Cleaning and Stain Removal - Peanut Oil on Bare Concrete

I have an area of about 20 square feet of bare concrete (no paint, coatings or other treatments) that had peanut oil inadvertently spilled onto it -- last year. Now the oil has basically embedded itself into the concrete and looks really nasty.

I have a small power washer (1600psi) but it does very little in the way of removing this stain. I also have a power scrubber, which seems like a more viable option at this point. My concern is that I don't want to use a harsh environmentally-evil detergent; I'm sure, for example, "Dawn" dishwashing detergent would lift the oil right out of there (especially when applied with the power scrubber and rinsed with the power washer) but I don't fancy a coating of "Dawn" on the lawn.

Options?

Check the label on the detergent. Most of them are biodegradable. You do need something that will soak into the concrete and emulsify the oil, lifting it to the surface so it can be washed away. You are dealing with a vegetable oil, which should be easier to clean up than dino oil. I don't believe that you will harm your grass or the environment. Just give it a good, diluting soak when you finish the concrete.

Get a bag of portland cement at the lumber yard. Pour it over the spill and leave it until it absorbs the oil. It's very hygroscopic (absorbs liquids) and will do the job over time. Just leave it alone: it's low labor, but takes time. Your power washer is likely driving the oil deeper into the concrete. Good luck