He was down in the sewage of Gotham City stinky and slimy air made it hard to breathe. Pipes and gutters were going deep down into the darkness. Batman turned on his night vision glasses "What is it?" - it was his first thought when he saw nests of rats all over the path. Rats were running under his feet and tried to bite him but the Bat suit protected Bruce Wayne from unnecessary stress. Still he felt soft flash of pushing rats with his steel toe shoes. Rats were squeaking and falling down to the stinky gutter and tried to swim. "No doubt whatever runs in those gutters is deadly to any life form" - thought Batman trying to see what was ahead of him. Nothing except rat. Computer was doing environmental scan and detected every possible chemical element but not in the consistency the Zone plant was producing.
It took quite a lot of time and resources to figure out what was even produced on that chemical plant. Getting ready to go under the City Batman did his research and all he could know about those stolen chemicals was that some parts of them had been used in atomic bombs or chemical weapons. Why a chemical resource such as the Zone plant was actually built in the city continued to be a good question but for the next time.
The computer shown the radiation and any dangerous evaporations were in almost normal level. "Sir, I detected a human voice approximately a hundred and fifty feet away. Do you want me to get directions?" - suddenly Batman heard voice in his ear.
"Humans in a sewage… they might be homeless or guys who stole the chemicals" - thought Batman and replied to the computer "Yes"
"Ok, Sir. This is the map directions I found as you see there is an obstacle approximately one hundred feet away"
-What is that obstacle? - Batman asked.
-The map is showing it's a wall, Sir.
-Any ways around?
-Only on the ground, Sir.
-Thank you. Keep the directions on my screen.
Batman continued his walk kicking rats and sneezing from time to time very quietly. He decided to walk to that obstacle on the map. And in the end it was a wall and he couldn't hear anything but hum of subway system. Every time a trait came closer to where Batman was standing everything around was shaking. It was dangerous to walk on slimy floors when ground was trembling from a train.
-Computer what is on the other side of the wall?
-The map shows a perpendicular tunnel and a subway station after that.
-I have to get back on my route. I need to get to the old school, computer.
-Getting previous directions.
Batman walked back and started almost from the beginning. He turned into different tunnel and then one more and one more. The tunnels where getting older and narrower as closer he was to the center of the city.
-Sir. - Batman heard a computer voice in his ear. - I detected a similar chemical consistency to the original sample. Approximately thirty feet away on your left.
When Batman first time went to that school and saw a pickup truck inside the basement he found a small chemical leak inside of a back of that truck. He took a sample.
Batman took a left turn and walked until he saw it with his own eyes. A small puddle of chemicals sitting on the edge of a gutter. It was brown and dark green in the same time.
-Do you see any track or steps? - Batman was carefully looking around and he found something what reminded about a dolly's tires.
-Yes, Sir. I am tracking tire's marks.
-Follow. - Batman gave a command and walked next to marks deeper into the narrow tunnel.