Part 5 – Wastewater Drainage
5.18 Pumping Stations
5.18.1 General
All equipment and/or components used for similar functions and purposes must be of the same design, make or model for ease of operation and maintenance. This includes new pumping stations. The requirements for the design of new pumping stations are detailed on Drawing TS 503.
Note: The MPDC Infrastructure Code of Practice provides useful guides for pump station layout.
5.18.2 Structural Stability
The pump station wet well shall be designed to have negative or zero buoyancy. Ground water level shall be assumed to be at ground level. The mass of the wet-well structure included in the stability analysis shall not include the associated mechanical and electrical components of the pump station. Nor can the soil friction forces of backfill around the wet well chamber be taken into account. Any additional weight needed shall be added in the form of mass concrete in the bottom of the chamber. The pump station drawings shall provide dimensions of the extent of mass concrete needed to counter buoyancy of the chamber.
5.18.3 Pumps, Rising Main, Delivery Point and Overflow
Pumps shall be Flygt MT pumps (medium head performance range) models CP or NP versions 3085, 3102, 3127 or 3152 or Homa equivalent for the 3152 models.
The pumping range shall be selected to give between 1 and 15 starts per hour at peak daily flow.
The pump system shall be an N + 1 system where N pumps are required for duty and a standby pump identical to the duty pumps shall be installed.
Exceptions to the duty plus one standby pump requirement can be made in small installations serving no more than 12 residential dwellings. In such installations the wet well shall be designed to have a minimum storage capacity sufficient to contain 12 hours of the catchment’s Average Daily Flow.
The rising main will be a minimum size of 80 mm and designed such that the minimum velocity, with one pump operating, is 1 m/s and the maximum velocity, with all duty pumps operating, is 3 m/s.
The point at which the pumping station is connected to Council’s system will be governed by the capacity of the network downstream from that point.
The emergency overflow pipeline shall be of sufficient capacity to carry peak wet weather flow from the station without surcharge. The inlet to the overflow pipe shall be baffled to restrict the entry of solid floatable material. This can normally be done using a 90 degree downturn bend.
The overflow pipe shall be from the pump station chamber to the nearest stormwater system. A backflow device shall be fitted where there is potential for stormwater to backflow into the pump well.
The upstream impacts of a pump station overflow shall be checked to ensure no overflow occurs elsewhere.
5.18.4 Pump Chamber, Valve Chamber and Manifolding
The layout of the pumping chamber, valve chamber and pipe work shall be similar to that shown on Drawing TS 503. The valve chamber shall be attached to the pumping chamber. Where the delivery point is within close proximity to the pumping station the valve chamber may be dispensed with and a separate rising main from each pump laid to the delivery point.
The floor of the pumping station shall be set at such a level below the inlet pipe so that the inlet pipe will not surcharge during the normal pump operation cycle.
The floor shall be designed to be of sufficient thickness to ensure that the pump station cannot become buoyant with groundwater at ground level and in any case not less than 600 mm thick.
Note: The MPDC Infrastructure Code of Practice provides useful information related to wastewater pumping stations
5.18.5 Pump Station Storage
Pump stations shall provide for wastewater storage in the event of pump failure, control malfunction, electricity outage etc.
A minimum of twelve hours storage at Average Daily Flow shall be provided before emergency overflow occurs. The required storage volume shall be provided in the volume of the wet well, plus any additional ancillary storage chambers, plus the volume of pipelines (below overflow level) draining to the facility. The wet well volume below pump switch off level shall be excluded from the calculation of available storage volume.
If necessary the required storage capacity can be obtained through use of an associated storage chamber constructed as an adjacent manhole haunched and connected to the wet well so as to completely drain into the wet well before the pump shuts off on the pump out cycle.
Preferably the storage volume shall be provided in the pumping wet well structure and upstream pipelines. Where this is impractical, additional storage can be provided in an additional manhole type structure adjoining the wet well. Or if this configuration is impractical, the storage shall be provided in a horizontal chamber made from large pipes.
5.18.6 Water Supply
A standard 630D MDPE pipeline as used for water supply rider mains shall be provided to the pump station. Wastewater pump stations are a “High Hazard” risk requiring reduced pressure zone type backflow prevention devices installed above ground level. The backflow prevention device is to be positioned adjacent to the electrical control cabinet.
5.18.7 Access
A permanent concrete all-weather vehicle access shall be provided to the pump station to allow maintenance vehicles to access wet wells.
