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Buildings
Debris Mountain Starts to Shrink
(enr.com
10/1/01)
By Nadine
M. Post and Debra K. Rubin
As hope of finding survivors dims more
than two weeks after the Sept. 11 attack on New York's World
Trade Center, officials and contractors are concentrating
new efforts on debris removal. But many don't expect a quick
pickup in the cleanup pace. There is concern about the proximity
of underground debris to the Twin Towers' foundation and continuing
sensitivity to recovering human remains and critical evidence.
Even so, participants are developing a site-wide debris management
plan that includes removal of an estimated 300,000 tons of
structural steel.
The core of what may become the cleanup master plan for
the wrecked site in lower Manhattan was delivered to the city's
Dept. of Design and Construction Sept. 22 by implosion consultant
Controlled Demolition Inc., Phoenix, Md. The 25-page "preliminary"
document offers a host of debris-related concerns and removal
ideas related to the site's key collapsed buildings and outlines
other project management issues, from site security and safety
to contractor relations and offsite debris disposal.
CDI was initially retained by Tully Construction Co. Inc.,
one of the site's four main cleanup management contractors,
to assess debris removal in its sector that includes the former
Two WTC and several smaller buildings. The site's other contractors
have also agreed to CDI's involvement, with the goal of creating
a site-wide master plan, says one contractor executive. "This
will await the official end of search and rescue," he
adds. At ENR presstime on Sept. 25, neither Mayor Rudolph
Giuliani nor city officials had made that pronouncement.
CDI contends that the progress of debris removal "must
be subservient" to retaining the structural integrity
of the slurry wall foundation. "The highest priority
and the great challenge in this emergency is to support the
slurry wall," says Mark Loizeaux, president.
The 1,000 x 500-ft foundation walls are intact, reports
George J. Tamaro, lead engineer on the Mueser Rutledge team.
Water inside seems to be related to rainfall and other sources,
but is not river water, he says. Tamaro adds that there is
"absolutely" a need for a slurry wall tieback system,
but not necessarily all around the "bathtub," which
covers 7.5 acres.
Because the structures in the eastern half of the site are
largely intact, CDI recommends them as the debris removal
starting point. Above grade, the firm's report recommends
conventional wrecking methods to remove 4 WTC down to the
slab. Conventional demolition of 5 WTC is not possible currently
because it would get in the way of debris removal operations
for the collapsed 7 WTC, which itself is a stand-alone operation.
The report says some torch work will be necessary to isolate
or downsize major structural steel debris. CDI recommends
liquid oxygen-propane torches to avoid the "weld-back"
of steel, which slows down operations.
Freestanding sections of the towers can "probably"
be pulled over using cables and heavy equipment, says CDI.
After the fall area is cleared, an excavator would progressively
rock the freestanding element to build "accelerating
harmonic response" until failure is achieved.
To accelerate progress, CDI also recommends attention to
restoring transit service in the area and development of "a
detailed sequence" for utility installation. The report
also urges improvements in how project officials interact
and communicate.
STACKING UP. While site concrete was largely pulverized into
fine dust, huge quantities of damaged structural steel lay
in tangled heaps throughout the former 16-acre WTC site. "I
saw I-beams stacked six stories high," says Allen Morse,
chief debris expert for the Army Corps of Engineers, a technical
advisor to the Federal Emergency Management Agency. He says
steel could make up as much as half of the site's estimated
1.2 million tons of wreckage. "You can't move machinery
around unless you plan for it," adds Morse.
To accelerate steel removal, Weeks Marine Inc. has created
two steel offloading areas that ramped up operations last
week to transport debris by barge for recycling. The sites
are located at Pier 25 on the Hudson River and at Pier 6 at
the tip of lower Manhattan (see map). The city's usual garbage
removal facilities, which is handling smaller site debris,
could not accommodate steel pieces.
Weeks was still dredging the Pier 25 site even as trucks
began delivering steel to the site for offloading by crane
to barges that can hold up to 3,000 tons. "That's equivalent
to 150 truckloads," says Weeks Senior Vice President
George Wittich. Business was slow at first as truckdrivers
maneuvered through the site and city streets and had to pass
muster with fbi officials checking for evidence. One site
source says security was beefed up after some drivers sold
steel privately to scrap dealers.
Wittich says the city has awarded contracts to two private
scrap dealers to handle 50,000 tons of steel. The rest is
expected to be used to create offshore artificial reefs or
head for "upland" disposal. While the company obtained
dredging permits in seemingly record time, environmental permits
for steel disposal have yet to be issued. "The rate that
the stuff can be brought to the reef is less than what's coming
out," says Weeks President Richard S. Weeks. Wittich
says larger steel debris, as big as 30 tons, may be used for
slurry wall stabilization.
Even with 45 Weeks employees on site and 24-hour-a-day operation,
the Corps called in help, awarding a $790,500 contract to
Great Lakes Dredge and Dock Co. to deepen the Pier 6 site.
But the CDI report contends that more disposal capability
is needed. "The existing barge terminal facilities must
be expanded...if there is any hope of accommodating the tremendous
volume of material that demolition contractors can move once
full production is under way," says the document.
The Corps is also seeking to ramp up debris sorting operations
at the Fresh Kills landfill in Staten Island, N.Y. On Sept.
25, it began testing a conveyor system, says Morse. He adds
that the U.S. Environmental Protection Agency is "writing
a plan" to manage hazardous waste recovered on site,
including freon, fuel and biomedical waste. "When we
run across it now, the stuff is being put in a holding area,"
he says.
But even as management plans move into high gear, project
participants are not optimistic that debris will disappear
fast. Morse estimates work could take eight months but CDI's
Loizeaux believes it could take up to 14 months. "The
debris stream will pick up, but it won't be huge," says
Morse. "It will still be a deliberate process."
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