I almost commented earlier today but since you pinged me I will. Yes lots of steel slag. Even down deep under our vegetable garden. 111th and Avenue M on the East Side is where I grew up. Most everyone in the neighborhood worked in the mills. Dad always fished in Lake Calumet from shore. A few times we had so much rain all the sewers backed up and we had water in the basement.
I remembered you saying that! When I lived in Chicago I had a friend who drove from Ravenswood down to USS in I think Sauganash? to work.
(Somewhere in the Cal-Sag canal area anyway!)