Tunnel and Reservoir Plan - Illinois Section of the American Society

It is one of the most ambitious
public works projects in North
America, yet it remains unseen and
unnoticed to most Chicagoans. The
Tunnel and Reservoir Plan (TARP),
commonly referred to as the Deep
Tunnel project, is currently being
constructed 200 to 360 feet below
Chicago and several suburbs. The
$3.5 billion project will create over
100 miles of tunnels and nearly 16
billion gallons of storage for the
combination of storm runoff water
with raw sewage in Chicago and
neighboring communities. TARP One mission of the Tunnel and Reservoir Plan is to construct reservoirs to
will solve two serious problems for receive and store excess flows from the creeks and streams in order to
the metropolitan area: waterway !L:"f.", waters from overflowing the channel banks and flooding the
porlution and the
n""¿irÉ äï",äIin ii,iå;,,:X:;:;",';9",!,bv the MWRDGO and obtained from
of 500,000 homes."¡rãric'
There are two types of sewer systems, separate and combined. In a separate sewer system there is one
network of sewer pipes designed to transport wastewater to the fieatment plant and a second network of
sewer pipes designed to transport stormwater to local waterways. Most newer communities have separate
sewer systems. In a combined system, the wastewater and stormwater are conveyed in one common network
of sewer pipes. Many older communities have combined sewer systems.
For communities with well-maintained separate systems, storms have limited impact on the system's
ability to convey wastewater to the treatment plant. However, in combined sewer systems heavy storms can
cause the combined waste stream to exceed the capacity of both the conveyance system and the wastewater
treatment plant. Chicago and other portions of the Metropolitan Water Reclamation Disftict of Greater Chicago
(IVIWRDGC, the district) service area have combined sewer systems.
Metropolitan Chicago grew rapidly after World War II, trading open land for pavement and buildings.
As a result, the amount of storm runoff to the combined sewer pipes dramatically increased and began to
60
overload the sewer system. This is why during heavy storms,
it
was not uncommon in Chicago to see (1) combined
wastewater back up into residential basements and (2)
discharges of combined wastewater to area rivers and
sffeams. By the mid-1960's, with ordinary rainfalls forcing
untreated water into local waterways and flooding
basements, the MWRDGC began searching for a
comprehensive solution.
TARP was the proposed flood control system selected
from over 50 alternatives examined and through the
cooperation of numerous agencies. Interestingly, one
alternative to TARP would have been to separate the sewer
system. This would have meant literally digging up nearly
every street in the City of Chicago and many of the older
nearby suburbs to install new storm sewer systems.
The development of huge, deep rock tunnels and
reservoirs that capture, convey and store combined sewage
until transferred to existing treafinent plants when capacity becomes available following storms was the
best and most cost-effective solution despite the unproven nature and large funds required. The primary
goals of TARP are to: protect Lake Michigan from river backflow pollution, alleviate inland waterway
pollution, provide an outlet for floodwaters to reduce basement sewage backups, comply with state and
federal CSO's water quality regulations, and achieve these goals cost-effectively.
Adopted by the District in 1972 and started under construction inI975,TARP serves a 375-square mile
combined sewer area that is home to 3.5 million residents and contains 13,500 miles of sewers. The City of
Chicago and 5l surrounding cities and villages also comprise this area, which has 438 CSO's locallyowned and 38 District sewer outfalls on area waterways. The major tunnel segments completed thus far
have performed well, shown significant side benefits and made TARP a worldwide model for urban water
Construction photo of a portion of
the TARP Tunnel along
the
Calumet Leg. The large air ducts
hanging from the ceiling were used
to supply fresh air to workers.
Photo provided by the MWRDGC
and obtained from the "1992
Citizens Reporf.
management.
TARP is the latest chapter in the storied history of sewer systems in Chicago. As the city rebuilt after the
disastrous fire of 1871 , diverse growth along the banks of the Chicago River produced tremendous amounts
of waste. Like many rivers in urban areas before the turn of the century the Chicago River served as a
public sewer. Refuse steadily flowed farther out into Lake Michigan, the city's water supply. Eventually
sewage was sucked into the intakes, contaminating the city's water and causing devastating epidemics and
killing thousands of Chicagoans.
Aplan was devised to divert contaminated water away from the lake and west to the Des Plaines River,
eventually flowing to the Mississþi River. In 1900, the Chicago Sanitary District (now the IvIWRDGC)
6T
reversed the flow of the Chicago River and constructed
the Chicago Sanitary and Ship Canal. Locks were later
installed at the lakefront intake point to control the
westward flow of lake water.
This æmporary solution kept drinking water clean, but
did little for the condition of the lakefront and area
waterways. The district constructed sewage fteatment
plants "to protect and preserve Lake Michigan,n'
redirecting the combined (raw sewage/storm water) sewer
pipes from open waterways to the new treatment plants.
Overflows to the waterways remained to provide
emergency discharges during large storm events. These
combined sewer outflows are the problem that TARPaims
to remedy.
TARP was designed in two phases. Phase I involves
This is a photo of a dropshaft where it intersects the TARP tunnel. Drop shafts extend
from the surface 200 to 300 feet down to the bottom of the TARP Tunnel. Photo provided
by the MWRDGC.
tunnel construction serving to control CSO pollution.
Phase IIis called the Chicagoland Underflow Plan (CUP)
and involves reservoir construction serving tocontrol
flooding. Construction has been staged so that individual
tunnel segments and reservoirs are placed in operation as
soon as they are completed.
After a huge rain storm, the combined runoff will be stored in three proposed reservoirs until such time as the water can be pumped out and treated before
it is released back into the waterway system. This photo shows the site of the 10.5 billion gallon Mcoook Reservoir. The anticipated completion date for the
first stage is 2009. Photo provided by the MWRDGC.
62
I
was the nation's first comprehensive CSO
a large urban area and was designed to
captüe 857o of CSO first-flush pollution. Four major
tunnel systems in and around Chicago comprise Phase
I: Mainstream, Calumet, Des Plaines and O'Hare/Upper
Des Plaines. Nearly all of the 109.4 miles of tunnels
have been completed to date. The deep tunnels range
in diameter from 8 to 33 feet and are 150 to 340 feet
deep. Phase I facilities also include three pumping
stations to dewater tunnels and reservoirs, over 250 drop
shafts 4 to 25 feet in diameter, over 600 near-surface
connecting and flow control structures and atunnel CSO
storage capacity of 2.4 billion gallons.
The Mainstream Tunnel, the largest Phase I project,
was the first to be completed. It consists of 40.5 miles
of tunnels extending fromWilmette, Illinois in the north
to the southern terminus in McCook, Illinois. One
hundred sixteen drop shafts convey sewage and storm
water to the tunnels, where they are carried to the
Mainstream Pumping Station. The flow is then pumped
to the District's West-Southwest Treatment Plant.
One of the largest underground pumping stations ever built, the Mainstream Station has six operational
pumps with space for two additional pumps. Located 370 feet below ground, four of the pumps have a total
capacity of 1,100 cubic feet per second (cfs) or 710 million gallons per day (mgd) and the remaining two
can pump 490 cfs or 316 mgd. This pumping capacity allows the facility to empty the entire Mainstream
Thnnel in less than two days.
The six pumps are housed in twin pumping chambers measuring 270 feetlong,64 feet wide and 90 feet
high. This configuration offers the flexibility of operating the pump chambers independently in four different
modes: Mode 1. Pump from the tunnels to the treatment plant. 2. Pump from the tunnels to the reservoir. 3.
Pump simultaneously from the tunnels to the reservoir and the treatment plant. 4. Pump from the reservoir.
The pumps are powered by two independent electric power sources to ensure the availability of unintemrpted
power and backed by diesel generators.
Phase IVCUP was intended primarily for flood control and consists of three large surface reservoirs. The
U.S.Army Corps of Engineers is designing and constructing this phase and determinedflood control volume
based on federal criteria. The O'Hare Reservoir, the smallest of the three, has a 350 million gallon capacity
and was completed in July 1998. The Thornton Reservoir will be built in two stages: a 3.1 billion gallon
Phase
control plan for
The picture above shows the 33.5foot diameter boring machine better
known asthe "Mole" mining machine.
It can bore through solid rock at a
rate of up to 14.9 feet per hour or 96
feet in a single 8-hour shift. Photo
provided by the MWRDGO.
63
"transistional reservoir" was built in the west lobe of the
Thornton quarry to provide flood relief for separate sewered
areas (the transitional reservoir was nominated for anASCE
award in 2003). The 4.8 billion gallon permanent reservoir
will be mined in the North Lobe with completion estimated
in 201,3, at which point the Transitional Reservoir will be
decommissioned and returned to an active quarry. The 10.5
billion gallon McCook Reservoir will be constructed in three
stages, each providing 3.5 billion gallons of storage. The
anticipated completion date for the first stage is 2009.
A project of this social and physical magnitude is bound
to produce remarkable engineering efforts. The same
underground tunneling technology used to mine the Deep
Tunnel was also employed in the famous tunnel, connecting
England and France under the English Channel. The 33.5This is a photo of the Mole Mining Machine in operation, breaking through into the tunnel
from the other side. Photo provided by the MWRDGC.
foot diameter tunnel boring machine (TBM) carves the tunnel,
depositing stone and soil onto a conveyor belt that runs back
through the tunnel and up to the surface. The joint venture
of Kenny Construction Company, Peter Kieweil Construction
Company and J.F. Shea Company Inc. (Kenny/IGewilShea)
averaged2D0 feet bored per day, but also set numerous mining
rate world records: best hour at 14.9 feet, best eight-hour
shift at 96 feet, best 24-horir day at 242 feet, best five-day
week at 1,064 feet and the best month at 3,993 feet.
Certain sections of the tunnel required the use of multiple
soft-ground and hard-rock TBM's. A concrete liner was
installed after boring and grouting the tunnel. The l2-inch
thick concrete liner was poured in telescoping forms,
permitting the full circle to be poured at once. Certain tunnel
sections required transporting the concrete along 3,000-foot
lines powered by S,O00-horespower pumps to the proper
location.
TARP has been praised throughout the professional
engineering and environmental community. Engineering
A 12-inch thick concrete liner is poured so water is unable to leach from the tunnel into
the surrounding rock. Notice the reinforcing bars. Photo provided by the MWRDGC.
&
News Record named TARP "One of the Top 125 Consfruction
Projects of the Past 125 Years" in 2000. TARP Phase I was
awarded
the Outstanding Civil
Engineering Achievement from ASCE
twice, first in 1986 and more recently in
1994. Additionally, the United States
Environmental Protection Agency
(USEPA) recognizedTARPas one of the
nation's top Clean Water Act success
stories
in 1997.
TARP construction costs are estimated
at $3.06 billion. At nearly $2.4 billion,
the tunnel and appurtenant facility costs
from Phase I comprise the majority of the
total project cost. By 200 t , $2.16 billion
in Phase I projects had been completed.
The Calumet Torrence Avenue Leg
Tunnel, which makes up the remaining
$222mtllion is nearing completion. The
District funds the project through
a
combination of annual allocations from
the USEPAandthe
Illinois legislature and
local matching funds. Phase II/CUP
Reservoirs will cost $674 million; by
2001,547 million of this total had been
used for the completed O'Hare Reservoir.
Reservoirs currently under final design
and
in the preliminary
stages of
construction constitute the remaining
$627 million. The U.S. Army Corps of
Engineers is supplying 75 percent ofthe
funding for the Phase II flood control
projects and the Disfict generates the remaining cost from the aforementioned sources.
A 1985 estimate credited TARP's detention storage, which reduces peak flows
and optimizes existing sewer and fteatment capacity, with eliminating the need for
$1.6 billion in treatment plant expansion and $692 million in new interceptor and
local relief sewers. TARP also serves the metropolitan area as a bypass conduit for
emergency interceptor and pump station repairs, for planned rehabilitation of
With each year that passes, the Chicago river and wateruay
system will become cleaner thanks to the TARP and CUP
system. ln this photo, boaters make the trek from inland
dry-docks and marinas along the Chicago River to Lake
Michigan. Photo provided by the MWRDGC.
65
interceptors and as an outlet during rising canal levels to prevent river backflows to the lake.
The quality of the water in the Chicago River and Lake Michigan has improved dramatically since the
inception of TARP 27 years ago. Fish populations have increased three-fold, with over 50 new species of
fish now inhabiting local urban waterways. The noticeably cleaner waterways have stimulated new
development and a boom in riverside land values as Chicago has witnessed office buildings, condominiums,
hotels, restaurants, riverwalks, canoe launches and marinas grow along the river. The clean waters of the
Chicago River have attracted vigorous recreational uses as well, including tourism, boating and fishing.
With little more than a decade left to the completion of TARPPhase II, Chicagoans can see the light at the
end of the tunnel: unpolluted waterways and reduction of basement sewage backups.
Resources
'"[unnel and Reseruoir Plan Mainstream Pumping S:tation," MWRDGC Brochure.
Robison, Ritia, "The Tunnel That Cleaned Up Chicago," Civil Engineering, ASCE, July, 1986.
Walsh, Michelle, '"TARP Continues Steadily, lnvisibly," Dodge Construction News, Chicago, December 1996.
Carder, Carol, "Chicago's Deep Tunnel," Compressed Air Magazine, 1997.
Zurad, Joseph T., Sobanski, Joseph P., and Rakoczay, Joseph R., "The Metropolitan Water Reclamation
District of Greater Chicago; For over a Century Our Goal ls Clear," ASCE Annual Conference, History and
Heritage Program, Houston, Texas, October 2001
.
'"[ARP Status Report," MWRDGC, Memo, January 1,2OO1.
'"[unnel and Reservoir Plan (TARP) Description/Scope," MWRDGC, Memo, July 11, 20O2.
66