First, you're going to have to read my entire post to see what I actually said before you can know how to answer. I mentioned a lot of things that you covered.
I've had the best soil experts in my area, including the soil conservation, lake designers, several respected contractors, and government agents, and etc. In the beginning I got a soil scientist to evaluate the lake area and he said it was ideal. We spent part of one afternoon driving around the site boring test holes with a tractor and an auger to check the soil composition and he said the dirt was excellent. How we missed ay sand, I 'll never know unless it was too deep for us to detect.
So I did build this lake the "right" way in the beginning, with a good contractor. Most people thought I "over-built" it
just to be on the safe side.
I've also done every thing we've done the "right" way since the leak was discovered. I've plated over the levee with 2-4' of clay. Later I did more test drilling and we dug out most of the levee to remove any sand that was there. I never noticed anything wrong with the fill dirt back at the time of construction, but they could have done it when I wasn't there. Regardless, there is no evidence of a leak there now.
While we were at it we did a secondary core ditch, even though there was no evidence it was leaking there, but we did it just to be on the safe side again.
We DID dig out all the sand in the sand pockets and veins we found, and packed it with clay. Then we plated over it with even more clay. You can't dig all the sand out, because every lake and pond in my state has sand in it somewhere. We took a back hoe and trenched around the areas we found sand pockets when we probed and backfilled and plated over them. We've already plated with clay, as you suggested.
I can only get down to my low pool level. If I get much beyond the pool level I'm afraid it would hurt the fish. Still, I think I may can add clay to that point to displace some of the water than might be causing some pressure. However, I've had soil and lake experts look at the lake and all of them say there is not enough head to force water out. It looks just like a perfectly good lake site in all regards.
As far as people not using plastic to line a lake, they do it all the time. I see lagoons and other lakes with a solid lining of plastic sheeting scattered around for many uses. People use plastic all the time for things like this, and they also build smaller ponds out of it for koi, too. Here's one example.
http://informedfarmers.com/using-liners-to-stop/ And as the article says, it's 100% effective at stopping leaks. There are companies who specialize in this very thing. There's even a tarp company out there that sells waterproof tarps that were used as billboard signs. They have customers that line leaky lake beds with them and it works.
As far as the solid layer of seamed 45 mil plastic, I don't have the budget for that, and if I did it would require me to drain all the fish out to do it.
I want to add more clay to the suspect areas, as I said in my post. Then add black plastic, and then add more clay on top of that.
I was mainly curious if anyone else here had tried using black plastic commonly found in hardware stores.
You did mentioned the pressure on a lake bottom that can contribute to water being forced out. That's another reason I'll be adding as much clay as I can before adding the plastic. The more soil I can get in the lake bed, the less water there will be, which should decrease the water pressure being exerted downward.
The main thing I wanted to ask here is if anyone else had used black plastic sheeting. I also wanted to know if anyone had info telling how long it will last sealed underground. Again, we all know it will hold water. I'm just curious to know for how long.
Thanks again.
DS
