William John

You answered right 😉.
GL

Knock a zero off the end of the price and i'll take it rofl

Personally I would dig out your area and if it is as you say clay like material then I would tamp the earth with a handmade wood tamp.
Or you could buy a metal tamp. That will compress the soil and create a natural bed capable of holding water long term. If once you try tamping and the bed of your pond still seems porous or brittle you would need to add something like clay, which you could find and dig up and transport to your pond. Mix clay in with your existing dirt and create a compressible layer. Then tamp that down. If hand tamping is not your thing you can rent a wacker packer, fire it up and bang it around your pond.
If that doesn't hold water still you could buy some cement mix and add it to your material. Cheaper than that fancy stuff you were mentioning.
Really it boils down to budget in the end. How much you want to spend versus how much labor you are willing to expend.
Good luck!

Congratulations on earning your acre the hard way Orin.
Best of luck in coming months building your Nirvana!

Jeff Higdon wrote:

 However, I got sprayed with some water that was in one of those tanks and it gave me a mild chemical burn.  That got me to thinking:  Do I really want to live with those chemicals in my house for the next 50 years?

 After looking online, I came up with www.repurposedmaterialsinc.com.  They sell 45 mil rubber roofing for $400 for about 2000 square feet.

 The only problem is the holes and irregular shapes.  I went and talked to a roofing contractor who installs it, and he told me of a tape you can buy to seam it, though I have not sourced that yet.

 They also sell billboard vinyls which could be used for many applications.

What about cleaning the liner from those tanks? I guess there is a trade off to consider there. Which is more efficient use of time and effort? Cleaning (if feasible) the "free*" liner versus patching the used roofing material.

I would think something similar to what is used to patch inner tubes for tires would work for the holes, cut outs. Labor intensive for sure depending on the material. Might would even make sense to trim that material in straight lengths then glue them together. That might would provide more installation control when repaired seams could get ripped off and end up with leakage.

* when i say free there is still a cost for moving, handling, storing, your time, etc.

Do you have any data on the vinyl? Thickness, cost, etc.

Thanks!