How Deep Should a Leach Field Be?

The pipes in a leach field may be at a depth of 6 inches to 4 feet. The trench in which the pipes are buried may be as deep as 6 feet.

Leach fields are an integral part to a successful septic system. A septic system works to remove waste from households and businesses and is often used in areas without access to municipal sewer systems. Septic systems carry water and waste from sinks, bathtubs, showers and toilets to a tank, in which bacteria break down the solid matter. New water flowing in displaces the water already in the tank, which flows to a leach field.

The leach field allows the water from the septic tank to filter back into the soil slowly so that bacteria in the soil can attack contaminants and prevent them from reaching the water table. The size of the leach field is determined by the absorption rate of the soil in the field and the amount of water that enters the field on a daily basis. Harder soils, such as those containing clay, have a slower absorption rate and as such the leach field has to be larger. Additionally, the pipes that transport the water to the field must be at an appropriate depth. Typical leach field trenches are from 4 to 6 feet deep. The bottom of the trench is filled with gravel or sand to a height of 2 to 3 feet. The minimum depth for leach field pipes is 6 inches.