Miami, like many cities around the country, is facing a crisis over sewage. Because of the high cost, Miami-Dade County has put off long-needed upgrades to its wastewater system. Now in one neighborhood, businesses can't expand and developers can't build because of a lack of sewage treatment capacity. The federal government has stepped in and is forcing Miami-Dade to spend more than $4 billion to upgrade its sewer system. But even that may not be enough. Environmental groups say the county needs to spend more on a robust system that takes into account sea-level rise expected because of global warming.