Oil contamination of soil often happens under outdoor storage tanks or from leaky heavy equipment such as skidders. A large patch of oil-contaminated soil could be a serious environmental condition. In such cases, we recommend hiring an environmental consultant to assess the site and provide recommendations. For minor spots, landowners can treat the soil themselves, as the oil will degrade with encouragement. Place the soil on a plastic tarp, and add manure (the nitrogen helps speed degradation). Turn the soil to aerate and mix every few months until the soil is clean again.