Alternative technology used as a system interlock must fulfill the provisions of this chapter.

(1) Human interlock. In lieu of an automatic interlock, a person may serve as a system interlock. The individual must continuously monitor the application, be alert throughout the application process, be immediately available to terminate the application in the event of equipment malfunction, and be knowledgeable about the operation of the irrigation and injection systems.

(2) Solenoid and check valve.

(a) The chemical injection line must contain either a normally closed solenoid-operated valve connected to the system interlock or a normally closed hydraulically operated valve that opens only when the main water line is adequately pressurized. A normally closed, solenoid-operated valve must be placed on the intake side of the injection pump, immediately adjacent to the application tank.

(b) The chemical injection line between the application tank and the metering device must contain an automatic, quick-closing check valve to prevent the flow of liquid back toward the application tank. The check valve must be placed immediately adjacent to the venturi chemical inlet.