Tutorial - Pump Tanks

Why do I have a pump tank?

In some cases, the septic system may include a pump tank.  Pump tanks are used whenever wastewater has to be discharged to a location which is uphill. Pump systems may also be required for large systems. Pressurized systems distribute the wastwater thoughout the entire drain field in evenly sized doses.  This provides more effective flow dispersal and treatment.

Flow can be delivered from the pump tank into the drain field by two principle methods.

Pump to Distribution Box (D-Box) with Gravity Flow Distribution 

The pump delivers flow to a D-box.  The flow is then distributed by gravity to the various sections of the drain field though 4-inch diameter (or larger) pipes.  This flow distribution is similar to the standard gravity (non-pump) systems, except that the system receives flow in large doses.  Note: this configuration typically requires a separate drain field vent to operate properly. 

Figure 4 – Septic System with Pump to D-box

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 Pump to Pressure Distribution Network 

The pump distributes the flow, under pressure, throughout the entire drain field through a network of smaller diameter pipes (typically 1-inch to 1.5-inch diameter).  This pipeline network has small perforations (commonly ¼-in holes) that spray the wastewater into the drain field stone.  The pressure distribution system provides more even distribution of flow throughout the entire drain field than other systems.

 Figure 5 – Septic System with Pump to Pressure Distribution

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The Advantage of Dosing the Drain Field

Both of the above pump systems provide dosing of the drain field. Dosing provides better treatment of the wastewater and extends the life of the drain field.  The dosing process rapidly soaks the entire drain field, then allows the drain field to rest (for hours at a time) between doses.  This process encourages healthy micro-organism "bio-mat" growth in the soil below the entire drain field, improving filtration.  The micro-organisms develop a higher metabolism (they get hungry) during the "rest period" resulting in more effective digestion of the wastewater.  In some states, regulations require a pump tank and pressure distribution for large systems or systems located near a sensitive area, for example near a lake or stream.  

Dosing may also be accomplished by Siphons or drip systems.  See Alternative Systems.

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