A wide array of solutions for diverse environmental problems
Bedding process during installation.
The thought of leaking underground
storage tanks typically
conjures up media articles detailing
contaminated wells,
major environmental clean-ups and
seemingly endless costs. This article addresses
the lessons that ZCL Composites
has learned about mitigating underground
storage and process tank leakage.
It will further invite the reader to
think “outside the box” in terms of additional
applications in other sectors.
The majority of underground tanks
installed in North America are located
at retail and commercial gasoline and
diesel outlets. This enormous number of
underground storage tanks did not come
into being overnight. Far from it. Mirroring
the opportunities created by the
“car in every garage” phenomenon, retail
gasoline stations proliferated, until
it seemed that there was one on every
corner.
Similarly, a large but likely inestimable
number of underground tanks exists
for applications ranging from chemical
storage to wastewater treatment. The
downside of this, of course, is that we
have been and continue to live with the
legacy of leaking underground tanks
contaminating our environment.
By and large, contamination due to
tank leakage has been attributable to
external and internal corrosion of the
tank walls in metallic tanks and permeation
and crack formation in concrete
tanks.
Over the past 25 years, technologies
intended to address and abate this problem
have been developed and accepted
for use. Without a doubt, the major technology
has been non-metallic fiberglass
reinforced plastic (FRP) underground
tanks. The use of chemically and electrically
stable materials ensures that not
only external but also internal corrosion
can be prevented.
How does this relate to
underground applications?
The exterior wall of an underground
storage tank can at any time be subjected
to varying conditions of pH, inorganic
chemicals, salinity, water table and even
stray electrical current. Acting alone or
in combination, these conditions can
result in the eventual degradation of unprotected
tank walls. Similar conditions
will attack protected tanks that have
been damaged or improperly maintained.
Degradation of underground storage
equipment occurs not only from the outside
of the vessel but also from the inside.
Unprotected steel tanks have been
found to suffer from the consequence
of water accumulation (from condensation)
and, in some cases, biological
byproducts if bottom sludge is present.
The rate of oxidation may be a slower
process but the end result is that the internal
surface of the tank will corrode.
Left unchecked, leakage will occur.
In underground concrete tanks, the
cement and steel reinforcements in the
form of rebar can be affected by both
soil conditions and the stored product.
Worse still, the release of the tank contents
may occur insidiously rather than
catastrophically. Consistent with the
“bury it and forget it” mentality, the first
evidence of a subsurface problem often
manifests itself as a contaminated well
or a visible plume at a drainage outfall.
At this point, the classic “investigate/
blame/clean up/pay out cycle” occurs.
Does anybody win?
The installation of any underground
equipment should be regarded as a longterm
investment intended to provide protection
against unnecessary environmental
mishaps and the associated liabilities.
Fiberglass tanks offer a variety of
benefits that address regulatory compliance
issues, insurance costs and protection
of land value, not to mention reduced
maintenance and upkeep costs.
Fiberglass tanks are fabricated using
a composite or laminate that consists of
glass reinforcements supporting a matrix
of polymers known as thermoset
resins. These resins are custom-tailored
for various applications using hydrocarbon
precursors derived from crude oil.
Once the resin backbone chains and
interchain linkages in the resins have
been formed, the resulting molecular
structure is capable of resisting attack
by oxidation (corrosion) and other
chemical reactions. In a thermoset resin
system, the formation of the plastic matrix
is irreversible and stable.
Properly selected, fiberglass tanks
can be regarded as chemically inert to
the underground environs and stored or
process contents. Properly designed, the
tanks are capable of withstanding the
mechanical stresses imposed by the
burial conditions. Investigations of storage
tanks unearthed after thirty years of
service reveal that the physical properties
of the laminates have regressed
minimally.
For an even higher degree of protection,
the double wall PreZerver tank was
developed. In essence, a tank within-atank,
the outer wall of this product provides
secondary containment over the
entire tank surface. More importantly,
the discreet space formed between the
inner and outer tank walls (interstitial
space) can be directly monitored by various
methods. Compared to more general
site monitoring wells, in the unlikely
event of a breach in the tank wall, the
detection time is significantly reduced.
This technology would be highly recommended
in locations that are environmentally
sensitive, near subsurface
structures or in critical storage applications.
Most underground tanks, regardless
of application will be subjected to interaction
with the external environment in
which they reside. But the nature of
stored or processed products may vary
over a wide spectrum, including:
Chemical storage in a tank that is
chemically resistant, non-contaminating,
impermeable and secure.
Sewage holding and processing in a
tank that is biologically inert and resistant
to biological byproducts.
Leachate collection, domestic and industrial
wastewater processing in a tank
that is resistant to a wide variety of waste
streams and water treatment chemicals.
Less obvious but no less important,
fiberglass tanks can be used as:
Reliable emergency spill containment
tanks that will always be ready when
needed. These tanks are typically used
where handling and transfer of hazardous
or toxic liquids is being performed.
Bulk water storage tanks can be fabricated
to hold more than 100,000 litres
each for emergency fire-fighting.
Protection of stored water supply for
domestic application, using food grade
resins resistant to treated water. Smooth
interior surfaces in fiberglass tanks reduce
biological build-up and are easier
to maintain.
In many cases, simple modifications
can be made to the tanks in situ, should
the occasion arise, the tanks can be
drained, exhumed and reused in other
locations subject to confirmation of their
integrity by inspection and test.
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