That is a very large area for a liner and will be expensive. If it is
seven feet deep and the soil is compacted it should be able to retain
sufficent level as a wildlife pond, depending the rainfall in your
area or if there is a natural spring feed.

I dug the hole years ago and compacted the soil, but when I fill it (water
from a well) the pond gets empty in a couple of days.

What is your plan for filtration? Is HDPE the stiffer, thinner stuff, also
called Permalon?

What do you mean with filtration?
Yes, HDPE is high density polyethylene (like Permalon)

Have you considered sodium bentonite? A natural lined pond is usually the
best choice for wildlife. Why do you say you have to use a liner?
Dave

I considered sodium bentonite, I' d like it, but it implies a lot of soil
moving and waterproofing is not 100% sure.



The main factors in the selection are duration and sturdiness ( maybe my
horse could decide to take a bath...)
anyway I plan to protect the bank with stones and gravel.

thanks to all

pp