My construction of a 1/2 acre pond has been a disaster and costly. I just want it finished.
I planned to put the pond in the downward slope between 2 hills with a damn on the downhill side. Seemed easy. I dug some sample holes and found the top 2 feet to be sand then clay, on the downhill side, but the uphill side was sand then stone, to the point where I couldn't dig deeper than 3ft and it was like concrete.
So my plan was to start the pond a bit lower from the uphill side where I could get about 3ft of water after lining with clay from the downhill side.
After digging out the trees and roots down to solid clay ( about 5ft) on the downhill side I began to fill in that 5ft x 20ft trench with clay from inside the pond area. I continued to elevate that with clay to about 20ft for my levee, spreading thin and packing as I went. Thats 20ft from the inside of the pond because I was getting the clay from the inside of the pond. The outside of the levee from natural ground is about 10ft.
From constructing this levee, I've used all my usable clay. I have none left to line my pond to seal it. The deeper I got in the clay area, the more rocks I found and what I'm guessing was compacted clay. It was flaky but I could snap them by hand. About 2ft of water is staying against my levee on the lowest side. It will get higher with rain, then fall back to that 2ft. We have been getting rain about once a week.
Its been 2 months since I stopped construction because I ran out of money for the project. I'm ready to get back on it but want some guidance. Obviously I picked the wrong location, but I have to make it work now. I've done the bucket test on the soils. The clay holds water until it evaporates, but the sandy areas won't hold water over night.
Whats my best plan of action next? Should I haul in clay to finish lining it. How deep to line it with clay? Mix in chemicals to form a seal?
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Do you have access to dirt that could be mixed with bentonite and used?

I have loads of the light sand I dug out. I used some of it for my driveway. It has small rocks it in but packs and dries hard. It doesn't hold much water. I can drive on it after a rain and barely leave tracks. Thats basically what the floor of the pond is. Mixed more with clay toward the down hill side. I can till in bentonite if need be. Would that be my cheapest route.

Bentonite is not a cure-all and its cost is determined by the nearness of your source. The same goes for trucking in native clay. You may want to read the Pond Boss threads on Soilfloc. (It may be your most affordable option.) Pond liners are expensive but may be the best solution. Is there a local experienced pond builder who could give you his input?
Are you digging your pond yourself? What equipment is being used? Are you using some method of soil compaction? How about some photos to help us see your project?

I hired a guy with a trackhoe and trackloader. He does plumbing work mostly but no experience on ponds. I'm pretty much just pointing the finger and he digs. I run my front end loader tractor and spread what he digs, raking out debris and packing with my tractor wheels. I've been searching online for bentonite but can't find anything local. Not much on pond experts either. I just moved to the area from out of state so I know no one here. I'm kinda at the mercy of goggle for local info.

I am not sure about getting bentonite in Alabama, but there might be a source. Try to find a drilling fluid company there. if not, then I know there are some in Mississippi. Trucks can haul up to 450 sks or 45,000 lbs, so transportation cost will depend on mileage. Cost will range somewhere around $18 to 20 bucks per 100 lbs for material. I believe if you undertreat your problem then it's better off to save your money or look for some local clays to haul in. No expert just a pond guy that deals in bentonite outside the pond area.

Call your nearest NRCS office (Natural Resources Conservation Service) in the USDA building. They have soil maps and know the best pond builders in the area. They can give you some guidance how to go forward.
Hindsight is 20-20, but if you can find more clay elsewhere on the property, that may be your best option to line the pond.

I would also contact teehjaeh57 here on the forum and ask him about Soil-Flock. That way you have multiple options and probably multiple price points to consider.