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What causes septic trench collapse?

If designed, constructed, and maintained correctly septic drainage trenches will provide years of effective wastewater removal. However, occasionally septic trenches fail, collapsing, blocking, or becoming compressed requiring immediate repairs, trench rehabilitation, or the creation of new trenches.

Your septic system septic trenches fail for a number of reasons but in all cases, this can result in a very smelly, boggy situation in your yard which can quickly lead to a serious hazard very quickly.

Common causes of absorption trench failure

Common issues occur due to factors such as the uneven distribution of treated liquid waste or heavy vehicles accessing the trench area.

Uneven wastewater distribution

A properly designed system will ensure the wastewater flows along the length of the trench evenly, allowing the treated water to absorb evenly into the surrounding area. However, if this is not the case and one area of the trench or trench system is being forced to take in the bulk of the wastewater problems can eventuate.

Issues can occur if one area of the trench system has soil which is more or less absorbent, if trenches are not level, or if pipe or arch perforations have become blocked.

Compacting of trenches

Trenches can become compacted due to pressure from heavy vehicles, large animals or even frequent foot traffic. This can result in the collapse of the arch or septic pipe preventing water from moving along the trench.

Compacting or collapsing of trenches can also occur when paving or driveways are constructed over the absorption trench area this can also cause the pipes to move, disrupting the required flow.

Excess water use

An increase in the expected wastewater volume from your home can flood the septic system with more liquid than the disposal area was designed to handle causing problems in the trenches due to flooding and excessive subsurface soakage.

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Blocked trenches

Trenches can become blocked due to failure of the protective layer allowing dirt and debris into the pipe or arch.

Another cause of blocked septic trenches is sludge and scum flowing from the septic tank into the absorption trenches. This is a common problem for septic systems which are not routinely pumped out, leading to an excess of sludge and scum in the tank.

Tree roots seek out rich sources of nutrients like those in the absorption trench area. If large trees or bushes are planted too close to septic trenches the roots can quickly cause blockages. To prevent this issue only grass or plants with shallow root systems should be planted over or near trenches

Signs of absorption trench problems:

  • Unpleasant smells
  • Excessively wet areas of grass or garden
  • Effluent surfacing
  • Pooling of stormwater
  • Cars or vehicles have been driving over the area
  • Paving or driveways have been constructed over the leach field
  • Drains, sink, bath, toilet or shower slow to drain
  • The septic tank needs frequent pumping (more than once a year)
  • Overgrowth of grass or plants in the trench area

Please note - sewage odours may occur at different times due to other factors such as an increase in wastewater load (extra washing, guests, etc) or if your system has just been installed.

Septic trench repairs

In some cases repairs can be carried out on your septic trench, however, often a failed or blocked trench will require a complete rehabilitation or if room permits a new trench altogether.

Your wastewater specialist will assess the problems with your septic system or absorption trenches and recommend the best repair method. If you have any queries concerning the content on this page, or would like to talk to us about your septic trench repairs, get in touch by calling 1300 722 517 or by completing a booking form.