Writing prompt Grade 11 English Language Arts
Explaining a PFAS Detection to Northbrook: An Explanatory Prompt
A grade 11 explanatory writing prompt: turn a fictional town's PFAS well results and treatment options into a plain-language explainer for residents.
Objectives
- Students will explain a contaminant detection accurately without overstating or minimizing what the results show.
- Students will organize an explanatory text so a reader can find the answer to a practical question quickly.
- Students will represent a regulation that is still changing without treating a proposal as settled law.
Vocabulary
- 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.
Also: blending, nondetect, compliance deadline
Teacher overview
Explanatory writing is hardest when the honest answer includes uncertainty, and a contaminant detection is that kind of subject, because the results are measured, the federal rule is still being revised, and residents want to know whether they should be concerned. This prompt gives students the well results, the current federal standard, and the treatment options facing the fictional town of Northbrook, and asks for a one-page explainer written for residents. Students frequently reach for reassurance or for alarm rather than for organization, so the rubric scores whether a reader could find, in order, what was measured, what the rule requires, and what happens next.
Prompt
Background: the fictional Northbrook Municipal Water system
Northbrook is a fictional town of 21,000 people that draws its drinking water from four wells. In the spring the utility sampled each well for per- and polyfluoroalkyl substances, a family of manufactured compounds usually shortened to PFAS. Two of the compounds in that family, PFOA and PFOS, are regulated in drinking water.
What the federal rule says
The maximum contaminant level for PFOA and for PFOS is 4.0 parts per trillion each, set in an April 2024 rule, and water systems must comply by April 2029. That rule is not finished changing. In May 2026 the Environmental Protection Agency proposed letting eligible systems apply for a two-year exemption, to April 2031. The exemption would not be automatic for every system, and the 4.0 limits would not change. A proposal is not a final rule, and this one was not final as of September 2026, so any explainer written now has to describe a requirement that exists alongside a proposed change to its timing.
Fictional spring sampling results, Northbrook Municipal Water
| Well | PFOA (parts per trillion) | PFOS (parts per trillion) | Share of town supply |
|---|---|---|---|
| Well 1 | Nondetect | Nondetect | 20 percent |
| Well 2 | 1.4 | Nondetect | 15 percent |
| Well 3 | 2.9 | 1.1 | 25 percent |
| Well 4 | 9.2 | 3.6 | 40 percent |
"Nondetect" means the laboratory found none at the level its method can measure.
Options the utility has described to the town board (fictional estimates)
- Install granular activated carbon treatment on Well 4. The utility estimates $3.4 million to build and about $210,000 a year to replace carbon and monitor.
- Take Well 4 out of service and increase pumping from Wells 1 and 3. This costs little to begin, yet the utility says the remaining wells cannot meet peak summer demand on their own.
- Blend Well 4 with Well 1 before the water enters the distribution system, lowering the combined concentration. The utility estimates $600,000 for the piping and controls, and notes that blending reduces concentration without removing anything.
- Connect to the neighboring Kettleridge regional system. The utility estimates $8.1 million for the transmission main and a purchased-water charge every year afterward.
Your task
Write a one-page explainer, four to six paragraphs, that the fictional Northbrook utility could mail to residents. Explain what was measured and where, what the federal standard is and what is currently proposed about its timing, what the utility's options are, and what a resident should expect next. Write for an adult reader who has no technical background and who wants a straight answer. Use the figures accurately, distinguish clearly between the rule and the proposal, and state plainly anything the results do not tell us.
Planning Organizer
Complete every row before you draft. The rows match the rubric criteria.
| Part of your explainer | What you will write | My notes |
|---|---|---|
| What was measured | The compounds, the wells, and the season, in one sentence. | |
| What the results show | The highest result and how it compares with the standard, stated precisely. | |
| What the standard is | The federal limit and its date, in the reader's words rather than the rule's. | |
| What is proposed | The proposed exemption from the compliance deadline, marked clearly as a proposal. | |
| What the options are | Two options with one advantage and one drawback each. | |
| What we do not know | One thing the sampling does not answer. | |
| What happens next | The concrete next step and when a reader will hear about it. |
Check two things before you draft.
- Every sentence in the "what we do not know" row should be something the background actually leaves open, not a general statement that science is uncertain.
- Your options row should include a drawback for each option, since an explainer that lists only advantages reads as persuasion rather than explanation.
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Exemplar & Rubric
Exemplar response (grade 11 level)
This spring the fictional Northbrook Municipal Water utility tested all four of its wells for PFOA and PFOS, two manufactured compounds in the PFAS family that are regulated in drinking water. Well 1 showed no detection of either compound. Well 2 showed 1.4 parts per trillion of PFOA. Well 3 showed 2.9 of PFOA and 1.1 of PFOS. Well 4, which supplies 40 percent of the town's water, showed 9.2 parts per trillion of PFOA and 3.6 of PFOS.
The federal maximum contaminant level for PFOA is 4.0 parts per trillion, and the level for PFOS is also 4.0. Well 4 is above the limit for PFOA and just below it for PFOS, and Wells 1, 2, and 3 are below the limit for both compounds. The limit was set in an April 2024 rule, and water systems must meet it by April 2029. The timing of that rule is currently under review: in May 2026 the Environmental Protection Agency proposed letting eligible water systems apply for a two-year exemption, to April 2031, without changing the limits themselves. That is a proposal rather than a final decision, and even if it is adopted, a system would have to apply and qualify, so residents should not assume Northbrook has until 2031.
Northbrook has four options, and none of them is free. Treating Well 4 with granular activated carbon would remove the compounds at the source; the utility estimates $3.4 million to build the system and about $210,000 a year to run it. Blending Well 4 with Well 1 would cost roughly $600,000 and lower the concentration reaching homes, though blending reduces a concentration rather than removing a compound. Taking Well 4 out of service costs almost nothing at first, yet the utility reports that the remaining wells cannot meet peak summer demand. Connecting to the neighboring Kettleridge system would cost about $8.1 million plus an annual charge for purchased water.
There are things this sampling does not tell us. It covers one season, so it does not show whether concentrations rise or fall through the year, and it does not identify where the compounds came from. It also does not describe any health effect for any individual person, because a drinking-water standard is written for long-term exposure across a population rather than for a single household.
The board expects to choose an option this fall, and the utility will sample all four wells again in the summer. Residents will receive the next round of results by mail, and the board's meeting date will be posted at the town office and on the utility's website. Anyone with questions before then can call the utility during business hours.
Rubric
| Criterion | Emerging | Developing | Proficient | Advanced |
|---|---|---|---|---|
| Accuracy of results | Misstates a value or compares a result with the wrong standard. | States the highest result correctly but reports the others loosely. | Reports the results accurately and compares them with the standard correctly. | Reports results accurately, compares them correctly, and notes which wells are below the limit as well as which are above. |
| Handling the regulation | Treats the proposed exemption as settled or as automatic for every system, or omits the standard. | States the standard but blurs the line between the rule and the proposal. | States the standard and identifies the two-year exemption explicitly as a proposal. | Does both and explains why the distinction matters to a reader deciding whether to act now. |
| Organization for the reader | Information appears in no usable order. | Order is mostly sequential but a reader must hunt for the practical answer. | Sections follow the reader's questions, and each paragraph has one job. | Order itself answers the reader's questions in the order they would ask them, with transitions that carry the logic. |
| Completeness and candor | Omits options or omits limits, and reassures without support. | Lists options but gives no drawbacks, or names no limits of the data. | Presents options with drawbacks and states at least one thing the data do not show. | Presents options with drawbacks, states the limits of the data precisely, and closes with a concrete next step and date. |
Differentiation
Support
Give these students the organizer with the "What was measured" and "What the standard is" rows completed, and reduce the explainer to four paragraphs. Provide a comparison frame for the results paragraph, such as "Well ___ measured ___ parts per trillion, which is ___ the limit of 4.0." Allow the options paragraph to be written as a labeled list before it is turned into prose.
Extension
Ask students to write the same information twice more: as a 300-character text alert and as a two-sentence script for the utility's phone recording. They then write a short reflection naming what each format forces them to drop, and argue which of the three versions a resident is most likely to act on.
ELL supports
Pre-teach nondetect, parts per trillion, blending, and compliance deadline with a labeled diagram of four wells feeding one pipe into a town, and post the terms with one-line definitions. Provide the organizer with sentence frames in every row. Allow students to explain the results table orally to a partner before writing, and permit the "what we do not know" row to be written as a question rather than a statement.
Extensions
Have students compare their explainer with a genuine consumer confidence report from a nearby utility, which most systems publish each year, and mark three places where the official document assumes knowledge their explainer supplies. A second option is a short revision exercise in which students rewrite their own opening paragraph for a different reader, such as a landlord with twelve tenants or a restaurant owner, and note in two sentences what changed and why.