No awards for walkers
If a runner walks in a running event, it doesn't matter. But if a walker runs in a walking event, it's cheating.
Don't give awards to walkers unless you can verify they walked the entire distance. Some walkers mix running and walking, others run the first mile and walk the rest.
Registration materials should require entrants to check off "run" or "walk." The walk is non-competitive. If you feel walkers should receive some recognition for their efforts, present all of them with finisher certificates or medals.
The walk should start after the run, so walkers and runners don't collide on the course. A separate chute should be set up for walkers and a digital clock placed there, so walkers can time themselves, if they choose. If you use a pull-tag results system, don't pull the tags of walkers.
Walkers should not be included in results and should not receive awards.