Restoring an unused bentonite liner

[steve/gridnot]

I found out the hard way on my first pond 35 years ago. It was 45'X 60' and 8' deep. I did it with bentonite about a foot thick. Locust trees punched holes in it the second year and before that it was a muddy mess. I put a garage in at that location and started making smaller ponds that I could manage. The bird seed idea I mentioned in my last communication, was from a helpful pond friend that didn't work. I've tried about every bottom and have had best success with liners.

As of late I was looking at a 150'X300' 12'deep one that a friend has.
It sits on the top of a hill and has a 14.5 mil pod skin liner. It's held water for a year and now he has the Koi fish bug. He put in a good bentinite base or it would be leaking from the weight. Its going to be expensive to make the water clear so he can see the fish. More fun for me on the never ending hobby.

I just wanted you to know that you have a good start going and there are a lot of ways to finish it.

 

[Catfishnut]

Gilbert,

The Bentonite will not "go away" so whatever was laid down initially is still there and still viable. However, the plant roots, even those of weeds and grasses will comprimise the seal of the bentonite. Since it does not retain water now, even from a heavy rain, that is conclusive that there is no seal.

The recommended application rate is 1-1.5 pounds per square foot for clay soils, 2-2.5 for sandy silt, 2.5 - 3.0 for silty sand, 3.5 - 4 for clean sand and 4 - 5 pounds per square foot for gravel bottomed ponds.

If the original pond bottom was a perfect, flat, circle 20 feet in diameter you would have an area of pi*r2 or near to 315 square feet. Obviously, a pond wouldn't have a simple flat bottom. It would have some depth making the shape more of a semi-sphere and the surface area a trig function of a sphere. A simple semi-sphere would have a surface area of 2*pi*r2 so the area should have been nearer to 630 square feet.

That area would have demanded 945 pounds of bentonite for a clay soil substrate and up to 3,150 pounds for a gravel substrate. If 5,000 pounds were applied, then either they were giving the bentonite a much greater safety margin or the pond is actually larger than you estimate. It would be better in this case if they overestimated the application rate or just "laid it on heavy".

If there are only simple weeds and grasses growing in the bed of the pond, then you should be able to refurbish the original bentonite liner. You need to apply a weed and brush killer to the entire area to kill the vegatation and then wait for it to dry thoroughly. The dead vegetation should be removed. Burn it, mow it, rake it, scythe it, whatever it takes. If there are any large diameter "woody" roots from large weeds or small trees, they will have to be pulled or dug out. These roots absolutely MUST be removed.

Once the area is clear of all vegetation, you will need to "till" the bentonite and the soil together. This may be problematic depending upon how much debris and silt has accumulated over these 20 years. You need to access the actual bentonite layer so that you can "stir" / "mix" and churn it like tilling your garden soil. This is going to be a lot of work. A LOT of work! You must do this so that the integrity of the bentonite layer is not comprimised. It needs to be consistently blended together with the existing soil, as if you were making concrete for a patio or a foundation footing.

Bentonite, sodium bentonite to be specific, will expand to 18 times its dry volume when wetted. Once wetted, it will retain that dimension and will basicallly form a "gasket" in the soil.

If you research sodium bentonite and lining ponds with the material on Google you will find lots of helpful information.

Gordy

 

[steve/gridnot]

One more reason I advocate the addition of some sort of a an over cover. You might find yourself stuck in the bentonite if you or any one wades into the pond.