Which method is NOT effective in controlling landfill fires?

Allowing natural combustion is not an effective method for controlling landfill fires because it permits the fire to continue burning without intervention. This results in prolonged combustion, which can lead to the release of harmful pollutants into the air and environment. Natural combustion does not address the fire but rather allows it to consume available materials, potentially increasing the fire's intensity and duration.

In contrast, separating burning refuse helps to isolate the fire, reducing the amount of combustible material and limiting the fire's spread. Covering the fire with soil can smother the flames by cutting off oxygen, which is essential for combustion. Injecting water is another common method that can extinguish fires by cooling the burning materials and depriving them of heat, thus controlling the combustion process. Each of these methods focuses on actively intervening in the combustion process to mitigate and control the fire's impact effectively.