So, oddly, my husband used to work at the trash burner portion of the MIRA plant back when it was owned by Covanta (2002-2004). There are two parts to the facility - where the trash is dumped/sorted/shredded and the incinerator. I've only been there a couple times, but I believe the part of the plant you were seeing from the dead end was the trash dumping/sorting portion of the plant. I'll confirm with DH when he gets home later.
The basic process is: trash gets dumped, then sorted, then shredded and then passed on a conveyor belt over to the incinerator where the steam/electricity is generated. If the bags got past the sorting and shredding, it would be an extremely difficult process to find any significant evidence. I'm really, really hoping that they were able to intercept the trash before sorting/shredding.