They've stopped the question asking due to overload...but I did see some useful info. Kinda bothers me now though /forums/images/graemlins/frown.gif I probably have a combination of these two:
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Failure of the Septic System from Overload or Poor Distribution
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If the soil surrounding and below the drainfield remains moist and not wet, the aerobic bacteria will dominate the drainfield and things are working fine. If the soil becomes saturated with sewage effluent or water, anaerobic (water breathing) bacteria from the effluent take over the drainfield. Then the treatment stops. The soil surrounding the drainfield becomes abnormally clogged with organic particles. The normal dark bacterial film (biomat) found below and around normally operating drainfields, becomes thick and totally waterproof. The soil stops absorbing effluent and ponding above ground usually occurs. Failure is also often accompanied by a "sewage odor."
A completely failed system generally must be replaced in a fresh location. If the drainfield is abandoned for a year or more, it probably will recover. In replacing a failed gravity drainfield, it is wise to put in a valve (bull run valve) to allow switching back to the old drainfield as a backup.
A septic system can be deliberately made to fail simply by turning on any tap in the house and leaving it running for a week or so. The excess volume of effluent will flood and fail the drainfield by killing the aerobic bacteria in the drainfield. This is why it is always important to repair hissing (leaking) toilets and even dripping taps in a home on a septic system.
Poor distribution of the effluent in the drainfield causes local patches of failure, reducing the effective area of the drainfield. This is why pressure systems are more reliable than gravity systems. Pressure distribution is almost always required in complex systems and poor soil conditions.
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Failure of the Septic System from Poor Soil
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Generally the best soil in which to build your septic system is undisturbed medium sand. Very fine sands, and darker organic (loamy) soils are second best. Silt, a very fine soil with a smooth texture like talcum powder is even less absorptive. There is simply less space between the particles to hold and pass water.
Clay, and extremely fine clay-like soils are poorer for septic systems. The poorer the soil, generally, the larger the drainfield due to the slow rate of absorption. Finer soils formed from ancient stream and lake beds can be compacted, and layered. Fine bands of silt and clay can spoil otherwise good sandy soils.
Also, coarse gravelly soils can be too porous allowing the flow of effluent from the drainfield to penetrate deep into the soil too quickly. This places the effluent below the plant root portion of the soil. This upper soil zone is where treatment must happen because of the presence of oxygen and aerobic bacteria.
Even when soil is good, it may not be deep enough to allow a system to be built (usually a minimum of four to five feet deep). Septic systems in shallow soil above a layer of solid rock, or above a shallow water table may not be approved by the local health department. Sometimes an alternative system such as a mound may be allowed if soil is too shallow.
If the soil is poor, or too shallow, why not bring in some good soil to replace it? Once ordinary dirt from a site has been disturbed or moved, it will not support proper septic functioning. The soil will fail in a few weeks. This is just one of the mysteries of soil. This applies to natural sand, dredging spoils, potting soil and all imported dirt. Once soil is left undisturbed for a few thousand years, microorganisms and other large and small forces of nature create a condition called soil structure. This naturally changes the soil making it suitable for use as a treatment medium. A designer or soil expert is trained and experienced at determining soil structure by throwing a hand pick at the soil face, and by feeling (texturing) the soil and other tests. Most home-owners and do-it-yourselfers would not be able to recognize poor soil structure and should not determine system size in areas known to have poor soil.
