Irrigation System on a Hillside with a Booster Pump
A hillside vineyard irrigates 30 acres with a system fed from a municipal main. A booster pump at the low point raises pressure to 110 psi to reach the upper rows. The irrigation main runs uphill and includes chemigation injection for fertilizer and pesticides. Several quick-coupler valves sit at low points where ponded water collects after rain. The owner wants to use a pressure vacuum breaker (PVB) at the service because it is cheaper than an RPZ and does not discharge. The municipal cross-connection program requires protection commensurate with the hazard and prohibits certain devices where backpressure can occur. The system also has a buried line that crosses a creek. The inspector must evaluate the proposal and the overall protection scheme.
1. Evaluate the PVB proposal given the booster pump, chemigation, and elevation profile. What protection is appropriate?
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The PVB is not acceptable here.
A PVB protects against backsiphonage only. It relies on a float that closes when supply pressure drops, and it must be installed above the highest downstream outlet. This system has a booster pump that can raise pressure to 110 psi, creating backpressure. A PVB cannot protect against backpressure, and its air inlet cannot open against downstream pressure. The chemigation injection adds a health hazard (fertilizer and pesticide), which is a high hazard regardless of the pump.
The appropriate protection is a reduced-pressure principle assembly or an air gap at the service, sized for the system's flow and pressure. The RPZ handles both backsiphonage and backpressure and is rated for health hazards. If discharge is a concern, an air gap with a break tank is an alternative. The assembly must be installed where it is accessible and where relief discharge can drain safely.
Additionally, the quick-coupler valves at low points need individual protection (hose-connection vacuum breakers or a protected loop), and the creek crossing should be evaluated for a possible cross-connection if the buried line can siphon. The inspector should reject the PVB in writing and require a high-hazard assembly before the irrigation season begins.
2. Describe how you would assess the creek crossing and the low-point quick couplers, and what records you would require.
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Creek crossing: A buried irrigation line crossing a stream can become a cross-connection if the pipe is submerged or if a break allows creek water to enter. The assessment should determine burial depth, pipe material, and whether the line is under continuous positive pressure. If the line can be drained or lose pressure, creek water could be drawn in. The safest approach is to keep the line pressurized and protected by the service assembly, or to install a separate RPZ on the branch that crosses the creek. The crossing should be marked and inspected after flood events.
Low-point quick couplers: These are hose connections that can be submerged in ponded water. Each should have a hose-connection vacuum breaker or be served by a protected loop. The couplers should be raised above expected ponding, or the area should be drained so standing water cannot submerge them.
Records to require:
- As-built drawings showing the service assembly, booster pump, chemigation point, creek crossing, and coupler locations.
- Test reports for the service assembly and any branch assemblies.
- Chemigation permit or injection equipment documentation.
- A maintenance log for the booster pump and couplers.
- A written hazard assessment signed by the owner.
The inspector should schedule a follow-up inspection after the rainy season to confirm the low points and crossing remain protected.