I am a geotechnical engineer and design and build ponds.
First off, the dam looks like its 25-30 tall, with steep side slopes. Unless you have very good material, that is pushing the limits of slope stability. I typically shoot for 1/2 slopes on the upstream and 1/3 slopes downstream. These yield a good factor of safety in most soils. Second, from the pictures the soil looks to be too dry as it is placed. This would not allow much compaction and would very likely results in seems in the core with a high potetial for seepage.
If this was my pond, I would drain it down to the level of the bulge, dig out the area of the buldge and see whats going on with the soils there. Find a soils engineer in your area. He can save you alot of heartburn.
John Schenne
