Holding Their Water
Precast tanks offer superior wastewater/water
storage solutions.
By Leslie Lichtenberg
The Eagle Hunt Effluent Storage
Tank in Chester County, Pa., is a circular precast
post-tensioned concrete tank that serves as
a large detention basin for treated water. Located
in the upscale residential community of Eagle
Hunt, a neighborhood of about 130 homes in Chester
Springs, the 2.2-million-gallon tank provided
a cost-effective, maintenance-free water storage
tank with extreme durability and structural
integrity. Because of its high visibility in
a residential development, the 108-by-36-foot
structure also met the aesthetic standards of
the project owner, Pulte Homes.
“The original
designs called for the tank to be installed
in a lagoon at the entrance to the development,”
explained Fred Ebert of RF Preston Engineering,
Bluebell, Pa. “By using a concrete tank,
we were able to move it to a top corner of the
site closer to the spray field, which not only
saved us about 10,000 feet of force main, but
also enabled the builder to actually add building
lots to the project,” he added.
Precast concrete was chosen
for the tank’s wall panels over other
materials for many reasons, including a considerable
reduction in cost. Because concrete does not
require many of the labor-intensive, high-maintenance
applications typically associated with steel
tanks, such as sandblasting and exterior coating,
precast was considered a cost-effective, virtually
maintenance-free alternative. In addition, the
engineer and owner preferred the AWWA D-115
construction methods over less stringent AWWA
D-110 concrete or cast-in-place concrete for
reasons associated with cost and longevity.
“For this project, we
were representing the interests of the largest
residential home builder in the country,”
said Dave Beiler, sales manager for Dutchland
Inc. in Gap, Pa, manufacturers and installers
of the Eagle Hunt Effluent Storage Tank. Not
only was pricing an issue, but also cost-effectiveness.
“The high costs of inspection and maintenance
made precast the most sensible choice for our
customer,” explained Beiler, adding that
the concrete in this type of structure does
not require interior or exterior coatings, as
is often the case with steel tanks, which can
deteriorate and discolor when exposed to the
outdoors.
Another benefit of precast
tanks is that they are not limited to aboveground
installation, as are steel tanks. Two-thirds
of the Eagle Hunt tank is underground and therefore
out of sight of adjacent homes, the closest
of which is 50 feet.
“Partial in-ground installation
was another aesthetic advantage associated with
this tank that enabled the builder to sell premium
homes in the community without a problem,”
said Ebert.
Working on a tight schedule,
Dutchland was able to design, manufacture and
install the Eagle Hunt Storage Tank in short
order. The use of precast concrete also expedited
the on-site erection time for the $600,000 project,
which began in March 2003 and was completed
approximately six months later.
An extremely high measure
of quality control is yet another advantage
of using precast concrete walls for a project
of this size and scope. Unlike cast-in-place
walls, which are cast vertically, the wall panels
for the Eagle Hunt tank were cast in molds horizontally,
thereby ensuring precision in concrete consolidation
and reinforcement positioning. At the site,
bearing pads and shims were placed in the keyways,
and the wall panels were placed on the base
slab. Post-tensioning provided not only active
reinforcement of the concrete, but also a dense
and watertight exterior. The post-tensioning
was achieved through the use of tension duct
extensions, which were placed and sealed between
the wall panels. Once the tendons were threaded
into the ducts, vertical joints were formed
and certified PTI (Post-Tensioning Institute)
personnel administered circumferential post-tensioning.
Using post-tensioned concrete ensures that the
tank is held in constant compression and allows
for minimal deflection and cracking.
The wall panels are constructed
as one continuous thickness, rather than applying
multiple layers of shot crete and cables (as
done for AWWA D-110 concrete tanks), providing
a more consistent and durable finish.
A similar project designed,
manufactured and installed by Dutchland is the
Long Run Pump Station in Irwin, Pa. In North
Huntington Township, a community of about 30,000
residents, two precast concrete post-tensioned
tanks were built to supplement the operation
of an existing 600,000-gallon tank and to help
provide equalization of water flow in the event
of storm surges. A new circular tank measuring
40 feet in diameter is used as a wet well to
hold submersible pumps, while a rectangular
structure holds 3 million gallons of water.
Precast concrete post-tensioned rectangular
structures are typically built for a variety
of wastewater treatment applications, as was
the case with the Long Run Pump Station.
“Because this
is an older community with a long history of
problems with stormwater inflow, these tanks
were built to supplement our sanitary sewage
system,” explained Kate Petrosky of the
North Huntington Township Municipal Authority,
owners of the project. “The purpose of
the tank is to retain excess water until the
pump station can catch up with it and send it
to the treatment plant.”
Cost was the primary factor
in choosing precast over cast-in-place concrete
for this $5 million project. Flexibility was
also critical in allowing the tank to be installed
during the winter months. Overall, the project,
which took approximately a year and a half to
complete, proved to be a longer and more complex
job than the Eagle Hunt project.
The rectangular tank, measuring
65 feet wide and approximately 250 feet long,
was constructed of precast concrete walls, corners
and tees, which were set on a cast-in-place
slab. “Although weather was not a factor
in the pouring of the walls and top of the tank,
it was factor in pouring the floor and sealing
the tank,” said Rich Hinkle of Glenn Engineering
& Associates, engineers on the Long Run
Pump Station.
The panels were set in place
and alignment was checked with laser equipment.
Like the Eagle Hunt Storage Tank, all walls
were cast horizontally in steel forms and exterior
coatings were not required. The rectangular
retention tank was installed 30 feet deep in
the ground. Again, post-tensioning provided
active reinforcement through internal ducts
cast within the tank walls.
The advantages of precast
concrete in both the Eagle Hunt Effluent Storage
Tank and the Long Run Pump Station centered
on a high level of quality control throughout
the fabrication process; cost effectiveness
owing to savings on time, labor and maintenance;
and an overall aesthetically pleasing product.
As environmental solutions
for water storage and wastewater treatment,
these precast post-tensioned tanks offer superior
functionality and durability that cannot be
matched when using steel, cast-in-place concrete
or other alternative materials.
Project Profile
Project Name:
Eagle Hunt Effluent
Storage Tank
Owner:
Pulte Homes, Trevose,
Pa.
Engineer: R.F.
Preston Engineering, Bluebell, Pa.
Contractor/Precaster:
Dutchland Inc., Gap,
Pa.*
Project Name:
Long Run Pump
Station
Owner: North
Huntington Township Municipal Authority, Westmoreland
County, Pa.
Engineer:
Glenn Engineering
& Associates Ltd., North Huntington, Pa.
Contractor/Precaster: Dutchland Inc., Gap, Pa.*
*Dutchland Inc.
is a certified plant under NPCA’s Quality
Assurance/Plant Certification program.
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