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Reading passage Grade 7 English Language Arts

The Mussels That Watch the Whitmore Gap Water Intake

A grade 7 informational passage on live-animal biomonitoring at a river water intake, with seven questions mixing stated facts and inference about false alarms.

Objectives

  1. Students will locate stated facts about how a river intake is monitored.
  2. Students will infer why an early-warning system uses living animals as well as instruments.
  3. Students will explain the tradeoff a false alarm creates for plant operators.

Vocabulary

Turbidity
Turbidity is a measure of how cloudy or murky water looks because of tiny particles floating in it. Clear water has low turbidity, and muddy water has high turbidity.

Also: intake, biomonitoring, sensor, false alarm

Teacher overview

This original informational passage describes how a fictional river water plant watches its intake, first with instruments and then with tanks of living mussels and small fish that react to trouble the instruments were not built to find. The text runs about six hundred words and is organized as a problem, a partial solution, and a limit. It pairs well with a class discussion of false alarms, since the passage ends on a decision the plant staff have to make without complete information.

The Mussels That Watch the Whitmore Gap Water Intake — Grade 7 English Language Arts
Name: ____________________________ Date: ______________

Passage

Watching the Water Before It Comes In

The Whitmore Gap Water Treatment Plant draws from the Sowerby River, in the fictional town of Whitmore Gap, through a pipe that reaches out below the surface. Whatever floats down the river reaches that pipe first. The place where the water enters is called the intake, and everything the plant does afterward depends on what the intake lets in.

Instruments watch the water day and night. One sensor measures turbidity, which is how cloudy the water is. Cloudy water can hide germs and can clog the filters faster, and under federal rules the finished water leaving a conventional plant has to stay at or below 0.3 NTU in most monthly samples, so operators watch the river to learn what the filters will have to handle. Another sensor measures pH. A third measures conductivity, which rises when the water carries more dissolved material, such as road salt after a February storm.

Those instruments are good at what they measure. The trouble is that each one measures only what it was built to measure. A truck could spill a chemical upstream that does not change the cloudiness, the pH, or the conductivity by much. The sensors would report a normal river while something harmful drifted toward the pipe.

So the plant keeps living animals in two tanks fed by river water. One tank holds freshwater mussels. The other holds small fish. Mussels sit with their shells slightly open while they feed, and they close when the water bothers them. Fish swim steadily when they are comfortable, and they change how they move when they are not. Thin sensors track the shells and the fish. A computer records what normal looks like over weeks.

When enough animals react at the same time, the computer raises an alarm. The rule at Whitmore Gap is that several animals must respond together within a short window, because one mussel closing means nothing at all. Any single animal might be resting, sick, or simply old. A group reacting at once is harder to explain away.

An alarm reports that something in the river has changed without identifying what it is, and the next decision belongs to people. An operator can close the intake and run the plant on stored water in the clearwell and the tanks for a few hours. That buys time to sample the river and send the sample to a laboratory. It also uses up the town's reserve, and the reserve is what the town would need if a main broke that same afternoon.

That is the tradeoff the staff live with. Closing the intake for a false alarm costs stored water and staff hours. Not closing it when the alarm was right costs far more. The plant's written procedure says to close first and ask questions after, and the operators keep a log of every alarm, the action taken, and what the laboratory found.

Most alarms turn out to be nothing serious, since warm weather can make the mussels sluggish and a power flicker can unsettle the fish. Over three years, the Whitmore Gap log recorded fourteen alarms and one real event, a fuel spill from an overturned tanker upstream. The intake closed eleven minutes after the alarm, and the spill passed the pipe while the valve was shut.

The staff do not describe the animals as a replacement for the instruments. They describe them as a second kind of attention, since the sensors report on the properties someone thought to measure, while the mussels and the fish react to conditions no one predicted.

Questions

  1. According to the passage, what three properties do the instruments at the intake measure?
  2. What do the mussels do when the water bothers them?
  3. Why does the plant require several animals to react before an alarm is raised?
  4. Explain why instruments alone might miss a chemical spill upstream. Use a detail from the passage.
  5. What does an operator give up by closing the intake? Cite the paragraph that explains it.
  6. The plant's procedure says to close the intake first and ask questions after. Explain why the staff chose that rule, using the tradeoff described in the passage.
  7. The passage ends by calling the animals a second kind of attention. Explain what that phrase means, using two details from the text.

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: Turbidity, pH, and conductivity.
    The second paragraph names all three and explains what each one shows.
  2. Answer: They close their shells.
    The fourth paragraph states that mussels sit with shells slightly open while feeding and close when the water bothers them.
  3. Answer: Because one animal might be resting, sick, or old, so a single reaction means nothing.
    The fifth paragraph explains that a group reacting at once is harder to explain away.
  4. Answer: A spilled chemical may not change cloudiness, pH, or conductivity enough for the sensors to notice.
    The third paragraph states that each instrument measures only what it was built to measure.
  5. Answer: Stored water from the clearwell and tanks, along with staff time.
    The paragraph about closing the intake explains that the reserve is what the town would need if a main broke the same day.
  6. Answer: Being wrong about a real event costs far more than being wrong about a false alarm.
    Accept any answer that weighs the small cost of stored water against the larger risk of letting contaminated water into the plant.
  7. Answer: The animals notice trouble the instruments were never designed to detect.
    Strong answers pair the statement that instruments measure only what they were built to measure with the mussel and fish behavior that changes for reasons no one predicted.

Differentiation

Support

Read the passage aloud in two parts, stopping after the paragraph about the instruments to ask what problem is coming. Give students a copy with the four ideas labeled in the margin as instruments, animals, alarm rule, and tradeoff, and reduce the set to questions 1 through 5.

Extension

Ask students to write the entry an operator would put in the log after the fuel spill, including what was observed, what action was taken, and what the laboratory later confirmed. A second option asks students to argue whether fourteen alarms with one real event is a good record, and to say what other information they would need.

ELL supports

Pre-teach "intake," "sensor," and "alarm" with a simple left-to-right sketch of the river, the pipe, the tanks, and the plant. Show a photograph of a freshwater mussel with its shell slightly open. Allow questions 1 and 2 to be answered with single words or phrases, and provide the frame "The animals help because ___" for question 7.

Extensions

Students research one other early-warning system that uses living things, such as canaries once used in mines, then write a short paragraph comparing what the living detector notices with what an instrument notices, using the passage as one of their two sources.