Hi Jake,I'm in Canada so the processes might be different but I would think you need to factor in the potential for environmental assessment and clean up.

If oil prices change, if the environmental regulations are modified, if they run low on water... they go bust overnight.Also, there is no hope of salvaging those units.

i've seen and heard of phase ones....what is the phase one environmental report, and why is it important to get on a larger property but unheard of for smaller ones?

Could be a major battle with the neighbors, utility companies, environmental surveys, whatever.Start by calling the planning and zoning commission and discussing the property with them.

@Jon Klaus, there's a huge difference between simple environmentally sensitive portions of a parcel, and hillside lots in the coastal areas, where we have earthquakes!

Things that used to be called "drainage" or "swamp land" now can be deemed homes to fairy shriimp, or listed as environmentally sensitive, and "wetlands".

However some lawsuits (like environmental issues) still can target the owners (for deeper pocket).

We are dealing with people that have a conscious.  

If the contractor told him 70k, and he doesn't mention to us anything about mold, lead or asbestos yet he still gives us a list of repairs to be made them I'm thinking it's pretty safe to assume that none of those repairs include the aforementioned environmental issues you're now asking about. 

@Daniel Moctezuma, I don't have any direct experience but the problem that I see is if the tank leaked you may have an environmental clean up on your hands (need to clean up the soil as well) - it may not be as "simple" as only removing the tank.