Tunnel and Reservoir Plan - Illinois Section of the American Society
Transcription
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