Geosynthetics June/July 2020 - 9

SCRAP OR RECYCLED POLYMER

COMPOSITE LINER

Q: The Delaware Department of Natural
Resources and Environmental Control has
expressed concern that up to 2% rework/
regrind is permitted in the manufacture of
new geomembrane sheets. Understanding
the industry standard is 10%, and the large
number of completed projects in which
the 10% spec has been followed with
acceptable performance, we would like
your input on the issue.

Q: I just spoke with Andrew Aho at the
Geosynthetic Materials Association (GMA)
regarding a large water feature we are going
to install at Edgewood Lodge in South Lake
Tahoe, Calif. He suggested sending you an
email for technical assistance. We are proposing
to construct a water feature with a width and
length of 25 × 30 feet (7.6 × 9.1 m) composed
of large boulders piled on top of each other,
having a weight of 35 to 40 tons (32 to 36
tonnes). Normally we use just a pond liner
covered with boulders as the base. However,
we want this to last far beyond the expected
warranty of 15 to 20 years. Therefore, I have
researched using a geomembrane with a
geosynthetic clay liner and a geogrid.

A: Please realize that we need to get our
wording consistent and precise. In section
4, Material Classification and Formulation, of
GRI-GM13 specification for HDPE, section 4.3
states that "The resin shall be virgin material
with no more than 10% rework. If rework is
used, it must be a similar HDPE as the parent
material." Furthermore, section 4.4 states that
"No post-consumer resin (PCR) of any type
shall be added to the formulation."
For starters, regrind is not discussed here and
is too vague for an ASTM or ISO definition.
Rework to most in the industry is edge trim,
which is ground and then reintroduced into
the hopper of the extruder. In most cases,
it never leaves the factory and has never
touched the floor. Regrind has enough
processing aid-antioxidant package in it to
survive several passes through the extruder
without significant thermal degradation. We
did an extensive study when GRI-GM13 was
originally written to arrive at this number. It
appears that the test of time (30 years) has
corroborated this decision.
In addition to your question there often
come inquiries like, "If we re-pelletize HDPE
geomembrane scrap and use it at max 10%
back into manufacturing of the same parent
geomembrane, would we be in compliance
with section 4.3 of the specification?" o this
we answer, "no." The intent of section 4.3 of
the GRI-GM13 when written was edge trim.
If one re-pelletizes HDPE geomembrane
"scrap" and uses it back into manufacturing
of HDPE geomembrane, the formulation
could be off due to out-of-conformance
"scrap," traceability issues, dirt, moisture
and many other noncompliant factors.
We realize that re-pelletize equipment has
made strides in efficiency and performance
over the last several years. However, we
think that geomembranes are used in
critical applications and need to last a
long time. This is no place for scrap or
recycled polymer.

It would be appreciated if you give us advice
on the design. Keep in mind Tahoe is at 6,200
feet (1,890 m) elevation in the Sierra Nevada
Mountains. Average low temperatures are
19˚F (-7˚C) in the winter and average highs are
78˚F (26˚C) in July. However, the water will be
heated and kept at a constant temperature no
less than about 50˚F (10˚C).
A: I agree that a composite liner
(geomembrane/geosynthetic clay liner)
sounds like a good idea for your application.
It is like a belts-and-suspenders approach
with redundancy. I would suggest a
puncture protection geotextile over the
geomembrane (heavy needlepunched
nonwoven 12-16 ounces per square yard)
instead of the geogrid. You are not looking
for reinforcement. You want to protect the
geomembrane against puncture.
Good news! Such a liner system, if designed
and installed correctly, should last much
longer than 20 years, possibly into the 100plus range.

ETHYLENE VINYL ALCOHOL
COPOLYMER (EVOH)
Q: We're designing a landfill to manage
soils affected by petroleum for a major oil
company. The typical petroleum concentration
in soil is expected to be on the order of 10,000
ppm (10,000 mg/kg). However, petroleum is
only expected to contact the high-density
polyethylene (HDPE) when dissolved in
leachate. That being said, our local regulators
have expressed concern about the potential
for the HDPE to degrade when exposed to the
petroleum in this situation. I would appreciate
if you could provide, or point me toward,
research that has been performed on this topic.

A: Existing geomembranes made of
polymers, such as HDPE, linear low
density polyethylene (LLDPE) and flexible
polypropylene (fPP), offer excellent
hydraulic resistance and act as a barrier to
heavy metals; however, the barrier to many
other contaminants can be significantly
improved through use of ethylene vinyl
alcohol copolymer (EVOH), a random
copolymer of ethylene and vinyl alcohol,
which has extremely high resistance
to the migration of greenhouse gases,
hydrocarbons and organic solvents.
EVAL EVOH is manufactured by Kuraray
America Inc., Pasadena, Texas. I would
search out the following two references
for its effectiveness and justification for
use in your project.
Armstrong S. (2012). "Performance of model
geosynthetics for containment of volatile organic
compounds in landfill applications." Proc., Global Waste
Symposium, Phoenix, Ariz.
McWatters, R. S., and Rowe, R. K. (2015). "Permeation
of volatile organic compound through EVOH thin film
membranes and coextruded LLDPE/EVOH/LLDPE
geomembranes." J. Geotech. Geoenviron. Eng., 141, 14.
doi: 10.1061/(ASCE)GT. 1943-5606.0001209.

WARNING BARRIER/SEPARATOR
Q: We are looking for a geosynthetic
that would discourage a contractor from
digging up contaminated soil. Do you
have a suggestion?
A: With government policy leading to an
increase in the development of brownfield
sites, the decision is often made to contain
hazards underground instead of removing or
neutralizing them. In these cases, it's vital that
adequate warning is put into place to protect
against future excavations.
There are several such products on the market.
Most seem to be bright vivid orange and act as
a warning barrier/separator. See the following
references for details of the contamination
indicator providing long-lasting deterrent at
Rocky Mountain Arsenal near Denver, Colo.
Zornberg, J. G. (2010). "Geosynthetic capillary barriers."
Invited keynote lecture, Proc., First International GSI-Asia
Geosynthetics Conf., Taichung, Taiwan, 13-28.
Kiel, R. et al. (2018). "Design of evapotranspirative (ET)
covers at the Rocky Mountain Arsenal." Proc., SWANA
Conf., Denver, Colo. G

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Geosynthetics June/July 2020

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