Main Break, Loss of Pressure, and a Boil Order Decision

Yes. Three things line up:

1. Pressure. System pressure fell to 11 psi and stayed there for nearly three hours. The operating threshold is 20 psi: below that, the main is no longer reliably under positive pressure and can draw in groundwater, soil, or backflow from a private service. A break that drains a main also lets contamination in through the break itself.
2. Chlorine residual was already marginal at 0.35 mg/L against a 0.6-1.0 mg/L target, so you cannot argue the water stayed protected.
3. The SCADA point is not the worst case. The transmitter sits on a nearby 8-inch main; the low-pressure pocket may be larger than the reading suggests, especially at the far end of the isolated area behind the PRVs.

Scope it to the area that lost pressure or was isolated, not the whole system - you must be able to flush and sample what you cover. Then: notify the Illinois EPA, notify every affected customer door-to-door and through the media/alert system using the boil-order language the state approves, post notices at businesses, and tell people what to do and when they will hear back.

Contrast case: a contained repair on a main that is shut down and stays above 20 psi, with no loss of residual, generally does not need an advisory.

All of the following, in order:

• Repair and disinfection. Disinfect the replacement pipe and the open ends per AWWA C651 practice - spray or swab with a strong hypochlorite solution, or slug-chlorinate the main - then close and charge.
• Flush. Unidirectional flushing from a clean source to clear sediment, air, and dirty water, working from the source out to the dead ends and taking care not to stir up downstream mains.
• Verify residual and pressure throughout the affected area, not just at the break site. If residual has not returned to your target, you are not done.
• Two consecutive rounds of bacteriological samples, at least 24 hours apart, all absent for total coliform and E. coli, from representative points including the repair site, the far end of the isolated area, and any dead ends - with chlorine residual recorded at each site.
• Confirm no remaining low-pressure pockets behind the PRVs and no customers still isolated.

Nothing gets lifted on the basis of one clean set. Document every step and keep the Illinois EPA informed as you go; the advisory is lifted only after the state-approved protocol is satisfied.

• Gas service within the excavation. A marked 2-inch plastic gas line in the same crossing is a hard stop. The JULIE (811) locate ticket must be current - Illinois requires notice of two business days - and within the tolerance zone you hand-dig only, no mechanical equipment. If anyone smells gas or hears escaping product: stop, evacuate the area, remove ignition sources, call the gas utility.
• Trench collapse. Six feet deep, standing water, a storm sewer 3 ft away: the soil is likely Type C, which means sloping at 1.5H:1V, benching, or a trench box - never a vertical wall. Dewater (GFCI-protected pump, cords out of the water), keep spoil and equipment back at least 2 ft from the edge, and provide a ladder within 25 ft of anyone in the trench. OSHA excavation rules apply to a "quick" nighttime repair exactly as they do to a planned one.
• Traffic. A four-way intersection going heavy after 6 a.m.: advance warning signs, cones, flaggers or a temporary signal, and a lane-closure plan that follows the MUTCD. Consider whether the repair can be staged to avoid the peak.
• Storm sewer and contamination. Standing water mixed with sewage-capable storm flow; gloves, eye protection, and hygiene before eating; check tetanus status.
• Confined space. If anyone must enter a valve vault, the permit-required confined space program applies.
• Night work. Lighting, high-visibility apparel, and a spotter for equipment backing.