The type of contamination is important. Some things can be cleaned up and it will never be a problem, small underground gas tank for example. Others you can’t ever get rid of. Your info is not complete enough to really say.
You can put in the contract the seller pays for the phase I & II and all clean up if needed. Then if there is a chance it will come back and the cost to clean up is not affordable, walk away.
From the little info you gave, the deal would have to amazing to go through the effort.
You will need to have professionsals look at it and give estimates.
I would only proceed with a Phase 1. If you think it likely that the property is contaminated, I’d just put that cost back on the seller and make him/her pay for it. Tell him/her that if the property checks out clean, that the investment in the Phase 1 (about $1,000) will be an asset to them. If the property is contaminated, then I’d probably make them do all the remediation (and/or just walk away from the deal).
There can be many hidden costs with cleaning up contamination. But the biggest may be your time. What is your time worth? You are likely to miss other great deals if you are spending time cleaning up a property.
I’d probably not touch a property until it was certified 100% clean. There are just too many other good deals out there to mess with a contaminated property.
There is no adequate protection for pollution related to USt’s if they have leaked if you purchase a property. That being said, I actually look for parks with these types of problems. You have to be able to afford the capital it will take to fix the park because no bank is going to loan you money.