Stevens,
I'm jumping into this conversation a little late but soil borings/test holes would give you some great insight on what it looks like "down there". Give them a shot.
As for the discussions regarding the permits and process revolving around this I feel you should proceed cautiously. Once the DEQ genie is out of the bottle that prick will never go back in. My dealings with them have been less than fruitful.
I spoke with a retired NRCS individual I know about getting a DEQ permit for digging some deeper holes in my existing pond. He said it "it shouldn't be a problem but after a career of dealing with those folks don't do it as they will look for any reason to deny a permit and usually find a reason". He recommended no notification in my case, off the record of course. He now works part time in retirement for a group that does wildlife habitat projects and still feels that way. The DEQ attitude and reach scares me to death. This is the same pond that the said group did a habitat improvement project of putting in a dam and water level control device to raise the water level a few feet. This private group paid for the work and water control device as long as I agreed to keep it in for a minimum of 10 years.
In my case I don't know how I am going to proceed yet, most likely it is heading to a poor ending. My 26 acre pond averages 5-7' deep I have all the paperwork filed from the original project and will attempt to use this as some sort of leverage for digging some deeper holes for fish. Sort of a �hey I did this as a wildlife benefit how about a project for some fish�.
My viewpoint is a little different than most on here and I may catch some flak for it but that is my opinion. Not trying to falsely scare you, just think it through. Just my $.02 and I have my fire pants on in anticipation of some hot flames. Good luck.
Bryan