Lesson plan Grade 10 Science
Fernvale's PFAS Wells: Evaluating an Advanced Treatment Solution
A grade 10 lesson where students compare well test results to the federal PFAS limit and evaluate a proposed carbon-filter treatment upgrade.
Objectives
- Students will compare PFAS test results to the federal maximum contaminant level to determine compliance.
- Students will apply a stated treatment removal rate to calculate a treated-water contaminant concentration.
- Students will evaluate a proposed advanced treatment technology by naming at least one trade-off it involves.
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.
- 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.
- Granular activated carbon
- Small black grains of specially treated carbon that grab contaminants as water flows through them. Utilities use big tanks of it to remove PFAS, bad tastes, and odors.
Teacher overview
Fernvale (a fictional town used for this lesson) recently found PFAS, a group of manufactured chemicals that persist in the environment, above the federal limit in two of its four water supply wells. This lesson has students compare well test results to the federal maximum contaminant level (MCL) for PFOA and PFOS, then evaluate a proposed treatment upgrade using granular activated carbon (GAC), a technology that adsorbs PFAS molecules onto carbon particles. A common misconception is that the legal limit marks a sharp line between safe and unsafe water; EPA's health-based goal for PFOA and PFOS is zero, and the 4.0 parts per trillion limit is set near the lowest level laboratories can reliably measure, so this lesson helps students reason carefully about that scale.
Procedure
Hook (5 min): Write "4.0 parts per trillion" on the board and ask students to estimate, using only place value, how small that concentration is compared to 4.0 parts per million or 4.0 parts per thousand. Discuss briefly.
Direct instruction (15 min): Explain what PFAS are, why they are called persistent chemicals that break down very slowly in the environment, and that the federal MCL for PFOA and PFOS is 4.0 parts per trillion each, with water systems required to comply by April 2029. Add that in May 2026 EPA proposed letting eligible systems apply for a two-year exemption, to April 2031, which would not change the 4.0 ppt limit; the proposal was not final as of September 2026. Introduce granular activated carbon (GAC) filtration as one proven technology for removing PFAS from water, in which PFAS molecules stick to the surface of activated carbon particles as water passes through a filter bed.
Guided practice (15 min): Present a table of PFOA test results, in parts per trillion, from four wells in the fictional town of Fernvale:
| Well | PFOA (ppt) |
|---|---|
| Well 1 | 3.1 |
| Well 2 | 6.8 |
| Well 3 | 4.0 |
| Well 4 | 11.4 |
In pairs, students identify which wells exceed the 4.0 ppt MCL and calculate by how many ppt each exceeds it (Question 1).
Independent practice (10 min): For Well 4's raw PFOA level (11.4 ppt), students apply a hypothetical GAC removal rate of 92 percent, used for this lesson, to calculate the treated concentration (Question 2), then state whether the treated water would comply with the MCL.
Closure / exit ticket (5 min): Students answer one question on an index card (Question 3): "Name one trade-off, other than the treatment technology's PFAS removal itself, that a utility must weigh when deciding whether to install a new treatment system like GAC filtration." Collect and scan responses for a reasoned trade-off, such as cost, ongoing carbon replacement, or monitoring, before dismissal.
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Answer Key
- Answer: Wells 2 and 4 exceed the limit.
Well 2 (6.8 ppt) exceeds the 4.0 ppt MCL by 2.8 ppt, and Well 4 (11.4 ppt) exceeds it by 7.4 ppt. Well 3 (4.0 ppt) sits exactly at the limit, and Well 1 (3.1 ppt) is below it. - Answer: about 0.91 ppt; compliant.
11.4 ppt × (1 − 0.92) = 11.4 × 0.08 = 0.912, which rounds to about 0.91 ppt, well below the 4.0 ppt MCL. - Answer: model response.
A reasonable trade-off is ongoing cost: GAC filters must be monitored and their carbon media replaced or regenerated on a schedule once it becomes saturated with PFAS, which adds a recurring expense beyond the initial installation.
Differentiation
Support (below grade level)
Provide the MCL comparison for the fictional town's Well 1 as a fully worked example, showing that 3.1 ppt is below 4.0 ppt and therefore compliant, before students evaluate Wells 2 through 4 on their own, and allow calculators for the removal-rate calculation.
Extension (above grade level)
Ask students to calculate the minimum GAC removal rate that would bring Well 4's water (11.4 ppt) down to exactly half the MCL (2.0 ppt), and explain why a utility might target a level below the legal limit rather than just barely meeting it.
ELL supports
Pre-teach "PFAS," "parts per trillion," and "filtration" with a simple diagram showing water passing through a carbon filter bed and PFAS molecules sticking to the carbon. Allow students to answer the independent-practice question using the diagram and numbers rather than full sentences.