Chicago’s permanent residents have a complicated relationship with the region’s waterways. Since the founding of the city, Lake Michigan, the Chicago River, and the city’s numerous other waterways and wetlands have been essential sources of everything from drinking water to industrial fodder. But concentrating millions of people along the banks of the water supply created a real problem for wastewater disposal, famously influencing the decision to reverse the Chicago River and the construction of the Sanitary and Ship Canal in 1900.
Nevertheless, reversing the river did not solve the region’s water problems. Among the persistent complications is the legacy of a combined sewer system. The system, which carries wastewater and stormwater, directs them to the region’s water treatment plants, where they are cleaned and then released into the area’s waterways. However, heavy rainstorms overwhelm the system, during which the combined sewage and stormwater are emptied into the area’s watercourses—and sometimes residents’ basements—before they can be treated. Residents primarily experience the subsequent pollution through beach closures, but the discharge affects the regional ecosystem in untold ways.
Started more than 40 years ago, the Tunnel and Reservoir Plan (TARP) is a goliath project designed to mitigate this problem by reducing the number of times when untreated sewage must be released into the area’s waterways. During periods of heavy precipitation, rain is diverted into the Deep Tunnel, a network of more than 100 miles of conduits as wide as 33 feet in diameter and deep as 350 feet below ground. The tunnels channel the effluent and rainwater into large reservoirs, which store the combined wastewater until it can be treated by the plants—and then released into the waterways.
These photographs present the three major portions of the southeastern section of the system: the Deep Tunnel, the Thornton Reservoir, and the Calumet Water Reclamation Plant. These interconnected facilities serve large portions of Chicago and its south suburban communities.
The portion of the Deep Tunnel shown here is the final 1,000 feet of a 36-mile system that leads to the reservoir approximately 325 feet below ground. When photographed, workers were finishing the installation of the 100-ton steel gates that control the flow of water in and out of the reservoir.
The Thornton Reservoir itself is being constructed from one of the world’s largest aggregate quarries and will hold 7.9 billion gallons of water when complete.
The final section is the Calumet Water Reclamation Plant and its underground pump room, which pumps the water out of Deep Tunnel and the reservoir to be treated and then discharged into the Little Calumet River.
The reservoir went online on November 26 and 27, 2015, during which it captured about 300 million gallons of water, enough to fill 15 feet of water from the reservoir floor. After decades of work and more than $1 billion spent during this phase (almost $4 billion in total), it is time to evaluate the effects that this portion of TARP will have on the quality of the region’s drinking water, the quality of the area waterways, and our resilience to flooding.