Septic Repair - Drainfield Options
Rehabilitation options for failed drain fields depend on the cause of failure.
Drain field failure due to flooding
High groundwater, surface flooding, or discharge of high volumes of water to the system can drown the bacteria in a drain field and seal the bottom of the drain field. It may be possible to recover the existing drain field by a combination of improvements that could include:
- Lowering groundwater in the region by use of a curtain drain.
- Removing opportunities for surface runoff to enter the system. Re-grading the site to direct surface runoff away from the septic tank and drain-field.
- Removing the source of high flow into the system. This may include removing a sump pump discharging to the system, fixing leaking fixtures, removing a hot tub discharge connection from the system, etc.
- Rehabilitating the failed system by improving aeration. This could include:
adding a drain field vent (passive system)
adding power ventilation to a drain field vent
adding a bubbler aeration system to the septic tank.
Improving aeration will not save a drain field that is subject to other stresses, like high groundwater or plugging due to paint or clay-like particles.
- Rehabilitating the failed drain field by adding super-charged aerobic organisms. This option may work if combined with aeration and removing sources of flooding, as discussed above.
Plumbing vs. Pumping
Flooded drain fields are often caused by high groundwater. Most commonly, these systems would be replaced with a raised drain field (mounded system). Design is based on site evaluation to ensure that the replacement drain field is placed well above the seasonal high water table. Site grading must also direct surface runoff away from the drain field.
A pump tank may be required to lift the wastewater from an existing septic tank or building sewer to the raised drain field. Pump tanks with pumps and controls are expensive components that require regular inspection and maintenance. In some cases, the system designer can avoid the need for a pump tank by raising the house interior plumbing. Raising the house plumbing is a design option that is often overlooked. The option of modifying the plumbing can save significant construction cost as well as minimize operating expenses.
Drain field failure due to carry-over of fats, oil & grease from septic tank
When fats, oils and grease flow up and over ("carry-over") the top of the septic tank outlet baffle, they then enter the D-box and the drain field. This can seal the bottom of the drain field, flooding the system and drowning the bacteria. Many times, this condition can be rehabilitated by the following combination of improvements:
- Adding aeration to the septic tank. See Septic Tank Aerators.
- Re-seeding the system with super-charged aerobic organisms. This option may work if the organisms are designed to attack fats, oils and grease.
The best chance to correct this failure uses both techniques together.
The property owner or system designer needs to address the cause of carry-over from the septic tank. A larger septic tank, grease trap, and outlet filter are some of the options to control carry-over of fats, oil and grease.
Drain field failure due to clay/silt, water softener backwash, paint, or poisons
If any of these contribute to drain field failure, rehabilitation efforts probably will not work. There are some chemical additives which are advertised to rehabilitate any plugged drain field. Our understanding is that the more aggressive of these may provide only temporary improvement.
In most cases, the cause of drain field failure is at least partly attributable to more than one of the items listed above. Owners want a solution that is guaranteed to work. Therefore, most designers will move directly to replacement of the drain field rather than attempting rehabilitation. State or local codes may not allow for drain field rehabilitation.
For additional information see Plugged Drain-field - How did this happen?
For more detailed information regarding rehabilitation additives, see Additives- Septic Helpers