ponddreamer,

I think I would get a civil engineer out as soon as possible to look at it. The integrity of your dam may be in question and downstream concerns may be pertinent.

Your problem is exactly why I am not a fan of stand pipes and would never have one...or anything artificial in an earthen dam.

The repair measures are drastic, sorry to say, much like starting all over. Hopefully, an engineer will find a less drastic solution for you.