Most household waste sites generate methane gas, which is a by-product of the breakdown of waste matter. It is perfectly normal/acceptable to many local authorities and goes on at what was our local waste landfill site. There are no bad smells coming from it and any excess gas is burnt off. After about 10-15 years or so the gas will have gone and the site becomes inert and can then be put back to some use. The only drawback I can see is that the site itself can be a danger to anyone who trespasses onto it while gas is being collected but then again who would want to.
