Pond Boss Forums Thread Like Summary - I think I have a leak around the overflow pipe

Wasn’t sure exactly where to post this. Hopefully this is the correct place. This is the first time in years my pond is full. I’ve noticed it really seems to drop quickly when completely full. It’s down about 4” now, which would have been fantastic a few months ago, because it was almost 2 feet down. I was back at the base of the dam looking for any evidence of a leak. There was a trickle of water in the old ravine we dammed up to build the pond. It didn’t appear to be coming out at the base of the dam. When walking around back there, which is very brushy with briars and poison ivy, I stepped near where the drain pipe comes out at the base of the dam. My foot sank in to deep mud, with water coming to the surface. It almost has to be from water seeping along the pipe.
The guys that built the dam put in the pipe. I was there 10 years ago when they put it in. They put collars on it to block seepage. I’m not sure they’re in the right places, and I’m fairly certain they didn’t get the clay packed in tight enough around the pipe and collars.
I’ve dug it out around the head of the pipe and packed in kitty litter, and soil floc. I thought it was fixed, or at least slowed down. Now I’m not so sure. Maybe from being so low for so long, the leaking area has opened back up.
I’m thinking of getting a hold of some heavy plastic and trying to fit it around the pipe at the inflow. Cinch it very tightly around the pipe. Then spread the plastic out maybe 8 feet down into the water and along the water line. Then dumping clay on top of the plastic.
Any thoughts on this being a viable solution? Any better ideas?
Just an FYI, I was told by a member here (Rex Rainman) many years ago, that this was probably my situation. His recommendation was to completely remove the drain pipe, and put in a siphoning system. I elected not to go that direction. The soil above the pipe at the top of the dam, definitely settled where the pipe goes through. That indicated to Rex that the pipe wasn’t packed in properly, and why he suspected a leak.

You don't need an entire unit of SeekLeak - waste of money for a project that small, I'd just alternate compacted hydrated clay and bentonite layer after layer and you'll be fine. Might be a good project in July/August when water level drops. The bad thing about a spillway leak is they will, due to physics and the fact water is a universal solvent, get worse annually. The good thing is they only leak when the pond is full...if one considers that a good thing. Way better than a dam or hydrostatic basin leak, anyhow. We already improved that leak for you, thankfully. At the end of the day, I wouldn't lose much sleep over it - but address when it's convenient. 50# bag of sodium bentonite powder will likely be enough - $13.

Right at the face of the dam where the pipe enters the dirt is gonna be pretty hard to seal off, if it was me I would try to go about ten twelve ft behind that and dig down around the pipe, try to get above but close to one of the seep collars, and compact really good clay along with generous amounts of bentonite and use a plate compactor to pack it really good all the way up past the water level at a minimum.
I have sealed several minor leaks off that way.
At that depth it is more likely to stay moist whereas at the surface it will dry and crack much worse.

Good Luck!

I was going to type a comment similar to gehajake's. I believe he has proposed probably the best solution.

However, I think you need to be certain you have correctly identified the problem. I like that your pond goes down 4" very quickly when full and then the water level drop more slowly. Can you confirm that behavior?

Put an easily-read measuring stick in the pond and note the daily water drop after the pond is full. If the pond drops the first 4" very quickly and then slows under nearly identical evaporation conditions, then I suspect you have a pipe seepage leak very high in the face of the dam. That is absolutely the best place to have it!

As to your top seal solutions: Clay actually expands in contact with water, as does bentonite (a specific type of clay). Unfortunately, these clays then shrink (and crack) when they are desiccated during exposure to air. Soil floc (and its near cousins) are types of cross-linked polymers that also swell when exposed to water. However, I do NOT know if they subsequently shrink after long-term exposure to air. (You might need to send a PM to TJ?) If his product also shrinks, then I don't think you can create a "top seal" at your drain pipe with those types of materials since they will all crack after multiple wet/dry cycles.

Concrete does not have that property, but I still think it would be a poor material to create a top seal - without some additional labor. Dry cement mixture does expand as it is hydrating with water, but it then begins contracting slightly as it cures. Therefore, your sealed concrete around the pipe may still let a tiny bit of water through after it cures. However, the good thing about concrete is that it is erosion proof in your application. Once compacted clay and soil materials develop a tiny water flow path, it tends to get bigger over time as a few particles lining the path eventually get dislodged and washed away. Concrete does NOT suffer from that particular problem.

I might try a cheap fix first? Dig out the dam face with shovels as deeply as you can along the pipe. Then use wood (or well-compacted) clay to create your concrete form. I would then rough up the pipe and spread the heavy black mastic they use to seal concrete water pipe (bell and lip). If you can't find that, use the black roofing mastic with embedded fibers. Spread your sealer to ensure 360 degree coverage plus coverage for all of the concrete thickness around the length of the pipe plus an extra inch that will stick out into the air. Then pour your concrete "collar" at the top of the drain pipe. After the concrete has cured, use a putty knife to push the exposed mastic down into the pipe/concrete circumferential joint.

(If you do have some membrane type material similar to a pond liner, you could even line the bottom of your "form" with a sheet fitted tight to the pipe like a traditional anti-seep collar.)

If that concrete "top seal" doesn't work, then I would go to gehajake's solution and expose a much longer section of the outlet pipe with a mini-excavator and try creating a good seal across a larger length of the troubled area.

I don’t think concrete will cure all the way to the center if you just dump it into the ground and hope there is enough water to penetrate the whole thing before the shell cures. Just eat your Wheaties, get a friend, and mix up one bag at a time and keep dumping the mix in. Standard concrete takes quite some time to cure, longer than it will take you to mix several bags up.

Of note, you cannot go too think, as the heat of curing can cause the concrete to crack. I don’t know what that limit would be.

I am starting to think that plastic pipe for a drain is problematic from a thermal expansion point of view. If the soils are warn surrounding the pipe in the dam center, but cold water flows through, the pipe may shrink enough to allow water to make its way along the outer edge despite a good installation. Sure the collars should stop it, but only if the soils around the collar are well packed, which seems difficult to do below the pipe. Maybe it would be ideal to box in the collars with concrete when installing? Even if it is just the lower half to seal the collars that are difficult to pack.

Also, concrete may stick to the plastic at first, but a shrinking cold pipe may still pull away.

My experience with Quikcrete was not a positive one. That stuff cures way too fast and runs hot. I used it to set in block windows for my basement, and I didn’t move fast enough for that crap to harden before the windows were in. Next thing I knew I was the sad owner of a new hammer drill,

Use plain old concrete mix, it will give you time to work it.

I'd place a 5 gal bucket in the pond in very shallow water. Fill it to the brim, and monitor rainfall vs. evaporation rate in the bucket vs. rainfall + runoff -evaporation and possible leakage in the pond.

Spillway leak due to poorly compacted clay around pipe and perhaps no antiseep collars installed. Clay must be HAND TAMPED around pipe and as collars.

Fixing is simple in my experience: Either drain pond 2-3' or wait for Summer drop and excavate as much material as possible from pipe on pond side. Compact layer of clay followed by layer of SeekLeak polymer or Sodium Bentonite, and keep adding these compacted layers until original excavated material has been replaced. Resolved hundreds of spillway leaks this way - process take a couple hours.

I have limited concrete work experience, but I have observed some terribly weak and flaky concrete where guys tried the "dry bag" wall and in other circumstances.

I have done dry Quikcrete mix for 4x4 fenceposts and had zero problems. However, I expect the cured concrete still had cracks in it deep underground. In that application, the cracks are no harm, because you still couldn't pull the fencepost free (unless the cracks created a perfect upwards bevel).

I have mixed small batches of concrete in a shallow mixing tub with a concrete hoe. (The tubs are cheap at your big box store.) I have also rented the rotary mixers for slightly larger jobs. ($50 for the weekend?) You either need 120VAC at the site, or your own generator.

As to monitoring the water level, I couldn't remember if you lived at your pond or not.

Do you have a game camera with a time lapse feature? If so, set it up to take photos every 8 hours from a location where you can read the water staff in your pond. That should get you good data over a month where hopefully, your pond fills and then goes down a few times.

Lol, some shrinkage is normal!

Speaking of, good clay shrinkage is what Im referring to, when it dries out it will shrink and you will have cracks, hopefully it has filled the pond up long enough, and kept adding a little to be able to get that clay swelled up to its full potential.

That crap gets tight as a drum when its dampened just right. Our old Missouri clay gets as tight as any of it around I suppose. its crazy the amount of ponds and lagoons I have messed with over the years, when you have a 40 yr old body of water and you get under the silt and scrape a few inches of clay off you are on solid, seems like almost dry, clay that you can barely tell its been under water for a week. you can literally drive a loaded dump truck across it.