Im not sure if Dave has examples of it causing a leak, but IMHO if you dont drill any holes in dam, and the others have the same dirt as the rest of the bottom, I would not be afraid of it. So if you start drilling and all the sudden small rocks come up, or a dramatic change in color/consistency of clay I would stop. Also you probably wont need a deep hole, not sure what size auger your tractor has. I would say a little wider and shorter than a 5 gal bucket.
