Graphic organizer Grade 10 Engineering & Design
Driftlow Avenue New Main: A Commissioning Sequence Organizer
A grade 10 sequence organizer for putting a fictional new water main into service, pairing each construction step with its acceptance test and its failure path.
Objectives
- Students will sequence the ten steps that take a new water main from excavation to acceptance.
- Students will state the acceptance test and pass criterion that closes out each construction step.
- Students will distinguish steps that protect the pipe from steps that protect public health.
Vocabulary
- Disinfection
- Disinfection is the step that kills or disables germs in water so it is safe to drink. Water plants usually disinfect with chlorine, ultraviolet light, or ozone.
Also: commissioning, thrust restraint, allowable leakage, bacteriological clearance, record drawings
Teacher overview
A new water main is not finished when the last joint is made, because the pipe still has to prove itself against a written specification before any water reaches a customer. This organizer is a ten-step sequence chain, read top to bottom, with a test column and a failure column beside each step. The sequence structure is the point, since every step has an acceptance test that must pass before the next step begins, and a crew that flushes out the chlorinated water before the 24-hour hold is complete has to disinfect the main again. Roughly half of the steps below produce paperwork and test results rather than visible work in the trench.
Organizer
Read the project specification, then complete the three empty columns for every step. Work top to bottom.
Project specification. Driftlow Avenue is a fictional street project. The utility is installing 1,800 feet of new 12-inch main. The specification requires a pressure and leakage test held at 150 psi for two hours, with makeup water at or below the allowable leakage calculated for the length, diameter, and test pressure. Disinfection uses chlorinated water at 25 mg/L free chlorine held for 24 hours, with at least 10 mg/L free chlorine remaining at the end of the hold. Clearance requires two sets of bacteriological samples taken 24 hours apart, both absent for total coliform.
| Step | What the crew does | Why the step exists | Acceptance test and pass criterion | What happens if it fails |
|---|---|---|---|---|
| 1 | Locate and mark existing buried utilities | |||
| 2 | Excavate and place the bedding | |||
| 3 | Lay and join the pipe | |||
| 4 | Install thrust restraint at bends, tees, and valves | |||
| 5 | Backfill partially, leaving joints exposed | |||
| 6 | Run the pressure and leakage test | |||
| 7 | Disinfect the main | |||
| 8 | Dechlorinate and flush | |||
| 9 | Collect bacteriological clearance samples | |||
| 10 | Tie in, turn over valves, and submit record drawings |
Closing prompt. Two steps in this sequence protect public health rather than protecting the pipe. Name them and explain what each one prevents.
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Completed Exemplar
Project specification. The fictional Driftlow Avenue project installs 1,800 feet of 12-inch main under the specification described in the organizer.
| Step | What the crew does | Why the step exists | Acceptance test and pass criterion | What happens if it fails |
|---|---|---|---|---|
| 1 | Locate and mark existing buried utilities | A strike on a gas, electric, or sewer line is dangerous and stops the job | Every utility in the corridor is located and marked before any excavation begins | Work stops until the locate is complete and the marks are verified in the field |
| 2 | Excavate and place the bedding | Pipe supported unevenly cracks under load, even when the pipe itself is sound | Bedding material, depth, and grade are checked at set intervals along the trench | The crew removes and replaces the bedding to grade before any pipe is laid |
| 3 | Lay and join the pipe | A joint that is not fully seated leaks or pulls apart under pressure | Each joint is homed and its deflection is within the manufacturer's stated limit | The joint is pulled apart, cleaned, and remade before the next length is laid |
| 4 | Install thrust restraint at bends, tees, and valves | Water changing direction pushes hard on the fitting, and an unrestrained bend can blow out of the trench | Restraint type and size match the design at every fitting shown on the plan | The fitting is excavated and the restraint is corrected before pressure is applied |
| 5 | Backfill partially, leaving joints exposed | Cover holds the pipe in place during the test while exposed joints stay visible for inspection | Cover is placed along the barrel of the pipe with every joint left open to view | Backfill is removed until the joints can be seen during the test |
| 6 | Run the pressure and leakage test | The test proves that the joints and restraint hold before the trench is closed | The main holds 150 psi for two hours and makeup water stays at or below the allowable leakage | The crew locates and repairs the leak, then repeats the full two-hour test |
| 7 | Disinfect the main | Construction leaves soil, groundwater, and handling contamination inside the pipe | Chlorinated water at 25 mg/L free chlorine is held 24 hours with at least 10 mg/L remaining at the end | The main is refilled and rechlorinated, and the hold is repeated from the start |
| 8 | Dechlorinate and flush | Water at disinfection strength would harm fish and aquatic life if it reached a stream or storm drain | The discharge is neutralized before it leaves the site, and flushing continues until the main's residual matches the rest of the system | Treatment and flushing continue, and the discharge point is corrected before more water is released |
| 9 | Collect bacteriological clearance samples | Chlorine residual alone does not prove the main is free of coliform bacteria | Two sample sets taken 24 hours apart are both absent for total coliform | The main is disinfected and flushed again, and both sample sets are collected again |
| 10 | Tie in, turn over valves, and submit record drawings | Crews need accurate records to find and operate the new valves, and a valve missing from the maps may not be closed quickly during a break | Every new valve is exercised and located, and the record drawings and mapping data are accepted | The main is not accepted into service until the records and valve locations are complete |
Closing prompt. Steps 7 and 9 protect public health rather than the pipe. Disinfection kills organisms introduced while the pipe sat open in a trench, and the bacteriological clearance samples prove that the disinfection worked before anyone drinks the water. Step 8 protects the environment rather than the pipe, since heavily chlorinated water is toxic to fish, and a strong answer may name it as a third public-protection step.
Differentiation
Support
Give these students the "Why the step exists" column already filled in, so their work begins with the acceptance test. Provide a matching bank of the ten pass criteria in scrambled order and have students place each one beside the step it closes out, then write only the failure column in their own words.
Extension
Ask these students to identify which two steps could be run out of order without harming the result, and to explain why every other pair is locked in sequence. Have them also write an eleventh row for a step the fictional Driftlow Avenue specification leaves out, such as a final tap and service transfer, with its own acceptance test.
ELL supports
Provide a labeled trench cross-section showing bedding, pipe, joint, thrust block, and backfill, and a simple flow arrow diagram of the ten steps in order. Post a term strip pairing commissioning with putting into service, clearance with permission to use, residual with chlorine still present, and record drawings with the final map of what was built.
Extensions
Have students obtain a construction inspection checklist from a public works department or a state drinking water program and compare its steps with the ten in this organizer, noting which steps their local document splits into more than one line. Students can also research how a utility handles a positive coliform sample on a new main and write the decision path as a branching diagram beside step 9.