Methane is a natrually occuring gas that is found in any landfill. But it is also a potentially explosive gas when it is in certain high concentrations. According to Missouri DNR those concentrations are generally between 5% and 15% by volume. And even then the gas would need an ignition, such as fire or a flammable flash.
The gas is also colorless and odorless and also has the capacity to seep into homes nearby. Again, in high concentrations methane can displace oxygen and cause a threat to health.
Cases of methane in landfills, such as in the Weber Landfill, are closely monitored so that levels can never get to a dangerous level. The next step will b e to vent the methane into the air safely.