Federal, state, tribal and local agencies will be gathered at Riverfront Park and the Fort Dalles Readiness Center in The Dalles on Wednesday to conduct a mass rescue operation exercise.  The Coast Guard is running the exercise that will help first responder agencies to evaluate search and rescue procedures and coordination, interagency Incident Command System response, triage accountability processes, and joint communications procedures and capabilities.  The scenario to be practiced involves a large passenger vessel that runs hard aground near Three Mile Rapids, which causes mass injuries and forces passengers into the Columbia River without lifejackets.