Get the professional opinion of a PA registered civil engineer. There will be a "PE" after the name.

Shop around until you find someone conversant in subsoils engineering. Most of these problems can be engineered around, particulary in the price range mentioned.

I am currently living in a home which was built on a supposedly "unbuildable" waterlogged lot. Still here after 17 years. I got a PE to solve my problem.

And BTW a PE can and will override the local building inspector's opinion.