- Function
- Provide temporary storage within a wastewater system
- Possible deposits
- Settled solids and retained debris
- Operating constraint
- Changing inflow and weather
- Separate asset
- Not the same as a clean surface-water attenuation tank
Storm storage in wastewater systems
A storm-storage tank in a wastewater system may receive sewage or mixed wastewater during high flows. The word “storm” is not evidence that the tank contains only clean rainwater or that it is equivalent to a surface-water attenuation tank.
The tank’s connections, controls and filling conditions define its role in the system. They also show whether unexpected inflow is possible while it is out of normal service.
Sediment and debris after storm events
After stored wastewater drains or is returned to the system, sediment and debris may remain. The amount and location depend on tank design, previous filling and the way the storage is operated.
Flushing equipment, outlets and level devices may be affected by retained material. Cleaning around a blocked outlet or failed control does not itself resolve the equipment fault.
Weather, inflow and isolation
Weather and the system’s ability to manage incoming flow affect when the tank can be taken out of service. A tank that is dry when work begins may still receive wastewater if conditions change.
Material removed from the tank and any washwater need a route suitable for what they contain. Confined-space and sewage-exposure hazards must be assessed by competent people, with isolation and access controls suited to the installation.
Return to service
The completion record should identify the areas cleaned, any deposits left in place and equipment observations relevant to the next filling event. The site’s operating controls govern return to service; cleaning alone does not confirm that outlets, level controls or other equipment are working correctly.