How Deep Should a Septic Leach Field Be?

Municipal water facilities provide sewer removal for homes connected to the system. For homeowners outside the system, normally in rural areas, a septic system installed on the property is the only alternative. The system includes the septic tank and a leach, or drainage field. Numerous standards exist for the installation of the field, including the depth of the pipes.

...
Installing the septic tank is the first step towards a complete system.

Leach Field Size

The leach field is the end result of the septic system. Drain lines run from the septic tank to the field where perforated pipes are buried with the holes facing down so the wastewater seeps into the soil. The size of the leach field depends on the size of the home, the anticipated water usage and the ability of the soil to percolate. Percolation refers to the ability of the soil to drain water which varies depending upon soil type.

Diagram

Locate leach fields in open spaces that contain sufficient room and will be easy to access in the event of repair or replacement. Designing a leach field involves spacing the perforated pipe for proper drainage. Trenches for the pipes contain gravel and may be as long as 100 feet. Each trench is 1-3 feet wide with 6 feet between each trench.

Depth

Place the pipes in the leach field a minimum of 6 inches and most likely between 18 to 36 inches deep according to the Clemson Cooperative Extension. Each leach field requires an individual design as soil and water tables vary from state to state and within states. An example is the state of Maine where the seasonal high water table can be less than 36 inches which requires the leach field bed to be raised up according to Green Environmental Engineering.

Landscaping

The depth of the leach field impacts the type of landscaping on the surface ground above the field. Know the depth of your leach field and the type of root systems for any plants on the surface. Select plants or grasses with shallow root systems. Roots and pipes make a poor combination in a leach field.