I have a pond leak that is almost identical to the one described by Katana. About six years ago my wife and I purchased some property that had an existing pond. From what I've been told the pond has been on the property for quite a while (the size of trees behind the grade, which may have weakened the integrity of the dam attest to this fact). In an effort to cheaply increase the size and surface area of the pond I installed a culvert at a higher elevation than the previous run-off. The spring-fed pond slowly filled to this new level and I was happy. For a little while at least. The pond soon began quickly draining to well below the original level. Eventually I was able to see and hear where the pond was losing water. It appeared to be in an area that was less muddy and more sandy than the rest of the pond (I'm assuming that it is close to an area with more sandstone). Using thick pond liner and bentonite I patched the hole. The pond filled and then quickly drained again revealing a new hole close to the original. This same scenario of a patch sealing the pond, the pond rising, and then a subsequent draining to a new hole (each time the hole has been about four inches in diameter) has been repeated several times. All of the subsequent holes are in the same general area. I believe that the pressure of the pond rising eventually causes a new area in the pond to open up and find a new access to the one "drain". I believe that overall the pond is in good shape. If I could find some way to fill in the length of the drain instead of merely patching the access to it I think my problem would be solved (but what do I know?). Is there some way to fill in more of the leak so that the pressure caused by the pond filling doesn't result in the forming of a new hole?

I see that several commented to a post submitted by Katana (who describes a leak similar to mine) and suggested that concrete should be used. What's the best way to do this? Is there a particular kind of concrete that should be used? With previous patches I've used powdered Bentonite. Without using a liner in conjunction with the Bentonite the pond pressure eventually eats through the 'patch'. Would a pelletized type of Bentonite that would be carried far into the depths of the drain (between the hole and the back of the dam) work better? Any help/advice is GREATLY appreciated!