If Rimrock Dam was to fail after a big earthquake, downtown Yakima and the cities of Wapato and Toppenish would be under water. It would be a major emergency. The Yakima County Office of Emergency Management wants to be prepared just in case that ever does happen. The office is conducting a tabletop exercise today to educate first responders on how they would help. The exercise will be held in the new emergency operations center located at 2403 S. 18th Street in Union Gap. The exercise will occur between 10:00 a.m. and 2:00 p.m. today.