Download Digging In To Deliver Clean Water

THE CONSTRUCTION WEEKLY
June 15, 2009
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enr.com
Engineering News-Record
WATER WORKS
New York City
tucks massive
290-mgd water
filtration plant
under Bronx
golf course
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Cover Story Drinking Water
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By Jack Buehrer
Digging In To Deliver
U
nder an extremely tight deadline mandated by the U.S. Environmental Protection Agency, New York City is building its
first-ever water filtration plant, which, once operational in
2012, will end a long, costly and often controversial saga that began
nearly two decades ago.
Originally estimated at $992 million, the now $2.8-billion Croton Water
Filtration Plant entailed more than 10 years of planning before contractors broke
ground in early 2007. But unlike the breakneck, 51-month construction schedule,
the idea for the 290-million-gallon-per-day plant has been slowly gestating in
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New York since 1989, the year EPA
began requiring filtration for all surface
drinking water.
“They talked about it for years,”
says Bernard Daly, who is managing the
project for the New York City Dept. of
Environmental Protection. “Now we’re
being very aggressive. It’s the driving
part of the project.”
Enacted in 1989, the Surface Water
Treatment Rule requires all public surface
water systems to achieve 99.9% removal
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NYC takes
$2.8-billion
drinking water
filtration plant
100 ft below
grade
r Clean Water
of bacteria, Giardia lamblia cysts and
viruses and a maximum contaminant level
of 1 nephelometric turbidity units. Like
some other big cities that did not filter
drinking water, New York City applied
for and received a “filtration avoidance”
for water that came from the Catskill/
Delaware watershed, the western region
of the city’s large 19-reservoir water
system. But in 1993, EPA ordered the
eastern portion of the system, the Croton
watershed, be filtered and disinfected
because of its consistent exposure
to stormwater runoff and pollution.
Construction of what now is estimated to
be a $2.8 billion project—spread over 10
separate contracts—is expected to bring
the Croton system up to EPA standards
while supplying about 10% of the city’s
drinking water under normal conditions
and more than 30% during drought
conditions. In all, the plant will have the
capacity to treat 290 million gallons of
water per day.
Located about 15 miles northeast
of midtown Manhattan, the plant is
being built between 80 ft and 100 ft
underground across a 9-acre footprint at
a golf course, located in the southeastern
corner of Van Cortlandt Park in the
Bronx. Raw water conveyed through the
New Croton Aqueduct in Westchester
County will enter the plant via gravity
through an 865-ft, 12-ft-dia tunnel
constructed as part of three-tunnel
contract, which created one intake and
two outflow lines by boring and blasting
through more than a mile of hard rock.
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Layers. Once crews have a section of the
foundation set, they go vertical, resulting in a
tiered site that is at base slab in some areas
and roof level in others.
WATER CONVEYANCE ROUTE
N.Y.
N.J.
Jerome
Park
Reservoir
Van
Cortlandt
Park
Plant
site
Ma
nha
ttan
Bronx
Queens
Brooklyn
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Conn.
PHOTO BY THE NEW YORK DAILY NEWS/HOWARD SIMMONS; MAP BY NANCY SOULLIARD FOR ENR
New Croto
n Aqueduc
t
Croton
watershed
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FILTRATION PROCESS
Screw compressor
Raw water passes through dissolved-air-floatation filters and Saturators
receives standard UV treatment before being released into
the city’s water system at Jerome Park Reservoir.
DAF recycle
Rawwater
pump
station
Overflow Flocculators
Weir Stage 1 Stage 2
DAF filters
Troughs
Raw water
from
New Croton
Aqueduct
DAF
recycle
pumps
High level
(pumped)
Backwash tanks
Mixer 1
Mixer 2
Media
Mixer 3
UV
Sleeve valves
Filter to waste
Air scour
Waste backwash storage
Backwash
pump
Floated
solids
buffer
tanks
Mixed-solids
storage tank
Low level
(gravity)
Treated-water
pump station
Force main to Hunts Point WPCP
Waste backwash
recycle pumps
Residuals transfer pumps
SOURCE: NEW YORK CITY DEP
added at each train’s final water weir—
including hydrofluosilicic acid to prevent
tooth decay and sodium hydroxide for
additional pH adjustment—treated water
will be discharged through two 108-in.dia outflow tunnels, leading to the Jerome
Park reservoir for distribution.
The Metcalf and Eddy/Hazen &
Sawyer team designed a beefed-up, castin-place reinforced-concrete structure
that was required to be flexible enough to
be folded into a relatively small site and
strong enough to support three 9-acre
levels while also holding the earth load
above the plant. The design was created
by converting 2D drawings into a 3D
model, which was used primarily for
clash detection and resolution.
In 1997, the federal government sued
the city for failing to meet deadlines set
forth in the 1993 EPA ruling. The city
was originally given a 2006 deadline to
complete the plant as part of a federal
court consent decree that also required it
to pay a $1-million fine. The project was
slowed even more by lawsuits disputing
the plant’s location, chosen because of
its proximity to existing lines that send
water south to Manhattan and Queens.
Procurement Snags
As recently as February 2007, DEP
was being fined $30,000 a day by the
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Invisible. Once complete, the plant will be
covered by about 10 ft of fill and sodded over
to create a “living roof,” and driving range.
federal government for not having hired
a lead contractor to begin work. The
original low bidder, a consortium led
by Perini Corp., pulled out in spring
2007. By the time Skanska Northeast,
in joint venture with Queens-based
Tully Construction Co. Inc., signed the
$1.3-billion base contract in August 2007,
Schiavone Construction, Seacaucus, N.J.,
had already completed its $126-million
site-preparations contract.
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RENDERINGS COURTESY OF GRIMSHAW ARCHITECTS
When complete, the plant will be covered
with fill and replanted for use as a driving
range.
The 400,000-sq-ft plant, designed
under a $50-million contract by
a joint venture of Metcalf and Eddy
(now AECOM) and Hazen & Sawyer,
both New York City, is divided into
two identical but independent parallel
treatment trains, each able to treat at least
50% of the plant’s capacity. Raw water
will be boosted by four 55,400-gallonper-minute vertical turbine pumps, which
will propel it into three mixers that add
coagulants and polymers to help remove
solid particles. Sulfuric acid also is to be
added for pH correction and sodium
hypochlorite for disinfection.
Water will then move to 48 dissolvedair floatation tanks, 24 in each treatment
train. The 22-ft-x-36-ft open-top concrete
structures are stacked to reduce the size
of the plant’s footprint. Flocculators
force any coagulated solid particles to
float to the top to be skimmed off before
flow is sent through the filter.
“Stacking allowed us to effectively
treat the water as well as maximize the
space we had,” Daly says.
Filtered water will pass through a
sand-and-charcoal media on its way to 20
ultraviolet treatment units for disinfection.
After a final mixture of chemicals is
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Cover Story Drinking Water
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DEP would not provide specific
information on cost increases. A
spokesman says they are tied to “general
inflation in the construction industry
and the highly competitive labor market
in New York City. Cost increases are
consistent with similar increases on
many other heavy construction projects
nationally.”
To excavate the site to 80-ft to 100ft depths, Schiavone removed 186,000
cu yd of soil and 920,000 cu yd of rock,
constructing concrete secant wall where
the rock was high as well as soldier piles
in the deeper reaches.
“We came in and things were already
behind, and we were able to get going
right away because the site was ready,”
says John Crecco, project executive for
Skanska. “It’s rare that we come across
a project like this where the excavation
is done for us. We started at bedrock,
and we were able to hit the ground
running.”
In August 2007, Skanska-Tully began
placing the 4.5-ft-thick reinforced
concrete mat foundation using mass
concrete, which uses a larger aggregate
and lower cement content to better
control temperatures within the structure.
DEP required foundation walls between
20 ft and 40 ft high to be placed against
the existing rock face, which crews were
able to do using a one-face form system
that incorporates a vertical A-frame
design.
“At heights greater than 30 ft, we
used a specially designed A-frame since
that height has never been done before,”
says Crecco.
The upper-level perimeter walls
required a custom-designed, vertically
braced one-face wall-form system that
braces back to the buttresses, spaced at
20 ft.
“It allowed for the mechanical works
to proceed at the lower levels, while
we constructed the upper levels of the
structure,” Crecco adds.
Maintaining flexibility to keep both
mechanical and civil teams proceeding
simultaneously has been one of the
biggest challenges in fast-tracking. The
sequencing of each section of the site gives
a slight lag to the mechanical installation.
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PHOTO TOP BY THE NEW YORK DAILY NEWS/HOWARD SIMMONS; BOTTOM BY JACK BUEHRER FOR ENR
Tight Fit. Crews encountered existing water
lines while blasting a new raw-water tunnel
that connects the filtration plant to the New
Croton Aqueduct.
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As soon as openings
are created in the
structure, mechanical
teams begin installing
equipment and closing
it up. Then it’s on to
the next floor. As the
structure rises, “the
pipes follow,” says
Don Fusco, Skanska
vice president of
operations.
“We’re moving so
fast that as soon as
we have a portion of
the foundation set,
we go vertical in that
area,” he adds. “It’s
an extremely layered
site. We have the
roof poured in some
areas, and the baseslab is still being poured in others. It’s a
snapshot of various stages of a project.”
In addition to all mechanical work,
Skanska-Tully is self-performing concrete
operations, rebar and sitework. In all, the
joint venture is using 95% direct labor,
which has also helped keep the project
moving on schedule.
“This way, we didn’t have to go bid a
bunch of jobs, hire a bunch of subs and
manage a bunch of subs,” says Fusco.
Currently the team has about 650
workers on-site. Fusco anticipates total
manpower will peak around 850 “once
the mechanicals really get going.”
Access and site logistics have created
the biggest challenges on-site. The
massive 400,000-sq-ft footprint is still
considered small for a project so large
it requires nine cranes; the three tower
cranes and six crawlers are the most
cranes on any jobsite in the city, says
Skanska’s Crecco.
Skanska’s team early on built an access
ramp into the hole for direct delivery of
mechanicals and equipment. Once the
ramp was removed, the only access to the
site was by stairs or by hook.
“When we had the ramp, we were
able to get 95% of the foundation
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Massive. The 400,000sq-ft footprint has room
for nine cranes, more
than any other New York
City site.
“We started at
bedrock. We
were able to hit
the ground
running”
John Crecco, project
executive, Skanska
Northeast
“We’re being
very aggressive.
It’s the driving
part of the
project.”
Bernard Daly, project
manager, NYC Dept.
of Enironmental
Protection
slabs completed,” says Crecco. “With
sequencing, we were able to construct
about 10% of the roof level. That allowed
for greater access into the structure by
driving on the roof.”
Tunnels
A joint venture of Schiavone and John P.
Picone Inc., Lawrence, N.Y., completed
the 865-ft-long
raw-water tunnel
that connects to an
existing line from
the aqueduct. The
12-ft-dia tunnel was
built using drill-andblast techniques, and
crews were cautious
to avoid disrupting
water service of
nearby lines.
“We were clear of
all the underground
water lines,” says
Paul Scagnelli, chief engineer and
executive vice president for Schiavone.
“But they’re so close we had to be
extremely careful.”
The Schiavone-Picone contract
also included construction of the two
tunnels to move treated water to the
Jerome Park Reservoir, about a mile
away. Contractors used a 13.6-ft-dia
TBM to bore the 3,600-ft-long highservice and 4,270-ft-long low-service
treated-water tunnels through “pretty
hard rock all the way,” Scagnelli says.
But what has been one of the most
locally controversial components of the
project still awaits: In the fall, crews
are expected to start blasting rock at
the reservoir for the shaft and meter
chamber, a decision staunchly opposed
by the community and local leaders.
The shaft, which requires removal
of about 5,800 cu yd of rock, was
originally planned to be built using a
raise bore. When NYCDEP decided to
blast the shaft to speed up construction,
community members balked, filing a
lawsuit to block the change of plans.
Project officials say periodic blasting is
more efficient and less disruptive to the
community. 䡲
Reprinted from Engineering News-Record, June 15, 2009, copyright by The McGraw-Hill Companies, Inc. with all rights reserved.
This reprint implies no endorsement, either tacit or expressed, of any company, product, service or investment opportunity.
#1-26450083 Reprinted by The YGS Group, 717.399.1900. For more information visit www.theYGSgroup.com/reprints.
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