I dug 6 inches below the sidewalk grade, trucked out about 30 1-yard trucks of soil, packed in 4 inches of concrete base and 2 to 3 inches of gold-colored rocks.

Hi BP,I'm looking at a HUD property with BURIED OIL TANK and may also need MOLD Remediation in the garage and another room.My bigger concern is potential Oil tank leaks and soil remediation that can run thousands of $s.

Ask that the EM be sizable and that it is released to you after they complete some diligence like soils and a initial concept meeting with the city.Negotiate - whatever they offer - they are willing to pay more.

Howeverall plumbing is laid and the slap is poured over it thus it can be very expensive to repairThere are areas where the soil is said to be "massively expansive" and it expands or contracts with water. 

But I am not sure they are going to hit the sell button, because once they do they will never be able to get out of from underneath that.

Do not buy the property until that tank has been inspected, decommissioned and removed (and any soil or groundwater contamination cleaned up / remediated).TRUISM: If there's an underground oil tank, and it's steel, it leaked.

The only way to be sure it’s done right is to connect the drain from underneath.  

I know there is some testing going on in the soil outside, but what has always bothered me about this is the homeowners that might be living next door with peeling paint blowing onto my property.

Underneath there are 3 one bedroom one bathroom units that were renting for 600 each.

In many places the soil in this area is very rocky so digging can be very laborious or requires machinery.