Deep Tunnel is full — and more rain is coming
BY KIM JANSSEN Staff Reporterfirstname.lastname@example.org April 18, 2013 1:24PM
Updated: May 20, 2013 7:50PM
The Deep Tunnel is full and more rain is coming.
That’s the word from the Metropolitan Water Reclamation District, which operates the 109-mile long underground system designed to protect Chicago from flooding.
Though it’s not unusual for the 2.3 billion gallon system to hit capacity — it does so roughly twice a year — officials say that further rainfall could yet see the current floods rival the damage caused by Sept. 2008’s historically bad storm.
“We’re watching it closely,” said water district supervisor Ed Staudacher. “We are at the limits of a lot of our systems.”
The district has been deliberately drawing down levels on the North Shore Channel, the North Branch of the Chicago River, the Sanitary and Ship Canal and the Cal-Sag Canal since Monday to prepare for the storm, Staudacher said.
Still, the waterways had to remain deep enough to allow ships to pass. So when the deep tunnel filled up, sending overflow into the waterways, they too hit their maximum levels, and all three gates restricting the overflow from entering Lake Michigan were opened overnight — a relatively drastic move engineers take only once or twice every five years.
Opening the gates sent sewage into the lake, but Staudacher said that it was “very dilute” because the rawest sewage was captured by the Deep Tunnel. Most of the sewage released into the lake is “basically storm water,” he said.
Nonetheless, the Chicago Department of Water Management has increased the amount of chlorine it uses in its purification processes and is “aggressively monitoring” the quality of the drinking water it takes from the lake, spokesman Tom LaPorte said.
Commissioned in the 1970s, the $3 billion Deep Tunnel system was intended to keep Chicago’s streets and basements dry during storms, and to keep pollution out of the lake.
But though the tunnels were recently finally completed, not all of the reservoirs it was supposed to connect to have yet been built, and engineers still rely on the lake for sewage overflow following especially heavy storms like Wednesdays.