboratory procedures and practical field
methods for obtaining clay permeability data for use in
design.
Development of new concepts and protocols for early detec-
tion of site failures and corrective measures, and evalua-
tion of currently proposed systems (e.g., resistivity and
acoustical measurement methods) under actual conditions.
Development of technical basis and criteria for proper
design of ground water monitoring systems with respect to
number, location, and depth of monitoring wells.
Development of reliable, maintenance free, and retrofittable
techniques for monitoring the unsaturated (vadose) zone.
This should be supplemented with an effort to compile and
evaluate data on mobility, attenuation, and persistence of
waste constituents in both the vadose and saturated zones.
Development of reliable and cost-effective methods for pin-
pointing the location of liner leaks, repairing leaks (espe-
cially in landfills), and mending liners that have been in
contact with waste and/or the elements for a number of
years.
B.4 SUMMARY AND CONCLUSIONS OF THE "LINER STUDY" (1)
B.4.1 Objectives, Data Sources, and Scope
The Environmental Protection Agency's Office of Solid Waste
(OSW) is currently engaged in a review of the Part 264 land
disposal regulations (promulgated in July 1982 as Interim Final
Regulations) to determine if there are areas where regulatory
reform would be appropriate. One of the areas which is being
reviewed relates to the requirement that liners and caps for new
land disposal facilities prevent migration of waste during the
active life of the facility and minimize migration during the
post-closure care period. In this connection, and under a con-
tract with OSW, TRW has collected and reviewed data on liner
installation practices and has developed a data base on installa-
tion problems, applicable mitigation measures, and related R&D
needs. The data base presented herein consists of information
from the open literature supplemented by up-to-date data collec-
ted through some 40 interviews with technical experts in indus-
try, state regulatory agencies, trade/professional associations,
research organizations, and waste management companies. The
interviews with the experts had a much broader objective than
determining installation problems alone. They also covered other
problem areas such as liner design, manufacture, and fabrication,
which can be very critical in developing an adequate liner,
either alone or in combination with installation factors. The
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reports on the interviews have been assembled separately in a
Volume I entitled "Data Base Development: Perspectives of Indus-
try Experts, State Regulators, and Owners and Operators".
This Volume II report, which focuses only on liner
installation problems, contains the data base and the analysis
for answering two related questions of critical importance to EPA
in its review of the liner regulatory requirements. These
questions are as follows:
Can current technology and know-how allow construction and
installation of bottom liners and cap systems so that they
meet designed performance capabilities?
Are the proper technology and know-how actually used in
practice to produce installations that meet designed
performance capabilities?
As used in this report, the term "installation" refers to
all field activities related to preparation of- the site to re-
ceive the liner and the actual installation effort (i.e., liner
placement, compaction, seaming, backfill placement, etc.). The
liners which have been addressed are clay, flexible membrane
(FMLs), admixed, and sprayed-on liners. Since a number of issues
and practices are common to all liner types, in the following
discussion these points of commonality are highlighted first,
followed by a review of the issues specific to the individual
liner types. Research and development needs for addressing areas
of uncertainties are identified and a number of key overall
conclusions are presented.
B.4.2 Issues Common to Clay, FML, and Other Liner and Cap
Materials
Under existing regulations, land disposal facilities must be
constructed to include a bottom liner, waste piles and landfills
must include a leachate collection system, and closed facilities
must be capped. The operations associated with installing these
systems may be categorized broadly as follows:
Preparation of the foundation upon which the liner or cap
will be supported.
Placement of the liner or cap.
Construction of a leachate collection system as well as leak
detection system for facilities with double bottom liners.
Placement of backfill as protection for the liner or cap.
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Each step, with exception of actual placement of the liner
or cap, is generally common to installation operations at all
land disposal facilities no matter what type of material actually
constitutes the liner or cap. These common operations are
summarized briefly within this section while the steps associated
with actual placement of the liner or cap, which vary with the
type of material, are addressed in subsequent sections.
Preparation of Foundation--
The bottom liner should not be required anywhere in the
facility to lend structural support to the contained waste. The
liner largely derives its strength from the foundation such that
the integrity of the liner can be only as good as that of the
underlying foundation. Problems associated with constructing the
foundation generally are as follows:
Compaction to less than the required density (resulting
possibly in later differential settlement which can induce
stresses in the overlying liner).
Permitting the foundation to develop a moisture condition
that is incompatible with subsequent liner placement steps.
Inadequate surface finishing to reduce the potential for
liner puncture (this is generally a concern for FML only).
Inadequate sterilization of foundation soils to suppress the
growth of vegetation which can potentially penetrate the
liner.
There is little data (mostly from limited case studies) to
substantiate the quality of already constructed foundations and,
therefore, little basis on which to judge the adequacy or preva-
lence of typical construction practices. However, in general,
each of the listed problem areas should be manageable by properly
applying techniques and practices which are already used in
earthwork projects. It is the role of the quality assurance
program to ensure that such practices are actually utilized.
Also, certain consequences of the above-listed construction prob-
lems, if allowed to occur, can be readily identified and correc-
ted during subsequent operations in the overall facility develop-
ment. For example, substantial differential settlement occurring
shortly after construction or puncture of the liner by sharp
objects in the subgrade can be repaired during placement of the
liner or shortly thereafter.
Construction problems can also arise from factors which are
primarily design issues, and the quality assurance program
generally has little control over these. Some foundation designs
are incompatible with construction equipment and techniques, in
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particular sideslopes are sometimes specified too steep.
Developing a supporting surface for caps can be a more
difficult task than for the bottom liner because many wastes are
not easily compacted. As. for bottom liners, little data is
available regarding the adequacy of the supporting surface
prepared for caps.
Construction of Leachate Collection and Leak Detection Systems--
Leachate collection systems are required by the interim
regulations for waste piles and landfills to maintain the hydrau-
lic head of leachate over the liner below 30 cm. Leak detection
systems are installed in between the two liners of double-lined
facilities. The principal construction problems surrounding both
of these systems relate to the severe stresses that the collec-
tion pipes are subjected to during installation. The pipes for
leachate collection systems are laid close to the liner in an
appropriate bedding and are backfilled both to protect the pipes
from overlying stresses (the waste and vehicle traffic) and to
provide a suitable drainage course for the leachate. The magni-
tude of stress transmitted to a pipe by a load applied to the
overlying backfill is very sensitive to the depth of backfill.
Therefore, a pipe that is adequately protected by its final,
design depth of backfill may be highly susceptible to failure
until that depth is actually in place. Under most circumstances,
the leachate collection or leak detection piping network can
probably be installed without significant damage by applying very
careful techniques of backfill placement and by eliminating con-
struction equipment traffic over the pipes until the backfill has
been placed to its design depth. However, there is no data to
determine how successfully leachate collection or leak detection
systems are installed in practice.
Under some circumstances, it may be especially difficult to
construct the piping network without some damage to it and
possibly the liner. The configuration of the leachate collection
pipes and the vertical clearance over the liner are determined by
the allowable head of leachate over the liner and the
transmissivity of the backfill. When these factors require that
the collection pipes be closely spaced, it becomes difficult to
provide a backfill that will both protect the pipes and permit
flow of leachate to them. The backfill must also be so designed
that it does not clog the collection pipes.
An additional problem associated with leak detection systems
is that failure of a pipe can initiate piping of the sand or
other soil material between the two liners. Localized subsidence
is then likely, resulting possibly in a failure of the overlying
liner.
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Placement of Backfill
Backfill includes any cover material placed over a liner
(including over the leachate collection system for waste piles
and landfills as discussed) or cap to protect it from mechanical,
weather, or other environmental damage such as exposure to the
elements, vehicular or animal traffic, hot spots within a
landfill, etc. In the case of surface impoundments, the stresses
on the backfill can be especially severe as wave action is
usually involved. The principal problem associated with
installation of backfill over bottom liners and common to all
liner material types is placement of the backfill in such a
manner that it remains in place on the slopes. The degree to
which adequate practices are utilized is not documented.
Maintenance of a cover on the cap is considered the most
expensive element of post-closure care. As is the case for
development of a suitable supporting surface for the cap,
adequate compaction of the backfill is sometimes not possible due
to the condition of the underlying waste material. Many of the
problems associated with caps can be minimized, though not
eliminated, through proper design and operating practices; for
example: use of appropriate slopes, use of a soil cover capable
of supporting vegetation, seeding the area at the correct time of
the year, etc. While little hard data exists indicating the
adequacy of current construction techniques for caps, incidences
of erosion, sloughing, and subsidence have been reported.
B.4.3 Clay Liner and Caps
Many of the operations and therefore problems associated
with construction of a clay liner parallel those of the more
general earthwork operations applied during construction of the
foundation. Problems generally specific to clay liner
construction are as follows:
Where in-situ clays are involved--failing to detect and
remove discontinuities from the clay such as sand or silt
lenses, roots, rocks, etc.
Where recompacted emplaced soil liners are used--inadequate
protection of stockpiles from contamination.
Falling to attain the desired permeability which generally
results from the difficulty of ensuring that conditions in
the field closely meet those specified in the design
specifications.
Prevention of cracking, particularly by desiccation, between
the time that the liner is completed and when it is
backfilled or put directly into service.
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For facilities with in situ clay deposits (i.e., facilities
that rely upon in situ geological formations to contain wastes),
a potential problem is the presence of secondary permeabilities
(cracks, sand lenses, silt lenses, etc.) that provide potential
paths for transport of contaminants toward ground water. These
discontinuities, particularly silt lenses, are difficult to
detect. Over-excavation and recompaction (remolding) of the clay
results in a much more homogeneous barrier material. However,
certain natural clay deposits are not efficiently remolded due to
natural compression conditions. Thus, in determining- the
technology to be used for producing a soil liner, information on
both natural preconsolidation pressure of the soil and the
presence of discontinuities should be considered.
Stockpiles of clay to be used for liner or cap material
require special care to'avoid contamination, significant changes
in moisture content, or material loss by erosion. Mitigation
measures which have been used successfully in other earthwork
projects include covering the material (or seeding if it is to
remain in place for a significant length of time), inspection to
detect and remove contaminants, and addition of water if necessa-
ry to adjust moisture level to near optimum prior to placement.
Adequate compaction and therefore permeability requires that
the clay soil conditions closely approximate the design
specifications determined by laboratory testing. Potential
problems with the use of laboratory permeability tests to predict
hydraulic conductivity of the field liner include the following:
Samples may not be representative because the volume of soil
tested is minuscule compared with the volume of the soil
liner, composite samples produce less realistic results than
separate samples, or many laboratories often discard
deleterious substances in the samples.
In the field, clay clods up to one foot across are sometimes
found, but in the laboratory, clay clods are broken down
into smaller sizes. Permeability may be significantly
affected by the size of the clods of clay that exist in the
soil before it is compacted.
The lowest permeabilities correspond to the condition when
the soil is compacted at wet of optimum moisture content. It
is critical that the compaction moisture content of
laboratory samples match conditions in the field.
Permeability of compacted soil is also a function of the
compactive effort. If the compactive effort in the field is
less than in the laboratory, the field permeability may be
much higher than expected due to a shift in optimum moisture
content. It should be recognized that the method of
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compaction in the lab will never precisely reproduce
compaction in the field by heavy equipment.
There is little chance of obtaining representative
desiccation cracks which increase permeability in small,
undisturbed samples.
Use of the wrong permeate and excessive hydraulic gradients
are areas of potential problems in laboratory testing.
These problems can be mitigated by the use of laboratory
permeability tests for general guidance during final design in
conjunction with field permeability tests for construction
verification. Field tests can be conducted on individual lifts
of the compacted clay, or on the completed liner. Construction
should be inspected to ensure that deleterious materials are not
used, that moisture content and compactive effort are correct,
that large clay clods are adequately broken up, and that the
liner is not allowed to dry out. To prevent desiccation before
the liner is placed in service, a soil layer or synthetic
material should be placed atop the liner.
With exception of operations associated with reforming in
situ clays, the same problems occur for cap installation as for
bottom liner installation. However, clay cap compaction can be
particularly difficult as the underlying waste may be spongy.
For both clay liners and clay caps, the associated
installation problems can be largely overcome by using current
construction practices combined with a comprehensive quality
assurance program. Little data exists to rigorously evaluate the
adequacy of these practices or determine their prevalence.
B.4.4 Flexible Membrane Liner and Caps
Operations specific to installation of flexible membrane
liners and caps are storage and handling of the material, liner
placement, seaming, and certain aspects of backfilling.
Storage and Handling
Proper storage and handling of liner materials at the job
site is necessary to prevent their degradation due to exposure to
unfavorable weather, vandalism, and repeated folding and
unfolding. These potential problems can be handled by measures
such as storing the liner in a secured area; scheduling to reduce
time between delivery and placement of the liner; avoiding
unnecessary folding and unfolding; and inspecting materials to
identify and correct problems.
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Liner Placement
Problems associated with placement of the liner include:
Placement of panels in a wrong configuration (e.g., seams on
sideslopes oriented parallel rather than correctly
perpendicular to the side).
Placements that bridge a gap between two surfaces (e.g., at
penetrations).
Improper timing (for example, placement during inclement,
including windy, conditions).
Placement of the liner with little clearance between it and
the leachate collection pipes. This is often unavoidable
per the requirements of the leachate collection system, but
any ruptured pipe could potentially puncture the liner.
The problem of improper configuration can be avoided through
proper design (including identification of panels by number at
manufacture and fabrication) and strict adherence to design spe-
cifications. Bridging can be avoided by ensuring complete liner
contact with the supporting soil and proper compaction of the
subgrade around connections (to reduce subsequent settling).
anchoring during anchor trench backfilling can reduce liner dam-
age. Although data are not available to document incidences of
liner damage due to the above placement-related factors, the
problem of wind damage is reportedly to be widespread.
Seaming--
Seaming is perhaps the most critical operation in the
installation of FML liners and caps. The following are certain
factors of good seaming practice to avoid common problems:
Seaming procedures can vary for different liner materials
and for the same material produced by different
manufacturers. These differences should be carefully noted
as plans for the seaming operation are drawn up.
Experienced labor, at least at the foreman level, is
necessary to address adequately any unexpected problems.
Weather conditions should be compatible with the seaming
operations; in particular, excessive moisture, wind, and
extremes in temperature should be avoided.
Solvents or adhesives, where these are used to make the
bond, should be applied exactly as specified. Neither too
little nor an excess lends itself to adequate seam strength.
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Likewise, pressure should be applied to the seam in
accordance with specifications.
Slack and wrinkles should be removed, except those included
intentionally to allow for thermal expansion/contraction.
Special attention should be given to making connections
between the liner and structures.
Special precautions are required when new cap material is
seamed to old liner material. These include ensuring that
the bottom liner and cap are compatible when seamed, removal
of the surface cure from the bottom liner using solvents and
scrubbers, and repairing damage that the bottom liner
suffers when it is uncovered.
The technology for proper seaming is available, but there is
some evidence that FMLs are not always seamed properly in
practice. Seaming FMLs presents many opportunities for mistakes
and unintentional as well as deliberate deviations from
recommended practices. Use of reputable installers, development
of clear and concise specifications, and implementation of a
comprehensive quality assurance , program are essential to
constructing adequate seams.
Checking to ensure proper positioning of the liner panels,
clean seaming areas, proper overlaps, and suitable weather condi-
tions should be included among the quality assurance measures for
seaming. In addition, test seams should be made twice daily and
tested in shear and peel. All seams should be tested nondestruc-
tively over their full length. The nondestructive testing should
include both visual inspection and at least one other applicable
method (e.g., air lance, vacuum, or ultrasonic testing). Some
experts believe that while nondestructive testing is necessary,
it only provides information on the effectiveness of the seam
seal and not on the seam strength. Therefore, destructive
testing, whereby samples of the seams are removed and tested for
strength and quality in the field or laboratory, should also be
performed. Unless sampled seam areas are improperly patched,
destructive testing should not affect the liner integrity, as
feared by some who prefer to avoid such tests.
Placement of Backfill Over FML
No completely acceptable method exists for placing backfill
over FML; all methods are claimed to risk some damage to the
underlying liner. Extra care is needed when placing backfill to
avoid damage to the liner. Proper design, use of clear and
concise specifications, and an effective quality assurance pro-
gram to ensure adherence to specifications are essential but not
necessarily sufficient to install a properly functioning backfill
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without liner damage. The degree to which protective measures
are taken and to which damage occurs in actual facilities is not
documented.
B.4.5 Other Liners and Caps
Because they are used less often, the data base for other
liner and cap types is considerably smaller than that for FML and
clay. Other types of liner and cap materials reviewed in this
study are admixtures (bentonite-soil, mixtures, hydraulic asphalt
concrete, and asphalt-soil mixtures) and sprayed-ons (catalyti-
cally blown asphalt, emulsified asphalt, asphaltic rubber, and
urethane modified asphalt).
Installation problems unique to these liners relate largely
to on-site mixing and conditioning to develop the desired
material characteristics, and to application of the product to
the subgrade to develop a uniform liner of adequate thickness.
Because of the careful control which is required, a well-
conceived and implemented quality assurance program which ensures
compliance with product application requirements becomes
essential to constructing an adequate liner. However, the
adequacy of construction practices used to install specialty
liners and the prevalence of their use is not documented.
B.4.6 Key Overall Conclusions and Research and Development Needs
Conclusions
Based on the data base developed in this project, the
following conclusions can be drawn:
Little data is available to evaluate the adequacy of con-
struction and installation techniques for bottom liners and
caps, but based on the views of experts and limited case
studies reported in the literature, current technology and
know-how are believed sufficient to permit construction and
installation of systems capable of meeting design perform-
ance. This situation underlines the importance of the qua-
lity assurance/quality control programs to ensure that the
best available techniques are used during construction.
In general, the prevalence of specific installation
practices (as well as their direct impact on liner
performance) is not known. Installation problems are not
documented. but while little information is available in
the literature, [judgments by many experts interviewed
indicate that adequate installations often are not made.
Some information is also available in the form of reported
problems that occurred some time after construction is
completed. However, the connection of any such problem to a
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specific installation or construction operation is highly
uncertain. Reflecting this situation, research and
development should be directed toward systematic and
carefully developed studies to document cases of liner
successes and failures, and the installation and
construction techniques involved. Other research and
development needs identified are as follows.
Research and Development Needs--
General--
Observation of the installation and subsequent performance
of liners in actual field facilities or in "prototype" cells
dedicated to systematic studies. These studies could, for
example, address the behavior of liners and seams in deep
and shallow ponds and under a range of exposure conditions.
Scientific cause-and-effeet investigation and documentation
of the reported cases of liner failure (and successes).
Development of improved quality control tests and better
establishment of the correlation between test results and
actual performance.
Development of improved and standardized methods for
analyzing results from field and laboratory tests.
Investigation of the effectiveness of various soil steri-
lants and improved methods of application, and education of
the users on the capability of the various sterilants.
Determination of the most suitable configurations for
leachate collection systems to minimize potential for
failure during construction.
Evaluation of alternate designs and materials for leachate
collection and leak detection systems, including detection
systems which can locate the source of the leak.
Determination of maintenance practices most effective in
maintaining the long-term integrity of the backfill on a
cap.
Testing and evaluation of new materials and applications
(geotextiles for gas venting, for example), especially from
the perspective of installation techniques.
Investigation of use of chemicals such as lime or limestone
on top of the liner to effect in situ neutralization of
leachate and reduce liner-leachate incompatibility problems.
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Clays
Development of more reliable techniques for detecting subtle
discontinuities in in situ clays to ensure their removal.
Investigation of improved techniques and equipment for
uniformly distributing water to clay to develop optimal
moisture content.
Development of improved methods of determining permeability
both by field tests and by laboratory tests.
Development of methods to evaluate clay liners after
placement without violating the liner's integrity.
Assessment of the effect of subsidence on rate of
infiltration through caps.
Investigation of the possibility of using dispersants to
permit compaction of the clay to a higher density.
Development of better methods by which to evaluate
contaminant transport in fine grain soils, including in
fracture networks.
Flexible Membranes
Development of better design/construction criteria for con-
necting liners to concrete structures in impoundments.
Development of better sump systems for landfills to allow
more durable connections (the concept of a prefabricated
unit is considered worth investigating).
Definition of conditions where geotextiles can be cost-
effectively used in conjunction with reinforced and
unreinforced FML.
Investigation of substitutes to seaming (e.g., use of a
"mechanical zipper"), development of new seaming methods,
and test and evaluation to generate the technical basis for
more concise seaming specifications.
Investigation of the thickness and characteristics of
bedding and protective soil layers needed to protect the FML
from projections in the subgrade.
Other Liner and Cap Materials
Independent verification of data reported by suppliers on
installation problems and effectiveness of specialty liners.
191
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*PB86162104*
*BA*
BIN
INVOICE
SHIPTO
PAYMENT
M156
783008
1*798B3
NONE
06-22-99
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