The Los Angeles Times has an article on the 700-square mile Umatilla County, Oregon free wi-fi network (one of the largest in the US, but not the largest) which is used by the police, emergency workers, port shippers, and onion farmers:
The reason this wireless hot spot — believed to be one of the largest in the nation — was set up in the first place was not for those potential users, however. It was built as an emergency communications system in the event of a leak at the Umatilla Chemical Depot, where nearly 4,000 tons of sarin, mustard and other Cold War-era nerve gases are stored in concrete igloos.
The network cost $5 million to build and has so many uses for different kinds of businesses that it’s hard to believe this is good old wi-fi technology.