First off I'm in central TN. I had a run off pond dug 20+ years ago. The pond is about 200 ft across and in kind of a small valley with a dam at the deep part. At the time the guy who dug it said it might not hold water and he was partially right. It fills during the winter, stays full and drains in the spring. It used to pick a day and drain like someone pulled the plug on a bathtub, then stay dry all summer. There isn't much dirt at the shallow end and there are two large rocks showing. Average soil depth here is 3ft. Since I retired I have taken on the pond as a challenge. I first thought the dam was leaking so I added 60 yards of soil in the bottom at the base of the dam over two years. Now the pond fills partially during the year but always leaks slowly down. It usually fills to the exposed rocks in the shallow end which I took as a sign there wasn't enough/any dirt over the rocks. One possibility. The other thing I noticed was that on the back side of the dam sumac is growing, not the poison variety, but only halfway down from one end and top to bottom. Another sign? Back side of the dam isn't soggy.

I'm looking for suggestions as to the possible causes of the leaking

Did he cut a core trench? What is your soil like, is there very much clay?

If the soil is shallow, it may not provide enough of a deal to bedrock below that may be fractured. There are a few options to addressing leaks like lining the basin with clay, rubber liner, or hitting everything with SoilFloc. Rubber liners are pricey as heck, but simply don't leak. Clay requires having a good source available that is either on-site or nearby, and is applied with heavy equipment. SoilFloc is a polymer-based sealant, and may work in your circumstance, though I would recommend reaching out to TJ on this forum to have a chat to see what your options are.

Here to help anytime feel free to reach out anytime. Tj@hudlandmgmt.com

No they did not. I had forgotten about that. I had the pond dug about 20 years ago and new nothing about how it should be done. Asked around for a reputable person to do it. Needless to say I didn't get one but it took me years to figure that out. Its been a challenge ever since. Just low on the priority list.

I'll send you an email with pictures

I have read that you need about 8% clay. I know our soil is not loamy at all in the summer without rain it turns as hard as a rock and it is a clay color. Non scientific observation.

Try adding a bit of water to a handful, Try to roll it into a pencil and see if it stays together. If it breaks apart, add a bit more water and keep trying. If you can roll it into a pencil then it should have enough clay to compact and seal given the correct water content.

I will definitely try that. What a simple test. I love that kind of thing. Thanks again.

Jim

I want to say thanks to TJ. I talked to him tonight and he was soooooo helpful. Answered all my questions and some I didn't even know I had. I think he has set me on the path to solving my pond problems, even provided a suggestion on possible contractors. Turns out the sumac growing on the dam was indicative of the dam leaking. When I explained how the pond was built TJ explained that the guy who built the dam didn't compact it correctly among a bunch of other things. I should have done my homework better. I will keep the community up to date on the progress including pictures. May take a while but if the cost is reasonable I'm fixing it.