Miami-Dade’s biggest — and most vulnerable — sewage treatment plant is getting a big upgrade, which could help the county stop dumping tens of millions of gallons of wastewater into the ocean in the next few years. At a groundbreaking event on Thursday, county leaders praised the project as a step toward a “future-proofed county.” “We are making bold achievements to ensure we have a resilient future — we will and we must,” said Mayor Daniella Levine Cava. The wastewater treatment plant on Virginia Key has long been a poster child for the havoc sea level rise could wreak on Miami-Dade County’s …