Sorry your bentonite application probably won't work!

Time to think outside of the box.

If you think you can seal the bottom effectively, then maybe try a pond liner on vertical sides? If you cut your sides vertical, you could have a little more pond volume within your restricted space.

You could tuck the pond liner into a trench in the pond bottom and then backfill to anchor it. I think it would be very unlikely to get punctured since no animals or humans would be able to effectively put weight on it.


Alternatively, I have seen applications of cement modified soil. However, that material was used for erosion control in emergency spillways subject to erosive water flows. I have not personally seen it used in applications where perfect sealing is required.

I have attached an engineering paper from my files to give you a little more information if you have to go the "Cement Modified Soil" route.

chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://secement.org/wp-content/uploads/2017/04/EB242.pdf