Directions for Installing a Leach Field

Leach fields, sometimes referred to as a drain field, allow the fluids of a septic or sewer system to drain away. Septic systems with leach fields are often used in rural areas and in some suburban areas. The septic system is made up of a septic tank, where sewage solids break down into liquids, and the leach field, where the fluids soak into the ground.

Close-up of the leg of a man standing with a shovel in a yard
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Choosing the Site

A leach field is a rather simple item to install or construct, but it needs to be placed properly. The size of a leach field varies, depending on the percolation rate of the soil and the number of people in the household. Soil percolation is the rate that water soaks away and will depend on the composition of the soil. In many areas, soil testing is required.This also will determine the depth of the trenches for the leach field. Leach fields are usually placed near the septic tank to lessen the cost of installation, but need to be placed at least 30 yards from drinking water sources, such as wells.

Building the Field

After you've determined the leach field size and location, you will dig the trenches. Many leach fields are laid out as a number of parallel trenches connected by pipes to the septic tank. Trenches are commonly between 1 and 5 feet deep and 1 and 3 feet wide. These trenches are filled to within 6 inches of the top with gravel or pea rock. Pea rock is gravel screened so that all stones are at least the size of a pea.

Place perforated PVC pipe into the top of the gravel-filled trench. This pipe will carry the sewer effluent from the septic tank to the leach field and allow it to drain into the gravel-filled trench. From there it will work its way into the soil around it and eventually be absorbed away from the leach field. Place construction paper over the gravel and pipe arrangement in the trench before backfilling it in order to prevent the gravel from being clogged by soil working down from the top.

After the trenches are backfilled with top soil, the area can be replanted with grass. Avoid planting trees or shrubs in the area of the leach field as their roots can clog the pipes, causing sewage backup into the home.