Generally speaking before a pool project gets started we have a general idea whether or not we will hit bedrock and at what depth. Most municipalites have a GIS system that can provide you with a predicted soil type for your area. You can also contact your local building inspector to use as a resource as well.
That being said, there are instances where you can be surprised as well. In our area we typically do not have an issue with bedrock unless you are in the ledgeview area near De Pere WI or working in Door County north of Sturgeon Bay.
In those cases that we know we will hit bedrock we will have a plan in place to remove the bedrock and that will be incorporated into your cost that was provided to you. The removal of bed rock, or large stones usually involves the use of a hydraulic hammer attachedment and a large excavator that chips the rock out as needed. This adds to the cost and the time needed to complete the project, but bedrock does not mean you cannot build a pool. It will just take a few extra days.
When you run into buried debris by surprise on a job site you can expect to pay additional to have it removed. On average it may add about $3,500-$4,000.00 to remove bedrock from a pool dig site.
While smaller rocks can be dug out, it may take a little longer than expected to complete the excavation. In some cases it may be beneficial to excavate past the layer of rocks to a more consolidated material and backfill in engineered lifts to the point of your pool base. This can add from $800-$1,800.00 on average.
All in all, in most cases if we find unexpected debris in the pool site we typically have solutions to remedy the situation.