Classroom activity Grade 11 Engineering & Design

Halverstock Campus Cross-Connection Survey Rotation

A grade 11 station rotation where student inspectors survey six campus cross connections and select the minimum adequate backflow prevention assembly for each one.

Grade: Grade 11
Subject: Engineering & Design
Material: Classroom activity
Time: 50 min
Prep: Low prep
Materials: Six printed station cards, one per connection described in the handout, Clipboards or printed survey sheets, one per team, Timer, Drinking straw and a clear glass of water tinted with food coloring, for the opening demonstration

Standards

HS-ETS1-3 NGSS

Evaluate a solution to a complex real-world problem based on prioritized criteria and trade-offs that account for a range of constraints, including cost, safety, reliability, and aesthetics as well as possible social, cultural, and environmental impacts.

How this material aligns: Questions 1 through 5 and question 7 have students weigh hazard severity, the direction backflow could travel, and whether a connection is better eliminated than protected before selecting one assembly, which is the prioritized evaluation this standard describes.

All materials for HS-ETS1-3 →

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: The rotation breaks a whole-campus plumbing protection problem into six separate connection-level problems that each team solves independently, the decomposition this standard describes.

All materials for HS-ETS1-2 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-09-03.

Objectives

Students will classify a cross connection as a high or low degree of hazard.
Students will select the minimum adequate backflow prevention assembly for a given connection.
Students will justify why backpressure protection is required at specific connections.

Vocabulary

Cross-connection: A cross-connection is any place where drinking water pipes are linked to something dirty, like a garden hose left sitting in a bucket of soapy water. If the flow reverses, the dirty water can get sucked in.

Also: backsiphonage, backpressure, reduced pressure principle assembly, air gap

Teacher overview

This is a six-station rotation for a class working in teams of three or four, cast as a cross-connection control survey of a fictional secondary campus. Each station card describes one real connection between the building's drinking-water piping and something else, and each team decides whether the hazard is high or low, whether contamination could travel by backsiphonage or by backpressure, and which assembly from a fixed menu is the minimum adequate protection. The activity mirrors how a utility's cross-connection control program actually works, because inspectors survey a building connection by connection rather than judging the building as a whole. One misconception worth naming before the rotation begins is the belief that backflow can only happen when the city main loses pressure, which leads students to protect only against backsiphonage and to treat any building with steady supply pressure as safe. Boilers, pressure washers, and cooling tower circulating pumps all create pressure higher than the supply, so they push water backward even when the main is perfectly healthy.

Activity Directions

Before class, print the six station cards from the Student Handout and post them at six spread-out spots. Post the assembly menu where every team can see it: air gap, hose-connection vacuum breaker, pressure vacuum breaker, double check valve assembly, and reduced pressure principle assembly.
Open with a five-minute demonstration using a straw and a glass of colored water. Draw water up the straw to show backsiphonage, then blow gently to push water back down to show backpressure. Tell students that the survey menu contains assemblies that stop only one of those two directions.
Divide the class into six teams and assign each team a starting station. Give every team a survey sheet with columns for degree of hazard, direction of backflow, and selected assembly.
Run six rounds of five minutes. In each round a team reads its station card, records its three decisions, and writes one sentence of justification. Ring the timer and rotate teams one station clockwise.
Circulate during the rounds. When a team selects an assembly that stops only backsiphonage at a station with a pump or a boiler, ask them what happens if the downstream pressure rises above the supply pressure rather than correcting them directly.
The rotation ends when every team has visited all six stations, which takes thirty minutes of rotation time.
Bring the class back together and have each team report the station where its answer changed after discussion. Complete the handout questions individually or in pairs during the last ten minutes.
Close with two debrief questions. First, which station is best fixed by removing the connection rather than by installing an assembly, and why is that usually the cheaper answer over twenty years? Second, why does the district inspect and test assemblies every year instead of once at installation?

Halverstock Campus Cross-Connection Survey Rotation — Grade 11 Engineering & Design

Name: ____________________________ Date: ______________

Student Handout

You are working as cross-connection control inspectors for the fictional Oakhelm Water District, surveying the fictional Halverstock Regional High School campus. For each station, record the degree of hazard, the direction of backflow, and your selected assembly on your survey sheet. Then answer the numbered questions.

Assembly menu: air gap, hose-connection vacuum breaker, pressure vacuum breaker, double check valve assembly, reduced pressure principle assembly.

Station cards:

Station 1, athletic field irrigation. The irrigation main serves an injector that adds liquid fertilizer to the irrigation water. The injector pump can raise irrigation-side pressure above the building supply.
Station 2, boiler makeup line. The heating boiler runs a closed loop treated with a corrosion inhibitor and operates at 15 psi. A makeup line refills the loop from the drinking-water piping.
Station 3, fire sprinkler riser. The sprinkler system holds ordinary water with no antifreeze and no chemical additive. Water sits in the sprinkler piping for months at a time.
Station 4, kitchen dishwasher drain. The dishwasher drain hose is presently piped straight into the sanitary drain line with no separation.
Station 5, rooftop cooling tower. A makeup line feeds the tower, a biocide feeder treats the circulating water, and circulating pumps run whenever the chiller runs.
Station 6, greenhouse hose bib. A garden hose runs from a wall hose bib and its open end rests inside a tank of dilute plant nutrient solution.

Which assembly from the menu is the minimum adequate protection for the Station 1 irrigation connection?
Which assembly from the menu is the minimum adequate protection for the Station 2 boiler makeup line?
Which assembly from the menu is the minimum adequate protection for the Station 3 fire sprinkler riser?
Which assembly from the menu is the minimum adequate protection for the Station 5 cooling tower makeup line?
Which assembly from the menu is the minimum adequate protection for the Station 6 greenhouse hose bib?
Name the three stations where the water on the far side of the connection can be pushed back toward the building supply by pressure rather than pulled back by suction.
Which station's cross connection should be eliminated by separation instead of being protected with a testable assembly?
Explain why a pressure vacuum breaker would not give adequate protection on the Station 2 boiler makeup line.
Explain why the Station 3 sprinkler riser is treated as a lower degree of hazard than the Station 5 cooling tower.
Explain why the district tests installed assemblies every year rather than only at installation.

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: A reduced pressure principle assembly.
The fertilizer injector makes this a high degree of hazard because the contaminant is a chemical rather than a nuisance, and the injector pump can create backpressure, so the assembly must stop flow in both directions under continuous pressure.
Answer: A reduced pressure principle assembly.
Boiler treatment chemicals are a health hazard and the boiler operates above atmospheric pressure, so backpressure is the realistic failure path. Only a reduced pressure principle assembly is rated for a high hazard under continuous pressure.
Answer: A double check valve assembly.
Water standing in sprinkler piping is stale and unappealing but is not a health hazard when no antifreeze or additive is present, so this is a low degree of hazard. A double check valve assembly is the standard protection for a low-hazard connection held under continuous pressure.
Answer: A reduced pressure principle assembly.
The biocide makes the tower water a health hazard, and the circulating pumps can raise tower-side pressure above the supply, so the connection needs high-hazard protection against both backsiphonage and backpressure.
Answer: A hose-connection vacuum breaker.
A hose lying in a nutrient tank is a high-hazard connection, yet the hose bib is not under continuous downstream pressure, so a hose-connection vacuum breaker is the minimum adequate device. Keeping the hose end above the rim of the tank removes the connection entirely and is the better long-term fix.
Answer: Stations 1, 2, and 5.
The irrigation injector pump, the boiler, and the cooling tower circulating pumps each generate pressure on the downstream side that can exceed the supply pressure.
Answer: Station 4, the kitchen dishwasher drain.
Piping the drain through an air gap into a floor sink separates the two systems physically, so no assembly is needed and nothing has to be tested each year.
Answer: A pressure vacuum breaker stops only backsiphonage.
It opens to atmosphere when supply pressure drops, which does nothing when the boiler pushes treated water backward at a pressure higher than the supply.
Answer: The sprinkler system contains no added chemical.
Its water is a nuisance rather than a health hazard, while the cooling tower water carries a biocide that would be dangerous to drink, so the two connections sit at different degrees of hazard.
Answer: Assembly check valves and relief valves wear out silently.
A fouled seat or a weak spring gives no outward sign, so annual testing under known pressure is the only way to confirm the assembly still closes when it must.

Differentiation

Support

Give these teams a two-column reference card listing each assembly beside the backflow directions it stops and whether it may sit under continuous pressure. Walk Station 1 through with them as a worked model before the rotation starts so they carry the same three decisions into the remaining fictional stations.

Extension

Ask these students to price the six stations. Have them rank the fictional stations by the twenty-year cost of ownership, counting the purchase, the annual test, and the repair parts, then argue which connection the district should eliminate first on cost grounds rather than hazard grounds.

ELL supports

Provide a labeled diagram for each fictional station showing the supply pipe, the connection, and an arrow for the direction of possible backflow. Post the assembly names with a picture of each and allow students to answer questions 8 through 10 with the sentence frame "This device is not enough because ___."

Extensions

Have students survey a real building they know well, such as their own school or a family workplace, and list every place where drinking-water piping connects to something else. They should classify each connection as high or low hazard without naming any device, then compare their list against the fictional campus survey. As a second step, invite a cross-connection control inspector or a plumbing inspector to review the class list and describe how a real survey report is written and filed with the utility.