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Sunday, February 18, 2018

Failed Septic System?

What defines a failed septic system?

Most homeowners define a failed septic system as one that either periodically or continually backs-up into the house or overflows onto the ground in their yard. In short, the system is a continual or occasional nuisance. If neither of these events occur, most homeowners assume they have a good septic system. Although a system may be functional for the occupants, it may or may not meet the legal definition of a functioning septic system. The page will provide specific information on how the test is performed. The MOA defines a functioning as one that is capable of absorbing (not just accepting) 150 gallons per day per bedroom. This corresponds to the following:

  • 2 bedrooms: 300 gallons per day
  • 3 bedrooms: 450 gallons per day
  • 4 bedrooms: 600 gallons per day
  • 5 bedrooms: 750 gallons per day


Most 3 or 4 bedroom houses only have about 4-5 occupants in them and a total daily water usage of 200 to 250 gallons per day, which is significantly less than the absorption requirements established by the MOA. As a result, you may have a septic system that functions fine for your family, but is unable to meet the absorption requirements established by the MOA. The septic system adequacy test is very demanding. Statistically, about one out of every three systems is in a technical state of failure. Although that may not sound too optimistic, it is a fact.

What is the Average Life Span of a Septic System?

The average life span of a typical trench type is about 9-10 years. Bed type drainfields and mound systems typically don’t last quite as long as trench systems. There are systems which defy these statistics and fail much sooner or last much longer. Systems which last much longer typically were installed in good sandy, gravelly soils, were used moderately (small family), and were maintained ( pumped at least every 2 years). Systems which failed "prematurely" were typically installed in poorer soils (silts & clays), used more heavily (larger family), and/or were not maintained.

What Causes Drainfields to Fail?

- It is important to bear in mind that virtually all septic systems (except those with back-up drainfields and an ) will fail. The normal cause of failure is due to the buildup of a thick, pasty, black sludge, called a . The biomat is a biological growth that develops in the drainfield. The microbes in the drainfield consume the soluble organic material in the wastewater that comes from the septic tank and convert it to cell mass, the same way we convert food energy into fat and muscle. Over time this mass of bacteria builds up and plugs the interface between the drainrock in the field and the surrounding soil, preventing wastewater from percolating into the ground. The result: a drainfield that fills with water and backs-up into the house and/or overflows onto the ground. It is important to note that the cold ground temperatures, and the deep depths at which we install drainfields in Alaska (so as prevent freezing), which are oxygen deficient, hastens the build-up of the biomat, explaining why drainfields in colder climates don’t seem to last as long.

Other Factors

In addition, to old age, there are a number of reasons why systems fail. They include, but are not limited to, the following:

  • Undersized System: The design of a septic system is based upon a very limited amount of field testing. It is possible that the actual soils on which your system was installed are not as porous as the indicated. Consequently the drainfield was sized too small.
  • Poor Construction Practices: If the contractor drove equipment over the surface of the drainfield (particularly with wet silty/clayey soils), or installed silty (unclean) drainrock, the performance of the drainfield may have been significantly compromised.
  • You may have groundwater problems that were not identified during the design of your septic system. The done by the engineer may not have accurately identified the seasonal high groundwater table on your property. It is possible that during spring break-up and significant rainfall events that the groundwater rises to such an extent that the hydraulics of your septic system are significantly diminished.
  • If the was not pumped frequently enough, or not at all, it is likely that the solids collected in the septic tank to such an extent that some of them began to wash through the tank and into the drainfield. In some cases it is possible to jet clean the "muck" out of the drainfield and retest it successfully. You should consult with your engineer regarding this option.
  • Do you have any additional sources of water that may be hydraulically overloading the drainfield? Look for the following:
  1. Do you have leaking toilets (typically the "flapper" in the tank) or other fixtures?
  2. Is there a sump pump hooked up to the septic system?
  3. Do you have a water softener that is backwashing excessively?
  4. Did you just drain your 1000 gallon hot tub into the septic system?

If any of these conditions exist, they may be causing your septic system to be hydraulically overloaded. In some cases, if these sources of water are eliminated, and the system given several days to recover, it may be possible to retest the system successfully.

  • Excessive usage by residents: As mentioned previously, the average water use for a family is typically 200-250 gallons per day. If your family has been indiscriminate about water usage, this may have hastened the failure of the drainfield.
  • Did you use biological additives in your septic system? The EPA, ADEC, and the MOA all discourage the use of septic system additives (enzymes, yeasts, ect). There is no data proving that they do anything to enhance the performance of the system. In fact there is evidence that some additives contribute to drainfield failure.


My septic system is failed, so what are my options?

  • REJUVENATION - Attempt to jump start the septic system using chemical rejuvenation or the Terralift process. These methods have been used successfully in the past to get a septic system to pass an adequacy test, however, they should not be viewed as a long term solution. Neither process will correct problems associated with a bad design/installation, high groundwater, or poor soils. The cost for these treatments varies from about $1500-$2000 for chemical rejuvenation to $2500 for Terralifting. Our experience at GEG, Ltd. is that chemical treatment is more effective than Terralifting, and costs less. In order for either process to work you must have soils that are relatively porous (sands and gravels). If the soil contains significant amounts of clay or silt either treatment process has a poor success rate. Neither treatment should be considered a long term solution. If you are selling your house you will need to disclose to your engineer, the and the buyer that you utilized either of these rejuvenation methods. Upon doing so don’t be surprised if your buyer is not receptive to it.
  • UPGRADE THE SEPTIC SYSTEM - If you are looking for a long term solution to your onsite wastewater treatment needs, this is the option you should consider. When the new drainfield is constructed, an should be installed after the septic tank so that wastewater from the septic tank can be routed to either the old or new drainfield. When the new drainfield is being used, the old drainfield will have an opportunity to rest and recover. In fact, after several years with no usage it will recover virtually 100%. The alternator valve should then be switched periodically (about every 6 months) so that neither drainfield has an opportunity to develop a . The result is a system that should work indefinitely, assuming both drainfields were properly designed.

How is the septic adequacy test performed?

On to the Septic System Upgrade page

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