Solid Waste Disposal

A modern sanitary landfill is built in layers, bottom to top, before any trash arrives. First comes a thick liner of plastic and compacted clay, sealing the landfill off from the soil and groundwater below. As waste piles up and rain filters through it, it creates leachate, a contaminated liquid loaded with dissolved metals, salts, and organic compounds. Without the liner, leachate would sink straight into the water table. Instead, a drainage system collects it and pipes it out for treatment. Meanwhile, bacteria decomposing the buried waste produce methane, a potent greenhouse gas, so vertical vents capture and either burn it off or collect it for energy. Each day's waste gets covered with a layer of soil to keep out pests, smells, and rain, and the whole landfill is capped and sealed once it closes.

Incineration takes a different approach: burn the waste instead of burying it. A waste-to-energy incinerator can shrink trash volume by about 90 percent, and the heat released can spin turbines and generate electricity, which sounds like a clean trade. But combustion sends gases up the stack, including particulates, heavy metals, and other pollutants if the filtering technology is weak, and it leaves behind toxic ash that still needs a landfill of its own. So incineration does not erase waste's environmental cost, it redistributes it between air, ash, and land.

After a landfill closes, methane generation does not stop immediately. Decomposition continues underground for decades, with methane output typically peaking within the first few years after closure, then gradually declining over roughly 30 years as the buried waste runs out of material to break down. This links disposal directly to the atmospheric and water pollution chapters around it: landfills and incinerators are both downstream fixes for waste that dose-response thinking says would be better reduced, reused, or recycled before it ever needs a liner or a stack.