Below Ground Waste Water Collection Tank Calculations

Things to consider when calculating the size of a below ground collection tank:

  • Accumulated silt collection and retention capacity exists below the pump suction point to ensure appropriate (target once per year) time intervals are achieved between (costly) prescribed waste evacuations
  • Pump suction point is best terminated 600mm – 800mm above the base of the tank to allow for an acceptable volume of silt to build up in the base of the tank before it ends up being transferred through the pump into the oil water separator

This process extends the life of the pump and the duration between oil/water separator service and maintenance visits

  • The vertical distance between the pump suction point and the invert level of the inlet drain caters to retention of one hour of peak wash water volume, plus the first flush volume (where applicable for unroofed washbays)
  • First Flush being the area of the washbay x 10mm of rainfall (Industry Best Practice) falling on the catchment
  • Typical tank liquid retention capacities range from 1500 to 5000 (or greater for some applications) dependent on the location and size of the washbay catchment and wash-down flow rates
  • Pump suction lines are to include a barrel union to cater to future removal for service and maintenance purposes
  • Conduit and pump suction line connections within the tank are reachable  from the top of the tank when the access cover is removed to remove the necessity for confined space entry during equipment service and maintenance attendances

Little Holland is the approved Distributor of Fox Enviro & Wyuna Separation Technology products in Victoria, Southern NSW and South Australia