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What causes a septic system to fail, and how can I tell if mine is failing?

What causes a septic system to fail, and how can I tell if mine is failing?

  • A septic system most often fails because the soil absorption system (the leaching field or trench) stops accepting liquid.  This can occur due to clogging of the soil over time, or due to saturation of the surrounding soils with water from some other source (such as stormwater runoff from outside areas, or rising groundwater).
  • The symptoms of a failing septic system may include a noticeable slowing of drainage from toilets and fixtures that doesn’t go away after cleaning the pipes, and/or the “surfacing” of wastewater in your yard or nearby areas.  In extreme cases, wastewater may backflow into your home through floor drains, often while running a washing machine or some other fixture that uses a lot of water at one time.
  • “Surfacing” of wastewater is another common indicator of a septic system failure, and refers to seepage of wastewater from the ground surface.  A properly operating septic system will not result in any surface discharge of wastewater, or any odors.  Seeping wastewater will often appear near the failed septic system, or just downhill from it, especially in places where the natural ground surface has been disturbed through steep excavations or installation of retaining walls.  Seepage from a failed septic system will usually have an unpleasant odor, will cause areas of black or dark green slime, and will attract large numbers of flies.
  • Failure due to excessive stormwater runoff, a high water table, or an unforeseen layer of solid rock below the leaching field will occur fairly quickly after occupancy and is very difficult (or in some cases impossible) to fix.  This type of failure is usually the result of site conditions that were overlooked during design and construction.  This is why it is critical that the design of your home include both a percolation test and a deeper soil observation pit, in addition to an overall site assessment to look for risks related stormwater runoff and other characteristics associated with the site’s location within the overall landscape.  One of the primary responsibilities of your engineer or architect is to determine if such conditions exist prior to you committing funds for construction.  Therefore, it is important that you make sure the septic system is one of the first things your engineer or architect pays attention to, and is not just an afterthought based on previous designs in your neighborhood or other areas where they may have worked in the past.
  • Poor construction methods can also cause a rapid failure of a septic system, occurring shortly after occupancy.  Excavation of the leaching field or trench must be performed with care, particularly in the clayey soils of southern Guam.  The contractor must not compact the bottom of the excavation with the excavator bucket, or “smear” the sides, which can create a microscopic but nearly water-tight layer of compacted clay.  Some soils are so fragile that even the act of pouring in the stone aggregate (gravel) may compact the soil and create such water-tight layers, and require that the contractor first place a layer of sand to avoid such action.  In addition, contractors can damage an absorption system after it is constructed by driving over it.  Once a leaching field or trench is constructed, there should be no driving or parking on it in order to avoid this type of failure, especially in areas with slow-percolating soils such as Southern Guam.
  • Failure due to clogging usually happens over a longer period of time (often many years), and is more common in soils that have slower percolation rates (for example less than 1 inch per 30 minutes), or have a high clay content.  This type of failure is mostly caused by the occupants of the house and what they flush into the septic system, or how often and how well the system is maintained.

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