CHICAGO -- This largest of American lakefront cities has long relied on feats of engineering to keep its sewage away from Lake Michigan, its primary freshwater resource and recreational crown jewel.

In 1900, the Sanitary District of Chicago reversed the Chicago River's flow, sending wastewater from homes, businesses and streets west toward the Illinois and Mississippi rivers rather than continue to foul the city's waterfront along what today is Lakeshore Drive.

As Chicago grew over the next 110 years, so did its sewers -- morphing from a rudimentary straight-pipe sewage system into something far more complex, if only moderately cleaner. The conduit for the new plumbing system was the Chicago Sanitary and Ship Canal, which linked the Chicago and Calumet rivers to the Mississippi, which provided a trench for Chicago's wastewater to flow downstream.

Today's sewer network, built and maintained by the Metropolitan Water Reclamation District of Greater Chicago, is a behemoth among urban wastewater collection systems. Girded by more than 109 miles of deep underground pipe, Chicago's massive "Tunnel and Reservoir Plan" (TARP) ranks among the nation's largest public works projects, both in term of scale and cost, estimated at $3.58 billion.

But questions remain as to whether -- having installed all this -- Chicago can keep up with the increasingly stringent demands of Mother Nature, especially as climate change ushers in greater weather instability marked by repeated record precipitation events.

The heaviest rain in Chicago history, a 6.86-inch deluge on July 23, 2011, put its so-called Deep Tunnel system to its toughest test yet. It flunked, and sewer managers were forced to relieve flooding by opening outfalls to the Chicago River and Lake Michigan, allowing tens of millions of gallons of filthy, bacteria-laden stormwater to pour into local waterways, including along the swimming beaches that line Lakeshore Drive.

The 2011 storm was only slightly larger than two previous record rainfalls -- on July 23 and 24, 2010, and Sept. 13, 2008. Those storms, too, produced severe flooding that overtopped highways and streets, filled underground parking garages and basements, and triggered similar spoutings of untreated sewage into the lake and river.

Dubbed "City of the Big Shoulders" in 1916 by its most famous poet, Carl Sandburg, Chicago had never seen anything like these. Experts say the rising frequency and intensity of rain events has changed many Chicagoans' assumptions about what climatologists call the "100-year storm," or the rain event that has a 1 percent chance of occurring in any given year. And for many more, climate change became more a reality than a theory.

"Certainly, it has put our residents in a new frame of mind," said David St. Pierre, executive director of the Metropolitan Water Reclamation District (MWRD), which he joined in June 2011 after two decades managing wastewater systems in Atlanta and St. Louis.

Tunnels working as designed
Since last year's floods, St. Pierre said, he has attended numerous public meetings to field Chicagoans' complaints about chronic flooding and offer reassurance that the district's multibillion-dollar TARP system is working as designed. The problem, he tells residents, is that the region's first-line sewers are overwhelmed by the high volume of stormwater rushing off streets, sidewalks and parking lots.

That surging wastewater is unable to move quickly enough into interceptor sewers that feed water to the 2.3-billion-gallon-capacity Deep Tunnel system, where it can be routed to treatment plants before discharge into the Sanitary and Ship Canal. The result is that stormwater rises in low-lying areas and backs up into homes and buildings across the region, creating an environmental and public health hazard.

"You have a whole system that carries water to TARP, and you can't logistically enlarge every pipe," St. Pierre said in a recent interview. "So you really have to think about different ways to manage water, including developing a kind of hybrid where we keep water out of the [sewers] and modulate it, so the system can handle flows gradually over time."

Such a system is under construction at sites south of downtown Chicago, where MWRD and the Army Corps of Engineers are building two of the largest catch basins ever conceived. The basins, essentially deep quarries hollowed out by dynamite and earth excavators, will be able to hold an estimated 15 billion gallons of stormwater, which engineers believe should contain runoff from virtually any storm event.

When completed in 2029, the two new reservoirs, known as Thornton and McCook, will join an existing 350-million-gallon catch basin near O'Hare International Airport that since 1998 has helped avoid $250 million in flood damage, according to MWRD officials.

Last year, the Obama administration solidified that plan under a consent decree among the Justice Department, U.S. EPA, the Illinois EPA and MWRD. The agreement, which is awaiting court approval, came years after U.S. EPA first notified Chicago authorities of MWRD's massive Clean Water Act violations and imposed a new timetable for completing the reservoirs.

According to MWRD, most of the reservoir capacity -- roughly 11 billion gallons -- will be in place by 2017, including the 7.9-billion-gallon Thornton reservoir, which will trap sewer overflows from the highly industrialized Calumet-Saganashkee Channel, which links the Port of Chicago to the Chicago Sanitary and Ship Canal.

Reservoirs added, but construction moves slowly
But environmental groups, some of which have fought for decades to force MWRD to eliminate combined sewer overflows, remain dissatisfied with the settlement as drafted. They want a federal judge to require more of MWRD, including that the Thornton and McCook reservoirs be finished on a much shorter timetable than the consent decree currently allows.

Jessica Dexter, a staff attorney with the Chicago-based Environmental Law & Policy Center, said TARP, which was conceived in 1972 -- the same year the Clean Water Act became law -- has become an administrative dead weight that MWRD has been unable or unwilling to carry through to completion.

"Over the course of years, the deadlines keep slipping back and back and back," Dexter said of the plan. "We think they can be more ambitious with it."

The Deep Tunnel portion of TARP, for example, came online in 2006, after decades of start-and-stop excavation work that was subject to changing political and budgetary priorities.

Among their complaints, outlined in a March 21 letter to the Justice Department, is that federal regulators simply endorsed MWRD's "status quo" planning schedule for completing the reservoirs by 2029, which would make TARP a 57-year project.

By comparison, the nation's largest public works project, Boston's Central Artery/Tunnel, or "Big Dig," was conceived around the same time as TARP and completed in 2007 at a cost of roughly $15 billion.

Dexter and other critics say there's no reason to spend another 17 years digging reservoirs when Chicago's stormwater management challenges are growing more daunting by the year. If TARP is to be the first line of defense against sewer overflows, the argument goes, it should be deployed much faster.

"We need to finish what we started in 1972, and do it as quickly as we can," Dexter said.

Part of the problem, according to critics like the Environmental Law & Policy Center and the Natural Resources Defense Council, is that the reservoir construction schedule is tied to a vendor contract that allows excavation to speed up or slow down based on how quickly the limestone being mined from Thornton and McCook sites can be sold.

In a recent blog post, NRDC's Ann Alexander said U.S. EPA has taken a kid-glove approach to Chicago's CSO problem that contrasts with its actions in similar settlements with cities like St. Louis, Indianapolis and Kansas City.

Will the first line of defense hold?
Rather than impose tough cleanup terms on MWRD, Alexander wrote, EPA "has traded away its strong legal case in exchange for a promise from the District to simply carry on with its grindingly slow work to address the sewer overflows -- without even requiring a showing that the work is going to solve the problem."

MWRD officials acknowledge the work plan allows contractors flexibility in when and where to mine rock. But they maintain construction is moving at the proper pace based on timelines agreed to by the district and the Army Corps of Engineers, which is responsible for designing and building the reservoirs.

Since 2008, when full-scale mining began at McCook, the district has removed about 7.6 million cubic yards of overburden at the reservoir site, states a Dec. 1, 2011, status report on the TARP project.

On a recent visit to the McCook reservoir site, there was little evidence of a major excavation under way, although the size and scale of the reservoir were evident from the deep-terraced pit. From the rim of the pit, a lone bulldozer chugged along 10 or more stories below the surface. And at the opposite end of the reservoir site, a large hole had been punched through a sidewall where the outfall lines were to be constructed.

Responding to criticisms that construction was happening too slowly, St. Pierre said the schedule "is based on aggressive mining rates."

Time will tell if the solution is aggressive enough.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500