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Influent Pumping Overview
The Wenatchee WWTP influent pumping station receives raw wastewater from the City's service area and conveys it to the Headworks.
Theory of Operation
Raw wastewater flows through perforated plate screens before entering the influent pump station wet well from which six influent pumps can draw flow from. All of the pumps are vertical centrifugal non-clog pumps of varying size.  Pumps 1 and 2 intake through a 12-inch line from the wet well and discharge to the Headworks. Pumps 3 and 4 intake through a 16-inch line and also discharge to the Headworks.  Raw sewage pumps 5 and 6 discharge to a 24-inch pipeline connected to the flow equalization basin.

Wenatchee WWTP Design Criteria
Parameter Criteria
Monthly average flow (max month)5.5 MGD
Daily average flow3.2 MGD
Peak hydraulic capacity15 MGD
BOD influent loading13,006 lbs/day
Total Suspended Solids13,111 lbs/day
TKN influent loading1,800 lbs/day

Flow entering the treatment plant is conveyed to the influent junction box by 18, 36, or 42- inch interceptor sewers. The influent next passes through two perforated plate screens before entering the raw sewage pump station wet well, where the flow is split into two channels.  Pumps 1-4 discharge to the headworks, while pumps 5 and 6 discharge to the flow equalization basin.

The capacities and horsepower of the six influent pumps are:

      Pump 1   2,820 gpm @ 43' TDH, 40 hp
      Pump 2   2,820 gpm @ 43' TDH, 40 hp
      Pump 3   1,500 gpm @ 26' TDH, 20 hp
      Pump 4   2,500 gpm @ 26' TDH, 25 hp
      Pump 5   5,000 gpm @ 25' TDH, 40 hp
      Pump 6   6,000 gpm @ 25' TDH, 50 hp

Raw sewage pumps 1 and 2 are controlled by variable frequency drive units, while raw sewage pumps 3 - 6 are constant speed pumps. When the local switch and the SCADA switch are in Auto, the following program in the PLC controls the operation of the influent pumps:

Pumps 1 and 2 operate in a duty/standby configuration. Under dry weather flows, either pump 1 or pump 2 operates and is controlled by a VFD to maintain an operator-adjustable wet well set point. If the VFD-controlled pump fails, then the standby VFD pump starts. If pump  1 or 2 are unable to maintain the wet well setpoint, then pump 3 or 4 starts. Raw sewage pumps 3 and 4 operate in a lead/lag configuration. An operator selects in SCADA which pump operates in lead. If pump 3 is selected as lead, then it starts if the VFD-controlled pump is unable to maintain the wet well set point. If the wet well continues to increase after pump 3 is running, then pump 4 starts as a lag constant speed pump. If the lead VFD-controlled pump fails during this operation, then the standby VFD pumps starts. If one VFD and both lag pumps are unable to maintain wet well level, then the standby VFD pump will start. This high-flow scenario has pumps 1 - 4 pumping to the Headworks. If these four pumps are unable to maintain wet well level, then pump 5 or 6 starts and sends flow to the Equalization Basin. Pumps 5 and 6 operate in a duty/standby configuration. If pump 5 is selected as lead and it fails during operation, pump 6 starts.

Flow Equalization


Flow equalization is implemented to reduce hydraulic impacts of peak flows through the plant. The equalization basin is used when flows exceed approximately 11 MGD.  Raw sewage pumps 5 and 6 discharge to a 24-inch pipeline that feeds the flow equalization basin. A single submersible pump rated for 700 gpm (1 mgd) pumps the contents of the flow equalization basin back into the influent sewer after the high flow event ends.
The flow equalization basin is located west across the road from the WWTP.

The flow equalization consists of a 24-inch influent pipeline from the raw sewage pump station, a membrane lined basin with sand filled membrane tubes, a concrete sump, a simplex submersible pump station with local controls, and a 4-inch discharge pipeline. Following a flow equalization event, a flushing valve can be opened to flush city water (isolated by a backflow preventer) into the pipeline to displace dilute raw sewage in the pipeline. Sodium hypochlorite can be dosed into this same water using the RAS chlorination pump.
Flow Equalization Basin
The flow equalization basin has a capacity of 1.7 million gallons below elevation 639.0 (NAVD88).
Flow Equalization Effluent Pump
The equalization basin effluent pump is a simplex pump in a 72-inch diameter manhole and is removable using a guide rail system.

Item Design Criteria
Flow Equalization Basin
Number of units 1
Type Lined pond
Capacity 1.7 million gallons
Flow Equalization Pump
Number of units 1
Type Submersible non-clog
Capacity 700 gpm
Motor HP 10 HP
Motor type Constant speed

The Influent Pumping Station system includes the following equipment:
  • Vertical centrifugal non-clog influent pumps
  • Wet well level instrument
  • Wet well odor control
Vertical Centrifugal Non-Clog Influent Pumps 6
  Six vertical centrifugal pumps are located in the pump room, with extended shafts connected to the motors installed upstairs in the motor room. The pump shafts have an intermediate bearing support and guards. Two pumps are controlled by VFDs located in the motor room.  Each pump uses seal water controlled by a solenoid valve that opens when the pump is running.  Pumps 1 - 4 are supplied from the wet well and pump raw wastewater to the headworks.  Pumps 5 & 6 are supplied from the wet well and pump raw wastewater to the equalization basin.
Wet Well Level Instrument 6
An ultrasonic level indicator monitors the level of the influent wet well. 
Wet Well Odor Control6
Foul air is drawn from the covered wet well by fan F-42004 and pushed through the primary clarifiers to the inlet of biofilter supply fan F-31031A. The biofilter supply fan then pushes the combined foul air stream to Biofilter 2. 

A detailed description of the system is provided under the Odor Control section of the eOM.

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Last Updated: 6/3/2014 7:42:40 AM
Version 4.0.1