Lastly, an alternative to removal is decommissioning. 

What is the likely hood of it being contaminated if it has already been decommissioned?

Background:  I'm 35, NYS Real Estate Salesperson, Accounts Payable Specialist at a local power plant (scheduled to decommission in 2018) , and Amateur flipper.

Have the tank tested to determine whether it's leaking.Seller normally pays to decommission the tank prior to selling.This is not an insurmountable problem.

Then I added a 5th unit (that was there but was "decommissioned") and after getting it rented out, I had the property reappraised.

You can call the city and ask if about the permits that have been pulled.My thoughts on the property, if it really is being sold as a 4plex (one of the rooms being decommissioned then it makes for a great House-Hack play for sure.  

Patrick is talking about Vancouver BC.. not Vancouver WA.Tsunami are not an issue as you are 60 miles inland... the nuclear reactors were all decommission 25 years ago...

They can also be from old bridges that have been decommissioned.

If it is a masonry fireplace, then there are ways to "decommission" it so it cannot be used to burn wood.

Perhaps if a bunch of other neighbors want to do likewise, and split the cost, it might make sense.And Jeffrey said you have to take the oil tank out - I don't believe that is required, since I see many decommissioned oil tanks being left inside houses that are gas heated.