Short answers, pulled from the story.
A landfill is a site for the disposal of waste materials, including municipal solid waste. It is the oldest and most common form of waste disposal, though the systematic burial of waste with daily, intermediate, and final covers only began in the 1940s. Sanitary landfills as engineered facilities gained wide use in the 1960s and 1970s.
Landfills produce mainly methane and carbon dioxide through anaerobic digestion of organic waste. On average, about half of landfill gas by volume is methane. Landfills are the third largest emitter of methane worldwide, and methane has a global warming potential of 29.8 times that of carbon dioxide over a 100-year period.
Leachate forms when precipitation or water released by decomposing waste percolates through landfill material, picking up organic matter, heavy metals, and other contaminants. If it escapes containment, it can pollute groundwater and aquifers. The largest leachate quality problem is ammonium nitrogen, which can accumulate to concentrations of several thousand milligrams per liter.
The five phases are Initial Adjustment (aerobic biodegradation while oxygen is present), Transition (oxygen is consumed and anaerobic conditions develop), Acid Formation (volatile fatty acids accumulate and leachate pH drops from about 7.5 to 5.6), Methane Fermentation (the longest phase, producing methane and carbon dioxide), and Final Maturation and Stabilization (microbial activity slows, methane nearly disappears, and organic matter converts to humic-like compounds).
Aftercare duration has been estimated from several decades up to eternity. In the Netherlands, aftercare costs are estimated at more than 20 million euros per landfill. Aftercare involves maintaining liners, capturing greenhouse gases, and treating leachate after the site is capped and closed.
Germany, Austria, Sweden, Denmark, Belgium, the Netherlands, and Switzerland have all banned the disposal of untreated waste in landfills. Most European Union member states also have laws banning or severely restricting household trash disposal via landfills, in compliance with the European Landfill Directive.