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Debate kit Grade 6 Science

Marchbold's PFAS Choice: Blend the Wells or Add Carbon

A grade 6 science debate on how a fictional town should cut PFAS in its well water, with two-sided evidence on blending and on carbon filters.

Objectives

  1. Students will explain the difference between diluting a contaminant and removing it.
  2. Students will build an argument from a monitoring record about which method a town should use.
  3. Students will rebut an opposing claim by naming the specific measurement that weakens it.

Vocabulary

PFAS
A large family of human-made chemicals used in things like nonstick pans, waterproof fabric, and firefighting foam. They are called forever chemicals because they take a very long time to break down.
Parts per trillion
A unit for measuring extremely small amounts of a chemical in water. PFAS limits are set in parts per trillion because these chemicals matter even in tiny doses.
Activated carbon
Activated carbon is a special charcoal full of microscopic holes that grab and hold chemicals as water flows past. It is the same material used in many home water filter pitchers.

Also: blending, reporting limit, well field

Teacher overview

This debate runs as a water board hearing across two class periods. Two teams of five argue over how a fictional town should handle PFAS in one of its well fields, a moderator keeps time, and the rest of the class sits as the board and votes. The question is genuinely open, because one plan takes the chemical out of the water while the other spreads the same amount of it through a larger supply, and each plan costs something different. A misconception to name before students read the evidence is the assumption that boiling water, or letting it sit, gets rid of a contaminant they cannot see or taste. Boiling drives off water vapor and leaves the PFAS behind, so the concentration goes up rather than down. Students who carry that idea into the hearing will treat both plans as equally good at removal, and they will miss the strongest argument on each side.

Marchbold's PFAS Choice: Blend the Wells or Add Carbon — Grade 6 Science
Name: ____________________________ Date: ______________

Resolution & Background

Resolution: "The town of Marchbold should build a carbon treatment plant at the Orrelby Road wells rather than blend that water with water from the Redlow well field."

Marchbold is a fictional town of about 9,000 people. Its water comes from two well fields. The Orrelby Road field sits downhill from an old fire training ground. The Redlow field sits three miles away on the other side of a ridge. Everything about Marchbold in this kit is fictional and was written for this debate.

PFAS are a family of human-made chemicals used in firefighting foam, stain guards, and nonstick coatings. They do not break down easily in soil or water, so they build up over time. EPA has set the limit for two of them, PFOA and PFOS, at 4.0 parts per trillion each. That rule became final in April 2024, and water systems must meet it by April 2029. In May 2026 EPA proposed letting eligible systems apply for a two-year exemption, which would give them until April 2031. The exemption would not be automatic for every system, and the 4.0 ppt limit would not change. The proposal was not yet final as of September 2026, so the deadline is still in motion.

A part per trillion is a very small share, yet the limit is a legal requirement the town has to meet. Marchbold has two ways to meet it. It can blend, which means mixing Orrelby water with clean Redlow water until the level in the mixed water drops below the limit. Or it can treat, which means running Orrelby water through a bed of activated carbon that holds the PFAS on its surface. Carbon beds wear out and must be swapped.

Roles. Five students argue for the carbon plant. Five argue for blending. One student moderates and keeps time. Everyone else serves as the water board, writes questions on index cards, and votes at the end.

Format. Each team gives a four-minute opening. Teams then take six minutes to prepare. Each team gives a three-minute rebuttal and a two-minute closing. The board asks four questions from the cards, then votes. Each team turns in its written opening and its rebuttal notes.

Evidence File

Every reading below comes from a fictional Marchbold record written for this debate, except where an outside source is named.

Case for building the carbon plant

  1. Blending does not destroy PFAS or take it out of the water. The same amount of chemical leaves the plant each day; it is only spread through more gallons. A carbon bed holds the PFAS on its surface, so the water that leaves the bed carries less of it. (Source: a fictional plant chemist's memo written for this debate.)
  2. The town lab has tested both fields for three years. Orrelby Road water runs near 16 ppt of PFOA. Redlow water comes back below the lab's reporting limit. (Source: a fictional town lab record.)
  3. To reach 4.0 ppt by blending, Marchbold must mix one gallon of Orrelby water with three gallons of Redlow water. That lands the town exactly at the limit with nothing to spare. A single high result would put the town over. (Source: a fictional plant chemist's memo.)
  4. The federal limit for PFOA and PFOS is 4.0 parts per trillion each. It is a rule, not a target. (Source: EPA PFAS National Primary Drinking Water Regulation.)
  5. In a fictional six-month pilot, Orrelby water ran through a carbon column at the plant. Every monthly sample of the treated water came back below the reporting limit. (Source: a fictional pilot test report.)
  6. Demand rises in July. A fictional pumping record shows Redlow alone cannot carry the town through a hot week, so the town would have to pull more Orrelby water and the blend would slip. (Source: a fictional pumping record.)

Case for blending instead

  1. Blending can start within a month. It needs a valve, a meter, and daily readings by an operator. The carbon plant would take about three years to design, fund, and build, and residents drink the water during those three years. (Source: a fictional town engineer's schedule.)
  2. Cost is real and it falls on ratepayers. A fictional engineering estimate puts the carbon plant at $4,600,000 to build and about $310,000 a year to run, mostly for swapping out spent carbon. Blending would cost the town far less. (Source: a fictional engineering estimate.)
  3. Spent carbon does not disappear. The fictional estimate expects about 12 tons a year to be hauled away for burning or reuse, which moves the PFAS somewhere else rather than ending it. (Source: the same fictional estimate.)
  4. Three years of fictional town lab results show Orrelby holding steady between 15 and 17 ppt, with no upward trend. A steady source is easier to blend against than a rising one. (Source: a fictional town lab record.)
  5. Marchbold already loses about one gallon in six to leaks. A fictional water loss audit found that fixing the worst two miles of pipe would free up enough Redlow water to hold the blend through July. (Source: a fictional water loss audit.)
  6. The compliance date is April 2029, but in May 2026 EPA proposed letting eligible systems apply for two more years, to April 2031. The proposal is not final. A town that blends now and watches its numbers can decide later whether treatment is still needed. (Source: EPA PFAS National Primary Drinking Water Regulation; EPA proposed extension rule, May 2026.)

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

Rubric
Criterion Emerging Developing Proficient Advanced
Use of evidence States a position without evidence from the file Names one piece of evidence but does not say what it shows Names at least two pieces of evidence and explains what each shows about Marchbold's water Names several pieces, explains each, and says which measurement matters most and why
Dilution versus removal Treats blending and carbon as the same kind of fix States that the two plans differ without explaining how Explains that blending spreads the same amount of PFAS while carbon holds it out of the water Explains the difference and applies it to a specific number in the record, such as the one-to-three blend ratio
Rebuttal Does not respond to the other team Responds in general terms without naming evidence Answers a specific opposing point using a named measurement or record Answers more than one opposing point and explains why the team's own evidence carries more weight
Delivery and organization Hard to follow; no clear order Has an order, but transitions are unclear Follows a clear claim, evidence, and conclusion structure within the time limit Clear, well paced, and responsive to the board's questions as well as to the opening arguments

Differentiation

Support

Give these students an evidence card carrying only the two strongest points for their side, printed in larger type with the measurement circled. Provide rebuttal frames such as "The other team said ___, but the fictional lab record shows ___." Allow them to read a written opening rather than speak from notes, and let two students share one speaking role. A drawing helps here: two beakers, one blended and one filtered, with the same starting water.

Extension

Ask a pair to serve as fact-checkers rather than debaters. Their job is to flag any moment a speaker states something the evidence file does not say, and to report at the end which claims went past the record. A second option is to draft the board's written decision, naming the reason for the vote and one condition the board attaches, such as a monitoring schedule.

ELL supports

Pre-teach "blend," "well field," "carbon," "reporting limit," and "parts per trillion" with a labeled drawing of two wells joining at a mixing tank. Provide a bilingual glossary card. Allow students to deliver their part from a written script, and give extra preparation time before the rebuttal round. Accept a labeled drawing as part of a closing statement.

Extensions

Have students look up whether their own state posts PFAS results for local water systems, and report what units the results use and how those units compare with the federal limit. A second option is to sketch the fictional Marchbold system as a flow diagram, with both wells, the mixing point, and the proposed carbon beds, then mark the one spot where a sample would tell the board whether the chosen plan is working.