Frostmere's Winter Road Decision

Compare snow-clearing plans that could help protect a town's stream.

1. Investigate the Town's Problem

Read the report. Use its observations and science ideas to answer the questions.

A Report for Frostmere's Town Council

Each winter, Frostmere's road crew clears snow from town streets. The crew also spreads road salt to help melt ice. Street drains carry meltwater through pipes to Willow Brook. The town water office explains that road salt dissolves in water and can travel with that water. Too much dissolved salt can harm some freshwater plants and animals. The council wants to compare ways to clear pavement while limiting the salt used.

A plow pushes snow off pavement. A salt spreader drops salt through adjustable openings. Workers can calibrate a spreader by collecting and weighing what it releases over a measured area, then adjusting its settings. Without checks, a spreader may release more salt than workers intend. The road crew proposed three plans. Plan A used salt without plowing first. Plan B used a plow followed by the usual salt treatment. Plan C used a plow followed by a calibrated, lower-salt treatment.

During one storm, trained adults tested the plans on three separate strips in a vehicle-training yard closed to traffic. Each strip covered 100 square meters. The strips had the same pavement, slope, starting snow depth, and temperature. Workers used the same kind of salt and began the treatments at the same time. They changed the clearing plan and recorded the salt applied. The graph shows the amount used per square meter, not the total for each strip.

Workers marked 20 equal squares on each strip. After 30 minutes, they counted squares with completely exposed pavement. Plan A cleared 18 squares. Plans B and C each cleared 20 squares. For this trial, the council's clearing goal was at least 19 clear squares. Its salt-use goal was no more than 20 grams per square meter. Meeting the trial's clearing goal did not prove that a plan would work in every storm.

The trial did not measure salt in Willow Brook or study stream animals. Before making a town-wide decision, the water office proposed more road trials and stream checks through the winter. Workers could collect water above and below a street-drain outlet at the same times. They could measure dissolved salt and observe small stream animals. The council would consider these records along with road-clearing results, rather than judging a plan by salt use alone.

Why should the town water office help evaluate a road-clearing plan?

A. Salt stays on pavement, so only the road crew needs to track it.
B. Salt can leave the road in meltwater and affect life in the brook.
C. Salt becomes harmless as soon as it can no longer be seen.
D. Salt melts snow by changing it into fresh water without salt.

Which choice helped make the comparison of the three plans fair?

A. Giving the lower-salt plan a thinner starting layer of snow
B. Checking each plan after a different amount of time
C. Testing the salt-only plan on a much smaller strip
D. Using equal-sized strips with the same starting conditions

How could plowing before spreading salt help the town reduce its salt use?

A. It takes away snow that otherwise would need to melt.
B. It removes dissolved salt from water already in the brook.
C. It changes road salt into a material that cannot dissolve.
D. It keeps all later meltwater from entering street drains.

Select the two reasons this trial alone cannot show that a plan protects the brook throughout the winter.

The plans were tested during only one storm.The workers used the same kind of salt.The trial did not measure effects in the brook.The workers checked all strips after 30 minutes.

Considering only the goal of at least 19 clear squares after 30 minutes, which plans met that goal?

A. Plans A and B
B. Plans A and C
C. Plans B and C
D. Plans A, B, and C

2. Compare the Test Results

Use the graph and the report together. The bars show salt used on each square meter of pavement.

How many fewer grams of salt per square meter did Plan C use than Plan A? grams per square meter

A council member says, "Plans B and C cleared the same number of squares, so they used resources equally well." Which response best uses the evidence?

A. The member is right because clear-square counts measure salt use.
B. Plan B used less salt because its bar is taller than Plan C's.
C. Neither plan can be compared because both included a plow.
D. Plan C reached the same clearing result while using less salt.

The town wants to learn whether the plans also work during much colder storms. Which next investigation would provide the most useful comparison?

A. Test only Plan C in colder weather and compare it with Plan A's warmer-weather result.
B. Repeat all three plans in colder weather using matched strips and the same checking time.
C. Test Plan A in deep snow and Plan C in shallow snow during the next cold storm.
D. Repeat the graph's salt measurements without checking whether the pavement clears.

Which result from later trials would most strongly show that Plan C needs improvement before wider use?

A. It repeatedly clears only 16 of 20 squares after 30 minutes.
B. It clears all 20 squares in several additional storms.
C. Its spreader continues to deliver 15 grams per square meter.
D. Its collected meltwater contains less dissolved salt than Plan B's.

3. Advise the Community

Judge the plans using both town goals. Support written answers with evidence from the page.

10.

The council wants at least 19 clear squares after 30 minutes and no more than 20 grams of salt per square meter. Which plan met both goals in this trial?

A. Plan A, because its larger salt amount makes up for fewer clear squares
B. Plan B, because clearing every square makes the salt limit unnecessary
C. Plan C, because it cleared every square and stayed below the salt limit
D. No plan, because each one missed at least one of the council's goals

11.

Why would collecting water both above and below the street-drain outlet be more useful than collecting water only below it?

A. It would prove that every bit of salt below the outlet came from that drain.
B. It would help compare water entering the area with water after the drain joins it.
C. It would remove dissolved salt before it could reach small stream animals.
D. It would let the crew stop measuring how much salt it spreads on roads.

12.

The crew wants to find out whether it can use even less salt than Plan C. Describe a fair comparison of Plan C with a lower-salt plan. Name what to change, two things to keep the same, and what to measure to check whether the clearing goal is still met.

13.

Which plan should the council choose for a larger, closely monitored trial? Support your recommendation with a salt-use number and a clearing result. Explain how the plan could help protect the brook, and name one uncertainty the town should investigate.