Pond Boss Forums POND CONSTRUCTION Soil questions extreme leak - solutions?

I need some advice as I'll be the first to admit I'm not a pond building expert. I looked at a 2-acre lake this weekend that won't hold water. Actually to be technically correct, it's just a dry hole in the ground with a small puddle in the deepest area. The owner wants to seal it, but didn't like the $35k price tag he got from the bentonite folks, particularly with no guarantee.

Upon examination of the site and pictures of the construction, I determined that the dam appears to have been constructed with a clay core and the leak is no likely going through the dam, but more likely under it. The lake was constructed on a small creekbed. It's quite deep, 15-25' over 75% of the area, but it leaks all the way down in a couple of weeks. It has filled and drained numerous times in the two years since it was dug.

The contractor dug through quite a bit of good clay which was used in the dam, but dug the lake down to bedrock in most places. Several trees were left in place on pedestals (for lack of a better term) to serve as cover. All of the timber was put back into the lake when construction was complete. So what is left is a big hole in the ground, with dead timber everywhere.

My assessment is this: The pond was dug too deep (obviously) and the clay that should have been used to line the basin was instead used to core an excessively large dam. The bedrock in the basin is probably fractured, and the water is leaking through some large cracks and surfacing about 250 yards downhill past the dam. Some leakage may be occurring elsewhere, but the rapidity of leak-down, combined with the fact that the lake goes almost dry, leads me to believe that the leak(s) are in the bottom of the basin.

So what to do? Bentonite or a liner appears to be too expensive for the landowner to stomach. Obviously whatever course he takes, the dead timber needs to be removed. The trees on pedestals look cool, but could they be contributing somehow to the leak? They'll probably have to go if the basin is sealed.

I've looked at the ESS-13 website, but I'm not convinced that it will work to seal cracked bedrock. It looks like additional clay has to be brought in regardless for this product to work. Has anyone used this product in a similar situation with success?

Perhaps the most straight-forward solution would be to truck in clay and line the bottom of the tank. A reduction in depth would not be an issue, because it is already plenty deep. A loss of 5' even would not be a problem. Would this work, and if so, how much of a clay blanket would be needed?

One last question. He indicated that a neighbor built a large lake and lined it with caliche when constructed. He compacted it and wetted it. I saw the lake, it's full and apparantly stays that way. Has anyone heard of this technique? The concept is that it sets up like concrete and forms a barrier that way. The reason he asked is that I believe he can obtain the same caliche for his lake. Might this work?

Sorry for the length of my post. This one's a doozy!

Fishman,

Not seeing the site, your client needs to do one of three things: 1)import enough clay to line the entire pond; 2) install a pond liner (best alternative) or 3)live with a dry hole because he doesn't want to spend the money. Unfortunately, most people don't understand there is no such thing as free advice or a free lunch.

GOOD LUCK!

In addition to this bad situation, how thick does the clay need to be on the bottom ?

I would recommend a clay blanket of at least 4 feet deep. This blanket MUST be compacted using a sheep's foot. This is crucial in the success of the clay blanket. And the clay must be compacted at a 90-95% ratio. Any thing less than that would not be substantial. However, I must include a disclaimer again in this post...I have not seen the pond site.

Thanks for the replies so far.

Trent, when you say a 90-95% ratio, I presume you mean compacting the clay to a density of 90-95% of what it was before it was dug up. Is this correct?

Any other thoughts about clay vs. other methods?

Fishman,

When I talk about a compaction ratio, I am referring to a percentage of the total density that particular soil can achieve. The ratio is not relative to any other prior condition of the soil.

Does that make sense? I tried to find the best terms to use that would make this difficult concept of soil properties easy to understand.

Sorry...I forgot to answer your other question...clay vs. other methods. Again, keeping in mind my disclaimer...the best and most long term method with the highest chance for success is the pond liner and a backfill of 3 feet of soil. Of course, this is the most expensive.

Without having seen the pond, it's difficult for me to recommend any other methods.

trees suck up alot of water, all of it (eventualy) is evaporated out through the leaves. I've heard that some trees can "drink" 40 gallons of water a day. I don't know how much water trees loose a day but is it enough to make a diffrence? Should you be careful about planting trees near your pond?

Not sure about trees but when my neighbor and I straitened our common property line beside my pond and moved it about 12 ft towards his property I found that about 15 large oak,hickory and maple that were on his side of the fence moved to my side of the fence and being within 25 ft of my pond they became firewood! I did notice that my water levels went from a 1 inch drop per day down to 3/8 to 1/2 inch per day so I assume that the trees were soaking alot of water out of my 1/3 acre pond.

Bob

I was wondering about caliche too. USDS biologist that surveyed our site remarked that caliche is actually quite porous and wouldn't seal. Info I've seen elsewhere indicates it might. I don't know, wish someone did?