City right-of-way: can I place a porta potty for my construction site?

My construction site is on a narrow downtown lot with no room for a portable toilet. The only available space is the public sidewalk right in front. I need one standard portable toilet for a crew of 10 workers, Monday through Friday for about eight weeks. No food or alcohol is involved. The sidewalk is concrete and level, and a vacuum truck could park in the street about 15 feet away. I'm not sure if this is allowed or what permits I'd need from the city. Has anyone dealt with placing a unit in the right-of-way? Do I need an ADA-compliant unit even for a small crew?