Veolia Water North America-West, the federal government’s contractor tasked with maintaining its wastewater treatment plant at the U.S.-Mexico border, is the subject of a new lawsuit alleging failure to contain crossborder sewage. On Monday, the Coronado Unified School District sued the plant operator and its former manager, Mark Wippler, marking the first time a school district joins local municipalities, environmental groups and homeowners that are suing and previously sued the international engineering company and federal government. San Diego-based Frantz Law Group, which opened a mass tort case late last year over similar claims, is representing the school district. It’s unclear whether other South County school districts may join or follow suit.