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Classroom activity Grade 10 Science

Ferrowdale Main Break: An Operations Tabletop

A 55-minute grade 10 tabletop exercise where student crews isolate a broken water main in timed rounds and calculate lost water, tank drawdown, and zone pressure.

Objectives

  1. Students will identify which valves isolate a broken main segment and count the customers affected.
  2. Students will calculate water lost from a break and from tank storage during an outage.
  3. Students will explain the sampling step required before a repaired main returns to service.

Vocabulary

Pressure zone
A pressure zone is a section of a water system that a utility manages separately because it sits at a different elevation than the rest of the town. Utilities create pressure zones so that water pressure stays safe and steady for everyone, whether they live at the bottom of a hill or near the top.
Boil water advisory
A public notice telling people to boil tap water before drinking it because germs may have entered the pipes, often after a main break or a loss of pressure.

Also: isolation valve, flushing, bacteriological sample

Teacher overview

A crew responding to a broken water main works under time pressure, and several of its decisions depend on arithmetic done on the spot. The crew decides which valves to close, counts how many customers that choice puts out of water, and estimates how long the storage tank can hold pressure. This tabletop exercise runs in three timed rounds for teams of four, with each student holding one role in the fictional Ferrowdale Water Department. Teams work the same numbers a night shift would work, and the exercise ends with the sampling step that determines when the neighborhood gets its water back.

Activity Directions

  1. Before class, print one handout per student and one set of four role cards per team. Every place, valve, and figure in this exercise is invented for the fictional Ferrowdale system.
  2. Briefing (8 min): Assign roles within each team of four: shift operator at the control desk, distribution supervisor, crew lead in the field, and public information officer. Explain that a pressure zone is a section of the system whose pressure is set by the water level in one tank, so the pressure at each service depends on its elevation, that closing valves isolates a segment, and that pressure below roughly 20 psi can let contamination enter a pipe. Point students to the segment table on the handout.
  3. Round 1, the call (10 min): Read the scene aloud. At 2:10 a.m. the fictional Ferrowdale control desk sees the Elm Zone tank dropping fast, and a resident reports water crossing Alder Street. The break is on Segment C. Teams decide which valves to close and answer handout items 1 and 2. The shift operator reports the decision aloud to you before the timer sounds.
  4. Round 2, the complication (10 min): Announce that valve V4 will not seat and cannot be closed, so the crew must close V5 instead. Teams answer handout items 3 and 4 and decide whether to notify the elementary school, which opens at 7 a.m. The public information officer drafts a two-sentence notice.
  5. Round 3, return to service (12 min): Announce that the repair is complete at 6:40 a.m. Teams answer handout items 5 through 8, then decide in what order to flush, sample, and reopen valves. The crew lead reads the team's order aloud.
  6. Debrief (15 min): Collect the handouts and discuss two questions with the whole class. First, which Round 2 decision affected the most customers, and how would the team justify it to a resident? Second, why does the utility hold the segment out of service until a laboratory result comes back, even when the water looks clear? Close by asking each team to name the role they found hardest.
Ferrowdale Main Break: An Operations Tabletop — Grade 10 Science
Name: ____________________________ Date: ______________

Student Handout

Suppose you are on the night shift for the fictional Ferrowdale Water Department. Every valve, customer count, and figure below is invented for this exercise. Use 0.433 psi per foot of water and 7.48 gallons per cubic foot. Cylinder volume equals 0.785 x diameter squared x depth.

Segment Valves that isolate it Customers served
A V1 and V2 120
B V2 and V3 85
C V3 and V4 210
D V4 and V5 60
E V5 and V6 145
  1. The break is on Segment C. Using the table, name the two valves the crew must close to isolate it.
  2. Using the table, state how many customers lose water when Segment C alone is isolated.
  3. Valve V4 will not seat, so the crew closes V5 instead of V4. Using the table, state how many customers lose water when Segments C and D are both isolated.
  4. The break flowed at 350 gpm for 3 hours and 30 minutes before the crew isolated it. Calculate the volume lost, in gallons.
  5. The Elm Zone tank is a cylinder 60 feet in diameter, and its water level fell 4.0 feet during the break. Calculate the volume that left storage, in gallons.
  6. Calculate the pressure at the highest service in the Elm Zone when the tank's water surface stands 134 feet above that service.
  7. After the repair the crew flushes the segment at 900 gpm for 25 minutes. Calculate the volume of water used for flushing, in gallons.
  8. Explain why the crew collects a bacteriological sample before returning Segment C to service, even when the flushed water runs clear.

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: V3 and V4. The table lists V3 and V4 as the valves that isolate Segment C.
  2. Answer: 210 customers. The table lists 210 customers served by Segment C.
  3. Answer: 270 customers. Closing V3 and V5 isolates Segment C and Segment D together, and 210 + 60 = 270 customers.
  4. Answer: 73,500 gallons. Three hours and thirty minutes is 210 minutes, and 350 gpm x 210 minutes = 73,500 gallons.
  5. Answer: 84,554 gallons. Volume = 0.785 x 60 x 60 x 4.0 = 11,304 cubic feet, and 11,304 x 7.48 = 84,554 gallons.
  6. Answer: 58.0 psi. Pressure = 134 feet x 0.433 psi per foot = 58.0 psi.
  7. Answer: 22,500 gallons. Flushing volume = 900 gpm x 25 minutes = 22,500 gallons.
  8. Answer: Clear water is not proof of safe water. While the main was open and depressurized, soil and standing water around the trench could have entered the pipe, and the bacteria that matter are far too small to see. The sample tests for indicator organisms that would show that contamination reached the pipe, and the laboratory result is the only evidence the utility can give the health department that the repair is safe to put back in service.

Differentiation

Support

Give these students a printed copy of the segment table with the break location already circled, and work item 1 with them before Round 1 begins. Provide the three formulas they will need on a card and allow a calculator throughout.

Extension

Ask teams to redesign the Elm Zone valve layout so that a break in the middle of Segment C would take fewer customers out of service, and to explain what the utility would have to spend to make that change. Have them name one drawback of adding more valves.

ELL supports

Pre-teach "valve," "isolate," "segment," and "flush" with a simple line diagram showing the six valves and five segments before the briefing. Provide the sentence frame "We closed valve ___ and valve ___ because ___," and allow teams to discuss in their home languages during the rounds.