Gases have been being extracted from garbage landfills for over 20 years now.
A sewage treatment plant I frequently drive past has a tall flare stack. Be nice if they could use the gas for something productive.
Growing up near San Francisco Bay, there was a garbage dump on the bay. Many years after it closed, the music producer Bill Graham decided to build a pretty good music venue on it. The venue has many seats, and a large, sloping grass area in the back. No one had thought about all of the natural gas percolating below the grass. As concert audiences tend to do, they lit up cigarettes, and, no doubt, smoked other things. Well, the gas rising through the soil reached the discarded matches, cigarettes, and lit on fire. No significant fires, but quite a few surprises. They closed the venue, installed a system to redirect the natural gas away, and resumed operations.