I've got a well established pond, about 7 acres, in Texas that was build before I bought the property. The pond leaks from the bottom, under the dam, and the transmitted water is evident about 25 yards behind the dam. I'm a Civil Engineer with lots of experience with reservoirs and earthwork; however, solving a leak is more of an art than a science I've found out! I've inspected the dam - solid. The pond still holds a lot of water - about 18' deep despite the severe drought. I'm suspicious of a lens of gravel or sandy material at the bottom of the pond that is is providing the transmissivity of the the water from the bottom, under the dam (I don't know about any key-way) where it becomes exposed down-gradient of the dam. When the water surface in the pond is down, like it is now, there is no noticeable flow under the dam (i.e. no found water behind the dam). When the water level in the lake is high, there is a good bit of standing water behind the dam. This is obviously related to the hydrostatic pressure on the transmitting material.

So.... I'm looking for a solution that doesn't require me to pump drain the pond, kill all my fish, etc. Question: Would adding a lot of sodium bentonite directly into the pond at the deepest point (likely leak location) be an effective solution? How well do those sodium bentonite slurry solutions help solve this? Or is adding sodium bentonite to an existing pond just a placebo?

Thanks for any advice, answers, or counsel. All the best,

No luck sealing my damn. Waisted money for me. Ended up having to drain and put in 18" clay liner.

Of all the people here on the forum that have had leaky ponds and have used bentonite in the way that you describe, I can't remember of one coming back saying that it was a permanent fix.

Wow... Thanks for the replies. Those are pretty damning (excuse the pun) comments on the use of sodium bentonite. I'll keep thinking then. A very, very, expensive solution would be to construct a slurry wall behind the dam below the transmitting material. Another way would be to drill a well nearby, install a solar or windmill pump, and hope the daily pumping into the lake matches the leak flow rate thereby keeping a constant water balance. Mmmm... I wish there was a simple pill I could toss off the dock to solve this... Thanks again.

If sodium bentonite was an economical solution, wouldn't everyone just dig a hole and then add the stuff?

The Porter County NRCS, in sandy soil with excavated ponds, recommends digging a trench completely around the pond, down to the groundwater level. Then they drop a sheet of visqueen in the trench, backfilling as they go. They bring the visqueen as close to ground level as they can. They said that slows the leaking of ponds.

I don't know if that would be a viable option for you or not. It doesn't 100% seal the pond, but it slows down the leakage.

I've tried bentonite on 3 different ponds with leaky, sandy bottoms with no positive result. I used a LOT of it, tilled it in, etc.

I do have a friend that had the oil co that he worked for bring the used mud(bentonite) from a well and dump copious amounts on the bottom of his leaky pond. That worked but I have no idea what it would have cost in that quantity.

I used bentonite in my pond and it fixed the leak. But I did drain the pond, tilled it in, and compacted the heck out of it. I have decent clay and used 1lb/sqft of bentonite.

The first time I carried a bag of bintonite my age was 18 my next birthday will be number 62. In 1988 we put lots of the mud on top of a drainage pipe that was under a lake. We knew where the line was and just dumped the stuff on top of it. That stopped the water loss. THAT IS THE ONLY TIME IT WORKED WITHOUT IT BEING INSTALLED PROPELY.
Every other method has been tried. At least once. No good results have ever come from the slurry. Twice customers have had access to a good supply of the slurry; they talked me into letting them try it. No good results
Otto

I have had slurry (aqua gel drilling mud mixed with water) work on a pond with a stray sand lens. Did what Mike described (dumped the slurry via pvc over the sand area)and it stopped the leak. I assume the slurry was pulled into the sand lens and mixed with the sand to form a clay/sand mix. It worked and stayed fixed for as long as we had the property (25 years).

My installation worked because I followed the directions from Mike. Thanks again Mike.