Pond Boss Forums POND CONSTRUCTION Soil questions New Pond w/Bentonite - Not Holding

Had a new pond constructed in the Texas Hill country about 2 weeks ago. Filled up about 1 week ago to "target" level and then turn pump off (on Saturday, 9/20). Went out today and the pond level is signficantly down. I measured down about 14feet from the edge of the "target" level to the new water level (not this is not straight feet dropage...just measured from last water mark to now). The pond circumference is about 395 feet. Average water depth is about 5 feet...max depth is about 11 feet. Best I can tell the bentonite was placed in the botton and up the walls (just not sure how much was put up the walls)

The constructor used 45,000/lbs of bentonite. I thought the process was pretty sound...he tilled the bentonite into the clay, compacted the soil and then we filled. It filled well to the "target" level but has now dropped significanty. Based on the dimensions is this enough bentonite?

The soil area where water was filled to has large cracks...does this mean anything?

Hi Mr James, and welcome to the forum.

Since we can't even begin to estimate volume without more info, Bentonite absorbs a large amount of water to swell!

How was your pond "compacted"? Was the bentonite moistened and equipment like a sheepsfoot roller used? Was the bentonite kept moist once compacted until full?

The large "cracks" are from the moisture in the soil/bentonite being released. These areas may need to be reworked and compacted before they will seal now (depending on many variables).

Thanks for reply Rainmain...the compactor was large steel smooth drum type roller that was pulled behind a tractor. It was not a sheepsfoot roller.

The bentonite was not moistened before compaction. It was tilled into the soil and compacted...then the pond sat for about 1-2 days before I could start the filling process. Why is keeping the bentonite moist necessary? How does this make a difference?

Regarding the differences between the two types of compactors.

Think of a piece of fabric with all the individual threads knitted together.

Now think of a ream of paper with all the pieces laying on top of one another.

The former was compacted with a sheepsfoot, the latter with a smooth drum type compactor.

When using the smooth compactor, if water penetrates one layer, it can move horizontally all over the pond until it finds another way to penetrate the 2nd layer, etc., etc.

Another question, how thick was the layer of dirt/bentonite that was being compacted?

I would estimate the level to be about 4 - 6 inches. The bentonite was tilled into the soil and then the soil/bentonite was compacted. So the soil that was compacted was just what the tiller kicked up

Also, can you comment on why the bentonite needs to be kept moist?

Im not an expert but seems it would work best if moist becuase it would be sticky and seal its self better.

It expands when wet.

Understand it expands when wet. But why does it need to be moist when spreading it.

Seems like it would be better to spread dry and get thoroughly mixed then wet it. Also why does it need to be kept moist as the pond is being filled.

I didn't know that it had to be. I've never heard that.

Mr James, the bentonite is best distributed and mixed in when the soils are fairly dry, but to be compacted well, it needs to be moist (not wet). Bentonite holds a lot of moisture, and as you know, expands a lot. If you get parts moist, and they dry, you get the massive cracks that extend well beyond your bentonite thickness, like the cracks you described having were water levels dropped.