It's a delicate operation when you're lifting a stainless steel wheel gate that weighs 54 tons; no room for error. And this is just part of four huge wheel gates being lowered down this drop shaft - 300 feet down - where they will permanently reside in the deep tunnel. They will be raised and lowered to regulate the flow of storm and waste water through this last section and into the north lobe of the Thornton Quarry.
"It's the largest dirty water reservoir in the world, or it will be when it comes on line at the end of the month," said Kevin Fitzpatrick, MWRD project engineer.
At full capacity, this section of the quarry can hold nearly 8 billion gallons of water. There will be times, engineers say, when it will be filled after extremely heavy rains. What that means is there is another big place to put the stinky sewer and storm water that has caused flooding headaches on the far South Side and surrounding suburbs for years.
MORE VIDEO: Thornton Quarry drone footage
"We don't say it's a cure-all for everything, but it's gonna make a huge difference in about 500,000 people tied to this reservoir," Fitzpatrick said.
So this functions as a giant bathtub - a dirty bathtub as it were, but to work, all the quarry walls had to be sealed with grout.
That meant drilling 150 miles worth of 3-inch holes around the perimeter of the quarry and shooting in pressurized grout. No ground water leaking in or stinky water leaking out.
And at the bottom of the quarry, which looks like a train tunnel, is a 30-foot diameter tube that leads back to where the wheel gates will be. When the quarry fills, the gates will go down to keep the bathtub from overflowing.
"About 20 times a year we anticipate water coming in here after a storm. After the storm, we pump it to our Calumet water treatment plant, where it's cleaned and put back in the waterway," Fitzpatrick said.
More stinky water in the big bathtub, less in basements - that's the idea.
Operations are scheduled to start first of next month to place the rest of the gates.