tetrahydrofuran
Detected in the landfill...detected in the well...hmmm...
What precisely would DEP require as a "clear indication" that it came from the landfill ? What other possible sources for this substance exist in that area ? They may be able to quibble over bacteria and iron...but tetrahydrofuran ???
This is a solvent and degreaser...it does not appear naturally in the ground.