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Worksheet Grade 10 Health & Consumer Science

Above the Limit: Reading a Home PFAS Result and a Rule in Motion

A grade 10 consumer worksheet where students compare a fictional home's PFOA and PFOS results to the 4.0 ppt limit and interpret a proposed compliance deadline exemption.

Objectives

  1. Students will compare PFOA and PFOS results to the maximum contaminant level in parts per trillion.
  2. Students will explain why a home result above a limit differs from a utility rule violation during a phase-in.

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.
Point-of-use filter
A small filter at a single faucet, like a pitcher filter or one that attaches to the tap. Certified filters can remove lead or PFAS from the water a family drinks.

Also: compliance deadline

Teacher overview

PFAS are a family of long-lasting chemicals now regulated in drinking water at very low levels, measured in parts per trillion. The federal limit for two of them, PFOA and PFOS, is 4.0 ppt each, and EPA has proposed letting some utilities apply for more time to meet it. This worksheet follows the fictional Nakamura household as they read a private lab result and compare it to the limit, and it asks students to reason about what a result above the limit does and does not mean while the rule is still phasing in.

Above the Limit: Reading a Home PFAS Result and a Rule in Motion — Grade 10 Health & Consumer Science
Name: ____________________________ Date: ______________

Student Worksheet

Use the results below for the fictional Nakamura household in the town of Fernbrook. The readings are invented for this exercise; the 4.0 ppt limit is the real federal maximum contaminant level.

  • PFOA measured 12 ppt.
  • PFOS measured 6 ppt.
  • The maximum contaminant level for PFOA and for PFOS is 4.0 ppt each.
  1. By how many ppt does the PFOA result of 12 ppt exceed the 4.0 ppt limit?
  2. By how many ppt does the PFOS result of 6 ppt exceed the 4.0 ppt limit?
  3. How many times the 4.0 ppt limit is the PFOA result of 12 ppt? Divide to find out.
  4. A certified filter removes at least 90 percent of PFOA. Applied to the 12 ppt result, what is the highest level that could remain?
  5. After that reduction, is the treated PFOA at or below the 4.0 ppt limit, and by how much?
  6. The 2024 rule set the 4.0 ppt limit and an April 2029 compliance deadline. In May 2026 EPA proposed letting eligible utilities apply for an exemption to April 2031; the proposal is not yet final. How many additional years would that exemption give an eligible utility?
  7. Explain why the Nakamura household's 12 ppt home result does not, by itself, mean their utility is breaking the rule right now.
  8. The limit is written in parts per trillion, not parts per million. Explain in your own words how much smaller a part per trillion is.
  9. Based on both results, list two reasonable steps the household could take.

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

Answer Key

All readings below refer to the fictional Nakamura household.

  1. Answer: 8 ppt.
    The PFOA result is 12 ppt and the limit is 4.0 ppt: 12 - 4.0 = 8 ppt above.
  2. Answer: 2 ppt.
    The PFOS result is 6 ppt: 6 - 4.0 = 2 ppt above the limit.
  3. Answer: 3 times.
    Divide the result by the limit: 12 / 4.0 = 3, so PFOA is three times the limit.
  4. Answer: 1.2 ppt.
    Removing at least 90 percent leaves at most 10 percent: 12 x 0.10 = 1.2 ppt remaining.
  5. Answer: 2.8 ppt below.
    The 1.2 ppt treated level is at or below the 4.0 ppt limit, clearing it by 4.0 - 1.2 = 2.8 ppt.
  6. Answer: 2 years.
    An exemption from April 2029 to April 2031 adds 2031 - 2029 = 2 years.
  7. Answer: A home result is not a utility compliance number.
    Utilities are judged against the rule on a schedule that is still phasing in, and by required sampling at set points, so one household's private result does not by itself show a current violation.
  8. Answer: A part per trillion is a million times smaller.
    A part per trillion is one million times smaller than a part per million (and one thousand times smaller than a part per billion), so the PFAS limit flags amounts far tinier than most other drinking-water standards.
  9. Answer: Confirm the result and treat the water.
    Reasonable steps include retesting to confirm the reading and installing a certified filter, such as reverse osmosis or a filter rated for PFAS, for drinking and cooking water.

Differentiation

Support

Provide a number line marked at 4.0 ppt with the two readings placed on it, so students see "above the limit" before subtracting. Model item 1 as a worked example and allow a calculator.

Extension

Ask students to find the smallest whole-number percent removal a filter would need to bring the 12 ppt PFOA result to the 4.0 ppt limit or below, and to show the inequality they solved.

ELL supports

Pre-teach "PFAS," "limit," "parts per trillion," and "compliance deadline" with short definitions and a simple scale comparing a million to a trillion. Allow items 7, 8, and 9 to be answered with short phrases.