INSURING GEOMEMBRANE-LINED CONTAINMENT FACILITIES: SOME OF THE THINGS YOU
NEED TO KNOW
Ian D. Peggs
I-CORP INTERNATIONAL, Inc.
Lining a steep slope valley landfill – it must not leak!
INTRODUCTION
Containment systems incorporating plastic liners (geomembranes) are now effectively
a regulated requirement for hazardous waste, municipal solid waste, and wastewater
treatment plants around the world. Geomembranes are also used to contain valuable
products (such as gold, copper, lithium), to waterproof dams and tunnels, to line
irrigation canals, and to preclude the contamination of infiltrating rainwater. Failures
of such containment systems can result in multimillion-dollar remediation projects and
years of litigation to define financial culpability. This is unfortunate when most of the
problems that have occurred could have been prevented with a little more, alreadyknown, knowledge and effort, and at minor cost.
It is imperative that those who prepare construction contracts and those who provide
construction and operations insurance coverage understand containment systems in
order to adequately and cost-effectively protect their clients and themselves.
One of the major problems is that geomembranes are sold and bought as commodity
products. In many applications they are commodities but in others they assuredly
aren’t. It is usually in the latter more critical applications that problems occur.
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In this paper we will outline some of the failures that have occurred and explain how
some of the differences in only one aspect of geomembrane specification (surface
modification – roughness, adhesion, impermeability, color) can be the difference
between acceptable and problematic performance. The same principle applies to
other aspects of lining systems and to all construction projects in general.
GEOMEMBRANE CHARACTERISTICS
Geomembranes are thin flexible sheets of plastic typically between 0.020 and 0.100 in.
(0.5 to 2.5 mm) thick, 6 to 30 ft (2 to 10 m) wide, and 650 to 1750 ft (210 to 570 m) long.
Smaller rigid sheets up to about 0.25 in. (6 mm) thick are used to line concrete tanks
and basins.
Rolls of geomembrane are conventionally welded together to cover very large areas
(up to 250 acres [100 ha]) by thermal fusion, extrusion of a narrow molten bead of the
same plastic over the edge of the top overlapping sheet, or by adhesion bonding.
When properly done the fusion and extrusion seams cannot be peeled apart, while the
conventional adhesively bonded seams generally can be peeled apart. However,
provided the peeling force exceeds a specified value they are considered
acceptable. This apparent dichotomy of standards has resulted in thermal
fusion/extrusion fusion being the preferred welding method, although, as will be shown,
new chemical surface-modification technology enables equally strong adhesive
bonding. A book could be written on welding techniques, seam test methods, and
seam specifications, but this is not the topic of this paper.
There are many different materials from which geomembranes are made, but at
present high density polyethylene (HDPE) is the predominant material – polyvinyl
chloride (PVC), polypropylene (PP), and alloys of up to three or four polymers (plastics)
are also available. Each has its own characteristic properties that make it more or less
suitable than other materials in different applications, such that there is no longer a
need to design an installation for a specific geomembrane material. HDPE has
excellent general chemical resistance and high strength, but there are chemicals in
which it will stress crack. It also has low deformation capabilities. It has a high
expansion coefficient that causes it to expand and form waves in the sun, and pull tight
(become stressed) at low temperatures. On the other hand PVC has a lower strength,
but has high deformation capabilities, and does not stress crack. However, unlike
HDPE, it must be covered to protect it against degradation (stiffening then cracking) by
thermal exposure and ultraviolet radiation. PP has a combination of HDPE and PVC
properties – it does not stress crack, it is tolerant of deformation, and can be left
exposed to sunlight. It has half the expansion coefficient of HDPE and is much easier to
weld.
Clearly, there is not one geomembrane material that is applicable in all installations.
HDPE would come close, but that way of thinking has become its Achilles’ heel. One
associated difficulty is that HDPE geomembranes are made from many different HDPE
resins with the consequence that the final products can vary by a factor of about 500 in
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their long-term mechanical durabilities. Hence, there is a need to distinguish between
the commodity product, such as for a golf course pond, and the more critical product
required to contain a hazardous waste liquid. The consequences of failure are very
different in these two installations so should the same material installed to the same
specifications be used in both? The liner for the latter should be far more durable.
Liners are installed to prevent leakage. However, while clay liners may be expected to
leak somewhat, geomembrane liners are generally held to a far higher standard and
are not expected to leak at all. Despite this, it is United States Environmental Protection
Agency policy to assume that all single geomembrane liners will leak to some small
degree and that the lining system should be capable of handling such leakage, hence
the requirement for a double lining system in hazardous waste facilities. The maximum
allowable leakage rate through the primary (upper) liner is typically 20 gal/acre.day
(200 l/ha.day). Both liners have the same number of flaws, but provided the leakage is
removed from the secondary (lower) liner it will not have the constant liquid head on it
that the primary (upper) liner does. While the primary liner might constantly “leak” the
secondary liner does not leak at all. Therefore, the total lining system does not leak.
This is the same principle for why the double-hulled ship does not sink - provided the
space between the hulls is pumped.
CASE HISTORY 1 – WASTEWATER TREATMENT PLANT
A major international corporation lined a concrete basin in its wastewater treatment
plant with a double liner of thick (too thick, too rigid) HDPE geomembrane. When
filled, a few discrete drips persistently came out of the leakage collection system
between the two liners. The contractor was called in to make repairs – the leak
became worse. After a second call-back the leak was continuous. The corporation
was not aware of the virtual impossibility of making a leak tight liner and requiring
repairs only succeeded in making an acceptable installation unacceptable. How
easy it would have been to recirculate a few drips back into the basin. The basin is
about to be replaced with a large stainless steel tank. Now, who caused the problem?
The design engineer for specifying a product that was more difficult to install than
others? The installer for not installing a totally leak free liner? The owner for requiring
that unnecessary repairs be made? Or even the regulator for making it easy to get a
permit for HDPE when another less familiar material, but one that requires more
deliberation, might have been more appropriate? It should not necessarily be
assumed that if a Professional Engineer has stamped the drawings and the State has
given a permit that a lining system will function as expected. And whose expectations
are we to consider – do they understand geomembrane technology?
SURFACE TREATMENTS
As indicated, HDPE is considered the geomembrane material of choice at present, but
there are many different HDPEs, just as there are many different automobiles – some
perform better or more reliably than others. In addition, there are several different
surface treatments both chemical and physical that can be given to HDPE
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geomembranes that will improve their performance in different circumstances. Not
only will these treatments improve performance, they will allow HDPE to be used in
circumstances in which a conventional “commodity” untreated HDPE geomembrane
would fail. The most traditional of these surface treatments is a physical roughening
(texturing) of the surface to provide more friction. Such geomembranes will not slide
on steeper slopes, nor will the material on top of the geomembrane slip on the
geomembrane. However the latter can be undesirable.
CASE HISTORY 2 – LANDFILL BOTTOM LINER
A new landfill cell had been constructed in the fall. On the side slopes the State
required that the sand layer be increased in depth to provide better insulation of the
clay under the double geomembrane during the cold winter. The lower
geomembrane was textured on the bottom and smooth on top. The upper
geomembrane was textured on both sides. Within a few days of adding the sand the
slopes started moving downwards, all the upper layers sliding on the smooth top
surface of the lower geomembrane Figure 1. It should have been clear that this might
happen with the added weight of sand.
Figure 1. Structure of lining system that pulled out of anchor trench
and slipped on smooth top surface of secondary (bottom) liner.
This event also identifies an advantage of having a geomembrane with a smooth top
surface – material slides on it rather than sticking to it and tearing it so that it leaks. The
liner can be used again. Alternatively, if sticking occurs but the induced stress is
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insufficient to cause the geomembrane to tear, the lower long-term stress may
ultimately result in stress cracking – a brittle fracture at a constant stress lower than the
short term break strength of the material - akin to a steady load fatigue failure. Who
was responsible for this failure? The state for requiring the additional sand? The owner
who might have added the sand without informing the engineer, or the engineer who
allowed the sand to be placed?
TEXTURED SURFACES
Further, and to complicate the practical performance of friction enhancement by
texturing, there are several methods of achieving a surface texture. As a result the
nature of the roughened surface is quite variable (see Figure 2). In the most
predominant method the surface is roughened during the primary geomembrane
extrusion process to look like a rough ocean with variable high waves. With the
specification of a minimum geomembrane thickness, it is required that more plastic is
used to ensure that the lowest valley of the rough surface will not be lower than the
minimum thickness. For equivalent thicknesses of rough and smooth materials the
break strength and elongation properties of the textured product are lower than those
for the smooth product. Thus the roughness compromises the strength of the material.
Two other processes require the thermal bonding of a surface texture (short fine
filaments or a powder) in a secondary process. In this case the minimum thickness of
the geomembrane is well established (the thickness of the smooth sheet), however the
durability of the surface texture bond is variable. It is a compromise between sufficient
bonding to prevent the added texture from being scraped off (losing its purpose) and
not overheating the bond to minimize the potential for local stress cracking over the
long term. Thus, these two types of texture do not significantly affect the short-term
break stress and elongation of the sheet as might be measured for quality control and
quality assurance conformance testing.
All three of these processes produce a random structure that is impossible to fully
control both in terms of height of texture and distribution. A fourth method is
calendering, in which the still warm and soft extruded sheet is rolled between profiled
rollers that form a controlled reproducible pattern of cones, ridges, waves, or other
raised features on the surface. In this process the minimum thickness of the sheet is
well established, and the surface texturing is integral with the body of the sheet – it is not
welded to the sheet. These textures are well-characterized.
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Figure 2.
Textured geomembranes (previous page) – nitrogen (top), powder
(middle), spray (bottom) calendered (above).
For practical performance characteristics it is important to note that all of these profiles
do not develop the same interface shear strength characteristics with all possible
components of a lining system. The short filaments interact extremely well with the felttype geotextile cushions but not as well with subgrade clays. On the other hand, the
cones and ridges of calendered products perform well with clays but not as well with
geotextiles. Thus, it is very important to perform interface shear strength (friction) tests
with the actual textured geomembrane proposed for the project against the actual site
soils and adjacent geosynthetic layers. One of the more commonly-occurring failures
is for cover soil to slide down the slopes on landfill caps (Figure 3) when the soil
becomes saturated with rainwater because interface shear tests were performed in the
laboratory with dry materials rather than with wet materials.
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Figure 3.
Cover soil slippage on landfill cap
WHITE SURFACES
The second most traditional modified surface is a white surface which reflects sunlight
better than black and results in the temperature of the liner being about 20oC cooler.
However, one does need sunglasses to work on such a liner! Expansion and wrinkling
during installation are minimized, better enabling the geomembrane to be placed flat
against a clay subgrade and to achieve the 1000 times better impermeability that is
designed to occur with an intimate contact composite lining system. If the
geomembrane and clay are not in the specified 100% contact a defect in the
geomembrane will not be effectively plugged by the adjacent clay, and water will be
allowed to flow in the non-contact areas, thereby having a larger area of clay, and
associated flaws, to flow through. If there are wrinkles in the liner that are folded over
when the cover layers are placed on the liner, it is possible that the stresses generated
by folding will ultimately cause the liner to crack and leak. A wrinkle or fold will also
prevent leachate from a landfill draining away to the sump where it can be removed.
Therefore, leachate will build up right at a location where the liner might crack. When
bulldozers operate on the soil liner above a wrinkled geomembrane liner the possibility
is increased that the bulldozer blade or tracks might catch on the top of a wrinkle and
damage the liner, again at the location where leachate will collect – and leak.
However, a white surface layer does not contain the same carbon black that provides
the clear polyethylene resin with its excellent resistance to ultraviolet radiation. So
while wrinkling problems are improved, UV resistance is compromised. Thus a white
liner should not typically be left exposed. With another swing of the pendulum, the
thin white layer makes it easy to see where the geomembrane has been damaged on
the surface and the black bulk of the geomembrane has been exposed, as shown in
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Figure 4. Clearly, the pros and cons of any geomembrane material and any surface
treatment need careful evaluation, again outlining the significant differences between
commodity and specialty applications.
Figure 4. Scratch and puncture damage easily visible on white surface. Scratch
below and parallel to black scratch is not as deep.
CASE HISTORY #3 – CAST-IN CONCRETE LINER
Thick HDPE panels with studs on the back were cast into the concrete wall of a
corrosive, valuable-liquid, containment facility. The gaps between the rigidly held
panels were too wide to weld them together with a fillet extrusion bead so a loose cap
strip was placed over the gap and welded on either side. In service the liquids were
absorbed by the HDPE causing the cap to swell along the surface layer. The loose
panel bowed outwards tending to lift and peel the edge welds off the rigidly held sheet
on the wall, as shown schematically in Figure 5. The welds separated and started to
leak.
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Figure 5.
Schematic of liner swelling to cause seam separation (Fluoroseal)
The installer was held accountable for making poor welds. However, the HDPE was
clearly incompatible with the liquid otherwise absorption swelling would not have
occurred. Normal geomembrane design philosophy is that the geomembrane shall
not be stressed; it simply should act as a barrier. Normal geomembrane weld testing
practice is that out of five test specimens cut from a weld sample only four must pass
destructive testing – an allowed failure rate of 20%. This is only tolerated since seams
are not expected to be stressed in service. However, in the concrete basin 100% of
the welds were stressed, so it is not surprising that some failed – the 20% often expected
to fail, unless more stringent specifications are imposed. Unfortunately, in this case, the
absorbed liquids made it very difficult to make good repairs on the liner, since the
owner did not want to shut the facility down in order to provide time for the absorbed
liquids to evaporate. Who was responsible? The engineer for specifying a liner
material that was incompatible with the liquids? The installer for poor workmanship or
for average workmanship on a facility that would experience stresses he never
expected? Or, the owner for not allowing time for adequate repairs?
As investigations of this liner behavior were underway, stress cracking failures started to
occur at wrinkles and locations of stress on a large section of liner that was not cast into
the concrete. The liquid was oxidizing the surface of the HDPE and initiating cracks.
The open cracks resulted in accelerated oxidation and accelerated cracking, the
cracks finally penetrating the geomembrane.
This was an extremely costly problem for all parties.
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SURFACE FLUORINATION
This leads to the third and probably most interesting surface modification – a chemical
fluorination treatment that allows HDPE to be used in liquid environments that would
otherwise be absorbed in the surface layers, eventually to diffuse right through the
HDPE. Gasoline will diffuse through conventional polyethylene and condense as a
liquid on the far side – apparently “leaking”. However, several car manufacturer are
able to use light, strong, HDPE gas tanks because the inside surface has been
fluorinated, thereby providing a barrier to gasoline absorption and subsequent diffusion
(see Figure 6). Such a treatment would probably have prevented the problems shown
in Figure 5, and at minimal cost compared to the cost of the events that actually
ensued – for all parties and their insurance companies.
Figure 6.
Schematic of surface fluorination (Fluoroseal)
Testing by Sangam et al. (2001) on the resistance of fluorinated HDPE geomembranes in
municipal sold waste landfills to typical benzene, toluene, ethyl benzene, and xylene
concentrations in leachate show that the fluorination treatment decreases the
permeability of these solvents through the liner by factors between 2.6 and 4.8. This is
equivalent to increasing the thickness of the clay layer under the geomembrane from 2
ft (600 mm) to 5 ft (1.5 m). Thus the barrier performance of geomembranes to
aggressive landfill liquids, and associated protection of groundwater, can be
significantly improved by a simple surface treatment.
However, not only does the fluorine surface treatment improve the barrier performance
of the HDPE liner, the surface chemical treatment also enables it to be adhesively
bonded to itself and to concrete and metal surfaces. In its untreated form HDPE
geomembranes have very smooth surfaces to which almost nothing will stick for any
length of time. In addition very low molecular weight components of the HDPE will rise
to the surface effectively coating the surface with a waxy layer that makes adhesion
very difficult. Even when HDPE geomembranes are thermally welded the waxes on
the surface must be removed by grinding for extrusion welding, and are scraped off by
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the hot wedge during thermal fusion welding. Welding, particularly extrusion welding
as is invariably used for repairs and detail work, requires specialized equipment with an
experienced operator. Thus, making repairs can be costly and time-consuming if
equipment and operators have to be brought in to remote sites for the simplest welding
repair. Now, with fluorinated surfaces, a repair patch can be added by a local
laborer using a two-part epoxy adhesive.
The same epoxy adhesive can be used to bond HDPE geomembrane to concrete and
steel over 100% of the contact area. In pull-off tests break occurs within the concrete
rather than on the HDPE/concrete interface, as shown in Figure 7. Thus, the adhesive
bond to the plastic is stronger than the adhesive itself. This provides superior sealing
when compared to using mechanical batten strips and rubber gaskets where bolts are
fasted on 6 in. or more centers and where leaks often occur at 90 degree corners
where the strips are butted together and where bolts cannot be placed right at the
ends, for maximum clamping effect. Not only does the adhesive make the bond, it
also fills any roughness in the concrete surface thereby improving the quality of the seal.
Figure 7.
Peeled specimen; adhesive bond is stronger than concrete (Fluoroseal)
Geomembranes can be welded to “lock strips” of the same plastic material cast into
the edge of the concrete, but there can still be problems with eventual leakage along
the plastic/concrete interface of the lock strip, and joints in the lock strip, particularly at
corners, have to be carefully welded. And while the bonded width of an extruded
bead might only be 0.5 or 0.75 in. on the top of the bottom sheet, the width of an
adhesive bond could be several inches, thereby decreasing the possibility of the
adhesive bond shearing apart.
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The adhesive bond can also be made underwater, which opens up many different
technical opportunities and which necessitates a re-thinking of underwater liner
construction and operating policies in major projects such as waterproofing the
upstream faces of concrete dams which have cracked and are leaking. Increasingly,
such dams are repaired with loose geomembranes mechanically fastened to the dam
face with periodic vertical stainless steel channels. In a multiple liner welding process
the channels are in turn covered by geomembrane and made waterproof. Then the
liner is attached to the side and base of the dam face with stainless steel batten strips.
Until recently, such repairs have required a complete draining of the reservoir, a very
time-consuming and costly procedure. One prototype project has been performed by
the US Army Corps of Engineers to line a dam face underwater, but again this is a very
costly procedure requiring some precise drilling and fitting work under very difficult
circumstances. And, since the liner is not fully bonded to the dam face, a geotextile
or geonet drainage layer is required between liner and concrete to allow any leakage
through the liner to be drained away and removed. If this leakage is not removed the
liner is not effective. Thus it becomes important to test the installed liner for leakage
before the reservoir is filled.
Alternatively, the fluorination surface treatment allows the liner to be adhered directly
to the face of the dam without any vertical channels and additional seams, and
without the batten strip around the edges. It can also be installed without having to
remove water from the reservoir. In fact the properties of the epoxy adhesive, when
spread on the concrete face of the dam, cause water underneath the epoxy to be
expelled away from the concrete surface, thus enabling 100% intimate coverage of the
concrete. Cavities in the concrete are filled and protrusions are provided with
circumferential filling resulting in more uniform support for the liner. And since there is
no gap between the concrete and liner there is no need for additional layers to
provide a drainage capability. If there is a pinhole in the liner water does not fill the
space between the liner and dam, the water in the pinhole is plugged by the epoxy.
Construction is easier, there are fewer potentially problematic procedures, and ultimate
risks are lower.
Such a system of 100% adhesion to concrete rather than the periodic attachment of
the cast-in liner, and the ability to fully adhere a cap strip would have prevented many
of the problems in Case History #3. In fact, with the larger, thinner geomembrane
rolls, there would have been no requirement for welds between panels on the walls.
On a more mundane, but still important level, is the ability to easily and effectively line
concrete basins in wastewater treatment plants and hog, dairy, and cattle farms.
Additional benefits of surface fluorination are added protection against oxidation and
the initiation of stress cracking, probably the predominant failure mechanisms in
exposed HDPE geomembranes.
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CONDUCTIVE SURFACE LAYERS
The fourth surface treatment is done on the underside of a liner – the surface layer is
made electrically conductive by the addition of a higher proportion of carbon black.
This facilitates a final electrical test for pinholes in the liner just as the corrosion
protection coating on a high-pressure gas transmission line is tested for pinholes, the
potential site for aggressive corrosion to occur. An electric potential is applied
between the conductive coating on the underside of the liner and a brass brush that is
dragged over the surface of the liner. At a pinhole, where there is no resistance
provided by the plastic layer, there is a spark discharge which can be seen, heard, and
otherwise recorded. Thus holes through the liner, and even some thin spots, can be
detected and repaired before liquid is placed on the liner and actual leakage occurs.
This should provide insurance companies and contract attorneys a benchmark to show
that construction has been satisfactorily performed. It will also provide a benchmark
beyond which subsequent problems are likely covered under an operations policy
rather than a construction policy.
Actually, pinholes are rarely the problem in liners - the major problems are stone
puncture holes and gashes caused by bulldozers and other mechanical equipment
that are simply covered over. This too could be the subject of another paper.
Such a conductive surface layer also helps in the performance of a “water-lance” type
of leak survey where positively charged water is directed on to the liner surface such
that when it penetrates a hole and contacts the negatively charged conductive layer
current flows and can be recorded. Leaks can be pinpointed. Typically, the
subgrade soil would be used as the negatively charged layer, but where there is a
wrinkle in the liner and the liner is not in contact with the subgrade the water lance
survey would be ineffective. Incorporating the conductive layer in the geomembrane
obviates this problem – the liner and conductive layer are always in contact.
CASE HISTORY #4 – VERY LARGE POND LINER
The division between construction and operations phases in relation to insurance
protection was demonstrated in a very large single liner pond facility that was felt to be
leaking since the production process was not meeting its expected yields. Visual
surveys were performed and locations of suspected leakage identified. The hard
crystalline salt deposit on top of the liner was removed and identical linear “cuts” were
found in the liner at all suspect locations. The owner suspected sabotage during the
insured construction phase. There was no operational insurance. The owner naturally
made the claim that damage occurred during construction. After an extensive very
costly investigation it was concluded that the act of removing liner cover material to
expose the liner damage was itself causing the damage noted, and that other
problems in the pond, not related to the liner, were causing deficiencies in the process.
In addition there were many features of the design and activities during the
construction process that resulted in extensive damage to the lining system that was not
covered by liquid but that would become leaks as the facility expanded according to
the design. The investigation revealed that the insurance company had not had the
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design reviewed for its effectiveness and constructability, and had not required any
monitoring of construction to confirm that what was required was properly done and
that changes in design would not compromise the quality of the liner.
The predominant cause of liner failures at present, as investigated by this author, is a
lack of sufficient knowledge of liner materials performance by design engineers. Civil
and geotechnical engineers, even electrical engineers, with insufficient work in their
own fields are expanding into the perceived lucrative environmental protection field to
work with these “simple sheets of plastic that conform to the shape of the ground, that
are completely impermeable, and that just need heating and pressing together to
make a waterproof joint” – the true commodity product as promoted by the
geomembrane industry. It is not as simple as this.
CASE HISTORY #5 – WASTEWATER TREATMENT PONDS
An extreme example of inadequate engineering knowledge involves an engineering
group working its first geosynthetic clay liner (GCL) at a water treatment plant where
the maximum leakage rate allowed through the liner was 500 gallons per acre.day (see
Figure 8).
Figure 8. Wastewater treatment pond
The engineer calculated the leakage rate given the liner specifications and the depth
of water to be contained. The leakage rate was too high. He asked the
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manufacturer of the GCL if the calculations had been done correctly – the
manufacturer said they had, and confirmed that the proposed liner would not work.
The engineer found an earlier brochure from the manufacturer’s literature that had a
lower permeability specification that would just allow the allowable leakage rate to be
met. The engineer asked the manufacturer if they would guarantee the lower number
– the manufacturer declined. The engineer asked the manufacturer for the lowest
number they would guarantee. The manufacturer obliged but the number was still not
low enough to provide an acceptable leakage rate. Then the engineer remembered
that for half the year the groundwater level would be higher than the floor of the
ponds, thereby reducing the head on the liner (technically this was not a proper
assumption) and therefore reducing the driving force for leakage. The reduced
hydraulic head just brought the leak rate into compliance with the regulations. The
engineer proceeded with the construction of several ponds.
A full-scale hydrotest, with the pond full to 11 ft, was required to demonstrate
compliance with the regulations. When there was 7 ft of water in the ponds the water
level could be raised no further - they were leaking faster than they could be filled!
Clearly, said the engineer and owner, the installer had installed a defective lining
system – the material was defective or the installation had damaged the liner – we will
not pay. Subsequent investigation revealed the leakage rate calculations described
above together with the fact that there were rocks in the cover soil up to 10 in. long
when the GCL manufacturer’s guidelines required no stones larger than 1 in. in contact
with the GCL. In addition there should be more than 80% fines in the soil – there was
actually only 10%. As a result the liner was not uniformly confined between the two soil
layers. Consequently, there were many abrasion and puncture holes in the GCL. The
design engineer was finally held accountable and the ponds were lined with
geomembranes, as should have been done in the first place.
A contract between the owner and general contractor should never have been
approved, nor should the engineer have been allowed to proceed with such a lining
system. There was no effective peer review of the design performed for any of the
project parties. And the review performed for the engineer was totally ignored. The
project should not have been allowed to proceed. Nor should insurance coverage
have been provided.
CASE HISTORY #6 – LINER MANUFACTURING
In a case of a different kind, a North American distributor/installer of a Europeanmanufactured HDPE cast-in concrete liner (CIL) thought it might be more economical
to have the sheet produced in North America and to weld on the studs themselves.
However, the European HDPE resin was not available in the USA. A full disclosure of the
properties of the original resin, the method of welding on the studs, the product
specifications required, service conditions of the sheet, and the mode of installation,
were provided to potential manufacturers of the sheet. A manufacturer promising
“equal or better” performance was selected to make sheet. Six months after their
construction the first three installations failed catastrophically by stress cracking at every
weld. Once again the installer was faulted for obvious improper welding. It was
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subsequently found that the resin used to make the sheet had an extremely low stress
cracking resistance and that the added heat of welding was sufficient to initiate stress
cracks that slowly (over 6 months) propagated through the sheet resulting in cracking
and extensive leaking.
Responsibility? The fabricator, working with HDPE should certainly have been aware of
the need for good stress cracking resistance, the single most important performance
parameter of HDPE products, but one that does not appear on conventional
specification sheets. However, the sheet manufacturer, having been provided with all
material specifications, installation procedures, and operating conditions, should have
been far more knowledgeable of the requirement for good stress cracking resistance
and the performance of its products. The costs to all parties, not only financial but also
in reputation, was very high and all because a confirmatory test costing $250 was not
performed.
It is interesting to note that the sheet in this case history, although not having a
conductive back surface, was electrically tested for leaks when installed – copper wires
were installed behind the welds. Leaks were repaired, but the added heat of the
repair process simply made the material even more susceptible to stress cracking!
Had the same sheet been fluorinated it would have been possible to attach large
panels to the walls without seams, to make joints with an epoxy adhesive therefore
without heating, and the surface would not have been as susceptible to stress crack
initiation.
Typically, we continue to see that materials problems are initiated on surfaces and work
their way inwards until ultimate failure occurs. Many times the agency that initiates the
problem cannot be avoided since it is the thing we are trying to contain. Therefore, if
the surface of the material can be beneficially modified to prevent the initiation of the
problem and to optimize the performance of the containment system, it is worth doing.
SUMMARY
As geomembrane-based lining systems become more accepted by owners and
regulators so too are the numbers of failures increasing. Approximately 60 % of failures
are due to inadequate designs, 20% to poor installation, 10% to inferior materials, and
10% to miscellaneous items. Therefore, with a little extra knowledge of the performance
characteristics of the different liner materials and a knowledge of the surface
treatments that can be given to improve the applicability of the geomembrane
material of choice (HDPE), a significant impact on 70% of presently occurring failures
could be made.
These treatments allow the safer use of HDPE geomembranes on slopes, they minimize
expansion and contraction problems, they allow easier testing for the presence and
location of leaks, and they allow the safer containment of organic liquids, the ability to
fully bond HDPE with more security to concrete and steel structures and to itself, and
the ability to bond to concrete and steel underwater.
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The insurance and legal (contract) professions can take the following simple steps to
better assure the quality of any geomembrane containment installation and its longterm satisfactory performance:

Require the review of all material specifications, project specifications, and
project drawings, by an experienced independent engineer who is not likely
to provide negative criticism for competition’s sake

Require the review of candidate contractors to ensure they have a level of
experience commensurate with the criticality of the project

Consider the preparation of a documented construction quality assurance
plan.

Require experienced construction quality assurance monitors to be on site
when the liner is being installed to ensure compliance with the project
specifications and to ensure that workmanship is of adequate quality.
The cost of such a proactive program is far less than the costs of dealing with a failure
and an environmental disaster.
REFERENCES
Sangam, H.P., Rowe, R.K., Cadwallader, M.W., and Kastelic, J.R., “Effects of HDPE
Geomembrane Fluorination on the Diffusive Migration of MSW Organic Contaminants”,
Geosynthetics Conference 2001, IFAI, Roseville, MN, pp163-176.
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