What is a Septic System?

A septic system is a sewage treatment and disposal system buried in the ground. It is composed of a septic tank and a leach field or trench.

Household sewage (wastewater from sinks, toilets, showers, washing machines, garbage disposals and dishwashers) generally flows by gravity into the septic tank. There, heavier particles settle to the bottom and scum rises to the top. Bacteria in the tank help break down some of the solids.

Baffles within the tank improve sludge settling and prevent scum from floating out of the tank. Effluent (liquid) flows to the leach field, where it is distributed over crushed gravel or absorbent soil.

The liquid typically Includes contaminants such as nitrates, phosphorus, disease-causing bacteria and viruses, dissolved metals, detergents and solvents. The septic tank and leach field provide minimal treatment for these contaminants. Generally, phosphorus and dissolved metals are bound up by the soil; although, sand and gravel may not effectively remove these pollutants. Nitrates and solvents are diluted in groundwater. Bacteria and viruses are filtered by the soil or die off.

But septic systems can fail due to poor design or construction, to overloading or to inadequate maintenance.