Biodegradeable products are good but they will not help you comply with the by-law. It's not the detergent that they are worried about, it is the automotive dirt/grime/grease that goes into the run-off.

There are mats that you can drive over - it collects all the waste water when you wash your car but then you still have to dispose of it. Canadian guy patented this technology I think. You can find it in industrial supply stores.

The waste water can be recovered and the detergent can even be reused using some of the newer water recovery equipment. The water ends up about 99.999% pure again. This technology is about $20K for a small unit.