You're thinking of man hole covers. They are for different uses. If hill's camp had searched for covers which say "Sewer" on them, they would have dumped in the appropriate pipes- semi legally.
A storm drain has a grid cover so that water on the street can drain in there. The ones in my town drain into the creek. If hill's camp had dumped in my area, they would have contaminated NYC drinking water...and the owner on whose property is the storm drain, would have been fined millions.
The pipes I was talking about are the ones on campers and RV’s and should have covers on them. I’m saying it was a deliberate act since several things have to be done before the dump can proceed.