How Septic Systems Work

A septic system is a self-contained, underground wastewater treatment system, usually used when a house has no access to city sewer. Septic systems operate on a fundamental concept: water in, water out. If you flush three gallons down the drain, three gallons will immediately leave the tank and travel to the leach field. Because miles of sewer lines are not needed, on-site systems are less disruptive to the environment. These systems are less costly to operate than the large municipal treatment plants and tend to be more efficient.

A septic system consists of two main parts: a septic tank and a leach field (or drain field).  A septic tank is water tight and generally made from metal, concrete or fiberglass. Waste water flows from the house to the tank. The tank treats the wastewater by holding it in the tank long enough for the solids to settle out of the effluent (water) and fall to the bottom of the tank. This is called SLUDGE.

Solids that are lighter than water: grease, oil, laundry lint, and garbage- remain floating on the top of the water. This is called the SCUM layer. The middle layer, which should take up most of the volume in the tank, is called EFFLUENT. This is the layer of grey water that flows into the leach field. The layers of scum and sludge remain in the tank where enzymes and bacteria work to break them down. The scum and sludge that cannot be broken down remain in the tank until the tank is cleaned and pumped.

When the grey water leaves the septic tank, it travels to the leach/drain field. Typically the grey water flows from the tank to a distribution box and then through a solid (non-perforated) pipe. From there, it flows to another box or out to multiple leach lines. These lines can be 12 inches -36 inches deep depending on soil type. Historically, trenches were filed with drain rock. Today, however, many different proprietary products are used. The water trickles down through the drain media to the bottom of the trench and millions of microbes in the soil work to process the pathogens (bacteria and viruses), thus breaking down the organic matter. The water is then purified and returned to the aquifer.

Check out our Video Gallery for a more in depth look at Leach Field Anatomy and Drain Field Anatomy.