Analyze an environmental problem doing calculations

Composting and landfill methane

Units 8 and 9
10 points
About 24 minutes

You can use a calculator on this question, just like on exam day.

You work through an environmental scenario using numbers: set up and solve calculations (showing your work), then explain the science and propose solutions. Several of the 10 points come from the calculations, usually one for the setup and one for the answer. On the exam: Question 3 of 3 in the 70-minute free-response section (Section II is 40% of the exam score).

The question

A city of 250,000 people generates an average of 2.2 kg of municipal solid waste per person per day. Food scraps and yard waste make up 30% of this waste by mass. All of the city's waste currently goes to a sanitary landfill. The city plans a composting program that would divert 60% of the food scraps and yard waste from the landfill. (1 metric ton = 1,000 kg; 1 year = 365 days)

Suggested time: 24 minutes

Your answers are saved in this browser as you type.

Part (a)

2 points

Calculate the mass of municipal solid waste the city generates in one year, in metric tons. Show your work.

Your answer to part (a)

0 / 2,500 characters

Part (b)

2 points

Calculate the mass of food scraps and yard waste, in metric tons, that the composting program would divert from the landfill each year. Show your work.

Your answer to part (b)

0 / 2,500 characters

Part (c)

2 points

Each metric ton of food scraps and yard waste buried in the landfill eventually releases 0.04 metric tons of methane (CH₄). Methane has a global warming potential (GWP) of 28. Calculate the yearly greenhouse gas emissions avoided by the composting program, expressed as CO₂-equivalent. Show your work.

Your answer to part (c)

0 / 2,500 characters

Part (d)

1 point

Explain why food waste buried in a landfill produces methane.

Your answer to part (d)

0 / 2,500 characters

Part (e)

1 point

Describe one design feature of a sanitary landfill that protects groundwater.

Your answer to part (e)

0 / 2,500 characters

Part (f)

1 point

Propose one realistic way the city could reduce the environmental impact of the methane still produced by the landfill.

Your answer to part (f)

0 / 2,500 characters

Part (g)

1 point

Explain how the solution you proposed in part (f) would reduce the landfill's contribution to climate change.

Your answer to part (g)

0 / 2,500 characters

Checking scoring…

Scoring it yourself shows you the rubric, examples and a model answer. Try writing your answer first.