Worksheet Grade 9 Health & Consumer Science

The Renslow Well PFAS Report: A Parts-per-Trillion Worksheet

Grade 9 consumer-health worksheet reading a fictional well's PFAS results against the 4.0 ppt limit, with percent-of-limit and trace-concentration math.

Grade: Grade 9
Subject: Health & Consumer Science
Material: Worksheet
Time: 35 min
Prep: No prep
Materials: None

Standards

HSN-Q.A.1 Common Core Math

Use units as a way to understand problems and to guide the solution of multi-step problems; choose and interpret units consistently in formulas; choose and interpret the scale and the origin in graphs and data displays.

How this material aligns: Students carry parts-per-trillion values through comparisons to the limit and a nanogram-per-liter conversion, keeping the trace-concentration units consistent from the lab report to the daily intake.

All materials for HSN-Q.A.1 →

HSN-Q.A.3 Common Core Math

Choose a level of accuracy appropriate to limitations on measurement when reporting quantities.

How this material aligns: Items 3, 4, and 8 ask students to round percent-of-limit and post-treatment results to a whole percent or a hundredth of a ppt.

All materials for HSN-Q.A.3 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-23.

Objectives

Students will compare PFAS test results to a maximum contaminant level in parts per trillion.
Students will interpret a percent of the limit and a removal rate to judge whether treated water meets the standard.

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.
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.
Reverse osmosis: Reverse osmosis cleans water by pushing it through a membrane with holes so tiny that salt and most other dissolved things cannot fit through. It can even turn seawater into fresh water.

Also: part per trillion

Teacher overview

PFAS are a group of long-lasting chemicals now regulated in drinking water, and their limits are set in parts per trillion, a very small unit that can be hard to picture. The federal maximum contaminant level for PFOA and for PFOS is 4.0 ppt each. This worksheet has students read a fictional test report from the Renslow family's private well, compare each result to the limit, and check whether a home treatment system would bring the water into range. Apart from the 4.0 ppt limit and the rule dates, every number comes from the fictional figures stated in the items.

The Renslow Well PFAS Report: A Parts-per-Trillion Worksheet — Grade 9 Health & Consumer Science

Name: ____________________________ Date: ______________

Student Worksheet

Suppose the Renslow family tested their private well. The fictional lab report showed PFOA at 6.2 ppt and PFOS at 3.5 ppt. The federal limit for each of these chemicals is 4.0 ppt. Show your work.

The PFOA result was 6.2 ppt and the limit is 4.0 ppt. How many ppt above the limit is the PFOA result?
The PFOS result was 3.5 ppt, with the same 4.0 ppt limit. How many ppt below the limit is the PFOS result?
What percent of the 4.0 ppt limit is the 6.2 ppt PFOA result? Round to the nearest whole percent.
What percent of the 4.0 ppt limit is the 3.5 ppt PFOS result? Round to the nearest whole percent.
Which chemical, PFOA or PFOS, tested above its limit in the Renslow well?
Chemists often write 1 ppt as 1 nanogram per liter. How many nanograms of PFOA are in 1 liter of the well water at 6.2 ppt?
The family drinks 2 liters of this water per day. How many nanograms of PFOA does that add up to in one day?
A reverse-osmosis system is rated to remove 95 percent of PFOA. Starting from 6.2 ppt, how many ppt of PFOA would remain after treatment? Round to the nearest hundredth.
Is the treated result from item 8 below the 4.0 ppt limit, and by how many ppt?
EPA set these limits in 2024 and gave public water systems until 2029 to meet them. In 2026 EPA proposed letting eligible systems apply for an exemption to 2031, and that proposal is not yet final. Federal limits apply to public water systems, not private wells. Explain what this means for the Renslows as they decide whether to treat their well water now.

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

Answer Key

The Renslow well results below are fictional figures built into the scenario.

Answer: 2.2 ppt. 6.2 ppt minus the 4.0 ppt limit equals 2.2 ppt above the limit.
Answer: 0.5 ppt. 4.0 ppt minus the 3.5 ppt result equals 0.5 ppt below the limit.
Answer: 155 percent. 6.2 divided by 4.0 is 1.55, which is 155 percent of the limit.
Answer: 88 percent. 3.5 divided by 4.0 is 0.875, which rounds to 88 percent of the limit.
Answer: PFOA. Its 6.2 ppt result is above the 4.0 ppt limit, while the 3.5 ppt PFOS result is below it.
Answer: 6.2 nanograms. Since 1 ppt equals 1 nanogram per liter, 6.2 ppt equals 6.2 nanograms in 1 liter.
Answer: 12.4 nanograms. 6.2 nanograms per liter times 2 liters equals 12.4 nanograms per day.
Answer: 0.31 ppt. Removing 95 percent leaves 5 percent, and 6.2 times 0.05 equals 0.31 ppt remaining.
Answer: Below, by 3.69 ppt. The treated 0.31 ppt is under the 4.0 ppt limit, and 4.0 minus 0.31 equals 3.69 ppt.
Answer: No federal deadline applies to a private well, so the Renslows are responsible for testing and treating their own water. The 4.0 ppt limit is still a useful health benchmark, and because their PFOA result is above it, treating now is the safer choice however the public-system deadline changes.

Differentiation

Support

Provide a number line marked in ppt from zero to ten, with the 4.0 ppt limit drawn as a bold line, and have students plot the two results on it before answering items 1 and 2. Allow calculators for the percent items.

Extension

Ask students to find the removal rate a filter would need so that the fictional 6.2 ppt PFOA result lands exactly at the 4.0 ppt limit, and explain why a family would want a margin below the limit rather than exactly at it.

ELL supports

Pre-teach "part per trillion," "limit," and "remove" with a simple visual of a large tank and a single drop. Provide a sentence frame for item 5: "The chemical above its limit is ___ because its result of ___ ppt is more than 4.0 ppt."