Although it does not come up often, occassionally I discover evirnmental concerns while inspecting homes.  The two most come items are :

1) Abandoned Wells
2) Abandoned Fuel Oil Tanks (often buried outside the home)

Each of these can create significant liability for the buyer.
1) Abandoned Wells – The state of minnesota requires that all wells not durrently functioning must be either repaired to working order or the equipment, including drop pipe and pump must be pulled and the well casing must be sealed (filled with a concrete product from the bottom to the top by a licensed contractor.  Typical costs range from $500.00 to $1500.00.

Obviously it is important that your home inspector know what this equipment looks like and to be particullarly alert in areas where this is common.  This would be areas or homes that city water was brought in after the home was built.

2) Abandoned fuel tanks.  Abandoned fuel tanks must also be removed by a licensed contractor.  However, this process can be complicated be cause the soil around and below the tank must be tested for contamination from leaks or spills.  If leaks or spills are found thens a more indepth and expensive proecess must be undergone.  Cost could be in the thousands.
Typically the only clue that a buried tank is present is two small pipe protruding from the grouns.  One of the pipes is a filler tube and the other is a vent tube.