Thanks Rainman. Before I built this lake around 1993 I had a soil scientist come and test the ground and we had a tractor and augered a lot of test holes all around the general perimeter and in the proposed lake bed itself, to see what the soil composition was. All of it was excellent. No one suspected any problem with the good clay soil we hit everywhere, and one hill over is another lake with the same clay soil and it's held water like a rain barrell since 1942. No one had any concerns about the quality of the clay soil I would be using. And this includes the local federal government agencies that help design and build lakes.
To fast forward, a few years later I raised the levee (we had a more than adequate core ditch and we roughed up the new levee, knocked the top off, etc to have a textbook foundation to add to.) I've had the levee tested and had other experts out to check things and they did more boring, this time on the levee and found an area that was moist and was of the soil composition to allow water to seep through. I believe they called it "moving material" through the levee. I'm guessing the previous contractor hit a pocket of sand and small sandstone and a little of that got hauled in for the levee and that is the root cause of the leak.
In 2008 I drained the lake completely. We plated the front with 4 feet of top quality clay soil and the whole levee got at least 2 feet of it all down the front side. The suspected problem area got 4 feet and it was packed well. I pumped the lake back up later that winter and into the next spring and by the end of the summer it had seeped back down to the original level. I pumped it up again this past winter and now it's dropped about 6-8 feet again. It seems to drop about 15-24 inches per month, and more in the hot dry late summer. It hits a certain point and then seems to stop draining and then the water level stabilizes. The deepest part of the lake is right off the levee where my depth finder shows it to be 27 feet deep. Without getting into a lot calculations and speculations, there's a big head of water pressure on the levee and I'm sure it has one heck of a static line angling down through it. But the suspected leaky area is not there. It's away from the deep part where the head pressure should be the greatest, and is back toward the other end of the levee. We've pretty much eliminted the leak being near the center of the levee. The back side is dry there with no visible surface moisture.
I'm runnnig out of options, so now I'm considering Bentonite and/or Pondseal, and the pond liner. I thought about getting a track hoe that can reach down 12-15 feet to dig a core from the top of the levee in the area where the sand was found last time. We could trench down the levee and if we do hit sand, then we could dig it all out and replace with good clay soil and maybe even a mix of Bentonite and/or Pondseal clay to go with it. I think I figured that such a cut of around 75 feet, 3-4 feet wide, and 12-15 feet deep shouldn't need but about 500 yards of clay-dirt to fill and pack. But I think we could isolate it down to an area about 15-25 feet.
If the trouble is not in this suspect area that is about 50-75' long, then I don't know where else to look. The backside of the levee in this location was always wet and willows sprouted and grew here and no place else. I'd have to send pictures to explain, but suffice it to say that I can pretty well narrow it down to this 50-75 foot section, as did the soil scientist who bored the test holes on the levee, and the others that came out to examine and assess the levee.
The pond liner idea came up recently when I was searching for ways to fix a leaky pond. Believe me, I've tried all the routine things and this has been going on to one degree or another, since it was built in the 1990s. The pond liner is around $700, and that is the one listed as 15 x 100 and 45 mil thick. I thought that would be a big enough overlap, and since the lake is down about 8 feet now that I could add that to the front regardless. But if I do I'd have to forego the Bentonite and/or Pondseal on the front-water side of the levee or either mix it in and wet it and let it set and then add the pond liner on top later.
We've run out of the easy things do to, and really the hard things too. I probably added 5,000 yards of dirt to the levee in the 2008 construction and I can't tell that it improved one thing.
So...I'm branching out on the internet now to see if someone has an idea we've overlooked. In the next year or two I've got to either fix it or just learn to live with the level it drains to and stays at. We're convinced there is no sink hole in the lake bed because it drains to a certain point and stops. It's there now, and that's why I want to do something now while we can see everything and have the water low enough to get to work. The question is...but what work to do? The only thing I haven't tried is making a cut down the levee and packing it with top quality material, maybe even bentonite, or add Bentonite to the front side, and maybe add a a pond liner on top of that.
Any further suggestions will be appreciated.
