Looking for a Few Good Tanks
A Marine Corps base selects precast
for its fuel farm.
By Joy LePree
Quantico Marine Corps Base
in Quantico, Va., was looking for a few good
oil/water separator tanks. A project that would
expand and upgrade the site’s fuel farm
area, which is used to store fuel oil and aviation
fuel, called for repairs to the containment
dikes and piping, a new fuel truck parking area,
and the replacement of loading and unloading
pumps. David Heid, Quantico’s project
engineer, realized that the existing oil/water
separator would have to be replaced as well
because it did not have the capacity to handle
the stormwater runoff from the expansion. Two
precast concrete tanks were installed for the
project: a 9,500-gallon tank to house the oil/water
separator and a 1,900-gallon storage tank to
contain the oil removed by the separator.
Precast pros
While the pre-existing
tanks for this application were made of steel,
project engineers at Quantico originally specified
the use of cast-in-place concrete for the new
tanks because it was a less expensive material
than steel. However, the contractor asked Heid
to consider using precast concrete for the application.
“The contractor suggested
that precast tanks would be faster and easier
to install because they wouldn’t require
extra forming time,” says Heid. “So
we ultimately decided to go with two precast
tanks because they could be installed with less
disruption to the operation of the fuel farm.”
Precast concrete is favored
in storage tank applications over other possible
materials, such as cast-in-place concrete and
steel, for a variety of other reasons. “While
steel is often chosen as a material for storage
tank applications, it’s not really the
best material available,” says George
Reisner, a representative for Modern Precast
Concrete, the Ottsville, Pa.-based manufacturer
of the storage tanks.
“Steel corrodes, so
if it is used in underground storage tank applications,
the tanks must be double-walled steel tanks
with all types of leak detection equipment and
very expensive level-monitoring equipment and
monitors for the spaces between the walls,”
says Reisner. “When you factor all this
in, simple precast tanks are generally cheaper
than steel tanks and are very competitive in
price when compared to steel separator tanks.
Cast-in-place concrete is
not ideal in these applications because it is
difficult to cast the underground tanks, according
to Reisner. “You have to place the forms
in the ground and you must precisely position
the forms that will make the holes for the inlet
and outlet manifold. This is a very difficult
and labor-intensive undertaking, which often
makes cast-in-place concrete a more costly option
than precast concrete.”
Quantico’s separator
system
Quantico’s oil/water
separator system was devised to handle the stormwater
runoff in the fuel farm area, where the two
tanks are mounted adjacent to each other. The
9,500-gallon tank houses the separator, while
the 1,900-gallon tank stores of the oil that
is skimmed off by the separator. “The
oil/water separator allows the rain to run off
and flow slowly through a series of baffles
in the separator,” says Heid. “The
clean water is allowed to exit into the stormwater
system. The oil that is captured floats to the
top of the tank and enters a draw-off pipe,
then flows into the waste oil storage tank where
it is stored until it is pumped out and disposed
of.”
The tanks used in Quantico’s
oil/water separator system were cast at Modern’s
plant using standard tank forms and were trucked
to the site where they were installed in the
ground. A crane set the base tank in the excavation
and placed a series of risers on top of the
base while sealant was applied between each
layer. Then the separator tank, which was precast
as one piece, was placed inside the finished
tank. The internal surfaces of both tanks were
coated with an oil-resistant epoxy to prevent
oil absorption by the concrete.
Topless tanks
What made this project
somewhat unique was that both tanks were to
remain topless. “Normally there’s
a lid with manhole access to the surface, but
this job did not require a lid for either tank
– they are simply open tanks,” notes
Reisner.
“We thought the open-top
configuration of the oil/water separator and
the storage tank would permit easier monitoring
and maintenance,” says Heid. “So
what we have are two tanks that sit a few inches
above ground level. They are both covered with
a grate to prevent people from falling in, but
you can walk on the tanks and look inside to
see if they are functioning properly.”
The tanks have never had a
warranty type issue and they are operating as
they should be, says Heid. “Precast was
the right choice for this application.”
Project Profile
Project:
Oil/water separator tanks
Owner:
Quantico Marine Corps Base, Quantico, Va.
Engineer:
David Heid, Quantico
Marine Corps Base
Contractor:
Whiting-Turner
Contracting Co., Baltimore
Precast
Manufacturer: Modern
Precast Concrete, Ottsville, Pa.*
*Modern
Precast Concrete is a certified plant under
NPCA’s Quality Assurance/Plant Certification
program.
