Where does our rubbish actually go, and what does it do once it gets there?
Topic 8.9 Solid Waste Disposal: describe the main methods of solid waste disposal and their environmental impacts.
A focused answer to APES Topic 8.9, covering municipal solid waste, sanitary landfills and their design (liners, leachate, methane), incineration and waste-to-energy, ocean dumping and e-waste, the impacts of each, and the role of hazardous waste, with a worked landfill capacity calculation.
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What this topic is asking
The College Board (Topic 8.9) wants you to describe the main methods of solid waste disposal and their environmental impacts.
Landfills and leachate
Decomposing waste in the oxygen-poor landfill produces methane, a potent greenhouse gas, which is collected and either flared or burned for energy.
Incineration and waste-to-energy
E-waste and hazardous waste
Why this matters
Solid waste disposal connects Unit 8 to urbanization (cities generate the most waste), to groundwater pollution (leachate), and to air pollution (incineration, Unit 7) and climate (landfill methane, Unit 9). It sets up Topic 8.10, where reducing, reusing and recycling cut the waste that must be disposed of in the first place.
Try this
Q1. Identify the contaminated liquid that forms as water percolates through landfill waste. [1 point]
- Cue. Leachate.
Q2. Explain one advantage and one disadvantage of incinerating solid waste. [2 points]
- Cue. Advantage: incineration greatly reduces waste volume and can generate electricity (waste-to-energy). Disadvantage: it releases air pollutants and leaves toxic ash that must still be disposed of.
Exam-style practice questions
Practice questions written in the style of College Board exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AP 2021 (style)4 marksSection II (FRQ). (a) Describe two features of a sanitary landfill that protect the environment. (b) Explain what leachate is and why it is a concern. (c) Identify one advantage and one disadvantage of incinerating solid waste. (d) Explain one problem with electronic waste (e-waste).Show worked answer →
A 4-point FRQ on solid waste disposal.
(a) Describe (1 point): any two of a bottom liner to stop leachate escaping, a leachate collection system, daily soil cover, and methane collection.
(b) Explain (1 point): leachate is the liquid that forms as water percolates through waste, picking up dissolved and suspended contaminants; if it escapes it can pollute groundwater.
(c) Identify (1 point): advantage such as reducing waste volume or generating energy (waste-to-energy); disadvantage such as releasing air pollutants and toxic ash.
(d) Explain (1 point): e-waste contains toxic heavy metals (lead, mercury, cadmium) that leach from landfills or harm workers when dismantled, especially in developing countries.
Markers reward two valid landfill features, the contaminant-laden-liquid definition of leachate, a valid incineration advantage and disadvantage, and a valid e-waste problem.
AP 2018 (style)1 marksSection I (multiple choice). The liquid that forms when water percolates through buried waste in a landfill, potentially contaminating groundwater, is called: (A) leachate (B) effluent (C) sludge (D) runoff. Justify your choice.Show worked answer →
A 1-point MCQ on landfills. The answer is (A).
Leachate is the contaminated liquid produced as water percolates down through buried waste, dissolving and carrying pollutants; if it is not collected it can reach and contaminate groundwater. Effluent (B) is discharged wastewater, sludge (C) is the solid residue from treatment, and runoff (D) is surface water flow. The trap is confusing leachate with other water terms; leachate specifically forms inside a landfill.
Related dot points
- Topic 8.10 Waste Reduction Methods: describe methods of reducing waste, including the waste hierarchy, recycling and composting.
A focused answer to APES Topic 8.10, covering the waste hierarchy (reduce, reuse, recycle), source reduction, recycling and its limits, composting, the role of legislation and economics, and how these cut disposal and resource use, with a worked recycling diversion calculation.
- Topic 8.11 Sewage Treatment: describe the stages of sewage treatment and explain how they reduce water pollution.
A focused answer to APES Topic 8.11, covering the primary, secondary and tertiary stages of sewage treatment, what each removes, the role of disinfection, sludge handling, why untreated sewage is dangerous, and the link to eutrophication and pathogens, with a worked BOD reduction calculation.
- Topic 8.1 Sources of Pollution: distinguish point and non-point sources of pollution and identify major types of pollutants.
A focused answer to APES Topic 8.1, covering the distinction between point and non-point sources of pollution, examples of each, why non-point sources are harder to control, the major pollutant types, and how this shapes management, with a worked load calculation.
- Topic 8.2 Human Impacts on Ecosystems: explain how pollution and other human activities disrupt ecosystems and harm organisms.
A focused answer to APES Topic 8.2, covering how pollution, oil spills, plastic, heavy metals and habitat disturbance disrupt ecosystems, the idea of ecological tolerance and indirect effects through food webs, coral reef damage, and ecosystem recovery, with a worked species-loss reasoning example.
- Topic 5.10 Urbanization: explain the environmental effects of urbanization, including impervious surfaces, runoff, the urban heat island, sprawl and saltwater intrusion.
A focused answer to APES Topic 5.10, covering urbanization, impervious surfaces and increased runoff, the urban heat island effect, urban sprawl, depletion and saltwater intrusion, and the benefits of smart growth, with a worked impervious-surface calculation.
Sources & how we know this
- AP Environmental Science Course and Exam Description — College Board (2020)