How to deal with water possibly contaminated with machine oil?

My wife and I have a ~20 acre farm that we are trying to develop along permaculture principles.

We have a 1/4 mile gravel road on the property that leads downhill to a circle at the house. It transports a lot of rain water that we want to divert to growing areas and possibly a pond. The circle itself has about four vehicles parked at it, plus a refueling station for the tractor, plus a planned wash station to take mud and frozen winter slush off the vehicles and tractor.

I would like to design a drainage system at the circle that can isolate the possibly contaminated water and divert it further downhill for some kind of treatment. We have another 1/4 mile of forest and creeks below the house.

Thanks for any resources or ideas!

I would look into using mushrooms to remediate. I'm new to this forum, but I bet there is a thread on mycroremediation. The wikipedia article here has the basics plus references to other article on the topic by the experts.

I think you're looking at a settling pond/swamp. Winter slush is very likely going to contain salt though. Plan for that.
See if your terrain works to make an area to catch and hold the runoff, plant with all the local swampy plants the same as for black water treatment.

I would think in terms of a trench/pit/pond/constructed wetland, lined or not, featuring wood chips where the runoff is to be received. Wood is broken down by a large diversity of adaptable microbes.....mushroom mycelia among them....that can easily make the switch to digesting petrochemicals. Around and in this area you can grow an assortment of non-food plants (although I have read an article about woodchips inoculated with oyster mushrooms that did produce edible, residue-free mushrooms even when the woodchips were doused with diesel!) Firewood coppice and basketry materials come first to mind. I suppose there is still some danger from lead, especially if the area has been receiving drainage from vehicles from the time of leaded gasoline, and this is not broken down by microbes or plants. A chemical test might clarify this if you have the money for it.

some cures here for phytoremediation oil and slideshow Phytoremediation science< some serious stuff. Sunflowers and hemp have shown great promise with toxins, including radiation.