Septic Tank Water Ingress

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In this video we will be looking at what happens when your septic tank is affected by water ingress.

The purpose of a septic tank is one of settlement and separation. This process is most effective when the septic tank is in a state or period of inactivity.

When the foul waste water settles in the septic tank, the solids in the water break down and separate into 3 distinct layers.
As the septic tank collects the waste from the property, less dense waste material floats to the surface to form a scum layer. The more dense waste material sinks to the bottom of the tank, forming sludge. The partially clarified liquor from between the two layers is allowed into the outfall drainage field or soakaway
Septic tanks operate on the basis of hydraulic displacement. This means that the same amount of liquid that enters that tank, causes the same amount of liquid to exit the tank, regardless of the length of time the liquid has been detained in the tank to achieve settlement and separation.

If the structure of the septic tank is compromised by an external force, ground water could be forced into the tank via a breech in the tank wall. The uncontrolled inflow of groundwater causes turbulence of the otherwise quiescent conditions, causing the originally settled matter to go back into suspension and ultimately is discharged into the soakaway.

When the wrong type of waste enters the soakaway system, the solid material contained within the discharge fills the voids in the surrounding soil of the drainage field or soakaway. This cannot be undone and any further treatment of the waste will be prevented as the system has become choked and exhausted.

The soakaway system will continue to fill with the waste from the septic tank and either quickly backs up through the system and into the property, or finds its way to ground level and starts to pool on the surface above the soakaway.

If your septic tank is backing up, or you have noticed waste pooling above the system, call UKDP today on 01628 788 600 or visit our website at to arrange a septic tank investigation.