Describe how a modern sanitary landfill is engineered, compare landfilling to incineration, and apply the waste hierarchy to rank management options.
A modern sanitary landfill is a carefully engineered structure, not simply a hole in the ground: compacted layers of waste sit atop a bottom liner (clay and/or synthetic material) designed to prevent leachate -- contaminated liquid that percolates down through the waste -- from reaching groundwater, paired with a leachate collection system and, often, a methane capture system. Decomposing organic waste in a landfill's low-oxygen environment produces methane, a potent greenhouse gas from Week 24; some landfills capture this methane and burn it to generate electricity, turning a liability into a partial resource. Incineration ("waste-to-energy") burns waste to reduce its volume dramatically, often by 80 to 90%, and can generate electricity from the heat, but requires real air-pollution control equipment (connecting back to Week 22's criteria pollutants) and produces ash that still needs its own disposal.
The waste hierarchy, often drawn as an inverted pyramid, ranks management options from most to least preferred: reduce (avoid creating the waste at all) is best, then reuse (use an item again), then recycle or compost (recover the material), then recover energy (incineration with energy capture), and finally dispose (landfill) as the last resort. A common misconception is treating recycling as the top of this hierarchy, when reduce and reuse both rank above it.
Mastery looks like: They can explain the function of a landfill's liner and methane-capture system, calculate percent composition from a given waste sample, and correctly rank a list of actions using the waste hierarchy.
Common stumbles: Believing recycling is the top-ranked waste-hierarchy action rather than reduce and reuse; assuming landfills are unengineered, unregulated holes in the ground.