I have searched this site pretty hard and cannot find a problem quite like mine. So here I go. I bought this property with the pond already on it from what I understand it is about 30 years old and has never held water to the top. It is about 3/4 acre and ranges from 5 to 11 ft deep depending on the amount of rain we have and what time of the year. So this year I decided to get a local excavator in and do some digging to see what we find. We went on the top of the damn and dug down on the back side. I’d say we got to about 10 ft down from the top of the damn and ran into some grey looking material which he called organic material and we soon started to see some seepage coming out and we are pretty sure it’s like this along the whole damn. The top material is pretty good clay but I’m thinking whomever built it just damned up a hill side. On top on top soil? But not sure my one neighbor swore he cored it in. The damn is about 80 yards long and I’d say about 35 yards of it always seemed moist and had some of those water plants on it. We then decided to cut the damn and drain it and come back in a few months and rebuild the damn correctly. Since he left I have been slowly shoveling out a small trench to get the pond completely drained. As I got further out in the muck I noticed I started hitting rock/sandstone only about 8 inches deep. So I feel like this maybe a problem? I still think the water was leaking thru the damn but could some of this also be seeping thru the sand stone? Here are few of my questions I cannot afford a liner for the whole pond. Has any one ever tried just putting one on the bottom and toeing it into the damn. Should I not even worry about this same stone?
Few little facts. Located in central Missouri. When pond is pretty full a garden hose can keep up with the leak. Never have seen running water just a big area always moist.
Thanks again any advice will be greatly appreciated. Tried adding pictures but it won’t let me
Curious....could you excavate the sandstone at the bottom and find good clay from somewhere else on the property with "good clay"
I think they call this a borrow pit....what you pull out of the pit goes in the pond / dam and what comes out of the pond....straight to the borrow pit.
I don't have any experience with liners. Will leave that to one of the more experienced guys.
Good time to do it right while the pond is empty for sure.
Yes, loose rock or a layer of sandstone are BOTH bad news!
One possibility is that they planned a core trench, but then hit a layer of rock and just did "the best they could" over the rock layer.
Another possibility, is that they encountered a lot of large chunks of rock and did not clear them from the pond bottom and dam area. You cannot compact material containing large rocks. When the rocks have enough point-to-point contacts, they begin to form a load-bearing framework. At that point, the clay material between the rocks can no longer be compacted any further.
Finally, as you suggested, the sandstone itself could be permeable (capable of allowing fluid flows). If there is not a well-compacted clay blanket over a ledge of permeable rock, then that can provide a pathway for a leak. Some sandstones and limestones in Missouri are impermeable rock that would hold water. However, if such a rock layer is jointed or fractured, it will still allow water to pass.
That is the bad news. The good news is that if your pond is only leaking a little, then your probably have some good clay material available for your use.
Generally, a foot of good clay-bearing material that was properly compacted in 6" lifts with the correct moisture content, will seal over any leaky rock layers for a pond up to 10' deep. (If you are going to build deeper, then you made need to thicken your clay blanket on the bottom in the deepest spots.)
My advice would be to keep working to get your pond drained and dry enough for you to walk around. I would then build a poor-boy probe with some re-bar. (You will need to weld a tee or a loop, to tap or pull out your probe when it gets stuck.) Then walk around your pond basin with your probe and a little 3 or 4# sledge hammer and try to find your rock.
If you see any exposed rock, that is a problem. If you hit rock 3-6" down, that is also a problem. If you find areas more than 12" to rock, good.
If you find areas several feet to rock, then maybe take some samples with your shovel. If it is at least 25% clay with no rock, perhaps you can deepen the pond in that spot and steal some of that material to fix your problem spots.
Does your pond only leak down to a certain level when full, and then quit leaking at that point?
If so, then still several possibilities.
- Could have a leak out of the side of the pond somewhere but high up in the bank.
- Could have a nearly impermeable leak in the bottom of the pond - that only allows water to pass when the pond is full and the "extra" hydrostatic pressure can push through some water. When the water level subsides enough to lower the hydrostatic pressure the leak ceases or is significantly reduced.
- Could be they just did a poor job on some aspect of the core trench. That could be poor compaction. However, perhaps they just ran out of clay-rich material and did not build the core trench up high enough and just added some crappy material with a high organic content to get the dam high enough.
(I think the third possibility is the most likely, based on your observation of moist ground on the back side of the dam.)
All of my writing above is some wild speculation. Keep probing and digging at your pond. If you can clearly define the problem, there are some people on Pond Boss that can offer some pretty good solutions.
Thanks alot for reply. I also added some pictures let me know if you think of anything else. I will definitely make a probe and try that out. Just not sure how much its goin to cost to bring in that much clay. I might have to also wait a year and let it dry out. I wish the guy who is doing the work would get back with me but he is just so busy its hard to get in touch with him.
The only rock I see in your dam trench is near the pond side water level. If that is correct, that is fine. MANY ponds have rock placed on the dam facing the pond after the dam is constructed.
I do not see any significant rock issues in your dam core. (Unless you are seeing rock in person?)
Even your core fill looks fine to me.
Most organic material in the soil or in the muck at the bottom of a pond is black. (Usually because it is isolated from oxygen and aerobic bacteria.) However, not all black material is organic muck!
I have black subsoil material on my farm. It is almost 100% clay. It packs very well, and has such a low organic content that it will not degrade over time.
Can you grab some of that black material in Pic #3? Wet it a little and try to make a small snowball. If you can pack it, that is good clay. Generally, if you grab black "muck" organic material from the bottom of an old pond it will not pack.
Can you go to a safe part of your trench and deftly make some cuts with a shovel into the side walls? (Trench safety first!) If you see large rough layers, that is constructed by the pond builder. For example, if they built up the core in 6" lifts, you might see that a little as they pushed in some slightly different colored material each time.
However, when you start to see very fine layering in your shovel cuts, that means you are into naturally deposited material. You are then below the core trench excavation and back fill.
More wild speculation from a guy not on the site:
I do not see a "rock problem" as I described in my previous long comment. (It might be there, and I am not seeing it in the pictures. You are the eyeballs on the ground.) It does sound like you do have some minor leakage through the dam. That may be due to an imperfectly constructed core trench. It may even be due to a properly constructed core trench! Even expert pond builders do not give leak guarantees. The soil materials they work with are too variable, such that pro builders sometimes have to go back in and find and repair leaks.
(Was your neighbor the pond builder? If he says he put in a core trench, that still sounds likely true at this point. However, if your site is "clay poor", then perhaps there was a little bit of forced skimping on either the height or the width of the core trench?)
Dam leaks are notoriously difficult to find. I believe they are usually found by very delicate excavating on the back side of the dam while the pond is full. (I am a geologist, NOT a dam construction expert.)
Perhaps search the archives and read some of the "dam leaking" threads. Some of those contain excellent histories about finding a leak and then repairing the leak.
Ive done some dam works that didn't work...and now some dam work that is pretty darn good. Your's doesn't look too bad and the amount of work you might have to do it "fix" a lek that can be topped up with a hose might be false economy - ie. cheaper to keep topped up with a garden hose.
From my new experience, clay gravel (which it looks like you have) is pretty darn good and can seal up very well. In my limited experience opinion I'd just top it up and enjoy it unless you have deep pockets..... If I were to try to "fix " it I'd excavate a trench just in front of the water side of the dam and clay face it with an excavator then entire length - but again lots of money and youll still lose water through evaporation.
Oh, and from the way your material is drying out there is a good clay content in it.
Just my 2 cents after about 50K in work over the last few years.
I will definitely try some of the stuff you mentioned. And no the neighbor was not the builder was just around when it was built.
And the pictures don't show the sand stone i am talking about. its out more in the real loose material that you sink to your shins/knee in. nasty smelly stuff right at waters edge in the pictures. If i dig out in that that's when i hit a bunch of that rock about 8 inches deep or so.
And the grey dirt does pack well seems to have a lot of clay structure to it. But i am also finding small roots (looks like corn hair) very small and also some tree bark. When we dug the hole on the back side of the damn and after about 30 seconds we could see water start trickling out and running down the wall. so im pretty confident its leaking thru that layer of grey dirt. But could it we taking that sand stone and then dispersing through that ? I dont know i just hate to put this much money in it and have the same problem. I also really would hate to fill it in because we use it so much. Im just alittle nervous to rebuild the whole damn and its all stemming from that rock.
Also when i say it leaks a garden hose a day thats at about 1/2 to 3/4 full. once it gets full it goes down pretty quick i assume because of the pressure.
Sorry should of explained better. The garden hose to keep it full only works when its about 1/2 to 3/4 full. When its completely full i cant keep up with it. And i also cant afford to run my well 24/7 i did it one month and jumps my electric bill up 200 dollars. And the well cant keep up when we are doing laundry/dishes or showers because i have to run two hoses to it other wise my well pump will just keep cycling on and off.
No i dont have deep pockets its just something we have been struggling with that last 12 years and we dont ever plan on moving so my wife and I decided to give it a try. but i want to give it my best try and not skimp on anything. Just trying to due some research before i pay him all this money and we have the same problem.
Based on your description, it does sound like there is organic material in the dark clay.
Organic material in the core trench is a big no-no.
Perhaps there was a small pond there 30 years ago, they scraped the clay and organic debris out of that pond basin for the material in the dam core they built back then. (Reason doesn't matter.)
If there was a 1" diameter branch in the core trench material, and that has now decayed to create a water pathway, then that alone could create a leak that your garden hose cannot keep up with at full pool. Further, there could also be additional tiny leaks where small root networks were in the compacted fill, but have now decayed and created a perfect leak path ... shaped just like a tree root system.
You might need another core trench either to the pond side or the back side of the centerline of your dam. I don't know which side is optimal since you are moving beyond my expertise.
Perhaps you could get by just trenching and repairing the 35 yards that is consistently moist?
A core trench is also sometimes called a "keyway". That is because it locks the dam into place to resist the pressure of the water in a full pond trying to push the dam downslope.
IMO, your dam is probably "structurally sound" for that purpose. You just need to improve the "seal" in your dam. If you do try to repair only a portion of the dam, then any secondary clay trench must be tied to the existing clay in the core. Otherwise, the water will hit your barrier through the pre-existing leaks, and then move sideways until it can find a new path around your repairs.
P.S. There is also a member that is a leak expert (teehjaeh57). He sells a commercial product that can seal leaky ponds in some situations.
He also does free advice/consulting on pond leaks for members. You might contact him for more advice. I don't think his product would seal a 1" pipe (like my decayed tree branch speculation). However, his product would probably work on multiple tiny leaks (like my tree hair roots speculation).
Sorry late to the party - yes I continue to provide consulting for any pond building, rehab, or leak abatement projects and my time has always been and will always be free to our Pond Boss family. Happy to help however I can.
Dam and main basin hydrostatic leaks respond well to polymer treatments, but I'd need to learn a lot more before I'd recommend spending a penny. Often times we can address leak issues without any money spent...just takes time to compile data, analyze, and huddle for a strategy.
Feel free to reach out anytime!
TJ
tj@hudlandmgmt.com 402.730.4897
Many men go fishing all of their lives without knowing that it is not fish they are after. ~ Henry David Thoreau
In your pictures it shows your pond drained down pro over 2/3rd of the way, my first mode of action would be to keep a log of your water level at that point, if the water keeps going down, or leaking out, even at that level it is a huge chance that your core trench and or the sand stone layer is compromised, which will be a much bigger problem to address, along with, you guessed it, much bigger expense.
If the water level, where it's at right now seems to be holding reasonably steady, that would be good news, from there on up should be a lot more economical to rectify.
I have sealed off several small bodies of water that were leaking in the top half of a dam, and even down to a rock layer, by digging a cross trench, much like have pictured, and recompacting it back in with a quality clay, mixed with a generous amount of bentonite. But you may be able to seal it off with the product that Teehjaeh has without having to do the excavation, that would be wonderful as we all know, excavating costs these days are astronomical.
Good Luck!
All the really good ideas I've ever had came to me while I was milking a cow.
Sorry about your leaking pond, I share your difficulties though not nearly as bad as it used to be. The polymer treatments slowed it considerably to an acceptable rate.
Some thinking outside the box is if your dam has some good clay in it, use the top foot or two to create a seal on the bottom. Perhaps the original builder got a bit too ambitious and dug too deep. The pond may not wind up quite so deep in the end, but maybe more consistent to a reasonable level and the lowered dam will be achievable for a fill.
The rock on the bottom across such a large area is very likely to have cracks in which water can escape. Imagine a bunch of tightly packed large bricks with no mortar. Water will go where it can.
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