(1) A person shall not serve as a human interlock for chemigation equipment.

(2) A person with knowledge of the operation of both the irrigation and injection systems may function as a system interlock during fertigation: Provided that the person remains on-site to continuously monitor the application and is immediately available to terminate the application in the event of any equipment malfunction.

(3) 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.