Landfill Methane Pressure Releaser

Picture reference. I don't know the professional, or industry name for this piece of equipment, so I'll call it a Landfill Methane Pressure Releaser. I've seen similar ones called either a landfill gas recovery well or landfill gas pressure release valve. But there are quite a few different styles and types, so I don't know if they are all performing the same function. This one was located on a landfill in the UK. Near Coleshill. Every now and then it makes a loud hissing noise. This, I think, is the methane gas from deep underground where the rubbish has been buried being released or captured. Gave me quite a fright the first time I was ever near one. I never knew what it was, and I didn't expect it to start hissing randomly. This picture was taken with the Panasonic FZ50.