The scare quotes need to go away. Run-of-the-mill functions as a single adjective, and as such, it needs to be hyphenated. I did change the wording slightly in the second sentence so it would be grammatically correct, etc., without having to break that sentenced into more than one. (I think run-of-the-mill may not be the best way to describe something out of the ordinary — a chemical spill into the water supply is not an everyday occurrence — even if events are going as one would expect in such an uncommon situation.)
The first sentence of the second paragraph is compound, so it requires a comma. If you have more than one sentence joined by conjunctions, you need commas for all of them. (Yes, that three-part sentence is passive voice. How do you know it isn’t by zombies? 🙂 Also, there are times when passive voice is better than active, times when what was done is more important than who did it.) Use italics, not all-caps, for extra emphasis.
There has been a chemical spill in your local water supply. At first, things seem to be run-of-the-mill, with people affected being checked and quickly released from the hospital, but soon it’s a different story.
The chemical is something unknown, and within a week, people are getting sick and dying. Not only that, but for some unknown reason, it appears to be spreading. The city has been cordoned off, curfews have been issued, and the police are everywhere. Is it really a chemical spill? Is the apocalypse finally here?