Pond Boss Forums POND CONSTRUCTION Building a dam Anti-seep collar: 100% Bentonite vs. PVC Collar

I have a pond and didn't pay close enough attention to the anti-seepage collar around inlet pipe. Now I'm draining pond due to seepage along pipe exiting from the pond.

So, I'd like to get it right the second time around and would appreciate your expertise.

Bentonite Option 1:
Since I already have 50 bags of sodium bentonite, I'd like to use it if possible to create an anti-seep collar. My inlet pipe is 8" PVC and I would like to know if a 4'x4'x18" form around center line of existing pipe and then filled with 100% sodium bentonite (no soil mix) will create a proper anti-seep collar. Finally, I would compact around the collar with jumping jack compactor. The full pond water level is 24" above pipe. I would leave the wood form in place to rot so as not to disturb the compaction.

As a test, I got a 16 oz plastic cup, punched holes it the bottom, added 1" of chipped stone, then 1 cup of bentonite and filled to the brim with water. So far not a drip has come out the bottom of the cup.

PVC Collar Option 2:
Or is it better to buy a 4'x4'x 1/4" HDPE manufactured collar. ScheibDrainage makes one that bolts around existing pipe.

PVC + Bentonite Collar Option 3:
Or should I use the PVC collar PLUS the bentonite form against the PVC collar on the pond side?

Thank you!

If it were mine, I would use the PVC + Bentonite - Option 3. since you have ample bentonite, a second bentonite collar further down the pipe would act as insurance.

Thank you for your reply.

I know option 1 (bentonite) is more expensive than option 2 (pvc) and combining the two is more effective than either one alone.

But if you had to choose only one option, are they about the same in effectiveness and longevity or is one option clearly better than the other? Why?

Concrete poured around the pipe would make a suitable collar. The hardest part would be the digging of the void around the pipe in which to pour the concrete............ Given the history of your situation, I'd be afraid that a collar made solely of bentonite may eventually fail.

If it were me.... and I was already having to dig it back up...... AND I KNEW option 3 was the best........ there is no way in hail I would do it any other way!

Just a FYI, I have two PVC seep collars on my 12" pipe. They were installed on the pipe correctly, but not packed in clay, and compacted correctly. There is a leak running along side the pipe when the water level exceeds the spot where the pipe comes out of the dam. The pipe is angled upwards fairly substantially. I think the water runs down the original trench dug to place the pipe.
I'm going to try the polymer approach to stop the seep. I'm hoping to avoid the draining and rebuilding..
I'd go with option #3 if I had a chance to do it all over again.
Or go with a siphon system.
Jeff

See this informative link:

my $.02

I'm a belt and suspenders type of guy when it comes to ponds. If I'm going to the expense and hassle of re-digging the overflow pipe, I would use multiple methods. Sure it will be more expensive than only one method. But what would it cost to dig it up again?

Also, remember that it's not only the anti-seep collar, it's how the dirt is placed back around the overflow pipe as SetterGuy has found out.....

Brettski, thank you for the great article.

Okay, so here is my plan:

1. Already drained pond
2. Dig 2' on all sides of 8" pipe. I will use judgement under the pipe and if I hit solid ground or clay, I won't dig past that point.
3. Then I will build concrete form of about 4'x4'x1' and fill with concrete.
4. After 7 days cure time, I will remove forms and I will also add a PVC collar 4'x4'x1/4" about 1' away from concrete collar.
5. I will apply mastic (foundation coating) all around the PVC and concrete collars.
6. Then I will begin compacting (6" at a time) around both collars with rented "jumping jack" compactor.
7. I will manually compact the 1' void between the collars but only to about 6" depth.
8. As I compact around the collars, I will add pure bentonite to the 1' void between the PVC collar and concrete collar.

Your critiques are most welcomed since I don't start the digging for 5 days.

If space and equipment permits, I would add soil floc or bentonite to the material that was removed from the area around the pipe, incorporate it all together, and compact as you stated as the material is replaced around the pipe.

vs. just replacing and repacking the material around the pipe after the anti-seep collars were added.

Belt and suspenders, remember?

You may need to add some moisture to the material as you repack it and refill the hole. Proper moisture in the soil is important for good compaction.

I would NOT suggest adding pure bentonite! There are a few grades of bentonite also...some swell little, while other swell a LOT. You'll need a swelling bentonite, BUT, what swell with moisture, also shrinks, and that creates cracks and voids! If you go through a dry spell, and the bentonite has dried, shrunk, and levy behind voids, and then you get a large rain event that causes water to flow through voids, you could have a bigger problem, even a sudden breech.

It's best to mix the bentonite into moisture holding soils/substrates at proper percentages.

Consider contacting Mike Otto at Otto's Dirt Service and ask Mike's advice on how to best compact around drain pipes...also consider buying his book, "Just Add Water".

Great advice, thank you everyone.