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Lesson plan Grade 11 Science

Marrow Creek's Forever Chemicals: PFAS Bonds and Treatment Trade-offs

Grade 11 students connect carbon-fluorine bond strength to PFAS persistence, compare fictional well results to the federal limit, and evaluate treatment options.

Objectives

  1. Students will explain why the carbon-fluorine bond makes PFAS chemically persistent.
  2. Students will calculate well results as a percent of the federal maximum contaminant level.
  3. Students will evaluate PFAS treatment options using named trade-off criteria such as cost, safety, and reliability.

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.
Carbon-fluorine bond
The very strong chemical bond between carbon and fluorine atoms in PFAS molecules. It is the reason these chemicals last so long in the environment.
Maximum contaminant level (MCL)
A maximum contaminant level, or MCL, is the highest amount of a certain substance that federal rules allow in drinking water. Water systems test regularly to prove their water stays under each limit.

Also: persistent, adsorption

Teacher overview

PFAS compounds earned the nickname "forever chemicals" because of how they are built at the molecular level, and this lesson starts from that chemistry before moving to the policy questions communities face when PFAS shows up in drinking water. Marrow Creek (a fictional town created for this lesson) has three wells with different PFAS results, giving students a concrete case for applying the federal limit and weighing treatment trade-offs. A common misconception this lesson addresses directly: students often think "trace amounts" of a chemical are automatically safe to ignore, without connecting that assumption to the specific chemistry, the carbon-fluorine bond, that makes PFAS resist the natural breakdown processes that remove most other pollutants over time.

Procedure

Hook (5 min): Write "forever chemicals" on the board and ask students to guess, based on the name alone, what property of these chemicals it might be describing at the molecular level.

Direct instruction (15 min): Explain that PFAS molecules contain many carbon-fluorine bonds, among the strongest single bonds in organic chemistry, which is why PFAS resist the natural chemical and biological breakdown that removes most organic pollutants from soil and water over time. Note common sources (firefighting foam, nonstick and stain-resistant coatings) and that PFAS can persist in the environment and accumulate in the body. Introduce the federal maximum contaminant level: 4.0 parts per trillion each for PFOA and PFOS, set in an April 2024 rule, with compliance required by April 2029. In May 2026 EPA proposed letting eligible systems apply for a two-year exemption, to April 2031. That would not be an automatic extension for every system, the 4.0 ppt limits would not change, and the proposal was not yet final as of September 2026, a sign that the regulation is still actively in motion.

Guided practice (15 min): Present Marrow Creek's three well results (a fictional data set created for this lesson): Well A at 6.4 ppt, Well B at 3.2 ppt, and Well C at 4.8 ppt (each a PFOA result). Work through calculating each well's result as a percent of the 4.0 ppt limit as a class.

Independent practice (10 min): Students rank the three wells by urgency of action and, for the well needing the most urgent response, choose one treatment technology to evaluate first from a provided list (granular activated carbon adsorption, ion exchange, or reverse osmosis), justifying the choice using at least two named criteria: cost, safety, reliability, or environmental impact.

Closure / exit ticket (5 min): Students answer one question on an index card: "Carbon-fluorine bonds resist natural breakdown. Explain in one sentence why that chemistry fact makes PFAS cleanup a longer-term problem than stopping the source alone would solve."

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: 160 percent of the limit. Well A: 6.4 ÷ 4.0 × 100 = 160%.
  2. Answer: 80 percent of the limit. Well B: 3.2 ÷ 4.0 × 100 = 80%.
  3. Answer: 120 percent of the limit. Well C: 4.8 ÷ 4.0 × 100 = 120%.
  4. Exit ticket answer: Answers will vary. A strong answer explains that because carbon-fluorine bonds resist natural breakdown, PFAS already sitting in soil and groundwater will keep re-entering wells for years after a source is shut off, so treatment has to keep running at the wells even after source control begins.

Differentiation

Support (below grade level)

Provide the percent-of-limit formula already set up (result ÷ 4.0 × 100) with Well A worked as a full example, so students only need to substitute Wells B and C. Provide the list of four treatment-evaluation criteria as a printed checklist for independent practice.

Extension (above grade level)

Ask students to research one specific trade-off between granular activated carbon and reverse osmosis for PFAS removal, and to write a short paragraph recommending one for Well A, citing at least two criteria.

ELL supports

Pre-teach "persistent," "bond," and "limit" using a simple diagram comparing a weak bond (breaks apart over time) to a strong carbon-fluorine bond (stays intact). Allow the ranking task in independent practice to be shown as a numbered list with short justification phrases rather than full sentences.