Septic Systems With Alternating Drainfields

Have you ever heard of a septic system consisting of a septic tank and two drainfields? This is known as the alternating drainfield method.

The idea is simple: rest one drainfield while using the other. The septic system owner is usually experiencing septic tank problems or fearful they may soon appear. After research and consultation, the decision to install a second drainfield is made and construction begins.

What ends up happening is a second drain field is installed in the yard. A bull run valve is placed in-line between the two drain fields. The wastewater from the septic tank is diverted to the new drain field, allowing the old drain field to rest. During this resting period, the food source for the biomat in the first (older) drainfield is cut off.

Remember the biomat? The biomat is a living organism made up of anaerobic bacteria and its byproduct. It lives off of organic matter present in wastewater. It causes the most common symptoms of a failing septic systems: sewage ponding on the ground above the drain field, ponding about the septic tank cover, elevated tank levels, or backups into the house. The biomat grows at the infiltrative surface of the drainfield. It will first begin growing at the bottom of the drain field, sealing it off and preventing water from passing back to the ground and the water table. The wastewater collects at the bottom of the drainfield, saturating the gravel bed below the soil.

Eventually the biomat will grow up the sidewalls to the surface of the ground. At that point, sewage ponding on the ground above the drain field, elevated tank levels, or backups in the house, or any combination of these symptoms occurs.

The alternating drainfield strategy is supposed to help homeowners deal with the biomat. Unfortunately, it can take several years for a resting drain field to rid itself of a mature biomat. Even worse, the bull run valve will eventually be open to both drainfields, ultimately leading both to failure.

The real problem is the anaerobic bacterial environment present in the septic system. Unfortunately, most septic tanks and drainfields contain the perfect environment for anaerobic bacteria and the biomat to thrive. This because the anaerobic system will only reduce the organic material by about 30 to 40% in the septic tank, leaving the drain field to  60% to 70% of the work – a steady and abundant food source for a biomat to thrive.

A better way to address the septic system problems and drainfield failure is to convert the septic tank to an aerobic environment. A controlled introduction of oxygen into the septic tank will allow aerobic bacteria present in human waste to explode in population.  After the conversion, the organic material in the septic tank is reduced by 90% or more, leaving the drainfield to do only 10% of the work. Significantly cleaner water flows to the drainfield, starving the biomat. Like any other living organism in nature, if the food source is cut off, the organism will die. In this case, the biomat breaks down and the drainfield becomes permeable again.

A carefully controlled conversion of a septic tank to an aerobic environment is a better solution to septic system problems than installing the expensive alternating drainfield.

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