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4.12.1.2. If an air vent pipe is provided, it shall extend twelve (12) inches <br /> above the ground surface, inverted in a downward direction, <br /> and the end shall be covered with 16-mesh screening. <br /> 4.12.2. The fill pipe on a gravel packed well shall be water tight, extend twelve <br /> (12) inches above the ground surface, and be provided with a watertight <br /> threaded cap. <br /> 4.12.3. If a commercially produced sanitary seal is used, a sounding tube will be <br /> required if the sanitary seal, approved by the Director, is designed with a <br /> means of entrance into the well for chlorinating and sounding. <br /> 4.13. SAMPLING TAP <br /> 4.13.1. A non-threaded tap shall be installed for the purpose of obtaining water <br /> for laboratory examination between the well head and the check valve or <br /> within 3 feet of the well head. <br /> 4.14. BACKFLOW PREVENTION <br /> 4.14.1. All pump discharge pipes shall be installed with approved protective <br /> devices to prevent backflow and/or back siphonage into a well. A <br /> properly designed air gap may be considered an acceptable protective <br /> device for agricultural wells. <br /> 4.14.2. No person shall install any equipment or mechanism that uses chemical <br /> feeders or injectors without an approved backflow prevention device. <br /> 4.14.3. Backflow prevention is required when drinking water supplies are <br /> involved, as prescribed in Title 17, California Code of Regulations. <br /> 4.14.4. No person shall make a connection or allow one to exist between pipes or <br /> conduits carrying domestic water supplied by any public or private water <br /> service system, and any pipes, conduits, or fixtures containing or carrying <br /> water from any other source or containing or carrying water which has <br /> been used for any purpose whatsoever, or any piping carrying chemicals, <br /> liquids, gases, or any substances whatsoever, unless there is provided a <br /> backflow prevention device approved for potential hazard. <br /> 4.14.5. Agricultural discharge pipes utilizing an air gap for backflow prevention <br /> shall maintain an air gap equal to the size of the discharge pipe, but not <br /> less than 6 inches. The discharge pipe shall also have two - '/4 inch slit <br /> extending 6 inches from the bottom of the pipe and opposite each other. <br /> EHD 43-03 Page 15 of 27 WELL STANDARDS <br /> 10/9/07 <br />