Sorry about the leak. If you are considering removing the pond, then I think fixing the leak needs to be the #1 priority. I would be sad indeed to have a house overlooking a pond and then have to lose the pond.
Do you have enough watershed (surface area) that will direct rainwater into the pond? If so, does your pond water level go up after good rains and then subside rapidly over the next few days? Does it usually come down almost to exactly the same elevation?
A spring in the basin of a pond will act as either a water inlet or a water outlet. For a well-connected spring, the water level in your pond will always equilibrate to the "potentiometric surface" of the spring. (That is the stabilized water level if you dug a hole down to the spring and then measured it the next day.) On my farm, the water level might only go up a foot above the spring horizon, but in some places it can be as great as 8 feet.
Were you on site when the pond was constructed? When I dig on my farm, it is easy to see when I reach the level of the spring in the side of the trench. The water starts seeping, but I can always see where the clay overlies the sandy streak that is the horizon of the spring. Sometimes the sand layer is only 1" thick, but still produces prodigious water. Sometimes the sand layer is several feet thick and I have to quit digging before getting through because my trench is collapsing.
I do not know if the spring would be visible in the side slope of your pond. However, if you can completely drain the pond, then I think you may be able to locate the spring horizon if you get hot, dry weather so the rest of your pond basin is no longer damp.
If the spring is high in the side slope of your pond, then it MIGHT be possible to save your fish in the remaining deep pool and fix the pond with some bentonite and compaction equipment. However, it is very difficult to run your heavy equipment with water (and slick clay) in the basin.
There are a few success stories of sprinkling bentonite and it migrating into the leak and then swelling enough to stop the leak. However, there are some commercial products that are usually even more effective for that application.
There is a member on the forum that does free consulting on pond leaks with the handle of teehjaeh57. (He also sells a commercial solution, but is very willing to just give expert advice to people with leaking ponds.) You can search for his handle and send a private message or email him at
[email protected]. He may be very busy right now due to all of the current pond activity.
If the application is feasible, you might be able to apply his product in your pond with the existing water and fish and either stop or significantly slow the leak.
If that is not feasible than you can probably still seal your pond the "old school" way. Drain it and let it dry. Hopefully you can see the spring inlet/outlet horizon. Disc or tractor rototill all of the pond slope or pond bottom where you observe the spring, plus a wide "safety" margin. If you have good clay, you can then use compaction equipment and moisture to seal the spring horizon that you just disrupted. Scrape up some additional clay from the bottom of the pond and put an additional 6" thick compacted clay blanket over your spring.
If you do NOT have a good clay in the pond basin (or nearby), then you could add bentonite after the disc/rototill step. Then do your compaction. You then need to mostly re-fill the pond in a single step. Any good water source? If the bentonite and clay seal goes through repeated cycles of wetting and drying, then it can develop significant cracks.
Hope that adds some more information for you to process on your pond plans.
