Reprinted from Research Reports: Septic Tank/Water Softener by the University of Wisconsin and The Geological and Natural History University of Wisconsin/Extension.

The Below diagram is an example of a typical single compartment septic tank.

The sewage enters at one end which is properly baffled to prevent bypass flow and reduce turbulence. In the main part of the tank, less buoyant solids settle tothe bottom of the tank, and the lighter than water oils, greases and solids rise to the top. Under ideal conditions, much of the soluble organic matter, heavy solids and floating greases are digested by the bacteria normally present in the sewage. Since these bacteria operate in the absence of air, this digestive process is called "anaerobic."

Ideally, by the time the wastewater passes through the baffled outlet of the septic tank, through the distribution box and into the disposal field, most of the suspended solids and organic matter have been removed. The water then is passed into the drain field in which perforated pipe or tile with open joints allow the water to trickle out into the trenches. These trenches are commonly bedded with gravel or crushed stone which further distributes the water as it is applied to the soil absorption field.

The most frequent questions asked of the industry researchers in regard to possible adverse effects of water conditioning equipment are:

• Is the salt-brine discharged from a water softener toxic to the bacteria in a septic system?
• What effect does the flow rate and volume of backwash and regeneration water discharged from a softener have on the settling and floatation process by reducing the digestion time in the septic tank,thus causing carry-over of solids into the drain field?
• Since sodium is contained in the regeneration solutions of softeners and sodium is known to cause certain soils to swell and thus reduce the percolation (hydraulic conductivity) of water through the soil, how severe is this effect on the soil going to be?

Studies conducted at the University of Wisconsin - Madison,and the National Sanitation Foundation confirmed the results of earlier studies and agreed with assumptions and conclusions of the water conditioning industry.

• These tests confirmed that water softener waste effluents acrually exert a beneficial influence on a septic tank by stimulating biological action and caused no operational problems in the typical anaerobic or aerobic septic tanks.
• The volume of softener wastes (about 50 gallons per regeneration) are added to the septic tank slowly and are not of sufficient volume to cause any deleterious hydraulic load problems in septic tank systems.
• Water softener regenerational wastes not only should not interfere with septic tank system drain field soil percolation but actually might improve soil percolation.