With this being an earthen pond, the question I have is what purpose does it serve. Is it a small fishery pond, a woodland habitat pond, etc.
I have never heard of Bentonite failing to work if it was applied correctly and the existing soil had enough clay content.
Are they planning on back-filling soil over the liner to ensure a healthy Benthic layer is maintained?
EPDM may not be necessary, if indeed a liner is mandated. Polyethylene or Polypropylene would be easier to install because of the lighter weight of the material. Polyethylene is the better choice, IMO, for it is considerably more flexible than Polypropylene though not as much as ERPM.
Some more details would help.
"Everybody is ignorant, only on different subjects." - Will Rogers