oil stain on concrete

I've been asked to clean an hydraulic oil spill/stain from a concrete slab, easy enough - lots of degreaser and hot water, do it several times over a week to allow for more oil to rise to the surface. But, this will be ground down and polished to expose the aggregate, then sealed. I have told those concerned that we won't know how successful the cleaning is until the conc is ground down (about 5mm).
What I would like your thoughts on is - should I tell the site foreman to forget about the stain untill the grinding is done, and I then chemical/steam clean what stain is there? I'm not sure if there is any point cleaning concrete that is going to be ground off anyway.
The spill happened on Sat. and nothing was done to it until Monday, when it was covered in sand. I went to inspect it this morning (Wednesday) but the site foreman had dumped a truckload of gravel on it (because he couldn't find anywhere else to put it and didn't know I had been called) and I won't have acces to the stain untill Tuesday. This give the oil lots of time to soak in.
So, should I start cleaning on Tuesday or wait untill the grinding is done and then work on what is left? The more I think about it the more waiting seems the most economical (for them, not for me) and sensible.
Thanks for your thoughts.
deep oil stain

Thanks Walter,
Coincidence would have it that I posted that artice.

The big issue with this stain is that the concrete will be ground off to expose the aggregate, then polished and have a clean sealer applied. The end result should be no stain and the floor (of someones million dollar town house).

I should get to see how bad it is on Tuesday, will decide then, & take some photos.

Thanks again


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