If other businesses have contaminents that have leaked into your soil that could be a huge development problem.You might want a developer consultant who knows that market to discuss further.I know nothing of Washington.

They are junk, some are contaminated as mentioned above, and they are more like crappy travel trailers.Stay away unless you like losing money and sanity.

What is the process if removed a underground oil tank and the soil is contaminated?

I will point out that on a small build it may not be worth that money because the "test" they do is not a soil sample or boring of the land, it is a research into the property to determine if a laundry facility or auto body shop or some contaminate / polluting type of business or entity was once on that lot a long time ago.

This soil contamination is not likely to be covered by insurance. 

The main problem is if there is a leak and soil is contaminated.

I came across an REO with disclosed soil contamination.  

With raw land, there are only a few questions that you can askSize of land, zoning, any known contamination?

. - Leave untouched as much of the remaining land as possible - both for a greater feeling of privacy and exclusivity for the resort guests and owners, as well as for environmentally responsible development.Pulling all of the expense figures out of thin air, I would pay 125mil for the property.The main concern for due diligence would be environmental contamination from previous activity - both military and research facilities.

Also if the property is older there could be asbestos or other contaminants and then demo can be more expensive because of additional regulations required.