I've done quite a bit of research on ways to seal in general, and also a lot of on-site examination. Also had a good contractor meet to look over the situation.
I calculated that the pump I use pours in around 85,000 gallons of water a day. They water level rise varies as it fills, but 2-4 inches a day is a fair guess. With the pump off, the water level drops about half that fast in the beginning. So, that's conservatively 30,000 - 40,000 of water a day the lake loses. We've mowed the levee again and there is no sign of water seepage anywhere behind the levee or in the drainage ditch. I plated the front of the dam with 2-4 feet of good clay soil in 2008. In 2009 and 2010, I can't tell it has slowed the leak at all. Therefore, for now we've eliminated the levee itself as a likely spot for the leak.
I've walked a lot of shoreline back and forth and we've used a post hole digger and a metal probe. What surprised us, and especially me (since I've known that land pretty well for years), is that the far side of the shore, opposite the levee, it as solid as can be expected from the main point and running on the northeast side of the southern cove all the way to the back. We did a lot of probing and it hits solid ground a few inches down. We never did hit a pure sand pocket.
However, on the southeast shoreline of the north cove, we could push the probe out of site. It appears that a vein or layer or strata of sand runs through that hill and on into the hollow where the water backs up. We could pull back from the shore and go up hill a bit and dig with a post hole digger and within seconds it would start filling with water once we were deep enough to be at the elevation of the current lake level. There was a band at least 15 feet wide and 200 or more feet long where we hit this kind of sand.
The contractor thinks we need to get a big track hoe and start digging on the north east edge of the cover which runs to the levee. We probed that shore for 200 or more feet also and usually hit solid clay within 6-12 inches. Rarely did we push the probe easily its full length like we did on the other side.
The water may be seeping into the sandy hill and re-routing under the lake or into a sand strata that gets into the hill adjoining the levee and then stay underground from then on. He feels that a good core ditch there will stop it. And it may. But I think we need to run a core ditch, or maybe even better, plate the sandy hillside with 1-2 feet of good clay soil. The more we investigate, the more I'm convinved we need to treat both shorelines of that cove in order to 1) stop water from seeping into the sandy hillside and re-routing itself underground by plating it solid with good clay soil 2) stop any seepage into the other (opposite) hillside that runs into the levee with a core ditch and more clay plating.
This particularly sandy hillside is hard to walk to, and it's fairly steep, and it's also on the far side that can't be mowed, so none of us ever suspected it, nor saw any evidence of, this amount of sand. All other areas had been tested fairly well and eliminated as the source of the leak.
I think this is going to be far beyond reinforcing the levee anymore. Now we're looking at plating up to 400 feet long and maybe 20 feet wide on both shores.
This is the latest on the saga of the leaky lake. We're hoping to investigate more for now to see how much we need to treat, but also have plans to start work around October 1 once I drop the water about 3 more feet with my drain pipe and give it some time to dry.
Still hoping for more ideas, if any of you would like to comment.
