I'm reposting this here from another thread, as suggested by another member.

I'm really having a hard time with getting a local pond builder and have gone the NRCS route with no success.

I wish an expert pond builder would chime in with some advice, that has actually repaired a large ledge leak.

"I priced out more Benonite clay yesterday, since I haven't had any luck finding a blue clay source. Maybe if I pack the open ledge with a ton and a half of Benonite in 6 inch lifts I can stop it? The area is only about 20 feet in diameter where I couldn't compact the soil when I mixed in the Benonite two years ago. This would even allow me to have a deeper pond.

The first time I back filled at least four feet of soil over the area. The next time I mixed in the Benonite and compacted over the whole basin. Which left me with the soft area I couldn't compact."