What Causes Septic Systems to Fail?
Septic systems that are failing on the surface of the ground are fairly easy to detect using obvious signs such as:
- Raw sewage on the ground (areas that remain wet after rain events or appear without precipitation)
- Septic odor
- Slowly draining pipes
- Sewage backing up into the house
- Abnormal grass growth such as green blobs not in line with pipes, random patches of lush growth, and bulls-eye patterns (dead areas surrounded by green growth).
The grass in this picture outlines the septic tank (this indicates seepage around the tank) and the beginning of the drainfield lines. Also, this system is not protected from car traffic.
Septic systems that are failing below the surface of the ground are much more difficult to detect without visual inspections or the use of groundwater monitoring or dye tracer studies. These subsurface failures may be impacting groundwater and surface waters that are closely hydrologically connected.
Several factors contribute to septic system failure and may occur alone or in combination:
Age - Septic systems that were permitted under the old "perc" method may have been built in soils that would not be permitted under today's standards. Or they may have been placed deeper, and thus closer to the water table, than they would be placed today. Also, the longer a system has gone without maintenance, the greater the likelihood it will fail.
Abuse - which can come in many forms:
- Excessive water (also called hydraulic overload) from surface water that flows over the drainfield (downspouts or poor grading), to leaky water fixtures, to doing laundry all in one day can cause system failure.
- Physical Damage from driving, paving, or building over the system can cause the soil to compact and reduce oxygen flow to the soil or can even break tank lids or pipes.
- Improper disposal of many items down the drain that can upset the settling and digestion that occurs in the septic tank, or clog up the trenches and soil in the drainfield. A list of these items plus other "do's and don'ts" can be found on the Septic System Maintenance fact sheet listed under Homeowner Education.
Improper Design and Construction - can doom a system from the beginning. Fortunately, the DHEC Division of Onsite Wastewater Management has a uniform, statewide program for the permitting of septic systems and staff are professionally trained and evaluated. Once again, older systems designed and installed under the "perc" evaluation method and even homemade systems may be more prone to failure. Also, a system that has been designed for a four bedroom home (hydraulic design for 8 people) which is then turned into rental property that "sleeps 12" will be undersized and very prone to failure due to hydraulic overload (too much water).*
Bedrooms: 4
Baths: 3
Pool: Community Pool
Location: Seacrest Beach North
Occupants: 12
Square Footage: 2400
Beach Distance: 400 yards
*This house photo and specifications are from an Internet advertisement.
A system that has been designed properly also must be installed properly. Tanks in backwards, drainfield components unlevel, soil compacted by heavy equipment, and wet soil smeared (and thus sealed) during excavation are just some examples of what can go wrong during installation.
Lack of Maintenance - is probably the most common cause of failure. As the solids levels build up in the tank to an excessive level they can be forced into the drainfield and evenutally clog the gravel and soil. As a result, wastewater may either back up into the house or erupt on the surface of the ground. System failure can also be caused by missing, broken, or degraded tee fittings or baffles in the septic tank. These fittings are designed to slow down the inflow and outflow of wastewater which in turn allows for the primary digestion and separation of solids, grease, and scum from the clarified layer of wastewater. If maintenance is not done before problems occur, then the correction of problems most likely will be more extensive and expensive.