Yuck!
I read something that you might want to try. Since it's Sunday it may be a while before the city can respond.

Cleaning Wet Paint Spills

It is much easier to clean up fresh, wet paint. Speed is the key here. As soon as you spill paint on concrete, act immediately. Whether it is water- or oil-based, first absorb as much as possible. If you're outside, use dirt. Cat litter, sand and potting soil work as well. If it's just a few drips, quickly rubbing a little dirt into it may be all that is needed. For larger spills, sweep the absorbent material and paint mix up, and use the appropriate solvent to clean the area. Using a hose and a stiff bristled brush is effective for water-based paint.