Pressure Loss and a Submerged Tanker Hose
An 8-inch cast-iron main serves a residential zone through a pressure-reducing valve set at 65 psi. At 10:15 a contractor filling a 5,000-gallon tanker from a hydrant 900 feet from the PRV reports low flow; the hydrant pressure gauge reads 38 psi. Within an hour, 12 customers call about discolored water, and the chlorine residual at a nearby sample station falls from 0.9 to 0.15 mg/L. The zone has a 250,000-gallon elevated tank at 42% level, and a 6-inch dead-end main with a closed valve separates the area from a commercial laundry that has a boiler feed line and a fire sprinkler system. The contractor's tanker has no air gap and the fill hose was submerged in the tanker. No main break is visible. The system has a written cross-connection control program but no records of the laundry's backflow assemblies.
1. What is your first priority and what immediate actions do you take at the hydrant and zone?
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My first priority is stopping a possible contamination path and protecting public health. I would order the contractor to stop filling immediately and close the hydrant valve. I would treat the submerged hose and missing air gap as a high-hazard cross-connection until proven otherwise, because the tanker contents are unknown and pressure at the hydrant has dropped. I would notify the utility supervisor and the state primacy agency, check the PRV and elevated tank level to understand whether low pressure is local or zone-wide, and isolate the hydrant branch if valves allow. I would collect chlorine, turbidity, and bacteriological samples near the hydrant and at control sites, and ask the contractor what the tanker last carried. I would not let the contractor flush the hose into the street or drain the tanker into the system. If pressure reversed or contamination is confirmed, I would prepare a precautionary boil-water notice with the agency.
2. How would you determine whether the low chlorine and discoloration are caused by a cross-connection versus a main break or valve issue?
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I would build a pressure and flow history first: PRV inlet and outlet pressures, tank level trend, hydrant flow, and whether nearby valves or the laundry's closed valve moved. A 38 psi reading is low but still positive, so back-siphonage would require a pressure drop at the point of connection; the submerged hose and no air gap make that plausible if the main lost pressure. Discoloration and chlorine loss can also come from sediment resuspension during high hydrant flow or from a partially closed valve. I would isolate the laundry service and test its backflow assemblies, inspect for a boiler feed connection, and sample the main upstream and downstream of the hydrant. A tracer or chemical analysis of the tanker contents would help. I would check for a hidden main break by comparing zone flows and listening for leaks. If the laundry has an unprotected boiler feed line, I would keep it isolated until corrected.
3. Outline a flushing and sampling plan before lifting any precautionary notice.
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I would flush unidirectionally from the source toward the dead ends, starting at the hydrant and moving to the affected streets, while measuring chlorine and turbidity at each outlet. Flushing should be coordinated with the tank level and PRV so the zone does not lose pressure. I would clean and disinfect the hydrant and tanker connection area, then collect bacteriological samples at the affected sites, the laundry service, and unaffected control locations. I would test for chlorine residual, turbidity, and any contaminant suggested by the tanker's previous cargo. If a boil-water notice was issued, I would follow the state protocol, which typically requires two consecutive rounds of negative samples separated by at least 24 hours, plus restored chlorine residual. I would document flush volumes, sample locations, times, and results, and get agency concurrence before lifting the notice.