I agree with Dave...I don't think the plastic will work either. I'd get on the phone today and call your contractor who is so proud of his construction and tell him to fix it!
I actually had a similar situation recently on a pond I expanded myself. It leaked badly and was in danger of washing out. For a discussion of that situation see the following:
http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=3;t=000079 I can say that the repairs from the backside on the new construction have worked 100%...the repairs of the existing dam which was plagued by animal dens and tree roots was a different problem.
I packed in good clay, very carefully and very thoroughly with a small dozer. It was a much better solution than draining the pond and essentially starting over...but pay close heed to the warnings of others who said that it may not work. Your situation is different than mine and what worked for me may not work for you....but it is certainly worth a try before draining and starting over, or jumping off the dam
Let us know how it goes.
