Few weeks ago we came home to a VERY strong odor, smelled like oil, and found out in the basement there was a lot of oil in the sump pump. After a few days of a lot of rain the majority of the oil is gone but the smell is still here. The plumber came and had no idea why this happened. Why do you think oil got into the sump, is our house sitting on oil? We still see some signs of oil coming in from the tubing in the ground and there is nothing outside to show us that someone spilled oil in our yard. HELP! What do you think?

Maybe heating oil? Maybe you or your neighbor has a buried oil tank that's leaking?

How do you heat your home?
Is there any neighbor heating with oil in the area?
Is there any gas station close by?
Are you or anyone else in the area using well water?
Is there an abandoned oil tank in your yard that you do not know is there?

I would contact the township right away. Any oil found in ground water is a concern.

A few years back we had a client that had this same issue. It turns out the house four doors away had a leak in their tank and it traveled through the ground and ended up in their sump pit. The entire area had to be dug up and cleaned out. The entire foundation of their home had to be removed including basement floor.
Also did a well test on another home with a gas station located 1/4 mile away. Found hydocarbons in well water. It turned out to be the gas station tanks were leaking. Another major clean up project.

This is a very serious issue. Call township TODAY!

http://www.fredericksburg.com/News/FLS/2002/042002/04222002/585209
A few years ago, a petroleum company in Culpeper, VA bought a man's house "and dismantled it...as part of a cleanup effort that became necessary after a company deliveryman poured about 550 gallons of heating oil into the basement."