Main Break, Low Pressure, and a Boil Water Notice
At 09:15, a contractor strikes a 12-inch cast-iron main on a business loop. The break floods a parking lot and undermines pavement. The zone serving 620 connections, a 120-bed nursing home, and a food processing plant loses pressure; the logger at the nearest hydrant records 8 psi for an estimated 2.5 hours before the main is isolated. Repair is complete at 18:40, and pressure is restored at 19:10. The system's standard procedure requires a boil water notice when pressure falls below 20 psi. Chlorine residual at the nearest sample station before the break was 0.7 mg/L; after repair it is 0.3 mg/L. The state requires two consecutive negative bacteriological samples 24 hours apart before lifting a boil water notice. The food plant is in the middle of a production run, and the nursing home has 12 residents on dialysis.
1. Do you issue a boil water notice, and what immediate actions follow?
Read the worked answer
Yes-issue a boil water notice. The zone lost pressure to 8 psi for 2.5 hours, well below the 20-psi threshold, and a main break can draw contaminants into the pipe.
- Notify the state immediately and issue the notice to all 620 connections, the nursing home, and the food plant. Use door hangers, phone, and media.
- Isolate and repair the main. Keep the area barricaded and dewatered.
- Flush the repaired main and the zone to remove sediment and stale water. Start at the break and move outward.
- Increase chlorine residual to the system's target for new mains, and measure at representative points.
- Sample for total coliform and E. coli after repair and flushing. The state requires two consecutive negative sets 24 hours apart before lifting the notice.
- Tell customers to boil water for one minute or use bottled water for drinking, cooking, ice, and brushing teeth. Include the nursing home and food plant explicitly.
Do not lift the notice just because pressure is back. The notice is about contamination risk, not convenience.
2. Describe the main disinfection, flushing, and bacteriological sampling plan after the repair.
Read the worked answer
Disinfect the repaired pipe and prove it with samples.
- Clean and swab the broken ends and any replacement pipe. Keep debris and groundwater out of the main.
- Apply a chlorine solution to the repaired section-typically 50 mg/L for 24 hours or 100 mg/L for 1 hour, per the system's standard-then flush until the residual is at the normal system level. Check the state's specific requirement.
- Flush at a controlled rate to avoid surges and discolored water. Flush hydrants downstream and at the dead ends.
- Collect bacteriological samples from the repair area and representative points in the zone. The state requires two consecutive negative sets 24 hours apart. Do not composite samples.
- Measure chlorine at each sample point. A residual of at least 0.2 mg/L (or the system's target) supports the barrier.
- Document the repair, disinfection concentration, contact time, flush volumes, and sample results.
If any sample is positive, repeat the disinfection and sampling and keep the notice in place. Notify the state before lifting.
3. What specific guidance do you give the nursing home and food plant, and what criteria lift the notice?
Read the worked answer
Give each customer instructions matched to their risk.
- Nursing home: Provide bottled water for drinking, food preparation, and oral care. The 12 dialysis residents need water that meets dialysis standards; the clinic should use its emergency plan or suspend treatment until pressure and chlorine are stable. Do not assume the notice covers dialysis-call them.
- Food plant: The plant must stop using the water for product, cleaning, or ice unless it has an approved treatment step. It may need to discard product made during the notice. Inspect with the state food program.
- Lift the notice only when two consecutive negative bacteriological sets 24 hours apart are complete, chlorine residual is restored throughout the zone, and the state agrees. Then issue a rescission notice with the same distribution list.
Keep a log of who was notified and when. If the food plant or nursing home cannot comply, the system should provide alternative water. The legal duty is to notify, but the practical duty is to make sure the sensitive customers heard it.