Hi all, my one acre pond has finally filled. I have a 8” drain going thru the dam that has started to leak on the back side of the dam about 30 feet from the waters edge. The pipe is about 2 feet under water and has a mortar collar poured around it on the water slope. The top of the collar is in about a foot of water and the bottom in about 2 1/2 feet. I also built in a ball valve at the end of the pipe for draining purposes.

Unfortunately, a few weeks ago when the water was lower the pond iced then the snow melt pushed the ice up under the drain end and lifted the pipe assembly about 4 inches. The mortar collar essentially was raised up above the pond slope exposing a small gap under the pipe. Today, a week later, I notice a very soft spot where the water is seeping out on the back slope.

My best immediate guess of a plan is to get two or three hundred pounds of bentonite and try to seal around the mortar collar. I have access to “bentonite chips” and “bentonite powder” from a local Facebook vendor.

What do you think of the plan? Also, form of bentonite would be best?

Thanks in advance fo the help, Tony

No anti-seep collars?

No collars

I agree with Theo, you might have a "channel" along the pipe created by the pipe moving in the fill clay. A collar 10-15' into the dam would probably stop the water from working its way along the pipe.

If the gap of the channel is very small, then the swelling bentonite MAY work. If the gap is too large, then the bentonite may just wash out.

Is the pipe just a lateral with a slight slope? How far underground is your pipe? Those parameters will probably change the advice if you have to go with an "invasive" repair.

I'd go with the chips vs. powder.

Then this summer when the water is lower, fix the problem so it doesn't happen again this upcoming winter.

Welcome to the forum!

Pipe is a lateral with a slight slope. At the crown of the dam it is probably 3 1/2 to 4 ft deep.

I will try to apply bentonite chips this evening to see if I can stop the leak around the collar.

If the water is lower than the pipe in the summer would it be possible to dig down around the pipe at the crown of the dam and construct a sand filter for a permanent fix?

How would a sand filter fix it permanently?

Good, not too deep.

If the bentonite (fingers crossed) doesn't work, then you are probably going to have to do some excavating repairs next time your water level is down.

Where frost heaving is a problem, most people run a deeper lateral line and then use a stand pipe as a riser. The ice can't pull up very readily on the exterior of a smooth, vertical pipe.

One option is to dig back past your mortar collar and cut your pipe. Install a 22.5 or 45 ell, a straight section going downwards, another ell (same as previous), a straight section going horizontal, a 90 ell, and then your riser. The top of the riser will still set your pond level. (The advantage is that you could easily change the water level by just temporarily installing a pipe collar and small section of pipe above the existing top.) Bury the first ell back under your dam and rebuild your slope.

The solution above should help with your frost-heaving problem. However, it will be more prone to plugging! You will definitely need an effective trash rack designed to screen out your most typical debris.

Another option is to dig back into your dam a fair distance and install a nice anti-seep collar. Tamp well and re-pack your clay around your drain pipe from the collar all of the way back to the lake inlet before you bury.

Hopefully, someone has some more elegant solutions.

I address spillway leaks with clay/polymer layers compacted by hand and with the few projects completed they were successful. If you prefer using bentonite I suggest the same method, high plasticity clay layers and bentonite compacted to achieve a seal. Anti seep collars are always strongly recommended. If you want to reach out to discuss I’m happy to chat anytime.

I highly recommend the polymer product that TJ has. It works wonders. If the bentonite doesn't work, try that stuff.

Thanks for the continued responses.

First, I’m going to eliminate future ice lifting the pipe problems by adding a small bubbler from my aeration system to run in the winter under the pipe area to prevent ice.

Second, I pick up 300 lbs of bentonite chips tonight (similar to Aquablok) and will apply around the pipe in a 4 foot radius tomorrow afternoon. Will add more if needed.

Third, what is the polymer product that TJ uses? If the bentonite isn’t effective I would like to try that.

Soilfloc.

Also if you look for TJ posts using the search function, it is: teehjaeh57


Finally, the bubbler idea sounds good. Stops ice heaving around your outlet and adds a little oxygen. Win-win!

Owning a pond is a joy, but as this thread illustrates, it can also be one dam thing after another.

Reach out anytime, as a volunteer here my time is always free to the Pond Boss family. If you elect to go the polymer route I can source a PB forum discount, too.

tj@hudlandmgmt.com

Think I may have isolated the problem.

I spread 300 lbs of bentonite chips around mortar cap surrounding the drain pipe but the leak didn’t stop. Today I decided to open the drain valve and lower the water a bit to see the pipe and mortar better. I discovered that when the ice pressured the pipe, it actually opened a significant gap between the mortar cap and the PVC.

Draining the pond another half a foot and will seal the gap between the pipe and the mortar shield tomorrow. I’m pretty sure that is the source of the problem and am hoping this will solve the issue.

I am optimistic that you have now pinned down the problem.

Hopefully, you can create a leak-proof repair and then your pond will be fully ready to go for the spring rains!

Spread another 300 lbs of Bentonite chips mixed with dirt over and around the mortar repair yesterday. Should know in a few days if fixes worked - I think they will.

Wishing you luck

Well friends, the repairs worked. Seep has dried up as a result of fixing the cracked mortar collar with hydraulic cement and covering the face of the pipe penetration with 300 lbs of bentonite chips (coated gravel). I’ll be installing a small bubbler near the overflow so the ice won’t lift the pipe and re-open the leak in following winters.

A tip for using bentonite chips - mix 50-50 with dirt prior to spreading. The bentonite goes further and the dirt gives the swelled up bentonite “snot” more body.

Thanks for all the help!

Tony

I am glad that your repair worked!

Thanks for posting the update and the good advice on proper "snot" repair procedures.

Great thread!