Household wastewater enters into the septic tank where solids are separated. Heavier solids will settle to the bottom of the tank forming a layer of sludge. Lighter materials, like fats and grease, float to the surface, forming a scum layer.
Then a transformation process begins, called anaerobic action. Naturally occurring bacteria (anaerobes) slowly digest the sewage into liquid and gaseous forms. Sludge and scum that are not digested stay within the tank and are not allowed to flow to the Sand Filter or Drain Field.
As the sludge and grease build up, the efficiency of the anaerobic action decreases. At a measured level it becomes necessary to have the septic tank pumped.
If the sewage effluent cannot be absorbed into the soil near the drain field, it will backup and overflow onto the surface of the ground. There are four major causes:
High Water Table – during rainy periods the groundwater table rises. If the table rises into the drain field, sewage may be forced up to the surface of the ground. This is usually the result of an improperly located drain field.
Soil Clogging – If sludge or scum from the septic tank overflows into the drain field, the soil and drain field pipes become clogged. (this is not the case with systems that use Sand Filters) When clogging occurs this usually means that the drain field must be replaced. However, this may not always be the case and some corrective actions may be applied.
Mineral Deposits – If the soil in the drain field area is continuously wet or flooded due to high water tables or excessive sewage flow, mineral deposits will form and clog the soil. Again, there may be some corrective actions applied.
Roots – the roots of certain trees and shrubs planted over a drain filed can enter and block pipes. Removal of these plants is required and corrective action taken. Plants to avoid are are dogwood trees, poplar, willow and cottonwood. It is highly recommended that grass turf be planted over the drain field as this is a shallow root plant and will help to take moisture from the ground and the system.