There is a fast ride on Tuesday and Thursday mornings (averaging 20-24 mph). As for Sunday rides, I know that Rapha does a group ride, as well as Bike Rack (6:30 am fast ride; 8:30 no drop ride). I was out there yesterday and there were groups everywhere.
That said, we are always looking for someone to step up and organize more DCTC group workouts. Tuan used to do a Sunday morning ride for years with a large following. I am not aware that he is leading it this season. Perhaps this might be something you are interested in organizing. I bet you could get a good following 🙂