@Allan Smith I don't understand what people mean when they keep saying "water lines" but a sewer lateral is not just a water line, when it breaks it releases raw sewage into the ground water.

Usually, only heating oil USTs associated with commercial properties are regulated. thus, most home heating oil tanks may and often are taken out of service without any oversight from state regulators.Second- the rules that are in effect for heating oil tanks are usually less stringent than for diesel or gasoline tanks since heating oil tends to thicker and may not migrate as far. as a result, many states just require tanks to be cleaned out. they may also require the tanks to be filled with sand or concrete to prevent collapse. but sampling may not be required.Third- the key to determining if a tank has leaked is to collect soil samples from around and beneath the tank (groundwater also if groundwater is shallow). another quick way to see if a tank is leaking is to "dip" it with a stick that has a paste that turns color in the presence of water. generally, if water has gotten into a tank, it can mean oil has leaked out of the tank (although a certain amount of condensation may be present even where there is no leak so this is not a infallible test).Fourth- if there is currently a tank in the basement, ask the owner if there used to be a buried tank (a/k/a underground storage tank).Fifth, If the tank has impacted the soil, the cleanup generally varies from $25K to $50K though the costs will depend ont he depth of the contamination. i once had a home with a heated pool that had pressurized piping and used diesel. the contamination went down 40 feet and the consultant went crazy excavating the soil to the tune of $400K!!!

However, soil and groundwater results are below the cleanup criteria in your State.  

Pollution to the ground water could impact neighbor's wells.

I'm on the fence about this one...The REO property I'm interested in is in a subdivision that the ground water is partially contaminated by THC from a manufacturing plant.

Where I'm at right now: I have spoken directly to the Director of Public Works and he says that he must speak with someone in the Groundwater Management Department (whom I have also spoken with directly) to see what type of system can be done and give me a timeline.

There have been no issues since and I knew I was relieved when the inspector said it was just above ground water not able to get away from the house. 

The majority of underground tanks (up to 80%) leak and if it does then you have soil and potentially ground water contamination to deal with.

They run for miles and collect alot of groundwater.

This is South Florida, so we have a very high water table, and in the summer when it rains a lot, the water table is so high, that if you drain all the water from the pool, the hydrostatic pressure of the water in the surrounding ground will actually push the concrete pool's shell out of the ground.If one fills the pool with water, will it settle back down as the ground water recedes during a dry spell?