Main Break, Precautionary Notice, and Restoring Service
At 2:10 a.m. on a Sunday, a 12-inch unlined cast iron main installed in 1952 breaks under a residential street. Normal pressure is 40 psi; pressure in the area falls to about 12 psi before the crew isolates the break. Twenty-two services are out, including a K-8 school and a 60-bed assisted-living facility. The repair replaces 300 feet of pipe and will finish around 8 p.m. The system uses chlorinated groundwater leaving the plant at 1.1 mg/L free chlorine. The crew finds the break washed out, with soil and road salt visible in the trench. There is no hydrant at the repair site; the nearest is 600 feet away.
1. Do you issue a boil water notice, and how do you justify and deliver it?
Read the worked answer
Yes. Issue a precautionary boil water notice for the affected area.
The deciding fact is the 12 psi. When pressure in a main drops below 20 psi, the pipe can draw in groundwater and soil through the break, joints, and any cross-connection, because the system is no longer reliably under positive pressure. Here there is visible contaminated soil and road salt sitting against an open 1952 unlined main, which makes the risk concrete rather than theoretical.
Delivery must cover everyone.
- Hand delivery to the 22 affected services, not just a notice on a utility website. Include the school and the assisted-living facility, which need direct notification because they serve populations that cannot easily act on a general announcement.
- Coordinate with the school district and the facility administrator so they can plan for Monday, including food service and any medical equipment that uses water.
- Notify the state regulatory office as required by your permit, with the location, cause, affected area, and expected duration.
Write the notice plainly: boil vigorously for one minute and cool before drinking, cooking, brushing teeth, or making ice; use bottled water for infant formula; dishwashing and bathing guidance included; do not rely on a home filter.
What does not justify skipping it: the water is chlorinated. Chlorine residual is not a substitute for positive pressure, and residual in the main is exactly what you cannot verify when the main is open to the ground.
2. Write the disinfection and sampling steps for the 300-foot replacement, with the volume and the amount of 12.5 percent hypochlorite needed for a 50 mg/L dose.
Read the worked answer
Volume of the new pipe:
- 12-inch pipe: area = 0.7854 x 1.0^2 = 0.785 sq ft
- 0.785 sq ft x 300 ft = 236 cubic feet
- 236 cu ft x 7.48 = about 1,760 gallons
Chlorine needed for 50 mg/L:
- lb Cl2 = gallons x 8.34 x mg/L / 1,000,000 = 1,760 x 8.34 x 50 / 1,000,000 = 0.735 lb
- 12.5 percent sodium hypochlorite holds about 1.3 lb of available chlorine per gallon
- 0.735 / 1.3 = about 0.6 gallon
Sequence:
- Keep the repaired section isolated. Swab the interior and fittings with a strong hypochlorite solution as it is assembled, and keep the open ends plugged when work stops.
- Fill with chlorinated water to the target concentration and hold for the required contact time, verifying residual at the far end of the section before discharging it.
- Flush to waste with dechlorination where required, until chlorine residual and turbidity are stable and match the rest of the system.
- Collect bacteriological samples from the repaired section per the state's requirements, then restore service.
Judgement point: the section will not be out of service for 24 hours of contact time and then a full sampling cycle with 22 customers and a school waiting. Restore service once the section is chlorinated, flushed, and sampled, and let the boil water notice carry the public health protection until the lab results clear. That is the reason the notice exists.
3. What must be verified before the notice can be lifted, and what commonly goes wrong when pressure is restored?
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To lift the notice, all of these:
- Two consecutive sets of satisfactory bacteriological samples collected at least 24 hours apart from the affected area, with no total coliform and no E. coli, and adequate free chlorine residual at the time of collection. Confirm the exact rescission criteria and reporting steps with the state before you tell customers it is over.
- Free chlorine residual restored and confirmed at the ends of the affected area, not just at the plant.
- System pressure restored above 20 psi throughout, including the far ends.
- Flushing until turbidity and color are stable, with dechlorination where the discharge requires it.
What goes wrong on restoration:
- Valves left closed. A valve that was shut to isolate the break and never reopened turns part of the area into a stagnant dead end with no residual, right after you told everyone the water was fine. Use a valve list from the isolation and check each one.
- Full-open valves on an empty main. Opening too fast sends a pressure surge through 1952 cast iron and can break a second main, and it stirs sediment that turns into dirty-water complaints for a week. Open slowly and vent air.
- Sediment and discoloration. Flush in one direction and tell customers to run a cold tap before doing laundry.
- Building plumbing and cross-connections. At the school and the assisted-living facility, confirm backflow protection and that internal fixtures have been flushed after the outage.
- Paperwork. The notice, the delivery list, the sampling results, and the rescission notice all belong in the file; reconstructing them after the fact is where utilities lose enforcement cases.