LDCRS FLOW FROM DOUBLE-LINED LANDFILLS
AND
SURFACE IMPOUNDMENTS
by
Rudolph Bonaparte and Beth A. Gross
GeoSyntec Consultants
Atlanta, Georgia 30342
Contract No. 68-CO-0068
Project Officer
Mr. Robert E. Landreth
Risk Reduction Engineering Laboratory
Cincinnati, Ohio 45268
RISK REDUCTION ENGINEERING LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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'*",
4
DISCLAIMER
The information in this document has been funded by the U.S. Environmental Protection Agency
(EPA) under Contract No. 68-CO-0068, Work Assignment No. 35 to Eastern Research Group, Inc. It
has been subjected to the Agency's peer and administrative reviews, and it has been approved for
publication as an EPA document. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
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FOREWORD
Today's rapidly developing and changing technologies and industrial products and practices
frequently carry with them the increased generation of materials that, if improperly dealt with, can
threaten both public health and the environment. The U.S. Environmental Protection Agency is
charged by Congress with protecting the Nation's land, air, and water resource. Under a mandate of
national environmental laws, the agency strives to formulate and implement actions leading to a
compatible balance between human activities and the ability of natural systems to support and nurture
life. These laws direct the EPA to perform research to define our environmental problems, measure
the impacts, and search for solutions. :
The Risk Reduction Engineering Laboratory is responsible for planning, implementing, and
managing research, development, and demonstration programs to provide an authoritative,!defensible
engineering basis in support of the policies, programs, and regulations of the EPA with irespect to
drinking water, wastewater, pesticides, toxic substances, solid and hazardous wastes, and Superf und-
related activities.
This report provides the field data to support the Agency's recent final rule on liner leak detection
(40 CFR 260, 264, 265, 270, and 271). The data illustrates that waste management facilities can be
constructed with minimal leakage rates provided that quality control and quality assurance programs
are used.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
in
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ABSTRACT
This report presents field data on the measured flows of liquid from the leakage detection,
collection, and removal systems (LDCRSs) of 28 double-lined landfill facilities and eight double-lined
surface impoundment facilities. For each facility, information on design and operation is presented,
as is an evaluation of the sources of the measured flow. Potential sources include leakage through the
top liner, precipitation that percolates into the LDCRS during construction, water that infiltrates through
the bottom liner and enters the LDCRS, and consolidation of any clay component of the top liner. From
the evaluation, conclusions are drawn regarding the frequency of occurrence, sources, and rates of
liquid flows from the LDCRSs of double-liner systems. Conclusions are as follows:
• LDCRSs frequently exhibit flows from one or several of the aforementioned sources;
« all of the landfill cells constructed with geomembrane top liners appear to have exhibited top
liner leakage; cells with composite top liners typically exhibited LDCRS flows attributable to
consolidation water, except for composite liners constructed with geosynthetic-clay liners
(GCLs) for which there is little, if any, consolidation water;
«> about 60 percent of the surface impoundment ponds constructed with geomembrane top
liners appear to have exhibited top liner leakage; the lower incidence of top liner leakage for
ponds than for landfill cells may be attributed to the use of ponding tests and/or leak location
surveys during construction of the ponds to identify geomembrane defects and allow their
repair;
• flow rates from the LDCRSs of the landfills are generally within the range that would be
expected, based on currently available methods of analysis for liner system performance;
flow rates from the LDCRSs of ponds constructed with geomembrane top liners are lower
than would be calculated using available analysis methods because the use of ponding tests
and leak location surveys, followed by geomembrane repair, resulted in fewer geomembrane
liner defects than assumed in the analysis methods; and
• facilities constructed with a rigorous construction quality assurance program typically meet
EPA recommended action leakage rates (ALRs) of 1,000 Iphd (100 gpad) for landfills and
10,000 Iphd (1,000 gpad) for ponds; however, flow rates higher .than these ALRs
occasionally occur at landfills with composite top liners and ponds that have geomembrane
top liner defects.
This report was submitted in fulfillment of Contract No. 68-CO-0068, Work Assignment No. 35,
by GeoSyntec Consultants under the sponsorship of EPA. The report covers work completed through
September 1992.
IV
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CONTENTS
DISCLAIMER ii
FOREWORD ,. . Hi
ABSTRACT iv
FIGURES vii
TABLES viii
ACKNOWLEDGEMENTS \ ix
1. INTRODUCTION 1
1.1 Purpose of the Report 1
1.2 Organization of the Report 2
1.3 Definitions 2
1.3.1 Landfills and Surface Impoundments 2
1.3.2 Liner, Lining System, and Double-Liner System '. . . 3
1.3.3 Double-Liner System Components 3
2. CONCLUSIONS 7
3. RECOMMENDATIONS . 9
3.1 Introduction 9
3.2 Available Data . 9
3.3 Data Evaluation 10
4. POTENTIAL SOURCES OF LIQUIDS IN LDCRSs 11
4.1 Introduction 11
4.2 Top Liner Leakage 11
4.3 Construction Water 14
4.4 Compression Water ; 15
4.5 Consolidation Water 16
4.6 Infiltration Water ' 18
5. DATA FROM LDCRSs OF OPERATING UNITS 19
5.1 Data Collection Methodology 19
5.2 Description of Operating Units • 19
5.3 Measurement of Flow from LDCRSs 41
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CONTENTS (continued)
6. RESULTS AND DISCUSSION 43
6.1 Methodology for Evaluating Measured Flow 43
6.2 Review of Data -. 44
6.2.1 Group I Facilities . . 44
6.2.2 Group II Facilities 47
6.2.3 Group III Facilities . 49
6.2.4 Group IV Facilities 51
6.3 Interpretation of Data 53
6.3.1 Group I and Group II Landfills 53
6.3.2 Group III and Group IV Landfills 55
REFERENCES 57
APPENDIX A REGULATORY BACKGROUND 59
VI
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FIGURES
Number Page
1 Typical double-liner systems for leachate containment in landfills 4
2 Definitions and terminology for double-liner system components 6
3 Potential sources of flow from LDCRSs 12
VII
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TABLES
Number Page
1 Calculated top liner leakage rates due to leakage through holes
in a geomembrane ; 13
2 General information on double-lined landfills 20
3 Details of landfill double-liner systems 23
4 Measured flow rates from the LDCRSs of the double-lined landfills 26
5 General information on double-lined surface impoundments '. . . . . 34
6 Details of surface impoundment double-liner systems 35
7 Measured flow rates from the LDCRSs of the double-lined surface
impoundments 36
8 Characterization of 93 individually monitored cells and ponds 40
9 Number of facilities in each group . 40
10 Comparison of measured flow rates at Group I and II landfills 54
11 Comparison of measured flow rates at Group III and IV landfills 56
VIII
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ACKNOWLEDGEMENTS
This report was prepared under the guidance of the EPA, Office of Research and
Development. The EPA Task Manager overseeing preparation of the report was Mr. Robert E.
Landreth. An earlier version of this report was prepared for the EPA Office of Solid Waste; EPA Task
Managers for the earlier report were Messrs. Alessi D. Otte and William Kline. The support and
contributions of Messrs. Landreth, Otte, and Kline to this work are appreciated. The authors would
also like to thank Dr. J.P. Giroud of GeoSyntec Consultants for his review of the report, i
IX
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SECTION 1
INTRODUCTION
1.1 PURPOSE OF THE REPORT
Liquid flows have been observed from the leakage detection, collection, and removal systems
(LDCRSs) of many double-lined landfill and surface impoundment units. Regulatory authorities and
others have sometimes assumed that these flows are due solely to leakage through the top liner and
are, therefore, a cause for concern and action. The flows, however, can be due to sources other than
top liner leakage.
The purpose of this report is to summarize and evaluate field data on the measured flows of
liquid from the LDCRSs of 28 double-lined landfills and eight double-lined surface impoundments. The
report was originally prepared to provide technical support for EPA's proposed Liner/Leak Detection
System Rule of 29 May 1987. In this proposed rule, EPA introduced the concept of action leakage
rate (ALR) which was defined as (52 FR 20222) "the rate of leakage from the top liner into the LDCRS
that triggers interaction between the owner or operator and the Agency to determine the appropriate
response action for the leakage". Under the proposed rule, the facility owner or operator could
establish an ALR as a value specified by EPA or by developing a site-specific ALR. The ALR value
specified by EPA was proposed to be in the range of 5 to 20 gallons/acre/day (gpad). This report was
initiated to provide technical support to EPA for selection of a specific ALR value. Interim results of
the investigation of LDCRS flow rates were presented by Bonaparte and Gross [1990]. In their paper,
Bonaparte and Gross conclude that while an ALR of 50 Iphd (5 gpad) is too restrictive, an ALR of 200
Iphd (20 gpad) appears to be reasonable for facilities constructed to present standards with rigorous
construction quality assurance. (NOTE: For simplicity, in this report it is assumed that 1 gpad = 10
Iphd. More precisely, however, 1 gpad = 9.3 Iphd.)
The proposed Liner/Leak Detection System Rule was finalized on 29 January 1992 (57 FR
3462). The original ALR concept was not included in the final rule, and the ALR was redefined as (57
FR 3462) "the maximum design leakage rate that the leak detection system can remove without the
fluid head on the bottom liner exceeding one foot". The value of the ALR in the final rule is site-
specific. Additionally, as"stated in the preamble to the final rule (57 FR 3474), "the Agency believes
that units meeting the minimum technical requirements would not require action leakage rates below
100 gpad for landfills and waste piles and 1000 gpad for surface impoundments". These flow rates,
1
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which are referred to as EPA's "recommended action leakage rates" in the preamble to final rule, are
significantly higher (i.e., approximately one to two orders of magnitude higher) than the ALR values
considered under EPA's proposed rule of 29 May 1987. As will be shown in this report, the facilities
considered in this report typically exhibited LDCRS flows less than the ALR values in the final rule.
1.2 ORGANIZATION OF THE REPORT \ ' •
The organization of this report is as follows:
• conclusions on the analysis and interpretation of the LDCRS flow rate data are
presented in Section 2; '
• recommendations for future research related to the information presented herein are
presented in Section 3; '
• potential sources of liquid flows from LDCRSs are described in Section 4;
• data on measured flows from the LDCRSs of double-lined landfills and surface
impoundments are presented in Section 5; and
• analysis and interpretation of the LDCRS flow rate data is presented in Section 6.
I
The regulatory developments that led to the final ALR concept are presented in Appendix A
of this report.
1.3 DEFINITIONS '
1.3.1 Landfills and Surface Impoundments \
Landfills and surface impoundments are land-based units that contain solid wastes, and liquid
wastes or sludges, respectively. The goal of the lining system in these units is to minimize, to the
extent achievable, the migration of hazardous constituents out of the units. >
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1.3.2 Liner, Lining System, and Double-Liner System
A liner is a low-permeability barrier used to impede liquid or gas flow. As discussed in Giroud
[1984] and EPA [1987], no currently available liner is totally impermeable. Since no liner is
impermeable, liquid containment within a landfill or surface impoundment unit can only result from a
combination of liners and drainage layers performing complementary functions. Liners impede the flow
of liquid out of the unit. Drainage layers collect and convey the liquid towards controlled collection
points (sumps) where the liquid can be removed from the unit. Combinations of liners and drainage
layers in the units are called lining systems.
A double-liner system is a lining system which includes two liners with a leakage detection,
collection, and removal system (LDCRS) between the liners. For landfills, a leachate collection and
removal system (LCRS) is placed above the top liner. For surface impoundments, there is no need or
regulatory requirement for a LCRS above the top liner. The majority of double-liner systems being
constructed today have either geomembrane or composite top and bottom liners (where a composite
liner consists of a geomembrane placed directly on top of a low-permeability soil layer or geosynthetic
clay liner (GCL)) with a LDCRS between the two liners. Older lining systems constructed with low-
permeability soil liners alone are not considered in this report.
1.3.3 Double-Liner System Components
Figure 1 illustrates typical double-liner systems used to contain leachate in landfills. Double-
liner systems used to contain liquid in surface impoundments are similar to those shown in Figure 1,
except that surface impoundments do not require an LCRS drainage layer above the top liner. (Waste
piles are a third type of land-based containment unit and are similar to landfills except that they only
contain solid wastes temporarily. Waste piles are mentioned briefly in this report for completeness
since they are subject to most of the same regulations as landfills.) The double-liner systems shown
in Figure 1 incorporate the liner types (i.e., geomembrane liners and composite liners) and the drainage
materials types (i.e., granular materials, geonets, or other geosynthetics) used to construct landfills,
waste piles, and surface impoundments. The types of liners and drainage materials used in double-liner
systems significantly influence the frequencies of occurrence, sources, and rates of flow from LDCRSs.
Therefore, different liner and drainage material types will be considered in this report.
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SAND LCRS
DRAINAGE LAYER.
SAND LDCRS
DRAINAGE LAYER
PROTECTIVE
COVER SOIL
GEOMEMBRANE
TOP LINER
COMPOSITE
BOTTOM
' LINER
GEONET LCRS
DRAINAGE LAYER
COMPOSITE
TOP LINER
COMPOSITE
BOTTOM
LINER
GEONET LDCRS
DRAINAGE LAYER
Figure 1. Typical double-liner systems for leachate containment in landfills.
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f
In this report, the parameters used to describe the design features of double-liner systems
are (Figure 2): i = slope gradient (dimensionless); kdt = hydraulic conductivity of the LCRS drainage
material (cm/s); Tdt = thickness of the LCRS drainage material (m (ft)); Tflt = thickness of the
geomembrane component of the top liner (mm (mil)); kst = hydraulic conductivity of the compacted
low-permeability soil or geosynthetic clay liner (GCL) component of the top liner {cm/s); T3t = thickness
of the compacted low-permeability soil or GCL component of the top liner (m (ft)); k,, = hydraulic
conductivity of the LDCRS drainage material (cm/s); Tdb = thickness of the LDCRS drainage material
(m (ft)); TBb = thickness of the geomembrane component of the bottom liner (mm (mil)); k.b =
hydraulic conductivity of the compacted low-permeability soil component of the bottom liner (cm/s);
and Tsb = thickness of the compacted low-permeability soil component of the bottom liner (m (ft)).
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LCRS DRAINAGE LAYER
TOP LINER
LDCRS DRAINAGE LAYER
BOTTOM LINER
Figure 2. Definitions and terminology for double-liner system components,
(Note: k = hydraulic conductivity; T = thickness; and ;
± = slope gradient.) _ !
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SECTION 2
CONCLUSIONS
Using the data for landfills and surface impoundments presented in Section 5 of this report,
and the data analysis and interpretation presented in Section 6, the following conclusions are drawn
with respect to LDCRS flows from double-lined waste containment facilities.
• LDCRSs frequently exhibit flows that may be due to top liner leakage or other
sources such as construction water, consolidation water, and infiltration water.
LDCRS flow rate data presented in Tables 4 and 7, for landfills and surface
impoundments, respectively, demonstrate the frequencies of occurrence and rates
of flow from these sources.
• All of the landfill cells reviewed in this report that were constructed with
geomembrane top liners appear to have exhibited top liner leakage. Based on the
available data, the average and maximum flow rates attributable to top liner leakage
at active cells that had geomembrane top liners and construction quality assurance
(CQA) programs were less than 1,000 Iphd (100 gpad). Typically, flow rates from
these units were less than 200 Iphd (20 gpad). For cells without CQA programs,
both average and maximum flow rates attributable to top liner leakage were
frequently more than 1,000 Iphd (100 gpad). Maximum flow rates, which often
occurred shortly after storm events, were typically several times greater than the
average flow rates.
• Only about 60 percent of the surface impoundment ponds reviewed in this report
that were constructed with geomembrane top liners appear to have exhibited top
liner leakage. In general, the measured flows from the ponds were less than 300
Iphd (30 gpad). The lower incidence of top liner leakage for ponds than for landfill
cells may be attributed to the use of ponding tests and/or leak location surveys
during construction of the ponds to identify geomembrane defects and allow their
repair. Additionally, when flows were observed during operation of a pond, defects
were often located and repaired. Thus, significant LDCRS flows from ponds were
often of limited duration (i.e., until the pond was repaired).
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Facilities having a composite top liner incorporating a layer of clay almost always
exhibited LDCRS flows due to consolidation water. Flows attributable to primary
consolidation of the clay occurred while the facilities were active. Continuing flows
after facility closure are potentially attributable to water expelled during secondary
compression of the clay layer (secondary compression water). Average measured
flow rates attributable to consolidation water ranged up to 1,300 Iphd (130 gpad),
although most rates were less than 300 Iphd (30 gpad); average measured flow
rates potentially attributable to secondary compression water ranged from 30 to 380
Iphd (3 to 38 gpad).
Leakage rate calculations performed using the method of Giroud and Bonaparte
[1989a,b] provide a reasonable upper bound on observed flow rates attributable to
top liner leakage at landfills with .geomembrane top liners. However, ;the method
greatly overpredicts top liner leakage rates at impoundments with geomembrarie top
liners. It appears that the primary reason for the overprediction is that |the number
and/or frequency of geomembrane holes assumed by Giroud and Bonaparte are too
high for the considered surface impoundments and period of monitoring. Based on
the data in this report, the use of ponding tests and leak location surveys, followed
by geomembrane repair, reduces the frequency and/or size of geomembrane holes
below the number often assumed for leakage rate calculations (i.e., :3 to 5 per
hectare (1 to 2 per acre)).
The calculation methods presented by Gross et al. [1990] for! estimating
consolidation water and construction water flow rates appear to give, reasonable
order-of-magnitude estimates of flows attributable to these sources.
Based on an analysis of the data presented in Tables 4 and 7, facilities with double-
liner systems constructed with a rigorous CQA program will typically meet the EPA
recommended action leakage rates of 1,000 Iphd (100 gpad) for landfills and 10,000
I
Iphd (1,000 gpad) for surface impoundments. For landfills with composite top liners,
' flows due to consolidation water may occasionally be greater than 1,000 Iphd (100
gpad). For surface impoundments that have defects in the geomembrane top liner,
flow rates may temporarily be higher than 10,000 Iphd (1,000 gpad).; However,
repair of the defects will usually decrease flows to below triggering levels (i.e., less
than 10,000 Iphd (1,000 gpad)). '
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SECTION 3
RECOMMENDATIONS
3.1 INTRODUCTION
The information contained in this report is intended to provide a preliminary understanding
of how landfill and surface impoundments are performing with respect to liquid containment and
environmental protection. To increase this understanding, it is recommended that additional studies
be undertaken. The purpose of this section of the report is to present recommendations for future
studies to expand the information contained in this report. In developing the recommendations,
emphasis is placed on those studies appearing to have the best potential to provide useful results and
that can be performed with data currently accessible to EPA.
3.2 AVAILABLE DATA
As a starting point for the additional studies, data should be obtained from the waste
management units described in this report and other units that have designs meeting, or at least
reasonably consistent with, existing EPA regulations. Information should be collected directly from the
owners/operators of the units, as well as from EPA files. The data that should be gathered for each
unit include:
• type of unit and design details, geographic location, hydrogeologic setting, waste
characteristics, key dates in the life of the unit (e.g., construction, operation,
closure), and operations and maintenance information;
• LCRS monitoring data (liquid quantity and chemical quality);
• LDCRS monitoring data (liquid quantity and chemical quality);
• unsaturated zone monitoring data (liquid quantity and chemical quality), if it exists;
• ground-water quality monitoring data;
• rainfall monitoring data; and
• results of any special evaluations or testing, such as geomembrane coupon testing.
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3.3 DATA EVALUATION
The available data for landfills, waste piles, and surface impoundments should be collected,
analyzed, interpreted and cataloged. The cataloging effort should be designed to create a permanent
data base, available for interested parties, that can be periodically updated in the future. The analyses
and interpretation of the data should be intended to systematically address the following questions.
• What quantity and chemical quality of leachate is generated in the units, both during
and after closure? i
• How does the quantity and chemical quality of leachate vary geographically?
• What impact is EPA's land disposal restrictions (i.e., 40 CFR 268) having on leachate
quantity and chemical quality? :
• What is the quantity and chemical quality of the liquid flows from the LDCRSs of the
units?
I i
• What are the sources of the liquid flows from the LDCRSs? '•
• What conclusions can be drawn from the available LDCRS data on the performance
of top liners and, by extrapolation, on the performance of the entire liner system?
• What is the risk of the liquid flows from the LDCRS on human health and the
environment?
• Is there any indication from the available data that the LCRSs or LDCRSs are clogged
or otherwise not functioning adequately?
• Is there any indication that units with one type of LCRS or LDCRS rdesign are
performing better than units with a different type of design?
• Does available ground-water quality monitoring data or other available imonitoring
data (such as unsaturated zone monitoring data) provide any indication!of leakage
from a unit? :
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SECTION 4
POTENTIAL SOURCES OF LIQUIDS IN LDCRSs
4.1 INTRODUCTION
To evaluate LDCRS flow data, the potential sources of flow must first be identified. Flow
can be due to top liner leakage, water from precipitation or other sources that percolates into the
LDCRS during construction ("construction water"), water expelled from a granular LDCRS due to
compression of the LDCRS ("compression water"), water squeezed out of the clay component of a
composite top liner as a result of clay consolidation ("consolidation water"), and water that infiltrates
the bottom liner and enters the LDCRS ("infiltration water") [Gross et al., 1990]. Each of these
potential sources of flow is depicted in Figure 3 and is described below.
4.2 TOP LINER LEAKAGE
All of the top liners considered in this report include geomembranes (i.e., they are either
geomembrane liners or composite liners). Leakage through liners constructed with geomembranes
occurs essentially as a result of flow through defects in the geomembrane. Occasional small defects
in geomembranes may result from manufacturing, but are more likely to result from during or after
geomembrane installation. Equations to calculate steady-state leakage rates through liners constructed
with geomembranes due to flow through holes were developed in EPA [1987], based on the analytical
and experimental studies by Faure [1979, 1984], Sherard [1985], Fukuoka [1985, 1986], and Brown
et al. [1987]. The equations were later modified by Bonaparte et al. [1989], Giroud and Bonaparte
[1989a,b], and Giroud et al. [1989; 1992]. Based on these equations, the rate of flow through
geomembrane holes is dependent on the liquid head on the geomembrane, the hydraulic conductivities
of the soil layers immediately underlying and overlying the geomembrane, the size and frequency of
occurrence of holes in the geomembrane, and, for composite liners, the quality of the contact between
the geomembrane and underlying soil layer (which is a function of the quality of construction).
Table 1 presents the results of calculations using the equations for flow through holes in a
geomembrane to obtain top liner leakage rates per unit area of liner. For the calculations, it was
assumed that the soil layer underlying the geomembrane is 0.9 m (3 ft) thick, and the GCL underlying
the geomembrane is 6 mm (0.25 in.) thick. It was further assumed that the geomembrane was
carefully constructed and had only five small holes per hectare (2 small holes per acre), with each hole
having an area of 3 x 10~6 m2 (5 x 10~3 in2), and that good quality contact existed between the
geomembrane and underlying soil layer or GCL (assumptions consistent with those of Giroud and
Bonaparte [1989a,b]).
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GROUND-WATER TABLE
Q = TOTAL FLOW
Q = AtB+C+D
POTENTIAL SOURCE:
A = TOP LINER LEAKAGE
B = CONSTRUCTION WATER AND COMPRESSION WATER
C = CONSOLIDATION WATER
D = INFILTRATION WATER
Figure 3. Potential sources of flow from LDCRSs (from Bonaparte arid
Gross [1990]). ;
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Table 1. Calculated top liner leakage rates due to leakage through holes in a geomembrane (qT,
Iphd). (Values obtained using equations from Bonaparte et al. [1989] and Giroud et al.
[1992], and the following input parameters: N = number of geomembrane holes per
unit area = 5 holes/hectare (2 holes/acre); a = area of geomembrane hole = 3 x 10"6
m2 (5 x 10'3 in2}; kmin = minimum of kdb or kat; and ht = liquid head on liner. Good
o.uality contact exists between the geomembrane and underlying soil layer or
geosynthetic clay liner (GCL). The thickness of the soil layer is 0.9 m (3 ft), and the
thickness of the GCL is 6 mm (0.25 in.).)
Conductivity
kmln (cm/s)
io-9
10-8
10'7
10'6
1 0'5
10'4
io-3
TO'2
io-1
1
Liquid Head on Liner, ht (m (ft))
0.03 (0.1)
Soil Layer
-
0.05
0.3
1
8
40
200
400
600
600
GCL
0.01
0.06
-
-
-
-
-
-
-
-
0.3 (1)
Soil Layer
-
0.4
2
10
60
300
1000
1500
2000
2000
GCL
0.2
1
-
-
-
-
-
-
-
-
3.0 (10)
Soil Layer
-
3
20
90
500
2600
5200
6200
6300
6300
GCL
10
80
-
-
_
_
-
_
-
-
13
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From inspection of Table 1, it can be seen that calculated steady-state top liner leakage rates
through composite liners (based on a hydraulic conductivity (kmln) of the clay or GCL component of the
composite liner of 10~7 cm/s or less) range from 0,01 to 90 Iphd (0.001 to 9 gpad). In contrast,
calculated leakage rates through geomembrane liners underlain by drainage materials (with the
hydraulic conductivity of the drainage material kmin > 10"2 cm/s) range from 400 to 6,300 Iphd (40
to 630 gpad). The calculated leakage rates for geomembrane top liners are about two to five orders
of magnitude greater than those calculated for composite top liners. A further contrast between
composite liners and geomembrane liners lies in the fact that it can take from several months to many
years for liquid to flow through the clay component of a composite liner or several daysj to several
years for liquid to flow through the GCL component of a composite liner, whereas flow through a hole
in a geomembrane liner underlain by a drainage material occurs almost instantaneously. It can also be
observed from Table 1 that composite liners incorporating GCLs are most effective at minimizing
leakage when subjected to liquid heads of 0.3 m (1 ft) or less, which are typical for landfills. When
subjected to higher liquid heads, such as those that occur in surface impoundments (e.g., 3 ;m (10 ft)),
the effectiveness of composite liners incorporating GCLs decreases somewhat due to the high hydraulic
gradient across the GCL [Giroud et al., 1992].
4.3 CONSTRUCTION WATER
The primary source of construction water in a LDCRS is precipitation that percolates into the
LDCRS prior to placement of the top liner. Of this water, some may be retained in the drainage
material by capillary tension, and the rest will flow by gravity from the LDCRS.
The maximum time required for gravity drainage of construction water from a LDCRS can be
estimated using Darcy's equation, as follows:
) (Equation 1)
where: tc = maximum time for gravity drainage of construction water (s); Lf = maximum length of
flow path (m (ft)); i = slope gradient (dimensionless); and ndb = porosity of the LDCRS drainage
material (dimensionless).
The maximum volumetric moisture content of a drainage material due to capillarity Is referred
to as its specific retention, sr. The specific retention of a drainage material is dependent on the size
distribution and shape of the material's pores. The specific retention of a geonet drainage layer is zero;
the specific retention of a coarse gravel is almost zero. A medium to coarse sand hasja specific
retention on the order of 0.08 [Linsley et al., 1975]. If the volumetric moisture content, !wv, of the
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LDCRS drainage material at the end of construction is less than its specific retention (i.e., if wv < sr),
there will be no drainage of construction water. If, however, the volumetric moisture content of the
material at the end of construction is greater than its specific retention (i.e., if wr > sr), water will drain
from the layer until the volumetric moisture content equals the specific retention (i.e., wr = sr).
The volume of water per unit area of liner that drains from the LDCRS by gravity can be
estimated using the following equation:
vc = Tdb (wv - sr) = Tdb (S ndb - s,) (Equation 2)
where: vc = volume of construction water per unit area of liner that drains from the LDCRS by gravity
(m (ft)); wv = volumetric moisture content of drainage material at end of construction {dimensionless);
sr = specific retention of drainage material (dimensionless); and S = degree of saturation of drainage
material at end of construction (dimensionless)'.
The average LDCRS flow rate per unit area of liner, qc (Iphd (gpad)), due to construction
water is given by:
Qc = vc I tc (Equation 3)
Gross et al. [1990] presented the results of calculations to quantify potential construction
water flow rates and durations for a typical landfill cell. The results indicate that the flow rate is
directly proportional to kdb and the duration of flow is inversely proportional to kdb. Thus, with a high-
permeability drainage material, such as a clean gravel or geonet (e.g., kdb > 1 cm/s), the flow rate after
a precipitation event can be large (e.g., 200,000 Iphd (20,000 gpad)) but of very short duration (e.g.,
less than one day). In contrast, with a lower-permeability drainage material, such as a fine to medium
sand (e.g., kdb = 10~2 cm/s), the rate of flow of construction water will be smaller (e.g., 2,000 Iphd
(200 gpad)), but the duration of flow will be quite long (e.g., more than 100 days). In the latter case,
construction water may still be draining from a facility well after the start of operation.
4.4 COMPRESSION WATER
As a LDCRS constructed of a granular material compresses under the weight of the overlying
waste or impounded liquid, the pore volume and porosity of the LDCRS decrease. Simultaneously, the
capillary tension of water in the pores of the material increases as the soil particles take on a denser
packing.
15
-------
When a granular LDCRS material retaining water by capillary tension compresses, the volume
!
of water per unit area of liner that drains from the LDCRS can be calculated using the following
equation:
v£ = ev s, Tdb = (Aav I Ec)sr Tdb (Equation 4)
where: VE = volume of water per unit area of liner that drains from the LDCRS by gravity (m (ft));
ev = compressive strain of the LDCRS drainage material (dimensionless); Acrv = change1 in vertical
stress due to placement of waste (kPa (psf)); and E0 = constrained modulus of the drainage material
(kPa (psf)). Equation 4 was derived using the conservative assumption that there is no increase in
f
specific retention of the granular material as it compresses under the weight of the overlying waste.
Equation 4 can only be used if the volumetric water content of the material is greater than or equal to
its specific retention (i.e., wv >: sr). If the volumetric water content of the material is less than the
material's specific retention (i.e., wv < sr). Equation 4 is not valid since liquid may not be released as
a result of compression.
Calculations in Gross et al. [1990] indicate that the flow rate of compression water from a
i
granular drainage material initially at its specific retention is small (e.g., 1 to 20 Iphd (0.1 to 2 gpad))
and is frequently negligible in comparison to potential flow rates from other sources. ;
4.5 CONSOLIDATION WATER ! .
Two general categories of low-permeability soil layers must be considered: (i) relatively thick
(0.5 to 1.5-m (1.5 to 5-ft) thick) layers of compacted natural clay or bentonite-treated soil; and (ii) thin
(6-mm (0.25 in.) thick) GCLs. During filling of a landfill or surface impoundment, soil layersiin the first
category will consolidate and expel water into the adjacent LDCRS drainage layer. GCLs, however,
are placed in a dry state and will not contribute additional liquid to the LDCRS.
An upper bound of the rate at which water is expelled from a clay layer can be obtained by
assuming the clay layer is initially saturated. With this assumption, the occurrence of consolidation
|
water can be quantified using the classical theory of one-dimensional consolidation [Terzaghi, 1943].
This theory uses the consolidation time factor, T, defined as:
T = f£ (Equation 5)
H2
where: T = consolidation time factor at time t (dimensionless); t = elapsed time since instantaneous
load application (s); H = length of drainage path (m (ft)); and cv = coefficient of consolidation (rn2/s
16
-------
(ft2/s)). The theory also establishes a relationship between the consolidation time factor T and the
degree of consolidation U. . .
Schiffman [1957] modified the classical theory of one-dimensional consolidation to account
for a constant rate of load application. In his work, Schiffman established a relationship between the
degree of consolidation U and the consolidation time factor T. This relationship was later used by
Giroud [1983] to determine the maximum rate of consolidation Rmax (defined as dU/dT) for a constant
rate of load application. For flow rate calculations, it can be assumed that the rate of filling of a unit
is constant between t = 0 and t = tf, where t, is the time required to fill the landfill or surface
impoundment. It can also be assumed that the pore water within the clay layer drains to the LDCRS
drainage layer (i.e., the maximum length of the drainage path for pore water is equal to the thickness
of the clay layer).
For most landfill and many surface impoundment applications, the time factor, Tf, at the end
of filling (obtained using Equation 5 with t = tf) is larger than one. As shown by Giroud [1983], when
Tf > 1, almost all of the consolidation water has been expelled at time t = t, (i.e., at the end of waste
placement or surface impoundment filling) and Rmax = 1 /Tf.
Giroud [1983] has established the following equation to calculate the maximum rate of water
expulsion from a consolidating clay layer subjected to a constant rate of load application:
gs = Aff" **! /?max (Equation 6)
Pw 9 I st
where: qs = maximum flow rate from the LDCRS per unit area of liner due to consolidation water (m/s
(ft/s)); Aav = vertical stress due to the weight of waste (kPa (psf)); pw = density of water (kg/m3
(lb/ft3)); g = acceleration of gravity (m/s2 (ft/s2)); and Rmax = maximum rate of consolidation. Equation
6 is conservative because it assumes that the clay is initially saturated. In most cases, clay layers are
compacted to a degree of saturation between 75 and 90 percent.
Calculations presented in Gross et al. [1990] suggest that the flow rate due to consolidation
water may range from 10 to 1,500 Iphd (on the order of 1 to 150 gpad). Higher flow rates are
associated with more compressible soils, faster rates of load application, and larger consolidation
stresses. The calculations also indicate that, for most landfills that receive waste at a steady rate over
one or more years, the end of primary consolidation will approximately coincide with the end of the
active life of the landfill.
17
-------
It should be noted that, as described by Bonaparte and Gross [1990], water from secondary
compression of a clay layer may persist after the end of primary consolidation. In general, soils that
exhibit relatively high consolidation, such as high plasticity clays, will also exhibit relatively high
secondary compression. As a consequence, for some plastic clay materials compacted wet of
optimum moisture content, water due to secondary compression may be a significant souijce of liquid
flow after the end of a facility's active life. Calculated secondary compression flow rates are in the
range of 10 to 100 Iphd (on the order of 1 to 10 gpad). These flow rates may persist over the entire
post-closure period of the facility, albeit at a progressively decreasing rate. ;
4.6 INFILTRATION WATER
Infiltration water can migrate through defects in the geomembrane component of ithe bottom
liner into the LDCRS if there is a sustained ground-water table above the base of the bottom liner or
if the bottom liner is a composite liner with a clay layer that is undergoing consolidation or secondary
compression. The calculation results given in Table 1 can be used to estimate infiltration rates if it is
assumed that the rate of flow through the liner is independent of the direction of flow (i.e., up or
down). In this case, kmln in Table 1 corresponds to the hydraulic conductivity of the soil immediately
underlying the geomembrane component of the bottom liner. From Table 1, the quantity of infiltration
through composite bottom liners (i.e., ksb < 10"6 cm/s) constructed with clay layers will be relatively
small and will only occur after water saturates the clay layer. In contrast, infiltration rates through
i
geomembrane bottom liners underlain by relatively permeable soils can be very large and will occur
quickly.
18
-------
SECTION 5
DATA FROM LDCRSs OF OPERATING UNITS
5.1 DATA COLLECTION METHODOLOGY
The data presented in this report were obtained from engineering drawings, project
specifications, operation records, and interviews with facility owners and operators and regulatory
agencies. With respect to flow data, in most cases only data on LDCRS flow rates were available; data
on LCRS flow rates and on the chemical quality of flows from the LDCRS and LCRS were typically not
available. Efforts were made to obtain data from operating and closed landfills and from facilities
constructed with different types of lining systems (e.g., geomembrane top liners versus composite top
liners, and sand LDCRS drainage layers versus geonet LDCRS drainage layers), constructed with and
without third-party construction quality assurance (CQA) programs, and located in different climatic
regions. For the purpose of this report, a facility was considered to be closed if it was covered with
a soil layer or geomembrane. Very little data were obtained from closed facilities, and approximately
86 percent of the facilities were constructed under a third-party CQA program. In addition,
approximately 96 percent of the landfill facilities are located in relatively moist climatic regions. All
other things being equal, larger flow rates would be expected from the LDCRSs of operating or closed
landfills located in relatively moist climatic regions than from operating or closed landfills, respectively,
located in drier climatic regions, since there is less leachate production in drier climates. Based on the
characteristics of the data base, the measured flow rates presented in this report likely represent the
higher end of the range of flows that might occur from landfills constructed under third-party CQA
programs.
5.2 DESCRIPTION OF OPERATING UNITS
LDCRS flow rate data have been collected from 28 double-lined landfill facilities (containing
76 individually monitored landfill cells) and eight double-lined surface impoundment facilities (containing
17 individually monitored ponds). The data, along with information on each of the facilities, are
presented in Tables 2 through 7. These tables include all of data reported by Bonaparte and Gross
[1990], as well as additional data that the authors were able to obtain since the preparation of the
cited reference. Tables 2 and 3 present general information and double-liner system properties,
respectively, for the 28 landfill facilities. Tables 5 and 6 present the same information for the eight
surface impoundment facilities. It should be noted that the double-liner system properties given in
Tables 3 and 6 were obtained from the previously-listed sources; they are, not measured properties.
19
-------
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38
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Tables 4 and 7, respectively, present the LDCRS flow rate data for the landfill and surface
impoundment facilities. Data are summarised for two different time periods: (i) just after the end of
construction, when the influence of construction water on the flow rates would be greatest; and (ii)
during the active life of the facility. Where possible, flow rates are reported at different time intervals
during the active life. The authors found only limited data on flow rates after landfill closure. The data
corresponding to closed landfill conditions are specially noted in Table 4.
A characterization of the monitored cells and ponds is presented in Table 8. It can be seen
that about 40 percent of the monitored cells and ponds have geomembrane top liners, while the
remaining 60 percent have composite top liners. About 40 percent of the monitored cells and ponds
have sand LDCRSs, while the remaining 60 percent have geonet LDCRSs. (Some of the facilities listed
in Table 8 as having a geonet LDCRS may actually have a geocomposite LDCRS consisting of a geonet
with a geotextile bonded to its top surface. However, for the purposes of this report, geocomposite
LDCRSs are considered functionally equivalent to geonet LDCRSs.) Most of the units are located at
sites where the ground-water table is below the unit base; however, in a few cases, the relationship
between the unit base and the ground-water table is unknown. For purposes of this report, it is
assumed that infiltration of ground water did not contribute to the LDCRS flows at any of the units.
For all units, the bottom liner included a geomembrane; in most cases, the bottom liner was a
composite. Therefore, for most facilities, a small amount of the water expelled during consolidation
of the soil component of the bottom liner could infiltrate the LDCRS through a hole in the
geomembrane component of the bottom liner. This small amount of water is considered to be
negligible for the purpose of this report. Also, for most facilities, the collection efficiency of the
LDCRSs at the monitored facilities should be very high (i.e., very little of the liquid in the LDCRS should
have migrated into the bottom liner).
It should be noted that only 13 of the 28 landfill facilities and three of the eight surface
impoundment facilities have lining systems that appear to meet the minimum design requirements of
EPA's final rule of 29 January 1992 (described in Appendix A). The minimum design requirements of
the final rule include the following: (i) a composite bottom liner consisting of a geomembrane and a 0.9
m (3 ft) thick compacted clay layer with a hydraulic conductivity no greater than 1 x TO"7 cm/s; (ii) a
minimum LDCRS bottom slope of 1 percent; (iii) for granular LDCRS drainage media, a minimum
thickness of 30 cm (12 in.) and a minimum hydraulic conductivity of 1 x 10~2 cm/s for landfills and
1 x 1Q'1 cm/s for surface impoundments; and (iv) for synthetic LDCRS drainage media, a minimum
39
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TableS. Characterization of 93 individually monitored cells and ponds. [Note: Gmb = gebmembrane;
Cmp = composite; Below = ground-water table below base of facility.]
Cells
Ponds
Cells and
Ponds
Top
Liner
Gmb
25
11
36
Cmp
51
6
57
LDCRS
Sand
32
7
39
Geonet
44
10
54
Ground-Water
Table
Below
74
15
89
Unknown
2
2
: 4
Table 9. Number of facilities in each group.
Group
No.
I
II
III
IV
Top
Liner
Geomembrane
Geomembrane
Composite
Composite
LDCRS
Geonet
Sand
Geonet
Sand
Number of
Cells and Ponds
13 ;
23
41 ;
16
40
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hydraulic transmissivity of 3 x 10'5 m2/s for landfills and 3 x 10"4 m2/s for surface impoundments. The
main reason that some of the facilities do not meet the requirements of the final rule is that the
compacted clay component of the bottom liner is less than 0.9 m (3 ft) thick or has a hydraulic
conductivity greater than 1x10"7 cm/s.
To interpret the data, it is convenient to group the monitored facilities by the type of top liner
(i.e., geomembrane versus composite) and type of LDCRS (i.e., sand versus geonet). With this
grouping, the potential sources of flow for cells and ponds in any group are basically the same (Table
9). The flow rate data are interpreted for each group of facilities in Section 6.
5.3 MEASUREMENT OF FLOW FROM LDCRSs
Under EPA's final rule of 29 January 1992, owners and operators of hazardous waste
landfills and surface impoundments are required to monitor the rate of flow from the LDCRS of the
facilities on a weekly basis during the active life of the facilities (including the closure period) and
monthly or quarterly during the post-closure period. For the majority of the facilities presented in this
report, liquid flows from the LDCRSs of operating units were measured daily or weekly. However, the
available data were typically weekly or monthly flow volumes, or flow rates.
The flow rate data for each facility are given in Table 4 for landfills and Table 7 for surface
impoundments. Where there is sufficient data to evaluate the temporal variation in flow, both average
and maximum flow rates are reported. Average flow rates are typically reported for one or more
months. Maximum flow rates are reported as the maximum weekly or monthly flow rate over a given
time interval, except as noted. When possible, the maximum flow rates are based on a maximum
weekly flow rate. It is preferable to report the maximum flow rates based on a weekly time interval,
as this is the time interval required by EPA for monitoring of LDCRS flow rates at active units. With
this information, conclusions can be drawn on the .maximum LDCRS flow rates that may occur on a
weekly basis at other land disposal units.
The techniques for measuring LDCRS flow rates at the landfill and surface impoundment
facilities presented in this report range from the relatively simple, such as calculating the flow
quantities based on changes in liquid depth in the LDCRS sump, to relatively complex, such as
measuring flows using tipping buckets and flumes and recording the flow data with automated data-
logging systems. The different methods used to measure LDCRS flow rates at the facilities in the
report were as follows:
41
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• estimating the volume of liquid pumped from the sump by multiplying the sump area
by the change in the liquid depth in the sump and dividing volume of liquid by the
time between liquid depth measurements;
• measuring volume indirectly by multiplying the pumping time by the pump capacity
and dividing by the time since the last pumping event; !
• estimating the volume of liquid removed from the LDCRS sump during a certain
period of time by multiplying the number of times the pump automatically activated
by the volume of liquid that is stored in the sump between the "pump on"! and "pump
off" levels, and dividing the estimated volume of liquid by the length of the
considered time period;
• measuring the flow rate manually at a given point in time, using a bucket and
stopwatch {at gravity flow outlets); '
• measuring the liquid volume in the LDCRS by opening the drain lines and allowing the
liquid to flow by gravity into a graduated container and dividing the volume of liquid
by the time since the last measurement event (at gravity flow outlets);
• using flow meters equipped with mechanical accumulators or automatic data-logging
systems and dividing the change in flow volume by the time since the last
measurement event; and
• using'tipping buckets and flumes, with automatic flow data acquisition systems (at
gravjty flow outlets). > ; :
• _.•".-•/> . • _ - • - i - . ... • • •. • . - t-
• '.' ,'•'••••••";•'•". ••'•'•"-.•'•'.' '/'••'• x: [
The most common method used to measured LDCRS flow rates at the facilities presented
in this report involved using a flow meter equipped with a mechanical accumulator and dividing the
change in flow volume by the time since the last measurement event. :
42
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SECTION 6
RESULTS AND DISCUSSION
6.1 METHODOLOGY FOR EVALUATING MEASURED FLOW
In this section of the report, the sources of flow from the LDCRSs of operating facilities
within each of the four groups identified in Table 9 are evaluated by comparing the measured flow
rates for a specific time period with the calculated flow rates from different sources during the same
time period. This methodology for evaluating the source of measured flow has been described by
Gross et al. [1990] as follows.
• Identify the potential sources of flow based on double-liner system design, climatic
and hydrogeologic setting, and operating history.
• Calculate the flow rates from each potential source.
• Calculate the time frame for flow from each potential source.
• Evaluate the potential sources of flow by comparing measured flow rates to
calculated flow rates at specific points in time.
Additionally, comparisons of the chemical constituents in liquids contained in surface
impoundments or leachates from landfills with the chemical constituents in the flows from the LDCRSs
often provide insight into whether a source of the flow is top liner leakage.
The interpretation methodology described above was used to evaluate the sources of flow
from the 93 individually monitored cells and ponds presented in Tables 2 through 7. A review of the
data on measured flow rates from the four groups of facilities and an interpretation of the data are
provided in the remainder of this section of the report.
43
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6.2 REVIEW OF DATA •;
6.2.1 Group I Facilities
Introduction
Group I facilities were constructed with geomembrane top liners and geonet LDCRS drainage
layers. There are three landfill facilities (seven cells) and two surface impoundment facilities (six
ponds) in this group. End of construction flow rate data are available for four landfill cells and all
surface impoundment ponds. In addition, data are available for all cells and ponds duringitheir active
lives. No data for closed cells are available.
The only potential source of flow from the LDCRSs of the Group I facilities is top liner leakage
and any small amount of construction water that drains from granular collection trenches in the LDCRS
during the early active life of the facilities.
Landfills
For the four Group I cells for which end of construction data is available, average measured
flow rates ranged from 3 to 470 Iphd (0.3 to 47 gpad), and maximum weekly measured flow rates
ranged from 10 to 560 Iphd (1 to 56 gpad). These flows are primarily attributed to construction water
draining from granular collection trenches and top liner leakage.
All seven cells from the three Group I landfills appear to have exhibited top liner leakage
during their active lives, with average flow rates ranging from 0 to 220 Iphd (0 to 22 gpad). Maximum
weekly flow rates of 110 to 860 Iphd (11 to 86 gpad) and maximum monthly flow rates of 20 to 160
Iphd (2 to 16 gpad) were measured for these cells. These maximum flow rates are up to about seven
times greater than the average values. The maximum LDCRS flows typically corresponded jto high flow
rates from the LCRSs, which usually occurred shortly ( e.g., from a few days to a few weeks) after
storm events. It should also be noted that all of the Group I landfills are located in relatively moist
climatic regions. All other things being equal, smaller rates of top liner leakage would be bxpected at
facilities located in dry climates where leachate production rates are low.
44
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Surface Impoundments
Of the six Group 1 ponds, only two (i.e.. Surface Impoundment E, Pond 2 and Surface
Impoundment F) have exhibited flow since the start of operation. One pond (i.e.. Surface
Impoundment E, Pond 2) exhibited no flows until a 20-mm (1-in.) long defect developed along a
geomembrane seam on the side slope of the pond. Flow through the defect averaged 30,000 Iphd
(3,000 gpad). Flow was not observed after the defect was repaired. The other pond (i.e.. Surface
Impoundment F) initially exhibited an average flow of 1,380 Iphd (138 gpad} at 0.5 months after
construction. The flow was due, in part, to top liner leakage. After a geomembrane defect was
discovered and repaired and the LDCRS was flushed with water, the flow rate decreased steadily with
time and was very low (i.e., about 2 Iphd (0.2 gpad}) from two to eight months after the end of
construction. Based on a chemical analysis of the LDCRS flow for a primary constituent in the pond
liquids, the flow observed during this time can be attributed to flush water slowly draining from the
LDCRS. At nine months, the geomembrane top liner was damaged and the average flow rate increased
to 950 Iphd (95 gpad). The geomembrane was repaired, a ponding test was performed to locate any
additional geomembrane defects, and the LDCRS was again flushed with water. After this repair, the
flow rates decreased with time and remained very low from 10 to 52 months after the end of
construction. By several months after the repair, the flows appeared to be just flush water based on
chemical analysis.
At 53 months, the maximum liquid height in Pond 2 of Impoundment E was increased to a
. higher level. Based on the increased flow rate and on chemical analysis of constituents in the flow,
it was determined that top liner leakage was again occurring. Since the observed leakage coincided
with an increase in the maximum liquid height in the pond, it is likely the pond had a geomembrane top
liner defect on its side slope. The liquid height in the pond was decreased and the LDCRS was again
flushed. Chemical characteristics of the LDCRS liquids went back to normal (i.e., a primary chemical
constituent in the pond liquids was not detected in the LDCRS liquids) within several months. The
LDCRS flow rates again decreased and remained low until 88 months after the end of construction.
Prior to 88 months, beginning at 81 months, top liner leakage again began occurring based on testing
of chemical constituents in the LDCRS flow. At 88 months, the average flow rate increased rapidly
to 250 Iphd (25 gpad), and the facility was taken out of service. An investigation of the top liner
indicated that the geomembrane had a number of small holes which were located primarily on the base
of the pond. It was also reported by the surface impoundment owner that the scrim of the
geomembrane was exposed in a number of places and the strength properties of the geomembrane
were significantly less (i.e., 50 percent or less) than the specified original properties of the
geomembrane. A new geomembrane comprised of the same polymer as the old geomembrane was
45
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installed over the old geomembrane. The owner reported that the new geomembrane had a different
formulation than the old geomembrane, which was installed in 1983.
One reason for the absence of top liner leakage at four of the Group I ponds and only four
occurrences of top liner leakage at the other two Group I ponds is that these facilities were all
subjected to ponding tests and/or leak location surveys as part of the owners' internal or third-party
CQA program. It was reported that geomembrane holes identified during the leak location surveys
and/or ponding tests were repaired. Additionally, geomembrane holes that developed during operation
were typically repaired.
It is interesting to note that none of the geomembrane top liners at the Group I surface
impoundments were protected by an overlying protective soil layer or other material.
Comparison Between Observed and Calculated Leakage Rates For Landfills and Surface Impoundments
It is useful to compare the observed top liner leakage rates at the monitored landfills and
surface impoundments to the calculated top liner leakage rates. For the Group I landfills, the observed
flow rates are, on average, somewhat smaller than the calculated top liner leakage rate of 600 Iphd
(60 gpad) given in Table 1 for ht = 0.03 m {0.1 ft) and kmin > 1 cm/s. However, the calculated value
appears to represent a reasonable upper bound of the observed values. In contrast, observed flow
rates from,the Group I ponds are typically much smaller than the calculated top leakage rate of..6,300
Iphd (630 gpad) given in Table 1 for ht = 3 m (10 ft) and kmin > 1 cm/s.
Giroud and Bonaparte [1989a,b] presented evidence suggesting that a geomembrane hole
frequency of 3 to 5 holes per hectare (1 to 2 holes per acre) and a geomembrane hole size of 3 x 10"6
m2 (3 x 10"5 ft2) may be assumed for calculating "representative" flow rates due ito holes in
geomembranes installed using rigorous CQA programs. It is apparent from the observations of the
monitored surface impoundments that the foregoing assumptions regarding the frequency and/or size
of geomembrane holes may, in some cases, be too conservative for geomembrane installations that
include ponding tests and/or leak location surveys as part of a CQA program and the repair of
geomembrane holes that develop during operation. The use of these techniques reduced the frequency
and/or size of geomembrane holes in the Group I surface impoundments in this study below the values
assumed by Giroud and Bonaparte. Their assumptions were based on analyses of the performance of
geomembranes that had not been subjected to ponding tests, leak location surveys, and/or
geomembrane repair during operation.
46
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6.2.2 Group II Facilities
Introduction
Group II facilities were constructed with geomembrane top liners and sand LDCRS drainage
layers. There are seven landfill facilities (18 cells) and three surface impoundment facilities (five ponds)
in this group, with all of the facilities located in relatively moist climatic regions. End of construction
data are available for 16 of the landfill cells and two of the surface impoundments. Data are also
available for 16 of the cells and all of the ponds during their active lives, and for two closed cells.
*u
The potential sources of flow from the LDCRSs of the Group II facilities are construction
water and top liner leakage.
Landfills
For the 16 Group II cells for which end of construction data are available, the hydraulic
conductivity of the LDCRS drainage material is in the range of 10'3 to 10'1 cm/s. For this range of
hydraulic conductivity, drainage of construction water could have occurred for about one day to one
year after installation of the top liner. AH 16 of the landfill cells show LDCRS flows shortly after
construction. The average measured flow rates at the end of construction ranged from 60 to 17,000
Iphd (6 to 1,700 gpad), with seven of the cells exhibiting average flow rates of 1,000 Iphd (100 gpad)
or more. The maximum end of construction flow rates for the cells ranged from 440 to 32,000 Iphd
(44 to 3,200 gpad), with two of the cells exhibiting maximum flow rates of more than 10,000 Iphd
(1,000 gpad). These maximum values were up to eight times greater than the average values.
Excluding the four cells of Landfill J (discussed subsequently), the remaining 12 Group II cells
for which data are available exhibited flows during their active lives which are thought to be due to
top liner leakage. The average flow rates from the 12 cells potentially attributable to top.liner leakage
ranged from 0 to 2,200 Iphd (0 to 220 gpad), with the maximum flow rates being up to about five
times larger than the average values. The maximum monthly flow rates ranged from 0.4 to 3,300 Iphd
(0.04 to 330 gpad), and the maximum weekly flow rates ranged from 0 to 4,300 Iphd (0 to 430 gpad).
It is noted that top liner leakage has clearly occurred at Cell 1 of Landfill V. A slope failure occurred
at this facility shortly after construction. The failure was confined to the lining system on the 12-m
(40-ft) high, 3H:1 V (horizontalrvertical) side slope. The failure involved the downslope sliding of the
0.6-m (2-ft) thick sand LCRS drainage layer and underlying geotextile cushion layer on the HOPE
geomembrane top liner. Flow from the cell had not been monitored prior to the failure. Shortly after
the failure, however, the flow rate from the LDCRS was found to be almost 1,500 Iphd (150 gpad)!
47
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The lining system was subsequently repaired, and the flow rate from the LDCRS decreased. At 22
months after the end of construction, the average measured flow rate from the cell was 200 Iphd
{20 gpad). Interestingly, the six cells at which CQA programs were not implemented (i.e;, Landfills L
and Q) had larger flow rates attributable to top liner leakage (i.e., averaging from 130 to 2,200 Iphd
(13 to 220 gpad)) than the cells at which CQA programs were implemented (i.e., averaging from 0.1
to 200 Iphd (0.01 to 20 gpad). ; ' • '.
As discussed by Bonaparte and Gross [1990], Landfill J is a special Group II facility because
I
it was constructed with the compacted clay component of the bottom liner above, rather than below
(as is usual), the geomembrane component. In addition, at Landfill J the LDCRS is continuous between
cells, thereby allowing flow to cross from one cell to the next. A detailed analysis of LDCRS flows
from the Landfill J cells was presented by Gross et al. [1990]. Their analysis indicated average
construction water flow rates of 60 to 17,000 Iphd (6 to 1,700 gpad) for the cells. Average
consolidation water flow rates from the four Landfill J cells ranged from 6 Iphd (0.6 gpad) for Cell 3,
which was filled slowly over 18 months, to 1,700 Iphd (170 gpad) from Cell 1, which wasjfilled in one
month. The relatively high average flow rate of 2,700 Iphd (270 gpad) observed for Cell 3 at 30
months after construction was due to flooding of the LDCRS in an adjacent cell for a leak location
survey. Based on an analysis of chemical constituents in flow from the LDCRSs and LCRSs, the top
liners at two of the four Landfill J cells (i.e., Cell 1 and Cell 4) leaked. In the case of Cell 1, no top
liner leakage was observed until several years after closure, at which time an average flow from the
LDCRS of 140 Iphd (14 gpad) commenced. In the case of Cell 4, no top liner leakage was observed
until about 24 months after construction, when the LDCRS began experiencing an average flow of
\
about 120 Iphd (12 gpad). An evaluation of the methods used to construct Cells 1 and 4 resulted in
the conclusion that the most likely cause of top liner leakage was the development of a hole at the
LCRS pipe penetration of the geomembrane top liner in these cells.
Surface Impoundments
For the two Group II surface impoundments ponds for which end of construction flow data
available, the hydraulic conductivity of the LDCRS drainage material is about 10"2 cm/s. For this value
of hydraulic conductivity, drainage of construction water could have occurred for several months after
installation of the top liner. The average measured flow rates at the end of construction, for the two
ponds were 990 and 1,020 Iphd (99 and 102 gpad), and the maximum monthly flow rates were 1,230
and 1,300 Iphd (123 and 130 gpad).
Three of the five ponds from the Group II surface impoundments had average flow rates
during their active lives potentially attributable to top liner leakage and construction water of 20 to 250
48 :
-------
Iphd (2 to 25 gpad), and maximum monthly flow rates of 90 to 310 Iphd (9 to 31 gpad). Ponding tests
or leak location surveys were reportedly performed as part of the CQA program at all of these ponds.
The remaining two ponds {i.e.. Ponds 2 and 3 of Surface Impoundment H) had average flow rates
potentially attributable to top liner leakage of 230 to 19,780 Iphd (23 to 1,978 gpad), and maximum
•monthly flow rates of 300 to 27,440 Iphd (30 to 2,744 gpad). It should be noted that leak location
surveys were performed in both of the ponds before they were put into operation. The results of
chemical quality testing of the LDCRS liquids indicated that top liner leakage was occurring in both of
these ponds shortly after the ponds were put into operation. At 25 months, the geomembrane top
liners in the two ponds were repaired. After 25 months, the average measured flow rates from these
two ponds decreased significantly and ranged from 400 to 440 Iphd (40 to 44 gpad).
Comparison Between Observed and Calculated Leakage Rates for Surface Impoundments
Similar to the Group I ponds, flow rates from the Group II ponds were typically much smaller
than the calculated leakage rate through a geomembrane hole of 6,300 Iphd (630 gpad) given in
Table 1 for h = 3 m (10 ft) and kmln > 1 cm/s. The exception to this is for Ponds 2 and 3 of Surface
Impoundment H, which experienced significantly higher flows than the other ponds. After the
geomembrane top liners in the two ponds were repaired, however, the flow rates from these ponds
became more consistent with the measured flow rates from the other ponds.
6.2.3 Group III Facilities
Introduction
Group III facilities were constructed with composite top liners and geonet LDCRS drainage
layers. There are ten landfill facilities (37 cells) and two surface impoundment facilities (four ponds)
in this group. End of construction data are available for seven landfill cells and two surface
impoundment ponds. In addition, data are available for 31 cells and three ponds during their active
lives, and for 17 closed cells.
For the Group III facilities, top liner leakage rates should be low and should not occur for
some period after construction (due to the containment capabilities of composite top liners). Since
geonets were used in the LDCRS drainage layers of these facilities, there should not be any
construction water (except for a small amount of water that drains from granular collection trenches
in the LDCRS). Therefore, flows from the LDCRSs of Group 111 facilities should result primarily from
consolidation of the clay component of the top liner.
49
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Landfills
For the seven Group 111 cells for which end of construction data is available, average
measured flow rates ranged from 0 to 1,900 Iphd (6 to 190 gpad), and maximum measured flow rates
ranged from 0 to 6,400 Iphd (0 to 640 gpad). These flows are attributed to construction water
draining from granular collection trenches and consolidation water.
With one exception, all of the 31 Group III landfill cells for which data are available exhibited
flows from their LDCRSs during their active lives. Average flow rates during the active lives of these
I '
cells ranged from 0 to 1,300 Iphd (0 to 130 gpad); with 15 of the 31 cells exhibiting flows less than
200 Iphd (20 gpad), 24 of the cells exhibiting flows less than 500 Iphd (50 gpad), and 28 of the cells
exhibiting flows less than 1,000 Iphd (100 gpad). Based on the calculated breakthrough times for
seepage through the top liner, the LDCRS flows from these cells during their active lives are primarily
I
attributable to consolidation water. The flow rates are consistent with the calculated range of values
for flows due to consolidation water of 1 to 1,500 Iphd (1 to 150 gpad) reported in Section 4.5.
For the 17 Group III cells that are closed or covered with a geomembrane or soil layer (i.e..
Landfill F, Cells 1 to 4, Landfill G, Cells 1 to 6, Landfill H, Cell 1, and Landfill T, Cells 1 to 6), ongoing
LDCRS flows may be due to continuing consolidation or secondary compression of the clay component
of the top liner. In addition, a portion of the flows from Landfills H and T, which have a geomembrane
top liner on their side slopes, may be due to top liner leakage. While there is no direct'evidence of
leakage through the composite top liner of any of the closed cells (i.e., there is no chemical constituent
data for the LDCRS), the possibility of minor top liner leakage cannot be ruled out because the LCRS
at the facilities continues to produce liquid, and the calculated breakthrough time for the clay
component of the composite top liner is less than the time period between the start of the active life
and the recording of the LDCRS flows.
Surface Impoundments
For the two Group III ponds for which end of construction data is available, the average
measured flow rates were 53 and 1,590 (5.3 to 159 gpad). These flows are attributed to construction
water draining from granular collection trenches and consolidation water.
The three Group III ponds that have data from their active lives exhibited average measured
LDCRS flow rates ranging from 0 to 960 Iphd (0 to 96 gpad), and maximum monthly flow nates ranging
from 0 to 1,380 Iphd (0 to 138 gpad). The flows from these ponds are primarily attributed to
consolidation water. Top liner leakage is thought to have occurred for one pond (Le., Surface
50
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Impoundment C, Pond 2). For this pond the average measured flow rate increased from 4 to 960 Iphd
{0.4 to 96 gpad) after the liquid height in the pond was increased at 38 months after the end of
construction. It cannot be determined from the available information how flow entered the LDCRS in
such a short time period after the liquid height in the pond was increased as the top liner was a
composite on the base and side slopes. A geomembrane top liner defect was found on the side slope
of the pond and repaired. Subsequently, the average flow rate decreased to 40 Iphd (4 gpad).
Flow Rate Over Time
For both landfill and surface impoundment facilities it is interesting to observe how the flow
rate of consolidation water from a facility decreases over time (e.g.. Landfill T, Cell 9 and Surface
Impoundment C, Pond 3). For example, for Landfill T, Cell 9, the average flow rate at about seven to
twelve months after construction was 230 Iphd {23 gpad). By 13 to 1 8 months, the average flow rate
had decreased to 150 Iphd (15 gpad). The flow decreased still further over time and was 20 Iphd {2
gpad) at 26 to 30 months after construction.
6.2.4 Group IV Facilities
Introduction
Group IV facilities were constructed with composite top liners and sand LDCRS drainage
layers. There are eight landfill facilities (14 cells) and one surface impoundment facility (two ponds)
in this group. End of construction data are available for ten landfill .cells. Data are also available for
twelve cells and all surface impoundment ponds during their active lives. No data for closed cells are
available.
At the end of construction, flows from the LDCRSs of the Group IV facilities should be due
primarily to drainage of construction water. Subsequently, consolidation water will contribute to the
flow from those facilities in which a conventional compacted clay layer was used in the composite top
liner. For one of the facilities (Landfill I), a 6-mm (0.25-in.) thick GCL was placed directly under the
geomembrane. This GCL is installed with the bentonite in a dry state. The bentonite in the GCL
hydrates in the presence of water, thereby forming a low-permeability barrier. Due to its thinness,
consolidation water from the GCL should not be a source of significant flow from the LDCRS of this
facility.
51
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Landfills i
Seven of the 14 Group IV cells have a layer of compacted clay as the soil component of the
composite top liner, and seven have a GCL.
At the Group IV facilities for which end of construction flow rate data is available (i.e., nine
landfill cells), the hydraulic conductivity of the drainage material is on the order of 10"2 cm/s. For this
value of hydraulic conductivity, drainage of construction water could have occurred for several months
after installation of the top liner. Flow rate data at the end of construction are available for three cells
with a compacted clay layer in their composite top liner. For these three cells, the average measured
flow rates were 0, 15, and 23,300 Iphd (0, 1.5, and 2,330 gpad). The average measured flow rates
at the end of construction for the seven Group IV cells that were constructed with a GCL in their
composite top liner ranged from 0 to 890 Iphd (0 to!89 gpad), with five of the cells exhibiting average
flow rates of less than 100 Iphd (10 gpad). The jmaximum weekly flow rate for thesejseven cells
ranged from 0 to 2,900 Iphd (0 to 290 gpad). ;
Flow rate data are available for five active cells with a compacted clay layer as a component
of the composite top liner. Average measured flow rates from the LDCRSs of these cells ranged from
40 to 500 Iphd (4 to 50 gpad). Three of the five cells exhibited flows of less than 200 Iphd (20 gpad).
These flow rates are consistent with the range of flow rates attributed to consolidation water observed
for the Group III cells.
Flow rate data are available for seven active cells with a GCL as a component of the
composite top liner. In one of the seven cells, no LDCRS flow was observed. For five of the six cells
exhibiting flow, average flow rates of 50 Iphd (5 gpad) or less were observed. For the remaining cell,
an average flow of 120 Iphd (12 gpad) or less was observed. Maximum weekly flows for the seven
cells were 430 Iphd (43 gpad) or less. These flow rates could be accounted for by a combination of
compression and continuing drainage of the sand LDCRS drainage layer or leakage through the
geomembrane top liner on the side slopes of the cells (the GCL only extends over the base of the cells).
Surface Impoundments
Both Group IV ponds were constructed with a composite top liner on the base slope and a
geomembrane top liner on the side slope. Average measured flow rates from one of the ponds (i.e..
Surface Impoundment B, Pond 1) ranged from 2 to 1,120 Iphd (0.2 to 112 gpad) during the active life
of the pond. The maximum monthly flow rates from this pond ranged from 7 to 1,340 (0.7 to 134
gpad). These flows are primarily attributed to consolidation water and leakage through the
52
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geomembrane top liner on the side slope of the pond. It is known that top liner leakage was occurring
in this pond during 35 to 37 months after the end of construction based on analysis of LDCRS flow
for chemical constituents found in the pond liquid. This incidence of top liner leakage coincided with
an increase in the liquid level in the pond. The LDCRS flow rate decreased when the liquid level was
lowered. It therefore appears that the geomembrane top liner on the pond side slope had a defect.
The flow rate from the LDCRS of the second pond (i.e.. Surface Impoundment B, Pond 2) was zero
from 20 to 43 months after construction; for this latter pond, consolidation water flows apparently
ceased prior to flow rate measurement and quantifiable top liner leakage did not occur.
6.3 INTERPRETATION OF DATA
6.3.1 Group I and Group II Landfills
It is interesting to compare the flows attributable to top liner leakage for the Group I and II
landfills (excluding Landfill J). For this comparison, the 21 landfill cells have been subdivided into those
that had a CQA program (14 cells) and those that did not have a CQA program (seven cells). From
Table 10, it can be seen that of the 14 cells that had a CQA program, six had average flow rates less
than 50 Iphd (5 gpad), and eleven had average flow rates less than 200 Iphd (20 gpad). All 14 cells
that had a CQA program exhibited both average and maximum flow rates less than 1,000 Iphd (100
gpad), which is EPA's recommended action leakage rate value for landfills. Of the seven cells that did
not have a CQA program, one cell had a average flow rate less than 200 Iphd (20 gpad), and five cells
exhibited average flow rates greater than 1,000 Iphd (100 gpad). For the cells without a CQA program
for which maximum flow rate data is available (i.e., six cells), all of the cells exhibited maximum flow
rates of up to 500 Iphd (50 gpad) or more, and four of the cells exhibited maximum flow rates of over
1,000 Iphd (100 gpad).
On the basis of the limited available flow rate data, it appears that cells with properly
constructed geomembrane top liners that have undergone CQA monitoring will consistently limit top
liner leakage to a value of less than 1,000 Iphd (100 gpad). From the data in Table 10, it also appears
that implementation of a CQA program during construction significantly reduces top liner leakage rates
in comparison to facilities that do not have a CQA program.
53
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Table 10. Comparison of average and maximum measured flow rates at Group I and il landfills
[Notes: Excludes Landfill J].
LDCRS Flow Rates for
Landfills With CQA
Less than 50 Iphd
From 50 to 200 Iphd
From 200 to 500 Iphd
From 500 to 1 ,000 Iphd
More than 1 ,000 Iphd
LDCRS Flow Rates for
Landfills Without CQA
Less than 50 Iphd
From 50 to 200 Iphd •
From 200 to 500 Iphd
From 500 to 1 ,000 Iphd
More than 1 ,000 Iphd
Average
6
5
2
1
"
Average
1
1
5
Maximum
Monthly
5
4
-
- .
'
Maximum
Monthly
-
-
-
-
-
Maximum
Weekly
i-
1
1
;3
-
Maximum
Weekly
-
'-
:-
2
4
54
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6.3.2 Group III and Group IV Landfills
As was done with the Group I and II landfills, the flows from the LDCRSs of the Group III and
IV landfills (excluding Landfill I) can also be compared (Table 11). In the case of Group I and II landfills,
flows from the LDCRSs were due primarily to top liner leakage. For Group III and IV landfills, flows
were primarily due to consolidation water.
From Table 11, it can be seen that 39 of the 42 Group III and IV landfill cells for which data
exist have average consolidation water flow rates of less than 1,000 Iphd (100 gpad), and 36 of the
42 cells have average consolidation water flow rates less than 500 Iphd (50 gpad). Maximum flow
rates are somewhat higher, with 26 of the 37 cells for which data is available exhibiting maximum
flows less than 1,000 Iphd (100 gpad), which is EPA's recommended action leakage rate for landfills.
From these flow rates, it appears that landfills with composite top liners may occasionally exhibit
LDCRS flow rates exceeding 1,000 Iphd (100 gpad). While consolidation water is not necessarily an
environmental concern, EPA intends to consider all flow from the LDCRS as top liner leakage unless
it is demonstrated (in a response action plan) to be from another source. The above interpretations,
however, should be interpreted cautiously because consolidation water flow rates vary with time and
the reported values may not be maximums.
55
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Table 11. Comparison of average and maximum measured flow rates at Group III and IV
landfills [Notes: Excludes Landfill I].
LDCRS Flow Rates for
Landfills With CQA
Less than 50 Iphd
From 50 to 200 Iphd
From 200 to 500 Iphd
From 500 to 1 ,000 Iphd
More than 1 ,000 Iphd
LDCRS Flow Rates for
Landfills Without CQA
Less than 50 Iphd
From 50 to 200 Iphd
From 200 to 500 Iphd
From 500 to 1 ,000 Iphd
More than 1,000 Iphd
Average
7
14
TO;
3:
3
Average
-
1
2 i
2
- !
Maximum
Monthly
2
8
5
-
3
Maximum
Monthly
-
-
2
1
2
Maximum
Weekly
'-
1
3
4
J3
i
Maximum
Weekly
'.-
-
-
-
,-
56
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REFERENCES
Bonaparte, R., Giroud, J.P., and Gross, B.A., "Rates of Leakage Through Landfill Liners", Proceedings,
Geosynthetics '89, San Diego, Feb 1989, Vol. 1, pp. 18-29.
Bonaparte, R. and Gross, B.A., "Field Behavior of Double-Liner Systems", Waste Containment Systems:
Construction, Regulation, and Performance, Geotechnical Special Publication No. 26, American Society
of Civil Engineers, New York, 1990, pp. 52-83.
Brown, K.W., Thomas, J.C., Lytton, R.L., Jayawickrama, P., and Bahrt, S.C., "Quantification of Leak
Rates Through Holes in Landfill Liners", EPA Report CR 810940, Cincinnati, 1987, 147 p.
EPA, "Background Document: Proposed Liner and Leak Detection Rule", EPA\530-SW-87-015,
prepared by GeoSyntec Consultants, May 1987, 526 p.
Faure, Y.H., "Nappes E'tanches: De'bit et Forme de t'Ecolement en Cas de Fru/te", thesis, University
of Grenoble, France, Dec 1979, 263 pp. (in French)
Faure, Y.H., "Design of Drain Beneath Geomembranes: Discharge Estimation and Flow Patterns in
Case of Leak", Proceedings, International Conference on Geomembranes, Denver, Vol. 2, June 1984,
pp. 463-468.
Fukuoka, M., "Outline of Large Scale Model Test on Waterproof Membrane", unpublished report, May
1985,24pp.
Fukuoka, M., "Large Scale Permeability Tests f or Geomembrane-Subgrade System", Proceedings, Third
International Conference on Geotextiles, Vienna, Austria, Vol. 3, April 1986, pp. 917-922.
Giroud, J.P., "Geotextile Drainage Layers for Soil Consolidation", Civil Engineering for Practicing and
Design Engineers, Vol. II, 1983, pp. 275-295.
Giroud, J.P., "Impermeability: The Myth and a Rational Approach", Proceedings, International
Conference on Geomembranes, Denver, Vol. 1, June 1984, pp. 157-162.
Giroud, J.P. and Bonaparte, R., "Leakage Through Liners Constructed with Geomembranes - Part I.
Geomembrane Liners", Geotextiles and Geomembranes, Vol. 8, No. 1, 1989a, pp. 27-67.
57
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A
9
Giroud, J.P. and Bonaparte, R., "Leakage Through Liners Constructed with Geomembranes - Part II.
Composite Liners", Geotextiles and Geomembranes, VoL 8, No. 2, 1989b, pp. 78-111.
Giroud, J.P., Khatami, A., and Badu-Tweneboah, K., "Evaluation of the Rate of Leakage Through
Composite Liners", Geotextiles and Geomembranes, Vol. 8, No. 4, 1989, pp. 337-340.
Giroud, J.P., Badu-Tweneboah, and Bonaparte, R., "Rate of Leakage Through a Composite Liner Due
to Geomembrane Defects", Geotextiles and Geomembranes, Vol. 11, No. 1, 1992, pp. 1-28.
Gross, B.A., Bonaparte, R., and Giroud, J.P., "Evaluation of Flow from Landfill Leakagfe Detection
Layers", Proceedings, Fourth International Conference on Geotextiles, Vol. 2, The Hague> Jun 1990,
pp. 481-486.
Jayawickrama, P., Brown, K.W., Thomas, J.C., and Lytton, R.L., "Leakage.Rates Through Flaws in
Geomembrane Liners", Journal of Environmental Engineering, ASCE, Vol. 114, No. 6, Dec 1988, pp.
1401-1420. ' | . i
Linsley, R.K., Jr., Kohler, M.A., and Paulhus, J.H., "Hydrology for Engineers", McGraw-Hill, Inc., New
York, NY, 1975, 482 p. i
i
Schiffman, R.L., "Consolidation of Soil Under Time Dependent Loading and Varying Permeability",
Highway Research Board Proceedings No. 37, 1958, pp. 584-617.
Sherard, J.L., "The Upstream Zone in Concrete-Face Rockfill Dams", Proceedings of a Symposium on
Concrete Faces Rockfill Dams - Design, Construction, and Performance, sponsored by the Geotechnical
Engineering Division of the American Society of Civil Engineers, ed. J. Barry Cooks and James L.
Sherard, Detroit, Oct 1985, pp. 618-641. ;
Terzaghi, K., Theoretical Soil Mechanics, John Wiley and Sons, Inc., New York, 1943, 527 p.
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A.. REGULATORY BACKGROUND
A.1 INTRODUCTION
The purpose of this appendix to the report is to describe regulatory developments under the
Resource Conservation and Recovery Act (RCRA) of 21 October 1976 that led to the design criteria
for leakage detection, collection, and removal systems (LDCRSs) and the action leakage rate (ALR)
concept in EPA's final rule of 29 January 1992.
A.2 EPA FINAL RULE OF 26 JULY 1982
Minimum technology requirements for lining systems.at hazardous waste landfill, waste pile,
and surface impoundment units were first promulgated by EPA on 26 July 1982 (47 FR 32274). (A
"unit" was defined in the preamble to the final rule as "the contiguous area of land on or in which
waste is placed".) These requirements (in amendments to Chapter 40 Sections 264 and 265 to the
Code of Federal Regulations (CFR) (i.e., 40 CFR 265 and 266)) included: (i) a single liner "that is
designed, constructed, and installed to prevent any migration of wastes" out of the unit during the
active life (including the closure period) of the unit; and (ii) for landfills and waste piles, a leachate
collection system that limited the leachate depth over the liner to 0.3 m (1 ft). In the preamble to the
EPA final rule of 26 July 1982, EPA recognized that the requirement that a liner "prevent any migration
of wastes out of a unit" would dictate the type of liner that could be used. For landfills, EPA only
recognized geomembranes as being able to meet this standard. For surface impoundments and waste
piles that were closed by removing or decontaminating wastes and waste residues, a compacted soil
liner or geomembrane could be used. The EPA final rule of 26 July 1982 also required monitoring and
inspection of liners during their construction and installation.
A.3 HSWA AMENDMENTS OF 8 NOVEMBER 1984 TO RCRA
In the 8 November 1984 Hazardous and Solid Waste Amendments (HSWA) to RCRA,
Congress imposed the first double-liner requirements for hazardous waste landfills and surface
impoundments. Under Sections 3004(o)(1)(A) and 3015 of HSWA, certain landfill and surface
impoundment units were required to have "two or more liners and a leachate collection system above
(in the case of a landfill) and between the liners". The leachate collection system between the top and
bottom liners was referred to as the "leak detection system". Although waste pile units were not
required to have a double-liner system, certain waste piles were required to have a leak detection
59
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system. Under Section 3004(o)(4)(B) of HSWA, the leak detection system for the units was required
"to be capable of detecting leaks of hazardous constituents at the earliest practicable time". Section
3004{o)(5)(B) of HSWA allowed the use of a particular liner system (i.e., "a top finer designed,
operated and constructed of materials to prevent the migration of any constituents into such liner
during the period such facility remains in operation (including any post-closure monitoring period)" and
a bottom liner consisting of a "3-foot thick layer ofrecompacted clay or other natural material with a
permeability of no more than 1 x Iff7 centimeter per second") until EPA issued regulations lor guidance
to meet the requirements of HSWA. HSWA also listed deadlines for EPA to promulgate regulations or
issue guidance documents for double-liner systems. ;
A.4 EPA DRAFT GUIDANCE OF 24 MAY 1985 ,
In response to the requirement of HWSA that EPA to promulgate regulations or issue
guidance documents for double-liner systems, EPA issued a guidance document on 24' May 1985
entitled "Draft, Minimum Technology Guidance on Double Liner Systems for Landfills and Surface
Impoundments - Design, Construction, and Operation" (EPA/530-SW-85-014). This| draft EPA
document provided guidance on liner system designs, in addition to the design in Section 3004{o)(5)(B)
of RCRA as amended by HSWA (hereafter referred to as RCRA), that met the requirements of Section
3004(o)(1)(A) of RCRA. Two double-liner systems were described in the draft EPA guidance
document. The first double-liner system included a geomembrane top liner and a composite bottom
liner. The second double-liner system included a geomembrane top liner and a low-permeability soil
bottom liner. The document also provided guidance on construction quality assurance (CQA)
procedures for the various liner system components to ensure, to the degree possible, that the
constructed facility met the design specifications and performance requirements.
In both double-liner systems described in the EPA draft guidance document, the thickness
of the geomembrane top liner was at least 0.75 mm (30 mil) if the geomembrane was covered by a
protective soil layer or waste after installation or 1.1> mm (45 mil) if the geomembrane was feft exposed
for an extended period or operated without a protective soil layer. The geomembrane top liner was
also chemically resistant to degradation by waste and leachate and met certain other requirements.
I
The two double-liner systems described in the draft EPA guidance document differed only
in their bottom liners. The first bottom liner was a composite liner comprising a geomembrane upper
component and a compacted low-permeability soil layer lower component. The geomembrane
component of the bottom liner met requirements similar to those for the geomembrane top liner. The
soil component of the bottom liner was at least 0.9-m (3-ft) thick and had a saturated hydraulic
60 '
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conductivity of no more than 1 x 10'7 cm/s. The second bottom liner described in the draft EPA
guidance document was a compacted soil liner that met the requirements of the bottom liner allowed
by HSWA! According to EPA, this liner had a saturated hydraulic conductivity of no more than 1 x
10~7 cm/s, had a minimum thickness of 0.9 m (3 ft), and was of sufficient thickness to "prevent the
migration of any constituent through the liner during the facility's active life and post-closure care
period".
In both of the double-liner systems described in the draft EPA guidance document, the top
liner of landfill units was overlain by a "primary" leachate collection system consisting of a 0.3-m (1 -ft)
thick (minimum) granular drainage layer that had a saturated hydraulic conductivity of not less than
1 x 10"2 cm/s, was placed with a minimum slope of two percent, and was chemically resistant to
degradation by waste and leachate. A synthetic drainage layer, such as a geonet, could be used in
lieu of a granular drainage layer if it was shown to be equivalent to, of more effective than, a granular
drainage layer meeting the minimum requirements. In any case, the leachate collection system was
designed to limit the leachate depth on the top liner to 0.3 m (1 ft) to meet the EPA final rule of 26
July 1982.
In both double-liner systems described in the EPA draft guidance document, a "secondary"
leachate collection system was included between the top and bottom liners. This secondary leachate
collection system was designed to rapidly detect, collect, and remove liquids that enter the system so
as to "produce little or no head of liquid on the bottom liner". The secondary leachate collection
system described by EPA was basically the same as the primary leachate collection system (i.e., a 0.3-
m (1-ft) thick (minimum) granular drainage layer that had a minimum saturated hydraulic conductivity
of 1 x 10"2 cm/s, was placed with a minimum slope of 2 percent, and was chemically resistant to
degradation by waste and leachate). EPA also indicated in the document that a synthetic drainage
layer, such as a geonet, could be used in lieu of a granular drainage layer if it was shown to be
equivalent to a granular drainage layer meeting the minimum requirements.
A.5 EPA FINAL RULE OF 15 JULY 1985
On 15 July 1985, EPA issued a final rule (50 FR 28702) amending existing regulations to
reflect those statutory provisions of HSWA that took effect immediately or shortly after its enactment.
This rule incorporated into the existing regulations (i.e., into 40 CFR 264 and 265) the HSWA
provisions (under Section 3004(o)(5)(B) of RCRA) requiring that, until EPA issued regulations
implementing the double-liner system requirements of Sections 3004(o)(1)(A) and 3015 of RCRA,
certain facilities must have a double-liner system that meets or exceeds the specific requirements of
the provisions. The 15 July 1985 rule required facilities to have a top liner and a compacted soil
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bottom liner (i.e., the liner system allowed by Section 3004(o){5)(B) of RCRA). For landfills, the top
liner was required to be a geomembrane, but for surface impoundments the top liner ;could be a
compacted soil layer or a geomembrane. The bottom liner was deemed to satisfy the HSWA provisions
if it was "constructed of at least a 3-foot thick layer of recompacted clay or other natural material with
a permeability of no more than 1 x 10'7 centimeter per second". The rule also required a leachate
collection system between the top and bottom liners at surface impoundments and landfills and above
the top liner at landfills. . \
A.6 EPA PROPOSED RULE OF 28 MARCH 1986 '
On 28 March 1986, EPA promulgated regulations on double-liner systems as required by
HSWA. The proposed rule contained minimum technology requirements for double-liner systems and
leachate collection and removal systems (51 FR 10706). This proposed rule, commonly]referred to
as the proposed "Double-Liner and Leachate Collection System Rule" or simply the "Double-Liner Rule",
would, when finalized, amend the double-liner system requirements of 40 CFR 264 and 265.
The minimum technology requirements in the proposed Double-Liner Rule were! essentially
those of the draft EPA guidance document of 24 May 1985. Two double-liner system options were
provided in the proposed rule (51 FR 10709). Both incorporated geomembrane top liners; however,
one option allowed a compacted soil bottom liner, while the other option allowed a composite bottom
liner. There was no minimum thickness requirement for the geomembrane top liner given in the
regulations.
The compacted soil bottom liner option closely resembled the design standard^ of Section
3004{o)(5)(B) of RCRA, as codified in the EPA final rule of 15 July 1985. The compacted soil bottom
liner of the proposed rule differed from that of the standard of Section 3004(o)(5)(B) in that it required
the bottom liner to not only meet a minimum design requirement (i.e., be at least 0.9-m (3-fjt) thick and
have a hydraulic conductivity of no more than 1 x 10"7 cm/s), but also meet a minimum performance
standard (i.e., prevent the migration of any constituent through the liner during the facility's active life
and post-closure care period). This performance standard was similar to that presented in the draft
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EPA guidance document of 24 May 1985. The composite bottom liner option of the proposed Double-
Liner Rule was also similar to that in .the draft EPA guidance document, with the exception that no
minimum thickness was specified in the proposed rule for the geomembrane or compacted soil
component of the composite bottom liner. However, in the preamble (51 FR 10710) to the proposed
rule of 28 March 1986 EPA noted that the soil component should be at least 0.9-m (S-ft)ithick. The
proposed rule required the compacted soil component to have a hydraulic conductivity of no more than
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1x10" cm/s and to minimize the migration of any constituent through the geomembrane component
of the liner if a defect were to develop in the geomembrane prior to the end of the post-closure care
period of the facility.
The proposed rule also provided minimum requirements for the leachate collection and
removal system above the top liner of landfills and between the top and bottom liners of landfills and
surface impoundments. Consistent with the EPA final rule of 26 July 1982 and draft EPA guidance
document of 24 May 1985, the LCRS above the top liner was required to be designed, constructed,
and operated to collect and remove leachate and ensure that the leachate head on the top liner did not
exceed 0.3 m (1 ft). In addition, the LCRS between the top and bottom liners was required to be
"designed, constructed, maintained, and operated to detect, collect, and remove liquids that may leak
through any area of the top liner during the active life and post-closure care period". No hydraulic
conductivity requirement for the LCRSs was given in the proposed rule.
A.7 EPA NOTICE OF 17 APRIL 1987
On 17 April 1987, EPA issued "Hazardous Waste Management System; Minimum Technology
Requirements: Notice of Availability of Information" (52 FR 12566). The notice contained data on the
two bottom liner designs (i.e., compacted soil liner and composite liner) presented in the EPA proposed
rule of 28 March 1986. In this notice, EPA compared the two liner systems with respect to leak
detection performance characteristics, leachate collection efficiency, and leachate migration into and
through the liner. Based on the data, EPA concluded that the proposed composite bottom liner
contained leachate and enhanced leachate collection significantly better than the proposed compacted
soil bottom liner. Based on the information in this notice, along with the minimum technology
requirements of the proposed "Liner/Leak Detection System Rule", EPA decided that the final "Double-
Liner Rule" would only allow the use of a composite bottom liner (i.e., a compacted soil bottom liner
will not be allowed).
A.8 EPA PROPOSED RULE OF 29 MAY 1987
On 29 May 1987, EPA proposed minimum technology requirements for LDCRSs at certain
land disposal units (52 FR 20218). These requirements were intended to meet the previously
mentioned statutory provisions in Section 3004(o)(4)(A) of RCRA that specifically call for EPA to
establish minimum standards for "leak detection systems". The proposed rule, commonly referred to
as the "Liner/Leak Detection System Rule" or simply "Leak Detection System Rule", required all new
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landfills, surface impoundments, and waste piles to have an approved LDCRS that was capable of
detecting leakage "at the earliest practicable time". The proposed rule also required waste piles to
meet essentially the same double-liner system requirements as landfills. Lastly, the proposed rule
codified CQA requirements for landfills, waste piles, and surface impoundments.
The proposed Liner/Leak Detection System Rule contained both minimum design
specifications and minimum performance requirements for the LDCRS. The minimum design
requirements consisted of: (i) a minimum bottom slope of 2 percent; (ii) for granular drainage media,
a minimum thickness of 30 cm (12 in.) and a minimum hydraulic conductivity of 1 cm/s^and (iii) for
synthetic drainage media, a minimum hydraulic transmissivity of 5 x 10"4 m2/s. The performance
requirements consisted of: (i) a minimum leak detection sensitivity of 10 Iphd (1 gpadj; and (ii) a
maximum steady-state leak detection time of 1 day. , ,;
In the proposed Liner/Leak Detection System Rule of 29 May 1987, EPA introduced the
concept of an action leakage rate (ALR), which was defined as (52 FR 20222) "the rate of leakage
from the top liner into the LCRS that triggers interaction between the owner or operator and the
Agency to determine the appropriate response action for the leakage". EPA proposed to establish the
ALR as follows: |
"(1) Using a standard value of (EPA is proposing to select a final value
from the range of 5-20 gallons/acre/day); or
(2) A review by the Regional Administrator of an owner or operator
demonstration, and a finding by the Regional Administrator, that a site-specific top
liner action leakage rate is appropriate for initiating review of the actual leakage rate
to determine if a response action^ is necessary. The site-specific top liner action
leakage rate demonstration must be based on allowing only very small isolated
leakage through the top liner that does not affect the overall performance of the top
liner."
The concepts of rapid and extremely large leakage (RLL) and response action plan (RAP) were
also introduced in the proposed Liner/Leak Detection System Rule. The RLL was defined as (52 FR
20237) "the maximum design leakage rate that the LDCRS can remove under gravity flow conditions
(i. e., without the fluid head on the bottom liner exceeding one foot of water in granular leak detection
systems and without the fluid head exceeding the thickness of synthetic leak detection systems)."
The RAP was defined as (52 FR 20222) a plan "which consists of an assessment of the. reason for
leakage, the current conditions of the unit components..., the potential for migration out of the. unit
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of hazardous waste constituents at levels exceeding health-based standards, and an assessment of the
effectiveness of various responses."
A.9 EPA FINAL RULE OF 29 JANUARY 1992
On 29 January 1992, EPA finalized the proposed rules of 28 March 1986 and 29 May 1987
(i.e., the Double-Liner Rule and the Leak Detection System Rule). This final rule (57 FR 3462) amended
the double-liner and LDCRS requirements of 40 CFR 264 and 265 for certain land disposal units,
including some waste piles. The final rule also codified CQA requirements for landfills, waste piles,
and surface impoundments.
The double-liner system and LCRS required in the final rule are essentially the same as those
presented in the proposed 28 March 1986 rule. The double-liner system requirements can be satisfied
by a geomembrane top liner and composite bottom liner consisting of a geomembrane upper
component and 0.9-m (3-ft) thick compacted soil layer lower component with a hydraulic conductivity
of no more than 1 x 10~7 cm/s. The LCRS requirements can be met by a drainage system that limits
the depth of leachate over the top liner to 0.3 m (1 ft).
The LDCRS requirements in the final rule are somewhat different than those presented in the
proposed EPA rule of 29 May 1987. In the final rule, the design requirements consist of the following:
(i) a minimum bottom slope of one percent; (ii) for granular drainage media, a minimum thickness of
0.3 m (1 ft) and a minimum hydraulic conductivity of 1 x 10~2 cm/s for landfills and waste piles and
1 x 10'1 cm/s for surface impoundments; and (iii) for synthetic drainage media, a minimum hydraulic
transmissivity of 3 x 10"5 m2/s for landfills and waste piles and 3 x 10'4 m2/s for surface
impoundments. The previously-mentioned performance requirements given in the 29 May 1987
proposed rule for LDCRSs were not promulgated in the final rule.
In the final rule of 29 January 1992, EPA included the RAP concept and combined the ALR
and RLL concepts of the proposed 27 May 1987 rule. In the final rule the RLL was renamed the ALR
and defined as (57 FR 3474) "the maximum design leakage rate that the leak detection system can
remove without the fluid head on the bottom liner exceeding one foot". As stated in the preamble to
the final rule, "the Agency believes that units meeting the minimum technical requirements would not
require leakage rates below 100 gpad for landfills and waste piles and 1,000 gpad for surface
impoundments". However, EPA also indicated in the preamble that they recognize "that a number of
site-specific factors affect the maximum flow capacity of a leak detection system, and owners or
operators may want to propose alternative action leakage rates".
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