DS-6.9 Wastewater Pump Stations

Drawing Ref: T660, T661, T662, T663, T664, T665, T666, T667, T668, T669, T670, T671, T672, T673, T674, T675, T676, T677, T678, T679, T680, T681, T682, T683

City Plan Performance Standard: Appendix 12C

Each wastewater management system shall be designed and constructed to ensure:
1. Pump stations or network structures (e.g. manholes) located within the stormwater management system’s secondary flowpath (excluding Road Zone and vehicle and pedestrian accessways) shall have a finished lid level of 500mm above the design flow of the flowpath or the level of ponding.
Wastewater pump stations shall be used only where gravity reticulation cannot optimally serve the entire catchment.
1. Pump stations shall be located on a separate lot specific for that purpose. That lot shall:
2. Be vested in Council;
3. Be provided with all weather access of not less than 3 metres wide;
4. Include a clear area of 5 metres x 5 metres to enable installation of a biofilter.
Safe, reasonable and practical access shall be provided to the wastewater management system for its maintenance.

Wastewater pump stations convey wastewater from developed areas where natural landform and gradients do not allow for a gravity system to be used. It is important that’s factors affecting a pump station’s operation are understood as the effect of an overflow on the surrounding area and/or watercourses is unacceptable due to important cultural, ecological and environmental implications as well as public health and pollution issues.

Detailed design shall be required at the time of Infrastructure Development Works Approval. Where no Infrastructure Development Works Approval is required Council approval shall be obtained at a time required by Council and before the construction of the system.

DS-6.9.1 Calculation of Flows

The following shall apply:

The pump station shall be sized to accommodate pumped flows from the total foreseeable contributing catchment.
Each pump shall be sized such that the duty pump is capable of pumping the maximum design peak flow, calculated in accordance with DS-6.4.1 Calculation of Flows.

DS-6.9.2 Freeboard

The pump station finished lid levels shall be located no less than 300mm above the 100 year return period storm event (1%AEP) flood level.

DS-6.9.3 Wet Well and Storage Chamber

Drawing Ref: T660, T661, T662, T663, T664, T665, T666, T667, T668, T669

The following shall apply:

These shall be as specified in the Standard Drawings.
Pump stations and vents shall be located to avoid being a noise or odour nuisance to occupants of buildings or likely building sites.
Wet wells and storage chambers shall be designed to accommodate all anticipated loadings and safely accommodate all maintenance and operations vehicles and personnel.
The wet well operational volume (volume between duty pump start and stop level) shall be designed at full catchment average dry weather inflow to limit pump starts to a maximum of 15 an hour based on the following formula:

Operational Volume (litres) = 900 x Q
N
Q = Pumping Rate (l/s)
N = Number of starts per hour
Operational depth shall be a minimum of 1.5m measured from the invert of the inlet pipe.

The design and construction of the wet and storage well foundations shall ensure that no more than 10mm effective long term total or differential settlement of the completed structure occurs and a factor of safety of 1.25 against flotation is obtained. Effects on adjoining infrastructure must be considered.
A geotechnical investigation report may be required by Council at the time of the application for Resource Consent or the development plan approval.
In determining the appropriate wet well diameter the minimum clearance between individual pumps and side clearances shall comply with the manufacturer’s recommendations.
A minimum clearance of 100mm all round the well shall be provided at the lid entrance.
Where a separate well is considered necessary to accommodate emergency storage volume it shall be designed to direct all flow to the outlet point and be self cleansing.
A hinged entry safety grill shall be fitted immediately under the wet well chamber lids.

DS-6.9.4 Pump Station Inlet Pipe

The following shall apply:

The invert level of the gravity inlet pipe and emergency storage well shall be a minimum of 100mm above the standby pump start level to prevent surcharge of the system during normal operation.
Only one gravity pipe may discharge into the wet well and must include an isolation valve. Where multiple inflows occur they must discharge to a receiving manhole, then into the wet well.

DS-6.9.5 Pump Selection

In calculating the system head losses the effects of all bends and fittings beyond the pump discharge bend shall be allowed for, together with rising main friction losses. Calculations of friction loss shall be carried out based on roughness ‘Ks’ values of 1.5mm and 0.5mm to ensure that the selected pump is capable of operating over this range of duty points. (Colebrook White formula). Where the discharge is to an existing rising main, the head shall be calculated to include the operating head in the existing rising main. Council approval is required for any discharge into an existing rising main.
The system static head shall be based on the difference in level between the flange of the pump discharge bend and the highest point on the rising main system.
The pump and rising main selection shall ensure the minimum velocity in the rising main is 1.0m/sec and the maximum 2.0m/sec (at peak design discharge rate).
In selecting pumps the operating conditions shall correspond as closely as possible with the point of maximum pump efficiency. However final pump selection must be approved by the Council to facilitate some standardisation of pump model and impellor type and sizes.
Standard pump stations shall include 2 identical submersible Wastewater pumps, one as a duty pump and the other as a standby. Larger pump stations may require additional pumps.
The pump type shall be as specified in AM-6 Wastewater.

DS-6.9.6 Impellers

To prevent unnecessary blockage all pumps shall be fitted with an ‘N" impeller approved by the Council. Where a mini pump station is constructed to service 5 lots or less, some departure from the IDC may be acceptable. However, approval is required from Council.

DS-6.9.7 Power Supply

Drawing Ref: T672, T673, T674, T675, T676, T677, T678, T679, T680, T681, T682, T683

All pumps shall be operated from a three-phase electrical power supply system.

DS-6.9.8 Control and Alarm Levels

Control and alarms levels shall be as outlined in Table 6.6: Control and Alarm Levels.

Table 6.6: Control and Alarm Levels

Control Type	Level
Low level alarm	Set to activate if the water level drops below cut out level for more than 1 minute
Pump stop level	Minimum submergence level of pumps
Duty pump start level	150mm below incoming wastewater invert level
Standby pump start level	100mm above duty cut-in level
High level alarm	100mm above stand-by cut-in level
Critical alarm	100mm below spill level

DS-6.9.9 Emergency Storage

The following shall apply:

A total of 9 hours emergency storage must be provided upstream of the pumping station. This volume may include the upstream pipelines and manholes in calculating storage design but only after approval has been received from Council.
Specifically designed emergency storage chambers may be required to supplement the volume provided by the collection system.

Definitions in this section

AEP

Council

Design

Development works approval