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Worksheet Grade 6 Social Studies & Civics

Barrow County's Nutrient Trading Plan: Comparing Two Costs

A grade 6 worksheet comparing the cost of paying farmers for buffer strips against upgrading a treatment plant to meet a fictional county's nitrogen target.

Objectives

  1. Students will calculate the total cost of two different pollution-reduction approaches using given per-unit rates.
  2. Students will calculate a percent savings by comparing two total costs.
  3. Students will explain how a single policy choice can affect different groups differently.

Vocabulary

Key words: nutrient trading, buffer strip, runoff, cost-benefit

Teacher overview

Fertilizer that washes off farm fields carries nitrogen into rivers and lakes, where it can feed algae blooms that use up oxygen fish need. This worksheet uses a fictional county, Barrow County, to explore a real strategy some communities use to address this problem: a nutrient trading program, in which a wastewater treatment plant can meet part of its pollution-reduction target by paying nearby farmers to reduce runoff instead of upgrading its own equipment. A common misconception is that the "cheapest" fix for a pollution problem must always be a technology upgrade at the source; this worksheet's numbers are built so students discover that is not always true.

Barrow County's Nutrient Trading Plan: Comparing Two Costs — Grade 6 Social Studies & Civics
Name: ____________________________ Date: ______________

Student Worksheet

Suppose Barrow County's wastewater treatment plant must reduce the nitrogen it releases by 5,000 pounds per year to meet a new permit limit. The county is comparing two ways to reach that target.

Option A: Buffer strips. Farmers can plant strips of grass and shrubs along field edges. These buffer strips catch runoff before it reaches the river. Each acre of buffer strip reduces nitrogen runoff by 20 pounds per year. The county would pay farmers $150 per acre per year to plant and maintain the strips.

Option B: Plant upgrade. The treatment plant could instead install new equipment that removes nitrogen directly, at a cost of $10.00 per pound removed.

  1. How many acres of buffer strips would farmers need to plant to reduce the full 5,000 pounds of nitrogen the county needs?
  2. At $150 per acre per year, what would the county pay farmers in total for that many acres of buffer strips (Option A)?
  3. At $10.00 per pound, what would the plant upgrade (Option B) cost to remove the full 5,000 pounds directly?
  4. Which option costs Barrow County less money in total, and by how much?
  5. Buffer strips and a plant upgrade cost different amounts. They also affect people differently. Describe one way Option A affects farmers. Then describe one way Option B affects ratepayers, the people who pay the treatment plant's bills.
  6. What percent less does the county spend by choosing buffer strips (Option A) instead of the plant upgrade (Option B)?
  7. Suppose only 150 acres of farmland are available for buffer strips. How many pounds of nitrogen would that amount of buffer strip actually remove?
  8. The county uses all 150 available acres of buffer strips but still needs to remove more nitrogen. How many more pounds must it remove some other way? What would it cost at the plant's $10.00-per-pound rate?

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key
  1. Answer: 250 acres.
    5,000 lbs ÷ 20 lbs/acre = 250 acres.
  2. Answer: $37,500.
    250 acres × $150/acre = $37,500.
  3. Answer: $50,000.
    5,000 lbs × $10.00/lb = $50,000.
  4. Answer: Option A, by $12,500.
    $50,000 (Option B) − $37,500 (Option A) = $12,500 less for buffer strips.
  5. Answer: Answers will vary. A strong response notes that farmers under Option A receive payments that help cover their land and maintenance costs but must give up some field space, while ratepayers under Option B would likely see the plant's higher equipment cost passed on through their water bills.
  6. Answer: 25 percent.
    $12,500 ÷ $50,000 × 100 = 25 percent.
  7. Answer: 3,000 lbs.
    150 acres × 20 lbs/acre = 3,000 pounds.
  8. Answer: 2,000 lbs, costing $20,000.
    The county still needs 5,000 − 3,000 = 2,000 pounds removed. At $10.00 per pound, 2,000 × $10.00 = $20,000.

Differentiation

Support (below grade level)

Provide a simple two-column chart labeled "Option A" and "Option B" with the per-unit rates already written in, and work through item 1 together as a class before students complete items 2 through 4 independently.

Extension (above grade level)

Using the fictional Barrow County numbers, ask students to find the buffer strip cost per pound of nitrogen removed and the plant upgrade cost per pound, then explain in writing why comparing the two rates directly tells the same story as comparing the two total costs.

ELL supports

Pre-teach "buffer strip," "runoff," and "permit" with a simple diagram showing rain washing fertilizer off a field, through a strip of plants, and into a river. Provide the numbers from the word problem already extracted into a labeled table so students can locate each value before calculating.