Fertilizer Injection, an Overdue RPZ, and a Missing Hose-Bibb Vacuum Breaker
A 12-acre wholesale nursery has a 4-inch municipal water service. The service enters a booster pump room and then feeds both the office/restroom and an irrigation system. The irrigation system includes a 55-gallon tank of liquid fertilizer and a wetting agent, injected by a 1/2-hp chemical pump into the irrigation main downstream of a 2-inch reduced-pressure principle assembly (RPZ) at the service. The RPZ was tested 14 months ago. During a main break last week, the irrigation main lost pressure and the chemical pump continued to run for about 20 minutes. The nursery's handyman replaced a leaking hose bibb on the office wall with a plain sillcock and removed the old screw-on vacuum breaker because it sprayed. The local health department has now asked for a cross-connection survey. The owner argues that the RPZ at the meter already protects everything.
1. Classify the hazard and evaluate the owner's claim that the meter RPZ protects everything.
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The fertilizer and wetting agent are at least a non-health hazard and may be a health hazard depending on the product's toxicity and concentration. The meter RPZ is a containment device: it protects the public main from backflow out of the nursery, but it does not protect the nursery's internal potable piping, the office restroom, or any hose bibb downstream of it. During the main break, the irrigation main lost pressure while the chemical pump continued to run, so backsiphonage could have pulled fertilizer into the irrigation main and, through any unprotected connection, into the building water system. The RPZ being 14 months old is also a violation of the usual annual testing requirement, so its condition is not proven. The owner's claim is therefore wrong: containment at the meter does not replace isolation protection at the point of cross-connection. A separate RPZ or an air gap is needed at the irrigation takeoff, and the internal potable system needs protection.
2. What corrections are required at the hose bibb and at the chemical injection point?
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The plain sillcock must be replaced or fitted with a listed hose-bibb vacuum breaker, such as an ASSE 1011 device, or replaced with a self-draining freeze-proof sillcock that has integral backflow protection. Removing the old vacuum breaker because it sprayed is not acceptable; the correct response is to repair or replace it, not delete it. At the chemical injection point, the injection pump must discharge downstream of an air gap or an RPZ, and the injection line should have a functioning check valve and a solenoid or low-level cutoff that stops injection when the irrigation pump is off or the tank is empty. The chemical tank should have secondary containment, and the injection point should be labeled. Because the chemical pump ran during a pressure loss, the system should be treated as potentially contaminated until flushed, disinfected, and sampled under health-department direction.
3. Outline the immediate response and the retest/documentation plan after the backflow incident.
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Immediately stop use of the potable water for drinking or food preparation, notify the health department and the water utility, and isolate the irrigation system from the building supply. Have a certified tester inspect and retest the RPZ; repair or replace any failed check or relief valve, then retest before returning it to service. Flush and disinfect the affected potable piping using an approved procedure, then collect bacteriological and chemical samples as directed. Replace or verify the injection-line check valve and add the solenoid interlock. Document the event with photos, the RPZ test report, the chemical product safety data sheets, the flush/disinfection record, and the sample results. Finally, establish an annual RPZ testing schedule and a cross-connection survey of all hose bibbs, sinks, and chemical-mixing points.