Creative

In this case, it still does. In many other cities, equivalent neighborhoods were occasionally entirely uprooted. In Chicago, they essentially built a wall around it instead. I made another one with Hawaii, where almost everything even tangentially related to China, including all private and personal property, all land, even names, were nationalized.

By "deal with petroleum pollution products" I don't necessarily mean that it was meant to reduce pollution, but that it happened to do so. The microbes may have been made to reclaim or produce oil, which was an extremely hot commodity. China attacked Alaska for the stuff, and the US attacked mainland China too. Of course, the Dregs may have also been partially developed as a weapon, as most things were in the setting. Perhaps to act as a pest that consume and degrade enemy resources.

The BoS in the region is generally more collaborative than those of either the West or East, working with the local population quite equitably despite their typical dogmatic nature. There are also several rogue groups of soldiers left behind after the main BoS forces left for the East. They arrived in the city with a fleet of Airships, and only a few made it out. One Airship, the Argos, was destroyed nortwest of the Chicago Loop, by the USS Cradley. A few others were destroyed by AA weapons at O'Hare. The only one that managed to get to East Coast was the Prydwen, and that's because it was built at Adam's Airforce Base in Maryland. This left many soldiers stranded. A few of them became bandits essentially. Some deserted to the Enclave, however well that might have turned out. And others went AWOL.

The Faithful of Thoria are known to be quite reserved with radiation compared to the rather cultish Children of Atom. The Thorians prefer to hoard radiohazards rather than spread them. So, they've collected nuclear waste from all over the region and piled it up in the Crater. They actually have a deal with Stickney to take the radioactive junk they filter out of the water. They do the same with other nuclear tech too, such as x-ray machines, radiotherapy machines, NMR, nuclear weapons, etc. As a whole though, they're tolerated, though the BoS dislikes having to deal with them.

The Enclave has a rather dominant position in the city, with control of several covert facilities, some of them functional, as well as the USS Crowdley. The BoS did manage to severely damage the ship, causing its beaching, but it's presumably not completely derelict. The Enclave in Chicago never got ahold of their leadership on the West Coast, so they're going along with their current plans of securing all assets they can in Chicago. Which is why they were able to give the BoS a good run for their money. They've managed to eek out a presence on the surface though, where they continue to skirmish with the Brotherhood frequently.

In this setting, I figure Chicago maintained some level of its past industry, with the Union Stockyards still being in use, or at least a new refurbished version of them. There's also a major Post Office Department ground facility in the city, which serves to connect many offices around the state. Many of the settlers and raiders around the city are descendants of these individuals. But also for the national guardsman who were left in control of what was left of the city when the Army remnants bailed. Eventually, the attrition rate became so much that they gave up.