George, I looked into Bentonite for sealing my pond when I renovated it in 2009. At that time, IIRC the Bentonite material bill (not including labor to "install" it) would have been in the $30K range when you added in shipping. That's why I have a fluctuating water level in my groundwater pond and why I'm doing my due diligence in researching a well for my pond.

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).