Thanks all for your input.

Ryan, in the long run, I would agree that letting the pond drain, removing the pipe and rebuilding the dam would be the best option. Our problem is the dam is our driveway and the only way in and out. We could move to a hotel for a week or so if necessary for the repairs; but, due to health reasons of a live-in in-law, our neighbors could not.

When you suggest pumping grout in, are you talking from the pond side or the drain end on the other side of the dam. What kind of grout should be used and what should I be looking for in a contractor?

Jsec, the water is now only a couple of inches above the rim of the vertical pipe. We are hoping we can pump it out once the water drops below the level of the rim but our hunch is the vertical pipe lost its integrity somewhere around the 90 joint down below so it may not pump out but we are going to give it a try.Thanks for the suggestion.

Essup, when you say 'culvert' are you talking about the old outflow 12" pipe or the vertical stand pipe?

Thanks again to all for your input.

Regards,
Paul