Backflow prevention

- Winter 1999 "Update" Newsletter Article -

Backflow prevention

CIT publication discusses issues of chemigation and backflow in irrigated agriculture

Pressurized irrigation systems, featuring the use of drip lines, microsprayers and sprinklers for water delivery, continue to gain popularity in California agriculture as water-use efficiency becomes more crucial. An added benefit of pressurized systems is the capability of using "chemigation" methods for delivering fertilizers and other materials to crops, notes Center for Irrigation Technology (CIT) Director David Zoldoske in a new publication discussing chemigation and backflow devices. The publication is titled "Backflow Prevention and Safety Devices for Chemigation" and is available through CIT. Coauthor, along with Zoldoske, is former CIT Director Ken Solomon.

The authors provide updated information on the types of backflow equipment currently available. Categories include irrigation pipeline equipment, injection line equipment, injection line equipment used with a Venturi injector, and power and system interlocks. Also provided are specifications for agricultural chemigation valves, failure rates of double check valves, and additional safety considerations.

Chemigation simply means injecting some kind of chemical or substance into an irrigation system prior to applying the water, Zoldoske explains. The material is delivered to the crop roots along with the water. Benefits include economical application, potential for frequent, precise applications to match seasonal crop needs, and a reduction in soil compaction and mechanical damage to crops due to less frequent tractor work.

With the growth of chemigation, however, a new concern has arisen - backflow prevention.

"Water must be protected from contamination from chemicals introduced downstream (in the irrigation line)," Zoldoske notes. With all the "bad press" growers have received in recent years concerning pesticide residues and groundwater pollution, it's not surprising that government has started legislating controls. Several states, such as Minnesota and Nebraska, have taken the lead in requiring protection on all agricultural well heads. These "chemigation valves," as they are referred to, are designed to stop the mixture of water and chemical from draining or siphoning back into the irrigation water source.

Some governmental and other agencies differ in their requirements for backflow prevention depending on whether the system is used strictly for fertigation, or for application of more toxic biocides. However, CIT recommends that any chemigation system be fitted with protective equipment commensurate with the most hazardous class of chemicals, i.e., biocides.

"The rationale is that since the equipment for injection of fertilizers is the same as for the injection of biocides, fertigation systems are potentially chemigation systems. Unless an inspector is present during each irrigation event, there is no way to enforce a ban on the injection of biocides. Therefore, all injection systems should be treated as biocide injection systems, and protected accordingly," Zoldoske stated.

Backflow prevention devices and other equipment listed in the new publication are described and rated, where field information is available. The publication may be viewed in CIT's Research Publications section

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