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New Challenges: Lining
Wastewater Pond with Steel Plate
Guest article by Paul Windham, VP, Fisher Tank Company
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Fisher Tank Company of Chester, PA
and Lexington, SC, has been building aboveground steel water
storage tanks for over 40 years. But when a good customer says,
"how about building an in-ground storage tank?," a good
contractor listens. And that's exactly what happened when DSM
Chemicals, Inc. of Augusta, GA. called on Fisher to line a 14'
deep x 260' diameter wastewater treatment pond near the Savannah
River with steel plate.
many wastewater treatment ponds around the country, the pond had
early on shown signs of ageing. The walls and bottom of the 1 ½
acre lagoon, lined with one-inch thick gunite over an HDPE plastic
liner, had gradually weakened. Rather than risk a leak, DSM
management had switched to aboveground steel storage tanks 10
years before. As production at the company increased, DSM decided
to build a new facility to recycle caprolactum from used
carpeting. That's when management realized its 10-year-old above
ground storage tanks lacked the capacity to handle the additional
load from the new recycling facility.
A new storage tank was not a good
option. Cost was one deterrent: a new tank would have cost
anywhere from $1 to 1.5 million. Time was another: no one wanted
to delay the opening of the new recycling plant. Once again, the
on-site pond was placed on a front burner. The old pond had
several things going for it. It was, first of all, big enough to
do the job: it had a capacity of 10 million gallons. Moreover, all
the ancillary pumps, piping and processing equipment were already
there. By using the existing impoundment instead of building a new
tank, management estimated it could save as much as $1 million.
But cost and time were only two
considerations. Management of the environmentally conscious
company wanted assurances that the pond could perform safely,
without risk of leaks. Accordingly, they insisted on lining the
walls and bottom of the earthen impoundment with steel plate.
was the safest way to go. Gunite has a history of cracking and,
over a period of time, could leak. For that reason, chemicals and
oils are never stored in concrete. Steel, of course, is
non-porous; it will contain anything from water to nuclear
reactors. Since management would not tolerate any leaching of the
product into the soil, steel was the most secure option.
To perform the work in the tight
timeframe mandated, Fisher, which had erected DSM's existing
aboveground steel wastewater tanks, mobilized two 10-man crews to
work two 10-hour shifts. "What we did here," explained
Windham, "is similar to what they do with nuclear waste
landfills. The original HDPE liner and gunite covering were left
in place. Where there were holes, cracks or voids, a suitable fill
was used to cover them."
Once the bottom and walls were
prepared, it was time to move the steel plates to the site.
Employing rubber-tired rough terrain cranes, Fisher Tank personnel
began lowering the heavy 8-foot by 20-foot carbon steel plates
into the excavation and positioning them on the floor and walls of
the embankment. Because of the pond's large size and the gradual
slope of the sides, forming of the steel plates was unnecessary;
they could be laid in place as is.
Since specs called for a liner that
was 100% steel to guard against any possible leakage, Fisher Tank
personnel employed continuous welding along the seams: using the
automatic submerged arc welding process, workers joined the plates
along the long seams; the short seams were welded with the manual
shielded-arc process. Plates were lap welded from topside. After
the welding was completed, vacuum box testing of all welds was
performed to ensure that the lining was leak-proof. Fisher Tank
personnel conducted the test in much the same way they test
conventional aboveground steel tank bottoms in compliance with
Finally, the plates were
sandblasted and the entire steel liner was coated with an
anti-corrosion epoxy. As a further precaution against the
corrosive effect of the wastewater, management of the chemical
company also directed Fisher Tank to apply a steel covering to
piping and other accessories inside the tank -- anything that
would come in contact with the waste. For this purpose, special
pieces were designed and fabricated at Fisher's Lexington, SC
The success of the
project validated management's decision to use the old
impoundment. Since completion of the work, DSM has experienced
neither leaks nor liner problems, according to a company
spokesman. With the steel-lined lagoon on-line, DSM almost doubled
its treatment capacity.
"When we only used the two
tanks, " Dan Skedsvold, DSM Chemicals' senior environmental
specialist, pointed out, "we had six million gallons of
aeration capacity. Converting the impoundment increased this by
4.5-million gallons, bringing the total at the site to over 10
million gallons. The new facility, like the other two tanks,
handles about 850,000 gallons of water each day. Wastewater has a
residence time of only one day throughout the plant before we
discharge it into the river, absolutely clean."
For more information contact our
- Mr. Paul Windham
Fisher Tank Company
3131 West 4th Street
Chester, PA 19013
Web site: http://www.fishertank.com/
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