If it's concrete use Premiere Products "Force" which costs circa £8 - £10 / 5 ltr. Make sure you scrape off as much of the oily gunk as possible first, apply the chemical as per the manufacturer's instructions, leave to dwell, agitate with a deck scrub then hot wash off.
As Roger so rightly says, if any of the resultant slurry goes into the drainage system your in big trouble both financially and reputation wise. What you need to do is block the drains off (sandbags) and pick up the slurry with a wet vac then dump it into a 45 gallon drum so you can skim off the oil.
By the look of the blue plastic containers your customer has an expensive waste disposal job here. You might get away with just adding your oily waste to the containers for them to get rid of.
Remember to add 'clean up time' to the job as everything will need cleaning down afterwards from your boots to your hoses to your wet vac.