Backflow Assembly Selection at a Commercial Irrigation Connection
A commercial property has a dedicated 2-inch irrigation service tapped from the municipal main. The irrigation system includes pop-up spray heads, a fertigation injection system using a chemical tank and pump, and a hose bib at the riser. The property also has a fire sprinkler system on a separate service. The contractor installs a 2-inch double check valve assembly on the irrigation service and a 2-inch reduced-pressure principle assembly on the fire line. The water purveyor requires the highest level of protection for the irrigation service because of the chemical injection. The double check assembly is installed in a below-grade vault that floods seasonally. The inspector must determine whether the installation meets cross-connection requirements.
1. Determine whether the double check valve assembly is the correct device for the irrigation service and explain the hazard classification.
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No. Chemical injection (fertigation) creates a health hazard because a backflow event could introduce chemicals into the potable supply. A double check valve assembly only protects against low-hazard (pollution) backflow and is not acceptable where a health hazard exists. The correct device is a reduced-pressure principle assembly (or an air gap), which provides protection against both backflow and backsiphonage for high-hazard connections. The hose bib at the riser is also an unprotected cross connection unless it is a hose-connection vacuum breaker or the riser is protected upstream. The fire line RPZ is appropriate for a high-hazard connection. The fix is to replace the double check with an RPZ on the irrigation service, keep the chemical injection protected by an air gap or RPZ, and ensure the hose bib has an approved vacuum breaker.
2. The double check assembly sits in a vault that floods. Assess the installation and testing implications.
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A double check valve assembly is not designed to be submerged; a flooding vault can allow contaminated water to enter the assembly through the test cocks and clearances, defeating the protection. Even an RPZ must be installed so that the relief port and test cocks are not subject to flooding or backpressure, and the assembly must be drainable and accessible for testing and maintenance. The installation should be relocated above grade or into a properly drained, non-flooding enclosure, with the required clearance and a drain for the RPZ relief discharge. Testing must be performed by a certified tester with the required gauges, and the results submitted to the purveyor; a submerged or inaccessible assembly cannot be reliably tested. The inspector should require relocation and re-testing before approval.