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The requirements are specified in the Arizona Department of Environmental Quality's (ADEQ) Engineering Bulletin No. 10, "Guidelines for the Construction of Water Systems," Chapter 6, Section E.6.
In addition to the installation of overflow piping with a 16-mesh corrosion resistant screen, MCESD also allows the use of alternative designs such as the use of counter-weighted flapper valves or self-sealing valves that will open and close automatically when an overflow occurs.
In all cases, overflows shall have a 16-mesh corrosion resistant screen installed or provide a mechanical means of sealing the overflow opening to prevent the ingress of birds and insects.
If the overflow from a storage vessel is not connected to a sewer or storm water system, a suitable means of onsite containment must be included in the design. Onsite retention basins with riprap line channels and sides are typically used to contain an overflow and prevent erosion. Care should be taken in the design to insure that underground vaults and access points are not located in close proximity to overflow channels or retention basins. For more information, download the Guidelines for the Construction of Water Systems (PDF).