Geosynthetic Liner Systems for Municipal Solid Waste Landfills: An Inadequate Technology for Protection of Groundwater Quality
G. Fred Lee, PhD, PE and Anne Jones-Lee, PhD
G. Fred Lee & Associates
El Macero, California
Waste Management & Research published a paper by Fluet et al. entitled, "A Review of
Geosynthetic Liner System Technology" in its March 1992 issue. The geosynthetic liner system
technology that they addressed was an engineered containment system for use in lined "dry
tomb" landfills in which are placed untreated municipal solid waste (MSW). The "dry tomb"
landfilling approach relies on a cover system to in theory keep the wastes dry and a liner system
(liner and leachate collection and removal system) to collect and remove leachate. The
performance of a "dry tomb" landfill depends on the functioning of the cover and of the liner
system for as long as the wastes represent a threat.
The Fluet et al. review suggests to the reader that flexible membrane liner systems of the type
being constructed today in municipal solid waste landfills will protect groundwater quality from
pollution by landfill leachate. Critical examination of the Fluet et al. (1992) review article,
however, reveals that they omitted from their discussion some of the most important topics that
need to be considered in an evaluation of the efficacy of landfill liner systems in providing truly
long-term protection of groundwater quality. Those neglected topics contribute to the
assessment of:
whether the liner system will prevent groundwater pollution for as long as the wastes
represent a threat to groundwater quality.
The incorporation of liners or liner systems of any kind into landfill designs was borne from the
knowledge that landfills will generate leachate that will pollute the groundwater with which it
comes in contact. Therefore, a review of the ability of geosynthetic liner systems to prevent the
pollution of groundwater for as long as the wastes represent a threat is the major essential aspect
of a review of that technology. In their abstract Fluet et al. made appropriate observations about
the common discrepancy between meeting design guidelines of regulations and the achievement
of protection of groundwater quality. The paper itself, however, focused on the design
components of a geosynthetic liner "system" without adequate consideration of the realities of
the use of such systems in landfill applications and the manner in which such systems will
eventually fail to protect groundwater quality. The review should be recognized as missing that
critical component.
Presented below is a discussion of key issues that should be considered in evaluating the efficacy
of a proposed landfill liner system.
Regulatory Requirements
Fluet et al. (1992) noted in the abstract regarding regulatory requirements,
"Regarding regulatory considerations, the paper discusses how liner systems must be selected
and designed in conformance with regulatory performance standards in order to ensure
long-term protection of the environment, and notes that many American state regulations for
municipal waste landfills include minimum design guidelines that may be inadequate to meet the
state's performance standards."
The US EPA October 9, 1991 Subtitle D regulations governing municipal solid waste landfills stated with regard to performance standards,
"The rule's standard requires that an approved State's program be capable of protecting ground
water that is currently used or reasonably expected to be used for drinking water at the relevant
point of compliance [i.e., 150 m from waste management unit boundary on land owned by the
owner of the unit]."
Those regulations also stated,
"The design must ensure that the concentration values listed in Table 1 of this section will not be
exceeded in the uppermost aquifer at the relevant point of compliance..."
The US EPA also specified that the landfill liner and cover shall consist of a composite liner, the
uppermost component of which must be a 30-mil (7.6-mm) (minimum) flexible membrane liner
(FML) and the lower component of which must be at least a 2-ft (0.6-m) layer of soil compacted
to achieve a hydraulic conductivity of no more than 1x10-7 cm/sec. If the FML is high density
polyethylene, it must be at least 60-mil (15.2-mm) thick. The FML component must also be
installed in direct and uniform contact with the compacted soil component.
The state of California Chapter 15 regulations governing municipal solid waste landfills require
that the landfill containment system be sufficient to protect groundwater quality for as long as
the wastes represent a threat. Lee and Jones-Lee (1991) have reviewed the potential threat that
municipal solid wastes and their leachates represent to the use groundwaters for domestic water
supply. The following conclusions were evident.
MSW's and their leachates contain a wide variety of chemical constituents in high concentrations
that can readily render a groundwater and associated aquifer unsuitable for domestic water
supply purposes.
A small amount of MSW leachate can pollute very large amounts of groundwater rendering them
unusable for domestic water supply purposes.
Because of the large amounts of unidentified, unscrutinized, unregulated non-conventional pollutants in MSW leachate, any contamination of a groundwater by MSW leachate should cause the groundwater to be considered unsuitable for domestic water supply use.
Inorganic salts, heavy metals, non-degradable organics and non-degradable organic residues
associated with leachate from lined "dry tomb" MSW landfills will represent a threat to
groundwater quality indefinitely, i.e., forever.
Therefore, MSW will be a threat to groundwater quality for as long as it remains buried, and
hence engineered groundwater protection systems must function properly forever in order to
achieve long-term protection of groundwater quality.
While the US EPA municipal landfill regulations address only a few so-called "hazardous
chemicals" in groundwater, the state of California requires protection of groundwater quality
from all chemicals that can impair its uses. Total dissolved solids (TDS), hardness, alkalinity,
chloride, sulfate, etc. present in MSW leachate can readily pollute groundwaters, impairing their
use. While the US EPA regulations do not prohibit impairment from those types of pollutants,
the state of California regulations do prohibit such impairment.
The authors agree with Fluet et al.'s (1992) observation that a geosynthetic or any other type of
liner system that is used for municipal solid waste landfills needs to achieve the performance
standards set forth by the regulations. In California that means that the geosynthetic liner system
has to provide for the unequivocal protection of groundwater quality for as long as the wastes
represent a threat, i.e., forever. Fluet et al. (1992) also noted that the minimum design standards
in many states are not adequate to achieve the performance standards. California is one such
state because of the manner in which the "minimum design standards" requirement is being
interpreted. The Chapter 15 regulations explicitly state that the liner (or liner system) must be
capable of preventing degradation of the waters of the state, have a permeability equal to or less
than 1x10-6 cm/sec, and be of sufficient thickness to prevent vertical migration of fluid (including
waste in leachate) to the waters of the state causing degradation.
While the Chapter 15 regulations state that the minimum design standards are whatever is
necessary to achieve the performance standard of groundwater quality protection, regulatory
agencies have allowed landfill applicants and their consultants to interpret those regulations to
mean that a liner design of a 1-ft (0.3-m) layer of soil compacted to achieve a permeability of
1x10-6 cm/sec is the design standard for municipal landfills. It is such lack of enforcement of the
Chapter 15 requirements in the state of California by the regulatory agencies that is allowing the
construction of inadequate liner systems. It may therefore be concluded that even where the
regulations make it clear that the performance standards shall be achieved, the implementation of
the regulations at the regional or local level may well not provide that degree of protection.
Because of the current and growing importance of groundwater for domestic supply, and because
once polluted with municipal landfill leachate, groundwaters and associated aquifers cannot be
restored to provide a reliable water supply, it is the authors' view that the performance standards
must require protection from impairment of groundwater for as long as the wastes represent a
threat. Since the wastes will be a threat forever, the geosynthetic (or other) liner system used in a
landfill must be able to perform perfectly forever as a barrier to leachate migration through it.
Any landfill liner system that does not achieve that level of protection is allowing today's society
to enjoy garbage disposal for cheaper-than-real cost at the expense of the public health,
groundwater resources and economic and other welfare of future generations.
An important observation about such well-intentioned performance standards for municipal
landfills is that no material or engineered component can be ensured to last forever, i.e., for as
long as the wastes represent a threat to groundwater quality. This is especially critical for
components that are buried beneath hundreds of feet or meters of garbage and/or otherwise not
amenable to routine and thorough inspection, repair, and replacement. The authors have seen
this dilemma "addressed" in a number of different ways, each inadequate to ensure protection of
groundwater resources. Technical issues of claims such as that the wastes and hazards will
"degrade," that groundwater monitoring programs will provide advance warning of pollution,
that liner systems provide redundancies for protection, that only cap maintenance is of
significance to groundwater quality protection, and that only "small amounts" of leachate will
leak through modern liner systems, have been addressed elsewhere (Lee and Jones-Lee, 1991,
1992a, 1992b).
Geosynthetic Liner System Leakage
There is a myth developing that because a "liner system" contains a number of components, none
of the individual components has to be fail-safe to provide protection. In discussing the theme of
their paper, the difference between "liners" and "liner systems," Fluet et al. (1992) noted,
"In fact, since liners depend solely on their material properties to inhibit flow of fluids through
them, it is impossible to construct large scale liners that do not leak. However, this does not
mean that landfills must leak, because landfills constructed with liner systems consisting of one
or more liner(s) and leachate collection layer(s) can be constructed with de minimis or no
leakage. Liner systems are able to succeed where simple liners fail, because, whereas liners
depend solely on material properties, liner systems utilize both engineering design and material
properties to prevent leakage."
There is a variety of mechanisms by which failure of not only liners but also leachate collection
and removal systems will inevitably occur (Lee and Jones-Lee, 1992a). The integrity of most
such systems is governed by the integrity of a synthetic liner, itself imperfect and subject to
penetration and deterioration. Clogging of the leachate collection and removal system is another
mechanism becoming recognized as problematic in maintaining their performance.
In their discussion of the role of the leachate collection systems in liner system design to
"prevent" groundwater pollution, Fluet et al. tried to develop an analogy between the design of a
landfill liner system and that of a ship's hull. They did not discuss, however, at least one very
significant difference between a ship's hull design and a landfill liner design, namely that a ship's
hull is accessible for and subjected to inspection, maintenance, and repair. Further, even a
well-maintained ship does not have to be kept sea-worthy forever. A landfill liner is buried
under often hundreds of feet (or meters) of solid wastes and cannot be inspected and cannot be
repaired without waste exhumation. The landfill liner must function perfectly forever if it is
going to prevent groundwater pollution for as long as the wastes represent a threat.
Fluet et al.'s (1992) paper was reportedly originally submitted to Waste Management & Research
in February 1990. Subsequent to that time, a considerable amount of new information has been
published on landfill liner leakage. That information was recently reviewed and summarized by
Lee and Jones-Lee (1992a). As they pointed out, for example, Bonaparte and Gross (1990)
reported,
"Based on the data in this study, an action leakage rate of 50 lphd [liters per hectare per day] is
too restrictive and presents a performance standard that, if promulgated by US EPA, frequently
will not be met by facilities that were constructed to present standards with rigorous third-party
CQA [Construction Quality Assurance] programs. An action leakage rate of 200 lphd appears to
be reasonable for landfills that have been constructed using rigorous third-party CQA
programs."
Further, the US EPA (1989) stated,
"EPA realizes that even with a good construction quality assurance plan, flexible membrane
liners (FMLs) will allow some liquid transmission either through water vapor permeation of an
intact FML, or through small pinholes or tears in a slightly flawed FML. Leakage rates
resulting from these mechanisms can range from less than 1 to 300 gallons per acre per day
(gal/acre/day) [9 to 2800 lphd]."
In January 1992 the US EPA released its regulations regarding de minimis - or "accepted" -
leakage rates for hazardous waste landfills. There seems to be general agreement that a de
minimis leakage rate of less than 20 gals/acre/day [200 lphd] would be very difficult to achieve
when the liner system is new (US EPA, 1992). US EPA (1992) did not recommend a fixed de
minimum leakage rate.
Lee and Jones-Lee (1992a) pointed out that de minimis leakage rates should be based on
protection of groundwater quality, not on what can be routinely achieved with a particular
existing technology of FML's and compacted soil liner systems. They also discussed the fact that
the existing liner system materials were selected not because they have a demonstrated ability to
provide groundwater quality protection for as long as wastes represent a threat. Landfills are
built with the least expensive materials and systems that will allow them to be approved by the
regulators. A de minimis leakage rate should represent a rate of leakage that will not, under any
reasonable circumstance, result in groundwater pollution that can impair the uses of the
groundwater for domestic or other purposes. The establishment of de minimis leakage rates
based on the performance of geosynthetic liner systems that can be routinely achieved is
technically invalid and highly inappropriate. If that, or any other, liner system cannot perform to
prevent groundwater pollution, that liner system cannot be considered to meet the performance
standard of protection of groundwater quality for as long as the wastes represent a threat.
It is concluded that leakage of municipal landfill leachate at a rate of 20 gal/acre/day [200 lphd]
can pollute millions of gallons of groundwater daily, rendering it and the associated areas of the
aquifer unsuitable for domestic water supply. Therefore, shortly after a geosynthetic liner system
is put into service, it may fail to protect groundwater quality from pollution by municipal landfill
leachate.
Long-Term Performance of Geosynthetic Liner Systems
Fluet et al. (1992) did not properly address the expectations for long-term performance of FML's
and compacted soil as effective liners, or of the long-term performance of "liner systems." They
simply stated in this regard:
"Geosynthetic liner systems have performed very well and should continue to provide society
with a cost effective and safe means of containing waste. The foreseeable dangers lie not with
the geosynthetic liner systems but with untrained designers, careless contractors, imprudent
operators and unknowledgable regulators. Any of these can result in inappropriate geosynthetic
liner systems and the resulting problems reflect poorly on all of us. Let us all commit to
designing, installing, operating, and approving the types of geosynthetic liner systems which will
reflect well on all concerned and, most importantly, will protect the environment well into the
future."
First, the issue is not protection of the environment simply "well into the future." The regulatory,
and indeed the groundwater quality protection, requirements are not met by the liner system's
working for awhile and deteriorating sufficiently to allow widespread pollution. US (federal)
requirements do not explicitly specify a performance duration but they imply that the
performance duration has no time limit on it. The state of California regulations are explicit in
requiring protection for as long as the wastes represent a threat. Therefore, claiming protection
"well into the future" as Fluet et al. have done is not only inadequate, but also highly misleading.
By that choice of language, Fluet et al. tacitly acknowledge that they cannot claim that
geosynthetic liner systems will meet performance requirements to protect groundwater quality
for as long as the wastes in the landfill represent a threat.
The ensuing notation of the vulnerability of groundwater quality protection components of
landfill systems to "untrained designers, careless contractors, imprudent operators and
unknowledgable regulators" expresses a fundamental, and fatal, flaw of the "dry tomb" lined
landfilling approach. While systems may be able to be conceived that should in theory protect
groundwater quality ad infinitum, they will always be subject to human error, carelessness, and
societal neglect. If there is vulnerability to these types of human error in the development and
operation of a new landfill, they can only be assumed to multiply once the landfill is closed and
the landfill company is relieved of responsibility for it or society "forgets" that the area is a
landfill. However, even if the design, construction and operation of landfills with geosynthetic
liner systems were to be done without error or imperfection, the liner system will, based on the
Second Law of Thermodynamics, eventually fail to prevent leakage of leachate to pollute
groundwater. Thus, the issues of inadequate design, construction, operation, etc. associated with
geosynthetic liner systems, only speak to when groundwater pollution will occur, not to whether
it will occur. The less attention to perfection in design, construction, and operation, the earlier it
may be expected to fail. Since groundwater needs to be protected from landfill leachate for as
long as the waste represents a threat, pollution that does not occur for 50 years is as much of
concern as pollution that occurs after 5 years.
Key Findings on Issue of Long-Term Protection
Based on their review of the recent literature, characteristics of municipal solid wastes and their
leachates, and the characteristics and research on the long-term performance of FML's and
compacted soil layers, and other liner system components, Lee and Jones-Lee (1992a) drew the
following conclusions about the expected performance of geosynthetic liner systems.
Geomembrane liner systems, including those with composite liners and covers, will typically
leak leachate shortly after being placed in service at a rate sufficient to pollute groundwater,
impairing its use, and the use of that part of the aquifer, for domestic water supply purposes.
The leachate retention capabilities of geomembrane liner systems will deteriorate over time,
leading to an increase in the rate of leachate migration through the liner and pollution of
groundwater with conventional, non-conventional, and hazardous pollutants.
Geomembrane liner systems cannot be expected to perform perfectly - i.e., prevent groundwater
pollution - for as long as the waste represents a threat to groundwater quality.
Geosynthetic liner systems are often designed, constructed, and operated at the lowest cost
possible. Once a landfill is put into service, there is no opportunity to inspect, repair, or replace
system components as they deteriorate or fail. Therefore, the system components must function
perfectly for as long as the wastes represent a threat, i.e., forever.
The geomembrane liner systems of the type being used today, including those with
double-composite liner systems, is a flawed technology that will not provide for groundwater
quality protection from pollution by municipal landfill leachate.
Conclusion
Fluet et al. should have discussed the ability of geosynthetic liner systems of the type they
describe to unequivocally prevent groundwater pollution for as long as the wastes represent a
threat. Since those systems cannot be relied upon to provide that level and duration of
protection, must be considered to be a flawed technological approach. A review of the literature
(Lee and Jones-Lee, 1992a) shows that contrary to statements made by Fluet et al. (1992),
geomembrane liner systems have not performed well, nor would they be expected to provide the
necessary protection of groundwater quality for as long as the wastes represent a threat.
References
Bonaparte, R., and Gross, B., "Field Behavior of Double-Liner Systems," IN: Waste
Containment Systems: Construction, Regulation, and Performance, Geotechnical Special
Publication no. 26, ASCE, New York, pp. 52-83 (1990).
Fluet, J. E., Badu-Tweneboah, K., Khatami, A., "A Review of Geosynthetic Liner System
Technology," Waste Management & Research, 10:47-65 (1992).
Lee, G. F., and Jones-Lee, A., "Groundwater Pollution by Municipal Landfills: Leachate
Composition, Detection, and Its Water Quality Significance," Proceedings National Water Well
Association's Fifth National Outdoor Action Conference, Las Vegas, NV, May (1991).
Lee, G. F., and Jones-Lee, A., "Municipal Solid Waste Management by Lined 'Dry Tomb'
Landfills: A Flawed Technological Approach for Protection of Groundwater Quality," Report of
G. Fred Lee & Associates, Short-Course Notes for Landfills and Groundwater Quality Protection
Issues Short Course, University Extension, University of California, Davis (1992a).
Lee, G. F., and Jones-Lee, A., "Groundwater Quality Monitoring at Lined Landfills: It's Time to
Stop Deceiving Ourselves and the Public," Workshop on Dry Tomb Landfills: Problems and
Suggested Alternative Approaches," National Ground Water Association Outdoor Action
Conference, Las Vegas, NV (1992b).
US EPA, "Requirements for Hazardous Waste Landfill Design, Construction, and Closure,"
EPA/625/4-89/022, US EPA Center for Environmental Research Information, Office of Research
and Development, Cincinnati, OH, August (1989).
US EPA, "Liners and Leak Detection Systems for Hazardous Waste Land Disposal Units; Final Rule," Federal Register 57:3462-3497, 40 CFR Parts 260, 264, 265, 270, 271, January 29 (1992).
Reference as:"Lee, G. F. and Jones-Lee, A., 'Geosynthetic Liner Systems for Municipal Solid Waste Landfills: An Inadequate Technology for Protection of Groundwater Quality,' Waste Management & Research, 11:354-360 (1993)."
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