Oil Tank and Concrete Removal

I understand the first step is hiring X-ray services to locate the tank…but is this necessary if I plan to have the concrete removed from the entire yard ? The yard is 50×84 – a lot of concrete! Where would I get an estimate of cost to do this? What are the chances and expenses involved if there is an oil leak? I understand it is the seller’s responsibility, but “as is” is asked as a condition of sale. I would appreciate any advice.