🎯⭐ INTERACTIVE LESSON

Solid & Hazardous Waste

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Solid & Hazardous Waste - Complete Interactive Lesson

Part 1: What Is Waste? Streams, Composition & Generation

🗑️ Solid & Hazardous Waste

Part 1 of 7 — What Is Waste? Streams, Composition & Generation

Topics in This Part

Section
Defining Solid vs. Hazardous Waste
The Major Waste Streams
What's in Municipal Solid Waste (MSW)
Who Generates the Most

🔑 Key Concept: "Waste" is just material we have decided has no further value — but that decision is economic and cultural, not physical. The exam rewards you for knowing where waste comes from, what it's made of, and how the waste hierarchy ranks our options for dealing with it.

Solid Waste vs. Hazardous Waste

Term	Definition	Examples
Solid waste	Any discarded material that is not a liquid or gas (the everyday "trash")	Packaging, food scraps, yard trimmings, paper, old furniture
Municipal solid waste (MSW)	The fraction of solid waste collected from homes, schools, and businesses	The contents of your curbside bin
Hazardous waste	Waste that is ignitable, corrosive, reactive, or toxic — dangerous to health/environment	Solvents, batteries, pesticides, motor oil, many electronics
E-waste	Discarded electronics (a fast-growing, often hazardous stream)	Phones, laptops, TVs, circuit boards

A crucial scale point: MSW is only a small slice of all waste. Industrial, mining, and agricultural wastes vastly outweigh household trash by mass — but MSW is the part individuals control directly.

💡 "Solid" is a legal category, not a physical one. Under U.S. law (RCRA), a "solid waste" can include certain liquids and sludges. For the AP exam, focus on the function: solid waste = the discarded materials of everyday life; hazardous waste = the dangerous subset defined by the four characteristics you'll meet in Part 5.

Concept Check 🎯

The Major Waste Streams

Where does waste actually come from? By mass, most U.S. waste is never in your trash can:

Waste Stream	Source	Relative Mass
Mining waste	Tailings, overburden from extracting ore	Largest
Agricultural waste	Crop residue, manure	Very large
Industrial waste	Manufacturing byproducts	Large
Municipal solid waste (MSW)	Homes, schools, businesses	Small (but visible)

⚠️ Common misconception: Most people picture "waste" as household garbage, but mining and agriculture produce far more waste by mass than all the world's households combined. MSW gets the attention because it's collected publicly and is what consumers can change.

What's Inside Municipal Solid Waste

EPA tracks the composition of U.S. MSW as generated (before recycling). The biggest categories:

Material	Approx. share of MSW (by mass)
Paper & paperboard	~23%
Food waste	~22%
Plastics	~13%
Yard trimmings	~12%
Metals	~9%
Wood	~6%
Glass, textiles, rubber, other	remainder

🔑 Two key takeaways for the exam: (1) Paper and food waste are the two largest components of MSW. (2) A huge share of MSW is organic (paper, food, yard trimmings, wood) — material that could be composted or recycled instead of buried, which is the central argument of the waste hierarchy in Part 4.

Sort the Waste Stream 🔽

Use what you know about MSW composition and waste streams.

How Much Do We Generate?

The United States generates roughly 4.9 pounds of MSW per person per day — among the highest rates in the world. Generation rises with:

Affluence / income (more buying → more discarding)
Industrialization & urbanization
Packaging and single-use culture

Country type	Typical per-capita waste
Wealthy, industrialized (U.S.)	High
Rapidly developing	Rising fast
Low-income	Lower (but often poorly managed)

💡 Affluence cuts both ways. Wealthier nations generate more waste per person, but they also have the resources for sanitary landfills, recycling, and regulation. Poorer nations often generate less per person but lack safe disposal — leading to open dumps and burning.

Per-Capita Math 🧮

Use the U.S. rate of about 4.9 pounds of MSW per person per day.

1) About how many pounds of MSW does one American generate in a 7-day week? (round to the nearest whole number) 2) A town has 10,000 residents. About how many pounds of MSW does the whole town generate in a single day? (enter the number)

Part 2: Sanitary Landfills

🗑️ Solid & Hazardous Waste

Part 2 of 7 — Sanitary Landfills

🔑 The Idea: A modern sanitary landfill is not a hole full of garbage — it is an engineered containment system designed to keep two things from escaping: leachate (toxic liquid) below, and methane (explosive greenhouse gas) above.

Anatomy of a Sanitary Landfill

Garbage is dumped, compacted, and covered with soil daily. The whole pile sits inside an engineered "bathtub":

Component	Job
Clay + plastic (geomembrane) liner	Bottom barrier that stops liquids from reaching groundwater
Leachate collection system	Pipes that drain and pump out the toxic liquid for treatment
Methane recovery wells	Capture the gas produced as buried organics decompose
Daily soil cover	Reduces odor, pests, and blowing litter
Final cap (clay + soil + vegetation)	Seals the top when full; sheds rainwater
Monitoring wells	Test surrounding groundwater for leaks

💡 going into groundwater, and coming into the air. Every design feature targets one of these two escapes.

Part 3: Incineration & Waste-to-Energy

🗑️ Solid & Hazardous Waste

Part 3 of 7 — Incineration & Waste-to-Energy

🔑 The Idea: Incineration burns waste. Its great advantage is drastic volume reduction; its great cost is air pollution and toxic ash. Modern "waste-to-energy" (WTE) plants try to capture the benefit (energy) while controlling the cost (emissions).

How Incineration Works

In mass burn incineration, mixed MSW is burned at high temperature. The result:

Outcome	Detail
Volume reduction	Cuts waste volume by ~80–90% and mass by ~75%
Energy recovery (WTE)	Heat boils water → steam → spins a turbine → electricity
Bottom ash	Heavier residue left in the furnace (less toxic)
Fly ash	Light ash trapped by air-pollution controls — concentrated toxics (heavy metals, dioxins)
Air emissions	Without controls: dioxins, heavy metals (e.g., mercury), particulates, acid gases

⚠️ The ash paradox: Incineration shrinks the of waste enormously, but the remaining — it concentrates heavy metals and dioxins and must itself be disposed of carefully (often in a lined hazardous-waste landfill). Burning doesn't make toxics disappear; it concentrates them.

Part 4: The Waste Hierarchy: Reduce, Reuse, Recycle, Compost

🗑️ Solid & Hazardous Waste

Part 4 of 7 — The Waste Hierarchy: Reduce, Reuse, Recycle, Compost

🔑 The Idea: Not all waste strategies are equal. The waste-management hierarchy ranks them from best to worst. The order is the single most important concept in this unit — and the top of the list (source reduction) beats everything below it.

The Waste Hierarchy (Best → Worst)

Rank	Strategy	What it means
1 (best)	Source reduction / Reduce	Make/buy less; less packaging; durable goods
2	Reuse	Use an item again as-is (refillable bottle, donated furniture)
3	Recycle / Compost	Reprocess materials into new products; compost organics
4	Energy recovery	Waste-to-energy incineration
5 (worst)	Disposal	Landfill or plain incineration

Part 5: Hazardous Waste, E-Waste & Superfund

🗑️ Solid & Hazardous Waste

Part 5 of 7 — Hazardous Waste, E-Waste & Superfund

🔑 The Idea: Some waste is too dangerous for an ordinary landfill. Hazardous waste is defined by four characteristics and governed by its own laws — RCRA (for active, "cradle-to-grave" tracking) and CERCLA/Superfund (for cleaning up the toxic sins of the past).

The Four Characteristics of Hazardous Waste

Under RCRA, a waste is hazardous if it shows any of four characteristics. A handy mnemonic is I-C-R-T:

Characteristic	Meaning	Example
I — Ignitable	Catches fire easily (low flash point)	Gasoline, solvents, alcohol
C — Corrosive	Strong acid or base (pH ≤ 2 or ≥ 12.5)	Battery acid, drain cleaner
R — Reactive	Unstable; can explode or release toxic gas	Explosives, some peroxides
T — Toxic	Harmful or fatal when ingested/absorbed	Heavy metals (lead, mercury), pesticides

Part 6: Plastics, Ocean Pollution & Global Waste

🗑️ Solid & Hazardous Waste

Part 6 of 7 — Plastics, Ocean Pollution & Global Waste

🔑 The Idea: Waste does not stay where we put it. Plastics in particular persist for centuries, break into microplastics, and accumulate in the ocean — turning a local disposal choice into a global, transboundary problem.

Why Plastics Are Special

Plastics are cheap, light, and durable — and that durability is exactly the problem once they become waste:

Property	Consequence
Non-biodegradable	Persists for hundreds of years; doesn't rot like paper or food
Photodegrades into fragments	Sunlight breaks it into ever-smaller microplastics (< 5 mm)
Made from fossil fuels	Production adds to CO₂ and depends on petroleum
Many incompatible resin types	Hard to recycle; much is downcycled or landfilled
Lightweight & buoyant	Easily blows/washes into waterways and floats to sea

⚠️ Microplastics are the long tail of the plastic problem. Big items break into tiny fragments that are eaten by plankton and fish, up the food chain, and have been found in seafood, salt, drinking water, and human blood.

Part 7: Integrated Management, Economics & Mastery Check

🗑️ Solid & Hazardous Waste

Part 7 of 7 — Integrated Management, Economics & Mastery Check

You now know the waste streams, landfills, incineration, the waste hierarchy, hazardous waste and Superfund, and the global plastic problem. This final part ties them together with integrated waste management and policy/economics — then a mixed review and an Exit Quiz.

Integrated Waste Management

No single method solves everything, so real-world systems combine them in hierarchy order:

$\underbrace{\text{Reduce} \rightarrow \text{Reuse} \rightarrow \text{Recycle/Compost}}_{\text{shrink the stream first}} \rightarrow \underbrace{\text{Energy recovery} \rightarrow \text{Landfill}}_{\text{handle what's left}}$

The two enemies:

Leachate: The Liquid Threat

Leachate is the contaminated liquid that forms when rainwater percolates down through the buried waste, dissolving chemicals, heavy metals, and organic compounds along the way.

$\text{Rainwater} \;+\; \text{buried waste} \;\longrightarrow\; \text{leachate (toxic liquid)}$

If the liner fails, leachate can contaminate the groundwater / aquifer below — the most serious landfill pollution risk. That is why a sanitary landfill has:

A double liner (compacted clay plus a plastic geomembrane)
A leachate collection layer of pipes that drains the liquid to be treated
Monitoring wells around the perimeter to detect any leak early

⚠️ Exam favorite: The primary reason landfills are lined and monitored is to protect groundwater from leachate. An open dump (no liner) lets leachate flow straight into the water table — the key contrast with a sanitary landfill.

Concept Check 🎯

Methane: The Gas Threat

As buried organic waste (food, paper, yard trimmings) decomposes without oxygen — anaerobically — bacteria produce landfill gas, which is roughly half methane (CH₄) and half carbon dioxide (CO₂).

$\text{Organic waste} \xrightarrow{\text{anaerobic bacteria}} \text{CH}_4 \;+\; \text{CO}_2$

Methane is a problem for two reasons:

Explosion / fire hazard if it builds up.
Potent greenhouse gas — methane traps far more heat per molecule than CO₂ (over a ~100-year window, roughly 25–30× stronger).

The fix: methane recovery wells collect the gas. It can then be flared (burned off) or, better, burned to generate electricity — turning a pollutant into an energy source.

🔑 Best-case outcome: Captured landfill methane is used as fuel. This both prevents a potent greenhouse gas from escaping and produces energy, which is why landfill-gas-to-energy is considered a win-win.

Match Component to Function 🔽

Putting Numbers on Landfill Gas

Engineers size methane-recovery systems using two facts:

Landfill gas is roughly half methane, half CO₂ by volume, so the methane you can capture is about 50% of the total gas collected.
Each ton of methane that escapes carries the warming punch of roughly 25 tons of CO₂ over a century.

Multiplying those out shows why capture is worth the investment — even a modest gas-collection system prevents a large amount of CO₂-equivalent warming.

💡 Setup: The math below uses the 50% rule and the 25× warming factor. Keep them straight — one is a volume split, the other a warming-potency multiplier.

Landfill Gas Math 🧮

Landfill gas is roughly 50% methane (CH₄) and 50% carbon dioxide (CO₂) by volume.

1) A landfill captures 800,000 cubic meters of landfill gas in a year. About how many cubic meters of that are methane? (enter the number) 2) Methane traps about 25 times as much heat per unit as CO₂. If 100 tons of methane escape uncaptured, that is equivalent to how many tons of CO₂ in warming potential? (enter the number)

fly ash is often hazardous

Concept Check 🎯

Waste-to-Energy (WTE)

A waste-to-energy plant is an incinerator that recovers the heat to make electricity:

$\text{Waste} \xrightarrow{\text{burn}} \text{heat} \rightarrow \text{steam} \rightarrow \text{turbine} \rightarrow \text{electricity}$

Pros of WTE	Cons of WTE
Massive volume reduction (saves landfill space)	Air emissions (require scrubbers, precipitators, filters)
Generates electricity	Toxic fly ash must be landfilled
Reduces methane that landfilling organics would make	High capital cost to build
Can recover metals from ash	May discourage recycling (needs a steady fuel supply of trash)

💡 The recycling tension: A WTE plant is a big investment that needs a constant stream of burnable trash to pay off. Critics argue this can create a perverse incentive to keep generating waste rather than reduce and recycle it — placing WTE below recycling in the waste hierarchy (Part 4).

Incineration Trade-offs 🔽

How Much Volume Does Burning Save?

The headline number for incineration is volume reduction. A modern incinerator typically removes about 90% of the waste volume, leaving roughly 10% behind as ash.

$\text{Ash volume} \;\approx\; (1 - 0.90) \times \text{original volume} \;=\; 0.10 \times \text{original}$

That tenfold shrink is why cities short on landfill space turn to incineration despite the air-pollution and ash costs.

⚠️ Don't confuse volume reduction with making waste disappear. The mass shrinks less than the volume (~75% vs. ~90%), and the toxics concentrate into the ash that remains.

Volume-Reduction Math 🧮

Suppose an incinerator reduces waste volume by 90%.

1) A city sends 5,000 cubic meters of waste to the incinerator. After burning, about how many cubic meters of ash remain? (enter the number) 2) That leftover ash is what percent of the original volume? (enter just the number, e.g. 25 for 25%)

🔑 Why "reduce" is #1: The cheapest, cleanest waste is the waste never created. Source reduction avoids all the downstream costs — collection, processing, emissions, and disposal — at once. Everything below it is just managing waste that already exists.

💡 Memory tool — the 3 Rs in order: Reduce → Reuse → Recycle. They are listed in priority order on purpose. Recycling is good, but it is the third choice, not the first.

Concept Check 🎯

Recycling: Closed vs. Open Loop

Recycling reprocesses used materials into new products, saving raw materials and energy. There are two kinds:

Type	Meaning	Example
Closed-loop	Material becomes the same product again, repeatedly	Aluminum can → aluminum can
Open-loop (downcycling)	Material becomes a different, lower-grade product	Plastic bottle → carpet fiber or park bench

Why recycling helps the environment:

Saves energy (recycling aluminum uses ~95% less energy than making it from bauxite ore)
Conserves raw materials / mineral resources
Reduces landfill volume and mining/logging impacts

Why it isn't perfect:

Contamination (food, wrong materials) ruins batches
Some materials (most plastics) degrade each cycle → only downcyclable
Economics: recycling only happens at scale when there's a market for the recovered material

💡 Aluminum is the recycling superstar: it's infinitely closed-loop recyclable and saves ~95% of the energy versus virgin production. Glass and metals recycle well; mixed plastics are the hardest because there are many incompatible resin types.

Composting: Recycling for Organics

Composting is the controlled aerobic (with oxygen) decomposition of organic waste — food scraps, yard trimmings, paper — into a nutrient-rich soil amendment (humus).

$\text{Organic waste} + \text{O}_2 \xrightarrow{\text{aerobic microbes}} \text{compost (humus)} + \text{CO}_2 + \text{heat}$

Benefit of Composting	Why It Matters
Diverts organics from landfills	~30–40% of MSW is compostable organics
Avoids landfill methane	Aerobic composting makes CO₂, not the worse greenhouse gas CH₄
Returns nutrients to soil	Reduces need for synthetic fertilizer
Improves soil water retention	Healthier, more drought-resistant soil

⚠️ Aerobic vs. anaerobic — a key contrast: Composting (with oxygen) produces mostly CO₂. The same organics buried in an oxygen-poor landfill decompose anaerobically and produce methane (CH₄) — a far stronger greenhouse gas. Composting therefore has a real climate advantage over landfilling food and yard waste.

Classify Each Action 🔽

Match each action to the correct level of the waste hierarchy or recycling type.

Measuring Recycling

Two quick formulas come up constantly on the exam:

$\text{Recycling rate} \;=\; \frac{\text{mass recycled}}{\text{total MSW generated}} \times 100\%$

$\text{Energy saved} \;=\; (\text{fraction saved}) \times (\text{energy to make from virgin ore})$

Recycling aluminum saves about 95% of the energy needed to make it from raw bauxite ore — the single biggest energy savings of any common recyclable, and the reason aluminum cans are so valuable to collect.

💡 Watch the denominators: a recycling rate divides by total waste generated, not by the amount landfilled. Mixing those up is a common free-response error.

Recycling-Rate Math 🧮

1) A city generates 200,000 tons of MSW per year and recycles 60,000 tons of it. What is its recycling rate, as a percent? (enter just the number, e.g. 25 for 25%) 2) Recycling 1 ton of aluminum saves about 95% of the energy needed to make it from ore. If making 1 ton from ore takes 200 units of energy, how many units are saved by recycling instead? (enter the number)

💡 Mnemonic: "I See Real Trouble" = Ignitable, Corrosive, Reactive, Toxic. If a waste has even one of these, it's legally hazardous and must be handled under special rules.

Concept Check 🎯

E-Waste: A Fast-Growing Hazard

Electronic waste (e-waste) — old phones, computers, and TVs — is the fastest-growing waste stream in the world. It is a double-edged problem:

E-Waste Contains...	Concern
Toxic metals (lead, mercury, cadmium)	Poison soil and water if dumped/burned
Brominated flame retardants	Persistent, bioaccumulative toxins
Valuable metals (gold, copper, rare earths)	Worth recovering — "urban mining"

The danger is concentrated in informal recycling, often in developing nations, where workers burn or acid-bath electronics to recover metals — releasing toxic fumes and contaminating local communities.

⚠️ The export problem: Wealthy nations sometimes ship e-waste to poorer countries where labor is cheap and rules are weak. This shifts the toxic burden onto vulnerable communities — a classic environmental justice issue. The Basel Convention is the international treaty meant to restrict such hazardous-waste exports.

Concept Check 🎯

Two Landmark U.S. Laws

Law	Nickname	What It Does
RCRA (1976)	Resource Conservation and Recovery Act	Regulates hazardous waste "cradle to grave" — tracks it from generation to disposal at active facilities
CERCLA (1980)	Superfund	Funds cleanup of abandoned toxic-waste sites; makes polluters pay

RCRA is forward-looking: it manages waste being produced right now so it doesn't become tomorrow's disaster. CERCLA/Superfund is backward-looking: it cleans up already-abandoned contaminated sites and can hold responsible parties liable.

🔑 The "polluter pays" principle: Superfund is built on the idea that those responsible for contamination should pay to clean it up. When no responsible party can be found, a federal trust fund covers the cost — so the public isn't simply left with the bill.

Love Canal: The Site That Created Superfund

The Love Canal disaster (Niagara Falls, NY) is the textbook case:

In the 1940s–50s, a company buried ~21,000 tons of toxic chemical waste in an old canal, then capped it.
The land was later sold (for $1) and a school and neighborhood were built on top.
By the 1970s, chemicals were oozing into basements and yards; residents reported high rates of illness and birth defects.
President Carter declared a federal emergency; hundreds of families were evacuated.
The outrage led Congress to pass CERCLA (Superfund) in 1980, and Love Canal became one of the first sites on the National Priorities List.

💡 Why it matters for the exam: Love Canal is the standard example linking improper hazardous-waste disposal → public-health crisis → the creation of Superfund. If a question asks why CERCLA exists, Love Canal is the answer.

Match the Law / Concept 🔽

Concept Check 🎯

The Ocean Garbage Patches

Ocean currents (gyres) sweep floating debris into massive accumulation zones. The most famous is the Great Pacific Garbage Patch, a soup of plastic and microplastics concentrated by the North Pacific gyre.

Marine Plastic Harm	Mechanism
Entanglement	Animals trapped in nets, six-pack rings, rope
Ingestion	Turtles eat bags (look like jellyfish); seabirds fill stomachs with plastic
Microplastic uptake	Plastics enter the base of the food web
Chemical transport	Plastics adsorb and carry toxins across the ocean

Most ocean plastic originates on land — from littering, mismanaged waste, and rivers carrying trash to sea — not from ships.

💡 Solution direction: Because most marine plastic comes from land-based mismanaged waste, the most effective fixes are upstream: reduce single-use plastics, improve waste collection in coastal nations, and capture trash in rivers before it reaches the ocean.

Ocean Plastic Logic 🔽

Global Waste & Environmental Justice

How waste is handled varies enormously by wealth:

Setting	Typical Disposal	Risk
Developed nations	Sanitary landfills, WTE, formal recycling	Lower direct exposure
Developing nations	Open dumps, open burning, informal recycling	Leachate, smoke, disease, exposure

An open dump is unlined and uncovered — leachate flows freely into groundwater, waste is often burned (releasing dioxins), and people may live and scavenge on the dump itself.

Two equity problems recur:

Exporting waste (e-waste, plastics) from rich to poor nations shifts the hazard onto those least able to handle it.
Siting landfills, incinerators, and dumps near poor and marginalized communities within a country.

⚠️ Environmental justice: The burdens of waste disposal frequently fall hardest on low-income communities and communities of color, both internationally (waste exports) and domestically (facility siting). The AP exam expects you to recognize this pattern.

Concept Check 🎯

Reduce→Reuse→Recycle/Compost

handle what’s leftEnergy recovery→Landfill

Prevent as much waste as possible (source reduction).
Divert recyclables and organics (recycling + composting).
Recover energy from the combustible remainder (WTE).
Landfill only the final, unavoidable residue.

🔑 The whole unit in one sentence: Push waste up the hierarchy — prevent and divert first, and use disposal (landfill/incineration) only as the last resort for what truly can't be reduced, reused, or recycled.

Policy Tools & Economics

Why don't people just reduce waste on their own? Often because disposal is artificially cheap — the price of throwing something away doesn't include its full environmental cost. Policy tools fix this:

Tool	How It Works
Pay-as-you-throw (PAYT)	Charge households by the bag/bin → strong incentive to reduce & recycle
Bottle bills / deposits	Refundable deposit on containers → boosts return & recycling rates
Extended Producer Responsibility (EPR)	Makes manufacturers responsible for end-of-life of their products → designs for recyclability
Bans / fees	Plastic-bag bans, landfill bans on organics/e-waste
Recycling mandates & markets	Require recycling; support markets for recovered materials

💡 Why "pay-as-you-throw" works: When trash is free or flat-rate, there's no reason to generate less. Charging per bag makes the cost of waste visible to the person creating it — and people respond by reducing and recycling more. It internalizes the externality.

Match Policy to Effect 🔽

Waste-Diversion Math 🧮

A city of 50,000 people generates 100,000 tons of MSW per year.

1) After a pay-as-you-throw program, total generation drops by 20%. How many tons does the city generate now? (enter the number) 2) Of that reduced amount, the city recycles and composts 40,000 tons. What is the new diversion (recycling + composting) rate, as a percent of current generation? (enter just the number, e.g. 25 for 25%)

Quick Reference

Concept	Key fact
Biggest waste stream (mass)	Mining, then agriculture/industry; MSW is small
Biggest MSW components	Paper and food waste (much of MSW is organic)
U.S. per-capita MSW	~4.9 lb/person/day
Sanitary landfill	Liner + leachate collection (groundwater) + methane wells
Leachate	Toxic liquid → threatens groundwater
Landfill methane	Anaerobic decay → CH₄ (potent greenhouse gas; capture for energy)
Incineration	~80–90% volume reduction; toxic fly ash; WTE makes electricity
Waste hierarchy	Reduce → Reuse → Recycle/Compost → Energy → Landfill
Composting	Aerobic → CO₂ + humus (avoids landfill methane)
Hazardous waste	I-C-R-T: Ignitable, Corrosive, Reactive, Toxic
RCRA vs. CERCLA	RCRA = cradle-to-grave (active); CERCLA/Superfund = cleanup of abandoned sites
Love Canal	Buried toxics under a neighborhood → created Superfund
Plastics	Non-biodegradable → microplastics; ocean gyres; land-based sources

⚠️ Top traps: reduce is #1 (not recycle); incineration shrinks volume but makes toxic fly ash; landfill methane is anaerobic (composting is aerobic); RCRA ≠ CERCLA; most ocean plastic comes from land.

Mixed Practice 🎯

Exit Quiz ✅

Answer all three to finish the lesson.