Classroom activity Grade 9 Science

Wickhollow Main Break: A Valve Isolation Simulation

A 45-minute grade 9 activity where crews of students isolate a break on a fictional water main, count customers cut off, and size the flushing and disinfection work.

Grade: Grade 9
Subject: Science
Material: Classroom activity
Time: 45 min
Prep: Moderate prep
Materials: Printed Student Handout, one per student, One sheet of chart paper or 11-by-17-inch paper per crew for the map sketch, Calculators, Eight index cards per crew to mark valves

Standards

HS-ETS1-2 NGSS

Design a solution to a complex real-world problem by breaking it down into smaller, more manageable problems that can be solved through engineering.

How this material aligns: Crews handle the restoration of service as four smaller problems, isolating the broken segment, repairing it, disinfecting and flushing it, and returning it to service, and they solve the quantitative piece of each, which is the decomposition of a complex problem this standard describes.

All materials for HS-ETS1-2 →

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 inches to feet, cubic feet to gallons, and gallons to million gallons through the pipe volume and chlorine dosing steps, choosing units consistently.

All materials for HSN-Q.A.1 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-10-12.

Objectives

Students will choose a valve closure plan and count the service connections it takes out.
Students will calculate the volume of an isolated main and the chlorine needed to disinfect it.
Students will convert a tank height to pressure and compare it with a minimum pressure.

Vocabulary

Key words: distribution main, isolation valve, service connection, flushing, chlorine dose, head

Teacher overview

When a water main breaks, a utility crew has to solve four problems in order: stop the water, get the broken pipe out of service, disinfect the repair, and put the main back without sending dirty water to customers. This activity puts crews of three or four students on a fictional street grid in the fictional town of Wickhollow, where a break has opened on one segment and two different valve plans would both stop it. Every choice the crews make has a number attached, so the debrief compares plans on customers affected rather than on preference. The activity mirrors the real decision, because closing a valve is the only way to isolate a pipe, and each valve closed puts more people out of water.

Activity Directions

1. Setup and map sketch (7 min). Form crews of three or four. Give each student the Student Handout and give each crew a sheet of chart paper and eight index cards labeled Valve 1 through Valve 8. Crews use the loop layout table in the handout to sketch the north loop as a rectangle: the supply tee at the northwest corner, the eight valves in order clockwise around the rectangle, and each of the seven segments labeled with its letter, length, and number of service connections. Crews then place the valve cards face up on their sketch and flip a card face down to show a closed valve. Read the situation aloud: a fictional break has opened on Segment C of the north loop, water is surfacing in the street, and the crew has to isolate it.

2. Round one, choose an isolation plan (10 min). Each crew studies its map sketch and picks one of the two plans printed in the Student Handout. Plan A closes Valve 4 and Valve 5, which isolates Segment C alone. Plan B closes Valve 3 and Valve 6, which isolates Segments B, C, and D together. Tell crews that the fictional utility's records show Valve 4 has not been operated in twelve years and sits under a repaved section of street, so it may not seat fully. Crews flip the cards for the valves they close and write one sentence saying why they chose that plan.

3. Round two, crew calculations (15 min). Crews complete items 1 through 8 in the Student Handout, dividing the work so that two students handle the volume and chlorine items while the others handle the pressure and customer items, then check each other. Circulate and watch for two common errors: leaving the pipe diameter in inches inside the volume formula, and forgetting to convert gallons to million gallons before using the pounds formula.

4. Round three, order of restoration (6 min). Each crew writes the four steps of returning the main to service in the correct order: isolate the segment, drain and repair the pipe, disinfect and flush, then reopen the valves slowly and confirm pressure. Crews that finish early explain why reopening a valve quickly can stir up sediment and cause dirty water complaints across the neighborhood.

5. Debrief (7 min). The activity ends when every crew has posted its plan choice and its answer to item 7. Ask two questions. First: Plan B takes many more customers out of service, so why would a crew ever choose it? Second: if the fictional utility exercised its valves once a year, which of these two plans would become the obvious choice, and why? Close by naming valve exercising as the routine maintenance that determines how much of the system a crew has to shut down during the next break.

Wickhollow Main Break: A Valve Isolation Simulation — Grade 9 Science

Name: ____________________________ Date: ______________

Student Handout

The Wickhollow north loop. In this fictional town, the north loop is an 8-inch water main that runs in a rectangle around a group of four blocks, bounded by Ferris Street on the north, Kettle Avenue on the east, Mill Street on the south, and Ash Avenue on the west. A 12-inch supply main from the Wickhollow tank joins the loop at a tee at the corner of Ferris Street and Ash Avenue. The supply main has its own valve, which stays open during this activity.

Valves 1 through 8 divide the loop into seven segments. Valve 1 and Valve 8 sit on either side of the tee, so no pipe and no customers lie between them. Each segment has its own service connections, which are the pipes running to individual homes and businesses. The table lists the loop in order, going clockwise from the tee.

Segment	Between valves	Street	Length	Service connections
G	Valve 1 and Valve 2	Ferris Street	760 feet	21
A	Valve 2 and Valve 3	Ferris Street, ending at the Kettle Avenue corner	640 feet	19
B	Valve 3 and Valve 4	Kettle Avenue	720 feet	24
C	Valve 4 and Valve 5	Kettle Avenue around the corner onto Mill Street	900 feet	38
D	Valve 5 and Valve 6	Mill Street	810 feet	31
E	Valve 6 and Valve 7	Mill Street around the corner onto Ash Avenue	560 feet	17
F	Valve 7 and Valve 8	Ash Avenue, back to the tee	650 feet	26

Sketching the map. Draw a large rectangle with Ferris Street along the top. Mark the tee at the top left corner, then mark Valve 1 just to the right of the tee and Valve 8 just below it. Working clockwise from Valve 1, mark Valves 2 through 7 so that the segments fall in the order shown in the table, and label each segment with its letter, length, and service connections.

How water moves in the loop. Water enters the loop only at the tee and can travel around the rectangle in either direction. When a crew closes two valves, the segments between them lose water, while every other segment still has an open path back to the tee and stays in service.

The break is on Segment C. Plan A closes Valve 4 and Valve 5. Plan B closes Valve 3 and Valve 6.

Use these tools. Pipe volume in cubic feet equals 0.785 times the diameter in feet squared times the length in feet. One cubic foot holds 7.48 gallons. Pounds of chemical equals concentration in mg/L times volume in million gallons times 8.34. One foot of water height equals 0.433 psi. The 8-inch main has a diameter of 0.667 feet. Round volumes in gallons to the nearest gallon, chemical weights to two decimal places, and all other answers to one decimal place.

Find the volume of Segment C in gallons, using a diameter of 0.667 feet and a length of 900 feet.
After the repair, the crew fills Segment C with water dosed at 25 mg/L of chlorine. Using your answer to item 1, how many pounds of chlorine does that take?
The water level in the fictional Wickhollow tank stands 62 feet above the low point of the north loop. What is the pressure at that low point, in psi?
Most states require at least 20 psi in the distribution system. How many psi above that minimum is the low point of the loop?
How many service connections lose water under Plan A?
How many service connections lose water under Plan B?
How many more service connections lose water under Plan B than under Plan A?
To flush the repaired segment, the crew moves three pipe volumes through a hydrant at 350 gpm. Using your answer to item 1, how many minutes does the flushing take?

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

Answer Key

Answer: 2351 gallons. Volume equals 0.785 times 0.667 squared times 900, which is 0.785 times 0.444889 times 900, or about 314.3 cubic feet. Multiply by 7.48 gallons per cubic foot to get about 2,351 gallons.
Answer: 0.49 pounds. Convert 2,351 gallons to 0.002351 million gallons, then apply the pounds formula: 25 times 0.002351 times 8.34 equals about 0.49 pounds of chlorine.
Answer: 26.8 psi. Multiply the height of water above the point by 0.433 psi per foot: 62 times 0.433 equals 26.846, or about 26.8 psi.
Answer: 6.8 psi. Subtract the minimum from the calculated pressure: 26.8 minus 20 equals 6.8 psi of margin above the minimum.
Answer: 38 connections. Plan A isolates Segment C alone, and Segment C carries 38 service connections.
Answer: 93 connections. Plan B isolates Segments B, C, and D together, so 24 plus 38 plus 31 equals 93 service connections.
Answer: 55 connections. Subtract the Plan A total from the Plan B total: 93 minus 38 equals 55 additional connections out of service.
Answer: 20.2 minutes. Three pipe volumes is 3 times 2,351, or 7,053 gallons, and 7,053 divided by 350 gallons per minute is about 20.2 minutes.

Differentiation

Support

Give these crews the diameter already squared and the cubic-foot volume already computed for item 1, so the work begins at the conversion to gallons. Provide a unit checklist that names the required unit for each step: feet, cubic feet, gallons, million gallons, pounds. Assign these crews the customer-count items first so they begin with a successful result.

Extension

Ask these crews to find the segment of the fictional loop where a break would take the fewest customers out of service, name the two valves they would close, and justify the answer with the connection counts in the table. The expected answer is Segment E, isolated by closing Valve 6 and Valve 7, which takes 17 connections out of service; Segment A, with 19, is next. They can also calculate the pounds of chlorine that Plan B's longer isolated length would require if all three segments had to be disinfected, using the same 8-inch diameter and 25 mg/L dose. Segments B, C, and D total 2,430 feet, which holds about 848.6 cubic feet, or 6,348 gallons, so the dose takes 25 times 0.006348 times 8.34, or about 1.32 pounds of chlorine.

ELL supports

Pre-teach "valve," "isolate," "service connection," "flush," and "dose" by walking crews through the map and pointing to each feature before the first round. Provide a picture glossary card at each seat, and give a sentence frame for the round one justification: "Our crew closed Valve ___ and Valve ___ because ___."

Extensions

Have crews redesign the fictional north loop by adding two more valves anywhere they choose, then recalculate how many service connections a break on the longest segment would take out under their new layout. Ask each crew to state the trade-off in one sentence, since every added valve is another piece of equipment the utility has to buy, find, and exercise every year.