That is even easier to fix than sand in the bottom!

If you still have silty-clay material on site, or you still have good material in the bottom of the pond, then you just need clay blankets to seal that sand layer.

For a water depth of 10' or less, two six-inch lifts of compacted clay should be sufficient.



This type of compactor can easily roll up and back down your pond side slopes. Rental in my area is only $1,500/day. (The transport fee would be around $200 each way for me.)

Cat CP44 Vibratory Soil Compactor

You might be able to do the entirety of a 1-acre pond in two days? You would also need a small-medium dozer pushing material onto the side slopes. It could perhaps be accomplished in a single day if the sand layer is only present in part of the pond slopes.

You also need to wet the clay blanket material to the correct moisture content for optimal compaction. Is there still water in the bottom of your pond basin? You can use that to spray the dozed material after each load.

I would definitely ask the geo engineer what moisture content was their target for the detention pond, and if there is an easy way for you to estimate moisture content on your project.

Finally, do you have a small tractor with a disc attachment? After sealing the sand layer, I would recommend discing the other side slopes and the bottom of the pond in a few passes with different orientations. Wet that as needed, and then roll the heck out of that while your compaction equipment is still on site. Hopefully, that will give you a pretty tightly sealed pond.