In response to EPA’s 1991 landfill rules that pushed the industry to larger facilities, landfill operator’s today pile and compact trash on the ground into giant mounds in the shape of a four sided pyramid. As originally contemplated, these mounds of trash were encased in liners to keep the wastes dry so contaminants would not be mobilized to leak into groundwater, along with monitoring systems at the site perimeter in an effort to detect leaks. Little thought had been given to landfill gas.
But, because the garbage was being capped and packed down in these covered landfills often hundreds of feet deep, the wastes were substantially sealed off from the air, unlike the situation in the shallow and porous, open dumps. Practically for the first time, a new environment was created deep inside the mountains of trash in which microbes that could live in an oxygen starved, or anaerobic, environment, took over.