Bentonite will only be needed if you have poor soil and no clay content. A good grain man/operator will no how much to remove and re pack sides . Remember do not treat it like a swimming pool leave some of the silt behind to line bottom. If you get strong inflow this is what stirs up silt,put some large stones at entry point to diffuse and break up flow.
The inflow slashway into pond should be lined with rock up the sides and bottom this will help aerate water coming in.

Good Luck Scott


Scott Trava
Catskill Pond
http://catskillpond.com
scott@catskillpond.com
Returning Catskill Waters To A Simpler Time
EST. 1923