I was recently talking to the grounds supervisor of a property a few miles from my home that is owned by a very wealthy local business man. I was asking him about the ponds on the property and he was telling me about the one that is 8 acres and won't hold water so I began to ask him if he had tried bentonite, clay,etc. After a few minutes it became obvious that this is a serious problem. It appears they have tried liners that have gotten sucked down in the hole it's so big and had even resorted to putting big blocks of concrete down the hole. I'm afraid they may have a little cave under there and not a sinkhole. This area is known for having a lot of sinkholes and caves and it doesn't look like he had anybody really survey this area before building. I don't know how you would know if there is a sink hole or cave under where you would like to build a site but if there is a way I would sure like to hear about it. As well if anyone has any advice that I can apply to this guys plight I would appreciate it. Since I've never actually seen the pond I am trying to hook up with the grounds man in the next few days. When I go over there it would be nice to have a little more knowledge. I have contacted the county USDA agent who is going to get back in touch with me today.

You might try talking to the local US Geological Survey (USGS) office. They should have some relevant information. Another source would be the Geology department at a nearby college or university. Many privately owned caves have been mapped by local geologists and you might get lucky on this one. A couple of calls should yield some info.

If sinkholes are common, someone will know about them. Engineers won't allow structures to be built where soils are questionable, or if subsoils won't support what is to be constructed.
And, drilling a few test holes might shed some light on the question.

As it turns out the owner apparently had the USGS or USDA do tests on the site prior to building and they recommended not building it there as they believed sink holes or a small cave was underneath but they built it anyway. Knowing this changed my opinion of the entire situation; the guy seems to have more money than sense imo. Maybe he has learned a valuable lesson. I don't know since I've yet to talk to him about it. With several hundred acres I'm sure he can find another site to build that would work.