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1. Is emergency power required for sewer collection system lift stations?

Yes in most cases. Maricopa County Environmental Health Code (MCEHC) Chapter I, Section 2, Regulation 5 states: "For systems that treat, or which are designed to treat greater than 10,000 gallons/day, a standby power source shall be provided at all sewage treatment systems and/or pump stations where a temporary power failure may allow a discharge of raw or partially treated sewage. Standby power may be via a standby generator, separate feeders from separate substations, a loop feeder on separate transformers from a common substation, or a high-level alarm with portable generators. Standby power also shall be provided to any sewage treatment systems and/or pump stations, regardless of size, if a temporary power failure may allow a discharge into surface waters classified as 'Unique Waters', by the Arizona Department of Environmental Quality."

This is also a requirement for obtaining a Type 4 General Aquifer Protection Permit for a sewer collection system as described in Arizona Administrative Code R18-9-E301.D.5f. For more information, please call 602-506-1058.

2. What are the design requirements for venting wet wells, dry wells, basins, tanks and reservoirs?

All wet wells, dry wells, basins, tanks and reservoirs require venting. Wet and dry wells require forced ventilation and basins, tanks and reservoirs require normal ventilation.

Wet wells require 12 continuous air changes per hour or 60 intermittent air changes per hour based on the volume of the head space above the minimum sewage level. Dry wells require 6 continuous air changes per hour or 30 intermittent air changes per hour based on the volume of the dry well.

Wet wells and dry wells are usually vented by force draft fans or blowers in combination with odor control devices located on the ventilation discharge from the wet or dry well. National Fire Protection Association (NFPA) Section 820 specifies that all continuous ventilation systems should be fitted with flow detection devices connected to an alarm system to indicate ventilation system failure.

Basins, tanks and reservoirs are usually vented using inverted 'U' type, 'chair' or cross-flow vents using normal air currents. In all cases, vents shall have a 16-mesh corrosion resistant screen installed to prevent the ingress of birds and insects. For more information, please call 602-506-1058.

3. What are the design requirements for wet well, basin, tank or reservoir overflows?

Overflows of wastewater must be contained and not allowed to spill onto the ground. A suitable means of onsite containment must be included in the design.

Counterweighted flapper valves or self-sealing valves which open and close automatically when an overflow occurs must be installed on the end of the overflow discharge pipe to control odors and prevent the ingress of birds and insects. For more information, please call 602-506-1058.